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Revision 1.309 by root, Thu Oct 21 09:23:21 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	=head1 EXAMPLE PROGRAM	9	=head2 EXAMPLE PROGRAM
10		10
		11	// a single header file is required
11	#include <ev.h>	12	#include <ev.h>
12		13
		14	#include <stdio.h> // for puts
		15
		16	// every watcher type has its own typedef'd struct
		17	// with the name ev_TYPE
13	ev_io stdin_watcher;	18	ev_io stdin_watcher;
14	ev_timer timeout_watcher;	19	ev_timer timeout_watcher;
15		20
16	/* called when data readable on stdin */	21	// all watcher callbacks have a similar signature
		22	// this callback is called when data is readable on stdin
17	static void	23	static void
18	stdin_cb (EV_P_ struct ev_io *w, int revents)	24	stdin_cb (EV_P_ ev_io *w, int revents)
19	{	25	{
20	/* puts ("stdin ready"); */	26	puts ("stdin ready");
21	ev_io_stop (EV_A_ w); /* just a syntax example */	27	// for one-shot events, one must manually stop the watcher
22	ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */	28	// with its corresponding stop function.
		29	ev_io_stop (EV_A_ w);
		30
		31	// this causes all nested ev_loop's to stop iterating
		32	ev_unloop (EV_A_ EVUNLOOP_ALL);
23	}	33	}
24		34
		35	// another callback, this time for a time-out
25	static void	36	static void
26	timeout_cb (EV_P_ struct ev_timer *w, int revents)	37	timeout_cb (EV_P_ ev_timer *w, int revents)
27	{	38	{
28	/* puts ("timeout"); */	39	puts ("timeout");
29	ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */	40	// this causes the innermost ev_loop to stop iterating
		41	ev_unloop (EV_A_ EVUNLOOP_ONE);
30	}	42	}
31		43
32	int	44	int
33	main (void)	45	main (void)
34	{	46	{
		47	// use the default event loop unless you have special needs
35	struct ev_loop *loop = ev_default_loop (0);	48	struct ev_loop *loop = ev_default_loop (0);
36		49
37	/* initialise an io watcher, then start it */	50	// initialise an io watcher, then start it
		51	// this one will watch for stdin to become readable
38	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);
39	ev_io_start (loop, &stdin_watcher);	53	ev_io_start (loop, &stdin_watcher);
40		54
		55	// initialise a timer watcher, then start it
41	/* simple non-repeating 5.5 second timeout */	56	// simple non-repeating 5.5 second timeout
42	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);	57	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
43	ev_timer_start (loop, &timeout_watcher);	58	ev_timer_start (loop, &timeout_watcher);
44		59
45	/* loop till timeout or data ready */	60	// now wait for events to arrive
46	ev_loop (loop, 0);	61	ev_loop (loop, 0);
47		62
		63	// unloop was called, so exit
48	return 0;	64	return 0;
49	}	65	}
50		66
51	=head1 DESCRIPTION	67	=head1 ABOUT THIS DOCUMENT
52		68
		69	This document documents the libev software package.
		70
53	The newest version of this document is also available as a html-formatted	71	The newest version of this document is also available as an html-formatted
54	web page you might find easier to navigate when reading it for the first	72	web page you might find easier to navigate when reading it for the first
55	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
56		84
57	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
58	file descriptor being readable or a timeout occuring), and it will manage	86	file descriptor being readable or a timeout occurring), and it will manage
59	these event sources and provide your program with events.	87	these event sources and provide your program with events.
60		88
61	To do this, it must take more or less complete control over your process	89	To do this, it must take more or less complete control over your process
62	(or thread) by executing the I<event loop> handler, and will then	90	(or thread) by executing the I<event loop> handler, and will then
63	communicate events via a callback mechanism.	91	communicate events via a callback mechanism.
…		…
65	You register interest in certain events by registering so-called I<event	93	You register interest in certain events by registering so-called I<event
66	watchers>, which are relatively small C structures you initialise with the	94	watchers>, which are relatively small C structures you initialise with the
67	details of the event, and then hand it over to libev by I<starting> the	95	details of the event, and then hand it over to libev by I<starting> the
68	watcher.	96	watcher.
69		97
70	=head1 FEATURES	98	=head2 FEATURES
71		99
72	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
73	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	101	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
74	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
75	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	103	(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
76	with customised rescheduling (C<ev_periodic>), synchronous signals	104	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative
77	(C<ev_signal>), process status change events (C<ev_child>), and event	105	timers (C<ev_timer>), absolute timers with customised rescheduling
78	watchers dealing with the event loop mechanism itself (C<ev_idle>,	106	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
79	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as	107	change events (C<ev_child>), and event watchers dealing with the event
80	file watchers (C<ev_stat>) and even limited support for fork events	108	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
81	(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>).
82		111
83	It also is quite fast (see this	112	It also is quite fast (see this
84	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
85	for example).	114	for example).
86		115
87	=head1 CONVENTIONS	116	=head2 CONVENTIONS
88		117
89	Libev is very configurable. In this manual the default configuration will	118	Libev is very configurable. In this manual the default (and most common)
90	be described, which supports multiple event loops. For more info about	119	configuration will be described, which supports multiple event loops. For
91	various configuration options please have a look at B<EMBED> section in	120	more info about various configuration options please have a look at
92	this manual. If libev was configured without support for multiple event	121	B<EMBED> section in this manual. If libev was configured without support
93	loops, then all functions taking an initial argument of name C<loop>	122	for multiple event loops, then all functions taking an initial argument of
94	(which is always of type C<struct ev_loop *>) will not have this argument.	123	name C<loop> (which is always of type C<struct ev_loop *>) will not have
		124	this argument.
95		125
96	=head1 TIME REPRESENTATION	126	=head2 TIME REPRESENTATION
97		127
98	Libev represents time as a single floating point number, representing the	128	Libev represents time as a single floating point number, representing
99	(fractional) number of seconds since the (POSIX) epoch (somewhere near	129	the (fractional) number of seconds since the (POSIX) epoch (in practise
100	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
101	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
102	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
103	it, you should treat it as such.	133	any calculations on it, you should treat it as some floating point value.
		134
		135	Unlike the name component C<stamp> might indicate, it is also used for
		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
104		158
105	=head1 GLOBAL FUNCTIONS	159	=head1 GLOBAL FUNCTIONS
106		160
107	These functions can be called anytime, even before initialising the	161	These functions can be called anytime, even before initialising the
108	library in any way.	162	library in any way.
…		…
112	=item ev_tstamp ev_time ()	166	=item ev_tstamp ev_time ()
113		167
114	Returns the current time as libev would use it. Please note that the	168	Returns the current time as libev would use it. Please note that the
115	C<ev_now> function is usually faster and also often returns the timestamp	169	C<ev_now> function is usually faster and also often returns the timestamp
116	you actually want to know.	170	you actually want to know.
		171
		172	=item ev_sleep (ev_tstamp interval)
		173
		174	Sleep for the given interval: The current thread will be blocked until
		175	either it is interrupted or the given time interval has passed. Basically
		176	this is a sub-second-resolution C<sleep ()>.
117		177
118	=item int ev_version_major ()	178	=item int ev_version_major ()
119		179
120	=item int ev_version_minor ()	180	=item int ev_version_minor ()
121		181
…		…
132	as this indicates an incompatible change. Minor versions are usually	192	as this indicates an incompatible change. Minor versions are usually
133	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
134	not a problem.	194	not a problem.
135		195
136	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
137	version.	197	version (note, however, that this will not detect ABI mismatches :).
138		198
139	assert (("libev version mismatch",	199	assert (("libev version mismatch",
140	ev_version_major () == EV_VERSION_MAJOR	200	ev_version_major () == EV_VERSION_MAJOR
141	&& ev_version_minor () >= EV_VERSION_MINOR));	201	&& ev_version_minor () >= EV_VERSION_MINOR));
142		202
143	=item unsigned int ev_supported_backends ()	203	=item unsigned int ev_supported_backends ()
144		204
145	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_*>
146	value) compiled into this binary of libev (independent of their	206	value) compiled into this binary of libev (independent of their
…		…
148	a description of the set values.	208	a description of the set values.
149		209
150	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
151	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
152		212
153	assert (("sorry, no epoll, no sex",	213	assert (("sorry, no epoll, no sex",
154	ev_supported_backends () & EVBACKEND_EPOLL));	214	ev_supported_backends () & EVBACKEND_EPOLL));
155		215
156	=item unsigned int ev_recommended_backends ()	216	=item unsigned int ev_recommended_backends ()
157		217
158	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
159	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
160	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
161	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
162	(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
163	libev will probe for if you specify no backends explicitly.	223	libev will probe for if you specify no backends explicitly.
164		224
165	=item unsigned int ev_embeddable_backends ()	225	=item unsigned int ev_embeddable_backends ()
166		226
…		…
170	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	230	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
171	recommended ones.	231	recommended ones.
172		232
173	See the description of C<ev_embed> watchers for more info.	233	See the description of C<ev_embed> watchers for more info.
174		234
175	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	235	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
176		236
177	Sets the allocation function to use (the prototype is similar - the	237	Sets the allocation function to use (the prototype is similar - the
178	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
179	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
180	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
181	potentially destructive action. The default is your system realloc	241	or take some potentially destructive action.
182	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.
183		246
184	You could override this function in high-availability programs to, say,	247	You could override this function in high-availability programs to, say,
185	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,
186	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.
187		250
188	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
189	retries).	252	retries (example requires a standards-compliant C<realloc>).
190		253
191	static void *	254	static void *
192	persistent_realloc (void *ptr, size_t size)	255	persistent_realloc (void *ptr, size_t size)
193	{	256	{
194	for (;;)	257	for (;;)
…		…
203	}	266	}
204		267
205	...	268	...
206	ev_set_allocator (persistent_realloc);	269	ev_set_allocator (persistent_realloc);
207		270
208	=item ev_set_syserr_cb (void (*cb)(const char *msg));	271	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
209		272
210	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
211	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
212	indicating the system call or subsystem causing the problem. If this	275	indicating the system call or subsystem causing the problem. If this
213	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
214	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
215	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
216	(such as abort).	279	(such as abort).
217		280
218	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.
…		…
229		292
230	=back	293	=back
231		294
232	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	295	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
233		296
234	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>
235	types of such loops, the I<default> loop, which supports signals and child	298	is I<not> optional in this case, as there is also an C<ev_loop>
236	events, and dynamically created loops which do not.	299	I<function>).
237		300
238	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
239	in your main thread (or in a separate thread) and for each thread you	302	supports signals and child events, and dynamically created loops which do
240	create, you also create another event loop. Libev itself does no locking	303	not.
241	whatsoever, so if you mix calls to the same event loop in different
242	threads, make sure you lock (this is usually a bad idea, though, even if
243	done correctly, because it's hideous and inefficient).
244		304
245	=over 4	305	=over 4
246		306
247	=item struct ev_loop *ev_default_loop (unsigned int flags)	307	=item struct ev_loop *ev_default_loop (unsigned int flags)
248		308
…		…
252	flags. If that is troubling you, check C<ev_backend ()> afterwards).	312	flags. If that is troubling you, check C<ev_backend ()> afterwards).
253		313
254	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
255	function.	315	function.
256		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
		321	The default loop is the only loop that can handle C<ev_signal> and
		322	C<ev_child> watchers, and to do this, it always registers a handler
		323	for C<SIGCHLD>. If this is a problem for your application you can either
		324	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
		325	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
		326	C<ev_default_init>.
		327
257	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
258	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	329	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
259		330
260	The following flags are supported:	331	The following flags are supported:
261		332
…		…
266	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
267	thing, believe me).	338	thing, believe me).
268		339
269	=item C<EVFLAG_NOENV>	340	=item C<EVFLAG_NOENV>
270		341
271	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
272	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
273	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	344	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
274	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
275	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
276	around bugs.	347	around bugs.
277		348
278	=item C<EVFLAG_FORKCHECK>	349	=item C<EVFLAG_FORKCHECK>
279		350
280	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
281	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.
282	enabling this flag.
283		353
284	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,
285	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
286	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
287	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
288	without a syscall and thus I<very> fast, but my Linux system also has	358	without a system call and thus I<very> fast, but my GNU/Linux system also has
289	C<pthread_atfork> which is even faster).	359	C<pthread_atfork> which is even faster).
290		360
291	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
292	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
293	flag.	363	flag.
294		364
295	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>
296	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.
297		387
298	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	388	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
299		389
300	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
301	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,
302	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
303	using this backend. It doesn't scale too well (O(highest_fd)), but its usually	393	using this backend. It doesn't scale too well (O(highest_fd)), but its
304	the fastest backend for a low number of fds.	394	usually the fastest backend for a low number of (low-numbered :) fds.
		395
		396	To get good performance out of this backend you need a high amount of
		397	parallelism (most of the file descriptors should be busy). If you are
		398	writing a server, you should C<accept ()> in a loop to accept as many
		399	connections as possible during one iteration. You might also want to have
		400	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		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).
305		406
306	=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)
307		408
308	And this is your standard poll(2) backend. It's more complicated than	409	And this is your standard poll(2) backend. It's more complicated
309	select, but handles sparse fds better and has no artificial limit on the	410	than select, but handles sparse fds better and has no artificial
310	number of fds you can use (except it will slow down considerably with a	411	limit on the number of fds you can use (except it will slow down
311	lot of inactive fds). It scales similarly to select, i.e. O(total_fds).	412	considerably with a lot of inactive fds). It scales similarly to select,
		413	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		414	performance tips.
		415
		416	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		417	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
312		418
313	=item C<EVBACKEND_EPOLL> (value 4, Linux)	419	=item C<EVBACKEND_EPOLL> (value 4, Linux)
314		420
		421	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		422	kernels).
		423
315	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,
316	but it scales phenomenally better. While poll and select usually scale like	425	but it scales phenomenally better. While poll and select usually scale
317	O(total_fds) where n is the total number of fds (or the highest fd), epoll scales	426	like O(total_fds) where n is the total number of fds (or the highest fd),
318	either O(1) or O(active_fds).	427	epoll scales either O(1) or O(active_fds).
319		428
		429	The epoll mechanism deserves honorable mention as the most misdesigned
		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...).
		447
320	While stopping and starting an I/O watcher in the same iteration will	448	While stopping, setting and starting an I/O watcher in the same iteration
321	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
322	(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
323	best to avoid that. Also, dup()ed file descriptors might not work very	451	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
324	well if you register events for both fds.	452	file descriptors might not work very well if you register events for both
		453	file descriptors.
325		454
326	Please note that epoll sometimes generates spurious notifications, so you	455	Best performance from this backend is achieved by not unregistering all
327	need to use non-blocking I/O or other means to avoid blocking when no data	456	watchers for a file descriptor until it has been closed, if possible,
328	(or space) is available.	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.
		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
		467	While nominally embeddable in other event loops, this feature is broken in
		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>.
329		472
330	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	473	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
331		474
332	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
333	was broken on all BSDs except NetBSD (usually it doesn't work with	476	was broken on all BSDs except NetBSD (usually it doesn't work reliably
334	anything but sockets and pipes, except on Darwin, where of course its	477	with anything but sockets and pipes, except on Darwin, where of course
335	completely useless). For this reason its 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
336	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
337	C<EVBACKEND_KQUEUE>).	482	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		483	system like NetBSD.
		484
		485	You still can embed kqueue into a normal poll or select backend and use it
		486	only for sockets (after having made sure that sockets work with kqueue on
		487	the target platform). See C<ev_embed> watchers for more info.
338		488
339	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
340	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
341	course). While starting and stopping an I/O watcher does not cause an	491	course). While stopping, setting and starting an I/O watcher does never
342	extra syscall as with epoll, it still adds up to four event changes per	492	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
343	incident, so its best to avoid that.	493	two event changes per incident. Support for C<fork ()> is very bad (but
		494	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		495	cases
		496
		497	This backend usually performs well under most conditions.
		498
		499	While nominally embeddable in other event loops, this doesn't work
		500	everywhere, so you might need to test for this. And since it is broken
		501	almost everywhere, you should only use it when you have a lot of sockets
		502	(for which it usually works), by embedding it into another event loop
		503	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
		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>.
344		509
345	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	510	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
346		511
347	This is not implemented yet (and might never be).	512	This is not implemented yet (and might never be, unless you send me an
		513	implementation). According to reports, C</dev/poll> only supports sockets
		514	and is not embeddable, which would limit the usefulness of this backend
		515	immensely.
348		516
349	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	517	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
350		518
351	This uses the Solaris 10 port mechanism. As with everything on Solaris,	519	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
352	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)).
353		521
354	Please note that solaris ports can result in a lot of spurious	522	Please note that Solaris event ports can deliver a lot of spurious
355	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
356	blocking when no data (or space) is available.	524	blocking when no data (or space) is available.
		525
		526	While this backend scales well, it requires one system call per active
		527	file descriptor per loop iteration. For small and medium numbers of file
		528	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		529	might perform better.
		530
		531	On the positive side, with the exception of the spurious readiness
		532	notifications, this backend actually performed fully to specification
		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>.
357		538
358	=item C<EVBACKEND_ALL>	539	=item C<EVBACKEND_ALL>
359		540
360	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
361	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
362	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	543	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
363		544
		545	It is definitely not recommended to use this flag.
		546
364	=back	547	=back
365		548
366	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,
367	backends will be tried (in the reverse order as given here). If none are	550	then only these backends will be tried (in the reverse order as listed
368	specified, most compiled-in backend will be tried, usually in reverse	551	here). If none are specified, all backends in C<ev_recommended_backends
369	order of their flag values :)	552	()> will be tried.
370		553
371	The most typical usage is like this:	554	Example: This is the most typical usage.
372		555
373	if (!ev_default_loop (0))	556	if (!ev_default_loop (0))
374	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	557	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
375		558
376	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
377	environment settings to be taken into account:	560	environment settings to be taken into account:
378		561
379	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	562	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
380		563
381	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
382	available (warning, breaks stuff, best use only with your own private	565	used if available (warning, breaks stuff, best use only with your own
383	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):
384		568
385	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	569	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
386		570
387	=item struct ev_loop *ev_loop_new (unsigned int flags)	571	=item struct ev_loop *ev_loop_new (unsigned int flags)
388		572
389	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
390	always distinct from the default loop. Unlike the default loop, it cannot	574	always distinct from the default loop.
391	handle signal and child watchers, and attempts to do so will be greeted by	575
392	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.
393		579
394	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.
395		581
396	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	582	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
397	if (!epoller)	583	if (!epoller)
398	fatal ("no epoll found here, maybe it hides under your chair");	584	fatal ("no epoll found here, maybe it hides under your chair");
399		585
400	=item ev_default_destroy ()	586	=item ev_default_destroy ()
401		587
402	Destroys the default loop again (frees all memory and kernel state	588	Destroys the default loop (frees all memory and kernel state etc.). None
403	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
404	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
405	responsibility to either stop all watchers cleanly yoursef I<before>	591	either stop all watchers cleanly yourself I<before> calling this function,
406	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
407	the easiest thing, youc na just ignore the watchers and/or C<free ()> them	593	can just ignore the watchers and/or C<free ()> them for example).
408	for example).	594
		595	Note that certain global state, such as signal state (and installed signal
		596	handlers), will not be freed by this function, and related watchers (such
		597	as signal and child watchers) would need to be stopped manually.
		598
		599	In general it is not advisable to call this function except in the
		600	rare occasion where you really need to free e.g. the signal handling
		601	pipe fds. If you need dynamically allocated loops it is better to use
		602	C<ev_loop_new> and C<ev_loop_destroy>.
409		603
410	=item ev_loop_destroy (loop)	604	=item ev_loop_destroy (loop)
411		605
412	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
413	earlier call to C<ev_loop_new>.	607	earlier call to C<ev_loop_new>.
414		608
415	=item ev_default_fork ()	609	=item ev_default_fork ()
416		610
		611	This function sets a flag that causes subsequent C<ev_loop> iterations
417	This function reinitialises the kernel state for backends that have	612	to reinitialise the kernel state for backends that have one. Despite the
418	one. Despite the name, you can call it anytime, but it makes most sense	613	name, you can call it anytime, but it makes most sense after forking, in
419	after forking, in either the parent or child process (or both, but that	614	the child process (or both child and parent, but that again makes little
420	again makes little sense).	615	sense). You I<must> call it in the child before using any of the libev
		616	functions, and it will only take effect at the next C<ev_loop> iteration.
421		617
422	You I<must> call this function in the child process after forking if and	618	Again, you I<have> to call it on I<any> loop that you want to re-use after
423	only if you want to use the event library in both processes. If you just	619	a fork, I<even if you do not plan to use the loop in the parent>. This is
424	fork+exec, you don't have to call it.	620	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		621	during fork.
		622
		623	On the other hand, you only need to call this function in the child
		624	process if and only if you want to use the event loop in the child. If you
		625	just fork+exec or create a new loop in the child, you don't have to call
		626	it at all.
425		627
426	The function itself is quite fast and it's usually not a problem to call	628	The function itself is quite fast and it's usually not a problem to call
427	it just in case after a fork. To make this easy, the function will fit in	629	it just in case after a fork. To make this easy, the function will fit in
428	quite nicely into a call to C<pthread_atfork>:	630	quite nicely into a call to C<pthread_atfork>:
429		631
430	pthread_atfork (0, 0, ev_default_fork);	632	pthread_atfork (0, 0, ev_default_fork);
431		633
432	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
433	without calling this function, so if you force one of those backends you
434	do not need to care.
435
436	=item ev_loop_fork (loop)	634	=item ev_loop_fork (loop)
437		635
438	Like C<ev_default_fork>, but acts on an event loop created by	636	Like C<ev_default_fork>, but acts on an event loop created by
439	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	637	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
440	after fork, and how you do this is entirely your own problem.	638	after fork that you want to re-use in the child, and how you keep track of
		639	them is entirely your own problem.
441		640
		641	=item int ev_is_default_loop (loop)
		642
		643	Returns true when the given loop is, in fact, the default loop, and false
		644	otherwise.
		645
442	=item unsigned int ev_loop_count (loop)	646	=item unsigned int ev_iteration (loop)
443		647
444	Returns the count of loop iterations for the loop, which is identical to	648	Returns the current iteration count for the loop, which is identical to
445	the number of times libev did poll for new events. It starts at C<0> and	649	the number of times libev did poll for new events. It starts at C<0> and
446	happily wraps around with enough iterations.	650	happily wraps around with enough iterations.
447		651
448	This value can sometimes be useful as a generation counter of sorts (it	652	This value can sometimes be useful as a generation counter of sorts (it
449	"ticks" the number of loop iterations), as it roughly corresponds with	653	"ticks" the number of loop iterations), as it roughly corresponds with
450	C<ev_prepare> and C<ev_check> calls.	654	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		655	prepare and check phases.
		656
		657	=item unsigned int ev_depth (loop)
		658
		659	Returns the number of times C<ev_loop> was entered minus the number of
		660	times C<ev_loop> was exited, in other words, the recursion depth.
		661
		662	Outside C<ev_loop>, this number is zero. In a callback, this number is
		663	C<1>, unless C<ev_loop> was invoked recursively (or from another thread),
		664	in which case it is higher.
		665
		666	Leaving C<ev_loop> abnormally (setjmp/longjmp, cancelling the thread
		667	etc.), doesn't count as "exit" - consider this as a hint to avoid such
		668	ungentleman behaviour unless it's really convenient.
451		669
452	=item unsigned int ev_backend (loop)	670	=item unsigned int ev_backend (loop)
453		671
454	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	672	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
455	use.	673	use.
…		…
458		676
459	Returns the current "event loop time", which is the time the event loop	677	Returns the current "event loop time", which is the time the event loop
460	received events and started processing them. This timestamp does not	678	received events and started processing them. This timestamp does not
461	change as long as callbacks are being processed, and this is also the base	679	change as long as callbacks are being processed, and this is also the base
462	time used for relative timers. You can treat it as the timestamp of the	680	time used for relative timers. You can treat it as the timestamp of the
463	event occuring (or more correctly, libev finding out about it).	681	event occurring (or more correctly, libev finding out about it).
		682
		683	=item ev_now_update (loop)
		684
		685	Establishes the current time by querying the kernel, updating the time
		686	returned by C<ev_now ()> in the progress. This is a costly operation and
		687	is usually done automatically within C<ev_loop ()>.
		688
		689	This function is rarely useful, but when some event callback runs for a
		690	very long time without entering the event loop, updating libev's idea of
		691	the current time is a good idea.
		692
		693	See also L<The special problem of time updates> in the C<ev_timer> section.
		694
		695	=item ev_suspend (loop)
		696
		697	=item ev_resume (loop)
		698
		699	These two functions suspend and resume a loop, for use when the loop is
		700	not used for a while and timeouts should not be processed.
		701
		702	A typical use case would be an interactive program such as a game: When
		703	the user presses C<^Z> to suspend the game and resumes it an hour later it
		704	would be best to handle timeouts as if no time had actually passed while
		705	the program was suspended. This can be achieved by calling C<ev_suspend>
		706	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		707	C<ev_resume> directly afterwards to resume timer processing.
		708
		709	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		710	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		711	will be rescheduled (that is, they will lose any events that would have
		712	occurred while suspended).
		713
		714	After calling C<ev_suspend> you B<must not> call I<any> function on the
		715	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		716	without a previous call to C<ev_suspend>.
		717
		718	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		719	event loop time (see C<ev_now_update>).
464		720
465	=item ev_loop (loop, int flags)	721	=item ev_loop (loop, int flags)
466		722
467	Finally, this is it, the event handler. This function usually is called	723	Finally, this is it, the event handler. This function usually is called
468	after you initialised all your watchers and you want to start handling	724	after you have initialised all your watchers and you want to start
469	events.	725	handling events.
470		726
471	If the flags argument is specified as C<0>, it will not return until	727	If the flags argument is specified as C<0>, it will not return until
472	either no event watchers are active anymore or C<ev_unloop> was called.	728	either no event watchers are active anymore or C<ev_unloop> was called.
473		729
474	Please note that an explicit C<ev_unloop> is usually better than	730	Please note that an explicit C<ev_unloop> is usually better than
475	relying on all watchers to be stopped when deciding when a program has	731	relying on all watchers to be stopped when deciding when a program has
476	finished (especially in interactive programs), but having a program that	732	finished (especially in interactive programs), but having a program
477	automatically loops as long as it has to and no longer by virtue of	733	that automatically loops as long as it has to and no longer by virtue
478	relying on its watchers stopping correctly is a thing of beauty.	734	of relying on its watchers stopping correctly, that is truly a thing of
		735	beauty.
479		736
480	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	737	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
481	those events and any outstanding ones, but will not block your process in	738	those events and any already outstanding ones, but will not block your
482	case there are no events and will return after one iteration of the loop.	739	process in case there are no events and will return after one iteration of
		740	the loop.
483		741
484	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	742	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
485	neccessary) and will handle those and any outstanding ones. It will block	743	necessary) and will handle those and any already outstanding ones. It
486	your process until at least one new event arrives, and will return after	744	will block your process until at least one new event arrives (which could
487	one iteration of the loop. This is useful if you are waiting for some	745	be an event internal to libev itself, so there is no guarantee that a
488	external event in conjunction with something not expressible using other	746	user-registered callback will be called), and will return after one
		747	iteration of the loop.
		748
		749	This is useful if you are waiting for some external event in conjunction
		750	with something not expressible using other libev watchers (i.e. "roll your
489	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	751	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
490	usually a better approach for this kind of thing.	752	usually a better approach for this kind of thing.
