ViewVC Help

View File | Revision Log | Show Annotations | Download File

/cvs/libev/ev.pod

Comparing libev/ev.pod (file contents):
Revision 1.102 by root, Sat Dec 22 16:21:25 2007 UTC vs.
Revision 1.434 by root, Tue May 6 13:24:39 2014 UTC

		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
6		8
7	#include <ev.h>	9	#include <ev.h>
8		10
9	=head1 EXAMPLE PROGRAM	11	=head2 EXAMPLE PROGRAM
10		12
		13	// a single header file is required
11	#include <ev.h>	14	#include <ev.h>
12		15
		16	#include <stdio.h> // for puts
		17
		18	// every watcher type has its own typedef'd struct
		19	// with the name ev_TYPE
13	ev_io stdin_watcher;	20	ev_io stdin_watcher;
14	ev_timer timeout_watcher;	21	ev_timer timeout_watcher;
15		22
16	/* called when data readable on stdin */	23	// all watcher callbacks have a similar signature
		24	// this callback is called when data is readable on stdin
17	static void	25	static void
18	stdin_cb (EV_P_ struct ev_io *w, int revents)	26	stdin_cb (EV_P_ ev_io *w, int revents)
19	{	27	{
20	/* puts ("stdin ready"); */	28	puts ("stdin ready");
21	ev_io_stop (EV_A_ w); /* just a syntax example */	29	// for one-shot events, one must manually stop the watcher
22	ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */	30	// with its corresponding stop function.
		31	ev_io_stop (EV_A_ w);
		32
		33	// this causes all nested ev_run's to stop iterating
		34	ev_break (EV_A_ EVBREAK_ALL);
23	}	35	}
24		36
		37	// another callback, this time for a time-out
25	static void	38	static void
26	timeout_cb (EV_P_ struct ev_timer *w, int revents)	39	timeout_cb (EV_P_ ev_timer *w, int revents)
27	{	40	{
28	/* puts ("timeout"); */	41	puts ("timeout");
29	ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */	42	// this causes the innermost ev_run to stop iterating
		43	ev_break (EV_A_ EVBREAK_ONE);
30	}	44	}
31		45
32	int	46	int
33	main (void)	47	main (void)
34	{	48	{
35	struct ev_loop *loop = ev_default_loop (0);	49	// use the default event loop unless you have special needs
		50	struct ev_loop *loop = EV_DEFAULT;
36		51
37	/* initialise an io watcher, then start it */	52	// initialise an io watcher, then start it
		53	// this one will watch for stdin to become readable
38	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);
39	ev_io_start (loop, &stdin_watcher);	55	ev_io_start (loop, &stdin_watcher);
40		56
		57	// initialise a timer watcher, then start it
41	/* simple non-repeating 5.5 second timeout */	58	// simple non-repeating 5.5 second timeout
42	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);	59	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
43	ev_timer_start (loop, &timeout_watcher);	60	ev_timer_start (loop, &timeout_watcher);
44		61
45	/* loop till timeout or data ready */	62	// now wait for events to arrive
46	ev_loop (loop, 0);	63	ev_run (loop, 0);
47		64
		65	// break was called, so exit
48	return 0;	66	return 0;
49	}	67	}
50		68
51	=head1 DESCRIPTION	69	=head1 ABOUT THIS DOCUMENT
52		70
		71	This document documents the libev software package.
		72
53	The newest version of this document is also available as a html-formatted	73	The newest version of this document is also available as an html-formatted
54	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
55	time: L<http://cvs.schmorp.de/libev/ev.html>.	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
56		94
57	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
58	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
59	these event sources and provide your program with events.	97	these event sources and provide your program with events.
60		98
…		…
65	You register interest in certain events by registering so-called I<event	103	You register interest in certain events by registering so-called I<event
66	watchers>, which are relatively small C structures you initialise with the	104	watchers>, which are relatively small C structures you initialise with the
67	details of the event, and then hand it over to libev by I<starting> the	105	details of the event, and then hand it over to libev by I<starting> the
68	watcher.	106	watcher.
69		107
70	=head1 FEATURES	108	=head2 FEATURES
71		109
72	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
73	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	111	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
74	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
75	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	113	(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
76	with customised rescheduling (C<ev_periodic>), synchronous signals	114	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative
77	(C<ev_signal>), process status change events (C<ev_child>), and event	115	timers (C<ev_timer>), absolute timers with customised rescheduling
78	watchers dealing with the event loop mechanism itself (C<ev_idle>,	116	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
79	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
80	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
81	(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>).
82		121
83	It also is quite fast (see this	122	It also is quite fast (see this
84	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
85	for example).	124	for example).
86		125
87	=head1 CONVENTIONS	126	=head2 CONVENTIONS
88		127
89	Libev is very configurable. In this manual the default configuration will	128	Libev is very configurable. In this manual the default (and most common)
90	be described, which supports multiple event loops. For more info about	129	configuration will be described, which supports multiple event loops. For
91	various configuration options please have a look at B<EMBED> section in	130	more info about various configuration options please have a look at
92	this manual. If libev was configured without support for multiple event	131	B<EMBED> section in this manual. If libev was configured without support
93	loops, then all functions taking an initial argument of name C<loop>	132	for multiple event loops, then all functions taking an initial argument of
94	(which is always of type C<struct ev_loop *>) will not have this argument.	133	name C<loop> (which is always of type C<struct ev_loop *>) will not have
		134	this argument.
95		135
96	=head1 TIME REPRESENTATION	136	=head2 TIME REPRESENTATION
97		137
98	Libev represents time as a single floating point number, representing the	138	Libev represents time as a single floating point number, representing
99	(fractional) number of seconds since the (POSIX) epoch (somewhere near	139	the (fractional) number of seconds since the (POSIX) epoch (in practice
100	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
101	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
102	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
103	it, you should treat it as some floatingpoint value. Unlike the name	143	any calculations on it, you should treat it as some floating point value.
		144
104	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
105	throughout libev.	146	time differences (e.g. delays) throughout libev.
		147
		148	=head1 ERROR HANDLING
		149
		150	Libev knows three classes of errors: operating system errors, usage errors
		151	and internal errors (bugs).
		152
		153	When libev catches an operating system error it cannot handle (for example
		154	a system call indicating a condition libev cannot fix), it calls the callback
		155	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		156	abort. The default is to print a diagnostic message and to call C<abort
		157	()>.
		158
		159	When libev detects a usage error such as a negative timer interval, then
		160	it will print a diagnostic message and abort (via the C<assert> mechanism,
		161	so C<NDEBUG> will disable this checking): these are programming errors in
		162	the libev caller and need to be fixed there.
		163
		164	Libev also has a few internal error-checking C<assert>ions, and also has
		165	extensive consistency checking code. These do not trigger under normal
		166	circumstances, as they indicate either a bug in libev or worse.
		167
106		168
107	=head1 GLOBAL FUNCTIONS	169	=head1 GLOBAL FUNCTIONS
108		170
109	These functions can be called anytime, even before initialising the	171	These functions can be called anytime, even before initialising the
110	library in any way.	172	library in any way.
…		…
113		175
114	=item ev_tstamp ev_time ()	176	=item ev_tstamp ev_time ()
115		177
116	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
117	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
118	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>.
119		182
120	=item ev_sleep (ev_tstamp interval)	183	=item ev_sleep (ev_tstamp interval)
121		184
122	Sleep for the given interval: The current thread will be blocked until	185	Sleep for the given interval: The current thread will be blocked
123	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
124	this is a subsecond-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 >>).
125		194
126	=item int ev_version_major ()	195	=item int ev_version_major ()
127		196
128	=item int ev_version_minor ()	197	=item int ev_version_minor ()
129		198
…		…
140	as this indicates an incompatible change. Minor versions are usually	209	as this indicates an incompatible change. Minor versions are usually
141	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
142	not a problem.	211	not a problem.
143		212
144	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
145	version.	214	version (note, however, that this will not detect other ABI mismatches,
		215	such as LFS or reentrancy).
146		216
147	assert (("libev version mismatch",	217	assert (("libev version mismatch",
148	ev_version_major () == EV_VERSION_MAJOR	218	ev_version_major () == EV_VERSION_MAJOR
149	&& ev_version_minor () >= EV_VERSION_MINOR));	219	&& ev_version_minor () >= EV_VERSION_MINOR));
150		220
151	=item unsigned int ev_supported_backends ()	221	=item unsigned int ev_supported_backends ()
152		222
153	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	223	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
154	value) compiled into this binary of libev (independent of their	224	value) compiled into this binary of libev (independent of their
…		…
156	a description of the set values.	226	a description of the set values.
157		227
158	Example: make sure we have the epoll method, because yeah this is cool and	228	Example: make sure we have the epoll method, because yeah this is cool and
159	a must have and can we have a torrent of it please!!!11	229	a must have and can we have a torrent of it please!!!11
160		230
161	assert (("sorry, no epoll, no sex",	231	assert (("sorry, no epoll, no sex",
162	ev_supported_backends () & EVBACKEND_EPOLL));	232	ev_supported_backends () & EVBACKEND_EPOLL));
163		233
164	=item unsigned int ev_recommended_backends ()	234	=item unsigned int ev_recommended_backends ()
165		235
166	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
167	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
168	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
169	most BSDs and will not be autodetected unless you explicitly request it	240	and will not be auto-detected unless you explicitly request it (assuming
170	(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
171	libev will probe for if you specify no backends explicitly.	242	probe for if you specify no backends explicitly.
172		243
173	=item unsigned int ev_embeddable_backends ()	244	=item unsigned int ev_embeddable_backends ()
174		245
175	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
176	is the theoretical, all-platform, value. To find which backends	247	value is platform-specific but can include backends not available on the
177	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
178	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	249	the current system, you would need to look at C<ev_embeddable_backends ()
179	recommended ones.	250	& ev_supported_backends ()>, likewise for recommended ones.
180		251
181	See the description of C<ev_embed> watchers for more info.	252	See the description of C<ev_embed> watchers for more info.
182		253
183	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	254	=item ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())
184		255
185	Sets the allocation function to use (the prototype is similar - the	256	Sets the allocation function to use (the prototype is similar - the
186	semantics is identical - to the realloc C function). It is used to	257	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
187	allocate and free memory (no surprises here). If it returns zero when	258	used to allocate and free memory (no surprises here). If it returns zero
188	memory needs to be allocated, the library might abort or take some	259	when memory needs to be allocated (C<size != 0>), the library might abort
189	potentially destructive action. The default is your system realloc	260	or take some potentially destructive action.
190	function.	261
		262	Since some systems (at least OpenBSD and Darwin) fail to implement
		263	correct C<realloc> semantics, libev will use a wrapper around the system
		264	C<realloc> and C<free> functions by default.
191		265
192	You could override this function in high-availability programs to, say,	266	You could override this function in high-availability programs to, say,
193	free some memory if it cannot allocate memory, to use a special allocator,	267	free some memory if it cannot allocate memory, to use a special allocator,
194	or even to sleep a while and retry until some memory is available.	268	or even to sleep a while and retry until some memory is available.
195		269
196	Example: Replace the libev allocator with one that waits a bit and then	270	Example: Replace the libev allocator with one that waits a bit and then
197	retries).	271	retries (example requires a standards-compliant C<realloc>).
198		272
199	static void *	273	static void *
200	persistent_realloc (void *ptr, size_t size)	274	persistent_realloc (void *ptr, size_t size)
201	{	275	{
202	for (;;)	276	for (;;)
…		…
211	}	285	}
212		286
213	...	287	...
214	ev_set_allocator (persistent_realloc);	288	ev_set_allocator (persistent_realloc);
215		289
216	=item ev_set_syserr_cb (void (*cb)(const char *msg));	290	=item ev_set_syserr_cb (void (*cb)(const char *msg) throw ())
217		291
218	Set the callback function to call on a retryable syscall error (such	292	Set the callback function to call on a retryable system call error (such
219	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
220	indicating the system call or subsystem causing the problem. If this	294	indicating the system call or subsystem causing the problem. If this
221	callback is set, then libev will expect it to remedy the sitution, no	295	callback is set, then libev will expect it to remedy the situation, no
222	matter what, when it returns. That is, libev will generally retry the	296	matter what, when it returns. That is, libev will generally retry the
223	requested operation, or, if the condition doesn't go away, do bad stuff	297	requested operation, or, if the condition doesn't go away, do bad stuff
224	(such as abort).	298	(such as abort).
225		299
226	Example: This is basically the same thing that libev does internally, too.	300	Example: This is basically the same thing that libev does internally, too.
…		…
233	}	307	}
234		308
235	...	309	...
236	ev_set_syserr_cb (fatal_error);	310	ev_set_syserr_cb (fatal_error);
237		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
238	=back	325	=back
239		326
240	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	327	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
241		328
242	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
243	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
244	events, and dynamically created loops which do not.	331	libev 3 had an C<ev_loop> function colliding with the struct name).
245		332
246	If you use threads, a common model is to run the default event loop	333	The library knows two types of such loops, the I<default> loop, which
247	in your main thread (or in a separate thread) and for each thread you	334	supports child process events, and dynamically created event loops which
248	create, you also create another event loop. Libev itself does no locking	335	do not.
249	whatsoever, so if you mix calls to the same event loop in different
250	threads, make sure you lock (this is usually a bad idea, though, even if
251	done correctly, because it's hideous and inefficient).
252		336
253	=over 4	337	=over 4
254		338
255	=item struct ev_loop *ev_default_loop (unsigned int flags)	339	=item struct ev_loop *ev_default_loop (unsigned int flags)
256		340
257	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
258	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
259	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
260	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".
261		351
262	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
263	function.	353	function (or via the C<EV_DEFAULT> macro).
		354
		355	Note that this function is I<not> thread-safe, so if you want to use it
		356	from multiple threads, you have to employ some kind of mutex (note also
		357	that this case is unlikely, as loops cannot be shared easily between
		358	threads anyway).
		359
		360	The default loop is the only loop that can handle C<ev_child> watchers,
		361	and to do this, it always registers a handler for C<SIGCHLD>. If this is
		362	a problem for your application you can either create a dynamic loop with
		363	C<ev_loop_new> which doesn't do that, or you can simply overwrite the
		364	C<SIGCHLD> signal handler I<after> calling 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.
264		384
265	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
266	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>).
267		387
268	The following flags are supported:	388	The following flags are supported:
…		…
274	The default flags value. Use this if you have no clue (it's the right	394	The default flags value. Use this if you have no clue (it's the right
275	thing, believe me).	395	thing, believe me).
276		396
277	=item C<EVFLAG_NOENV>	397	=item C<EVFLAG_NOENV>
278		398
279	If this flag bit is ored 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
280	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
281	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	401	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
282	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
283	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
284	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).
285		407
286	=item C<EVFLAG_FORKCHECK>	408	=item C<EVFLAG_FORKCHECK>
287		409
288	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
289	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.
290	enabling this flag.
291		412
292	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,
293	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
294	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
295	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
296	without a syscall and thus I<very> fast, but my Linux system also has	417	without a system call and thus I<very> fast, but my GNU/Linux system also has
297	C<pthread_atfork> which is even faster).	418	C<pthread_atfork> which is even faster).
298		419
299	The big advantage of this flag is that you can forget about fork (and	420	The big advantage of this flag is that you can forget about fork (and
300	forget about forgetting to tell libev about forking) when you use this	421	forget about forgetting to tell libev about forking) when you use this
301	flag.	422	flag.
302		423
303	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>	424	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
304	environment variable.	425	environment variable.
		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.
305		461
306	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	462	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
307		463
308	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
309	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,
310	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
311	using this backend. It doesn't scale too well (O(highest_fd)), but its	467	using this backend. It doesn't scale too well (O(highest_fd)), but its
312	usually the fastest backend for a low number of (low-numbered :) fds.	468	usually the fastest backend for a low number of (low-numbered :) fds.
313		469
314	To get good performance out of this backend you need a high amount of	470	To get good performance out of this backend you need a high amount of
315	parallelity (most of the file descriptors should be busy). If you are	471	parallelism (most of the file descriptors should be busy). If you are
316	writing a server, you should C<accept ()> in a loop to accept as many	472	writing a server, you should C<accept ()> in a loop to accept as many
317	connections as possible during one iteration. You might also want to have	473	connections as possible during one iteration. You might also want to have
318	a look at C<ev_set_io_collect_interval ()> to increase the amount of	474	a look at C<ev_set_io_collect_interval ()> to increase the amount of
319	readyness notifications you get per iteration.	475	readiness notifications you get per iteration.
		476
		477	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		478	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		479	C<exceptfds> set on that platform).
320		480
321	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	481	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
322		482
323	And this is your standard poll(2) backend. It's more complicated	483	And this is your standard poll(2) backend. It's more complicated
324	than select, but handles sparse fds better and has no artificial	484	than select, but handles sparse fds better and has no artificial
325	limit on the number of fds you can use (except it will slow down	485	limit on the number of fds you can use (except it will slow down
326	considerably with a lot of inactive fds). It scales similarly to select,	486	considerably with a lot of inactive fds). It scales similarly to select,
327	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for	487	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
328	performance tips.	488	performance tips.
329		489
		490	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		491	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
		492
330	=item C<EVBACKEND_EPOLL> (value 4, Linux)	493	=item C<EVBACKEND_EPOLL> (value 4, Linux)
331		494
		495	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		496	kernels).
		497
332	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
333	but it scales phenomenally better. While poll and select usually scale	499	it scales phenomenally better. While poll and select usually scale like
334	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
335	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).
336	of shortcomings, such as silently dropping events in some hard-to-detect	502
337	cases and rewiring a syscall per fd change, no fork support and bad	503	The epoll mechanism deserves honorable mention as the most misdesigned
338	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...
339		530
340	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
341	will result in some caching, there is still a syscall per such incident	532	will result in some caching, there is still a system call per such
342	(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
343	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
344	very well if you register events for both fds.	535	file descriptors might not work very well if you register events for both
345		536	file descriptors.
346	Please note that epoll sometimes generates spurious notifications, so you
347	need to use non-blocking I/O or other means to avoid blocking when no data
348	(or space) is available.
349		537
350	Best performance from this backend is achieved by not unregistering all	538	Best performance from this backend is achieved by not unregistering all
351	watchers for a file descriptor until it has been closed, if possible, i.e.	539	watchers for a file descriptor until it has been closed, if possible,
352	keep at least one watcher active per fd at all times.	540	i.e. keep at least one watcher active per fd at all times. Stopping and
		541	starting a watcher (without re-setting it) also usually doesn't cause
		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.
353		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.
		549
354	While nominally embeddeble in other event loops, this feature is broken in	550	While nominally embeddable in other event loops, this feature is broken in
355	all kernel versions tested so far.	551	all kernel versions tested so far.
		552
		553	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		554	C<EVBACKEND_POLL>.
356		555
357	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	556	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
358		557
359	Kqueue deserves special mention, as at the time of this writing, it	558	Kqueue deserves special mention, as at the time of this writing, it
360	was broken on all BSDs except NetBSD (usually it doesn't work reliably	559	was broken on all BSDs except NetBSD (usually it doesn't work reliably
361	with anything but sockets and pipes, except on Darwin, where of course	560	with anything but sockets and pipes, except on Darwin, where of course
362	it's completely useless). For this reason it's not being "autodetected"	561	it's completely useless). Unlike epoll, however, whose brokenness
		562	is by design, these kqueue bugs can (and eventually will) be fixed
		563	without API changes to existing programs. For this reason it's not being
363	unless you explicitly specify it explicitly in the flags (i.e. using	564	"auto-detected" unless you explicitly specify it in the flags (i.e. using
364	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)	565	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
365	system like NetBSD.	566	system like NetBSD.
366		567
367	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
368	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
369	the target platform). See C<ev_embed> watchers for more info.	570	the target platform). See C<ev_embed> watchers for more info.
370		571
371	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
372	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
373	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
374	cause an extra syscall 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
375	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
376	drops fds silently in similarly hard-to-detect cases.	578	drops fds silently in similarly hard-to-detect cases.
377		579
378	This backend usually performs well under most conditions.	580	This backend usually performs well under most conditions.
379		581
380	While nominally embeddable in other event loops, this doesn't work	582	While nominally embeddable in other event loops, this doesn't work
381	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
382	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
383	(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
384	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for	586	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
385	sockets.	587	also broken on OS X)) and, did I mention it, using it only for sockets.
		588
		589	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		590	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		591	C<NOTE_EOF>.
386		592
387	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	593	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
388		594
389	This is not implemented yet (and might never be, unless you send me an	595	This is not implemented yet (and might never be, unless you send me an
390	implementation). According to reports, C</dev/poll> only supports sockets	596	implementation). According to reports, C</dev/poll> only supports sockets
…		…
394	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	600	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
395		601
396	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,
397	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)).
398		604
399	Please note that solaris event ports can deliver a lot of spurious
400	notifications, so you need to use non-blocking I/O or other means to avoid
401	blocking when no data (or space) is available.
402
403	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
404	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
405	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	607	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
406	might perform better.	608	might perform better.
407		609
		610	On the positive side, this backend actually performed fully to
		611	specification in all tests and is fully embeddable, which is a rare feat
		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.
		624
		625	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		626	C<EVBACKEND_POLL>.
		627
408	=item C<EVBACKEND_ALL>	628	=item C<EVBACKEND_ALL>
409		629
410	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
411	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
412	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	632	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
413		633
414	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).
415		643
416	=back	644	=back
417		645
418	If one or more of these are ored into the flags value, then only these	646	If one or more of the backend flags are or'ed into the flags value,
419	backends will be tried (in the reverse order as given here). If none are	647	then only these backends will be tried (in the reverse order as listed
420	specified, most compiled-in backend will be tried, usually in reverse	648	here). If none are specified, all backends in C<ev_recommended_backends
421	order of their flag values :)	649	()> will be tried.
422
423	The most typical usage is like this:
424
425	if (!ev_default_loop (0))
426	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
427
428	Restrict libev to the select and poll backends, and do not allow
429	environment settings to be taken into account:
430
431	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
432
433	Use whatever libev has to offer, but make sure that kqueue is used if
434	available (warning, breaks stuff, best use only with your own private
435	event loop and only if you know the OS supports your types of fds):
436
437	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
438
439	=item struct ev_loop *ev_loop_new (unsigned int flags)
440
441	Similar to C<ev_default_loop>, but always creates a new event loop that is
442	always distinct from the default loop. Unlike the default loop, it cannot
443	handle signal and child watchers, and attempts to do so will be greeted by
444	undefined behaviour (or a failed assertion if assertions are enabled).
445		650
446	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.
447		652
448	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	653	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
449	if (!epoller)	654	if (!epoller)
450	fatal ("no epoll found here, maybe it hides under your chair");	655	fatal ("no epoll found here, maybe it hides under your chair");
451		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
452	=item ev_default_destroy ()	662	=item ev_loop_destroy (loop)
453		663
454	Destroys the default loop again (frees all memory and kernel state	664	Destroys an event loop object (frees all memory and kernel state
455	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
456	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
457	responsibility to either stop all watchers cleanly yoursef I<before>	667	responsibility to either stop all watchers cleanly yourself I<before>
458	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
459	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
460	for example).	670	for example).
461		671
462	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
463	this function, and related watchers (such as signal and child watchers)	673	handlers), will not be freed by this function, and related watchers (such
464	would need to be stopped manually.	674	as signal and child watchers) would need to be stopped manually.
465		675
466	In general it is not advisable to call this function except in the	676	This function is normally used on loop objects allocated by
467	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.
468	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>
469	C<ev_loop_new> and C<ev_loop_destroy>).	683	and C<ev_loop_destroy>.
470		684
471	=item ev_loop_destroy (loop)	685	=item ev_loop_fork (loop)
472		686
473	Like C<ev_default_destroy>, but destroys an event loop created by an	687	This function sets a flag that causes subsequent C<ev_run> iterations
474	earlier call to C<ev_loop_new>.
475
476	=item ev_default_fork ()
477
478	This function reinitialises the kernel state for backends that have	688	to reinitialise the kernel state for backends that have one. Despite
479	one. Despite the name, you can call it anytime, but it makes most sense	689	the name, you can call it anytime you are allowed to start or stop
480	after forking, in either the parent or child process (or both, but that	690	watchers (except inside an C<ev_prepare> callback), but it makes most
481	again makes little sense).	691	sense after forking, in the child process. You I<must> call it (or use
		692	C<EVFLAG_FORKCHECK>) in the child before resuming or calling C<ev_run>.
482		693
483	You I<must> call this function in the child process after forking if and	694	Again, you I<have> to call it on I<any> loop that you want to re-use after
484	only if you want to use the event library in both processes. If you just	695	a fork, I<even if you do not plan to use the loop in the parent>. This is
485	fork+exec, you don't have to call it.	696	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		697	during fork.
		698
		699	On the other hand, you only need to call this function in the child
		700	process if and only if you want to use the event loop in the child. If
		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).
486		705
487	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
488	it just in case after a fork. To make this easy, the function will fit in	707	it just in case after a fork.
489	quite nicely into a call to C<pthread_atfork>:
490		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	...
491	pthread_atfork (0, 0, ev_default_fork);	719	pthread_atfork (0, 0, post_fork_child);
492		720
493	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use	721	=item int ev_is_default_loop (loop)
494	without calling this function, so if you force one of those backends you
495	do not need to care.
496		722
497	=item ev_loop_fork (loop)	723	Returns true when the given loop is, in fact, the default loop, and false
		724	otherwise.
498		725
499	Like C<ev_default_fork>, but acts on an event loop created by
500	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
501	after fork, and how you do this is entirely your own problem.
502
503	=item unsigned int ev_loop_count (loop)	726	=item unsigned int ev_iteration (loop)
504		727
505	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
506	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>
507	happily wraps around with enough iterations.	730	and happily wraps around with enough iterations.
508		731
509	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
510	"ticks" the number of loop iterations), as it roughly corresponds with	733	"ticks" the number of loop iterations), as it roughly corresponds with
511	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.
512		750
513	=item unsigned int ev_backend (loop)	751	=item unsigned int ev_backend (loop)
514		752
515	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
516	use.	754	use.
…		…
521	received events and started processing them. This timestamp does not	759	received events and started processing them. This timestamp does not
522	change as long as callbacks are being processed, and this is also the base	760	change as long as callbacks are being processed, and this is also the base
523	time used for relative timers. You can treat it as the timestamp of the	761	time used for relative timers. You can treat it as the timestamp of the
524	event occurring (or more correctly, libev finding out about it).	762	event occurring (or more correctly, libev finding out about it).
525		763
		764	=item ev_now_update (loop)
		765
		766	Establishes the current time by querying the kernel, updating the time
		767	returned by C<ev_now ()> in the progress. This is a costly operation and
		768	is usually done automatically within C<ev_run ()>.
		769
		770	This function is rarely useful, but when some event callback runs for a
		771	very long time without entering the event loop, updating libev's idea of
		772	the current time is a good idea.
		773
		774	See also L</The special problem of time updates> in the C<ev_timer> section.
		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
526	=item ev_loop (loop, int flags)	802	=item bool ev_run (loop, int flags)
527		803
528	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
529	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
530	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>.
531		809
532	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
533	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.
534		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
535	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
536	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
537	finished (especially in interactive programs), but having a program that	820	finished (especially in interactive programs), but having a program
538	automatically loops as long as it has to and no longer by virtue of	821	that automatically loops as long as it has to and no longer by virtue
539	relying on its watchers stopping correctly is a thing of beauty.	822	of relying on its watchers stopping correctly, that is truly a thing of
		823	beauty.
540		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
541	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
542	those events and any outstanding ones, but will not block your process in	831	those events and any already outstanding ones, but will not wait and
543	case there are no events and will return after one iteration of the loop.	832	block your process in case there are no events and will return after one
		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.
