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Revision 1.101 by ayin, Sat Dec 22 14:11:25 2007 UTC vs.
Revision 1.253 by root, Tue Jul 14 18:33:48 2009 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	Familarity 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>), relative timers (C<ev_timer>), absolute timers
…		…
82		110
83	It also is quite fast (see this	111	It also is quite fast (see this
84	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent	112	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
85	for example).	113	for example).
86		114
87	=head1 CONVENTIONS	115	=head2 CONVENTIONS
88		116
89	Libev is very configurable. In this manual the default configuration will	117	Libev is very configurable. In this manual the default (and most common)
90	be described, which supports multiple event loops. For more info about	118	configuration will be described, which supports multiple event loops. For
91	various configuration options please have a look at B<EMBED> section in	119	more info about various configuration options please have a look at
92	this manual. If libev was configured without support for multiple event	120	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>	121	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.	122	name C<loop> (which is always of type C<ev_loop *>) will not have
		123	this argument.
95		124
96	=head1 TIME REPRESENTATION	125	=head2 TIME REPRESENTATION
97		126
98	Libev represents time as a single floating point number, representing the	127	Libev represents time as a single floating point number, representing
99	(fractional) number of seconds since the (POSIX) epoch (somewhere near	128	the (fractional) number of seconds since the (POSIX) epoch (somewhere
100	the beginning of 1970, details are complicated, don't ask). This type is	129	near the beginning of 1970, details are complicated, don't ask). This
101	called C<ev_tstamp>, which is what you should use too. It usually aliases	130	type is called C<ev_tstamp>, which is what you should use too. It usually
102	to the C<double> type in C, and when you need to do any calculations on	131	aliases to the C<double> type in C. When you need to do any calculations
103	it, you should treat it as some floatingpoint value. Unlike the name	132	on it, you should treat it as some floating point value. Unlike the name
104	component C<stamp> might indicate, it is also used for time differences	133	component C<stamp> might indicate, it is also used for time differences
105	throughout libev.	134	throughout libev.
		135
		136	=head1 ERROR HANDLING
		137
		138	Libev knows three classes of errors: operating system errors, usage errors
		139	and internal errors (bugs).
		140
		141	When libev catches an operating system error it cannot handle (for example
		142	a system call indicating a condition libev cannot fix), it calls the callback
		143	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		144	abort. The default is to print a diagnostic message and to call C<abort
		145	()>.
		146
		147	When libev detects a usage error such as a negative timer interval, then
		148	it will print a diagnostic message and abort (via the C<assert> mechanism,
		149	so C<NDEBUG> will disable this checking): these are programming errors in
		150	the libev caller and need to be fixed there.
		151
		152	Libev also has a few internal error-checking C<assert>ions, and also has
		153	extensive consistency checking code. These do not trigger under normal
		154	circumstances, as they indicate either a bug in libev or worse.
		155
106		156
107	=head1 GLOBAL FUNCTIONS	157	=head1 GLOBAL FUNCTIONS
108		158
109	These functions can be called anytime, even before initialising the	159	These functions can be called anytime, even before initialising the
110	library in any way.	160	library in any way.
…		…
119		169
120	=item ev_sleep (ev_tstamp interval)	170	=item ev_sleep (ev_tstamp interval)
121		171
122	Sleep for the given interval: The current thread will be blocked until	172	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	173	either it is interrupted or the given time interval has passed. Basically
124	this is a subsecond-resolution C<sleep ()>.	174	this is a sub-second-resolution C<sleep ()>.
125		175
126	=item int ev_version_major ()	176	=item int ev_version_major ()
127		177
128	=item int ev_version_minor ()	178	=item int ev_version_minor ()
129		179
…		…
142	not a problem.	192	not a problem.
143		193
144	Example: Make sure we haven't accidentally been linked against the wrong	194	Example: Make sure we haven't accidentally been linked against the wrong
145	version.	195	version.
146		196
147	assert (("libev version mismatch",	197	assert (("libev version mismatch",
148	ev_version_major () == EV_VERSION_MAJOR	198	ev_version_major () == EV_VERSION_MAJOR
149	&& ev_version_minor () >= EV_VERSION_MINOR));	199	&& ev_version_minor () >= EV_VERSION_MINOR));
150		200
151	=item unsigned int ev_supported_backends ()	201	=item unsigned int ev_supported_backends ()
152		202
153	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	203	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
154	value) compiled into this binary of libev (independent of their	204	value) compiled into this binary of libev (independent of their
…		…
156	a description of the set values.	206	a description of the set values.
157		207
158	Example: make sure we have the epoll method, because yeah this is cool and	208	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	209	a must have and can we have a torrent of it please!!!11
160		210
161	assert (("sorry, no epoll, no sex",	211	assert (("sorry, no epoll, no sex",
162	ev_supported_backends () & EVBACKEND_EPOLL));	212	ev_supported_backends () & EVBACKEND_EPOLL));
163		213
164	=item unsigned int ev_recommended_backends ()	214	=item unsigned int ev_recommended_backends ()
165		215
166	Return the set of all backends compiled into this binary of libev and also	216	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	217	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	218	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	219	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	220	(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.	221	libev will probe for if you specify no backends explicitly.
172		222
173	=item unsigned int ev_embeddable_backends ()	223	=item unsigned int ev_embeddable_backends ()
174		224
…		…
178	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	228	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
179	recommended ones.	229	recommended ones.
180		230
181	See the description of C<ev_embed> watchers for more info.	231	See the description of C<ev_embed> watchers for more info.
182		232
183	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	233	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
184		234
185	Sets the allocation function to use (the prototype is similar - the	235	Sets the allocation function to use (the prototype is similar - the
186	semantics is identical - to the realloc C function). It is used to	236	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	237	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	238	when memory needs to be allocated (C<size != 0>), the library might abort
189	potentially destructive action. The default is your system realloc	239	or take some potentially destructive action.
190	function.	240
		241	Since some systems (at least OpenBSD and Darwin) fail to implement
		242	correct C<realloc> semantics, libev will use a wrapper around the system
		243	C<realloc> and C<free> functions by default.
191		244
192	You could override this function in high-availability programs to, say,	245	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,	246	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.	247	or even to sleep a while and retry until some memory is available.
195		248
196	Example: Replace the libev allocator with one that waits a bit and then	249	Example: Replace the libev allocator with one that waits a bit and then
197	retries).	250	retries (example requires a standards-compliant C<realloc>).
198		251
199	static void *	252	static void *
200	persistent_realloc (void *ptr, size_t size)	253	persistent_realloc (void *ptr, size_t size)
201	{	254	{
202	for (;;)	255	for (;;)
…		…
211	}	264	}
212		265
213	...	266	...
214	ev_set_allocator (persistent_realloc);	267	ev_set_allocator (persistent_realloc);
215		268
216	=item ev_set_syserr_cb (void (*cb)(const char *msg));	269	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
217		270
218	Set the callback function to call on a retryable syscall error (such	271	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	272	as failed select, poll, epoll_wait). The message is a printable string
220	indicating the system call or subsystem causing the problem. If this	273	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	274	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	275	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	276	requested operation, or, if the condition doesn't go away, do bad stuff
224	(such as abort).	277	(such as abort).
225		278
226	Example: This is basically the same thing that libev does internally, too.	279	Example: This is basically the same thing that libev does internally, too.
…		…
237		290
238	=back	291	=back
239		292
240	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	293	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
241		294
242	An event loop is described by a C<struct ev_loop *>. The library knows two	295	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	296	is I<not> optional in this case, as there is also an C<ev_loop>
244	events, and dynamically created loops which do not.	297	I<function>).
245		298
246	If you use threads, a common model is to run the default event loop	299	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	300	supports signals and child events, and dynamically created loops which do
248	create, you also create another event loop. Libev itself does no locking	301	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		302
253	=over 4	303	=over 4
254		304
255	=item struct ev_loop *ev_default_loop (unsigned int flags)	305	=item struct ev_loop *ev_default_loop (unsigned int flags)
256		306
…		…
260	flags. If that is troubling you, check C<ev_backend ()> afterwards).	310	flags. If that is troubling you, check C<ev_backend ()> afterwards).
261		311
262	If you don't know what event loop to use, use the one returned from this	312	If you don't know what event loop to use, use the one returned from this
263	function.	313	function.
264		314
		315	Note that this function is I<not> thread-safe, so if you want to use it
		316	from multiple threads, you have to lock (note also that this is unlikely,
		317	as loops cannot be shared easily between threads anyway).
		318
		319	The default loop is the only loop that can handle C<ev_signal> and
		320	C<ev_child> watchers, and to do this, it always registers a handler
		321	for C<SIGCHLD>. If this is a problem for your application you can either
		322	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
		323	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
		324	C<ev_default_init>.
		325
265	The flags argument can be used to specify special behaviour or specific	326	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>).	327	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
267		328
268	The following flags are supported:	329	The following flags are supported:
269		330
…		…
274	The default flags value. Use this if you have no clue (it's the right	335	The default flags value. Use this if you have no clue (it's the right
275	thing, believe me).	336	thing, believe me).
276		337
277	=item C<EVFLAG_NOENV>	338	=item C<EVFLAG_NOENV>
278		339
279	If this flag bit is ored into the flag value (or the program runs setuid	340	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	341	or setgid) then libev will I<not> look at the environment variable
281	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	342	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
282	override the flags completely if it is found in the environment. This is	343	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	344	useful to try out specific backends to test their performance, or to work
284	around bugs.	345	around bugs.
…		…
290	enabling this flag.	351	enabling this flag.
291		352
292	This works by calling C<getpid ()> on every iteration of the loop,	353	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	354	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	355	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	356	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	357	without a system call and thus I<very> fast, but my GNU/Linux system also has
297	C<pthread_atfork> which is even faster).	358	C<pthread_atfork> which is even faster).
298		359
299	The big advantage of this flag is that you can forget about fork (and	360	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	361	forget about forgetting to tell libev about forking) when you use this
301	flag.	362	flag.
302		363
303	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>	364	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
304	environment variable.	365	environment variable.
305		366
306	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	367	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
307		368
308	This is your standard select(2) backend. Not I<completely> standard, as	369	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,	370	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	371	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	372	using this backend. It doesn't scale too well (O(highest_fd)), but its
312	the fastest backend for a low number of fds.	373	usually the fastest backend for a low number of (low-numbered :) fds.
		374
		375	To get good performance out of this backend you need a high amount of
		376	parallelism (most of the file descriptors should be busy). If you are
		377	writing a server, you should C<accept ()> in a loop to accept as many
		378	connections as possible during one iteration. You might also want to have
		379	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		380	readiness notifications you get per iteration.
		381
		382	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		383	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		384	C<exceptfds> set on that platform).
313		385
314	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	386	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
315		387
316	And this is your standard poll(2) backend. It's more complicated than	388	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	389	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	390	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).	391	considerably with a lot of inactive fds). It scales similarly to select,
		392	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		393	performance tips.
		394
		395	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		396	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
320		397
321	=item C<EVBACKEND_EPOLL> (value 4, Linux)	398	=item C<EVBACKEND_EPOLL> (value 4, Linux)
322		399
323	For few fds, this backend is a bit little slower than poll and select,	400	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	401	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),	402	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	403	epoll scales either O(1) or O(active_fds).
327	of shortcomings, such as silently dropping events in some hard-to-detect	404
328	cases and rewiring a syscall per fd change, no fork support and bad	405	The epoll mechanism deserves honorable mention as the most misdesigned
329	support for dup:	406	of the more advanced event mechanisms: mere annoyances include silently
		407	dropping file descriptors, requiring a system call per change per file
		408	descriptor (and unnecessary guessing of parameters), problems with dup and
		409	so on. The biggest issue is fork races, however - if a program forks then
		410	I<both> parent and child process have to recreate the epoll set, which can
		411	take considerable time (one syscall per file descriptor) and is of course
		412	hard to detect.
		413
		414	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		415	of course I<doesn't>, and epoll just loves to report events for totally
		416	I<different> file descriptors (even already closed ones, so one cannot
		417	even remove them from the set) than registered in the set (especially
		418	on SMP systems). Libev tries to counter these spurious notifications by
		419	employing an additional generation counter and comparing that against the
		420	events to filter out spurious ones, recreating the set when required.
330		421
331	While stopping, setting and starting an I/O watcher in the same iteration	422	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	423	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	424	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	425	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
335	very well if you register events for both fds.	426	file descriptors might not work very well if you register events for both
		427	file descriptors.
336		428
337	Please note that epoll sometimes generates spurious notifications, so you	429	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	430	watchers for a file descriptor until it has been closed, if possible,
339	(or space) is available.	431	i.e. keep at least one watcher active per fd at all times. Stopping and
		432	starting a watcher (without re-setting it) also usually doesn't cause
		433	extra overhead. A fork can both result in spurious notifications as well
		434	as in libev having to destroy and recreate the epoll object, which can
		435	take considerable time and thus should be avoided.
		436
		437	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		438	faster than epoll for maybe up to a hundred file descriptors, depending on
		439	the usage. So sad.
		440
		441	While nominally embeddable in other event loops, this feature is broken in
		442	all kernel versions tested so far.
		443
		444	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		445	C<EVBACKEND_POLL>.