491		753
492	Here are the gory details of what C<ev_loop> does:	754	Here are the gory details of what C<ev_loop> does:
493		755
494	- Before the first iteration, call any pending watchers.	756	- Before the first iteration, call any pending watchers.
495	* If there are no active watchers (reference count is zero), return.	757	* If EVFLAG_FORKCHECK was used, check for a fork.
496	- Queue all prepare watchers and then call all outstanding watchers.	758	- If a fork was detected (by any means), queue and call all fork watchers.
		759	- Queue and call all prepare watchers.
497	- If we have been forked, recreate the kernel state.	760	- If we have been forked, detach and recreate the kernel state
		761	as to not disturb the other process.
498	- Update the kernel state with all outstanding changes.	762	- Update the kernel state with all outstanding changes.
499	- Update the "event loop time".	763	- Update the "event loop time" (ev_now ()).
500	- Calculate for how long to block.	764	- Calculate for how long to sleep or block, if at all
		765	(active idle watchers, EVLOOP_NONBLOCK or not having
		766	any active watchers at all will result in not sleeping).
		767	- Sleep if the I/O and timer collect interval say so.
501	- Block the process, waiting for any events.	768	- Block the process, waiting for any events.
502	- Queue all outstanding I/O (fd) events.	769	- Queue all outstanding I/O (fd) events.
503	- Update the "event loop time" and do time jump handling.	770	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
504	- Queue all outstanding timers.	771	- Queue all expired timers.
505	- Queue all outstanding periodics.	772	- Queue all expired periodics.
506	- If no events are pending now, queue all idle watchers.	773	- Unless any events are pending now, queue all idle watchers.
507	- Queue all check watchers.	774	- Queue all check watchers.
508	- Call all queued watchers in reverse order (i.e. check watchers first).	775	- Call all queued watchers in reverse order (i.e. check watchers first).
509	Signals and child watchers are implemented as I/O watchers, and will	776	Signals and child watchers are implemented as I/O watchers, and will
510	be handled here by queueing them when their watcher gets executed.	777	be handled here by queueing them when their watcher gets executed.
511	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	778	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
512	were used, return, otherwise continue with step *.	779	were used, or there are no active watchers, return, otherwise
		780	continue with step *.
513		781
514	Example: Queue some jobs and then loop until no events are outsanding	782	Example: Queue some jobs and then loop until no events are outstanding
515	anymore.	783	anymore.
516		784
517	... queue jobs here, make sure they register event watchers as long	785	... queue jobs here, make sure they register event watchers as long
518	... as they still have work to do (even an idle watcher will do..)	786	... as they still have work to do (even an idle watcher will do..)
519	ev_loop (my_loop, 0);	787	ev_loop (my_loop, 0);
520	... jobs done. yeah!	788	... jobs done or somebody called unloop. yeah!
521		789
522	=item ev_unloop (loop, how)	790	=item ev_unloop (loop, how)
523		791
524	Can be used to make a call to C<ev_loop> return early (but only after it	792	Can be used to make a call to C<ev_loop> return early (but only after it
525	has processed all outstanding events). The C<how> argument must be either	793	has processed all outstanding events). The C<how> argument must be either
526	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	794	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
527	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	795	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
528		796
		797	This "unloop state" will be cleared when entering C<ev_loop> again.
		798
		799	It is safe to call C<ev_unloop> from outside any C<ev_loop> calls.
		800
529	=item ev_ref (loop)	801	=item ev_ref (loop)
530		802
531	=item ev_unref (loop)	803	=item ev_unref (loop)
532		804
533	Ref/unref can be used to add or remove a reference count on the event	805	Ref/unref can be used to add or remove a reference count on the event
534	loop: Every watcher keeps one reference, and as long as the reference	806	loop: Every watcher keeps one reference, and as long as the reference
535	count is nonzero, C<ev_loop> will not return on its own. If you have	807	count is nonzero, C<ev_loop> will not return on its own.
536	a watcher you never unregister that should not keep C<ev_loop> from	808
537	returning, ev_unref() after starting, and ev_ref() before stopping it. For	809	This is useful when you have a watcher that you never intend to
		810	unregister, but that nevertheless should not keep C<ev_loop> from
		811	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		812	before stopping it.
		813
538	example, libev itself uses this for its internal signal pipe: It is not	814	As an example, libev itself uses this for its internal signal pipe: It
539	visible to the libev user and should not keep C<ev_loop> from exiting if	815	is not visible to the libev user and should not keep C<ev_loop> from
540	no event watchers registered by it are active. It is also an excellent	816	exiting if no event watchers registered by it are active. It is also an
541	way to do this for generic recurring timers or from within third-party	817	excellent way to do this for generic recurring timers or from within
542	libraries. Just remember to I<unref after start> and I<ref before stop>.	818	third-party libraries. Just remember to I<unref after start> and I<ref
		819	before stop> (but only if the watcher wasn't active before, or was active
		820	before, respectively. Note also that libev might stop watchers itself
		821	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		822	in the callback).
543		823
544	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	824	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
545	running when nothing else is active.	825	running when nothing else is active.
546		826
547	struct ev_signal exitsig;	827	ev_signal exitsig;
548	ev_signal_init (&exitsig, sig_cb, SIGINT);	828	ev_signal_init (&exitsig, sig_cb, SIGINT);
549	ev_signal_start (loop, &exitsig);	829	ev_signal_start (loop, &exitsig);
550	evf_unref (loop);	830	evf_unref (loop);
551		831
552	Example: For some weird reason, unregister the above signal handler again.	832	Example: For some weird reason, unregister the above signal handler again.
553		833
554	ev_ref (loop);	834	ev_ref (loop);
555	ev_signal_stop (loop, &exitsig);	835	ev_signal_stop (loop, &exitsig);
		836
		837	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		838
		839	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		840
		841	These advanced functions influence the time that libev will spend waiting
		842	for events. Both time intervals are by default C<0>, meaning that libev
		843	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		844	latency.
		845
		846	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		847	allows libev to delay invocation of I/O and timer/periodic callbacks
		848	to increase efficiency of loop iterations (or to increase power-saving
		849	opportunities).
		850
		851	The idea is that sometimes your program runs just fast enough to handle
		852	one (or very few) event(s) per loop iteration. While this makes the
		853	program responsive, it also wastes a lot of CPU time to poll for new
		854	events, especially with backends like C<select ()> which have a high
		855	overhead for the actual polling but can deliver many events at once.
		856
		857	By setting a higher I<io collect interval> you allow libev to spend more
		858	time collecting I/O events, so you can handle more events per iteration,
		859	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		860	C<ev_timer>) will be not affected. Setting this to a non-null value will
		861	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		862	sleep time ensures that libev will not poll for I/O events more often then
		863	once per this interval, on average.
		864
		865	Likewise, by setting a higher I<timeout collect interval> you allow libev
		866	to spend more time collecting timeouts, at the expense of increased
		867	latency/jitter/inexactness (the watcher callback will be called
		868	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		869	value will not introduce any overhead in libev.
		870
		871	Many (busy) programs can usually benefit by setting the I/O collect
		872	interval to a value near C<0.1> or so, which is often enough for
		873	interactive servers (of course not for games), likewise for timeouts. It
		874	usually doesn't make much sense to set it to a lower value than C<0.01>,
		875	as this approaches the timing granularity of most systems. Note that if
		876	you do transactions with the outside world and you can't increase the
		877	parallelity, then this setting will limit your transaction rate (if you
		878	need to poll once per transaction and the I/O collect interval is 0.01,
		879	then you can't do more than 100 transactions per second).
		880
		881	Setting the I<timeout collect interval> can improve the opportunity for
		882	saving power, as the program will "bundle" timer callback invocations that
		883	are "near" in time together, by delaying some, thus reducing the number of
		884	times the process sleeps and wakes up again. Another useful technique to
		885	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		886	they fire on, say, one-second boundaries only.
		887
		888	Example: we only need 0.1s timeout granularity, and we wish not to poll
		889	more often than 100 times per second:
		890
		891	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		892	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		893
		894	=item ev_invoke_pending (loop)
		895
		896	This call will simply invoke all pending watchers while resetting their
		897	pending state. Normally, C<ev_loop> does this automatically when required,
		898	but when overriding the invoke callback this call comes handy.
		899
		900	=item int ev_pending_count (loop)
		901
		902	Returns the number of pending watchers - zero indicates that no watchers
		903	are pending.
		904
		905	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		906
		907	This overrides the invoke pending functionality of the loop: Instead of
		908	invoking all pending watchers when there are any, C<ev_loop> will call
		909	this callback instead. This is useful, for example, when you want to
		910	invoke the actual watchers inside another context (another thread etc.).
		911
		912	If you want to reset the callback, use C<ev_invoke_pending> as new
		913	callback.
		914
		915	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		916
		917	Sometimes you want to share the same loop between multiple threads. This
		918	can be done relatively simply by putting mutex_lock/unlock calls around
		919	each call to a libev function.
		920
		921	However, C<ev_loop> can run an indefinite time, so it is not feasible to
		922	wait for it to return. One way around this is to wake up the loop via
		923	C<ev_unloop> and C<av_async_send>, another way is to set these I<release>
		924	and I<acquire> callbacks on the loop.
		925
		926	When set, then C<release> will be called just before the thread is
		927	suspended waiting for new events, and C<acquire> is called just
		928	afterwards.
		929
		930	Ideally, C<release> will just call your mutex_unlock function, and
		931	C<acquire> will just call the mutex_lock function again.
		932
		933	While event loop modifications are allowed between invocations of
		934	C<release> and C<acquire> (that's their only purpose after all), no
		935	modifications done will affect the event loop, i.e. adding watchers will
		936	have no effect on the set of file descriptors being watched, or the time
		937	waited. Use an C<ev_async> watcher to wake up C<ev_loop> when you want it
		938	to take note of any changes you made.
		939
		940	In theory, threads executing C<ev_loop> will be async-cancel safe between
		941	invocations of C<release> and C<acquire>.
		942
		943	See also the locking example in the C<THREADS> section later in this
		944	document.
		945
		946	=item ev_set_userdata (loop, void *data)
		947
		948	=item ev_userdata (loop)
		949
		950	Set and retrieve a single C<void *> associated with a loop. When
		951	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		952	C<0.>
		953
		954	These two functions can be used to associate arbitrary data with a loop,
		955	and are intended solely for the C<invoke_pending_cb>, C<release> and
		956	C<acquire> callbacks described above, but of course can be (ab-)used for
		957	any other purpose as well.
		958
		959	=item ev_verify (loop)
		960
		961	This function only does something when C<EV_VERIFY> support has been
		962	compiled in, which is the default for non-minimal builds. It tries to go
		963	through all internal structures and checks them for validity. If anything
		964	is found to be inconsistent, it will print an error message to standard
		965	error and call C<abort ()>.
		966
		967	This can be used to catch bugs inside libev itself: under normal
		968	circumstances, this function will never abort as of course libev keeps its
		969	data structures consistent.
556		970
557	=back	971	=back
558		972
559		973
560	=head1 ANATOMY OF A WATCHER	974	=head1 ANATOMY OF A WATCHER
		975
		976	In the following description, uppercase C<TYPE> in names stands for the
		977	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		978	watchers and C<ev_io_start> for I/O watchers.
561		979
562	A watcher is a structure that you create and register to record your	980	A watcher is a structure that you create and register to record your
563	interest in some event. For instance, if you want to wait for STDIN to	981	interest in some event. For instance, if you want to wait for STDIN to
564	become readable, you would create an C<ev_io> watcher for that:	982	become readable, you would create an C<ev_io> watcher for that:
565		983
566	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	984	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
567	{	985	{
568	ev_io_stop (w);	986	ev_io_stop (w);
569	ev_unloop (loop, EVUNLOOP_ALL);	987	ev_unloop (loop, EVUNLOOP_ALL);
570	}	988	}
571		989
572	struct ev_loop *loop = ev_default_loop (0);	990	struct ev_loop *loop = ev_default_loop (0);
		991
573	struct ev_io stdin_watcher;	992	ev_io stdin_watcher;
		993
574	ev_init (&stdin_watcher, my_cb);	994	ev_init (&stdin_watcher, my_cb);
575	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	995	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
576	ev_io_start (loop, &stdin_watcher);	996	ev_io_start (loop, &stdin_watcher);
		997
577	ev_loop (loop, 0);	998	ev_loop (loop, 0);
578		999
579	As you can see, you are responsible for allocating the memory for your	1000	As you can see, you are responsible for allocating the memory for your
580	watcher structures (and it is usually a bad idea to do this on the stack,	1001	watcher structures (and it is I<usually> a bad idea to do this on the
581	although this can sometimes be quite valid).	1002	stack).
		1003
		1004	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1005	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
582		1006
583	Each watcher structure must be initialised by a call to C<ev_init	1007	Each watcher structure must be initialised by a call to C<ev_init
584	(watcher *, callback)>, which expects a callback to be provided. This	1008	(watcher *, callback)>, which expects a callback to be provided. This
585	callback gets invoked each time the event occurs (or, in the case of io	1009	callback gets invoked each time the event occurs (or, in the case of I/O
586	watchers, each time the event loop detects that the file descriptor given	1010	watchers, each time the event loop detects that the file descriptor given
587	is readable and/or writable).	1011	is readable and/or writable).
588		1012
589	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1013	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
590	with arguments specific to this watcher type. There is also a macro	1014	macro to configure it, with arguments specific to the watcher type. There
591	to combine initialisation and setting in one call: C<< ev_<type>_init	1015	is also a macro to combine initialisation and setting in one call: C<<
592	(watcher *, callback, ...) >>.	1016	ev_TYPE_init (watcher *, callback, ...) >>.
593		1017
594	To make the watcher actually watch out for events, you have to start it	1018	To make the watcher actually watch out for events, you have to start it
595	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1019	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
596	*) >>), and you can stop watching for events at any time by calling the	1020	*) >>), and you can stop watching for events at any time by calling the
597	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1021	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
598		1022
599	As long as your watcher is active (has been started but not stopped) you	1023	As long as your watcher is active (has been started but not stopped) you
600	must not touch the values stored in it. Most specifically you must never	1024	must not touch the values stored in it. Most specifically you must never
601	reinitialise it or call its C<set> macro.	1025	reinitialise it or call its C<ev_TYPE_set> macro.
602		1026
603	Each and every callback receives the event loop pointer as first, the	1027	Each and every callback receives the event loop pointer as first, the
604	registered watcher structure as second, and a bitset of received events as	1028	registered watcher structure as second, and a bitset of received events as
605	third argument.	1029	third argument.
606		1030
…		…
615	=item C<EV_WRITE>	1039	=item C<EV_WRITE>
616		1040
617	The file descriptor in the C<ev_io> watcher has become readable and/or	1041	The file descriptor in the C<ev_io> watcher has become readable and/or
618	writable.	1042	writable.
619		1043
620	=item C<EV_TIMEOUT>	1044	=item C<EV_TIMER>
621		1045
622	The C<ev_timer> watcher has timed out.	1046	The C<ev_timer> watcher has timed out.
623		1047
624	=item C<EV_PERIODIC>	1048	=item C<EV_PERIODIC>
625		1049
…		…
660	=item C<EV_FORK>	1084	=item C<EV_FORK>
661		1085
662	The event loop has been resumed in the child process after fork (see	1086	The event loop has been resumed in the child process after fork (see
663	C<ev_fork>).	1087	C<ev_fork>).
664		1088
		1089	=item C<EV_ASYNC>
		1090
		1091	The given async watcher has been asynchronously notified (see C<ev_async>).
		1092
		1093	=item C<EV_CUSTOM>
		1094
		1095	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1096	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1097
665	=item C<EV_ERROR>	1098	=item C<EV_ERROR>
666		1099
667	An unspecified error has occured, the watcher has been stopped. This might	1100	An unspecified error has occurred, the watcher has been stopped. This might
668	happen because the watcher could not be properly started because libev	1101	happen because the watcher could not be properly started because libev
669	ran out of memory, a file descriptor was found to be closed or any other	1102	ran out of memory, a file descriptor was found to be closed or any other
		1103	problem. Libev considers these application bugs.
		1104
670	problem. You best act on it by reporting the problem and somehow coping	1105	You best act on it by reporting the problem and somehow coping with the
671	with the watcher being stopped.	1106	watcher being stopped. Note that well-written programs should not receive
		1107	an error ever, so when your watcher receives it, this usually indicates a
		1108	bug in your program.
672		1109
673	Libev will usually signal a few "dummy" events together with an error,	1110	Libev will usually signal a few "dummy" events together with an error, for
674	for example it might indicate that a fd is readable or writable, and if	1111	example it might indicate that a fd is readable or writable, and if your
675	your callbacks is well-written it can just attempt the operation and cope	1112	callbacks is well-written it can just attempt the operation and cope with
676	with the error from read() or write(). This will not work in multithreaded	1113	the error from read() or write(). This will not work in multi-threaded
677	programs, though, so beware.	1114	programs, though, as the fd could already be closed and reused for another
		1115	thing, so beware.
678		1116
679	=back	1117	=back
680		1118
681	=head2 GENERIC WATCHER FUNCTIONS	1119	=head2 GENERIC WATCHER FUNCTIONS
682
683	In the following description, C<TYPE> stands for the watcher type,
684	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
685		1120
686	=over 4	1121	=over 4
687		1122
688	=item C<ev_init> (ev_TYPE *watcher, callback)	1123	=item C<ev_init> (ev_TYPE *watcher, callback)
689		1124
…		…
695	which rolls both calls into one.	1130	which rolls both calls into one.
696		1131
697	You can reinitialise a watcher at any time as long as it has been stopped	1132	You can reinitialise a watcher at any time as long as it has been stopped
698	(or never started) and there are no pending events outstanding.	1133	(or never started) and there are no pending events outstanding.
699		1134
700	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1135	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
701	int revents)>.	1136	int revents)>.
702		1137
		1138	Example: Initialise an C<ev_io> watcher in two steps.
		1139
		1140	ev_io w;
		1141	ev_init (&w, my_cb);
		1142	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1143
703	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1144	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
704		1145
705	This macro initialises the type-specific parts of a watcher. You need to	1146	This macro initialises the type-specific parts of a watcher. You need to
706	call C<ev_init> at least once before you call this macro, but you can	1147	call C<ev_init> at least once before you call this macro, but you can
707	call C<ev_TYPE_set> any number of times. You must not, however, call this	1148	call C<ev_TYPE_set> any number of times. You must not, however, call this
708	macro on a watcher that is active (it can be pending, however, which is a	1149	macro on a watcher that is active (it can be pending, however, which is a
709	difference to the C<ev_init> macro).	1150	difference to the C<ev_init> macro).
710		1151
711	Although some watcher types do not have type-specific arguments	1152	Although some watcher types do not have type-specific arguments
712	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1153	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
713		1154
		1155	See C<ev_init>, above, for an example.
		1156
714	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1157	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
715		1158
716	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1159	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
717	calls into a single call. This is the most convinient method to initialise	1160	calls into a single call. This is the most convenient method to initialise
718	a watcher. The same limitations apply, of course.	1161	a watcher. The same limitations apply, of course.
719		1162
		1163	Example: Initialise and set an C<ev_io> watcher in one step.
		1164
		1165	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1166
720	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1167	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
721		1168
722	Starts (activates) the given watcher. Only active watchers will receive	1169	Starts (activates) the given watcher. Only active watchers will receive
723	events. If the watcher is already active nothing will happen.	1170	events. If the watcher is already active nothing will happen.
724		1171
		1172	Example: Start the C<ev_io> watcher that is being abused as example in this
		1173	whole section.
		1174
		1175	ev_io_start (EV_DEFAULT_UC, &w);
		1176
725	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1177	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
726		1178
727	Stops the given watcher again (if active) and clears the pending	1179	Stops the given watcher if active, and clears the pending status (whether
		1180	the watcher was active or not).
		1181
728	status. It is possible that stopped watchers are pending (for example,	1182	It is possible that stopped watchers are pending - for example,
729	non-repeating timers are being stopped when they become pending), but	1183	non-repeating timers are being stopped when they become pending - but
730	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1184	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
731	you want to free or reuse the memory used by the watcher it is therefore a	1185	pending. If you want to free or reuse the memory used by the watcher it is
732	good idea to always call its C<ev_TYPE_stop> function.	1186	therefore a good idea to always call its C<ev_TYPE_stop> function.
733		1187
734	=item bool ev_is_active (ev_TYPE *watcher)	1188	=item bool ev_is_active (ev_TYPE *watcher)
735		1189
736	Returns a true value iff the watcher is active (i.e. it has been started	1190	Returns a true value iff the watcher is active (i.e. it has been started
737	and not yet been stopped). As long as a watcher is active you must not modify	1191	and not yet been stopped). As long as a watcher is active you must not modify
…		…
753	=item ev_cb_set (ev_TYPE *watcher, callback)	1207	=item ev_cb_set (ev_TYPE *watcher, callback)
754		1208
755	Change the callback. You can change the callback at virtually any time	1209	Change the callback. You can change the callback at virtually any time
756	(modulo threads).	1210	(modulo threads).
757		1211
758	=item ev_set_priority (ev_TYPE *watcher, priority)	1212	=item ev_set_priority (ev_TYPE *watcher, int priority)
759		1213
760	=item int ev_priority (ev_TYPE *watcher)	1214	=item int ev_priority (ev_TYPE *watcher)
761		1215
762	Set and query the priority of the watcher. The priority is a small	1216	Set and query the priority of the watcher. The priority is a small
763	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1217	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
764	(default: C<-2>). Pending watchers with higher priority will be invoked	1218	(default: C<-2>). Pending watchers with higher priority will be invoked
765	before watchers with lower priority, but priority will not keep watchers	1219	before watchers with lower priority, but priority will not keep watchers
766	from being executed (except for C<ev_idle> watchers).	1220	from being executed (except for C<ev_idle> watchers).
767		1221
768	This means that priorities are I<only> used for ordering callback
769	invocation after new events have been received. This is useful, for
770	example, to reduce latency after idling, or more often, to bind two
771	watchers on the same event and make sure one is called first.
772
773	If you need to suppress invocation when higher priority events are pending	1222	If you need to suppress invocation when higher priority events are pending
774	you need to look at C<ev_idle> watchers, which provide this functionality.	1223	you need to look at C<ev_idle> watchers, which provide this functionality.
775		1224
776	You I<must not> change the priority of a watcher as long as it is active or	1225	You I<must not> change the priority of a watcher as long as it is active or
777	pending.	1226	pending.
778		1227
		1228	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1229	fine, as long as you do not mind that the priority value you query might
		1230	or might not have been clamped to the valid range.
		1231
779	The default priority used by watchers when no priority has been set is	1232	The default priority used by watchers when no priority has been set is
780	always C<0>, which is supposed to not be too high and not be too low :).	1233	always C<0>, which is supposed to not be too high and not be too low :).
781		1234
782	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1235	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
783	fine, as long as you do not mind that the priority value you query might	1236	priorities.
784	or might not have been adjusted to be within valid range.
785		1237
786	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1238	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
787		1239
788	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1240	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
789	C<loop> nor C<revents> need to be valid as long as the watcher callback	1241	C<loop> nor C<revents> need to be valid as long as the watcher callback
790	can deal with that fact.	1242	can deal with that fact, as both are simply passed through to the
		1243	callback.
791		1244
792	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1245	=item int ev_clear_pending (loop, ev_TYPE *watcher)
793		1246
794	If the watcher is pending, this function returns clears its pending status	1247	If the watcher is pending, this function clears its pending status and
795	and returns its C<revents> bitset (as if its callback was invoked). If the	1248	returns its C<revents> bitset (as if its callback was invoked). If the
796	watcher isn't pending it does nothing and returns C<0>.	1249	watcher isn't pending it does nothing and returns C<0>.
797		1250
		1251	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1252	callback to be invoked, which can be accomplished with this function.
		1253
		1254	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1255
		1256	Feeds the given event set into the event loop, as if the specified event
		1257	had happened for the specified watcher (which must be a pointer to an
		1258	initialised but not necessarily started event watcher). Obviously you must
		1259	not free the watcher as long as it has pending events.
		1260
		1261	Stopping the watcher, letting libev invoke it, or calling
		1262	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1263	not started in the first place.
		1264
		1265	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1266	functions that do not need a watcher.
		1267
798	=back	1268	=back
799		1269
800		1270
801	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1271	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
802		1272
803	Each watcher has, by default, a member C<void *data> that you can change	1273	Each watcher has, by default, a member C<void *data> that you can change
804	and read at any time, libev will completely ignore it. This can be used	1274	and read at any time: libev will completely ignore it. This can be used
805	to associate arbitrary data with your watcher. If you need more data and	1275	to associate arbitrary data with your watcher. If you need more data and
806	don't want to allocate memory and store a pointer to it in that data	1276	don't want to allocate memory and store a pointer to it in that data
807	member, you can also "subclass" the watcher type and provide your own	1277	member, you can also "subclass" the watcher type and provide your own
808	data:	1278	data:
809		1279
810	struct my_io	1280	struct my_io
811	{	1281	{
812	struct ev_io io;	1282	ev_io io;
813	int otherfd;	1283	int otherfd;
814	void *somedata;	1284	void *somedata;
815	struct whatever *mostinteresting;	1285	struct whatever *mostinteresting;
816	}	1286	};
		1287
		1288	...
		1289	struct my_io w;
		1290	ev_io_init (&w.io, my_cb, fd, EV_READ);
817		1291
818	And since your callback will be called with a pointer to the watcher, you	1292	And since your callback will be called with a pointer to the watcher, you
819	can cast it back to your own type:	1293	can cast it back to your own type:
820		1294
821	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1295	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
822	{	1296	{
823	struct my_io *w = (struct my_io *)w_;	1297	struct my_io *w = (struct my_io *)w_;
824	...	1298	...
825	}	1299	}
826		1300
827	More interesting and less C-conformant ways of casting your callback type	1301	More interesting and less C-conformant ways of casting your callback type
828	instead have been omitted.	1302	instead have been omitted.
829		1303
830	Another common scenario is having some data structure with multiple	1304	Another common scenario is to use some data structure with multiple
831	watchers:	1305	embedded watchers:
832		1306
833	struct my_biggy	1307	struct my_biggy
834	{	1308	{
835	int some_data;	1309	int some_data;
836	ev_timer t1;	1310	ev_timer t1;
837	ev_timer t2;	1311	ev_timer t2;
838	}	1312	}
839		1313
840	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1314	In this case getting the pointer to C<my_biggy> is a bit more
841	you need to use C<offsetof>:	1315	complicated: Either you store the address of your C<my_biggy> struct
		1316	in the C<data> member of the watcher (for woozies), or you need to use
		1317	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1318	programmers):
842		1319
843	#include <stddef.h>	1320	#include <stddef.h>
844		1321
845	static void	1322	static void
846	t1_cb (EV_P_ struct ev_timer *w, int revents)	1323	t1_cb (EV_P_ ev_timer *w, int revents)
847	{	1324	{
848	struct my_biggy big = (struct my_biggy *	1325	struct my_biggy big = (struct my_biggy *)
849	(((char *)w) - offsetof (struct my_biggy, t1));	1326	(((char *)w) - offsetof (struct my_biggy, t1));
850	}	1327	}
851		1328
852	static void	1329	static void
853	t2_cb (EV_P_ struct ev_timer *w, int revents)	1330	t2_cb (EV_P_ ev_timer *w, int revents)
854	{	1331	{
855	struct my_biggy big = (struct my_biggy *	1332	struct my_biggy big = (struct my_biggy *)
856	(((char *)w) - offsetof (struct my_biggy, t2));	1333	(((char *)w) - offsetof (struct my_biggy, t2));
857	}	1334	}
		1335
		1336	=head2 WATCHER PRIORITY MODELS
		1337
		1338	Many event loops support I<watcher priorities>, which are usually small
		1339	integers that influence the ordering of event callback invocation
		1340	between watchers in some way, all else being equal.
