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Revision 1.305 by root, Thu Oct 14 05:07:04 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 occurring), 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
…		…
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 some floatingpoint value. Unlike the name	133	any calculations on it, you should treat it as some floating point value.
		134
104	component C<stamp> might indicate, it is also used for time differences	135	Unlike the name component C<stamp> might indicate, it is also used for
105	throughout libev.	136	time differences (e.g. delays) throughout libev.
		137
		138	=head1 ERROR HANDLING
		139
		140	Libev knows three classes of errors: operating system errors, usage errors
		141	and internal errors (bugs).
		142
		143	When libev catches an operating system error it cannot handle (for example
		144	a system call indicating a condition libev cannot fix), it calls the callback
		145	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		146	abort. The default is to print a diagnostic message and to call C<abort
		147	()>.
		148
		149	When libev detects a usage error such as a negative timer interval, then
		150	it will print a diagnostic message and abort (via the C<assert> mechanism,
		151	so C<NDEBUG> will disable this checking): these are programming errors in
		152	the libev caller and need to be fixed there.
		153
		154	Libev also has a few internal error-checking C<assert>ions, and also has
		155	extensive consistency checking code. These do not trigger under normal
		156	circumstances, as they indicate either a bug in libev or worse.
		157
106		158
107	=head1 GLOBAL FUNCTIONS	159	=head1 GLOBAL FUNCTIONS
108		160
109	These functions can be called anytime, even before initialising the	161	These functions can be called anytime, even before initialising the
110	library in any way.	162	library in any way.
…		…
119		171
120	=item ev_sleep (ev_tstamp interval)	172	=item ev_sleep (ev_tstamp interval)
121		173
122	Sleep for the given interval: The current thread will be blocked until	174	Sleep for the given interval: The current thread will be blocked until
123	either it is interrupted or the given time interval has passed. Basically	175	either it is interrupted or the given time interval has passed. Basically
124	this is a subsecond-resolution C<sleep ()>.	176	this is a sub-second-resolution C<sleep ()>.
125		177
126	=item int ev_version_major ()	178	=item int ev_version_major ()
127		179
128	=item int ev_version_minor ()	180	=item int ev_version_minor ()
129		181
…		…
140	as this indicates an incompatible change. Minor versions are usually	192	as this indicates an incompatible change. Minor versions are usually
141	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
142	not a problem.	194	not a problem.
143		195
144	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
145	version.	197	version (note, however, that this will not detect ABI mismatches :).
146		198
147	assert (("libev version mismatch",	199	assert (("libev version mismatch",
148	ev_version_major () == EV_VERSION_MAJOR	200	ev_version_major () == EV_VERSION_MAJOR
149	&& ev_version_minor () >= EV_VERSION_MINOR));	201	&& ev_version_minor () >= EV_VERSION_MINOR));
150		202
151	=item unsigned int ev_supported_backends ()	203	=item unsigned int ev_supported_backends ()
152		204
153	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_*>
154	value) compiled into this binary of libev (independent of their	206	value) compiled into this binary of libev (independent of their
…		…
156	a description of the set values.	208	a description of the set values.
157		209
158	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
159	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
160		212
161	assert (("sorry, no epoll, no sex",	213	assert (("sorry, no epoll, no sex",
162	ev_supported_backends () & EVBACKEND_EPOLL));	214	ev_supported_backends () & EVBACKEND_EPOLL));
163		215
164	=item unsigned int ev_recommended_backends ()	216	=item unsigned int ev_recommended_backends ()
165		217
166	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
167	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
168	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
169	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
170	(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
171	libev will probe for if you specify no backends explicitly.	223	libev will probe for if you specify no backends explicitly.
172		224
173	=item unsigned int ev_embeddable_backends ()	225	=item unsigned int ev_embeddable_backends ()
174		226
…		…
178	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	230	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
179	recommended ones.	231	recommended ones.
180		232
181	See the description of C<ev_embed> watchers for more info.	233	See the description of C<ev_embed> watchers for more info.
182		234
183	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	235	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
184		236
185	Sets the allocation function to use (the prototype is similar - the	237	Sets the allocation function to use (the prototype is similar - the
186	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
187	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
188	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
189	potentially destructive action. The default is your system realloc	241	or take some potentially destructive action.
190	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.
191		246
192	You could override this function in high-availability programs to, say,	247	You could override this function in high-availability programs to, say,
193	free some memory if it cannot allocate memory, to use a special allocator,	248	free some memory if it cannot allocate memory, to use a special allocator,
194	or even to sleep a while and retry until some memory is available.	249	or even to sleep a while and retry until some memory is available.
195		250
196	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
197	retries).	252	retries (example requires a standards-compliant C<realloc>).
198		253
199	static void *	254	static void *
200	persistent_realloc (void *ptr, size_t size)	255	persistent_realloc (void *ptr, size_t size)
201	{	256	{
202	for (;;)	257	for (;;)
…		…
211	}	266	}
212		267
213	...	268	...
214	ev_set_allocator (persistent_realloc);	269	ev_set_allocator (persistent_realloc);
215		270
216	=item ev_set_syserr_cb (void (*cb)(const char *msg));	271	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
217		272
218	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
219	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
220	indicating the system call or subsystem causing the problem. If this	275	indicating the system call or subsystem causing the problem. If this
221	callback is set, then libev will expect it to remedy the sitution, no	276	callback is set, then libev will expect it to remedy the situation, no
222	matter what, when it returns. That is, libev will generally retry the	277	matter what, when it returns. That is, libev will generally retry the
223	requested operation, or, if the condition doesn't go away, do bad stuff	278	requested operation, or, if the condition doesn't go away, do bad stuff
224	(such as abort).	279	(such as abort).
225		280
226	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.
…		…
237		292
238	=back	293	=back
239		294
240	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	295	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
241		296
242	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>
243	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>
244	events, and dynamically created loops which do not.	299	I<function>).
245		300
246	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
247	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
248	create, you also create another event loop. Libev itself does no locking	303	not.
249	whatsoever, so if you mix calls to the same event loop in different
250	threads, make sure you lock (this is usually a bad idea, though, even if
251	done correctly, because it's hideous and inefficient).
252		304
253	=over 4	305	=over 4
254		306
255	=item struct ev_loop *ev_default_loop (unsigned int flags)	307	=item struct ev_loop *ev_default_loop (unsigned int flags)
256		308
…		…
260	flags. If that is troubling you, check C<ev_backend ()> afterwards).	312	flags. If that is troubling you, check C<ev_backend ()> afterwards).
261		313
262	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
263	function.	315	function.
264		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
265	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
266	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>).
267		330
268	The following flags are supported:	331	The following flags are supported:
269		332
…		…
274	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
275	thing, believe me).	338	thing, believe me).
276		339
277	=item C<EVFLAG_NOENV>	340	=item C<EVFLAG_NOENV>
278		341
279	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
280	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
281	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	344	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
282	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
283	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
284	around bugs.	347	around bugs.
285		348
286	=item C<EVFLAG_FORKCHECK>	349	=item C<EVFLAG_FORKCHECK>
287		350
288	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
289	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.
290	enabling this flag.
291		353
292	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,
293	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
294	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
295	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
296	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
297	C<pthread_atfork> which is even faster).	359	C<pthread_atfork> which is even faster).
298		360
299	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
300	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
301	flag.	363	flag.
302		364
303	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>
304	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.
305		387
306	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	388	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
307		389
308	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
309	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,
310	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
311	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
312	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).
313		406
314	=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)
315		408
316	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
317	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
318	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
319	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>.
320		418
321	=item C<EVBACKEND_EPOLL> (value 4, Linux)	419	=item C<EVBACKEND_EPOLL> (value 4, Linux)
		420
		421	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		422	kernels).
322		423
323	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,
324	but it scales phenomenally better. While poll and select usually scale	425	but it scales phenomenally better. While poll and select usually scale
325	like O(total_fds) where n is the total number of fds (or the highest fd),	426	like O(total_fds) where n is the total number of fds (or the highest fd),
326	epoll scales either O(1) or O(active_fds). The epoll design has a number	427	epoll scales either O(1) or O(active_fds).
327	of shortcomings, such as silently dropping events in some hard-to-detect	428
328	cases and rewiring a syscall per fd change, no fork support and bad	429	The epoll mechanism deserves honorable mention as the most misdesigned
329	support for dup:	430	of the more advanced event mechanisms: mere annoyances include silently
		431	dropping file descriptors, requiring a system call per change per file
		432	descriptor (and unnecessary guessing of parameters), problems with dup and
		433	so on. The biggest issue is fork races, however - if a program forks then
		434	I<both> parent and child process have to recreate the epoll set, which can
		435	take considerable time (one syscall per file descriptor) and is of course
		436	hard to detect.
		437
		438	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		439	of course I<doesn't>, and epoll just loves to report events for totally
		440	I<different> file descriptors (even already closed ones, so one cannot
		441	even remove them from the set) than registered in the set (especially
		442	on SMP systems). Libev tries to counter these spurious notifications by
		443	employing an additional generation counter and comparing that against the
		444	events to filter out spurious ones, recreating the set when required.
330		445
331	While stopping, setting and starting an I/O watcher in the same iteration	446	While stopping, setting and starting an I/O watcher in the same iteration
332	will result in some caching, there is still a syscall per such incident	447	will result in some caching, there is still a system call per such
333	(because the fd could point to a different file description now), so its	448	incident (because the same I<file descriptor> could point to a different
334	best to avoid that. Also, C<dup ()>'ed file descriptors might not work	449	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
335	very well if you register events for both fds.	450	file descriptors might not work very well if you register events for both
		451	file descriptors.
336		452
337	Please note that epoll sometimes generates spurious notifications, so you	453	Best performance from this backend is achieved by not unregistering all
338	need to use non-blocking I/O or other means to avoid blocking when no data	454	watchers for a file descriptor until it has been closed, if possible,
339	(or space) is available.	455	i.e. keep at least one watcher active per fd at all times. Stopping and
		456	starting a watcher (without re-setting it) also usually doesn't cause
		457	extra overhead. A fork can both result in spurious notifications as well
		458	as in libev having to destroy and recreate the epoll object, which can
		459	take considerable time and thus should be avoided.
		460
		461	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		462	faster than epoll for maybe up to a hundred file descriptors, depending on
		463	the usage. So sad.
		464
		465	While nominally embeddable in other event loops, this feature is broken in
		466	all kernel versions tested so far.
		467
		468	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		469	C<EVBACKEND_POLL>.
340		470
341	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	471	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
342		472
343	Kqueue deserves special mention, as at the time of this writing, it	473	Kqueue deserves special mention, as at the time of this writing, it
344	was broken on I<all> BSDs (usually it doesn't work with anything but	474	was broken on all BSDs except NetBSD (usually it doesn't work reliably
345	sockets and pipes, except on Darwin, where of course it's completely	475	with anything but sockets and pipes, except on Darwin, where of course
346	useless. On NetBSD, it seems to work for all the FD types I tested, so it	476	it's completely useless). Unlike epoll, however, whose brokenness
347	is used by default there). For this reason it's not being "autodetected"	477	is by design, these kqueue bugs can (and eventually will) be fixed
		478	without API changes to existing programs. For this reason it's not being
348	unless you explicitly specify it explicitly in the flags (i.e. using	479	"auto-detected" unless you explicitly specify it in the flags (i.e. using
349	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)	480	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
350	system like NetBSD.	481	system like NetBSD.
351		482
		483	You still can embed kqueue into a normal poll or select backend and use it
		484	only for sockets (after having made sure that sockets work with kqueue on
		485	the target platform). See C<ev_embed> watchers for more info.
		486
352	It scales in the same way as the epoll backend, but the interface to the	487	It scales in the same way as the epoll backend, but the interface to the
353	kernel is more efficient (which says nothing about its actual speed,	488	kernel is more efficient (which says nothing about its actual speed, of
354	of course). While stopping, setting and starting an I/O watcher does	489	course). While stopping, setting and starting an I/O watcher does never
355	never cause an extra syscall as with epoll, it still adds up to two event	490	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
356	changes per incident, support for C<fork ()> is very bad and it drops fds	491	two event changes per incident. Support for C<fork ()> is very bad (but
357	silently in similarly hard-to-detetc cases.	492	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		493	cases
		494
		495	This backend usually performs well under most conditions.
		496
		497	While nominally embeddable in other event loops, this doesn't work
		498	everywhere, so you might need to test for this. And since it is broken
		499	almost everywhere, you should only use it when you have a lot of sockets
		500	(for which it usually works), by embedding it into another event loop
		501	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
		502	also broken on OS X)) and, did I mention it, using it only for sockets.
		503
		504	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		505	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		506	C<NOTE_EOF>.
358		507
359	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	508	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
360		509
361	This is not implemented yet (and might never be).	510	This is not implemented yet (and might never be, unless you send me an
		511	implementation). According to reports, C</dev/poll> only supports sockets
		512	and is not embeddable, which would limit the usefulness of this backend
		513	immensely.
362		514
363	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	515	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
364		516
365	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	517	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
366	it's really slow, but it still scales very well (O(active_fds)).	518	it's really slow, but it still scales very well (O(active_fds)).
367		519
368	Please note that solaris event ports can deliver a lot of spurious	520	Please note that Solaris event ports can deliver a lot of spurious
369	notifications, so you need to use non-blocking I/O or other means to avoid	521	notifications, so you need to use non-blocking I/O or other means to avoid
370	blocking when no data (or space) is available.	522	blocking when no data (or space) is available.
		523
		524	While this backend scales well, it requires one system call per active
		525	file descriptor per loop iteration. For small and medium numbers of file
		526	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		527	might perform better.
		528
		529	On the positive side, with the exception of the spurious readiness
		530	notifications, this backend actually performed fully to specification
		531	in all tests and is fully embeddable, which is a rare feat among the
		532	OS-specific backends (I vastly prefer correctness over speed hacks).
		533
		534	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		535	C<EVBACKEND_POLL>.
371		536
372	=item C<EVBACKEND_ALL>	537	=item C<EVBACKEND_ALL>
373		538
374	Try all backends (even potentially broken ones that wouldn't be tried	539	Try all backends (even potentially broken ones that wouldn't be tried
375	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	540	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
376	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	541	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
377		542
		543	It is definitely not recommended to use this flag.
		544
378	=back	545	=back
379		546
380	If one or more of these are ored into the flags value, then only these	547	If one or more of the backend flags are or'ed into the flags value,
381	backends will be tried (in the reverse order as given here). If none are	548	then only these backends will be tried (in the reverse order as listed
382	specified, most compiled-in backend will be tried, usually in reverse	549	here). If none are specified, all backends in C<ev_recommended_backends
383	order of their flag values :)	550	()> will be tried.
384		551
385	The most typical usage is like this:	552	Example: This is the most typical usage.
386		553
387	if (!ev_default_loop (0))	554	if (!ev_default_loop (0))
388	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	555	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
389		556
390	Restrict libev to the select and poll backends, and do not allow	557	Example: Restrict libev to the select and poll backends, and do not allow
391	environment settings to be taken into account:	558	environment settings to be taken into account:
392		559
393	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	560	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
394		561
395	Use whatever libev has to offer, but make sure that kqueue is used if	562	Example: Use whatever libev has to offer, but make sure that kqueue is
396	available (warning, breaks stuff, best use only with your own private	563	used if available (warning, breaks stuff, best use only with your own
397	event loop and only if you know the OS supports your types of fds):	564	private event loop and only if you know the OS supports your types of
		565	fds):
398		566
399	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	567	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
400		568
401	=item struct ev_loop *ev_loop_new (unsigned int flags)	569	=item struct ev_loop *ev_loop_new (unsigned int flags)
402		570
403	Similar to C<ev_default_loop>, but always creates a new event loop that is	571	Similar to C<ev_default_loop>, but always creates a new event loop that is
404	always distinct from the default loop. Unlike the default loop, it cannot	572	always distinct from the default loop.
405	handle signal and child watchers, and attempts to do so will be greeted by	573
406	undefined behaviour (or a failed assertion if assertions are enabled).	574	Note that this function I<is> thread-safe, and one common way to use
		575	libev with threads is indeed to create one loop per thread, and using the
		576	default loop in the "main" or "initial" thread.
407		577
408	Example: Try to create a event loop that uses epoll and nothing else.	578	Example: Try to create a event loop that uses epoll and nothing else.
409		579
410	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	580	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
411	if (!epoller)	581	if (!epoller)
412	fatal ("no epoll found here, maybe it hides under your chair");	582	fatal ("no epoll found here, maybe it hides under your chair");
413		583
414	=item ev_default_destroy ()	584	=item ev_default_destroy ()
415		585
416	Destroys the default loop again (frees all memory and kernel state	586	Destroys the default loop (frees all memory and kernel state etc.). None
417	etc.). None of the active event watchers will be stopped in the normal	587	of the active event watchers will be stopped in the normal sense, so
418	sense, so e.g. C<ev_is_active> might still return true. It is your	588	e.g. C<ev_is_active> might still return true. It is your responsibility to
419	responsibility to either stop all watchers cleanly yoursef I<before>	589	either stop all watchers cleanly yourself I<before> calling this function,
420	calling this function, or cope with the fact afterwards (which is usually	590	or cope with the fact afterwards (which is usually the easiest thing, you
421	the easiest thing, you can just ignore the watchers and/or C<free ()> them	591	can just ignore the watchers and/or C<free ()> them for example).
422	for example).
423		592
424	Note that certain global state, such as signal state, will not be freed by	593	Note that certain global state, such as signal state (and installed signal
425	this function, and related watchers (such as signal and child watchers)	594	handlers), will not be freed by this function, and related watchers (such
426	would need to be stopped manually.	595	as signal and child watchers) would need to be stopped manually.
427		596
428	In general it is not advisable to call this function except in the	597	In general it is not advisable to call this function except in the
429	rare occasion where you really need to free e.g. the signal handling	598	rare occasion where you really need to free e.g. the signal handling
430	pipe fds. If you need dynamically allocated loops it is better to use	599	pipe fds. If you need dynamically allocated loops it is better to use
431	C<ev_loop_new> and C<ev_loop_destroy>).	600	C<ev_loop_new> and C<ev_loop_destroy>.
432		601
433	=item ev_loop_destroy (loop)	602	=item ev_loop_destroy (loop)
434		603
435	Like C<ev_default_destroy>, but destroys an event loop created by an	604	Like C<ev_default_destroy>, but destroys an event loop created by an
436	earlier call to C<ev_loop_new>.	605	earlier call to C<ev_loop_new>.
437		606
438	=item ev_default_fork ()	607	=item ev_default_fork ()
439		608
		609	This function sets a flag that causes subsequent C<ev_loop> iterations
440	This function reinitialises the kernel state for backends that have	610	to reinitialise the kernel state for backends that have one. Despite the
441	one. Despite the name, you can call it anytime, but it makes most sense	611	name, you can call it anytime, but it makes most sense after forking, in
442	after forking, in either the parent or child process (or both, but that	612	the child process (or both child and parent, but that again makes little
443	again makes little sense).	613	sense). You I<must> call it in the child before using any of the libev
		614	functions, and it will only take effect at the next C<ev_loop> iteration.
444		615
445	You I<must> call this function in the child process after forking if and	616	Again, you I<have> to call it on I<any> loop that you want to re-use after
446	only if you want to use the event library in both processes. If you just	617	a fork, I<even if you do not plan to use the loop in the parent>. This is
447	fork+exec, you don't have to call it.	618	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
		619	during fork.
		620
		621	On the other hand, you only need to call this function in the child
		622	process if and only if you want to use the event loop in the child. If you
		623	just fork+exec or create a new loop in the child, you don't have to call
		624	it at all.
448		625
449	The function itself is quite fast and it's usually not a problem to call	626	The function itself is quite fast and it's usually not a problem to call
450	it just in case after a fork. To make this easy, the function will fit in	627	it just in case after a fork. To make this easy, the function will fit in
451	quite nicely into a call to C<pthread_atfork>:	628	quite nicely into a call to C<pthread_atfork>:
452		629
453	pthread_atfork (0, 0, ev_default_fork);	630	pthread_atfork (0, 0, ev_default_fork);
454		631
455	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
456	without calling this function, so if you force one of those backends you
457	do not need to care.
458
459	=item ev_loop_fork (loop)	632	=item ev_loop_fork (loop)
460		633
461	Like C<ev_default_fork>, but acts on an event loop created by	634	Like C<ev_default_fork>, but acts on an event loop created by
462	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	635	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
463	after fork, and how you do this is entirely your own problem.	636	after fork that you want to re-use in the child, and how you keep track of
		637	them is entirely your own problem.
464		638
		639	=item int ev_is_default_loop (loop)
		640
		641	Returns true when the given loop is, in fact, the default loop, and false
		642	otherwise.
		643
465	=item unsigned int ev_loop_count (loop)	644	=item unsigned int ev_iteration (loop)
466		645
467	Returns the count of loop iterations for the loop, which is identical to	646	Returns the current iteration count for the loop, which is identical to
468	the number of times libev did poll for new events. It starts at C<0> and	647	the number of times libev did poll for new events. It starts at C<0> and
469	happily wraps around with enough iterations.	648	happily wraps around with enough iterations.
470		649
471	This value can sometimes be useful as a generation counter of sorts (it	650	This value can sometimes be useful as a generation counter of sorts (it
472	"ticks" the number of loop iterations), as it roughly corresponds with	651	"ticks" the number of loop iterations), as it roughly corresponds with
473	C<ev_prepare> and C<ev_check> calls.	652	C<ev_prepare> and C<ev_check> calls - and is incremented between the
		653	prepare and check phases.
		654
		655	=item unsigned int ev_depth (loop)
		656
		657	Returns the number of times C<ev_loop> was entered minus the number of
		658	times C<ev_loop> was exited, in other words, the recursion depth.
		659
		660	Outside C<ev_loop>, this number is zero. In a callback, this number is
		661	C<1>, unless C<ev_loop> was invoked recursively (or from another thread),
		662	in which case it is higher.
		663
		664	Leaving C<ev_loop> abnormally (setjmp/longjmp, cancelling the thread
		665	etc.), doesn't count as "exit" - consider this as a hint to avoid such
		666	ungentleman behaviour unless it's really convenient.
474		667
475	=item unsigned int ev_backend (loop)	668	=item unsigned int ev_backend (loop)
476		669
477	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	670	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
478	use.	671	use.
…		…
483	received events and started processing them. This timestamp does not	676	received events and started processing them. This timestamp does not
484	change as long as callbacks are being processed, and this is also the base	677	change as long as callbacks are being processed, and this is also the base
485	time used for relative timers. You can treat it as the timestamp of the	678	time used for relative timers. You can treat it as the timestamp of the
486	event occurring (or more correctly, libev finding out about it).	679	event occurring (or more correctly, libev finding out about it).
487		680
		681	=item ev_now_update (loop)
		682
		683	Establishes the current time by querying the kernel, updating the time
		684	returned by C<ev_now ()> in the progress. This is a costly operation and
		685	is usually done automatically within C<ev_loop ()>.
		686
		687	This function is rarely useful, but when some event callback runs for a
		688	very long time without entering the event loop, updating libev's idea of
		689	the current time is a good idea.
		690
		691	See also L<The special problem of time updates> in the C<ev_timer> section.
		692
		693	=item ev_suspend (loop)
		694
		695	=item ev_resume (loop)
		696
		697	These two functions suspend and resume a loop, for use when the loop is
		698	not used for a while and timeouts should not be processed.
		699
		700	A typical use case would be an interactive program such as a game: When
		701	the user presses C<^Z> to suspend the game and resumes it an hour later it
		702	would be best to handle timeouts as if no time had actually passed while
		703	the program was suspended. This can be achieved by calling C<ev_suspend>
		704	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		705	C<ev_resume> directly afterwards to resume timer processing.
		706
		707	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		708	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		709	will be rescheduled (that is, they will lose any events that would have
		710	occurred while suspended).
		711
		712	After calling C<ev_suspend> you B<must not> call I<any> function on the
		713	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		714	without a previous call to C<ev_suspend>.
		715
		716	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		717	event loop time (see C<ev_now_update>).
		718
488	=item ev_loop (loop, int flags)	719	=item ev_loop (loop, int flags)
489		720
490	Finally, this is it, the event handler. This function usually is called	721	Finally, this is it, the event handler. This function usually is called
491	after you initialised all your watchers and you want to start handling	722	after you have initialised all your watchers and you want to start
492	events.	723	handling events.
493		724
494	If the flags argument is specified as C<0>, it will not return until	725	If the flags argument is specified as C<0>, it will not return until
495	either no event watchers are active anymore or C<ev_unloop> was called.	726	either no event watchers are active anymore or C<ev_unloop> was called.
496		727
497	Please note that an explicit C<ev_unloop> is usually better than	728	Please note that an explicit C<ev_unloop> is usually better than
498	relying on all watchers to be stopped when deciding when a program has	729	relying on all watchers to be stopped when deciding when a program has
499	finished (especially in interactive programs), but having a program that	730	finished (especially in interactive programs), but having a program
500	automatically loops as long as it has to and no longer by virtue of	731	that automatically loops as long as it has to and no longer by virtue
501	relying on its watchers stopping correctly is a thing of beauty.	732	of relying on its watchers stopping correctly, that is truly a thing of
		733	beauty.
502		734
503	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	735	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
504	those events and any outstanding ones, but will not block your process in	736	those events and any already outstanding ones, but will not block your
505	case there are no events and will return after one iteration of the loop.	737	process in case there are no events and will return after one iteration of
		738	the loop.
506		739
507	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	740	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
508	neccessary) and will handle those and any outstanding ones. It will block	741	necessary) and will handle those and any already outstanding ones. It
509	your process until at least one new event arrives, and will return after	742	will block your process until at least one new event arrives (which could
510	one iteration of the loop. This is useful if you are waiting for some	743	be an event internal to libev itself, so there is no guarantee that a
511	external event in conjunction with something not expressible using other	744	user-registered callback will be called), and will return after one
		745	iteration of the loop.
		746
		747	This is useful if you are waiting for some external event in conjunction
		748	with something not expressible using other libev watchers (i.e. "roll your
512	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	749	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
513	usually a better approach for this kind of thing.	750	usually a better approach for this kind of thing.
514		751
515	Here are the gory details of what C<ev_loop> does:	752	Here are the gory details of what C<ev_loop> does:
516		753
517	- Before the first iteration, call any pending watchers.	754	- Before the first iteration, call any pending watchers.
518	* If there are no active watchers (reference count is zero), return.	755	* If EVFLAG_FORKCHECK was used, check for a fork.
519	- Queue all prepare watchers and then call all outstanding watchers.	756	- If a fork was detected (by any means), queue and call all fork watchers.
		757	- Queue and call all prepare watchers.
520	- If we have been forked, recreate the kernel state.	758	- If we have been forked, detach and recreate the kernel state
		759	as to not disturb the other process.
521	- Update the kernel state with all outstanding changes.	760	- Update the kernel state with all outstanding changes.
522	- Update the "event loop time".	761	- Update the "event loop time" (ev_now ()).
523	- Calculate for how long to block.	762	- Calculate for how long to sleep or block, if at all
		763	(active idle watchers, EVLOOP_NONBLOCK or not having
		764	any active watchers at all will result in not sleeping).
		765	- Sleep if the I/O and timer collect interval say so.
524	- Block the process, waiting for any events.	766	- Block the process, waiting for any events.
525	- Queue all outstanding I/O (fd) events.	767	- Queue all outstanding I/O (fd) events.