544		835
545	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
546	neccessary) and will handle those and any outstanding ones. It will block	837	necessary) and will handle those and any already outstanding ones. It
547	your process until at least one new event arrives, and will return after	838	will block your process until at least one new event arrives (which could
548	one iteration of the loop. This is useful if you are waiting for some	839	be an event internal to libev itself, so there is no guarantee that a
549	external event in conjunction with something not expressible using other	840	user-registered callback will be called), and will return after one
		841	iteration of the loop.
		842
		843	This is useful if you are waiting for some external event in conjunction
		844	with something not expressible using other libev watchers (i.e. "roll your
550	libev watchers. 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
551	usually a better approach for this kind of thing.	846	usually a better approach for this kind of thing.
552		847
553	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):
554		851
		852	- Increment loop depth.
		853	- Reset the ev_break status.
555	- Before the first iteration, call any pending watchers.	854	- Before the first iteration, call any pending watchers.
556	* If there are no active watchers (reference count is zero), return.	855	LOOP:
557	- Queue all prepare watchers and then call all outstanding watchers.	856	- If EVFLAG_FORKCHECK was used, check for a fork.
		857	- If a fork was detected (by any means), queue and call all fork watchers.
		858	- Queue and call all prepare watchers.
		859	- If ev_break was called, goto FINISH.
558	- If we have been forked, recreate the kernel state.	860	- If we have been forked, detach and recreate the kernel state
		861	as to not disturb the other process.
559	- Update the kernel state with all outstanding changes.	862	- Update the kernel state with all outstanding changes.
560	- Update the "event loop time".	863	- Update the "event loop time" (ev_now ()).
561	- Calculate for how long to block.	864	- Calculate for how long to sleep or block, if at all
		865	(active idle watchers, EVRUN_NOWAIT or not having
		866	any active watchers at all will result in not sleeping).
		867	- Sleep if the I/O and timer collect interval say so.
		868	- Increment loop iteration counter.
562	- Block the process, waiting for any events.	869	- Block the process, waiting for any events.
563	- Queue all outstanding I/O (fd) events.	870	- Queue all outstanding I/O (fd) events.
564	- Update the "event loop time" and do time jump handling.	871	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
565	- Queue all outstanding timers.	872	- Queue all expired timers.
566	- Queue all outstanding periodics.	873	- Queue all expired periodics.
567	- If no events are pending now, queue all idle watchers.	874	- Queue all idle watchers with priority higher than that of pending events.
568	- Queue all check watchers.	875	- Queue all check watchers.
569	- 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).
570	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
571	be handled here by queueing them when their watcher gets executed.	878	be handled here by queueing them when their watcher gets executed.
572	- 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
573	were used, return, otherwise continue with step *.	880	were used, or there are no active watchers, goto FINISH, otherwise
		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.
574		886
575	Example: Queue some jobs and then loop until no events are outsanding	887	Example: Queue some jobs and then loop until no events are outstanding
576	anymore.	888	anymore.
577		889
578	... queue jobs here, make sure they register event watchers as long	890	... queue jobs here, make sure they register event watchers as long
579	... 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..)
580	ev_loop (my_loop, 0);	892	ev_run (my_loop, 0);
581	... jobs done. yeah!	893	... jobs done or somebody called break. yeah!
582		894
583	=item ev_unloop (loop, how)	895	=item ev_break (loop, how)
584		896
585	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
586	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
587	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
588	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.
		901
		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.
589		906
590	=item ev_ref (loop)	907	=item ev_ref (loop)
591		908
592	=item ev_unref (loop)	909	=item ev_unref (loop)
593		910
594	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
595	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
596	count is nonzero, C<ev_loop> will not return on its own. If you have	913	count is nonzero, C<ev_run> will not return on its own.
597	a watcher you never unregister that should not keep C<ev_loop> from	914
598	returning, ev_unref() after starting, and ev_ref() before stopping it. For	915	This is useful when you have a watcher that you never intend to
		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>
		918	before stopping it.
		919
599	example, libev itself uses this for its internal signal pipe: It is not	920	As an example, libev itself uses this for its internal signal pipe: It
600	visible to the libev user and should not keep C<ev_loop> from exiting if	921	is not visible to the libev user and should not keep C<ev_run> from
601	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
602	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
603	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
		925	before stop> (but only if the watcher wasn't active before, or was active
		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).
604		929
605	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>
606	running when nothing else is active.	931	running when nothing else is active.
607		932
608	struct ev_signal exitsig;	933	ev_signal exitsig;
609	ev_signal_init (&exitsig, sig_cb, SIGINT);	934	ev_signal_init (&exitsig, sig_cb, SIGINT);
610	ev_signal_start (loop, &exitsig);	935	ev_signal_start (loop, &exitsig);
611	evf_unref (loop);	936	ev_unref (loop);
612		937
613	Example: For some weird reason, unregister the above signal handler again.	938	Example: For some weird reason, unregister the above signal handler again.
614		939
615	ev_ref (loop);	940	ev_ref (loop);
616	ev_signal_stop (loop, &exitsig);	941	ev_signal_stop (loop, &exitsig);
617		942
618	=item ev_set_io_collect_interval (loop, ev_tstamp interval)	943	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
619		944
620	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)	945	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
621		946
622	These advanced functions influence the time that libev will spend waiting	947	These advanced functions influence the time that libev will spend waiting
623	for events. Both are by default C<0>, meaning that libev will try to	948	for events. Both time intervals are by default C<0>, meaning that libev
624	invoke timer/periodic callbacks and I/O callbacks with minimum latency.	949	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		950	latency.
625		951
626	Setting these to a higher value (the C<interval> I<must> be >= C<0>)	952	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
627	allows libev to delay invocation of I/O and timer/periodic callbacks to	953	allows libev to delay invocation of I/O and timer/periodic callbacks
628	increase efficiency of loop iterations.	954	to increase efficiency of loop iterations (or to increase power-saving
		955	opportunities).
629		956
630	The background is that sometimes your program runs just fast enough to	957	The idea is that sometimes your program runs just fast enough to handle
631	handle one (or very few) event(s) per loop iteration. While this makes	958	one (or very few) event(s) per loop iteration. While this makes the
632	the program responsive, it also wastes a lot of CPU time to poll for new	959	program responsive, it also wastes a lot of CPU time to poll for new
633	events, especially with backends like C<select ()> which have a high	960	events, especially with backends like C<select ()> which have a high
634	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.
635		962
636	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
637	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,
638	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
639	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
640	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).
641		971
642	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
643	to spend more time collecting timeouts, at the expense of increased	973	to spend more time collecting timeouts, at the expense of increased
644	latency (the watcher callback will be called later). C<ev_io> watchers	974	latency/jitter/inexactness (the watcher callback will be called
645	will not be affected. Setting this to a non-null value will not introduce	975	later). C<ev_io> watchers will not be affected. Setting this to a non-null
646	any overhead in libev.	976	value will not introduce any overhead in libev.
647		977
648	Many (busy) programs can usually benefit by setting the io collect	978	Many (busy) programs can usually benefit by setting the I/O collect
649	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
650	interactive servers (of course not for games), likewise for timeouts. It	980	interactive servers (of course not for games), likewise for timeouts. It
651	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>,
652	as this approsaches 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).
		987
		988	Setting the I<timeout collect interval> can improve the opportunity for
		989	saving power, as the program will "bundle" timer callback invocations that
		990	are "near" in time together, by delaying some, thus reducing the number of
		991	times the process sleeps and wakes up again. Another useful technique to
		992	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		993	they fire on, say, one-second boundaries only.
		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
		1070	=item ev_verify (loop)
		1071
		1072	This function only does something when C<EV_VERIFY> support has been
		1073	compiled in, which is the default for non-minimal builds. It tries to go
		1074	through all internal structures and checks them for validity. If anything
		1075	is found to be inconsistent, it will print an error message to standard
		1076	error and call C<abort ()>.
		1077
		1078	This can be used to catch bugs inside libev itself: under normal
		1079	circumstances, this function will never abort as of course libev keeps its
		1080	data structures consistent.
653		1081
654	=back	1082	=back
655		1083
656		1084
657	=head1 ANATOMY OF A WATCHER	1085	=head1 ANATOMY OF A WATCHER
658		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
659	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
660	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
661	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:
662		1095
663	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)
664	{	1097	{
665	ev_io_stop (w);	1098	ev_io_stop (w);
666	ev_unloop (loop, EVUNLOOP_ALL);	1099	ev_break (loop, EVBREAK_ALL);
667	}	1100	}
668		1101
669	struct ev_loop *loop = ev_default_loop (0);	1102	struct ev_loop *loop = ev_default_loop (0);
		1103
670	struct ev_io stdin_watcher;	1104	ev_io stdin_watcher;
		1105
671	ev_init (&stdin_watcher, my_cb);	1106	ev_init (&stdin_watcher, my_cb);
672	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1107	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
673	ev_io_start (loop, &stdin_watcher);	1108	ev_io_start (loop, &stdin_watcher);
		1109
674	ev_loop (loop, 0);	1110	ev_run (loop, 0);
675		1111
676	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
677	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
678	although this can sometimes be quite valid).	1114	stack).
679		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
680	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
681	(watcher *, callback)>, which expects a callback to be provided. This	1120	*, callback)>, which expects a callback to be provided. This callback is
682	callback gets invoked each time the event occurs (or, in the case of io	1121	invoked each time the event occurs (or, in the case of I/O watchers, each
683	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
684	is readable and/or writable).	1123	and/or writable).
685		1124
686	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 *, ...) >>
687	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
688	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<<
689	(watcher *, callback, ...) >>.	1128	ev_TYPE_init (watcher *, callback, ...) >>.
690		1129
691	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
692	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
693	*) >>), 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
694	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1133	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
695		1134
696	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
697	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
698	reinitialise it or call its C<set> macro.	1137	reinitialise it or call its C<ev_TYPE_set> macro.
699		1138
700	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
701	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
702	third argument.	1141	third argument.
703		1142
…		…
712	=item C<EV_WRITE>	1151	=item C<EV_WRITE>
713		1152
714	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
715	writable.	1154	writable.
716		1155
717	=item C<EV_TIMEOUT>	1156	=item C<EV_TIMER>
718		1157
719	The C<ev_timer> watcher has timed out.	1158	The C<ev_timer> watcher has timed out.
720		1159
721	=item C<EV_PERIODIC>	1160	=item C<EV_PERIODIC>
722		1161
…		…
740		1179
741	=item C<EV_PREPARE>	1180	=item C<EV_PREPARE>
742		1181
743	=item C<EV_CHECK>	1182	=item C<EV_CHECK>
744		1183
745	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
746	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)
747	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
748	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
749	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
750	(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
751	C<ev_loop> from blocking).	1195	blocking).
752		1196
753	=item C<EV_EMBED>	1197	=item C<EV_EMBED>
754		1198
755	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.
756		1200
757	=item C<EV_FORK>	1201	=item C<EV_FORK>
758		1202
759	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
760	C<ev_fork>).	1204	C<ev_fork>).
761		1205
		1206	=item C<EV_CLEANUP>
		1207
		1208	The event loop is about to be destroyed (see C<ev_cleanup>).
		1209
		1210	=item C<EV_ASYNC>
		1211
		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>).
		1218
762	=item C<EV_ERROR>	1219	=item C<EV_ERROR>
763		1220
764	An unspecified error has occured, the watcher has been stopped. This might	1221	An unspecified error has occurred, the watcher has been stopped. This might
765	happen because the watcher could not be properly started because libev	1222	happen because the watcher could not be properly started because libev
766	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
767	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
768	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.
769		1230
770	Libev will usually signal a few "dummy" events together with an error,	1231	Libev will usually signal a few "dummy" events together with an error, for
771	for example it might indicate that a fd is readable or writable, and if	1232	example it might indicate that a fd is readable or writable, and if your
772	your callbacks is well-written it can just attempt the operation and cope	1233	callbacks is well-written it can just attempt the operation and cope with
773	with the error from read() or write(). This will not work in multithreaded	1234	the error from read() or write(). This will not work in multi-threaded
774	programs, though, so beware.	1235	programs, though, as the fd could already be closed and reused for another
		1236	thing, so beware.
775		1237
776	=back	1238	=back
777		1239
778	=head2 GENERIC WATCHER FUNCTIONS	1240	=head2 GENERIC WATCHER FUNCTIONS
779
780	In the following description, C<TYPE> stands for the watcher type,
781	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
782		1241
783	=over 4	1242	=over 4
784		1243
785	=item C<ev_init> (ev_TYPE *watcher, callback)	1244	=item C<ev_init> (ev_TYPE *watcher, callback)
786		1245
…		…
792	which rolls both calls into one.	1251	which rolls both calls into one.
793		1252
794	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
795	(or never started) and there are no pending events outstanding.	1254	(or never started) and there are no pending events outstanding.
796		1255
797	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,
798	int revents)>.	1257	int revents)>.
799		1258
		1259	Example: Initialise an C<ev_io> watcher in two steps.
		1260
		1261	ev_io w;
		1262	ev_init (&w, my_cb);
		1263	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1264
800	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1265	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
801		1266
802	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
803	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
804	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
805	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
806	difference to the C<ev_init> macro).	1271	difference to the C<ev_init> macro).
807		1272
808	Although some watcher types do not have type-specific arguments	1273	Although some watcher types do not have type-specific arguments
809	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1274	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
810		1275
		1276	See C<ev_init>, above, for an example.
		1277
811	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1278	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
812		1279
813	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1280	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
814	calls into a single call. This is the most convinient method to initialise	1281	calls into a single call. This is the most convenient method to initialise
815	a watcher. The same limitations apply, of course.	1282	a watcher. The same limitations apply, of course.
816		1283
		1284	Example: Initialise and set an C<ev_io> watcher in one step.
		1285
		1286	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1287
817	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1288	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
818		1289
819	Starts (activates) the given watcher. Only active watchers will receive	1290	Starts (activates) the given watcher. Only active watchers will receive
820	events. If the watcher is already active nothing will happen.	1291	events. If the watcher is already active nothing will happen.
821		1292
		1293	Example: Start the C<ev_io> watcher that is being abused as example in this
		1294	whole section.
		1295
		1296	ev_io_start (EV_DEFAULT_UC, &w);
		1297
822	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1298	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
823		1299
824	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
825	status. It is possible that stopped watchers are pending (for example,	1303	It is possible that stopped watchers are pending - for example,
826	non-repeating timers are being stopped when they become pending), but	1304	non-repeating timers are being stopped when they become pending - but
827	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
828	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
829	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.
830		1308
831	=item bool ev_is_active (ev_TYPE *watcher)	1309	=item bool ev_is_active (ev_TYPE *watcher)
832		1310
833	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
834	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
…		…
845		1323
846	=item callback ev_cb (ev_TYPE *watcher)	1324	=item callback ev_cb (ev_TYPE *watcher)
847		1325
848	Returns the callback currently set on the watcher.	1326	Returns the callback currently set on the watcher.
849		1327
850	=item ev_cb_set (ev_TYPE *watcher, callback)	1328	=item ev_set_cb (ev_TYPE *watcher, callback)
851		1329
852	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
853	(modulo threads).	1331	(modulo threads).
854		1332
855	=item ev_set_priority (ev_TYPE *watcher, priority)	1333	=item ev_set_priority (ev_TYPE *watcher, int priority)
856		1334
857	=item int ev_priority (ev_TYPE *watcher)	1335	=item int ev_priority (ev_TYPE *watcher)
858		1336
859	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
860	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>
861	(default: C<-2>). Pending watchers with higher priority will be invoked	1339	(default: C<-2>). Pending watchers with higher priority will be invoked
862	before watchers with lower priority, but priority will not keep watchers	1340	before watchers with lower priority, but priority will not keep watchers
863	from being executed (except for C<ev_idle> watchers).	1341	from being executed (except for C<ev_idle> watchers).
864		1342
865	This means that priorities are I<only> used for ordering callback
866	invocation after new events have been received. This is useful, for
867	example, to reduce latency after idling, or more often, to bind two
868	watchers on the same event and make sure one is called first.
869
870	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
871	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.
872		1345
873	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
874	pending.	1347	pending.
875		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
876	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
877	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 :).
878		1355
879	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
880	fine, as long as you do not mind that the priority value you query might	1357	priorities.
881	or might not have been adjusted to be within valid range.
882		1358
883	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1359	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
884		1360
885	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
886	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
887	can deal with that fact.	1363	can deal with that fact, as both are simply passed through to the
		1364	callback.
888		1365
889	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1366	=item int ev_clear_pending (loop, ev_TYPE *watcher)
890		1367
891	If the watcher is pending, this function returns clears its pending status	1368	If the watcher is pending, this function clears its pending status and
892	and returns its C<revents> bitset (as if its callback was invoked). If the	1369	returns its C<revents> bitset (as if its callback was invoked). If the
893	watcher isn't pending it does nothing and returns C<0>.	1370	watcher isn't pending it does nothing and returns C<0>.
894		1371
		1372	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1373	callback to be invoked, which can be accomplished with this function.
		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
895	=back	1389	=back
896		1390
		1391	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
		1392	OWN COMPOSITE WATCHERS> idioms.
897		1393
898	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1394	=head2 WATCHER STATES
899		1395
900	Each watcher has, by default, a member C<void *data> that you can change	1396	There are various watcher states mentioned throughout this manual -
901	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
902	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
903	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".
904	member, you can also "subclass" the watcher type and provide your own
905	data:
906		1400
907	struct my_io	1401	=over 4
908	{
909	struct ev_io io;
910	int otherfd;
911	void *somedata;
912	struct whatever *mostinteresting;
913	}
914		1402
915	And since your callback will be called with a pointer to the watcher, you	1403	=item initialised
916	can cast it back to your own type:
917		1404
918	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1405	Before a watcher can be registered with the event loop it has to be
919	{	1406	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
920	struct my_io *w = (struct my_io *)w_;	1407	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
921	...
922	}
923		1408
924	More interesting and less C-conformant ways of casting your callback type	1409	In this state it is simply some block of memory that is suitable for
925	instead have been omitted.	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.
926		1413
927	Another common scenario is having some data structure with multiple	1414	=item started/running/active
928	watchers:
929		1415
930	struct my_biggy	1416	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
931	{	1417	property of the event loop, and is actively waiting for events. While in
932	int some_data;	1418	this state it cannot be accessed (except in a few documented ways), moved,
933	ev_timer t1;	1419	freed or anything else - the only legal thing is to keep a pointer to it,
934	ev_timer t2;	1420	and call libev functions on it that are documented to work on active watchers.
935	}
936		1421
937	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1422	=item pending
938	you need to use C<offsetof>:
939		1423
940	#include <stddef.h>	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.
941		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
942	static void	1524	static void
943	t1_cb (EV_P_ struct ev_timer *w, int revents)	1525	io_cb (EV_P_ ev_io *w, int revents)
944	{	1526	{
945	struct my_biggy big = (struct my_biggy *	1527	// stop the I/O watcher, we received the event, but
946	(((char *)w) - offsetof (struct my_biggy, t1));	1528	// are not yet ready to handle it.
		1529	ev_io_stop (EV_A_ w);
		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);
947	}	1535	}
948		1536
949	static void	1537	static void
950	t2_cb (EV_P_ struct ev_timer *w, int revents)	1538	idle_cb (EV_P_ ev_idle *w, int revents)
951	{	1539	{
952	struct my_biggy big = (struct my_biggy *	1540	// actual processing
953	(((char *)w) - offsetof (struct my_biggy, t2));	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);
954	}	1546	}
		1547
		1548	// initialisation
		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);
		1552
		1553	In the "real" world, it might also be beneficial to start a timer, so that
		1554	low-priority connections can not be locked out forever under load. This
		1555	enables your program to keep a lower latency for important connections
		1556	during short periods of high load, while not completely locking out less
		1557	important ones.
955		1558
956		1559
957	=head1 WATCHER TYPES	1560	=head1 WATCHER TYPES
958		1561
959	This section describes each watcher in detail, but will not repeat	1562	This section describes each watcher in detail, but will not repeat
…		…
983	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
984	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
985	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
986	required if you know what you are doing).	1589	required if you know what you are doing).
987		1590
988	You have to be careful with dup'ed file descriptors, though. Some backends
989	(the linux epoll backend is a notable example) cannot handle dup'ed file
990	descriptors correctly if you register interest in two or more fds pointing
991	to the same underlying file/socket/etc. description (that is, they share
992	the same underlying "file open").
993
994	If you must do this, then force the use of a known-to-be-good backend
995	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
996	C<EVBACKEND_POLL>).
997
998	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
999	receive "spurious" readyness notifications, that is your callback might	1592	receive "spurious" readiness notifications, that is, your callback might
1000	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
1001	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
1002	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
1003	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
1004	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1005	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1597	preferable to a program hanging until some data arrives.
1006		1598
1007	If you cannot run the fd in non-blocking mode (for example you should not	1599	If you cannot run the fd in non-blocking mode (for example you should
1008	play around with an Xlib connection), then you have to seperately re-test	1600	not play around with an Xlib connection), then you have to separately
1009	whether a file descriptor is really ready with a known-to-be good interface	1601	re-test whether a file descriptor is really ready with a known-to-be good
1010	such as poll (fortunately in our Xlib example, Xlib already does this on	1602	interface such as poll (fortunately in the case of Xlib, it already does
1011	its own, so its quite safe to use).	1603	this on its own, so its quite safe to use). Some people additionally
		1604	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1605	indefinitely.
		1606
		1607	But really, best use non-blocking mode.
1012		1608
1013	=head3 The special problem of disappearing file descriptors	1609	=head3 The special problem of disappearing file descriptors
1014		1610
1015	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1611	Some backends (e.g. kqueue, epoll) need to be told about closing a file
1016	descriptor (either by calling C<close> explicitly or by any other means,	1612	descriptor (either due to calling C<close> explicitly or any other means,
1017	such as C<dup>). The reason is that you register interest in some file	1613	such as C<dup2>). The reason is that you register interest in some file
1018	descriptor, but when it goes away, the operating system will silently drop	1614	descriptor, but when it goes away, the operating system will silently drop
1019	this interest. If another file descriptor with the same number then is	1615	this interest. If another file descriptor with the same number then is
1020	registered with libev, there is no efficient way to see that this is, in	1616	registered with libev, there is no efficient way to see that this is, in
1021	fact, a different file descriptor.	1617	fact, a different file descriptor.
1022		1618
…		…
1032	optimisations to libev.	1628	optimisations to libev.
1033		1629
1034	=head3 The special problem of dup'ed file descriptors	1630	=head3 The special problem of dup'ed file descriptors
1035		1631
1036	Some backends (e.g. epoll), cannot register events for file descriptors,	1632	Some backends (e.g. epoll), cannot register events for file descriptors,
1037	but only events for the underlying file descriptions. That menas when you	1633	but only events for the underlying file descriptions. That means when you
1038	have C<dup ()>'ed file descriptors and register events for them, only one	1634	have C<dup ()>'ed file descriptors or weirder constellations, and register
1039	file descriptor might actually receive events.	1635	events for them, only one file descriptor might actually receive events.
1040		1636
1041	There is no workaorund possible except not registering events	1637	There is no workaround possible except not registering events
1042	for potentially C<dup ()>'ed file descriptors or to resort to	1638	for potentially C<dup ()>'ed file descriptors, or to resort to
1043	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1639	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		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.
1044		1673
1045	=head3 The special problem of fork	1674	=head3 The special problem of fork
1046		1675
1047	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
1048	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
1049	it in the child.	1678	it in the child if you want to continue to use it in the child.
1050		1679
1051	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
1052	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
1053	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1682	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1054	C<EVBACKEND_POLL>.
1055		1683
		1684	=head3 The special problem of SIGPIPE
		1685
		1686	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1687	when writing to a pipe whose other end has been closed, your program gets
		1688	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1689	this is sensible behaviour, for daemons, this is usually undesirable.
		1690
		1691	So when you encounter spurious, unexplained daemon exits, make sure you
		1692	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1693	somewhere, as that would have given you a big clue).
		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.
1056		1733
1057	=head3 Watcher-Specific Functions	1734	=head3 Watcher-Specific Functions
1058		1735
1059	=over 4	1736	=over 4
1060		1737
1061	=item ev_io_init (ev_io *, callback, int fd, int events)	1738	=item ev_io_init (ev_io *, callback, int fd, int events)
1062		1739
1063	=item ev_io_set (ev_io *, int fd, int events)	1740	=item ev_io_set (ev_io *, int fd, int events)
1064		1741
1065	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1742	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
1066	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1743	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
1067	C<EV_READ | EV_WRITE> to receive the given events.	1744	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
1068		1745
1069	=item int fd [read-only]	1746	=item int fd [read-only]
1070		1747
1071	The file descriptor being watched.	1748	The file descriptor being watched.
1072		1749
1073	=item int events [read-only]	1750	=item int events [read-only]
1074		1751
1075	The events being watched.	1752	The events being watched.
1076		1753
1077	=back	1754	=back
		1755
		1756	=head3 Examples
1078		1757
1079	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
1080	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
1081	attempt to read a whole line in the callback.	1760	attempt to read a whole line in the callback.
1082		1761
1083	static void	1762	static void
1084	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)
1085	{	1764	{
1086	ev_io_stop (loop, w);	1765	ev_io_stop (loop, w);
1087	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1766	.. read from stdin here (or from w->fd) and handle any I/O errors
1088	}	1767	}
1089		1768
1090	...	1769	...
1091	struct ev_loop *loop = ev_default_init (0);	1770	struct ev_loop *loop = ev_default_init (0);
1092	struct ev_io stdin_readable;	1771	ev_io stdin_readable;
1093	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);
1094	ev_io_start (loop, &stdin_readable);	1773	ev_io_start (loop, &stdin_readable);
1095	ev_loop (loop, 0);	1774	ev_run (loop, 0);
1096		1775
1097		1776
1098	=head2 C<ev_timer> - relative and optionally repeating timeouts	1777	=head2 C<ev_timer> - relative and optionally repeating timeouts
1099		1778
1100	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
1101	given time, and optionally repeating in regular intervals after that.	1780	given time, and optionally repeating in regular intervals after that.
1102		1781
1103	The timers are based on real time, that is, if you register an event that	1782	The timers are based on real time, that is, if you register an event that
1104	times out after an hour and you reset your system clock to last years	1783	times out after an hour and you reset your system clock to January last
1105	time, it will still time out after (roughly) and hour. "Roughly" because	1784	year, it will still time out after (roughly) one hour. "Roughly" because
1106	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1785	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1107	monotonic clock option helps a lot here).	1786	monotonic clock option helps a lot here).
		1787
		1788	The callback is guaranteed to be invoked only I<after> its timeout has
		1789	passed (not I<at>, so on systems with very low-resolution clocks this
		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.
		2021
		2022	=head3 The special problem of time updates
		2023
		2024	Establishing the current time is a costly operation (it usually takes
		2025	at least one system call): EV therefore updates its idea of the current
		2026	time only before and after C<ev_run> collects new events, which causes a
		2027	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		2028	lots of events in one iteration.
1108		2029
1109	The relative timeouts are calculated relative to the C<ev_now ()>	2030	The relative timeouts are calculated relative to the C<ev_now ()>
1110	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
1111	of the event triggering whatever timeout you are modifying/starting. If	2032	of the event triggering whatever timeout you are modifying/starting. If
1112	you suspect event processing to be delayed and you I<need> to base the timeout	2033	you suspect event processing to be delayed and you I<need> to base the
1113	on the current time, use something like this to adjust for this:	2034	timeout on the current time, use something like the following to adjust
		2035	for it:
1114		2036
1115	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2037	ev_timer_set (&timer, after + (ev_time () - ev_now ()), 0.);
1116		2038
1117	The callback is guarenteed to be invoked only when its timeout has passed,	2039	If the event loop is suspended for a long time, you can also force an
1118	but if multiple timers become ready during the same loop iteration then	2040	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1119	order of execution is undefined.	2041	()>, although that will push the event time of all outstanding events
		2042	further into the future.