340		446
341	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	447	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
342		448
343	Kqueue deserves special mention, as at the time of this writing, it	449	Kqueue deserves special mention, as at the time of this writing, it
344	was broken on all BSDs except NetBSD (usually it doesn't work reliably	450	was broken on all BSDs except NetBSD (usually it doesn't work reliably
345	with anything but sockets and pipes, except on Darwin, where of course	451	with anything but sockets and pipes, except on Darwin, where of course
346	it's completely useless). For this reason it's not being "autodetected"	452	it's completely useless). Unlike epoll, however, whose brokenness
		453	is by design, these kqueue bugs can (and eventually will) be fixed
		454	without API changes to existing programs. For this reason it's not being
347	unless you explicitly specify it explicitly in the flags (i.e. using	455	"auto-detected" unless you explicitly specify it in the flags (i.e. using
348	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)	456	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
349	system like NetBSD.	457	system like NetBSD.
350		458
351	You still can embed kqueue into a normal poll or select backend and use it	459	You still can embed kqueue into a normal poll or select backend and use it
352	only for sockets (after having made sure that sockets work with kqueue on	460	only for sockets (after having made sure that sockets work with kqueue on
353	the target platform). See C<ev_embed> watchers for more info.	461	the target platform). See C<ev_embed> watchers for more info.
354		462
355	It scales in the same way as the epoll backend, but the interface to the	463	It scales in the same way as the epoll backend, but the interface to the
356	kernel is more efficient (which says nothing about its actual speed, of	464	kernel is more efficient (which says nothing about its actual speed, of
357	course). While stopping, setting and starting an I/O watcher does never	465	course). While stopping, setting and starting an I/O watcher does never
358	cause an extra syscall as with C<EVBACKEND_EPOLL>, it still adds up to	466	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
359	two event changes per incident, support for C<fork ()> is very bad and it	467	two event changes per incident. Support for C<fork ()> is very bad (but
360	drops fds silently in similarly hard-to-detect cases.	468	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		469	cases
		470
		471	This backend usually performs well under most conditions.
		472
		473	While nominally embeddable in other event loops, this doesn't work
		474	everywhere, so you might need to test for this. And since it is broken
		475	almost everywhere, you should only use it when you have a lot of sockets
		476	(for which it usually works), by embedding it into another event loop
		477	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
		478	also broken on OS X)) and, did I mention it, using it only for sockets.
		479
		480	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		481	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		482	C<NOTE_EOF>.
361		483
362	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	484	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
363		485
364	This is not implemented yet (and might never be).	486	This is not implemented yet (and might never be, unless you send me an
		487	implementation). According to reports, C</dev/poll> only supports sockets
		488	and is not embeddable, which would limit the usefulness of this backend
		489	immensely.
365		490
366	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	491	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
367		492
368	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	493	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
369	it's really slow, but it still scales very well (O(active_fds)).	494	it's really slow, but it still scales very well (O(active_fds)).
370		495
371	Please note that solaris event ports can deliver a lot of spurious	496	Please note that Solaris event ports can deliver a lot of spurious
372	notifications, so you need to use non-blocking I/O or other means to avoid	497	notifications, so you need to use non-blocking I/O or other means to avoid
373	blocking when no data (or space) is available.	498	blocking when no data (or space) is available.
		499
		500	While this backend scales well, it requires one system call per active
		501	file descriptor per loop iteration. For small and medium numbers of file
		502	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		503	might perform better.
		504
		505	On the positive side, with the exception of the spurious readiness
		506	notifications, this backend actually performed fully to specification
		507	in all tests and is fully embeddable, which is a rare feat among the
		508	OS-specific backends (I vastly prefer correctness over speed hacks).
		509
		510	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		511	C<EVBACKEND_POLL>.
374		512
375	=item C<EVBACKEND_ALL>	513	=item C<EVBACKEND_ALL>
376		514
377	Try all backends (even potentially broken ones that wouldn't be tried	515	Try all backends (even potentially broken ones that wouldn't be tried
378	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	516	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
379	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	517	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
380		518
		519	It is definitely not recommended to use this flag.
		520
381	=back	521	=back
382		522
383	If one or more of these are ored into the flags value, then only these	523	If one or more of these are or'ed into the flags value, then only these
384	backends will be tried (in the reverse order as given here). If none are	524	backends will be tried (in the reverse order as listed here). If none are
385	specified, most compiled-in backend will be tried, usually in reverse	525	specified, all backends in C<ev_recommended_backends ()> will be tried.
386	order of their flag values :)
387		526
388	The most typical usage is like this:	527	Example: This is the most typical usage.
389		528
390	if (!ev_default_loop (0))	529	if (!ev_default_loop (0))
391	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	530	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
392		531
393	Restrict libev to the select and poll backends, and do not allow	532	Example: Restrict libev to the select and poll backends, and do not allow
394	environment settings to be taken into account:	533	environment settings to be taken into account:
395		534
396	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	535	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
397		536
398	Use whatever libev has to offer, but make sure that kqueue is used if	537	Example: Use whatever libev has to offer, but make sure that kqueue is
399	available (warning, breaks stuff, best use only with your own private	538	used if available (warning, breaks stuff, best use only with your own
400	event loop and only if you know the OS supports your types of fds):	539	private event loop and only if you know the OS supports your types of
		540	fds):
401		541
402	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	542	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
403		543
404	=item struct ev_loop *ev_loop_new (unsigned int flags)	544	=item struct ev_loop *ev_loop_new (unsigned int flags)
405		545
406	Similar to C<ev_default_loop>, but always creates a new event loop that is	546	Similar to C<ev_default_loop>, but always creates a new event loop that is
407	always distinct from the default loop. Unlike the default loop, it cannot	547	always distinct from the default loop. Unlike the default loop, it cannot
408	handle signal and child watchers, and attempts to do so will be greeted by	548	handle signal and child watchers, and attempts to do so will be greeted by
409	undefined behaviour (or a failed assertion if assertions are enabled).	549	undefined behaviour (or a failed assertion if assertions are enabled).
410		550
		551	Note that this function I<is> thread-safe, and the recommended way to use
		552	libev with threads is indeed to create one loop per thread, and using the
		553	default loop in the "main" or "initial" thread.
		554
411	Example: Try to create a event loop that uses epoll and nothing else.	555	Example: Try to create a event loop that uses epoll and nothing else.
412		556
413	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	557	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
414	if (!epoller)	558	if (!epoller)
415	fatal ("no epoll found here, maybe it hides under your chair");	559	fatal ("no epoll found here, maybe it hides under your chair");
416		560
417	=item ev_default_destroy ()	561	=item ev_default_destroy ()
418		562
419	Destroys the default loop again (frees all memory and kernel state	563	Destroys the default loop again (frees all memory and kernel state
420	etc.). None of the active event watchers will be stopped in the normal	564	etc.). None of the active event watchers will be stopped in the normal
421	sense, so e.g. C<ev_is_active> might still return true. It is your	565	sense, so e.g. C<ev_is_active> might still return true. It is your
422	responsibility to either stop all watchers cleanly yoursef I<before>	566	responsibility to either stop all watchers cleanly yourself I<before>
423	calling this function, or cope with the fact afterwards (which is usually	567	calling this function, or cope with the fact afterwards (which is usually
424	the easiest thing, you can just ignore the watchers and/or C<free ()> them	568	the easiest thing, you can just ignore the watchers and/or C<free ()> them
425	for example).	569	for example).
426		570
427	Note that certain global state, such as signal state, will not be freed by	571	Note that certain global state, such as signal state (and installed signal
428	this function, and related watchers (such as signal and child watchers)	572	handlers), will not be freed by this function, and related watchers (such
429	would need to be stopped manually.	573	as signal and child watchers) would need to be stopped manually.
430		574
431	In general it is not advisable to call this function except in the	575	In general it is not advisable to call this function except in the
432	rare occasion where you really need to free e.g. the signal handling	576	rare occasion where you really need to free e.g. the signal handling
433	pipe fds. If you need dynamically allocated loops it is better to use	577	pipe fds. If you need dynamically allocated loops it is better to use
434	C<ev_loop_new> and C<ev_loop_destroy>).	578	C<ev_loop_new> and C<ev_loop_destroy>).
…		…
438	Like C<ev_default_destroy>, but destroys an event loop created by an	582	Like C<ev_default_destroy>, but destroys an event loop created by an
439	earlier call to C<ev_loop_new>.	583	earlier call to C<ev_loop_new>.
440		584
441	=item ev_default_fork ()	585	=item ev_default_fork ()
442		586
		587	This function sets a flag that causes subsequent C<ev_loop> iterations
443	This function reinitialises the kernel state for backends that have	588	to reinitialise the kernel state for backends that have one. Despite the
444	one. Despite the name, you can call it anytime, but it makes most sense	589	name, you can call it anytime, but it makes most sense after forking, in
445	after forking, in either the parent or child process (or both, but that	590	the child process (or both child and parent, but that again makes little
446	again makes little sense).	591	sense). You I<must> call it in the child before using any of the libev
		592	functions, and it will only take effect at the next C<ev_loop> iteration.
447		593
448	You I<must> call this function in the child process after forking if and	594	On the other hand, you only need to call this function in the child
449	only if you want to use the event library in both processes. If you just	595	process if and only if you want to use the event library in the child. If
450	fork+exec, you don't have to call it.	596	you just fork+exec, you don't have to call it at all.
451		597
452	The function itself is quite fast and it's usually not a problem to call	598	The function itself is quite fast and it's usually not a problem to call
453	it just in case after a fork. To make this easy, the function will fit in	599	it just in case after a fork. To make this easy, the function will fit in
454	quite nicely into a call to C<pthread_atfork>:	600	quite nicely into a call to C<pthread_atfork>:
455		601
456	pthread_atfork (0, 0, ev_default_fork);	602	pthread_atfork (0, 0, ev_default_fork);
457		603
458	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
459	without calling this function, so if you force one of those backends you
460	do not need to care.
461
462	=item ev_loop_fork (loop)	604	=item ev_loop_fork (loop)
463		605
464	Like C<ev_default_fork>, but acts on an event loop created by	606	Like C<ev_default_fork>, but acts on an event loop created by
465	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	607	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
466	after fork, and how you do this is entirely your own problem.	608	after fork that you want to re-use in the child, and how you do this is
		609	entirely your own problem.
		610
		611	=item int ev_is_default_loop (loop)
		612
		613	Returns true when the given loop is, in fact, the default loop, and false
		614	otherwise.
467		615
468	=item unsigned int ev_loop_count (loop)	616	=item unsigned int ev_loop_count (loop)
469		617
470	Returns the count of loop iterations for the loop, which is identical to	618	Returns the count of loop iterations for the loop, which is identical to
471	the number of times libev did poll for new events. It starts at C<0> and	619	the number of times libev did poll for new events. It starts at C<0> and
472	happily wraps around with enough iterations.	620	happily wraps around with enough iterations.
473		621
474	This value can sometimes be useful as a generation counter of sorts (it	622	This value can sometimes be useful as a generation counter of sorts (it
475	"ticks" the number of loop iterations), as it roughly corresponds with	623	"ticks" the number of loop iterations), as it roughly corresponds with
476	C<ev_prepare> and C<ev_check> calls.	624	C<ev_prepare> and C<ev_check> calls.
		625
		626	=item unsigned int ev_loop_depth (loop)
		627
		628	Returns the number of times C<ev_loop> was entered minus the number of
		629	times C<ev_loop> was exited, in other words, the recursion depth.
		630
		631	Outside C<ev_loop>, this number is zero. In a callback, this number is
		632	C<1>, unless C<ev_loop> was invoked recursively (or from another thread),
		633	in which case it is higher.
		634
		635	Leaving C<ev_loop> abnormally (setjmp/longjmp, cancelling the thread
		636	etc.), doesn't count as exit.
477		637
478	=item unsigned int ev_backend (loop)	638	=item unsigned int ev_backend (loop)
479		639
480	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	640	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
481	use.	641	use.
…		…
486	received events and started processing them. This timestamp does not	646	received events and started processing them. This timestamp does not
487	change as long as callbacks are being processed, and this is also the base	647	change as long as callbacks are being processed, and this is also the base
488	time used for relative timers. You can treat it as the timestamp of the	648	time used for relative timers. You can treat it as the timestamp of the
489	event occurring (or more correctly, libev finding out about it).	649	event occurring (or more correctly, libev finding out about it).
490		650
		651	=item ev_now_update (loop)
		652
		653	Establishes the current time by querying the kernel, updating the time
		654	returned by C<ev_now ()> in the progress. This is a costly operation and
		655	is usually done automatically within C<ev_loop ()>.
		656
		657	This function is rarely useful, but when some event callback runs for a
		658	very long time without entering the event loop, updating libev's idea of
		659	the current time is a good idea.
		660
		661	See also L<The special problem of time updates> in the C<ev_timer> section.
		662
		663	=item ev_suspend (loop)
		664
		665	=item ev_resume (loop)
		666
		667	These two functions suspend and resume a loop, for use when the loop is
		668	not used for a while and timeouts should not be processed.
		669
		670	A typical use case would be an interactive program such as a game: When
		671	the user presses C<^Z> to suspend the game and resumes it an hour later it
		672	would be best to handle timeouts as if no time had actually passed while
		673	the program was suspended. This can be achieved by calling C<ev_suspend>
		674	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		675	C<ev_resume> directly afterwards to resume timer processing.
		676
		677	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		678	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		679	will be rescheduled (that is, they will lose any events that would have
		680	occured while suspended).
		681
		682	After calling C<ev_suspend> you B<must not> call I<any> function on the
		683	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		684	without a previous call to C<ev_suspend>.
		685
		686	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		687	event loop time (see C<ev_now_update>).
		688
491	=item ev_loop (loop, int flags)	689	=item ev_loop (loop, int flags)
492		690
493	Finally, this is it, the event handler. This function usually is called	691	Finally, this is it, the event handler. This function usually is called
494	after you initialised all your watchers and you want to start handling	692	after you initialised all your watchers and you want to start handling
495	events.	693	events.