526	- Update the "event loop time" and do time jump handling.	768	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
527	- Queue all outstanding timers.	769	- Queue all expired timers.
528	- Queue all outstanding periodics.	770	- Queue all expired periodics.
529	- If no events are pending now, queue all idle watchers.	771	- Unless any events are pending now, queue all idle watchers.
530	- Queue all check watchers.	772	- Queue all check watchers.
531	- Call all queued watchers in reverse order (i.e. check watchers first).	773	- Call all queued watchers in reverse order (i.e. check watchers first).
532	Signals and child watchers are implemented as I/O watchers, and will	774	Signals and child watchers are implemented as I/O watchers, and will
533	be handled here by queueing them when their watcher gets executed.	775	be handled here by queueing them when their watcher gets executed.
534	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	776	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
535	were used, return, otherwise continue with step *.	777	were used, or there are no active watchers, return, otherwise
		778	continue with step *.
536		779
537	Example: Queue some jobs and then loop until no events are outsanding	780	Example: Queue some jobs and then loop until no events are outstanding
538	anymore.	781	anymore.
539		782
540	... queue jobs here, make sure they register event watchers as long	783	... queue jobs here, make sure they register event watchers as long
541	... as they still have work to do (even an idle watcher will do..)	784	... as they still have work to do (even an idle watcher will do..)
542	ev_loop (my_loop, 0);	785	ev_loop (my_loop, 0);
543	... jobs done. yeah!	786	... jobs done or somebody called unloop. yeah!
544		787
545	=item ev_unloop (loop, how)	788	=item ev_unloop (loop, how)
546		789
547	Can be used to make a call to C<ev_loop> return early (but only after it	790	Can be used to make a call to C<ev_loop> return early (but only after it
548	has processed all outstanding events). The C<how> argument must be either	791	has processed all outstanding events). The C<how> argument must be either
549	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	792	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
550	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	793	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
551		794
		795	This "unloop state" will be cleared when entering C<ev_loop> again.
		796
		797	It is safe to call C<ev_unloop> from outside any C<ev_loop> calls.
		798
552	=item ev_ref (loop)	799	=item ev_ref (loop)
553		800
554	=item ev_unref (loop)	801	=item ev_unref (loop)
555		802
556	Ref/unref can be used to add or remove a reference count on the event	803	Ref/unref can be used to add or remove a reference count on the event
557	loop: Every watcher keeps one reference, and as long as the reference	804	loop: Every watcher keeps one reference, and as long as the reference
558	count is nonzero, C<ev_loop> will not return on its own. If you have	805	count is nonzero, C<ev_loop> will not return on its own.
559	a watcher you never unregister that should not keep C<ev_loop> from	806
560	returning, ev_unref() after starting, and ev_ref() before stopping it. For	807	This is useful when you have a watcher that you never intend to
		808	unregister, but that nevertheless should not keep C<ev_loop> from
		809	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		810	before stopping it.
		811
561	example, libev itself uses this for its internal signal pipe: It is not	812	As an example, libev itself uses this for its internal signal pipe: It
562	visible to the libev user and should not keep C<ev_loop> from exiting if	813	is not visible to the libev user and should not keep C<ev_loop> from
563	no event watchers registered by it are active. It is also an excellent	814	exiting if no event watchers registered by it are active. It is also an
564	way to do this for generic recurring timers or from within third-party	815	excellent way to do this for generic recurring timers or from within
565	libraries. Just remember to I<unref after start> and I<ref before stop>.	816	third-party libraries. Just remember to I<unref after start> and I<ref
		817	before stop> (but only if the watcher wasn't active before, or was active
		818	before, respectively. Note also that libev might stop watchers itself
		819	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		820	in the callback).
566		821
567	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	822	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
568	running when nothing else is active.	823	running when nothing else is active.
569		824
570	struct ev_signal exitsig;	825	ev_signal exitsig;
571	ev_signal_init (&exitsig, sig_cb, SIGINT);	826	ev_signal_init (&exitsig, sig_cb, SIGINT);
572	ev_signal_start (loop, &exitsig);	827	ev_signal_start (loop, &exitsig);
573	evf_unref (loop);	828	evf_unref (loop);
574		829
575	Example: For some weird reason, unregister the above signal handler again.	830	Example: For some weird reason, unregister the above signal handler again.
576		831
577	ev_ref (loop);	832	ev_ref (loop);
578	ev_signal_stop (loop, &exitsig);	833	ev_signal_stop (loop, &exitsig);
579		834
580	=item ev_set_io_collect_interval (loop, ev_tstamp interval)	835	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
581		836
582	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)	837	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
583		838
584	These advanced functions influence the time that libev will spend waiting	839	These advanced functions influence the time that libev will spend waiting
585	for events. Both are by default C<0>, meaning that libev will try to	840	for events. Both time intervals are by default C<0>, meaning that libev
586	invoke timer/periodic callbacks and I/O callbacks with minimum latency.	841	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		842	latency.
587		843
588	Setting these to a higher value (the C<interval> I<must> be >= C<0>)	844	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
589	allows libev to delay invocation of I/O and timer/periodic callbacks to	845	allows libev to delay invocation of I/O and timer/periodic callbacks
590	increase efficiency of loop iterations.	846	to increase efficiency of loop iterations (or to increase power-saving
		847	opportunities).
591		848
592	The background is that sometimes your program runs just fast enough to	849	The idea is that sometimes your program runs just fast enough to handle
593	handle one (or very few) event(s) per loop iteration. While this makes	850	one (or very few) event(s) per loop iteration. While this makes the
594	the program responsive, it also wastes a lot of CPU time to poll for new	851	program responsive, it also wastes a lot of CPU time to poll for new
595	events, especially with backends like C<select ()> which have a high	852	events, especially with backends like C<select ()> which have a high
596	overhead for the actual polling but can deliver many events at once.	853	overhead for the actual polling but can deliver many events at once.
597		854
598	By setting a higher I<io collect interval> you allow libev to spend more	855	By setting a higher I<io collect interval> you allow libev to spend more
599	time collecting I/O events, so you can handle more events per iteration,	856	time collecting I/O events, so you can handle more events per iteration,
600	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	857	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
601	C<ev_timer>) will be not affected. Setting this to a non-null bvalue will	858	C<ev_timer>) will be not affected. Setting this to a non-null value will
602	introduce an additional C<ev_sleep ()> call into most loop iterations.	859	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		860	sleep time ensures that libev will not poll for I/O events more often then
		861	once per this interval, on average.
603		862
604	Likewise, by setting a higher I<timeout collect interval> you allow libev	863	Likewise, by setting a higher I<timeout collect interval> you allow libev
605	to spend more time collecting timeouts, at the expense of increased	864	to spend more time collecting timeouts, at the expense of increased
606	latency (the watcher callback will be called later). C<ev_io> watchers	865	latency/jitter/inexactness (the watcher callback will be called
607	will not be affected. Setting this to a non-null value will not introduce	866	later). C<ev_io> watchers will not be affected. Setting this to a non-null
608	any overhead in libev.	867	value will not introduce any overhead in libev.
609		868
610	Many (busy) programs can usually benefit by setting the io collect	869	Many (busy) programs can usually benefit by setting the I/O collect
611	interval to a value near C<0.1> or so, which is often enough for	870	interval to a value near C<0.1> or so, which is often enough for
612	interactive servers (of course not for games), likewise for timeouts. It	871	interactive servers (of course not for games), likewise for timeouts. It
613	usually doesn't make much sense to set it to a lower value than C<0.01>,	872	usually doesn't make much sense to set it to a lower value than C<0.01>,
614	as this approsaches the timing granularity of most systems.	873	as this approaches the timing granularity of most systems. Note that if
		874	you do transactions with the outside world and you can't increase the
		875	parallelity, then this setting will limit your transaction rate (if you
		876	need to poll once per transaction and the I/O collect interval is 0.01,
		877	then you can't do more than 100 transactions per second).
		878
		879	Setting the I<timeout collect interval> can improve the opportunity for
		880	saving power, as the program will "bundle" timer callback invocations that
		881	are "near" in time together, by delaying some, thus reducing the number of
		882	times the process sleeps and wakes up again. Another useful technique to
		883	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		884	they fire on, say, one-second boundaries only.
		885
		886	Example: we only need 0.1s timeout granularity, and we wish not to poll
		887	more often than 100 times per second:
		888
		889	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		890	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		891
		892	=item ev_invoke_pending (loop)
		893
		894	This call will simply invoke all pending watchers while resetting their
		895	pending state. Normally, C<ev_loop> does this automatically when required,
		896	but when overriding the invoke callback this call comes handy.
		897
		898	=item int ev_pending_count (loop)
		899
		900	Returns the number of pending watchers - zero indicates that no watchers
		901	are pending.
		902
		903	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		904
		905	This overrides the invoke pending functionality of the loop: Instead of
		906	invoking all pending watchers when there are any, C<ev_loop> will call
		907	this callback instead. This is useful, for example, when you want to
		908	invoke the actual watchers inside another context (another thread etc.).
		909
		910	If you want to reset the callback, use C<ev_invoke_pending> as new
		911	callback.
		912
		913	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		914
		915	Sometimes you want to share the same loop between multiple threads. This
		916	can be done relatively simply by putting mutex_lock/unlock calls around
		917	each call to a libev function.
		918
		919	However, C<ev_loop> can run an indefinite time, so it is not feasible to
		920	wait for it to return. One way around this is to wake up the loop via
		921	C<ev_unloop> and C<av_async_send>, another way is to set these I<release>
		922	and I<acquire> callbacks on the loop.
		923
		924	When set, then C<release> will be called just before the thread is
		925	suspended waiting for new events, and C<acquire> is called just
		926	afterwards.
		927
		928	Ideally, C<release> will just call your mutex_unlock function, and
		929	C<acquire> will just call the mutex_lock function again.
		930
		931	While event loop modifications are allowed between invocations of
		932	C<release> and C<acquire> (that's their only purpose after all), no
		933	modifications done will affect the event loop, i.e. adding watchers will
		934	have no effect on the set of file descriptors being watched, or the time
		935	waited. Use an C<ev_async> watcher to wake up C<ev_loop> when you want it
		936	to take note of any changes you made.
		937
		938	In theory, threads executing C<ev_loop> will be async-cancel safe between
		939	invocations of C<release> and C<acquire>.
		940
		941	See also the locking example in the C<THREADS> section later in this
		942	document.
		943
		944	=item ev_set_userdata (loop, void *data)
		945
		946	=item ev_userdata (loop)
		947
		948	Set and retrieve a single C<void *> associated with a loop. When
		949	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		950	C<0.>
		951
		952	These two functions can be used to associate arbitrary data with a loop,
		953	and are intended solely for the C<invoke_pending_cb>, C<release> and
		954	C<acquire> callbacks described above, but of course can be (ab-)used for
		955	any other purpose as well.
		956
		957	=item ev_loop_verify (loop)
		958
		959	This function only does something when C<EV_VERIFY> support has been
		960	compiled in, which is the default for non-minimal builds. It tries to go
		961	through all internal structures and checks them for validity. If anything
		962	is found to be inconsistent, it will print an error message to standard
		963	error and call C<abort ()>.
		964
		965	This can be used to catch bugs inside libev itself: under normal
		966	circumstances, this function will never abort as of course libev keeps its
		967	data structures consistent.
615		968
616	=back	969	=back
617		970
618		971
619	=head1 ANATOMY OF A WATCHER	972	=head1 ANATOMY OF A WATCHER
		973
		974	In the following description, uppercase C<TYPE> in names stands for the
		975	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		976	watchers and C<ev_io_start> for I/O watchers.
620		977
621	A watcher is a structure that you create and register to record your	978	A watcher is a structure that you create and register to record your
622	interest in some event. For instance, if you want to wait for STDIN to	979	interest in some event. For instance, if you want to wait for STDIN to
623	become readable, you would create an C<ev_io> watcher for that:	980	become readable, you would create an C<ev_io> watcher for that:
624		981
625	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	982	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
626	{	983	{
627	ev_io_stop (w);	984	ev_io_stop (w);
628	ev_unloop (loop, EVUNLOOP_ALL);	985	ev_unloop (loop, EVUNLOOP_ALL);
629	}	986	}
630		987
631	struct ev_loop *loop = ev_default_loop (0);	988	struct ev_loop *loop = ev_default_loop (0);
		989
632	struct ev_io stdin_watcher;	990	ev_io stdin_watcher;
		991
633	ev_init (&stdin_watcher, my_cb);	992	ev_init (&stdin_watcher, my_cb);
634	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	993	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
635	ev_io_start (loop, &stdin_watcher);	994	ev_io_start (loop, &stdin_watcher);
		995
636	ev_loop (loop, 0);	996	ev_loop (loop, 0);
637		997
638	As you can see, you are responsible for allocating the memory for your	998	As you can see, you are responsible for allocating the memory for your
639	watcher structures (and it is usually a bad idea to do this on the stack,	999	watcher structures (and it is I<usually> a bad idea to do this on the
640	although this can sometimes be quite valid).	1000	stack).
		1001
		1002	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		1003	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
641		1004
642	Each watcher structure must be initialised by a call to C<ev_init	1005	Each watcher structure must be initialised by a call to C<ev_init
643	(watcher *, callback)>, which expects a callback to be provided. This	1006	(watcher *, callback)>, which expects a callback to be provided. This
644	callback gets invoked each time the event occurs (or, in the case of io	1007	callback gets invoked each time the event occurs (or, in the case of I/O
645	watchers, each time the event loop detects that the file descriptor given	1008	watchers, each time the event loop detects that the file descriptor given
646	is readable and/or writable).	1009	is readable and/or writable).
647		1010
648	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1011	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
649	with arguments specific to this watcher type. There is also a macro	1012	macro to configure it, with arguments specific to the watcher type. There
650	to combine initialisation and setting in one call: C<< ev_<type>_init	1013	is also a macro to combine initialisation and setting in one call: C<<
651	(watcher *, callback, ...) >>.	1014	ev_TYPE_init (watcher *, callback, ...) >>.
652		1015
653	To make the watcher actually watch out for events, you have to start it	1016	To make the watcher actually watch out for events, you have to start it
654	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1017	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
655	*) >>), and you can stop watching for events at any time by calling the	1018	*) >>), and you can stop watching for events at any time by calling the
656	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1019	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
657		1020
658	As long as your watcher is active (has been started but not stopped) you	1021	As long as your watcher is active (has been started but not stopped) you
659	must not touch the values stored in it. Most specifically you must never	1022	must not touch the values stored in it. Most specifically you must never
660	reinitialise it or call its C<set> macro.	1023	reinitialise it or call its C<ev_TYPE_set> macro.
661		1024
662	Each and every callback receives the event loop pointer as first, the	1025	Each and every callback receives the event loop pointer as first, the
663	registered watcher structure as second, and a bitset of received events as	1026	registered watcher structure as second, and a bitset of received events as
664	third argument.	1027	third argument.
665		1028
…		…
674	=item C<EV_WRITE>	1037	=item C<EV_WRITE>
675		1038
676	The file descriptor in the C<ev_io> watcher has become readable and/or	1039	The file descriptor in the C<ev_io> watcher has become readable and/or
677	writable.	1040	writable.
678		1041
679	=item C<EV_TIMEOUT>	1042	=item C<EV_TIMER>
680		1043
681	The C<ev_timer> watcher has timed out.	1044	The C<ev_timer> watcher has timed out.
682		1045
683	=item C<EV_PERIODIC>	1046	=item C<EV_PERIODIC>
684		1047
…		…
719	=item C<EV_FORK>	1082	=item C<EV_FORK>
720		1083
721	The event loop has been resumed in the child process after fork (see	1084	The event loop has been resumed in the child process after fork (see
722	C<ev_fork>).	1085	C<ev_fork>).
723		1086
		1087	=item C<EV_ASYNC>
		1088
		1089	The given async watcher has been asynchronously notified (see C<ev_async>).
		1090
		1091	=item C<EV_CUSTOM>
		1092
		1093	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1094	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1095
724	=item C<EV_ERROR>	1096	=item C<EV_ERROR>
725		1097
726	An unspecified error has occured, the watcher has been stopped. This might	1098	An unspecified error has occurred, the watcher has been stopped. This might
727	happen because the watcher could not be properly started because libev	1099	happen because the watcher could not be properly started because libev
728	ran out of memory, a file descriptor was found to be closed or any other	1100	ran out of memory, a file descriptor was found to be closed or any other
		1101	problem. Libev considers these application bugs.
		1102
729	problem. You best act on it by reporting the problem and somehow coping	1103	You best act on it by reporting the problem and somehow coping with the
730	with the watcher being stopped.	1104	watcher being stopped. Note that well-written programs should not receive
		1105	an error ever, so when your watcher receives it, this usually indicates a
		1106	bug in your program.
731		1107
732	Libev will usually signal a few "dummy" events together with an error,	1108	Libev will usually signal a few "dummy" events together with an error, for
733	for example it might indicate that a fd is readable or writable, and if	1109	example it might indicate that a fd is readable or writable, and if your
734	your callbacks is well-written it can just attempt the operation and cope	1110	callbacks is well-written it can just attempt the operation and cope with
735	with the error from read() or write(). This will not work in multithreaded	1111	the error from read() or write(). This will not work in multi-threaded
736	programs, though, so beware.	1112	programs, though, as the fd could already be closed and reused for another
		1113	thing, so beware.
737		1114
738	=back	1115	=back
739		1116
740	=head2 GENERIC WATCHER FUNCTIONS	1117	=head2 GENERIC WATCHER FUNCTIONS
741
742	In the following description, C<TYPE> stands for the watcher type,
743	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
744		1118
745	=over 4	1119	=over 4
746		1120
747	=item C<ev_init> (ev_TYPE *watcher, callback)	1121	=item C<ev_init> (ev_TYPE *watcher, callback)
748		1122
…		…
754	which rolls both calls into one.	1128	which rolls both calls into one.
755		1129
756	You can reinitialise a watcher at any time as long as it has been stopped	1130	You can reinitialise a watcher at any time as long as it has been stopped
757	(or never started) and there are no pending events outstanding.	1131	(or never started) and there are no pending events outstanding.
758		1132
759	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1133	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
760	int revents)>.	1134	int revents)>.
761		1135
		1136	Example: Initialise an C<ev_io> watcher in two steps.
		1137
		1138	ev_io w;
		1139	ev_init (&w, my_cb);
		1140	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1141
762	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1142	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
763		1143
764	This macro initialises the type-specific parts of a watcher. You need to	1144	This macro initialises the type-specific parts of a watcher. You need to
765	call C<ev_init> at least once before you call this macro, but you can	1145	call C<ev_init> at least once before you call this macro, but you can
766	call C<ev_TYPE_set> any number of times. You must not, however, call this	1146	call C<ev_TYPE_set> any number of times. You must not, however, call this
767	macro on a watcher that is active (it can be pending, however, which is a	1147	macro on a watcher that is active (it can be pending, however, which is a
768	difference to the C<ev_init> macro).	1148	difference to the C<ev_init> macro).
769		1149
770	Although some watcher types do not have type-specific arguments	1150	Although some watcher types do not have type-specific arguments
771	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1151	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
772		1152
		1153	See C<ev_init>, above, for an example.
		1154
773	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1155	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
774		1156
775	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1157	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
776	calls into a single call. This is the most convinient method to initialise	1158	calls into a single call. This is the most convenient method to initialise
777	a watcher. The same limitations apply, of course.	1159	a watcher. The same limitations apply, of course.
778		1160
		1161	Example: Initialise and set an C<ev_io> watcher in one step.
		1162
		1163	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1164
779	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1165	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
780		1166
781	Starts (activates) the given watcher. Only active watchers will receive	1167	Starts (activates) the given watcher. Only active watchers will receive
782	events. If the watcher is already active nothing will happen.	1168	events. If the watcher is already active nothing will happen.
783		1169
		1170	Example: Start the C<ev_io> watcher that is being abused as example in this
		1171	whole section.
		1172
		1173	ev_io_start (EV_DEFAULT_UC, &w);
		1174
784	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1175	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
785		1176
786	Stops the given watcher again (if active) and clears the pending	1177	Stops the given watcher if active, and clears the pending status (whether
		1178	the watcher was active or not).
		1179
787	status. It is possible that stopped watchers are pending (for example,	1180	It is possible that stopped watchers are pending - for example,
788	non-repeating timers are being stopped when they become pending), but	1181	non-repeating timers are being stopped when they become pending - but
789	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1182	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
790	you want to free or reuse the memory used by the watcher it is therefore a	1183	pending. If you want to free or reuse the memory used by the watcher it is
791	good idea to always call its C<ev_TYPE_stop> function.	1184	therefore a good idea to always call its C<ev_TYPE_stop> function.
792		1185
793	=item bool ev_is_active (ev_TYPE *watcher)	1186	=item bool ev_is_active (ev_TYPE *watcher)
794		1187
795	Returns a true value iff the watcher is active (i.e. it has been started	1188	Returns a true value iff the watcher is active (i.e. it has been started
796	and not yet been stopped). As long as a watcher is active you must not modify	1189	and not yet been stopped). As long as a watcher is active you must not modify
…		…
812	=item ev_cb_set (ev_TYPE *watcher, callback)	1205	=item ev_cb_set (ev_TYPE *watcher, callback)
813		1206
814	Change the callback. You can change the callback at virtually any time	1207	Change the callback. You can change the callback at virtually any time
815	(modulo threads).	1208	(modulo threads).
816		1209
817	=item ev_set_priority (ev_TYPE *watcher, priority)	1210	=item ev_set_priority (ev_TYPE *watcher, int priority)
818		1211
819	=item int ev_priority (ev_TYPE *watcher)	1212	=item int ev_priority (ev_TYPE *watcher)
820		1213
821	Set and query the priority of the watcher. The priority is a small	1214	Set and query the priority of the watcher. The priority is a small
822	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1215	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
823	(default: C<-2>). Pending watchers with higher priority will be invoked	1216	(default: C<-2>). Pending watchers with higher priority will be invoked
824	before watchers with lower priority, but priority will not keep watchers	1217	before watchers with lower priority, but priority will not keep watchers
825	from being executed (except for C<ev_idle> watchers).	1218	from being executed (except for C<ev_idle> watchers).
826		1219
827	This means that priorities are I<only> used for ordering callback
828	invocation after new events have been received. This is useful, for
829	example, to reduce latency after idling, or more often, to bind two
830	watchers on the same event and make sure one is called first.
831
832	If you need to suppress invocation when higher priority events are pending	1220	If you need to suppress invocation when higher priority events are pending
833	you need to look at C<ev_idle> watchers, which provide this functionality.	1221	you need to look at C<ev_idle> watchers, which provide this functionality.
834		1222
835	You I<must not> change the priority of a watcher as long as it is active or	1223	You I<must not> change the priority of a watcher as long as it is active or
836	pending.	1224	pending.
837		1225
		1226	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1227	fine, as long as you do not mind that the priority value you query might
		1228	or might not have been clamped to the valid range.
		1229
838	The default priority used by watchers when no priority has been set is	1230	The default priority used by watchers when no priority has been set is
839	always C<0>, which is supposed to not be too high and not be too low :).	1231	always C<0>, which is supposed to not be too high and not be too low :).
840		1232
841	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1233	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
842	fine, as long as you do not mind that the priority value you query might	1234	priorities.
843	or might not have been adjusted to be within valid range.
844		1235
845	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1236	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
846		1237
847	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1238	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
848	C<loop> nor C<revents> need to be valid as long as the watcher callback	1239	C<loop> nor C<revents> need to be valid as long as the watcher callback
849	can deal with that fact.	1240	can deal with that fact, as both are simply passed through to the
		1241	callback.
850		1242
851	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1243	=item int ev_clear_pending (loop, ev_TYPE *watcher)
852		1244
853	If the watcher is pending, this function returns clears its pending status	1245	If the watcher is pending, this function clears its pending status and
854	and returns its C<revents> bitset (as if its callback was invoked). If the	1246	returns its C<revents> bitset (as if its callback was invoked). If the
855	watcher isn't pending it does nothing and returns C<0>.	1247	watcher isn't pending it does nothing and returns C<0>.
856		1248
		1249	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1250	callback to be invoked, which can be accomplished with this function.
		1251
		1252	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1253
		1254	Feeds the given event set into the event loop, as if the specified event
		1255	had happened for the specified watcher (which must be a pointer to an
		1256	initialised but not necessarily started event watcher). Obviously you must
		1257	not free the watcher as long as it has pending events.
		1258
		1259	Stopping the watcher, letting libev invoke it, or calling
		1260	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1261	not started in the first place.
		1262
		1263	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1264	functions that do not need a watcher.
		1265
857	=back	1266	=back
858		1267
859		1268
860	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1269	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
861		1270
862	Each watcher has, by default, a member C<void *data> that you can change	1271	Each watcher has, by default, a member C<void *data> that you can change
863	and read at any time, libev will completely ignore it. This can be used	1272	and read at any time: libev will completely ignore it. This can be used
864	to associate arbitrary data with your watcher. If you need more data and	1273	to associate arbitrary data with your watcher. If you need more data and
865	don't want to allocate memory and store a pointer to it in that data	1274	don't want to allocate memory and store a pointer to it in that data
866	member, you can also "subclass" the watcher type and provide your own	1275	member, you can also "subclass" the watcher type and provide your own
867	data:	1276	data:
868		1277
869	struct my_io	1278	struct my_io
870	{	1279	{
871	struct ev_io io;	1280	ev_io io;
872	int otherfd;	1281	int otherfd;
873	void *somedata;	1282	void *somedata;
874	struct whatever *mostinteresting;	1283	struct whatever *mostinteresting;
875	}	1284	};
		1285
		1286	...
		1287	struct my_io w;
		1288	ev_io_init (&w.io, my_cb, fd, EV_READ);
876		1289
877	And since your callback will be called with a pointer to the watcher, you	1290	And since your callback will be called with a pointer to the watcher, you
878	can cast it back to your own type:	1291	can cast it back to your own type:
879		1292
880	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1293	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
881	{	1294	{
882	struct my_io *w = (struct my_io *)w_;	1295	struct my_io *w = (struct my_io *)w_;
883	...	1296	...
884	}	1297	}
885		1298
886	More interesting and less C-conformant ways of casting your callback type	1299	More interesting and less C-conformant ways of casting your callback type
887	instead have been omitted.	1300	instead have been omitted.
888		1301
889	Another common scenario is having some data structure with multiple	1302	Another common scenario is to use some data structure with multiple
890	watchers:	1303	embedded watchers:
891		1304
892	struct my_biggy	1305	struct my_biggy
893	{	1306	{
894	int some_data;	1307	int some_data;
895	ev_timer t1;	1308	ev_timer t1;
896	ev_timer t2;	1309	ev_timer t2;
897	}	1310	}
898		1311
899	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1312	In this case getting the pointer to C<my_biggy> is a bit more
900	you need to use C<offsetof>:	1313	complicated: Either you store the address of your C<my_biggy> struct
		1314	in the C<data> member of the watcher (for woozies), or you need to use
		1315	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1316	programmers):
901		1317
902	#include <stddef.h>	1318	#include <stddef.h>
903		1319
904	static void	1320	static void
905	t1_cb (EV_P_ struct ev_timer *w, int revents)	1321	t1_cb (EV_P_ ev_timer *w, int revents)
906	{	1322	{
907	struct my_biggy big = (struct my_biggy *	1323	struct my_biggy big = (struct my_biggy *)
908	(((char *)w) - offsetof (struct my_biggy, t1));	1324	(((char *)w) - offsetof (struct my_biggy, t1));
909	}	1325	}
910		1326
911	static void	1327	static void
912	t2_cb (EV_P_ struct ev_timer *w, int revents)	1328	t2_cb (EV_P_ ev_timer *w, int revents)
913	{	1329	{
914	struct my_biggy big = (struct my_biggy *	1330	struct my_biggy big = (struct my_biggy *)
915	(((char *)w) - offsetof (struct my_biggy, t2));	1331	(((char *)w) - offsetof (struct my_biggy, t2));
916	}	1332	}
		1333
		1334	=head2 WATCHER PRIORITY MODELS
		1335
		1336	Many event loops support I<watcher priorities>, which are usually small
		1337	integers that influence the ordering of event callback invocation
		1338	between watchers in some way, all else being equal.