		2043
		2044	=head3 The special problem of unsynchronised clocks
		2045
		2046	Modern systems have a variety of clocks - libev itself uses the normal
		2047	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2048	jumps).
		2049
		2050	Neither of these clocks is synchronised with each other or any other clock
		2051	on the system, so C<ev_time ()> might return a considerably different time
		2052	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2053	a call to C<gettimeofday> might return a second count that is one higher
		2054	than a directly following call to C<time>.
		2055
		2056	The moral of this is to only compare libev-related timestamps with
		2057	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2058	a second or so.
		2059
		2060	One more problem arises due to this lack of synchronisation: if libev uses
		2061	the system monotonic clock and you compare timestamps from C<ev_time>
		2062	or C<ev_now> from when you started your timer and when your callback is
		2063	invoked, you will find that sometimes the callback is a bit "early".
		2064
		2065	This is because C<ev_timer>s work in real time, not wall clock time, so
		2066	libev makes sure your callback is not invoked before the delay happened,
		2067	I<measured according to the real time>, not the system clock.
		2068
		2069	If your timeouts are based on a physical timescale (e.g. "time out this
		2070	connection after 100 seconds") then this shouldn't bother you as it is
		2071	exactly the right behaviour.
		2072
		2073	If you want to compare wall clock/system timestamps to your timers, then
		2074	you need to use C<ev_periodic>s, as these are based on the wall clock
		2075	time, where your comparisons will always generate correct results.
		2076
		2077	=head3 The special problems of suspended animation
		2078
		2079	When you leave the server world it is quite customary to hit machines that
		2080	can suspend/hibernate - what happens to the clocks during such a suspend?
		2081
		2082	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		2083	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		2084	to run until the system is suspended, but they will not advance while the
		2085	system is suspended. That means, on resume, it will be as if the program
		2086	was frozen for a few seconds, but the suspend time will not be counted
		2087	towards C<ev_timer> when a monotonic clock source is used. The real time
		2088	clock advanced as expected, but if it is used as sole clocksource, then a
		2089	long suspend would be detected as a time jump by libev, and timers would
		2090	be adjusted accordingly.
		2091
		2092	I would not be surprised to see different behaviour in different between
		2093	operating systems, OS versions or even different hardware.
		2094
		2095	The other form of suspend (job control, or sending a SIGSTOP) will see a
		2096	time jump in the monotonic clocks and the realtime clock. If the program
		2097	is suspended for a very long time, and monotonic clock sources are in use,
		2098	then you can expect C<ev_timer>s to expire as the full suspension time
		2099	will be counted towards the timers. When no monotonic clock source is in
		2100	use, then libev will again assume a timejump and adjust accordingly.
		2101
		2102	It might be beneficial for this latter case to call C<ev_suspend>
		2103	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		2104	deterministic behaviour in this case (you can do nothing against
		2105	C<SIGSTOP>).
1120		2106
1121	=head3 Watcher-Specific Functions and Data Members	2107	=head3 Watcher-Specific Functions and Data Members
1122		2108
1123	=over 4	2109	=over 4
1124		2110
1125	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2111	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1126		2112
1127	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2113	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1128		2114
1129	Configure the timer to trigger after C<after> seconds. If C<repeat> is	2115	Configure the timer to trigger after C<after> seconds. If C<repeat>
1130	C<0.>, then it will automatically be stopped. If it is positive, then the	2116	is C<0.>, then it will automatically be stopped once the timeout is
1131	timer will automatically be configured to trigger again C<repeat> seconds	2117	reached. If it is positive, then the timer will automatically be
1132	later, again, and again, until stopped manually.	2118	configured to trigger again C<repeat> seconds later, again, and again,
		2119	until stopped manually.
1133		2120
1134	The timer itself will do a best-effort at avoiding drift, that is, if you	2121	The timer itself will do a best-effort at avoiding drift, that is, if
1135	configure a timer to trigger every 10 seconds, then it will trigger at	2122	you configure a timer to trigger every 10 seconds, then it will normally
1136	exactly 10 second intervals. If, however, your program cannot keep up with	2123	trigger at exactly 10 second intervals. If, however, your program cannot
1137	the timer (because it takes longer than those 10 seconds to do stuff) the	2124	keep up with the timer (because it takes longer than those 10 seconds to
1138	timer will not fire more than once per event loop iteration.	2125	do stuff) the timer will not fire more than once per event loop iteration.
1139		2126
1140	=item ev_timer_again (loop)	2127	=item ev_timer_again (loop, ev_timer *)
1141		2128
1142	This will act as if the timer timed out and restart it again if it is	2129	This will act as if the timer timed out, and restarts it again if it is
1143	repeating. The exact semantics are:	2130	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2131	timeout to the C<repeat> value and calling C<ev_timer_start>.
1144		2132
		2133	The exact semantics are as in the following rules, all of which will be
		2134	applied to the watcher:
		2135
		2136	=over 4
		2137
1145	If the timer is pending, its pending status is cleared.	2138	=item If the timer is pending, the pending status is always cleared.
1146		2139
1147	If the timer is started but nonrepeating, stop it (as if it timed out).	2140	=item If the timer is started but non-repeating, stop it (as if it timed
		2141	out, without invoking it).
1148		2142
1149	If the timer is repeating, either start it if necessary (with the	2143	=item If the timer is repeating, make the C<repeat> value the new timeout
1150	C<repeat> value), or reset the running timer to the C<repeat> value.	2144	and start the timer, if necessary.
1151		2145
1152	This sounds a bit complicated, but here is a useful and typical	2146	=back
1153	example: Imagine you have a tcp connection and you want a so-called idle
1154	timeout, that is, you want to be called when there have been, say, 60
1155	seconds of inactivity on the socket. The easiest way to do this is to
1156	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1157	C<ev_timer_again> each time you successfully read or write some data. If
1158	you go into an idle state where you do not expect data to travel on the
1159	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1160	automatically restart it if need be.
1161		2147
1162	That means you can ignore the C<after> value and C<ev_timer_start>	2148	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
1163	altogether and only ever use the C<repeat> value and C<ev_timer_again>:	2149	usage example.
1164		2150
1165	ev_timer_init (timer, callback, 0., 5.);	2151	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1166	ev_timer_again (loop, timer);
1167	...
1168	timer->again = 17.;
1169	ev_timer_again (loop, timer);
1170	...
1171	timer->again = 10.;
1172	ev_timer_again (loop, timer);
1173		2152
1174	This is more slightly efficient then stopping/starting the timer each time	2153	Returns the remaining time until a timer fires. If the timer is active,
1175	you want to modify its timeout value.	2154	then this time is relative to the current event loop time, otherwise it's
		2155	the timeout value currently configured.
		2156
		2157	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
		2158	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		2159	will return C<4>. When the timer expires and is restarted, it will return
		2160	roughly C<7> (likely slightly less as callback invocation takes some time,
		2161	too), and so on.
1176		2162
1177	=item ev_tstamp repeat [read-write]	2163	=item ev_tstamp repeat [read-write]
1178		2164
1179	The current C<repeat> value. Will be used each time the watcher times out	2165	The current C<repeat> value. Will be used each time the watcher times out
1180	or C<ev_timer_again> is called and determines the next timeout (if any),	2166	or C<ev_timer_again> is called, and determines the next timeout (if any),
1181	which is also when any modifications are taken into account.	2167	which is also when any modifications are taken into account.
1182		2168
1183	=back	2169	=back
1184		2170
		2171	=head3 Examples
		2172
1185	Example: Create a timer that fires after 60 seconds.	2173	Example: Create a timer that fires after 60 seconds.
1186		2174
1187	static void	2175	static void
1188	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2176	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1189	{	2177	{
1190	.. one minute over, w is actually stopped right here	2178	.. one minute over, w is actually stopped right here
1191	}	2179	}
1192		2180
1193	struct ev_timer mytimer;	2181	ev_timer mytimer;
1194	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	2182	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1195	ev_timer_start (loop, &mytimer);	2183	ev_timer_start (loop, &mytimer);
1196		2184
1197	Example: Create a timeout timer that times out after 10 seconds of	2185	Example: Create a timeout timer that times out after 10 seconds of
1198	inactivity.	2186	inactivity.
1199		2187
1200	static void	2188	static void
1201	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2189	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1202	{	2190	{
1203	.. ten seconds without any activity	2191	.. ten seconds without any activity
1204	}	2192	}
1205		2193
1206	struct ev_timer mytimer;	2194	ev_timer mytimer;
1207	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	2195	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1208	ev_timer_again (&mytimer); /* start timer */	2196	ev_timer_again (&mytimer); /* start timer */
1209	ev_loop (loop, 0);	2197	ev_run (loop, 0);
1210		2198
1211	// and in some piece of code that gets executed on any "activity":	2199	// and in some piece of code that gets executed on any "activity":
1212	// reset the timeout to start ticking again at 10 seconds	2200	// reset the timeout to start ticking again at 10 seconds
1213	ev_timer_again (&mytimer);	2201	ev_timer_again (&mytimer);
1214		2202
1215		2203
1216	=head2 C<ev_periodic> - to cron or not to cron?	2204	=head2 C<ev_periodic> - to cron or not to cron?
1217		2205
1218	Periodic watchers are also timers of a kind, but they are very versatile	2206	Periodic watchers are also timers of a kind, but they are very versatile
1219	(and unfortunately a bit complex).	2207	(and unfortunately a bit complex).
1220		2208
1221	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	2209	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1222	but on wallclock time (absolute time). You can tell a periodic watcher	2210	relative time, the physical time that passes) but on wall clock time
1223	to trigger "at" some specific point in time. For example, if you tell a	2211	(absolute time, the thing you can read on your calender or clock). The
1224	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	2212	difference is that wall clock time can run faster or slower than real
1225	+ 10.>) and then reset your system clock to the last year, then it will	2213	time, and time jumps are not uncommon (e.g. when you adjust your
1226	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	2214	wrist-watch).
1227	roughly 10 seconds later).
1228		2215
1229	They can also be used to implement vastly more complex timers, such as	2216	You can tell a periodic watcher to trigger after some specific point
1230	triggering an event on each midnight, local time or other, complicated,	2217	in time: for example, if you tell a periodic watcher to trigger "in 10
1231	rules.	2218	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2219	not a delay) and then reset your system clock to January of the previous
		2220	year, then it will take a year or more to trigger the event (unlike an
		2221	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2222	it, as it uses a relative timeout).
1232		2223
		2224	C<ev_periodic> watchers can also be used to implement vastly more complex
		2225	timers, such as triggering an event on each "midnight, local time", or
		2226	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		2227	those cannot react to time jumps.
		2228
1233	As with timers, the callback is guarenteed to be invoked only when the	2229	As with timers, the callback is guaranteed to be invoked only when the
1234	time (C<at>) has been passed, but if multiple periodic timers become ready	2230	point in time where it is supposed to trigger has passed. If multiple
1235	during the same loop iteration then order of execution is undefined.	2231	timers become ready during the same loop iteration then the ones with
		2232	earlier time-out values are invoked before ones with later time-out values
		2233	(but this is no longer true when a callback calls C<ev_run> recursively).
1236		2234
1237	=head3 Watcher-Specific Functions and Data Members	2235	=head3 Watcher-Specific Functions and Data Members
1238		2236
1239	=over 4	2237	=over 4
1240		2238
1241	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2239	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1242		2240
1243	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2241	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1244		2242
1245	Lots of arguments, lets sort it out... There are basically three modes of	2243	Lots of arguments, let's sort it out... There are basically three modes of
1246	operation, and we will explain them from simplest to complex:	2244	operation, and we will explain them from simplest to most complex:
1247		2245
1248	=over 4	2246	=over 4
1249		2247
1250	=item * absolute timer (at = time, interval = reschedule_cb = 0)	2248	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1251		2249
1252	In this configuration the watcher triggers an event at the wallclock time	2250	In this configuration the watcher triggers an event after the wall clock
1253	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	2251	time C<offset> has passed. It will not repeat and will not adjust when a
1254	that is, if it is to be run at January 1st 2011 then it will run when the	2252	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1255	system time reaches or surpasses this time.	2253	will be stopped and invoked when the system clock reaches or surpasses
		2254	this point in time.
1256		2255
1257	=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	2256	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1258		2257
1259	In this mode the watcher will always be scheduled to time out at the next	2258	In this mode the watcher will always be scheduled to time out at the next
1260	C<at + N * interval> time (for some integer N, which can also be negative)	2259	C<offset + N * interval> time (for some integer N, which can also be
1261	and then repeat, regardless of any time jumps.	2260	negative) and then repeat, regardless of any time jumps. The C<offset>
		2261	argument is merely an offset into the C<interval> periods.
1262		2262
1263	This can be used to create timers that do not drift with respect to system	2263	This can be used to create timers that do not drift with respect to the
1264	time:	2264	system clock, for example, here is an C<ev_periodic> that triggers each
		2265	hour, on the hour (with respect to UTC):
1265		2266
1266	ev_periodic_set (&periodic, 0., 3600., 0);	2267	ev_periodic_set (&periodic, 0., 3600., 0);
1267		2268
1268	This doesn't mean there will always be 3600 seconds in between triggers,	2269	This doesn't mean there will always be 3600 seconds in between triggers,
1269	but only that the the callback will be called when the system time shows a	2270	but only that the callback will be called when the system time shows a
1270	full hour (UTC), or more correctly, when the system time is evenly divisible	2271	full hour (UTC), or more correctly, when the system time is evenly divisible
1271	by 3600.	2272	by 3600.
1272		2273
1273	Another way to think about it (for the mathematically inclined) is that	2274	Another way to think about it (for the mathematically inclined) is that
1274	C<ev_periodic> will try to run the callback in this mode at the next possible	2275	C<ev_periodic> will try to run the callback in this mode at the next possible
1275	time where C<time = at (mod interval)>, regardless of any time jumps.	2276	time where C<time = offset (mod interval)>, regardless of any time jumps.
1276		2277
1277	For numerical stability it is preferable that the C<at> value is near	2278	The C<interval> I<MUST> be positive, and for numerical stability, the
1278	C<ev_now ()> (the current time), but there is no range requirement for	2279	interval value should be higher than C<1/8192> (which is around 100
1279	this value.	2280	microseconds) and C<offset> should be higher than C<0> and should have
		2281	at most a similar magnitude as the current time (say, within a factor of
		2282	ten). Typical values for offset are, in fact, C<0> or something between
		2283	C<0> and C<interval>, which is also the recommended range.
1280		2284
		2285	Note also that there is an upper limit to how often a timer can fire (CPU
		2286	speed for example), so if C<interval> is very small then timing stability
		2287	will of course deteriorate. Libev itself tries to be exact to be about one
		2288	millisecond (if the OS supports it and the machine is fast enough).
		2289
1281	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	2290	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1282		2291
1283	In this mode the values for C<interval> and C<at> are both being	2292	In this mode the values for C<interval> and C<offset> are both being
1284	ignored. Instead, each time the periodic watcher gets scheduled, the	2293	ignored. Instead, each time the periodic watcher gets scheduled, the
1285	reschedule callback will be called with the watcher as first, and the	2294	reschedule callback will be called with the watcher as first, and the
1286	current time as second argument.	2295	current time as second argument.
1287		2296
1288	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2297	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1289	ever, or make any event loop modifications>. If you need to stop it,	2298	or make ANY other event loop modifications whatsoever, unless explicitly
1290	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	2299	allowed by documentation here>.
1291	starting an C<ev_prepare> watcher, which is legal).
1292		2300
		2301	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		2302	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		2303	only event loop modification you are allowed to do).
		2304
1293	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	2305	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1294	ev_tstamp now)>, e.g.:	2306	*w, ev_tstamp now)>, e.g.:
1295		2307
		2308	static ev_tstamp
1296	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2309	my_rescheduler (ev_periodic *w, ev_tstamp now)
1297	{	2310	{
1298	return now + 60.;	2311	return now + 60.;
1299	}	2312	}
1300		2313
1301	It must return the next time to trigger, based on the passed time value	2314	It must return the next time to trigger, based on the passed time value
1302	(that is, the lowest time value larger than to the second argument). It	2315	(that is, the lowest time value larger than to the second argument). It
1303	will usually be called just before the callback will be triggered, but	2316	will usually be called just before the callback will be triggered, but
1304	might be called at other times, too.	2317	might be called at other times, too.
1305		2318
1306	NOTE: I<< This callback must always return a time that is later than the	2319	NOTE: I<< This callback must always return a time that is higher than or
1307	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	2320	equal to the passed C<now> value >>.
1308		2321
1309	This can be used to create very complex timers, such as a timer that	2322	This can be used to create very complex timers, such as a timer that
1310	triggers on each midnight, local time. To do this, you would calculate the	2323	triggers on "next midnight, local time". To do this, you would calculate the
1311	next midnight after C<now> and return the timestamp value for this. How	2324	next midnight after C<now> and return the timestamp value for this. How
1312	you do this is, again, up to you (but it is not trivial, which is the main	2325	you do this is, again, up to you (but it is not trivial, which is the main
1313	reason I omitted it as an example).	2326	reason I omitted it as an example).
1314		2327
1315	=back	2328	=back
…		…
1319	Simply stops and restarts the periodic watcher again. This is only useful	2332	Simply stops and restarts the periodic watcher again. This is only useful
1320	when you changed some parameters or the reschedule callback would return	2333	when you changed some parameters or the reschedule callback would return
1321	a different time than the last time it was called (e.g. in a crond like	2334	a different time than the last time it was called (e.g. in a crond like
1322	program when the crontabs have changed).	2335	program when the crontabs have changed).
1323		2336
		2337	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2338
		2339	When active, returns the absolute time that the watcher is supposed
		2340	to trigger next. This is not the same as the C<offset> argument to
		2341	C<ev_periodic_set>, but indeed works even in interval and manual
		2342	rescheduling modes.
		2343
1324	=item ev_tstamp offset [read-write]	2344	=item ev_tstamp offset [read-write]
1325		2345
1326	When repeating, this contains the offset value, otherwise this is the	2346	When repeating, this contains the offset value, otherwise this is the
1327	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	2347	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2348	although libev might modify this value for better numerical stability).
1328		2349
1329	Can be modified any time, but changes only take effect when the periodic	2350	Can be modified any time, but changes only take effect when the periodic
1330	timer fires or C<ev_periodic_again> is being called.	2351	timer fires or C<ev_periodic_again> is being called.
1331		2352
1332	=item ev_tstamp interval [read-write]	2353	=item ev_tstamp interval [read-write]
1333		2354
1334	The current interval value. Can be modified any time, but changes only	2355	The current interval value. Can be modified any time, but changes only
1335	take effect when the periodic timer fires or C<ev_periodic_again> is being	2356	take effect when the periodic timer fires or C<ev_periodic_again> is being
1336	called.	2357	called.
1337		2358
1338	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2359	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1339		2360
1340	The current reschedule callback, or C<0>, if this functionality is	2361	The current reschedule callback, or C<0>, if this functionality is
1341	switched off. Can be changed any time, but changes only take effect when	2362	switched off. Can be changed any time, but changes only take effect when
1342	the periodic timer fires or C<ev_periodic_again> is being called.	2363	the periodic timer fires or C<ev_periodic_again> is being called.
1343		2364
1344	=item ev_tstamp at [read-only]
1345
1346	When active, contains the absolute time that the watcher is supposed to
1347	trigger next.
1348
1349	=back	2365	=back
1350		2366
		2367	=head3 Examples
		2368
1351	Example: Call a callback every hour, or, more precisely, whenever the	2369	Example: Call a callback every hour, or, more precisely, whenever the
1352	system clock is divisible by 3600. The callback invocation times have	2370	system time is divisible by 3600. The callback invocation times have
1353	potentially a lot of jittering, but good long-term stability.	2371	potentially a lot of jitter, but good long-term stability.
1354		2372
1355	static void	2373	static void
1356	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2374	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1357	{	2375	{
1358	... its now a full hour (UTC, or TAI or whatever your clock follows)	2376	... its now a full hour (UTC, or TAI or whatever your clock follows)
1359	}	2377	}
1360		2378
1361	struct ev_periodic hourly_tick;	2379	ev_periodic hourly_tick;
1362	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2380	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1363	ev_periodic_start (loop, &hourly_tick);	2381	ev_periodic_start (loop, &hourly_tick);
1364		2382
1365	Example: The same as above, but use a reschedule callback to do it:	2383	Example: The same as above, but use a reschedule callback to do it:
1366		2384
1367	#include <math.h>	2385	#include <math.h>
1368		2386
1369	static ev_tstamp	2387	static ev_tstamp
1370	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2388	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1371	{	2389	{
1372	return fmod (now, 3600.) + 3600.;	2390	return now + (3600. - fmod (now, 3600.));
1373	}	2391	}
1374		2392
1375	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2393	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1376		2394
1377	Example: Call a callback every hour, starting now:	2395	Example: Call a callback every hour, starting now:
1378		2396
1379	struct ev_periodic hourly_tick;	2397	ev_periodic hourly_tick;
1380	ev_periodic_init (&hourly_tick, clock_cb,	2398	ev_periodic_init (&hourly_tick, clock_cb,
1381	fmod (ev_now (loop), 3600.), 3600., 0);	2399	fmod (ev_now (loop), 3600.), 3600., 0);
1382	ev_periodic_start (loop, &hourly_tick);	2400	ev_periodic_start (loop, &hourly_tick);
1383		2401
1384		2402
1385	=head2 C<ev_signal> - signal me when a signal gets signalled!	2403	=head2 C<ev_signal> - signal me when a signal gets signalled!
1386		2404
1387	Signal watchers will trigger an event when the process receives a specific	2405	Signal watchers will trigger an event when the process receives a specific
1388	signal one or more times. Even though signals are very asynchronous, libev	2406	signal one or more times. Even though signals are very asynchronous, libev
1389	will try it's best to deliver signals synchronously, i.e. as part of the	2407	will try its best to deliver signals synchronously, i.e. as part of the
1390	normal event processing, like any other event.	2408	normal event processing, like any other event.
1391		2409
		2410	If you want signals to be delivered truly asynchronously, just use
		2411	C<sigaction> as you would do without libev and forget about sharing
		2412	the signal. You can even use C<ev_async> from a signal handler to
		2413	synchronously wake up an event loop.
		2414
1392	You can configure as many watchers as you like per signal. Only when the	2415	You can configure as many watchers as you like for the same signal, but
1393	first watcher gets started will libev actually register a signal watcher	2416	only within the same loop, i.e. you can watch for C<SIGINT> in your
1394	with the kernel (thus it coexists with your own signal handlers as long	2417	default loop and for C<SIGIO> in another loop, but you cannot watch for
1395	as you don't register any with libev). Similarly, when the last signal	2418	C<SIGINT> in both the default loop and another loop at the same time. At
1396	watcher for a signal is stopped libev will reset the signal handler to	2419	the moment, C<SIGCHLD> is permanently tied to the default loop.
1397	SIG_DFL (regardless of what it was set to before).	2420
		2421	Only after the first watcher for a signal is started will libev actually
		2422	register something with the kernel. It thus coexists with your own signal
		2423	handlers as long as you don't register any with libev for the same signal.
		2424
		2425	If possible and supported, libev will install its handlers with
		2426	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2427	not be unduly interrupted. If you have a problem with system calls getting
		2428	interrupted by signals you can block all signals in an C<ev_check> watcher
		2429	and unblock them in an C<ev_prepare> watcher.
		2430
		2431	=head3 The special problem of inheritance over fork/execve/pthread_create
		2432
		2433	Both the signal mask (C<sigprocmask>) and the signal disposition
		2434	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2435	stopping it again), that is, libev might or might not block the signal,
		2436	and might or might not set or restore the installed signal handler (but
		2437	see C<EVFLAG_NOSIGMASK>).
		2438
		2439	While this does not matter for the signal disposition (libev never
		2440	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2441	C<execve>), this matters for the signal mask: many programs do not expect
		2442	certain signals to be blocked.
		2443
		2444	This means that before calling C<exec> (from the child) you should reset
		2445	the signal mask to whatever "default" you expect (all clear is a good
		2446	choice usually).
		2447
		2448	The simplest way to ensure that the signal mask is reset in the child is
		2449	to install a fork handler with C<pthread_atfork> that resets it. That will
		2450	catch fork calls done by libraries (such as the libc) as well.
		2451
		2452	In current versions of libev, the signal will not be blocked indefinitely
		2453	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2454	the window of opportunity for problems, it will not go away, as libev
		2455	I<has> to modify the signal mask, at least temporarily.
		2456
		2457	So I can't stress this enough: I<If you do not reset your signal mask when
		2458	you expect it to be empty, you have a race condition in your code>. This
		2459	is not a libev-specific thing, this is true for most event libraries.
		2460
		2461	=head3 The special problem of threads signal handling
		2462
		2463	POSIX threads has problematic signal handling semantics, specifically,
		2464	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2465	threads in a process block signals, which is hard to achieve.
		2466
		2467	When you want to use sigwait (or mix libev signal handling with your own
		2468	for the same signals), you can tackle this problem by globally blocking
		2469	all signals before creating any threads (or creating them with a fully set
		2470	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2471	loops. Then designate one thread as "signal receiver thread" which handles
		2472	these signals. You can pass on any signals that libev might be interested
		2473	in by calling C<ev_feed_signal>.
1398		2474
1399	=head3 Watcher-Specific Functions and Data Members	2475	=head3 Watcher-Specific Functions and Data Members
1400		2476
1401	=over 4	2477	=over 4
1402		2478
…		…
1411		2487
1412	The signal the watcher watches out for.	2488	The signal the watcher watches out for.
1413		2489
1414	=back	2490	=back
1415		2491
		2492	=head3 Examples
		2493
		2494	Example: Try to exit cleanly on SIGINT.
		2495
		2496	static void
		2497	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2498	{
		2499	ev_break (loop, EVBREAK_ALL);
		2500	}
		2501
		2502	ev_signal signal_watcher;
		2503	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2504	ev_signal_start (loop, &signal_watcher);
		2505
1416		2506
1417	=head2 C<ev_child> - watch out for process status changes	2507	=head2 C<ev_child> - watch out for process status changes
1418		2508
1419	Child watchers trigger when your process receives a SIGCHLD in response to	2509	Child watchers trigger when your process receives a SIGCHLD in response to
1420	some child status changes (most typically when a child of yours dies).	2510	some child status changes (most typically when a child of yours dies or
		2511	exits). It is permissible to install a child watcher I<after> the child
		2512	has been forked (which implies it might have already exited), as long
		2513	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2514	forking and then immediately registering a watcher for the child is fine,
		2515	but forking and registering a watcher a few event loop iterations later or
		2516	in the next callback invocation is not.
		2517
		2518	Only the default event loop is capable of handling signals, and therefore
		2519	you can only register child watchers in the default event loop.
		2520
		2521	Due to some design glitches inside libev, child watchers will always be
		2522	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2523	libev)
		2524
		2525	=head3 Process Interaction
		2526
		2527	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2528	initialised. This is necessary to guarantee proper behaviour even if the
		2529	first child watcher is started after the child exits. The occurrence
		2530	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2531	synchronously as part of the event loop processing. Libev always reaps all
		2532	children, even ones not watched.
