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Revision 1.137 by root, Sun Mar 16 16:42:56 2008 UTC vs.
Revision 1.316 by root, Fri Oct 22 09:34:01 2010 UTC

…		…
2		2
3	libev - a high performance full-featured event loop written in C	3	libev - a high performance full-featured event loop written in C
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
8		8
9	=head2 EXAMPLE PROGRAM	9	=head2 EXAMPLE PROGRAM
10		10
11	// a single header file is required	11	// a single header file is required
12	#include <ev.h>	12	#include <ev.h>
13		13
		14	#include <stdio.h> // for puts
		15
14	// every watcher type has its own typedef'd struct	16	// every watcher type has its own typedef'd struct
15	// with the name ev_<type>	17	// with the name ev_TYPE
16	ev_io stdin_watcher;	18	ev_io stdin_watcher;
17	ev_timer timeout_watcher;	19	ev_timer timeout_watcher;
18		20
19	// all watcher callbacks have a similar signature	21	// all watcher callbacks have a similar signature
20	// this callback is called when data is readable on stdin	22	// this callback is called when data is readable on stdin
21	static void	23	static void
22	stdin_cb (EV_P_ struct ev_io *w, int revents)	24	stdin_cb (EV_P_ ev_io *w, int revents)
23	{	25	{
24	puts ("stdin ready");	26	puts ("stdin ready");
25	// for one-shot events, one must manually stop the watcher	27	// for one-shot events, one must manually stop the watcher
26	// with its corresponding stop function.	28	// with its corresponding stop function.
27	ev_io_stop (EV_A_ w);	29	ev_io_stop (EV_A_ w);
28		30
29	// this causes all nested ev_loop's to stop iterating	31	// this causes all nested ev_run's to stop iterating
30	ev_unloop (EV_A_ EVUNLOOP_ALL);	32	ev_break (EV_A_ EVBREAK_ALL);
31	}	33	}
32		34
33	// another callback, this time for a time-out	35	// another callback, this time for a time-out
34	static void	36	static void
35	timeout_cb (EV_P_ struct ev_timer *w, int revents)	37	timeout_cb (EV_P_ ev_timer *w, int revents)
36	{	38	{
37	puts ("timeout");	39	puts ("timeout");
38	// this causes the innermost ev_loop to stop iterating	40	// this causes the innermost ev_run to stop iterating
39	ev_unloop (EV_A_ EVUNLOOP_ONE);	41	ev_break (EV_A_ EVBREAK_ONE);
40	}	42	}
41		43
42	int	44	int
43	main (void)	45	main (void)
44	{	46	{
45	// use the default event loop unless you have special needs	47	// use the default event loop unless you have special needs
46	struct ev_loop *loop = ev_default_loop (0);	48	struct ev_loop *loop = ev_default_loop (0);
47		49
48	// initialise an io watcher, then start it	50	// initialise an io watcher, then start it
49	// this one will watch for stdin to become readable	51	// this one will watch for stdin to become readable
50	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);	52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
51	ev_io_start (loop, &stdin_watcher);	53	ev_io_start (loop, &stdin_watcher);
52		54
53	// initialise a timer watcher, then start it	55	// initialise a timer watcher, then start it
54	// simple non-repeating 5.5 second timeout	56	// simple non-repeating 5.5 second timeout
55	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);	57	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
56	ev_timer_start (loop, &timeout_watcher);	58	ev_timer_start (loop, &timeout_watcher);
57		59
58	// now wait for events to arrive	60	// now wait for events to arrive
59	ev_loop (loop, 0);	61	ev_run (loop, 0);
60		62
61	// unloop was called, so exit	63	// unloop was called, so exit
62	return 0;	64	return 0;
63	}	65	}
64		66
65	=head1 DESCRIPTION	67	=head1 ABOUT THIS DOCUMENT
		68
		69	This document documents the libev software package.
66		70
67	The newest version of this document is also available as an html-formatted	71	The newest version of this document is also available as an html-formatted
68	web page you might find easier to navigate when reading it for the first	72	web page you might find easier to navigate when reading it for the first
69	time: L<http://cvs.schmorp.de/libev/ev.html>.	73	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		74
		75	While this document tries to be as complete as possible in documenting
		76	libev, its usage and the rationale behind its design, it is not a tutorial
		77	on event-based programming, nor will it introduce event-based programming
		78	with libev.
		79
		80	Familiarity with event based programming techniques in general is assumed
		81	throughout this document.
		82
		83	=head1 ABOUT LIBEV
70		84
71	Libev is an event loop: you register interest in certain events (such as a	85	Libev is an event loop: you register interest in certain events (such as a
72	file descriptor being readable or a timeout occurring), and it will manage	86	file descriptor being readable or a timeout occurring), and it will manage
73	these event sources and provide your program with events.	87	these event sources and provide your program with events.
74		88
…		…
84	=head2 FEATURES	98	=head2 FEATURES
85		99
86	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	100	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
87	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	101	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
88	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	102	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
89	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	103	(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
90	with customised rescheduling (C<ev_periodic>), synchronous signals	104	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative
91	(C<ev_signal>), process status change events (C<ev_child>), and event	105	timers (C<ev_timer>), absolute timers with customised rescheduling
92	watchers dealing with the event loop mechanism itself (C<ev_idle>,	106	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
93	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as	107	change events (C<ev_child>), and event watchers dealing with the event
94	file watchers (C<ev_stat>) and even limited support for fork events	108	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
95	(C<ev_fork>).	109	C<ev_check> watchers) as well as file watchers (C<ev_stat>) and even
		110	limited support for fork events (C<ev_fork>).
96		111
97	It also is quite fast (see this	112	It also is quite fast (see this
98	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent	113	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
99	for example).	114	for example).
100		115
…		…
108	name C<loop> (which is always of type C<struct ev_loop *>) will not have	123	name C<loop> (which is always of type C<struct ev_loop *>) will not have
109	this argument.	124	this argument.
110		125
111	=head2 TIME REPRESENTATION	126	=head2 TIME REPRESENTATION
112		127
113	Libev represents time as a single floating point number, representing the	128	Libev represents time as a single floating point number, representing
114	(fractional) number of seconds since the (POSIX) epoch (somewhere near	129	the (fractional) number of seconds since the (POSIX) epoch (in practise
115	the beginning of 1970, details are complicated, don't ask). This type is	130	somewhere near the beginning of 1970, details are complicated, don't
116	called C<ev_tstamp>, which is what you should use too. It usually aliases	131	ask). This type is called C<ev_tstamp>, which is what you should use
117	to the C<double> type in C, and when you need to do any calculations on	132	too. It usually aliases to the C<double> type in C. When you need to do
118	it, you should treat it as some floatingpoint value. Unlike the name	133	any calculations on it, you should treat it as some floating point value.
		134
119	component C<stamp> might indicate, it is also used for time differences	135	Unlike the name component C<stamp> might indicate, it is also used for
120	throughout libev.	136	time differences (e.g. delays) throughout libev.
		137
		138	=head1 ERROR HANDLING
		139
		140	Libev knows three classes of errors: operating system errors, usage errors
		141	and internal errors (bugs).
		142
		143	When libev catches an operating system error it cannot handle (for example
		144	a system call indicating a condition libev cannot fix), it calls the callback
		145	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		146	abort. The default is to print a diagnostic message and to call C<abort
		147	()>.
		148
		149	When libev detects a usage error such as a negative timer interval, then
		150	it will print a diagnostic message and abort (via the C<assert> mechanism,
		151	so C<NDEBUG> will disable this checking): these are programming errors in
		152	the libev caller and need to be fixed there.
		153
		154	Libev also has a few internal error-checking C<assert>ions, and also has
		155	extensive consistency checking code. These do not trigger under normal
		156	circumstances, as they indicate either a bug in libev or worse.
		157
121		158
122	=head1 GLOBAL FUNCTIONS	159	=head1 GLOBAL FUNCTIONS
123		160
124	These functions can be called anytime, even before initialising the	161	These functions can be called anytime, even before initialising the
125	library in any way.	162	library in any way.
…		…
134		171
135	=item ev_sleep (ev_tstamp interval)	172	=item ev_sleep (ev_tstamp interval)
136		173
137	Sleep for the given interval: The current thread will be blocked until	174	Sleep for the given interval: The current thread will be blocked until
138	either it is interrupted or the given time interval has passed. Basically	175	either it is interrupted or the given time interval has passed. Basically
139	this is a subsecond-resolution C<sleep ()>.	176	this is a sub-second-resolution C<sleep ()>.
140		177
141	=item int ev_version_major ()	178	=item int ev_version_major ()
142		179
143	=item int ev_version_minor ()	180	=item int ev_version_minor ()
144		181
…		…
155	as this indicates an incompatible change. Minor versions are usually	192	as this indicates an incompatible change. Minor versions are usually
156	compatible to older versions, so a larger minor version alone is usually	193	compatible to older versions, so a larger minor version alone is usually
157	not a problem.	194	not a problem.
158		195
159	Example: Make sure we haven't accidentally been linked against the wrong	196	Example: Make sure we haven't accidentally been linked against the wrong
160	version.	197	version (note, however, that this will not detect ABI mismatches :).
161		198
162	assert (("libev version mismatch",	199	assert (("libev version mismatch",
163	ev_version_major () == EV_VERSION_MAJOR	200	ev_version_major () == EV_VERSION_MAJOR
164	&& ev_version_minor () >= EV_VERSION_MINOR));	201	&& ev_version_minor () >= EV_VERSION_MINOR));
165		202
166	=item unsigned int ev_supported_backends ()	203	=item unsigned int ev_supported_backends ()
167		204
168	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	205	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
169	value) compiled into this binary of libev (independent of their	206	value) compiled into this binary of libev (independent of their
…		…
171	a description of the set values.	208	a description of the set values.
172		209
173	Example: make sure we have the epoll method, because yeah this is cool and	210	Example: make sure we have the epoll method, because yeah this is cool and
174	a must have and can we have a torrent of it please!!!11	211	a must have and can we have a torrent of it please!!!11
175		212
176	assert (("sorry, no epoll, no sex",	213	assert (("sorry, no epoll, no sex",
177	ev_supported_backends () & EVBACKEND_EPOLL));	214	ev_supported_backends () & EVBACKEND_EPOLL));
178		215
179	=item unsigned int ev_recommended_backends ()	216	=item unsigned int ev_recommended_backends ()
180		217
181	Return the set of all backends compiled into this binary of libev and also	218	Return the set of all backends compiled into this binary of libev and also
182	recommended for this platform. This set is often smaller than the one	219	recommended for this platform. This set is often smaller than the one
183	returned by C<ev_supported_backends>, as for example kqueue is broken on	220	returned by C<ev_supported_backends>, as for example kqueue is broken on
184	most BSDs and will not be autodetected unless you explicitly request it	221	most BSDs and will not be auto-detected unless you explicitly request it
185	(assuming you know what you are doing). This is the set of backends that	222	(assuming you know what you are doing). This is the set of backends that
186	libev will probe for if you specify no backends explicitly.	223	libev will probe for if you specify no backends explicitly.
187		224
188	=item unsigned int ev_embeddable_backends ()	225	=item unsigned int ev_embeddable_backends ()
189		226
…		…
193	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	230	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
194	recommended ones.	231	recommended ones.
195		232
196	See the description of C<ev_embed> watchers for more info.	233	See the description of C<ev_embed> watchers for more info.
197		234
198	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	235	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
199		236
200	Sets the allocation function to use (the prototype is similar - the	237	Sets the allocation function to use (the prototype is similar - the
201	semantics is identical - to the realloc C function). It is used to	238	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
202	allocate and free memory (no surprises here). If it returns zero when	239	used to allocate and free memory (no surprises here). If it returns zero
203	memory needs to be allocated, the library might abort or take some	240	when memory needs to be allocated (C<size != 0>), the library might abort
204	potentially destructive action. The default is your system realloc	241	or take some potentially destructive action.
205	function.	242
		243	Since some systems (at least OpenBSD and Darwin) fail to implement
		244	correct C<realloc> semantics, libev will use a wrapper around the system
		245	C<realloc> and C<free> functions by default.
206		246
207	You could override this function in high-availability programs to, say,	247	You could override this function in high-availability programs to, say,
208	free some memory if it cannot allocate memory, to use a special allocator,	248	free some memory if it cannot allocate memory, to use a special allocator,
209	or even to sleep a while and retry until some memory is available.	249	or even to sleep a while and retry until some memory is available.
210		250
211	Example: Replace the libev allocator with one that waits a bit and then	251	Example: Replace the libev allocator with one that waits a bit and then
212	retries).	252	retries (example requires a standards-compliant C<realloc>).
213		253
214	static void *	254	static void *
215	persistent_realloc (void *ptr, size_t size)	255	persistent_realloc (void *ptr, size_t size)
216	{	256	{
217	for (;;)	257	for (;;)
…		…
226	}	266	}
227		267
228	...	268	...
229	ev_set_allocator (persistent_realloc);	269	ev_set_allocator (persistent_realloc);
230		270
231	=item ev_set_syserr_cb (void (*cb)(const char *msg));	271	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
232		272
233	Set the callback function to call on a retryable syscall error (such	273	Set the callback function to call on a retryable system call error (such
234	as failed select, poll, epoll_wait). The message is a printable string	274	as failed select, poll, epoll_wait). The message is a printable string
235	indicating the system call or subsystem causing the problem. If this	275	indicating the system call or subsystem causing the problem. If this
236	callback is set, then libev will expect it to remedy the sitution, no	276	callback is set, then libev will expect it to remedy the situation, no
237	matter what, when it returns. That is, libev will generally retry the	277	matter what, when it returns. That is, libev will generally retry the
238	requested operation, or, if the condition doesn't go away, do bad stuff	278	requested operation, or, if the condition doesn't go away, do bad stuff
239	(such as abort).	279	(such as abort).
240		280
241	Example: This is basically the same thing that libev does internally, too.	281	Example: This is basically the same thing that libev does internally, too.
…		…
252		292
253	=back	293	=back
254		294
255	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	295	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
256		296
257	An event loop is described by a C<struct ev_loop *>. The library knows two	297	An event loop is described by a C<struct ev_loop *> (the C<struct> is
258	types of such loops, the I<default> loop, which supports signals and child	298	I<not> optional in this case unless libev 3 compatibility is disabled, as
259	events, and dynamically created loops which do not.	299	libev 3 had an C<ev_loop> function colliding with the struct name).
260		300
261	If you use threads, a common model is to run the default event loop	301	The library knows two types of such loops, the I<default> loop, which
262	in your main thread (or in a separate thread) and for each thread you	302	supports signals and child events, and dynamically created event loops
263	create, you also create another event loop. Libev itself does no locking	303	which do not.
264	whatsoever, so if you mix calls to the same event loop in different
265	threads, make sure you lock (this is usually a bad idea, though, even if
266	done correctly, because it's hideous and inefficient).
267		304
268	=over 4	305	=over 4
269		306
270	=item struct ev_loop *ev_default_loop (unsigned int flags)	307	=item struct ev_loop *ev_default_loop (unsigned int flags)
271		308
…		…
275	flags. If that is troubling you, check C<ev_backend ()> afterwards).	312	flags. If that is troubling you, check C<ev_backend ()> afterwards).
276		313
277	If you don't know what event loop to use, use the one returned from this	314	If you don't know what event loop to use, use the one returned from this
278	function.	315	function.
279		316
		317	Note that this function is I<not> thread-safe, so if you want to use it
		318	from multiple threads, you have to lock (note also that this is unlikely,
		319	as loops cannot be shared easily between threads anyway).
		320
280	The default loop is the only loop that can handle C<ev_signal> and	321	The default loop is the only loop that can handle C<ev_signal> and
281	C<ev_child> watchers, and to do this, it always registers a handler	322	C<ev_child> watchers, and to do this, it always registers a handler
282	for C<SIGCHLD>. If this is a problem for your app you can either	323	for C<SIGCHLD>. If this is a problem for your application you can either
283	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you	324	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
284	can simply overwrite the C<SIGCHLD> signal handler I<after> calling	325	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
285	C<ev_default_init>.	326	C<ev_default_init>.
286		327
287	The flags argument can be used to specify special behaviour or specific	328	The flags argument can be used to specify special behaviour or specific
…		…
296	The default flags value. Use this if you have no clue (it's the right	337	The default flags value. Use this if you have no clue (it's the right
297	thing, believe me).	338	thing, believe me).
298		339
299	=item C<EVFLAG_NOENV>	340	=item C<EVFLAG_NOENV>
300		341
301	If this flag bit is ored into the flag value (or the program runs setuid	342	If this flag bit is or'ed into the flag value (or the program runs setuid
302	or setgid) then libev will I<not> look at the environment variable	343	or setgid) then libev will I<not> look at the environment variable
303	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	344	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
304	override the flags completely if it is found in the environment. This is	345	override the flags completely if it is found in the environment. This is
305	useful to try out specific backends to test their performance, or to work	346	useful to try out specific backends to test their performance, or to work
306	around bugs.	347	around bugs.
307		348
308	=item C<EVFLAG_FORKCHECK>	349	=item C<EVFLAG_FORKCHECK>
309		350
310	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after	351	Instead of calling C<ev_loop_fork> manually after a fork, you can also
311	a fork, you can also make libev check for a fork in each iteration by	352	make libev check for a fork in each iteration by enabling this flag.
312	enabling this flag.
313		353
314	This works by calling C<getpid ()> on every iteration of the loop,	354	This works by calling C<getpid ()> on every iteration of the loop,
315	and thus this might slow down your event loop if you do a lot of loop	355	and thus this might slow down your event loop if you do a lot of loop
316	iterations and little real work, but is usually not noticeable (on my	356	iterations and little real work, but is usually not noticeable (on my
317	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence	357	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
318	without a syscall and thus I<very> fast, but my GNU/Linux system also has	358	without a system call and thus I<very> fast, but my GNU/Linux system also has
319	C<pthread_atfork> which is even faster).	359	C<pthread_atfork> which is even faster).
320		360
321	The big advantage of this flag is that you can forget about fork (and	361	The big advantage of this flag is that you can forget about fork (and
322	forget about forgetting to tell libev about forking) when you use this	362	forget about forgetting to tell libev about forking) when you use this
323	flag.	363	flag.
324		364
325	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>	365	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
326	environment variable.	366	environment variable.
		367
		368	=item C<EVFLAG_NOINOTIFY>
		369
		370	When this flag is specified, then libev will not attempt to use the
		371	I<inotify> API for it's C<ev_stat> watchers. Apart from debugging and
		372	testing, this flag can be useful to conserve inotify file descriptors, as
		373	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		374
		375	=item C<EVFLAG_SIGNALFD>
		376
		377	When this flag is specified, then libev will attempt to use the
		378	I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This API
		379	delivers signals synchronously, which makes it both faster and might make
		380	it possible to get the queued signal data. It can also simplify signal
		381	handling with threads, as long as you properly block signals in your
		382	threads that are not interested in handling them.
		383
		384	Signalfd will not be used by default as this changes your signal mask, and
		385	there are a lot of shoddy libraries and programs (glib's threadpool for
		386	example) that can't properly initialise their signal masks.
327		387
328	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	388	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
329		389
330	This is your standard select(2) backend. Not I<completely> standard, as	390	This is your standard select(2) backend. Not I<completely> standard, as
331	libev tries to roll its own fd_set with no limits on the number of fds,	391	libev tries to roll its own fd_set with no limits on the number of fds,
332	but if that fails, expect a fairly low limit on the number of fds when	392	but if that fails, expect a fairly low limit on the number of fds when
333	using this backend. It doesn't scale too well (O(highest_fd)), but its	393	using this backend. It doesn't scale too well (O(highest_fd)), but its
334	usually the fastest backend for a low number of (low-numbered :) fds.	394	usually the fastest backend for a low number of (low-numbered :) fds.
335		395
336	To get good performance out of this backend you need a high amount of	396	To get good performance out of this backend you need a high amount of
337	parallelity (most of the file descriptors should be busy). If you are	397	parallelism (most of the file descriptors should be busy). If you are
338	writing a server, you should C<accept ()> in a loop to accept as many	398	writing a server, you should C<accept ()> in a loop to accept as many
339	connections as possible during one iteration. You might also want to have	399	connections as possible during one iteration. You might also want to have
340	a look at C<ev_set_io_collect_interval ()> to increase the amount of	400	a look at C<ev_set_io_collect_interval ()> to increase the amount of
341	readyness notifications you get per iteration.	401	readiness notifications you get per iteration.
		402
		403	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		404	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		405	C<exceptfds> set on that platform).
342		406
343	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	407	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
344		408
345	And this is your standard poll(2) backend. It's more complicated	409	And this is your standard poll(2) backend. It's more complicated
346	than select, but handles sparse fds better and has no artificial	410	than select, but handles sparse fds better and has no artificial
347	limit on the number of fds you can use (except it will slow down	411	limit on the number of fds you can use (except it will slow down
348	considerably with a lot of inactive fds). It scales similarly to select,	412	considerably with a lot of inactive fds). It scales similarly to select,
349	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for	413	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
350	performance tips.	414	performance tips.
351		415
		416	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		417	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
		418
352	=item C<EVBACKEND_EPOLL> (value 4, Linux)	419	=item C<EVBACKEND_EPOLL> (value 4, Linux)
		420
		421	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		422	kernels).
353		423
354	For few fds, this backend is a bit little slower than poll and select,	424	For few fds, this backend is a bit little slower than poll and select,
355	but it scales phenomenally better. While poll and select usually scale	425	but it scales phenomenally better. While poll and select usually scale
356	like O(total_fds) where n is the total number of fds (or the highest fd),	426	like O(total_fds) where n is the total number of fds (or the highest fd),
357	epoll scales either O(1) or O(active_fds). The epoll design has a number	427	epoll scales either O(1) or O(active_fds).
358	of shortcomings, such as silently dropping events in some hard-to-detect	428
359	cases and rewiring a syscall per fd change, no fork support and bad	429	The epoll mechanism deserves honorable mention as the most misdesigned
360	support for dup.	430	of the more advanced event mechanisms: mere annoyances include silently
		431	dropping file descriptors, requiring a system call per change per file
		432	descriptor (and unnecessary guessing of parameters), problems with dup and
		433	so on. The biggest issue is fork races, however - if a program forks then
		434	I<both> parent and child process have to recreate the epoll set, which can
		435	take considerable time (one syscall per file descriptor) and is of course
		436	hard to detect.
		437
		438	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		439	of course I<doesn't>, and epoll just loves to report events for totally
		440	I<different> file descriptors (even already closed ones, so one cannot
		441	even remove them from the set) than registered in the set (especially
		442	on SMP systems). Libev tries to counter these spurious notifications by
		443	employing an additional generation counter and comparing that against the
		444	events to filter out spurious ones, recreating the set when required. Last
		445	not least, it also refuses to work with some file descriptors which work
		446	perfectly fine with C<select> (files, many character devices...).
361		447
362	While stopping, setting and starting an I/O watcher in the same iteration	448	While stopping, setting and starting an I/O watcher in the same iteration
363	will result in some caching, there is still a syscall per such incident	449	will result in some caching, there is still a system call per such
364	(because the fd could point to a different file description now), so its	450	incident (because the same I<file descriptor> could point to a different
365	best to avoid that. Also, C<dup ()>'ed file descriptors might not work	451	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
366	very well if you register events for both fds.	452	file descriptors might not work very well if you register events for both
367		453	file descriptors.
368	Please note that epoll sometimes generates spurious notifications, so you
369	need to use non-blocking I/O or other means to avoid blocking when no data
370	(or space) is available.
371		454
372	Best performance from this backend is achieved by not unregistering all	455	Best performance from this backend is achieved by not unregistering all
373	watchers for a file descriptor until it has been closed, if possible, i.e.	456	watchers for a file descriptor until it has been closed, if possible,
374	keep at least one watcher active per fd at all times.	457	i.e. keep at least one watcher active per fd at all times. Stopping and
		458	starting a watcher (without re-setting it) also usually doesn't cause
		459	extra overhead. A fork can both result in spurious notifications as well
		460	as in libev having to destroy and recreate the epoll object, which can
		461	take considerable time and thus should be avoided.
375		462
		463	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		464	faster than epoll for maybe up to a hundred file descriptors, depending on
		465	the usage. So sad.
		466
376	While nominally embeddeble in other event loops, this feature is broken in	467	While nominally embeddable in other event loops, this feature is broken in
377	all kernel versions tested so far.	468	all kernel versions tested so far.
		469
		470	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		471	C<EVBACKEND_POLL>.
378		472
379	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	473	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
380		474
381	Kqueue deserves special mention, as at the time of this writing, it	475	Kqueue deserves special mention, as at the time of this writing, it
382	was broken on all BSDs except NetBSD (usually it doesn't work reliably	476	was broken on all BSDs except NetBSD (usually it doesn't work reliably
383	with anything but sockets and pipes, except on Darwin, where of course	477	with anything but sockets and pipes, except on Darwin, where of course
384	it's completely useless). For this reason it's not being "autodetected"	478	it's completely useless). Unlike epoll, however, whose brokenness
		479	is by design, these kqueue bugs can (and eventually will) be fixed
		480	without API changes to existing programs. For this reason it's not being
385	unless you explicitly specify it explicitly in the flags (i.e. using	481	"auto-detected" unless you explicitly specify it in the flags (i.e. using
386	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)	482	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
387	system like NetBSD.	483	system like NetBSD.
388		484
389	You still can embed kqueue into a normal poll or select backend and use it	485	You still can embed kqueue into a normal poll or select backend and use it
390	only for sockets (after having made sure that sockets work with kqueue on	486	only for sockets (after having made sure that sockets work with kqueue on
391	the target platform). See C<ev_embed> watchers for more info.	487	the target platform). See C<ev_embed> watchers for more info.
392		488
393	It scales in the same way as the epoll backend, but the interface to the	489	It scales in the same way as the epoll backend, but the interface to the
394	kernel is more efficient (which says nothing about its actual speed, of	490	kernel is more efficient (which says nothing about its actual speed, of
395	course). While stopping, setting and starting an I/O watcher does never	491	course). While stopping, setting and starting an I/O watcher does never
396	cause an extra syscall as with C<EVBACKEND_EPOLL>, it still adds up to	492	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
397	two event changes per incident, support for C<fork ()> is very bad and it	493	two event changes per incident. Support for C<fork ()> is very bad (but
398	drops fds silently in similarly hard-to-detect cases.	494	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		495	cases
399		496
400	This backend usually performs well under most conditions.	497	This backend usually performs well under most conditions.
401		498
402	While nominally embeddable in other event loops, this doesn't work	499	While nominally embeddable in other event loops, this doesn't work
403	everywhere, so you might need to test for this. And since it is broken	500	everywhere, so you might need to test for this. And since it is broken
404	almost everywhere, you should only use it when you have a lot of sockets	501	almost everywhere, you should only use it when you have a lot of sockets
405	(for which it usually works), by embedding it into another event loop	502	(for which it usually works), by embedding it into another event loop
406	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for	503	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
407	sockets.	504	also broken on OS X)) and, did I mention it, using it only for sockets.
		505
		506	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		507	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		508	C<NOTE_EOF>.
408		509
409	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	510	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
410		511
411	This is not implemented yet (and might never be, unless you send me an	512	This is not implemented yet (and might never be, unless you send me an
412	implementation). According to reports, C</dev/poll> only supports sockets	513	implementation). According to reports, C</dev/poll> only supports sockets
…		…
416	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	517	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
417		518
418	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	519	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
419	it's really slow, but it still scales very well (O(active_fds)).	520	it's really slow, but it still scales very well (O(active_fds)).
420		521
421	Please note that solaris event ports can deliver a lot of spurious	522	Please note that Solaris event ports can deliver a lot of spurious
422	notifications, so you need to use non-blocking I/O or other means to avoid	523	notifications, so you need to use non-blocking I/O or other means to avoid
423	blocking when no data (or space) is available.	524	blocking when no data (or space) is available.
424		525
425	While this backend scales well, it requires one system call per active	526	While this backend scales well, it requires one system call per active
426	file descriptor per loop iteration. For small and medium numbers of file	527	file descriptor per loop iteration. For small and medium numbers of file
427	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	528	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
428	might perform better.	529	might perform better.
429		530
430	On the positive side, ignoring the spurious readyness notifications, this	531	On the positive side, with the exception of the spurious readiness
431	backend actually performed to specification in all tests and is fully	532	notifications, this backend actually performed fully to specification
432	embeddable, which is a rare feat among the OS-specific backends.	533	in all tests and is fully embeddable, which is a rare feat among the
		534	OS-specific backends (I vastly prefer correctness over speed hacks).
		535
		536	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		537	C<EVBACKEND_POLL>.
433		538
434	=item C<EVBACKEND_ALL>	539	=item C<EVBACKEND_ALL>
435		540
436	Try all backends (even potentially broken ones that wouldn't be tried	541	Try all backends (even potentially broken ones that wouldn't be tried
437	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	542	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
…		…
439		544
440	It is definitely not recommended to use this flag.	545	It is definitely not recommended to use this flag.
441		546
442	=back	547	=back
443		548
444	If one or more of these are ored into the flags value, then only these	549	If one or more of the backend flags are or'ed into the flags value,
445	backends will be tried (in the reverse order as listed here). If none are	550	then only these backends will be tried (in the reverse order as listed
446	specified, all backends in C<ev_recommended_backends ()> will be tried.	551	here). If none are specified, all backends in C<ev_recommended_backends
		552	()> will be tried.
447		553
448	The most typical usage is like this:	554	Example: This is the most typical usage.
449		555
450	if (!ev_default_loop (0))	556	if (!ev_default_loop (0))
451	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	557	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
452		558
453	Restrict libev to the select and poll backends, and do not allow	559	Example: Restrict libev to the select and poll backends, and do not allow
454	environment settings to be taken into account:	560	environment settings to be taken into account:
455		561
456	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	562	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
457		563
458	Use whatever libev has to offer, but make sure that kqueue is used if	564	Example: Use whatever libev has to offer, but make sure that kqueue is
459	available (warning, breaks stuff, best use only with your own private	565	used if available (warning, breaks stuff, best use only with your own
460	event loop and only if you know the OS supports your types of fds):	566	private event loop and only if you know the OS supports your types of
		567	fds):
461		568
462	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	569	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
463		570
464	=item struct ev_loop *ev_loop_new (unsigned int flags)	571	=item struct ev_loop *ev_loop_new (unsigned int flags)
465		572
466	Similar to C<ev_default_loop>, but always creates a new event loop that is	573	Similar to C<ev_default_loop>, but always creates a new event loop that is
467	always distinct from the default loop. Unlike the default loop, it cannot	574	always distinct from the default loop.
468	handle signal and child watchers, and attempts to do so will be greeted by	575
469	undefined behaviour (or a failed assertion if assertions are enabled).	576	Note that this function I<is> thread-safe, and one common way to use
		577	libev with threads is indeed to create one loop per thread, and using the
		578	default loop in the "main" or "initial" thread.