		1339
		1340	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1341	description for the more technical details such as the actual priority
		1342	range.
		1343
		1344	There are two common ways how these these priorities are being interpreted
		1345	by event loops:
		1346
		1347	In the more common lock-out model, higher priorities "lock out" invocation
		1348	of lower priority watchers, which means as long as higher priority
		1349	watchers receive events, lower priority watchers are not being invoked.
		1350
		1351	The less common only-for-ordering model uses priorities solely to order
		1352	callback invocation within a single event loop iteration: Higher priority
		1353	watchers are invoked before lower priority ones, but they all get invoked
		1354	before polling for new events.
		1355
		1356	Libev uses the second (only-for-ordering) model for all its watchers
		1357	except for idle watchers (which use the lock-out model).
		1358
		1359	The rationale behind this is that implementing the lock-out model for
		1360	watchers is not well supported by most kernel interfaces, and most event
		1361	libraries will just poll for the same events again and again as long as
		1362	their callbacks have not been executed, which is very inefficient in the
		1363	common case of one high-priority watcher locking out a mass of lower
		1364	priority ones.
		1365
		1366	Static (ordering) priorities are most useful when you have two or more
		1367	watchers handling the same resource: a typical usage example is having an
		1368	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1369	timeouts. Under load, data might be received while the program handles
		1370	other jobs, but since timers normally get invoked first, the timeout
		1371	handler will be executed before checking for data. In that case, giving
		1372	the timer a lower priority than the I/O watcher ensures that I/O will be
		1373	handled first even under adverse conditions (which is usually, but not
		1374	always, what you want).
		1375
		1376	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1377	will only be executed when no same or higher priority watchers have
		1378	received events, they can be used to implement the "lock-out" model when
		1379	required.
		1380
		1381	For example, to emulate how many other event libraries handle priorities,
		1382	you can associate an C<ev_idle> watcher to each such watcher, and in
		1383	the normal watcher callback, you just start the idle watcher. The real
		1384	processing is done in the idle watcher callback. This causes libev to
		1385	continuously poll and process kernel event data for the watcher, but when
		1386	the lock-out case is known to be rare (which in turn is rare :), this is
		1387	workable.
		1388
		1389	Usually, however, the lock-out model implemented that way will perform
		1390	miserably under the type of load it was designed to handle. In that case,
		1391	it might be preferable to stop the real watcher before starting the
		1392	idle watcher, so the kernel will not have to process the event in case
		1393	the actual processing will be delayed for considerable time.
		1394
		1395	Here is an example of an I/O watcher that should run at a strictly lower
		1396	priority than the default, and which should only process data when no
		1397	other events are pending:
		1398
		1399	ev_idle idle; // actual processing watcher
		1400	ev_io io; // actual event watcher
		1401
		1402	static void
		1403	io_cb (EV_P_ ev_io *w, int revents)
		1404	{
		1405	// stop the I/O watcher, we received the event, but
		1406	// are not yet ready to handle it.
		1407	ev_io_stop (EV_A_ w);
		1408
		1409	// start the idle watcher to handle the actual event.
		1410	// it will not be executed as long as other watchers
		1411	// with the default priority are receiving events.
		1412	ev_idle_start (EV_A_ &idle);
		1413	}
		1414
		1415	static void
		1416	idle_cb (EV_P_ ev_idle *w, int revents)
		1417	{
		1418	// actual processing
		1419	read (STDIN_FILENO, ...);
		1420
		1421	// have to start the I/O watcher again, as
		1422	// we have handled the event
		1423	ev_io_start (EV_P_ &io);
		1424	}
		1425
		1426	// initialisation
		1427	ev_idle_init (&idle, idle_cb);
		1428	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1429	ev_io_start (EV_DEFAULT_ &io);
		1430
		1431	In the "real" world, it might also be beneficial to start a timer, so that
		1432	low-priority connections can not be locked out forever under load. This
		1433	enables your program to keep a lower latency for important connections
		1434	during short periods of high load, while not completely locking out less
		1435	important ones.
917		1436
918		1437
919	=head1 WATCHER TYPES	1438	=head1 WATCHER TYPES
920		1439
921	This section describes each watcher in detail, but will not repeat	1440	This section describes each watcher in detail, but will not repeat
…		…
945	In general you can register as many read and/or write event watchers per	1464	In general you can register as many read and/or write event watchers per
946	fd as you want (as long as you don't confuse yourself). Setting all file	1465	fd as you want (as long as you don't confuse yourself). Setting all file
947	descriptors to non-blocking mode is also usually a good idea (but not	1466	descriptors to non-blocking mode is also usually a good idea (but not
948	required if you know what you are doing).	1467	required if you know what you are doing).
949		1468
950	You have to be careful with dup'ed file descriptors, though. Some backends	1469	If you cannot use non-blocking mode, then force the use of a
951	(the linux epoll backend is a notable example) cannot handle dup'ed file	1470	known-to-be-good backend (at the time of this writing, this includes only
952	descriptors correctly if you register interest in two or more fds pointing	1471	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
953	to the same underlying file/socket/etc. description (that is, they share	1472	descriptors for which non-blocking operation makes no sense (such as
954	the same underlying "file open").	1473	files) - libev doesn't guarantee any specific behaviour in that case.
955
956	If you must do this, then force the use of a known-to-be-good backend
957	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
958	C<EVBACKEND_POLL>).
959		1474
960	Another thing you have to watch out for is that it is quite easy to	1475	Another thing you have to watch out for is that it is quite easy to
961	receive "spurious" readyness notifications, that is your callback might	1476	receive "spurious" readiness notifications, that is your callback might
962	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1477	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
963	because there is no data. Not only are some backends known to create a	1478	because there is no data. Not only are some backends known to create a
964	lot of those (for example solaris ports), it is very easy to get into	1479	lot of those (for example Solaris ports), it is very easy to get into
965	this situation even with a relatively standard program structure. Thus	1480	this situation even with a relatively standard program structure. Thus
966	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1481	it is best to always use non-blocking I/O: An extra C<read>(2) returning
967	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1482	C<EAGAIN> is far preferable to a program hanging until some data arrives.
968		1483
969	If you cannot run the fd in non-blocking mode (for example you should not	1484	If you cannot run the fd in non-blocking mode (for example you should
970	play around with an Xlib connection), then you have to seperately re-test	1485	not play around with an Xlib connection), then you have to separately
971	whether a file descriptor is really ready with a known-to-be good interface	1486	re-test whether a file descriptor is really ready with a known-to-be good
972	such as poll (fortunately in our Xlib example, Xlib already does this on	1487	interface such as poll (fortunately in our Xlib example, Xlib already
973	its own, so its quite safe to use).	1488	does this on its own, so its quite safe to use). Some people additionally
		1489	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1490	indefinitely.
		1491
		1492	But really, best use non-blocking mode.
974		1493
975	=head3 The special problem of disappearing file descriptors	1494	=head3 The special problem of disappearing file descriptors
976		1495
977	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1496	Some backends (e.g. kqueue, epoll) need to be told about closing a file
978	descriptor (either by calling C<close> explicitly or by any other means,	1497	descriptor (either due to calling C<close> explicitly or any other means,
979	such as C<dup>). The reason is that you register interest in some file	1498	such as C<dup2>). The reason is that you register interest in some file
980	descriptor, but when it goes away, the operating system will silently drop	1499	descriptor, but when it goes away, the operating system will silently drop
981	this interest. If another file descriptor with the same number then is	1500	this interest. If another file descriptor with the same number then is
982	registered with libev, there is no efficient way to see that this is, in	1501	registered with libev, there is no efficient way to see that this is, in
983	fact, a different file descriptor.	1502	fact, a different file descriptor.
984		1503
…		…
994	optimisations to libev.	1513	optimisations to libev.
995		1514
996	=head3 The special problem of dup'ed file descriptors	1515	=head3 The special problem of dup'ed file descriptors
997		1516
998	Some backends (e.g. epoll), cannot register events for file descriptors,	1517	Some backends (e.g. epoll), cannot register events for file descriptors,
999	but only events for the underlying file descriptions. That menas when you	1518	but only events for the underlying file descriptions. That means when you
1000	have C<dup ()>'ed file descriptors and register events for them, only one	1519	have C<dup ()>'ed file descriptors or weirder constellations, and register
1001	file descriptor might actually receive events.	1520	events for them, only one file descriptor might actually receive events.
1002		1521
1003	There is no workaorund possible except not registering events	1522	There is no workaround possible except not registering events
1004	for potentially C<dup ()>'ed file descriptors or to resort to	1523	for potentially C<dup ()>'ed file descriptors, or to resort to
1005	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1524	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1006		1525
1007	=head3 The special problem of fork	1526	=head3 The special problem of fork
1008		1527
1009	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1528	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
…		…
1013	To support fork in your programs, you either have to call	1532	To support fork in your programs, you either have to call
1014	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1533	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
1015	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1534	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
1016	C<EVBACKEND_POLL>.	1535	C<EVBACKEND_POLL>.
1017		1536
		1537	=head3 The special problem of SIGPIPE
		1538
		1539	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1540	when writing to a pipe whose other end has been closed, your program gets
		1541	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1542	this is sensible behaviour, for daemons, this is usually undesirable.
		1543
		1544	So when you encounter spurious, unexplained daemon exits, make sure you
		1545	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1546	somewhere, as that would have given you a big clue).
		1547
		1548	=head3 The special problem of accept()ing when you can't
		1549
		1550	Many implementations of the POSIX C<accept> function (for example,
		1551	found in post-2004 Linux) have the peculiar behaviour of not removing a
		1552	connection from the pending queue in all error cases.
		1553
		1554	For example, larger servers often run out of file descriptors (because
		1555	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1556	rejecting the connection, leading to libev signalling readiness on
		1557	the next iteration again (the connection still exists after all), and
		1558	typically causing the program to loop at 100% CPU usage.
		1559
		1560	Unfortunately, the set of errors that cause this issue differs between
		1561	operating systems, there is usually little the app can do to remedy the
		1562	situation, and no known thread-safe method of removing the connection to
		1563	cope with overload is known (to me).
		1564
		1565	One of the easiest ways to handle this situation is to just ignore it
		1566	- when the program encounters an overload, it will just loop until the
		1567	situation is over. While this is a form of busy waiting, no OS offers an
		1568	event-based way to handle this situation, so it's the best one can do.
		1569
		1570	A better way to handle the situation is to log any errors other than
		1571	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1572	messages, and continue as usual, which at least gives the user an idea of
		1573	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1574	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1575	usage.
		1576
		1577	If your program is single-threaded, then you could also keep a dummy file
		1578	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1579	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1580	close that fd, and create a new dummy fd. This will gracefully refuse
		1581	clients under typical overload conditions.
		1582
		1583	The last way to handle it is to simply log the error and C<exit>, as
		1584	is often done with C<malloc> failures, but this results in an easy
		1585	opportunity for a DoS attack.
1018		1586
1019	=head3 Watcher-Specific Functions	1587	=head3 Watcher-Specific Functions
1020		1588
1021	=over 4	1589	=over 4
1022		1590
1023	=item ev_io_init (ev_io *, callback, int fd, int events)	1591	=item ev_io_init (ev_io *, callback, int fd, int events)
1024		1592
1025	=item ev_io_set (ev_io *, int fd, int events)	1593	=item ev_io_set (ev_io *, int fd, int events)
1026		1594
1027	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1595	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
1028	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1596	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
1029	C<EV_READ | EV_WRITE> to receive the given events.	1597	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
1030		1598
1031	=item int fd [read-only]	1599	=item int fd [read-only]
1032		1600
1033	The file descriptor being watched.	1601	The file descriptor being watched.
1034		1602
1035	=item int events [read-only]	1603	=item int events [read-only]
1036		1604
1037	The events being watched.	1605	The events being watched.
1038		1606
1039	=back	1607	=back
		1608
		1609	=head3 Examples
1040		1610
1041	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1611	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1042	readable, but only once. Since it is likely line-buffered, you could	1612	readable, but only once. Since it is likely line-buffered, you could
1043	attempt to read a whole line in the callback.	1613	attempt to read a whole line in the callback.
1044		1614
1045	static void	1615	static void
1046	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1616	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1047	{	1617	{
1048	ev_io_stop (loop, w);	1618	ev_io_stop (loop, w);
1049	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1619	.. read from stdin here (or from w->fd) and handle any I/O errors
1050	}	1620	}
1051		1621
1052	...	1622	...
1053	struct ev_loop *loop = ev_default_init (0);	1623	struct ev_loop *loop = ev_default_init (0);
1054	struct ev_io stdin_readable;	1624	ev_io stdin_readable;
1055	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1625	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1056	ev_io_start (loop, &stdin_readable);	1626	ev_io_start (loop, &stdin_readable);
1057	ev_loop (loop, 0);	1627	ev_loop (loop, 0);
1058		1628
1059		1629
1060	=head2 C<ev_timer> - relative and optionally repeating timeouts	1630	=head2 C<ev_timer> - relative and optionally repeating timeouts
1061		1631
1062	Timer watchers are simple relative timers that generate an event after a	1632	Timer watchers are simple relative timers that generate an event after a
1063	given time, and optionally repeating in regular intervals after that.	1633	given time, and optionally repeating in regular intervals after that.
1064		1634
1065	The timers are based on real time, that is, if you register an event that	1635	The timers are based on real time, that is, if you register an event that
1066	times out after an hour and you reset your system clock to last years	1636	times out after an hour and you reset your system clock to January last
1067	time, it will still time out after (roughly) and hour. "Roughly" because	1637	year, it will still time out after (roughly) one hour. "Roughly" because
1068	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1638	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1069	monotonic clock option helps a lot here).	1639	monotonic clock option helps a lot here).
		1640
		1641	The callback is guaranteed to be invoked only I<after> its timeout has
		1642	passed (not I<at>, so on systems with very low-resolution clocks this
		1643	might introduce a small delay). If multiple timers become ready during the
		1644	same loop iteration then the ones with earlier time-out values are invoked
		1645	before ones of the same priority with later time-out values (but this is
		1646	no longer true when a callback calls C<ev_loop> recursively).
		1647
		1648	=head3 Be smart about timeouts
		1649
		1650	Many real-world problems involve some kind of timeout, usually for error
		1651	recovery. A typical example is an HTTP request - if the other side hangs,
		1652	you want to raise some error after a while.
		1653
		1654	What follows are some ways to handle this problem, from obvious and
		1655	inefficient to smart and efficient.
		1656
		1657	In the following, a 60 second activity timeout is assumed - a timeout that
		1658	gets reset to 60 seconds each time there is activity (e.g. each time some
		1659	data or other life sign was received).
		1660
		1661	=over 4
		1662
		1663	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1664
		1665	This is the most obvious, but not the most simple way: In the beginning,
		1666	start the watcher:
		1667
		1668	ev_timer_init (timer, callback, 60., 0.);
		1669	ev_timer_start (loop, timer);
		1670
		1671	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1672	and start it again:
		1673
		1674	ev_timer_stop (loop, timer);
		1675	ev_timer_set (timer, 60., 0.);
		1676	ev_timer_start (loop, timer);
		1677
		1678	This is relatively simple to implement, but means that each time there is
		1679	some activity, libev will first have to remove the timer from its internal
		1680	data structure and then add it again. Libev tries to be fast, but it's
		1681	still not a constant-time operation.
		1682
		1683	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1684
		1685	This is the easiest way, and involves using C<ev_timer_again> instead of
		1686	C<ev_timer_start>.
		1687
		1688	To implement this, configure an C<ev_timer> with a C<repeat> value
		1689	of C<60> and then call C<ev_timer_again> at start and each time you
		1690	successfully read or write some data. If you go into an idle state where
		1691	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1692	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1693
		1694	That means you can ignore both the C<ev_timer_start> function and the
		1695	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1696	member and C<ev_timer_again>.
		1697
		1698	At start:
		1699
		1700	ev_init (timer, callback);
		1701	timer->repeat = 60.;
		1702	ev_timer_again (loop, timer);
		1703
		1704	Each time there is some activity:
		1705
		1706	ev_timer_again (loop, timer);
		1707
		1708	It is even possible to change the time-out on the fly, regardless of
		1709	whether the watcher is active or not:
		1710
		1711	timer->repeat = 30.;
		1712	ev_timer_again (loop, timer);
		1713
		1714	This is slightly more efficient then stopping/starting the timer each time
		1715	you want to modify its timeout value, as libev does not have to completely
		1716	remove and re-insert the timer from/into its internal data structure.
		1717
		1718	It is, however, even simpler than the "obvious" way to do it.
		1719
		1720	=item 3. Let the timer time out, but then re-arm it as required.
		1721
		1722	This method is more tricky, but usually most efficient: Most timeouts are
		1723	relatively long compared to the intervals between other activity - in
		1724	our example, within 60 seconds, there are usually many I/O events with
		1725	associated activity resets.
		1726
		1727	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1728	but remember the time of last activity, and check for a real timeout only
		1729	within the callback:
		1730
		1731	ev_tstamp last_activity; // time of last activity
		1732
		1733	static void
		1734	callback (EV_P_ ev_timer *w, int revents)
		1735	{
		1736	ev_tstamp now = ev_now (EV_A);
		1737	ev_tstamp timeout = last_activity + 60.;
		1738
		1739	// if last_activity + 60. is older than now, we did time out
		1740	if (timeout < now)
		1741	{
		1742	// timeout occurred, take action
		1743	}
		1744	else
		1745	{
		1746	// callback was invoked, but there was some activity, re-arm
		1747	// the watcher to fire in last_activity + 60, which is
		1748	// guaranteed to be in the future, so "again" is positive:
		1749	w->repeat = timeout - now;
		1750	ev_timer_again (EV_A_ w);
		1751	}
		1752	}
		1753
		1754	To summarise the callback: first calculate the real timeout (defined
		1755	as "60 seconds after the last activity"), then check if that time has
		1756	been reached, which means something I<did>, in fact, time out. Otherwise
		1757	the callback was invoked too early (C<timeout> is in the future), so
		1758	re-schedule the timer to fire at that future time, to see if maybe we have
		1759	a timeout then.
		1760
		1761	Note how C<ev_timer_again> is used, taking advantage of the
		1762	C<ev_timer_again> optimisation when the timer is already running.
		1763
		1764	This scheme causes more callback invocations (about one every 60 seconds
		1765	minus half the average time between activity), but virtually no calls to
		1766	libev to change the timeout.
		1767
		1768	To start the timer, simply initialise the watcher and set C<last_activity>
		1769	to the current time (meaning we just have some activity :), then call the
		1770	callback, which will "do the right thing" and start the timer:
		1771
		1772	ev_init (timer, callback);
		1773	last_activity = ev_now (loop);
		1774	callback (loop, timer, EV_TIMER);
		1775
		1776	And when there is some activity, simply store the current time in
		1777	C<last_activity>, no libev calls at all:
		1778
		1779	last_activity = ev_now (loop);
		1780
		1781	This technique is slightly more complex, but in most cases where the
		1782	time-out is unlikely to be triggered, much more efficient.
		1783
		1784	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1785	callback :) - just change the timeout and invoke the callback, which will
		1786	fix things for you.
		1787
		1788	=item 4. Wee, just use a double-linked list for your timeouts.
		1789
		1790	If there is not one request, but many thousands (millions...), all
		1791	employing some kind of timeout with the same timeout value, then one can
		1792	do even better:
		1793
		1794	When starting the timeout, calculate the timeout value and put the timeout
		1795	at the I<end> of the list.
		1796
		1797	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1798	the list is expected to fire (for example, using the technique #3).
		1799
		1800	When there is some activity, remove the timer from the list, recalculate
		1801	the timeout, append it to the end of the list again, and make sure to
		1802	update the C<ev_timer> if it was taken from the beginning of the list.
		1803
		1804	This way, one can manage an unlimited number of timeouts in O(1) time for
		1805	starting, stopping and updating the timers, at the expense of a major
		1806	complication, and having to use a constant timeout. The constant timeout
		1807	ensures that the list stays sorted.
		1808
		1809	=back
		1810
		1811	So which method the best?
		1812
		1813	Method #2 is a simple no-brain-required solution that is adequate in most
		1814	situations. Method #3 requires a bit more thinking, but handles many cases
		1815	better, and isn't very complicated either. In most case, choosing either
		1816	one is fine, with #3 being better in typical situations.
		1817
		1818	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1819	rather complicated, but extremely efficient, something that really pays
		1820	off after the first million or so of active timers, i.e. it's usually
		1821	overkill :)
		1822
		1823	=head3 The special problem of time updates
		1824
		1825	Establishing the current time is a costly operation (it usually takes at
		1826	least two system calls): EV therefore updates its idea of the current
		1827	time only before and after C<ev_loop> collects new events, which causes a
		1828	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1829	lots of events in one iteration.
1070		1830
1071	The relative timeouts are calculated relative to the C<ev_now ()>	1831	The relative timeouts are calculated relative to the C<ev_now ()>
1072	time. This is usually the right thing as this timestamp refers to the time	1832	time. This is usually the right thing as this timestamp refers to the time
1073	of the event triggering whatever timeout you are modifying/starting. If	1833	of the event triggering whatever timeout you are modifying/starting. If
1074	you suspect event processing to be delayed and you I<need> to base the timeout	1834	you suspect event processing to be delayed and you I<need> to base the
1075	on the current time, use something like this to adjust for this:	1835	timeout on the current time, use something like this to adjust for this:
1076		1836
1077	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1837	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1078		1838
1079	The callback is guarenteed to be invoked only when its timeout has passed,	1839	If the event loop is suspended for a long time, you can also force an
1080	but if multiple timers become ready during the same loop iteration then	1840	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1081	order of execution is undefined.	1841	()>.
		1842
		1843	=head3 The special problems of suspended animation
		1844
		1845	When you leave the server world it is quite customary to hit machines that
		1846	can suspend/hibernate - what happens to the clocks during such a suspend?
		1847
		1848	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1849	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1850	to run until the system is suspended, but they will not advance while the
		1851	system is suspended. That means, on resume, it will be as if the program
		1852	was frozen for a few seconds, but the suspend time will not be counted
		1853	towards C<ev_timer> when a monotonic clock source is used. The real time
		1854	clock advanced as expected, but if it is used as sole clocksource, then a
		1855	long suspend would be detected as a time jump by libev, and timers would
		1856	be adjusted accordingly.
		1857
		1858	I would not be surprised to see different behaviour in different between
		1859	operating systems, OS versions or even different hardware.
		1860
		1861	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1862	time jump in the monotonic clocks and the realtime clock. If the program
		1863	is suspended for a very long time, and monotonic clock sources are in use,
		1864	then you can expect C<ev_timer>s to expire as the full suspension time
		1865	will be counted towards the timers. When no monotonic clock source is in
		1866	use, then libev will again assume a timejump and adjust accordingly.
		1867
		1868	It might be beneficial for this latter case to call C<ev_suspend>
		1869	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1870	deterministic behaviour in this case (you can do nothing against
		1871	C<SIGSTOP>).
1082		1872
1083	=head3 Watcher-Specific Functions and Data Members	1873	=head3 Watcher-Specific Functions and Data Members
1084		1874
1085	=over 4	1875	=over 4
1086		1876
1087	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1877	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1088		1878
1089	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1879	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1090		1880
1091	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1881	Configure the timer to trigger after C<after> seconds. If C<repeat>
1092	C<0.>, then it will automatically be stopped. If it is positive, then the	1882	is C<0.>, then it will automatically be stopped once the timeout is
1093	timer will automatically be configured to trigger again C<repeat> seconds	1883	reached. If it is positive, then the timer will automatically be
1094	later, again, and again, until stopped manually.	1884	configured to trigger again C<repeat> seconds later, again, and again,
		1885	until stopped manually.
1095		1886
1096	The timer itself will do a best-effort at avoiding drift, that is, if you	1887	The timer itself will do a best-effort at avoiding drift, that is, if
1097	configure a timer to trigger every 10 seconds, then it will trigger at	1888	you configure a timer to trigger every 10 seconds, then it will normally
1098	exactly 10 second intervals. If, however, your program cannot keep up with	1889	trigger at exactly 10 second intervals. If, however, your program cannot
1099	the timer (because it takes longer than those 10 seconds to do stuff) the	1890	keep up with the timer (because it takes longer than those 10 seconds to
1100	timer will not fire more than once per event loop iteration.	1891	do stuff) the timer will not fire more than once per event loop iteration.
1101		1892
1102	=item ev_timer_again (loop)	1893	=item ev_timer_again (loop, ev_timer *)
1103		1894
1104	This will act as if the timer timed out and restart it again if it is	1895	This will act as if the timer timed out and restart it again if it is
1105	repeating. The exact semantics are:	1896	repeating. The exact semantics are:
1106		1897
1107	If the timer is pending, its pending status is cleared.	1898	If the timer is pending, its pending status is cleared.
1108		1899
1109	If the timer is started but nonrepeating, stop it (as if it timed out).	1900	If the timer is started but non-repeating, stop it (as if it timed out).
1110		1901
1111	If the timer is repeating, either start it if necessary (with the	1902	If the timer is repeating, either start it if necessary (with the
1112	C<repeat> value), or reset the running timer to the C<repeat> value.	1903	C<repeat> value), or reset the running timer to the C<repeat> value.
1113		1904
1114	This sounds a bit complicated, but here is a useful and typical	1905	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1115	example: Imagine you have a tcp connection and you want a so-called idle	1906	usage example.
1116	timeout, that is, you want to be called when there have been, say, 60
1117	seconds of inactivity on the socket. The easiest way to do this is to
1118	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1119	C<ev_timer_again> each time you successfully read or write some data. If
1120	you go into an idle state where you do not expect data to travel on the
1121	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1122	automatically restart it if need be.
1123		1907
1124	That means you can ignore the C<after> value and C<ev_timer_start>	1908	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1125	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1126		1909
1127	ev_timer_init (timer, callback, 0., 5.);	1910	Returns the remaining time until a timer fires. If the timer is active,
1128	ev_timer_again (loop, timer);	1911	then this time is relative to the current event loop time, otherwise it's
1129	...	1912	the timeout value currently configured.
1130	timer->again = 17.;
1131	ev_timer_again (loop, timer);
1132	...
1133	timer->again = 10.;
1134	ev_timer_again (loop, timer);
1135		1913
1136	This is more slightly efficient then stopping/starting the timer each time	1914	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
1137	you want to modify its timeout value.	1915	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		1916	will return C<4>. When the timer expires and is restarted, it will return
		1917	roughly C<7> (likely slightly less as callback invocation takes some time,
		1918	too), and so on.