		1341
		1342	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1343	description for the more technical details such as the actual priority
		1344	range.
		1345
		1346	There are two common ways how these these priorities are being interpreted
		1347	by event loops:
		1348
		1349	In the more common lock-out model, higher priorities "lock out" invocation
		1350	of lower priority watchers, which means as long as higher priority
		1351	watchers receive events, lower priority watchers are not being invoked.
		1352
		1353	The less common only-for-ordering model uses priorities solely to order
		1354	callback invocation within a single event loop iteration: Higher priority
		1355	watchers are invoked before lower priority ones, but they all get invoked
		1356	before polling for new events.
		1357
		1358	Libev uses the second (only-for-ordering) model for all its watchers
		1359	except for idle watchers (which use the lock-out model).
		1360
		1361	The rationale behind this is that implementing the lock-out model for
		1362	watchers is not well supported by most kernel interfaces, and most event
		1363	libraries will just poll for the same events again and again as long as
		1364	their callbacks have not been executed, which is very inefficient in the
		1365	common case of one high-priority watcher locking out a mass of lower
		1366	priority ones.
		1367
		1368	Static (ordering) priorities are most useful when you have two or more
		1369	watchers handling the same resource: a typical usage example is having an
		1370	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1371	timeouts. Under load, data might be received while the program handles
		1372	other jobs, but since timers normally get invoked first, the timeout
		1373	handler will be executed before checking for data. In that case, giving
		1374	the timer a lower priority than the I/O watcher ensures that I/O will be
		1375	handled first even under adverse conditions (which is usually, but not
		1376	always, what you want).
		1377
		1378	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1379	will only be executed when no same or higher priority watchers have
		1380	received events, they can be used to implement the "lock-out" model when
		1381	required.
		1382
		1383	For example, to emulate how many other event libraries handle priorities,
		1384	you can associate an C<ev_idle> watcher to each such watcher, and in
		1385	the normal watcher callback, you just start the idle watcher. The real
		1386	processing is done in the idle watcher callback. This causes libev to
		1387	continuously poll and process kernel event data for the watcher, but when
		1388	the lock-out case is known to be rare (which in turn is rare :), this is
		1389	workable.
		1390
		1391	Usually, however, the lock-out model implemented that way will perform
		1392	miserably under the type of load it was designed to handle. In that case,
		1393	it might be preferable to stop the real watcher before starting the
		1394	idle watcher, so the kernel will not have to process the event in case
		1395	the actual processing will be delayed for considerable time.
		1396
		1397	Here is an example of an I/O watcher that should run at a strictly lower
		1398	priority than the default, and which should only process data when no
		1399	other events are pending:
		1400
		1401	ev_idle idle; // actual processing watcher
		1402	ev_io io; // actual event watcher
		1403
		1404	static void
		1405	io_cb (EV_P_ ev_io *w, int revents)
		1406	{
		1407	// stop the I/O watcher, we received the event, but
		1408	// are not yet ready to handle it.
		1409	ev_io_stop (EV_A_ w);
		1410
		1411	// start the idle watcher to handle the actual event.
		1412	// it will not be executed as long as other watchers
		1413	// with the default priority are receiving events.
		1414	ev_idle_start (EV_A_ &idle);
		1415	}
		1416
		1417	static void
		1418	idle_cb (EV_P_ ev_idle *w, int revents)
		1419	{
		1420	// actual processing
		1421	read (STDIN_FILENO, ...);
		1422
		1423	// have to start the I/O watcher again, as
		1424	// we have handled the event
		1425	ev_io_start (EV_P_ &io);
		1426	}
		1427
		1428	// initialisation
		1429	ev_idle_init (&idle, idle_cb);
		1430	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1431	ev_io_start (EV_DEFAULT_ &io);
		1432
		1433	In the "real" world, it might also be beneficial to start a timer, so that
		1434	low-priority connections can not be locked out forever under load. This
		1435	enables your program to keep a lower latency for important connections
		1436	during short periods of high load, while not completely locking out less
		1437	important ones.
858		1438
859		1439
860	=head1 WATCHER TYPES	1440	=head1 WATCHER TYPES
861		1441
862	This section describes each watcher in detail, but will not repeat	1442	This section describes each watcher in detail, but will not repeat
…		…
886	In general you can register as many read and/or write event watchers per	1466	In general you can register as many read and/or write event watchers per
887	fd as you want (as long as you don't confuse yourself). Setting all file	1467	fd as you want (as long as you don't confuse yourself). Setting all file
888	descriptors to non-blocking mode is also usually a good idea (but not	1468	descriptors to non-blocking mode is also usually a good idea (but not
889	required if you know what you are doing).	1469	required if you know what you are doing).
890		1470
891	You have to be careful with dup'ed file descriptors, though. Some backends	1471	If you cannot use non-blocking mode, then force the use of a
892	(the linux epoll backend is a notable example) cannot handle dup'ed file	1472	known-to-be-good backend (at the time of this writing, this includes only
893	descriptors correctly if you register interest in two or more fds pointing	1473	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
894	to the same underlying file/socket/etc. description (that is, they share	1474	descriptors for which non-blocking operation makes no sense (such as
895	the same underlying "file open").	1475	files) - libev doesn't guarantee any specific behaviour in that case.
896
897	If you must do this, then force the use of a known-to-be-good backend
898	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
899	C<EVBACKEND_POLL>).
900		1476
901	Another thing you have to watch out for is that it is quite easy to	1477	Another thing you have to watch out for is that it is quite easy to
902	receive "spurious" readyness notifications, that is your callback might	1478	receive "spurious" readiness notifications, that is your callback might
903	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1479	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
904	because there is no data. Not only are some backends known to create a	1480	because there is no data. Not only are some backends known to create a
905	lot of those (for example solaris ports), it is very easy to get into	1481	lot of those (for example Solaris ports), it is very easy to get into
906	this situation even with a relatively standard program structure. Thus	1482	this situation even with a relatively standard program structure. Thus
907	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1483	it is best to always use non-blocking I/O: An extra C<read>(2) returning
908	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1484	C<EAGAIN> is far preferable to a program hanging until some data arrives.
909		1485
910	If you cannot run the fd in non-blocking mode (for example you should not	1486	If you cannot run the fd in non-blocking mode (for example you should
911	play around with an Xlib connection), then you have to seperately re-test	1487	not play around with an Xlib connection), then you have to separately
912	whether a file descriptor is really ready with a known-to-be good interface	1488	re-test whether a file descriptor is really ready with a known-to-be good
913	such as poll (fortunately in our Xlib example, Xlib already does this on	1489	interface such as poll (fortunately in our Xlib example, Xlib already
914	its own, so its quite safe to use).	1490	does this on its own, so its quite safe to use). Some people additionally
		1491	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1492	indefinitely.
		1493
		1494	But really, best use non-blocking mode.
915		1495
916	=head3 The special problem of disappearing file descriptors	1496	=head3 The special problem of disappearing file descriptors
917		1497
918	Some backends (e.g kqueue, epoll) need to be told about closing a file	1498	Some backends (e.g. kqueue, epoll) need to be told about closing a file
919	descriptor (either by calling C<close> explicitly or by any other means,	1499	descriptor (either due to calling C<close> explicitly or any other means,
920	such as C<dup>). The reason is that you register interest in some file	1500	such as C<dup2>). The reason is that you register interest in some file
921	descriptor, but when it goes away, the operating system will silently drop	1501	descriptor, but when it goes away, the operating system will silently drop
922	this interest. If another file descriptor with the same number then is	1502	this interest. If another file descriptor with the same number then is
923	registered with libev, there is no efficient way to see that this is, in	1503	registered with libev, there is no efficient way to see that this is, in
924	fact, a different file descriptor.	1504	fact, a different file descriptor.
925		1505
…		…
932		1512
933	This is how one would do it normally anyway, the important point is that	1513	This is how one would do it normally anyway, the important point is that
934	the libev application should not optimise around libev but should leave	1514	the libev application should not optimise around libev but should leave
935	optimisations to libev.	1515	optimisations to libev.
936		1516
		1517	=head3 The special problem of dup'ed file descriptors
		1518
		1519	Some backends (e.g. epoll), cannot register events for file descriptors,
		1520	but only events for the underlying file descriptions. That means when you
		1521	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1522	events for them, only one file descriptor might actually receive events.
		1523
		1524	There is no workaround possible except not registering events
		1525	for potentially C<dup ()>'ed file descriptors, or to resort to
		1526	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1527
		1528	=head3 The special problem of fork
		1529
		1530	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1531	useless behaviour. Libev fully supports fork, but needs to be told about
		1532	it in the child.
		1533
		1534	To support fork in your programs, you either have to call
		1535	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1536	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1537	C<EVBACKEND_POLL>.
		1538
		1539	=head3 The special problem of SIGPIPE
		1540
		1541	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1542	when writing to a pipe whose other end has been closed, your program gets
		1543	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1544	this is sensible behaviour, for daemons, this is usually undesirable.
		1545
		1546	So when you encounter spurious, unexplained daemon exits, make sure you
		1547	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1548	somewhere, as that would have given you a big clue).
		1549
		1550	=head3 The special problem of accept()ing when you can't
		1551
		1552	Many implementations of the POSIX C<accept> function (for example,
		1553	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1554	connection from the pending queue in all error cases.
		1555
		1556	For example, larger servers often run out of file descriptors (because
		1557	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1558	rejecting the connection, leading to libev signalling readiness on
		1559	the next iteration again (the connection still exists after all), and
		1560	typically causing the program to loop at 100% CPU usage.
		1561
		1562	Unfortunately, the set of errors that cause this issue differs between
		1563	operating systems, there is usually little the app can do to remedy the
		1564	situation, and no known thread-safe method of removing the connection to
		1565	cope with overload is known (to me).
		1566
		1567	One of the easiest ways to handle this situation is to just ignore it
		1568	- when the program encounters an overload, it will just loop until the
		1569	situation is over. While this is a form of busy waiting, no OS offers an
		1570	event-based way to handle this situation, so it's the best one can do.
		1571
		1572	A better way to handle the situation is to log any errors other than
		1573	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1574	messages, and continue as usual, which at least gives the user an idea of
		1575	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1576	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1577	usage.
		1578
		1579	If your program is single-threaded, then you could also keep a dummy file
		1580	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1581	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1582	close that fd, and create a new dummy fd. This will gracefully refuse
		1583	clients under typical overload conditions.
		1584
		1585	The last way to handle it is to simply log the error and C<exit>, as
		1586	is often done with C<malloc> failures, but this results in an easy
		1587	opportunity for a DoS attack.
937		1588
938	=head3 Watcher-Specific Functions	1589	=head3 Watcher-Specific Functions
939		1590
940	=over 4	1591	=over 4
941		1592
942	=item ev_io_init (ev_io *, callback, int fd, int events)	1593	=item ev_io_init (ev_io *, callback, int fd, int events)
943		1594
944	=item ev_io_set (ev_io *, int fd, int events)	1595	=item ev_io_set (ev_io *, int fd, int events)
945		1596
946	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1597	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
947	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1598	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
948	C<EV_READ | EV_WRITE> to receive the given events.	1599	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
949		1600
950	=item int fd [read-only]	1601	=item int fd [read-only]
951		1602
952	The file descriptor being watched.	1603	The file descriptor being watched.
953		1604
954	=item int events [read-only]	1605	=item int events [read-only]
955		1606
956	The events being watched.	1607	The events being watched.
957		1608
958	=back	1609	=back
		1610
		1611	=head3 Examples
959		1612
960	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1613	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
961	readable, but only once. Since it is likely line-buffered, you could	1614	readable, but only once. Since it is likely line-buffered, you could
962	attempt to read a whole line in the callback.	1615	attempt to read a whole line in the callback.
963		1616
964	static void	1617	static void
965	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1618	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
966	{	1619	{
967	ev_io_stop (loop, w);	1620	ev_io_stop (loop, w);
968	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1621	.. read from stdin here (or from w->fd) and handle any I/O errors
969	}	1622	}
970		1623
971	...	1624	...
972	struct ev_loop *loop = ev_default_init (0);	1625	struct ev_loop *loop = ev_default_init (0);
973	struct ev_io stdin_readable;	1626	ev_io stdin_readable;
974	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1627	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
975	ev_io_start (loop, &stdin_readable);	1628	ev_io_start (loop, &stdin_readable);
976	ev_loop (loop, 0);	1629	ev_loop (loop, 0);
977		1630
978		1631
979	=head2 C<ev_timer> - relative and optionally repeating timeouts	1632	=head2 C<ev_timer> - relative and optionally repeating timeouts
980		1633
981	Timer watchers are simple relative timers that generate an event after a	1634	Timer watchers are simple relative timers that generate an event after a
982	given time, and optionally repeating in regular intervals after that.	1635	given time, and optionally repeating in regular intervals after that.
983		1636
984	The timers are based on real time, that is, if you register an event that	1637	The timers are based on real time, that is, if you register an event that
985	times out after an hour and you reset your system clock to last years	1638	times out after an hour and you reset your system clock to January last
986	time, it will still time out after (roughly) and hour. "Roughly" because	1639	year, it will still time out after (roughly) one hour. "Roughly" because
987	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1640	detecting time jumps is hard, and some inaccuracies are unavoidable (the
988	monotonic clock option helps a lot here).	1641	monotonic clock option helps a lot here).
		1642
		1643	The callback is guaranteed to be invoked only I<after> its timeout has
		1644	passed (not I<at>, so on systems with very low-resolution clocks this
		1645	might introduce a small delay). If multiple timers become ready during the
		1646	same loop iteration then the ones with earlier time-out values are invoked
		1647	before ones of the same priority with later time-out values (but this is
		1648	no longer true when a callback calls C<ev_loop> recursively).
		1649
		1650	=head3 Be smart about timeouts
		1651
		1652	Many real-world problems involve some kind of timeout, usually for error
		1653	recovery. A typical example is an HTTP request - if the other side hangs,
		1654	you want to raise some error after a while.
		1655
		1656	What follows are some ways to handle this problem, from obvious and
		1657	inefficient to smart and efficient.
		1658
		1659	In the following, a 60 second activity timeout is assumed - a timeout that
		1660	gets reset to 60 seconds each time there is activity (e.g. each time some
		1661	data or other life sign was received).
		1662
		1663	=over 4
		1664
		1665	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1666
		1667	This is the most obvious, but not the most simple way: In the beginning,
		1668	start the watcher:
		1669
		1670	ev_timer_init (timer, callback, 60., 0.);
		1671	ev_timer_start (loop, timer);
		1672
		1673	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1674	and start it again:
		1675
		1676	ev_timer_stop (loop, timer);
		1677	ev_timer_set (timer, 60., 0.);
		1678	ev_timer_start (loop, timer);
		1679
		1680	This is relatively simple to implement, but means that each time there is
		1681	some activity, libev will first have to remove the timer from its internal
		1682	data structure and then add it again. Libev tries to be fast, but it's
		1683	still not a constant-time operation.
		1684
		1685	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1686
		1687	This is the easiest way, and involves using C<ev_timer_again> instead of
		1688	C<ev_timer_start>.
		1689
		1690	To implement this, configure an C<ev_timer> with a C<repeat> value
		1691	of C<60> and then call C<ev_timer_again> at start and each time you
		1692	successfully read or write some data. If you go into an idle state where
		1693	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1694	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1695
		1696	That means you can ignore both the C<ev_timer_start> function and the
		1697	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1698	member and C<ev_timer_again>.
		1699
		1700	At start:
		1701
		1702	ev_init (timer, callback);
		1703	timer->repeat = 60.;
		1704	ev_timer_again (loop, timer);
		1705
		1706	Each time there is some activity:
		1707
		1708	ev_timer_again (loop, timer);
		1709
		1710	It is even possible to change the time-out on the fly, regardless of
		1711	whether the watcher is active or not:
		1712
		1713	timer->repeat = 30.;
		1714	ev_timer_again (loop, timer);
		1715
		1716	This is slightly more efficient then stopping/starting the timer each time
		1717	you want to modify its timeout value, as libev does not have to completely
		1718	remove and re-insert the timer from/into its internal data structure.
		1719
		1720	It is, however, even simpler than the "obvious" way to do it.
		1721
		1722	=item 3. Let the timer time out, but then re-arm it as required.
		1723
		1724	This method is more tricky, but usually most efficient: Most timeouts are
		1725	relatively long compared to the intervals between other activity - in
		1726	our example, within 60 seconds, there are usually many I/O events with
		1727	associated activity resets.
		1728
		1729	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1730	but remember the time of last activity, and check for a real timeout only
		1731	within the callback:
		1732
		1733	ev_tstamp last_activity; // time of last activity
		1734
		1735	static void
		1736	callback (EV_P_ ev_timer *w, int revents)
		1737	{
		1738	ev_tstamp now = ev_now (EV_A);
		1739	ev_tstamp timeout = last_activity + 60.;
		1740
		1741	// if last_activity + 60. is older than now, we did time out
		1742	if (timeout < now)
		1743	{
		1744	// timeout occurred, take action
		1745	}
		1746	else
		1747	{
		1748	// callback was invoked, but there was some activity, re-arm
		1749	// the watcher to fire in last_activity + 60, which is
		1750	// guaranteed to be in the future, so "again" is positive:
		1751	w->repeat = timeout - now;
		1752	ev_timer_again (EV_A_ w);
		1753	}
		1754	}
		1755
		1756	To summarise the callback: first calculate the real timeout (defined
		1757	as "60 seconds after the last activity"), then check if that time has
		1758	been reached, which means something I<did>, in fact, time out. Otherwise
		1759	the callback was invoked too early (C<timeout> is in the future), so
		1760	re-schedule the timer to fire at that future time, to see if maybe we have
		1761	a timeout then.
		1762
		1763	Note how C<ev_timer_again> is used, taking advantage of the
		1764	C<ev_timer_again> optimisation when the timer is already running.
		1765
		1766	This scheme causes more callback invocations (about one every 60 seconds
		1767	minus half the average time between activity), but virtually no calls to
		1768	libev to change the timeout.
		1769
		1770	To start the timer, simply initialise the watcher and set C<last_activity>
		1771	to the current time (meaning we just have some activity :), then call the
		1772	callback, which will "do the right thing" and start the timer:
		1773
		1774	ev_init (timer, callback);
		1775	last_activity = ev_now (loop);
		1776	callback (loop, timer, EV_TIMER);
		1777
		1778	And when there is some activity, simply store the current time in
		1779	C<last_activity>, no libev calls at all:
		1780
		1781	last_activity = ev_now (loop);
		1782
		1783	This technique is slightly more complex, but in most cases where the
		1784	time-out is unlikely to be triggered, much more efficient.
		1785
		1786	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1787	callback :) - just change the timeout and invoke the callback, which will
		1788	fix things for you.
		1789
		1790	=item 4. Wee, just use a double-linked list for your timeouts.
		1791
		1792	If there is not one request, but many thousands (millions...), all
		1793	employing some kind of timeout with the same timeout value, then one can
		1794	do even better:
		1795
		1796	When starting the timeout, calculate the timeout value and put the timeout
		1797	at the I<end> of the list.
		1798
		1799	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1800	the list is expected to fire (for example, using the technique #3).
		1801
		1802	When there is some activity, remove the timer from the list, recalculate
		1803	the timeout, append it to the end of the list again, and make sure to
		1804	update the C<ev_timer> if it was taken from the beginning of the list.
		1805
		1806	This way, one can manage an unlimited number of timeouts in O(1) time for
		1807	starting, stopping and updating the timers, at the expense of a major
		1808	complication, and having to use a constant timeout. The constant timeout
		1809	ensures that the list stays sorted.
		1810
		1811	=back
		1812
		1813	So which method the best?
		1814
		1815	Method #2 is a simple no-brain-required solution that is adequate in most
		1816	situations. Method #3 requires a bit more thinking, but handles many cases
		1817	better, and isn't very complicated either. In most case, choosing either
		1818	one is fine, with #3 being better in typical situations.
		1819
		1820	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1821	rather complicated, but extremely efficient, something that really pays
		1822	off after the first million or so of active timers, i.e. it's usually
		1823	overkill :)
		1824
		1825	=head3 The special problem of time updates
		1826
		1827	Establishing the current time is a costly operation (it usually takes at
		1828	least two system calls): EV therefore updates its idea of the current
		1829	time only before and after C<ev_loop> collects new events, which causes a
		1830	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1831	lots of events in one iteration.
989		1832
990	The relative timeouts are calculated relative to the C<ev_now ()>	1833	The relative timeouts are calculated relative to the C<ev_now ()>
991	time. This is usually the right thing as this timestamp refers to the time	1834	time. This is usually the right thing as this timestamp refers to the time
992	of the event triggering whatever timeout you are modifying/starting. If	1835	of the event triggering whatever timeout you are modifying/starting. If
993	you suspect event processing to be delayed and you I<need> to base the timeout	1836	you suspect event processing to be delayed and you I<need> to base the
994	on the current time, use something like this to adjust for this:	1837	timeout on the current time, use something like this to adjust for this:
995		1838
996	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1839	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
997		1840
998	The callback is guarenteed to be invoked only when its timeout has passed,	1841	If the event loop is suspended for a long time, you can also force an
999	but if multiple timers become ready during the same loop iteration then	1842	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1000	order of execution is undefined.	1843	()>.
		1844
		1845	=head3 The special problems of suspended animation
		1846
		1847	When you leave the server world it is quite customary to hit machines that
		1848	can suspend/hibernate - what happens to the clocks during such a suspend?
		1849
		1850	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1851	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1852	to run until the system is suspended, but they will not advance while the
		1853	system is suspended. That means, on resume, it will be as if the program
		1854	was frozen for a few seconds, but the suspend time will not be counted
		1855	towards C<ev_timer> when a monotonic clock source is used. The real time
		1856	clock advanced as expected, but if it is used as sole clocksource, then a
		1857	long suspend would be detected as a time jump by libev, and timers would
		1858	be adjusted accordingly.
		1859
		1860	I would not be surprised to see different behaviour in different between
		1861	operating systems, OS versions or even different hardware.
		1862
		1863	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1864	time jump in the monotonic clocks and the realtime clock. If the program
		1865	is suspended for a very long time, and monotonic clock sources are in use,
		1866	then you can expect C<ev_timer>s to expire as the full suspension time
		1867	will be counted towards the timers. When no monotonic clock source is in
		1868	use, then libev will again assume a timejump and adjust accordingly.
		1869
		1870	It might be beneficial for this latter case to call C<ev_suspend>
		1871	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1872	deterministic behaviour in this case (you can do nothing against
		1873	C<SIGSTOP>).
1001		1874
1002	=head3 Watcher-Specific Functions and Data Members	1875	=head3 Watcher-Specific Functions and Data Members
1003		1876
1004	=over 4	1877	=over 4
1005		1878
1006	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1879	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1007		1880
1008	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1881	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1009		1882
1010	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1883	Configure the timer to trigger after C<after> seconds. If C<repeat>
1011	C<0.>, then it will automatically be stopped. If it is positive, then the	1884	is C<0.>, then it will automatically be stopped once the timeout is
1012	timer will automatically be configured to trigger again C<repeat> seconds	1885	reached. If it is positive, then the timer will automatically be
1013	later, again, and again, until stopped manually.	1886	configured to trigger again C<repeat> seconds later, again, and again,
		1887	until stopped manually.
1014		1888
1015	The timer itself will do a best-effort at avoiding drift, that is, if you	1889	The timer itself will do a best-effort at avoiding drift, that is, if
1016	configure a timer to trigger every 10 seconds, then it will trigger at	1890	you configure a timer to trigger every 10 seconds, then it will normally
1017	exactly 10 second intervals. If, however, your program cannot keep up with	1891	trigger at exactly 10 second intervals. If, however, your program cannot
1018	the timer (because it takes longer than those 10 seconds to do stuff) the	1892	keep up with the timer (because it takes longer than those 10 seconds to
1019	timer will not fire more than once per event loop iteration.	1893	do stuff) the timer will not fire more than once per event loop iteration.
1020		1894
1021	=item ev_timer_again (loop)	1895	=item ev_timer_again (loop, ev_timer *)
1022		1896
1023	This will act as if the timer timed out and restart it again if it is	1897	This will act as if the timer timed out and restart it again if it is
1024	repeating. The exact semantics are:	1898	repeating. The exact semantics are:
1025		1899
1026	If the timer is pending, its pending status is cleared.	1900	If the timer is pending, its pending status is cleared.
1027		1901
1028	If the timer is started but nonrepeating, stop it (as if it timed out).	1902	If the timer is started but non-repeating, stop it (as if it timed out).
1029		1903
1030	If the timer is repeating, either start it if necessary (with the	1904	If the timer is repeating, either start it if necessary (with the
1031	C<repeat> value), or reset the running timer to the C<repeat> value.	1905	C<repeat> value), or reset the running timer to the C<repeat> value.
1032		1906
1033	This sounds a bit complicated, but here is a useful and typical	1907	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1034	example: Imagine you have a tcp connection and you want a so-called idle	1908	usage example.
1035	timeout, that is, you want to be called when there have been, say, 60
1036	seconds of inactivity on the socket. The easiest way to do this is to
1037	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1038	C<ev_timer_again> each time you successfully read or write some data. If
1039	you go into an idle state where you do not expect data to travel on the
1040	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1041	automatically restart it if need be.
1042		1909
1043	That means you can ignore the C<after> value and C<ev_timer_start>	1910	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1044	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1045		1911
1046	ev_timer_init (timer, callback, 0., 5.);	1912	Returns the remaining time until a timer fires. If the timer is active,
1047	ev_timer_again (loop, timer);	1913	then this time is relative to the current event loop time, otherwise it's
1048	...	1914	the timeout value currently configured.
1049	timer->again = 17.;
1050	ev_timer_again (loop, timer);
1051	...
1052	timer->again = 10.;
1053	ev_timer_again (loop, timer);
1054		1915
1055	This is more slightly efficient then stopping/starting the timer each time	1916	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
1056	you want to modify its timeout value.	1917	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		1918	will return C<4>. When the timer expires and is restarted, it will return
		1919	roughly C<7> (likely slightly less as callback invocation takes some time,
		1920	too), and so on.
1057		1921
1058	=item ev_tstamp repeat [read-write]	1922	=item ev_tstamp repeat [read-write]
1059		1923
1060	The current C<repeat> value. Will be used each time the watcher times out	1924	The current C<repeat> value. Will be used each time the watcher times out
1061	or C<ev_timer_again> is called and determines the next timeout (if any),	1925	or C<ev_timer_again> is called, and determines the next timeout (if any),
1062	which is also when any modifications are taken into account.	1926	which is also when any modifications are taken into account.
1063		1927
1064	=back	1928	=back
1065		1929
		1930	=head3 Examples
		1931
1066	Example: Create a timer that fires after 60 seconds.	1932	Example: Create a timer that fires after 60 seconds.
1067		1933
1068	static void	1934	static void
1069	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1935	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1070	{	1936	{
1071	.. one minute over, w is actually stopped right here	1937	.. one minute over, w is actually stopped right here
1072	}	1938	}
1073		1939
1074	struct ev_timer mytimer;	1940	ev_timer mytimer;
1075	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1941	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1076	ev_timer_start (loop, &mytimer);	1942	ev_timer_start (loop, &mytimer);
1077		1943
1078	Example: Create a timeout timer that times out after 10 seconds of	1944	Example: Create a timeout timer that times out after 10 seconds of
1079	inactivity.	1945	inactivity.