…		…
497	If the flags argument is specified as C<0>, it will not return until	695	If the flags argument is specified as C<0>, it will not return until
498	either no event watchers are active anymore or C<ev_unloop> was called.	696	either no event watchers are active anymore or C<ev_unloop> was called.
499		697
500	Please note that an explicit C<ev_unloop> is usually better than	698	Please note that an explicit C<ev_unloop> is usually better than
501	relying on all watchers to be stopped when deciding when a program has	699	relying on all watchers to be stopped when deciding when a program has
502	finished (especially in interactive programs), but having a program that	700	finished (especially in interactive programs), but having a program
503	automatically loops as long as it has to and no longer by virtue of	701	that automatically loops as long as it has to and no longer by virtue
504	relying on its watchers stopping correctly is a thing of beauty.	702	of relying on its watchers stopping correctly, that is truly a thing of
		703	beauty.
505		704
506	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	705	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
507	those events and any outstanding ones, but will not block your process in	706	those events and any already outstanding ones, but will not block your
508	case there are no events and will return after one iteration of the loop.	707	process in case there are no events and will return after one iteration of
		708	the loop.
509		709
510	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	710	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
511	neccessary) and will handle those and any outstanding ones. It will block	711	necessary) and will handle those and any already outstanding ones. It
512	your process until at least one new event arrives, and will return after	712	will block your process until at least one new event arrives (which could
513	one iteration of the loop. This is useful if you are waiting for some	713	be an event internal to libev itself, so there is no guarantee that a
514	external event in conjunction with something not expressible using other	714	user-registered callback will be called), and will return after one
		715	iteration of the loop.
		716
		717	This is useful if you are waiting for some external event in conjunction
		718	with something not expressible using other libev watchers (i.e. "roll your
515	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	719	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
516	usually a better approach for this kind of thing.	720	usually a better approach for this kind of thing.
517		721
518	Here are the gory details of what C<ev_loop> does:	722	Here are the gory details of what C<ev_loop> does:
519		723
520	- Before the first iteration, call any pending watchers.	724	- Before the first iteration, call any pending watchers.
521	* If there are no active watchers (reference count is zero), return.	725	* If EVFLAG_FORKCHECK was used, check for a fork.
522	- Queue all prepare watchers and then call all outstanding watchers.	726	- If a fork was detected (by any means), queue and call all fork watchers.
		727	- Queue and call all prepare watchers.
523	- If we have been forked, recreate the kernel state.	728	- If we have been forked, detach and recreate the kernel state
		729	as to not disturb the other process.
524	- Update the kernel state with all outstanding changes.	730	- Update the kernel state with all outstanding changes.
525	- Update the "event loop time".	731	- Update the "event loop time" (ev_now ()).
526	- Calculate for how long to block.	732	- Calculate for how long to sleep or block, if at all
		733	(active idle watchers, EVLOOP_NONBLOCK or not having
		734	any active watchers at all will result in not sleeping).
		735	- Sleep if the I/O and timer collect interval say so.
527	- Block the process, waiting for any events.	736	- Block the process, waiting for any events.
528	- Queue all outstanding I/O (fd) events.	737	- Queue all outstanding I/O (fd) events.
529	- Update the "event loop time" and do time jump handling.	738	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
530	- Queue all outstanding timers.	739	- Queue all expired timers.
531	- Queue all outstanding periodics.	740	- Queue all expired periodics.
532	- If no events are pending now, queue all idle watchers.	741	- Unless any events are pending now, queue all idle watchers.
533	- Queue all check watchers.	742	- Queue all check watchers.
534	- Call all queued watchers in reverse order (i.e. check watchers first).	743	- Call all queued watchers in reverse order (i.e. check watchers first).
535	Signals and child watchers are implemented as I/O watchers, and will	744	Signals and child watchers are implemented as I/O watchers, and will
536	be handled here by queueing them when their watcher gets executed.	745	be handled here by queueing them when their watcher gets executed.
537	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	746	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
538	were used, return, otherwise continue with step *.	747	were used, or there are no active watchers, return, otherwise
		748	continue with step *.
539		749
540	Example: Queue some jobs and then loop until no events are outsanding	750	Example: Queue some jobs and then loop until no events are outstanding
541	anymore.	751	anymore.
542		752
543	... queue jobs here, make sure they register event watchers as long	753	... queue jobs here, make sure they register event watchers as long
544	... as they still have work to do (even an idle watcher will do..)	754	... as they still have work to do (even an idle watcher will do..)
545	ev_loop (my_loop, 0);	755	ev_loop (my_loop, 0);
546	... jobs done. yeah!	756	... jobs done or somebody called unloop. yeah!
547		757
548	=item ev_unloop (loop, how)	758	=item ev_unloop (loop, how)
549		759
550	Can be used to make a call to C<ev_loop> return early (but only after it	760	Can be used to make a call to C<ev_loop> return early (but only after it
551	has processed all outstanding events). The C<how> argument must be either	761	has processed all outstanding events). The C<how> argument must be either
552	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	762	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
553	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	763	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
554		764
		765	This "unloop state" will be cleared when entering C<ev_loop> again.
		766
		767	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
		768
555	=item ev_ref (loop)	769	=item ev_ref (loop)
556		770
557	=item ev_unref (loop)	771	=item ev_unref (loop)
558		772
559	Ref/unref can be used to add or remove a reference count on the event	773	Ref/unref can be used to add or remove a reference count on the event
560	loop: Every watcher keeps one reference, and as long as the reference	774	loop: Every watcher keeps one reference, and as long as the reference
561	count is nonzero, C<ev_loop> will not return on its own. If you have	775	count is nonzero, C<ev_loop> will not return on its own.
		776
562	a watcher you never unregister that should not keep C<ev_loop> from	777	If you have a watcher you never unregister that should not keep C<ev_loop>
563	returning, ev_unref() after starting, and ev_ref() before stopping it. For	778	from returning, call ev_unref() after starting, and ev_ref() before
		779	stopping it.
		780
564	example, libev itself uses this for its internal signal pipe: It is not	781	As an example, libev itself uses this for its internal signal pipe: It
565	visible to the libev user and should not keep C<ev_loop> from exiting if	782	is not visible to the libev user and should not keep C<ev_loop> from
566	no event watchers registered by it are active. It is also an excellent	783	exiting if no event watchers registered by it are active. It is also an
567	way to do this for generic recurring timers or from within third-party	784	excellent way to do this for generic recurring timers or from within
568	libraries. Just remember to I<unref after start> and I<ref before stop>.	785	third-party libraries. Just remember to I<unref after start> and I<ref
		786	before stop> (but only if the watcher wasn't active before, or was active
		787	before, respectively. Note also that libev might stop watchers itself
		788	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		789	in the callback).
569		790
570	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	791	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
571	running when nothing else is active.	792	running when nothing else is active.
572		793
573	struct ev_signal exitsig;	794	ev_signal exitsig;
574	ev_signal_init (&exitsig, sig_cb, SIGINT);	795	ev_signal_init (&exitsig, sig_cb, SIGINT);
575	ev_signal_start (loop, &exitsig);	796	ev_signal_start (loop, &exitsig);
576	evf_unref (loop);	797	evf_unref (loop);
577		798
578	Example: For some weird reason, unregister the above signal handler again.	799	Example: For some weird reason, unregister the above signal handler again.
579		800
580	ev_ref (loop);	801	ev_ref (loop);
581	ev_signal_stop (loop, &exitsig);	802	ev_signal_stop (loop, &exitsig);
582		803
583	=item ev_set_io_collect_interval (loop, ev_tstamp interval)	804	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
584		805
585	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)	806	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
586		807
587	These advanced functions influence the time that libev will spend waiting	808	These advanced functions influence the time that libev will spend waiting
588	for events. Both are by default C<0>, meaning that libev will try to	809	for events. Both time intervals are by default C<0>, meaning that libev
589	invoke timer/periodic callbacks and I/O callbacks with minimum latency.	810	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		811	latency.
590		812
591	Setting these to a higher value (the C<interval> I<must> be >= C<0>)	813	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
592	allows libev to delay invocation of I/O and timer/periodic callbacks to	814	allows libev to delay invocation of I/O and timer/periodic callbacks
593	increase efficiency of loop iterations.	815	to increase efficiency of loop iterations (or to increase power-saving
		816	opportunities).
594		817
595	The background is that sometimes your program runs just fast enough to	818	The idea is that sometimes your program runs just fast enough to handle
596	handle one (or very few) event(s) per loop iteration. While this makes	819	one (or very few) event(s) per loop iteration. While this makes the
597	the program responsive, it also wastes a lot of CPU time to poll for new	820	program responsive, it also wastes a lot of CPU time to poll for new
598	events, especially with backends like C<select ()> which have a high	821	events, especially with backends like C<select ()> which have a high
599	overhead for the actual polling but can deliver many events at once.	822	overhead for the actual polling but can deliver many events at once.
600		823
601	By setting a higher I<io collect interval> you allow libev to spend more	824	By setting a higher I<io collect interval> you allow libev to spend more
602	time collecting I/O events, so you can handle more events per iteration,	825	time collecting I/O events, so you can handle more events per iteration,
603	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	826	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
604	C<ev_timer>) will be not affected. Setting this to a non-null value will	827	C<ev_timer>) will be not affected. Setting this to a non-null value will
605	introduce an additional C<ev_sleep ()> call into most loop iterations.	828	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		829	sleep time ensures that libev will not poll for I/O events more often then
		830	once per this interval, on average.
606		831
607	Likewise, by setting a higher I<timeout collect interval> you allow libev	832	Likewise, by setting a higher I<timeout collect interval> you allow libev
608	to spend more time collecting timeouts, at the expense of increased	833	to spend more time collecting timeouts, at the expense of increased
609	latency (the watcher callback will be called later). C<ev_io> watchers	834	latency/jitter/inexactness (the watcher callback will be called
610	will not be affected. Setting this to a non-null value will not introduce	835	later). C<ev_io> watchers will not be affected. Setting this to a non-null
611	any overhead in libev.	836	value will not introduce any overhead in libev.
612		837
613	Many (busy) programs can usually benefit by setting the io collect	838	Many (busy) programs can usually benefit by setting the I/O collect
614	interval to a value near C<0.1> or so, which is often enough for	839	interval to a value near C<0.1> or so, which is often enough for
615	interactive servers (of course not for games), likewise for timeouts. It	840	interactive servers (of course not for games), likewise for timeouts. It
616	usually doesn't make much sense to set it to a lower value than C<0.01>,	841	usually doesn't make much sense to set it to a lower value than C<0.01>,
617	as this approsaches the timing granularity of most systems.	842	as this approaches the timing granularity of most systems. Note that if
		843	you do transactions with the outside world and you can't increase the
		844	parallelity, then this setting will limit your transaction rate (if you
		845	need to poll once per transaction and the I/O collect interval is 0.01,
		846	then you can't do more than 100 transations per second).
		847
		848	Setting the I<timeout collect interval> can improve the opportunity for
		849	saving power, as the program will "bundle" timer callback invocations that
		850	are "near" in time together, by delaying some, thus reducing the number of
		851	times the process sleeps and wakes up again. Another useful technique to
		852	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		853	they fire on, say, one-second boundaries only.
		854
		855	Example: we only need 0.1s timeout granularity, and we wish not to poll
		856	more often than 100 times per second:
		857
		858	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		859	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		860
		861	=item ev_invoke_pending (loop)
		862
		863	This call will simply invoke all pending watchers while resetting their
		864	pending state. Normally, C<ev_loop> does this automatically when required,
		865	but when overriding the invoke callback this call comes handy.
		866
		867	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		868
		869	This overrides the invoke pending functionality of the loop: Instead of
		870	invoking all pending watchers when there are any, C<ev_loop> will call
		871	this callback instead. This is useful, for example, when you want to
		872	invoke the actual watchers inside another context (another thread etc.).
		873
		874	If you want to reset the callback, use C<ev_invoke_pending> as new
		875	callback.
		876
		877	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		878
		879	Sometimes you want to share the same loop between multiple threads. This
		880	can be done relatively simply by putting mutex_lock/unlock calls around
		881	each call to a libev function.
		882
		883	However, C<ev_loop> can run an indefinite time, so it is not feasible to
		884	wait for it to return. One way around this is to wake up the loop via
		885	C<ev_unloop> and C<av_async_send>, another way is to set these I<release>
		886	and I<acquire> callbacks on the loop.
		887
		888	When set, then C<release> will be called just before the thread is
		889	suspended waiting for new events, and C<acquire> is called just
		890	afterwards.
		891
		892	Ideally, C<release> will just call your mutex_unlock function, and
		893	C<acquire> will just call the mutex_lock function again.
		894
		895	=item ev_set_userdata (loop, void *data)
		896
		897	=item ev_userdata (loop)
		898
		899	Set and retrieve a single C<void *> associated with a loop. When
		900	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		901	C<0.>
		902
		903	These two functions can be used to associate arbitrary data with a loop,
		904	and are intended solely for the C<invoke_pending_cb>, C<release> and
		905	C<acquire> callbacks described above, but of course can be (ab-)used for
		906	any other purpose as well.
		907
		908	=item ev_loop_verify (loop)
		909
		910	This function only does something when C<EV_VERIFY> support has been
		911	compiled in, which is the default for non-minimal builds. It tries to go
		912	through all internal structures and checks them for validity. If anything
		913	is found to be inconsistent, it will print an error message to standard
		914	error and call C<abort ()>.