1138		1919
1139	=item ev_tstamp repeat [read-write]	1920	=item ev_tstamp repeat [read-write]
1140		1921
1141	The current C<repeat> value. Will be used each time the watcher times out	1922	The current C<repeat> value. Will be used each time the watcher times out
1142	or C<ev_timer_again> is called and determines the next timeout (if any),	1923	or C<ev_timer_again> is called, and determines the next timeout (if any),
1143	which is also when any modifications are taken into account.	1924	which is also when any modifications are taken into account.
1144		1925
1145	=back	1926	=back
1146		1927
		1928	=head3 Examples
		1929
1147	Example: Create a timer that fires after 60 seconds.	1930	Example: Create a timer that fires after 60 seconds.
1148		1931
1149	static void	1932	static void
1150	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1933	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1151	{	1934	{
1152	.. one minute over, w is actually stopped right here	1935	.. one minute over, w is actually stopped right here
1153	}	1936	}
1154		1937
1155	struct ev_timer mytimer;	1938	ev_timer mytimer;
1156	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1939	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1157	ev_timer_start (loop, &mytimer);	1940	ev_timer_start (loop, &mytimer);
1158		1941
1159	Example: Create a timeout timer that times out after 10 seconds of	1942	Example: Create a timeout timer that times out after 10 seconds of
1160	inactivity.	1943	inactivity.
1161		1944
1162	static void	1945	static void
1163	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1946	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1164	{	1947	{
1165	.. ten seconds without any activity	1948	.. ten seconds without any activity
1166	}	1949	}
1167		1950
1168	struct ev_timer mytimer;	1951	ev_timer mytimer;
1169	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1952	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1170	ev_timer_again (&mytimer); /* start timer */	1953	ev_timer_again (&mytimer); /* start timer */
1171	ev_loop (loop, 0);	1954	ev_loop (loop, 0);
1172		1955
1173	// and in some piece of code that gets executed on any "activity":	1956	// and in some piece of code that gets executed on any "activity":
1174	// reset the timeout to start ticking again at 10 seconds	1957	// reset the timeout to start ticking again at 10 seconds
1175	ev_timer_again (&mytimer);	1958	ev_timer_again (&mytimer);
1176		1959
1177		1960
1178	=head2 C<ev_periodic> - to cron or not to cron?	1961	=head2 C<ev_periodic> - to cron or not to cron?
1179		1962
1180	Periodic watchers are also timers of a kind, but they are very versatile	1963	Periodic watchers are also timers of a kind, but they are very versatile
1181	(and unfortunately a bit complex).	1964	(and unfortunately a bit complex).
1182		1965
1183	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1966	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1184	but on wallclock time (absolute time). You can tell a periodic watcher	1967	relative time, the physical time that passes) but on wall clock time
1185	to trigger "at" some specific point in time. For example, if you tell a	1968	(absolute time, the thing you can read on your calender or clock). The
1186	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	1969	difference is that wall clock time can run faster or slower than real
1187	+ 10.>) and then reset your system clock to the last year, then it will	1970	time, and time jumps are not uncommon (e.g. when you adjust your
1188	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1971	wrist-watch).
1189	roughly 10 seconds later).
1190		1972
1191	They can also be used to implement vastly more complex timers, such as	1973	You can tell a periodic watcher to trigger after some specific point
1192	triggering an event on each midnight, local time or other, complicated,	1974	in time: for example, if you tell a periodic watcher to trigger "in 10
1193	rules.	1975	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1976	not a delay) and then reset your system clock to January of the previous
		1977	year, then it will take a year or more to trigger the event (unlike an
		1978	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1979	it, as it uses a relative timeout).
1194		1980
		1981	C<ev_periodic> watchers can also be used to implement vastly more complex
		1982	timers, such as triggering an event on each "midnight, local time", or
		1983	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1984	those cannot react to time jumps.
		1985
1195	As with timers, the callback is guarenteed to be invoked only when the	1986	As with timers, the callback is guaranteed to be invoked only when the
1196	time (C<at>) has been passed, but if multiple periodic timers become ready	1987	point in time where it is supposed to trigger has passed. If multiple
1197	during the same loop iteration then order of execution is undefined.	1988	timers become ready during the same loop iteration then the ones with
		1989	earlier time-out values are invoked before ones with later time-out values
		1990	(but this is no longer true when a callback calls C<ev_loop> recursively).
1198		1991
1199	=head3 Watcher-Specific Functions and Data Members	1992	=head3 Watcher-Specific Functions and Data Members
1200		1993
1201	=over 4	1994	=over 4
1202		1995
1203	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1996	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1204		1997
1205	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1998	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1206		1999
1207	Lots of arguments, lets sort it out... There are basically three modes of	2000	Lots of arguments, let's sort it out... There are basically three modes of
1208	operation, and we will explain them from simplest to complex:	2001	operation, and we will explain them from simplest to most complex:
1209		2002
1210	=over 4	2003	=over 4
1211		2004
1212	=item * absolute timer (at = time, interval = reschedule_cb = 0)	2005	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1213		2006
1214	In this configuration the watcher triggers an event at the wallclock time	2007	In this configuration the watcher triggers an event after the wall clock
1215	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	2008	time C<offset> has passed. It will not repeat and will not adjust when a
1216	that is, if it is to be run at January 1st 2011 then it will run when the	2009	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1217	system time reaches or surpasses this time.	2010	will be stopped and invoked when the system clock reaches or surpasses
		2011	this point in time.
1218		2012
1219	=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	2013	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1220		2014
1221	In this mode the watcher will always be scheduled to time out at the next	2015	In this mode the watcher will always be scheduled to time out at the next
1222	C<at + N * interval> time (for some integer N, which can also be negative)	2016	C<offset + N * interval> time (for some integer N, which can also be
1223	and then repeat, regardless of any time jumps.	2017	negative) and then repeat, regardless of any time jumps. The C<offset>
		2018	argument is merely an offset into the C<interval> periods.
1224		2019
1225	This can be used to create timers that do not drift with respect to system	2020	This can be used to create timers that do not drift with respect to the
1226	time:	2021	system clock, for example, here is an C<ev_periodic> that triggers each
		2022	hour, on the hour (with respect to UTC):
1227		2023
1228	ev_periodic_set (&periodic, 0., 3600., 0);	2024	ev_periodic_set (&periodic, 0., 3600., 0);
1229		2025
1230	This doesn't mean there will always be 3600 seconds in between triggers,	2026	This doesn't mean there will always be 3600 seconds in between triggers,
1231	but only that the the callback will be called when the system time shows a	2027	but only that the callback will be called when the system time shows a
1232	full hour (UTC), or more correctly, when the system time is evenly divisible	2028	full hour (UTC), or more correctly, when the system time is evenly divisible
1233	by 3600.	2029	by 3600.
1234		2030
1235	Another way to think about it (for the mathematically inclined) is that	2031	Another way to think about it (for the mathematically inclined) is that
1236	C<ev_periodic> will try to run the callback in this mode at the next possible	2032	C<ev_periodic> will try to run the callback in this mode at the next possible
1237	time where C<time = at (mod interval)>, regardless of any time jumps.	2033	time where C<time = offset (mod interval)>, regardless of any time jumps.
1238		2034
1239	For numerical stability it is preferable that the C<at> value is near	2035	For numerical stability it is preferable that the C<offset> value is near
1240	C<ev_now ()> (the current time), but there is no range requirement for	2036	C<ev_now ()> (the current time), but there is no range requirement for
1241	this value.	2037	this value, and in fact is often specified as zero.
1242		2038
		2039	Note also that there is an upper limit to how often a timer can fire (CPU
		2040	speed for example), so if C<interval> is very small then timing stability
		2041	will of course deteriorate. Libev itself tries to be exact to be about one
		2042	millisecond (if the OS supports it and the machine is fast enough).
		2043
1243	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	2044	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1244		2045
1245	In this mode the values for C<interval> and C<at> are both being	2046	In this mode the values for C<interval> and C<offset> are both being
1246	ignored. Instead, each time the periodic watcher gets scheduled, the	2047	ignored. Instead, each time the periodic watcher gets scheduled, the
1247	reschedule callback will be called with the watcher as first, and the	2048	reschedule callback will be called with the watcher as first, and the
1248	current time as second argument.	2049	current time as second argument.
1249		2050
1250	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2051	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1251	ever, or make any event loop modifications>. If you need to stop it,	2052	or make ANY other event loop modifications whatsoever, unless explicitly
1252	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	2053	allowed by documentation here>.
1253	starting an C<ev_prepare> watcher, which is legal).
1254		2054
		2055	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		2056	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		2057	only event loop modification you are allowed to do).
		2058
1255	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	2059	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1256	ev_tstamp now)>, e.g.:	2060	*w, ev_tstamp now)>, e.g.:
1257		2061
		2062	static ev_tstamp
1258	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2063	my_rescheduler (ev_periodic *w, ev_tstamp now)
1259	{	2064	{
1260	return now + 60.;	2065	return now + 60.;
1261	}	2066	}
1262		2067
1263	It must return the next time to trigger, based on the passed time value	2068	It must return the next time to trigger, based on the passed time value
1264	(that is, the lowest time value larger than to the second argument). It	2069	(that is, the lowest time value larger than to the second argument). It
1265	will usually be called just before the callback will be triggered, but	2070	will usually be called just before the callback will be triggered, but
1266	might be called at other times, too.	2071	might be called at other times, too.
1267		2072
1268	NOTE: I<< This callback must always return a time that is later than the	2073	NOTE: I<< This callback must always return a time that is higher than or
1269	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	2074	equal to the passed C<now> value >>.
1270		2075
1271	This can be used to create very complex timers, such as a timer that	2076	This can be used to create very complex timers, such as a timer that
1272	triggers on each midnight, local time. To do this, you would calculate the	2077	triggers on "next midnight, local time". To do this, you would calculate the
1273	next midnight after C<now> and return the timestamp value for this. How	2078	next midnight after C<now> and return the timestamp value for this. How
1274	you do this is, again, up to you (but it is not trivial, which is the main	2079	you do this is, again, up to you (but it is not trivial, which is the main
1275	reason I omitted it as an example).	2080	reason I omitted it as an example).
1276		2081
1277	=back	2082	=back
…		…
1281	Simply stops and restarts the periodic watcher again. This is only useful	2086	Simply stops and restarts the periodic watcher again. This is only useful
1282	when you changed some parameters or the reschedule callback would return	2087	when you changed some parameters or the reschedule callback would return
1283	a different time than the last time it was called (e.g. in a crond like	2088	a different time than the last time it was called (e.g. in a crond like
1284	program when the crontabs have changed).	2089	program when the crontabs have changed).
1285		2090
		2091	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2092
		2093	When active, returns the absolute time that the watcher is supposed
		2094	to trigger next. This is not the same as the C<offset> argument to
		2095	C<ev_periodic_set>, but indeed works even in interval and manual
		2096	rescheduling modes.
		2097
1286	=item ev_tstamp offset [read-write]	2098	=item ev_tstamp offset [read-write]
1287		2099
1288	When repeating, this contains the offset value, otherwise this is the	2100	When repeating, this contains the offset value, otherwise this is the
1289	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	2101	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2102	although libev might modify this value for better numerical stability).
1290		2103
1291	Can be modified any time, but changes only take effect when the periodic	2104	Can be modified any time, but changes only take effect when the periodic
1292	timer fires or C<ev_periodic_again> is being called.	2105	timer fires or C<ev_periodic_again> is being called.
1293		2106
1294	=item ev_tstamp interval [read-write]	2107	=item ev_tstamp interval [read-write]
1295		2108
1296	The current interval value. Can be modified any time, but changes only	2109	The current interval value. Can be modified any time, but changes only
1297	take effect when the periodic timer fires or C<ev_periodic_again> is being	2110	take effect when the periodic timer fires or C<ev_periodic_again> is being
1298	called.	2111	called.
1299		2112
1300	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2113	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1301		2114
1302	The current reschedule callback, or C<0>, if this functionality is	2115	The current reschedule callback, or C<0>, if this functionality is
1303	switched off. Can be changed any time, but changes only take effect when	2116	switched off. Can be changed any time, but changes only take effect when
1304	the periodic timer fires or C<ev_periodic_again> is being called.	2117	the periodic timer fires or C<ev_periodic_again> is being called.
1305		2118
1306	=item ev_tstamp at [read-only]
1307
1308	When active, contains the absolute time that the watcher is supposed to
1309	trigger next.
1310
1311	=back	2119	=back
1312		2120
		2121	=head3 Examples
		2122
1313	Example: Call a callback every hour, or, more precisely, whenever the	2123	Example: Call a callback every hour, or, more precisely, whenever the
1314	system clock is divisible by 3600. The callback invocation times have	2124	system time is divisible by 3600. The callback invocation times have
1315	potentially a lot of jittering, but good long-term stability.	2125	potentially a lot of jitter, but good long-term stability.
1316		2126
1317	static void	2127	static void
1318	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2128	clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1319	{	2129	{
1320	... its now a full hour (UTC, or TAI or whatever your clock follows)	2130	... its now a full hour (UTC, or TAI or whatever your clock follows)
1321	}	2131	}
1322		2132
1323	struct ev_periodic hourly_tick;	2133	ev_periodic hourly_tick;
1324	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2134	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1325	ev_periodic_start (loop, &hourly_tick);	2135	ev_periodic_start (loop, &hourly_tick);
1326		2136
1327	Example: The same as above, but use a reschedule callback to do it:	2137	Example: The same as above, but use a reschedule callback to do it:
1328		2138
1329	#include <math.h>	2139	#include <math.h>
1330		2140
1331	static ev_tstamp	2141	static ev_tstamp
1332	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2142	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1333	{	2143	{
1334	return fmod (now, 3600.) + 3600.;	2144	return now + (3600. - fmod (now, 3600.));
1335	}	2145	}
1336		2146
1337	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2147	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1338		2148
1339	Example: Call a callback every hour, starting now:	2149	Example: Call a callback every hour, starting now:
1340		2150
1341	struct ev_periodic hourly_tick;	2151	ev_periodic hourly_tick;
1342	ev_periodic_init (&hourly_tick, clock_cb,	2152	ev_periodic_init (&hourly_tick, clock_cb,
1343	fmod (ev_now (loop), 3600.), 3600., 0);	2153	fmod (ev_now (loop), 3600.), 3600., 0);
1344	ev_periodic_start (loop, &hourly_tick);	2154	ev_periodic_start (loop, &hourly_tick);
1345		2155
1346		2156
1347	=head2 C<ev_signal> - signal me when a signal gets signalled!	2157	=head2 C<ev_signal> - signal me when a signal gets signalled!
1348		2158
1349	Signal watchers will trigger an event when the process receives a specific	2159	Signal watchers will trigger an event when the process receives a specific
1350	signal one or more times. Even though signals are very asynchronous, libev	2160	signal one or more times. Even though signals are very asynchronous, libev
1351	will try it's best to deliver signals synchronously, i.e. as part of the	2161	will try it's best to deliver signals synchronously, i.e. as part of the
1352	normal event processing, like any other event.	2162	normal event processing, like any other event.
1353		2163
		2164	If you want signals to be delivered truly asynchronously, just use
		2165	C<sigaction> as you would do without libev and forget about sharing
		2166	the signal. You can even use C<ev_async> from a signal handler to
		2167	synchronously wake up an event loop.
		2168
1354	You can configure as many watchers as you like per signal. Only when the	2169	You can configure as many watchers as you like for the same signal, but
		2170	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2171	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2172	C<SIGINT> in both the default loop and another loop at the same time. At
		2173	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2174
1355	first watcher gets started will libev actually register a signal watcher	2175	When the first watcher gets started will libev actually register something
1356	with the kernel (thus it coexists with your own signal handlers as long	2176	with the kernel (thus it coexists with your own signal handlers as long as
1357	as you don't register any with libev). Similarly, when the last signal	2177	you don't register any with libev for the same signal).
1358	watcher for a signal is stopped libev will reset the signal handler to	2178
1359	SIG_DFL (regardless of what it was set to before).	2179	If possible and supported, libev will install its handlers with
		2180	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
		2181	not be unduly interrupted. If you have a problem with system calls getting
		2182	interrupted by signals you can block all signals in an C<ev_check> watcher
		2183	and unblock them in an C<ev_prepare> watcher.
		2184
		2185	=head3 The special problem of inheritance over fork/execve/pthread_create
		2186
		2187	Both the signal mask (C<sigprocmask>) and the signal disposition
		2188	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2189	stopping it again), that is, libev might or might not block the signal,
		2190	and might or might not set or restore the installed signal handler.
		2191
		2192	While this does not matter for the signal disposition (libev never
		2193	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2194	C<execve>), this matters for the signal mask: many programs do not expect
		2195	certain signals to be blocked.
		2196
		2197	This means that before calling C<exec> (from the child) you should reset
		2198	the signal mask to whatever "default" you expect (all clear is a good
		2199	choice usually).
		2200
		2201	The simplest way to ensure that the signal mask is reset in the child is
		2202	to install a fork handler with C<pthread_atfork> that resets it. That will
		2203	catch fork calls done by libraries (such as the libc) as well.
		2204
		2205	In current versions of libev, the signal will not be blocked indefinitely
		2206	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2207	the window of opportunity for problems, it will not go away, as libev
		2208	I<has> to modify the signal mask, at least temporarily.
		2209
		2210	So I can't stress this enough: I<If you do not reset your signal mask when
		2211	you expect it to be empty, you have a race condition in your code>. This
		2212	is not a libev-specific thing, this is true for most event libraries.
1360		2213
1361	=head3 Watcher-Specific Functions and Data Members	2214	=head3 Watcher-Specific Functions and Data Members
1362		2215
1363	=over 4	2216	=over 4
1364		2217
…		…
1373		2226
1374	The signal the watcher watches out for.	2227	The signal the watcher watches out for.
1375		2228
1376	=back	2229	=back
1377		2230
		2231	=head3 Examples
		2232
		2233	Example: Try to exit cleanly on SIGINT.
		2234
		2235	static void
		2236	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2237	{
		2238	ev_unloop (loop, EVUNLOOP_ALL);
		2239	}
		2240
		2241	ev_signal signal_watcher;
		2242	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2243	ev_signal_start (loop, &signal_watcher);
		2244
1378		2245
1379	=head2 C<ev_child> - watch out for process status changes	2246	=head2 C<ev_child> - watch out for process status changes
1380		2247
1381	Child watchers trigger when your process receives a SIGCHLD in response to	2248	Child watchers trigger when your process receives a SIGCHLD in response to
1382	some child status changes (most typically when a child of yours dies).	2249	some child status changes (most typically when a child of yours dies or
		2250	exits). It is permissible to install a child watcher I<after> the child
		2251	has been forked (which implies it might have already exited), as long
		2252	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2253	forking and then immediately registering a watcher for the child is fine,
		2254	but forking and registering a watcher a few event loop iterations later or
		2255	in the next callback invocation is not.
		2256
		2257	Only the default event loop is capable of handling signals, and therefore
		2258	you can only register child watchers in the default event loop.
		2259
		2260	Due to some design glitches inside libev, child watchers will always be
		2261	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2262	libev)
		2263
		2264	=head3 Process Interaction
		2265
		2266	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2267	initialised. This is necessary to guarantee proper behaviour even if the
		2268	first child watcher is started after the child exits. The occurrence
		2269	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2270	synchronously as part of the event loop processing. Libev always reaps all
		2271	children, even ones not watched.
		2272
		2273	=head3 Overriding the Built-In Processing
		2274
		2275	Libev offers no special support for overriding the built-in child
		2276	processing, but if your application collides with libev's default child
		2277	handler, you can override it easily by installing your own handler for
		2278	C<SIGCHLD> after initialising the default loop, and making sure the
		2279	default loop never gets destroyed. You are encouraged, however, to use an
		2280	event-based approach to child reaping and thus use libev's support for
		2281	that, so other libev users can use C<ev_child> watchers freely.
		2282
		2283	=head3 Stopping the Child Watcher
		2284
		2285	Currently, the child watcher never gets stopped, even when the
		2286	child terminates, so normally one needs to stop the watcher in the
		2287	callback. Future versions of libev might stop the watcher automatically
		2288	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2289	problem).
1383		2290
1384	=head3 Watcher-Specific Functions and Data Members	2291	=head3 Watcher-Specific Functions and Data Members
1385		2292
1386	=over 4	2293	=over 4
1387		2294
1388	=item ev_child_init (ev_child *, callback, int pid)	2295	=item ev_child_init (ev_child *, callback, int pid, int trace)
1389		2296
1390	=item ev_child_set (ev_child *, int pid)	2297	=item ev_child_set (ev_child *, int pid, int trace)
1391		2298
1392	Configures the watcher to wait for status changes of process C<pid> (or	2299	Configures the watcher to wait for status changes of process C<pid> (or
1393	I<any> process if C<pid> is specified as C<0>). The callback can look	2300	I<any> process if C<pid> is specified as C<0>). The callback can look
1394	at the C<rstatus> member of the C<ev_child> watcher structure to see	2301	at the C<rstatus> member of the C<ev_child> watcher structure to see
1395	the status word (use the macros from C<sys/wait.h> and see your systems	2302	the status word (use the macros from C<sys/wait.h> and see your systems
1396	C<waitpid> documentation). The C<rpid> member contains the pid of the	2303	C<waitpid> documentation). The C<rpid> member contains the pid of the
1397	process causing the status change.	2304	process causing the status change. C<trace> must be either C<0> (only
		2305	activate the watcher when the process terminates) or C<1> (additionally
		2306	activate the watcher when the process is stopped or continued).
1398		2307
1399	=item int pid [read-only]	2308	=item int pid [read-only]
1400		2309
1401	The process id this watcher watches out for, or C<0>, meaning any process id.	2310	The process id this watcher watches out for, or C<0>, meaning any process id.
1402		2311
…		…
1409	The process exit/trace status caused by C<rpid> (see your systems	2318	The process exit/trace status caused by C<rpid> (see your systems
1410	C<waitpid> and C<sys/wait.h> documentation for details).	2319	C<waitpid> and C<sys/wait.h> documentation for details).
1411		2320
1412	=back	2321	=back
1413		2322
1414	Example: Try to exit cleanly on SIGINT and SIGTERM.	2323	=head3 Examples
1415		2324
		2325	Example: C<fork()> a new process and install a child handler to wait for
		2326	its completion.
		2327
		2328	ev_child cw;
		2329
1416	static void	2330	static void
1417	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2331	child_cb (EV_P_ ev_child *w, int revents)
1418	{	2332	{
1419	ev_unloop (loop, EVUNLOOP_ALL);	2333	ev_child_stop (EV_A_ w);
		2334	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1420	}	2335	}
1421		2336
1422	struct ev_signal signal_watcher;	2337	pid_t pid = fork ();
1423	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2338
1424	ev_signal_start (loop, &sigint_cb);	2339	if (pid < 0)
		2340	// error
		2341	else if (pid == 0)
		2342	{
		2343	// the forked child executes here
		2344	exit (1);
		2345	}
		2346	else
		2347	{
		2348	ev_child_init (&cw, child_cb, pid, 0);
		2349	ev_child_start (EV_DEFAULT_ &cw);
		2350	}
1425		2351
1426		2352
1427	=head2 C<ev_stat> - did the file attributes just change?	2353	=head2 C<ev_stat> - did the file attributes just change?
1428		2354
1429	This watches a filesystem path for attribute changes. That is, it calls	2355	This watches a file system path for attribute changes. That is, it calls
1430	C<stat> regularly (or when the OS says it changed) and sees if it changed	2356	C<stat> on that path in regular intervals (or when the OS says it changed)
1431	compared to the last time, invoking the callback if it did.	2357	and sees if it changed compared to the last time, invoking the callback if
		2358	it did.
1432		2359
1433	The path does not need to exist: changing from "path exists" to "path does	2360	The path does not need to exist: changing from "path exists" to "path does
1434	not exist" is a status change like any other. The condition "path does	2361	not exist" is a status change like any other. The condition "path does not
1435	not exist" is signified by the C<st_nlink> field being zero (which is	2362	exist" (or more correctly "path cannot be stat'ed") is signified by the
1436	otherwise always forced to be at least one) and all the other fields of	2363	C<st_nlink> field being zero (which is otherwise always forced to be at
1437	the stat buffer having unspecified contents.	2364	least one) and all the other fields of the stat buffer having unspecified
		2365	contents.
1438		2366
1439	The path I<should> be absolute and I<must not> end in a slash. If it is	2367	The path I<must not> end in a slash or contain special components such as
		2368	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1440	relative and your working directory changes, the behaviour is undefined.	2369	your working directory changes, then the behaviour is undefined.
1441		2370
1442	Since there is no standard to do this, the portable implementation simply	2371	Since there is no portable change notification interface available, the
1443	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2372	portable implementation simply calls C<stat(2)> regularly on the path
1444	can specify a recommended polling interval for this case. If you specify	2373	to see if it changed somehow. You can specify a recommended polling
1445	a polling interval of C<0> (highly recommended!) then a I<suitable,	2374	interval for this case. If you specify a polling interval of C<0> (highly
1446	unspecified default> value will be used (which you can expect to be around	2375	recommended!) then a I<suitable, unspecified default> value will be used
1447	five seconds, although this might change dynamically). Libev will also	2376	(which you can expect to be around five seconds, although this might
1448	impose a minimum interval which is currently around C<0.1>, but thats	2377	change dynamically). Libev will also impose a minimum interval which is
1449	usually overkill.	2378	currently around C<0.1>, but that's usually overkill.
1450		2379
1451	This watcher type is not meant for massive numbers of stat watchers,	2380	This watcher type is not meant for massive numbers of stat watchers,
1452	as even with OS-supported change notifications, this can be	2381	as even with OS-supported change notifications, this can be
1453	resource-intensive.	2382	resource-intensive.
1454		2383
1455	At the time of this writing, only the Linux inotify interface is	2384	At the time of this writing, the only OS-specific interface implemented
1456	implemented (implementing kqueue support is left as an exercise for the	2385	is the Linux inotify interface (implementing kqueue support is left as an
1457	reader). Inotify will be used to give hints only and should not change the	2386	exercise for the reader. Note, however, that the author sees no way of
1458	semantics of C<ev_stat> watchers, which means that libev sometimes needs	2387	implementing C<ev_stat> semantics with kqueue, except as a hint).
1459	to fall back to regular polling again even with inotify, but changes are	2388
1460	usually detected immediately, and if the file exists there will be no	2389	=head3 ABI Issues (Largefile Support)
1461	polling.	2390
		2391	Libev by default (unless the user overrides this) uses the default
		2392	compilation environment, which means that on systems with large file
		2393	support disabled by default, you get the 32 bit version of the stat
		2394	structure. When using the library from programs that change the ABI to
		2395	use 64 bit file offsets the programs will fail. In that case you have to
		2396	compile libev with the same flags to get binary compatibility. This is
		2397	obviously the case with any flags that change the ABI, but the problem is
		2398	most noticeably displayed with ev_stat and large file support.
		2399
		2400	The solution for this is to lobby your distribution maker to make large
		2401	file interfaces available by default (as e.g. FreeBSD does) and not
		2402	optional. Libev cannot simply switch on large file support because it has
		2403	to exchange stat structures with application programs compiled using the
		2404	default compilation environment.
		2405
		2406	=head3 Inotify and Kqueue
		2407
		2408	When C<inotify (7)> support has been compiled into libev and present at
		2409	runtime, it will be used to speed up change detection where possible. The
		2410	inotify descriptor will be created lazily when the first C<ev_stat>
		2411	watcher is being started.