470		579
471	Example: Try to create a event loop that uses epoll and nothing else.	580	Example: Try to create a event loop that uses epoll and nothing else.
472		581
473	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	582	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
474	if (!epoller)	583	if (!epoller)
475	fatal ("no epoll found here, maybe it hides under your chair");	584	fatal ("no epoll found here, maybe it hides under your chair");
476		585
477	=item ev_default_destroy ()	586	=item ev_default_destroy ()
478		587
479	Destroys the default loop again (frees all memory and kernel state	588	Destroys the default loop (frees all memory and kernel state etc.). None
480	etc.). None of the active event watchers will be stopped in the normal	589	of the active event watchers will be stopped in the normal sense, so
481	sense, so e.g. C<ev_is_active> might still return true. It is your	590	e.g. C<ev_is_active> might still return true. It is your responsibility to
482	responsibility to either stop all watchers cleanly yoursef I<before>	591	either stop all watchers cleanly yourself I<before> calling this function,
483	calling this function, or cope with the fact afterwards (which is usually	592	or cope with the fact afterwards (which is usually the easiest thing, you
484	the easiest thing, you can just ignore the watchers and/or C<free ()> them	593	can just ignore the watchers and/or C<free ()> them for example).
485	for example).
486		594
487	Note that certain global state, such as signal state, will not be freed by	595	Note that certain global state, such as signal state (and installed signal
488	this function, and related watchers (such as signal and child watchers)	596	handlers), will not be freed by this function, and related watchers (such
489	would need to be stopped manually.	597	as signal and child watchers) would need to be stopped manually.
490		598
491	In general it is not advisable to call this function except in the	599	In general it is not advisable to call this function except in the
492	rare occasion where you really need to free e.g. the signal handling	600	rare occasion where you really need to free e.g. the signal handling
493	pipe fds. If you need dynamically allocated loops it is better to use	601	pipe fds. If you need dynamically allocated loops it is better to use
494	C<ev_loop_new> and C<ev_loop_destroy>).	602	C<ev_loop_new> and C<ev_loop_destroy>.
495		603
496	=item ev_loop_destroy (loop)	604	=item ev_loop_destroy (loop)
497		605
498	Like C<ev_default_destroy>, but destroys an event loop created by an	606	Like C<ev_default_destroy>, but destroys an event loop created by an
499	earlier call to C<ev_loop_new>.	607	earlier call to C<ev_loop_new>.
500		608
501	=item ev_default_fork ()	609	=item ev_default_fork ()
502		610
503	This function sets a flag that causes subsequent C<ev_loop> iterations	611	This function sets a flag that causes subsequent C<ev_run> iterations
504	to reinitialise the kernel state for backends that have one. Despite the	612	to reinitialise the kernel state for backends that have one. Despite the
505	name, you can call it anytime, but it makes most sense after forking, in	613	name, you can call it anytime, but it makes most sense after forking, in
506	the child process (or both child and parent, but that again makes little	614	the child process (or both child and parent, but that again makes little
507	sense). You I<must> call it in the child before using any of the libev	615	sense). You I<must> call it in the child before using any of the libev
508	functions, and it will only take effect at the next C<ev_loop> iteration.	616	functions, and it will only take effect at the next C<ev_run> iteration.
		617
		618	Again, you I<have> to call it on I<any> loop that you want to re-use after
		619	a fork, I<even if you do not plan to use the loop in the parent>. This is
		620	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		621	during fork.
509		622
510	On the other hand, you only need to call this function in the child	623	On the other hand, you only need to call this function in the child
511	process if and only if you want to use the event library in the child. If	624	process if and only if you want to use the event loop in the child. If
512	you just fork+exec, you don't have to call it at all.	625	you just fork+exec or create a new loop in the child, you don't have to
		626	call it at all (in fact, C<epoll> is so badly broken that it makes a
		627	difference, but libev will usually detect this case on its own and do a
		628	costly reset of the backend).
513		629
514	The function itself is quite fast and it's usually not a problem to call	630	The function itself is quite fast and it's usually not a problem to call
515	it just in case after a fork. To make this easy, the function will fit in	631	it just in case after a fork. To make this easy, the function will fit in
516	quite nicely into a call to C<pthread_atfork>:	632	quite nicely into a call to C<pthread_atfork>:
517		633
…		…
519		635
520	=item ev_loop_fork (loop)	636	=item ev_loop_fork (loop)
521		637
522	Like C<ev_default_fork>, but acts on an event loop created by	638	Like C<ev_default_fork>, but acts on an event loop created by
523	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	639	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
524	after fork, and how you do this is entirely your own problem.	640	after fork that you want to re-use in the child, and how you keep track of
		641	them is entirely your own problem.
525		642
526	=item int ev_is_default_loop (loop)	643	=item int ev_is_default_loop (loop)
527		644
528	Returns true when the given loop actually is the default loop, false otherwise.	645	Returns true when the given loop is, in fact, the default loop, and false
		646	otherwise.
529		647
530	=item unsigned int ev_loop_count (loop)	648	=item unsigned int ev_iteration (loop)
531		649
532	Returns the count of loop iterations for the loop, which is identical to	650	Returns the current iteration count for the event loop, which is identical
533	the number of times libev did poll for new events. It starts at C<0> and	651	to the number of times libev did poll for new events. It starts at C<0>
534	happily wraps around with enough iterations.	652	and happily wraps around with enough iterations.
535		653
536	This value can sometimes be useful as a generation counter of sorts (it	654	This value can sometimes be useful as a generation counter of sorts (it
537	"ticks" the number of loop iterations), as it roughly corresponds with	655	"ticks" the number of loop iterations), as it roughly corresponds with
538	C<ev_prepare> and C<ev_check> calls.	656	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		657	prepare and check phases.
		658
		659	=item unsigned int ev_depth (loop)
		660
		661	Returns the number of times C<ev_run> was entered minus the number of
		662	times C<ev_run> was exited, in other words, the recursion depth.
		663
		664	Outside C<ev_run>, this number is zero. In a callback, this number is
		665	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
		666	in which case it is higher.
		667
		668	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread
		669	etc.), doesn't count as "exit" - consider this as a hint to avoid such
		670	ungentleman-like behaviour unless it's really convenient.
539		671
540	=item unsigned int ev_backend (loop)	672	=item unsigned int ev_backend (loop)
541		673
542	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	674	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
543	use.	675	use.
…		…
548	received events and started processing them. This timestamp does not	680	received events and started processing them. This timestamp does not
549	change as long as callbacks are being processed, and this is also the base	681	change as long as callbacks are being processed, and this is also the base
550	time used for relative timers. You can treat it as the timestamp of the	682	time used for relative timers. You can treat it as the timestamp of the
551	event occurring (or more correctly, libev finding out about it).	683	event occurring (or more correctly, libev finding out about it).
552		684
		685	=item ev_now_update (loop)
		686
		687	Establishes the current time by querying the kernel, updating the time
		688	returned by C<ev_now ()> in the progress. This is a costly operation and
		689	is usually done automatically within C<ev_run ()>.
		690
		691	This function is rarely useful, but when some event callback runs for a
		692	very long time without entering the event loop, updating libev's idea of
		693	the current time is a good idea.
		694
		695	See also L<The special problem of time updates> in the C<ev_timer> section.
		696
		697	=item ev_suspend (loop)
		698
		699	=item ev_resume (loop)
		700
		701	These two functions suspend and resume an event loop, for use when the
		702	loop is not used for a while and timeouts should not be processed.
		703
		704	A typical use case would be an interactive program such as a game: When
		705	the user presses C<^Z> to suspend the game and resumes it an hour later it
		706	would be best to handle timeouts as if no time had actually passed while
		707	the program was suspended. This can be achieved by calling C<ev_suspend>
		708	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		709	C<ev_resume> directly afterwards to resume timer processing.
		710
		711	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		712	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		713	will be rescheduled (that is, they will lose any events that would have
		714	occurred while suspended).
		715
		716	After calling C<ev_suspend> you B<must not> call I<any> function on the
		717	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		718	without a previous call to C<ev_suspend>.
		719
		720	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		721	event loop time (see C<ev_now_update>).
		722
553	=item ev_loop (loop, int flags)	723	=item ev_run (loop, int flags)
554		724
555	Finally, this is it, the event handler. This function usually is called	725	Finally, this is it, the event handler. This function usually is called
556	after you initialised all your watchers and you want to start handling	726	after you have initialised all your watchers and you want to start
557	events.	727	handling events. It will ask the operating system for any new events, call
		728	the watcher callbacks, an then repeat the whole process indefinitely: This
		729	is why event loops are called I<loops>.
558		730
559	If the flags argument is specified as C<0>, it will not return until	731	If the flags argument is specified as C<0>, it will keep handling events
560	either no event watchers are active anymore or C<ev_unloop> was called.	732	until either no event watchers are active anymore or C<ev_break> was
		733	called.
561		734
562	Please note that an explicit C<ev_unloop> is usually better than	735	Please note that an explicit C<ev_break> is usually better than
563	relying on all watchers to be stopped when deciding when a program has	736	relying on all watchers to be stopped when deciding when a program has
564	finished (especially in interactive programs), but having a program that	737	finished (especially in interactive programs), but having a program
565	automatically loops as long as it has to and no longer by virtue of	738	that automatically loops as long as it has to and no longer by virtue
566	relying on its watchers stopping correctly is a thing of beauty.	739	of relying on its watchers stopping correctly, that is truly a thing of
		740	beauty.
567		741
568	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	742	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
569	those events and any outstanding ones, but will not block your process in	743	those events and any already outstanding ones, but will not wait and
570	case there are no events and will return after one iteration of the loop.	744	block your process in case there are no events and will return after one
		745	iteration of the loop. This is sometimes useful to poll and handle new
		746	events while doing lengthy calculations, to keep the program responsive.
571		747
572	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	748	A flags value of C<EVRUN_ONCE> will look for new events (waiting if
573	neccessary) and will handle those and any outstanding ones. It will block	749	necessary) and will handle those and any already outstanding ones. It
574	your process until at least one new event arrives, and will return after	750	will block your process until at least one new event arrives (which could
575	one iteration of the loop. This is useful if you are waiting for some	751	be an event internal to libev itself, so there is no guarantee that a
576	external event in conjunction with something not expressible using other	752	user-registered callback will be called), and will return after one
		753	iteration of the loop.
		754
		755	This is useful if you are waiting for some external event in conjunction
		756	with something not expressible using other libev watchers (i.e. "roll your
577	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	757	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
578	usually a better approach for this kind of thing.	758	usually a better approach for this kind of thing.
579		759
580	Here are the gory details of what C<ev_loop> does:	760	Here are the gory details of what C<ev_run> does:
581		761
		762	- Increment loop depth.
		763	- Reset the ev_break status.
582	- Before the first iteration, call any pending watchers.	764	- Before the first iteration, call any pending watchers.
		765	LOOP:
583	* If EVFLAG_FORKCHECK was used, check for a fork.	766	- If EVFLAG_FORKCHECK was used, check for a fork.
584	- If a fork was detected, queue and call all fork watchers.	767	- If a fork was detected (by any means), queue and call all fork watchers.
585	- Queue and call all prepare watchers.	768	- Queue and call all prepare watchers.
		769	- If ev_break was called, goto FINISH.
586	- If we have been forked, recreate the kernel state.	770	- If we have been forked, detach and recreate the kernel state
		771	as to not disturb the other process.
587	- Update the kernel state with all outstanding changes.	772	- Update the kernel state with all outstanding changes.
588	- Update the "event loop time".	773	- Update the "event loop time" (ev_now ()).
589	- Calculate for how long to sleep or block, if at all	774	- Calculate for how long to sleep or block, if at all
590	(active idle watchers, EVLOOP_NONBLOCK or not having	775	(active idle watchers, EVRUN_NOWAIT or not having
591	any active watchers at all will result in not sleeping).	776	any active watchers at all will result in not sleeping).
592	- Sleep if the I/O and timer collect interval say so.	777	- Sleep if the I/O and timer collect interval say so.
		778	- Increment loop iteration counter.
593	- Block the process, waiting for any events.	779	- Block the process, waiting for any events.
594	- Queue all outstanding I/O (fd) events.	780	- Queue all outstanding I/O (fd) events.
595	- Update the "event loop time" and do time jump handling.	781	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
596	- Queue all outstanding timers.	782	- Queue all expired timers.
597	- Queue all outstanding periodics.	783	- Queue all expired periodics.
598	- If no events are pending now, queue all idle watchers.	784	- Queue all idle watchers with priority higher than that of pending events.
599	- Queue all check watchers.	785	- Queue all check watchers.
600	- Call all queued watchers in reverse order (i.e. check watchers first).	786	- Call all queued watchers in reverse order (i.e. check watchers first).
601	Signals and child watchers are implemented as I/O watchers, and will	787	Signals and child watchers are implemented as I/O watchers, and will
602	be handled here by queueing them when their watcher gets executed.	788	be handled here by queueing them when their watcher gets executed.
603	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	789	- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
604	were used, or there are no active watchers, return, otherwise	790	were used, or there are no active watchers, goto FINISH, otherwise
605	continue with step *.	791	continue with step LOOP.
		792	FINISH:
		793	- Reset the ev_break status iff it was EVBREAK_ONE.
		794	- Decrement the loop depth.
		795	- Return.
606		796
607	Example: Queue some jobs and then loop until no events are outstanding	797	Example: Queue some jobs and then loop until no events are outstanding
608	anymore.	798	anymore.
609		799
610	... queue jobs here, make sure they register event watchers as long	800	... queue jobs here, make sure they register event watchers as long
611	... as they still have work to do (even an idle watcher will do..)	801	... as they still have work to do (even an idle watcher will do..)
612	ev_loop (my_loop, 0);	802	ev_run (my_loop, 0);
613	... jobs done. yeah!	803	... jobs done or somebody called unloop. yeah!
614		804
615	=item ev_unloop (loop, how)	805	=item ev_break (loop, how)
616		806
617	Can be used to make a call to C<ev_loop> return early (but only after it	807	Can be used to make a call to C<ev_run> return early (but only after it
618	has processed all outstanding events). The C<how> argument must be either	808	has processed all outstanding events). The C<how> argument must be either
619	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	809	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
620	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	810	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
621		811
622	This "unloop state" will be cleared when entering C<ev_loop> again.	812	This "unloop state" will be cleared when entering C<ev_run> again.
		813
		814	It is safe to call C<ev_break> from outside any C<ev_run> calls. ##TODO##
623		815
624	=item ev_ref (loop)	816	=item ev_ref (loop)
625		817
626	=item ev_unref (loop)	818	=item ev_unref (loop)
627		819
628	Ref/unref can be used to add or remove a reference count on the event	820	Ref/unref can be used to add or remove a reference count on the event
629	loop: Every watcher keeps one reference, and as long as the reference	821	loop: Every watcher keeps one reference, and as long as the reference
630	count is nonzero, C<ev_loop> will not return on its own. If you have	822	count is nonzero, C<ev_run> will not return on its own.
631	a watcher you never unregister that should not keep C<ev_loop> from	823
632	returning, ev_unref() after starting, and ev_ref() before stopping it. For	824	This is useful when you have a watcher that you never intend to
		825	unregister, but that nevertheless should not keep C<ev_run> from
		826	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		827	before stopping it.
		828
633	example, libev itself uses this for its internal signal pipe: It is not	829	As an example, libev itself uses this for its internal signal pipe: It
634	visible to the libev user and should not keep C<ev_loop> from exiting if	830	is not visible to the libev user and should not keep C<ev_run> from
635	no event watchers registered by it are active. It is also an excellent	831	exiting if no event watchers registered by it are active. It is also an
636	way to do this for generic recurring timers or from within third-party	832	excellent way to do this for generic recurring timers or from within
637	libraries. Just remember to I<unref after start> and I<ref before stop>	833	third-party libraries. Just remember to I<unref after start> and I<ref
638	(but only if the watcher wasn't active before, or was active before,	834	before stop> (but only if the watcher wasn't active before, or was active
639	respectively).	835	before, respectively. Note also that libev might stop watchers itself
		836	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		837	in the callback).
640		838
641	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	839	Example: Create a signal watcher, but keep it from keeping C<ev_run>
642	running when nothing else is active.	840	running when nothing else is active.
643		841
644	struct ev_signal exitsig;	842	ev_signal exitsig;
645	ev_signal_init (&exitsig, sig_cb, SIGINT);	843	ev_signal_init (&exitsig, sig_cb, SIGINT);
646	ev_signal_start (loop, &exitsig);	844	ev_signal_start (loop, &exitsig);
647	evf_unref (loop);	845	evf_unref (loop);
648		846
649	Example: For some weird reason, unregister the above signal handler again.	847	Example: For some weird reason, unregister the above signal handler again.
650		848
651	ev_ref (loop);	849	ev_ref (loop);
652	ev_signal_stop (loop, &exitsig);	850	ev_signal_stop (loop, &exitsig);
653		851
654	=item ev_set_io_collect_interval (loop, ev_tstamp interval)	852	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
655		853
656	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)	854	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
657		855
658	These advanced functions influence the time that libev will spend waiting	856	These advanced functions influence the time that libev will spend waiting
659	for events. Both are by default C<0>, meaning that libev will try to	857	for events. Both time intervals are by default C<0>, meaning that libev
660	invoke timer/periodic callbacks and I/O callbacks with minimum latency.	858	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		859	latency.
661		860
662	Setting these to a higher value (the C<interval> I<must> be >= C<0>)	861	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
663	allows libev to delay invocation of I/O and timer/periodic callbacks to	862	allows libev to delay invocation of I/O and timer/periodic callbacks
664	increase efficiency of loop iterations.	863	to increase efficiency of loop iterations (or to increase power-saving
		864	opportunities).
665		865
666	The background is that sometimes your program runs just fast enough to	866	The idea is that sometimes your program runs just fast enough to handle
667	handle one (or very few) event(s) per loop iteration. While this makes	867	one (or very few) event(s) per loop iteration. While this makes the
668	the program responsive, it also wastes a lot of CPU time to poll for new	868	program responsive, it also wastes a lot of CPU time to poll for new
669	events, especially with backends like C<select ()> which have a high	869	events, especially with backends like C<select ()> which have a high
670	overhead for the actual polling but can deliver many events at once.	870	overhead for the actual polling but can deliver many events at once.
671		871
672	By setting a higher I<io collect interval> you allow libev to spend more	872	By setting a higher I<io collect interval> you allow libev to spend more
673	time collecting I/O events, so you can handle more events per iteration,	873	time collecting I/O events, so you can handle more events per iteration,
674	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	874	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
675	C<ev_timer>) will be not affected. Setting this to a non-null value will	875	C<ev_timer>) will be not affected. Setting this to a non-null value will
676	introduce an additional C<ev_sleep ()> call into most loop iterations.	876	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		877	sleep time ensures that libev will not poll for I/O events more often then
		878	once per this interval, on average.
677		879
678	Likewise, by setting a higher I<timeout collect interval> you allow libev	880	Likewise, by setting a higher I<timeout collect interval> you allow libev
679	to spend more time collecting timeouts, at the expense of increased	881	to spend more time collecting timeouts, at the expense of increased
680	latency (the watcher callback will be called later). C<ev_io> watchers	882	latency/jitter/inexactness (the watcher callback will be called
681	will not be affected. Setting this to a non-null value will not introduce	883	later). C<ev_io> watchers will not be affected. Setting this to a non-null
682	any overhead in libev.	884	value will not introduce any overhead in libev.
683		885
684	Many (busy) programs can usually benefit by setting the io collect	886	Many (busy) programs can usually benefit by setting the I/O collect
685	interval to a value near C<0.1> or so, which is often enough for	887	interval to a value near C<0.1> or so, which is often enough for
686	interactive servers (of course not for games), likewise for timeouts. It	888	interactive servers (of course not for games), likewise for timeouts. It
687	usually doesn't make much sense to set it to a lower value than C<0.01>,	889	usually doesn't make much sense to set it to a lower value than C<0.01>,
688	as this approsaches the timing granularity of most systems.	890	as this approaches the timing granularity of most systems. Note that if
		891	you do transactions with the outside world and you can't increase the
		892	parallelity, then this setting will limit your transaction rate (if you
		893	need to poll once per transaction and the I/O collect interval is 0.01,
		894	then you can't do more than 100 transactions per second).
		895
		896	Setting the I<timeout collect interval> can improve the opportunity for
		897	saving power, as the program will "bundle" timer callback invocations that
		898	are "near" in time together, by delaying some, thus reducing the number of
		899	times the process sleeps and wakes up again. Another useful technique to
		900	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		901	they fire on, say, one-second boundaries only.
		902
		903	Example: we only need 0.1s timeout granularity, and we wish not to poll
		904	more often than 100 times per second:
		905
		906	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		907	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		908
		909	=item ev_invoke_pending (loop)
		910
		911	This call will simply invoke all pending watchers while resetting their
		912	pending state. Normally, C<ev_run> does this automatically when required,
		913	but when overriding the invoke callback this call comes handy. This
		914	function can be invoked from a watcher - this can be useful for example
		915	when you want to do some lengthy calculation and want to pass further
		916	event handling to another thread (you still have to make sure only one
		917	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
		918
		919	=item int ev_pending_count (loop)
		920
		921	Returns the number of pending watchers - zero indicates that no watchers
		922	are pending.
		923
		924	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		925
		926	This overrides the invoke pending functionality of the loop: Instead of
		927	invoking all pending watchers when there are any, C<ev_run> will call
		928	this callback instead. This is useful, for example, when you want to
		929	invoke the actual watchers inside another context (another thread etc.).
		930
		931	If you want to reset the callback, use C<ev_invoke_pending> as new
		932	callback.
		933
		934	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		935
		936	Sometimes you want to share the same loop between multiple threads. This
		937	can be done relatively simply by putting mutex_lock/unlock calls around
		938	each call to a libev function.
		939
		940	However, C<ev_run> can run an indefinite time, so it is not feasible
		941	to wait for it to return. One way around this is to wake up the event
		942	loop via C<ev_break> and C<av_async_send>, another way is to set these
		943	I<release> and I<acquire> callbacks on the loop.
		944
		945	When set, then C<release> will be called just before the thread is
		946	suspended waiting for new events, and C<acquire> is called just
		947	afterwards.
		948
		949	Ideally, C<release> will just call your mutex_unlock function, and
		950	C<acquire> will just call the mutex_lock function again.
		951
		952	While event loop modifications are allowed between invocations of
		953	C<release> and C<acquire> (that's their only purpose after all), no
		954	modifications done will affect the event loop, i.e. adding watchers will
		955	have no effect on the set of file descriptors being watched, or the time
		956	waited. Use an C<ev_async> watcher to wake up C<ev_run> when you want it
		957	to take note of any changes you made.
		958
		959	In theory, threads executing C<ev_run> will be async-cancel safe between
		960	invocations of C<release> and C<acquire>.
		961
		962	See also the locking example in the C<THREADS> section later in this
		963	document.
		964
		965	=item ev_set_userdata (loop, void *data)
		966
		967	=item ev_userdata (loop)
		968
		969	Set and retrieve a single C<void *> associated with a loop. When
		970	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		971	C<0.>
		972
		973	These two functions can be used to associate arbitrary data with a loop,
		974	and are intended solely for the C<invoke_pending_cb>, C<release> and
		975	C<acquire> callbacks described above, but of course can be (ab-)used for
		976	any other purpose as well.
		977
		978	=item ev_verify (loop)
		979
		980	This function only does something when C<EV_VERIFY> support has been
		981	compiled in, which is the default for non-minimal builds. It tries to go
		982	through all internal structures and checks them for validity. If anything
		983	is found to be inconsistent, it will print an error message to standard
		984	error and call C<abort ()>.
		985
		986	This can be used to catch bugs inside libev itself: under normal
		987	circumstances, this function will never abort as of course libev keeps its
		988	data structures consistent.
689		989
690	=back	990	=back
691		991
692		992
693	=head1 ANATOMY OF A WATCHER	993	=head1 ANATOMY OF A WATCHER
694		994
		995	In the following description, uppercase C<TYPE> in names stands for the
		996	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		997	watchers and C<ev_io_start> for I/O watchers.
		998
695	A watcher is a structure that you create and register to record your	999	A watcher is an opaque structure that you allocate and register to record
696	interest in some event. For instance, if you want to wait for STDIN to	1000	your interest in some event. To make a concrete example, imagine you want
697	become readable, you would create an C<ev_io> watcher for that:	1001	to wait for STDIN to become readable, you would create an C<ev_io> watcher
		1002	for that:
698		1003
699	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1004	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
700	{	1005	{
701	ev_io_stop (w);	1006	ev_io_stop (w);
702	ev_unloop (loop, EVUNLOOP_ALL);	1007	ev_break (loop, EVBREAK_ALL);
703	}	1008	}
704		1009
705	struct ev_loop *loop = ev_default_loop (0);	1010	struct ev_loop *loop = ev_default_loop (0);
		1011
706	struct ev_io stdin_watcher;	1012	ev_io stdin_watcher;
		1013
707	ev_init (&stdin_watcher, my_cb);	1014	ev_init (&stdin_watcher, my_cb);
708	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	1015	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
709	ev_io_start (loop, &stdin_watcher);	1016	ev_io_start (loop, &stdin_watcher);
		1017
710	ev_loop (loop, 0);	1018	ev_run (loop, 0);
711		1019
712	As you can see, you are responsible for allocating the memory for your	1020	As you can see, you are responsible for allocating the memory for your
713	watcher structures (and it is usually a bad idea to do this on the stack,	1021	watcher structures (and it is I<usually> a bad idea to do this on the
714	although this can sometimes be quite valid).	1022	stack).
715		1023
		1024	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1025	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
		1026
716	Each watcher structure must be initialised by a call to C<ev_init	1027	Each watcher structure must be initialised by a call to C<ev_init (watcher
717	(watcher *, callback)>, which expects a callback to be provided. This	1028	*, callback)>, which expects a callback to be provided. This callback is
718	callback gets invoked each time the event occurs (or, in the case of io	1029	invoked each time the event occurs (or, in the case of I/O watchers, each
719	watchers, each time the event loop detects that the file descriptor given	1030	time the event loop detects that the file descriptor given is readable
720	is readable and/or writable).	1031	and/or writable).
721		1032
722	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1033	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
723	with arguments specific to this watcher type. There is also a macro	1034	macro to configure it, with arguments specific to the watcher type. There
724	to combine initialisation and setting in one call: C<< ev_<type>_init	1035	is also a macro to combine initialisation and setting in one call: C<<
725	(watcher *, callback, ...) >>.	1036	ev_TYPE_init (watcher *, callback, ...) >>.
726		1037
727	To make the watcher actually watch out for events, you have to start it	1038	To make the watcher actually watch out for events, you have to start it
728	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1039	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
729	*) >>), and you can stop watching for events at any time by calling the	1040	*) >>), and you can stop watching for events at any time by calling the
730	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1041	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
731		1042
732	As long as your watcher is active (has been started but not stopped) you	1043	As long as your watcher is active (has been started but not stopped) you
733	must not touch the values stored in it. Most specifically you must never	1044	must not touch the values stored in it. Most specifically you must never
734	reinitialise it or call its C<set> macro.	1045	reinitialise it or call its C<ev_TYPE_set> macro.
735		1046
736	Each and every callback receives the event loop pointer as first, the	1047	Each and every callback receives the event loop pointer as first, the
737	registered watcher structure as second, and a bitset of received events as	1048	registered watcher structure as second, and a bitset of received events as
738	third argument.	1049	third argument.
739		1050
…		…
748	=item C<EV_WRITE>	1059	=item C<EV_WRITE>
749		1060
750	The file descriptor in the C<ev_io> watcher has become readable and/or	1061	The file descriptor in the C<ev_io> watcher has become readable and/or
751	writable.	1062	writable.
752		1063
753	=item C<EV_TIMEOUT>	1064	=item C<EV_TIMER>
754		1065
755	The C<ev_timer> watcher has timed out.	1066	The C<ev_timer> watcher has timed out.
756		1067
757	=item C<EV_PERIODIC>	1068	=item C<EV_PERIODIC>
758		1069
…		…
776		1087
777	=item C<EV_PREPARE>	1088	=item C<EV_PREPARE>
778		1089
779	=item C<EV_CHECK>	1090	=item C<EV_CHECK>
780		1091
781	All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts	1092	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts
782	to gather new events, and all C<ev_check> watchers are invoked just after	1093	to gather new events, and all C<ev_check> watchers are invoked just after
783	C<ev_loop> has gathered them, but before it invokes any callbacks for any	1094	C<ev_run> has gathered them, but before it invokes any callbacks for any
784	received events. Callbacks of both watcher types can start and stop as	1095	received events. Callbacks of both watcher types can start and stop as
785	many watchers as they want, and all of them will be taken into account	1096	many watchers as they want, and all of them will be taken into account
786	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1097	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
787	C<ev_loop> from blocking).	1098	C<ev_run> from blocking).
788		1099
789	=item C<EV_EMBED>	1100	=item C<EV_EMBED>
790		1101
791	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1102	The embedded event loop specified in the C<ev_embed> watcher needs attention.
792		1103
…		…
797		1108
798	=item C<EV_ASYNC>	1109	=item C<EV_ASYNC>
799		1110
800	The given async watcher has been asynchronously notified (see C<ev_async>).	1111	The given async watcher has been asynchronously notified (see C<ev_async>).
801		1112
		1113	=item C<EV_CUSTOM>
		1114
		1115	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1116	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1117
802	=item C<EV_ERROR>	1118	=item C<EV_ERROR>
803		1119
804	An unspecified error has occured, the watcher has been stopped. This might	1120	An unspecified error has occurred, the watcher has been stopped. This might
805	happen because the watcher could not be properly started because libev	1121	happen because the watcher could not be properly started because libev
806	ran out of memory, a file descriptor was found to be closed or any other	1122	ran out of memory, a file descriptor was found to be closed or any other
		1123	problem. Libev considers these application bugs.
		1124
807	problem. You best act on it by reporting the problem and somehow coping	1125	You best act on it by reporting the problem and somehow coping with the
808	with the watcher being stopped.	1126	watcher being stopped. Note that well-written programs should not receive
		1127	an error ever, so when your watcher receives it, this usually indicates a
		1128	bug in your program.
809		1129
810	Libev will usually signal a few "dummy" events together with an error,	1130	Libev will usually signal a few "dummy" events together with an error, for
811	for example it might indicate that a fd is readable or writable, and if	1131	example it might indicate that a fd is readable or writable, and if your
812	your callbacks is well-written it can just attempt the operation and cope	1132	callbacks is well-written it can just attempt the operation and cope with
813	with the error from read() or write(). This will not work in multithreaded	1133	the error from read() or write(). This will not work in multi-threaded
814	programs, though, so beware.	1134	programs, though, as the fd could already be closed and reused for another
		1135	thing, so beware.
815		1136
816	=back	1137	=back
817		1138
		1139	=head2 WATCHER STATES
		1140
		1141	There are various watcher states mentioned throughout this manual -
		1142	active, pending and so on. In this section these states and the rules to
		1143	transition between them will be described in more detail - and while these
		1144	rules might look complicated, they usually do "the right thing".