		2533
		2534	=head3 Overriding the Built-In Processing
		2535
		2536	Libev offers no special support for overriding the built-in child
		2537	processing, but if your application collides with libev's default child
		2538	handler, you can override it easily by installing your own handler for
		2539	C<SIGCHLD> after initialising the default loop, and making sure the
		2540	default loop never gets destroyed. You are encouraged, however, to use an
		2541	event-based approach to child reaping and thus use libev's support for
		2542	that, so other libev users can use C<ev_child> watchers freely.
		2543
		2544	=head3 Stopping the Child Watcher
		2545
		2546	Currently, the child watcher never gets stopped, even when the
		2547	child terminates, so normally one needs to stop the watcher in the
		2548	callback. Future versions of libev might stop the watcher automatically
		2549	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2550	problem).
1421		2551
1422	=head3 Watcher-Specific Functions and Data Members	2552	=head3 Watcher-Specific Functions and Data Members
1423		2553
1424	=over 4	2554	=over 4
1425		2555
1426	=item ev_child_init (ev_child *, callback, int pid)	2556	=item ev_child_init (ev_child *, callback, int pid, int trace)
1427		2557
1428	=item ev_child_set (ev_child *, int pid)	2558	=item ev_child_set (ev_child *, int pid, int trace)
1429		2559
1430	Configures the watcher to wait for status changes of process C<pid> (or	2560	Configures the watcher to wait for status changes of process C<pid> (or
1431	I<any> process if C<pid> is specified as C<0>). The callback can look	2561	I<any> process if C<pid> is specified as C<0>). The callback can look
1432	at the C<rstatus> member of the C<ev_child> watcher structure to see	2562	at the C<rstatus> member of the C<ev_child> watcher structure to see
1433	the status word (use the macros from C<sys/wait.h> and see your systems	2563	the status word (use the macros from C<sys/wait.h> and see your systems
1434	C<waitpid> documentation). The C<rpid> member contains the pid of the	2564	C<waitpid> documentation). The C<rpid> member contains the pid of the
1435	process causing the status change.	2565	process causing the status change. C<trace> must be either C<0> (only
		2566	activate the watcher when the process terminates) or C<1> (additionally
		2567	activate the watcher when the process is stopped or continued).
1436		2568
1437	=item int pid [read-only]	2569	=item int pid [read-only]
1438		2570
1439	The process id this watcher watches out for, or C<0>, meaning any process id.	2571	The process id this watcher watches out for, or C<0>, meaning any process id.
1440		2572
…		…
1447	The process exit/trace status caused by C<rpid> (see your systems	2579	The process exit/trace status caused by C<rpid> (see your systems
1448	C<waitpid> and C<sys/wait.h> documentation for details).	2580	C<waitpid> and C<sys/wait.h> documentation for details).
1449		2581
1450	=back	2582	=back
1451		2583
1452	Example: Try to exit cleanly on SIGINT and SIGTERM.	2584	=head3 Examples
1453		2585
		2586	Example: C<fork()> a new process and install a child handler to wait for
		2587	its completion.
		2588
		2589	ev_child cw;
		2590
1454	static void	2591	static void
1455	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2592	child_cb (EV_P_ ev_child *w, int revents)
1456	{	2593	{
1457	ev_unloop (loop, EVUNLOOP_ALL);	2594	ev_child_stop (EV_A_ w);
		2595	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1458	}	2596	}
1459		2597
1460	struct ev_signal signal_watcher;	2598	pid_t pid = fork ();
1461	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2599
1462	ev_signal_start (loop, &sigint_cb);	2600	if (pid < 0)
		2601	// error
		2602	else if (pid == 0)
		2603	{
		2604	// the forked child executes here
		2605	exit (1);
		2606	}
		2607	else
		2608	{
		2609	ev_child_init (&cw, child_cb, pid, 0);
		2610	ev_child_start (EV_DEFAULT_ &cw);
		2611	}
1463		2612
1464		2613
1465	=head2 C<ev_stat> - did the file attributes just change?	2614	=head2 C<ev_stat> - did the file attributes just change?
1466		2615
1467	This watches a filesystem path for attribute changes. That is, it calls	2616	This watches a file system path for attribute changes. That is, it calls
1468	C<stat> regularly (or when the OS says it changed) and sees if it changed	2617	C<stat> on that path in regular intervals (or when the OS says it changed)
1469	compared to the last time, invoking the callback if it did.	2618	and sees if it changed compared to the last time, invoking the callback
		2619	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2620	happen after the watcher has been started will be reported.
1470		2621
1471	The path does not need to exist: changing from "path exists" to "path does	2622	The path does not need to exist: changing from "path exists" to "path does
1472	not exist" is a status change like any other. The condition "path does	2623	not exist" is a status change like any other. The condition "path does not
1473	not exist" is signified by the C<st_nlink> field being zero (which is	2624	exist" (or more correctly "path cannot be stat'ed") is signified by the
1474	otherwise always forced to be at least one) and all the other fields of	2625	C<st_nlink> field being zero (which is otherwise always forced to be at
1475	the stat buffer having unspecified contents.	2626	least one) and all the other fields of the stat buffer having unspecified
		2627	contents.
1476		2628
1477	The path I<should> be absolute and I<must not> end in a slash. If it is	2629	The path I<must not> end in a slash or contain special components such as
		2630	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1478	relative and your working directory changes, the behaviour is undefined.	2631	your working directory changes, then the behaviour is undefined.
1479		2632
1480	Since there is no standard to do this, the portable implementation simply	2633	Since there is no portable change notification interface available, the
1481	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2634	portable implementation simply calls C<stat(2)> regularly on the path
1482	can specify a recommended polling interval for this case. If you specify	2635	to see if it changed somehow. You can specify a recommended polling
1483	a polling interval of C<0> (highly recommended!) then a I<suitable,	2636	interval for this case. If you specify a polling interval of C<0> (highly
1484	unspecified default> value will be used (which you can expect to be around	2637	recommended!) then a I<suitable, unspecified default> value will be used
1485	five seconds, although this might change dynamically). Libev will also	2638	(which you can expect to be around five seconds, although this might
1486	impose a minimum interval which is currently around C<0.1>, but thats	2639	change dynamically). Libev will also impose a minimum interval which is
1487	usually overkill.	2640	currently around C<0.1>, but that's usually overkill.
1488		2641
1489	This watcher type is not meant for massive numbers of stat watchers,	2642	This watcher type is not meant for massive numbers of stat watchers,
1490	as even with OS-supported change notifications, this can be	2643	as even with OS-supported change notifications, this can be
1491	resource-intensive.	2644	resource-intensive.
1492		2645
1493	At the time of this writing, only the Linux inotify interface is	2646	At the time of this writing, the only OS-specific interface implemented
1494	implemented (implementing kqueue support is left as an exercise for the	2647	is the Linux inotify interface (implementing kqueue support is left as an
1495	reader). Inotify will be used to give hints only and should not change the	2648	exercise for the reader. Note, however, that the author sees no way of
1496	semantics of C<ev_stat> watchers, which means that libev sometimes needs	2649	implementing C<ev_stat> semantics with kqueue, except as a hint).
1497	to fall back to regular polling again even with inotify, but changes are	2650
1498	usually detected immediately, and if the file exists there will be no	2651	=head3 ABI Issues (Largefile Support)
1499	polling.	2652
		2653	Libev by default (unless the user overrides this) uses the default
		2654	compilation environment, which means that on systems with large file
		2655	support disabled by default, you get the 32 bit version of the stat
		2656	structure. When using the library from programs that change the ABI to
		2657	use 64 bit file offsets the programs will fail. In that case you have to
		2658	compile libev with the same flags to get binary compatibility. This is
		2659	obviously the case with any flags that change the ABI, but the problem is
		2660	most noticeably displayed with ev_stat and large file support.
		2661
		2662	The solution for this is to lobby your distribution maker to make large
		2663	file interfaces available by default (as e.g. FreeBSD does) and not
		2664	optional. Libev cannot simply switch on large file support because it has
		2665	to exchange stat structures with application programs compiled using the
		2666	default compilation environment.
		2667
		2668	=head3 Inotify and Kqueue
		2669
		2670	When C<inotify (7)> support has been compiled into libev and present at
		2671	runtime, it will be used to speed up change detection where possible. The
		2672	inotify descriptor will be created lazily when the first C<ev_stat>
		2673	watcher is being started.
		2674
		2675	Inotify presence does not change the semantics of C<ev_stat> watchers
		2676	except that changes might be detected earlier, and in some cases, to avoid
		2677	making regular C<stat> calls. Even in the presence of inotify support
		2678	there are many cases where libev has to resort to regular C<stat> polling,
		2679	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2680	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2681	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2682	xfs are fully working) libev usually gets away without polling.
		2683
		2684	There is no support for kqueue, as apparently it cannot be used to
		2685	implement this functionality, due to the requirement of having a file
		2686	descriptor open on the object at all times, and detecting renames, unlinks
		2687	etc. is difficult.
		2688
		2689	=head3 C<stat ()> is a synchronous operation
		2690
		2691	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2692	the process. The exception are C<ev_stat> watchers - those call C<stat
		2693	()>, which is a synchronous operation.
		2694
		2695	For local paths, this usually doesn't matter: unless the system is very
		2696	busy or the intervals between stat's are large, a stat call will be fast,
		2697	as the path data is usually in memory already (except when starting the
		2698	watcher).
		2699
		2700	For networked file systems, calling C<stat ()> can block an indefinite
		2701	time due to network issues, and even under good conditions, a stat call
		2702	often takes multiple milliseconds.
		2703
		2704	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2705	paths, although this is fully supported by libev.
		2706
		2707	=head3 The special problem of stat time resolution
		2708
		2709	The C<stat ()> system call only supports full-second resolution portably,
		2710	and even on systems where the resolution is higher, most file systems
		2711	still only support whole seconds.
		2712
		2713	That means that, if the time is the only thing that changes, you can
		2714	easily miss updates: on the first update, C<ev_stat> detects a change and
		2715	calls your callback, which does something. When there is another update
		2716	within the same second, C<ev_stat> will be unable to detect unless the
		2717	stat data does change in other ways (e.g. file size).
		2718
		2719	The solution to this is to delay acting on a change for slightly more
		2720	than a second (or till slightly after the next full second boundary), using
		2721	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2722	ev_timer_again (loop, w)>).
		2723
		2724	The C<.02> offset is added to work around small timing inconsistencies
		2725	of some operating systems (where the second counter of the current time
		2726	might be be delayed. One such system is the Linux kernel, where a call to
		2727	C<gettimeofday> might return a timestamp with a full second later than
		2728	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2729	update file times then there will be a small window where the kernel uses
		2730	the previous second to update file times but libev might already execute
		2731	the timer callback).
1500		2732
1501	=head3 Watcher-Specific Functions and Data Members	2733	=head3 Watcher-Specific Functions and Data Members
1502		2734
1503	=over 4	2735	=over 4
1504		2736
…		…
1510	C<path>. The C<interval> is a hint on how quickly a change is expected to	2742	C<path>. The C<interval> is a hint on how quickly a change is expected to
1511	be detected and should normally be specified as C<0> to let libev choose	2743	be detected and should normally be specified as C<0> to let libev choose
1512	a suitable value. The memory pointed to by C<path> must point to the same	2744	a suitable value. The memory pointed to by C<path> must point to the same
1513	path for as long as the watcher is active.	2745	path for as long as the watcher is active.
1514		2746
1515	The callback will be receive C<EV_STAT> when a change was detected,	2747	The callback will receive an C<EV_STAT> event when a change was detected,
1516	relative to the attributes at the time the watcher was started (or the	2748	relative to the attributes at the time the watcher was started (or the
1517	last change was detected).	2749	last change was detected).
1518		2750
1519	=item ev_stat_stat (ev_stat *)	2751	=item ev_stat_stat (loop, ev_stat *)
1520		2752
1521	Updates the stat buffer immediately with new values. If you change the	2753	Updates the stat buffer immediately with new values. If you change the
1522	watched path in your callback, you could call this fucntion to avoid	2754	watched path in your callback, you could call this function to avoid
1523	detecting this change (while introducing a race condition). Can also be	2755	detecting this change (while introducing a race condition if you are not
1524	useful simply to find out the new values.	2756	the only one changing the path). Can also be useful simply to find out the
		2757	new values.
1525		2758
1526	=item ev_statdata attr [read-only]	2759	=item ev_statdata attr [read-only]
1527		2760
1528	The most-recently detected attributes of the file. Although the type is of	2761	The most-recently detected attributes of the file. Although the type is
1529	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2762	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1530	suitable for your system. If the C<st_nlink> member is C<0>, then there	2763	suitable for your system, but you can only rely on the POSIX-standardised
		2764	members to be present. If the C<st_nlink> member is C<0>, then there was
1531	was some error while C<stat>ing the file.	2765	some error while C<stat>ing the file.
1532		2766
1533	=item ev_statdata prev [read-only]	2767	=item ev_statdata prev [read-only]
1534		2768
1535	The previous attributes of the file. The callback gets invoked whenever	2769	The previous attributes of the file. The callback gets invoked whenever
1536	C<prev> != C<attr>.	2770	C<prev> != C<attr>, or, more precisely, one or more of these members
		2771	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2772	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1537		2773
1538	=item ev_tstamp interval [read-only]	2774	=item ev_tstamp interval [read-only]
1539		2775
1540	The specified interval.	2776	The specified interval.
1541		2777
1542	=item const char *path [read-only]	2778	=item const char *path [read-only]
1543		2779
1544	The filesystem path that is being watched.	2780	The file system path that is being watched.
1545		2781
1546	=back	2782	=back
1547		2783
		2784	=head3 Examples
		2785
1548	Example: Watch C</etc/passwd> for attribute changes.	2786	Example: Watch C</etc/passwd> for attribute changes.
1549		2787
1550	static void	2788	static void
1551	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2789	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1552	{	2790	{
1553	/* /etc/passwd changed in some way */	2791	/* /etc/passwd changed in some way */
1554	if (w->attr.st_nlink)	2792	if (w->attr.st_nlink)
1555	{	2793	{
1556	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2794	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1557	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2795	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1558	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2796	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1559	}	2797	}
1560	else	2798	else
1561	/* you shalt not abuse printf for puts */	2799	/* you shalt not abuse printf for puts */
1562	puts ("wow, /etc/passwd is not there, expect problems. "	2800	puts ("wow, /etc/passwd is not there, expect problems. "
1563	"if this is windows, they already arrived\n");	2801	"if this is windows, they already arrived\n");
1564	}	2802	}
1565		2803
1566	...	2804	...
1567	ev_stat passwd;	2805	ev_stat passwd;
1568		2806
1569	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	2807	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1570	ev_stat_start (loop, &passwd);	2808	ev_stat_start (loop, &passwd);
		2809
		2810	Example: Like above, but additionally use a one-second delay so we do not
		2811	miss updates (however, frequent updates will delay processing, too, so
		2812	one might do the work both on C<ev_stat> callback invocation I<and> on
		2813	C<ev_timer> callback invocation).
		2814
		2815	static ev_stat passwd;
		2816	static ev_timer timer;
		2817
		2818	static void
		2819	timer_cb (EV_P_ ev_timer *w, int revents)
		2820	{
		2821	ev_timer_stop (EV_A_ w);
		2822
		2823	/* now it's one second after the most recent passwd change */
		2824	}
		2825
		2826	static void
		2827	stat_cb (EV_P_ ev_stat *w, int revents)
		2828	{
		2829	/* reset the one-second timer */
		2830	ev_timer_again (EV_A_ &timer);
		2831	}
		2832
		2833	...
		2834	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2835	ev_stat_start (loop, &passwd);
		2836	ev_timer_init (&timer, timer_cb, 0., 1.02);
1571		2837
1572		2838
1573	=head2 C<ev_idle> - when you've got nothing better to do...	2839	=head2 C<ev_idle> - when you've got nothing better to do...
1574		2840
1575	Idle watchers trigger events when no other events of the same or higher	2841	Idle watchers trigger events when no other events of the same or higher
1576	priority are pending (prepare, check and other idle watchers do not	2842	priority are pending (prepare, check and other idle watchers do not count
1577	count).	2843	as receiving "events").
1578		2844
1579	That is, as long as your process is busy handling sockets or timeouts	2845	That is, as long as your process is busy handling sockets or timeouts
1580	(or even signals, imagine) of the same or higher priority it will not be	2846	(or even signals, imagine) of the same or higher priority it will not be
1581	triggered. But when your process is idle (or only lower-priority watchers	2847	triggered. But when your process is idle (or only lower-priority watchers
1582	are pending), the idle watchers are being called once per event loop	2848	are pending), the idle watchers are being called once per event loop
…		…
1589	Apart from keeping your process non-blocking (which is a useful	2855	Apart from keeping your process non-blocking (which is a useful
1590	effect on its own sometimes), idle watchers are a good place to do	2856	effect on its own sometimes), idle watchers are a good place to do
1591	"pseudo-background processing", or delay processing stuff to after the	2857	"pseudo-background processing", or delay processing stuff to after the
1592	event loop has handled all outstanding events.	2858	event loop has handled all outstanding events.
1593		2859
		2860	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2861
		2862	As long as there is at least one active idle watcher, libev will never
		2863	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2864	For this to work, the idle watcher doesn't need to be invoked at all - the
		2865	lowest priority will do.
		2866
		2867	This mode of operation can be useful together with an C<ev_check> watcher,
		2868	to do something on each event loop iteration - for example to balance load
		2869	between different connections.
		2870
		2871	See L</Abusing an ev_check watcher for its side-effect> for a longer
		2872	example.
		2873
1594	=head3 Watcher-Specific Functions and Data Members	2874	=head3 Watcher-Specific Functions and Data Members
1595		2875
1596	=over 4	2876	=over 4
1597		2877
1598	=item ev_idle_init (ev_signal *, callback)	2878	=item ev_idle_init (ev_idle *, callback)
1599		2879
1600	Initialises and configures the idle watcher - it has no parameters of any	2880	Initialises and configures the idle watcher - it has no parameters of any
1601	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2881	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1602	believe me.	2882	believe me.
1603		2883
1604	=back	2884	=back
1605		2885
		2886	=head3 Examples
		2887
1606	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2888	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1607	callback, free it. Also, use no error checking, as usual.	2889	callback, free it. Also, use no error checking, as usual.
1608		2890
1609	static void	2891	static void
1610	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2892	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1611	{	2893	{
		2894	// stop the watcher
		2895	ev_idle_stop (loop, w);
		2896
		2897	// now we can free it
1612	free (w);	2898	free (w);
		2899
1613	// now do something you wanted to do when the program has	2900	// now do something you wanted to do when the program has
1614	// no longer asnything immediate to do.	2901	// no longer anything immediate to do.
1615	}	2902	}
1616		2903
1617	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2904	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1618	ev_idle_init (idle_watcher, idle_cb);	2905	ev_idle_init (idle_watcher, idle_cb);
1619	ev_idle_start (loop, idle_cb);	2906	ev_idle_start (loop, idle_watcher);
1620		2907
1621		2908
1622	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2909	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1623		2910
1624	Prepare and check watchers are usually (but not always) used in tandem:	2911	Prepare and check watchers are often (but not always) used in pairs:
1625	prepare watchers get invoked before the process blocks and check watchers	2912	prepare watchers get invoked before the process blocks and check watchers
1626	afterwards.	2913	afterwards.
1627		2914
1628	You I<must not> call C<ev_loop> or similar functions that enter	2915	You I<must not> call C<ev_run> (or similar functions that enter the
1629	the current event loop from either C<ev_prepare> or C<ev_check>	2916	current event loop) or C<ev_loop_fork> from either C<ev_prepare> or
1630	watchers. Other loops than the current one are fine, however. The	2917	C<ev_check> watchers. Other loops than the current one are fine,
1631	rationale behind this is that you do not need to check for recursion in	2918	however. The rationale behind this is that you do not need to check
1632	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2919	for recursion in those watchers, i.e. the sequence will always be
1633	C<ev_check> so if you have one watcher of each kind they will always be	2920	C<ev_prepare>, blocking, C<ev_check> so if you have one watcher of each
1634	called in pairs bracketing the blocking call.	2921	kind they will always be called in pairs bracketing the blocking call.
1635		2922
1636	Their main purpose is to integrate other event mechanisms into libev and	2923	Their main purpose is to integrate other event mechanisms into libev and
1637	their use is somewhat advanced. This could be used, for example, to track	2924	their use is somewhat advanced. They could be used, for example, to track
1638	variable changes, implement your own watchers, integrate net-snmp or a	2925	variable changes, implement your own watchers, integrate net-snmp or a
1639	coroutine library and lots more. They are also occasionally useful if	2926	coroutine library and lots more. They are also occasionally useful if
1640	you cache some data and want to flush it before blocking (for example,	2927	you cache some data and want to flush it before blocking (for example,
1641	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2928	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1642	watcher).	2929	watcher).
1643		2930
1644	This is done by examining in each prepare call which file descriptors need	2931	This is done by examining in each prepare call which file descriptors
1645	to be watched by the other library, registering C<ev_io> watchers for	2932	need to be watched by the other library, registering C<ev_io> watchers
1646	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2933	for them and starting an C<ev_timer> watcher for any timeouts (many
1647	provide just this functionality). Then, in the check watcher you check for	2934	libraries provide exactly this functionality). Then, in the check watcher,
1648	any events that occured (by checking the pending status of all watchers	2935	you check for any events that occurred (by checking the pending status
1649	and stopping them) and call back into the library. The I/O and timer	2936	of all watchers and stopping them) and call back into the library. The
1650	callbacks will never actually be called (but must be valid nevertheless,	2937	I/O and timer callbacks will never actually be called (but must be valid
1651	because you never know, you know?).	2938	nevertheless, because you never know, you know?).
1652		2939
1653	As another example, the Perl Coro module uses these hooks to integrate	2940	As another example, the Perl Coro module uses these hooks to integrate
1654	coroutines into libev programs, by yielding to other active coroutines	2941	coroutines into libev programs, by yielding to other active coroutines
1655	during each prepare and only letting the process block if no coroutines	2942	during each prepare and only letting the process block if no coroutines
1656	are ready to run (it's actually more complicated: it only runs coroutines	2943	are ready to run (it's actually more complicated: it only runs coroutines
1657	with priority higher than or equal to the event loop and one coroutine	2944	with priority higher than or equal to the event loop and one coroutine
1658	of lower priority, but only once, using idle watchers to keep the event	2945	of lower priority, but only once, using idle watchers to keep the event
1659	loop from blocking if lower-priority coroutines are active, thus mapping	2946	loop from blocking if lower-priority coroutines are active, thus mapping
1660	low-priority coroutines to idle/background tasks).	2947	low-priority coroutines to idle/background tasks).
1661		2948
1662	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2949	When used for this purpose, it is recommended to give C<ev_check> watchers
1663	priority, to ensure that they are being run before any other watchers	2950	highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
		2951	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		2952	watchers).
		2953
1664	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2954	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1665	too) should not activate ("feed") events into libev. While libev fully	2955	activate ("feed") events into libev. While libev fully supports this, they
1666	supports this, they will be called before other C<ev_check> watchers	2956	might get executed before other C<ev_check> watchers did their job. As
1667	did their job. As C<ev_check> watchers are often used to embed other	2957	C<ev_check> watchers are often used to embed other (non-libev) event
1668	(non-libev) event loops those other event loops might be in an unusable	2958	loops those other event loops might be in an unusable state until their
1669	state until their C<ev_check> watcher ran (always remind yourself to	2959	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1670	coexist peacefully with others).	2960	others).
		2961
		2962	=head3 Abusing an C<ev_check> watcher for its side-effect
		2963
		2964	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		2965	useful because they are called once per event loop iteration. For
		2966	example, if you want to handle a large number of connections fairly, you
		2967	normally only do a bit of work for each active connection, and if there
		2968	is more work to do, you wait for the next event loop iteration, so other
		2969	connections have a chance of making progress.
		2970
		2971	Using an C<ev_check> watcher is almost enough: it will be called on the
		2972	next event loop iteration. However, that isn't as soon as possible -
		2973	without external events, your C<ev_check> watcher will not be invoked.
		2974
		2975	This is where C<ev_idle> watchers come in handy - all you need is a
		2976	single global idle watcher that is active as long as you have one active
		2977	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		2978	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		2979	invoked. Neither watcher alone can do that.
1671		2980
1672	=head3 Watcher-Specific Functions and Data Members	2981	=head3 Watcher-Specific Functions and Data Members
1673		2982
1674	=over 4	2983	=over 4
1675		2984
…		…
1677		2986
1678	=item ev_check_init (ev_check *, callback)	2987	=item ev_check_init (ev_check *, callback)
1679		2988
1680	Initialises and configures the prepare or check watcher - they have no	2989	Initialises and configures the prepare or check watcher - they have no
1681	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2990	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1682	macros, but using them is utterly, utterly and completely pointless.	2991	macros, but using them is utterly, utterly, utterly and completely
		2992	pointless.
1683		2993
1684	=back	2994	=back
		2995
		2996	=head3 Examples
1685		2997
1686	There are a number of principal ways to embed other event loops or modules	2998	There are a number of principal ways to embed other event loops or modules
1687	into libev. Here are some ideas on how to include libadns into libev	2999	into libev. Here are some ideas on how to include libadns into libev
1688	(there is a Perl module named C<EV::ADNS> that does this, which you could	3000	(there is a Perl module named C<EV::ADNS> that does this, which you could
1689	use for an actually working example. Another Perl module named C<EV::Glib>	3001	use as a working example. Another Perl module named C<EV::Glib> embeds a
1690	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV	3002	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1691	into the Glib event loop).	3003	Glib event loop).
1692		3004
1693	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	3005	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1694	and in a check watcher, destroy them and call into libadns. What follows	3006	and in a check watcher, destroy them and call into libadns. What follows
1695	is pseudo-code only of course. This requires you to either use a low	3007	is pseudo-code only of course. This requires you to either use a low
1696	priority for the check watcher or use C<ev_clear_pending> explicitly, as	3008	priority for the check watcher or use C<ev_clear_pending> explicitly, as
1697	the callbacks for the IO/timeout watchers might not have been called yet.	3009	the callbacks for the IO/timeout watchers might not have been called yet.
1698		3010
1699	static ev_io iow [nfd];	3011	static ev_io iow [nfd];
1700	static ev_timer tw;	3012	static ev_timer tw;
1701		3013
1702	static void	3014	static void
1703	io_cb (ev_loop *loop, ev_io *w, int revents)	3015	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1704	{	3016	{
1705	}	3017	}
1706		3018
1707	// create io watchers for each fd and a timer before blocking	3019	// create io watchers for each fd and a timer before blocking
1708	static void	3020	static void
1709	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	3021	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1710	{	3022	{
1711	int timeout = 3600000;	3023	int timeout = 3600000;
1712	struct pollfd fds [nfd];	3024	struct pollfd fds [nfd];
1713	// actual code will need to loop here and realloc etc.	3025	// actual code will need to loop here and realloc etc.