		915
		916	This can be used to catch bugs inside libev itself: under normal
		917	circumstances, this function will never abort as of course libev keeps its
		918	data structures consistent.
618		919
619	=back	920	=back
620		921
621		922
622	=head1 ANATOMY OF A WATCHER	923	=head1 ANATOMY OF A WATCHER
		924
		925	In the following description, uppercase C<TYPE> in names stands for the
		926	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		927	watchers and C<ev_io_start> for I/O watchers.
623		928
624	A watcher is a structure that you create and register to record your	929	A watcher is a structure that you create and register to record your
625	interest in some event. For instance, if you want to wait for STDIN to	930	interest in some event. For instance, if you want to wait for STDIN to
626	become readable, you would create an C<ev_io> watcher for that:	931	become readable, you would create an C<ev_io> watcher for that:
627		932
628	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	933	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
629	{	934	{
630	ev_io_stop (w);	935	ev_io_stop (w);
631	ev_unloop (loop, EVUNLOOP_ALL);	936	ev_unloop (loop, EVUNLOOP_ALL);
632	}	937	}
633		938
634	struct ev_loop *loop = ev_default_loop (0);	939	struct ev_loop *loop = ev_default_loop (0);
		940
635	struct ev_io stdin_watcher;	941	ev_io stdin_watcher;
		942
636	ev_init (&stdin_watcher, my_cb);	943	ev_init (&stdin_watcher, my_cb);
637	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	944	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
638	ev_io_start (loop, &stdin_watcher);	945	ev_io_start (loop, &stdin_watcher);
		946
639	ev_loop (loop, 0);	947	ev_loop (loop, 0);
640		948
641	As you can see, you are responsible for allocating the memory for your	949	As you can see, you are responsible for allocating the memory for your
642	watcher structures (and it is usually a bad idea to do this on the stack,	950	watcher structures (and it is I<usually> a bad idea to do this on the
643	although this can sometimes be quite valid).	951	stack).
		952
		953	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		954	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
644		955
645	Each watcher structure must be initialised by a call to C<ev_init	956	Each watcher structure must be initialised by a call to C<ev_init
646	(watcher *, callback)>, which expects a callback to be provided. This	957	(watcher *, callback)>, which expects a callback to be provided. This
647	callback gets invoked each time the event occurs (or, in the case of io	958	callback gets invoked each time the event occurs (or, in the case of I/O
648	watchers, each time the event loop detects that the file descriptor given	959	watchers, each time the event loop detects that the file descriptor given
649	is readable and/or writable).	960	is readable and/or writable).
650		961
651	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	962	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
652	with arguments specific to this watcher type. There is also a macro	963	macro to configure it, with arguments specific to the watcher type. There
653	to combine initialisation and setting in one call: C<< ev_<type>_init	964	is also a macro to combine initialisation and setting in one call: C<<
654	(watcher *, callback, ...) >>.	965	ev_TYPE_init (watcher *, callback, ...) >>.
655		966
656	To make the watcher actually watch out for events, you have to start it	967	To make the watcher actually watch out for events, you have to start it
657	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	968	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
658	*) >>), and you can stop watching for events at any time by calling the	969	*) >>), and you can stop watching for events at any time by calling the
659	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	970	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
660		971
661	As long as your watcher is active (has been started but not stopped) you	972	As long as your watcher is active (has been started but not stopped) you
662	must not touch the values stored in it. Most specifically you must never	973	must not touch the values stored in it. Most specifically you must never
663	reinitialise it or call its C<set> macro.	974	reinitialise it or call its C<ev_TYPE_set> macro.
664		975
665	Each and every callback receives the event loop pointer as first, the	976	Each and every callback receives the event loop pointer as first, the
666	registered watcher structure as second, and a bitset of received events as	977	registered watcher structure as second, and a bitset of received events as
667	third argument.	978	third argument.
668		979
…		…
722	=item C<EV_FORK>	1033	=item C<EV_FORK>
723		1034
724	The event loop has been resumed in the child process after fork (see	1035	The event loop has been resumed in the child process after fork (see
725	C<ev_fork>).	1036	C<ev_fork>).
726		1037
		1038	=item C<EV_ASYNC>
		1039
		1040	The given async watcher has been asynchronously notified (see C<ev_async>).
		1041
		1042	=item C<EV_CUSTOM>
		1043
		1044	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1045	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1046
727	=item C<EV_ERROR>	1047	=item C<EV_ERROR>
728		1048
729	An unspecified error has occured, the watcher has been stopped. This might	1049	An unspecified error has occurred, the watcher has been stopped. This might
730	happen because the watcher could not be properly started because libev	1050	happen because the watcher could not be properly started because libev
731	ran out of memory, a file descriptor was found to be closed or any other	1051	ran out of memory, a file descriptor was found to be closed or any other
		1052	problem. Libev considers these application bugs.
		1053
732	problem. You best act on it by reporting the problem and somehow coping	1054	You best act on it by reporting the problem and somehow coping with the
733	with the watcher being stopped.	1055	watcher being stopped. Note that well-written programs should not receive
		1056	an error ever, so when your watcher receives it, this usually indicates a
		1057	bug in your program.
734		1058
735	Libev will usually signal a few "dummy" events together with an error,	1059	Libev will usually signal a few "dummy" events together with an error, for
736	for example it might indicate that a fd is readable or writable, and if	1060	example it might indicate that a fd is readable or writable, and if your
737	your callbacks is well-written it can just attempt the operation and cope	1061	callbacks is well-written it can just attempt the operation and cope with
738	with the error from read() or write(). This will not work in multithreaded	1062	the error from read() or write(). This will not work in multi-threaded
739	programs, though, so beware.	1063	programs, though, as the fd could already be closed and reused for another
		1064	thing, so beware.
740		1065
741	=back	1066	=back
742		1067
743	=head2 GENERIC WATCHER FUNCTIONS	1068	=head2 GENERIC WATCHER FUNCTIONS
744
745	In the following description, C<TYPE> stands for the watcher type,
746	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
747		1069
748	=over 4	1070	=over 4
749		1071
750	=item C<ev_init> (ev_TYPE *watcher, callback)	1072	=item C<ev_init> (ev_TYPE *watcher, callback)
751		1073
…		…
757	which rolls both calls into one.	1079	which rolls both calls into one.
758		1080
759	You can reinitialise a watcher at any time as long as it has been stopped	1081	You can reinitialise a watcher at any time as long as it has been stopped
760	(or never started) and there are no pending events outstanding.	1082	(or never started) and there are no pending events outstanding.
761		1083
762	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1084	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
763	int revents)>.	1085	int revents)>.
		1086
		1087	Example: Initialise an C<ev_io> watcher in two steps.
		1088
		1089	ev_io w;
		1090	ev_init (&w, my_cb);
		1091	ev_io_set (&w, STDIN_FILENO, EV_READ);
764		1092
765	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1093	=item C<ev_TYPE_set> (ev_TYPE *, [args])
766		1094
767	This macro initialises the type-specific parts of a watcher. You need to	1095	This macro initialises the type-specific parts of a watcher. You need to
768	call C<ev_init> at least once before you call this macro, but you can	1096	call C<ev_init> at least once before you call this macro, but you can
…		…
771	difference to the C<ev_init> macro).	1099	difference to the C<ev_init> macro).
772		1100
773	Although some watcher types do not have type-specific arguments	1101	Although some watcher types do not have type-specific arguments
774	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1102	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
775		1103
		1104	See C<ev_init>, above, for an example.
		1105
776	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1106	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
777		1107
778	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1108	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
779	calls into a single call. This is the most convinient method to initialise	1109	calls into a single call. This is the most convenient method to initialise
780	a watcher. The same limitations apply, of course.	1110	a watcher. The same limitations apply, of course.
		1111
		1112	Example: Initialise and set an C<ev_io> watcher in one step.
		1113
		1114	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
781		1115
782	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1116	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
783		1117
784	Starts (activates) the given watcher. Only active watchers will receive	1118	Starts (activates) the given watcher. Only active watchers will receive
785	events. If the watcher is already active nothing will happen.	1119	events. If the watcher is already active nothing will happen.
786		1120
		1121	Example: Start the C<ev_io> watcher that is being abused as example in this
		1122	whole section.
		1123
		1124	ev_io_start (EV_DEFAULT_UC, &w);
		1125
787	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1126	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
788		1127
789	Stops the given watcher again (if active) and clears the pending	1128	Stops the given watcher if active, and clears the pending status (whether
		1129	the watcher was active or not).
		1130
790	status. It is possible that stopped watchers are pending (for example,	1131	It is possible that stopped watchers are pending - for example,
791	non-repeating timers are being stopped when they become pending), but	1132	non-repeating timers are being stopped when they become pending - but
792	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1133	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
793	you want to free or reuse the memory used by the watcher it is therefore a	1134	pending. If you want to free or reuse the memory used by the watcher it is
794	good idea to always call its C<ev_TYPE_stop> function.	1135	therefore a good idea to always call its C<ev_TYPE_stop> function.
795		1136
796	=item bool ev_is_active (ev_TYPE *watcher)	1137	=item bool ev_is_active (ev_TYPE *watcher)
797		1138
798	Returns a true value iff the watcher is active (i.e. it has been started	1139	Returns a true value iff the watcher is active (i.e. it has been started
799	and not yet been stopped). As long as a watcher is active you must not modify	1140	and not yet been stopped). As long as a watcher is active you must not modify
…		…
825	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1166	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
826	(default: C<-2>). Pending watchers with higher priority will be invoked	1167	(default: C<-2>). Pending watchers with higher priority will be invoked
827	before watchers with lower priority, but priority will not keep watchers	1168	before watchers with lower priority, but priority will not keep watchers
828	from being executed (except for C<ev_idle> watchers).	1169	from being executed (except for C<ev_idle> watchers).
829		1170
830	This means that priorities are I<only> used for ordering callback
831	invocation after new events have been received. This is useful, for
832	example, to reduce latency after idling, or more often, to bind two
833	watchers on the same event and make sure one is called first.
834
835	If you need to suppress invocation when higher priority events are pending	1171	If you need to suppress invocation when higher priority events are pending
836	you need to look at C<ev_idle> watchers, which provide this functionality.	1172	you need to look at C<ev_idle> watchers, which provide this functionality.
837		1173
838	You I<must not> change the priority of a watcher as long as it is active or	1174	You I<must not> change the priority of a watcher as long as it is active or
839	pending.	1175	pending.
840		1176
		1177	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1178	fine, as long as you do not mind that the priority value you query might
		1179	or might not have been clamped to the valid range.
		1180
841	The default priority used by watchers when no priority has been set is	1181	The default priority used by watchers when no priority has been set is
842	always C<0>, which is supposed to not be too high and not be too low :).	1182	always C<0>, which is supposed to not be too high and not be too low :).
843		1183
844	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1184	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
845	fine, as long as you do not mind that the priority value you query might	1185	priorities.
846	or might not have been adjusted to be within valid range.
847		1186
848	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1187	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
849		1188
850	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1189	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
851	C<loop> nor C<revents> need to be valid as long as the watcher callback	1190	C<loop> nor C<revents> need to be valid as long as the watcher callback
852	can deal with that fact.	1191	can deal with that fact, as both are simply passed through to the
		1192	callback.
853		1193
854	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1194	=item int ev_clear_pending (loop, ev_TYPE *watcher)
855		1195
856	If the watcher is pending, this function returns clears its pending status	1196	If the watcher is pending, this function clears its pending status and
857	and returns its C<revents> bitset (as if its callback was invoked). If the	1197	returns its C<revents> bitset (as if its callback was invoked). If the
858	watcher isn't pending it does nothing and returns C<0>.	1198	watcher isn't pending it does nothing and returns C<0>.
859		1199
		1200	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1201	callback to be invoked, which can be accomplished with this function.
		1202
860	=back	1203	=back
861		1204
862		1205
863	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1206	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
864		1207
865	Each watcher has, by default, a member C<void *data> that you can change	1208	Each watcher has, by default, a member C<void *data> that you can change
866	and read at any time, libev will completely ignore it. This can be used	1209	and read at any time: libev will completely ignore it. This can be used
867	to associate arbitrary data with your watcher. If you need more data and	1210	to associate arbitrary data with your watcher. If you need more data and
868	don't want to allocate memory and store a pointer to it in that data	1211	don't want to allocate memory and store a pointer to it in that data
869	member, you can also "subclass" the watcher type and provide your own	1212	member, you can also "subclass" the watcher type and provide your own
870	data:	1213	data:
871		1214
872	struct my_io	1215	struct my_io
873	{	1216	{
874	struct ev_io io;	1217	ev_io io;
875	int otherfd;	1218	int otherfd;
876	void *somedata;	1219	void *somedata;
877	struct whatever *mostinteresting;	1220	struct whatever *mostinteresting;
878	}	1221	};
		1222
		1223	...
		1224	struct my_io w;
		1225	ev_io_init (&w.io, my_cb, fd, EV_READ);
879		1226
880	And since your callback will be called with a pointer to the watcher, you	1227	And since your callback will be called with a pointer to the watcher, you
881	can cast it back to your own type:	1228	can cast it back to your own type:
882		1229
883	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1230	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
884	{	1231	{
885	struct my_io *w = (struct my_io *)w_;	1232	struct my_io *w = (struct my_io *)w_;
886	...	1233	...
887	}	1234	}
888		1235
889	More interesting and less C-conformant ways of casting your callback type	1236	More interesting and less C-conformant ways of casting your callback type
890	instead have been omitted.	1237	instead have been omitted.