		1145
		1146	=over 4
		1147
		1148	=item initialiased
		1149
		1150	Before a watcher can be registered with the event looop it has to be
		1151	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
		1152	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
		1153
		1154	In this state it is simply some block of memory that is suitable for use
		1155	in an event loop. It can be moved around, freed, reused etc. at will.
		1156
		1157	=item started/running/active
		1158
		1159	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
		1160	property of the event loop, and is actively waiting for events. While in
		1161	this state it cannot be accessed (except in a few documented ways), moved,
		1162	freed or anything else - the only legal thing is to keep a pointer to it,
		1163	and call libev functions on it that are documented to work on active watchers.
		1164
		1165	=item pending
		1166
		1167	If a watcher is active and libev determines that an event it is interested
		1168	in has occurred (such as a timer expiring), it will become pending. It will
		1169	stay in this pending state until either it is stopped or its callback is
		1170	about to be invoked, so it is not normally pending inside the watcher
		1171	callback.
		1172
		1173	The watcher might or might not be active while it is pending (for example,
		1174	an expired non-repeating timer can be pending but no longer active). If it
		1175	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
		1176	but it is still property of the event loop at this time, so cannot be
		1177	moved, freed or reused. And if it is active the rules described in the
		1178	previous item still apply.
		1179
		1180	It is also possible to feed an event on a watcher that is not active (e.g.
		1181	via C<ev_feed_event>), in which case it becomes pending without being
		1182	active.
		1183
		1184	=item stopped
		1185
		1186	A watcher can be stopped implicitly by libev (in which case it might still
		1187	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
		1188	latter will clear any pending state the watcher might be in, regardless
		1189	of whether it was active or not, so stopping a watcher explicitly before
		1190	freeing it is often a good idea.
		1191
		1192	While stopped (and not pending) the watcher is essentially in the
		1193	initialised state, that is it can be reused, moved, modified in any way
		1194	you wish.
		1195
		1196	=back
		1197
818	=head2 GENERIC WATCHER FUNCTIONS	1198	=head2 GENERIC WATCHER FUNCTIONS
819
820	In the following description, C<TYPE> stands for the watcher type,
821	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
822		1199
823	=over 4	1200	=over 4
824		1201
825	=item C<ev_init> (ev_TYPE *watcher, callback)	1202	=item C<ev_init> (ev_TYPE *watcher, callback)
826		1203
…		…
832	which rolls both calls into one.	1209	which rolls both calls into one.
833		1210
834	You can reinitialise a watcher at any time as long as it has been stopped	1211	You can reinitialise a watcher at any time as long as it has been stopped
835	(or never started) and there are no pending events outstanding.	1212	(or never started) and there are no pending events outstanding.
836		1213
837	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1214	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
838	int revents)>.	1215	int revents)>.
839		1216
		1217	Example: Initialise an C<ev_io> watcher in two steps.
		1218
		1219	ev_io w;
		1220	ev_init (&w, my_cb);
		1221	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1222
840	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1223	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
841		1224
842	This macro initialises the type-specific parts of a watcher. You need to	1225	This macro initialises the type-specific parts of a watcher. You need to
843	call C<ev_init> at least once before you call this macro, but you can	1226	call C<ev_init> at least once before you call this macro, but you can
844	call C<ev_TYPE_set> any number of times. You must not, however, call this	1227	call C<ev_TYPE_set> any number of times. You must not, however, call this
845	macro on a watcher that is active (it can be pending, however, which is a	1228	macro on a watcher that is active (it can be pending, however, which is a
846	difference to the C<ev_init> macro).	1229	difference to the C<ev_init> macro).
847		1230
848	Although some watcher types do not have type-specific arguments	1231	Although some watcher types do not have type-specific arguments
849	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1232	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
850		1233
		1234	See C<ev_init>, above, for an example.
		1235
851	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1236	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
852		1237
853	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1238	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
854	calls into a single call. This is the most convinient method to initialise	1239	calls into a single call. This is the most convenient method to initialise
855	a watcher. The same limitations apply, of course.	1240	a watcher. The same limitations apply, of course.
856		1241
		1242	Example: Initialise and set an C<ev_io> watcher in one step.
		1243
		1244	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1245
857	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1246	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
858		1247
859	Starts (activates) the given watcher. Only active watchers will receive	1248	Starts (activates) the given watcher. Only active watchers will receive
860	events. If the watcher is already active nothing will happen.	1249	events. If the watcher is already active nothing will happen.
861		1250
		1251	Example: Start the C<ev_io> watcher that is being abused as example in this
		1252	whole section.
		1253
		1254	ev_io_start (EV_DEFAULT_UC, &w);
		1255
862	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1256	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
863		1257
864	Stops the given watcher again (if active) and clears the pending	1258	Stops the given watcher if active, and clears the pending status (whether
		1259	the watcher was active or not).
		1260
865	status. It is possible that stopped watchers are pending (for example,	1261	It is possible that stopped watchers are pending - for example,
866	non-repeating timers are being stopped when they become pending), but	1262	non-repeating timers are being stopped when they become pending - but
867	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1263	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
868	you want to free or reuse the memory used by the watcher it is therefore a	1264	pending. If you want to free or reuse the memory used by the watcher it is
869	good idea to always call its C<ev_TYPE_stop> function.	1265	therefore a good idea to always call its C<ev_TYPE_stop> function.
870		1266
871	=item bool ev_is_active (ev_TYPE *watcher)	1267	=item bool ev_is_active (ev_TYPE *watcher)
872		1268
873	Returns a true value iff the watcher is active (i.e. it has been started	1269	Returns a true value iff the watcher is active (i.e. it has been started
874	and not yet been stopped). As long as a watcher is active you must not modify	1270	and not yet been stopped). As long as a watcher is active you must not modify
…		…
890	=item ev_cb_set (ev_TYPE *watcher, callback)	1286	=item ev_cb_set (ev_TYPE *watcher, callback)
891		1287
892	Change the callback. You can change the callback at virtually any time	1288	Change the callback. You can change the callback at virtually any time
893	(modulo threads).	1289	(modulo threads).
894		1290
895	=item ev_set_priority (ev_TYPE *watcher, priority)	1291	=item ev_set_priority (ev_TYPE *watcher, int priority)
896		1292
897	=item int ev_priority (ev_TYPE *watcher)	1293	=item int ev_priority (ev_TYPE *watcher)
898		1294
899	Set and query the priority of the watcher. The priority is a small	1295	Set and query the priority of the watcher. The priority is a small
900	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1296	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
901	(default: C<-2>). Pending watchers with higher priority will be invoked	1297	(default: C<-2>). Pending watchers with higher priority will be invoked
902	before watchers with lower priority, but priority will not keep watchers	1298	before watchers with lower priority, but priority will not keep watchers
903	from being executed (except for C<ev_idle> watchers).	1299	from being executed (except for C<ev_idle> watchers).
904		1300
905	This means that priorities are I<only> used for ordering callback
906	invocation after new events have been received. This is useful, for
907	example, to reduce latency after idling, or more often, to bind two
908	watchers on the same event and make sure one is called first.
909
910	If you need to suppress invocation when higher priority events are pending	1301	If you need to suppress invocation when higher priority events are pending
911	you need to look at C<ev_idle> watchers, which provide this functionality.	1302	you need to look at C<ev_idle> watchers, which provide this functionality.
912		1303
913	You I<must not> change the priority of a watcher as long as it is active or	1304	You I<must not> change the priority of a watcher as long as it is active or
914	pending.	1305	pending.
915		1306
		1307	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1308	fine, as long as you do not mind that the priority value you query might
		1309	or might not have been clamped to the valid range.
		1310
916	The default priority used by watchers when no priority has been set is	1311	The default priority used by watchers when no priority has been set is
917	always C<0>, which is supposed to not be too high and not be too low :).	1312	always C<0>, which is supposed to not be too high and not be too low :).
918		1313
919	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1314	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
920	fine, as long as you do not mind that the priority value you query might	1315	priorities.
921	or might not have been adjusted to be within valid range.
922		1316
923	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1317	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
924		1318
925	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1319	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
926	C<loop> nor C<revents> need to be valid as long as the watcher callback	1320	C<loop> nor C<revents> need to be valid as long as the watcher callback
927	can deal with that fact.	1321	can deal with that fact, as both are simply passed through to the
		1322	callback.
928		1323
929	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1324	=item int ev_clear_pending (loop, ev_TYPE *watcher)
930		1325
931	If the watcher is pending, this function returns clears its pending status	1326	If the watcher is pending, this function clears its pending status and
932	and returns its C<revents> bitset (as if its callback was invoked). If the	1327	returns its C<revents> bitset (as if its callback was invoked). If the
933	watcher isn't pending it does nothing and returns C<0>.	1328	watcher isn't pending it does nothing and returns C<0>.
934		1329
		1330	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1331	callback to be invoked, which can be accomplished with this function.
		1332
		1333	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1334
		1335	Feeds the given event set into the event loop, as if the specified event
		1336	had happened for the specified watcher (which must be a pointer to an
		1337	initialised but not necessarily started event watcher). Obviously you must
		1338	not free the watcher as long as it has pending events.
		1339
		1340	Stopping the watcher, letting libev invoke it, or calling
		1341	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1342	not started in the first place.
		1343
		1344	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1345	functions that do not need a watcher.
		1346
935	=back	1347	=back
936		1348
937		1349
938	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1350	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
939		1351
940	Each watcher has, by default, a member C<void *data> that you can change	1352	Each watcher has, by default, a member C<void *data> that you can change
941	and read at any time, libev will completely ignore it. This can be used	1353	and read at any time: libev will completely ignore it. This can be used
942	to associate arbitrary data with your watcher. If you need more data and	1354	to associate arbitrary data with your watcher. If you need more data and
943	don't want to allocate memory and store a pointer to it in that data	1355	don't want to allocate memory and store a pointer to it in that data
944	member, you can also "subclass" the watcher type and provide your own	1356	member, you can also "subclass" the watcher type and provide your own
945	data:	1357	data:
946		1358
947	struct my_io	1359	struct my_io
948	{	1360	{
949	struct ev_io io;	1361	ev_io io;
950	int otherfd;	1362	int otherfd;
951	void *somedata;	1363	void *somedata;
952	struct whatever *mostinteresting;	1364	struct whatever *mostinteresting;
953	}	1365	};
		1366
		1367	...
		1368	struct my_io w;
		1369	ev_io_init (&w.io, my_cb, fd, EV_READ);
954		1370
955	And since your callback will be called with a pointer to the watcher, you	1371	And since your callback will be called with a pointer to the watcher, you
956	can cast it back to your own type:	1372	can cast it back to your own type:
957		1373
958	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1374	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
959	{	1375	{
960	struct my_io *w = (struct my_io *)w_;	1376	struct my_io *w = (struct my_io *)w_;
961	...	1377	...
962	}	1378	}
963		1379
964	More interesting and less C-conformant ways of casting your callback type	1380	More interesting and less C-conformant ways of casting your callback type
965	instead have been omitted.	1381	instead have been omitted.
966		1382
967	Another common scenario is having some data structure with multiple	1383	Another common scenario is to use some data structure with multiple
968	watchers:	1384	embedded watchers:
969		1385
970	struct my_biggy	1386	struct my_biggy
971	{	1387	{
972	int some_data;	1388	int some_data;
973	ev_timer t1;	1389	ev_timer t1;
974	ev_timer t2;	1390	ev_timer t2;
975	}	1391	}
976		1392
977	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1393	In this case getting the pointer to C<my_biggy> is a bit more
978	you need to use C<offsetof>:	1394	complicated: Either you store the address of your C<my_biggy> struct
		1395	in the C<data> member of the watcher (for woozies), or you need to use
		1396	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1397	programmers):
979		1398
980	#include <stddef.h>	1399	#include <stddef.h>
981		1400
982	static void	1401	static void
983	t1_cb (EV_P_ struct ev_timer *w, int revents)	1402	t1_cb (EV_P_ ev_timer *w, int revents)
984	{	1403	{
985	struct my_biggy big = (struct my_biggy *	1404	struct my_biggy big = (struct my_biggy *)
986	(((char *)w) - offsetof (struct my_biggy, t1));	1405	(((char *)w) - offsetof (struct my_biggy, t1));
987	}	1406	}
988		1407
989	static void	1408	static void
990	t2_cb (EV_P_ struct ev_timer *w, int revents)	1409	t2_cb (EV_P_ ev_timer *w, int revents)
991	{	1410	{
992	struct my_biggy big = (struct my_biggy *	1411	struct my_biggy big = (struct my_biggy *)
993	(((char *)w) - offsetof (struct my_biggy, t2));	1412	(((char *)w) - offsetof (struct my_biggy, t2));
994	}	1413	}
		1414
		1415	=head2 WATCHER PRIORITY MODELS
		1416
		1417	Many event loops support I<watcher priorities>, which are usually small
		1418	integers that influence the ordering of event callback invocation
		1419	between watchers in some way, all else being equal.
		1420
		1421	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1422	description for the more technical details such as the actual priority
		1423	range.
		1424
		1425	There are two common ways how these these priorities are being interpreted
		1426	by event loops:
		1427
		1428	In the more common lock-out model, higher priorities "lock out" invocation
		1429	of lower priority watchers, which means as long as higher priority
		1430	watchers receive events, lower priority watchers are not being invoked.
		1431
		1432	The less common only-for-ordering model uses priorities solely to order
		1433	callback invocation within a single event loop iteration: Higher priority
		1434	watchers are invoked before lower priority ones, but they all get invoked
		1435	before polling for new events.
		1436
		1437	Libev uses the second (only-for-ordering) model for all its watchers
		1438	except for idle watchers (which use the lock-out model).
		1439
		1440	The rationale behind this is that implementing the lock-out model for
		1441	watchers is not well supported by most kernel interfaces, and most event
		1442	libraries will just poll for the same events again and again as long as
		1443	their callbacks have not been executed, which is very inefficient in the
		1444	common case of one high-priority watcher locking out a mass of lower
		1445	priority ones.
		1446
		1447	Static (ordering) priorities are most useful when you have two or more
		1448	watchers handling the same resource: a typical usage example is having an
		1449	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1450	timeouts. Under load, data might be received while the program handles
		1451	other jobs, but since timers normally get invoked first, the timeout
		1452	handler will be executed before checking for data. In that case, giving
		1453	the timer a lower priority than the I/O watcher ensures that I/O will be
		1454	handled first even under adverse conditions (which is usually, but not
		1455	always, what you want).
		1456
		1457	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1458	will only be executed when no same or higher priority watchers have
		1459	received events, they can be used to implement the "lock-out" model when
		1460	required.
		1461
		1462	For example, to emulate how many other event libraries handle priorities,
		1463	you can associate an C<ev_idle> watcher to each such watcher, and in
		1464	the normal watcher callback, you just start the idle watcher. The real
		1465	processing is done in the idle watcher callback. This causes libev to
		1466	continuously poll and process kernel event data for the watcher, but when
		1467	the lock-out case is known to be rare (which in turn is rare :), this is
		1468	workable.
		1469
		1470	Usually, however, the lock-out model implemented that way will perform
		1471	miserably under the type of load it was designed to handle. In that case,
		1472	it might be preferable to stop the real watcher before starting the
		1473	idle watcher, so the kernel will not have to process the event in case
		1474	the actual processing will be delayed for considerable time.
		1475
		1476	Here is an example of an I/O watcher that should run at a strictly lower
		1477	priority than the default, and which should only process data when no
		1478	other events are pending:
		1479
		1480	ev_idle idle; // actual processing watcher
		1481	ev_io io; // actual event watcher
		1482
		1483	static void
		1484	io_cb (EV_P_ ev_io *w, int revents)
		1485	{
		1486	// stop the I/O watcher, we received the event, but
		1487	// are not yet ready to handle it.
		1488	ev_io_stop (EV_A_ w);
		1489
		1490	// start the idle watcher to handle the actual event.
		1491	// it will not be executed as long as other watchers
		1492	// with the default priority are receiving events.
		1493	ev_idle_start (EV_A_ &idle);
		1494	}
		1495
		1496	static void
		1497	idle_cb (EV_P_ ev_idle *w, int revents)
		1498	{
		1499	// actual processing
		1500	read (STDIN_FILENO, ...);
		1501
		1502	// have to start the I/O watcher again, as
		1503	// we have handled the event
		1504	ev_io_start (EV_P_ &io);
		1505	}
		1506
		1507	// initialisation
		1508	ev_idle_init (&idle, idle_cb);
		1509	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1510	ev_io_start (EV_DEFAULT_ &io);
		1511
		1512	In the "real" world, it might also be beneficial to start a timer, so that
		1513	low-priority connections can not be locked out forever under load. This
		1514	enables your program to keep a lower latency for important connections
		1515	during short periods of high load, while not completely locking out less
		1516	important ones.
995		1517
996		1518
997	=head1 WATCHER TYPES	1519	=head1 WATCHER TYPES
998		1520
999	This section describes each watcher in detail, but will not repeat	1521	This section describes each watcher in detail, but will not repeat
…		…
1023	In general you can register as many read and/or write event watchers per	1545	In general you can register as many read and/or write event watchers per
1024	fd as you want (as long as you don't confuse yourself). Setting all file	1546	fd as you want (as long as you don't confuse yourself). Setting all file
1025	descriptors to non-blocking mode is also usually a good idea (but not	1547	descriptors to non-blocking mode is also usually a good idea (but not
1026	required if you know what you are doing).	1548	required if you know what you are doing).
1027		1549
1028	If you must do this, then force the use of a known-to-be-good backend	1550	If you cannot use non-blocking mode, then force the use of a
1029	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and	1551	known-to-be-good backend (at the time of this writing, this includes only
1030	C<EVBACKEND_POLL>).	1552	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
		1553	descriptors for which non-blocking operation makes no sense (such as
		1554	files) - libev doesn't guarantee any specific behaviour in that case.
1031		1555
1032	Another thing you have to watch out for is that it is quite easy to	1556	Another thing you have to watch out for is that it is quite easy to
1033	receive "spurious" readyness notifications, that is your callback might	1557	receive "spurious" readiness notifications, that is your callback might
1034	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1558	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1035	because there is no data. Not only are some backends known to create a	1559	because there is no data. Not only are some backends known to create a
1036	lot of those (for example solaris ports), it is very easy to get into	1560	lot of those (for example Solaris ports), it is very easy to get into
1037	this situation even with a relatively standard program structure. Thus	1561	this situation even with a relatively standard program structure. Thus
1038	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1562	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1039	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1563	C<EAGAIN> is far preferable to a program hanging until some data arrives.
1040		1564
1041	If you cannot run the fd in non-blocking mode (for example you should not	1565	If you cannot run the fd in non-blocking mode (for example you should
1042	play around with an Xlib connection), then you have to seperately re-test	1566	not play around with an Xlib connection), then you have to separately
1043	whether a file descriptor is really ready with a known-to-be good interface	1567	re-test whether a file descriptor is really ready with a known-to-be good
1044	such as poll (fortunately in our Xlib example, Xlib already does this on	1568	interface such as poll (fortunately in our Xlib example, Xlib already
1045	its own, so its quite safe to use).	1569	does this on its own, so its quite safe to use). Some people additionally
		1570	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1571	indefinitely.
		1572
		1573	But really, best use non-blocking mode.
1046		1574
1047	=head3 The special problem of disappearing file descriptors	1575	=head3 The special problem of disappearing file descriptors
1048		1576
1049	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1577	Some backends (e.g. kqueue, epoll) need to be told about closing a file
1050	descriptor (either by calling C<close> explicitly or by any other means,	1578	descriptor (either due to calling C<close> explicitly or any other means,
1051	such as C<dup>). The reason is that you register interest in some file	1579	such as C<dup2>). The reason is that you register interest in some file
1052	descriptor, but when it goes away, the operating system will silently drop	1580	descriptor, but when it goes away, the operating system will silently drop
1053	this interest. If another file descriptor with the same number then is	1581	this interest. If another file descriptor with the same number then is
1054	registered with libev, there is no efficient way to see that this is, in	1582	registered with libev, there is no efficient way to see that this is, in
1055	fact, a different file descriptor.	1583	fact, a different file descriptor.
1056		1584
…		…
1085	To support fork in your programs, you either have to call	1613	To support fork in your programs, you either have to call
1086	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1614	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
1087	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1615	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
1088	C<EVBACKEND_POLL>.	1616	C<EVBACKEND_POLL>.
1089		1617
		1618	=head3 The special problem of SIGPIPE
		1619
		1620	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1621	when writing to a pipe whose other end has been closed, your program gets
		1622	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1623	this is sensible behaviour, for daemons, this is usually undesirable.
		1624
		1625	So when you encounter spurious, unexplained daemon exits, make sure you
		1626	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1627	somewhere, as that would have given you a big clue).
		1628
		1629	=head3 The special problem of accept()ing when you can't
		1630
		1631	Many implementations of the POSIX C<accept> function (for example,
		1632	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1633	connection from the pending queue in all error cases.
		1634
		1635	For example, larger servers often run out of file descriptors (because
		1636	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1637	rejecting the connection, leading to libev signalling readiness on
		1638	the next iteration again (the connection still exists after all), and
		1639	typically causing the program to loop at 100% CPU usage.
		1640
		1641	Unfortunately, the set of errors that cause this issue differs between
		1642	operating systems, there is usually little the app can do to remedy the
		1643	situation, and no known thread-safe method of removing the connection to
		1644	cope with overload is known (to me).
		1645
		1646	One of the easiest ways to handle this situation is to just ignore it
		1647	- when the program encounters an overload, it will just loop until the
		1648	situation is over. While this is a form of busy waiting, no OS offers an
		1649	event-based way to handle this situation, so it's the best one can do.
		1650
		1651	A better way to handle the situation is to log any errors other than
		1652	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1653	messages, and continue as usual, which at least gives the user an idea of
		1654	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1655	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1656	usage.
		1657
		1658	If your program is single-threaded, then you could also keep a dummy file
		1659	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1660	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1661	close that fd, and create a new dummy fd. This will gracefully refuse
		1662	clients under typical overload conditions.
		1663
		1664	The last way to handle it is to simply log the error and C<exit>, as
		1665	is often done with C<malloc> failures, but this results in an easy
		1666	opportunity for a DoS attack.
1090		1667
1091	=head3 Watcher-Specific Functions	1668	=head3 Watcher-Specific Functions
1092		1669
1093	=over 4	1670	=over 4
1094		1671
1095	=item ev_io_init (ev_io *, callback, int fd, int events)	1672	=item ev_io_init (ev_io *, callback, int fd, int events)
1096		1673
1097	=item ev_io_set (ev_io *, int fd, int events)	1674	=item ev_io_set (ev_io *, int fd, int events)
1098		1675
1099	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1676	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
1100	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1677	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
1101	C<EV_READ | EV_WRITE> to receive the given events.	1678	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
1102		1679
1103	=item int fd [read-only]	1680	=item int fd [read-only]
1104		1681
1105	The file descriptor being watched.	1682	The file descriptor being watched.
1106		1683
…		…
1114		1691
1115	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1692	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1116	readable, but only once. Since it is likely line-buffered, you could	1693	readable, but only once. Since it is likely line-buffered, you could
1117	attempt to read a whole line in the callback.	1694	attempt to read a whole line in the callback.
1118		1695
1119	static void	1696	static void
1120	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1697	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1121	{	1698	{
1122	ev_io_stop (loop, w);	1699	ev_io_stop (loop, w);
1123	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1700	.. read from stdin here (or from w->fd) and handle any I/O errors
1124	}	1701	}
1125		1702
1126	...	1703	...
1127	struct ev_loop *loop = ev_default_init (0);	1704	struct ev_loop *loop = ev_default_init (0);
1128	struct ev_io stdin_readable;	1705	ev_io stdin_readable;
1129	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1706	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1130	ev_io_start (loop, &stdin_readable);	1707	ev_io_start (loop, &stdin_readable);
1131	ev_loop (loop, 0);	1708	ev_run (loop, 0);
1132		1709
1133		1710
1134	=head2 C<ev_timer> - relative and optionally repeating timeouts	1711	=head2 C<ev_timer> - relative and optionally repeating timeouts
1135		1712
1136	Timer watchers are simple relative timers that generate an event after a	1713	Timer watchers are simple relative timers that generate an event after a
1137	given time, and optionally repeating in regular intervals after that.	1714	given time, and optionally repeating in regular intervals after that.
1138		1715
1139	The timers are based on real time, that is, if you register an event that	1716	The timers are based on real time, that is, if you register an event that
1140	times out after an hour and you reset your system clock to last years	1717	times out after an hour and you reset your system clock to January last
1141	time, it will still time out after (roughly) and hour. "Roughly" because	1718	year, it will still time out after (roughly) one hour. "Roughly" because
1142	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1719	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1143	monotonic clock option helps a lot here).	1720	monotonic clock option helps a lot here).
		1721
		1722	The callback is guaranteed to be invoked only I<after> its timeout has
		1723	passed (not I<at>, so on systems with very low-resolution clocks this
		1724	might introduce a small delay). If multiple timers become ready during the
		1725	same loop iteration then the ones with earlier time-out values are invoked
		1726	before ones of the same priority with later time-out values (but this is
		1727	no longer true when a callback calls C<ev_run> recursively).
		1728
		1729	=head3 Be smart about timeouts
		1730
		1731	Many real-world problems involve some kind of timeout, usually for error
		1732	recovery. A typical example is an HTTP request - if the other side hangs,
		1733	you want to raise some error after a while.
		1734
		1735	What follows are some ways to handle this problem, from obvious and
		1736	inefficient to smart and efficient.
		1737
		1738	In the following, a 60 second activity timeout is assumed - a timeout that
		1739	gets reset to 60 seconds each time there is activity (e.g. each time some
		1740	data or other life sign was received).
		1741
		1742	=over 4
		1743
		1744	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1745
		1746	This is the most obvious, but not the most simple way: In the beginning,
		1747	start the watcher:
		1748
		1749	ev_timer_init (timer, callback, 60., 0.);
		1750	ev_timer_start (loop, timer);
		1751
		1752	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1753	and start it again:
		1754
		1755	ev_timer_stop (loop, timer);
		1756	ev_timer_set (timer, 60., 0.);
		1757	ev_timer_start (loop, timer);
		1758
		1759	This is relatively simple to implement, but means that each time there is
		1760	some activity, libev will first have to remove the timer from its internal
		1761	data structure and then add it again. Libev tries to be fast, but it's
		1762	still not a constant-time operation.
		1763
		1764	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1765
		1766	This is the easiest way, and involves using C<ev_timer_again> instead of
		1767	C<ev_timer_start>.
		1768
		1769	To implement this, configure an C<ev_timer> with a C<repeat> value
		1770	of C<60> and then call C<ev_timer_again> at start and each time you
		1771	successfully read or write some data. If you go into an idle state where
		1772	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1773	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1774
		1775	That means you can ignore both the C<ev_timer_start> function and the
		1776	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1777	member and C<ev_timer_again>.
		1778
		1779	At start:
		1780
		1781	ev_init (timer, callback);
		1782	timer->repeat = 60.;
		1783	ev_timer_again (loop, timer);
		1784
		1785	Each time there is some activity:
		1786
		1787	ev_timer_again (loop, timer);
		1788
		1789	It is even possible to change the time-out on the fly, regardless of
		1790	whether the watcher is active or not:
		1791
		1792	timer->repeat = 30.;
		1793	ev_timer_again (loop, timer);
		1794
		1795	This is slightly more efficient then stopping/starting the timer each time
		1796	you want to modify its timeout value, as libev does not have to completely
		1797	remove and re-insert the timer from/into its internal data structure.
		1798
		1799	It is, however, even simpler than the "obvious" way to do it.
		1800
		1801	=item 3. Let the timer time out, but then re-arm it as required.
		1802
		1803	This method is more tricky, but usually most efficient: Most timeouts are
		1804	relatively long compared to the intervals between other activity - in
		1805	our example, within 60 seconds, there are usually many I/O events with
		1806	associated activity resets.
		1807
		1808	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1809	but remember the time of last activity, and check for a real timeout only
		1810	within the callback:
		1811
		1812	ev_tstamp last_activity; // time of last activity
		1813
		1814	static void
		1815	callback (EV_P_ ev_timer *w, int revents)
		1816	{
		1817	ev_tstamp now = ev_now (EV_A);
		1818	ev_tstamp timeout = last_activity + 60.;
		1819
		1820	// if last_activity + 60. is older than now, we did time out
		1821	if (timeout < now)
		1822	{
		1823	// timeout occurred, take action
		1824	}
		1825	else
		1826	{
		1827	// callback was invoked, but there was some activity, re-arm
		1828	// the watcher to fire in last_activity + 60, which is
		1829	// guaranteed to be in the future, so "again" is positive:
		1830	w->repeat = timeout - now;
		1831	ev_timer_again (EV_A_ w);
		1832	}
		1833	}
		1834
		1835	To summarise the callback: first calculate the real timeout (defined
		1836	as "60 seconds after the last activity"), then check if that time has
		1837	been reached, which means something I<did>, in fact, time out. Otherwise
		1838	the callback was invoked too early (C<timeout> is in the future), so
		1839	re-schedule the timer to fire at that future time, to see if maybe we have
		1840	a timeout then.
		1841
		1842	Note how C<ev_timer_again> is used, taking advantage of the
		1843	C<ev_timer_again> optimisation when the timer is already running.
		1844
		1845	This scheme causes more callback invocations (about one every 60 seconds
		1846	minus half the average time between activity), but virtually no calls to
		1847	libev to change the timeout.
		1848
		1849	To start the timer, simply initialise the watcher and set C<last_activity>
		1850	to the current time (meaning we just have some activity :), then call the
		1851	callback, which will "do the right thing" and start the timer:
		1852
		1853	ev_init (timer, callback);
		1854	last_activity = ev_now (loop);
		1855	callback (loop, timer, EV_TIMER);
		1856
		1857	And when there is some activity, simply store the current time in
		1858	C<last_activity>, no libev calls at all:
		1859
		1860	last_activity = ev_now (loop);
		1861
		1862	This technique is slightly more complex, but in most cases where the
		1863	time-out is unlikely to be triggered, much more efficient.
		1864
		1865	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1866	callback :) - just change the timeout and invoke the callback, which will
		1867	fix things for you.
		1868
		1869	=item 4. Wee, just use a double-linked list for your timeouts.
		1870
		1871	If there is not one request, but many thousands (millions...), all
		1872	employing some kind of timeout with the same timeout value, then one can
		1873	do even better:
		1874
		1875	When starting the timeout, calculate the timeout value and put the timeout
		1876	at the I<end> of the list.
		1877
		1878	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1879	the list is expected to fire (for example, using the technique #3).
		1880
		1881	When there is some activity, remove the timer from the list, recalculate
		1882	the timeout, append it to the end of the list again, and make sure to
		1883	update the C<ev_timer> if it was taken from the beginning of the list.