1714	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	3026	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1715		3027
1716	/* the callback is illegal, but won't be called as we stop during check */	3028	/* the callback is illegal, but won't be called as we stop during check */
1717	ev_timer_init (&tw, 0, timeout * 1e-3);	3029	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1718	ev_timer_start (loop, &tw);	3030	ev_timer_start (loop, &tw);
1719		3031
1720	// create one ev_io per pollfd	3032	// create one ev_io per pollfd
1721	for (int i = 0; i < nfd; ++i)	3033	for (int i = 0; i < nfd; ++i)
1722	{	3034	{
1723	ev_io_init (iow + i, io_cb, fds [i].fd,	3035	ev_io_init (iow + i, io_cb, fds [i].fd,
1724	((fds [i].events & POLLIN ? EV_READ : 0)	3036	((fds [i].events & POLLIN ? EV_READ : 0)
1725	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	3037	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1726		3038
1727	fds [i].revents = 0;	3039	fds [i].revents = 0;
1728	ev_io_start (loop, iow + i);	3040	ev_io_start (loop, iow + i);
1729	}	3041	}
1730	}	3042	}
1731		3043
1732	// stop all watchers after blocking	3044	// stop all watchers after blocking
1733	static void	3045	static void
1734	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	3046	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1735	{	3047	{
1736	ev_timer_stop (loop, &tw);	3048	ev_timer_stop (loop, &tw);
1737		3049
1738	for (int i = 0; i < nfd; ++i)	3050	for (int i = 0; i < nfd; ++i)
1739	{	3051	{
1740	// set the relevant poll flags	3052	// set the relevant poll flags
1741	// could also call adns_processreadable etc. here	3053	// could also call adns_processreadable etc. here
1742	struct pollfd *fd = fds + i;	3054	struct pollfd *fd = fds + i;
1743	int revents = ev_clear_pending (iow + i);	3055	int revents = ev_clear_pending (iow + i);
1744	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;	3056	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1745	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;	3057	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1746		3058
1747	// now stop the watcher	3059	// now stop the watcher
1748	ev_io_stop (loop, iow + i);	3060	ev_io_stop (loop, iow + i);
1749	}	3061	}
1750		3062
1751	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	3063	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1752	}	3064	}
1753		3065
1754	Method 2: This would be just like method 1, but you run C<adns_afterpoll>	3066	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
1755	in the prepare watcher and would dispose of the check watcher.	3067	in the prepare watcher and would dispose of the check watcher.
1756		3068
1757	Method 3: If the module to be embedded supports explicit event	3069	Method 3: If the module to be embedded supports explicit event
1758	notification (adns does), you can also make use of the actual watcher	3070	notification (libadns does), you can also make use of the actual watcher
1759	callbacks, and only destroy/create the watchers in the prepare watcher.	3071	callbacks, and only destroy/create the watchers in the prepare watcher.
1760		3072
1761	static void	3073	static void
1762	timer_cb (EV_P_ ev_timer *w, int revents)	3074	timer_cb (EV_P_ ev_timer *w, int revents)
1763	{	3075	{
1764	adns_state ads = (adns_state)w->data;	3076	adns_state ads = (adns_state)w->data;
1765	update_now (EV_A);	3077	update_now (EV_A);
1766		3078
1767	adns_processtimeouts (ads, &tv_now);	3079	adns_processtimeouts (ads, &tv_now);
1768	}	3080	}
1769		3081
1770	static void	3082	static void
1771	io_cb (EV_P_ ev_io *w, int revents)	3083	io_cb (EV_P_ ev_io *w, int revents)
1772	{	3084	{
1773	adns_state ads = (adns_state)w->data;	3085	adns_state ads = (adns_state)w->data;
1774	update_now (EV_A);	3086	update_now (EV_A);
1775		3087
1776	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);	3088	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
1777	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);	3089	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
1778	}	3090	}
1779		3091
1780	// do not ever call adns_afterpoll	3092	// do not ever call adns_afterpoll
1781		3093
1782	Method 4: Do not use a prepare or check watcher because the module you	3094	Method 4: Do not use a prepare or check watcher because the module you
1783	want to embed is too inflexible to support it. Instead, youc na override	3095	want to embed is not flexible enough to support it. Instead, you can
1784	their poll function. The drawback with this solution is that the main	3096	override their poll function. The drawback with this solution is that the
1785	loop is now no longer controllable by EV. The C<Glib::EV> module does	3097	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
1786	this.	3098	this approach, effectively embedding EV as a client into the horrible
		3099	libglib event loop.
1787		3100
1788	static gint	3101	static gint
1789	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	3102	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1790	{	3103	{
1791	int got_events = 0;	3104	int got_events = 0;
1792		3105
1793	for (n = 0; n < nfds; ++n)	3106	for (n = 0; n < nfds; ++n)
1794	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events	3107	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1795		3108
1796	if (timeout >= 0)	3109	if (timeout >= 0)
1797	// create/start timer	3110	// create/start timer
1798		3111
1799	// poll	3112	// poll
1800	ev_loop (EV_A_ 0);	3113	ev_run (EV_A_ 0);
1801		3114
1802	// stop timer again	3115	// stop timer again
1803	if (timeout >= 0)	3116	if (timeout >= 0)
1804	ev_timer_stop (EV_A_ &to);	3117	ev_timer_stop (EV_A_ &to);
1805		3118
1806	// stop io watchers again - their callbacks should have set	3119	// stop io watchers again - their callbacks should have set
1807	for (n = 0; n < nfds; ++n)	3120	for (n = 0; n < nfds; ++n)
1808	ev_io_stop (EV_A_ iow [n]);	3121	ev_io_stop (EV_A_ iow [n]);
1809		3122
1810	return got_events;	3123	return got_events;
1811	}	3124	}
1812		3125
1813		3126
1814	=head2 C<ev_embed> - when one backend isn't enough...	3127	=head2 C<ev_embed> - when one backend isn't enough...
1815		3128
1816	This is a rather advanced watcher type that lets you embed one event loop	3129	This is a rather advanced watcher type that lets you embed one event loop
…		…
1822	prioritise I/O.	3135	prioritise I/O.
1823		3136
1824	As an example for a bug workaround, the kqueue backend might only support	3137	As an example for a bug workaround, the kqueue backend might only support
1825	sockets on some platform, so it is unusable as generic backend, but you	3138	sockets on some platform, so it is unusable as generic backend, but you
1826	still want to make use of it because you have many sockets and it scales	3139	still want to make use of it because you have many sockets and it scales
1827	so nicely. In this case, you would create a kqueue-based loop and embed it	3140	so nicely. In this case, you would create a kqueue-based loop and embed
1828	into your default loop (which might use e.g. poll). Overall operation will	3141	it into your default loop (which might use e.g. poll). Overall operation
1829	be a bit slower because first libev has to poll and then call kevent, but	3142	will be a bit slower because first libev has to call C<poll> and then
1830	at least you can use both at what they are best.	3143	C<kevent>, but at least you can use both mechanisms for what they are
		3144	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1831		3145
1832	As for prioritising I/O: rarely you have the case where some fds have	3146	As for prioritising I/O: under rare circumstances you have the case where
1833	to be watched and handled very quickly (with low latency), and even	3147	some fds have to be watched and handled very quickly (with low latency),
1834	priorities and idle watchers might have too much overhead. In this case	3148	and even priorities and idle watchers might have too much overhead. In
1835	you would put all the high priority stuff in one loop and all the rest in	3149	this case you would put all the high priority stuff in one loop and all
1836	a second one, and embed the second one in the first.	3150	the rest in a second one, and embed the second one in the first.
1837		3151
1838	As long as the watcher is active, the callback will be invoked every time	3152	As long as the watcher is active, the callback will be invoked every
1839	there might be events pending in the embedded loop. The callback must then	3153	time there might be events pending in the embedded loop. The callback
1840	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	3154	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1841	their callbacks (you could also start an idle watcher to give the embedded	3155	sweep and invoke their callbacks (the callback doesn't need to invoke the
1842	loop strictly lower priority for example). You can also set the callback	3156	C<ev_embed_sweep> function directly, it could also start an idle watcher
1843	to C<0>, in which case the embed watcher will automatically execute the	3157	to give the embedded loop strictly lower priority for example).
1844	embedded loop sweep.
1845		3158
1846	As long as the watcher is started it will automatically handle events. The	3159	You can also set the callback to C<0>, in which case the embed watcher
1847	callback will be invoked whenever some events have been handled. You can	3160	will automatically execute the embedded loop sweep whenever necessary.
1848	set the callback to C<0> to avoid having to specify one if you are not
1849	interested in that.
1850		3161
1851	Also, there have not currently been made special provisions for forking:	3162	Fork detection will be handled transparently while the C<ev_embed> watcher
1852	when you fork, you not only have to call C<ev_loop_fork> on both loops,	3163	is active, i.e., the embedded loop will automatically be forked when the
1853	but you will also have to stop and restart any C<ev_embed> watchers	3164	embedding loop forks. In other cases, the user is responsible for calling
1854	yourself.	3165	C<ev_loop_fork> on the embedded loop.
1855		3166
1856	Unfortunately, not all backends are embeddable, only the ones returned by	3167	Unfortunately, not all backends are embeddable: only the ones returned by
1857	C<ev_embeddable_backends> are, which, unfortunately, does not include any	3168	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1858	portable one.	3169	portable one.
1859		3170
1860	So when you want to use this feature you will always have to be prepared	3171	So when you want to use this feature you will always have to be prepared
1861	that you cannot get an embeddable loop. The recommended way to get around	3172	that you cannot get an embeddable loop. The recommended way to get around
1862	this is to have a separate variables for your embeddable loop, try to	3173	this is to have a separate variables for your embeddable loop, try to
1863	create it, and if that fails, use the normal loop for everything:	3174	create it, and if that fails, use the normal loop for everything.
1864		3175
1865	struct ev_loop *loop_hi = ev_default_init (0);	3176	=head3 C<ev_embed> and fork
1866	struct ev_loop *loop_lo = 0;
1867	struct ev_embed embed;
1868
1869	// see if there is a chance of getting one that works
1870	// (remember that a flags value of 0 means autodetection)
1871	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1872	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1873	: 0;
1874		3177
1875	// if we got one, then embed it, otherwise default to loop_hi	3178	While the C<ev_embed> watcher is running, forks in the embedding loop will
1876	if (loop_lo)	3179	automatically be applied to the embedded loop as well, so no special
1877	{	3180	fork handling is required in that case. When the watcher is not running,
1878	ev_embed_init (&embed, 0, loop_lo);	3181	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1879	ev_embed_start (loop_hi, &embed);	3182	as applicable.
1880	}
1881	else
1882	loop_lo = loop_hi;
1883		3183
1884	=head3 Watcher-Specific Functions and Data Members	3184	=head3 Watcher-Specific Functions and Data Members
1885		3185
1886	=over 4	3186	=over 4
1887		3187
1888	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3188	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
1889		3189
1890	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)	3190	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
1891		3191
1892	Configures the watcher to embed the given loop, which must be	3192	Configures the watcher to embed the given loop, which must be
1893	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3193	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1894	invoked automatically, otherwise it is the responsibility of the callback	3194	invoked automatically, otherwise it is the responsibility of the callback
1895	to invoke it (it will continue to be called until the sweep has been done,	3195	to invoke it (it will continue to be called until the sweep has been done,
1896	if you do not want thta, you need to temporarily stop the embed watcher).	3196	if you do not want that, you need to temporarily stop the embed watcher).
1897		3197
1898	=item ev_embed_sweep (loop, ev_embed *)	3198	=item ev_embed_sweep (loop, ev_embed *)
1899		3199
1900	Make a single, non-blocking sweep over the embedded loop. This works	3200	Make a single, non-blocking sweep over the embedded loop. This works
1901	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	3201	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
1902	apropriate way for embedded loops.	3202	appropriate way for embedded loops.
1903		3203
1904	=item struct ev_loop *other [read-only]	3204	=item struct ev_loop *other [read-only]
1905		3205
1906	The embedded event loop.	3206	The embedded event loop.
1907		3207
1908	=back	3208	=back
		3209
		3210	=head3 Examples
		3211
		3212	Example: Try to get an embeddable event loop and embed it into the default
		3213	event loop. If that is not possible, use the default loop. The default
		3214	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		3215	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		3216	used).
		3217
		3218	struct ev_loop *loop_hi = ev_default_init (0);
		3219	struct ev_loop *loop_lo = 0;
		3220	ev_embed embed;
		3221
		3222	// see if there is a chance of getting one that works
		3223	// (remember that a flags value of 0 means autodetection)
		3224	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		3225	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		3226	: 0;
		3227
		3228	// if we got one, then embed it, otherwise default to loop_hi
		3229	if (loop_lo)
		3230	{
		3231	ev_embed_init (&embed, 0, loop_lo);
		3232	ev_embed_start (loop_hi, &embed);
		3233	}
		3234	else
		3235	loop_lo = loop_hi;
		3236
		3237	Example: Check if kqueue is available but not recommended and create
		3238	a kqueue backend for use with sockets (which usually work with any
		3239	kqueue implementation). Store the kqueue/socket-only event loop in
		3240	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		3241
		3242	struct ev_loop *loop = ev_default_init (0);
		3243	struct ev_loop *loop_socket = 0;
		3244	ev_embed embed;
		3245
		3246	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		3247	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		3248	{
		3249	ev_embed_init (&embed, 0, loop_socket);
		3250	ev_embed_start (loop, &embed);
		3251	}
		3252
		3253	if (!loop_socket)
		3254	loop_socket = loop;
		3255
		3256	// now use loop_socket for all sockets, and loop for everything else
1909		3257
1910		3258
1911	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3259	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
1912		3260
1913	Fork watchers are called when a C<fork ()> was detected (usually because	3261	Fork watchers are called when a C<fork ()> was detected (usually because
1914	whoever is a good citizen cared to tell libev about it by calling	3262	whoever is a good citizen cared to tell libev about it by calling
1915	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the	3263	C<ev_loop_fork>). The invocation is done before the event loop blocks next
1916	event loop blocks next and before C<ev_check> watchers are being called,	3264	and before C<ev_check> watchers are being called, and only in the child
1917	and only in the child after the fork. If whoever good citizen calling	3265	after the fork. If whoever good citizen calling C<ev_default_fork> cheats
1918	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3266	and calls it in the wrong process, the fork handlers will be invoked, too,
1919	handlers will be invoked, too, of course.	3267	of course.
		3268
		3269	=head3 The special problem of life after fork - how is it possible?
		3270
		3271	Most uses of C<fork ()> consist of forking, then some simple calls to set
		3272	up/change the process environment, followed by a call to C<exec()>. This
		3273	sequence should be handled by libev without any problems.
		3274
		3275	This changes when the application actually wants to do event handling
		3276	in the child, or both parent in child, in effect "continuing" after the
		3277	fork.
		3278
		3279	The default mode of operation (for libev, with application help to detect
		3280	forks) is to duplicate all the state in the child, as would be expected
		3281	when I<either> the parent I<or> the child process continues.
		3282
		3283	When both processes want to continue using libev, then this is usually the
		3284	wrong result. In that case, usually one process (typically the parent) is
		3285	supposed to continue with all watchers in place as before, while the other
		3286	process typically wants to start fresh, i.e. without any active watchers.
		3287
		3288	The cleanest and most efficient way to achieve that with libev is to
		3289	simply create a new event loop, which of course will be "empty", and
		3290	use that for new watchers. This has the advantage of not touching more
		3291	memory than necessary, and thus avoiding the copy-on-write, and the
		3292	disadvantage of having to use multiple event loops (which do not support
		3293	signal watchers).
		3294
		3295	When this is not possible, or you want to use the default loop for
		3296	other reasons, then in the process that wants to start "fresh", call
		3297	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
		3298	Destroying the default loop will "orphan" (not stop) all registered
		3299	watchers, so you have to be careful not to execute code that modifies
		3300	those watchers. Note also that in that case, you have to re-register any
		3301	signal watchers.
1920		3302
1921	=head3 Watcher-Specific Functions and Data Members	3303	=head3 Watcher-Specific Functions and Data Members
1922		3304
1923	=over 4	3305	=over 4
1924		3306
1925	=item ev_fork_init (ev_signal *, callback)	3307	=item ev_fork_init (ev_fork *, callback)
1926		3308
1927	Initialises and configures the fork watcher - it has no parameters of any	3309	Initialises and configures the fork watcher - it has no parameters of any
1928	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,	3310	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
1929	believe me.	3311	really.
1930		3312
1931	=back	3313	=back
1932		3314
1933		3315
		3316	=head2 C<ev_cleanup> - even the best things end
		3317
		3318	Cleanup watchers are called just before the event loop is being destroyed
		3319	by a call to C<ev_loop_destroy>.
		3320
		3321	While there is no guarantee that the event loop gets destroyed, cleanup
		3322	watchers provide a convenient method to install cleanup hooks for your
		3323	program, worker threads and so on - you just to make sure to destroy the
		3324	loop when you want them to be invoked.
		3325
		3326	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3327	all other watchers, they do not keep a reference to the event loop (which
		3328	makes a lot of sense if you think about it). Like all other watchers, you
		3329	can call libev functions in the callback, except C<ev_cleanup_start>.
		3330
		3331	=head3 Watcher-Specific Functions and Data Members
		3332
		3333	=over 4
		3334
		3335	=item ev_cleanup_init (ev_cleanup *, callback)
		3336
		3337	Initialises and configures the cleanup watcher - it has no parameters of
		3338	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3339	pointless, I assure you.
		3340
		3341	=back
		3342
		3343	Example: Register an atexit handler to destroy the default loop, so any
		3344	cleanup functions are called.
		3345
		3346	static void
		3347	program_exits (void)
		3348	{
		3349	ev_loop_destroy (EV_DEFAULT_UC);
		3350	}
		3351
		3352	...
		3353	atexit (program_exits);
		3354
		3355
		3356	=head2 C<ev_async> - how to wake up an event loop
		3357
		3358	In general, you cannot use an C<ev_loop> from multiple threads or other
		3359	asynchronous sources such as signal handlers (as opposed to multiple event
		3360	loops - those are of course safe to use in different threads).
		3361
		3362	Sometimes, however, you need to wake up an event loop you do not control,
		3363	for example because it belongs to another thread. This is what C<ev_async>
		3364	watchers do: as long as the C<ev_async> watcher is active, you can signal
		3365	it by calling C<ev_async_send>, which is thread- and signal safe.
		3366
		3367	This functionality is very similar to C<ev_signal> watchers, as signals,
		3368	too, are asynchronous in nature, and signals, too, will be compressed
		3369	(i.e. the number of callback invocations may be less than the number of
		3370	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
		3371	of "global async watchers" by using a watcher on an otherwise unused
		3372	signal, and C<ev_feed_signal> to signal this watcher from another thread,
		3373	even without knowing which loop owns the signal.
		3374
		3375	=head3 Queueing
		3376
		3377	C<ev_async> does not support queueing of data in any way. The reason
		3378	is that the author does not know of a simple (or any) algorithm for a
		3379	multiple-writer-single-reader queue that works in all cases and doesn't
		3380	need elaborate support such as pthreads or unportable memory access
		3381	semantics.
		3382
		3383	That means that if you want to queue data, you have to provide your own
		3384	queue. But at least I can tell you how to implement locking around your
		3385	queue:
		3386
		3387	=over 4
		3388
		3389	=item queueing from a signal handler context
		3390
		3391	To implement race-free queueing, you simply add to the queue in the signal
		3392	handler but you block the signal handler in the watcher callback. Here is
		3393	an example that does that for some fictitious SIGUSR1 handler:
		3394
		3395	static ev_async mysig;
		3396
		3397	static void
		3398	sigusr1_handler (void)
		3399	{
		3400	sometype data;
		3401
		3402	// no locking etc.
		3403	queue_put (data);
		3404	ev_async_send (EV_DEFAULT_ &mysig);
		3405	}
		3406
		3407	static void
		3408	mysig_cb (EV_P_ ev_async *w, int revents)
		3409	{
		3410	sometype data;
		3411	sigset_t block, prev;
		3412
		3413	sigemptyset (&block);
		3414	sigaddset (&block, SIGUSR1);
		3415	sigprocmask (SIG_BLOCK, &block, &prev);
		3416
		3417	while (queue_get (&data))
		3418	process (data);
		3419
		3420	if (sigismember (&prev, SIGUSR1)
		3421	sigprocmask (SIG_UNBLOCK, &block, 0);
		3422	}
		3423
		3424	(Note: pthreads in theory requires you to use C<pthread_setmask>
		3425	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		3426	either...).
		3427
		3428	=item queueing from a thread context
		3429
		3430	The strategy for threads is different, as you cannot (easily) block
		3431	threads but you can easily preempt them, so to queue safely you need to
		3432	employ a traditional mutex lock, such as in this pthread example:
		3433
		3434	static ev_async mysig;
		3435	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		3436
		3437	static void
		3438	otherthread (void)
		3439	{
		3440	// only need to lock the actual queueing operation
		3441	pthread_mutex_lock (&mymutex);
		3442	queue_put (data);
		3443	pthread_mutex_unlock (&mymutex);
		3444
		3445	ev_async_send (EV_DEFAULT_ &mysig);
		3446	}
		3447
		3448	static void
		3449	mysig_cb (EV_P_ ev_async *w, int revents)
		3450	{
		3451	pthread_mutex_lock (&mymutex);
		3452
		3453	while (queue_get (&data))
		3454	process (data);
		3455
		3456	pthread_mutex_unlock (&mymutex);
		3457	}
		3458
		3459	=back
		3460
		3461
		3462	=head3 Watcher-Specific Functions and Data Members
		3463
		3464	=over 4
		3465
		3466	=item ev_async_init (ev_async *, callback)
		3467
		3468	Initialises and configures the async watcher - it has no parameters of any
		3469	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		3470	trust me.
		3471
		3472	=item ev_async_send (loop, ev_async *)
		3473
		3474	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		3475	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3476	returns.
		3477
		3478	Unlike C<ev_feed_event>, this call is safe to do from other threads,
		3479	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
		3480	embedding section below on what exactly this means).
		3481
		3482	Note that, as with other watchers in libev, multiple events might get
		3483	compressed into a single callback invocation (another way to look at
		3484	this is that C<ev_async> watchers are level-triggered: they are set on
		3485	C<ev_async_send>, reset when the event loop detects that).
		3486
		3487	This call incurs the overhead of at most one extra system call per event
		3488	loop iteration, if the event loop is blocked, and no syscall at all if
		3489	the event loop (or your program) is processing events. That means that
		3490	repeated calls are basically free (there is no need to avoid calls for
		3491	performance reasons) and that the overhead becomes smaller (typically
		3492	zero) under load.
		3493
		3494	=item bool = ev_async_pending (ev_async *)
		3495
		3496	Returns a non-zero value when C<ev_async_send> has been called on the
		3497	watcher but the event has not yet been processed (or even noted) by the
		3498	event loop.
		3499
		3500	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3501	the loop iterates next and checks for the watcher to have become active,
		3502	it will reset the flag again. C<ev_async_pending> can be used to very
		3503	quickly check whether invoking the loop might be a good idea.
		3504
		3505	Not that this does I<not> check whether the watcher itself is pending,
		3506	only whether it has been requested to make this watcher pending: there
		3507	is a time window between the event loop checking and resetting the async
		3508	notification, and the callback being invoked.
		3509
		3510	=back
		3511
		3512
1934	=head1 OTHER FUNCTIONS	3513	=head1 OTHER FUNCTIONS
1935		3514
1936	There are some other functions of possible interest. Described. Here. Now.	3515	There are some other functions of possible interest. Described. Here. Now.
1937		3516
1938	=over 4	3517	=over 4
1939		3518
1940	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3519	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1941		3520
1942	This function combines a simple timer and an I/O watcher, calls your	3521	This function combines a simple timer and an I/O watcher, calls your
1943	callback on whichever event happens first and automatically stop both	3522	callback on whichever event happens first and automatically stops both
1944	watchers. This is useful if you want to wait for a single event on an fd	3523	watchers. This is useful if you want to wait for a single event on an fd
1945	or timeout without having to allocate/configure/start/stop/free one or	3524	or timeout without having to allocate/configure/start/stop/free one or
1946	more watchers yourself.	3525	more watchers yourself.
1947		3526
1948	If C<fd> is less than 0, then no I/O watcher will be started and events	3527	If C<fd> is less than 0, then no I/O watcher will be started and the
1949	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3528	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1950	C<events> set will be craeted and started.	3529	the given C<fd> and C<events> set will be created and started.
1951		3530
1952	If C<timeout> is less than 0, then no timeout watcher will be	3531	If C<timeout> is less than 0, then no timeout watcher will be
1953	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3532	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1954	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3533	repeat = 0) will be started. C<0> is a valid timeout.
1955	dubious value.
1956		3534
1957	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3535	The callback has the type C<void (*cb)(int revents, void *arg)> and is
1958	passed an C<revents> set like normal event callbacks (a combination of	3536	passed an C<revents> set like normal event callbacks (a combination of
1959	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3537	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
1960	value passed to C<ev_once>:	3538	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3539	a timeout and an io event at the same time - you probably should give io
		3540	events precedence.
1961		3541
		3542	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3543
1962	static void stdin_ready (int revents, void *arg)	3544	static void stdin_ready (int revents, void *arg)
		3545	{
		3546	if (revents & EV_READ)
		3547	/* stdin might have data for us, joy! */;
		3548	else if (revents & EV_TIMER)
		3549	/* doh, nothing entered */;
		3550	}
		3551
		3552	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
		3553
		3554	=item ev_feed_fd_event (loop, int fd, int revents)
		3555
		3556	Feed an event on the given fd, as if a file descriptor backend detected
		3557	the given events.
		3558
		3559	=item ev_feed_signal_event (loop, int signum)
		3560
		3561	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
		3562	which is async-safe.
		3563
		3564	=back
		3565
		3566
		3567	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3568
		3569	This section explains some common idioms that are not immediately
		3570	obvious. Note that examples are sprinkled over the whole manual, and this
		3571	section only contains stuff that wouldn't fit anywhere else.
		3572
		3573	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3574
		3575	Each watcher has, by default, a C<void *data> member that you can read
		3576	or modify at any time: libev will completely ignore it. This can be used
		3577	to associate arbitrary data with your watcher. If you need more data and
		3578	don't want to allocate memory separately and store a pointer to it in that
		3579	data member, you can also "subclass" the watcher type and provide your own
		3580	data:
		3581
		3582	struct my_io
		3583	{
		3584	ev_io io;
		3585	int otherfd;
		3586	void *somedata;
		3587	struct whatever *mostinteresting;
		3588	};
		3589
		3590	...
		3591	struct my_io w;
		3592	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3593
		3594	And since your callback will be called with a pointer to the watcher, you
		3595	can cast it back to your own type:
		3596
		3597	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3598	{
		3599	struct my_io *w = (struct my_io *)w_;
		3600	...
		3601	}
		3602
		3603	More interesting and less C-conformant ways of casting your callback
		3604	function type instead have been omitted.
		3605
		3606	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3607
		3608	Another common scenario is to use some data structure with multiple
		3609	embedded watchers, in effect creating your own watcher that combines
		3610	multiple libev event sources into one "super-watcher":
		3611
		3612	struct my_biggy
		3613	{
		3614	int some_data;
		3615	ev_timer t1;
		3616	ev_timer t2;
		3617	}
		3618
		3619	In this case getting the pointer to C<my_biggy> is a bit more
		3620	complicated: Either you store the address of your C<my_biggy> struct in
		3621	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3622	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3623	real programmers):
		3624
		3625	#include <stddef.h>
		3626
		3627	static void
		3628	t1_cb (EV_P_ ev_timer *w, int revents)
		3629	{
		3630	struct my_biggy big = (struct my_biggy *)
		3631	(((char *)w) - offsetof (struct my_biggy, t1));
		3632	}
		3633
		3634	static void
		3635	t2_cb (EV_P_ ev_timer *w, int revents)
		3636	{
		3637	struct my_biggy big = (struct my_biggy *)
		3638	(((char *)w) - offsetof (struct my_biggy, t2));
		3639	}
		3640
		3641	=head2 AVOIDING FINISHING BEFORE RETURNING
		3642
		3643	Often you have structures like this in event-based programs:
		3644
		3645	callback ()
1963	{	3646	{
1964	if (revents & EV_TIMEOUT)	3647	free (request);
1965	/* doh, nothing entered */;
1966	else if (revents & EV_READ)
1967	/* stdin might have data for us, joy! */;
1968	}	3648	}
1969		3649
1970	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3650	request = start_new_request (..., callback);
1971		3651
1972	=item ev_feed_event (ev_loop *, watcher *, int revents)	3652	The intent is to start some "lengthy" operation. The C<request> could be
		3653	used to cancel the operation, or do other things with it.