		2412
		2413	Inotify presence does not change the semantics of C<ev_stat> watchers
		2414	except that changes might be detected earlier, and in some cases, to avoid
		2415	making regular C<stat> calls. Even in the presence of inotify support
		2416	there are many cases where libev has to resort to regular C<stat> polling,
		2417	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2418	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2419	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2420	xfs are fully working) libev usually gets away without polling.
		2421
		2422	There is no support for kqueue, as apparently it cannot be used to
		2423	implement this functionality, due to the requirement of having a file
		2424	descriptor open on the object at all times, and detecting renames, unlinks
		2425	etc. is difficult.
		2426
		2427	=head3 C<stat ()> is a synchronous operation
		2428
		2429	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2430	the process. The exception are C<ev_stat> watchers - those call C<stat
		2431	()>, which is a synchronous operation.
		2432
		2433	For local paths, this usually doesn't matter: unless the system is very
		2434	busy or the intervals between stat's are large, a stat call will be fast,
		2435	as the path data is usually in memory already (except when starting the
		2436	watcher).
		2437
		2438	For networked file systems, calling C<stat ()> can block an indefinite
		2439	time due to network issues, and even under good conditions, a stat call
		2440	often takes multiple milliseconds.
		2441
		2442	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2443	paths, although this is fully supported by libev.
		2444
		2445	=head3 The special problem of stat time resolution
		2446
		2447	The C<stat ()> system call only supports full-second resolution portably,
		2448	and even on systems where the resolution is higher, most file systems
		2449	still only support whole seconds.
		2450
		2451	That means that, if the time is the only thing that changes, you can
		2452	easily miss updates: on the first update, C<ev_stat> detects a change and
		2453	calls your callback, which does something. When there is another update
		2454	within the same second, C<ev_stat> will be unable to detect unless the
		2455	stat data does change in other ways (e.g. file size).
		2456
		2457	The solution to this is to delay acting on a change for slightly more
		2458	than a second (or till slightly after the next full second boundary), using
		2459	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2460	ev_timer_again (loop, w)>).
		2461
		2462	The C<.02> offset is added to work around small timing inconsistencies
		2463	of some operating systems (where the second counter of the current time
		2464	might be be delayed. One such system is the Linux kernel, where a call to
		2465	C<gettimeofday> might return a timestamp with a full second later than
		2466	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2467	update file times then there will be a small window where the kernel uses
		2468	the previous second to update file times but libev might already execute
		2469	the timer callback).
1462		2470
1463	=head3 Watcher-Specific Functions and Data Members	2471	=head3 Watcher-Specific Functions and Data Members
1464		2472
1465	=over 4	2473	=over 4
1466		2474
…		…
1472	C<path>. The C<interval> is a hint on how quickly a change is expected to	2480	C<path>. The C<interval> is a hint on how quickly a change is expected to
1473	be detected and should normally be specified as C<0> to let libev choose	2481	be detected and should normally be specified as C<0> to let libev choose
1474	a suitable value. The memory pointed to by C<path> must point to the same	2482	a suitable value. The memory pointed to by C<path> must point to the same
1475	path for as long as the watcher is active.	2483	path for as long as the watcher is active.
1476		2484
1477	The callback will be receive C<EV_STAT> when a change was detected,	2485	The callback will receive an C<EV_STAT> event when a change was detected,
1478	relative to the attributes at the time the watcher was started (or the	2486	relative to the attributes at the time the watcher was started (or the
1479	last change was detected).	2487	last change was detected).
1480		2488
1481	=item ev_stat_stat (ev_stat *)	2489	=item ev_stat_stat (loop, ev_stat *)
1482		2490
1483	Updates the stat buffer immediately with new values. If you change the	2491	Updates the stat buffer immediately with new values. If you change the
1484	watched path in your callback, you could call this fucntion to avoid	2492	watched path in your callback, you could call this function to avoid
1485	detecting this change (while introducing a race condition). Can also be	2493	detecting this change (while introducing a race condition if you are not
1486	useful simply to find out the new values.	2494	the only one changing the path). Can also be useful simply to find out the
		2495	new values.
1487		2496
1488	=item ev_statdata attr [read-only]	2497	=item ev_statdata attr [read-only]
1489		2498
1490	The most-recently detected attributes of the file. Although the type is of	2499	The most-recently detected attributes of the file. Although the type is
1491	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2500	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1492	suitable for your system. If the C<st_nlink> member is C<0>, then there	2501	suitable for your system, but you can only rely on the POSIX-standardised
		2502	members to be present. If the C<st_nlink> member is C<0>, then there was
1493	was some error while C<stat>ing the file.	2503	some error while C<stat>ing the file.
1494		2504
1495	=item ev_statdata prev [read-only]	2505	=item ev_statdata prev [read-only]
1496		2506
1497	The previous attributes of the file. The callback gets invoked whenever	2507	The previous attributes of the file. The callback gets invoked whenever
1498	C<prev> != C<attr>.	2508	C<prev> != C<attr>, or, more precisely, one or more of these members
		2509	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2510	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1499		2511
1500	=item ev_tstamp interval [read-only]	2512	=item ev_tstamp interval [read-only]
1501		2513
1502	The specified interval.	2514	The specified interval.
1503		2515
1504	=item const char *path [read-only]	2516	=item const char *path [read-only]
1505		2517
1506	The filesystem path that is being watched.	2518	The file system path that is being watched.
1507		2519
1508	=back	2520	=back
1509		2521
		2522	=head3 Examples
		2523
1510	Example: Watch C</etc/passwd> for attribute changes.	2524	Example: Watch C</etc/passwd> for attribute changes.
1511		2525
1512	static void	2526	static void
1513	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2527	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1514	{	2528	{
1515	/* /etc/passwd changed in some way */	2529	/* /etc/passwd changed in some way */
1516	if (w->attr.st_nlink)	2530	if (w->attr.st_nlink)
1517	{	2531	{
1518	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2532	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1519	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2533	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1520	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2534	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1521	}	2535	}
1522	else	2536	else
1523	/* you shalt not abuse printf for puts */	2537	/* you shalt not abuse printf for puts */
1524	puts ("wow, /etc/passwd is not there, expect problems. "	2538	puts ("wow, /etc/passwd is not there, expect problems. "
1525	"if this is windows, they already arrived\n");	2539	"if this is windows, they already arrived\n");
1526	}	2540	}
1527		2541
1528	...	2542	...
1529	ev_stat passwd;	2543	ev_stat passwd;
1530		2544
1531	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	2545	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1532	ev_stat_start (loop, &passwd);	2546	ev_stat_start (loop, &passwd);
		2547
		2548	Example: Like above, but additionally use a one-second delay so we do not
		2549	miss updates (however, frequent updates will delay processing, too, so
		2550	one might do the work both on C<ev_stat> callback invocation I<and> on
		2551	C<ev_timer> callback invocation).
		2552
		2553	static ev_stat passwd;
		2554	static ev_timer timer;
		2555
		2556	static void
		2557	timer_cb (EV_P_ ev_timer *w, int revents)
		2558	{
		2559	ev_timer_stop (EV_A_ w);
		2560
		2561	/* now it's one second after the most recent passwd change */
		2562	}
		2563
		2564	static void
		2565	stat_cb (EV_P_ ev_stat *w, int revents)
		2566	{
		2567	/* reset the one-second timer */
		2568	ev_timer_again (EV_A_ &timer);
		2569	}
		2570
		2571	...
		2572	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2573	ev_stat_start (loop, &passwd);
		2574	ev_timer_init (&timer, timer_cb, 0., 1.02);
1533		2575
1534		2576
1535	=head2 C<ev_idle> - when you've got nothing better to do...	2577	=head2 C<ev_idle> - when you've got nothing better to do...
1536		2578
1537	Idle watchers trigger events when no other events of the same or higher	2579	Idle watchers trigger events when no other events of the same or higher
1538	priority are pending (prepare, check and other idle watchers do not	2580	priority are pending (prepare, check and other idle watchers do not count
1539	count).	2581	as receiving "events").
1540		2582
1541	That is, as long as your process is busy handling sockets or timeouts	2583	That is, as long as your process is busy handling sockets or timeouts
1542	(or even signals, imagine) of the same or higher priority it will not be	2584	(or even signals, imagine) of the same or higher priority it will not be
1543	triggered. But when your process is idle (or only lower-priority watchers	2585	triggered. But when your process is idle (or only lower-priority watchers
1544	are pending), the idle watchers are being called once per event loop	2586	are pending), the idle watchers are being called once per event loop
…		…
1555		2597
1556	=head3 Watcher-Specific Functions and Data Members	2598	=head3 Watcher-Specific Functions and Data Members
1557		2599
1558	=over 4	2600	=over 4
1559		2601
1560	=item ev_idle_init (ev_signal *, callback)	2602	=item ev_idle_init (ev_idle *, callback)
1561		2603
1562	Initialises and configures the idle watcher - it has no parameters of any	2604	Initialises and configures the idle watcher - it has no parameters of any
1563	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2605	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1564	believe me.	2606	believe me.
1565		2607
1566	=back	2608	=back
1567		2609
		2610	=head3 Examples
		2611
1568	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2612	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1569	callback, free it. Also, use no error checking, as usual.	2613	callback, free it. Also, use no error checking, as usual.
1570		2614
1571	static void	2615	static void
1572	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2616	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1573	{	2617	{
1574	free (w);	2618	free (w);
1575	// now do something you wanted to do when the program has	2619	// now do something you wanted to do when the program has
1576	// no longer asnything immediate to do.	2620	// no longer anything immediate to do.
1577	}	2621	}
1578		2622
1579	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2623	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1580	ev_idle_init (idle_watcher, idle_cb);	2624	ev_idle_init (idle_watcher, idle_cb);
1581	ev_idle_start (loop, idle_cb);	2625	ev_idle_start (loop, idle_watcher);
1582		2626
1583		2627
1584	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2628	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1585		2629
1586	Prepare and check watchers are usually (but not always) used in tandem:	2630	Prepare and check watchers are usually (but not always) used in pairs:
1587	prepare watchers get invoked before the process blocks and check watchers	2631	prepare watchers get invoked before the process blocks and check watchers
1588	afterwards.	2632	afterwards.
1589		2633
1590	You I<must not> call C<ev_loop> or similar functions that enter	2634	You I<must not> call C<ev_loop> or similar functions that enter
1591	the current event loop from either C<ev_prepare> or C<ev_check>	2635	the current event loop from either C<ev_prepare> or C<ev_check>
…		…
1594	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2638	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1595	C<ev_check> so if you have one watcher of each kind they will always be	2639	C<ev_check> so if you have one watcher of each kind they will always be
1596	called in pairs bracketing the blocking call.	2640	called in pairs bracketing the blocking call.
1597		2641
1598	Their main purpose is to integrate other event mechanisms into libev and	2642	Their main purpose is to integrate other event mechanisms into libev and
1599	their use is somewhat advanced. This could be used, for example, to track	2643	their use is somewhat advanced. They could be used, for example, to track
1600	variable changes, implement your own watchers, integrate net-snmp or a	2644	variable changes, implement your own watchers, integrate net-snmp or a
1601	coroutine library and lots more. They are also occasionally useful if	2645	coroutine library and lots more. They are also occasionally useful if
1602	you cache some data and want to flush it before blocking (for example,	2646	you cache some data and want to flush it before blocking (for example,
1603	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2647	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1604	watcher).	2648	watcher).
1605		2649
1606	This is done by examining in each prepare call which file descriptors need	2650	This is done by examining in each prepare call which file descriptors
1607	to be watched by the other library, registering C<ev_io> watchers for	2651	need to be watched by the other library, registering C<ev_io> watchers
1608	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2652	for them and starting an C<ev_timer> watcher for any timeouts (many
1609	provide just this functionality). Then, in the check watcher you check for	2653	libraries provide exactly this functionality). Then, in the check watcher,
1610	any events that occured (by checking the pending status of all watchers	2654	you check for any events that occurred (by checking the pending status
1611	and stopping them) and call back into the library. The I/O and timer	2655	of all watchers and stopping them) and call back into the library. The
1612	callbacks will never actually be called (but must be valid nevertheless,	2656	I/O and timer callbacks will never actually be called (but must be valid
1613	because you never know, you know?).	2657	nevertheless, because you never know, you know?).
1614		2658
1615	As another example, the Perl Coro module uses these hooks to integrate	2659	As another example, the Perl Coro module uses these hooks to integrate
1616	coroutines into libev programs, by yielding to other active coroutines	2660	coroutines into libev programs, by yielding to other active coroutines
1617	during each prepare and only letting the process block if no coroutines	2661	during each prepare and only letting the process block if no coroutines
1618	are ready to run (it's actually more complicated: it only runs coroutines	2662	are ready to run (it's actually more complicated: it only runs coroutines
…		…
1621	loop from blocking if lower-priority coroutines are active, thus mapping	2665	loop from blocking if lower-priority coroutines are active, thus mapping
1622	low-priority coroutines to idle/background tasks).	2666	low-priority coroutines to idle/background tasks).
1623		2667
1624	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2668	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1625	priority, to ensure that they are being run before any other watchers	2669	priority, to ensure that they are being run before any other watchers
		2670	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2671
1626	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2672	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1627	too) should not activate ("feed") events into libev. While libev fully	2673	activate ("feed") events into libev. While libev fully supports this, they
1628	supports this, they will be called before other C<ev_check> watchers did	2674	might get executed before other C<ev_check> watchers did their job. As
1629	their job. As C<ev_check> watchers are often used to embed other event	2675	C<ev_check> watchers are often used to embed other (non-libev) event
1630	loops those other event loops might be in an unusable state until their	2676	loops those other event loops might be in an unusable state until their
1631	C<ev_check> watcher ran (always remind yourself to coexist peacefully with	2677	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1632	others).	2678	others).
1633		2679
1634	=head3 Watcher-Specific Functions and Data Members	2680	=head3 Watcher-Specific Functions and Data Members
…		…
1639		2685
1640	=item ev_check_init (ev_check *, callback)	2686	=item ev_check_init (ev_check *, callback)
1641		2687
1642	Initialises and configures the prepare or check watcher - they have no	2688	Initialises and configures the prepare or check watcher - they have no
1643	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2689	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1644	macros, but using them is utterly, utterly and completely pointless.	2690	macros, but using them is utterly, utterly, utterly and completely
		2691	pointless.
1645		2692
1646	=back	2693	=back
		2694
		2695	=head3 Examples
1647		2696
1648	There are a number of principal ways to embed other event loops or modules	2697	There are a number of principal ways to embed other event loops or modules
1649	into libev. Here are some ideas on how to include libadns into libev	2698	into libev. Here are some ideas on how to include libadns into libev
1650	(there is a Perl module named C<EV::ADNS> that does this, which you could	2699	(there is a Perl module named C<EV::ADNS> that does this, which you could
1651	use for an actually working example. Another Perl module named C<EV::Glib>	2700	use as a working example. Another Perl module named C<EV::Glib> embeds a
1652	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV	2701	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1653	into the Glib event loop).	2702	Glib event loop).
1654		2703
1655	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	2704	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1656	and in a check watcher, destroy them and call into libadns. What follows	2705	and in a check watcher, destroy them and call into libadns. What follows
1657	is pseudo-code only of course. This requires you to either use a low	2706	is pseudo-code only of course. This requires you to either use a low
1658	priority for the check watcher or use C<ev_clear_pending> explicitly, as	2707	priority for the check watcher or use C<ev_clear_pending> explicitly, as
1659	the callbacks for the IO/timeout watchers might not have been called yet.	2708	the callbacks for the IO/timeout watchers might not have been called yet.
1660		2709
1661	static ev_io iow [nfd];	2710	static ev_io iow [nfd];
1662	static ev_timer tw;	2711	static ev_timer tw;
1663		2712
1664	static void	2713	static void
1665	io_cb (ev_loop *loop, ev_io *w, int revents)	2714	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1666	{	2715	{
1667	}	2716	}
1668		2717
1669	// create io watchers for each fd and a timer before blocking	2718	// create io watchers for each fd and a timer before blocking
1670	static void	2719	static void
1671	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2720	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1672	{	2721	{
1673	int timeout = 3600000;	2722	int timeout = 3600000;
1674	struct pollfd fds [nfd];	2723	struct pollfd fds [nfd];
1675	// actual code will need to loop here and realloc etc.	2724	// actual code will need to loop here and realloc etc.
1676	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2725	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1677		2726
1678	/* the callback is illegal, but won't be called as we stop during check */	2727	/* the callback is illegal, but won't be called as we stop during check */
1679	ev_timer_init (&tw, 0, timeout * 1e-3);	2728	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1680	ev_timer_start (loop, &tw);	2729	ev_timer_start (loop, &tw);
1681		2730
1682	// create one ev_io per pollfd	2731	// create one ev_io per pollfd
1683	for (int i = 0; i < nfd; ++i)	2732	for (int i = 0; i < nfd; ++i)
1684	{	2733	{
1685	ev_io_init (iow + i, io_cb, fds [i].fd,	2734	ev_io_init (iow + i, io_cb, fds [i].fd,
1686	((fds [i].events & POLLIN ? EV_READ : 0)	2735	((fds [i].events & POLLIN ? EV_READ : 0)
1687	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2736	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1688		2737
1689	fds [i].revents = 0;	2738	fds [i].revents = 0;
1690	ev_io_start (loop, iow + i);	2739	ev_io_start (loop, iow + i);
1691	}	2740	}
1692	}	2741	}
1693		2742
1694	// stop all watchers after blocking	2743	// stop all watchers after blocking
1695	static void	2744	static void
1696	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2745	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1697	{	2746	{
1698	ev_timer_stop (loop, &tw);	2747	ev_timer_stop (loop, &tw);
1699		2748
1700	for (int i = 0; i < nfd; ++i)	2749	for (int i = 0; i < nfd; ++i)
1701	{	2750	{
1702	// set the relevant poll flags	2751	// set the relevant poll flags
1703	// could also call adns_processreadable etc. here	2752	// could also call adns_processreadable etc. here
1704	struct pollfd *fd = fds + i;	2753	struct pollfd *fd = fds + i;
1705	int revents = ev_clear_pending (iow + i);	2754	int revents = ev_clear_pending (iow + i);
1706	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;	2755	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1707	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;	2756	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1708		2757
1709	// now stop the watcher	2758	// now stop the watcher
1710	ev_io_stop (loop, iow + i);	2759	ev_io_stop (loop, iow + i);
1711	}	2760	}
1712		2761
1713	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2762	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1714	}	2763	}
1715		2764
1716	Method 2: This would be just like method 1, but you run C<adns_afterpoll>	2765	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
1717	in the prepare watcher and would dispose of the check watcher.	2766	in the prepare watcher and would dispose of the check watcher.
1718		2767
1719	Method 3: If the module to be embedded supports explicit event	2768	Method 3: If the module to be embedded supports explicit event
1720	notification (adns does), you can also make use of the actual watcher	2769	notification (libadns does), you can also make use of the actual watcher
1721	callbacks, and only destroy/create the watchers in the prepare watcher.	2770	callbacks, and only destroy/create the watchers in the prepare watcher.
1722		2771
1723	static void	2772	static void
1724	timer_cb (EV_P_ ev_timer *w, int revents)	2773	timer_cb (EV_P_ ev_timer *w, int revents)
1725	{	2774	{
1726	adns_state ads = (adns_state)w->data;	2775	adns_state ads = (adns_state)w->data;
1727	update_now (EV_A);	2776	update_now (EV_A);
1728		2777
1729	adns_processtimeouts (ads, &tv_now);	2778	adns_processtimeouts (ads, &tv_now);
1730	}	2779	}
1731		2780
1732	static void	2781	static void
1733	io_cb (EV_P_ ev_io *w, int revents)	2782	io_cb (EV_P_ ev_io *w, int revents)
1734	{	2783	{
1735	adns_state ads = (adns_state)w->data;	2784	adns_state ads = (adns_state)w->data;
1736	update_now (EV_A);	2785	update_now (EV_A);
1737		2786
1738	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);	2787	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
1739	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);	2788	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
1740	}	2789	}
1741		2790
1742	// do not ever call adns_afterpoll	2791	// do not ever call adns_afterpoll
1743		2792
1744	Method 4: Do not use a prepare or check watcher because the module you	2793	Method 4: Do not use a prepare or check watcher because the module you
1745	want to embed is too inflexible to support it. Instead, youc na override	2794	want to embed is not flexible enough to support it. Instead, you can
1746	their poll function. The drawback with this solution is that the main	2795	override their poll function. The drawback with this solution is that the
1747	loop is now no longer controllable by EV. The C<Glib::EV> module does	2796	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
1748	this.	2797	this approach, effectively embedding EV as a client into the horrible
		2798	libglib event loop.
1749		2799
1750	static gint	2800	static gint
1751	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	2801	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1752	{	2802	{
1753	int got_events = 0;	2803	int got_events = 0;
1754		2804
1755	for (n = 0; n < nfds; ++n)	2805	for (n = 0; n < nfds; ++n)
1756	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events	2806	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1757		2807
1758	if (timeout >= 0)	2808	if (timeout >= 0)
1759	// create/start timer	2809	// create/start timer
1760		2810
1761	// poll	2811	// poll
1762	ev_loop (EV_A_ 0);	2812	ev_loop (EV_A_ 0);
1763		2813
1764	// stop timer again	2814	// stop timer again
1765	if (timeout >= 0)	2815	if (timeout >= 0)
1766	ev_timer_stop (EV_A_ &to);	2816	ev_timer_stop (EV_A_ &to);
1767		2817
1768	// stop io watchers again - their callbacks should have set	2818	// stop io watchers again - their callbacks should have set
1769	for (n = 0; n < nfds; ++n)	2819	for (n = 0; n < nfds; ++n)
1770	ev_io_stop (EV_A_ iow [n]);	2820	ev_io_stop (EV_A_ iow [n]);
1771		2821
1772	return got_events;	2822	return got_events;
1773	}	2823	}
1774		2824
1775		2825
1776	=head2 C<ev_embed> - when one backend isn't enough...	2826	=head2 C<ev_embed> - when one backend isn't enough...
1777		2827
1778	This is a rather advanced watcher type that lets you embed one event loop	2828	This is a rather advanced watcher type that lets you embed one event loop
1779	into another (currently only C<ev_io> events are supported in the embedded	2829	into another (currently only C<ev_io> events are supported in the embedded
1780	loop, other types of watchers might be handled in a delayed or incorrect	2830	loop, other types of watchers might be handled in a delayed or incorrect
1781	fashion and must not be used). (See portability notes, below).	2831	fashion and must not be used).
1782		2832
1783	There are primarily two reasons you would want that: work around bugs and	2833	There are primarily two reasons you would want that: work around bugs and
1784	prioritise I/O.	2834	prioritise I/O.
1785		2835
1786	As an example for a bug workaround, the kqueue backend might only support	2836	As an example for a bug workaround, the kqueue backend might only support
1787	sockets on some platform, so it is unusable as generic backend, but you	2837	sockets on some platform, so it is unusable as generic backend, but you
1788	still want to make use of it because you have many sockets and it scales	2838	still want to make use of it because you have many sockets and it scales
1789	so nicely. In this case, you would create a kqueue-based loop and embed it	2839	so nicely. In this case, you would create a kqueue-based loop and embed
1790	into your default loop (which might use e.g. poll). Overall operation will	2840	it into your default loop (which might use e.g. poll). Overall operation
1791	be a bit slower because first libev has to poll and then call kevent, but	2841	will be a bit slower because first libev has to call C<poll> and then
1792	at least you can use both at what they are best.	2842	C<kevent>, but at least you can use both mechanisms for what they are
		2843	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1793		2844
1794	As for prioritising I/O: rarely you have the case where some fds have	2845	As for prioritising I/O: under rare circumstances you have the case where
1795	to be watched and handled very quickly (with low latency), and even	2846	some fds have to be watched and handled very quickly (with low latency),
1796	priorities and idle watchers might have too much overhead. In this case	2847	and even priorities and idle watchers might have too much overhead. In
1797	you would put all the high priority stuff in one loop and all the rest in	2848	this case you would put all the high priority stuff in one loop and all
1798	a second one, and embed the second one in the first.	2849	the rest in a second one, and embed the second one in the first.
1799		2850
1800	As long as the watcher is active, the callback will be invoked every time	2851	As long as the watcher is active, the callback will be invoked every
1801	there might be events pending in the embedded loop. The callback must then	2852	time there might be events pending in the embedded loop. The callback
1802	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2853	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1803	their callbacks (you could also start an idle watcher to give the embedded	2854	sweep and invoke their callbacks (the callback doesn't need to invoke the
1804	loop strictly lower priority for example). You can also set the callback	2855	C<ev_embed_sweep> function directly, it could also start an idle watcher
1805	to C<0>, in which case the embed watcher will automatically execute the	2856	to give the embedded loop strictly lower priority for example).
1806	embedded loop sweep.
1807		2857
1808	As long as the watcher is started it will automatically handle events. The	2858	You can also set the callback to C<0>, in which case the embed watcher
1809	callback will be invoked whenever some events have been handled. You can	2859	will automatically execute the embedded loop sweep whenever necessary.
1810	set the callback to C<0> to avoid having to specify one if you are not
1811	interested in that.
1812		2860
1813	Also, there have not currently been made special provisions for forking:	2861	Fork detection will be handled transparently while the C<ev_embed> watcher
1814	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2862	is active, i.e., the embedded loop will automatically be forked when the
1815	but you will also have to stop and restart any C<ev_embed> watchers	2863	embedding loop forks. In other cases, the user is responsible for calling
1816	yourself.	2864	C<ev_loop_fork> on the embedded loop.
1817		2865
1818	Unfortunately, not all backends are embeddable, only the ones returned by	2866	Unfortunately, not all backends are embeddable: only the ones returned by
1819	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2867	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1820	portable one.	2868	portable one.
1821		2869
1822	So when you want to use this feature you will always have to be prepared	2870	So when you want to use this feature you will always have to be prepared
1823	that you cannot get an embeddable loop. The recommended way to get around	2871	that you cannot get an embeddable loop. The recommended way to get around
1824	this is to have a separate variables for your embeddable loop, try to	2872	this is to have a separate variables for your embeddable loop, try to
1825	create it, and if that fails, use the normal loop for everything:	2873	create it, and if that fails, use the normal loop for everything.
1826		2874
1827	struct ev_loop *loop_hi = ev_default_init (0);	2875	=head3 C<ev_embed> and fork
1828	struct ev_loop *loop_lo = 0;
1829	struct ev_embed embed;
1830
1831	// see if there is a chance of getting one that works
1832	// (remember that a flags value of 0 means autodetection)
1833	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1834	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1835	: 0;
1836		2876
1837	// if we got one, then embed it, otherwise default to loop_hi	2877	While the C<ev_embed> watcher is running, forks in the embedding loop will
1838	if (loop_lo)	2878	automatically be applied to the embedded loop as well, so no special
1839	{	2879	fork handling is required in that case. When the watcher is not running,
1840	ev_embed_init (&embed, 0, loop_lo);	2880	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1841	ev_embed_start (loop_hi, &embed);	2881	as applicable.
1842	}
1843	else
1844	loop_lo = loop_hi;
1845
1846	=head2 Portability notes
1847
1848	Kqueue is nominally embeddable, but this is broken on all BSDs that I
1849	tried, in various ways. Usually the embedded event loop will simply never
1850	receive events, sometimes it will only trigger a few times, sometimes in a
1851	loop. Epoll is also nominally embeddable, but many Linux kernel versions
1852	will always eport the epoll fd as ready, even when no events are pending.