1080		1946
1081	static void	1947	static void
1082	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1948	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1083	{	1949	{
1084	.. ten seconds without any activity	1950	.. ten seconds without any activity
1085	}	1951	}
1086		1952
1087	struct ev_timer mytimer;	1953	ev_timer mytimer;
1088	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1954	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1089	ev_timer_again (&mytimer); /* start timer */	1955	ev_timer_again (&mytimer); /* start timer */
1090	ev_loop (loop, 0);	1956	ev_loop (loop, 0);
1091		1957
1092	// and in some piece of code that gets executed on any "activity":	1958	// and in some piece of code that gets executed on any "activity":
1093	// reset the timeout to start ticking again at 10 seconds	1959	// reset the timeout to start ticking again at 10 seconds
1094	ev_timer_again (&mytimer);	1960	ev_timer_again (&mytimer);
1095		1961
1096		1962
1097	=head2 C<ev_periodic> - to cron or not to cron?	1963	=head2 C<ev_periodic> - to cron or not to cron?
1098		1964
1099	Periodic watchers are also timers of a kind, but they are very versatile	1965	Periodic watchers are also timers of a kind, but they are very versatile
1100	(and unfortunately a bit complex).	1966	(and unfortunately a bit complex).
1101		1967
1102	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1968	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1103	but on wallclock time (absolute time). You can tell a periodic watcher	1969	relative time, the physical time that passes) but on wall clock time
1104	to trigger "at" some specific point in time. For example, if you tell a	1970	(absolute time, the thing you can read on your calender or clock). The
1105	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	1971	difference is that wall clock time can run faster or slower than real
1106	+ 10.>) and then reset your system clock to the last year, then it will	1972	time, and time jumps are not uncommon (e.g. when you adjust your
1107	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1973	wrist-watch).
1108	roughly 10 seconds later).
1109		1974
1110	They can also be used to implement vastly more complex timers, such as	1975	You can tell a periodic watcher to trigger after some specific point
1111	triggering an event on each midnight, local time or other, complicated,	1976	in time: for example, if you tell a periodic watcher to trigger "in 10
1112	rules.	1977	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1978	not a delay) and then reset your system clock to January of the previous
		1979	year, then it will take a year or more to trigger the event (unlike an
		1980	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1981	it, as it uses a relative timeout).
1113		1982
		1983	C<ev_periodic> watchers can also be used to implement vastly more complex
		1984	timers, such as triggering an event on each "midnight, local time", or
		1985	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1986	those cannot react to time jumps.
		1987
1114	As with timers, the callback is guarenteed to be invoked only when the	1988	As with timers, the callback is guaranteed to be invoked only when the
1115	time (C<at>) has been passed, but if multiple periodic timers become ready	1989	point in time where it is supposed to trigger has passed. If multiple
1116	during the same loop iteration then order of execution is undefined.	1990	timers become ready during the same loop iteration then the ones with
		1991	earlier time-out values are invoked before ones with later time-out values
		1992	(but this is no longer true when a callback calls C<ev_loop> recursively).
1117		1993
1118	=head3 Watcher-Specific Functions and Data Members	1994	=head3 Watcher-Specific Functions and Data Members
1119		1995
1120	=over 4	1996	=over 4
1121		1997
1122	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1998	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1123		1999
1124	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	2000	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1125		2001
1126	Lots of arguments, lets sort it out... There are basically three modes of	2002	Lots of arguments, let's sort it out... There are basically three modes of
1127	operation, and we will explain them from simplest to complex:	2003	operation, and we will explain them from simplest to most complex:
1128		2004
1129	=over 4	2005	=over 4
1130		2006
1131	=item * absolute timer (at = time, interval = reschedule_cb = 0)	2007	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1132		2008
1133	In this configuration the watcher triggers an event at the wallclock time	2009	In this configuration the watcher triggers an event after the wall clock
1134	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	2010	time C<offset> has passed. It will not repeat and will not adjust when a
1135	that is, if it is to be run at January 1st 2011 then it will run when the	2011	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1136	system time reaches or surpasses this time.	2012	will be stopped and invoked when the system clock reaches or surpasses
		2013	this point in time.
1137		2014
1138	=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	2015	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1139		2016
1140	In this mode the watcher will always be scheduled to time out at the next	2017	In this mode the watcher will always be scheduled to time out at the next
1141	C<at + N * interval> time (for some integer N, which can also be negative)	2018	C<offset + N * interval> time (for some integer N, which can also be
1142	and then repeat, regardless of any time jumps.	2019	negative) and then repeat, regardless of any time jumps. The C<offset>
		2020	argument is merely an offset into the C<interval> periods.
1143		2021
1144	This can be used to create timers that do not drift with respect to system	2022	This can be used to create timers that do not drift with respect to the
1145	time:	2023	system clock, for example, here is an C<ev_periodic> that triggers each
		2024	hour, on the hour (with respect to UTC):
1146		2025
1147	ev_periodic_set (&periodic, 0., 3600., 0);	2026	ev_periodic_set (&periodic, 0., 3600., 0);
1148		2027
1149	This doesn't mean there will always be 3600 seconds in between triggers,	2028	This doesn't mean there will always be 3600 seconds in between triggers,
1150	but only that the the callback will be called when the system time shows a	2029	but only that the callback will be called when the system time shows a
1151	full hour (UTC), or more correctly, when the system time is evenly divisible	2030	full hour (UTC), or more correctly, when the system time is evenly divisible
1152	by 3600.	2031	by 3600.
1153		2032
1154	Another way to think about it (for the mathematically inclined) is that	2033	Another way to think about it (for the mathematically inclined) is that
1155	C<ev_periodic> will try to run the callback in this mode at the next possible	2034	C<ev_periodic> will try to run the callback in this mode at the next possible
1156	time where C<time = at (mod interval)>, regardless of any time jumps.	2035	time where C<time = offset (mod interval)>, regardless of any time jumps.
1157		2036
1158	For numerical stability it is preferable that the C<at> value is near	2037	For numerical stability it is preferable that the C<offset> value is near
1159	C<ev_now ()> (the current time), but there is no range requirement for	2038	C<ev_now ()> (the current time), but there is no range requirement for
1160	this value.	2039	this value, and in fact is often specified as zero.
1161		2040
		2041	Note also that there is an upper limit to how often a timer can fire (CPU
		2042	speed for example), so if C<interval> is very small then timing stability
		2043	will of course deteriorate. Libev itself tries to be exact to be about one
		2044	millisecond (if the OS supports it and the machine is fast enough).
		2045
1162	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	2046	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1163		2047
1164	In this mode the values for C<interval> and C<at> are both being	2048	In this mode the values for C<interval> and C<offset> are both being
1165	ignored. Instead, each time the periodic watcher gets scheduled, the	2049	ignored. Instead, each time the periodic watcher gets scheduled, the
1166	reschedule callback will be called with the watcher as first, and the	2050	reschedule callback will be called with the watcher as first, and the
1167	current time as second argument.	2051	current time as second argument.
1168		2052
1169	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2053	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1170	ever, or make any event loop modifications>. If you need to stop it,	2054	or make ANY other event loop modifications whatsoever, unless explicitly
1171	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	2055	allowed by documentation here>.
1172	starting an C<ev_prepare> watcher, which is legal).
1173		2056
		2057	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		2058	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		2059	only event loop modification you are allowed to do).
		2060
1174	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	2061	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1175	ev_tstamp now)>, e.g.:	2062	*w, ev_tstamp now)>, e.g.:
1176		2063
		2064	static ev_tstamp
1177	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2065	my_rescheduler (ev_periodic *w, ev_tstamp now)
1178	{	2066	{
1179	return now + 60.;	2067	return now + 60.;
1180	}	2068	}
1181		2069
1182	It must return the next time to trigger, based on the passed time value	2070	It must return the next time to trigger, based on the passed time value
1183	(that is, the lowest time value larger than to the second argument). It	2071	(that is, the lowest time value larger than to the second argument). It
1184	will usually be called just before the callback will be triggered, but	2072	will usually be called just before the callback will be triggered, but
1185	might be called at other times, too.	2073	might be called at other times, too.
1186		2074
1187	NOTE: I<< This callback must always return a time that is later than the	2075	NOTE: I<< This callback must always return a time that is higher than or
1188	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	2076	equal to the passed C<now> value >>.
1189		2077
1190	This can be used to create very complex timers, such as a timer that	2078	This can be used to create very complex timers, such as a timer that
1191	triggers on each midnight, local time. To do this, you would calculate the	2079	triggers on "next midnight, local time". To do this, you would calculate the
1192	next midnight after C<now> and return the timestamp value for this. How	2080	next midnight after C<now> and return the timestamp value for this. How
1193	you do this is, again, up to you (but it is not trivial, which is the main	2081	you do this is, again, up to you (but it is not trivial, which is the main
1194	reason I omitted it as an example).	2082	reason I omitted it as an example).
1195		2083
1196	=back	2084	=back
…		…
1200	Simply stops and restarts the periodic watcher again. This is only useful	2088	Simply stops and restarts the periodic watcher again. This is only useful
1201	when you changed some parameters or the reschedule callback would return	2089	when you changed some parameters or the reschedule callback would return
1202	a different time than the last time it was called (e.g. in a crond like	2090	a different time than the last time it was called (e.g. in a crond like
1203	program when the crontabs have changed).	2091	program when the crontabs have changed).
1204		2092
		2093	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2094
		2095	When active, returns the absolute time that the watcher is supposed
		2096	to trigger next. This is not the same as the C<offset> argument to
		2097	C<ev_periodic_set>, but indeed works even in interval and manual
		2098	rescheduling modes.
		2099
1205	=item ev_tstamp offset [read-write]	2100	=item ev_tstamp offset [read-write]
1206		2101
1207	When repeating, this contains the offset value, otherwise this is the	2102	When repeating, this contains the offset value, otherwise this is the
1208	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	2103	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2104	although libev might modify this value for better numerical stability).
1209		2105
1210	Can be modified any time, but changes only take effect when the periodic	2106	Can be modified any time, but changes only take effect when the periodic
1211	timer fires or C<ev_periodic_again> is being called.	2107	timer fires or C<ev_periodic_again> is being called.
1212		2108
1213	=item ev_tstamp interval [read-write]	2109	=item ev_tstamp interval [read-write]
1214		2110
1215	The current interval value. Can be modified any time, but changes only	2111	The current interval value. Can be modified any time, but changes only
1216	take effect when the periodic timer fires or C<ev_periodic_again> is being	2112	take effect when the periodic timer fires or C<ev_periodic_again> is being
1217	called.	2113	called.
1218		2114
1219	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2115	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1220		2116
1221	The current reschedule callback, or C<0>, if this functionality is	2117	The current reschedule callback, or C<0>, if this functionality is
1222	switched off. Can be changed any time, but changes only take effect when	2118	switched off. Can be changed any time, but changes only take effect when
1223	the periodic timer fires or C<ev_periodic_again> is being called.	2119	the periodic timer fires or C<ev_periodic_again> is being called.
1224		2120
1225	=back	2121	=back
1226		2122
		2123	=head3 Examples
		2124
1227	Example: Call a callback every hour, or, more precisely, whenever the	2125	Example: Call a callback every hour, or, more precisely, whenever the
1228	system clock is divisible by 3600. The callback invocation times have	2126	system time is divisible by 3600. The callback invocation times have
1229	potentially a lot of jittering, but good long-term stability.	2127	potentially a lot of jitter, but good long-term stability.
1230		2128
1231	static void	2129	static void
1232	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2130	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1233	{	2131	{
1234	... its now a full hour (UTC, or TAI or whatever your clock follows)	2132	... its now a full hour (UTC, or TAI or whatever your clock follows)
1235	}	2133	}
1236		2134
1237	struct ev_periodic hourly_tick;	2135	ev_periodic hourly_tick;
1238	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2136	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1239	ev_periodic_start (loop, &hourly_tick);	2137	ev_periodic_start (loop, &hourly_tick);
1240		2138
1241	Example: The same as above, but use a reschedule callback to do it:	2139	Example: The same as above, but use a reschedule callback to do it:
1242		2140
1243	#include <math.h>	2141	#include <math.h>
1244		2142
1245	static ev_tstamp	2143	static ev_tstamp
1246	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2144	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1247	{	2145	{
1248	return fmod (now, 3600.) + 3600.;	2146	return now + (3600. - fmod (now, 3600.));
1249	}	2147	}
1250		2148
1251	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2149	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1252		2150
1253	Example: Call a callback every hour, starting now:	2151	Example: Call a callback every hour, starting now:
1254		2152
1255	struct ev_periodic hourly_tick;	2153	ev_periodic hourly_tick;
1256	ev_periodic_init (&hourly_tick, clock_cb,	2154	ev_periodic_init (&hourly_tick, clock_cb,
1257	fmod (ev_now (loop), 3600.), 3600., 0);	2155	fmod (ev_now (loop), 3600.), 3600., 0);
1258	ev_periodic_start (loop, &hourly_tick);	2156	ev_periodic_start (loop, &hourly_tick);
1259		2157
1260		2158
1261	=head2 C<ev_signal> - signal me when a signal gets signalled!	2159	=head2 C<ev_signal> - signal me when a signal gets signalled!
1262		2160
1263	Signal watchers will trigger an event when the process receives a specific	2161	Signal watchers will trigger an event when the process receives a specific
1264	signal one or more times. Even though signals are very asynchronous, libev	2162	signal one or more times. Even though signals are very asynchronous, libev
1265	will try it's best to deliver signals synchronously, i.e. as part of the	2163	will try it's best to deliver signals synchronously, i.e. as part of the
1266	normal event processing, like any other event.	2164	normal event processing, like any other event.
1267		2165
		2166	If you want signals to be delivered truly asynchronously, just use
		2167	C<sigaction> as you would do without libev and forget about sharing
		2168	the signal. You can even use C<ev_async> from a signal handler to
		2169	synchronously wake up an event loop.
		2170
1268	You can configure as many watchers as you like per signal. Only when the	2171	You can configure as many watchers as you like for the same signal, but
		2172	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2173	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2174	C<SIGINT> in both the default loop and another loop at the same time. At
		2175	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2176
1269	first watcher gets started will libev actually register a signal watcher	2177	When the first watcher gets started will libev actually register something
1270	with the kernel (thus it coexists with your own signal handlers as long	2178	with the kernel (thus it coexists with your own signal handlers as long as
1271	as you don't register any with libev). Similarly, when the last signal	2179	you don't register any with libev for the same signal).
1272	watcher for a signal is stopped libev will reset the signal handler to	2180
1273	SIG_DFL (regardless of what it was set to before).	2181	If possible and supported, libev will install its handlers with
		2182	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2183	not be unduly interrupted. If you have a problem with system calls getting
		2184	interrupted by signals you can block all signals in an C<ev_check> watcher
		2185	and unblock them in an C<ev_prepare> watcher.
		2186
		2187	=head3 The special problem of inheritance over fork/execve/pthread_create
		2188
		2189	Both the signal mask (C<sigprocmask>) and the signal disposition
		2190	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2191	stopping it again), that is, libev might or might not block the signal,
		2192	and might or might not set or restore the installed signal handler.
		2193
		2194	While this does not matter for the signal disposition (libev never
		2195	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2196	C<execve>), this matters for the signal mask: many programs do not expect
		2197	certain signals to be blocked.
		2198
		2199	This means that before calling C<exec> (from the child) you should reset
		2200	the signal mask to whatever "default" you expect (all clear is a good
		2201	choice usually).
		2202
		2203	The simplest way to ensure that the signal mask is reset in the child is
		2204	to install a fork handler with C<pthread_atfork> that resets it. That will
		2205	catch fork calls done by libraries (such as the libc) as well.
		2206
		2207	In current versions of libev, the signal will not be blocked indefinitely
		2208	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2209	the window of opportunity for problems, it will not go away, as libev
		2210	I<has> to modify the signal mask, at least temporarily.
		2211
		2212	So I can't stress this enough: I<If you do not reset your signal mask when
		2213	you expect it to be empty, you have a race condition in your code>. This
		2214	is not a libev-specific thing, this is true for most event libraries.
1274		2215
1275	=head3 Watcher-Specific Functions and Data Members	2216	=head3 Watcher-Specific Functions and Data Members
1276		2217
1277	=over 4	2218	=over 4
1278		2219
…		…
1287		2228
1288	The signal the watcher watches out for.	2229	The signal the watcher watches out for.
1289		2230
1290	=back	2231	=back
1291		2232
		2233	=head3 Examples
		2234
		2235	Example: Try to exit cleanly on SIGINT.
		2236
		2237	static void
		2238	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2239	{
		2240	ev_unloop (loop, EVUNLOOP_ALL);
		2241	}
		2242
		2243	ev_signal signal_watcher;
		2244	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2245	ev_signal_start (loop, &signal_watcher);
		2246
1292		2247
1293	=head2 C<ev_child> - watch out for process status changes	2248	=head2 C<ev_child> - watch out for process status changes
1294		2249
1295	Child watchers trigger when your process receives a SIGCHLD in response to	2250	Child watchers trigger when your process receives a SIGCHLD in response to
1296	some child status changes (most typically when a child of yours dies).	2251	some child status changes (most typically when a child of yours dies or
		2252	exits). It is permissible to install a child watcher I<after> the child
		2253	has been forked (which implies it might have already exited), as long
		2254	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2255	forking and then immediately registering a watcher for the child is fine,
		2256	but forking and registering a watcher a few event loop iterations later or
		2257	in the next callback invocation is not.
		2258
		2259	Only the default event loop is capable of handling signals, and therefore
		2260	you can only register child watchers in the default event loop.
		2261
		2262	Due to some design glitches inside libev, child watchers will always be
		2263	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2264	libev)
		2265
		2266	=head3 Process Interaction
		2267
		2268	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2269	initialised. This is necessary to guarantee proper behaviour even if the
		2270	first child watcher is started after the child exits. The occurrence
		2271	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2272	synchronously as part of the event loop processing. Libev always reaps all
		2273	children, even ones not watched.
		2274
		2275	=head3 Overriding the Built-In Processing
		2276
		2277	Libev offers no special support for overriding the built-in child
		2278	processing, but if your application collides with libev's default child
		2279	handler, you can override it easily by installing your own handler for
		2280	C<SIGCHLD> after initialising the default loop, and making sure the
		2281	default loop never gets destroyed. You are encouraged, however, to use an
		2282	event-based approach to child reaping and thus use libev's support for
		2283	that, so other libev users can use C<ev_child> watchers freely.
		2284
		2285	=head3 Stopping the Child Watcher
		2286
		2287	Currently, the child watcher never gets stopped, even when the
		2288	child terminates, so normally one needs to stop the watcher in the
		2289	callback. Future versions of libev might stop the watcher automatically
		2290	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2291	problem).
1297		2292
1298	=head3 Watcher-Specific Functions and Data Members	2293	=head3 Watcher-Specific Functions and Data Members
1299		2294
1300	=over 4	2295	=over 4
1301		2296
1302	=item ev_child_init (ev_child *, callback, int pid)	2297	=item ev_child_init (ev_child *, callback, int pid, int trace)
1303		2298
1304	=item ev_child_set (ev_child *, int pid)	2299	=item ev_child_set (ev_child *, int pid, int trace)
1305		2300
1306	Configures the watcher to wait for status changes of process C<pid> (or	2301	Configures the watcher to wait for status changes of process C<pid> (or
1307	I<any> process if C<pid> is specified as C<0>). The callback can look	2302	I<any> process if C<pid> is specified as C<0>). The callback can look
1308	at the C<rstatus> member of the C<ev_child> watcher structure to see	2303	at the C<rstatus> member of the C<ev_child> watcher structure to see
1309	the status word (use the macros from C<sys/wait.h> and see your systems	2304	the status word (use the macros from C<sys/wait.h> and see your systems
1310	C<waitpid> documentation). The C<rpid> member contains the pid of the	2305	C<waitpid> documentation). The C<rpid> member contains the pid of the
1311	process causing the status change.	2306	process causing the status change. C<trace> must be either C<0> (only
		2307	activate the watcher when the process terminates) or C<1> (additionally
		2308	activate the watcher when the process is stopped or continued).
1312		2309
1313	=item int pid [read-only]	2310	=item int pid [read-only]
1314		2311
1315	The process id this watcher watches out for, or C<0>, meaning any process id.	2312	The process id this watcher watches out for, or C<0>, meaning any process id.
1316		2313
…		…
1323	The process exit/trace status caused by C<rpid> (see your systems	2320	The process exit/trace status caused by C<rpid> (see your systems
1324	C<waitpid> and C<sys/wait.h> documentation for details).	2321	C<waitpid> and C<sys/wait.h> documentation for details).
1325		2322
1326	=back	2323	=back
1327		2324
1328	Example: Try to exit cleanly on SIGINT and SIGTERM.	2325	=head3 Examples
1329		2326
		2327	Example: C<fork()> a new process and install a child handler to wait for
		2328	its completion.
		2329
		2330	ev_child cw;
		2331
1330	static void	2332	static void
1331	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2333	child_cb (EV_P_ ev_child *w, int revents)
1332	{	2334	{
1333	ev_unloop (loop, EVUNLOOP_ALL);	2335	ev_child_stop (EV_A_ w);
		2336	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1334	}	2337	}
1335		2338
1336	struct ev_signal signal_watcher;	2339	pid_t pid = fork ();
1337	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2340
1338	ev_signal_start (loop, &sigint_cb);	2341	if (pid < 0)
		2342	// error
		2343	else if (pid == 0)
		2344	{
		2345	// the forked child executes here
		2346	exit (1);
		2347	}
		2348	else
		2349	{
		2350	ev_child_init (&cw, child_cb, pid, 0);
		2351	ev_child_start (EV_DEFAULT_ &cw);
		2352	}
1339		2353
1340		2354
1341	=head2 C<ev_stat> - did the file attributes just change?	2355	=head2 C<ev_stat> - did the file attributes just change?
1342		2356
1343	This watches a filesystem path for attribute changes. That is, it calls	2357	This watches a file system path for attribute changes. That is, it calls
1344	C<stat> regularly (or when the OS says it changed) and sees if it changed	2358	C<stat> on that path in regular intervals (or when the OS says it changed)
1345	compared to the last time, invoking the callback if it did.	2359	and sees if it changed compared to the last time, invoking the callback if
		2360	it did.
1346		2361
1347	The path does not need to exist: changing from "path exists" to "path does	2362	The path does not need to exist: changing from "path exists" to "path does
1348	not exist" is a status change like any other. The condition "path does	2363	not exist" is a status change like any other. The condition "path does not
1349	not exist" is signified by the C<st_nlink> field being zero (which is	2364	exist" (or more correctly "path cannot be stat'ed") is signified by the
1350	otherwise always forced to be at least one) and all the other fields of	2365	C<st_nlink> field being zero (which is otherwise always forced to be at
1351	the stat buffer having unspecified contents.	2366	least one) and all the other fields of the stat buffer having unspecified
		2367	contents.
1352		2368
1353	The path I<should> be absolute and I<must not> end in a slash. If it is	2369	The path I<must not> end in a slash or contain special components such as
		2370	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1354	relative and your working directory changes, the behaviour is undefined.	2371	your working directory changes, then the behaviour is undefined.
1355		2372
1356	Since there is no standard to do this, the portable implementation simply	2373	Since there is no portable change notification interface available, the
1357	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2374	portable implementation simply calls C<stat(2)> regularly on the path
1358	can specify a recommended polling interval for this case. If you specify	2375	to see if it changed somehow. You can specify a recommended polling
1359	a polling interval of C<0> (highly recommended!) then a I<suitable,	2376	interval for this case. If you specify a polling interval of C<0> (highly
1360	unspecified default> value will be used (which you can expect to be around	2377	recommended!) then a I<suitable, unspecified default> value will be used
1361	five seconds, although this might change dynamically). Libev will also	2378	(which you can expect to be around five seconds, although this might
1362	impose a minimum interval which is currently around C<0.1>, but thats	2379	change dynamically). Libev will also impose a minimum interval which is
1363	usually overkill.	2380	currently around C<0.1>, but that's usually overkill.
1364		2381
1365	This watcher type is not meant for massive numbers of stat watchers,	2382	This watcher type is not meant for massive numbers of stat watchers,
1366	as even with OS-supported change notifications, this can be	2383	as even with OS-supported change notifications, this can be
1367	resource-intensive.	2384	resource-intensive.
1368		2385
1369	At the time of this writing, only the Linux inotify interface is	2386	At the time of this writing, the only OS-specific interface implemented
1370	implemented (implementing kqueue support is left as an exercise for the	2387	is the Linux inotify interface (implementing kqueue support is left as an
1371	reader). Inotify will be used to give hints only and should not change the	2388	exercise for the reader. Note, however, that the author sees no way of
1372	semantics of C<ev_stat> watchers, which means that libev sometimes needs	2389	implementing C<ev_stat> semantics with kqueue, except as a hint).
1373	to fall back to regular polling again even with inotify, but changes are	2390
1374	usually detected immediately, and if the file exists there will be no	2391	=head3 ABI Issues (Largefile Support)
1375	polling.	2392
		2393	Libev by default (unless the user overrides this) uses the default
		2394	compilation environment, which means that on systems with large file
		2395	support disabled by default, you get the 32 bit version of the stat
		2396	structure. When using the library from programs that change the ABI to
		2397	use 64 bit file offsets the programs will fail. In that case you have to
		2398	compile libev with the same flags to get binary compatibility. This is
		2399	obviously the case with any flags that change the ABI, but the problem is
		2400	most noticeably displayed with ev_stat and large file support.
		2401
		2402	The solution for this is to lobby your distribution maker to make large
		2403	file interfaces available by default (as e.g. FreeBSD does) and not
		2404	optional. Libev cannot simply switch on large file support because it has
		2405	to exchange stat structures with application programs compiled using the
		2406	default compilation environment.
		2407
		2408	=head3 Inotify and Kqueue
		2409
		2410	When C<inotify (7)> support has been compiled into libev and present at
		2411	runtime, it will be used to speed up change detection where possible. The
		2412	inotify descriptor will be created lazily when the first C<ev_stat>
		2413	watcher is being started.
		2414
		2415	Inotify presence does not change the semantics of C<ev_stat> watchers
		2416	except that changes might be detected earlier, and in some cases, to avoid
		2417	making regular C<stat> calls. Even in the presence of inotify support
		2418	there are many cases where libev has to resort to regular C<stat> polling,
		2419	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2420	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2421	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2422	xfs are fully working) libev usually gets away without polling.
		2423
		2424	There is no support for kqueue, as apparently it cannot be used to
		2425	implement this functionality, due to the requirement of having a file
		2426	descriptor open on the object at all times, and detecting renames, unlinks
		2427	etc. is difficult.
		2428
		2429	=head3 C<stat ()> is a synchronous operation
		2430
		2431	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2432	the process. The exception are C<ev_stat> watchers - those call C<stat
		2433	()>, which is a synchronous operation.
		2434
		2435	For local paths, this usually doesn't matter: unless the system is very
		2436	busy or the intervals between stat's are large, a stat call will be fast,
		2437	as the path data is usually in memory already (except when starting the
		2438	watcher).