1973		3654
1974	Feeds the given event set into the event loop, as if the specified event	3655	It's not uncommon to have code paths in C<start_new_request> that
1975	had happened for the specified watcher (which must be a pointer to an	3656	immediately invoke the callback, for example, to report errors. Or you add
1976	initialised but not necessarily started event watcher).	3657	some caching layer that finds that it can skip the lengthy aspects of the
		3658	operation and simply invoke the callback with the result.
1977		3659
1978	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3660	The problem here is that this will happen I<before> C<start_new_request>
		3661	has returned, so C<request> is not set.
1979		3662
1980	Feed an event on the given fd, as if a file descriptor backend detected	3663	Even if you pass the request by some safer means to the callback, you
1981	the given events it.	3664	might want to do something to the request after starting it, such as
		3665	canceling it, which probably isn't working so well when the callback has
		3666	already been invoked.
1982		3667
1983	=item ev_feed_signal_event (ev_loop *loop, int signum)	3668	A common way around all these issues is to make sure that
		3669	C<start_new_request> I<always> returns before the callback is invoked. If
		3670	C<start_new_request> immediately knows the result, it can artificially
		3671	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3672	example, or more sneakily, by reusing an existing (stopped) watcher and
		3673	pushing it into the pending queue:
1984		3674
1985	Feed an event as if the given signal occured (C<loop> must be the default	3675	ev_set_cb (watcher, callback);
1986	loop!).	3676	ev_feed_event (EV_A_ watcher, 0);
1987		3677
1988	=back	3678	This way, C<start_new_request> can safely return before the callback is
		3679	invoked, while not delaying callback invocation too much.
		3680
		3681	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3682
		3683	Often (especially in GUI toolkits) there are places where you have
		3684	I<modal> interaction, which is most easily implemented by recursively
		3685	invoking C<ev_run>.
		3686
		3687	This brings the problem of exiting - a callback might want to finish the
		3688	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3689	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3690	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3691	other combination: In these cases, a simple C<ev_break> will not work.
		3692
		3693	The solution is to maintain "break this loop" variable for each C<ev_run>
		3694	invocation, and use a loop around C<ev_run> until the condition is
		3695	triggered, using C<EVRUN_ONCE>:
		3696
		3697	// main loop
		3698	int exit_main_loop = 0;
		3699
		3700	while (!exit_main_loop)
		3701	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3702
		3703	// in a modal watcher
		3704	int exit_nested_loop = 0;
		3705
		3706	while (!exit_nested_loop)
		3707	ev_run (EV_A_ EVRUN_ONCE);
		3708
		3709	To exit from any of these loops, just set the corresponding exit variable:
		3710
		3711	// exit modal loop
		3712	exit_nested_loop = 1;
		3713
		3714	// exit main program, after modal loop is finished
		3715	exit_main_loop = 1;
		3716
		3717	// exit both
		3718	exit_main_loop = exit_nested_loop = 1;
		3719
		3720	=head2 THREAD LOCKING EXAMPLE
		3721
		3722	Here is a fictitious example of how to run an event loop in a different
		3723	thread from where callbacks are being invoked and watchers are
		3724	created/added/removed.
		3725
		3726	For a real-world example, see the C<EV::Loop::Async> perl module,
		3727	which uses exactly this technique (which is suited for many high-level
		3728	languages).
		3729
		3730	The example uses a pthread mutex to protect the loop data, a condition
		3731	variable to wait for callback invocations, an async watcher to notify the
		3732	event loop thread and an unspecified mechanism to wake up the main thread.
		3733
		3734	First, you need to associate some data with the event loop:
		3735
		3736	typedef struct {
		3737	mutex_t lock; /* global loop lock */
		3738	ev_async async_w;
		3739	thread_t tid;
		3740	cond_t invoke_cv;
		3741	} userdata;
		3742
		3743	void prepare_loop (EV_P)
		3744	{
		3745	// for simplicity, we use a static userdata struct.
		3746	static userdata u;
		3747
		3748	ev_async_init (&u->async_w, async_cb);
		3749	ev_async_start (EV_A_ &u->async_w);
		3750
		3751	pthread_mutex_init (&u->lock, 0);
		3752	pthread_cond_init (&u->invoke_cv, 0);
		3753
		3754	// now associate this with the loop
		3755	ev_set_userdata (EV_A_ u);
		3756	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3757	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3758
		3759	// then create the thread running ev_run
		3760	pthread_create (&u->tid, 0, l_run, EV_A);
		3761	}
		3762
		3763	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3764	solely to wake up the event loop so it takes notice of any new watchers
		3765	that might have been added:
		3766
		3767	static void
		3768	async_cb (EV_P_ ev_async *w, int revents)
		3769	{
		3770	// just used for the side effects
		3771	}
		3772
		3773	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3774	protecting the loop data, respectively.
		3775
		3776	static void
		3777	l_release (EV_P)
		3778	{
		3779	userdata *u = ev_userdata (EV_A);
		3780	pthread_mutex_unlock (&u->lock);
		3781	}
		3782
		3783	static void
		3784	l_acquire (EV_P)
		3785	{
		3786	userdata *u = ev_userdata (EV_A);
		3787	pthread_mutex_lock (&u->lock);
		3788	}
		3789
		3790	The event loop thread first acquires the mutex, and then jumps straight
		3791	into C<ev_run>:
		3792
		3793	void *
		3794	l_run (void *thr_arg)
		3795	{
		3796	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3797
		3798	l_acquire (EV_A);
		3799	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3800	ev_run (EV_A_ 0);
		3801	l_release (EV_A);
		3802
		3803	return 0;
		3804	}
		3805
		3806	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3807	signal the main thread via some unspecified mechanism (signals? pipe
		3808	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3809	have been called (in a while loop because a) spurious wakeups are possible
		3810	and b) skipping inter-thread-communication when there are no pending
		3811	watchers is very beneficial):
		3812
		3813	static void
		3814	l_invoke (EV_P)
		3815	{
		3816	userdata *u = ev_userdata (EV_A);
		3817
		3818	while (ev_pending_count (EV_A))
		3819	{
		3820	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3821	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3822	}
		3823	}
		3824
		3825	Now, whenever the main thread gets told to invoke pending watchers, it
		3826	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3827	thread to continue:
		3828
		3829	static void
		3830	real_invoke_pending (EV_P)
		3831	{
		3832	userdata *u = ev_userdata (EV_A);
		3833
		3834	pthread_mutex_lock (&u->lock);
		3835	ev_invoke_pending (EV_A);
		3836	pthread_cond_signal (&u->invoke_cv);
		3837	pthread_mutex_unlock (&u->lock);
		3838	}
		3839
		3840	Whenever you want to start/stop a watcher or do other modifications to an
		3841	event loop, you will now have to lock:
		3842
		3843	ev_timer timeout_watcher;
		3844	userdata *u = ev_userdata (EV_A);
		3845
		3846	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3847
		3848	pthread_mutex_lock (&u->lock);
		3849	ev_timer_start (EV_A_ &timeout_watcher);
		3850	ev_async_send (EV_A_ &u->async_w);
		3851	pthread_mutex_unlock (&u->lock);
		3852
		3853	Note that sending the C<ev_async> watcher is required because otherwise
		3854	an event loop currently blocking in the kernel will have no knowledge
		3855	about the newly added timer. By waking up the loop it will pick up any new
		3856	watchers in the next event loop iteration.
		3857
		3858	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3859
		3860	While the overhead of a callback that e.g. schedules a thread is small, it
		3861	is still an overhead. If you embed libev, and your main usage is with some
		3862	kind of threads or coroutines, you might want to customise libev so that
		3863	doesn't need callbacks anymore.
		3864
		3865	Imagine you have coroutines that you can switch to using a function
		3866	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3867	and that due to some magic, the currently active coroutine is stored in a
		3868	global called C<current_coro>. Then you can build your own "wait for libev
		3869	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3870	the differing C<;> conventions):
		3871
		3872	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3873	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3874
		3875	That means instead of having a C callback function, you store the
		3876	coroutine to switch to in each watcher, and instead of having libev call
		3877	your callback, you instead have it switch to that coroutine.
		3878
		3879	A coroutine might now wait for an event with a function called
		3880	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3881	matter when, or whether the watcher is active or not when this function is
		3882	called):
		3883
		3884	void
		3885	wait_for_event (ev_watcher *w)
		3886	{
		3887	ev_set_cb (w, current_coro);
		3888	switch_to (libev_coro);
		3889	}
		3890
		3891	That basically suspends the coroutine inside C<wait_for_event> and
		3892	continues the libev coroutine, which, when appropriate, switches back to
		3893	this or any other coroutine.
		3894
		3895	You can do similar tricks if you have, say, threads with an event queue -
		3896	instead of storing a coroutine, you store the queue object and instead of
		3897	switching to a coroutine, you push the watcher onto the queue and notify
		3898	any waiters.
		3899
		3900	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		3901	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3902
		3903	// my_ev.h
		3904	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3905	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);
		3906	#include "../libev/ev.h"
		3907
		3908	// my_ev.c
		3909	#define EV_H "my_ev.h"
		3910	#include "../libev/ev.c"
		3911
		3912	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3913	F<my_ev.c> into your project. When properly specifying include paths, you
		3914	can even use F<ev.h> as header file name directly.
1989		3915
1990		3916
1991	=head1 LIBEVENT EMULATION	3917	=head1 LIBEVENT EMULATION
1992		3918
1993	Libev offers a compatibility emulation layer for libevent. It cannot	3919	Libev offers a compatibility emulation layer for libevent. It cannot
1994	emulate the internals of libevent, so here are some usage hints:	3920	emulate the internals of libevent, so here are some usage hints:
1995		3921
1996	=over 4	3922	=over 4
		3923
		3924	=item * Only the libevent-1.4.1-beta API is being emulated.
		3925
		3926	This was the newest libevent version available when libev was implemented,
		3927	and is still mostly unchanged in 2010.
1997		3928
1998	=item * Use it by including <event.h>, as usual.	3929	=item * Use it by including <event.h>, as usual.
1999		3930
2000	=item * The following members are fully supported: ev_base, ev_callback,	3931	=item * The following members are fully supported: ev_base, ev_callback,
2001	ev_arg, ev_fd, ev_res, ev_events.	3932	ev_arg, ev_fd, ev_res, ev_events.
…		…
2006		3937
2007	=item * Priorities are not currently supported. Initialising priorities	3938	=item * Priorities are not currently supported. Initialising priorities
2008	will fail and all watchers will have the same priority, even though there	3939	will fail and all watchers will have the same priority, even though there
2009	is an ev_pri field.	3940	is an ev_pri field.
2010		3941
		3942	=item * In libevent, the last base created gets the signals, in libev, the
		3943	base that registered the signal gets the signals.
		3944
2011	=item * Other members are not supported.	3945	=item * Other members are not supported.
2012		3946
2013	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3947	=item * The libev emulation is I<not> ABI compatible to libevent, you need
2014	to use the libev header file and library.	3948	to use the libev header file and library.
2015		3949
2016	=back	3950	=back
2017		3951
2018	=head1 C++ SUPPORT	3952	=head1 C++ SUPPORT
2019		3953
		3954	=head2 C API
		3955
		3956	The normal C API should work fine when used from C++: both ev.h and the
		3957	libev sources can be compiled as C++. Therefore, code that uses the C API
		3958	will work fine.
		3959
		3960	Proper exception specifications might have to be added to callbacks passed
		3961	to libev: exceptions may be thrown only from watcher callbacks, all
		3962	other callbacks (allocator, syserr, loop acquire/release and periodic
		3963	reschedule callbacks) must not throw exceptions, and might need a C<throw
		3964	()> specification. If you have code that needs to be compiled as both C
		3965	and C++ you can use the C<EV_THROW> macro for this:
		3966
		3967	static void
		3968	fatal_error (const char *msg) EV_THROW
		3969	{
		3970	perror (msg);
		3971	abort ();
		3972	}
		3973
		3974	...
		3975	ev_set_syserr_cb (fatal_error);
		3976
		3977	The only API functions that can currently throw exceptions are C<ev_run>,
		3978	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		3979	because it runs cleanup watchers).
		3980
		3981	Throwing exceptions in watcher callbacks is only supported if libev itself
		3982	is compiled with a C++ compiler or your C and C++ environments allow
		3983	throwing exceptions through C libraries (most do).
		3984
		3985	=head2 C++ API
		3986
2020	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3987	Libev comes with some simplistic wrapper classes for C++ that mainly allow
2021	you to use some convinience methods to start/stop watchers and also change	3988	you to use some convenience methods to start/stop watchers and also change
2022	the callback model to a model using method callbacks on objects.	3989	the callback model to a model using method callbacks on objects.
2023		3990
2024	To use it,	3991	To use it,
2025		3992
2026	#include <ev++.h>	3993	#include <ev++.h>
2027		3994
2028	This automatically includes F<ev.h> and puts all of its definitions (many	3995	This automatically includes F<ev.h> and puts all of its definitions (many
2029	of them macros) into the global namespace. All C++ specific things are	3996	of them macros) into the global namespace. All C++ specific things are
2030	put into the C<ev> namespace. It should support all the same embedding	3997	put into the C<ev> namespace. It should support all the same embedding
2031	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	3998	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
2033	Care has been taken to keep the overhead low. The only data member the C++	4000	Care has been taken to keep the overhead low. The only data member the C++
2034	classes add (compared to plain C-style watchers) is the event loop pointer	4001	classes add (compared to plain C-style watchers) is the event loop pointer
2035	that the watcher is associated with (or no additional members at all if	4002	that the watcher is associated with (or no additional members at all if
2036	you disable C<EV_MULTIPLICITY> when embedding libev).	4003	you disable C<EV_MULTIPLICITY> when embedding libev).
2037		4004
2038	Currently, functions, and static and non-static member functions can be	4005	Currently, functions, static and non-static member functions and classes
2039	used as callbacks. Other types should be easy to add as long as they only	4006	with C<operator ()> can be used as callbacks. Other types should be easy
2040	need one additional pointer for context. If you need support for other	4007	to add as long as they only need one additional pointer for context. If
2041	types of functors please contact the author (preferably after implementing	4008	you need support for other types of functors please contact the author
2042	it).	4009	(preferably after implementing it).
		4010
		4011	For all this to work, your C++ compiler either has to use the same calling
		4012	conventions as your C compiler (for static member functions), or you have
		4013	to embed libev and compile libev itself as C++.
2043		4014
2044	Here is a list of things available in the C<ev> namespace:	4015	Here is a list of things available in the C<ev> namespace:
2045		4016
2046	=over 4	4017	=over 4
2047		4018
…		…
2057	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	4028	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
2058		4029
2059	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4030	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
2060	the same name in the C<ev> namespace, with the exception of C<ev_signal>	4031	the same name in the C<ev> namespace, with the exception of C<ev_signal>
2061	which is called C<ev::sig> to avoid clashes with the C<signal> macro	4032	which is called C<ev::sig> to avoid clashes with the C<signal> macro
2062	defines by many implementations.	4033	defined by many implementations.
2063		4034
2064	All of those classes have these methods:	4035	All of those classes have these methods:
2065		4036
2066	=over 4	4037	=over 4
2067		4038
2068	=item ev::TYPE::TYPE ()	4039	=item ev::TYPE::TYPE ()
2069		4040
2070	=item ev::TYPE::TYPE (struct ev_loop *)	4041	=item ev::TYPE::TYPE (loop)
2071		4042
2072	=item ev::TYPE::~TYPE	4043	=item ev::TYPE::~TYPE
2073		4044
2074	The constructor (optionally) takes an event loop to associate the watcher	4045	The constructor (optionally) takes an event loop to associate the watcher
2075	with. If it is omitted, it will use C<EV_DEFAULT>.	4046	with. If it is omitted, it will use C<EV_DEFAULT>.
…		…
2098	your compiler is good :), then the method will be fully inlined into the	4069	your compiler is good :), then the method will be fully inlined into the
2099	thunking function, making it as fast as a direct C callback.	4070	thunking function, making it as fast as a direct C callback.
2100		4071
2101	Example: simple class declaration and watcher initialisation	4072	Example: simple class declaration and watcher initialisation
2102		4073
2103	struct myclass	4074	struct myclass
2104	{	4075	{
2105	void io_cb (ev::io &w, int revents) { }	4076	void io_cb (ev::io &w, int revents) { }
2106	}	4077	}
2107		4078
2108	myclass obj;	4079	myclass obj;
2109	ev::io iow;	4080	ev::io iow;
2110	iow.set <myclass, &myclass::io_cb> (&obj);	4081	iow.set <myclass, &myclass::io_cb> (&obj);
		4082
		4083	=item w->set (object *)
		4084
		4085	This is a variation of a method callback - leaving out the method to call
		4086	will default the method to C<operator ()>, which makes it possible to use
		4087	functor objects without having to manually specify the C<operator ()> all
		4088	the time. Incidentally, you can then also leave out the template argument
		4089	list.
		4090
		4091	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		4092	int revents)>.
		4093
		4094	See the method-C<set> above for more details.
		4095
		4096	Example: use a functor object as callback.
		4097
		4098	struct myfunctor
		4099	{
		4100	void operator() (ev::io &w, int revents)
		4101	{
		4102	...
		4103	}
		4104	}
		4105
		4106	myfunctor f;
		4107
		4108	ev::io w;
		4109	w.set (&f);
2111		4110
2112	=item w->set<function> (void *data = 0)	4111	=item w->set<function> (void *data = 0)
2113		4112
2114	Also sets a callback, but uses a static method or plain function as	4113	Also sets a callback, but uses a static method or plain function as
2115	callback. The optional C<data> argument will be stored in the watcher's	4114	callback. The optional C<data> argument will be stored in the watcher's
…		…
2117		4116
2118	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	4117	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2119		4118
2120	See the method-C<set> above for more details.	4119	See the method-C<set> above for more details.
2121		4120
2122	Example:	4121	Example: Use a plain function as callback.
2123		4122
2124	static void io_cb (ev::io &w, int revents) { }	4123	static void io_cb (ev::io &w, int revents) { }
2125	iow.set <io_cb> ();	4124	iow.set <io_cb> ();
2126		4125
2127	=item w->set (struct ev_loop *)	4126	=item w->set (loop)
2128		4127
2129	Associates a different C<struct ev_loop> with this watcher. You can only	4128	Associates a different C<struct ev_loop> with this watcher. You can only
2130	do this when the watcher is inactive (and not pending either).	4129	do this when the watcher is inactive (and not pending either).
2131		4130
2132	=item w->set ([args])	4131	=item w->set ([arguments])
2133		4132
2134	Basically the same as C<ev_TYPE_set>, with the same args. Must be	4133	Basically the same as C<ev_TYPE_set> (except for C<ev::embed> watchers>),
		4134	with the same arguments. Either this method or a suitable start method
2135	called at least once. Unlike the C counterpart, an active watcher gets	4135	must be called at least once. Unlike the C counterpart, an active watcher
2136	automatically stopped and restarted when reconfiguring it with this	4136	gets automatically stopped and restarted when reconfiguring it with this
2137	method.	4137	method.
		4138
		4139	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4140	clashing with the C<set (loop)> method.
2138		4141
2139	=item w->start ()	4142	=item w->start ()
2140		4143
2141	Starts the watcher. Note that there is no C<loop> argument, as the	4144	Starts the watcher. Note that there is no C<loop> argument, as the
2142	constructor already stores the event loop.	4145	constructor already stores the event loop.
2143		4146
		4147	=item w->start ([arguments])
		4148
		4149	Instead of calling C<set> and C<start> methods separately, it is often
		4150	convenient to wrap them in one call. Uses the same type of arguments as
		4151	the configure C<set> method of the watcher.
		4152
2144	=item w->stop ()	4153	=item w->stop ()
2145		4154
2146	Stops the watcher if it is active. Again, no C<loop> argument.	4155	Stops the watcher if it is active. Again, no C<loop> argument.
2147		4156
2148	=item w->again () (C<ev::timer>, C<ev::periodic> only)	4157	=item w->again () (C<ev::timer>, C<ev::periodic> only)
…		…
2160		4169
2161	=back	4170	=back
2162		4171
2163	=back	4172	=back
2164		4173
2165	Example: Define a class with an IO and idle watcher, start one of them in	4174	Example: Define a class with two I/O and idle watchers, start the I/O
2166	the constructor.	4175	watchers in the constructor.
2167		4176
2168	class myclass	4177	class myclass
2169	{	4178	{
2170	ev_io io; void io_cb (ev::io &w, int revents);	4179	ev::io io ; void io_cb (ev::io &w, int revents);
		4180	ev::io io2 ; void io2_cb (ev::io &w, int revents);
2171	ev_idle idle void idle_cb (ev::idle &w, int revents);	4181	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2172		4182
2173	myclass ();	4183	myclass (int fd)
2174	}	4184	{
2175
2176	myclass::myclass (int fd)
2177	{
2178	io .set <myclass, &myclass::io_cb > (this);	4185	io .set <myclass, &myclass::io_cb > (this);
		4186	io2 .set <myclass, &myclass::io2_cb > (this);
2179	idle.set <myclass, &myclass::idle_cb> (this);	4187	idle.set <myclass, &myclass::idle_cb> (this);
2180		4188
2181	io.start (fd, ev::READ);	4189	io.set (fd, ev::WRITE); // configure the watcher
		4190	io.start (); // start it whenever convenient
		4191
		4192	io2.start (fd, ev::READ); // set + start in one call
		4193	}
2182	}	4194	};
		4195
		4196
		4197	=head1 OTHER LANGUAGE BINDINGS
		4198
		4199	Libev does not offer other language bindings itself, but bindings for a
		4200	number of languages exist in the form of third-party packages. If you know
		4201	any interesting language binding in addition to the ones listed here, drop
		4202	me a note.
		4203
		4204	=over 4
		4205
		4206	=item Perl
		4207
		4208	The EV module implements the full libev API and is actually used to test
		4209	libev. EV is developed together with libev. Apart from the EV core module,
		4210	there are additional modules that implement libev-compatible interfaces
		4211	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		4212	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		4213	and C<EV::Glib>).
		4214
		4215	It can be found and installed via CPAN, its homepage is at
		4216	L<http://software.schmorp.de/pkg/EV>.
		4217
		4218	=item Python
		4219
		4220	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		4221	seems to be quite complete and well-documented.
		4222
		4223	=item Ruby
		4224
		4225	Tony Arcieri has written a ruby extension that offers access to a subset
		4226	of the libev API and adds file handle abstractions, asynchronous DNS and
		4227	more on top of it. It can be found via gem servers. Its homepage is at
		4228	L<http://rev.rubyforge.org/>.
		4229
		4230	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		4231	makes rev work even on mingw.
		4232
		4233	=item Haskell
		4234
		4235	A haskell binding to libev is available at
		4236	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		4237
		4238	=item D
		4239
		4240	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		4241	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
		4242
		4243	=item Ocaml
		4244
		4245	Erkki Seppala has written Ocaml bindings for libev, to be found at
		4246	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		4247
		4248	=item Lua
		4249
		4250	Brian Maher has written a partial interface to libev for lua (at the
		4251	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		4252	L<http://github.com/brimworks/lua-ev>.
		4253
		4254	=item Javascript
		4255
		4256	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4257
		4258	=item Others
		4259
		4260	There are others, and I stopped counting.
		4261
		4262	=back
2183		4263
2184		4264
2185	=head1 MACRO MAGIC	4265	=head1 MACRO MAGIC
2186		4266
2187	Libev can be compiled with a variety of options, the most fundamantal	4267	Libev can be compiled with a variety of options, the most fundamental
2188	of which is C<EV_MULTIPLICITY>. This option determines whether (most)	4268	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2189	functions and callbacks have an initial C<struct ev_loop *> argument.	4269	functions and callbacks have an initial C<struct ev_loop *> argument.
2190		4270
2191	To make it easier to write programs that cope with either variant, the	4271	To make it easier to write programs that cope with either variant, the
2192	following macros are defined:	4272	following macros are defined:
…		…
2197		4277
2198	This provides the loop I<argument> for functions, if one is required ("ev	4278	This provides the loop I<argument> for functions, if one is required ("ev
2199	loop argument"). The C<EV_A> form is used when this is the sole argument,	4279	loop argument"). The C<EV_A> form is used when this is the sole argument,
2200	C<EV_A_> is used when other arguments are following. Example:	4280	C<EV_A_> is used when other arguments are following. Example:
2201		4281
2202	ev_unref (EV_A);	4282	ev_unref (EV_A);
2203	ev_timer_add (EV_A_ watcher);	4283	ev_timer_add (EV_A_ watcher);
2204	ev_loop (EV_A_ 0);	4284	ev_run (EV_A_ 0);
2205		4285
2206	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	4286	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2207	which is often provided by the following macro.	4287	which is often provided by the following macro.
2208		4288
2209	=item C<EV_P>, C<EV_P_>	4289	=item C<EV_P>, C<EV_P_>
2210		4290
2211	This provides the loop I<parameter> for functions, if one is required ("ev	4291	This provides the loop I<parameter> for functions, if one is required ("ev
2212	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	4292	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
2213	C<EV_P_> is used when other parameters are following. Example:	4293	C<EV_P_> is used when other parameters are following. Example:
2214		4294
2215	// this is how ev_unref is being declared	4295	// this is how ev_unref is being declared
2216	static void ev_unref (EV_P);	4296	static void ev_unref (EV_P);
2217		4297
2218	// this is how you can declare your typical callback	4298	// this is how you can declare your typical callback
2219	static void cb (EV_P_ ev_timer *w, int revents)	4299	static void cb (EV_P_ ev_timer *w, int revents)
2220		4300
2221	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	4301	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
2222	suitable for use with C<EV_A>.	4302	suitable for use with C<EV_A>.
2223		4303
2224	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4304	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2225		4305
2226	Similar to the other two macros, this gives you the value of the default	4306	Similar to the other two macros, this gives you the value of the default
2227	loop, if multiple loops are supported ("ev loop default").	4307	loop, if multiple loops are supported ("ev loop default"). The default loop
		4308	will be initialised if it isn't already initialised.
		4309
		4310	For non-multiplicity builds, these macros do nothing, so you always have
		4311	to initialise the loop somewhere.
		4312
		4313	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		4314
		4315	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		4316	default loop has been initialised (C<UC> == unchecked). Their behaviour
		4317	is undefined when the default loop has not been initialised by a previous
		4318	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		4319
		4320	It is often prudent to use C<EV_DEFAULT> when initialising the first
		4321	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
2228		4322
2229	=back	4323	=back
2230		4324
2231	Example: Declare and initialise a check watcher, utilising the above	4325	Example: Declare and initialise a check watcher, utilising the above
2232	macros so it will work regardless of whether multiple loops are supported	4326	macros so it will work regardless of whether multiple loops are supported
2233	or not.	4327	or not.
2234		4328
2235	static void	4329	static void
2236	check_cb (EV_P_ ev_timer *w, int revents)	4330	check_cb (EV_P_ ev_timer *w, int revents)
2237	{	4331	{
2238	ev_check_stop (EV_A_ w);	4332	ev_check_stop (EV_A_ w);
2239	}	4333	}
2240		4334
2241	ev_check check;	4335	ev_check check;
2242	ev_check_init (&check, check_cb);	4336	ev_check_init (&check, check_cb);
2243	ev_check_start (EV_DEFAULT_ &check);	4337	ev_check_start (EV_DEFAULT_ &check);
2244	ev_loop (EV_DEFAULT_ 0);	4338	ev_run (EV_DEFAULT_ 0);
2245		4339
2246	=head1 EMBEDDING	4340	=head1 EMBEDDING
2247		4341
2248	Libev can (and often is) directly embedded into host	4342	Libev can (and often is) directly embedded into host
2249	applications. Examples of applications that embed it include the Deliantra	4343	applications. Examples of applications that embed it include the Deliantra
…		…
2256	libev somewhere in your source tree).	4350	libev somewhere in your source tree).