1853
1854	While libev allows embedding these backends (they are contained in
1855	C<ev_embeddable_backends ()>), take extreme care that it will actually
1856	work.
1857
1858	When in doubt, create a dynamic event loop forced to use sockets (this
1859	usually works) and possibly another thread and a pipe or so to report to
1860	your main event loop.
1861		2882
1862	=head3 Watcher-Specific Functions and Data Members	2883	=head3 Watcher-Specific Functions and Data Members
1863		2884
1864	=over 4	2885	=over 4
1865		2886
…		…
1869		2890
1870	Configures the watcher to embed the given loop, which must be	2891	Configures the watcher to embed the given loop, which must be
1871	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	2892	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1872	invoked automatically, otherwise it is the responsibility of the callback	2893	invoked automatically, otherwise it is the responsibility of the callback
1873	to invoke it (it will continue to be called until the sweep has been done,	2894	to invoke it (it will continue to be called until the sweep has been done,
1874	if you do not want thta, you need to temporarily stop the embed watcher).	2895	if you do not want that, you need to temporarily stop the embed watcher).
1875		2896
1876	=item ev_embed_sweep (loop, ev_embed *)	2897	=item ev_embed_sweep (loop, ev_embed *)
1877		2898
1878	Make a single, non-blocking sweep over the embedded loop. This works	2899	Make a single, non-blocking sweep over the embedded loop. This works
1879	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	2900	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
1880	apropriate way for embedded loops.	2901	appropriate way for embedded loops.
1881		2902
1882	=item struct ev_loop *other [read-only]	2903	=item struct ev_loop *other [read-only]
1883		2904
1884	The embedded event loop.	2905	The embedded event loop.
1885		2906
1886	=back	2907	=back
		2908
		2909	=head3 Examples
		2910
		2911	Example: Try to get an embeddable event loop and embed it into the default
		2912	event loop. If that is not possible, use the default loop. The default
		2913	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2914	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2915	used).
		2916
		2917	struct ev_loop *loop_hi = ev_default_init (0);
		2918	struct ev_loop *loop_lo = 0;
		2919	ev_embed embed;
		2920
		2921	// see if there is a chance of getting one that works
		2922	// (remember that a flags value of 0 means autodetection)
		2923	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2924	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2925	: 0;
		2926
		2927	// if we got one, then embed it, otherwise default to loop_hi
		2928	if (loop_lo)
		2929	{
		2930	ev_embed_init (&embed, 0, loop_lo);
		2931	ev_embed_start (loop_hi, &embed);
		2932	}
		2933	else
		2934	loop_lo = loop_hi;
		2935
		2936	Example: Check if kqueue is available but not recommended and create
		2937	a kqueue backend for use with sockets (which usually work with any
		2938	kqueue implementation). Store the kqueue/socket-only event loop in
		2939	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2940
		2941	struct ev_loop *loop = ev_default_init (0);
		2942	struct ev_loop *loop_socket = 0;
		2943	ev_embed embed;
		2944
		2945	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2946	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2947	{
		2948	ev_embed_init (&embed, 0, loop_socket);
		2949	ev_embed_start (loop, &embed);
		2950	}
		2951
		2952	if (!loop_socket)
		2953	loop_socket = loop;
		2954
		2955	// now use loop_socket for all sockets, and loop for everything else
1887		2956
1888		2957
1889	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	2958	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
1890		2959
1891	Fork watchers are called when a C<fork ()> was detected (usually because	2960	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
1894	event loop blocks next and before C<ev_check> watchers are being called,	2963	event loop blocks next and before C<ev_check> watchers are being called,
1895	and only in the child after the fork. If whoever good citizen calling	2964	and only in the child after the fork. If whoever good citizen calling
1896	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2965	C<ev_default_fork> cheats and calls it in the wrong process, the fork
1897	handlers will be invoked, too, of course.	2966	handlers will be invoked, too, of course.
1898		2967
		2968	=head3 The special problem of life after fork - how is it possible?
		2969
		2970	Most uses of C<fork()> consist of forking, then some simple calls to set
		2971	up/change the process environment, followed by a call to C<exec()>. This
		2972	sequence should be handled by libev without any problems.
		2973
		2974	This changes when the application actually wants to do event handling
		2975	in the child, or both parent in child, in effect "continuing" after the
		2976	fork.
		2977
		2978	The default mode of operation (for libev, with application help to detect
		2979	forks) is to duplicate all the state in the child, as would be expected
		2980	when I<either> the parent I<or> the child process continues.
		2981
		2982	When both processes want to continue using libev, then this is usually the
		2983	wrong result. In that case, usually one process (typically the parent) is
		2984	supposed to continue with all watchers in place as before, while the other
		2985	process typically wants to start fresh, i.e. without any active watchers.
		2986
		2987	The cleanest and most efficient way to achieve that with libev is to
		2988	simply create a new event loop, which of course will be "empty", and
		2989	use that for new watchers. This has the advantage of not touching more
		2990	memory than necessary, and thus avoiding the copy-on-write, and the
		2991	disadvantage of having to use multiple event loops (which do not support
		2992	signal watchers).
		2993
		2994	When this is not possible, or you want to use the default loop for
		2995	other reasons, then in the process that wants to start "fresh", call
		2996	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2997	the default loop will "orphan" (not stop) all registered watchers, so you
		2998	have to be careful not to execute code that modifies those watchers. Note
		2999	also that in that case, you have to re-register any signal watchers.
		3000
1899	=head3 Watcher-Specific Functions and Data Members	3001	=head3 Watcher-Specific Functions and Data Members
1900		3002
1901	=over 4	3003	=over 4
1902		3004
1903	=item ev_fork_init (ev_signal *, callback)	3005	=item ev_fork_init (ev_signal *, callback)
…		…
1907	believe me.	3009	believe me.
1908		3010
1909	=back	3011	=back
1910		3012
1911		3013
		3014	=head2 C<ev_async> - how to wake up an event loop
		3015
		3016	In general, you cannot use an C<ev_loop> from multiple threads or other
		3017	asynchronous sources such as signal handlers (as opposed to multiple event
		3018	loops - those are of course safe to use in different threads).
		3019
		3020	Sometimes, however, you need to wake up an event loop you do not control,
		3021	for example because it belongs to another thread. This is what C<ev_async>
		3022	watchers do: as long as the C<ev_async> watcher is active, you can signal
		3023	it by calling C<ev_async_send>, which is thread- and signal safe.
		3024
		3025	This functionality is very similar to C<ev_signal> watchers, as signals,
		3026	too, are asynchronous in nature, and signals, too, will be compressed
		3027	(i.e. the number of callback invocations may be less than the number of
		3028	C<ev_async_sent> calls).
		3029
		3030	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		3031	just the default loop.
		3032
		3033	=head3 Queueing
		3034
		3035	C<ev_async> does not support queueing of data in any way. The reason
		3036	is that the author does not know of a simple (or any) algorithm for a
		3037	multiple-writer-single-reader queue that works in all cases and doesn't
		3038	need elaborate support such as pthreads or unportable memory access
		3039	semantics.
		3040
		3041	That means that if you want to queue data, you have to provide your own
		3042	queue. But at least I can tell you how to implement locking around your
		3043	queue:
		3044
		3045	=over 4
		3046
		3047	=item queueing from a signal handler context
		3048
		3049	To implement race-free queueing, you simply add to the queue in the signal
		3050	handler but you block the signal handler in the watcher callback. Here is
		3051	an example that does that for some fictitious SIGUSR1 handler:
		3052
		3053	static ev_async mysig;
		3054
		3055	static void
		3056	sigusr1_handler (void)
		3057	{
		3058	sometype data;
		3059
		3060	// no locking etc.
		3061	queue_put (data);
		3062	ev_async_send (EV_DEFAULT_ &mysig);
		3063	}
		3064
		3065	static void
		3066	mysig_cb (EV_P_ ev_async *w, int revents)
		3067	{
		3068	sometype data;
		3069	sigset_t block, prev;
		3070
		3071	sigemptyset (&block);
		3072	sigaddset (&block, SIGUSR1);
		3073	sigprocmask (SIG_BLOCK, &block, &prev);
		3074
		3075	while (queue_get (&data))
		3076	process (data);
		3077
		3078	if (sigismember (&prev, SIGUSR1)
		3079	sigprocmask (SIG_UNBLOCK, &block, 0);
		3080	}
		3081
		3082	(Note: pthreads in theory requires you to use C<pthread_setmask>
		3083	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		3084	either...).
		3085
		3086	=item queueing from a thread context
		3087
		3088	The strategy for threads is different, as you cannot (easily) block
		3089	threads but you can easily preempt them, so to queue safely you need to
		3090	employ a traditional mutex lock, such as in this pthread example:
		3091
		3092	static ev_async mysig;
		3093	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		3094
		3095	static void
		3096	otherthread (void)
		3097	{
		3098	// only need to lock the actual queueing operation
		3099	pthread_mutex_lock (&mymutex);
		3100	queue_put (data);
		3101	pthread_mutex_unlock (&mymutex);
		3102
		3103	ev_async_send (EV_DEFAULT_ &mysig);
		3104	}
		3105
		3106	static void
		3107	mysig_cb (EV_P_ ev_async *w, int revents)
		3108	{
		3109	pthread_mutex_lock (&mymutex);
		3110
		3111	while (queue_get (&data))
		3112	process (data);
		3113
		3114	pthread_mutex_unlock (&mymutex);
		3115	}
		3116
		3117	=back
		3118
		3119
		3120	=head3 Watcher-Specific Functions and Data Members
		3121
		3122	=over 4
		3123
		3124	=item ev_async_init (ev_async *, callback)
		3125
		3126	Initialises and configures the async watcher - it has no parameters of any
		3127	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		3128	trust me.
		3129
		3130	=item ev_async_send (loop, ev_async *)
		3131
		3132	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		3133	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		3134	C<ev_feed_event>, this call is safe to do from other threads, signal or
		3135	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		3136	section below on what exactly this means).
		3137
		3138	Note that, as with other watchers in libev, multiple events might get
		3139	compressed into a single callback invocation (another way to look at this
		3140	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3141	reset when the event loop detects that).
		3142
		3143	This call incurs the overhead of a system call only once per event loop
		3144	iteration, so while the overhead might be noticeable, it doesn't apply to
		3145	repeated calls to C<ev_async_send> for the same event loop.
		3146
		3147	=item bool = ev_async_pending (ev_async *)
		3148
		3149	Returns a non-zero value when C<ev_async_send> has been called on the
		3150	watcher but the event has not yet been processed (or even noted) by the
		3151	event loop.
		3152
		3153	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3154	the loop iterates next and checks for the watcher to have become active,
		3155	it will reset the flag again. C<ev_async_pending> can be used to very
		3156	quickly check whether invoking the loop might be a good idea.
		3157
		3158	Not that this does I<not> check whether the watcher itself is pending,
		3159	only whether it has been requested to make this watcher pending: there
		3160	is a time window between the event loop checking and resetting the async
		3161	notification, and the callback being invoked.
		3162
		3163	=back
		3164
		3165
1912	=head1 OTHER FUNCTIONS	3166	=head1 OTHER FUNCTIONS
1913		3167
1914	There are some other functions of possible interest. Described. Here. Now.	3168	There are some other functions of possible interest. Described. Here. Now.
1915		3169
1916	=over 4	3170	=over 4
1917		3171
1918	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3172	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1919		3173
1920	This function combines a simple timer and an I/O watcher, calls your	3174	This function combines a simple timer and an I/O watcher, calls your
1921	callback on whichever event happens first and automatically stop both	3175	callback on whichever event happens first and automatically stops both
1922	watchers. This is useful if you want to wait for a single event on an fd	3176	watchers. This is useful if you want to wait for a single event on an fd
1923	or timeout without having to allocate/configure/start/stop/free one or	3177	or timeout without having to allocate/configure/start/stop/free one or
1924	more watchers yourself.	3178	more watchers yourself.
1925		3179
1926	If C<fd> is less than 0, then no I/O watcher will be started and events	3180	If C<fd> is less than 0, then no I/O watcher will be started and the
1927	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3181	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1928	C<events> set will be craeted and started.	3182	the given C<fd> and C<events> set will be created and started.
1929		3183
1930	If C<timeout> is less than 0, then no timeout watcher will be	3184	If C<timeout> is less than 0, then no timeout watcher will be
1931	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3185	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1932	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3186	repeat = 0) will be started. C<0> is a valid timeout.
1933	dubious value.
1934		3187
1935	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3188	The callback has the type C<void (*cb)(int revents, void *arg)> and is
1936	passed an C<revents> set like normal event callbacks (a combination of	3189	passed an C<revents> set like normal event callbacks (a combination of
1937	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3190	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
1938	value passed to C<ev_once>:	3191	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3192	a timeout and an io event at the same time - you probably should give io
		3193	events precedence.
1939		3194
		3195	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3196
1940	static void stdin_ready (int revents, void *arg)	3197	static void stdin_ready (int revents, void *arg)
1941	{	3198	{
1942	if (revents & EV_TIMEOUT)
1943	/* doh, nothing entered */;
1944	else if (revents & EV_READ)	3199	if (revents & EV_READ)
1945	/* stdin might have data for us, joy! */;	3200	/* stdin might have data for us, joy! */;
		3201	else if (revents & EV_TIMER)
		3202	/* doh, nothing entered */;
1946	}	3203	}
1947		3204
1948	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3205	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1949		3206
1950	=item ev_feed_event (ev_loop *, watcher *, int revents)
1951
1952	Feeds the given event set into the event loop, as if the specified event
1953	had happened for the specified watcher (which must be a pointer to an
1954	initialised but not necessarily started event watcher).
1955
1956	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3207	=item ev_feed_fd_event (loop, int fd, int revents)
1957		3208
1958	Feed an event on the given fd, as if a file descriptor backend detected	3209	Feed an event on the given fd, as if a file descriptor backend detected
1959	the given events it.	3210	the given events it.
1960		3211
1961	=item ev_feed_signal_event (ev_loop *loop, int signum)	3212	=item ev_feed_signal_event (loop, int signum)
1962		3213
1963	Feed an event as if the given signal occured (C<loop> must be the default	3214	Feed an event as if the given signal occurred (C<loop> must be the default
1964	loop!).	3215	loop!).
1965		3216
1966	=back	3217	=back
1967		3218
1968		3219
…		…
1984		3235
1985	=item * Priorities are not currently supported. Initialising priorities	3236	=item * Priorities are not currently supported. Initialising priorities
1986	will fail and all watchers will have the same priority, even though there	3237	will fail and all watchers will have the same priority, even though there
1987	is an ev_pri field.	3238	is an ev_pri field.
1988		3239
		3240	=item * In libevent, the last base created gets the signals, in libev, the
		3241	first base created (== the default loop) gets the signals.
		3242
1989	=item * Other members are not supported.	3243	=item * Other members are not supported.
1990		3244
1991	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3245	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1992	to use the libev header file and library.	3246	to use the libev header file and library.
1993		3247
1994	=back	3248	=back
1995		3249
1996	=head1 C++ SUPPORT	3250	=head1 C++ SUPPORT
1997		3251
1998	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3252	Libev comes with some simplistic wrapper classes for C++ that mainly allow
1999	you to use some convinience methods to start/stop watchers and also change	3253	you to use some convenience methods to start/stop watchers and also change
2000	the callback model to a model using method callbacks on objects.	3254	the callback model to a model using method callbacks on objects.
2001		3255
2002	To use it,	3256	To use it,
2003		3257
2004	#include <ev++.h>	3258	#include <ev++.h>
2005		3259
2006	This automatically includes F<ev.h> and puts all of its definitions (many	3260	This automatically includes F<ev.h> and puts all of its definitions (many
2007	of them macros) into the global namespace. All C++ specific things are	3261	of them macros) into the global namespace. All C++ specific things are
2008	put into the C<ev> namespace. It should support all the same embedding	3262	put into the C<ev> namespace. It should support all the same embedding
2009	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	3263	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
2043		3297
2044	=over 4	3298	=over 4
2045		3299
2046	=item ev::TYPE::TYPE ()	3300	=item ev::TYPE::TYPE ()
2047		3301
2048	=item ev::TYPE::TYPE (struct ev_loop *)	3302	=item ev::TYPE::TYPE (loop)
2049		3303
2050	=item ev::TYPE::~TYPE	3304	=item ev::TYPE::~TYPE
2051		3305
2052	The constructor (optionally) takes an event loop to associate the watcher	3306	The constructor (optionally) takes an event loop to associate the watcher
2053	with. If it is omitted, it will use C<EV_DEFAULT>.	3307	with. If it is omitted, it will use C<EV_DEFAULT>.
…		…
2076	your compiler is good :), then the method will be fully inlined into the	3330	your compiler is good :), then the method will be fully inlined into the
2077	thunking function, making it as fast as a direct C callback.	3331	thunking function, making it as fast as a direct C callback.
2078		3332
2079	Example: simple class declaration and watcher initialisation	3333	Example: simple class declaration and watcher initialisation
2080		3334
2081	struct myclass	3335	struct myclass
2082	{	3336	{
2083	void io_cb (ev::io &w, int revents) { }	3337	void io_cb (ev::io &w, int revents) { }
2084	}	3338	}
2085		3339
2086	myclass obj;	3340	myclass obj;
2087	ev::io iow;	3341	ev::io iow;
2088	iow.set <myclass, &myclass::io_cb> (&obj);	3342	iow.set <myclass, &myclass::io_cb> (&obj);
		3343
		3344	=item w->set (object *)
		3345
		3346	This is a variation of a method callback - leaving out the method to call
		3347	will default the method to C<operator ()>, which makes it possible to use
		3348	functor objects without having to manually specify the C<operator ()> all
		3349	the time. Incidentally, you can then also leave out the template argument
		3350	list.
		3351
		3352	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3353	int revents)>.
		3354
		3355	See the method-C<set> above for more details.
		3356
		3357	Example: use a functor object as callback.
		3358
		3359	struct myfunctor
		3360	{
		3361	void operator() (ev::io &w, int revents)
		3362	{
		3363	...
		3364	}
		3365	}
		3366
		3367	myfunctor f;
		3368
		3369	ev::io w;
		3370	w.set (&f);
2089		3371
2090	=item w->set<function> (void *data = 0)	3372	=item w->set<function> (void *data = 0)
2091		3373
2092	Also sets a callback, but uses a static method or plain function as	3374	Also sets a callback, but uses a static method or plain function as
2093	callback. The optional C<data> argument will be stored in the watcher's	3375	callback. The optional C<data> argument will be stored in the watcher's
…		…
2095		3377
2096	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	3378	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2097		3379
2098	See the method-C<set> above for more details.	3380	See the method-C<set> above for more details.
2099		3381
2100	Example:	3382	Example: Use a plain function as callback.
2101		3383
2102	static void io_cb (ev::io &w, int revents) { }	3384	static void io_cb (ev::io &w, int revents) { }
2103	iow.set <io_cb> ();	3385	iow.set <io_cb> ();
2104		3386
2105	=item w->set (struct ev_loop *)	3387	=item w->set (loop)
2106		3388
2107	Associates a different C<struct ev_loop> with this watcher. You can only	3389	Associates a different C<struct ev_loop> with this watcher. You can only
2108	do this when the watcher is inactive (and not pending either).	3390	do this when the watcher is inactive (and not pending either).
2109		3391
2110	=item w->set ([args])	3392	=item w->set ([arguments])
2111		3393
2112	Basically the same as C<ev_TYPE_set>, with the same args. Must be	3394	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
2113	called at least once. Unlike the C counterpart, an active watcher gets	3395	called at least once. Unlike the C counterpart, an active watcher gets
2114	automatically stopped and restarted when reconfiguring it with this	3396	automatically stopped and restarted when reconfiguring it with this
2115	method.	3397	method.
2116		3398
2117	=item w->start ()	3399	=item w->start ()
…		…
2141	=back	3423	=back
2142		3424
2143	Example: Define a class with an IO and idle watcher, start one of them in	3425	Example: Define a class with an IO and idle watcher, start one of them in
2144	the constructor.	3426	the constructor.
2145		3427
2146	class myclass	3428	class myclass
2147	{	3429	{
2148	ev_io io; void io_cb (ev::io &w, int revents);	3430	ev::io io ; void io_cb (ev::io &w, int revents);
2149	ev_idle idle void idle_cb (ev::idle &w, int revents);	3431	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2150		3432
2151	myclass ();	3433	myclass (int fd)
2152	}	3434	{
2153
2154	myclass::myclass (int fd)
2155	{
2156	io .set <myclass, &myclass::io_cb > (this);	3435	io .set <myclass, &myclass::io_cb > (this);
2157	idle.set <myclass, &myclass::idle_cb> (this);	3436	idle.set <myclass, &myclass::idle_cb> (this);
2158		3437
2159	io.start (fd, ev::READ);	3438	io.start (fd, ev::READ);
		3439	}
2160	}	3440	};
		3441
		3442
		3443	=head1 OTHER LANGUAGE BINDINGS
		3444
		3445	Libev does not offer other language bindings itself, but bindings for a
		3446	number of languages exist in the form of third-party packages. If you know
		3447	any interesting language binding in addition to the ones listed here, drop
		3448	me a note.
		3449
		3450	=over 4
		3451
		3452	=item Perl
		3453
		3454	The EV module implements the full libev API and is actually used to test
		3455	libev. EV is developed together with libev. Apart from the EV core module,
		3456	there are additional modules that implement libev-compatible interfaces
		3457	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3458	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3459	and C<EV::Glib>).
		3460
		3461	It can be found and installed via CPAN, its homepage is at
		3462	L<http://software.schmorp.de/pkg/EV>.
		3463
		3464	=item Python
		3465
		3466	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3467	seems to be quite complete and well-documented.
		3468
		3469	=item Ruby
		3470
		3471	Tony Arcieri has written a ruby extension that offers access to a subset
		3472	of the libev API and adds file handle abstractions, asynchronous DNS and
		3473	more on top of it. It can be found via gem servers. Its homepage is at
		3474	L<http://rev.rubyforge.org/>.
		3475
		3476	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3477	makes rev work even on mingw.
		3478
		3479	=item Haskell
		3480
		3481	A haskell binding to libev is available at
		3482	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3483
		3484	=item D
		3485
		3486	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3487	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3488
		3489	=item Ocaml
		3490
		3491	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3492	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3493
		3494	=item Lua
		3495
		3496	Brian Maher has written a partial interface to libev for lua (at the
		3497	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		3498	L<http://github.com/brimworks/lua-ev>.
		3499
		3500	=back
2161		3501
2162		3502
2163	=head1 MACRO MAGIC	3503	=head1 MACRO MAGIC
2164		3504
2165	Libev can be compiled with a variety of options, the most fundamantal	3505	Libev can be compiled with a variety of options, the most fundamental
2166	of which is C<EV_MULTIPLICITY>. This option determines whether (most)	3506	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2167	functions and callbacks have an initial C<struct ev_loop *> argument.	3507	functions and callbacks have an initial C<struct ev_loop *> argument.
2168		3508
2169	To make it easier to write programs that cope with either variant, the	3509	To make it easier to write programs that cope with either variant, the
2170	following macros are defined:	3510	following macros are defined:
…		…
2175		3515
2176	This provides the loop I<argument> for functions, if one is required ("ev	3516	This provides the loop I<argument> for functions, if one is required ("ev
2177	loop argument"). The C<EV_A> form is used when this is the sole argument,	3517	loop argument"). The C<EV_A> form is used when this is the sole argument,
2178	C<EV_A_> is used when other arguments are following. Example:	3518	C<EV_A_> is used when other arguments are following. Example:
2179		3519
2180	ev_unref (EV_A);	3520	ev_unref (EV_A);
2181	ev_timer_add (EV_A_ watcher);	3521	ev_timer_add (EV_A_ watcher);
2182	ev_loop (EV_A_ 0);	3522	ev_loop (EV_A_ 0);
2183		3523
2184	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	3524	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2185	which is often provided by the following macro.	3525	which is often provided by the following macro.
2186		3526
2187	=item C<EV_P>, C<EV_P_>	3527	=item C<EV_P>, C<EV_P_>
2188		3528
2189	This provides the loop I<parameter> for functions, if one is required ("ev	3529	This provides the loop I<parameter> for functions, if one is required ("ev
2190	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	3530	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
2191	C<EV_P_> is used when other parameters are following. Example:	3531	C<EV_P_> is used when other parameters are following. Example:
2192		3532
2193	// this is how ev_unref is being declared	3533	// this is how ev_unref is being declared
2194	static void ev_unref (EV_P);	3534	static void ev_unref (EV_P);
2195		3535
2196	// this is how you can declare your typical callback	3536	// this is how you can declare your typical callback
2197	static void cb (EV_P_ ev_timer *w, int revents)	3537	static void cb (EV_P_ ev_timer *w, int revents)
2198		3538
2199	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	3539	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
2200	suitable for use with C<EV_A>.	3540	suitable for use with C<EV_A>.
2201		3541
2202	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3542	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2203		3543
2204	Similar to the other two macros, this gives you the value of the default	3544	Similar to the other two macros, this gives you the value of the default
2205	loop, if multiple loops are supported ("ev loop default").	3545	loop, if multiple loops are supported ("ev loop default").
		3546
		3547	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3548
		3549	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3550	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3551	is undefined when the default loop has not been initialised by a previous
		3552	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3553
		3554	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3555	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
2206		3556
2207	=back	3557	=back
2208		3558
2209	Example: Declare and initialise a check watcher, utilising the above	3559	Example: Declare and initialise a check watcher, utilising the above
2210	macros so it will work regardless of whether multiple loops are supported	3560	macros so it will work regardless of whether multiple loops are supported
2211	or not.	3561	or not.
2212		3562
2213	static void	3563	static void
2214	check_cb (EV_P_ ev_timer *w, int revents)	3564	check_cb (EV_P_ ev_timer *w, int revents)
2215	{	3565	{
2216	ev_check_stop (EV_A_ w);	3566	ev_check_stop (EV_A_ w);
2217	}	3567	}
2218		3568
2219	ev_check check;	3569	ev_check check;
2220	ev_check_init (&check, check_cb);	3570	ev_check_init (&check, check_cb);
2221	ev_check_start (EV_DEFAULT_ &check);	3571	ev_check_start (EV_DEFAULT_ &check);
2222	ev_loop (EV_DEFAULT_ 0);	3572	ev_loop (EV_DEFAULT_ 0);
2223		3573
2224	=head1 EMBEDDING	3574	=head1 EMBEDDING
2225		3575
2226	Libev can (and often is) directly embedded into host	3576	Libev can (and often is) directly embedded into host
2227	applications. Examples of applications that embed it include the Deliantra	3577	applications. Examples of applications that embed it include the Deliantra
…		…
2234	libev somewhere in your source tree).	3584	libev somewhere in your source tree).
2235		3585
2236	=head2 FILESETS	3586	=head2 FILESETS
2237		3587
2238	Depending on what features you need you need to include one or more sets of files	3588	Depending on what features you need you need to include one or more sets of files
2239	in your app.	3589	in your application.