		1884
		1885	This way, one can manage an unlimited number of timeouts in O(1) time for
		1886	starting, stopping and updating the timers, at the expense of a major
		1887	complication, and having to use a constant timeout. The constant timeout
		1888	ensures that the list stays sorted.
		1889
		1890	=back
		1891
		1892	So which method the best?
		1893
		1894	Method #2 is a simple no-brain-required solution that is adequate in most
		1895	situations. Method #3 requires a bit more thinking, but handles many cases
		1896	better, and isn't very complicated either. In most case, choosing either
		1897	one is fine, with #3 being better in typical situations.
		1898
		1899	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1900	rather complicated, but extremely efficient, something that really pays
		1901	off after the first million or so of active timers, i.e. it's usually
		1902	overkill :)
		1903
		1904	=head3 The special problem of time updates
		1905
		1906	Establishing the current time is a costly operation (it usually takes at
		1907	least two system calls): EV therefore updates its idea of the current
		1908	time only before and after C<ev_run> collects new events, which causes a
		1909	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1910	lots of events in one iteration.
1144		1911
1145	The relative timeouts are calculated relative to the C<ev_now ()>	1912	The relative timeouts are calculated relative to the C<ev_now ()>
1146	time. This is usually the right thing as this timestamp refers to the time	1913	time. This is usually the right thing as this timestamp refers to the time
1147	of the event triggering whatever timeout you are modifying/starting. If	1914	of the event triggering whatever timeout you are modifying/starting. If
1148	you suspect event processing to be delayed and you I<need> to base the timeout	1915	you suspect event processing to be delayed and you I<need> to base the
1149	on the current time, use something like this to adjust for this:	1916	timeout on the current time, use something like this to adjust for this:
1150		1917
1151	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1918	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1152		1919
1153	The callback is guarenteed to be invoked only when its timeout has passed,	1920	If the event loop is suspended for a long time, you can also force an
1154	but if multiple timers become ready during the same loop iteration then	1921	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1155	order of execution is undefined.	1922	()>.
		1923
		1924	=head3 The special problems of suspended animation
		1925
		1926	When you leave the server world it is quite customary to hit machines that
		1927	can suspend/hibernate - what happens to the clocks during such a suspend?
		1928
		1929	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1930	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1931	to run until the system is suspended, but they will not advance while the
		1932	system is suspended. That means, on resume, it will be as if the program
		1933	was frozen for a few seconds, but the suspend time will not be counted
		1934	towards C<ev_timer> when a monotonic clock source is used. The real time
		1935	clock advanced as expected, but if it is used as sole clocksource, then a
		1936	long suspend would be detected as a time jump by libev, and timers would
		1937	be adjusted accordingly.
		1938
		1939	I would not be surprised to see different behaviour in different between
		1940	operating systems, OS versions or even different hardware.
		1941
		1942	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1943	time jump in the monotonic clocks and the realtime clock. If the program
		1944	is suspended for a very long time, and monotonic clock sources are in use,
		1945	then you can expect C<ev_timer>s to expire as the full suspension time
		1946	will be counted towards the timers. When no monotonic clock source is in
		1947	use, then libev will again assume a timejump and adjust accordingly.
		1948
		1949	It might be beneficial for this latter case to call C<ev_suspend>
		1950	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1951	deterministic behaviour in this case (you can do nothing against
		1952	C<SIGSTOP>).
1156		1953
1157	=head3 Watcher-Specific Functions and Data Members	1954	=head3 Watcher-Specific Functions and Data Members
1158		1955
1159	=over 4	1956	=over 4
1160		1957
1161	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1958	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1162		1959
1163	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1960	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1164		1961
1165	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1962	Configure the timer to trigger after C<after> seconds. If C<repeat>
1166	C<0.>, then it will automatically be stopped. If it is positive, then the	1963	is C<0.>, then it will automatically be stopped once the timeout is
1167	timer will automatically be configured to trigger again C<repeat> seconds	1964	reached. If it is positive, then the timer will automatically be
1168	later, again, and again, until stopped manually.	1965	configured to trigger again C<repeat> seconds later, again, and again,
		1966	until stopped manually.
1169		1967
1170	The timer itself will do a best-effort at avoiding drift, that is, if you	1968	The timer itself will do a best-effort at avoiding drift, that is, if
1171	configure a timer to trigger every 10 seconds, then it will trigger at	1969	you configure a timer to trigger every 10 seconds, then it will normally
1172	exactly 10 second intervals. If, however, your program cannot keep up with	1970	trigger at exactly 10 second intervals. If, however, your program cannot
1173	the timer (because it takes longer than those 10 seconds to do stuff) the	1971	keep up with the timer (because it takes longer than those 10 seconds to
1174	timer will not fire more than once per event loop iteration.	1972	do stuff) the timer will not fire more than once per event loop iteration.
1175		1973
1176	=item ev_timer_again (loop, ev_timer *)	1974	=item ev_timer_again (loop, ev_timer *)
1177		1975
1178	This will act as if the timer timed out and restart it again if it is	1976	This will act as if the timer timed out and restart it again if it is
1179	repeating. The exact semantics are:	1977	repeating. The exact semantics are:
1180		1978
1181	If the timer is pending, its pending status is cleared.	1979	If the timer is pending, its pending status is cleared.
1182		1980
1183	If the timer is started but nonrepeating, stop it (as if it timed out).	1981	If the timer is started but non-repeating, stop it (as if it timed out).
1184		1982
1185	If the timer is repeating, either start it if necessary (with the	1983	If the timer is repeating, either start it if necessary (with the
1186	C<repeat> value), or reset the running timer to the C<repeat> value.	1984	C<repeat> value), or reset the running timer to the C<repeat> value.
1187		1985
1188	This sounds a bit complicated, but here is a useful and typical	1986	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1189	example: Imagine you have a tcp connection and you want a so-called idle	1987	usage example.
1190	timeout, that is, you want to be called when there have been, say, 60
1191	seconds of inactivity on the socket. The easiest way to do this is to
1192	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1193	C<ev_timer_again> each time you successfully read or write some data. If
1194	you go into an idle state where you do not expect data to travel on the
1195	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1196	automatically restart it if need be.
1197		1988
1198	That means you can ignore the C<after> value and C<ev_timer_start>	1989	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1199	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1200		1990
1201	ev_timer_init (timer, callback, 0., 5.);	1991	Returns the remaining time until a timer fires. If the timer is active,
1202	ev_timer_again (loop, timer);	1992	then this time is relative to the current event loop time, otherwise it's
1203	...	1993	the timeout value currently configured.
1204	timer->again = 17.;
1205	ev_timer_again (loop, timer);
1206	...
1207	timer->again = 10.;
1208	ev_timer_again (loop, timer);
1209		1994
1210	This is more slightly efficient then stopping/starting the timer each time	1995	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
1211	you want to modify its timeout value.	1996	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		1997	will return C<4>. When the timer expires and is restarted, it will return
		1998	roughly C<7> (likely slightly less as callback invocation takes some time,
		1999	too), and so on.
1212		2000
1213	=item ev_tstamp repeat [read-write]	2001	=item ev_tstamp repeat [read-write]
1214		2002
1215	The current C<repeat> value. Will be used each time the watcher times out	2003	The current C<repeat> value. Will be used each time the watcher times out
1216	or C<ev_timer_again> is called and determines the next timeout (if any),	2004	or C<ev_timer_again> is called, and determines the next timeout (if any),
1217	which is also when any modifications are taken into account.	2005	which is also when any modifications are taken into account.
1218		2006
1219	=back	2007	=back
1220		2008
1221	=head3 Examples	2009	=head3 Examples
1222		2010
1223	Example: Create a timer that fires after 60 seconds.	2011	Example: Create a timer that fires after 60 seconds.
1224		2012
1225	static void	2013	static void
1226	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2014	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1227	{	2015	{
1228	.. one minute over, w is actually stopped right here	2016	.. one minute over, w is actually stopped right here
1229	}	2017	}
1230		2018
1231	struct ev_timer mytimer;	2019	ev_timer mytimer;
1232	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	2020	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1233	ev_timer_start (loop, &mytimer);	2021	ev_timer_start (loop, &mytimer);
1234		2022
1235	Example: Create a timeout timer that times out after 10 seconds of	2023	Example: Create a timeout timer that times out after 10 seconds of
1236	inactivity.	2024	inactivity.
1237		2025
1238	static void	2026	static void
1239	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	2027	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1240	{	2028	{
1241	.. ten seconds without any activity	2029	.. ten seconds without any activity
1242	}	2030	}
1243		2031
1244	struct ev_timer mytimer;	2032	ev_timer mytimer;
1245	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	2033	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1246	ev_timer_again (&mytimer); /* start timer */	2034	ev_timer_again (&mytimer); /* start timer */
1247	ev_loop (loop, 0);	2035	ev_run (loop, 0);
1248		2036
1249	// and in some piece of code that gets executed on any "activity":	2037	// and in some piece of code that gets executed on any "activity":
1250	// reset the timeout to start ticking again at 10 seconds	2038	// reset the timeout to start ticking again at 10 seconds
1251	ev_timer_again (&mytimer);	2039	ev_timer_again (&mytimer);
1252		2040
1253		2041
1254	=head2 C<ev_periodic> - to cron or not to cron?	2042	=head2 C<ev_periodic> - to cron or not to cron?
1255		2043
1256	Periodic watchers are also timers of a kind, but they are very versatile	2044	Periodic watchers are also timers of a kind, but they are very versatile
1257	(and unfortunately a bit complex).	2045	(and unfortunately a bit complex).
1258		2046
1259	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	2047	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1260	but on wallclock time (absolute time). You can tell a periodic watcher	2048	relative time, the physical time that passes) but on wall clock time
1261	to trigger "at" some specific point in time. For example, if you tell a	2049	(absolute time, the thing you can read on your calender or clock). The
1262	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	2050	difference is that wall clock time can run faster or slower than real
1263	+ 10.>) and then reset your system clock to the last year, then it will	2051	time, and time jumps are not uncommon (e.g. when you adjust your
1264	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	2052	wrist-watch).
1265	roughly 10 seconds later).
1266		2053
1267	They can also be used to implement vastly more complex timers, such as	2054	You can tell a periodic watcher to trigger after some specific point
1268	triggering an event on each midnight, local time or other, complicated,	2055	in time: for example, if you tell a periodic watcher to trigger "in 10
1269	rules.	2056	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		2057	not a delay) and then reset your system clock to January of the previous
		2058	year, then it will take a year or more to trigger the event (unlike an
		2059	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		2060	it, as it uses a relative timeout).
1270		2061
		2062	C<ev_periodic> watchers can also be used to implement vastly more complex
		2063	timers, such as triggering an event on each "midnight, local time", or
		2064	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		2065	those cannot react to time jumps.
		2066
1271	As with timers, the callback is guarenteed to be invoked only when the	2067	As with timers, the callback is guaranteed to be invoked only when the
1272	time (C<at>) has been passed, but if multiple periodic timers become ready	2068	point in time where it is supposed to trigger has passed. If multiple
1273	during the same loop iteration then order of execution is undefined.	2069	timers become ready during the same loop iteration then the ones with
		2070	earlier time-out values are invoked before ones with later time-out values
		2071	(but this is no longer true when a callback calls C<ev_run> recursively).
1274		2072
1275	=head3 Watcher-Specific Functions and Data Members	2073	=head3 Watcher-Specific Functions and Data Members
1276		2074
1277	=over 4	2075	=over 4
1278		2076
1279	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	2077	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1280		2078
1281	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2079	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1282		2080
1283	Lots of arguments, lets sort it out... There are basically three modes of	2081	Lots of arguments, let's sort it out... There are basically three modes of
1284	operation, and we will explain them from simplest to complex:	2082	operation, and we will explain them from simplest to most complex:
1285		2083
1286	=over 4	2084	=over 4
1287		2085
1288	=item * absolute timer (at = time, interval = reschedule_cb = 0)	2086	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1289		2087
1290	In this configuration the watcher triggers an event at the wallclock time	2088	In this configuration the watcher triggers an event after the wall clock
1291	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	2089	time C<offset> has passed. It will not repeat and will not adjust when a
1292	that is, if it is to be run at January 1st 2011 then it will run when the	2090	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1293	system time reaches or surpasses this time.	2091	will be stopped and invoked when the system clock reaches or surpasses
		2092	this point in time.
1294		2093
1295	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	2094	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1296		2095
1297	In this mode the watcher will always be scheduled to time out at the next	2096	In this mode the watcher will always be scheduled to time out at the next
1298	C<at + N * interval> time (for some integer N, which can also be negative)	2097	C<offset + N * interval> time (for some integer N, which can also be
1299	and then repeat, regardless of any time jumps.	2098	negative) and then repeat, regardless of any time jumps. The C<offset>
		2099	argument is merely an offset into the C<interval> periods.
1300		2100
1301	This can be used to create timers that do not drift with respect to system	2101	This can be used to create timers that do not drift with respect to the
1302	time:	2102	system clock, for example, here is an C<ev_periodic> that triggers each
		2103	hour, on the hour (with respect to UTC):
1303		2104
1304	ev_periodic_set (&periodic, 0., 3600., 0);	2105	ev_periodic_set (&periodic, 0., 3600., 0);
1305		2106
1306	This doesn't mean there will always be 3600 seconds in between triggers,	2107	This doesn't mean there will always be 3600 seconds in between triggers,
1307	but only that the the callback will be called when the system time shows a	2108	but only that the callback will be called when the system time shows a
1308	full hour (UTC), or more correctly, when the system time is evenly divisible	2109	full hour (UTC), or more correctly, when the system time is evenly divisible
1309	by 3600.	2110	by 3600.
1310		2111
1311	Another way to think about it (for the mathematically inclined) is that	2112	Another way to think about it (for the mathematically inclined) is that
1312	C<ev_periodic> will try to run the callback in this mode at the next possible	2113	C<ev_periodic> will try to run the callback in this mode at the next possible
1313	time where C<time = at (mod interval)>, regardless of any time jumps.	2114	time where C<time = offset (mod interval)>, regardless of any time jumps.
1314		2115
1315	For numerical stability it is preferable that the C<at> value is near	2116	For numerical stability it is preferable that the C<offset> value is near
1316	C<ev_now ()> (the current time), but there is no range requirement for	2117	C<ev_now ()> (the current time), but there is no range requirement for
1317	this value.	2118	this value, and in fact is often specified as zero.
1318		2119
		2120	Note also that there is an upper limit to how often a timer can fire (CPU
		2121	speed for example), so if C<interval> is very small then timing stability
		2122	will of course deteriorate. Libev itself tries to be exact to be about one
		2123	millisecond (if the OS supports it and the machine is fast enough).
		2124
1319	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	2125	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1320		2126
1321	In this mode the values for C<interval> and C<at> are both being	2127	In this mode the values for C<interval> and C<offset> are both being
1322	ignored. Instead, each time the periodic watcher gets scheduled, the	2128	ignored. Instead, each time the periodic watcher gets scheduled, the
1323	reschedule callback will be called with the watcher as first, and the	2129	reschedule callback will be called with the watcher as first, and the
1324	current time as second argument.	2130	current time as second argument.
1325		2131
1326	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2132	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1327	ever, or make any event loop modifications>. If you need to stop it,	2133	or make ANY other event loop modifications whatsoever, unless explicitly
1328	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	2134	allowed by documentation here>.
1329	starting an C<ev_prepare> watcher, which is legal).
1330		2135
		2136	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		2137	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		2138	only event loop modification you are allowed to do).
		2139
1331	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	2140	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1332	ev_tstamp now)>, e.g.:	2141	*w, ev_tstamp now)>, e.g.:
1333		2142
		2143	static ev_tstamp
1334	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2144	my_rescheduler (ev_periodic *w, ev_tstamp now)
1335	{	2145	{
1336	return now + 60.;	2146	return now + 60.;
1337	}	2147	}
1338		2148
1339	It must return the next time to trigger, based on the passed time value	2149	It must return the next time to trigger, based on the passed time value
1340	(that is, the lowest time value larger than to the second argument). It	2150	(that is, the lowest time value larger than to the second argument). It
1341	will usually be called just before the callback will be triggered, but	2151	will usually be called just before the callback will be triggered, but
1342	might be called at other times, too.	2152	might be called at other times, too.
1343		2153
1344	NOTE: I<< This callback must always return a time that is later than the	2154	NOTE: I<< This callback must always return a time that is higher than or
1345	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	2155	equal to the passed C<now> value >>.
1346		2156
1347	This can be used to create very complex timers, such as a timer that	2157	This can be used to create very complex timers, such as a timer that
1348	triggers on each midnight, local time. To do this, you would calculate the	2158	triggers on "next midnight, local time". To do this, you would calculate the
1349	next midnight after C<now> and return the timestamp value for this. How	2159	next midnight after C<now> and return the timestamp value for this. How
1350	you do this is, again, up to you (but it is not trivial, which is the main	2160	you do this is, again, up to you (but it is not trivial, which is the main
1351	reason I omitted it as an example).	2161	reason I omitted it as an example).
1352		2162
1353	=back	2163	=back
…		…
1357	Simply stops and restarts the periodic watcher again. This is only useful	2167	Simply stops and restarts the periodic watcher again. This is only useful
1358	when you changed some parameters or the reschedule callback would return	2168	when you changed some parameters or the reschedule callback would return
1359	a different time than the last time it was called (e.g. in a crond like	2169	a different time than the last time it was called (e.g. in a crond like
1360	program when the crontabs have changed).	2170	program when the crontabs have changed).
1361		2171
		2172	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2173
		2174	When active, returns the absolute time that the watcher is supposed
		2175	to trigger next. This is not the same as the C<offset> argument to
		2176	C<ev_periodic_set>, but indeed works even in interval and manual
		2177	rescheduling modes.
		2178
1362	=item ev_tstamp offset [read-write]	2179	=item ev_tstamp offset [read-write]
1363		2180
1364	When repeating, this contains the offset value, otherwise this is the	2181	When repeating, this contains the offset value, otherwise this is the
1365	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	2182	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2183	although libev might modify this value for better numerical stability).
1366		2184
1367	Can be modified any time, but changes only take effect when the periodic	2185	Can be modified any time, but changes only take effect when the periodic
1368	timer fires or C<ev_periodic_again> is being called.	2186	timer fires or C<ev_periodic_again> is being called.
1369		2187
1370	=item ev_tstamp interval [read-write]	2188	=item ev_tstamp interval [read-write]
1371		2189
1372	The current interval value. Can be modified any time, but changes only	2190	The current interval value. Can be modified any time, but changes only
1373	take effect when the periodic timer fires or C<ev_periodic_again> is being	2191	take effect when the periodic timer fires or C<ev_periodic_again> is being
1374	called.	2192	called.
1375		2193
1376	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2194	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1377		2195
1378	The current reschedule callback, or C<0>, if this functionality is	2196	The current reschedule callback, or C<0>, if this functionality is
1379	switched off. Can be changed any time, but changes only take effect when	2197	switched off. Can be changed any time, but changes only take effect when
1380	the periodic timer fires or C<ev_periodic_again> is being called.	2198	the periodic timer fires or C<ev_periodic_again> is being called.
1381		2199
1382	=item ev_tstamp at [read-only]
1383
1384	When active, contains the absolute time that the watcher is supposed to
1385	trigger next.
1386
1387	=back	2200	=back
1388		2201
1389	=head3 Examples	2202	=head3 Examples
1390		2203
1391	Example: Call a callback every hour, or, more precisely, whenever the	2204	Example: Call a callback every hour, or, more precisely, whenever the
1392	system clock is divisible by 3600. The callback invocation times have	2205	system time is divisible by 3600. The callback invocation times have
1393	potentially a lot of jittering, but good long-term stability.	2206	potentially a lot of jitter, but good long-term stability.
1394		2207
1395	static void	2208	static void
1396	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2209	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1397	{	2210	{
1398	... its now a full hour (UTC, or TAI or whatever your clock follows)	2211	... its now a full hour (UTC, or TAI or whatever your clock follows)
1399	}	2212	}
1400		2213
1401	struct ev_periodic hourly_tick;	2214	ev_periodic hourly_tick;
1402	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2215	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1403	ev_periodic_start (loop, &hourly_tick);	2216	ev_periodic_start (loop, &hourly_tick);
1404		2217
1405	Example: The same as above, but use a reschedule callback to do it:	2218	Example: The same as above, but use a reschedule callback to do it:
1406		2219
1407	#include <math.h>	2220	#include <math.h>
1408		2221
1409	static ev_tstamp	2222	static ev_tstamp
1410	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2223	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1411	{	2224	{
1412	return fmod (now, 3600.) + 3600.;	2225	return now + (3600. - fmod (now, 3600.));
1413	}	2226	}
1414		2227
1415	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2228	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1416		2229
1417	Example: Call a callback every hour, starting now:	2230	Example: Call a callback every hour, starting now:
1418		2231
1419	struct ev_periodic hourly_tick;	2232	ev_periodic hourly_tick;
1420	ev_periodic_init (&hourly_tick, clock_cb,	2233	ev_periodic_init (&hourly_tick, clock_cb,
1421	fmod (ev_now (loop), 3600.), 3600., 0);	2234	fmod (ev_now (loop), 3600.), 3600., 0);
1422	ev_periodic_start (loop, &hourly_tick);	2235	ev_periodic_start (loop, &hourly_tick);
1423		2236
1424		2237
1425	=head2 C<ev_signal> - signal me when a signal gets signalled!	2238	=head2 C<ev_signal> - signal me when a signal gets signalled!
1426		2239
1427	Signal watchers will trigger an event when the process receives a specific	2240	Signal watchers will trigger an event when the process receives a specific
1428	signal one or more times. Even though signals are very asynchronous, libev	2241	signal one or more times. Even though signals are very asynchronous, libev
1429	will try it's best to deliver signals synchronously, i.e. as part of the	2242	will try it's best to deliver signals synchronously, i.e. as part of the
1430	normal event processing, like any other event.	2243	normal event processing, like any other event.
1431		2244
		2245	If you want signals to be delivered truly asynchronously, just use
		2246	C<sigaction> as you would do without libev and forget about sharing
		2247	the signal. You can even use C<ev_async> from a signal handler to
		2248	synchronously wake up an event loop.
		2249
1432	You can configure as many watchers as you like per signal. Only when the	2250	You can configure as many watchers as you like for the same signal, but
		2251	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2252	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2253	C<SIGINT> in both the default loop and another loop at the same time. At
		2254	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2255
1433	first watcher gets started will libev actually register a signal watcher	2256	When the first watcher gets started will libev actually register something
1434	with the kernel (thus it coexists with your own signal handlers as long	2257	with the kernel (thus it coexists with your own signal handlers as long as
1435	as you don't register any with libev). Similarly, when the last signal	2258	you don't register any with libev for the same signal).
1436	watcher for a signal is stopped libev will reset the signal handler to
1437	SIG_DFL (regardless of what it was set to before).
1438		2259
1439	If possible and supported, libev will install its handlers with	2260	If possible and supported, libev will install its handlers with
1440	C<SA_RESTART> behaviour enabled, so syscalls should not be unduly	2261	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
1441	interrupted. If you have a problem with syscalls getting interrupted by	2262	not be unduly interrupted. If you have a problem with system calls getting
1442	signals you can block all signals in an C<ev_check> watcher and unblock	2263	interrupted by signals you can block all signals in an C<ev_check> watcher
1443	them in an C<ev_prepare> watcher.	2264	and unblock them in an C<ev_prepare> watcher.
		2265
		2266	=head3 The special problem of inheritance over fork/execve/pthread_create
		2267
		2268	Both the signal mask (C<sigprocmask>) and the signal disposition
		2269	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2270	stopping it again), that is, libev might or might not block the signal,
		2271	and might or might not set or restore the installed signal handler.
		2272
		2273	While this does not matter for the signal disposition (libev never
		2274	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2275	C<execve>), this matters for the signal mask: many programs do not expect
		2276	certain signals to be blocked.
		2277
		2278	This means that before calling C<exec> (from the child) you should reset
		2279	the signal mask to whatever "default" you expect (all clear is a good
		2280	choice usually).
		2281
		2282	The simplest way to ensure that the signal mask is reset in the child is
		2283	to install a fork handler with C<pthread_atfork> that resets it. That will
		2284	catch fork calls done by libraries (such as the libc) as well.
		2285
		2286	In current versions of libev, the signal will not be blocked indefinitely
		2287	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2288	the window of opportunity for problems, it will not go away, as libev
		2289	I<has> to modify the signal mask, at least temporarily.
		2290
		2291	So I can't stress this enough: I<If you do not reset your signal mask when
		2292	you expect it to be empty, you have a race condition in your code>. This
		2293	is not a libev-specific thing, this is true for most event libraries.
1444		2294
1445	=head3 Watcher-Specific Functions and Data Members	2295	=head3 Watcher-Specific Functions and Data Members
1446		2296
1447	=over 4	2297	=over 4
1448		2298
…		…
1459		2309
1460	=back	2310	=back
1461		2311
1462	=head3 Examples	2312	=head3 Examples
1463		2313
1464	Example: Try to exit cleanly on SIGINT and SIGTERM.	2314	Example: Try to exit cleanly on SIGINT.
1465		2315
1466	static void	2316	static void
1467	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2317	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
1468	{	2318	{
1469	ev_unloop (loop, EVUNLOOP_ALL);	2319	ev_break (loop, EVBREAK_ALL);
1470	}	2320	}
1471		2321
1472	struct ev_signal signal_watcher;	2322	ev_signal signal_watcher;
1473	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2323	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1474	ev_signal_start (loop, &sigint_cb);	2324	ev_signal_start (loop, &signal_watcher);
1475		2325
1476		2326
1477	=head2 C<ev_child> - watch out for process status changes	2327	=head2 C<ev_child> - watch out for process status changes
1478		2328
1479	Child watchers trigger when your process receives a SIGCHLD in response to	2329	Child watchers trigger when your process receives a SIGCHLD in response to
1480	some child status changes (most typically when a child of yours dies). It	2330	some child status changes (most typically when a child of yours dies or
1481	is permissible to install a child watcher I<after> the child has been	2331	exits). It is permissible to install a child watcher I<after> the child
1482	forked (which implies it might have already exited), as long as the event	2332	has been forked (which implies it might have already exited), as long
1483	loop isn't entered (or is continued from a watcher).	2333	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2334	forking and then immediately registering a watcher for the child is fine,
		2335	but forking and registering a watcher a few event loop iterations later or
		2336	in the next callback invocation is not.
1484		2337
1485	Only the default event loop is capable of handling signals, and therefore	2338	Only the default event loop is capable of handling signals, and therefore
1486	you can only rgeister child watchers in the default event loop.	2339	you can only register child watchers in the default event loop.
		2340
		2341	Due to some design glitches inside libev, child watchers will always be
		2342	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2343	libev)
1487		2344
1488	=head3 Process Interaction	2345	=head3 Process Interaction
1489		2346
1490	Libev grabs C<SIGCHLD> as soon as the default event loop is	2347	Libev grabs C<SIGCHLD> as soon as the default event loop is
1491	initialised. This is necessary to guarantee proper behaviour even if	2348	initialised. This is necessary to guarantee proper behaviour even if the
1492	the first child watcher is started after the child exits. The occurance	2349	first child watcher is started after the child exits. The occurrence
1493	of C<SIGCHLD> is recorded asynchronously, but child reaping is done	2350	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
1494	synchronously as part of the event loop processing. Libev always reaps all	2351	synchronously as part of the event loop processing. Libev always reaps all
1495	children, even ones not watched.	2352	children, even ones not watched.
1496		2353
1497	=head3 Overriding the Built-In Processing	2354	=head3 Overriding the Built-In Processing
…		…
1501	handler, you can override it easily by installing your own handler for	2358	handler, you can override it easily by installing your own handler for
1502	C<SIGCHLD> after initialising the default loop, and making sure the	2359	C<SIGCHLD> after initialising the default loop, and making sure the
1503	default loop never gets destroyed. You are encouraged, however, to use an	2360	default loop never gets destroyed. You are encouraged, however, to use an
1504	event-based approach to child reaping and thus use libev's support for	2361	event-based approach to child reaping and thus use libev's support for
1505	that, so other libev users can use C<ev_child> watchers freely.	2362	that, so other libev users can use C<ev_child> watchers freely.
		2363
		2364	=head3 Stopping the Child Watcher
		2365
		2366	Currently, the child watcher never gets stopped, even when the
		2367	child terminates, so normally one needs to stop the watcher in the
		2368	callback. Future versions of libev might stop the watcher automatically
		2369	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2370	problem).
1506		2371
1507	=head3 Watcher-Specific Functions and Data Members	2372	=head3 Watcher-Specific Functions and Data Members
1508		2373
1509	=over 4	2374	=over 4
1510		2375
…		…
1539	=head3 Examples	2404	=head3 Examples
1540		2405
1541	Example: C<fork()> a new process and install a child handler to wait for	2406	Example: C<fork()> a new process and install a child handler to wait for
1542	its completion.	2407	its completion.
1543		2408
1544	ev_child cw;	2409	ev_child cw;
1545		2410
1546	static void	2411	static void
1547	child_cb (EV_P_ struct ev_child *w, int revents)	2412	child_cb (EV_P_ ev_child *w, int revents)
1548	{	2413	{
1549	ev_child_stop (EV_A_ w);	2414	ev_child_stop (EV_A_ w);
1550	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);	2415	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1551	}	2416	}
1552		2417
1553	pid_t pid = fork ();	2418	pid_t pid = fork ();
1554		2419
1555	if (pid < 0)	2420	if (pid < 0)
1556	// error	2421	// error
1557	else if (pid == 0)	2422	else if (pid == 0)
1558	{	2423	{
1559	// the forked child executes here	2424	// the forked child executes here
1560	exit (1);	2425	exit (1);
1561	}	2426	}
1562	else	2427	else
1563	{	2428	{
1564	ev_child_init (&cw, child_cb, pid, 0);	2429	ev_child_init (&cw, child_cb, pid, 0);
1565	ev_child_start (EV_DEFAULT_ &cw);	2430	ev_child_start (EV_DEFAULT_ &cw);
1566	}	2431	}
1567		2432
1568		2433
1569	=head2 C<ev_stat> - did the file attributes just change?	2434	=head2 C<ev_stat> - did the file attributes just change?
1570		2435
1571	This watches a filesystem path for attribute changes. That is, it calls	2436	This watches a file system path for attribute changes. That is, it calls
1572	C<stat> regularly (or when the OS says it changed) and sees if it changed	2437	C<stat> on that path in regular intervals (or when the OS says it changed)
1573	compared to the last time, invoking the callback if it did.	2438	and sees if it changed compared to the last time, invoking the callback if
		2439	it did.
1574		2440
1575	The path does not need to exist: changing from "path exists" to "path does	2441	The path does not need to exist: changing from "path exists" to "path does
1576	not exist" is a status change like any other. The condition "path does	2442	not exist" is a status change like any other. The condition "path does not
1577	not exist" is signified by the C<st_nlink> field being zero (which is	2443	exist" (or more correctly "path cannot be stat'ed") is signified by the
1578	otherwise always forced to be at least one) and all the other fields of	2444	C<st_nlink> field being zero (which is otherwise always forced to be at
1579	the stat buffer having unspecified contents.	2445	least one) and all the other fields of the stat buffer having unspecified
		2446	contents.