891		1238
892	Another common scenario is having some data structure with multiple	1239	Another common scenario is to use some data structure with multiple
893	watchers:	1240	embedded watchers:
894		1241
895	struct my_biggy	1242	struct my_biggy
896	{	1243	{
897	int some_data;	1244	int some_data;
898	ev_timer t1;	1245	ev_timer t1;
899	ev_timer t2;	1246	ev_timer t2;
900	}	1247	}
901		1248
902	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1249	In this case getting the pointer to C<my_biggy> is a bit more
903	you need to use C<offsetof>:	1250	complicated: Either you store the address of your C<my_biggy> struct
		1251	in the C<data> member of the watcher (for woozies), or you need to use
		1252	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1253	programmers):
904		1254
905	#include <stddef.h>	1255	#include <stddef.h>
906		1256
907	static void	1257	static void
908	t1_cb (EV_P_ struct ev_timer *w, int revents)	1258	t1_cb (EV_P_ ev_timer *w, int revents)
909	{	1259	{
910	struct my_biggy big = (struct my_biggy *	1260	struct my_biggy big = (struct my_biggy *)
911	(((char *)w) - offsetof (struct my_biggy, t1));	1261	(((char *)w) - offsetof (struct my_biggy, t1));
912	}	1262	}
913		1263
914	static void	1264	static void
915	t2_cb (EV_P_ struct ev_timer *w, int revents)	1265	t2_cb (EV_P_ ev_timer *w, int revents)
916	{	1266	{
917	struct my_biggy big = (struct my_biggy *	1267	struct my_biggy big = (struct my_biggy *)
918	(((char *)w) - offsetof (struct my_biggy, t2));	1268	(((char *)w) - offsetof (struct my_biggy, t2));
919	}	1269	}
		1270
		1271	=head2 WATCHER PRIORITY MODELS
		1272
		1273	Many event loops support I<watcher priorities>, which are usually small
		1274	integers that influence the ordering of event callback invocation
		1275	between watchers in some way, all else being equal.
		1276
		1277	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1278	description for the more technical details such as the actual priority
		1279	range.
		1280
		1281	There are two common ways how these these priorities are being interpreted
		1282	by event loops:
		1283
		1284	In the more common lock-out model, higher priorities "lock out" invocation
		1285	of lower priority watchers, which means as long as higher priority
		1286	watchers receive events, lower priority watchers are not being invoked.
		1287
		1288	The less common only-for-ordering model uses priorities solely to order
		1289	callback invocation within a single event loop iteration: Higher priority
		1290	watchers are invoked before lower priority ones, but they all get invoked
		1291	before polling for new events.
		1292
		1293	Libev uses the second (only-for-ordering) model for all its watchers
		1294	except for idle watchers (which use the lock-out model).
		1295
		1296	The rationale behind this is that implementing the lock-out model for
		1297	watchers is not well supported by most kernel interfaces, and most event
		1298	libraries will just poll for the same events again and again as long as
		1299	their callbacks have not been executed, which is very inefficient in the
		1300	common case of one high-priority watcher locking out a mass of lower
		1301	priority ones.
		1302
		1303	Static (ordering) priorities are most useful when you have two or more
		1304	watchers handling the same resource: a typical usage example is having an
		1305	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1306	timeouts. Under load, data might be received while the program handles
		1307	other jobs, but since timers normally get invoked first, the timeout
		1308	handler will be executed before checking for data. In that case, giving
		1309	the timer a lower priority than the I/O watcher ensures that I/O will be
		1310	handled first even under adverse conditions (which is usually, but not
		1311	always, what you want).
		1312
		1313	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1314	will only be executed when no same or higher priority watchers have
		1315	received events, they can be used to implement the "lock-out" model when
		1316	required.
		1317
		1318	For example, to emulate how many other event libraries handle priorities,
		1319	you can associate an C<ev_idle> watcher to each such watcher, and in
		1320	the normal watcher callback, you just start the idle watcher. The real
		1321	processing is done in the idle watcher callback. This causes libev to
		1322	continously poll and process kernel event data for the watcher, but when
		1323	the lock-out case is known to be rare (which in turn is rare :), this is
		1324	workable.
		1325
		1326	Usually, however, the lock-out model implemented that way will perform
		1327	miserably under the type of load it was designed to handle. In that case,
		1328	it might be preferable to stop the real watcher before starting the
		1329	idle watcher, so the kernel will not have to process the event in case
		1330	the actual processing will be delayed for considerable time.
		1331
		1332	Here is an example of an I/O watcher that should run at a strictly lower
		1333	priority than the default, and which should only process data when no
		1334	other events are pending:
		1335
		1336	ev_idle idle; // actual processing watcher
		1337	ev_io io; // actual event watcher
		1338
		1339	static void
		1340	io_cb (EV_P_ ev_io *w, int revents)
		1341	{
		1342	// stop the I/O watcher, we received the event, but
		1343	// are not yet ready to handle it.
		1344	ev_io_stop (EV_A_ w);
		1345
		1346	// start the idle watcher to ahndle the actual event.
		1347	// it will not be executed as long as other watchers
		1348	// with the default priority are receiving events.
		1349	ev_idle_start (EV_A_ &idle);
		1350	}
		1351
		1352	static void
		1353	idle_cb (EV_P_ ev_idle *w, int revents)
		1354	{
		1355	// actual processing
		1356	read (STDIN_FILENO, ...);
		1357
		1358	// have to start the I/O watcher again, as
		1359	// we have handled the event
		1360	ev_io_start (EV_P_ &io);
		1361	}
		1362
		1363	// initialisation
		1364	ev_idle_init (&idle, idle_cb);
		1365	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1366	ev_io_start (EV_DEFAULT_ &io);
		1367
		1368	In the "real" world, it might also be beneficial to start a timer, so that
		1369	low-priority connections can not be locked out forever under load. This
		1370	enables your program to keep a lower latency for important connections
		1371	during short periods of high load, while not completely locking out less
		1372	important ones.
920		1373
921		1374
922	=head1 WATCHER TYPES	1375	=head1 WATCHER TYPES
923		1376
924	This section describes each watcher in detail, but will not repeat	1377	This section describes each watcher in detail, but will not repeat
…		…
948	In general you can register as many read and/or write event watchers per	1401	In general you can register as many read and/or write event watchers per
949	fd as you want (as long as you don't confuse yourself). Setting all file	1402	fd as you want (as long as you don't confuse yourself). Setting all file
950	descriptors to non-blocking mode is also usually a good idea (but not	1403	descriptors to non-blocking mode is also usually a good idea (but not
951	required if you know what you are doing).	1404	required if you know what you are doing).
952		1405
953	You have to be careful with dup'ed file descriptors, though. Some backends	1406	If you cannot use non-blocking mode, then force the use of a
954	(the linux epoll backend is a notable example) cannot handle dup'ed file	1407	known-to-be-good backend (at the time of this writing, this includes only
955	descriptors correctly if you register interest in two or more fds pointing	1408	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
956	to the same underlying file/socket/etc. description (that is, they share	1409	descriptors for which non-blocking operation makes no sense (such as
957	the same underlying "file open").	1410	files) - libev doesn't guarentee any specific behaviour in that case.
958
959	If you must do this, then force the use of a known-to-be-good backend
960	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
961	C<EVBACKEND_POLL>).
962		1411
963	Another thing you have to watch out for is that it is quite easy to	1412	Another thing you have to watch out for is that it is quite easy to
964	receive "spurious" readyness notifications, that is your callback might	1413	receive "spurious" readiness notifications, that is your callback might
965	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1414	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
966	because there is no data. Not only are some backends known to create a	1415	because there is no data. Not only are some backends known to create a
967	lot of those (for example solaris ports), it is very easy to get into	1416	lot of those (for example Solaris ports), it is very easy to get into
968	this situation even with a relatively standard program structure. Thus	1417	this situation even with a relatively standard program structure. Thus
969	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1418	it is best to always use non-blocking I/O: An extra C<read>(2) returning
970	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1419	C<EAGAIN> is far preferable to a program hanging until some data arrives.
971		1420
972	If you cannot run the fd in non-blocking mode (for example you should not	1421	If you cannot run the fd in non-blocking mode (for example you should
973	play around with an Xlib connection), then you have to seperately re-test	1422	not play around with an Xlib connection), then you have to separately
974	whether a file descriptor is really ready with a known-to-be good interface	1423	re-test whether a file descriptor is really ready with a known-to-be good
975	such as poll (fortunately in our Xlib example, Xlib already does this on	1424	interface such as poll (fortunately in our Xlib example, Xlib already
976	its own, so its quite safe to use).	1425	does this on its own, so its quite safe to use). Some people additionally
		1426	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1427	indefinitely.
		1428
		1429	But really, best use non-blocking mode.
977		1430
978	=head3 The special problem of disappearing file descriptors	1431	=head3 The special problem of disappearing file descriptors
979		1432
980	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1433	Some backends (e.g. kqueue, epoll) need to be told about closing a file
981	descriptor (either by calling C<close> explicitly or by any other means,	1434	descriptor (either due to calling C<close> explicitly or any other means,
982	such as C<dup>). The reason is that you register interest in some file	1435	such as C<dup2>). The reason is that you register interest in some file
983	descriptor, but when it goes away, the operating system will silently drop	1436	descriptor, but when it goes away, the operating system will silently drop
984	this interest. If another file descriptor with the same number then is	1437	this interest. If another file descriptor with the same number then is
985	registered with libev, there is no efficient way to see that this is, in	1438	registered with libev, there is no efficient way to see that this is, in
986	fact, a different file descriptor.	1439	fact, a different file descriptor.
987		1440
…		…
997	optimisations to libev.	1450	optimisations to libev.
998		1451
999	=head3 The special problem of dup'ed file descriptors	1452	=head3 The special problem of dup'ed file descriptors
1000		1453
1001	Some backends (e.g. epoll), cannot register events for file descriptors,	1454	Some backends (e.g. epoll), cannot register events for file descriptors,
1002	but only events for the underlying file descriptions. That menas when you	1455	but only events for the underlying file descriptions. That means when you
1003	have C<dup ()>'ed file descriptors and register events for them, only one	1456	have C<dup ()>'ed file descriptors or weirder constellations, and register
1004	file descriptor might actually receive events.	1457	events for them, only one file descriptor might actually receive events.
1005		1458
1006	There is no workaorund possible except not registering events	1459	There is no workaround possible except not registering events
1007	for potentially C<dup ()>'ed file descriptors or to resort to	1460	for potentially C<dup ()>'ed file descriptors, or to resort to
1008	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1461	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1009		1462
1010	=head3 The special problem of fork	1463	=head3 The special problem of fork
1011		1464
1012	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1465	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
…		…
1016	To support fork in your programs, you either have to call	1469	To support fork in your programs, you either have to call
1017	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1470	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
1018	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1471	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
1019	C<EVBACKEND_POLL>.	1472	C<EVBACKEND_POLL>.
1020		1473
		1474	=head3 The special problem of SIGPIPE
		1475
		1476	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1477	when writing to a pipe whose other end has been closed, your program gets
		1478	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1479	this is sensible behaviour, for daemons, this is usually undesirable.
		1480
		1481	So when you encounter spurious, unexplained daemon exits, make sure you
		1482	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1483	somewhere, as that would have given you a big clue).
		1484
1021		1485
1022	=head3 Watcher-Specific Functions	1486	=head3 Watcher-Specific Functions
1023		1487
1024	=over 4	1488	=over 4
1025		1489
1026	=item ev_io_init (ev_io *, callback, int fd, int events)	1490	=item ev_io_init (ev_io *, callback, int fd, int events)
1027		1491
1028	=item ev_io_set (ev_io *, int fd, int events)	1492	=item ev_io_set (ev_io *, int fd, int events)
1029		1493
1030	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1494	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
1031	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1495	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
1032	C<EV_READ | EV_WRITE> to receive the given events.	1496	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
1033		1497
1034	=item int fd [read-only]	1498	=item int fd [read-only]
1035		1499
1036	The file descriptor being watched.	1500	The file descriptor being watched.
1037		1501
1038	=item int events [read-only]	1502	=item int events [read-only]
1039		1503
1040	The events being watched.	1504	The events being watched.
1041		1505
1042	=back	1506	=back
		1507
		1508	=head3 Examples
1043		1509
1044	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1510	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1045	readable, but only once. Since it is likely line-buffered, you could	1511	readable, but only once. Since it is likely line-buffered, you could
1046	attempt to read a whole line in the callback.	1512	attempt to read a whole line in the callback.
1047		1513
1048	static void	1514	static void
1049	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1515	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1050	{	1516	{
1051	ev_io_stop (loop, w);	1517	ev_io_stop (loop, w);
1052	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1518	.. read from stdin here (or from w->fd) and handle any I/O errors
1053	}	1519	}
1054		1520
1055	...	1521	...
1056	struct ev_loop *loop = ev_default_init (0);	1522	struct ev_loop *loop = ev_default_init (0);
1057	struct ev_io stdin_readable;	1523	ev_io stdin_readable;
1058	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1524	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1059	ev_io_start (loop, &stdin_readable);	1525	ev_io_start (loop, &stdin_readable);
1060	ev_loop (loop, 0);	1526	ev_loop (loop, 0);
1061		1527
1062		1528
1063	=head2 C<ev_timer> - relative and optionally repeating timeouts	1529	=head2 C<ev_timer> - relative and optionally repeating timeouts
1064		1530
1065	Timer watchers are simple relative timers that generate an event after a	1531	Timer watchers are simple relative timers that generate an event after a
1066	given time, and optionally repeating in regular intervals after that.	1532	given time, and optionally repeating in regular intervals after that.