2240		3590
2241	=head3 CORE EVENT LOOP	3591	=head3 CORE EVENT LOOP
2242		3592
2243	To include only the libev core (all the C<ev_*> functions), with manual	3593	To include only the libev core (all the C<ev_*> functions), with manual
2244	configuration (no autoconf):	3594	configuration (no autoconf):
2245		3595
2246	#define EV_STANDALONE 1	3596	#define EV_STANDALONE 1
2247	#include "ev.c"	3597	#include "ev.c"
2248		3598
2249	This will automatically include F<ev.h>, too, and should be done in a	3599	This will automatically include F<ev.h>, too, and should be done in a
2250	single C source file only to provide the function implementations. To use	3600	single C source file only to provide the function implementations. To use
2251	it, do the same for F<ev.h> in all files wishing to use this API (best	3601	it, do the same for F<ev.h> in all files wishing to use this API (best
2252	done by writing a wrapper around F<ev.h> that you can include instead and	3602	done by writing a wrapper around F<ev.h> that you can include instead and
2253	where you can put other configuration options):	3603	where you can put other configuration options):
2254		3604
2255	#define EV_STANDALONE 1	3605	#define EV_STANDALONE 1
2256	#include "ev.h"	3606	#include "ev.h"
2257		3607
2258	Both header files and implementation files can be compiled with a C++	3608	Both header files and implementation files can be compiled with a C++
2259	compiler (at least, thats a stated goal, and breakage will be treated	3609	compiler (at least, that's a stated goal, and breakage will be treated
2260	as a bug).	3610	as a bug).
2261		3611
2262	You need the following files in your source tree, or in a directory	3612	You need the following files in your source tree, or in a directory
2263	in your include path (e.g. in libev/ when using -Ilibev):	3613	in your include path (e.g. in libev/ when using -Ilibev):
2264		3614
2265	ev.h	3615	ev.h
2266	ev.c	3616	ev.c
2267	ev_vars.h	3617	ev_vars.h
2268	ev_wrap.h	3618	ev_wrap.h
2269		3619
2270	ev_win32.c required on win32 platforms only	3620	ev_win32.c required on win32 platforms only
2271		3621
2272	ev_select.c only when select backend is enabled (which is enabled by default)	3622	ev_select.c only when select backend is enabled (which is enabled by default)
2273	ev_poll.c only when poll backend is enabled (disabled by default)	3623	ev_poll.c only when poll backend is enabled (disabled by default)
2274	ev_epoll.c only when the epoll backend is enabled (disabled by default)	3624	ev_epoll.c only when the epoll backend is enabled (disabled by default)
2275	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	3625	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2276	ev_port.c only when the solaris port backend is enabled (disabled by default)	3626	ev_port.c only when the solaris port backend is enabled (disabled by default)
2277		3627
2278	F<ev.c> includes the backend files directly when enabled, so you only need	3628	F<ev.c> includes the backend files directly when enabled, so you only need
2279	to compile this single file.	3629	to compile this single file.
2280		3630
2281	=head3 LIBEVENT COMPATIBILITY API	3631	=head3 LIBEVENT COMPATIBILITY API
2282		3632
2283	To include the libevent compatibility API, also include:	3633	To include the libevent compatibility API, also include:
2284		3634
2285	#include "event.c"	3635	#include "event.c"
2286		3636
2287	in the file including F<ev.c>, and:	3637	in the file including F<ev.c>, and:
2288		3638
2289	#include "event.h"	3639	#include "event.h"
2290		3640
2291	in the files that want to use the libevent API. This also includes F<ev.h>.	3641	in the files that want to use the libevent API. This also includes F<ev.h>.
2292		3642
2293	You need the following additional files for this:	3643	You need the following additional files for this:
2294		3644
2295	event.h	3645	event.h
2296	event.c	3646	event.c
2297		3647
2298	=head3 AUTOCONF SUPPORT	3648	=head3 AUTOCONF SUPPORT
2299		3649
2300	Instead of using C<EV_STANDALONE=1> and providing your config in	3650	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2301	whatever way you want, you can also C<m4_include([libev.m4])> in your	3651	whatever way you want, you can also C<m4_include([libev.m4])> in your
2302	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	3652	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2303	include F<config.h> and configure itself accordingly.	3653	include F<config.h> and configure itself accordingly.
2304		3654
2305	For this of course you need the m4 file:	3655	For this of course you need the m4 file:
2306		3656
2307	libev.m4	3657	libev.m4
2308		3658
2309	=head2 PREPROCESSOR SYMBOLS/MACROS	3659	=head2 PREPROCESSOR SYMBOLS/MACROS
2310		3660
2311	Libev can be configured via a variety of preprocessor symbols you have to define	3661	Libev can be configured via a variety of preprocessor symbols you have to
2312	before including any of its files. The default is not to build for multiplicity	3662	define before including (or compiling) any of its files. The default in
2313	and only include the select backend.	3663	the absence of autoconf is documented for every option.
		3664
		3665	Symbols marked with "(h)" do not change the ABI, and can have different
		3666	values when compiling libev vs. including F<ev.h>, so it is permissible
		3667	to redefine them before including F<ev.h> without breaking compatibility
		3668	to a compiled library. All other symbols change the ABI, which means all
		3669	users of libev and the libev code itself must be compiled with compatible
		3670	settings.
2314		3671
2315	=over 4	3672	=over 4
2316		3673
2317	=item EV_STANDALONE	3674	=item EV_STANDALONE (h)
2318		3675
2319	Must always be C<1> if you do not use autoconf configuration, which	3676	Must always be C<1> if you do not use autoconf configuration, which
2320	keeps libev from including F<config.h>, and it also defines dummy	3677	keeps libev from including F<config.h>, and it also defines dummy
2321	implementations for some libevent functions (such as logging, which is not	3678	implementations for some libevent functions (such as logging, which is not
2322	supported). It will also not define any of the structs usually found in	3679	supported). It will also not define any of the structs usually found in
2323	F<event.h> that are not directly supported by the libev core alone.	3680	F<event.h> that are not directly supported by the libev core alone.
2324		3681
		3682	In standalone mode, libev will still try to automatically deduce the
		3683	configuration, but has to be more conservative.
		3684
2325	=item EV_USE_MONOTONIC	3685	=item EV_USE_MONOTONIC
2326		3686
2327	If defined to be C<1>, libev will try to detect the availability of the	3687	If defined to be C<1>, libev will try to detect the availability of the
2328	monotonic clock option at both compiletime and runtime. Otherwise no use	3688	monotonic clock option at both compile time and runtime. Otherwise no
2329	of the monotonic clock option will be attempted. If you enable this, you	3689	use of the monotonic clock option will be attempted. If you enable this,
2330	usually have to link against librt or something similar. Enabling it when	3690	you usually have to link against librt or something similar. Enabling it
2331	the functionality isn't available is safe, though, although you have	3691	when the functionality isn't available is safe, though, although you have
2332	to make sure you link against any libraries where the C<clock_gettime>	3692	to make sure you link against any libraries where the C<clock_gettime>
2333	function is hiding in (often F<-lrt>).	3693	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2334		3694
2335	=item EV_USE_REALTIME	3695	=item EV_USE_REALTIME
2336		3696
2337	If defined to be C<1>, libev will try to detect the availability of the	3697	If defined to be C<1>, libev will try to detect the availability of the
2338	realtime clock option at compiletime (and assume its availability at	3698	real-time clock option at compile time (and assume its availability
2339	runtime if successful). Otherwise no use of the realtime clock option will	3699	at runtime if successful). Otherwise no use of the real-time clock
2340	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3700	option will be attempted. This effectively replaces C<gettimeofday>
2341	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	3701	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2342	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	3702	correctness. See the note about libraries in the description of
		3703	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3704	C<EV_USE_CLOCK_SYSCALL>.
		3705
		3706	=item EV_USE_CLOCK_SYSCALL
		3707
		3708	If defined to be C<1>, libev will try to use a direct syscall instead
		3709	of calling the system-provided C<clock_gettime> function. This option
		3710	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3711	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3712	programs needlessly. Using a direct syscall is slightly slower (in
		3713	theory), because no optimised vdso implementation can be used, but avoids
		3714	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3715	higher, as it simplifies linking (no need for C<-lrt>).
2343		3716
2344	=item EV_USE_NANOSLEEP	3717	=item EV_USE_NANOSLEEP
2345		3718
2346	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	3719	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2347	and will use it for delays. Otherwise it will use C<select ()>.	3720	and will use it for delays. Otherwise it will use C<select ()>.
2348		3721
		3722	=item EV_USE_EVENTFD
		3723
		3724	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3725	available and will probe for kernel support at runtime. This will improve
		3726	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3727	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3728	2.7 or newer, otherwise disabled.
		3729
2349	=item EV_USE_SELECT	3730	=item EV_USE_SELECT
2350		3731
2351	If undefined or defined to be C<1>, libev will compile in support for the	3732	If undefined or defined to be C<1>, libev will compile in support for the
2352	C<select>(2) backend. No attempt at autodetection will be done: if no	3733	C<select>(2) backend. No attempt at auto-detection will be done: if no
2353	other method takes over, select will be it. Otherwise the select backend	3734	other method takes over, select will be it. Otherwise the select backend
2354	will not be compiled in.	3735	will not be compiled in.
2355		3736
2356	=item EV_SELECT_USE_FD_SET	3737	=item EV_SELECT_USE_FD_SET
2357		3738
2358	If defined to C<1>, then the select backend will use the system C<fd_set>	3739	If defined to C<1>, then the select backend will use the system C<fd_set>
2359	structure. This is useful if libev doesn't compile due to a missing	3740	structure. This is useful if libev doesn't compile due to a missing
2360	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	3741	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2361	exotic systems. This usually limits the range of file descriptors to some	3742	on exotic systems. This usually limits the range of file descriptors to
2362	low limit such as 1024 or might have other limitations (winsocket only	3743	some low limit such as 1024 or might have other limitations (winsocket
2363	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3744	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2364	influence the size of the C<fd_set> used.	3745	configures the maximum size of the C<fd_set>.
2365		3746
2366	=item EV_SELECT_IS_WINSOCKET	3747	=item EV_SELECT_IS_WINSOCKET
2367		3748
2368	When defined to C<1>, the select backend will assume that	3749	When defined to C<1>, the select backend will assume that
2369	select/socket/connect etc. don't understand file descriptors but	3750	select/socket/connect etc. don't understand file descriptors but
…		…
2371	be used is the winsock select). This means that it will call	3752	be used is the winsock select). This means that it will call
2372	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3753	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2373	it is assumed that all these functions actually work on fds, even	3754	it is assumed that all these functions actually work on fds, even
2374	on win32. Should not be defined on non-win32 platforms.	3755	on win32. Should not be defined on non-win32 platforms.
2375		3756
		3757	=item EV_FD_TO_WIN32_HANDLE(fd)
		3758
		3759	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3760	file descriptors to socket handles. When not defining this symbol (the
		3761	default), then libev will call C<_get_osfhandle>, which is usually
		3762	correct. In some cases, programs use their own file descriptor management,
		3763	in which case they can provide this function to map fds to socket handles.
		3764
		3765	=item EV_WIN32_HANDLE_TO_FD(handle)
		3766
		3767	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		3768	using the standard C<_open_osfhandle> function. For programs implementing
		3769	their own fd to handle mapping, overwriting this function makes it easier
		3770	to do so. This can be done by defining this macro to an appropriate value.
		3771
		3772	=item EV_WIN32_CLOSE_FD(fd)
		3773
		3774	If programs implement their own fd to handle mapping on win32, then this
		3775	macro can be used to override the C<close> function, useful to unregister
		3776	file descriptors again. Note that the replacement function has to close
		3777	the underlying OS handle.
		3778
2376	=item EV_USE_POLL	3779	=item EV_USE_POLL
2377		3780
2378	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3781	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2379	backend. Otherwise it will be enabled on non-win32 platforms. It	3782	backend. Otherwise it will be enabled on non-win32 platforms. It
2380	takes precedence over select.	3783	takes precedence over select.
2381		3784
2382	=item EV_USE_EPOLL	3785	=item EV_USE_EPOLL
2383		3786
2384	If defined to be C<1>, libev will compile in support for the Linux	3787	If defined to be C<1>, libev will compile in support for the Linux
2385	C<epoll>(7) backend. Its availability will be detected at runtime,	3788	C<epoll>(7) backend. Its availability will be detected at runtime,
2386	otherwise another method will be used as fallback. This is the	3789	otherwise another method will be used as fallback. This is the preferred
2387	preferred backend for GNU/Linux systems.	3790	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3791	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2388		3792
2389	=item EV_USE_KQUEUE	3793	=item EV_USE_KQUEUE
2390		3794
2391	If defined to be C<1>, libev will compile in support for the BSD style	3795	If defined to be C<1>, libev will compile in support for the BSD style
2392	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	3796	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2405	otherwise another method will be used as fallback. This is the preferred	3809	otherwise another method will be used as fallback. This is the preferred
2406	backend for Solaris 10 systems.	3810	backend for Solaris 10 systems.
2407		3811
2408	=item EV_USE_DEVPOLL	3812	=item EV_USE_DEVPOLL
2409		3813
2410	reserved for future expansion, works like the USE symbols above.	3814	Reserved for future expansion, works like the USE symbols above.
2411		3815
2412	=item EV_USE_INOTIFY	3816	=item EV_USE_INOTIFY
2413		3817
2414	If defined to be C<1>, libev will compile in support for the Linux inotify	3818	If defined to be C<1>, libev will compile in support for the Linux inotify
2415	interface to speed up C<ev_stat> watchers. Its actual availability will	3819	interface to speed up C<ev_stat> watchers. Its actual availability will
2416	be detected at runtime.	3820	be detected at runtime. If undefined, it will be enabled if the headers
		3821	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2417		3822
		3823	=item EV_ATOMIC_T
		3824
		3825	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3826	access is atomic with respect to other threads or signal contexts. No such
		3827	type is easily found in the C language, so you can provide your own type
		3828	that you know is safe for your purposes. It is used both for signal handler "locking"
		3829	as well as for signal and thread safety in C<ev_async> watchers.
		3830
		3831	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3832	(from F<signal.h>), which is usually good enough on most platforms.
		3833
2418	=item EV_H	3834	=item EV_H (h)
2419		3835
2420	The name of the F<ev.h> header file used to include it. The default if	3836	The name of the F<ev.h> header file used to include it. The default if
2421	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This	3837	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2422	can be used to virtually rename the F<ev.h> header file in case of conflicts.	3838	used to virtually rename the F<ev.h> header file in case of conflicts.
2423		3839
2424	=item EV_CONFIG_H	3840	=item EV_CONFIG_H (h)
2425		3841
2426	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	3842	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2427	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	3843	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2428	C<EV_H>, above.	3844	C<EV_H>, above.
2429		3845
2430	=item EV_EVENT_H	3846	=item EV_EVENT_H (h)
2431		3847
2432	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	3848	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2433	of how the F<event.h> header can be found.	3849	of how the F<event.h> header can be found, the default is C<"event.h">.
2434		3850
2435	=item EV_PROTOTYPES	3851	=item EV_PROTOTYPES (h)
2436		3852
2437	If defined to be C<0>, then F<ev.h> will not define any function	3853	If defined to be C<0>, then F<ev.h> will not define any function
2438	prototypes, but still define all the structs and other symbols. This is	3854	prototypes, but still define all the structs and other symbols. This is
2439	occasionally useful if you want to provide your own wrapper functions	3855	occasionally useful if you want to provide your own wrapper functions
2440	around libev functions.	3856	around libev functions.
…		…
2459	When doing priority-based operations, libev usually has to linearly search	3875	When doing priority-based operations, libev usually has to linearly search
2460	all the priorities, so having many of them (hundreds) uses a lot of space	3876	all the priorities, so having many of them (hundreds) uses a lot of space
2461	and time, so using the defaults of five priorities (-2 .. +2) is usually	3877	and time, so using the defaults of five priorities (-2 .. +2) is usually
2462	fine.	3878	fine.
2463		3879
2464	If your embedding app does not need any priorities, defining these both to	3880	If your embedding application does not need any priorities, defining these
2465	C<0> will save some memory and cpu.	3881	both to C<0> will save some memory and CPU.
2466		3882
2467	=item EV_PERIODIC_ENABLE	3883	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		3884	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		3885	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
2468		3886
2469	If undefined or defined to be C<1>, then periodic timers are supported. If	3887	If undefined or defined to be C<1> (and the platform supports it), then
2470	defined to be C<0>, then they are not. Disabling them saves a few kB of	3888	the respective watcher type is supported. If defined to be C<0>, then it
2471	code.	3889	is not. Disabling watcher types mainly saves code size.
2472		3890
2473	=item EV_IDLE_ENABLE	3891	=item EV_FEATURES
2474
2475	If undefined or defined to be C<1>, then idle watchers are supported. If
2476	defined to be C<0>, then they are not. Disabling them saves a few kB of
2477	code.
2478
2479	=item EV_EMBED_ENABLE
2480
2481	If undefined or defined to be C<1>, then embed watchers are supported. If
2482	defined to be C<0>, then they are not.
2483
2484	=item EV_STAT_ENABLE
2485
2486	If undefined or defined to be C<1>, then stat watchers are supported. If
2487	defined to be C<0>, then they are not.
2488
2489	=item EV_FORK_ENABLE
2490
2491	If undefined or defined to be C<1>, then fork watchers are supported. If
2492	defined to be C<0>, then they are not.
2493
2494	=item EV_MINIMAL
2495		3892
2496	If you need to shave off some kilobytes of code at the expense of some	3893	If you need to shave off some kilobytes of code at the expense of some
2497	speed, define this symbol to C<1>. Currently only used for gcc to override	3894	speed (but with the full API), you can define this symbol to request
2498	some inlining decisions, saves roughly 30% codesize of amd64.	3895	certain subsets of functionality. The default is to enable all features
		3896	that can be enabled on the platform.
		3897
		3898	A typical way to use this symbol is to define it to C<0> (or to a bitset
		3899	with some broad features you want) and then selectively re-enable
		3900	additional parts you want, for example if you want everything minimal,
		3901	but multiple event loop support, async and child watchers and the poll
		3902	backend, use this:
		3903
		3904	#define EV_FEATURES 0
		3905	#define EV_MULTIPLICITY 1
		3906	#define EV_USE_POLL 1
		3907	#define EV_CHILD_ENABLE 1
		3908	#define EV_ASYNC_ENABLE 1
		3909
		3910	The actual value is a bitset, it can be a combination of the following
		3911	values:
		3912
		3913	=over 4
		3914
		3915	=item C<1> - faster/larger code
		3916
		3917	Use larger code to speed up some operations.
		3918
		3919	Currently this is used to override some inlining decisions (enlarging the
		3920	code size by roughly 30% on amd64).
		3921
		3922	When optimising for size, use of compiler flags such as C<-Os> with
		3923	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
		3924	assertions.
		3925
		3926	=item C<2> - faster/larger data structures
		3927
		3928	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		3929	hash table sizes and so on. This will usually further increase code size
		3930	and can additionally have an effect on the size of data structures at
		3931	runtime.
		3932
		3933	=item C<4> - full API configuration
		3934
		3935	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		3936	enables multiplicity (C<EV_MULTIPLICITY>=1).
		3937
		3938	=item C<8> - full API
		3939
		3940	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		3941	details on which parts of the API are still available without this
		3942	feature, and do not complain if this subset changes over time.
		3943
		3944	=item C<16> - enable all optional watcher types
		3945
		3946	Enables all optional watcher types. If you want to selectively enable
		3947	only some watcher types other than I/O and timers (e.g. prepare,
		3948	embed, async, child...) you can enable them manually by defining
		3949	C<EV_watchertype_ENABLE> to C<1> instead.
		3950
		3951	=item C<32> - enable all backends
		3952
		3953	This enables all backends - without this feature, you need to enable at
		3954	least one backend manually (C<EV_USE_SELECT> is a good choice).
		3955
		3956	=item C<64> - enable OS-specific "helper" APIs
		3957
		3958	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		3959	default.
		3960
		3961	=back
		3962
		3963	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		3964	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		3965	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		3966	watchers, timers and monotonic clock support.
		3967
		3968	With an intelligent-enough linker (gcc+binutils are intelligent enough
		3969	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		3970	your program might be left out as well - a binary starting a timer and an
		3971	I/O watcher then might come out at only 5Kb.
		3972
		3973	=item EV_AVOID_STDIO
		3974
		3975	If this is set to C<1> at compiletime, then libev will avoid using stdio
		3976	functions (printf, scanf, perror etc.). This will increase the code size
		3977	somewhat, but if your program doesn't otherwise depend on stdio and your
		3978	libc allows it, this avoids linking in the stdio library which is quite
		3979	big.
		3980
		3981	Note that error messages might become less precise when this option is
		3982	enabled.
		3983
		3984	=item EV_NSIG
		3985
		3986	The highest supported signal number, +1 (or, the number of
		3987	signals): Normally, libev tries to deduce the maximum number of signals
		3988	automatically, but sometimes this fails, in which case it can be
		3989	specified. Also, using a lower number than detected (C<32> should be
		3990	good for about any system in existence) can save some memory, as libev
		3991	statically allocates some 12-24 bytes per signal number.
2499		3992
2500	=item EV_PID_HASHSIZE	3993	=item EV_PID_HASHSIZE
2501		3994
2502	C<ev_child> watchers use a small hash table to distribute workload by	3995	C<ev_child> watchers use a small hash table to distribute workload by
2503	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3996	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
2504	than enough. If you need to manage thousands of children you might want to	3997	usually more than enough. If you need to manage thousands of children you
2505	increase this value (I<must> be a power of two).	3998	might want to increase this value (I<must> be a power of two).
2506		3999
2507	=item EV_INOTIFY_HASHSIZE	4000	=item EV_INOTIFY_HASHSIZE
2508		4001
2509	C<ev_staz> watchers use a small hash table to distribute workload by	4002	C<ev_stat> watchers use a small hash table to distribute workload by
2510	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	4003	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
2511	usually more than enough. If you need to manage thousands of C<ev_stat>	4004	disabled), usually more than enough. If you need to manage thousands of
2512	watchers you might want to increase this value (I<must> be a power of	4005	C<ev_stat> watchers you might want to increase this value (I<must> be a
2513	two).	4006	power of two).
		4007
		4008	=item EV_USE_4HEAP
		4009
		4010	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4011	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		4012	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		4013	faster performance with many (thousands) of watchers.
		4014
		4015	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4016	will be C<0>.
		4017
		4018	=item EV_HEAP_CACHE_AT
		4019
		4020	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		4021	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		4022	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		4023	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		4024	but avoids random read accesses on heap changes. This improves performance
		4025	noticeably with many (hundreds) of watchers.
		4026
		4027	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4028	will be C<0>.
		4029
		4030	=item EV_VERIFY
		4031
		4032	Controls how much internal verification (see C<ev_loop_verify ()>) will
		4033	be done: If set to C<0>, no internal verification code will be compiled
		4034	in. If set to C<1>, then verification code will be compiled in, but not
		4035	called. If set to C<2>, then the internal verification code will be
		4036	called once per loop, which can slow down libev. If set to C<3>, then the
		4037	verification code will be called very frequently, which will slow down
		4038	libev considerably.
		4039
		4040	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
		4041	will be C<0>.
2514		4042
2515	=item EV_COMMON	4043	=item EV_COMMON
2516		4044
2517	By default, all watchers have a C<void *data> member. By redefining	4045	By default, all watchers have a C<void *data> member. By redefining
2518	this macro to a something else you can include more and other types of	4046	this macro to something else you can include more and other types of
2519	members. You have to define it each time you include one of the files,	4047	members. You have to define it each time you include one of the files,
2520	though, and it must be identical each time.	4048	though, and it must be identical each time.
2521		4049
2522	For example, the perl EV module uses something like this:	4050	For example, the perl EV module uses something like this:
2523		4051
2524	#define EV_COMMON \	4052	#define EV_COMMON \
2525	SV *self; /* contains this struct */ \	4053	SV *self; /* contains this struct */ \
2526	SV *cb_sv, *fh /* note no trailing ";" */	4054	SV *cb_sv, *fh /* note no trailing ";" */
2527		4055
2528	=item EV_CB_DECLARE (type)	4056	=item EV_CB_DECLARE (type)
2529		4057
2530	=item EV_CB_INVOKE (watcher, revents)	4058	=item EV_CB_INVOKE (watcher, revents)
2531		4059
…		…
2536	definition and a statement, respectively. See the F<ev.h> header file for	4064	definition and a statement, respectively. See the F<ev.h> header file for
2537	their default definitions. One possible use for overriding these is to	4065	their default definitions. One possible use for overriding these is to
2538	avoid the C<struct ev_loop *> as first argument in all cases, or to use	4066	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2539	method calls instead of plain function calls in C++.	4067	method calls instead of plain function calls in C++.
2540		4068
		4069	=back
		4070
2541	=head2 EXPORTED API SYMBOLS	4071	=head2 EXPORTED API SYMBOLS
2542		4072
2543	If you need to re-export the API (e.g. via a dll) and you need a list of	4073	If you need to re-export the API (e.g. via a DLL) and you need a list of
2544	exported symbols, you can use the provided F<Symbol.*> files which list	4074	exported symbols, you can use the provided F<Symbol.*> files which list
2545	all public symbols, one per line:	4075	all public symbols, one per line:
2546		4076
2547	Symbols.ev for libev proper	4077	Symbols.ev for libev proper
2548	Symbols.event for the libevent emulation	4078	Symbols.event for the libevent emulation
2549		4079
2550	This can also be used to rename all public symbols to avoid clashes with	4080	This can also be used to rename all public symbols to avoid clashes with
2551	multiple versions of libev linked together (which is obviously bad in	4081	multiple versions of libev linked together (which is obviously bad in
2552	itself, but sometimes it is inconvinient to avoid this).	4082	itself, but sometimes it is inconvenient to avoid this).
2553		4083
2554	A sed command like this will create wrapper C<#define>'s that you need to	4084	A sed command like this will create wrapper C<#define>'s that you need to
2555	include before including F<ev.h>:	4085	include before including F<ev.h>:
2556		4086
2557	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h	4087	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
…		…
2574	file.	4104	file.
2575		4105
2576	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	4106	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2577	that everybody includes and which overrides some configure choices:	4107	that everybody includes and which overrides some configure choices:
2578		4108
2579	#define EV_MINIMAL 1	4109	#define EV_FEATURES 8
2580	#define EV_USE_POLL 0	4110	#define EV_USE_SELECT 1
2581	#define EV_MULTIPLICITY 0
2582	#define EV_PERIODIC_ENABLE 0	4111	#define EV_PREPARE_ENABLE 1
		4112	#define EV_IDLE_ENABLE 1
2583	#define EV_STAT_ENABLE 0	4113	#define EV_SIGNAL_ENABLE 1
2584	#define EV_FORK_ENABLE 0	4114	#define EV_CHILD_ENABLE 1
		4115	#define EV_USE_STDEXCEPT 0
2585	#define EV_CONFIG_H <config.h>	4116	#define EV_CONFIG_H <config.h>
2586	#define EV_MINPRI 0
2587	#define EV_MAXPRI 0
2588		4117
2589	#include "ev++.h"	4118	#include "ev++.h"
2590		4119
2591	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4120	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2592		4121
2593	#include "ev_cpp.h"	4122	#include "ev_cpp.h"
2594	#include "ev.c"	4123	#include "ev.c"
2595		4124
		4125	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
2596		4126
		4127	=head2 THREADS AND COROUTINES
		4128
		4129	=head3 THREADS
		4130
		4131	All libev functions are reentrant and thread-safe unless explicitly
		4132	documented otherwise, but libev implements no locking itself. This means
		4133	that you can use as many loops as you want in parallel, as long as there
		4134	are no concurrent calls into any libev function with the same loop
		4135	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4136	of course): libev guarantees that different event loops share no data
		4137	structures that need any locking.