1580		2447
1581	The path I<should> be absolute and I<must not> end in a slash. If it is	2448	The path I<must not> end in a slash or contain special components such as
		2449	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1582	relative and your working directory changes, the behaviour is undefined.	2450	your working directory changes, then the behaviour is undefined.
1583		2451
1584	Since there is no standard to do this, the portable implementation simply	2452	Since there is no portable change notification interface available, the
1585	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2453	portable implementation simply calls C<stat(2)> regularly on the path
1586	can specify a recommended polling interval for this case. If you specify	2454	to see if it changed somehow. You can specify a recommended polling
1587	a polling interval of C<0> (highly recommended!) then a I<suitable,	2455	interval for this case. If you specify a polling interval of C<0> (highly
1588	unspecified default> value will be used (which you can expect to be around	2456	recommended!) then a I<suitable, unspecified default> value will be used
1589	five seconds, although this might change dynamically). Libev will also	2457	(which you can expect to be around five seconds, although this might
1590	impose a minimum interval which is currently around C<0.1>, but thats	2458	change dynamically). Libev will also impose a minimum interval which is
1591	usually overkill.	2459	currently around C<0.1>, but that's usually overkill.
1592		2460
1593	This watcher type is not meant for massive numbers of stat watchers,	2461	This watcher type is not meant for massive numbers of stat watchers,
1594	as even with OS-supported change notifications, this can be	2462	as even with OS-supported change notifications, this can be
1595	resource-intensive.	2463	resource-intensive.
1596		2464
1597	At the time of this writing, only the Linux inotify interface is	2465	At the time of this writing, the only OS-specific interface implemented
1598	implemented (implementing kqueue support is left as an exercise for the	2466	is the Linux inotify interface (implementing kqueue support is left as an
1599	reader). Inotify will be used to give hints only and should not change the	2467	exercise for the reader. Note, however, that the author sees no way of
1600	semantics of C<ev_stat> watchers, which means that libev sometimes needs	2468	implementing C<ev_stat> semantics with kqueue, except as a hint).
1601	to fall back to regular polling again even with inotify, but changes are
1602	usually detected immediately, and if the file exists there will be no
1603	polling.
1604		2469
1605	=head3 ABI Issues (Largefile Support)	2470	=head3 ABI Issues (Largefile Support)
1606		2471
1607	Libev by default (unless the user overrides this) uses the default	2472	Libev by default (unless the user overrides this) uses the default
1608	compilation environment, which means that on systems with optionally	2473	compilation environment, which means that on systems with large file
1609	disabled large file support, you get the 32 bit version of the stat	2474	support disabled by default, you get the 32 bit version of the stat
1610	structure. When using the library from programs that change the ABI to	2475	structure. When using the library from programs that change the ABI to
1611	use 64 bit file offsets the programs will fail. In that case you have to	2476	use 64 bit file offsets the programs will fail. In that case you have to
1612	compile libev with the same flags to get binary compatibility. This is	2477	compile libev with the same flags to get binary compatibility. This is
1613	obviously the case with any flags that change the ABI, but the problem is	2478	obviously the case with any flags that change the ABI, but the problem is
1614	most noticably with ev_stat and largefile support.	2479	most noticeably displayed with ev_stat and large file support.
1615		2480
1616	=head3 Inotify	2481	The solution for this is to lobby your distribution maker to make large
		2482	file interfaces available by default (as e.g. FreeBSD does) and not
		2483	optional. Libev cannot simply switch on large file support because it has
		2484	to exchange stat structures with application programs compiled using the
		2485	default compilation environment.
1617		2486
		2487	=head3 Inotify and Kqueue
		2488
1618	When C<inotify (7)> support has been compiled into libev (generally only	2489	When C<inotify (7)> support has been compiled into libev and present at
1619	available on Linux) and present at runtime, it will be used to speed up	2490	runtime, it will be used to speed up change detection where possible. The
1620	change detection where possible. The inotify descriptor will be created lazily	2491	inotify descriptor will be created lazily when the first C<ev_stat>
1621	when the first C<ev_stat> watcher is being started.	2492	watcher is being started.
1622		2493
1623	Inotify presense does not change the semantics of C<ev_stat> watchers	2494	Inotify presence does not change the semantics of C<ev_stat> watchers
1624	except that changes might be detected earlier, and in some cases, to avoid	2495	except that changes might be detected earlier, and in some cases, to avoid
1625	making regular C<stat> calls. Even in the presense of inotify support	2496	making regular C<stat> calls. Even in the presence of inotify support
1626	there are many cases where libev has to resort to regular C<stat> polling.	2497	there are many cases where libev has to resort to regular C<stat> polling,
		2498	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2499	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2500	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2501	xfs are fully working) libev usually gets away without polling.
1627		2502
1628	(There is no support for kqueue, as apparently it cannot be used to	2503	There is no support for kqueue, as apparently it cannot be used to
1629	implement this functionality, due to the requirement of having a file	2504	implement this functionality, due to the requirement of having a file
1630	descriptor open on the object at all times).	2505	descriptor open on the object at all times, and detecting renames, unlinks
		2506	etc. is difficult.
		2507
		2508	=head3 C<stat ()> is a synchronous operation
		2509
		2510	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2511	the process. The exception are C<ev_stat> watchers - those call C<stat
		2512	()>, which is a synchronous operation.
		2513
		2514	For local paths, this usually doesn't matter: unless the system is very
		2515	busy or the intervals between stat's are large, a stat call will be fast,
		2516	as the path data is usually in memory already (except when starting the
		2517	watcher).
		2518
		2519	For networked file systems, calling C<stat ()> can block an indefinite
		2520	time due to network issues, and even under good conditions, a stat call
		2521	often takes multiple milliseconds.
		2522
		2523	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2524	paths, although this is fully supported by libev.
1631		2525
1632	=head3 The special problem of stat time resolution	2526	=head3 The special problem of stat time resolution
1633		2527
1634	The C<stat ()> syscall only supports full-second resolution portably, and	2528	The C<stat ()> system call only supports full-second resolution portably,
1635	even on systems where the resolution is higher, many filesystems still	2529	and even on systems where the resolution is higher, most file systems
1636	only support whole seconds.	2530	still only support whole seconds.
1637		2531
1638	That means that, if the time is the only thing that changes, you might	2532	That means that, if the time is the only thing that changes, you can
1639	miss updates: on the first update, C<ev_stat> detects a change and calls	2533	easily miss updates: on the first update, C<ev_stat> detects a change and
1640	your callback, which does something. When there is another update within	2534	calls your callback, which does something. When there is another update
1641	the same second, C<ev_stat> will be unable to detect it.	2535	within the same second, C<ev_stat> will be unable to detect unless the
		2536	stat data does change in other ways (e.g. file size).
1642		2537
1643	The solution to this is to delay acting on a change for a second (or till	2538	The solution to this is to delay acting on a change for slightly more
1644	the next second boundary), using a roughly one-second delay C<ev_timer>	2539	than a second (or till slightly after the next full second boundary), using
1645	(C<ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)>). The C<.01>	2540	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
1646	is added to work around small timing inconsistencies of some operating	2541	ev_timer_again (loop, w)>).
1647	systems.	2542
		2543	The C<.02> offset is added to work around small timing inconsistencies
		2544	of some operating systems (where the second counter of the current time
		2545	might be be delayed. One such system is the Linux kernel, where a call to
		2546	C<gettimeofday> might return a timestamp with a full second later than
		2547	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2548	update file times then there will be a small window where the kernel uses
		2549	the previous second to update file times but libev might already execute
		2550	the timer callback).
1648		2551
1649	=head3 Watcher-Specific Functions and Data Members	2552	=head3 Watcher-Specific Functions and Data Members
1650		2553
1651	=over 4	2554	=over 4
1652		2555
…		…
1658	C<path>. The C<interval> is a hint on how quickly a change is expected to	2561	C<path>. The C<interval> is a hint on how quickly a change is expected to
1659	be detected and should normally be specified as C<0> to let libev choose	2562	be detected and should normally be specified as C<0> to let libev choose
1660	a suitable value. The memory pointed to by C<path> must point to the same	2563	a suitable value. The memory pointed to by C<path> must point to the same
1661	path for as long as the watcher is active.	2564	path for as long as the watcher is active.
1662		2565
1663	The callback will be receive C<EV_STAT> when a change was detected,	2566	The callback will receive an C<EV_STAT> event when a change was detected,
1664	relative to the attributes at the time the watcher was started (or the	2567	relative to the attributes at the time the watcher was started (or the
1665	last change was detected).	2568	last change was detected).
1666		2569
1667	=item ev_stat_stat (loop, ev_stat *)	2570	=item ev_stat_stat (loop, ev_stat *)
1668		2571
1669	Updates the stat buffer immediately with new values. If you change the	2572	Updates the stat buffer immediately with new values. If you change the
1670	watched path in your callback, you could call this fucntion to avoid	2573	watched path in your callback, you could call this function to avoid
1671	detecting this change (while introducing a race condition). Can also be	2574	detecting this change (while introducing a race condition if you are not
1672	useful simply to find out the new values.	2575	the only one changing the path). Can also be useful simply to find out the
		2576	new values.
1673		2577
1674	=item ev_statdata attr [read-only]	2578	=item ev_statdata attr [read-only]
1675		2579
1676	The most-recently detected attributes of the file. Although the type is of	2580	The most-recently detected attributes of the file. Although the type is
1677	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2581	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1678	suitable for your system. If the C<st_nlink> member is C<0>, then there	2582	suitable for your system, but you can only rely on the POSIX-standardised
		2583	members to be present. If the C<st_nlink> member is C<0>, then there was
1679	was some error while C<stat>ing the file.	2584	some error while C<stat>ing the file.
1680		2585
1681	=item ev_statdata prev [read-only]	2586	=item ev_statdata prev [read-only]
1682		2587
1683	The previous attributes of the file. The callback gets invoked whenever	2588	The previous attributes of the file. The callback gets invoked whenever
1684	C<prev> != C<attr>.	2589	C<prev> != C<attr>, or, more precisely, one or more of these members
		2590	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2591	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1685		2592
1686	=item ev_tstamp interval [read-only]	2593	=item ev_tstamp interval [read-only]
1687		2594
1688	The specified interval.	2595	The specified interval.
1689		2596
1690	=item const char *path [read-only]	2597	=item const char *path [read-only]
1691		2598
1692	The filesystem path that is being watched.	2599	The file system path that is being watched.
1693		2600
1694	=back	2601	=back
1695		2602
1696	=head3 Examples	2603	=head3 Examples
1697		2604
1698	Example: Watch C</etc/passwd> for attribute changes.	2605	Example: Watch C</etc/passwd> for attribute changes.
1699		2606
1700	static void	2607	static void
1701	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2608	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1702	{	2609	{
1703	/* /etc/passwd changed in some way */	2610	/* /etc/passwd changed in some way */
1704	if (w->attr.st_nlink)	2611	if (w->attr.st_nlink)
1705	{	2612	{
1706	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2613	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1707	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2614	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1708	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2615	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1709	}	2616	}
1710	else	2617	else
1711	/* you shalt not abuse printf for puts */	2618	/* you shalt not abuse printf for puts */
1712	puts ("wow, /etc/passwd is not there, expect problems. "	2619	puts ("wow, /etc/passwd is not there, expect problems. "
1713	"if this is windows, they already arrived\n");	2620	"if this is windows, they already arrived\n");
1714	}	2621	}
1715		2622
1716	...	2623	...
1717	ev_stat passwd;	2624	ev_stat passwd;
1718		2625
1719	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);	2626	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1720	ev_stat_start (loop, &passwd);	2627	ev_stat_start (loop, &passwd);
1721		2628
1722	Example: Like above, but additionally use a one-second delay so we do not	2629	Example: Like above, but additionally use a one-second delay so we do not
1723	miss updates (however, frequent updates will delay processing, too, so	2630	miss updates (however, frequent updates will delay processing, too, so
1724	one might do the work both on C<ev_stat> callback invocation I<and> on	2631	one might do the work both on C<ev_stat> callback invocation I<and> on
1725	C<ev_timer> callback invocation).	2632	C<ev_timer> callback invocation).
1726		2633
1727	static ev_stat passwd;	2634	static ev_stat passwd;
1728	static ev_timer timer;	2635	static ev_timer timer;
1729		2636
1730	static void	2637	static void
1731	timer_cb (EV_P_ ev_timer *w, int revents)	2638	timer_cb (EV_P_ ev_timer *w, int revents)
1732	{	2639	{
1733	ev_timer_stop (EV_A_ w);	2640	ev_timer_stop (EV_A_ w);
1734		2641
1735	/* now it's one second after the most recent passwd change */	2642	/* now it's one second after the most recent passwd change */
1736	}	2643	}
1737		2644
1738	static void	2645	static void
1739	stat_cb (EV_P_ ev_stat *w, int revents)	2646	stat_cb (EV_P_ ev_stat *w, int revents)
1740	{	2647	{
1741	/* reset the one-second timer */	2648	/* reset the one-second timer */
1742	ev_timer_again (EV_A_ &timer);	2649	ev_timer_again (EV_A_ &timer);
1743	}	2650	}
1744		2651
1745	...	2652	...
1746	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);	2653	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1747	ev_stat_start (loop, &passwd);	2654	ev_stat_start (loop, &passwd);
1748	ev_timer_init (&timer, timer_cb, 0., 1.01);	2655	ev_timer_init (&timer, timer_cb, 0., 1.02);
1749		2656
1750		2657
1751	=head2 C<ev_idle> - when you've got nothing better to do...	2658	=head2 C<ev_idle> - when you've got nothing better to do...
1752		2659
1753	Idle watchers trigger events when no other events of the same or higher	2660	Idle watchers trigger events when no other events of the same or higher
1754	priority are pending (prepare, check and other idle watchers do not	2661	priority are pending (prepare, check and other idle watchers do not count
1755	count).	2662	as receiving "events").
1756		2663
1757	That is, as long as your process is busy handling sockets or timeouts	2664	That is, as long as your process is busy handling sockets or timeouts
1758	(or even signals, imagine) of the same or higher priority it will not be	2665	(or even signals, imagine) of the same or higher priority it will not be
1759	triggered. But when your process is idle (or only lower-priority watchers	2666	triggered. But when your process is idle (or only lower-priority watchers
1760	are pending), the idle watchers are being called once per event loop	2667	are pending), the idle watchers are being called once per event loop
…		…
1771		2678
1772	=head3 Watcher-Specific Functions and Data Members	2679	=head3 Watcher-Specific Functions and Data Members
1773		2680
1774	=over 4	2681	=over 4
1775		2682
1776	=item ev_idle_init (ev_signal *, callback)	2683	=item ev_idle_init (ev_idle *, callback)
1777		2684
1778	Initialises and configures the idle watcher - it has no parameters of any	2685	Initialises and configures the idle watcher - it has no parameters of any
1779	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2686	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1780	believe me.	2687	believe me.
1781		2688
…		…
1784	=head3 Examples	2691	=head3 Examples
1785		2692
1786	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2693	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1787	callback, free it. Also, use no error checking, as usual.	2694	callback, free it. Also, use no error checking, as usual.
1788		2695
1789	static void	2696	static void
1790	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2697	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1791	{	2698	{
1792	free (w);	2699	free (w);
1793	// now do something you wanted to do when the program has	2700	// now do something you wanted to do when the program has
1794	// no longer anything immediate to do.	2701	// no longer anything immediate to do.
1795	}	2702	}
1796		2703
1797	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2704	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1798	ev_idle_init (idle_watcher, idle_cb);	2705	ev_idle_init (idle_watcher, idle_cb);
1799	ev_idle_start (loop, idle_cb);	2706	ev_idle_start (loop, idle_watcher);
1800		2707
1801		2708
1802	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2709	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1803		2710
1804	Prepare and check watchers are usually (but not always) used in tandem:	2711	Prepare and check watchers are usually (but not always) used in pairs:
1805	prepare watchers get invoked before the process blocks and check watchers	2712	prepare watchers get invoked before the process blocks and check watchers
1806	afterwards.	2713	afterwards.
1807		2714
1808	You I<must not> call C<ev_loop> or similar functions that enter	2715	You I<must not> call C<ev_run> or similar functions that enter
1809	the current event loop from either C<ev_prepare> or C<ev_check>	2716	the current event loop from either C<ev_prepare> or C<ev_check>
1810	watchers. Other loops than the current one are fine, however. The	2717	watchers. Other loops than the current one are fine, however. The
1811	rationale behind this is that you do not need to check for recursion in	2718	rationale behind this is that you do not need to check for recursion in
1812	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2719	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1813	C<ev_check> so if you have one watcher of each kind they will always be	2720	C<ev_check> so if you have one watcher of each kind they will always be
1814	called in pairs bracketing the blocking call.	2721	called in pairs bracketing the blocking call.
1815		2722
1816	Their main purpose is to integrate other event mechanisms into libev and	2723	Their main purpose is to integrate other event mechanisms into libev and
1817	their use is somewhat advanced. This could be used, for example, to track	2724	their use is somewhat advanced. They could be used, for example, to track
1818	variable changes, implement your own watchers, integrate net-snmp or a	2725	variable changes, implement your own watchers, integrate net-snmp or a
1819	coroutine library and lots more. They are also occasionally useful if	2726	coroutine library and lots more. They are also occasionally useful if
1820	you cache some data and want to flush it before blocking (for example,	2727	you cache some data and want to flush it before blocking (for example,
1821	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2728	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1822	watcher).	2729	watcher).
1823		2730
1824	This is done by examining in each prepare call which file descriptors need	2731	This is done by examining in each prepare call which file descriptors
1825	to be watched by the other library, registering C<ev_io> watchers for	2732	need to be watched by the other library, registering C<ev_io> watchers
1826	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2733	for them and starting an C<ev_timer> watcher for any timeouts (many
1827	provide just this functionality). Then, in the check watcher you check for	2734	libraries provide exactly this functionality). Then, in the check watcher,
1828	any events that occured (by checking the pending status of all watchers	2735	you check for any events that occurred (by checking the pending status
1829	and stopping them) and call back into the library. The I/O and timer	2736	of all watchers and stopping them) and call back into the library. The
1830	callbacks will never actually be called (but must be valid nevertheless,	2737	I/O and timer callbacks will never actually be called (but must be valid
1831	because you never know, you know?).	2738	nevertheless, because you never know, you know?).
1832		2739
1833	As another example, the Perl Coro module uses these hooks to integrate	2740	As another example, the Perl Coro module uses these hooks to integrate
1834	coroutines into libev programs, by yielding to other active coroutines	2741	coroutines into libev programs, by yielding to other active coroutines
1835	during each prepare and only letting the process block if no coroutines	2742	during each prepare and only letting the process block if no coroutines
1836	are ready to run (it's actually more complicated: it only runs coroutines	2743	are ready to run (it's actually more complicated: it only runs coroutines
…		…
1839	loop from blocking if lower-priority coroutines are active, thus mapping	2746	loop from blocking if lower-priority coroutines are active, thus mapping
1840	low-priority coroutines to idle/background tasks).	2747	low-priority coroutines to idle/background tasks).
1841		2748
1842	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2749	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1843	priority, to ensure that they are being run before any other watchers	2750	priority, to ensure that they are being run before any other watchers
		2751	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2752
1844	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2753	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1845	too) should not activate ("feed") events into libev. While libev fully	2754	activate ("feed") events into libev. While libev fully supports this, they
1846	supports this, they will be called before other C<ev_check> watchers	2755	might get executed before other C<ev_check> watchers did their job. As
1847	did their job. As C<ev_check> watchers are often used to embed other	2756	C<ev_check> watchers are often used to embed other (non-libev) event
1848	(non-libev) event loops those other event loops might be in an unusable	2757	loops those other event loops might be in an unusable state until their
1849	state until their C<ev_check> watcher ran (always remind yourself to	2758	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1850	coexist peacefully with others).	2759	others).
1851		2760
1852	=head3 Watcher-Specific Functions and Data Members	2761	=head3 Watcher-Specific Functions and Data Members
1853		2762
1854	=over 4	2763	=over 4
1855		2764
…		…
1857		2766
1858	=item ev_check_init (ev_check *, callback)	2767	=item ev_check_init (ev_check *, callback)
1859		2768
1860	Initialises and configures the prepare or check watcher - they have no	2769	Initialises and configures the prepare or check watcher - they have no
1861	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2770	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1862	macros, but using them is utterly, utterly and completely pointless.	2771	macros, but using them is utterly, utterly, utterly and completely
		2772	pointless.
1863		2773
1864	=back	2774	=back
1865		2775
1866	=head3 Examples	2776	=head3 Examples
1867		2777
1868	There are a number of principal ways to embed other event loops or modules	2778	There are a number of principal ways to embed other event loops or modules
1869	into libev. Here are some ideas on how to include libadns into libev	2779	into libev. Here are some ideas on how to include libadns into libev
1870	(there is a Perl module named C<EV::ADNS> that does this, which you could	2780	(there is a Perl module named C<EV::ADNS> that does this, which you could
1871	use for an actually working example. Another Perl module named C<EV::Glib>	2781	use as a working example. Another Perl module named C<EV::Glib> embeds a
1872	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV	2782	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1873	into the Glib event loop).	2783	Glib event loop).
1874		2784
1875	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	2785	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1876	and in a check watcher, destroy them and call into libadns. What follows	2786	and in a check watcher, destroy them and call into libadns. What follows
1877	is pseudo-code only of course. This requires you to either use a low	2787	is pseudo-code only of course. This requires you to either use a low
1878	priority for the check watcher or use C<ev_clear_pending> explicitly, as	2788	priority for the check watcher or use C<ev_clear_pending> explicitly, as
1879	the callbacks for the IO/timeout watchers might not have been called yet.	2789	the callbacks for the IO/timeout watchers might not have been called yet.
1880		2790
1881	static ev_io iow [nfd];	2791	static ev_io iow [nfd];
1882	static ev_timer tw;	2792	static ev_timer tw;
1883		2793
1884	static void	2794	static void
1885	io_cb (ev_loop *loop, ev_io *w, int revents)	2795	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1886	{	2796	{
1887	}	2797	}
1888		2798
1889	// create io watchers for each fd and a timer before blocking	2799	// create io watchers for each fd and a timer before blocking
1890	static void	2800	static void
1891	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2801	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1892	{	2802	{
1893	int timeout = 3600000;	2803	int timeout = 3600000;
1894	struct pollfd fds [nfd];	2804	struct pollfd fds [nfd];
1895	// actual code will need to loop here and realloc etc.	2805	// actual code will need to loop here and realloc etc.
1896	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2806	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1897		2807
1898	/* the callback is illegal, but won't be called as we stop during check */	2808	/* the callback is illegal, but won't be called as we stop during check */
1899	ev_timer_init (&tw, 0, timeout * 1e-3);	2809	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1900	ev_timer_start (loop, &tw);	2810	ev_timer_start (loop, &tw);
1901		2811
1902	// create one ev_io per pollfd	2812	// create one ev_io per pollfd
1903	for (int i = 0; i < nfd; ++i)	2813	for (int i = 0; i < nfd; ++i)
1904	{	2814	{
1905	ev_io_init (iow + i, io_cb, fds [i].fd,	2815	ev_io_init (iow + i, io_cb, fds [i].fd,
1906	((fds [i].events & POLLIN ? EV_READ : 0)	2816	((fds [i].events & POLLIN ? EV_READ : 0)
1907	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2817	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1908		2818
1909	fds [i].revents = 0;	2819	fds [i].revents = 0;
1910	ev_io_start (loop, iow + i);	2820	ev_io_start (loop, iow + i);
1911	}	2821	}
1912	}	2822	}
1913		2823
1914	// stop all watchers after blocking	2824	// stop all watchers after blocking
1915	static void	2825	static void
1916	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2826	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1917	{	2827	{
1918	ev_timer_stop (loop, &tw);	2828	ev_timer_stop (loop, &tw);
1919		2829
1920	for (int i = 0; i < nfd; ++i)	2830	for (int i = 0; i < nfd; ++i)
1921	{	2831	{
1922	// set the relevant poll flags	2832	// set the relevant poll flags
1923	// could also call adns_processreadable etc. here	2833	// could also call adns_processreadable etc. here
1924	struct pollfd *fd = fds + i;	2834	struct pollfd *fd = fds + i;
1925	int revents = ev_clear_pending (iow + i);	2835	int revents = ev_clear_pending (iow + i);
1926	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;	2836	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1927	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;	2837	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1928		2838
1929	// now stop the watcher	2839	// now stop the watcher
1930	ev_io_stop (loop, iow + i);	2840	ev_io_stop (loop, iow + i);
1931	}	2841	}
1932		2842
1933	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2843	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1934	}	2844	}
1935		2845
1936	Method 2: This would be just like method 1, but you run C<adns_afterpoll>	2846	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
1937	in the prepare watcher and would dispose of the check watcher.	2847	in the prepare watcher and would dispose of the check watcher.
1938		2848
1939	Method 3: If the module to be embedded supports explicit event	2849	Method 3: If the module to be embedded supports explicit event
1940	notification (adns does), you can also make use of the actual watcher	2850	notification (libadns does), you can also make use of the actual watcher
1941	callbacks, and only destroy/create the watchers in the prepare watcher.	2851	callbacks, and only destroy/create the watchers in the prepare watcher.
1942		2852
1943	static void	2853	static void
1944	timer_cb (EV_P_ ev_timer *w, int revents)	2854	timer_cb (EV_P_ ev_timer *w, int revents)
1945	{	2855	{
1946	adns_state ads = (adns_state)w->data;	2856	adns_state ads = (adns_state)w->data;
1947	update_now (EV_A);	2857	update_now (EV_A);
1948		2858
1949	adns_processtimeouts (ads, &tv_now);	2859	adns_processtimeouts (ads, &tv_now);
1950	}	2860	}
1951		2861
1952	static void	2862	static void
1953	io_cb (EV_P_ ev_io *w, int revents)	2863	io_cb (EV_P_ ev_io *w, int revents)
1954	{	2864	{
1955	adns_state ads = (adns_state)w->data;	2865	adns_state ads = (adns_state)w->data;
1956	update_now (EV_A);	2866	update_now (EV_A);
1957		2867
1958	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);	2868	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
1959	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);	2869	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
1960	}	2870	}
1961		2871
1962	// do not ever call adns_afterpoll	2872	// do not ever call adns_afterpoll
1963		2873
1964	Method 4: Do not use a prepare or check watcher because the module you	2874	Method 4: Do not use a prepare or check watcher because the module you
1965	want to embed is too inflexible to support it. Instead, youc na override	2875	want to embed is not flexible enough to support it. Instead, you can
1966	their poll function. The drawback with this solution is that the main	2876	override their poll function. The drawback with this solution is that the
1967	loop is now no longer controllable by EV. The C<Glib::EV> module does	2877	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
1968	this.	2878	this approach, effectively embedding EV as a client into the horrible
		2879	libglib event loop.
1969		2880
1970	static gint	2881	static gint
1971	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	2882	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1972	{	2883	{
1973	int got_events = 0;	2884	int got_events = 0;
1974		2885
1975	for (n = 0; n < nfds; ++n)	2886	for (n = 0; n < nfds; ++n)
1976	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events	2887	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1977		2888
1978	if (timeout >= 0)	2889	if (timeout >= 0)
1979	// create/start timer	2890	// create/start timer
1980		2891
1981	// poll	2892	// poll
1982	ev_loop (EV_A_ 0);	2893	ev_run (EV_A_ 0);
1983		2894
1984	// stop timer again	2895	// stop timer again
1985	if (timeout >= 0)	2896	if (timeout >= 0)
1986	ev_timer_stop (EV_A_ &to);	2897	ev_timer_stop (EV_A_ &to);
1987		2898
1988	// stop io watchers again - their callbacks should have set	2899	// stop io watchers again - their callbacks should have set
1989	for (n = 0; n < nfds; ++n)	2900	for (n = 0; n < nfds; ++n)
1990	ev_io_stop (EV_A_ iow [n]);	2901	ev_io_stop (EV_A_ iow [n]);
1991		2902
1992	return got_events;	2903	return got_events;
1993	}	2904	}
1994		2905
1995		2906
1996	=head2 C<ev_embed> - when one backend isn't enough...	2907	=head2 C<ev_embed> - when one backend isn't enough...
1997		2908
1998	This is a rather advanced watcher type that lets you embed one event loop	2909	This is a rather advanced watcher type that lets you embed one event loop
…		…
2004	prioritise I/O.	2915	prioritise I/O.
2005		2916
2006	As an example for a bug workaround, the kqueue backend might only support	2917	As an example for a bug workaround, the kqueue backend might only support
2007	sockets on some platform, so it is unusable as generic backend, but you	2918	sockets on some platform, so it is unusable as generic backend, but you
2008	still want to make use of it because you have many sockets and it scales	2919	still want to make use of it because you have many sockets and it scales
2009	so nicely. In this case, you would create a kqueue-based loop and embed it	2920	so nicely. In this case, you would create a kqueue-based loop and embed
2010	into your default loop (which might use e.g. poll). Overall operation will	2921	it into your default loop (which might use e.g. poll). Overall operation
2011	be a bit slower because first libev has to poll and then call kevent, but	2922	will be a bit slower because first libev has to call C<poll> and then
2012	at least you can use both at what they are best.	2923	C<kevent>, but at least you can use both mechanisms for what they are
		2924	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
2013		2925
2014	As for prioritising I/O: rarely you have the case where some fds have	2926	As for prioritising I/O: under rare circumstances you have the case where
2015	to be watched and handled very quickly (with low latency), and even	2927	some fds have to be watched and handled very quickly (with low latency),
2016	priorities and idle watchers might have too much overhead. In this case	2928	and even priorities and idle watchers might have too much overhead. In
2017	you would put all the high priority stuff in one loop and all the rest in	2929	this case you would put all the high priority stuff in one loop and all
2018	a second one, and embed the second one in the first.	2930	the rest in a second one, and embed the second one in the first.
2019		2931
2020	As long as the watcher is active, the callback will be invoked every time	2932	As long as the watcher is active, the callback will be invoked every
2021	there might be events pending in the embedded loop. The callback must then	2933	time there might be events pending in the embedded loop. The callback
2022	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2934	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
2023	their callbacks (you could also start an idle watcher to give the embedded	2935	sweep and invoke their callbacks (the callback doesn't need to invoke the
2024	loop strictly lower priority for example). You can also set the callback	2936	C<ev_embed_sweep> function directly, it could also start an idle watcher
2025	to C<0>, in which case the embed watcher will automatically execute the	2937	to give the embedded loop strictly lower priority for example).
2026	embedded loop sweep.
2027		2938
2028	As long as the watcher is started it will automatically handle events. The	2939	You can also set the callback to C<0>, in which case the embed watcher
2029	callback will be invoked whenever some events have been handled. You can	2940	will automatically execute the embedded loop sweep whenever necessary.