1067		1533
1068	The timers are based on real time, that is, if you register an event that	1534	The timers are based on real time, that is, if you register an event that
1069	times out after an hour and you reset your system clock to last years	1535	times out after an hour and you reset your system clock to January last
1070	time, it will still time out after (roughly) and hour. "Roughly" because	1536	year, it will still time out after (roughly) one hour. "Roughly" because
1071	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1537	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1072	monotonic clock option helps a lot here).	1538	monotonic clock option helps a lot here).
		1539
		1540	The callback is guaranteed to be invoked only I<after> its timeout has
		1541	passed (not I<at>, so on systems with very low-resolution clocks this
		1542	might introduce a small delay). If multiple timers become ready during the
		1543	same loop iteration then the ones with earlier time-out values are invoked
		1544	before ones of the same priority with later time-out values (but this is
		1545	no longer true when a callback calls C<ev_loop> recursively).
		1546
		1547	=head3 Be smart about timeouts
		1548
		1549	Many real-world problems involve some kind of timeout, usually for error
		1550	recovery. A typical example is an HTTP request - if the other side hangs,
		1551	you want to raise some error after a while.
		1552
		1553	What follows are some ways to handle this problem, from obvious and
		1554	inefficient to smart and efficient.
		1555
		1556	In the following, a 60 second activity timeout is assumed - a timeout that
		1557	gets reset to 60 seconds each time there is activity (e.g. each time some
		1558	data or other life sign was received).
		1559
		1560	=over 4
		1561
		1562	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1563
		1564	This is the most obvious, but not the most simple way: In the beginning,
		1565	start the watcher:
		1566
		1567	ev_timer_init (timer, callback, 60., 0.);
		1568	ev_timer_start (loop, timer);
		1569
		1570	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1571	and start it again:
		1572
		1573	ev_timer_stop (loop, timer);
		1574	ev_timer_set (timer, 60., 0.);
		1575	ev_timer_start (loop, timer);
		1576
		1577	This is relatively simple to implement, but means that each time there is
		1578	some activity, libev will first have to remove the timer from its internal
		1579	data structure and then add it again. Libev tries to be fast, but it's
		1580	still not a constant-time operation.
		1581
		1582	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1583
		1584	This is the easiest way, and involves using C<ev_timer_again> instead of
		1585	C<ev_timer_start>.
		1586
		1587	To implement this, configure an C<ev_timer> with a C<repeat> value
		1588	of C<60> and then call C<ev_timer_again> at start and each time you
		1589	successfully read or write some data. If you go into an idle state where
		1590	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1591	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1592
		1593	That means you can ignore both the C<ev_timer_start> function and the
		1594	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1595	member and C<ev_timer_again>.
		1596
		1597	At start:
		1598
		1599	ev_init (timer, callback);
		1600	timer->repeat = 60.;
		1601	ev_timer_again (loop, timer);
		1602
		1603	Each time there is some activity:
		1604
		1605	ev_timer_again (loop, timer);
		1606
		1607	It is even possible to change the time-out on the fly, regardless of
		1608	whether the watcher is active or not:
		1609
		1610	timer->repeat = 30.;
		1611	ev_timer_again (loop, timer);
		1612
		1613	This is slightly more efficient then stopping/starting the timer each time
		1614	you want to modify its timeout value, as libev does not have to completely
		1615	remove and re-insert the timer from/into its internal data structure.
		1616
		1617	It is, however, even simpler than the "obvious" way to do it.
		1618
		1619	=item 3. Let the timer time out, but then re-arm it as required.
		1620
		1621	This method is more tricky, but usually most efficient: Most timeouts are
		1622	relatively long compared to the intervals between other activity - in
		1623	our example, within 60 seconds, there are usually many I/O events with
		1624	associated activity resets.
		1625
		1626	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1627	but remember the time of last activity, and check for a real timeout only
		1628	within the callback:
		1629
		1630	ev_tstamp last_activity; // time of last activity
		1631
		1632	static void
		1633	callback (EV_P_ ev_timer *w, int revents)
		1634	{
		1635	ev_tstamp now = ev_now (EV_A);
		1636	ev_tstamp timeout = last_activity + 60.;
		1637
		1638	// if last_activity + 60. is older than now, we did time out
		1639	if (timeout < now)
		1640	{
		1641	// timeout occured, take action
		1642	}
		1643	else
		1644	{
		1645	// callback was invoked, but there was some activity, re-arm
		1646	// the watcher to fire in last_activity + 60, which is
		1647	// guaranteed to be in the future, so "again" is positive:
		1648	w->repeat = timeout - now;
		1649	ev_timer_again (EV_A_ w);
		1650	}
		1651	}
		1652
		1653	To summarise the callback: first calculate the real timeout (defined
		1654	as "60 seconds after the last activity"), then check if that time has
		1655	been reached, which means something I<did>, in fact, time out. Otherwise
		1656	the callback was invoked too early (C<timeout> is in the future), so
		1657	re-schedule the timer to fire at that future time, to see if maybe we have
		1658	a timeout then.
		1659
		1660	Note how C<ev_timer_again> is used, taking advantage of the
		1661	C<ev_timer_again> optimisation when the timer is already running.
		1662
		1663	This scheme causes more callback invocations (about one every 60 seconds
		1664	minus half the average time between activity), but virtually no calls to
		1665	libev to change the timeout.
		1666
		1667	To start the timer, simply initialise the watcher and set C<last_activity>
		1668	to the current time (meaning we just have some activity :), then call the
		1669	callback, which will "do the right thing" and start the timer:
		1670
		1671	ev_init (timer, callback);
		1672	last_activity = ev_now (loop);
		1673	callback (loop, timer, EV_TIMEOUT);
		1674
		1675	And when there is some activity, simply store the current time in
		1676	C<last_activity>, no libev calls at all:
		1677
		1678	last_actiivty = ev_now (loop);
		1679
		1680	This technique is slightly more complex, but in most cases where the
		1681	time-out is unlikely to be triggered, much more efficient.
		1682
		1683	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1684	callback :) - just change the timeout and invoke the callback, which will
		1685	fix things for you.
		1686
		1687	=item 4. Wee, just use a double-linked list for your timeouts.
		1688
		1689	If there is not one request, but many thousands (millions...), all
		1690	employing some kind of timeout with the same timeout value, then one can
		1691	do even better:
		1692
		1693	When starting the timeout, calculate the timeout value and put the timeout
		1694	at the I<end> of the list.
		1695
		1696	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1697	the list is expected to fire (for example, using the technique #3).
		1698
		1699	When there is some activity, remove the timer from the list, recalculate
		1700	the timeout, append it to the end of the list again, and make sure to
		1701	update the C<ev_timer> if it was taken from the beginning of the list.
		1702
		1703	This way, one can manage an unlimited number of timeouts in O(1) time for
		1704	starting, stopping and updating the timers, at the expense of a major
		1705	complication, and having to use a constant timeout. The constant timeout
		1706	ensures that the list stays sorted.
		1707
		1708	=back
		1709
		1710	So which method the best?
		1711
		1712	Method #2 is a simple no-brain-required solution that is adequate in most
		1713	situations. Method #3 requires a bit more thinking, but handles many cases
		1714	better, and isn't very complicated either. In most case, choosing either
		1715	one is fine, with #3 being better in typical situations.
		1716
		1717	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1718	rather complicated, but extremely efficient, something that really pays
		1719	off after the first million or so of active timers, i.e. it's usually
		1720	overkill :)
		1721
		1722	=head3 The special problem of time updates
		1723
		1724	Establishing the current time is a costly operation (it usually takes at
		1725	least two system calls): EV therefore updates its idea of the current
		1726	time only before and after C<ev_loop> collects new events, which causes a
		1727	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1728	lots of events in one iteration.
1073		1729
1074	The relative timeouts are calculated relative to the C<ev_now ()>	1730	The relative timeouts are calculated relative to the C<ev_now ()>
1075	time. This is usually the right thing as this timestamp refers to the time	1731	time. This is usually the right thing as this timestamp refers to the time
1076	of the event triggering whatever timeout you are modifying/starting. If	1732	of the event triggering whatever timeout you are modifying/starting. If
1077	you suspect event processing to be delayed and you I<need> to base the timeout	1733	you suspect event processing to be delayed and you I<need> to base the
1078	on the current time, use something like this to adjust for this:	1734	timeout on the current time, use something like this to adjust for this:
1079		1735
1080	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1736	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1081		1737
1082	The callback is guarenteed to be invoked only when its timeout has passed,	1738	If the event loop is suspended for a long time, you can also force an
1083	but if multiple timers become ready during the same loop iteration then	1739	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1084	order of execution is undefined.	1740	()>.
1085		1741
1086	=head3 Watcher-Specific Functions and Data Members	1742	=head3 Watcher-Specific Functions and Data Members
1087		1743
1088	=over 4	1744	=over 4
1089		1745
1090	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1746	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1091		1747
1092	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1748	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1093		1749
1094	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1750	Configure the timer to trigger after C<after> seconds. If C<repeat>
1095	C<0.>, then it will automatically be stopped. If it is positive, then the	1751	is C<0.>, then it will automatically be stopped once the timeout is
1096	timer will automatically be configured to trigger again C<repeat> seconds	1752	reached. If it is positive, then the timer will automatically be
1097	later, again, and again, until stopped manually.	1753	configured to trigger again C<repeat> seconds later, again, and again,
		1754	until stopped manually.
1098		1755
1099	The timer itself will do a best-effort at avoiding drift, that is, if you	1756	The timer itself will do a best-effort at avoiding drift, that is, if
1100	configure a timer to trigger every 10 seconds, then it will trigger at	1757	you configure a timer to trigger every 10 seconds, then it will normally
1101	exactly 10 second intervals. If, however, your program cannot keep up with	1758	trigger at exactly 10 second intervals. If, however, your program cannot
1102	the timer (because it takes longer than those 10 seconds to do stuff) the	1759	keep up with the timer (because it takes longer than those 10 seconds to
1103	timer will not fire more than once per event loop iteration.	1760	do stuff) the timer will not fire more than once per event loop iteration.
1104		1761
1105	=item ev_timer_again (loop)	1762	=item ev_timer_again (loop, ev_timer *)
1106		1763
1107	This will act as if the timer timed out and restart it again if it is	1764	This will act as if the timer timed out and restart it again if it is
1108	repeating. The exact semantics are:	1765	repeating. The exact semantics are:
1109		1766
1110	If the timer is pending, its pending status is cleared.	1767	If the timer is pending, its pending status is cleared.
1111		1768
1112	If the timer is started but nonrepeating, stop it (as if it timed out).	1769	If the timer is started but non-repeating, stop it (as if it timed out).
1113		1770
1114	If the timer is repeating, either start it if necessary (with the	1771	If the timer is repeating, either start it if necessary (with the
1115	C<repeat> value), or reset the running timer to the C<repeat> value.	1772	C<repeat> value), or reset the running timer to the C<repeat> value.
1116		1773
1117	This sounds a bit complicated, but here is a useful and typical	1774	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1118	example: Imagine you have a tcp connection and you want a so-called idle	1775	usage example.
1119	timeout, that is, you want to be called when there have been, say, 60
1120	seconds of inactivity on the socket. The easiest way to do this is to
1121	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1122	C<ev_timer_again> each time you successfully read or write some data. If
1123	you go into an idle state where you do not expect data to travel on the
1124	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1125	automatically restart it if need be.
1126
1127	That means you can ignore the C<after> value and C<ev_timer_start>
1128	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1129
1130	ev_timer_init (timer, callback, 0., 5.);
1131	ev_timer_again (loop, timer);
1132	...
1133	timer->again = 17.;
1134	ev_timer_again (loop, timer);
1135	...
1136	timer->again = 10.;
1137	ev_timer_again (loop, timer);
1138
1139	This is more slightly efficient then stopping/starting the timer each time
1140	you want to modify its timeout value.
1141		1776
1142	=item ev_tstamp repeat [read-write]	1777	=item ev_tstamp repeat [read-write]
1143		1778
1144	The current C<repeat> value. Will be used each time the watcher times out	1779	The current C<repeat> value. Will be used each time the watcher times out
1145	or C<ev_timer_again> is called and determines the next timeout (if any),	1780	or C<ev_timer_again> is called, and determines the next timeout (if any),
1146	which is also when any modifications are taken into account.	1781	which is also when any modifications are taken into account.
1147		1782
1148	=back	1783	=back
1149		1784
		1785	=head3 Examples
		1786
1150	Example: Create a timer that fires after 60 seconds.	1787	Example: Create a timer that fires after 60 seconds.
1151		1788
1152	static void	1789	static void
1153	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1790	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1154	{	1791	{
1155	.. one minute over, w is actually stopped right here	1792	.. one minute over, w is actually stopped right here
1156	}	1793	}
1157		1794
1158	struct ev_timer mytimer;	1795	ev_timer mytimer;
1159	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1796	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1160	ev_timer_start (loop, &mytimer);	1797	ev_timer_start (loop, &mytimer);
1161		1798
1162	Example: Create a timeout timer that times out after 10 seconds of	1799	Example: Create a timeout timer that times out after 10 seconds of
1163	inactivity.	1800	inactivity.