2257		4351
2258	=head2 FILESETS	4352	=head2 FILESETS
2259		4353
2260	Depending on what features you need you need to include one or more sets of files	4354	Depending on what features you need you need to include one or more sets of files
2261	in your app.	4355	in your application.
2262		4356
2263	=head3 CORE EVENT LOOP	4357	=head3 CORE EVENT LOOP
2264		4358
2265	To include only the libev core (all the C<ev_*> functions), with manual	4359	To include only the libev core (all the C<ev_*> functions), with manual
2266	configuration (no autoconf):	4360	configuration (no autoconf):
2267		4361
2268	#define EV_STANDALONE 1	4362	#define EV_STANDALONE 1
2269	#include "ev.c"	4363	#include "ev.c"
2270		4364
2271	This will automatically include F<ev.h>, too, and should be done in a	4365	This will automatically include F<ev.h>, too, and should be done in a
2272	single C source file only to provide the function implementations. To use	4366	single C source file only to provide the function implementations. To use
2273	it, do the same for F<ev.h> in all files wishing to use this API (best	4367	it, do the same for F<ev.h> in all files wishing to use this API (best
2274	done by writing a wrapper around F<ev.h> that you can include instead and	4368	done by writing a wrapper around F<ev.h> that you can include instead and
2275	where you can put other configuration options):	4369	where you can put other configuration options):
2276		4370
2277	#define EV_STANDALONE 1	4371	#define EV_STANDALONE 1
2278	#include "ev.h"	4372	#include "ev.h"
2279		4373
2280	Both header files and implementation files can be compiled with a C++	4374	Both header files and implementation files can be compiled with a C++
2281	compiler (at least, thats a stated goal, and breakage will be treated	4375	compiler (at least, that's a stated goal, and breakage will be treated
2282	as a bug).	4376	as a bug).
2283		4377
2284	You need the following files in your source tree, or in a directory	4378	You need the following files in your source tree, or in a directory
2285	in your include path (e.g. in libev/ when using -Ilibev):	4379	in your include path (e.g. in libev/ when using -Ilibev):
2286		4380
2287	ev.h	4381	ev.h
2288	ev.c	4382	ev.c
2289	ev_vars.h	4383	ev_vars.h
2290	ev_wrap.h	4384	ev_wrap.h
2291		4385
2292	ev_win32.c required on win32 platforms only	4386	ev_win32.c required on win32 platforms only
2293		4387
2294	ev_select.c only when select backend is enabled (which is enabled by default)	4388	ev_select.c only when select backend is enabled (which is enabled by default)
2295	ev_poll.c only when poll backend is enabled (disabled by default)	4389	ev_poll.c only when poll backend is enabled (disabled by default)
2296	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4390	ev_epoll.c only when the epoll backend is enabled (disabled by default)
2297	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	4391	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2298	ev_port.c only when the solaris port backend is enabled (disabled by default)	4392	ev_port.c only when the solaris port backend is enabled (disabled by default)
2299		4393
2300	F<ev.c> includes the backend files directly when enabled, so you only need	4394	F<ev.c> includes the backend files directly when enabled, so you only need
2301	to compile this single file.	4395	to compile this single file.
2302		4396
2303	=head3 LIBEVENT COMPATIBILITY API	4397	=head3 LIBEVENT COMPATIBILITY API
2304		4398
2305	To include the libevent compatibility API, also include:	4399	To include the libevent compatibility API, also include:
2306		4400
2307	#include "event.c"	4401	#include "event.c"
2308		4402
2309	in the file including F<ev.c>, and:	4403	in the file including F<ev.c>, and:
2310		4404
2311	#include "event.h"	4405	#include "event.h"
2312		4406
2313	in the files that want to use the libevent API. This also includes F<ev.h>.	4407	in the files that want to use the libevent API. This also includes F<ev.h>.
2314		4408
2315	You need the following additional files for this:	4409	You need the following additional files for this:
2316		4410
2317	event.h	4411	event.h
2318	event.c	4412	event.c
2319		4413
2320	=head3 AUTOCONF SUPPORT	4414	=head3 AUTOCONF SUPPORT
2321		4415
2322	Instead of using C<EV_STANDALONE=1> and providing your config in	4416	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2323	whatever way you want, you can also C<m4_include([libev.m4])> in your	4417	whatever way you want, you can also C<m4_include([libev.m4])> in your
2324	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	4418	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2325	include F<config.h> and configure itself accordingly.	4419	include F<config.h> and configure itself accordingly.
2326		4420
2327	For this of course you need the m4 file:	4421	For this of course you need the m4 file:
2328		4422
2329	libev.m4	4423	libev.m4
2330		4424
2331	=head2 PREPROCESSOR SYMBOLS/MACROS	4425	=head2 PREPROCESSOR SYMBOLS/MACROS
2332		4426
2333	Libev can be configured via a variety of preprocessor symbols you have to define	4427	Libev can be configured via a variety of preprocessor symbols you have to
2334	before including any of its files. The default is not to build for multiplicity	4428	define before including (or compiling) any of its files. The default in
2335	and only include the select backend.	4429	the absence of autoconf is documented for every option.
		4430
		4431	Symbols marked with "(h)" do not change the ABI, and can have different
		4432	values when compiling libev vs. including F<ev.h>, so it is permissible
		4433	to redefine them before including F<ev.h> without breaking compatibility
		4434	to a compiled library. All other symbols change the ABI, which means all
		4435	users of libev and the libev code itself must be compiled with compatible
		4436	settings.
2336		4437
2337	=over 4	4438	=over 4
2338		4439
		4440	=item EV_COMPAT3 (h)
		4441
		4442	Backwards compatibility is a major concern for libev. This is why this
		4443	release of libev comes with wrappers for the functions and symbols that
		4444	have been renamed between libev version 3 and 4.
		4445
		4446	You can disable these wrappers (to test compatibility with future
		4447	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		4448	sources. This has the additional advantage that you can drop the C<struct>
		4449	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		4450	typedef in that case.
		4451
		4452	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		4453	and in some even more future version the compatibility code will be
		4454	removed completely.
		4455
2339	=item EV_STANDALONE	4456	=item EV_STANDALONE (h)
2340		4457
2341	Must always be C<1> if you do not use autoconf configuration, which	4458	Must always be C<1> if you do not use autoconf configuration, which
2342	keeps libev from including F<config.h>, and it also defines dummy	4459	keeps libev from including F<config.h>, and it also defines dummy
2343	implementations for some libevent functions (such as logging, which is not	4460	implementations for some libevent functions (such as logging, which is not
2344	supported). It will also not define any of the structs usually found in	4461	supported). It will also not define any of the structs usually found in
2345	F<event.h> that are not directly supported by the libev core alone.	4462	F<event.h> that are not directly supported by the libev core alone.
2346		4463
		4464	In standalone mode, libev will still try to automatically deduce the
		4465	configuration, but has to be more conservative.
		4466
		4467	=item EV_USE_FLOOR
		4468
		4469	If defined to be C<1>, libev will use the C<floor ()> function for its
		4470	periodic reschedule calculations, otherwise libev will fall back on a
		4471	portable (slower) implementation. If you enable this, you usually have to
		4472	link against libm or something equivalent. Enabling this when the C<floor>
		4473	function is not available will fail, so the safe default is to not enable
		4474	this.
		4475
2347	=item EV_USE_MONOTONIC	4476	=item EV_USE_MONOTONIC
2348		4477
2349	If defined to be C<1>, libev will try to detect the availability of the	4478	If defined to be C<1>, libev will try to detect the availability of the
2350	monotonic clock option at both compiletime and runtime. Otherwise no use	4479	monotonic clock option at both compile time and runtime. Otherwise no
2351	of the monotonic clock option will be attempted. If you enable this, you	4480	use of the monotonic clock option will be attempted. If you enable this,
2352	usually have to link against librt or something similar. Enabling it when	4481	you usually have to link against librt or something similar. Enabling it
2353	the functionality isn't available is safe, though, although you have	4482	when the functionality isn't available is safe, though, although you have
2354	to make sure you link against any libraries where the C<clock_gettime>	4483	to make sure you link against any libraries where the C<clock_gettime>
2355	function is hiding in (often F<-lrt>).	4484	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2356		4485
2357	=item EV_USE_REALTIME	4486	=item EV_USE_REALTIME
2358		4487
2359	If defined to be C<1>, libev will try to detect the availability of the	4488	If defined to be C<1>, libev will try to detect the availability of the
2360	realtime clock option at compiletime (and assume its availability at	4489	real-time clock option at compile time (and assume its availability
2361	runtime if successful). Otherwise no use of the realtime clock option will	4490	at runtime if successful). Otherwise no use of the real-time clock
2362	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	4491	option will be attempted. This effectively replaces C<gettimeofday>
2363	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	4492	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2364	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	4493	correctness. See the note about libraries in the description of
		4494	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		4495	C<EV_USE_CLOCK_SYSCALL>.
		4496
		4497	=item EV_USE_CLOCK_SYSCALL
		4498
		4499	If defined to be C<1>, libev will try to use a direct syscall instead
		4500	of calling the system-provided C<clock_gettime> function. This option
		4501	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		4502	unconditionally pulls in C<libpthread>, slowing down single-threaded
		4503	programs needlessly. Using a direct syscall is slightly slower (in
		4504	theory), because no optimised vdso implementation can be used, but avoids
		4505	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		4506	higher, as it simplifies linking (no need for C<-lrt>).
2365		4507
2366	=item EV_USE_NANOSLEEP	4508	=item EV_USE_NANOSLEEP
2367		4509
2368	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	4510	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2369	and will use it for delays. Otherwise it will use C<select ()>.	4511	and will use it for delays. Otherwise it will use C<select ()>.
2370		4512
		4513	=item EV_USE_EVENTFD
		4514
		4515	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		4516	available and will probe for kernel support at runtime. This will improve
		4517	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		4518	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		4519	2.7 or newer, otherwise disabled.
		4520
2371	=item EV_USE_SELECT	4521	=item EV_USE_SELECT
2372		4522
2373	If undefined or defined to be C<1>, libev will compile in support for the	4523	If undefined or defined to be C<1>, libev will compile in support for the
2374	C<select>(2) backend. No attempt at autodetection will be done: if no	4524	C<select>(2) backend. No attempt at auto-detection will be done: if no
2375	other method takes over, select will be it. Otherwise the select backend	4525	other method takes over, select will be it. Otherwise the select backend
2376	will not be compiled in.	4526	will not be compiled in.
2377		4527
2378	=item EV_SELECT_USE_FD_SET	4528	=item EV_SELECT_USE_FD_SET
2379		4529
2380	If defined to C<1>, then the select backend will use the system C<fd_set>	4530	If defined to C<1>, then the select backend will use the system C<fd_set>
2381	structure. This is useful if libev doesn't compile due to a missing	4531	structure. This is useful if libev doesn't compile due to a missing
2382	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	4532	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2383	exotic systems. This usually limits the range of file descriptors to some	4533	on exotic systems. This usually limits the range of file descriptors to
2384	low limit such as 1024 or might have other limitations (winsocket only	4534	some low limit such as 1024 or might have other limitations (winsocket
2385	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	4535	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2386	influence the size of the C<fd_set> used.	4536	configures the maximum size of the C<fd_set>.
2387		4537
2388	=item EV_SELECT_IS_WINSOCKET	4538	=item EV_SELECT_IS_WINSOCKET
2389		4539
2390	When defined to C<1>, the select backend will assume that	4540	When defined to C<1>, the select backend will assume that
2391	select/socket/connect etc. don't understand file descriptors but	4541	select/socket/connect etc. don't understand file descriptors but
…		…
2393	be used is the winsock select). This means that it will call	4543	be used is the winsock select). This means that it will call
2394	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	4544	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2395	it is assumed that all these functions actually work on fds, even	4545	it is assumed that all these functions actually work on fds, even
2396	on win32. Should not be defined on non-win32 platforms.	4546	on win32. Should not be defined on non-win32 platforms.
2397		4547
		4548	=item EV_FD_TO_WIN32_HANDLE(fd)
		4549
		4550	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		4551	file descriptors to socket handles. When not defining this symbol (the
		4552	default), then libev will call C<_get_osfhandle>, which is usually
		4553	correct. In some cases, programs use their own file descriptor management,
		4554	in which case they can provide this function to map fds to socket handles.
		4555
		4556	=item EV_WIN32_HANDLE_TO_FD(handle)
		4557
		4558	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		4559	using the standard C<_open_osfhandle> function. For programs implementing
		4560	their own fd to handle mapping, overwriting this function makes it easier
		4561	to do so. This can be done by defining this macro to an appropriate value.
		4562
		4563	=item EV_WIN32_CLOSE_FD(fd)
		4564
		4565	If programs implement their own fd to handle mapping on win32, then this
		4566	macro can be used to override the C<close> function, useful to unregister
		4567	file descriptors again. Note that the replacement function has to close
		4568	the underlying OS handle.
		4569
		4570	=item EV_USE_WSASOCKET
		4571
		4572	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4573	communication socket, which works better in some environments. Otherwise,
		4574	the normal C<socket> function will be used, which works better in other
		4575	environments.
		4576
2398	=item EV_USE_POLL	4577	=item EV_USE_POLL
2399		4578
2400	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4579	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2401	backend. Otherwise it will be enabled on non-win32 platforms. It	4580	backend. Otherwise it will be enabled on non-win32 platforms. It
2402	takes precedence over select.	4581	takes precedence over select.
2403		4582
2404	=item EV_USE_EPOLL	4583	=item EV_USE_EPOLL
2405		4584
2406	If defined to be C<1>, libev will compile in support for the Linux	4585	If defined to be C<1>, libev will compile in support for the Linux
2407	C<epoll>(7) backend. Its availability will be detected at runtime,	4586	C<epoll>(7) backend. Its availability will be detected at runtime,
2408	otherwise another method will be used as fallback. This is the	4587	otherwise another method will be used as fallback. This is the preferred
2409	preferred backend for GNU/Linux systems.	4588	backend for GNU/Linux systems. If undefined, it will be enabled if the
		4589	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2410		4590
2411	=item EV_USE_KQUEUE	4591	=item EV_USE_KQUEUE
2412		4592
2413	If defined to be C<1>, libev will compile in support for the BSD style	4593	If defined to be C<1>, libev will compile in support for the BSD style
2414	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	4594	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2427	otherwise another method will be used as fallback. This is the preferred	4607	otherwise another method will be used as fallback. This is the preferred
2428	backend for Solaris 10 systems.	4608	backend for Solaris 10 systems.
2429		4609
2430	=item EV_USE_DEVPOLL	4610	=item EV_USE_DEVPOLL
2431		4611
2432	reserved for future expansion, works like the USE symbols above.	4612	Reserved for future expansion, works like the USE symbols above.
2433		4613
2434	=item EV_USE_INOTIFY	4614	=item EV_USE_INOTIFY
2435		4615
2436	If defined to be C<1>, libev will compile in support for the Linux inotify	4616	If defined to be C<1>, libev will compile in support for the Linux inotify
2437	interface to speed up C<ev_stat> watchers. Its actual availability will	4617	interface to speed up C<ev_stat> watchers. Its actual availability will
2438	be detected at runtime.	4618	be detected at runtime. If undefined, it will be enabled if the headers
		4619	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2439		4620
		4621	=item EV_NO_SMP
		4622
		4623	If defined to be C<1>, libev will assume that memory is always coherent
		4624	between threads, that is, threads can be used, but threads never run on
		4625	different cpus (or different cpu cores). This reduces dependencies
		4626	and makes libev faster.
		4627
		4628	=item EV_NO_THREADS
		4629
		4630	If defined to be C<1>, libev will assume that it will never be called from
		4631	different threads (that includes signal handlers), which is a stronger
		4632	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4633	libev faster.
		4634
		4635	=item EV_ATOMIC_T
		4636
		4637	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		4638	access is atomic with respect to other threads or signal contexts. No
		4639	such type is easily found in the C language, so you can provide your own
		4640	type that you know is safe for your purposes. It is used both for signal
		4641	handler "locking" as well as for signal and thread safety in C<ev_async>
		4642	watchers.
		4643
		4644	In the absence of this define, libev will use C<sig_atomic_t volatile>
		4645	(from F<signal.h>), which is usually good enough on most platforms.
		4646
2440	=item EV_H	4647	=item EV_H (h)
2441		4648
2442	The name of the F<ev.h> header file used to include it. The default if	4649	The name of the F<ev.h> header file used to include it. The default if
2443	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This	4650	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2444	can be used to virtually rename the F<ev.h> header file in case of conflicts.	4651	used to virtually rename the F<ev.h> header file in case of conflicts.
2445		4652
2446	=item EV_CONFIG_H	4653	=item EV_CONFIG_H (h)
2447		4654
2448	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	4655	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2449	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	4656	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2450	C<EV_H>, above.	4657	C<EV_H>, above.
2451		4658
2452	=item EV_EVENT_H	4659	=item EV_EVENT_H (h)
2453		4660
2454	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	4661	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2455	of how the F<event.h> header can be found.	4662	of how the F<event.h> header can be found, the default is C<"event.h">.
2456		4663
2457	=item EV_PROTOTYPES	4664	=item EV_PROTOTYPES (h)
2458		4665
2459	If defined to be C<0>, then F<ev.h> will not define any function	4666	If defined to be C<0>, then F<ev.h> will not define any function
2460	prototypes, but still define all the structs and other symbols. This is	4667	prototypes, but still define all the structs and other symbols. This is
2461	occasionally useful if you want to provide your own wrapper functions	4668	occasionally useful if you want to provide your own wrapper functions
2462	around libev functions.	4669	around libev functions.
…		…
2467	will have the C<struct ev_loop *> as first argument, and you can create	4674	will have the C<struct ev_loop *> as first argument, and you can create
2468	additional independent event loops. Otherwise there will be no support	4675	additional independent event loops. Otherwise there will be no support
2469	for multiple event loops and there is no first event loop pointer	4676	for multiple event loops and there is no first event loop pointer
2470	argument. Instead, all functions act on the single default loop.	4677	argument. Instead, all functions act on the single default loop.
2471		4678
		4679	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4680	default loop when multiplicity is switched off - you always have to
		4681	initialise the loop manually in this case.
		4682
2472	=item EV_MINPRI	4683	=item EV_MINPRI
2473		4684
2474	=item EV_MAXPRI	4685	=item EV_MAXPRI
2475		4686
2476	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4687	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
2481	When doing priority-based operations, libev usually has to linearly search	4692	When doing priority-based operations, libev usually has to linearly search
2482	all the priorities, so having many of them (hundreds) uses a lot of space	4693	all the priorities, so having many of them (hundreds) uses a lot of space
2483	and time, so using the defaults of five priorities (-2 .. +2) is usually	4694	and time, so using the defaults of five priorities (-2 .. +2) is usually
2484	fine.	4695	fine.
2485		4696
2486	If your embedding app does not need any priorities, defining these both to	4697	If your embedding application does not need any priorities, defining these
2487	C<0> will save some memory and cpu.	4698	both to C<0> will save some memory and CPU.
2488		4699
2489	=item EV_PERIODIC_ENABLE	4700	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		4701	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		4702	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
2490		4703
2491	If undefined or defined to be C<1>, then periodic timers are supported. If	4704	If undefined or defined to be C<1> (and the platform supports it), then
2492	defined to be C<0>, then they are not. Disabling them saves a few kB of	4705	the respective watcher type is supported. If defined to be C<0>, then it
2493	code.	4706	is not. Disabling watcher types mainly saves code size.
2494		4707
2495	=item EV_IDLE_ENABLE	4708	=item EV_FEATURES
2496
2497	If undefined or defined to be C<1>, then idle watchers are supported. If
2498	defined to be C<0>, then they are not. Disabling them saves a few kB of
2499	code.
2500
2501	=item EV_EMBED_ENABLE
2502
2503	If undefined or defined to be C<1>, then embed watchers are supported. If
2504	defined to be C<0>, then they are not.
2505
2506	=item EV_STAT_ENABLE
2507
2508	If undefined or defined to be C<1>, then stat watchers are supported. If
2509	defined to be C<0>, then they are not.
2510
2511	=item EV_FORK_ENABLE
2512
2513	If undefined or defined to be C<1>, then fork watchers are supported. If
2514	defined to be C<0>, then they are not.
2515
2516	=item EV_MINIMAL
2517		4709
2518	If you need to shave off some kilobytes of code at the expense of some	4710	If you need to shave off some kilobytes of code at the expense of some
2519	speed, define this symbol to C<1>. Currently only used for gcc to override	4711	speed (but with the full API), you can define this symbol to request
2520	some inlining decisions, saves roughly 30% codesize of amd64.	4712	certain subsets of functionality. The default is to enable all features
		4713	that can be enabled on the platform.
		4714
		4715	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4716	with some broad features you want) and then selectively re-enable
		4717	additional parts you want, for example if you want everything minimal,
		4718	but multiple event loop support, async and child watchers and the poll
		4719	backend, use this:
		4720
		4721	#define EV_FEATURES 0
		4722	#define EV_MULTIPLICITY 1
		4723	#define EV_USE_POLL 1
		4724	#define EV_CHILD_ENABLE 1
		4725	#define EV_ASYNC_ENABLE 1
		4726
		4727	The actual value is a bitset, it can be a combination of the following
		4728	values (by default, all of these are enabled):
		4729
		4730	=over 4
		4731
		4732	=item C<1> - faster/larger code
		4733
		4734	Use larger code to speed up some operations.
		4735
		4736	Currently this is used to override some inlining decisions (enlarging the
		4737	code size by roughly 30% on amd64).
		4738
		4739	When optimising for size, use of compiler flags such as C<-Os> with
		4740	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4741	assertions.
		4742
		4743	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4744	(e.g. gcc with C<-Os>).
		4745
		4746	=item C<2> - faster/larger data structures
		4747
		4748	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4749	hash table sizes and so on. This will usually further increase code size
		4750	and can additionally have an effect on the size of data structures at
		4751	runtime.
		4752
		4753	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4754	(e.g. gcc with C<-Os>).
		4755
		4756	=item C<4> - full API configuration
		4757
		4758	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4759	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4760
		4761	=item C<8> - full API
		4762
		4763	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4764	details on which parts of the API are still available without this
		4765	feature, and do not complain if this subset changes over time.
		4766
		4767	=item C<16> - enable all optional watcher types
		4768
		4769	Enables all optional watcher types. If you want to selectively enable
		4770	only some watcher types other than I/O and timers (e.g. prepare,
		4771	embed, async, child...) you can enable them manually by defining
		4772	C<EV_watchertype_ENABLE> to C<1> instead.
		4773
		4774	=item C<32> - enable all backends
		4775
		4776	This enables all backends - without this feature, you need to enable at
		4777	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4778
		4779	=item C<64> - enable OS-specific "helper" APIs
		4780
		4781	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4782	default.
		4783
		4784	=back
		4785
		4786	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4787	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4788	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4789	watchers, timers and monotonic clock support.
		4790
		4791	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4792	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4793	your program might be left out as well - a binary starting a timer and an
		4794	I/O watcher then might come out at only 5Kb.
		4795
		4796	=item EV_API_STATIC
		4797
		4798	If this symbol is defined (by default it is not), then all identifiers
		4799	will have static linkage. This means that libev will not export any
		4800	identifiers, and you cannot link against libev anymore. This can be useful
		4801	when you embed libev, only want to use libev functions in a single file,
		4802	and do not want its identifiers to be visible.
		4803
		4804	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4805	wants to use libev.
		4806
		4807	This option only works when libev is compiled with a C compiler, as C++
		4808	doesn't support the required declaration syntax.
		4809
		4810	=item EV_AVOID_STDIO
		4811
		4812	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4813	functions (printf, scanf, perror etc.). This will increase the code size
		4814	somewhat, but if your program doesn't otherwise depend on stdio and your
		4815	libc allows it, this avoids linking in the stdio library which is quite
		4816	big.
		4817
		4818	Note that error messages might become less precise when this option is
		4819	enabled.
		4820
		4821	=item EV_NSIG
		4822
		4823	The highest supported signal number, +1 (or, the number of
		4824	signals): Normally, libev tries to deduce the maximum number of signals
		4825	automatically, but sometimes this fails, in which case it can be
		4826	specified. Also, using a lower number than detected (C<32> should be
		4827	good for about any system in existence) can save some memory, as libev
		4828	statically allocates some 12-24 bytes per signal number.
2521		4829
2522	=item EV_PID_HASHSIZE	4830	=item EV_PID_HASHSIZE
2523		4831
2524	C<ev_child> watchers use a small hash table to distribute workload by	4832	C<ev_child> watchers use a small hash table to distribute workload by
2525	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	4833	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
2526	than enough. If you need to manage thousands of children you might want to	4834	usually more than enough. If you need to manage thousands of children you
2527	increase this value (I<must> be a power of two).	4835	might want to increase this value (I<must> be a power of two).
2528		4836
2529	=item EV_INOTIFY_HASHSIZE	4837	=item EV_INOTIFY_HASHSIZE
2530		4838
2531	C<ev_staz> watchers use a small hash table to distribute workload by	4839	C<ev_stat> watchers use a small hash table to distribute workload by
2532	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	4840	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
2533	usually more than enough. If you need to manage thousands of C<ev_stat>	4841	disabled), usually more than enough. If you need to manage thousands of
2534	watchers you might want to increase this value (I<must> be a power of	4842	C<ev_stat> watchers you might want to increase this value (I<must> be a
2535	two).	4843	power of two).
		4844
		4845	=item EV_USE_4HEAP
		4846
		4847	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4848	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		4849	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		4850	faster performance with many (thousands) of watchers.
		4851
		4852	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4853	will be C<0>.
		4854
		4855	=item EV_HEAP_CACHE_AT
		4856
		4857	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4858	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		4859	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		4860	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		4861	but avoids random read accesses on heap changes. This improves performance
		4862	noticeably with many (hundreds) of watchers.
		4863
		4864	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4865	will be C<0>.
		4866
		4867	=item EV_VERIFY
		4868
		4869	Controls how much internal verification (see C<ev_verify ()>) will
		4870	be done: If set to C<0>, no internal verification code will be compiled
		4871	in. If set to C<1>, then verification code will be compiled in, but not
		4872	called. If set to C<2>, then the internal verification code will be
		4873	called once per loop, which can slow down libev. If set to C<3>, then the
		4874	verification code will be called very frequently, which will slow down
		4875	libev considerably.
		4876
		4877	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4878	will be C<0>.
2536		4879
2537	=item EV_COMMON	4880	=item EV_COMMON
2538		4881
2539	By default, all watchers have a C<void *data> member. By redefining	4882	By default, all watchers have a C<void *data> member. By redefining
2540	this macro to a something else you can include more and other types of	4883	this macro to something else you can include more and other types of
2541	members. You have to define it each time you include one of the files,	4884	members. You have to define it each time you include one of the files,
2542	though, and it must be identical each time.	4885	though, and it must be identical each time.