2030	set the callback to C<0> to avoid having to specify one if you are not
2031	interested in that.
2032		2941
2033	Also, there have not currently been made special provisions for forking:	2942	Fork detection will be handled transparently while the C<ev_embed> watcher
2034	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2943	is active, i.e., the embedded loop will automatically be forked when the
2035	but you will also have to stop and restart any C<ev_embed> watchers	2944	embedding loop forks. In other cases, the user is responsible for calling
2036	yourself.	2945	C<ev_loop_fork> on the embedded loop.
2037		2946
2038	Unfortunately, not all backends are embeddable, only the ones returned by	2947	Unfortunately, not all backends are embeddable: only the ones returned by
2039	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2948	C<ev_embeddable_backends> are, which, unfortunately, does not include any
2040	portable one.	2949	portable one.
2041		2950
2042	So when you want to use this feature you will always have to be prepared	2951	So when you want to use this feature you will always have to be prepared
2043	that you cannot get an embeddable loop. The recommended way to get around	2952	that you cannot get an embeddable loop. The recommended way to get around
2044	this is to have a separate variables for your embeddable loop, try to	2953	this is to have a separate variables for your embeddable loop, try to
2045	create it, and if that fails, use the normal loop for everything.	2954	create it, and if that fails, use the normal loop for everything.
2046		2955
		2956	=head3 C<ev_embed> and fork
		2957
		2958	While the C<ev_embed> watcher is running, forks in the embedding loop will
		2959	automatically be applied to the embedded loop as well, so no special
		2960	fork handling is required in that case. When the watcher is not running,
		2961	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		2962	as applicable.
		2963
2047	=head3 Watcher-Specific Functions and Data Members	2964	=head3 Watcher-Specific Functions and Data Members
2048		2965
2049	=over 4	2966	=over 4
2050		2967
2051	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	2968	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
…		…
2054		2971
2055	Configures the watcher to embed the given loop, which must be	2972	Configures the watcher to embed the given loop, which must be
2056	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	2973	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
2057	invoked automatically, otherwise it is the responsibility of the callback	2974	invoked automatically, otherwise it is the responsibility of the callback
2058	to invoke it (it will continue to be called until the sweep has been done,	2975	to invoke it (it will continue to be called until the sweep has been done,
2059	if you do not want thta, you need to temporarily stop the embed watcher).	2976	if you do not want that, you need to temporarily stop the embed watcher).
2060		2977
2061	=item ev_embed_sweep (loop, ev_embed *)	2978	=item ev_embed_sweep (loop, ev_embed *)
2062		2979
2063	Make a single, non-blocking sweep over the embedded loop. This works	2980	Make a single, non-blocking sweep over the embedded loop. This works
2064	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	2981	similarly to C<ev_run (embedded_loop, EVRUN_NOWAIT)>, but in the most
2065	apropriate way for embedded loops.	2982	appropriate way for embedded loops.
2066		2983
2067	=item struct ev_loop *other [read-only]	2984	=item struct ev_loop *other [read-only]
2068		2985
2069	The embedded event loop.	2986	The embedded event loop.
2070		2987
…		…
2072		2989
2073	=head3 Examples	2990	=head3 Examples
2074		2991
2075	Example: Try to get an embeddable event loop and embed it into the default	2992	Example: Try to get an embeddable event loop and embed it into the default
2076	event loop. If that is not possible, use the default loop. The default	2993	event loop. If that is not possible, use the default loop. The default
2077	loop is stored in C<loop_hi>, while the mebeddable loop is stored in	2994	loop is stored in C<loop_hi>, while the embeddable loop is stored in
2078	C<loop_lo> (which is C<loop_hi> in the acse no embeddable loop can be	2995	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
2079	used).	2996	used).
2080		2997
2081	struct ev_loop *loop_hi = ev_default_init (0);	2998	struct ev_loop *loop_hi = ev_default_init (0);
2082	struct ev_loop *loop_lo = 0;	2999	struct ev_loop *loop_lo = 0;
2083	struct ev_embed embed;	3000	ev_embed embed;
2084		3001
2085	// see if there is a chance of getting one that works	3002	// see if there is a chance of getting one that works
2086	// (remember that a flags value of 0 means autodetection)	3003	// (remember that a flags value of 0 means autodetection)
2087	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3004	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2088	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3005	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
2089	: 0;	3006	: 0;
2090		3007
2091	// if we got one, then embed it, otherwise default to loop_hi	3008	// if we got one, then embed it, otherwise default to loop_hi
2092	if (loop_lo)	3009	if (loop_lo)
2093	{	3010	{
2094	ev_embed_init (&embed, 0, loop_lo);	3011	ev_embed_init (&embed, 0, loop_lo);
2095	ev_embed_start (loop_hi, &embed);	3012	ev_embed_start (loop_hi, &embed);
2096	}	3013	}
2097	else	3014	else
2098	loop_lo = loop_hi;	3015	loop_lo = loop_hi;
2099		3016
2100	Example: Check if kqueue is available but not recommended and create	3017	Example: Check if kqueue is available but not recommended and create
2101	a kqueue backend for use with sockets (which usually work with any	3018	a kqueue backend for use with sockets (which usually work with any
2102	kqueue implementation). Store the kqueue/socket-only event loop in	3019	kqueue implementation). Store the kqueue/socket-only event loop in
2103	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3020	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2104		3021
2105	struct ev_loop *loop = ev_default_init (0);	3022	struct ev_loop *loop = ev_default_init (0);
2106	struct ev_loop *loop_socket = 0;	3023	struct ev_loop *loop_socket = 0;
2107	struct ev_embed embed;	3024	ev_embed embed;
2108		3025
2109	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3026	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2110	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3027	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2111	{	3028	{
2112	ev_embed_init (&embed, 0, loop_socket);	3029	ev_embed_init (&embed, 0, loop_socket);
2113	ev_embed_start (loop, &embed);	3030	ev_embed_start (loop, &embed);
2114	}	3031	}
2115		3032
2116	if (!loop_socket)	3033	if (!loop_socket)
2117	loop_socket = loop;	3034	loop_socket = loop;
2118		3035
2119	// now use loop_socket for all sockets, and loop for everything else	3036	// now use loop_socket for all sockets, and loop for everything else
2120		3037
2121		3038
2122	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3039	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
2123		3040
2124	Fork watchers are called when a C<fork ()> was detected (usually because	3041	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
2127	event loop blocks next and before C<ev_check> watchers are being called,	3044	event loop blocks next and before C<ev_check> watchers are being called,
2128	and only in the child after the fork. If whoever good citizen calling	3045	and only in the child after the fork. If whoever good citizen calling
2129	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3046	C<ev_default_fork> cheats and calls it in the wrong process, the fork
2130	handlers will be invoked, too, of course.	3047	handlers will be invoked, too, of course.
2131		3048
		3049	=head3 The special problem of life after fork - how is it possible?
		3050
		3051	Most uses of C<fork()> consist of forking, then some simple calls to set
		3052	up/change the process environment, followed by a call to C<exec()>. This
		3053	sequence should be handled by libev without any problems.
		3054
		3055	This changes when the application actually wants to do event handling
		3056	in the child, or both parent in child, in effect "continuing" after the
		3057	fork.
		3058
		3059	The default mode of operation (for libev, with application help to detect
		3060	forks) is to duplicate all the state in the child, as would be expected
		3061	when I<either> the parent I<or> the child process continues.
		3062
		3063	When both processes want to continue using libev, then this is usually the
		3064	wrong result. In that case, usually one process (typically the parent) is
		3065	supposed to continue with all watchers in place as before, while the other
		3066	process typically wants to start fresh, i.e. without any active watchers.
		3067
		3068	The cleanest and most efficient way to achieve that with libev is to
		3069	simply create a new event loop, which of course will be "empty", and
		3070	use that for new watchers. This has the advantage of not touching more
		3071	memory than necessary, and thus avoiding the copy-on-write, and the
		3072	disadvantage of having to use multiple event loops (which do not support
		3073	signal watchers).
		3074
		3075	When this is not possible, or you want to use the default loop for
		3076	other reasons, then in the process that wants to start "fresh", call
		3077	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		3078	the default loop will "orphan" (not stop) all registered watchers, so you
		3079	have to be careful not to execute code that modifies those watchers. Note
		3080	also that in that case, you have to re-register any signal watchers.
		3081
2132	=head3 Watcher-Specific Functions and Data Members	3082	=head3 Watcher-Specific Functions and Data Members
2133		3083
2134	=over 4	3084	=over 4
2135		3085
2136	=item ev_fork_init (ev_signal *, callback)	3086	=item ev_fork_init (ev_signal *, callback)
…		…
2140	believe me.	3090	believe me.
2141		3091
2142	=back	3092	=back
2143		3093
2144		3094
2145	=head2 C<ev_async> - how to wake up another event loop	3095	=head2 C<ev_async> - how to wake up an event loop
2146		3096
2147	In general, you cannot use an C<ev_loop> from multiple threads or other	3097	In general, you cannot use an C<ev_run> from multiple threads or other
2148	asynchronous sources such as signal handlers (as opposed to multiple event	3098	asynchronous sources such as signal handlers (as opposed to multiple event
2149	loops - those are of course safe to use in different threads).	3099	loops - those are of course safe to use in different threads).
2150		3100
2151	Sometimes, however, you need to wake up another event loop you do not	3101	Sometimes, however, you need to wake up an event loop you do not control,
2152	control, for example because it belongs to another thread. This is what	3102	for example because it belongs to another thread. This is what C<ev_async>
2153	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you	3103	watchers do: as long as the C<ev_async> watcher is active, you can signal
2154	can signal it by calling C<ev_async_send>, which is thread- and signal	3104	it by calling C<ev_async_send>, which is thread- and signal safe.
2155	safe.
2156		3105
2157	This functionality is very similar to C<ev_signal> watchers, as signals,	3106	This functionality is very similar to C<ev_signal> watchers, as signals,
2158	too, are asynchronous in nature, and signals, too, will be compressed	3107	too, are asynchronous in nature, and signals, too, will be compressed
2159	(i.e. the number of callback invocations may be less than the number of	3108	(i.e. the number of callback invocations may be less than the number of
2160	C<ev_async_sent> calls).	3109	C<ev_async_sent> calls).
…		…
2165	=head3 Queueing	3114	=head3 Queueing
2166		3115
2167	C<ev_async> does not support queueing of data in any way. The reason	3116	C<ev_async> does not support queueing of data in any way. The reason
2168	is that the author does not know of a simple (or any) algorithm for a	3117	is that the author does not know of a simple (or any) algorithm for a
2169	multiple-writer-single-reader queue that works in all cases and doesn't	3118	multiple-writer-single-reader queue that works in all cases and doesn't
2170	need elaborate support such as pthreads.	3119	need elaborate support such as pthreads or unportable memory access
		3120	semantics.
2171		3121
2172	That means that if you want to queue data, you have to provide your own	3122	That means that if you want to queue data, you have to provide your own
2173	queue. But at least I can tell you would implement locking around your	3123	queue. But at least I can tell you how to implement locking around your
2174	queue:	3124	queue:
2175		3125
2176	=over 4	3126	=over 4
2177		3127
2178	=item queueing from a signal handler context	3128	=item queueing from a signal handler context
2179		3129
2180	To implement race-free queueing, you simply add to the queue in the signal	3130	To implement race-free queueing, you simply add to the queue in the signal
2181	handler but you block the signal handler in the watcher callback. Here is an example that does that for	3131	handler but you block the signal handler in the watcher callback. Here is
2182	some fictitiuous SIGUSR1 handler:	3132	an example that does that for some fictitious SIGUSR1 handler:
2183		3133
2184	static ev_async mysig;	3134	static ev_async mysig;
2185		3135
2186	static void	3136	static void
2187	sigusr1_handler (void)	3137	sigusr1_handler (void)
…		…
2253	=over 4	3203	=over 4
2254		3204
2255	=item ev_async_init (ev_async *, callback)	3205	=item ev_async_init (ev_async *, callback)
2256		3206
2257	Initialises and configures the async watcher - it has no parameters of any	3207	Initialises and configures the async watcher - it has no parameters of any
2258	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,	3208	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
2259	believe me.	3209	trust me.
2260		3210
2261	=item ev_async_send (loop, ev_async *)	3211	=item ev_async_send (loop, ev_async *)
2262		3212
2263	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3213	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
2264	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3214	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
2265	C<ev_feed_event>, this call is safe to do in other threads, signal or	3215	C<ev_feed_event>, this call is safe to do from other threads, signal or
2266	similar contexts (see the dicusssion of C<EV_ATOMIC_T> in the embedding	3216	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
2267	section below on what exactly this means).	3217	section below on what exactly this means).
2268		3218
		3219	Note that, as with other watchers in libev, multiple events might get
		3220	compressed into a single callback invocation (another way to look at this
		3221	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3222	reset when the event loop detects that).
		3223
2269	This call incurs the overhead of a syscall only once per loop iteration,	3224	This call incurs the overhead of a system call only once per event loop
2270	so while the overhead might be noticable, it doesn't apply to repeated	3225	iteration, so while the overhead might be noticeable, it doesn't apply to
2271	calls to C<ev_async_send>.	3226	repeated calls to C<ev_async_send> for the same event loop.
		3227
		3228	=item bool = ev_async_pending (ev_async *)
		3229
		3230	Returns a non-zero value when C<ev_async_send> has been called on the
		3231	watcher but the event has not yet been processed (or even noted) by the
		3232	event loop.
		3233
		3234	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3235	the loop iterates next and checks for the watcher to have become active,
		3236	it will reset the flag again. C<ev_async_pending> can be used to very
		3237	quickly check whether invoking the loop might be a good idea.
		3238
		3239	Not that this does I<not> check whether the watcher itself is pending,
		3240	only whether it has been requested to make this watcher pending: there
		3241	is a time window between the event loop checking and resetting the async
		3242	notification, and the callback being invoked.
2272		3243
2273	=back	3244	=back
2274		3245
2275		3246
2276	=head1 OTHER FUNCTIONS	3247	=head1 OTHER FUNCTIONS
…		…
2280	=over 4	3251	=over 4
2281		3252
2282	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3253	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
2283		3254
2284	This function combines a simple timer and an I/O watcher, calls your	3255	This function combines a simple timer and an I/O watcher, calls your
2285	callback on whichever event happens first and automatically stop both	3256	callback on whichever event happens first and automatically stops both
2286	watchers. This is useful if you want to wait for a single event on an fd	3257	watchers. This is useful if you want to wait for a single event on an fd
2287	or timeout without having to allocate/configure/start/stop/free one or	3258	or timeout without having to allocate/configure/start/stop/free one or
2288	more watchers yourself.	3259	more watchers yourself.
2289		3260
2290	If C<fd> is less than 0, then no I/O watcher will be started and events	3261	If C<fd> is less than 0, then no I/O watcher will be started and the
2291	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3262	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
2292	C<events> set will be craeted and started.	3263	the given C<fd> and C<events> set will be created and started.
2293		3264
2294	If C<timeout> is less than 0, then no timeout watcher will be	3265	If C<timeout> is less than 0, then no timeout watcher will be
2295	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3266	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
2296	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3267	repeat = 0) will be started. C<0> is a valid timeout.
2297	dubious value.
2298		3268
2299	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3269	The callback has the type C<void (*cb)(int revents, void *arg)> and is
2300	passed an C<revents> set like normal event callbacks (a combination of	3270	passed an C<revents> set like normal event callbacks (a combination of
2301	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3271	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
2302	value passed to C<ev_once>:	3272	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3273	a timeout and an io event at the same time - you probably should give io
		3274	events precedence.
2303		3275
		3276	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3277
2304	static void stdin_ready (int revents, void *arg)	3278	static void stdin_ready (int revents, void *arg)
2305	{	3279	{
2306	if (revents & EV_TIMEOUT)
2307	/* doh, nothing entered */;
2308	else if (revents & EV_READ)	3280	if (revents & EV_READ)
2309	/* stdin might have data for us, joy! */;	3281	/* stdin might have data for us, joy! */;
		3282	else if (revents & EV_TIMER)
		3283	/* doh, nothing entered */;
2310	}	3284	}
2311		3285
2312	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3286	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2313		3287
2314	=item ev_feed_event (ev_loop *, watcher *, int revents)
2315
2316	Feeds the given event set into the event loop, as if the specified event
2317	had happened for the specified watcher (which must be a pointer to an
2318	initialised but not necessarily started event watcher).
2319
2320	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3288	=item ev_feed_fd_event (loop, int fd, int revents)
2321		3289
2322	Feed an event on the given fd, as if a file descriptor backend detected	3290	Feed an event on the given fd, as if a file descriptor backend detected
2323	the given events it.	3291	the given events it.
2324		3292
2325	=item ev_feed_signal_event (ev_loop *loop, int signum)	3293	=item ev_feed_signal_event (loop, int signum)
2326		3294
2327	Feed an event as if the given signal occured (C<loop> must be the default	3295	Feed an event as if the given signal occurred (C<loop> must be the default
2328	loop!).	3296	loop!).
2329		3297
2330	=back	3298	=back
2331		3299
2332		3300
…		…
2348		3316
2349	=item * Priorities are not currently supported. Initialising priorities	3317	=item * Priorities are not currently supported. Initialising priorities
2350	will fail and all watchers will have the same priority, even though there	3318	will fail and all watchers will have the same priority, even though there
2351	is an ev_pri field.	3319	is an ev_pri field.
2352		3320
		3321	=item * In libevent, the last base created gets the signals, in libev, the
		3322	first base created (== the default loop) gets the signals.
		3323
2353	=item * Other members are not supported.	3324	=item * Other members are not supported.
2354		3325
2355	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3326	=item * The libev emulation is I<not> ABI compatible to libevent, you need
2356	to use the libev header file and library.	3327	to use the libev header file and library.
2357		3328
2358	=back	3329	=back
2359		3330
2360	=head1 C++ SUPPORT	3331	=head1 C++ SUPPORT
2361		3332
2362	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3333	Libev comes with some simplistic wrapper classes for C++ that mainly allow
2363	you to use some convinience methods to start/stop watchers and also change	3334	you to use some convenience methods to start/stop watchers and also change
2364	the callback model to a model using method callbacks on objects.	3335	the callback model to a model using method callbacks on objects.
2365		3336
2366	To use it,	3337	To use it,
2367		3338
2368	#include <ev++.h>	3339	#include <ev++.h>
2369		3340
2370	This automatically includes F<ev.h> and puts all of its definitions (many	3341	This automatically includes F<ev.h> and puts all of its definitions (many
2371	of them macros) into the global namespace. All C++ specific things are	3342	of them macros) into the global namespace. All C++ specific things are
2372	put into the C<ev> namespace. It should support all the same embedding	3343	put into the C<ev> namespace. It should support all the same embedding
2373	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	3344	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
2407		3378
2408	=over 4	3379	=over 4
2409		3380
2410	=item ev::TYPE::TYPE ()	3381	=item ev::TYPE::TYPE ()
2411		3382
2412	=item ev::TYPE::TYPE (struct ev_loop *)	3383	=item ev::TYPE::TYPE (loop)
2413		3384
2414	=item ev::TYPE::~TYPE	3385	=item ev::TYPE::~TYPE
2415		3386
2416	The constructor (optionally) takes an event loop to associate the watcher	3387	The constructor (optionally) takes an event loop to associate the watcher
2417	with. If it is omitted, it will use C<EV_DEFAULT>.	3388	with. If it is omitted, it will use C<EV_DEFAULT>.
…		…
2440	your compiler is good :), then the method will be fully inlined into the	3411	your compiler is good :), then the method will be fully inlined into the
2441	thunking function, making it as fast as a direct C callback.	3412	thunking function, making it as fast as a direct C callback.
2442		3413
2443	Example: simple class declaration and watcher initialisation	3414	Example: simple class declaration and watcher initialisation
2444		3415
2445	struct myclass	3416	struct myclass
2446	{	3417	{
2447	void io_cb (ev::io &w, int revents) { }	3418	void io_cb (ev::io &w, int revents) { }
2448	}	3419	}
2449		3420
2450	myclass obj;	3421	myclass obj;
2451	ev::io iow;	3422	ev::io iow;
2452	iow.set <myclass, &myclass::io_cb> (&obj);	3423	iow.set <myclass, &myclass::io_cb> (&obj);
		3424
		3425	=item w->set (object *)
		3426
		3427	This is a variation of a method callback - leaving out the method to call
		3428	will default the method to C<operator ()>, which makes it possible to use
		3429	functor objects without having to manually specify the C<operator ()> all
		3430	the time. Incidentally, you can then also leave out the template argument
		3431	list.
		3432
		3433	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3434	int revents)>.
		3435
		3436	See the method-C<set> above for more details.
		3437
		3438	Example: use a functor object as callback.
		3439
		3440	struct myfunctor
		3441	{
		3442	void operator() (ev::io &w, int revents)
		3443	{
		3444	...
		3445	}
		3446	}
		3447
		3448	myfunctor f;
		3449
		3450	ev::io w;
		3451	w.set (&f);
2453		3452
2454	=item w->set<function> (void *data = 0)	3453	=item w->set<function> (void *data = 0)
2455		3454
2456	Also sets a callback, but uses a static method or plain function as	3455	Also sets a callback, but uses a static method or plain function as
2457	callback. The optional C<data> argument will be stored in the watcher's	3456	callback. The optional C<data> argument will be stored in the watcher's
…		…
2459		3458
2460	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	3459	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2461		3460
2462	See the method-C<set> above for more details.	3461	See the method-C<set> above for more details.
2463		3462
2464	Example:	3463	Example: Use a plain function as callback.
2465		3464
2466	static void io_cb (ev::io &w, int revents) { }	3465	static void io_cb (ev::io &w, int revents) { }
2467	iow.set <io_cb> ();	3466	iow.set <io_cb> ();
2468		3467
2469	=item w->set (struct ev_loop *)	3468	=item w->set (loop)
2470		3469
2471	Associates a different C<struct ev_loop> with this watcher. You can only	3470	Associates a different C<struct ev_loop> with this watcher. You can only
2472	do this when the watcher is inactive (and not pending either).	3471	do this when the watcher is inactive (and not pending either).
2473		3472
2474	=item w->set ([args])	3473	=item w->set ([arguments])
2475		3474
2476	Basically the same as C<ev_TYPE_set>, with the same args. Must be	3475	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this
2477	called at least once. Unlike the C counterpart, an active watcher gets	3476	method or a suitable start method must be called at least once. Unlike the
2478	automatically stopped and restarted when reconfiguring it with this	3477	C counterpart, an active watcher gets automatically stopped and restarted
2479	method.	3478	when reconfiguring it with this method.
2480		3479
2481	=item w->start ()	3480	=item w->start ()
2482		3481
2483	Starts the watcher. Note that there is no C<loop> argument, as the	3482	Starts the watcher. Note that there is no C<loop> argument, as the
2484	constructor already stores the event loop.	3483	constructor already stores the event loop.
2485		3484
		3485	=item w->start ([arguments])
		3486
		3487	Instead of calling C<set> and C<start> methods separately, it is often
		3488	convenient to wrap them in one call. Uses the same type of arguments as
		3489	the configure C<set> method of the watcher.
		3490
2486	=item w->stop ()	3491	=item w->stop ()
2487		3492
2488	Stops the watcher if it is active. Again, no C<loop> argument.	3493	Stops the watcher if it is active. Again, no C<loop> argument.
2489		3494
2490	=item w->again () (C<ev::timer>, C<ev::periodic> only)	3495	=item w->again () (C<ev::timer>, C<ev::periodic> only)
…		…
2502		3507
2503	=back	3508	=back
2504		3509
2505	=back	3510	=back
2506		3511
2507	Example: Define a class with an IO and idle watcher, start one of them in	3512	Example: Define a class with two I/O and idle watchers, start the I/O
2508	the constructor.	3513	watchers in the constructor.
2509		3514
2510	class myclass	3515	class myclass
2511	{	3516	{
2512	ev::io io; void io_cb (ev::io &w, int revents);	3517	ev::io io ; void io_cb (ev::io &w, int revents);
		3518	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);
2513	ev:idle idle void idle_cb (ev::idle &w, int revents);	3519	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2514		3520
2515	myclass (int fd)	3521	myclass (int fd)
2516	{	3522	{
2517	io .set <myclass, &myclass::io_cb > (this);	3523	io .set <myclass, &myclass::io_cb > (this);
		3524	io2 .set <myclass, &myclass::io2_cb > (this);
2518	idle.set <myclass, &myclass::idle_cb> (this);	3525	idle.set <myclass, &myclass::idle_cb> (this);
2519		3526
2520	io.start (fd, ev::READ);	3527	io.set (fd, ev::WRITE); // configure the watcher
		3528	io.start (); // start it whenever convenient
		3529
		3530	io2.start (fd, ev::READ); // set + start in one call
2521	}	3531	}
2522	};	3532	};
2523		3533
2524		3534
2525	=head1 OTHER LANGUAGE BINDINGS	3535	=head1 OTHER LANGUAGE BINDINGS
2526		3536
2527	Libev does not offer other language bindings itself, but bindings for a	3537	Libev does not offer other language bindings itself, but bindings for a
2528	numbe rof languages exist in the form of third-party packages. If you know	3538	number of languages exist in the form of third-party packages. If you know
2529	any interesting language binding in addition to the ones listed here, drop	3539	any interesting language binding in addition to the ones listed here, drop
2530	me a note.	3540	me a note.
2531		3541
2532	=over 4	3542	=over 4
2533		3543
2534	=item Perl	3544	=item Perl
2535		3545
2536	The EV module implements the full libev API and is actually used to test	3546	The EV module implements the full libev API and is actually used to test
2537	libev. EV is developed together with libev. Apart from the EV core module,	3547	libev. EV is developed together with libev. Apart from the EV core module,
2538	there are additional modules that implement libev-compatible interfaces	3548	there are additional modules that implement libev-compatible interfaces
2539	to C<libadns> (C<EV::ADNS>), C<Net::SNMP> (C<Net::SNMP::EV>) and the	3549	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
2540	C<libglib> event core (C<Glib::EV> and C<EV::Glib>).	3550	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3551	and C<EV::Glib>).
2541		3552
2542	It can be found and installed via CPAN, its homepage is found at	3553	It can be found and installed via CPAN, its homepage is at
2543	L<http://software.schmorp.de/pkg/EV>.	3554	L<http://software.schmorp.de/pkg/EV>.
2544		3555
		3556	=item Python
		3557
		3558	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3559	seems to be quite complete and well-documented.
		3560
2545	=item Ruby	3561	=item Ruby
2546		3562
2547	Tony Arcieri has written a ruby extension that offers access to a subset	3563	Tony Arcieri has written a ruby extension that offers access to a subset
2548	of the libev API and adds filehandle abstractions, asynchronous DNS and	3564	of the libev API and adds file handle abstractions, asynchronous DNS and
2549	more on top of it. It can be found via gem servers. Its homepage is at	3565	more on top of it. It can be found via gem servers. Its homepage is at
2550	L<http://rev.rubyforge.org/>.	3566	L<http://rev.rubyforge.org/>.
2551		3567
		3568	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3569	makes rev work even on mingw.
		3570
		3571	=item Haskell
		3572
		3573	A haskell binding to libev is available at
		3574	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3575
2552	=item D	3576	=item D
2553		3577
2554	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	3578	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
2555	be found at L<http://git.llucax.com.ar/?p=software/ev.d.git;a=summary>.	3579	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3580
		3581	=item Ocaml
		3582
		3583	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3584	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3585
		3586	=item Lua
		3587
		3588	Brian Maher has written a partial interface to libev for lua (at the
		3589	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		3590	L<http://github.com/brimworks/lua-ev>.
2556		3591
2557	=back	3592	=back
2558		3593
2559		3594
2560	=head1 MACRO MAGIC	3595	=head1 MACRO MAGIC
2561		3596
2562	Libev can be compiled with a variety of options, the most fundamantal	3597	Libev can be compiled with a variety of options, the most fundamental
2563	of which is C<EV_MULTIPLICITY>. This option determines whether (most)	3598	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2564	functions and callbacks have an initial C<struct ev_loop *> argument.	3599	functions and callbacks have an initial C<struct ev_loop *> argument.
2565		3600
2566	To make it easier to write programs that cope with either variant, the	3601	To make it easier to write programs that cope with either variant, the
2567	following macros are defined:	3602	following macros are defined:
…		…
2572		3607
2573	This provides the loop I<argument> for functions, if one is required ("ev	3608	This provides the loop I<argument> for functions, if one is required ("ev
2574	loop argument"). The C<EV_A> form is used when this is the sole argument,	3609	loop argument"). The C<EV_A> form is used when this is the sole argument,
2575	C<EV_A_> is used when other arguments are following. Example:	3610	C<EV_A_> is used when other arguments are following. Example:
2576		3611
2577	ev_unref (EV_A);	3612	ev_unref (EV_A);
2578	ev_timer_add (EV_A_ watcher);	3613	ev_timer_add (EV_A_ watcher);
2579	ev_loop (EV_A_ 0);	3614	ev_run (EV_A_ 0);
2580		3615
2581	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	3616	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2582	which is often provided by the following macro.	3617	which is often provided by the following macro.
2583		3618
2584	=item C<EV_P>, C<EV_P_>	3619	=item C<EV_P>, C<EV_P_>
2585		3620
2586	This provides the loop I<parameter> for functions, if one is required ("ev	3621	This provides the loop I<parameter> for functions, if one is required ("ev
2587	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	3622	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
2588	C<EV_P_> is used when other parameters are following. Example:	3623	C<EV_P_> is used when other parameters are following. Example:
2589		3624
2590	// this is how ev_unref is being declared	3625	// this is how ev_unref is being declared
2591	static void ev_unref (EV_P);	3626	static void ev_unref (EV_P);
2592		3627
2593	// this is how you can declare your typical callback	3628	// this is how you can declare your typical callback
2594	static void cb (EV_P_ ev_timer *w, int revents)	3629	static void cb (EV_P_ ev_timer *w, int revents)
2595		3630
2596	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	3631	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
2597	suitable for use with C<EV_A>.	3632	suitable for use with C<EV_A>.
2598		3633
2599	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3634	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2600		3635
2601	Similar to the other two macros, this gives you the value of the default	3636	Similar to the other two macros, this gives you the value of the default
2602	loop, if multiple loops are supported ("ev loop default").	3637	loop, if multiple loops are supported ("ev loop default").
		3638
		3639	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3640
		3641	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3642	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3643	is undefined when the default loop has not been initialised by a previous
		3644	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3645
		3646	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3647	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
2603		3648
2604	=back	3649	=back
2605		3650
2606	Example: Declare and initialise a check watcher, utilising the above	3651	Example: Declare and initialise a check watcher, utilising the above
2607	macros so it will work regardless of whether multiple loops are supported	3652	macros so it will work regardless of whether multiple loops are supported
2608	or not.	3653	or not.