1164		1801
1165	static void	1802	static void
1166	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1803	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1167	{	1804	{
1168	.. ten seconds without any activity	1805	.. ten seconds without any activity
1169	}	1806	}
1170		1807
1171	struct ev_timer mytimer;	1808	ev_timer mytimer;
1172	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1809	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1173	ev_timer_again (&mytimer); /* start timer */	1810	ev_timer_again (&mytimer); /* start timer */
1174	ev_loop (loop, 0);	1811	ev_loop (loop, 0);
1175		1812
1176	// and in some piece of code that gets executed on any "activity":	1813	// and in some piece of code that gets executed on any "activity":
1177	// reset the timeout to start ticking again at 10 seconds	1814	// reset the timeout to start ticking again at 10 seconds
1178	ev_timer_again (&mytimer);	1815	ev_timer_again (&mytimer);
1179		1816
1180		1817
1181	=head2 C<ev_periodic> - to cron or not to cron?	1818	=head2 C<ev_periodic> - to cron or not to cron?
1182		1819
1183	Periodic watchers are also timers of a kind, but they are very versatile	1820	Periodic watchers are also timers of a kind, but they are very versatile
1184	(and unfortunately a bit complex).	1821	(and unfortunately a bit complex).
1185		1822
1186	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1823	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1187	but on wallclock time (absolute time). You can tell a periodic watcher	1824	relative time, the physical time that passes) but on wall clock time
1188	to trigger "at" some specific point in time. For example, if you tell a	1825	(absolute time, the thing you can read on your calender or clock). The
1189	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	1826	difference is that wall clock time can run faster or slower than real
1190	+ 10.>) and then reset your system clock to the last year, then it will	1827	time, and time jumps are not uncommon (e.g. when you adjust your
1191	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1828	wrist-watch).
1192	roughly 10 seconds later).
1193		1829
1194	They can also be used to implement vastly more complex timers, such as	1830	You can tell a periodic watcher to trigger after some specific point
1195	triggering an event on each midnight, local time or other, complicated,	1831	in time: for example, if you tell a periodic watcher to trigger "in 10
1196	rules.	1832	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1833	not a delay) and then reset your system clock to January of the previous
		1834	year, then it will take a year or more to trigger the event (unlike an
		1835	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1836	it, as it uses a relative timeout).
1197		1837
		1838	C<ev_periodic> watchers can also be used to implement vastly more complex
		1839	timers, such as triggering an event on each "midnight, local time", or
		1840	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1841	those cannot react to time jumps.
		1842
1198	As with timers, the callback is guarenteed to be invoked only when the	1843	As with timers, the callback is guaranteed to be invoked only when the
1199	time (C<at>) has been passed, but if multiple periodic timers become ready	1844	point in time where it is supposed to trigger has passed. If multiple
1200	during the same loop iteration then order of execution is undefined.	1845	timers become ready during the same loop iteration then the ones with
		1846	earlier time-out values are invoked before ones with later time-out values
		1847	(but this is no longer true when a callback calls C<ev_loop> recursively).
1201		1848
1202	=head3 Watcher-Specific Functions and Data Members	1849	=head3 Watcher-Specific Functions and Data Members
1203		1850
1204	=over 4	1851	=over 4
1205		1852
1206	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1853	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1207		1854
1208	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1855	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1209		1856
1210	Lots of arguments, lets sort it out... There are basically three modes of	1857	Lots of arguments, let's sort it out... There are basically three modes of
1211	operation, and we will explain them from simplest to complex:	1858	operation, and we will explain them from simplest to most complex:
1212		1859
1213	=over 4	1860	=over 4
1214		1861
1215	=item * absolute timer (at = time, interval = reschedule_cb = 0)	1862	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1216		1863
1217	In this configuration the watcher triggers an event at the wallclock time	1864	In this configuration the watcher triggers an event after the wall clock
1218	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1865	time C<offset> has passed. It will not repeat and will not adjust when a
1219	that is, if it is to be run at January 1st 2011 then it will run when the	1866	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1220	system time reaches or surpasses this time.	1867	will be stopped and invoked when the system clock reaches or surpasses
		1868	this point in time.
1221		1869
1222	=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	1870	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1223		1871
1224	In this mode the watcher will always be scheduled to time out at the next	1872	In this mode the watcher will always be scheduled to time out at the next
1225	C<at + N * interval> time (for some integer N, which can also be negative)	1873	C<offset + N * interval> time (for some integer N, which can also be
1226	and then repeat, regardless of any time jumps.	1874	negative) and then repeat, regardless of any time jumps. The C<offset>
		1875	argument is merely an offset into the C<interval> periods.
1227		1876
1228	This can be used to create timers that do not drift with respect to system	1877	This can be used to create timers that do not drift with respect to the
1229	time:	1878	system clock, for example, here is an C<ev_periodic> that triggers each
		1879	hour, on the hour (with respect to UTC):
1230		1880
1231	ev_periodic_set (&periodic, 0., 3600., 0);	1881	ev_periodic_set (&periodic, 0., 3600., 0);
1232		1882
1233	This doesn't mean there will always be 3600 seconds in between triggers,	1883	This doesn't mean there will always be 3600 seconds in between triggers,
1234	but only that the the callback will be called when the system time shows a	1884	but only that the callback will be called when the system time shows a
1235	full hour (UTC), or more correctly, when the system time is evenly divisible	1885	full hour (UTC), or more correctly, when the system time is evenly divisible
1236	by 3600.	1886	by 3600.
1237		1887
1238	Another way to think about it (for the mathematically inclined) is that	1888	Another way to think about it (for the mathematically inclined) is that
1239	C<ev_periodic> will try to run the callback in this mode at the next possible	1889	C<ev_periodic> will try to run the callback in this mode at the next possible
1240	time where C<time = at (mod interval)>, regardless of any time jumps.	1890	time where C<time = offset (mod interval)>, regardless of any time jumps.
1241		1891
1242	For numerical stability it is preferable that the C<at> value is near	1892	For numerical stability it is preferable that the C<offset> value is near
1243	C<ev_now ()> (the current time), but there is no range requirement for	1893	C<ev_now ()> (the current time), but there is no range requirement for
1244	this value.	1894	this value, and in fact is often specified as zero.
1245		1895
		1896	Note also that there is an upper limit to how often a timer can fire (CPU
		1897	speed for example), so if C<interval> is very small then timing stability
		1898	will of course deteriorate. Libev itself tries to be exact to be about one
		1899	millisecond (if the OS supports it and the machine is fast enough).
		1900
1246	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	1901	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1247		1902
1248	In this mode the values for C<interval> and C<at> are both being	1903	In this mode the values for C<interval> and C<offset> are both being
1249	ignored. Instead, each time the periodic watcher gets scheduled, the	1904	ignored. Instead, each time the periodic watcher gets scheduled, the
1250	reschedule callback will be called with the watcher as first, and the	1905	reschedule callback will be called with the watcher as first, and the
1251	current time as second argument.	1906	current time as second argument.
1252		1907
1253	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1908	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1254	ever, or make any event loop modifications>. If you need to stop it,	1909	or make ANY other event loop modifications whatsoever, unless explicitly
1255	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	1910	allowed by documentation here>.
1256	starting an C<ev_prepare> watcher, which is legal).
1257		1911
		1912	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1913	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1914	only event loop modification you are allowed to do).
		1915
1258	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1916	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1259	ev_tstamp now)>, e.g.:	1917	*w, ev_tstamp now)>, e.g.:
1260		1918
		1919	static ev_tstamp
1261	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1920	my_rescheduler (ev_periodic *w, ev_tstamp now)
1262	{	1921	{
1263	return now + 60.;	1922	return now + 60.;
1264	}	1923	}
1265		1924
1266	It must return the next time to trigger, based on the passed time value	1925	It must return the next time to trigger, based on the passed time value
1267	(that is, the lowest time value larger than to the second argument). It	1926	(that is, the lowest time value larger than to the second argument). It
1268	will usually be called just before the callback will be triggered, but	1927	will usually be called just before the callback will be triggered, but
1269	might be called at other times, too.	1928	might be called at other times, too.
1270		1929
1271	NOTE: I<< This callback must always return a time that is later than the	1930	NOTE: I<< This callback must always return a time that is higher than or
1272	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	1931	equal to the passed C<now> value >>.
1273		1932
1274	This can be used to create very complex timers, such as a timer that	1933	This can be used to create very complex timers, such as a timer that
1275	triggers on each midnight, local time. To do this, you would calculate the	1934	triggers on "next midnight, local time". To do this, you would calculate the
1276	next midnight after C<now> and return the timestamp value for this. How	1935	next midnight after C<now> and return the timestamp value for this. How
1277	you do this is, again, up to you (but it is not trivial, which is the main	1936	you do this is, again, up to you (but it is not trivial, which is the main
1278	reason I omitted it as an example).	1937	reason I omitted it as an example).
1279		1938
1280	=back	1939	=back
…		…
1284	Simply stops and restarts the periodic watcher again. This is only useful	1943	Simply stops and restarts the periodic watcher again. This is only useful
1285	when you changed some parameters or the reschedule callback would return	1944	when you changed some parameters or the reschedule callback would return
1286	a different time than the last time it was called (e.g. in a crond like	1945	a different time than the last time it was called (e.g. in a crond like
1287	program when the crontabs have changed).	1946	program when the crontabs have changed).
1288		1947
		1948	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1949
		1950	When active, returns the absolute time that the watcher is supposed
		1951	to trigger next. This is not the same as the C<offset> argument to
		1952	C<ev_periodic_set>, but indeed works even in interval and manual
		1953	rescheduling modes.
		1954
1289	=item ev_tstamp offset [read-write]	1955	=item ev_tstamp offset [read-write]
1290		1956
1291	When repeating, this contains the offset value, otherwise this is the	1957	When repeating, this contains the offset value, otherwise this is the
1292	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	1958	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		1959	although libev might modify this value for better numerical stability).
1293		1960
1294	Can be modified any time, but changes only take effect when the periodic	1961	Can be modified any time, but changes only take effect when the periodic
1295	timer fires or C<ev_periodic_again> is being called.	1962	timer fires or C<ev_periodic_again> is being called.
1296		1963
1297	=item ev_tstamp interval [read-write]	1964	=item ev_tstamp interval [read-write]
1298		1965
1299	The current interval value. Can be modified any time, but changes only	1966	The current interval value. Can be modified any time, but changes only
1300	take effect when the periodic timer fires or C<ev_periodic_again> is being	1967	take effect when the periodic timer fires or C<ev_periodic_again> is being
1301	called.	1968	called.
1302		1969
1303	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	1970	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1304		1971
1305	The current reschedule callback, or C<0>, if this functionality is	1972	The current reschedule callback, or C<0>, if this functionality is
1306	switched off. Can be changed any time, but changes only take effect when	1973	switched off. Can be changed any time, but changes only take effect when
1307	the periodic timer fires or C<ev_periodic_again> is being called.	1974	the periodic timer fires or C<ev_periodic_again> is being called.
1308		1975
1309	=item ev_tstamp at [read-only]
1310
1311	When active, contains the absolute time that the watcher is supposed to
1312	trigger next.
1313
1314	=back	1976	=back
1315		1977
		1978	=head3 Examples
		1979
1316	Example: Call a callback every hour, or, more precisely, whenever the	1980	Example: Call a callback every hour, or, more precisely, whenever the
1317	system clock is divisible by 3600. The callback invocation times have	1981	system time is divisible by 3600. The callback invocation times have
1318	potentially a lot of jittering, but good long-term stability.	1982	potentially a lot of jitter, but good long-term stability.
1319		1983
1320	static void	1984	static void
1321	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1985	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1322	{	1986	{
1323	... its now a full hour (UTC, or TAI or whatever your clock follows)	1987	... its now a full hour (UTC, or TAI or whatever your clock follows)
1324	}	1988	}
1325		1989
1326	struct ev_periodic hourly_tick;	1990	ev_periodic hourly_tick;
1327	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	1991	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1328	ev_periodic_start (loop, &hourly_tick);	1992	ev_periodic_start (loop, &hourly_tick);
1329		1993
1330	Example: The same as above, but use a reschedule callback to do it:	1994	Example: The same as above, but use a reschedule callback to do it:
1331		1995
1332	#include <math.h>	1996	#include <math.h>
1333		1997
1334	static ev_tstamp	1998	static ev_tstamp
1335	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	1999	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1336	{	2000	{
1337	return fmod (now, 3600.) + 3600.;	2001	return now + (3600. - fmod (now, 3600.));
1338	}	2002	}
1339		2003
1340	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2004	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1341		2005
1342	Example: Call a callback every hour, starting now:	2006	Example: Call a callback every hour, starting now:
1343		2007
1344	struct ev_periodic hourly_tick;	2008	ev_periodic hourly_tick;
1345	ev_periodic_init (&hourly_tick, clock_cb,	2009	ev_periodic_init (&hourly_tick, clock_cb,
1346	fmod (ev_now (loop), 3600.), 3600., 0);	2010	fmod (ev_now (loop), 3600.), 3600., 0);
1347	ev_periodic_start (loop, &hourly_tick);	2011	ev_periodic_start (loop, &hourly_tick);
1348		2012
1349		2013
1350	=head2 C<ev_signal> - signal me when a signal gets signalled!	2014	=head2 C<ev_signal> - signal me when a signal gets signalled!
1351		2015
1352	Signal watchers will trigger an event when the process receives a specific	2016	Signal watchers will trigger an event when the process receives a specific
1353	signal one or more times. Even though signals are very asynchronous, libev	2017	signal one or more times. Even though signals are very asynchronous, libev
1354	will try it's best to deliver signals synchronously, i.e. as part of the	2018	will try it's best to deliver signals synchronously, i.e. as part of the
1355	normal event processing, like any other event.	2019	normal event processing, like any other event.