		4138
		4139	Or to put it differently: calls with different loop parameters can be done
		4140	concurrently from multiple threads, calls with the same loop parameter
		4141	must be done serially (but can be done from different threads, as long as
		4142	only one thread ever is inside a call at any point in time, e.g. by using
		4143	a mutex per loop).
		4144
		4145	Specifically to support threads (and signal handlers), libev implements
		4146	so-called C<ev_async> watchers, which allow some limited form of
		4147	concurrency on the same event loop, namely waking it up "from the
		4148	outside".
		4149
		4150	If you want to know which design (one loop, locking, or multiple loops
		4151	without or something else still) is best for your problem, then I cannot
		4152	help you, but here is some generic advice:
		4153
		4154	=over 4
		4155
		4156	=item * most applications have a main thread: use the default libev loop
		4157	in that thread, or create a separate thread running only the default loop.
		4158
		4159	This helps integrating other libraries or software modules that use libev
		4160	themselves and don't care/know about threading.
		4161
		4162	=item * one loop per thread is usually a good model.
		4163
		4164	Doing this is almost never wrong, sometimes a better-performance model
		4165	exists, but it is always a good start.
		4166
		4167	=item * other models exist, such as the leader/follower pattern, where one
		4168	loop is handed through multiple threads in a kind of round-robin fashion.
		4169
		4170	Choosing a model is hard - look around, learn, know that usually you can do
		4171	better than you currently do :-)
		4172
		4173	=item * often you need to talk to some other thread which blocks in the
		4174	event loop.
		4175
		4176	C<ev_async> watchers can be used to wake them up from other threads safely
		4177	(or from signal contexts...).
		4178
		4179	An example use would be to communicate signals or other events that only
		4180	work in the default loop by registering the signal watcher with the
		4181	default loop and triggering an C<ev_async> watcher from the default loop
		4182	watcher callback into the event loop interested in the signal.
		4183
		4184	=back
		4185
		4186	=head4 THREAD LOCKING EXAMPLE
		4187
		4188	Here is a fictitious example of how to run an event loop in a different
		4189	thread than where callbacks are being invoked and watchers are
		4190	created/added/removed.
		4191
		4192	For a real-world example, see the C<EV::Loop::Async> perl module,
		4193	which uses exactly this technique (which is suited for many high-level
		4194	languages).
		4195
		4196	The example uses a pthread mutex to protect the loop data, a condition
		4197	variable to wait for callback invocations, an async watcher to notify the
		4198	event loop thread and an unspecified mechanism to wake up the main thread.
		4199
		4200	First, you need to associate some data with the event loop:
		4201
		4202	typedef struct {
		4203	mutex_t lock; /* global loop lock */
		4204	ev_async async_w;
		4205	thread_t tid;
		4206	cond_t invoke_cv;
		4207	} userdata;
		4208
		4209	void prepare_loop (EV_P)
		4210	{
		4211	// for simplicity, we use a static userdata struct.
		4212	static userdata u;
		4213
		4214	ev_async_init (&u->async_w, async_cb);
		4215	ev_async_start (EV_A_ &u->async_w);
		4216
		4217	pthread_mutex_init (&u->lock, 0);
		4218	pthread_cond_init (&u->invoke_cv, 0);
		4219
		4220	// now associate this with the loop
		4221	ev_set_userdata (EV_A_ u);
		4222	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4223	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4224
		4225	// then create the thread running ev_loop
		4226	pthread_create (&u->tid, 0, l_run, EV_A);
		4227	}
		4228
		4229	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4230	solely to wake up the event loop so it takes notice of any new watchers
		4231	that might have been added:
		4232
		4233	static void
		4234	async_cb (EV_P_ ev_async *w, int revents)
		4235	{
		4236	// just used for the side effects
		4237	}
		4238
		4239	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4240	protecting the loop data, respectively.
		4241
		4242	static void
		4243	l_release (EV_P)
		4244	{
		4245	userdata *u = ev_userdata (EV_A);
		4246	pthread_mutex_unlock (&u->lock);
		4247	}
		4248
		4249	static void
		4250	l_acquire (EV_P)
		4251	{
		4252	userdata *u = ev_userdata (EV_A);
		4253	pthread_mutex_lock (&u->lock);
		4254	}
		4255
		4256	The event loop thread first acquires the mutex, and then jumps straight
		4257	into C<ev_loop>:
		4258
		4259	void *
		4260	l_run (void *thr_arg)
		4261	{
		4262	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		4263
		4264	l_acquire (EV_A);
		4265	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4266	ev_loop (EV_A_ 0);
		4267	l_release (EV_A);
		4268
		4269	return 0;
		4270	}
		4271
		4272	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4273	signal the main thread via some unspecified mechanism (signals? pipe
		4274	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4275	have been called (in a while loop because a) spurious wakeups are possible
		4276	and b) skipping inter-thread-communication when there are no pending
		4277	watchers is very beneficial):
		4278
		4279	static void
		4280	l_invoke (EV_P)
		4281	{
		4282	userdata *u = ev_userdata (EV_A);
		4283
		4284	while (ev_pending_count (EV_A))
		4285	{
		4286	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4287	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4288	}
		4289	}
		4290
		4291	Now, whenever the main thread gets told to invoke pending watchers, it
		4292	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4293	thread to continue:
		4294
		4295	static void
		4296	real_invoke_pending (EV_P)
		4297	{
		4298	userdata *u = ev_userdata (EV_A);
		4299
		4300	pthread_mutex_lock (&u->lock);
		4301	ev_invoke_pending (EV_A);
		4302	pthread_cond_signal (&u->invoke_cv);
		4303	pthread_mutex_unlock (&u->lock);
		4304	}
		4305
		4306	Whenever you want to start/stop a watcher or do other modifications to an
		4307	event loop, you will now have to lock:
		4308
		4309	ev_timer timeout_watcher;
		4310	userdata *u = ev_userdata (EV_A);
		4311
		4312	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4313
		4314	pthread_mutex_lock (&u->lock);
		4315	ev_timer_start (EV_A_ &timeout_watcher);
		4316	ev_async_send (EV_A_ &u->async_w);
		4317	pthread_mutex_unlock (&u->lock);
		4318
		4319	Note that sending the C<ev_async> watcher is required because otherwise
		4320	an event loop currently blocking in the kernel will have no knowledge
		4321	about the newly added timer. By waking up the loop it will pick up any new
		4322	watchers in the next event loop iteration.
		4323
		4324	=head3 COROUTINES
		4325
		4326	Libev is very accommodating to coroutines ("cooperative threads"):
		4327	libev fully supports nesting calls to its functions from different
		4328	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		4329	different coroutines, and switch freely between both coroutines running
		4330	the loop, as long as you don't confuse yourself). The only exception is
		4331	that you must not do this from C<ev_periodic> reschedule callbacks.
		4332
		4333	Care has been taken to ensure that libev does not keep local state inside
		4334	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		4335	they do not call any callbacks.
		4336
		4337	=head2 COMPILER WARNINGS
		4338
		4339	Depending on your compiler and compiler settings, you might get no or a
		4340	lot of warnings when compiling libev code. Some people are apparently
		4341	scared by this.
		4342
		4343	However, these are unavoidable for many reasons. For one, each compiler
		4344	has different warnings, and each user has different tastes regarding
		4345	warning options. "Warn-free" code therefore cannot be a goal except when
		4346	targeting a specific compiler and compiler-version.
		4347
		4348	Another reason is that some compiler warnings require elaborate
		4349	workarounds, or other changes to the code that make it less clear and less
		4350	maintainable.
		4351
		4352	And of course, some compiler warnings are just plain stupid, or simply
		4353	wrong (because they don't actually warn about the condition their message
		4354	seems to warn about). For example, certain older gcc versions had some
		4355	warnings that resulted in an extreme number of false positives. These have
		4356	been fixed, but some people still insist on making code warn-free with
		4357	such buggy versions.
		4358
		4359	While libev is written to generate as few warnings as possible,
		4360	"warn-free" code is not a goal, and it is recommended not to build libev
		4361	with any compiler warnings enabled unless you are prepared to cope with
		4362	them (e.g. by ignoring them). Remember that warnings are just that:
		4363	warnings, not errors, or proof of bugs.
		4364
		4365
		4366	=head2 VALGRIND
		4367
		4368	Valgrind has a special section here because it is a popular tool that is
		4369	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		4370
		4371	If you think you found a bug (memory leak, uninitialised data access etc.)
		4372	in libev, then check twice: If valgrind reports something like:
		4373
		4374	==2274== definitely lost: 0 bytes in 0 blocks.
		4375	==2274== possibly lost: 0 bytes in 0 blocks.
		4376	==2274== still reachable: 256 bytes in 1 blocks.
		4377
		4378	Then there is no memory leak, just as memory accounted to global variables
		4379	is not a memleak - the memory is still being referenced, and didn't leak.
		4380
		4381	Similarly, under some circumstances, valgrind might report kernel bugs
		4382	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4383	although an acceptable workaround has been found here), or it might be
		4384	confused.
		4385
		4386	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		4387	make it into some kind of religion.
		4388
		4389	If you are unsure about something, feel free to contact the mailing list
		4390	with the full valgrind report and an explanation on why you think this
		4391	is a bug in libev (best check the archives, too :). However, don't be
		4392	annoyed when you get a brisk "this is no bug" answer and take the chance
		4393	of learning how to interpret valgrind properly.
		4394
		4395	If you need, for some reason, empty reports from valgrind for your project
		4396	I suggest using suppression lists.
		4397
		4398
		4399	=head1 PORTABILITY NOTES
		4400
		4401	=head2 GNU/LINUX 32 BIT LIMITATIONS
		4402
		4403	GNU/Linux is the only common platform that supports 64 bit file/large file
		4404	interfaces but I<disables> them by default.
		4405
		4406	That means that libev compiled in the default environment doesn't support
		4407	files larger than 2GiB or so, which mainly affects C<ev_stat> watchers.
		4408
		4409	Unfortunately, many programs try to work around this GNU/Linux issue
		4410	by enabling the large file API, which makes them incompatible with the
		4411	standard libev compiled for their system.
		4412
		4413	Likewise, libev cannot enable the large file API itself as this would
		4414	suddenly make it incompatible to the default compile time environment,
		4415	i.e. all programs not using special compile switches.
		4416
		4417	=head2 OS/X AND DARWIN BUGS
		4418
		4419	The whole thing is a bug if you ask me - basically any system interface
		4420	you touch is broken, whether it is locales, poll, kqueue or even the
		4421	OpenGL drivers.
		4422
		4423	=head3 C<kqueue> is buggy
		4424
		4425	The kqueue syscall is broken in all known versions - most versions support
		4426	only sockets, many support pipes.
		4427
		4428	Libev tries to work around this by not using C<kqueue> by default on
		4429	this rotten platform, but of course you can still ask for it when creating
		4430	a loop.
		4431
		4432	=head3 C<poll> is buggy
		4433
		4434	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
		4435	implementation by something calling C<kqueue> internally around the 10.5.6
		4436	release, so now C<kqueue> I<and> C<poll> are broken.
		4437
		4438	Libev tries to work around this by not using C<poll> by default on
		4439	this rotten platform, but of course you can still ask for it when creating
		4440	a loop.
		4441
		4442	=head3 C<select> is buggy
		4443
		4444	All that's left is C<select>, and of course Apple found a way to fuck this
		4445	one up as well: On OS/X, C<select> actively limits the number of file
		4446	descriptors you can pass in to 1024 - your program suddenly crashes when
		4447	you use more.
		4448
		4449	There is an undocumented "workaround" for this - defining
		4450	C<_DARWIN_UNLIMITED_SELECT>, which libev tries to use, so select I<should>
		4451	work on OS/X.
		4452
		4453	=head2 SOLARIS PROBLEMS AND WORKAROUNDS
		4454
		4455	=head3 C<errno> reentrancy
		4456
		4457	The default compile environment on Solaris is unfortunately so
		4458	thread-unsafe that you can't even use components/libraries compiled
		4459	without C<-D_REENTRANT> (as long as they use C<errno>), which, of course,
		4460	isn't defined by default.
		4461
		4462	If you want to use libev in threaded environments you have to make sure
		4463	it's compiled with C<_REENTRANT> defined.
		4464
		4465	=head3 Event port backend
		4466
		4467	The scalable event interface for Solaris is called "event ports". Unfortunately,
		4468	this mechanism is very buggy. If you run into high CPU usage, your program
		4469	freezes or you get a large number of spurious wakeups, make sure you have
		4470	all the relevant and latest kernel patches applied. No, I don't know which
		4471	ones, but there are multiple ones.
		4472
		4473	If you can't get it to work, you can try running the program by setting
		4474	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
		4475	C<select> backends.
		4476
		4477	=head2 AIX POLL BUG
		4478
		4479	AIX unfortunately has a broken C<poll.h> header. Libev works around
		4480	this by trying to avoid the poll backend altogether (i.e. it's not even
		4481	compiled in), which normally isn't a big problem as C<select> works fine
		4482	with large bitsets, and AIX is dead anyway.
		4483
		4484	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		4485
		4486	=head3 General issues
		4487
		4488	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		4489	requires, and its I/O model is fundamentally incompatible with the POSIX
		4490	model. Libev still offers limited functionality on this platform in
		4491	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		4492	descriptors. This only applies when using Win32 natively, not when using
		4493	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
		4494	as every compielr comes with a slightly differently broken/incompatible
		4495	environment.
		4496
		4497	Lifting these limitations would basically require the full
		4498	re-implementation of the I/O system. If you are into this kind of thing,
		4499	then note that glib does exactly that for you in a very portable way (note
		4500	also that glib is the slowest event library known to man).
		4501
		4502	There is no supported compilation method available on windows except
		4503	embedding it into other applications.
		4504
		4505	Sensible signal handling is officially unsupported by Microsoft - libev
		4506	tries its best, but under most conditions, signals will simply not work.
		4507
		4508	Not a libev limitation but worth mentioning: windows apparently doesn't
		4509	accept large writes: instead of resulting in a partial write, windows will
		4510	either accept everything or return C<ENOBUFS> if the buffer is too large,
		4511	so make sure you only write small amounts into your sockets (less than a
		4512	megabyte seems safe, but this apparently depends on the amount of memory
		4513	available).
		4514
		4515	Due to the many, low, and arbitrary limits on the win32 platform and
		4516	the abysmal performance of winsockets, using a large number of sockets
		4517	is not recommended (and not reasonable). If your program needs to use
		4518	more than a hundred or so sockets, then likely it needs to use a totally
		4519	different implementation for windows, as libev offers the POSIX readiness
		4520	notification model, which cannot be implemented efficiently on windows
		4521	(due to Microsoft monopoly games).
		4522
		4523	A typical way to use libev under windows is to embed it (see the embedding
		4524	section for details) and use the following F<evwrap.h> header file instead
		4525	of F<ev.h>:
		4526
		4527	#define EV_STANDALONE /* keeps ev from requiring config.h */
		4528	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		4529
		4530	#include "ev.h"
		4531
		4532	And compile the following F<evwrap.c> file into your project (make sure
		4533	you do I<not> compile the F<ev.c> or any other embedded source files!):
		4534
		4535	#include "evwrap.h"
		4536	#include "ev.c"
		4537
		4538	=head3 The winsocket C<select> function
		4539
		4540	The winsocket C<select> function doesn't follow POSIX in that it
		4541	requires socket I<handles> and not socket I<file descriptors> (it is
		4542	also extremely buggy). This makes select very inefficient, and also
		4543	requires a mapping from file descriptors to socket handles (the Microsoft
		4544	C runtime provides the function C<_open_osfhandle> for this). See the
		4545	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		4546	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		4547
		4548	The configuration for a "naked" win32 using the Microsoft runtime
		4549	libraries and raw winsocket select is:
		4550
		4551	#define EV_USE_SELECT 1
		4552	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		4553
		4554	Note that winsockets handling of fd sets is O(n), so you can easily get a
		4555	complexity in the O(n²) range when using win32.
		4556
		4557	=head3 Limited number of file descriptors
		4558
		4559	Windows has numerous arbitrary (and low) limits on things.
		4560
		4561	Early versions of winsocket's select only supported waiting for a maximum
		4562	of C<64> handles (probably owning to the fact that all windows kernels
		4563	can only wait for C<64> things at the same time internally; Microsoft
		4564	recommends spawning a chain of threads and wait for 63 handles and the
		4565	previous thread in each. Sounds great!).
		4566
		4567	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		4568	to some high number (e.g. C<2048>) before compiling the winsocket select
		4569	call (which might be in libev or elsewhere, for example, perl and many
		4570	other interpreters do their own select emulation on windows).
		4571
		4572	Another limit is the number of file descriptors in the Microsoft runtime
		4573	libraries, which by default is C<64> (there must be a hidden I<64>
		4574	fetish or something like this inside Microsoft). You can increase this
		4575	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		4576	(another arbitrary limit), but is broken in many versions of the Microsoft
		4577	runtime libraries. This might get you to about C<512> or C<2048> sockets
		4578	(depending on windows version and/or the phase of the moon). To get more,
		4579	you need to wrap all I/O functions and provide your own fd management, but
		4580	the cost of calling select (O(n²)) will likely make this unworkable.
		4581
		4582	=head2 PORTABILITY REQUIREMENTS
		4583
		4584	In addition to a working ISO-C implementation and of course the
		4585	backend-specific APIs, libev relies on a few additional extensions:
		4586
		4587	=over 4
		4588
		4589	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4590	calling conventions regardless of C<ev_watcher_type *>.
		4591
		4592	Libev assumes not only that all watcher pointers have the same internal
		4593	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4594	assumes that the same (machine) code can be used to call any watcher
		4595	callback: The watcher callbacks have different type signatures, but libev
		4596	calls them using an C<ev_watcher *> internally.
		4597
		4598	=item C<sig_atomic_t volatile> must be thread-atomic as well
		4599
		4600	The type C<sig_atomic_t volatile> (or whatever is defined as
		4601	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		4602	threads. This is not part of the specification for C<sig_atomic_t>, but is
		4603	believed to be sufficiently portable.
		4604
		4605	=item C<sigprocmask> must work in a threaded environment
		4606
		4607	Libev uses C<sigprocmask> to temporarily block signals. This is not
		4608	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		4609	pthread implementations will either allow C<sigprocmask> in the "main
		4610	thread" or will block signals process-wide, both behaviours would
		4611	be compatible with libev. Interaction between C<sigprocmask> and
		4612	C<pthread_sigmask> could complicate things, however.
		4613
		4614	The most portable way to handle signals is to block signals in all threads
		4615	except the initial one, and run the default loop in the initial thread as
		4616	well.
		4617
		4618	=item C<long> must be large enough for common memory allocation sizes
		4619
		4620	To improve portability and simplify its API, libev uses C<long> internally
		4621	instead of C<size_t> when allocating its data structures. On non-POSIX
		4622	systems (Microsoft...) this might be unexpectedly low, but is still at
		4623	least 31 bits everywhere, which is enough for hundreds of millions of
		4624	watchers.
		4625
		4626	=item C<double> must hold a time value in seconds with enough accuracy
		4627
		4628	The type C<double> is used to represent timestamps. It is required to
		4629	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		4630	enough for at least into the year 4000. This requirement is fulfilled by
		4631	implementations implementing IEEE 754, which is basically all existing
		4632	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4633	2200.
		4634
		4635	=back
		4636
		4637	If you know of other additional requirements drop me a note.
		4638
		4639
2597	=head1 COMPLEXITIES	4640	=head1 ALGORITHMIC COMPLEXITIES
2598		4641
2599	In this section the complexities of (many of) the algorithms used inside	4642	In this section the complexities of (many of) the algorithms used inside
2600	libev will be explained. For complexity discussions about backends see the	4643	libev will be documented. For complexity discussions about backends see
2601	documentation for C<ev_default_init>.	4644	the documentation for C<ev_default_init>.
2602		4645
2603	All of the following are about amortised time: If an array needs to be	4646	All of the following are about amortised time: If an array needs to be
2604	extended, libev needs to realloc and move the whole array, but this	4647	extended, libev needs to realloc and move the whole array, but this
2605	happens asymptotically never with higher number of elements, so O(1) might	4648	happens asymptotically rarer with higher number of elements, so O(1) might
2606	mean it might do a lengthy realloc operation in rare cases, but on average	4649	mean that libev does a lengthy realloc operation in rare cases, but on
2607	it is much faster and asymptotically approaches constant time.	4650	average it is much faster and asymptotically approaches constant time.
2608		4651
2609	=over 4	4652	=over 4
2610		4653
2611	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4654	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2612		4655
2613	This means that, when you have a watcher that triggers in one hour and	4656	This means that, when you have a watcher that triggers in one hour and
2614	there are 100 watchers that would trigger before that then inserting will	4657	there are 100 watchers that would trigger before that, then inserting will
2615	have to skip those 100 watchers.	4658	have to skip roughly seven (C<ld 100>) of these watchers.
2616		4659
2617	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	4660	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2618		4661
2619	That means that for changing a timer costs less than removing/adding them	4662	That means that changing a timer costs less than removing/adding them,
2620	as only the relative motion in the event queue has to be paid for.	4663	as only the relative motion in the event queue has to be paid for.
2621		4664
2622	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	4665	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
2623		4666
2624	These just add the watcher into an array or at the head of a list.	4667	These just add the watcher into an array or at the head of a list.
		4668
2625	=item Stopping check/prepare/idle watchers: O(1)	4669	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2626		4670
2627	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	4671	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2628		4672
2629	These watchers are stored in lists then need to be walked to find the	4673	These watchers are stored in lists, so they need to be walked to find the
2630	correct watcher to remove. The lists are usually short (you don't usually	4674	correct watcher to remove. The lists are usually short (you don't usually
2631	have many watchers waiting for the same fd or signal).	4675	have many watchers waiting for the same fd or signal: one is typical, two
		4676	is rare).
2632		4677
2633	=item Finding the next timer per loop iteration: O(1)	4678	=item Finding the next timer in each loop iteration: O(1)
		4679
		4680	By virtue of using a binary or 4-heap, the next timer is always found at a
		4681	fixed position in the storage array.
2634		4682
2635	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	4683	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2636		4684
2637	A change means an I/O watcher gets started or stopped, which requires	4685	A change means an I/O watcher gets started or stopped, which requires
2638	libev to recalculate its status (and possibly tell the kernel).	4686	libev to recalculate its status (and possibly tell the kernel, depending
		4687	on backend and whether C<ev_io_set> was used).
2639		4688
2640	=item Activating one watcher: O(1)	4689	=item Activating one watcher (putting it into the pending state): O(1)
2641		4690
2642	=item Priority handling: O(number_of_priorities)	4691	=item Priority handling: O(number_of_priorities)
2643		4692
2644	Priorities are implemented by allocating some space for each	4693	Priorities are implemented by allocating some space for each
2645	priority. When doing priority-based operations, libev usually has to	4694	priority. When doing priority-based operations, libev usually has to
2646	linearly search all the priorities.	4695	linearly search all the priorities, but starting/stopping and activating
		4696	watchers becomes O(1) with respect to priority handling.
		4697
		4698	=item Sending an ev_async: O(1)
		4699
		4700	=item Processing ev_async_send: O(number_of_async_watchers)
		4701
		4702	=item Processing signals: O(max_signal_number)
		4703
		4704	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4705	calls in the current loop iteration. Checking for async and signal events
		4706	involves iterating over all running async watchers or all signal numbers.
2647		4707
2648	=back	4708	=back
2649		4709
2650		4710
		4711	=head1 PORTING FROM LIBEV 3.X TO 4.X
		4712
		4713	The major version 4 introduced some minor incompatible changes to the API.
		4714
		4715	At the moment, the C<ev.h> header file tries to implement superficial
		4716	compatibility, so most programs should still compile. Those might be
		4717	removed in later versions of libev, so better update early than late.
		4718
		4719	=over 4
		4720
		4721	=item C<ev_loop_count> renamed to C<ev_iteration>
		4722
		4723	=item C<ev_loop_depth> renamed to C<ev_depth>
		4724
		4725	=item C<ev_loop_verify> renamed to C<ev_verify>
		4726
		4727	Most functions working on C<struct ev_loop> objects don't have an
		4728	C<ev_loop_> prefix, so it was removed. Note that C<ev_loop_fork> is
		4729	still called C<ev_loop_fork> because it would otherwise clash with the
		4730	C<ev_fork> typedef.
		4731
		4732	=item C<EV_TIMEOUT> renamed to C<EV_TIMER> in C<revents>
		4733
		4734	This is a simple rename - all other watcher types use their name
		4735	as revents flag, and now C<ev_timer> does, too.
		4736
		4737	Both C<EV_TIMER> and C<EV_TIMEOUT> symbols were present in 3.x versions
		4738	and continue to be present for the foreseeable future, so this is mostly a
		4739	documentation change.
		4740
		4741	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		4742
		4743	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		4744	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		4745	and work, but the library code will of course be larger.
		4746
		4747	=back
		4748
		4749
		4750	=head1 GLOSSARY
		4751
		4752	=over 4
		4753
		4754	=item active
		4755
		4756	A watcher is active as long as it has been started (has been attached to
		4757	an event loop) but not yet stopped (disassociated from the event loop).
		4758
		4759	=item application
		4760
		4761	In this document, an application is whatever is using libev.
		4762
		4763	=item callback
		4764
		4765	The address of a function that is called when some event has been
		4766	detected. Callbacks are being passed the event loop, the watcher that
		4767	received the event, and the actual event bitset.
		4768
		4769	=item callback invocation
		4770
		4771	The act of calling the callback associated with a watcher.
		4772
		4773	=item event
		4774
		4775	A change of state of some external event, such as data now being available
		4776	for reading on a file descriptor, time having passed or simply not having
		4777	any other events happening anymore.
		4778
		4779	In libev, events are represented as single bits (such as C<EV_READ> or
		4780	C<EV_TIMER>).
		4781
		4782	=item event library
		4783
		4784	A software package implementing an event model and loop.
		4785
		4786	=item event loop
		4787
		4788	An entity that handles and processes external events and converts them
		4789	into callback invocations.
		4790
		4791	=item event model
		4792
		4793	The model used to describe how an event loop handles and processes
		4794	watchers and events.
		4795
		4796	=item pending
		4797
		4798	A watcher is pending as soon as the corresponding event has been detected,
		4799	and stops being pending as soon as the watcher will be invoked or its
		4800	pending status is explicitly cleared by the application.
		4801
		4802	A watcher can be pending, but not active. Stopping a watcher also clears
		4803	its pending status.
		4804
		4805	=item real time
		4806
		4807	The physical time that is observed. It is apparently strictly monotonic :)
		4808
		4809	=item wall-clock time
		4810
		4811	The time and date as shown on clocks. Unlike real time, it can actually
		4812	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4813	clock.
		4814
		4815	=item watcher
		4816
		4817	A data structure that describes interest in certain events. Watchers need
		4818	to be started (attached to an event loop) before they can receive events.
		4819
		4820	=item watcher invocation
		4821
		4822	The act of calling the callback associated with a watcher.
		4823
		4824	=back
		4825
2651	=head1 AUTHOR	4826	=head1 AUTHOR
2652		4827
2653	Marc Lehmann <libev@schmorp.de>.	4828	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
2654		4829

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