2609		3654
2610	static void	3655	static void
2611	check_cb (EV_P_ ev_timer *w, int revents)	3656	check_cb (EV_P_ ev_timer *w, int revents)
2612	{	3657	{
2613	ev_check_stop (EV_A_ w);	3658	ev_check_stop (EV_A_ w);
2614	}	3659	}
2615		3660
2616	ev_check check;	3661	ev_check check;
2617	ev_check_init (&check, check_cb);	3662	ev_check_init (&check, check_cb);
2618	ev_check_start (EV_DEFAULT_ &check);	3663	ev_check_start (EV_DEFAULT_ &check);
2619	ev_loop (EV_DEFAULT_ 0);	3664	ev_run (EV_DEFAULT_ 0);
2620		3665
2621	=head1 EMBEDDING	3666	=head1 EMBEDDING
2622		3667
2623	Libev can (and often is) directly embedded into host	3668	Libev can (and often is) directly embedded into host
2624	applications. Examples of applications that embed it include the Deliantra	3669	applications. Examples of applications that embed it include the Deliantra
…		…
2631	libev somewhere in your source tree).	3676	libev somewhere in your source tree).
2632		3677
2633	=head2 FILESETS	3678	=head2 FILESETS
2634		3679
2635	Depending on what features you need you need to include one or more sets of files	3680	Depending on what features you need you need to include one or more sets of files
2636	in your app.	3681	in your application.
2637		3682
2638	=head3 CORE EVENT LOOP	3683	=head3 CORE EVENT LOOP
2639		3684
2640	To include only the libev core (all the C<ev_*> functions), with manual	3685	To include only the libev core (all the C<ev_*> functions), with manual
2641	configuration (no autoconf):	3686	configuration (no autoconf):
2642		3687
2643	#define EV_STANDALONE 1	3688	#define EV_STANDALONE 1
2644	#include "ev.c"	3689	#include "ev.c"
2645		3690
2646	This will automatically include F<ev.h>, too, and should be done in a	3691	This will automatically include F<ev.h>, too, and should be done in a
2647	single C source file only to provide the function implementations. To use	3692	single C source file only to provide the function implementations. To use
2648	it, do the same for F<ev.h> in all files wishing to use this API (best	3693	it, do the same for F<ev.h> in all files wishing to use this API (best
2649	done by writing a wrapper around F<ev.h> that you can include instead and	3694	done by writing a wrapper around F<ev.h> that you can include instead and
2650	where you can put other configuration options):	3695	where you can put other configuration options):
2651		3696
2652	#define EV_STANDALONE 1	3697	#define EV_STANDALONE 1
2653	#include "ev.h"	3698	#include "ev.h"
2654		3699
2655	Both header files and implementation files can be compiled with a C++	3700	Both header files and implementation files can be compiled with a C++
2656	compiler (at least, thats a stated goal, and breakage will be treated	3701	compiler (at least, that's a stated goal, and breakage will be treated
2657	as a bug).	3702	as a bug).
2658		3703
2659	You need the following files in your source tree, or in a directory	3704	You need the following files in your source tree, or in a directory
2660	in your include path (e.g. in libev/ when using -Ilibev):	3705	in your include path (e.g. in libev/ when using -Ilibev):
2661		3706
2662	ev.h	3707	ev.h
2663	ev.c	3708	ev.c
2664	ev_vars.h	3709	ev_vars.h
2665	ev_wrap.h	3710	ev_wrap.h
2666		3711
2667	ev_win32.c required on win32 platforms only	3712	ev_win32.c required on win32 platforms only
2668		3713
2669	ev_select.c only when select backend is enabled (which is enabled by default)	3714	ev_select.c only when select backend is enabled (which is enabled by default)
2670	ev_poll.c only when poll backend is enabled (disabled by default)	3715	ev_poll.c only when poll backend is enabled (disabled by default)
2671	ev_epoll.c only when the epoll backend is enabled (disabled by default)	3716	ev_epoll.c only when the epoll backend is enabled (disabled by default)
2672	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	3717	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2673	ev_port.c only when the solaris port backend is enabled (disabled by default)	3718	ev_port.c only when the solaris port backend is enabled (disabled by default)
2674		3719
2675	F<ev.c> includes the backend files directly when enabled, so you only need	3720	F<ev.c> includes the backend files directly when enabled, so you only need
2676	to compile this single file.	3721	to compile this single file.
2677		3722
2678	=head3 LIBEVENT COMPATIBILITY API	3723	=head3 LIBEVENT COMPATIBILITY API
2679		3724
2680	To include the libevent compatibility API, also include:	3725	To include the libevent compatibility API, also include:
2681		3726
2682	#include "event.c"	3727	#include "event.c"
2683		3728
2684	in the file including F<ev.c>, and:	3729	in the file including F<ev.c>, and:
2685		3730
2686	#include "event.h"	3731	#include "event.h"
2687		3732
2688	in the files that want to use the libevent API. This also includes F<ev.h>.	3733	in the files that want to use the libevent API. This also includes F<ev.h>.
2689		3734
2690	You need the following additional files for this:	3735	You need the following additional files for this:
2691		3736
2692	event.h	3737	event.h
2693	event.c	3738	event.c
2694		3739
2695	=head3 AUTOCONF SUPPORT	3740	=head3 AUTOCONF SUPPORT
2696		3741
2697	Instead of using C<EV_STANDALONE=1> and providing your config in	3742	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2698	whatever way you want, you can also C<m4_include([libev.m4])> in your	3743	whatever way you want, you can also C<m4_include([libev.m4])> in your
2699	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	3744	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2700	include F<config.h> and configure itself accordingly.	3745	include F<config.h> and configure itself accordingly.
2701		3746
2702	For this of course you need the m4 file:	3747	For this of course you need the m4 file:
2703		3748
2704	libev.m4	3749	libev.m4
2705		3750
2706	=head2 PREPROCESSOR SYMBOLS/MACROS	3751	=head2 PREPROCESSOR SYMBOLS/MACROS
2707		3752
2708	Libev can be configured via a variety of preprocessor symbols you have to define	3753	Libev can be configured via a variety of preprocessor symbols you have to
2709	before including any of its files. The default is not to build for multiplicity	3754	define before including (or compiling) any of its files. The default in
2710	and only include the select backend.	3755	the absence of autoconf is documented for every option.
		3756
		3757	Symbols marked with "(h)" do not change the ABI, and can have different
		3758	values when compiling libev vs. including F<ev.h>, so it is permissible
		3759	to redefine them before including F<ev.h> without breaking compatibility
		3760	to a compiled library. All other symbols change the ABI, which means all
		3761	users of libev and the libev code itself must be compiled with compatible
		3762	settings.
2711		3763
2712	=over 4	3764	=over 4
2713		3765
		3766	=item EV_COMPAT3 (h)
		3767
		3768	Backwards compatibility is a major concern for libev. This is why this
		3769	release of libev comes with wrappers for the functions and symbols that
		3770	have been renamed between libev version 3 and 4.
		3771
		3772	You can disable these wrappers (to test compatibility with future
		3773	versions) by defining C<EV_COMPAT3> to C<0> when compiling your
		3774	sources. This has the additional advantage that you can drop the C<struct>
		3775	from C<struct ev_loop> declarations, as libev will provide an C<ev_loop>
		3776	typedef in that case.
		3777
		3778	In some future version, the default for C<EV_COMPAT3> will become C<0>,
		3779	and in some even more future version the compatibility code will be
		3780	removed completely.
		3781
2714	=item EV_STANDALONE	3782	=item EV_STANDALONE (h)
2715		3783
2716	Must always be C<1> if you do not use autoconf configuration, which	3784	Must always be C<1> if you do not use autoconf configuration, which
2717	keeps libev from including F<config.h>, and it also defines dummy	3785	keeps libev from including F<config.h>, and it also defines dummy
2718	implementations for some libevent functions (such as logging, which is not	3786	implementations for some libevent functions (such as logging, which is not
2719	supported). It will also not define any of the structs usually found in	3787	supported). It will also not define any of the structs usually found in
2720	F<event.h> that are not directly supported by the libev core alone.	3788	F<event.h> that are not directly supported by the libev core alone.
2721		3789
		3790	In standalone mode, libev will still try to automatically deduce the
		3791	configuration, but has to be more conservative.
		3792
2722	=item EV_USE_MONOTONIC	3793	=item EV_USE_MONOTONIC
2723		3794
2724	If defined to be C<1>, libev will try to detect the availability of the	3795	If defined to be C<1>, libev will try to detect the availability of the
2725	monotonic clock option at both compiletime and runtime. Otherwise no use	3796	monotonic clock option at both compile time and runtime. Otherwise no
2726	of the monotonic clock option will be attempted. If you enable this, you	3797	use of the monotonic clock option will be attempted. If you enable this,
2727	usually have to link against librt or something similar. Enabling it when	3798	you usually have to link against librt or something similar. Enabling it
2728	the functionality isn't available is safe, though, although you have	3799	when the functionality isn't available is safe, though, although you have
2729	to make sure you link against any libraries where the C<clock_gettime>	3800	to make sure you link against any libraries where the C<clock_gettime>
2730	function is hiding in (often F<-lrt>).	3801	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2731		3802
2732	=item EV_USE_REALTIME	3803	=item EV_USE_REALTIME
2733		3804
2734	If defined to be C<1>, libev will try to detect the availability of the	3805	If defined to be C<1>, libev will try to detect the availability of the
2735	realtime clock option at compiletime (and assume its availability at	3806	real-time clock option at compile time (and assume its availability
2736	runtime if successful). Otherwise no use of the realtime clock option will	3807	at runtime if successful). Otherwise no use of the real-time clock
2737	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3808	option will be attempted. This effectively replaces C<gettimeofday>
2738	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	3809	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2739	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	3810	correctness. See the note about libraries in the description of
		3811	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3812	C<EV_USE_CLOCK_SYSCALL>.
		3813
		3814	=item EV_USE_CLOCK_SYSCALL
		3815
		3816	If defined to be C<1>, libev will try to use a direct syscall instead
		3817	of calling the system-provided C<clock_gettime> function. This option
		3818	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3819	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3820	programs needlessly. Using a direct syscall is slightly slower (in
		3821	theory), because no optimised vdso implementation can be used, but avoids
		3822	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3823	higher, as it simplifies linking (no need for C<-lrt>).
2740		3824
2741	=item EV_USE_NANOSLEEP	3825	=item EV_USE_NANOSLEEP
2742		3826
2743	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	3827	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2744	and will use it for delays. Otherwise it will use C<select ()>.	3828	and will use it for delays. Otherwise it will use C<select ()>.
2745		3829
		3830	=item EV_USE_EVENTFD
		3831
		3832	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3833	available and will probe for kernel support at runtime. This will improve
		3834	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3835	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3836	2.7 or newer, otherwise disabled.
		3837
2746	=item EV_USE_SELECT	3838	=item EV_USE_SELECT
2747		3839
2748	If undefined or defined to be C<1>, libev will compile in support for the	3840	If undefined or defined to be C<1>, libev will compile in support for the
2749	C<select>(2) backend. No attempt at autodetection will be done: if no	3841	C<select>(2) backend. No attempt at auto-detection will be done: if no
2750	other method takes over, select will be it. Otherwise the select backend	3842	other method takes over, select will be it. Otherwise the select backend
2751	will not be compiled in.	3843	will not be compiled in.
2752		3844
2753	=item EV_SELECT_USE_FD_SET	3845	=item EV_SELECT_USE_FD_SET
2754		3846
2755	If defined to C<1>, then the select backend will use the system C<fd_set>	3847	If defined to C<1>, then the select backend will use the system C<fd_set>
2756	structure. This is useful if libev doesn't compile due to a missing	3848	structure. This is useful if libev doesn't compile due to a missing
2757	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	3849	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2758	exotic systems. This usually limits the range of file descriptors to some	3850	on exotic systems. This usually limits the range of file descriptors to
2759	low limit such as 1024 or might have other limitations (winsocket only	3851	some low limit such as 1024 or might have other limitations (winsocket
2760	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3852	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2761	influence the size of the C<fd_set> used.	3853	configures the maximum size of the C<fd_set>.
2762		3854
2763	=item EV_SELECT_IS_WINSOCKET	3855	=item EV_SELECT_IS_WINSOCKET
2764		3856
2765	When defined to C<1>, the select backend will assume that	3857	When defined to C<1>, the select backend will assume that
2766	select/socket/connect etc. don't understand file descriptors but	3858	select/socket/connect etc. don't understand file descriptors but
…		…
2768	be used is the winsock select). This means that it will call	3860	be used is the winsock select). This means that it will call
2769	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3861	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2770	it is assumed that all these functions actually work on fds, even	3862	it is assumed that all these functions actually work on fds, even
2771	on win32. Should not be defined on non-win32 platforms.	3863	on win32. Should not be defined on non-win32 platforms.
2772		3864
2773	=item EV_FD_TO_WIN32_HANDLE	3865	=item EV_FD_TO_WIN32_HANDLE(fd)
2774		3866
2775	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map	3867	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
2776	file descriptors to socket handles. When not defining this symbol (the	3868	file descriptors to socket handles. When not defining this symbol (the
2777	default), then libev will call C<_get_osfhandle>, which is usually	3869	default), then libev will call C<_get_osfhandle>, which is usually
2778	correct. In some cases, programs use their own file descriptor management,	3870	correct. In some cases, programs use their own file descriptor management,
2779	in which case they can provide this function to map fds to socket handles.	3871	in which case they can provide this function to map fds to socket handles.
2780		3872
		3873	=item EV_WIN32_HANDLE_TO_FD(handle)
		3874
		3875	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		3876	using the standard C<_open_osfhandle> function. For programs implementing
		3877	their own fd to handle mapping, overwriting this function makes it easier
		3878	to do so. This can be done by defining this macro to an appropriate value.
		3879
		3880	=item EV_WIN32_CLOSE_FD(fd)
		3881
		3882	If programs implement their own fd to handle mapping on win32, then this
		3883	macro can be used to override the C<close> function, useful to unregister
		3884	file descriptors again. Note that the replacement function has to close
		3885	the underlying OS handle.
		3886
2781	=item EV_USE_POLL	3887	=item EV_USE_POLL
2782		3888
2783	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3889	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2784	backend. Otherwise it will be enabled on non-win32 platforms. It	3890	backend. Otherwise it will be enabled on non-win32 platforms. It
2785	takes precedence over select.	3891	takes precedence over select.
2786		3892
2787	=item EV_USE_EPOLL	3893	=item EV_USE_EPOLL
2788		3894
2789	If defined to be C<1>, libev will compile in support for the Linux	3895	If defined to be C<1>, libev will compile in support for the Linux
2790	C<epoll>(7) backend. Its availability will be detected at runtime,	3896	C<epoll>(7) backend. Its availability will be detected at runtime,
2791	otherwise another method will be used as fallback. This is the	3897	otherwise another method will be used as fallback. This is the preferred
2792	preferred backend for GNU/Linux systems.	3898	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3899	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2793		3900
2794	=item EV_USE_KQUEUE	3901	=item EV_USE_KQUEUE
2795		3902
2796	If defined to be C<1>, libev will compile in support for the BSD style	3903	If defined to be C<1>, libev will compile in support for the BSD style
2797	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	3904	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2810	otherwise another method will be used as fallback. This is the preferred	3917	otherwise another method will be used as fallback. This is the preferred
2811	backend for Solaris 10 systems.	3918	backend for Solaris 10 systems.
2812		3919
2813	=item EV_USE_DEVPOLL	3920	=item EV_USE_DEVPOLL
2814		3921
2815	reserved for future expansion, works like the USE symbols above.	3922	Reserved for future expansion, works like the USE symbols above.
2816		3923
2817	=item EV_USE_INOTIFY	3924	=item EV_USE_INOTIFY
2818		3925
2819	If defined to be C<1>, libev will compile in support for the Linux inotify	3926	If defined to be C<1>, libev will compile in support for the Linux inotify
2820	interface to speed up C<ev_stat> watchers. Its actual availability will	3927	interface to speed up C<ev_stat> watchers. Its actual availability will
2821	be detected at runtime.	3928	be detected at runtime. If undefined, it will be enabled if the headers
		3929	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2822		3930
2823	=item EV_ATOMIC_T	3931	=item EV_ATOMIC_T
2824		3932
2825	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	3933	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
2826	access is atomic with respect to other threads or signal contexts. No such	3934	access is atomic with respect to other threads or signal contexts. No such
2827	type is easily found in the C language, so you can provide your own type	3935	type is easily found in the C language, so you can provide your own type
2828	that you know is safe for your purposes. It is used both for signal handler "locking"	3936	that you know is safe for your purposes. It is used both for signal handler "locking"
2829	as well as for signal and thread safety in C<ev_async> watchers.	3937	as well as for signal and thread safety in C<ev_async> watchers.
2830		3938
2831	In the absense of this define, libev will use C<sig_atomic_t volatile>	3939	In the absence of this define, libev will use C<sig_atomic_t volatile>
2832	(from F<signal.h>), which is usually good enough on most platforms.	3940	(from F<signal.h>), which is usually good enough on most platforms.
2833		3941
2834	=item EV_H	3942	=item EV_H (h)
2835		3943
2836	The name of the F<ev.h> header file used to include it. The default if	3944	The name of the F<ev.h> header file used to include it. The default if
2837	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be	3945	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2838	used to virtually rename the F<ev.h> header file in case of conflicts.	3946	used to virtually rename the F<ev.h> header file in case of conflicts.
2839		3947
2840	=item EV_CONFIG_H	3948	=item EV_CONFIG_H (h)
2841		3949
2842	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	3950	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2843	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	3951	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2844	C<EV_H>, above.	3952	C<EV_H>, above.
2845		3953
2846	=item EV_EVENT_H	3954	=item EV_EVENT_H (h)
2847		3955
2848	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	3956	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2849	of how the F<event.h> header can be found, the default is C<"event.h">.	3957	of how the F<event.h> header can be found, the default is C<"event.h">.
2850		3958
2851	=item EV_PROTOTYPES	3959	=item EV_PROTOTYPES (h)
2852		3960
2853	If defined to be C<0>, then F<ev.h> will not define any function	3961	If defined to be C<0>, then F<ev.h> will not define any function
2854	prototypes, but still define all the structs and other symbols. This is	3962	prototypes, but still define all the structs and other symbols. This is
2855	occasionally useful if you want to provide your own wrapper functions	3963	occasionally useful if you want to provide your own wrapper functions
2856	around libev functions.	3964	around libev functions.
…		…
2875	When doing priority-based operations, libev usually has to linearly search	3983	When doing priority-based operations, libev usually has to linearly search
2876	all the priorities, so having many of them (hundreds) uses a lot of space	3984	all the priorities, so having many of them (hundreds) uses a lot of space
2877	and time, so using the defaults of five priorities (-2 .. +2) is usually	3985	and time, so using the defaults of five priorities (-2 .. +2) is usually
2878	fine.	3986	fine.
2879		3987
2880	If your embedding app does not need any priorities, defining these both to	3988	If your embedding application does not need any priorities, defining these
2881	C<0> will save some memory and cpu.	3989	both to C<0> will save some memory and CPU.
2882		3990
2883	=item EV_PERIODIC_ENABLE	3991	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		3992	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		3993	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
2884		3994
2885	If undefined or defined to be C<1>, then periodic timers are supported. If	3995	If undefined or defined to be C<1> (and the platform supports it), then
2886	defined to be C<0>, then they are not. Disabling them saves a few kB of	3996	the respective watcher type is supported. If defined to be C<0>, then it
2887	code.	3997	is not. Disabling watcher types mainly saves code size.
2888		3998
2889	=item EV_IDLE_ENABLE	3999	=item EV_FEATURES
2890
2891	If undefined or defined to be C<1>, then idle watchers are supported. If
2892	defined to be C<0>, then they are not. Disabling them saves a few kB of
2893	code.
2894
2895	=item EV_EMBED_ENABLE
2896
2897	If undefined or defined to be C<1>, then embed watchers are supported. If
2898	defined to be C<0>, then they are not.
2899
2900	=item EV_STAT_ENABLE
2901
2902	If undefined or defined to be C<1>, then stat watchers are supported. If
2903	defined to be C<0>, then they are not.
2904
2905	=item EV_FORK_ENABLE
2906
2907	If undefined or defined to be C<1>, then fork watchers are supported. If
2908	defined to be C<0>, then they are not.
2909
2910	=item EV_ASYNC_ENABLE
2911
2912	If undefined or defined to be C<1>, then async watchers are supported. If
2913	defined to be C<0>, then they are not.
2914
2915	=item EV_MINIMAL
2916		4000
2917	If you need to shave off some kilobytes of code at the expense of some	4001	If you need to shave off some kilobytes of code at the expense of some
2918	speed, define this symbol to C<1>. Currently only used for gcc to override	4002	speed (but with the full API), you can define this symbol to request
2919	some inlining decisions, saves roughly 30% codesize of amd64.	4003	certain subsets of functionality. The default is to enable all features
		4004	that can be enabled on the platform.
		4005
		4006	A typical way to use this symbol is to define it to C<0> (or to a bitset
		4007	with some broad features you want) and then selectively re-enable
		4008	additional parts you want, for example if you want everything minimal,
		4009	but multiple event loop support, async and child watchers and the poll
		4010	backend, use this:
		4011
		4012	#define EV_FEATURES 0
		4013	#define EV_MULTIPLICITY 1
		4014	#define EV_USE_POLL 1
		4015	#define EV_CHILD_ENABLE 1
		4016	#define EV_ASYNC_ENABLE 1
		4017
		4018	The actual value is a bitset, it can be a combination of the following
		4019	values:
		4020
		4021	=over 4
		4022
		4023	=item C<1> - faster/larger code
		4024
		4025	Use larger code to speed up some operations.
		4026
		4027	Currently this is used to override some inlining decisions (enlarging the
		4028	code size by roughly 30% on amd64).
		4029
		4030	When optimising for size, use of compiler flags such as C<-Os> with
		4031	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		4032	assertions.
		4033
		4034	=item C<2> - faster/larger data structures
		4035
		4036	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		4037	hash table sizes and so on. This will usually further increase code size
		4038	and can additionally have an effect on the size of data structures at
		4039	runtime.
		4040
		4041	=item C<4> - full API configuration
		4042
		4043	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		4044	enables multiplicity (C<EV_MULTIPLICITY>=1).
		4045
		4046	=item C<8> - full API
		4047
		4048	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		4049	details on which parts of the API are still available without this
		4050	feature, and do not complain if this subset changes over time.
		4051
		4052	=item C<16> - enable all optional watcher types
		4053
		4054	Enables all optional watcher types. If you want to selectively enable
		4055	only some watcher types other than I/O and timers (e.g. prepare,
		4056	embed, async, child...) you can enable them manually by defining
		4057	C<EV_watchertype_ENABLE> to C<1> instead.
		4058
		4059	=item C<32> - enable all backends
		4060
		4061	This enables all backends - without this feature, you need to enable at
		4062	least one backend manually (C<EV_USE_SELECT> is a good choice).
		4063
		4064	=item C<64> - enable OS-specific "helper" APIs
		4065
		4066	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		4067	default.
		4068
		4069	=back
		4070
		4071	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		4072	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		4073	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		4074	watchers, timers and monotonic clock support.
		4075
		4076	With an intelligent-enough linker (gcc+binutils are intelligent enough
		4077	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		4078	your program might be left out as well - a binary starting a timer and an
		4079	I/O watcher then might come out at only 5Kb.
		4080
		4081	=item EV_AVOID_STDIO
		4082
		4083	If this is set to C<1> at compiletime, then libev will avoid using stdio
		4084	functions (printf, scanf, perror etc.). This will increase the code size
		4085	somewhat, but if your program doesn't otherwise depend on stdio and your
		4086	libc allows it, this avoids linking in the stdio library which is quite
		4087	big.
		4088
		4089	Note that error messages might become less precise when this option is
		4090	enabled.
		4091
		4092	=item EV_NSIG
		4093
		4094	The highest supported signal number, +1 (or, the number of
		4095	signals): Normally, libev tries to deduce the maximum number of signals
		4096	automatically, but sometimes this fails, in which case it can be
		4097	specified. Also, using a lower number than detected (C<32> should be
		4098	good for about any system in existence) can save some memory, as libev
		4099	statically allocates some 12-24 bytes per signal number.
2920		4100
2921	=item EV_PID_HASHSIZE	4101	=item EV_PID_HASHSIZE
2922		4102
2923	C<ev_child> watchers use a small hash table to distribute workload by	4103	C<ev_child> watchers use a small hash table to distribute workload by
2924	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	4104	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
2925	than enough. If you need to manage thousands of children you might want to	4105	usually more than enough. If you need to manage thousands of children you
2926	increase this value (I<must> be a power of two).	4106	might want to increase this value (I<must> be a power of two).
2927		4107
2928	=item EV_INOTIFY_HASHSIZE	4108	=item EV_INOTIFY_HASHSIZE
2929		4109
2930	C<ev_stat> watchers use a small hash table to distribute workload by	4110	C<ev_stat> watchers use a small hash table to distribute workload by
2931	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	4111	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
2932	usually more than enough. If you need to manage thousands of C<ev_stat>	4112	disabled), usually more than enough. If you need to manage thousands of
2933	watchers you might want to increase this value (I<must> be a power of	4113	C<ev_stat> watchers you might want to increase this value (I<must> be a
2934	two).	4114	power of two).
		4115
		4116	=item EV_USE_4HEAP
		4117
		4118	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4119	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		4120	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		4121	faster performance with many (thousands) of watchers.
		4122
		4123	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4124	will be C<0>.
		4125
		4126	=item EV_HEAP_CACHE_AT
		4127
		4128	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4129	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		4130	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		4131	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		4132	but avoids random read accesses on heap changes. This improves performance
		4133	noticeably with many (hundreds) of watchers.
		4134
		4135	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4136	will be C<0>.
		4137
		4138	=item EV_VERIFY
		4139
		4140	Controls how much internal verification (see C<ev_verify ()>) will
		4141	be done: If set to C<0>, no internal verification code will be compiled
		4142	in. If set to C<1>, then verification code will be compiled in, but not
		4143	called. If set to C<2>, then the internal verification code will be
		4144	called once per loop, which can slow down libev. If set to C<3>, then the
		4145	verification code will be called very frequently, which will slow down
		4146	libev considerably.
		4147
		4148	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4149	will be C<0>.
2935		4150
2936	=item EV_COMMON	4151	=item EV_COMMON
2937		4152
2938	By default, all watchers have a C<void *data> member. By redefining	4153	By default, all watchers have a C<void *data> member. By redefining
2939	this macro to a something else you can include more and other types of	4154	this macro to something else you can include more and other types of
2940	members. You have to define it each time you include one of the files,	4155	members. You have to define it each time you include one of the files,
2941	though, and it must be identical each time.	4156	though, and it must be identical each time.
2942		4157
2943	For example, the perl EV module uses something like this:	4158	For example, the perl EV module uses something like this:
2944		4159
2945	#define EV_COMMON \	4160	#define EV_COMMON \
2946	SV *self; /* contains this struct */ \	4161	SV *self; /* contains this struct */ \
2947	SV *cb_sv, *fh /* note no trailing ";" */	4162	SV *cb_sv, *fh /* note no trailing ";" */
2948		4163
2949	=item EV_CB_DECLARE (type)	4164	=item EV_CB_DECLARE (type)
2950		4165
2951	=item EV_CB_INVOKE (watcher, revents)	4166	=item EV_CB_INVOKE (watcher, revents)
2952		4167
…		…
2957	definition and a statement, respectively. See the F<ev.h> header file for	4172	definition and a statement, respectively. See the F<ev.h> header file for
2958	their default definitions. One possible use for overriding these is to	4173	their default definitions. One possible use for overriding these is to
2959	avoid the C<struct ev_loop *> as first argument in all cases, or to use	4174	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2960	method calls instead of plain function calls in C++.	4175	method calls instead of plain function calls in C++.
2961		4176
		4177	=back
		4178
2962	=head2 EXPORTED API SYMBOLS	4179	=head2 EXPORTED API SYMBOLS
2963		4180
2964	If you need to re-export the API (e.g. via a dll) and you need a list of	4181	If you need to re-export the API (e.g. via a DLL) and you need a list of
2965	exported symbols, you can use the provided F<Symbol.*> files which list	4182	exported symbols, you can use the provided F<Symbol.*> files which list
2966	all public symbols, one per line:	4183	all public symbols, one per line:
2967		4184
2968	Symbols.ev for libev proper	4185	Symbols.ev for libev proper
2969	Symbols.event for the libevent emulation	4186	Symbols.event for the libevent emulation
2970		4187
2971	This can also be used to rename all public symbols to avoid clashes with	4188	This can also be used to rename all public symbols to avoid clashes with
2972	multiple versions of libev linked together (which is obviously bad in	4189	multiple versions of libev linked together (which is obviously bad in
2973	itself, but sometimes it is inconvinient to avoid this).	4190	itself, but sometimes it is inconvenient to avoid this).
2974		4191
2975	A sed command like this will create wrapper C<#define>'s that you need to	4192	A sed command like this will create wrapper C<#define>'s that you need to
2976	include before including F<ev.h>:	4193	include before including F<ev.h>:
2977		4194
2978	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h	4195	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
…		…
2995	file.	4212	file.
2996		4213
2997	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	4214	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2998	that everybody includes and which overrides some configure choices:	4215	that everybody includes and which overrides some configure choices:
2999		4216
3000	#define EV_MINIMAL 1	4217	#define EV_FEATURES 8
3001	#define EV_USE_POLL 0	4218	#define EV_USE_SELECT 1
3002	#define EV_MULTIPLICITY 0
3003	#define EV_PERIODIC_ENABLE 0	4219	#define EV_PREPARE_ENABLE 1
		4220	#define EV_IDLE_ENABLE 1
3004	#define EV_STAT_ENABLE 0	4221	#define EV_SIGNAL_ENABLE 1
3005	#define EV_FORK_ENABLE 0	4222	#define EV_CHILD_ENABLE 1
		4223	#define EV_USE_STDEXCEPT 0
3006	#define EV_CONFIG_H <config.h>	4224	#define EV_CONFIG_H <config.h>
3007	#define EV_MINPRI 0
3008	#define EV_MAXPRI 0
3009		4225
3010	#include "ev++.h"	4226	#include "ev++.h"
3011		4227
3012	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4228	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
3013		4229
3014	#include "ev_cpp.h"	4230	#include "ev_cpp.h"
3015	#include "ev.c"	4231	#include "ev.c"
3016		4232
		4233	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
3017		4234
3018	=head1 COMPLEXITIES	4235	=head2 THREADS AND COROUTINES
3019		4236
3020	In this section the complexities of (many of) the algorithms used inside	4237	=head3 THREADS
3021	libev will be explained. For complexity discussions about backends see the
3022	documentation for C<ev_default_init>.