		2439
		2440	For networked file systems, calling C<stat ()> can block an indefinite
		2441	time due to network issues, and even under good conditions, a stat call
		2442	often takes multiple milliseconds.
		2443
		2444	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2445	paths, although this is fully supported by libev.
		2446
		2447	=head3 The special problem of stat time resolution
		2448
		2449	The C<stat ()> system call only supports full-second resolution portably,
		2450	and even on systems where the resolution is higher, most file systems
		2451	still only support whole seconds.
		2452
		2453	That means that, if the time is the only thing that changes, you can
		2454	easily miss updates: on the first update, C<ev_stat> detects a change and
		2455	calls your callback, which does something. When there is another update
		2456	within the same second, C<ev_stat> will be unable to detect unless the
		2457	stat data does change in other ways (e.g. file size).
		2458
		2459	The solution to this is to delay acting on a change for slightly more
		2460	than a second (or till slightly after the next full second boundary), using
		2461	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2462	ev_timer_again (loop, w)>).
		2463
		2464	The C<.02> offset is added to work around small timing inconsistencies
		2465	of some operating systems (where the second counter of the current time
		2466	might be be delayed. One such system is the Linux kernel, where a call to
		2467	C<gettimeofday> might return a timestamp with a full second later than
		2468	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2469	update file times then there will be a small window where the kernel uses
		2470	the previous second to update file times but libev might already execute
		2471	the timer callback).
1376		2472
1377	=head3 Watcher-Specific Functions and Data Members	2473	=head3 Watcher-Specific Functions and Data Members
1378		2474
1379	=over 4	2475	=over 4
1380		2476
…		…
1386	C<path>. The C<interval> is a hint on how quickly a change is expected to	2482	C<path>. The C<interval> is a hint on how quickly a change is expected to
1387	be detected and should normally be specified as C<0> to let libev choose	2483	be detected and should normally be specified as C<0> to let libev choose
1388	a suitable value. The memory pointed to by C<path> must point to the same	2484	a suitable value. The memory pointed to by C<path> must point to the same
1389	path for as long as the watcher is active.	2485	path for as long as the watcher is active.
1390		2486
1391	The callback will be receive C<EV_STAT> when a change was detected,	2487	The callback will receive an C<EV_STAT> event when a change was detected,
1392	relative to the attributes at the time the watcher was started (or the	2488	relative to the attributes at the time the watcher was started (or the
1393	last change was detected).	2489	last change was detected).
1394		2490
1395	=item ev_stat_stat (ev_stat *)	2491	=item ev_stat_stat (loop, ev_stat *)
1396		2492
1397	Updates the stat buffer immediately with new values. If you change the	2493	Updates the stat buffer immediately with new values. If you change the
1398	watched path in your callback, you could call this fucntion to avoid	2494	watched path in your callback, you could call this function to avoid
1399	detecting this change (while introducing a race condition). Can also be	2495	detecting this change (while introducing a race condition if you are not
1400	useful simply to find out the new values.	2496	the only one changing the path). Can also be useful simply to find out the
		2497	new values.
1401		2498
1402	=item ev_statdata attr [read-only]	2499	=item ev_statdata attr [read-only]
1403		2500
1404	The most-recently detected attributes of the file. Although the type is of	2501	The most-recently detected attributes of the file. Although the type is
1405	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2502	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1406	suitable for your system. If the C<st_nlink> member is C<0>, then there	2503	suitable for your system, but you can only rely on the POSIX-standardised
		2504	members to be present. If the C<st_nlink> member is C<0>, then there was
1407	was some error while C<stat>ing the file.	2505	some error while C<stat>ing the file.
1408		2506
1409	=item ev_statdata prev [read-only]	2507	=item ev_statdata prev [read-only]
1410		2508
1411	The previous attributes of the file. The callback gets invoked whenever	2509	The previous attributes of the file. The callback gets invoked whenever
1412	C<prev> != C<attr>.	2510	C<prev> != C<attr>, or, more precisely, one or more of these members
		2511	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2512	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1413		2513
1414	=item ev_tstamp interval [read-only]	2514	=item ev_tstamp interval [read-only]
1415		2515
1416	The specified interval.	2516	The specified interval.
1417		2517
1418	=item const char *path [read-only]	2518	=item const char *path [read-only]
1419		2519
1420	The filesystem path that is being watched.	2520	The file system path that is being watched.
1421		2521
1422	=back	2522	=back
1423		2523
		2524	=head3 Examples
		2525
1424	Example: Watch C</etc/passwd> for attribute changes.	2526	Example: Watch C</etc/passwd> for attribute changes.
1425		2527
1426	static void	2528	static void
1427	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2529	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1428	{	2530	{
1429	/* /etc/passwd changed in some way */	2531	/* /etc/passwd changed in some way */
1430	if (w->attr.st_nlink)	2532	if (w->attr.st_nlink)
1431	{	2533	{
1432	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2534	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1433	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2535	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1434	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2536	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1435	}	2537	}
1436	else	2538	else
1437	/* you shalt not abuse printf for puts */	2539	/* you shalt not abuse printf for puts */
1438	puts ("wow, /etc/passwd is not there, expect problems. "	2540	puts ("wow, /etc/passwd is not there, expect problems. "
1439	"if this is windows, they already arrived\n");	2541	"if this is windows, they already arrived\n");
1440	}	2542	}
1441		2543
1442	...	2544	...
1443	ev_stat passwd;	2545	ev_stat passwd;
1444		2546
1445	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	2547	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1446	ev_stat_start (loop, &passwd);	2548	ev_stat_start (loop, &passwd);
		2549
		2550	Example: Like above, but additionally use a one-second delay so we do not
		2551	miss updates (however, frequent updates will delay processing, too, so
		2552	one might do the work both on C<ev_stat> callback invocation I<and> on
		2553	C<ev_timer> callback invocation).
		2554
		2555	static ev_stat passwd;
		2556	static ev_timer timer;
		2557
		2558	static void
		2559	timer_cb (EV_P_ ev_timer *w, int revents)
		2560	{
		2561	ev_timer_stop (EV_A_ w);
		2562
		2563	/* now it's one second after the most recent passwd change */
		2564	}
		2565
		2566	static void
		2567	stat_cb (EV_P_ ev_stat *w, int revents)
		2568	{
		2569	/* reset the one-second timer */
		2570	ev_timer_again (EV_A_ &timer);
		2571	}
		2572
		2573	...
		2574	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2575	ev_stat_start (loop, &passwd);
		2576	ev_timer_init (&timer, timer_cb, 0., 1.02);
1447		2577
1448		2578
1449	=head2 C<ev_idle> - when you've got nothing better to do...	2579	=head2 C<ev_idle> - when you've got nothing better to do...
1450		2580
1451	Idle watchers trigger events when no other events of the same or higher	2581	Idle watchers trigger events when no other events of the same or higher
1452	priority are pending (prepare, check and other idle watchers do not	2582	priority are pending (prepare, check and other idle watchers do not count
1453	count).	2583	as receiving "events").
1454		2584
1455	That is, as long as your process is busy handling sockets or timeouts	2585	That is, as long as your process is busy handling sockets or timeouts
1456	(or even signals, imagine) of the same or higher priority it will not be	2586	(or even signals, imagine) of the same or higher priority it will not be
1457	triggered. But when your process is idle (or only lower-priority watchers	2587	triggered. But when your process is idle (or only lower-priority watchers
1458	are pending), the idle watchers are being called once per event loop	2588	are pending), the idle watchers are being called once per event loop
…		…
1469		2599
1470	=head3 Watcher-Specific Functions and Data Members	2600	=head3 Watcher-Specific Functions and Data Members
1471		2601
1472	=over 4	2602	=over 4
1473		2603
1474	=item ev_idle_init (ev_signal *, callback)	2604	=item ev_idle_init (ev_idle *, callback)
1475		2605
1476	Initialises and configures the idle watcher - it has no parameters of any	2606	Initialises and configures the idle watcher - it has no parameters of any
1477	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2607	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1478	believe me.	2608	believe me.
1479		2609
1480	=back	2610	=back
1481		2611
		2612	=head3 Examples
		2613
1482	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2614	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1483	callback, free it. Also, use no error checking, as usual.	2615	callback, free it. Also, use no error checking, as usual.
1484		2616
1485	static void	2617	static void
1486	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2618	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1487	{	2619	{
1488	free (w);	2620	free (w);
1489	// now do something you wanted to do when the program has	2621	// now do something you wanted to do when the program has
1490	// no longer asnything immediate to do.	2622	// no longer anything immediate to do.
1491	}	2623	}
1492		2624
1493	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2625	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1494	ev_idle_init (idle_watcher, idle_cb);	2626	ev_idle_init (idle_watcher, idle_cb);
1495	ev_idle_start (loop, idle_cb);	2627	ev_idle_start (loop, idle_watcher);
1496		2628
1497		2629
1498	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2630	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1499		2631
1500	Prepare and check watchers are usually (but not always) used in tandem:	2632	Prepare and check watchers are usually (but not always) used in pairs:
1501	prepare watchers get invoked before the process blocks and check watchers	2633	prepare watchers get invoked before the process blocks and check watchers
1502	afterwards.	2634	afterwards.
1503		2635
1504	You I<must not> call C<ev_loop> or similar functions that enter	2636	You I<must not> call C<ev_loop> or similar functions that enter
1505	the current event loop from either C<ev_prepare> or C<ev_check>	2637	the current event loop from either C<ev_prepare> or C<ev_check>
…		…
1508	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2640	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1509	C<ev_check> so if you have one watcher of each kind they will always be	2641	C<ev_check> so if you have one watcher of each kind they will always be
1510	called in pairs bracketing the blocking call.	2642	called in pairs bracketing the blocking call.
1511		2643
1512	Their main purpose is to integrate other event mechanisms into libev and	2644	Their main purpose is to integrate other event mechanisms into libev and
1513	their use is somewhat advanced. This could be used, for example, to track	2645	their use is somewhat advanced. They could be used, for example, to track
1514	variable changes, implement your own watchers, integrate net-snmp or a	2646	variable changes, implement your own watchers, integrate net-snmp or a
1515	coroutine library and lots more. They are also occasionally useful if	2647	coroutine library and lots more. They are also occasionally useful if
1516	you cache some data and want to flush it before blocking (for example,	2648	you cache some data and want to flush it before blocking (for example,
1517	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2649	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1518	watcher).	2650	watcher).
1519		2651
1520	This is done by examining in each prepare call which file descriptors need	2652	This is done by examining in each prepare call which file descriptors
1521	to be watched by the other library, registering C<ev_io> watchers for	2653	need to be watched by the other library, registering C<ev_io> watchers
1522	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2654	for them and starting an C<ev_timer> watcher for any timeouts (many
1523	provide just this functionality). Then, in the check watcher you check for	2655	libraries provide exactly this functionality). Then, in the check watcher,
1524	any events that occured (by checking the pending status of all watchers	2656	you check for any events that occurred (by checking the pending status
1525	and stopping them) and call back into the library. The I/O and timer	2657	of all watchers and stopping them) and call back into the library. The
1526	callbacks will never actually be called (but must be valid nevertheless,	2658	I/O and timer callbacks will never actually be called (but must be valid
1527	because you never know, you know?).	2659	nevertheless, because you never know, you know?).
1528		2660
1529	As another example, the Perl Coro module uses these hooks to integrate	2661	As another example, the Perl Coro module uses these hooks to integrate
1530	coroutines into libev programs, by yielding to other active coroutines	2662	coroutines into libev programs, by yielding to other active coroutines
1531	during each prepare and only letting the process block if no coroutines	2663	during each prepare and only letting the process block if no coroutines
1532	are ready to run (it's actually more complicated: it only runs coroutines	2664	are ready to run (it's actually more complicated: it only runs coroutines
…		…
1535	loop from blocking if lower-priority coroutines are active, thus mapping	2667	loop from blocking if lower-priority coroutines are active, thus mapping
1536	low-priority coroutines to idle/background tasks).	2668	low-priority coroutines to idle/background tasks).
1537		2669
1538	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2670	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1539	priority, to ensure that they are being run before any other watchers	2671	priority, to ensure that they are being run before any other watchers
		2672	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2673
1540	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2674	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1541	too) should not activate ("feed") events into libev. While libev fully	2675	activate ("feed") events into libev. While libev fully supports this, they
1542	supports this, they will be called before other C<ev_check> watchers did	2676	might get executed before other C<ev_check> watchers did their job. As
1543	their job. As C<ev_check> watchers are often used to embed other event	2677	C<ev_check> watchers are often used to embed other (non-libev) event
1544	loops those other event loops might be in an unusable state until their	2678	loops those other event loops might be in an unusable state until their
1545	C<ev_check> watcher ran (always remind yourself to coexist peacefully with	2679	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1546	others).	2680	others).
1547		2681
1548	=head3 Watcher-Specific Functions and Data Members	2682	=head3 Watcher-Specific Functions and Data Members
…		…
1553		2687
1554	=item ev_check_init (ev_check *, callback)	2688	=item ev_check_init (ev_check *, callback)
1555		2689
1556	Initialises and configures the prepare or check watcher - they have no	2690	Initialises and configures the prepare or check watcher - they have no
1557	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2691	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1558	macros, but using them is utterly, utterly and completely pointless.	2692	macros, but using them is utterly, utterly, utterly and completely
		2693	pointless.
1559		2694
1560	=back	2695	=back
		2696
		2697	=head3 Examples
1561		2698
1562	There are a number of principal ways to embed other event loops or modules	2699	There are a number of principal ways to embed other event loops or modules
1563	into libev. Here are some ideas on how to include libadns into libev	2700	into libev. Here are some ideas on how to include libadns into libev
1564	(there is a Perl module named C<EV::ADNS> that does this, which you could	2701	(there is a Perl module named C<EV::ADNS> that does this, which you could
1565	use for an actually working example. Another Perl module named C<EV::Glib>	2702	use as a working example. Another Perl module named C<EV::Glib> embeds a
1566	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV	2703	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1567	into the Glib event loop).	2704	Glib event loop).
1568		2705
1569	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	2706	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1570	and in a check watcher, destroy them and call into libadns. What follows	2707	and in a check watcher, destroy them and call into libadns. What follows
1571	is pseudo-code only of course. This requires you to either use a low	2708	is pseudo-code only of course. This requires you to either use a low
1572	priority for the check watcher or use C<ev_clear_pending> explicitly, as	2709	priority for the check watcher or use C<ev_clear_pending> explicitly, as
1573	the callbacks for the IO/timeout watchers might not have been called yet.	2710	the callbacks for the IO/timeout watchers might not have been called yet.
1574		2711
1575	static ev_io iow [nfd];	2712	static ev_io iow [nfd];
1576	static ev_timer tw;	2713	static ev_timer tw;
1577		2714
1578	static void	2715	static void
1579	io_cb (ev_loop *loop, ev_io *w, int revents)	2716	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1580	{	2717	{
1581	}	2718	}
1582		2719
1583	// create io watchers for each fd and a timer before blocking	2720	// create io watchers for each fd and a timer before blocking
1584	static void	2721	static void
1585	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2722	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1586	{	2723	{
1587	int timeout = 3600000;	2724	int timeout = 3600000;
1588	struct pollfd fds [nfd];	2725	struct pollfd fds [nfd];
1589	// actual code will need to loop here and realloc etc.	2726	// actual code will need to loop here and realloc etc.
1590	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2727	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1591		2728
1592	/* the callback is illegal, but won't be called as we stop during check */	2729	/* the callback is illegal, but won't be called as we stop during check */
1593	ev_timer_init (&tw, 0, timeout * 1e-3);	2730	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1594	ev_timer_start (loop, &tw);	2731	ev_timer_start (loop, &tw);
1595		2732
1596	// create one ev_io per pollfd	2733	// create one ev_io per pollfd
1597	for (int i = 0; i < nfd; ++i)	2734	for (int i = 0; i < nfd; ++i)
1598	{	2735	{
1599	ev_io_init (iow + i, io_cb, fds [i].fd,	2736	ev_io_init (iow + i, io_cb, fds [i].fd,
1600	((fds [i].events & POLLIN ? EV_READ : 0)	2737	((fds [i].events & POLLIN ? EV_READ : 0)
1601	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2738	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1602		2739
1603	fds [i].revents = 0;	2740	fds [i].revents = 0;
1604	ev_io_start (loop, iow + i);	2741	ev_io_start (loop, iow + i);
1605	}	2742	}
1606	}	2743	}
1607		2744
1608	// stop all watchers after blocking	2745	// stop all watchers after blocking
1609	static void	2746	static void
1610	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2747	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1611	{	2748	{
1612	ev_timer_stop (loop, &tw);	2749	ev_timer_stop (loop, &tw);
1613		2750
1614	for (int i = 0; i < nfd; ++i)	2751	for (int i = 0; i < nfd; ++i)
1615	{	2752	{
1616	// set the relevant poll flags	2753	// set the relevant poll flags
1617	// could also call adns_processreadable etc. here	2754	// could also call adns_processreadable etc. here
1618	struct pollfd *fd = fds + i;	2755	struct pollfd *fd = fds + i;
1619	int revents = ev_clear_pending (iow + i);	2756	int revents = ev_clear_pending (iow + i);
1620	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;	2757	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1621	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;	2758	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1622		2759
1623	// now stop the watcher	2760	// now stop the watcher
1624	ev_io_stop (loop, iow + i);	2761	ev_io_stop (loop, iow + i);
1625	}	2762	}
1626		2763
1627	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2764	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1628	}	2765	}
1629		2766
1630	Method 2: This would be just like method 1, but you run C<adns_afterpoll>	2767	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
1631	in the prepare watcher and would dispose of the check watcher.	2768	in the prepare watcher and would dispose of the check watcher.
1632		2769
1633	Method 3: If the module to be embedded supports explicit event	2770	Method 3: If the module to be embedded supports explicit event
1634	notification (adns does), you can also make use of the actual watcher	2771	notification (libadns does), you can also make use of the actual watcher
1635	callbacks, and only destroy/create the watchers in the prepare watcher.	2772	callbacks, and only destroy/create the watchers in the prepare watcher.
1636		2773
1637	static void	2774	static void
1638	timer_cb (EV_P_ ev_timer *w, int revents)	2775	timer_cb (EV_P_ ev_timer *w, int revents)
1639	{	2776	{
1640	adns_state ads = (adns_state)w->data;	2777	adns_state ads = (adns_state)w->data;
1641	update_now (EV_A);	2778	update_now (EV_A);
1642		2779
1643	adns_processtimeouts (ads, &tv_now);	2780	adns_processtimeouts (ads, &tv_now);
1644	}	2781	}
1645		2782
1646	static void	2783	static void
1647	io_cb (EV_P_ ev_io *w, int revents)	2784	io_cb (EV_P_ ev_io *w, int revents)
1648	{	2785	{
1649	adns_state ads = (adns_state)w->data;	2786	adns_state ads = (adns_state)w->data;
1650	update_now (EV_A);	2787	update_now (EV_A);
1651		2788
1652	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);	2789	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
1653	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);	2790	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
1654	}	2791	}
1655		2792
1656	// do not ever call adns_afterpoll	2793	// do not ever call adns_afterpoll
1657		2794
1658	Method 4: Do not use a prepare or check watcher because the module you	2795	Method 4: Do not use a prepare or check watcher because the module you
1659	want to embed is too inflexible to support it. Instead, youc na override	2796	want to embed is not flexible enough to support it. Instead, you can
1660	their poll function. The drawback with this solution is that the main	2797	override their poll function. The drawback with this solution is that the
1661	loop is now no longer controllable by EV. The C<Glib::EV> module does	2798	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
1662	this.	2799	this approach, effectively embedding EV as a client into the horrible
		2800	libglib event loop.
1663		2801
1664	static gint	2802	static gint
1665	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	2803	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1666	{	2804	{
1667	int got_events = 0;	2805	int got_events = 0;
1668		2806
1669	for (n = 0; n < nfds; ++n)	2807	for (n = 0; n < nfds; ++n)
1670	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events	2808	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1671		2809
1672	if (timeout >= 0)	2810	if (timeout >= 0)
1673	// create/start timer	2811	// create/start timer
1674		2812
1675	// poll	2813	// poll
1676	ev_loop (EV_A_ 0);	2814	ev_loop (EV_A_ 0);
1677		2815
1678	// stop timer again	2816	// stop timer again
1679	if (timeout >= 0)	2817	if (timeout >= 0)
1680	ev_timer_stop (EV_A_ &to);	2818	ev_timer_stop (EV_A_ &to);
1681		2819
1682	// stop io watchers again - their callbacks should have set	2820	// stop io watchers again - their callbacks should have set
1683	for (n = 0; n < nfds; ++n)	2821	for (n = 0; n < nfds; ++n)
1684	ev_io_stop (EV_A_ iow [n]);	2822	ev_io_stop (EV_A_ iow [n]);
1685		2823
1686	return got_events;	2824	return got_events;
1687	}	2825	}
1688		2826
1689		2827
1690	=head2 C<ev_embed> - when one backend isn't enough...	2828	=head2 C<ev_embed> - when one backend isn't enough...
1691		2829
1692	This is a rather advanced watcher type that lets you embed one event loop	2830	This is a rather advanced watcher type that lets you embed one event loop
…		…
1698	prioritise I/O.	2836	prioritise I/O.
1699		2837
1700	As an example for a bug workaround, the kqueue backend might only support	2838	As an example for a bug workaround, the kqueue backend might only support
1701	sockets on some platform, so it is unusable as generic backend, but you	2839	sockets on some platform, so it is unusable as generic backend, but you
1702	still want to make use of it because you have many sockets and it scales	2840	still want to make use of it because you have many sockets and it scales
1703	so nicely. In this case, you would create a kqueue-based loop and embed it	2841	so nicely. In this case, you would create a kqueue-based loop and embed
1704	into your default loop (which might use e.g. poll). Overall operation will	2842	it into your default loop (which might use e.g. poll). Overall operation
1705	be a bit slower because first libev has to poll and then call kevent, but	2843	will be a bit slower because first libev has to call C<poll> and then
1706	at least you can use both at what they are best.	2844	C<kevent>, but at least you can use both mechanisms for what they are
		2845	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1707		2846
1708	As for prioritising I/O: rarely you have the case where some fds have	2847	As for prioritising I/O: under rare circumstances you have the case where
1709	to be watched and handled very quickly (with low latency), and even	2848	some fds have to be watched and handled very quickly (with low latency),
1710	priorities and idle watchers might have too much overhead. In this case	2849	and even priorities and idle watchers might have too much overhead. In
1711	you would put all the high priority stuff in one loop and all the rest in	2850	this case you would put all the high priority stuff in one loop and all
1712	a second one, and embed the second one in the first.	2851	the rest in a second one, and embed the second one in the first.
1713		2852
1714	As long as the watcher is active, the callback will be invoked every time	2853	As long as the watcher is active, the callback will be invoked every
1715	there might be events pending in the embedded loop. The callback must then	2854	time there might be events pending in the embedded loop. The callback
1716	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2855	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1717	their callbacks (you could also start an idle watcher to give the embedded	2856	sweep and invoke their callbacks (the callback doesn't need to invoke the
1718	loop strictly lower priority for example). You can also set the callback	2857	C<ev_embed_sweep> function directly, it could also start an idle watcher
1719	to C<0>, in which case the embed watcher will automatically execute the	2858	to give the embedded loop strictly lower priority for example).
1720	embedded loop sweep.
1721		2859
1722	As long as the watcher is started it will automatically handle events. The	2860	You can also set the callback to C<0>, in which case the embed watcher
1723	callback will be invoked whenever some events have been handled. You can	2861	will automatically execute the embedded loop sweep whenever necessary.
1724	set the callback to C<0> to avoid having to specify one if you are not
1725	interested in that.
1726		2862
1727	Also, there have not currently been made special provisions for forking:	2863	Fork detection will be handled transparently while the C<ev_embed> watcher
1728	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2864	is active, i.e., the embedded loop will automatically be forked when the
1729	but you will also have to stop and restart any C<ev_embed> watchers	2865	embedding loop forks. In other cases, the user is responsible for calling
1730	yourself.	2866	C<ev_loop_fork> on the embedded loop.
1731		2867
1732	Unfortunately, not all backends are embeddable, only the ones returned by	2868	Unfortunately, not all backends are embeddable: only the ones returned by
1733	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2869	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1734	portable one.	2870	portable one.
1735		2871
1736	So when you want to use this feature you will always have to be prepared	2872	So when you want to use this feature you will always have to be prepared
1737	that you cannot get an embeddable loop. The recommended way to get around	2873	that you cannot get an embeddable loop. The recommended way to get around
1738	this is to have a separate variables for your embeddable loop, try to	2874	this is to have a separate variables for your embeddable loop, try to
1739	create it, and if that fails, use the normal loop for everything:	2875	create it, and if that fails, use the normal loop for everything.
1740		2876
1741	struct ev_loop *loop_hi = ev_default_init (0);	2877	=head3 C<ev_embed> and fork
1742	struct ev_loop *loop_lo = 0;
1743	struct ev_embed embed;
1744
1745	// see if there is a chance of getting one that works
1746	// (remember that a flags value of 0 means autodetection)
1747	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1748	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1749	: 0;
1750		2878
1751	// if we got one, then embed it, otherwise default to loop_hi	2879	While the C<ev_embed> watcher is running, forks in the embedding loop will
1752	if (loop_lo)	2880	automatically be applied to the embedded loop as well, so no special
1753	{	2881	fork handling is required in that case. When the watcher is not running,
1754	ev_embed_init (&embed, 0, loop_lo);	2882	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1755	ev_embed_start (loop_hi, &embed);	2883	as applicable.
1756	}
1757	else
1758	loop_lo = loop_hi;
1759		2884
1760	=head3 Watcher-Specific Functions and Data Members	2885	=head3 Watcher-Specific Functions and Data Members
1761		2886
1762	=over 4	2887	=over 4
1763		2888
…		…
1767		2892
1768	Configures the watcher to embed the given loop, which must be	2893	Configures the watcher to embed the given loop, which must be
1769	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	2894	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1770	invoked automatically, otherwise it is the responsibility of the callback	2895	invoked automatically, otherwise it is the responsibility of the callback
1771	to invoke it (it will continue to be called until the sweep has been done,	2896	to invoke it (it will continue to be called until the sweep has been done,
1772	if you do not want thta, you need to temporarily stop the embed watcher).	2897	if you do not want that, you need to temporarily stop the embed watcher).
1773		2898
1774	=item ev_embed_sweep (loop, ev_embed *)	2899	=item ev_embed_sweep (loop, ev_embed *)
1775		2900
1776	Make a single, non-blocking sweep over the embedded loop. This works	2901	Make a single, non-blocking sweep over the embedded loop. This works
1777	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	2902	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
1778	apropriate way for embedded loops.	2903	appropriate way for embedded loops.
1779		2904
1780	=item struct ev_loop *loop [read-only]	2905	=item struct ev_loop *other [read-only]
1781		2906
1782	The embedded event loop.	2907	The embedded event loop.
1783		2908
1784	=back	2909	=back
		2910
		2911	=head3 Examples
		2912
		2913	Example: Try to get an embeddable event loop and embed it into the default
		2914	event loop. If that is not possible, use the default loop. The default
		2915	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2916	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2917	used).