2543		4886
2544	For example, the perl EV module uses something like this:	4887	For example, the perl EV module uses something like this:
2545		4888
2546	#define EV_COMMON \	4889	#define EV_COMMON \
2547	SV *self; /* contains this struct */ \	4890	SV *self; /* contains this struct */ \
2548	SV *cb_sv, *fh /* note no trailing ";" */	4891	SV *cb_sv, *fh /* note no trailing ";" */
2549		4892
2550	=item EV_CB_DECLARE (type)	4893	=item EV_CB_DECLARE (type)
2551		4894
2552	=item EV_CB_INVOKE (watcher, revents)	4895	=item EV_CB_INVOKE (watcher, revents)
2553		4896
…		…
2558	definition and a statement, respectively. See the F<ev.h> header file for	4901	definition and a statement, respectively. See the F<ev.h> header file for
2559	their default definitions. One possible use for overriding these is to	4902	their default definitions. One possible use for overriding these is to
2560	avoid the C<struct ev_loop *> as first argument in all cases, or to use	4903	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2561	method calls instead of plain function calls in C++.	4904	method calls instead of plain function calls in C++.
2562		4905
		4906	=back
		4907
2563	=head2 EXPORTED API SYMBOLS	4908	=head2 EXPORTED API SYMBOLS
2564		4909
2565	If you need to re-export the API (e.g. via a dll) and you need a list of	4910	If you need to re-export the API (e.g. via a DLL) and you need a list of
2566	exported symbols, you can use the provided F<Symbol.*> files which list	4911	exported symbols, you can use the provided F<Symbol.*> files which list
2567	all public symbols, one per line:	4912	all public symbols, one per line:
2568		4913
2569	Symbols.ev for libev proper	4914	Symbols.ev for libev proper
2570	Symbols.event for the libevent emulation	4915	Symbols.event for the libevent emulation
2571		4916
2572	This can also be used to rename all public symbols to avoid clashes with	4917	This can also be used to rename all public symbols to avoid clashes with
2573	multiple versions of libev linked together (which is obviously bad in	4918	multiple versions of libev linked together (which is obviously bad in
2574	itself, but sometimes it is inconvinient to avoid this).	4919	itself, but sometimes it is inconvenient to avoid this).
2575		4920
2576	A sed command like this will create wrapper C<#define>'s that you need to	4921	A sed command like this will create wrapper C<#define>'s that you need to
2577	include before including F<ev.h>:	4922	include before including F<ev.h>:
2578		4923
2579	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h	4924	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
…		…
2596	file.	4941	file.
2597		4942
2598	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	4943	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2599	that everybody includes and which overrides some configure choices:	4944	that everybody includes and which overrides some configure choices:
2600		4945
2601	#define EV_MINIMAL 1	4946	#define EV_FEATURES 8
2602	#define EV_USE_POLL 0	4947	#define EV_USE_SELECT 1
2603	#define EV_MULTIPLICITY 0
2604	#define EV_PERIODIC_ENABLE 0	4948	#define EV_PREPARE_ENABLE 1
		4949	#define EV_IDLE_ENABLE 1
2605	#define EV_STAT_ENABLE 0	4950	#define EV_SIGNAL_ENABLE 1
2606	#define EV_FORK_ENABLE 0	4951	#define EV_CHILD_ENABLE 1
		4952	#define EV_USE_STDEXCEPT 0
2607	#define EV_CONFIG_H <config.h>	4953	#define EV_CONFIG_H <config.h>
2608	#define EV_MINPRI 0
2609	#define EV_MAXPRI 0
2610		4954
2611	#include "ev++.h"	4955	#include "ev++.h"
2612		4956
2613	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4957	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2614		4958
2615	#include "ev_cpp.h"	4959	#include "ev_cpp.h"
2616	#include "ev.c"	4960	#include "ev.c"
2617		4961
		4962	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
2618		4963
		4964	=head2 THREADS AND COROUTINES
		4965
		4966	=head3 THREADS
		4967
		4968	All libev functions are reentrant and thread-safe unless explicitly
		4969	documented otherwise, but libev implements no locking itself. This means
		4970	that you can use as many loops as you want in parallel, as long as there
		4971	are no concurrent calls into any libev function with the same loop
		4972	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4973	of course): libev guarantees that different event loops share no data
		4974	structures that need any locking.
		4975
		4976	Or to put it differently: calls with different loop parameters can be done
		4977	concurrently from multiple threads, calls with the same loop parameter
		4978	must be done serially (but can be done from different threads, as long as
		4979	only one thread ever is inside a call at any point in time, e.g. by using
		4980	a mutex per loop).
		4981
		4982	Specifically to support threads (and signal handlers), libev implements
		4983	so-called C<ev_async> watchers, which allow some limited form of
		4984	concurrency on the same event loop, namely waking it up "from the
		4985	outside".
		4986
		4987	If you want to know which design (one loop, locking, or multiple loops
		4988	without or something else still) is best for your problem, then I cannot
		4989	help you, but here is some generic advice:
		4990
		4991	=over 4
		4992
		4993	=item * most applications have a main thread: use the default libev loop
		4994	in that thread, or create a separate thread running only the default loop.
		4995
		4996	This helps integrating other libraries or software modules that use libev
		4997	themselves and don't care/know about threading.
		4998
		4999	=item * one loop per thread is usually a good model.
		5000
		5001	Doing this is almost never wrong, sometimes a better-performance model
		5002	exists, but it is always a good start.
		5003
		5004	=item * other models exist, such as the leader/follower pattern, where one
		5005	loop is handed through multiple threads in a kind of round-robin fashion.
		5006
		5007	Choosing a model is hard - look around, learn, know that usually you can do
		5008	better than you currently do :-)
		5009
		5010	=item * often you need to talk to some other thread which blocks in the
		5011	event loop.
		5012
		5013	C<ev_async> watchers can be used to wake them up from other threads safely
		5014	(or from signal contexts...).
		5015
		5016	An example use would be to communicate signals or other events that only
		5017	work in the default loop by registering the signal watcher with the
		5018	default loop and triggering an C<ev_async> watcher from the default loop
		5019	watcher callback into the event loop interested in the signal.
		5020
		5021	=back
		5022
		5023	See also L</THREAD LOCKING EXAMPLE>.
		5024
		5025	=head3 COROUTINES
		5026
		5027	Libev is very accommodating to coroutines ("cooperative threads"):
		5028	libev fully supports nesting calls to its functions from different
		5029	coroutines (e.g. you can call C<ev_run> on the same loop from two
		5030	different coroutines, and switch freely between both coroutines running
		5031	the loop, as long as you don't confuse yourself). The only exception is
		5032	that you must not do this from C<ev_periodic> reschedule callbacks.
		5033
		5034	Care has been taken to ensure that libev does not keep local state inside
		5035	C<ev_run>, and other calls do not usually allow for coroutine switches as
		5036	they do not call any callbacks.
		5037
		5038	=head2 COMPILER WARNINGS
		5039
		5040	Depending on your compiler and compiler settings, you might get no or a
		5041	lot of warnings when compiling libev code. Some people are apparently
		5042	scared by this.
		5043
		5044	However, these are unavoidable for many reasons. For one, each compiler
		5045	has different warnings, and each user has different tastes regarding
		5046	warning options. "Warn-free" code therefore cannot be a goal except when
		5047	targeting a specific compiler and compiler-version.
		5048
		5049	Another reason is that some compiler warnings require elaborate
		5050	workarounds, or other changes to the code that make it less clear and less
		5051	maintainable.
		5052
		5053	And of course, some compiler warnings are just plain stupid, or simply
		5054	wrong (because they don't actually warn about the condition their message
		5055	seems to warn about). For example, certain older gcc versions had some
		5056	warnings that resulted in an extreme number of false positives. These have
		5057	been fixed, but some people still insist on making code warn-free with
		5058	such buggy versions.
		5059
		5060	While libev is written to generate as few warnings as possible,
		5061	"warn-free" code is not a goal, and it is recommended not to build libev
		5062	with any compiler warnings enabled unless you are prepared to cope with
		5063	them (e.g. by ignoring them). Remember that warnings are just that:
		5064	warnings, not errors, or proof of bugs.
		5065
		5066
		5067	=head2 VALGRIND
		5068
		5069	Valgrind has a special section here because it is a popular tool that is
		5070	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		5071
		5072	If you think you found a bug (memory leak, uninitialised data access etc.)
		5073	in libev, then check twice: If valgrind reports something like:
		5074
		5075	==2274== definitely lost: 0 bytes in 0 blocks.
		5076	==2274== possibly lost: 0 bytes in 0 blocks.
		5077	==2274== still reachable: 256 bytes in 1 blocks.
		5078
		5079	Then there is no memory leak, just as memory accounted to global variables
		5080	is not a memleak - the memory is still being referenced, and didn't leak.
		5081
		5082	Similarly, under some circumstances, valgrind might report kernel bugs
		5083	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		5084	although an acceptable workaround has been found here), or it might be
		5085	confused.
		5086
		5087	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		5088	make it into some kind of religion.
		5089
		5090	If you are unsure about something, feel free to contact the mailing list
		5091	with the full valgrind report and an explanation on why you think this
		5092	is a bug in libev (best check the archives, too :). However, don't be
		5093	annoyed when you get a brisk "this is no bug" answer and take the chance
		5094	of learning how to interpret valgrind properly.
		5095
		5096	If you need, for some reason, empty reports from valgrind for your project
		5097	I suggest using suppression lists.
		5098
		5099
		5100	=head1 PORTABILITY NOTES
		5101
		5102	=head2 GNU/LINUX 32 BIT LIMITATIONS
		5103
		5104	GNU/Linux is the only common platform that supports 64 bit file/large file
		5105	interfaces but I<disables> them by default.
		5106
		5107	That means that libev compiled in the default environment doesn't support
		5108	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
		5109
		5110	Unfortunately, many programs try to work around this GNU/Linux issue
		5111	by enabling the large file API, which makes them incompatible with the
		5112	standard libev compiled for their system.
		5113
		5114	Likewise, libev cannot enable the large file API itself as this would
		5115	suddenly make it incompatible to the default compile time environment,
		5116	i.e. all programs not using special compile switches.
		5117
		5118	=head2 OS/X AND DARWIN BUGS
		5119
		5120	The whole thing is a bug if you ask me - basically any system interface
		5121	you touch is broken, whether it is locales, poll, kqueue or even the
		5122	OpenGL drivers.
		5123
		5124	=head3 C<kqueue> is buggy
		5125
		5126	The kqueue syscall is broken in all known versions - most versions support
		5127	only sockets, many support pipes.
		5128
		5129	Libev tries to work around this by not using C<kqueue> by default on this
		5130	rotten platform, but of course you can still ask for it when creating a
		5131	loop - embedding a socket-only kqueue loop into a select-based one is
		5132	probably going to work well.
		5133
		5134	=head3 C<poll> is buggy
		5135
		5136	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		5137	implementation by something calling C<kqueue> internally around the 10.5.6
		5138	release, so now C<kqueue> I<and> C<poll> are broken.
		5139
		5140	Libev tries to work around this by not using C<poll> by default on
		5141	this rotten platform, but of course you can still ask for it when creating
		5142	a loop.
		5143
		5144	=head3 C<select> is buggy
		5145
		5146	All that's left is C<select>, and of course Apple found a way to fuck this
		5147	one up as well: On OS/X, C<select> actively limits the number of file
		5148	descriptors you can pass in to 1024 - your program suddenly crashes when
		5149	you use more.
		5150
		5151	There is an undocumented "workaround" for this - defining
		5152	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		5153	work on OS/X.
		5154
		5155	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		5156
		5157	=head3 C<errno> reentrancy
		5158
		5159	The default compile environment on Solaris is unfortunately so
		5160	thread-unsafe that you can't even use components/libraries compiled
		5161	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		5162	defined by default. A valid, if stupid, implementation choice.
		5163
		5164	If you want to use libev in threaded environments you have to make sure
		5165	it's compiled with C<_REENTRANT> defined.
		5166
		5167	=head3 Event port backend
		5168
		5169	The scalable event interface for Solaris is called "event
		5170	ports". Unfortunately, this mechanism is very buggy in all major
		5171	releases. If you run into high CPU usage, your program freezes or you get
		5172	a large number of spurious wakeups, make sure you have all the relevant
		5173	and latest kernel patches applied. No, I don't know which ones, but there
		5174	are multiple ones to apply, and afterwards, event ports actually work
		5175	great.
		5176
		5177	If you can't get it to work, you can try running the program by setting
		5178	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		5179	C<select> backends.
		5180
		5181	=head2 AIX POLL BUG
		5182
		5183	AIX unfortunately has a broken C<poll.h> header. Libev works around
		5184	this by trying to avoid the poll backend altogether (i.e. it's not even
		5185	compiled in), which normally isn't a big problem as C<select> works fine
		5186	with large bitsets on AIX, and AIX is dead anyway.
		5187
		5188	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		5189
		5190	=head3 General issues
		5191
		5192	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		5193	requires, and its I/O model is fundamentally incompatible with the POSIX
		5194	model. Libev still offers limited functionality on this platform in
		5195	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		5196	descriptors. This only applies when using Win32 natively, not when using
		5197	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		5198	as every compiler comes with a slightly differently broken/incompatible
		5199	environment.
		5200
		5201	Lifting these limitations would basically require the full
		5202	re-implementation of the I/O system. If you are into this kind of thing,
		5203	then note that glib does exactly that for you in a very portable way (note
		5204	also that glib is the slowest event library known to man).
		5205
		5206	There is no supported compilation method available on windows except
		5207	embedding it into other applications.
		5208
		5209	Sensible signal handling is officially unsupported by Microsoft - libev
		5210	tries its best, but under most conditions, signals will simply not work.
		5211
		5212	Not a libev limitation but worth mentioning: windows apparently doesn't
		5213	accept large writes: instead of resulting in a partial write, windows will
		5214	either accept everything or return C<ENOBUFS> if the buffer is too large,
		5215	so make sure you only write small amounts into your sockets (less than a
		5216	megabyte seems safe, but this apparently depends on the amount of memory
		5217	available).
		5218
		5219	Due to the many, low, and arbitrary limits on the win32 platform and
		5220	the abysmal performance of winsockets, using a large number of sockets
		5221	is not recommended (and not reasonable). If your program needs to use
		5222	more than a hundred or so sockets, then likely it needs to use a totally
		5223	different implementation for windows, as libev offers the POSIX readiness
		5224	notification model, which cannot be implemented efficiently on windows
		5225	(due to Microsoft monopoly games).
		5226
		5227	A typical way to use libev under windows is to embed it (see the embedding
		5228	section for details) and use the following F<evwrap.h> header file instead
		5229	of F<ev.h>:
		5230
		5231	#define EV_STANDALONE /* keeps ev from requiring config.h */
		5232	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		5233
		5234	#include "ev.h"
		5235
		5236	And compile the following F<evwrap.c> file into your project (make sure
		5237	you do I<not> compile the F<ev.c> or any other embedded source files!):
		5238
		5239	#include "evwrap.h"
		5240	#include "ev.c"
		5241
		5242	=head3 The winsocket C<select> function
		5243
		5244	The winsocket C<select> function doesn't follow POSIX in that it
		5245	requires socket I<handles> and not socket I<file descriptors> (it is
		5246	also extremely buggy). This makes select very inefficient, and also
		5247	requires a mapping from file descriptors to socket handles (the Microsoft
		5248	C runtime provides the function C<_open_osfhandle> for this). See the
		5249	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		5250	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		5251
		5252	The configuration for a "naked" win32 using the Microsoft runtime
		5253	libraries and raw winsocket select is:
		5254
		5255	#define EV_USE_SELECT 1
		5256	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		5257
		5258	Note that winsockets handling of fd sets is O(n), so you can easily get a
		5259	complexity in the O(n²) range when using win32.
		5260
		5261	=head3 Limited number of file descriptors
		5262
		5263	Windows has numerous arbitrary (and low) limits on things.
		5264
		5265	Early versions of winsocket's select only supported waiting for a maximum
		5266	of C<64> handles (probably owning to the fact that all windows kernels
		5267	can only wait for C<64> things at the same time internally; Microsoft
		5268	recommends spawning a chain of threads and wait for 63 handles and the
		5269	previous thread in each. Sounds great!).
		5270
		5271	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		5272	to some high number (e.g. C<2048>) before compiling the winsocket select
		5273	call (which might be in libev or elsewhere, for example, perl and many
		5274	other interpreters do their own select emulation on windows).
		5275
		5276	Another limit is the number of file descriptors in the Microsoft runtime
		5277	libraries, which by default is C<64> (there must be a hidden I<64>
		5278	fetish or something like this inside Microsoft). You can increase this
		5279	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		5280	(another arbitrary limit), but is broken in many versions of the Microsoft
		5281	runtime libraries. This might get you to about C<512> or C<2048> sockets
		5282	(depending on windows version and/or the phase of the moon). To get more,
		5283	you need to wrap all I/O functions and provide your own fd management, but
		5284	the cost of calling select (O(n²)) will likely make this unworkable.
		5285
		5286	=head2 PORTABILITY REQUIREMENTS
		5287
		5288	In addition to a working ISO-C implementation and of course the
		5289	backend-specific APIs, libev relies on a few additional extensions:
		5290
		5291	=over 4
		5292
		5293	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		5294	calling conventions regardless of C<ev_watcher_type *>.
		5295
		5296	Libev assumes not only that all watcher pointers have the same internal
		5297	structure (guaranteed by POSIX but not by ISO C for example), but it also
		5298	assumes that the same (machine) code can be used to call any watcher
		5299	callback: The watcher callbacks have different type signatures, but libev
		5300	calls them using an C<ev_watcher *> internally.
		5301
		5302	=item pointer accesses must be thread-atomic
		5303
		5304	Accessing a pointer value must be atomic, it must both be readable and
		5305	writable in one piece - this is the case on all current architectures.
		5306
		5307	=item C<sig_atomic_t volatile> must be thread-atomic as well
		5308
		5309	The type C<sig_atomic_t volatile> (or whatever is defined as
		5310	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		5311	threads. This is not part of the specification for C<sig_atomic_t>, but is
		5312	believed to be sufficiently portable.
		5313
		5314	=item C<sigprocmask> must work in a threaded environment
		5315
		5316	Libev uses C<sigprocmask> to temporarily block signals. This is not
		5317	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		5318	pthread implementations will either allow C<sigprocmask> in the "main
		5319	thread" or will block signals process-wide, both behaviours would
		5320	be compatible with libev. Interaction between C<sigprocmask> and
		5321	C<pthread_sigmask> could complicate things, however.
		5322
		5323	The most portable way to handle signals is to block signals in all threads
		5324	except the initial one, and run the signal handling loop in the initial
		5325	thread as well.
		5326
		5327	=item C<long> must be large enough for common memory allocation sizes
		5328
		5329	To improve portability and simplify its API, libev uses C<long> internally
		5330	instead of C<size_t> when allocating its data structures. On non-POSIX
		5331	systems (Microsoft...) this might be unexpectedly low, but is still at
		5332	least 31 bits everywhere, which is enough for hundreds of millions of
		5333	watchers.
		5334
		5335	=item C<double> must hold a time value in seconds with enough accuracy
		5336
		5337	The type C<double> is used to represent timestamps. It is required to
		5338	have at least 51 bits of mantissa (and 9 bits of exponent), which is
		5339	good enough for at least into the year 4000 with millisecond accuracy
		5340	(the design goal for libev). This requirement is overfulfilled by
		5341	implementations using IEEE 754, which is basically all existing ones.
		5342
		5343	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5344	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5345	is either obsolete or somebody patched it to use C<long double> or
		5346	something like that, just kidding).
		5347
		5348	=back
		5349
		5350	If you know of other additional requirements drop me a note.
		5351
		5352
2619	=head1 COMPLEXITIES	5353	=head1 ALGORITHMIC COMPLEXITIES
2620		5354
2621	In this section the complexities of (many of) the algorithms used inside	5355	In this section the complexities of (many of) the algorithms used inside
2622	libev will be explained. For complexity discussions about backends see the	5356	libev will be documented. For complexity discussions about backends see
2623	documentation for C<ev_default_init>.	5357	the documentation for C<ev_default_init>.
2624		5358
2625	All of the following are about amortised time: If an array needs to be	5359	All of the following are about amortised time: If an array needs to be
2626	extended, libev needs to realloc and move the whole array, but this	5360	extended, libev needs to realloc and move the whole array, but this
2627	happens asymptotically never with higher number of elements, so O(1) might	5361	happens asymptotically rarer with higher number of elements, so O(1) might
2628	mean it might do a lengthy realloc operation in rare cases, but on average	5362	mean that libev does a lengthy realloc operation in rare cases, but on
2629	it is much faster and asymptotically approaches constant time.	5363	average it is much faster and asymptotically approaches constant time.
2630		5364
2631	=over 4	5365	=over 4
2632		5366
2633	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	5367	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2634		5368
2635	This means that, when you have a watcher that triggers in one hour and	5369	This means that, when you have a watcher that triggers in one hour and
2636	there are 100 watchers that would trigger before that then inserting will	5370	there are 100 watchers that would trigger before that, then inserting will
2637	have to skip those 100 watchers.	5371	have to skip roughly seven (C<ld 100>) of these watchers.
2638		5372
2639	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	5373	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2640		5374
2641	That means that for changing a timer costs less than removing/adding them	5375	That means that changing a timer costs less than removing/adding them,
2642	as only the relative motion in the event queue has to be paid for.	5376	as only the relative motion in the event queue has to be paid for.
2643		5377
2644	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	5378	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
2645		5379
2646	These just add the watcher into an array or at the head of a list.	5380	These just add the watcher into an array or at the head of a list.
		5381
2647	=item Stopping check/prepare/idle watchers: O(1)	5382	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2648		5383
2649	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	5384	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2650		5385
2651	These watchers are stored in lists then need to be walked to find the	5386	These watchers are stored in lists, so they need to be walked to find the
2652	correct watcher to remove. The lists are usually short (you don't usually	5387	correct watcher to remove. The lists are usually short (you don't usually
2653	have many watchers waiting for the same fd or signal).	5388	have many watchers waiting for the same fd or signal: one is typical, two
		5389	is rare).
2654		5390
2655	=item Finding the next timer per loop iteration: O(1)	5391	=item Finding the next timer in each loop iteration: O(1)
		5392
		5393	By virtue of using a binary or 4-heap, the next timer is always found at a
		5394	fixed position in the storage array.
2656		5395
2657	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	5396	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2658		5397
2659	A change means an I/O watcher gets started or stopped, which requires	5398	A change means an I/O watcher gets started or stopped, which requires
2660	libev to recalculate its status (and possibly tell the kernel).	5399	libev to recalculate its status (and possibly tell the kernel, depending
		5400	on backend and whether C<ev_io_set> was used).
2661		5401
2662	=item Activating one watcher: O(1)	5402	=item Activating one watcher (putting it into the pending state): O(1)
2663		5403
2664	=item Priority handling: O(number_of_priorities)	5404	=item Priority handling: O(number_of_priorities)
2665		5405
2666	Priorities are implemented by allocating some space for each	5406	Priorities are implemented by allocating some space for each
2667	priority. When doing priority-based operations, libev usually has to	5407	priority. When doing priority-based operations, libev usually has to
2668	linearly search all the priorities.	5408	linearly search all the priorities, but starting/stopping and activating
		5409	watchers becomes O(1) with respect to priority handling.
		5410
		5411	=item Sending an ev_async: O(1)
		5412
		5413	=item Processing ev_async_send: O(number_of_async_watchers)
		5414
		5415	=item Processing signals: O(max_signal_number)
		5416
		5417	Sending involves a system call I<iff> there were no other C<ev_async_send>
		5418	calls in the current loop iteration and the loop is currently
		5419	blocked. Checking for async and signal events involves iterating over all
		5420	running async watchers or all signal numbers.
2669		5421
2670	=back	5422	=back
2671		5423
2672		5424
		5425	=head1 PORTING FROM LIBEV 3.X TO 4.X
		5426
		5427	The major version 4 introduced some incompatible changes to the API.
		5428
		5429	At the moment, the C<ev.h> header file provides compatibility definitions
		5430	for all changes, so most programs should still compile. The compatibility
		5431	layer might be removed in later versions of libev, so better update to the
		5432	new API early than late.
		5433
		5434	=over 4
		5435
		5436	=item C<EV_COMPAT3> backwards compatibility mechanism
		5437
		5438	The backward compatibility mechanism can be controlled by
		5439	C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
		5440	section.
		5441
		5442	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5443
		5444	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5445
		5446	ev_loop_destroy (EV_DEFAULT_UC);
		5447	ev_loop_fork (EV_DEFAULT);
		5448
		5449	=item function/symbol renames
		5450
		5451	A number of functions and symbols have been renamed:
		5452
		5453	ev_loop => ev_run
		5454	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		5455	EVLOOP_ONESHOT => EVRUN_ONCE
		5456
		5457	ev_unloop => ev_break
		5458	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		5459	EVUNLOOP_ONE => EVBREAK_ONE
		5460	EVUNLOOP_ALL => EVBREAK_ALL
		5461
		5462	EV_TIMEOUT => EV_TIMER
		5463
		5464	ev_loop_count => ev_iteration
		5465	ev_loop_depth => ev_depth
		5466	ev_loop_verify => ev_verify
		5467
		5468	Most functions working on C<struct ev_loop> objects don't have an
		5469	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		5470	associated constants have been renamed to not collide with the C<struct
		5471	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		5472	as all other watcher types. Note that C<ev_loop_fork> is still called
		5473	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		5474	typedef.
		5475
		5476	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		5477
		5478	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		5479	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		5480	and work, but the library code will of course be larger.
		5481
		5482	=back
		5483
		5484
		5485	=head1 GLOSSARY
		5486
		5487	=over 4
		5488
		5489	=item active
		5490
		5491	A watcher is active as long as it has been started and not yet stopped.
		5492	See L</WATCHER STATES> for details.
		5493
		5494	=item application
		5495
		5496	In this document, an application is whatever is using libev.
		5497
		5498	=item backend
		5499
		5500	The part of the code dealing with the operating system interfaces.
		5501
		5502	=item callback
		5503
		5504	The address of a function that is called when some event has been
		5505	detected. Callbacks are being passed the event loop, the watcher that
		5506	received the event, and the actual event bitset.
		5507
		5508	=item callback/watcher invocation
		5509
		5510	The act of calling the callback associated with a watcher.
		5511
		5512	=item event
		5513
		5514	A change of state of some external event, such as data now being available
		5515	for reading on a file descriptor, time having passed or simply not having
		5516	any other events happening anymore.
		5517
		5518	In libev, events are represented as single bits (such as C<EV_READ> or
		5519	C<EV_TIMER>).
		5520
		5521	=item event library
		5522
		5523	A software package implementing an event model and loop.
		5524
		5525	=item event loop
		5526
		5527	An entity that handles and processes external events and converts them
		5528	into callback invocations.
		5529
		5530	=item event model
		5531
		5532	The model used to describe how an event loop handles and processes
		5533	watchers and events.
		5534
		5535	=item pending
		5536
		5537	A watcher is pending as soon as the corresponding event has been
		5538	detected. See L</WATCHER STATES> for details.
		5539
		5540	=item real time
		5541
		5542	The physical time that is observed. It is apparently strictly monotonic :)
		5543
		5544	=item wall-clock time
		5545
		5546	The time and date as shown on clocks. Unlike real time, it can actually
		5547	be wrong and jump forwards and backwards, e.g. when you adjust your
		5548	clock.
		5549
		5550	=item watcher
		5551
		5552	A data structure that describes interest in certain events. Watchers need
		5553	to be started (attached to an event loop) before they can receive events.
		5554
		5555	=back
		5556
2673	=head1 AUTHOR	5557	=head1 AUTHOR
2674		5558
2675	Marc Lehmann <libev@schmorp.de>.	5559	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5560	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
2676		5561

Diff Legend

–	Removed lines
+	Added lines
<	Changed lines
>	Changed lines