3023		4238
3024	All of the following are about amortised time: If an array needs to be	4239	All libev functions are reentrant and thread-safe unless explicitly
3025	extended, libev needs to realloc and move the whole array, but this	4240	documented otherwise, but libev implements no locking itself. This means
3026	happens asymptotically never with higher number of elements, so O(1) might	4241	that you can use as many loops as you want in parallel, as long as there
3027	mean it might do a lengthy realloc operation in rare cases, but on average	4242	are no concurrent calls into any libev function with the same loop
3028	it is much faster and asymptotically approaches constant time.	4243	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4244	of course): libev guarantees that different event loops share no data
		4245	structures that need any locking.
		4246
		4247	Or to put it differently: calls with different loop parameters can be done
		4248	concurrently from multiple threads, calls with the same loop parameter
		4249	must be done serially (but can be done from different threads, as long as
		4250	only one thread ever is inside a call at any point in time, e.g. by using
		4251	a mutex per loop).
		4252
		4253	Specifically to support threads (and signal handlers), libev implements
		4254	so-called C<ev_async> watchers, which allow some limited form of
		4255	concurrency on the same event loop, namely waking it up "from the
		4256	outside".
		4257
		4258	If you want to know which design (one loop, locking, or multiple loops
		4259	without or something else still) is best for your problem, then I cannot
		4260	help you, but here is some generic advice:
3029		4261
3030	=over 4	4262	=over 4
3031		4263
3032	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4264	=item * most applications have a main thread: use the default libev loop
		4265	in that thread, or create a separate thread running only the default loop.
3033		4266
3034	This means that, when you have a watcher that triggers in one hour and	4267	This helps integrating other libraries or software modules that use libev
3035	there are 100 watchers that would trigger before that then inserting will	4268	themselves and don't care/know about threading.
3036	have to skip roughly seven (C<ld 100>) of these watchers.
3037		4269
3038	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)	4270	=item * one loop per thread is usually a good model.
3039		4271
3040	That means that changing a timer costs less than removing/adding them	4272	Doing this is almost never wrong, sometimes a better-performance model
3041	as only the relative motion in the event queue has to be paid for.	4273	exists, but it is always a good start.
3042		4274
3043	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)	4275	=item * other models exist, such as the leader/follower pattern, where one
		4276	loop is handed through multiple threads in a kind of round-robin fashion.
3044		4277
3045	These just add the watcher into an array or at the head of a list.	4278	Choosing a model is hard - look around, learn, know that usually you can do
		4279	better than you currently do :-)
3046		4280
3047	=item Stopping check/prepare/idle/fork/async watchers: O(1)	4281	=item * often you need to talk to some other thread which blocks in the
		4282	event loop.
3048		4283
3049	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	4284	C<ev_async> watchers can be used to wake them up from other threads safely
		4285	(or from signal contexts...).
3050		4286
3051	These watchers are stored in lists then need to be walked to find the	4287	An example use would be to communicate signals or other events that only
3052	correct watcher to remove. The lists are usually short (you don't usually	4288	work in the default loop by registering the signal watcher with the
3053	have many watchers waiting for the same fd or signal).	4289	default loop and triggering an C<ev_async> watcher from the default loop
3054		4290	watcher callback into the event loop interested in the signal.
3055	=item Finding the next timer in each loop iteration: O(1)
3056
3057	By virtue of using a binary heap, the next timer is always found at the
3058	beginning of the storage array.
3059
3060	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
3061
3062	A change means an I/O watcher gets started or stopped, which requires
3063	libev to recalculate its status (and possibly tell the kernel, depending
3064	on backend and wether C<ev_io_set> was used).
3065
3066	=item Activating one watcher (putting it into the pending state): O(1)
3067
3068	=item Priority handling: O(number_of_priorities)
3069
3070	Priorities are implemented by allocating some space for each
3071	priority. When doing priority-based operations, libev usually has to
3072	linearly search all the priorities, but starting/stopping and activating
3073	watchers becomes O(1) w.r.t. priority handling.
3074
3075	=item Sending an ev_async: O(1)
3076
3077	=item Processing ev_async_send: O(number_of_async_watchers)
3078
3079	=item Processing signals: O(max_signal_number)
3080
3081	Sending involves a syscall I<iff> there were no other C<ev_async_send>
3082	calls in the current loop iteration. Checking for async and signal events
3083	involves iterating over all running async watchers or all signal numbers.
3084		4291
3085	=back	4292	=back
3086		4293
		4294	=head4 THREAD LOCKING EXAMPLE
3087		4295
3088	=head1 Win32 platform limitations and workarounds	4296	Here is a fictitious example of how to run an event loop in a different
		4297	thread than where callbacks are being invoked and watchers are
		4298	created/added/removed.
		4299
		4300	For a real-world example, see the C<EV::Loop::Async> perl module,
		4301	which uses exactly this technique (which is suited for many high-level
		4302	languages).
		4303
		4304	The example uses a pthread mutex to protect the loop data, a condition
		4305	variable to wait for callback invocations, an async watcher to notify the
		4306	event loop thread and an unspecified mechanism to wake up the main thread.
		4307
		4308	First, you need to associate some data with the event loop:
		4309
		4310	typedef struct {
		4311	mutex_t lock; /* global loop lock */
		4312	ev_async async_w;
		4313	thread_t tid;
		4314	cond_t invoke_cv;
		4315	} userdata;
		4316
		4317	void prepare_loop (EV_P)
		4318	{
		4319	// for simplicity, we use a static userdata struct.
		4320	static userdata u;
		4321
		4322	ev_async_init (&u->async_w, async_cb);
		4323	ev_async_start (EV_A_ &u->async_w);
		4324
		4325	pthread_mutex_init (&u->lock, 0);
		4326	pthread_cond_init (&u->invoke_cv, 0);
		4327
		4328	// now associate this with the loop
		4329	ev_set_userdata (EV_A_ u);
		4330	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4331	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4332
		4333	// then create the thread running ev_loop
		4334	pthread_create (&u->tid, 0, l_run, EV_A);
		4335	}
		4336
		4337	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4338	solely to wake up the event loop so it takes notice of any new watchers
		4339	that might have been added:
		4340
		4341	static void
		4342	async_cb (EV_P_ ev_async *w, int revents)
		4343	{
		4344	// just used for the side effects
		4345	}
		4346
		4347	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4348	protecting the loop data, respectively.
		4349
		4350	static void
		4351	l_release (EV_P)
		4352	{
		4353	userdata *u = ev_userdata (EV_A);
		4354	pthread_mutex_unlock (&u->lock);
		4355	}
		4356
		4357	static void
		4358	l_acquire (EV_P)
		4359	{
		4360	userdata *u = ev_userdata (EV_A);
		4361	pthread_mutex_lock (&u->lock);
		4362	}
		4363
		4364	The event loop thread first acquires the mutex, and then jumps straight
		4365	into C<ev_run>:
		4366
		4367	void *
		4368	l_run (void *thr_arg)
		4369	{
		4370	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		4371
		4372	l_acquire (EV_A);
		4373	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4374	ev_run (EV_A_ 0);
		4375	l_release (EV_A);
		4376
		4377	return 0;
		4378	}
		4379
		4380	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4381	signal the main thread via some unspecified mechanism (signals? pipe
		4382	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4383	have been called (in a while loop because a) spurious wakeups are possible
		4384	and b) skipping inter-thread-communication when there are no pending
		4385	watchers is very beneficial):
		4386
		4387	static void
		4388	l_invoke (EV_P)
		4389	{
		4390	userdata *u = ev_userdata (EV_A);
		4391
		4392	while (ev_pending_count (EV_A))
		4393	{
		4394	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4395	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4396	}
		4397	}
		4398
		4399	Now, whenever the main thread gets told to invoke pending watchers, it
		4400	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4401	thread to continue:
		4402
		4403	static void
		4404	real_invoke_pending (EV_P)
		4405	{
		4406	userdata *u = ev_userdata (EV_A);
		4407
		4408	pthread_mutex_lock (&u->lock);
		4409	ev_invoke_pending (EV_A);
		4410	pthread_cond_signal (&u->invoke_cv);
		4411	pthread_mutex_unlock (&u->lock);
		4412	}
		4413
		4414	Whenever you want to start/stop a watcher or do other modifications to an
		4415	event loop, you will now have to lock:
		4416
		4417	ev_timer timeout_watcher;
		4418	userdata *u = ev_userdata (EV_A);
		4419
		4420	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4421
		4422	pthread_mutex_lock (&u->lock);
		4423	ev_timer_start (EV_A_ &timeout_watcher);
		4424	ev_async_send (EV_A_ &u->async_w);
		4425	pthread_mutex_unlock (&u->lock);
		4426
		4427	Note that sending the C<ev_async> watcher is required because otherwise
		4428	an event loop currently blocking in the kernel will have no knowledge
		4429	about the newly added timer. By waking up the loop it will pick up any new
		4430	watchers in the next event loop iteration.
		4431
		4432	=head3 COROUTINES
		4433
		4434	Libev is very accommodating to coroutines ("cooperative threads"):
		4435	libev fully supports nesting calls to its functions from different
		4436	coroutines (e.g. you can call C<ev_run> on the same loop from two
		4437	different coroutines, and switch freely between both coroutines running
		4438	the loop, as long as you don't confuse yourself). The only exception is
		4439	that you must not do this from C<ev_periodic> reschedule callbacks.
		4440
		4441	Care has been taken to ensure that libev does not keep local state inside
		4442	C<ev_run>, and other calls do not usually allow for coroutine switches as
		4443	they do not call any callbacks.
		4444
		4445	=head2 COMPILER WARNINGS
		4446
		4447	Depending on your compiler and compiler settings, you might get no or a
		4448	lot of warnings when compiling libev code. Some people are apparently
		4449	scared by this.
		4450
		4451	However, these are unavoidable for many reasons. For one, each compiler
		4452	has different warnings, and each user has different tastes regarding
		4453	warning options. "Warn-free" code therefore cannot be a goal except when
		4454	targeting a specific compiler and compiler-version.
		4455
		4456	Another reason is that some compiler warnings require elaborate
		4457	workarounds, or other changes to the code that make it less clear and less
		4458	maintainable.
		4459
		4460	And of course, some compiler warnings are just plain stupid, or simply
		4461	wrong (because they don't actually warn about the condition their message
		4462	seems to warn about). For example, certain older gcc versions had some
		4463	warnings that resulted in an extreme number of false positives. These have
		4464	been fixed, but some people still insist on making code warn-free with
		4465	such buggy versions.
		4466
		4467	While libev is written to generate as few warnings as possible,
		4468	"warn-free" code is not a goal, and it is recommended not to build libev
		4469	with any compiler warnings enabled unless you are prepared to cope with
		4470	them (e.g. by ignoring them). Remember that warnings are just that:
		4471	warnings, not errors, or proof of bugs.
		4472
		4473
		4474	=head2 VALGRIND
		4475
		4476	Valgrind has a special section here because it is a popular tool that is
		4477	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		4478
		4479	If you think you found a bug (memory leak, uninitialised data access etc.)
		4480	in libev, then check twice: If valgrind reports something like:
		4481
		4482	==2274== definitely lost: 0 bytes in 0 blocks.
		4483	==2274== possibly lost: 0 bytes in 0 blocks.
		4484	==2274== still reachable: 256 bytes in 1 blocks.
		4485
		4486	Then there is no memory leak, just as memory accounted to global variables
		4487	is not a memleak - the memory is still being referenced, and didn't leak.
		4488
		4489	Similarly, under some circumstances, valgrind might report kernel bugs
		4490	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4491	although an acceptable workaround has been found here), or it might be
		4492	confused.
		4493
		4494	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		4495	make it into some kind of religion.
		4496
		4497	If you are unsure about something, feel free to contact the mailing list
		4498	with the full valgrind report and an explanation on why you think this
		4499	is a bug in libev (best check the archives, too :). However, don't be
		4500	annoyed when you get a brisk "this is no bug" answer and take the chance
		4501	of learning how to interpret valgrind properly.
		4502
		4503	If you need, for some reason, empty reports from valgrind for your project
		4504	I suggest using suppression lists.
		4505
		4506
		4507	=head1 PORTABILITY NOTES
		4508
		4509	=head2 GNU/LINUX 32 BIT LIMITATIONS
		4510
		4511	GNU/Linux is the only common platform that supports 64 bit file/large file
		4512	interfaces but I<disables> them by default.
		4513
		4514	That means that libev compiled in the default environment doesn't support
		4515	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
		4516
		4517	Unfortunately, many programs try to work around this GNU/Linux issue
		4518	by enabling the large file API, which makes them incompatible with the
		4519	standard libev compiled for their system.
		4520
		4521	Likewise, libev cannot enable the large file API itself as this would
		4522	suddenly make it incompatible to the default compile time environment,
		4523	i.e. all programs not using special compile switches.
		4524
		4525	=head2 OS/X AND DARWIN BUGS
		4526
		4527	The whole thing is a bug if you ask me - basically any system interface
		4528	you touch is broken, whether it is locales, poll, kqueue or even the
		4529	OpenGL drivers.
		4530
		4531	=head3 C<kqueue> is buggy
		4532
		4533	The kqueue syscall is broken in all known versions - most versions support
		4534	only sockets, many support pipes.
		4535
		4536	Libev tries to work around this by not using C<kqueue> by default on this
		4537	rotten platform, but of course you can still ask for it when creating a
		4538	loop - embedding a socket-only kqueue loop into a select-based one is
		4539	probably going to work well.
		4540
		4541	=head3 C<poll> is buggy
		4542
		4543	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		4544	implementation by something calling C<kqueue> internally around the 10.5.6
		4545	release, so now C<kqueue> I<and> C<poll> are broken.
		4546
		4547	Libev tries to work around this by not using C<poll> by default on
		4548	this rotten platform, but of course you can still ask for it when creating
		4549	a loop.
		4550
		4551	=head3 C<select> is buggy
		4552
		4553	All that's left is C<select>, and of course Apple found a way to fuck this
		4554	one up as well: On OS/X, C<select> actively limits the number of file
		4555	descriptors you can pass in to 1024 - your program suddenly crashes when
		4556	you use more.
		4557
		4558	There is an undocumented "workaround" for this - defining
		4559	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		4560	work on OS/X.
		4561
		4562	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		4563
		4564	=head3 C<errno> reentrancy
		4565
		4566	The default compile environment on Solaris is unfortunately so
		4567	thread-unsafe that you can't even use components/libraries compiled
		4568	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
		4569	defined by default. A valid, if stupid, implementation choice.
		4570
		4571	If you want to use libev in threaded environments you have to make sure
		4572	it's compiled with C<_REENTRANT> defined.
		4573
		4574	=head3 Event port backend
		4575
		4576	The scalable event interface for Solaris is called "event
		4577	ports". Unfortunately, this mechanism is very buggy in all major
		4578	releases. If you run into high CPU usage, your program freezes or you get
		4579	a large number of spurious wakeups, make sure you have all the relevant
		4580	and latest kernel patches applied. No, I don't know which ones, but there
		4581	are multiple ones to apply, and afterwards, event ports actually work
		4582	great.
		4583
		4584	If you can't get it to work, you can try running the program by setting
		4585	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		4586	C<select> backends.
		4587
		4588	=head2 AIX POLL BUG
		4589
		4590	AIX unfortunately has a broken C<poll.h> header. Libev works around
		4591	this by trying to avoid the poll backend altogether (i.e. it's not even
		4592	compiled in), which normally isn't a big problem as C<select> works fine
		4593	with large bitsets on AIX, and AIX is dead anyway.
		4594
		4595	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		4596
		4597	=head3 General issues
3089		4598
3090	Win32 doesn't support any of the standards (e.g. POSIX) that libev	4599	Win32 doesn't support any of the standards (e.g. POSIX) that libev
3091	requires, and its I/O model is fundamentally incompatible with the POSIX	4600	requires, and its I/O model is fundamentally incompatible with the POSIX
3092	model. Libev still offers limited functionality on this platform in	4601	model. Libev still offers limited functionality on this platform in
3093	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	4602	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
3094	descriptors. This only applies when using Win32 natively, not when using	4603	descriptors. This only applies when using Win32 natively, not when using
3095	e.g. cygwin.	4604	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		4605	as every compielr comes with a slightly differently broken/incompatible
		4606	environment.
		4607
		4608	Lifting these limitations would basically require the full
		4609	re-implementation of the I/O system. If you are into this kind of thing,
		4610	then note that glib does exactly that for you in a very portable way (note
		4611	also that glib is the slowest event library known to man).
3096		4612
3097	There is no supported compilation method available on windows except	4613	There is no supported compilation method available on windows except
3098	embedding it into other applications.	4614	embedding it into other applications.
3099		4615
		4616	Sensible signal handling is officially unsupported by Microsoft - libev
		4617	tries its best, but under most conditions, signals will simply not work.
		4618
		4619	Not a libev limitation but worth mentioning: windows apparently doesn't
		4620	accept large writes: instead of resulting in a partial write, windows will
		4621	either accept everything or return C<ENOBUFS> if the buffer is too large,
		4622	so make sure you only write small amounts into your sockets (less than a
		4623	megabyte seems safe, but this apparently depends on the amount of memory
		4624	available).
		4625
3100	Due to the many, low, and arbitrary limits on the win32 platform and the	4626	Due to the many, low, and arbitrary limits on the win32 platform and
3101	abysmal performance of winsockets, using a large number of sockets is not	4627	the abysmal performance of winsockets, using a large number of sockets
3102	recommended (and not reasonable). If your program needs to use more than	4628	is not recommended (and not reasonable). If your program needs to use
3103	a hundred or so sockets, then likely it needs to use a totally different	4629	more than a hundred or so sockets, then likely it needs to use a totally
3104	implementation for windows, as libev offers the POSIX model, which cannot	4630	different implementation for windows, as libev offers the POSIX readiness
3105	be implemented efficiently on windows (microsoft monopoly games).	4631	notification model, which cannot be implemented efficiently on windows
		4632	(due to Microsoft monopoly games).
3106		4633
3107	=over 4	4634	A typical way to use libev under windows is to embed it (see the embedding
		4635	section for details) and use the following F<evwrap.h> header file instead
		4636	of F<ev.h>:
3108		4637
		4638	#define EV_STANDALONE /* keeps ev from requiring config.h */
		4639	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		4640
		4641	#include "ev.h"
		4642
		4643	And compile the following F<evwrap.c> file into your project (make sure
		4644	you do I<not> compile the F<ev.c> or any other embedded source files!):
		4645
		4646	#include "evwrap.h"
		4647	#include "ev.c"
		4648
3109	=item The winsocket select function	4649	=head3 The winsocket C<select> function
3110		4650
3111	The winsocket C<select> function doesn't follow POSIX in that it requires	4651	The winsocket C<select> function doesn't follow POSIX in that it
3112	socket I<handles> and not socket I<file descriptors>. This makes select	4652	requires socket I<handles> and not socket I<file descriptors> (it is
3113	very inefficient, and also requires a mapping from file descriptors	4653	also extremely buggy). This makes select very inefficient, and also
3114	to socket handles. See the discussion of the C<EV_SELECT_USE_FD_SET>,	4654	requires a mapping from file descriptors to socket handles (the Microsoft
3115	C<EV_SELECT_IS_WINSOCKET> and C<EV_FD_TO_WIN32_HANDLE> preprocessor	4655	C runtime provides the function C<_open_osfhandle> for this). See the
3116	symbols for more info.	4656	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		4657	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
3117		4658
3118	The configuration for a "naked" win32 using the microsoft runtime	4659	The configuration for a "naked" win32 using the Microsoft runtime
3119	libraries and raw winsocket select is:	4660	libraries and raw winsocket select is:
3120		4661
3121	#define EV_USE_SELECT 1	4662	#define EV_USE_SELECT 1
3122	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */	4663	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
3123		4664
3124	Note that winsockets handling of fd sets is O(n), so you can easily get a	4665	Note that winsockets handling of fd sets is O(n), so you can easily get a
3125	complexity in the O(n²) range when using win32.	4666	complexity in the O(n²) range when using win32.
3126		4667
3127	=item Limited number of file descriptors	4668	=head3 Limited number of file descriptors
3128		4669
3129	Windows has numerous arbitrary (and low) limits on things. Early versions	4670	Windows has numerous arbitrary (and low) limits on things.
3130	of winsocket's select only supported waiting for a max. of C<64> handles	4671
		4672	Early versions of winsocket's select only supported waiting for a maximum
3131	(probably owning to the fact that all windows kernels can only wait for	4673	of C<64> handles (probably owning to the fact that all windows kernels
3132	C<64> things at the same time internally; microsoft recommends spawning a	4674	can only wait for C<64> things at the same time internally; Microsoft
3133	chain of threads and wait for 63 handles and the previous thread in each).	4675	recommends spawning a chain of threads and wait for 63 handles and the
		4676	previous thread in each. Sounds great!).
3134		4677
3135	Newer versions support more handles, but you need to define C<FD_SETSIZE>	4678	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3136	to some high number (e.g. C<2048>) before compiling the winsocket select	4679	to some high number (e.g. C<2048>) before compiling the winsocket select
3137	call (which might be in libev or elsewhere, for example, perl does its own	4680	call (which might be in libev or elsewhere, for example, perl and many
3138	select emulation on windows).	4681	other interpreters do their own select emulation on windows).
3139		4682
3140	Another limit is the number of file descriptors in the microsoft runtime	4683	Another limit is the number of file descriptors in the Microsoft runtime
3141	libraries, which by default is C<64> (there must be a hidden I<64> fetish	4684	libraries, which by default is C<64> (there must be a hidden I<64>
3142	or something like this inside microsoft). You can increase this by calling	4685	fetish or something like this inside Microsoft). You can increase this
3143	C<_setmaxstdio>, which can increase this limit to C<2048> (another	4686	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
3144	arbitrary limit), but is broken in many versions of the microsoft runtime	4687	(another arbitrary limit), but is broken in many versions of the Microsoft
3145	libraries.
3146
3147	This might get you to about C<512> or C<2048> sockets (depending on	4688	runtime libraries. This might get you to about C<512> or C<2048> sockets
3148	windows version and/or the phase of the moon). To get more, you need to	4689	(depending on windows version and/or the phase of the moon). To get more,
3149	wrap all I/O functions and provide your own fd management, but the cost of	4690	you need to wrap all I/O functions and provide your own fd management, but
3150	calling select (O(n²)) will likely make this unworkable.	4691	the cost of calling select (O(n²)) will likely make this unworkable.
		4692
		4693	=head2 PORTABILITY REQUIREMENTS
		4694
		4695	In addition to a working ISO-C implementation and of course the
		4696	backend-specific APIs, libev relies on a few additional extensions:
		4697
		4698	=over 4
		4699
		4700	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4701	calling conventions regardless of C<ev_watcher_type *>.
		4702
		4703	Libev assumes not only that all watcher pointers have the same internal
		4704	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4705	assumes that the same (machine) code can be used to call any watcher
		4706	callback: The watcher callbacks have different type signatures, but libev
		4707	calls them using an C<ev_watcher *> internally.
		4708
		4709	=item C<sig_atomic_t volatile> must be thread-atomic as well
		4710
		4711	The type C<sig_atomic_t volatile> (or whatever is defined as
		4712	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		4713	threads. This is not part of the specification for C<sig_atomic_t>, but is
		4714	believed to be sufficiently portable.
		4715
		4716	=item C<sigprocmask> must work in a threaded environment
		4717
		4718	Libev uses C<sigprocmask> to temporarily block signals. This is not
		4719	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		4720	pthread implementations will either allow C<sigprocmask> in the "main
		4721	thread" or will block signals process-wide, both behaviours would
		4722	be compatible with libev. Interaction between C<sigprocmask> and
		4723	C<pthread_sigmask> could complicate things, however.
		4724
		4725	The most portable way to handle signals is to block signals in all threads
		4726	except the initial one, and run the default loop in the initial thread as
		4727	well.
		4728
		4729	=item C<long> must be large enough for common memory allocation sizes
		4730
		4731	To improve portability and simplify its API, libev uses C<long> internally
		4732	instead of C<size_t> when allocating its data structures. On non-POSIX
		4733	systems (Microsoft...) this might be unexpectedly low, but is still at
		4734	least 31 bits everywhere, which is enough for hundreds of millions of
		4735	watchers.
		4736
		4737	=item C<double> must hold a time value in seconds with enough accuracy
		4738
		4739	The type C<double> is used to represent timestamps. It is required to
		4740	have at least 51 bits of mantissa (and 9 bits of exponent), which is
		4741	good enough for at least into the year 4000 with millisecond accuracy
		4742	(the design goal for libev). This requirement is overfulfilled by
		4743	implementations using IEEE 754, which is basically all existing ones. With
		4744	IEEE 754 doubles, you get microsecond accuracy until at least 2200.
3151		4745
3152	=back	4746	=back
3153		4747
		4748	If you know of other additional requirements drop me a note.
		4749
		4750
		4751	=head1 ALGORITHMIC COMPLEXITIES
		4752
		4753	In this section the complexities of (many of) the algorithms used inside
		4754	libev will be documented. For complexity discussions about backends see
		4755	the documentation for C<ev_default_init>.
		4756
		4757	All of the following are about amortised time: If an array needs to be
		4758	extended, libev needs to realloc and move the whole array, but this
		4759	happens asymptotically rarer with higher number of elements, so O(1) might
		4760	mean that libev does a lengthy realloc operation in rare cases, but on
		4761	average it is much faster and asymptotically approaches constant time.
		4762
		4763	=over 4
		4764
		4765	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		4766
		4767	This means that, when you have a watcher that triggers in one hour and
		4768	there are 100 watchers that would trigger before that, then inserting will
		4769	have to skip roughly seven (C<ld 100>) of these watchers.
		4770
		4771	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		4772
		4773	That means that changing a timer costs less than removing/adding them,
		4774	as only the relative motion in the event queue has to be paid for.
		4775
		4776	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		4777
		4778	These just add the watcher into an array or at the head of a list.
		4779
		4780	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		4781
		4782	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		4783
		4784	These watchers are stored in lists, so they need to be walked to find the
		4785	correct watcher to remove. The lists are usually short (you don't usually
		4786	have many watchers waiting for the same fd or signal: one is typical, two
		4787	is rare).
		4788
		4789	=item Finding the next timer in each loop iteration: O(1)
		4790
		4791	By virtue of using a binary or 4-heap, the next timer is always found at a
		4792	fixed position in the storage array.
		4793
		4794	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		4795
		4796	A change means an I/O watcher gets started or stopped, which requires
		4797	libev to recalculate its status (and possibly tell the kernel, depending
		4798	on backend and whether C<ev_io_set> was used).
		4799
		4800	=item Activating one watcher (putting it into the pending state): O(1)
		4801
		4802	=item Priority handling: O(number_of_priorities)
		4803
		4804	Priorities are implemented by allocating some space for each
		4805	priority. When doing priority-based operations, libev usually has to
		4806	linearly search all the priorities, but starting/stopping and activating
		4807	watchers becomes O(1) with respect to priority handling.
		4808
		4809	=item Sending an ev_async: O(1)
		4810
		4811	=item Processing ev_async_send: O(number_of_async_watchers)
		4812
		4813	=item Processing signals: O(max_signal_number)
		4814
		4815	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4816	calls in the current loop iteration. Checking for async and signal events
		4817	involves iterating over all running async watchers or all signal numbers.
		4818
		4819	=back
		4820
		4821
		4822	=head1 PORTING FROM LIBEV 3.X TO 4.X
		4823
		4824	The major version 4 introduced some minor incompatible changes to the API.
		4825
		4826	At the moment, the C<ev.h> header file tries to implement superficial
		4827	compatibility, so most programs should still compile. Those might be
		4828	removed in later versions of libev, so better update early than late.
		4829
		4830	=over 4
		4831
		4832	=item function/symbol renames
		4833
		4834	A number of functions and symbols have been renamed:
		4835
		4836	ev_loop => ev_run
		4837	EVLOOP_NONBLOCK => EVRUN_NOWAIT
		4838	EVLOOP_ONESHOT => EVRUN_ONCE
		4839
		4840	ev_unloop => ev_break
		4841	EVUNLOOP_CANCEL => EVBREAK_CANCEL
		4842	EVUNLOOP_ONE => EVBREAK_ONE
		4843	EVUNLOOP_ALL => EVBREAK_ALL
		4844
		4845	EV_TIMEOUT => EV_TIMER
		4846
		4847	ev_loop_count => ev_iteration
		4848	ev_loop_depth => ev_depth
		4849	ev_loop_verify => ev_verify
		4850
		4851	Most functions working on C<struct ev_loop> objects don't have an
		4852	C<ev_loop_> prefix, so it was removed; C<ev_loop>, C<ev_unloop> and
		4853	associated constants have been renamed to not collide with the C<struct
		4854	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
		4855	as all other watcher types. Note that C<ev_loop_fork> is still called
		4856	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
		4857	typedef.
		4858
		4859	=item C<EV_COMPAT3> backwards compatibility mechanism
		4860
		4861	The backward compatibility mechanism can be controlled by
		4862	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
		4863	section.
		4864
		4865	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		4866
		4867	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		4868	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		4869	and work, but the library code will of course be larger.
		4870
		4871	=back
		4872
		4873
		4874	=head1 GLOSSARY
		4875
		4876	=over 4
		4877
		4878	=item active
		4879
		4880	A watcher is active as long as it has been started and not yet stopped.
		4881	See L<WATCHER STATES> for details.
		4882
		4883	=item application
		4884
		4885	In this document, an application is whatever is using libev.
		4886
		4887	=item backend
		4888
		4889	The part of the code dealing with the operating system interfaces.
		4890
		4891	=item callback
		4892
		4893	The address of a function that is called when some event has been
		4894	detected. Callbacks are being passed the event loop, the watcher that
		4895	received the event, and the actual event bitset.
		4896
		4897	=item callback/watcher invocation
		4898
		4899	The act of calling the callback associated with a watcher.
		4900
		4901	=item event
		4902
		4903	A change of state of some external event, such as data now being available
		4904	for reading on a file descriptor, time having passed or simply not having
		4905	any other events happening anymore.
		4906
		4907	In libev, events are represented as single bits (such as C<EV_READ> or
		4908	C<EV_TIMER>).
		4909
		4910	=item event library
		4911
		4912	A software package implementing an event model and loop.
		4913
		4914	=item event loop
		4915
		4916	An entity that handles and processes external events and converts them
		4917	into callback invocations.
		4918
		4919	=item event model
		4920
		4921	The model used to describe how an event loop handles and processes
		4922	watchers and events.
		4923
		4924	=item pending
		4925
		4926	A watcher is pending as soon as the corresponding event has been
		4927	detected. See L<WATCHER STATES> for details.
		4928
		4929	=item real time
		4930
		4931	The physical time that is observed. It is apparently strictly monotonic :)
		4932
		4933	=item wall-clock time
		4934
		4935	The time and date as shown on clocks. Unlike real time, it can actually
		4936	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4937	clock.
		4938
		4939	=item watcher
		4940
		4941	A data structure that describes interest in certain events. Watchers need
		4942	to be started (attached to an event loop) before they can receive events.
		4943
		4944	=back
3154		4945
3155	=head1 AUTHOR	4946	=head1 AUTHOR
3156		4947
3157	Marc Lehmann <libev@schmorp.de>.	4948	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
3158		4949

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