		2918
		2919	struct ev_loop *loop_hi = ev_default_init (0);
		2920	struct ev_loop *loop_lo = 0;
		2921	ev_embed embed;
		2922
		2923	// see if there is a chance of getting one that works
		2924	// (remember that a flags value of 0 means autodetection)
		2925	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2926	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2927	: 0;
		2928
		2929	// if we got one, then embed it, otherwise default to loop_hi
		2930	if (loop_lo)
		2931	{
		2932	ev_embed_init (&embed, 0, loop_lo);
		2933	ev_embed_start (loop_hi, &embed);
		2934	}
		2935	else
		2936	loop_lo = loop_hi;
		2937
		2938	Example: Check if kqueue is available but not recommended and create
		2939	a kqueue backend for use with sockets (which usually work with any
		2940	kqueue implementation). Store the kqueue/socket-only event loop in
		2941	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2942
		2943	struct ev_loop *loop = ev_default_init (0);
		2944	struct ev_loop *loop_socket = 0;
		2945	ev_embed embed;
		2946
		2947	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2948	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2949	{
		2950	ev_embed_init (&embed, 0, loop_socket);
		2951	ev_embed_start (loop, &embed);
		2952	}
		2953
		2954	if (!loop_socket)
		2955	loop_socket = loop;
		2956
		2957	// now use loop_socket for all sockets, and loop for everything else
1785		2958
1786		2959
1787	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	2960	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
1788		2961
1789	Fork watchers are called when a C<fork ()> was detected (usually because	2962	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
1792	event loop blocks next and before C<ev_check> watchers are being called,	2965	event loop blocks next and before C<ev_check> watchers are being called,
1793	and only in the child after the fork. If whoever good citizen calling	2966	and only in the child after the fork. If whoever good citizen calling
1794	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2967	C<ev_default_fork> cheats and calls it in the wrong process, the fork
1795	handlers will be invoked, too, of course.	2968	handlers will be invoked, too, of course.
1796		2969
		2970	=head3 The special problem of life after fork - how is it possible?
		2971
		2972	Most uses of C<fork()> consist of forking, then some simple calls to set
		2973	up/change the process environment, followed by a call to C<exec()>. This
		2974	sequence should be handled by libev without any problems.
		2975
		2976	This changes when the application actually wants to do event handling
		2977	in the child, or both parent in child, in effect "continuing" after the
		2978	fork.
		2979
		2980	The default mode of operation (for libev, with application help to detect
		2981	forks) is to duplicate all the state in the child, as would be expected
		2982	when I<either> the parent I<or> the child process continues.
		2983
		2984	When both processes want to continue using libev, then this is usually the
		2985	wrong result. In that case, usually one process (typically the parent) is
		2986	supposed to continue with all watchers in place as before, while the other
		2987	process typically wants to start fresh, i.e. without any active watchers.
		2988
		2989	The cleanest and most efficient way to achieve that with libev is to
		2990	simply create a new event loop, which of course will be "empty", and
		2991	use that for new watchers. This has the advantage of not touching more
		2992	memory than necessary, and thus avoiding the copy-on-write, and the
		2993	disadvantage of having to use multiple event loops (which do not support
		2994	signal watchers).
		2995
		2996	When this is not possible, or you want to use the default loop for
		2997	other reasons, then in the process that wants to start "fresh", call
		2998	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2999	the default loop will "orphan" (not stop) all registered watchers, so you
		3000	have to be careful not to execute code that modifies those watchers. Note
		3001	also that in that case, you have to re-register any signal watchers.
		3002
1797	=head3 Watcher-Specific Functions and Data Members	3003	=head3 Watcher-Specific Functions and Data Members
1798		3004
1799	=over 4	3005	=over 4
1800		3006
1801	=item ev_fork_init (ev_signal *, callback)	3007	=item ev_fork_init (ev_signal *, callback)
…		…
1805	believe me.	3011	believe me.
1806		3012
1807	=back	3013	=back
1808		3014
1809		3015
		3016	=head2 C<ev_async> - how to wake up an event loop
		3017
		3018	In general, you cannot use an C<ev_loop> from multiple threads or other
		3019	asynchronous sources such as signal handlers (as opposed to multiple event
		3020	loops - those are of course safe to use in different threads).
		3021
		3022	Sometimes, however, you need to wake up an event loop you do not control,
		3023	for example because it belongs to another thread. This is what C<ev_async>
		3024	watchers do: as long as the C<ev_async> watcher is active, you can signal
		3025	it by calling C<ev_async_send>, which is thread- and signal safe.
		3026
		3027	This functionality is very similar to C<ev_signal> watchers, as signals,
		3028	too, are asynchronous in nature, and signals, too, will be compressed
		3029	(i.e. the number of callback invocations may be less than the number of
		3030	C<ev_async_sent> calls).
		3031
		3032	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		3033	just the default loop.
		3034
		3035	=head3 Queueing
		3036
		3037	C<ev_async> does not support queueing of data in any way. The reason
		3038	is that the author does not know of a simple (or any) algorithm for a
		3039	multiple-writer-single-reader queue that works in all cases and doesn't
		3040	need elaborate support such as pthreads or unportable memory access
		3041	semantics.
		3042
		3043	That means that if you want to queue data, you have to provide your own
		3044	queue. But at least I can tell you how to implement locking around your
		3045	queue:
		3046
		3047	=over 4
		3048
		3049	=item queueing from a signal handler context
		3050
		3051	To implement race-free queueing, you simply add to the queue in the signal
		3052	handler but you block the signal handler in the watcher callback. Here is
		3053	an example that does that for some fictitious SIGUSR1 handler:
		3054
		3055	static ev_async mysig;
		3056
		3057	static void
		3058	sigusr1_handler (void)
		3059	{
		3060	sometype data;
		3061
		3062	// no locking etc.
		3063	queue_put (data);
		3064	ev_async_send (EV_DEFAULT_ &mysig);
		3065	}
		3066
		3067	static void
		3068	mysig_cb (EV_P_ ev_async *w, int revents)
		3069	{
		3070	sometype data;
		3071	sigset_t block, prev;
		3072
		3073	sigemptyset (&block);
		3074	sigaddset (&block, SIGUSR1);
		3075	sigprocmask (SIG_BLOCK, &block, &prev);
		3076
		3077	while (queue_get (&data))
		3078	process (data);
		3079
		3080	if (sigismember (&prev, SIGUSR1)
		3081	sigprocmask (SIG_UNBLOCK, &block, 0);
		3082	}
		3083
		3084	(Note: pthreads in theory requires you to use C<pthread_setmask>
		3085	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		3086	either...).
		3087
		3088	=item queueing from a thread context
		3089
		3090	The strategy for threads is different, as you cannot (easily) block
		3091	threads but you can easily preempt them, so to queue safely you need to
		3092	employ a traditional mutex lock, such as in this pthread example:
		3093
		3094	static ev_async mysig;
		3095	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		3096
		3097	static void
		3098	otherthread (void)
		3099	{
		3100	// only need to lock the actual queueing operation
		3101	pthread_mutex_lock (&mymutex);
		3102	queue_put (data);
		3103	pthread_mutex_unlock (&mymutex);
		3104
		3105	ev_async_send (EV_DEFAULT_ &mysig);
		3106	}
		3107
		3108	static void
		3109	mysig_cb (EV_P_ ev_async *w, int revents)
		3110	{
		3111	pthread_mutex_lock (&mymutex);
		3112
		3113	while (queue_get (&data))
		3114	process (data);
		3115
		3116	pthread_mutex_unlock (&mymutex);
		3117	}
		3118
		3119	=back
		3120
		3121
		3122	=head3 Watcher-Specific Functions and Data Members
		3123
		3124	=over 4
		3125
		3126	=item ev_async_init (ev_async *, callback)
		3127
		3128	Initialises and configures the async watcher - it has no parameters of any
		3129	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		3130	trust me.
		3131
		3132	=item ev_async_send (loop, ev_async *)
		3133
		3134	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		3135	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		3136	C<ev_feed_event>, this call is safe to do from other threads, signal or
		3137	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		3138	section below on what exactly this means).
		3139
		3140	Note that, as with other watchers in libev, multiple events might get
		3141	compressed into a single callback invocation (another way to look at this
		3142	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3143	reset when the event loop detects that).
		3144
		3145	This call incurs the overhead of a system call only once per event loop
		3146	iteration, so while the overhead might be noticeable, it doesn't apply to
		3147	repeated calls to C<ev_async_send> for the same event loop.
		3148
		3149	=item bool = ev_async_pending (ev_async *)
		3150
		3151	Returns a non-zero value when C<ev_async_send> has been called on the
		3152	watcher but the event has not yet been processed (or even noted) by the
		3153	event loop.
		3154
		3155	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3156	the loop iterates next and checks for the watcher to have become active,
		3157	it will reset the flag again. C<ev_async_pending> can be used to very
		3158	quickly check whether invoking the loop might be a good idea.
		3159
		3160	Not that this does I<not> check whether the watcher itself is pending,
		3161	only whether it has been requested to make this watcher pending: there
		3162	is a time window between the event loop checking and resetting the async
		3163	notification, and the callback being invoked.
		3164
		3165	=back
		3166
		3167
1810	=head1 OTHER FUNCTIONS	3168	=head1 OTHER FUNCTIONS
1811		3169
1812	There are some other functions of possible interest. Described. Here. Now.	3170	There are some other functions of possible interest. Described. Here. Now.
1813		3171
1814	=over 4	3172	=over 4
1815		3173
1816	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3174	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1817		3175
1818	This function combines a simple timer and an I/O watcher, calls your	3176	This function combines a simple timer and an I/O watcher, calls your
1819	callback on whichever event happens first and automatically stop both	3177	callback on whichever event happens first and automatically stops both
1820	watchers. This is useful if you want to wait for a single event on an fd	3178	watchers. This is useful if you want to wait for a single event on an fd
1821	or timeout without having to allocate/configure/start/stop/free one or	3179	or timeout without having to allocate/configure/start/stop/free one or
1822	more watchers yourself.	3180	more watchers yourself.
1823		3181
1824	If C<fd> is less than 0, then no I/O watcher will be started and events	3182	If C<fd> is less than 0, then no I/O watcher will be started and the
1825	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3183	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1826	C<events> set will be craeted and started.	3184	the given C<fd> and C<events> set will be created and started.
1827		3185
1828	If C<timeout> is less than 0, then no timeout watcher will be	3186	If C<timeout> is less than 0, then no timeout watcher will be
1829	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3187	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1830	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3188	repeat = 0) will be started. C<0> is a valid timeout.
1831	dubious value.
1832		3189
1833	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3190	The callback has the type C<void (*cb)(int revents, void *arg)> and is
1834	passed an C<revents> set like normal event callbacks (a combination of	3191	passed an C<revents> set like normal event callbacks (a combination of
1835	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3192	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
1836	value passed to C<ev_once>:	3193	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3194	a timeout and an io event at the same time - you probably should give io
		3195	events precedence.
1837		3196
		3197	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3198
1838	static void stdin_ready (int revents, void *arg)	3199	static void stdin_ready (int revents, void *arg)
1839	{	3200	{
1840	if (revents & EV_TIMEOUT)
1841	/* doh, nothing entered */;
1842	else if (revents & EV_READ)	3201	if (revents & EV_READ)
1843	/* stdin might have data for us, joy! */;	3202	/* stdin might have data for us, joy! */;
		3203	else if (revents & EV_TIMER)
		3204	/* doh, nothing entered */;
1844	}	3205	}
1845		3206
1846	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3207	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1847		3208
1848	=item ev_feed_event (ev_loop *, watcher *, int revents)
1849
1850	Feeds the given event set into the event loop, as if the specified event
1851	had happened for the specified watcher (which must be a pointer to an
1852	initialised but not necessarily started event watcher).
1853
1854	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3209	=item ev_feed_fd_event (loop, int fd, int revents)
1855		3210
1856	Feed an event on the given fd, as if a file descriptor backend detected	3211	Feed an event on the given fd, as if a file descriptor backend detected
1857	the given events it.	3212	the given events it.
1858		3213
1859	=item ev_feed_signal_event (ev_loop *loop, int signum)	3214	=item ev_feed_signal_event (loop, int signum)
1860		3215
1861	Feed an event as if the given signal occured (C<loop> must be the default	3216	Feed an event as if the given signal occurred (C<loop> must be the default
1862	loop!).	3217	loop!).
1863		3218
1864	=back	3219	=back
1865		3220
1866		3221
…		…
1882		3237
1883	=item * Priorities are not currently supported. Initialising priorities	3238	=item * Priorities are not currently supported. Initialising priorities
1884	will fail and all watchers will have the same priority, even though there	3239	will fail and all watchers will have the same priority, even though there
1885	is an ev_pri field.	3240	is an ev_pri field.
1886		3241
		3242	=item * In libevent, the last base created gets the signals, in libev, the
		3243	first base created (== the default loop) gets the signals.
		3244
1887	=item * Other members are not supported.	3245	=item * Other members are not supported.
1888		3246
1889	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3247	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1890	to use the libev header file and library.	3248	to use the libev header file and library.
1891		3249
1892	=back	3250	=back
1893		3251
1894	=head1 C++ SUPPORT	3252	=head1 C++ SUPPORT
1895		3253
1896	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3254	Libev comes with some simplistic wrapper classes for C++ that mainly allow
1897	you to use some convinience methods to start/stop watchers and also change	3255	you to use some convenience methods to start/stop watchers and also change
1898	the callback model to a model using method callbacks on objects.	3256	the callback model to a model using method callbacks on objects.
1899		3257
1900	To use it,	3258	To use it,
1901		3259
1902	#include <ev++.h>	3260	#include <ev++.h>
1903		3261
1904	This automatically includes F<ev.h> and puts all of its definitions (many	3262	This automatically includes F<ev.h> and puts all of its definitions (many
1905	of them macros) into the global namespace. All C++ specific things are	3263	of them macros) into the global namespace. All C++ specific things are
1906	put into the C<ev> namespace. It should support all the same embedding	3264	put into the C<ev> namespace. It should support all the same embedding
1907	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	3265	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
1941		3299
1942	=over 4	3300	=over 4
1943		3301
1944	=item ev::TYPE::TYPE ()	3302	=item ev::TYPE::TYPE ()
1945		3303
1946	=item ev::TYPE::TYPE (struct ev_loop *)	3304	=item ev::TYPE::TYPE (loop)
1947		3305
1948	=item ev::TYPE::~TYPE	3306	=item ev::TYPE::~TYPE
1949		3307
1950	The constructor (optionally) takes an event loop to associate the watcher	3308	The constructor (optionally) takes an event loop to associate the watcher
1951	with. If it is omitted, it will use C<EV_DEFAULT>.	3309	with. If it is omitted, it will use C<EV_DEFAULT>.
…		…
1974	your compiler is good :), then the method will be fully inlined into the	3332	your compiler is good :), then the method will be fully inlined into the
1975	thunking function, making it as fast as a direct C callback.	3333	thunking function, making it as fast as a direct C callback.
1976		3334
1977	Example: simple class declaration and watcher initialisation	3335	Example: simple class declaration and watcher initialisation
1978		3336
1979	struct myclass	3337	struct myclass
1980	{	3338	{
1981	void io_cb (ev::io &w, int revents) { }	3339	void io_cb (ev::io &w, int revents) { }
1982	}	3340	}
1983		3341
1984	myclass obj;	3342	myclass obj;
1985	ev::io iow;	3343	ev::io iow;
1986	iow.set <myclass, &myclass::io_cb> (&obj);	3344	iow.set <myclass, &myclass::io_cb> (&obj);
		3345
		3346	=item w->set (object *)
		3347
		3348	This is a variation of a method callback - leaving out the method to call
		3349	will default the method to C<operator ()>, which makes it possible to use
		3350	functor objects without having to manually specify the C<operator ()> all
		3351	the time. Incidentally, you can then also leave out the template argument
		3352	list.
		3353
		3354	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3355	int revents)>.
		3356
		3357	See the method-C<set> above for more details.
		3358
		3359	Example: use a functor object as callback.
		3360
		3361	struct myfunctor
		3362	{
		3363	void operator() (ev::io &w, int revents)
		3364	{
		3365	...
		3366	}
		3367	}
		3368
		3369	myfunctor f;
		3370
		3371	ev::io w;
		3372	w.set (&f);
1987		3373
1988	=item w->set<function> (void *data = 0)	3374	=item w->set<function> (void *data = 0)
1989		3375
1990	Also sets a callback, but uses a static method or plain function as	3376	Also sets a callback, but uses a static method or plain function as
1991	callback. The optional C<data> argument will be stored in the watcher's	3377	callback. The optional C<data> argument will be stored in the watcher's
…		…
1993		3379
1994	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	3380	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
1995		3381
1996	See the method-C<set> above for more details.	3382	See the method-C<set> above for more details.
1997		3383
1998	Example:	3384	Example: Use a plain function as callback.
1999		3385
2000	static void io_cb (ev::io &w, int revents) { }	3386	static void io_cb (ev::io &w, int revents) { }
2001	iow.set <io_cb> ();	3387	iow.set <io_cb> ();
2002		3388
2003	=item w->set (struct ev_loop *)	3389	=item w->set (loop)
2004		3390
2005	Associates a different C<struct ev_loop> with this watcher. You can only	3391	Associates a different C<struct ev_loop> with this watcher. You can only
2006	do this when the watcher is inactive (and not pending either).	3392	do this when the watcher is inactive (and not pending either).
2007		3393
2008	=item w->set ([args])	3394	=item w->set ([arguments])
2009		3395
2010	Basically the same as C<ev_TYPE_set>, with the same args. Must be	3396	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this
2011	called at least once. Unlike the C counterpart, an active watcher gets	3397	method or a suitable start method must be called at least once. Unlike the
2012	automatically stopped and restarted when reconfiguring it with this	3398	C counterpart, an active watcher gets automatically stopped and restarted
2013	method.	3399	when reconfiguring it with this method.
2014		3400
2015	=item w->start ()	3401	=item w->start ()
2016		3402
2017	Starts the watcher. Note that there is no C<loop> argument, as the	3403	Starts the watcher. Note that there is no C<loop> argument, as the
2018	constructor already stores the event loop.	3404	constructor already stores the event loop.
2019		3405
		3406	=item w->start ([arguments])
		3407
		3408	Instead of calling C<set> and C<start> methods separately, it is often
		3409	convenient to wrap them in one call. Uses the same type of arguments as
		3410	the configure C<set> method of the watcher.
		3411
2020	=item w->stop ()	3412	=item w->stop ()
2021		3413
2022	Stops the watcher if it is active. Again, no C<loop> argument.	3414	Stops the watcher if it is active. Again, no C<loop> argument.
2023		3415
2024	=item w->again () C<ev::timer>, C<ev::periodic> only	3416	=item w->again () (C<ev::timer>, C<ev::periodic> only)
2025		3417
2026	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding	3418	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
2027	C<ev_TYPE_again> function.	3419	C<ev_TYPE_again> function.
2028		3420
2029	=item w->sweep () C<ev::embed> only	3421	=item w->sweep () (C<ev::embed> only)
2030		3422
2031	Invokes C<ev_embed_sweep>.	3423	Invokes C<ev_embed_sweep>.
2032		3424
2033	=item w->update () C<ev::stat> only	3425	=item w->update () (C<ev::stat> only)
2034		3426
2035	Invokes C<ev_stat_stat>.	3427	Invokes C<ev_stat_stat>.
2036		3428
2037	=back	3429	=back
2038		3430
2039	=back	3431	=back
2040		3432
2041	Example: Define a class with an IO and idle watcher, start one of them in	3433	Example: Define a class with two I/O and idle watchers, start the I/O
2042	the constructor.	3434	watchers in the constructor.
2043		3435
2044	class myclass	3436	class myclass
2045	{	3437	{
2046	ev_io io; void io_cb (ev::io &w, int revents);	3438	ev::io io ; void io_cb (ev::io &w, int revents);
		3439	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);
2047	ev_idle idle void idle_cb (ev::idle &w, int revents);	3440	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2048		3441
2049	myclass ();	3442	myclass (int fd)
2050	}	3443	{
2051
2052	myclass::myclass (int fd)
2053	{
2054	io .set <myclass, &myclass::io_cb > (this);	3444	io .set <myclass, &myclass::io_cb > (this);
		3445	io2 .set <myclass, &myclass::io2_cb > (this);
2055	idle.set <myclass, &myclass::idle_cb> (this);	3446	idle.set <myclass, &myclass::idle_cb> (this);
2056		3447
2057	io.start (fd, ev::READ);	3448	io.set (fd, ev::WRITE); // configure the watcher
		3449	io.start (); // start it whenever convenient
		3450
		3451	io2.start (fd, ev::READ); // set + start in one call
		3452	}
2058	}	3453	};
		3454
		3455
		3456	=head1 OTHER LANGUAGE BINDINGS
		3457
		3458	Libev does not offer other language bindings itself, but bindings for a
		3459	number of languages exist in the form of third-party packages. If you know
		3460	any interesting language binding in addition to the ones listed here, drop
		3461	me a note.
		3462
		3463	=over 4
		3464
		3465	=item Perl
		3466
		3467	The EV module implements the full libev API and is actually used to test
		3468	libev. EV is developed together with libev. Apart from the EV core module,
		3469	there are additional modules that implement libev-compatible interfaces
		3470	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3471	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3472	and C<EV::Glib>).
		3473
		3474	It can be found and installed via CPAN, its homepage is at
		3475	L<http://software.schmorp.de/pkg/EV>.
		3476
		3477	=item Python
		3478
		3479	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3480	seems to be quite complete and well-documented.
		3481
		3482	=item Ruby
		3483
		3484	Tony Arcieri has written a ruby extension that offers access to a subset
		3485	of the libev API and adds file handle abstractions, asynchronous DNS and
		3486	more on top of it. It can be found via gem servers. Its homepage is at
		3487	L<http://rev.rubyforge.org/>.
		3488
		3489	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3490	makes rev work even on mingw.
		3491
		3492	=item Haskell
		3493
		3494	A haskell binding to libev is available at
		3495	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3496
		3497	=item D
		3498
		3499	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3500	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3501
		3502	=item Ocaml
		3503
		3504	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3505	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3506
		3507	=item Lua
		3508
		3509	Brian Maher has written a partial interface to libev for lua (at the
		3510	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		3511	L<http://github.com/brimworks/lua-ev>.
		3512
		3513	=back
2059		3514
2060		3515
2061	=head1 MACRO MAGIC	3516	=head1 MACRO MAGIC
2062		3517
2063	Libev can be compiled with a variety of options, the most fundemantal is	3518	Libev can be compiled with a variety of options, the most fundamental
2064	C<EV_MULTIPLICITY>. This option determines whether (most) functions and	3519	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2065	callbacks have an initial C<struct ev_loop *> argument.	3520	functions and callbacks have an initial C<struct ev_loop *> argument.
2066		3521
2067	To make it easier to write programs that cope with either variant, the	3522	To make it easier to write programs that cope with either variant, the
2068	following macros are defined:	3523	following macros are defined:
2069		3524
2070	=over 4	3525	=over 4
…		…
2073		3528
2074	This provides the loop I<argument> for functions, if one is required ("ev	3529	This provides the loop I<argument> for functions, if one is required ("ev
2075	loop argument"). The C<EV_A> form is used when this is the sole argument,	3530	loop argument"). The C<EV_A> form is used when this is the sole argument,
2076	C<EV_A_> is used when other arguments are following. Example:	3531	C<EV_A_> is used when other arguments are following. Example:
2077		3532
2078	ev_unref (EV_A);	3533	ev_unref (EV_A);
2079	ev_timer_add (EV_A_ watcher);	3534	ev_timer_add (EV_A_ watcher);
2080	ev_loop (EV_A_ 0);	3535	ev_loop (EV_A_ 0);
2081		3536
2082	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	3537	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2083	which is often provided by the following macro.	3538	which is often provided by the following macro.
2084		3539
2085	=item C<EV_P>, C<EV_P_>	3540	=item C<EV_P>, C<EV_P_>
2086		3541
2087	This provides the loop I<parameter> for functions, if one is required ("ev	3542	This provides the loop I<parameter> for functions, if one is required ("ev
2088	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	3543	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
2089	C<EV_P_> is used when other parameters are following. Example:	3544	C<EV_P_> is used when other parameters are following. Example:
2090		3545
2091	// this is how ev_unref is being declared	3546	// this is how ev_unref is being declared
2092	static void ev_unref (EV_P);	3547	static void ev_unref (EV_P);
2093		3548
2094	// this is how you can declare your typical callback	3549	// this is how you can declare your typical callback
2095	static void cb (EV_P_ ev_timer *w, int revents)	3550	static void cb (EV_P_ ev_timer *w, int revents)
2096		3551
2097	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	3552	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
2098	suitable for use with C<EV_A>.	3553	suitable for use with C<EV_A>.
2099		3554
2100	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3555	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2101		3556
2102	Similar to the other two macros, this gives you the value of the default	3557	Similar to the other two macros, this gives you the value of the default
2103	loop, if multiple loops are supported ("ev loop default").	3558	loop, if multiple loops are supported ("ev loop default").
		3559
		3560	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3561
		3562	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3563	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3564	is undefined when the default loop has not been initialised by a previous
		3565	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3566
		3567	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3568	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
2104		3569
2105	=back	3570	=back
2106		3571
2107	Example: Declare and initialise a check watcher, utilising the above	3572	Example: Declare and initialise a check watcher, utilising the above
2108	macros so it will work regardless of whether multiple loops are supported	3573	macros so it will work regardless of whether multiple loops are supported
2109	or not.	3574	or not.
2110		3575
2111	static void	3576	static void
2112	check_cb (EV_P_ ev_timer *w, int revents)	3577	check_cb (EV_P_ ev_timer *w, int revents)
2113	{	3578	{
2114	ev_check_stop (EV_A_ w);	3579	ev_check_stop (EV_A_ w);
2115	}	3580	}
2116		3581
2117	ev_check check;	3582	ev_check check;
2118	ev_check_init (&check, check_cb);	3583	ev_check_init (&check, check_cb);
2119	ev_check_start (EV_DEFAULT_ &check);	3584	ev_check_start (EV_DEFAULT_ &check);
2120	ev_loop (EV_DEFAULT_ 0);	3585	ev_loop (EV_DEFAULT_ 0);
2121		3586
2122	=head1 EMBEDDING	3587	=head1 EMBEDDING
2123		3588
2124	Libev can (and often is) directly embedded into host	3589	Libev can (and often is) directly embedded into host
2125	applications. Examples of applications that embed it include the Deliantra	3590	applications. Examples of applications that embed it include the Deliantra
2126	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)	3591	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
2127	and rxvt-unicode.	3592	and rxvt-unicode.
2128		3593
2129	The goal is to enable you to just copy the neecssary files into your	3594	The goal is to enable you to just copy the necessary files into your
2130	source directory without having to change even a single line in them, so	3595	source directory without having to change even a single line in them, so
2131	you can easily upgrade by simply copying (or having a checked-out copy of	3596	you can easily upgrade by simply copying (or having a checked-out copy of
2132	libev somewhere in your source tree).	3597	libev somewhere in your source tree).
2133		3598
2134	=head2 FILESETS	3599	=head2 FILESETS
2135		3600
2136	Depending on what features you need you need to include one or more sets of files	3601	Depending on what features you need you need to include one or more sets of files
2137	in your app.	3602	in your application.
2138		3603
2139	=head3 CORE EVENT LOOP	3604	=head3 CORE EVENT LOOP
2140		3605
2141	To include only the libev core (all the C<ev_*> functions), with manual	3606	To include only the libev core (all the C<ev_*> functions), with manual
2142	configuration (no autoconf):	3607	configuration (no autoconf):
2143		3608
2144	#define EV_STANDALONE 1	3609	#define EV_STANDALONE 1
2145	#include "ev.c"	3610	#include "ev.c"
2146		3611
2147	This will automatically include F<ev.h>, too, and should be done in a	3612	This will automatically include F<ev.h>, too, and should be done in a
2148	single C source file only to provide the function implementations. To use	3613	single C source file only to provide the function implementations. To use
2149	it, do the same for F<ev.h> in all files wishing to use this API (best	3614	it, do the same for F<ev.h> in all files wishing to use this API (best
2150	done by writing a wrapper around F<ev.h> that you can include instead and	3615	done by writing a wrapper around F<ev.h> that you can include instead and
2151	where you can put other configuration options):	3616	where you can put other configuration options):
2152		3617
2153	#define EV_STANDALONE 1	3618	#define EV_STANDALONE 1
2154	#include "ev.h"	3619	#include "ev.h"
2155		3620
2156	Both header files and implementation files can be compiled with a C++	3621	Both header files and implementation files can be compiled with a C++
2157	compiler (at least, thats a stated goal, and breakage will be treated	3622	compiler (at least, that's a stated goal, and breakage will be treated
2158	as a bug).	3623	as a bug).
2159		3624
2160	You need the following files in your source tree, or in a directory	3625	You need the following files in your source tree, or in a directory
2161	in your include path (e.g. in libev/ when using -Ilibev):	3626	in your include path (e.g. in libev/ when using -Ilibev):
2162		3627
2163	ev.h	3628	ev.h
2164	ev.c	3629	ev.c
2165	ev_vars.h	3630	ev_vars.h
2166	ev_wrap.h	3631	ev_wrap.h
2167		3632
2168	ev_win32.c required on win32 platforms only	3633	ev_win32.c required on win32 platforms only
2169		3634
2170	ev_select.c only when select backend is enabled (which is enabled by default)	3635	ev_select.c only when select backend is enabled (which is enabled by default)
2171	ev_poll.c only when poll backend is enabled (disabled by default)	3636	ev_poll.c only when poll backend is enabled (disabled by default)
2172	ev_epoll.c only when the epoll backend is enabled (disabled by default)	3637	ev_epoll.c only when the epoll backend is enabled (disabled by default)
2173	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	3638	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2174	ev_port.c only when the solaris port backend is enabled (disabled by default)	3639	ev_port.c only when the solaris port backend is enabled (disabled by default)
2175		3640
2176	F<ev.c> includes the backend files directly when enabled, so you only need	3641	F<ev.c> includes the backend files directly when enabled, so you only need
2177	to compile this single file.	3642	to compile this single file.
2178		3643
2179	=head3 LIBEVENT COMPATIBILITY API	3644	=head3 LIBEVENT COMPATIBILITY API
2180		3645
2181	To include the libevent compatibility API, also include:	3646	To include the libevent compatibility API, also include:
2182		3647
2183	#include "event.c"	3648	#include "event.c"
2184		3649
2185	in the file including F<ev.c>, and:	3650	in the file including F<ev.c>, and:
2186		3651
2187	#include "event.h"	3652	#include "event.h"
2188		3653
2189	in the files that want to use the libevent API. This also includes F<ev.h>.	3654	in the files that want to use the libevent API. This also includes F<ev.h>.
2190		3655
2191	You need the following additional files for this:	3656	You need the following additional files for this:
2192		3657
2193	event.h	3658	event.h
2194	event.c	3659	event.c
2195		3660
2196	=head3 AUTOCONF SUPPORT	3661	=head3 AUTOCONF SUPPORT
2197		3662
2198	Instead of using C<EV_STANDALONE=1> and providing your config in	3663	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2199	whatever way you want, you can also C<m4_include([libev.m4])> in your	3664	whatever way you want, you can also C<m4_include([libev.m4])> in your
2200	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	3665	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2201	include F<config.h> and configure itself accordingly.	3666	include F<config.h> and configure itself accordingly.
2202		3667
2203	For this of course you need the m4 file:	3668	For this of course you need the m4 file:
2204		3669
2205	libev.m4	3670	libev.m4
2206		3671
2207	=head2 PREPROCESSOR SYMBOLS/MACROS	3672	=head2 PREPROCESSOR SYMBOLS/MACROS
2208		3673
2209	Libev can be configured via a variety of preprocessor symbols you have to define	3674	Libev can be configured via a variety of preprocessor symbols you have to
2210	before including any of its files. The default is not to build for multiplicity	3675	define before including (or compiling) any of its files. The default in
2211	and only include the select backend.	3676	the absence of autoconf is documented for every option.
		3677
		3678	Symbols marked with "(h)" do not change the ABI, and can have different
		3679	values when compiling libev vs. including F<ev.h>, so it is permissible
		3680	to redefine them before including F<ev.h> without breaking compatibility
		3681	to a compiled library. All other symbols change the ABI, which means all
		3682	users of libev and the libev code itself must be compiled with compatible
		3683	settings.
2212		3684
2213	=over 4	3685	=over 4
2214		3686
2215	=item EV_STANDALONE	3687	=item EV_STANDALONE (h)
2216		3688
2217	Must always be C<1> if you do not use autoconf configuration, which	3689	Must always be C<1> if you do not use autoconf configuration, which
2218	keeps libev from including F<config.h>, and it also defines dummy	3690	keeps libev from including F<config.h>, and it also defines dummy
2219	implementations for some libevent functions (such as logging, which is not	3691	implementations for some libevent functions (such as logging, which is not
2220	supported). It will also not define any of the structs usually found in	3692	supported). It will also not define any of the structs usually found in
2221	F<event.h> that are not directly supported by the libev core alone.	3693	F<event.h> that are not directly supported by the libev core alone.
2222		3694
		3695	In standalone mode, libev will still try to automatically deduce the
		3696	configuration, but has to be more conservative.
		3697
2223	=item EV_USE_MONOTONIC	3698	=item EV_USE_MONOTONIC
2224		3699
2225	If defined to be C<1>, libev will try to detect the availability of the	3700	If defined to be C<1>, libev will try to detect the availability of the
2226	monotonic clock option at both compiletime and runtime. Otherwise no use	3701	monotonic clock option at both compile time and runtime. Otherwise no
2227	of the monotonic clock option will be attempted. If you enable this, you	3702	use of the monotonic clock option will be attempted. If you enable this,
2228	usually have to link against librt or something similar. Enabling it when	3703	you usually have to link against librt or something similar. Enabling it
2229	the functionality isn't available is safe, though, althoguh you have	3704	when the functionality isn't available is safe, though, although you have
2230	to make sure you link against any libraries where the C<clock_gettime>	3705	to make sure you link against any libraries where the C<clock_gettime>
2231	function is hiding in (often F<-lrt>).	3706	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2232		3707
2233	=item EV_USE_REALTIME	3708	=item EV_USE_REALTIME
2234		3709
2235	If defined to be C<1>, libev will try to detect the availability of the	3710	If defined to be C<1>, libev will try to detect the availability of the
2236	realtime clock option at compiletime (and assume its availability at	3711	real-time clock option at compile time (and assume its availability
2237	runtime if successful). Otherwise no use of the realtime clock option will	3712	at runtime if successful). Otherwise no use of the real-time clock
2238	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3713	option will be attempted. This effectively replaces C<gettimeofday>
2239	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See tzhe note about libraries	3714	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2240	in the description of C<EV_USE_MONOTONIC>, though.	3715	correctness. See the note about libraries in the description of
		3716	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3717	C<EV_USE_CLOCK_SYSCALL>.
		3718
		3719	=item EV_USE_CLOCK_SYSCALL
		3720
		3721	If defined to be C<1>, libev will try to use a direct syscall instead
		3722	of calling the system-provided C<clock_gettime> function. This option
		3723	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3724	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3725	programs needlessly. Using a direct syscall is slightly slower (in
		3726	theory), because no optimised vdso implementation can be used, but avoids
		3727	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3728	higher, as it simplifies linking (no need for C<-lrt>).
		3729
		3730	=item EV_USE_NANOSLEEP
		3731
		3732	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		3733	and will use it for delays. Otherwise it will use C<select ()>.
		3734
		3735	=item EV_USE_EVENTFD
		3736
		3737	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3738	available and will probe for kernel support at runtime. This will improve
		3739	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3740	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3741	2.7 or newer, otherwise disabled.
2241		3742
2242	=item EV_USE_SELECT	3743	=item EV_USE_SELECT
2243		3744
2244	If undefined or defined to be C<1>, libev will compile in support for the	3745	If undefined or defined to be C<1>, libev will compile in support for the
2245	C<select>(2) backend. No attempt at autodetection will be done: if no	3746	C<select>(2) backend. No attempt at auto-detection will be done: if no
2246	other method takes over, select will be it. Otherwise the select backend	3747	other method takes over, select will be it. Otherwise the select backend
2247	will not be compiled in.	3748	will not be compiled in.
2248		3749
2249	=item EV_SELECT_USE_FD_SET	3750	=item EV_SELECT_USE_FD_SET
2250		3751
2251	If defined to C<1>, then the select backend will use the system C<fd_set>	3752	If defined to C<1>, then the select backend will use the system C<fd_set>
2252	structure. This is useful if libev doesn't compile due to a missing	3753	structure. This is useful if libev doesn't compile due to a missing
2253	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	3754	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2254	exotic systems. This usually limits the range of file descriptors to some	3755	on exotic systems. This usually limits the range of file descriptors to
2255	low limit such as 1024 or might have other limitations (winsocket only	3756	some low limit such as 1024 or might have other limitations (winsocket
2256	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3757	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2257	influence the size of the C<fd_set> used.	3758	configures the maximum size of the C<fd_set>.
2258		3759
2259	=item EV_SELECT_IS_WINSOCKET	3760	=item EV_SELECT_IS_WINSOCKET
2260		3761
2261	When defined to C<1>, the select backend will assume that	3762	When defined to C<1>, the select backend will assume that
2262	select/socket/connect etc. don't understand file descriptors but	3763	select/socket/connect etc. don't understand file descriptors but
…		…
2264	be used is the winsock select). This means that it will call	3765	be used is the winsock select). This means that it will call
2265	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3766	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2266	it is assumed that all these functions actually work on fds, even	3767	it is assumed that all these functions actually work on fds, even
2267	on win32. Should not be defined on non-win32 platforms.	3768	on win32. Should not be defined on non-win32 platforms.
2268		3769
		3770	=item EV_FD_TO_WIN32_HANDLE(fd)
		3771
		3772	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3773	file descriptors to socket handles. When not defining this symbol (the
		3774	default), then libev will call C<_get_osfhandle>, which is usually
		3775	correct. In some cases, programs use their own file descriptor management,
		3776	in which case they can provide this function to map fds to socket handles.
		3777
		3778	=item EV_WIN32_HANDLE_TO_FD(handle)
		3779
		3780	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		3781	using the standard C<_open_osfhandle> function. For programs implementing
		3782	their own fd to handle mapping, overwriting this function makes it easier
		3783	to do so. This can be done by defining this macro to an appropriate value.
		3784
		3785	=item EV_WIN32_CLOSE_FD(fd)
		3786
		3787	If programs implement their own fd to handle mapping on win32, then this
		3788	macro can be used to override the C<close> function, useful to unregister
		3789	file descriptors again. Note that the replacement function has to close
		3790	the underlying OS handle.
		3791
2269	=item EV_USE_POLL	3792	=item EV_USE_POLL
2270		3793
2271	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3794	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2272	backend. Otherwise it will be enabled on non-win32 platforms. It	3795	backend. Otherwise it will be enabled on non-win32 platforms. It
2273	takes precedence over select.	3796	takes precedence over select.
2274		3797
2275	=item EV_USE_EPOLL	3798	=item EV_USE_EPOLL
2276		3799
2277	If defined to be C<1>, libev will compile in support for the Linux	3800	If defined to be C<1>, libev will compile in support for the Linux
2278	C<epoll>(7) backend. Its availability will be detected at runtime,	3801	C<epoll>(7) backend. Its availability will be detected at runtime,
2279	otherwise another method will be used as fallback. This is the	3802	otherwise another method will be used as fallback. This is the preferred
2280	preferred backend for GNU/Linux systems.	3803	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3804	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2281		3805
2282	=item EV_USE_KQUEUE	3806	=item EV_USE_KQUEUE
2283		3807
2284	If defined to be C<1>, libev will compile in support for the BSD style	3808	If defined to be C<1>, libev will compile in support for the BSD style
2285	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	3809	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2298	otherwise another method will be used as fallback. This is the preferred	3822	otherwise another method will be used as fallback. This is the preferred
2299	backend for Solaris 10 systems.	3823	backend for Solaris 10 systems.
2300		3824
2301	=item EV_USE_DEVPOLL	3825	=item EV_USE_DEVPOLL
2302		3826
2303	reserved for future expansion, works like the USE symbols above.	3827	Reserved for future expansion, works like the USE symbols above.
2304		3828
2305	=item EV_USE_INOTIFY	3829	=item EV_USE_INOTIFY
2306		3830
2307	If defined to be C<1>, libev will compile in support for the Linux inotify	3831	If defined to be C<1>, libev will compile in support for the Linux inotify
2308	interface to speed up C<ev_stat> watchers. Its actual availability will	3832	interface to speed up C<ev_stat> watchers. Its actual availability will
2309	be detected at runtime.	3833	be detected at runtime. If undefined, it will be enabled if the headers
		3834	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2310		3835
		3836	=item EV_ATOMIC_T
		3837
		3838	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3839	access is atomic with respect to other threads or signal contexts. No such
		3840	type is easily found in the C language, so you can provide your own type
		3841	that you know is safe for your purposes. It is used both for signal handler "locking"
		3842	as well as for signal and thread safety in C<ev_async> watchers.
		3843
		3844	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3845	(from F<signal.h>), which is usually good enough on most platforms.
		3846
2311	=item EV_H	3847	=item EV_H (h)
2312		3848
2313	The name of the F<ev.h> header file used to include it. The default if	3849	The name of the F<ev.h> header file used to include it. The default if
2314	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This	3850	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2315	can be used to virtually rename the F<ev.h> header file in case of conflicts.	3851	used to virtually rename the F<ev.h> header file in case of conflicts.
2316		3852
2317	=item EV_CONFIG_H	3853	=item EV_CONFIG_H (h)
2318		3854
2319	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	3855	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2320	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	3856	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2321	C<EV_H>, above.	3857	C<EV_H>, above.
2322		3858
2323	=item EV_EVENT_H	3859	=item EV_EVENT_H (h)
2324		3860
2325	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	3861	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2326	of how the F<event.h> header can be found.	3862	of how the F<event.h> header can be found, the default is C<"event.h">.
2327		3863
2328	=item EV_PROTOTYPES	3864	=item EV_PROTOTYPES (h)
2329		3865
2330	If defined to be C<0>, then F<ev.h> will not define any function	3866	If defined to be C<0>, then F<ev.h> will not define any function
2331	prototypes, but still define all the structs and other symbols. This is	3867	prototypes, but still define all the structs and other symbols. This is
2332	occasionally useful if you want to provide your own wrapper functions	3868	occasionally useful if you want to provide your own wrapper functions
2333	around libev functions.	3869	around libev functions.
…		…
2352	When doing priority-based operations, libev usually has to linearly search	3888	When doing priority-based operations, libev usually has to linearly search
2353	all the priorities, so having many of them (hundreds) uses a lot of space	3889	all the priorities, so having many of them (hundreds) uses a lot of space
2354	and time, so using the defaults of five priorities (-2 .. +2) is usually	3890	and time, so using the defaults of five priorities (-2 .. +2) is usually
2355	fine.	3891	fine.
2356		3892
2357	If your embedding app does not need any priorities, defining these both to	3893	If your embedding application does not need any priorities, defining these
2358	C<0> will save some memory and cpu.	3894	both to C<0> will save some memory and CPU.
2359		3895
2360	=item EV_PERIODIC_ENABLE	3896	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		3897	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		3898	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
2361		3899
2362	If undefined or defined to be C<1>, then periodic timers are supported. If	3900	If undefined or defined to be C<1> (and the platform supports it), then
2363	defined to be C<0>, then they are not. Disabling them saves a few kB of	3901	the respective watcher type is supported. If defined to be C<0>, then it
2364	code.	3902	is not. Disabling watcher types mainly saves code size.
2365		3903
2366	=item EV_IDLE_ENABLE	3904	=item EV_FEATURES
2367
2368	If undefined or defined to be C<1>, then idle watchers are supported. If
2369	defined to be C<0>, then they are not. Disabling them saves a few kB of
2370	code.
2371
2372	=item EV_EMBED_ENABLE
2373
2374	If undefined or defined to be C<1>, then embed watchers are supported. If
2375	defined to be C<0>, then they are not.
2376
2377	=item EV_STAT_ENABLE
2378
2379	If undefined or defined to be C<1>, then stat watchers are supported. If
2380	defined to be C<0>, then they are not.
2381
2382	=item EV_FORK_ENABLE
2383
2384	If undefined or defined to be C<1>, then fork watchers are supported. If
2385	defined to be C<0>, then they are not.
2386
2387	=item EV_MINIMAL
2388		3905
2389	If you need to shave off some kilobytes of code at the expense of some	3906	If you need to shave off some kilobytes of code at the expense of some
2390	speed, define this symbol to C<1>. Currently only used for gcc to override	3907	speed (but with the full API), you can define this symbol to request
2391	some inlining decisions, saves roughly 30% codesize of amd64.	3908	certain subsets of functionality. The default is to enable all features
		3909	that can be enabled on the platform.
		3910
		3911	A typical way to use this symbol is to define it to C<0> (or to a bitset
		3912	with some broad features you want) and then selectively re-enable
		3913	additional parts you want, for example if you want everything minimal,
		3914	but multiple event loop support, async and child watchers and the poll
		3915	backend, use this:
		3916
		3917	#define EV_FEATURES 0
		3918	#define EV_MULTIPLICITY 1
		3919	#define EV_USE_POLL 1
		3920	#define EV_CHILD_ENABLE 1
		3921	#define EV_ASYNC_ENABLE 1
		3922
		3923	The actual value is a bitset, it can be a combination of the following
		3924	values:
		3925
		3926	=over 4
		3927
		3928	=item C<1> - faster/larger code
		3929
		3930	Use larger code to speed up some operations.
		3931
		3932	Currently this is used to override some inlining decisions (enlarging the
		3933	code size by roughly 30% on amd64).
		3934
		3935	When optimising for size, use of compiler flags such as C<-Os> with
		3936	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		3937	assertions.
		3938
		3939	=item C<2> - faster/larger data structures
		3940
		3941	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		3942	hash table sizes and so on. This will usually further increase code size
		3943	and can additionally have an effect on the size of data structures at
		3944	runtime.
		3945
		3946	=item C<4> - full API configuration
		3947
		3948	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		3949	enables multiplicity (C<EV_MULTIPLICITY>=1).
		3950
		3951	=item C<8> - full API
		3952
		3953	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		3954	details on which parts of the API are still available without this
		3955	feature, and do not complain if this subset changes over time.
		3956
		3957	=item C<16> - enable all optional watcher types
		3958
		3959	Enables all optional watcher types. If you want to selectively enable
		3960	only some watcher types other than I/O and timers (e.g. prepare,
		3961	embed, async, child...) you can enable them manually by defining
		3962	C<EV_watchertype_ENABLE> to C<1> instead.
		3963
		3964	=item C<32> - enable all backends
		3965
		3966	This enables all backends - without this feature, you need to enable at
		3967	least one backend manually (C<EV_USE_SELECT> is a good choice).
		3968
		3969	=item C<64> - enable OS-specific "helper" APIs
		3970
		3971	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		3972	default.
		3973
		3974	=back
		3975
		3976	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		3977	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		3978	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		3979	watchers, timers and monotonic clock support.
		3980
		3981	With an intelligent-enough linker (gcc+binutils are intelligent enough
		3982	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		3983	your program might be left out as well - a binary starting a timer and an
		3984	I/O watcher then might come out at only 5Kb.
		3985
		3986	=item EV_AVOID_STDIO
		3987
		3988	If this is set to C<1> at compiletime, then libev will avoid using stdio
		3989	functions (printf, scanf, perror etc.). This will increase the code size
		3990	somewhat, but if your program doesn't otherwise depend on stdio and your
		3991	libc allows it, this avoids linking in the stdio library which is quite
		3992	big.
		3993
		3994	Note that error messages might become less precise when this option is
		3995	enabled.
		3996
		3997	=item EV_NSIG
		3998
		3999	The highest supported signal number, +1 (or, the number of
		4000	signals): Normally, libev tries to deduce the maximum number of signals
		4001	automatically, but sometimes this fails, in which case it can be
		4002	specified. Also, using a lower number than detected (C<32> should be
		4003	good for about any system in existence) can save some memory, as libev
		4004	statically allocates some 12-24 bytes per signal number.
2392		4005
2393	=item EV_PID_HASHSIZE	4006	=item EV_PID_HASHSIZE
2394		4007
2395	C<ev_child> watchers use a small hash table to distribute workload by	4008	C<ev_child> watchers use a small hash table to distribute workload by
2396	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	4009	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
2397	than enough. If you need to manage thousands of children you might want to	4010	usually more than enough. If you need to manage thousands of children you
2398	increase this value (I<must> be a power of two).	4011	might want to increase this value (I<must> be a power of two).
2399		4012
2400	=item EV_INOTIFY_HASHSIZE	4013	=item EV_INOTIFY_HASHSIZE
2401		4014
2402	C<ev_staz> watchers use a small hash table to distribute workload by	4015	C<ev_stat> watchers use a small hash table to distribute workload by
2403	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	4016	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
2404	usually more than enough. If you need to manage thousands of C<ev_stat>	4017	disabled), usually more than enough. If you need to manage thousands of
2405	watchers you might want to increase this value (I<must> be a power of	4018	C<ev_stat> watchers you might want to increase this value (I<must> be a
2406	two).	4019	power of two).
		4020
		4021	=item EV_USE_4HEAP
		4022
		4023	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4024	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		4025	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		4026	faster performance with many (thousands) of watchers.
		4027
		4028	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4029	will be C<0>.
		4030
		4031	=item EV_HEAP_CACHE_AT
		4032
		4033	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4034	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		4035	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		4036	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		4037	but avoids random read accesses on heap changes. This improves performance
		4038	noticeably with many (hundreds) of watchers.
		4039
		4040	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4041	will be C<0>.
		4042
		4043	=item EV_VERIFY
		4044
		4045	Controls how much internal verification (see C<ev_verify ()>) will
		4046	be done: If set to C<0>, no internal verification code will be compiled
		4047	in. If set to C<1>, then verification code will be compiled in, but not
		4048	called. If set to C<2>, then the internal verification code will be
		4049	called once per loop, which can slow down libev. If set to C<3>, then the
		4050	verification code will be called very frequently, which will slow down
		4051	libev considerably.
		4052
		4053	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4054	will be C<0>.
2407		4055
2408	=item EV_COMMON	4056	=item EV_COMMON
2409		4057
2410	By default, all watchers have a C<void *data> member. By redefining	4058	By default, all watchers have a C<void *data> member. By redefining
2411	this macro to a something else you can include more and other types of	4059	this macro to something else you can include more and other types of
2412	members. You have to define it each time you include one of the files,	4060	members. You have to define it each time you include one of the files,
2413	though, and it must be identical each time.	4061	though, and it must be identical each time.
2414		4062
2415	For example, the perl EV module uses something like this:	4063	For example, the perl EV module uses something like this:
2416		4064
2417	#define EV_COMMON \	4065	#define EV_COMMON \
2418	SV *self; /* contains this struct */ \	4066	SV *self; /* contains this struct */ \
2419	SV *cb_sv, *fh /* note no trailing ";" */	4067	SV *cb_sv, *fh /* note no trailing ";" */
2420		4068
2421	=item EV_CB_DECLARE (type)	4069	=item EV_CB_DECLARE (type)
2422		4070
2423	=item EV_CB_INVOKE (watcher, revents)	4071	=item EV_CB_INVOKE (watcher, revents)
2424		4072
2425	=item ev_set_cb (ev, cb)	4073	=item ev_set_cb (ev, cb)
2426		4074
2427	Can be used to change the callback member declaration in each watcher,	4075	Can be used to change the callback member declaration in each watcher,
2428	and the way callbacks are invoked and set. Must expand to a struct member	4076	and the way callbacks are invoked and set. Must expand to a struct member
2429	definition and a statement, respectively. See the F<ev.v> header file for	4077	definition and a statement, respectively. See the F<ev.h> header file for
2430	their default definitions. One possible use for overriding these is to	4078	their default definitions. One possible use for overriding these is to
2431	avoid the C<struct ev_loop *> as first argument in all cases, or to use	4079	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2432	method calls instead of plain function calls in C++.	4080	method calls instead of plain function calls in C++.
		4081
		4082	=back
		4083
		4084	=head2 EXPORTED API SYMBOLS
		4085
		4086	If you need to re-export the API (e.g. via a DLL) and you need a list of
		4087	exported symbols, you can use the provided F<Symbol.*> files which list
		4088	all public symbols, one per line:
		4089
		4090	Symbols.ev for libev proper
		4091	Symbols.event for the libevent emulation
		4092
		4093	This can also be used to rename all public symbols to avoid clashes with
		4094	multiple versions of libev linked together (which is obviously bad in
		4095	itself, but sometimes it is inconvenient to avoid this).
		4096
		4097	A sed command like this will create wrapper C<#define>'s that you need to
		4098	include before including F<ev.h>:
		4099
		4100	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		4101
		4102	This would create a file F<wrap.h> which essentially looks like this:
		4103
		4104	#define ev_backend myprefix_ev_backend
		4105	#define ev_check_start myprefix_ev_check_start
		4106	#define ev_check_stop myprefix_ev_check_stop
		4107	...
2433		4108
2434	=head2 EXAMPLES	4109	=head2 EXAMPLES
2435		4110
2436	For a real-world example of a program the includes libev	4111	For a real-world example of a program the includes libev
2437	verbatim, you can have a look at the EV perl module	4112	verbatim, you can have a look at the EV perl module
…		…
2442	file.	4117	file.
2443		4118
2444	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	4119	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2445	that everybody includes and which overrides some configure choices:	4120	that everybody includes and which overrides some configure choices:
2446		4121
2447	#define EV_MINIMAL 1	4122	#define EV_FEATURES 8
2448	#define EV_USE_POLL 0	4123	#define EV_USE_SELECT 1
2449	#define EV_MULTIPLICITY 0
2450	#define EV_PERIODIC_ENABLE 0	4124	#define EV_PREPARE_ENABLE 1
		4125	#define EV_IDLE_ENABLE 1
2451	#define EV_STAT_ENABLE 0	4126	#define EV_SIGNAL_ENABLE 1
2452	#define EV_FORK_ENABLE 0	4127	#define EV_CHILD_ENABLE 1
		4128	#define EV_USE_STDEXCEPT 0
2453	#define EV_CONFIG_H <config.h>	4129	#define EV_CONFIG_H <config.h>
2454	#define EV_MINPRI 0
2455	#define EV_MAXPRI 0
2456		4130
2457	#include "ev++.h"	4131	#include "ev++.h"
2458		4132
2459	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4133	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2460		4134
2461	#include "ev_cpp.h"	4135	#include "ev_cpp.h"
2462	#include "ev.c"	4136	#include "ev.c"
2463		4137
		4138	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
2464		4139
		4140	=head2 THREADS AND COROUTINES
		4141
		4142	=head3 THREADS
		4143
		4144	All libev functions are reentrant and thread-safe unless explicitly
		4145	documented otherwise, but libev implements no locking itself. This means
		4146	that you can use as many loops as you want in parallel, as long as there
		4147	are no concurrent calls into any libev function with the same loop
		4148	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4149	of course): libev guarantees that different event loops share no data
		4150	structures that need any locking.
		4151
		4152	Or to put it differently: calls with different loop parameters can be done
		4153	concurrently from multiple threads, calls with the same loop parameter
		4154	must be done serially (but can be done from different threads, as long as
		4155	only one thread ever is inside a call at any point in time, e.g. by using
		4156	a mutex per loop).
		4157
		4158	Specifically to support threads (and signal handlers), libev implements
		4159	so-called C<ev_async> watchers, which allow some limited form of
		4160	concurrency on the same event loop, namely waking it up "from the
		4161	outside".
		4162
		4163	If you want to know which design (one loop, locking, or multiple loops
		4164	without or something else still) is best for your problem, then I cannot
		4165	help you, but here is some generic advice:
		4166
		4167	=over 4
		4168
		4169	=item * most applications have a main thread: use the default libev loop
		4170	in that thread, or create a separate thread running only the default loop.
		4171
		4172	This helps integrating other libraries or software modules that use libev
		4173	themselves and don't care/know about threading.
		4174
		4175	=item * one loop per thread is usually a good model.
		4176
		4177	Doing this is almost never wrong, sometimes a better-performance model
		4178	exists, but it is always a good start.
		4179
		4180	=item * other models exist, such as the leader/follower pattern, where one
		4181	loop is handed through multiple threads in a kind of round-robin fashion.
		4182
		4183	Choosing a model is hard - look around, learn, know that usually you can do
		4184	better than you currently do :-)
		4185
		4186	=item * often you need to talk to some other thread which blocks in the
		4187	event loop.
		4188
		4189	C<ev_async> watchers can be used to wake them up from other threads safely
		4190	(or from signal contexts...).
		4191
		4192	An example use would be to communicate signals or other events that only
		4193	work in the default loop by registering the signal watcher with the
		4194	default loop and triggering an C<ev_async> watcher from the default loop
		4195	watcher callback into the event loop interested in the signal.
		4196
		4197	=back
		4198
		4199	=head4 THREAD LOCKING EXAMPLE
		4200
		4201	Here is a fictitious example of how to run an event loop in a different
		4202	thread than where callbacks are being invoked and watchers are
		4203	created/added/removed.
		4204
		4205	For a real-world example, see the C<EV::Loop::Async> perl module,
		4206	which uses exactly this technique (which is suited for many high-level
		4207	languages).
		4208
		4209	The example uses a pthread mutex to protect the loop data, a condition
		4210	variable to wait for callback invocations, an async watcher to notify the
		4211	event loop thread and an unspecified mechanism to wake up the main thread.
		4212
		4213	First, you need to associate some data with the event loop:
		4214
		4215	typedef struct {
		4216	mutex_t lock; /* global loop lock */
		4217	ev_async async_w;
		4218	thread_t tid;
		4219	cond_t invoke_cv;
		4220	} userdata;
		4221
		4222	void prepare_loop (EV_P)
		4223	{
		4224	// for simplicity, we use a static userdata struct.
		4225	static userdata u;
		4226
		4227	ev_async_init (&u->async_w, async_cb);
		4228	ev_async_start (EV_A_ &u->async_w);
		4229
		4230	pthread_mutex_init (&u->lock, 0);
		4231	pthread_cond_init (&u->invoke_cv, 0);
		4232
		4233	// now associate this with the loop
		4234	ev_set_userdata (EV_A_ u);
		4235	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4236	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4237
		4238	// then create the thread running ev_loop
		4239	pthread_create (&u->tid, 0, l_run, EV_A);
		4240	}
		4241
		4242	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4243	solely to wake up the event loop so it takes notice of any new watchers
		4244	that might have been added:
		4245
		4246	static void
		4247	async_cb (EV_P_ ev_async *w, int revents)
		4248	{
		4249	// just used for the side effects
		4250	}
		4251
		4252	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4253	protecting the loop data, respectively.
		4254
		4255	static void
		4256	l_release (EV_P)
		4257	{
		4258	userdata *u = ev_userdata (EV_A);
		4259	pthread_mutex_unlock (&u->lock);
		4260	}
		4261
		4262	static void
		4263	l_acquire (EV_P)
		4264	{
		4265	userdata *u = ev_userdata (EV_A);
		4266	pthread_mutex_lock (&u->lock);
		4267	}
		4268
		4269	The event loop thread first acquires the mutex, and then jumps straight
		4270	into C<ev_loop>:
		4271
		4272	void *
		4273	l_run (void *thr_arg)
		4274	{
		4275	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		4276
		4277	l_acquire (EV_A);
		4278	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4279	ev_loop (EV_A_ 0);
		4280	l_release (EV_A);
		4281
		4282	return 0;
		4283	}
		4284
		4285	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4286	signal the main thread via some unspecified mechanism (signals? pipe
		4287	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4288	have been called (in a while loop because a) spurious wakeups are possible
		4289	and b) skipping inter-thread-communication when there are no pending
		4290	watchers is very beneficial):
		4291
		4292	static void
		4293	l_invoke (EV_P)
		4294	{
		4295	userdata *u = ev_userdata (EV_A);
		4296
		4297	while (ev_pending_count (EV_A))
		4298	{
		4299	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4300	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4301	}
		4302	}
		4303
		4304	Now, whenever the main thread gets told to invoke pending watchers, it
		4305	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4306	thread to continue:
		4307
		4308	static void
		4309	real_invoke_pending (EV_P)
		4310	{
		4311	userdata *u = ev_userdata (EV_A);
		4312
		4313	pthread_mutex_lock (&u->lock);
		4314	ev_invoke_pending (EV_A);
		4315	pthread_cond_signal (&u->invoke_cv);
		4316	pthread_mutex_unlock (&u->lock);
		4317	}
		4318
		4319	Whenever you want to start/stop a watcher or do other modifications to an
		4320	event loop, you will now have to lock:
		4321
		4322	ev_timer timeout_watcher;
		4323	userdata *u = ev_userdata (EV_A);
		4324
		4325	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4326
		4327	pthread_mutex_lock (&u->lock);
		4328	ev_timer_start (EV_A_ &timeout_watcher);
		4329	ev_async_send (EV_A_ &u->async_w);
		4330	pthread_mutex_unlock (&u->lock);
		4331
		4332	Note that sending the C<ev_async> watcher is required because otherwise
		4333	an event loop currently blocking in the kernel will have no knowledge
		4334	about the newly added timer. By waking up the loop it will pick up any new
		4335	watchers in the next event loop iteration.
		4336
		4337	=head3 COROUTINES
		4338
		4339	Libev is very accommodating to coroutines ("cooperative threads"):
		4340	libev fully supports nesting calls to its functions from different
		4341	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		4342	different coroutines, and switch freely between both coroutines running
		4343	the loop, as long as you don't confuse yourself). The only exception is
		4344	that you must not do this from C<ev_periodic> reschedule callbacks.
		4345
		4346	Care has been taken to ensure that libev does not keep local state inside
		4347	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		4348	they do not call any callbacks.
		4349
		4350	=head2 COMPILER WARNINGS
		4351
		4352	Depending on your compiler and compiler settings, you might get no or a
		4353	lot of warnings when compiling libev code. Some people are apparently
		4354	scared by this.
		4355
		4356	However, these are unavoidable for many reasons. For one, each compiler
		4357	has different warnings, and each user has different tastes regarding
		4358	warning options. "Warn-free" code therefore cannot be a goal except when
		4359	targeting a specific compiler and compiler-version.
		4360
		4361	Another reason is that some compiler warnings require elaborate
		4362	workarounds, or other changes to the code that make it less clear and less
		4363	maintainable.
		4364
		4365	And of course, some compiler warnings are just plain stupid, or simply
		4366	wrong (because they don't actually warn about the condition their message
		4367	seems to warn about). For example, certain older gcc versions had some
		4368	warnings that resulted in an extreme number of false positives. These have
		4369	been fixed, but some people still insist on making code warn-free with
		4370	such buggy versions.
		4371
		4372	While libev is written to generate as few warnings as possible,
		4373	"warn-free" code is not a goal, and it is recommended not to build libev
		4374	with any compiler warnings enabled unless you are prepared to cope with
		4375	them (e.g. by ignoring them). Remember that warnings are just that:
		4376	warnings, not errors, or proof of bugs.
		4377
		4378
		4379	=head2 VALGRIND
		4380
		4381	Valgrind has a special section here because it is a popular tool that is
		4382	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		4383
		4384	If you think you found a bug (memory leak, uninitialised data access etc.)
		4385	in libev, then check twice: If valgrind reports something like:
		4386
		4387	==2274== definitely lost: 0 bytes in 0 blocks.
		4388	==2274== possibly lost: 0 bytes in 0 blocks.
		4389	==2274== still reachable: 256 bytes in 1 blocks.
		4390
		4391	Then there is no memory leak, just as memory accounted to global variables
		4392	is not a memleak - the memory is still being referenced, and didn't leak.
		4393
		4394	Similarly, under some circumstances, valgrind might report kernel bugs
		4395	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4396	although an acceptable workaround has been found here), or it might be
		4397	confused.
		4398
		4399	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		4400	make it into some kind of religion.
		4401
		4402	If you are unsure about something, feel free to contact the mailing list
		4403	with the full valgrind report and an explanation on why you think this
		4404	is a bug in libev (best check the archives, too :). However, don't be
		4405	annoyed when you get a brisk "this is no bug" answer and take the chance
		4406	of learning how to interpret valgrind properly.
		4407
		4408	If you need, for some reason, empty reports from valgrind for your project
		4409	I suggest using suppression lists.
		4410
		4411
		4412	=head1 PORTABILITY NOTES
		4413
		4414	=head2 GNU/LINUX 32 BIT LIMITATIONS
		4415
		4416	GNU/Linux is the only common platform that supports 64 bit file/large file
		4417	interfaces but I<disables> them by default.
		4418
		4419	That means that libev compiled in the default environment doesn't support
		4420	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
		4421
		4422	Unfortunately, many programs try to work around this GNU/Linux issue
		4423	by enabling the large file API, which makes them incompatible with the
		4424	standard libev compiled for their system.
		4425
		4426	Likewise, libev cannot enable the large file API itself as this would
		4427	suddenly make it incompatible to the default compile time environment,
		4428	i.e. all programs not using special compile switches.
		4429
		4430	=head2 OS/X AND DARWIN BUGS
		4431
		4432	The whole thing is a bug if you ask me - basically any system interface
		4433	you touch is broken, whether it is locales, poll, kqueue or even the
		4434	OpenGL drivers.
		4435
		4436	=head3 C<kqueue> is buggy
		4437
		4438	The kqueue syscall is broken in all known versions - most versions support
		4439	only sockets, many support pipes.
		4440
		4441	Libev tries to work around this by not using C<kqueue> by default on
		4442	this rotten platform, but of course you can still ask for it when creating
		4443	a loop.
		4444
		4445	=head3 C<poll> is buggy
		4446
		4447	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		4448	implementation by something calling C<kqueue> internally around the 10.5.6
		4449	release, so now C<kqueue> I<and> C<poll> are broken.
		4450
		4451	Libev tries to work around this by not using C<poll> by default on
		4452	this rotten platform, but of course you can still ask for it when creating
		4453	a loop.
		4454
		4455	=head3 C<select> is buggy
		4456
		4457	All that's left is C<select>, and of course Apple found a way to fuck this
		4458	one up as well: On OS/X, C<select> actively limits the number of file
		4459	descriptors you can pass in to 1024 - your program suddenly crashes when
		4460	you use more.
		4461
		4462	There is an undocumented "workaround" for this - defining
		4463	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		4464	work on OS/X.
		4465
		4466	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		4467
		4468	=head3 C<errno> reentrancy
		4469
		4470	The default compile environment on Solaris is unfortunately so
		4471	thread-unsafe that you can't even use components/libraries compiled
		4472	without C<-D_REENTRANT> (as long as they use C<errno>), which, of course,
		4473	isn't defined by default.
		4474
		4475	If you want to use libev in threaded environments you have to make sure
		4476	it's compiled with C<_REENTRANT> defined.
		4477
		4478	=head3 Event port backend
		4479
		4480	The scalable event interface for Solaris is called "event ports". Unfortunately,
		4481	this mechanism is very buggy. If you run into high CPU usage, your program
		4482	freezes or you get a large number of spurious wakeups, make sure you have
		4483	all the relevant and latest kernel patches applied. No, I don't know which
		4484	ones, but there are multiple ones.
		4485
		4486	If you can't get it to work, you can try running the program by setting
		4487	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		4488	C<select> backends.
		4489
		4490	=head2 AIX POLL BUG
		4491
		4492	AIX unfortunately has a broken C<poll.h> header. Libev works around
		4493	this by trying to avoid the poll backend altogether (i.e. it's not even
		4494	compiled in), which normally isn't a big problem as C<select> works fine
		4495	with large bitsets, and AIX is dead anyway.
		4496
		4497	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		4498
		4499	=head3 General issues
		4500
		4501	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		4502	requires, and its I/O model is fundamentally incompatible with the POSIX
		4503	model. Libev still offers limited functionality on this platform in
		4504	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		4505	descriptors. This only applies when using Win32 natively, not when using
		4506	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		4507	as every compielr comes with a slightly differently broken/incompatible
		4508	environment.
		4509
		4510	Lifting these limitations would basically require the full
		4511	re-implementation of the I/O system. If you are into this kind of thing,
		4512	then note that glib does exactly that for you in a very portable way (note
		4513	also that glib is the slowest event library known to man).
		4514
		4515	There is no supported compilation method available on windows except
		4516	embedding it into other applications.
		4517
		4518	Sensible signal handling is officially unsupported by Microsoft - libev
		4519	tries its best, but under most conditions, signals will simply not work.
		4520
		4521	Not a libev limitation but worth mentioning: windows apparently doesn't
		4522	accept large writes: instead of resulting in a partial write, windows will
		4523	either accept everything or return C<ENOBUFS> if the buffer is too large,
		4524	so make sure you only write small amounts into your sockets (less than a
		4525	megabyte seems safe, but this apparently depends on the amount of memory
		4526	available).
		4527
		4528	Due to the many, low, and arbitrary limits on the win32 platform and
		4529	the abysmal performance of winsockets, using a large number of sockets
		4530	is not recommended (and not reasonable). If your program needs to use
		4531	more than a hundred or so sockets, then likely it needs to use a totally
		4532	different implementation for windows, as libev offers the POSIX readiness
		4533	notification model, which cannot be implemented efficiently on windows
		4534	(due to Microsoft monopoly games).
		4535
		4536	A typical way to use libev under windows is to embed it (see the embedding
		4537	section for details) and use the following F<evwrap.h> header file instead
		4538	of F<ev.h>:
		4539
		4540	#define EV_STANDALONE /* keeps ev from requiring config.h */
		4541	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		4542
		4543	#include "ev.h"
		4544
		4545	And compile the following F<evwrap.c> file into your project (make sure
		4546	you do I<not> compile the F<ev.c> or any other embedded source files!):
		4547
		4548	#include "evwrap.h"
		4549	#include "ev.c"
		4550
		4551	=head3 The winsocket C<select> function
		4552
		4553	The winsocket C<select> function doesn't follow POSIX in that it
		4554	requires socket I<handles> and not socket I<file descriptors> (it is
		4555	also extremely buggy). This makes select very inefficient, and also
		4556	requires a mapping from file descriptors to socket handles (the Microsoft
		4557	C runtime provides the function C<_open_osfhandle> for this). See the
		4558	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		4559	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		4560
		4561	The configuration for a "naked" win32 using the Microsoft runtime
		4562	libraries and raw winsocket select is:
		4563
		4564	#define EV_USE_SELECT 1
		4565	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		4566
		4567	Note that winsockets handling of fd sets is O(n), so you can easily get a
		4568	complexity in the O(n²) range when using win32.
		4569
		4570	=head3 Limited number of file descriptors
		4571
		4572	Windows has numerous arbitrary (and low) limits on things.
		4573
		4574	Early versions of winsocket's select only supported waiting for a maximum
		4575	of C<64> handles (probably owning to the fact that all windows kernels
		4576	can only wait for C<64> things at the same time internally; Microsoft
		4577	recommends spawning a chain of threads and wait for 63 handles and the
		4578	previous thread in each. Sounds great!).
		4579
		4580	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		4581	to some high number (e.g. C<2048>) before compiling the winsocket select
		4582	call (which might be in libev or elsewhere, for example, perl and many
		4583	other interpreters do their own select emulation on windows).
		4584
		4585	Another limit is the number of file descriptors in the Microsoft runtime
		4586	libraries, which by default is C<64> (there must be a hidden I<64>
		4587	fetish or something like this inside Microsoft). You can increase this
		4588	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		4589	(another arbitrary limit), but is broken in many versions of the Microsoft
		4590	runtime libraries. This might get you to about C<512> or C<2048> sockets
		4591	(depending on windows version and/or the phase of the moon). To get more,
		4592	you need to wrap all I/O functions and provide your own fd management, but
		4593	the cost of calling select (O(n²)) will likely make this unworkable.
		4594
		4595	=head2 PORTABILITY REQUIREMENTS
		4596
		4597	In addition to a working ISO-C implementation and of course the
		4598	backend-specific APIs, libev relies on a few additional extensions:
		4599
		4600	=over 4
		4601
		4602	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4603	calling conventions regardless of C<ev_watcher_type *>.
		4604
		4605	Libev assumes not only that all watcher pointers have the same internal
		4606	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4607	assumes that the same (machine) code can be used to call any watcher
		4608	callback: The watcher callbacks have different type signatures, but libev
		4609	calls them using an C<ev_watcher *> internally.
		4610
		4611	=item C<sig_atomic_t volatile> must be thread-atomic as well
		4612
		4613	The type C<sig_atomic_t volatile> (or whatever is defined as
		4614	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		4615	threads. This is not part of the specification for C<sig_atomic_t>, but is
		4616	believed to be sufficiently portable.
		4617
		4618	=item C<sigprocmask> must work in a threaded environment
		4619
		4620	Libev uses C<sigprocmask> to temporarily block signals. This is not
		4621	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		4622	pthread implementations will either allow C<sigprocmask> in the "main
		4623	thread" or will block signals process-wide, both behaviours would
		4624	be compatible with libev. Interaction between C<sigprocmask> and
		4625	C<pthread_sigmask> could complicate things, however.
		4626
		4627	The most portable way to handle signals is to block signals in all threads
		4628	except the initial one, and run the default loop in the initial thread as
		4629	well.
		4630
		4631	=item C<long> must be large enough for common memory allocation sizes
		4632
		4633	To improve portability and simplify its API, libev uses C<long> internally
		4634	instead of C<size_t> when allocating its data structures. On non-POSIX
		4635	systems (Microsoft...) this might be unexpectedly low, but is still at
		4636	least 31 bits everywhere, which is enough for hundreds of millions of
		4637	watchers.
		4638
		4639	=item C<double> must hold a time value in seconds with enough accuracy
		4640
		4641	The type C<double> is used to represent timestamps. It is required to
		4642	have at least 51 bits of mantissa (and 9 bits of exponent), which is
		4643	good enough for at least into the year 4000 with millisecond accuracy
		4644	(the design goal for libev). This requirement is overfulfilled by
		4645	implementations using IEEE 754, which is basically all existing ones. With
		4646	IEEE 754 doubles, you get microsecond accuracy until at least 2200.
		4647
		4648	=back
		4649
		4650	If you know of other additional requirements drop me a note.
		4651
		4652
2465	=head1 COMPLEXITIES	4653	=head1 ALGORITHMIC COMPLEXITIES
2466		4654
2467	In this section the complexities of (many of) the algorithms used inside	4655	In this section the complexities of (many of) the algorithms used inside
2468	libev will be explained. For complexity discussions about backends see the	4656	libev will be documented. For complexity discussions about backends see
2469	documentation for C<ev_default_init>.	4657	the documentation for C<ev_default_init>.
2470		4658
2471	All of the following are about amortised time: If an array needs to be	4659	All of the following are about amortised time: If an array needs to be
2472	extended, libev needs to realloc and move the whole array, but this	4660	extended, libev needs to realloc and move the whole array, but this
2473	happens asymptotically never with higher number of elements, so O(1) might	4661	happens asymptotically rarer with higher number of elements, so O(1) might
2474	mean it might do a lengthy realloc operation in rare cases, but on average	4662	mean that libev does a lengthy realloc operation in rare cases, but on
2475	it is much faster and asymptotically approaches constant time.	4663	average it is much faster and asymptotically approaches constant time.
2476		4664
2477	=over 4	4665	=over 4
2478		4666
2479	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4667	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2480		4668
2481	This means that, when you have a watcher that triggers in one hour and	4669	This means that, when you have a watcher that triggers in one hour and
2482	there are 100 watchers that would trigger before that then inserting will	4670	there are 100 watchers that would trigger before that, then inserting will
2483	have to skip those 100 watchers.	4671	have to skip roughly seven (C<ld 100>) of these watchers.
2484		4672
2485	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	4673	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2486		4674
2487	That means that for changing a timer costs less than removing/adding them	4675	That means that changing a timer costs less than removing/adding them,
2488	as only the relative motion in the event queue has to be paid for.	4676	as only the relative motion in the event queue has to be paid for.
2489		4677
2490	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	4678	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
2491		4679
2492	These just add the watcher into an array or at the head of a list.	4680	These just add the watcher into an array or at the head of a list.
		4681
2493	=item Stopping check/prepare/idle watchers: O(1)	4682	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2494		4683
2495	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	4684	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2496		4685
2497	These watchers are stored in lists then need to be walked to find the	4686	These watchers are stored in lists, so they need to be walked to find the
2498	correct watcher to remove. The lists are usually short (you don't usually	4687	correct watcher to remove. The lists are usually short (you don't usually
2499	have many watchers waiting for the same fd or signal).	4688	have many watchers waiting for the same fd or signal: one is typical, two
		4689	is rare).
2500		4690
2501	=item Finding the next timer per loop iteration: O(1)	4691	=item Finding the next timer in each loop iteration: O(1)
		4692
		4693	By virtue of using a binary or 4-heap, the next timer is always found at a
		4694	fixed position in the storage array.
2502		4695
2503	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	4696	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2504		4697
2505	A change means an I/O watcher gets started or stopped, which requires	4698	A change means an I/O watcher gets started or stopped, which requires
2506	libev to recalculate its status (and possibly tell the kernel).	4699	libev to recalculate its status (and possibly tell the kernel, depending
		4700	on backend and whether C<ev_io_set> was used).
2507		4701
2508	=item Activating one watcher: O(1)	4702	=item Activating one watcher (putting it into the pending state): O(1)
2509		4703
2510	=item Priority handling: O(number_of_priorities)	4704	=item Priority handling: O(number_of_priorities)
2511		4705
2512	Priorities are implemented by allocating some space for each	4706	Priorities are implemented by allocating some space for each
2513	priority. When doing priority-based operations, libev usually has to	4707	priority. When doing priority-based operations, libev usually has to
2514	linearly search all the priorities.	4708	linearly search all the priorities, but starting/stopping and activating
		4709	watchers becomes O(1) with respect to priority handling.
		4710
		4711	=item Sending an ev_async: O(1)
		4712
		4713	=item Processing ev_async_send: O(number_of_async_watchers)
		4714
		4715	=item Processing signals: O(max_signal_number)
		4716
		4717	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4718	calls in the current loop iteration. Checking for async and signal events
		4719	involves iterating over all running async watchers or all signal numbers.
2515		4720
2516	=back	4721	=back
2517		4722
2518		4723
		4724	=head1 PORTING FROM LIBEV 3.X TO 4.X
		4725
		4726	The major version 4 introduced some minor incompatible changes to the API.
		4727
		4728	At the moment, the C<ev.h> header file tries to implement superficial
		4729	compatibility, so most programs should still compile. Those might be
		4730	removed in later versions of libev, so better update early than late.
		4731
		4732	=over 4
		4733
		4734	=item C<ev_loop_count> renamed to C<ev_iteration>
		4735
		4736	=item C<ev_loop_depth> renamed to C<ev_depth>
		4737
		4738	=item C<ev_loop_verify> renamed to C<ev_verify>
		4739
		4740	Most functions working on C<struct ev_loop> objects don't have an
		4741	C<ev_loop_> prefix, so it was removed. Note that C<ev_loop_fork> is
		4742	still called C<ev_loop_fork> because it would otherwise clash with the
		4743	C<ev_fork> typedef.
		4744
		4745	=item C<EV_TIMEOUT> renamed to C<EV_TIMER> in C<revents>
		4746
		4747	This is a simple rename - all other watcher types use their name
		4748	as revents flag, and now C<ev_timer> does, too.
		4749
		4750	Both C<EV_TIMER> and C<EV_TIMEOUT> symbols were present in 3.x versions
		4751	and continue to be present for the foreseeable future, so this is mostly a
		4752	documentation change.
		4753
		4754	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		4755
		4756	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		4757	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		4758	and work, but the library code will of course be larger.
		4759
		4760	=back
		4761
		4762
		4763	=head1 GLOSSARY
		4764
		4765	=over 4
		4766
		4767	=item active
		4768
		4769	A watcher is active as long as it has been started (has been attached to
		4770	an event loop) but not yet stopped (disassociated from the event loop).
		4771
		4772	=item application
		4773
		4774	In this document, an application is whatever is using libev.
		4775
		4776	=item callback
		4777
		4778	The address of a function that is called when some event has been
		4779	detected. Callbacks are being passed the event loop, the watcher that
		4780	received the event, and the actual event bitset.
		4781
		4782	=item callback invocation
		4783
		4784	The act of calling the callback associated with a watcher.
		4785
		4786	=item event
		4787
		4788	A change of state of some external event, such as data now being available
		4789	for reading on a file descriptor, time having passed or simply not having
		4790	any other events happening anymore.
		4791
		4792	In libev, events are represented as single bits (such as C<EV_READ> or
		4793	C<EV_TIMER>).
		4794
		4795	=item event library
		4796
		4797	A software package implementing an event model and loop.
		4798
		4799	=item event loop
		4800
		4801	An entity that handles and processes external events and converts them
		4802	into callback invocations.
		4803
		4804	=item event model
		4805
		4806	The model used to describe how an event loop handles and processes
		4807	watchers and events.
		4808
		4809	=item pending
		4810
		4811	A watcher is pending as soon as the corresponding event has been detected,
		4812	and stops being pending as soon as the watcher will be invoked or its
		4813	pending status is explicitly cleared by the application.
		4814
		4815	A watcher can be pending, but not active. Stopping a watcher also clears
		4816	its pending status.
		4817
		4818	=item real time
		4819
		4820	The physical time that is observed. It is apparently strictly monotonic :)
		4821
		4822	=item wall-clock time
		4823
		4824	The time and date as shown on clocks. Unlike real time, it can actually
		4825	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4826	clock.
		4827
		4828	=item watcher
		4829
		4830	A data structure that describes interest in certain events. Watchers need
		4831	to be started (attached to an event loop) before they can receive events.
		4832
		4833	=item watcher invocation
		4834
		4835	The act of calling the callback associated with a watcher.
		4836
		4837	=back
		4838
2519	=head1 AUTHOR	4839	=head1 AUTHOR
2520		4840
2521	Marc Lehmann <libev@schmorp.de>.	4841	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
2522		4842

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