1356		2020
		2021	If you want signals asynchronously, just use C<sigaction> as you would
		2022	do without libev and forget about sharing the signal. You can even use
		2023	C<ev_async> from a signal handler to synchronously wake up an event loop.
		2024
1357	You can configure as many watchers as you like per signal. Only when the	2025	You can configure as many watchers as you like per signal. Only when the
1358	first watcher gets started will libev actually register a signal watcher	2026	first watcher gets started will libev actually register a signal handler
1359	with the kernel (thus it coexists with your own signal handlers as long	2027	with the kernel (thus it coexists with your own signal handlers as long as
1360	as you don't register any with libev). Similarly, when the last signal	2028	you don't register any with libev for the same signal). Similarly, when
1361	watcher for a signal is stopped libev will reset the signal handler to	2029	the last signal watcher for a signal is stopped, libev will reset the
1362	SIG_DFL (regardless of what it was set to before).	2030	signal handler to SIG_DFL (regardless of what it was set to before).
		2031
		2032	If possible and supported, libev will install its handlers with
		2033	C<SA_RESTART> behaviour enabled, so system calls should not be unduly
		2034	interrupted. If you have a problem with system calls getting interrupted by
		2035	signals you can block all signals in an C<ev_check> watcher and unblock
		2036	them in an C<ev_prepare> watcher.
1363		2037
1364	=head3 Watcher-Specific Functions and Data Members	2038	=head3 Watcher-Specific Functions and Data Members
1365		2039
1366	=over 4	2040	=over 4
1367		2041
…		…
1376		2050
1377	The signal the watcher watches out for.	2051	The signal the watcher watches out for.
1378		2052
1379	=back	2053	=back
1380		2054
		2055	=head3 Examples
		2056
		2057	Example: Try to exit cleanly on SIGINT.
		2058
		2059	static void
		2060	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2061	{
		2062	ev_unloop (loop, EVUNLOOP_ALL);
		2063	}
		2064
		2065	ev_signal signal_watcher;
		2066	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2067	ev_signal_start (loop, &signal_watcher);
		2068
1381		2069
1382	=head2 C<ev_child> - watch out for process status changes	2070	=head2 C<ev_child> - watch out for process status changes
1383		2071
1384	Child watchers trigger when your process receives a SIGCHLD in response to	2072	Child watchers trigger when your process receives a SIGCHLD in response to
1385	some child status changes (most typically when a child of yours dies).	2073	some child status changes (most typically when a child of yours dies or
		2074	exits). It is permissible to install a child watcher I<after> the child
		2075	has been forked (which implies it might have already exited), as long
		2076	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2077	forking and then immediately registering a watcher for the child is fine,
		2078	but forking and registering a watcher a few event loop iterations later or
		2079	in the next callback invocation is not.
		2080
		2081	Only the default event loop is capable of handling signals, and therefore
		2082	you can only register child watchers in the default event loop.
		2083
		2084	Due to some design glitches inside libev, child watchers will always be
		2085	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2086	libev)
		2087
		2088	=head3 Process Interaction
		2089
		2090	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2091	initialised. This is necessary to guarantee proper behaviour even if
		2092	the first child watcher is started after the child exits. The occurrence
		2093	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2094	synchronously as part of the event loop processing. Libev always reaps all
		2095	children, even ones not watched.
		2096
		2097	=head3 Overriding the Built-In Processing
		2098
		2099	Libev offers no special support for overriding the built-in child
		2100	processing, but if your application collides with libev's default child
		2101	handler, you can override it easily by installing your own handler for
		2102	C<SIGCHLD> after initialising the default loop, and making sure the
		2103	default loop never gets destroyed. You are encouraged, however, to use an
		2104	event-based approach to child reaping and thus use libev's support for
		2105	that, so other libev users can use C<ev_child> watchers freely.
		2106
		2107	=head3 Stopping the Child Watcher
		2108
		2109	Currently, the child watcher never gets stopped, even when the
		2110	child terminates, so normally one needs to stop the watcher in the
		2111	callback. Future versions of libev might stop the watcher automatically
		2112	when a child exit is detected.
1386		2113
1387	=head3 Watcher-Specific Functions and Data Members	2114	=head3 Watcher-Specific Functions and Data Members
1388		2115
1389	=over 4	2116	=over 4
1390		2117
1391	=item ev_child_init (ev_child *, callback, int pid)	2118	=item ev_child_init (ev_child *, callback, int pid, int trace)
1392		2119
1393	=item ev_child_set (ev_child *, int pid)	2120	=item ev_child_set (ev_child *, int pid, int trace)
1394		2121
1395	Configures the watcher to wait for status changes of process C<pid> (or	2122	Configures the watcher to wait for status changes of process C<pid> (or
1396	I<any> process if C<pid> is specified as C<0>). The callback can look	2123	I<any> process if C<pid> is specified as C<0>). The callback can look
1397	at the C<rstatus> member of the C<ev_child> watcher structure to see	2124	at the C<rstatus> member of the C<ev_child> watcher structure to see
1398	the status word (use the macros from C<sys/wait.h> and see your systems	2125	the status word (use the macros from C<sys/wait.h> and see your systems
1399	C<waitpid> documentation). The C<rpid> member contains the pid of the	2126	C<waitpid> documentation). The C<rpid> member contains the pid of the
1400	process causing the status change.	2127	process causing the status change. C<trace> must be either C<0> (only
		2128	activate the watcher when the process terminates) or C<1> (additionally
		2129	activate the watcher when the process is stopped or continued).
1401		2130
1402	=item int pid [read-only]	2131	=item int pid [read-only]
1403		2132
1404	The process id this watcher watches out for, or C<0>, meaning any process id.	2133	The process id this watcher watches out for, or C<0>, meaning any process id.
1405		2134
…		…
1412	The process exit/trace status caused by C<rpid> (see your systems	2141	The process exit/trace status caused by C<rpid> (see your systems
1413	C<waitpid> and C<sys/wait.h> documentation for details).	2142	C<waitpid> and C<sys/wait.h> documentation for details).
1414		2143
1415	=back	2144	=back
1416		2145
1417	Example: Try to exit cleanly on SIGINT and SIGTERM.	2146	=head3 Examples
1418		2147
		2148	Example: C<fork()> a new process and install a child handler to wait for
		2149	its completion.
		2150
		2151	ev_child cw;
		2152
1419	static void	2153	static void
1420	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2154	child_cb (EV_P_ ev_child *w, int revents)
1421	{	2155	{
1422	ev_unloop (loop, EVUNLOOP_ALL);	2156	ev_child_stop (EV_A_ w);
		2157	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1423	}	2158	}
1424		2159
1425	struct ev_signal signal_watcher;	2160	pid_t pid = fork ();
1426	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2161
1427	ev_signal_start (loop, &sigint_cb);	2162	if (pid < 0)
		2163	// error
		2164	else if (pid == 0)
		2165	{
		2166	// the forked child executes here
		2167	exit (1);
		2168	}
		2169	else
		2170	{
		2171	ev_child_init (&cw, child_cb, pid, 0);
		2172	ev_child_start (EV_DEFAULT_ &cw);
		2173	}
1428		2174
1429		2175
1430	=head2 C<ev_stat> - did the file attributes just change?	2176	=head2 C<ev_stat> - did the file attributes just change?
1431		2177
1432	This watches a filesystem path for attribute changes. That is, it calls	2178	This watches a file system path for attribute changes. That is, it calls
1433	C<stat> regularly (or when the OS says it changed) and sees if it changed	2179	C<stat> on that path in regular intervals (or when the OS says it changed)
1434	compared to the last time, invoking the callback if it did.	2180	and sees if it changed compared to the last time, invoking the callback if
		2181	it did.
1435		2182
1436	The path does not need to exist: changing from "path exists" to "path does	2183	The path does not need to exist: changing from "path exists" to "path does
1437	not exist" is a status change like any other. The condition "path does	2184	not exist" is a status change like any other. The condition "path does not
1438	not exist" is signified by the C<st_nlink> field being zero (which is	2185	exist" (or more correctly "path cannot be stat'ed") is signified by the
1439	otherwise always forced to be at least one) and all the other fields of	2186	C<st_nlink> field being zero (which is otherwise always forced to be at
1440	the stat buffer having unspecified contents.	2187	least one) and all the other fields of the stat buffer having unspecified
		2188	contents.
1441		2189
1442	The path I<should> be absolute and I<must not> end in a slash. If it is	2190	The path I<must not> end in a slash or contain special components such as
		2191	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1443	relative and your working directory changes, the behaviour is undefined.	2192	your working directory changes, then the behaviour is undefined.
1444		2193
1445	Since there is no standard to do this, the portable implementation simply	2194	Since there is no portable change notification interface available, the
1446	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2195	portable implementation simply calls C<stat(2)> regularly on the path
1447	can specify a recommended polling interval for this case. If you specify	2196	to see if it changed somehow. You can specify a recommended polling
1448	a polling interval of C<0> (highly recommended!) then a I<suitable,	2197	interval for this case. If you specify a polling interval of C<0> (highly
1449	unspecified default> value will be used (which you can expect to be around	2198	recommended!) then a I<suitable, unspecified default> value will be used
1450	five seconds, although this might change dynamically). Libev will also	2199	(which you can expect to be around five seconds, although this might
1451	impose a minimum interval which is currently around C<0.1>, but thats	2200	change dynamically). Libev will also impose a minimum interval which is
1452	usually overkill.	2201	currently around C<0.1>, but that's usually overkill.
1453		2202
1454	This watcher type is not meant for massive numbers of stat watchers,	2203	This watcher type is not meant for massive numbers of stat watchers,
1455	as even with OS-supported change notifications, this can be	2204	as even with OS-supported change notifications, this can be
1456	resource-intensive.	2205	resource-intensive.
1457		2206
1458	At the time of this writing, only the Linux inotify interface is	2207	At the time of this writing, the only OS-specific interface implemented
1459	implemented (implementing kqueue support is left as an exercise for the	2208	is the Linux inotify interface (implementing kqueue support is left as an
1460	reader). Inotify will be used to give hints only and should not change the	2209	exercise for the reader. Note, however, that the author sees no way of
1461	semantics of C<ev_stat> watchers, which means that libev sometimes needs	2210	implementing C<ev_stat> semantics with kqueue, except as a hint).
1462	to fall back to regular polling again even with inotify, but changes are	2211
1463	usually detected immediately, and if the file exists there will be no	2212	=head3 ABI Issues (Largefile Support)
1464	polling.	2213
		2214	Libev by default (unless the user overrides this) uses the default
		2215	compilation environment, which means that on systems with large file
		2216	support disabled by default, you get the 32 bit version of the stat
		2217	structure. When using the library from programs that change the ABI to
		2218	use 64 bit file offsets the programs will fail. In that case you have to
		2219	compile libev with the same flags to get binary compatibility. This is
		2220	obviously the case with any flags that change the ABI, but the problem is
		2221	most noticeably displayed with ev_stat and large file support.
		2222
		2223	The solution for this is to lobby your distribution maker to make large
		2224	file interfaces available by default (as e.g. FreeBSD does) and not
		2225	optional. Libev cannot simply switch on large file support because it has
		2226	to exchange stat structures with application programs compiled using the
		2227	default compilation environment.
		2228
		2229	=head3 Inotify and Kqueue
		2230
		2231	When C<inotify (7)> support has been compiled into libev and present at
		2232	runtime, it will be used to speed up change detection where possible. The
		2233	inotify descriptor will be created lazily when the first C<ev_stat>
		2234	watcher is being started.
		2235
		2236	Inotify presence does not change the semantics of C<ev_stat> watchers
		2237	except that changes might be detected earlier, and in some cases, to avoid
		2238	making regular C<stat> calls. Even in the presence of inotify support
		2239	there are many cases where libev has to resort to regular C<stat> polling,
		2240	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2241	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2242	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2243	xfs are fully working) libev usually gets away without polling.
		2244
		2245	There is no support for kqueue, as apparently it cannot be used to
		2246	implement this functionality, due to the requirement of having a file
		2247	descriptor open on the object at all times, and detecting renames, unlinks
		2248	etc. is difficult.
		2249
		2250	=head3 C<stat ()> is a synchronous operation
		2251
		2252	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2253	the process. The exception are C<ev_stat> watchers - those call C<stat
		2254	()>, which is a synchronous operation.
		2255
		2256	For local paths, this usually doesn't matter: unless the system is very
		2257	busy or the intervals between stat's are large, a stat call will be fast,
		2258	as the path data is usually in memory already (except when starting the
		2259	watcher).
		2260
		2261	For networked file systems, calling C<stat ()> can block an indefinite
		2262	time due to network issues, and even under good conditions, a stat call
		2263	often takes multiple milliseconds.
		2264
		2265	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2266	paths, although this is fully supported by libev.
		2267
		2268	=head3 The special problem of stat time resolution
		2269
		2270	The C<stat ()> system call only supports full-second resolution portably,
		2271	and even on systems where the resolution is higher, most file systems
		2272	still only support whole seconds.
		2273
		2274	That means that, if the time is the only thing that changes, you can
		2275	easily miss updates: on the first update, C<ev_stat> detects a change and
		2276	calls your callback, which does something. When there is another update
		2277	within the same second, C<ev_stat> will be unable to detect unless the
		2278	stat data does change in other ways (e.g. file size).
		2279
		2280	The solution to this is to delay acting on a change for slightly more
		2281	than a second (or till slightly after the next full second boundary), using
		2282	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2283	ev_timer_again (loop, w)>).
		2284
		2285	The C<.02> offset is added to work around small timing inconsistencies
		2286	of some operating systems (where the second counter of the current time
		2287	might be be delayed. One such system is the Linux kernel, where a call to
		2288	C<gettimeofday> might return a timestamp with a full second later than
		2289	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2290	update file times then there will be a small window where the kernel uses
		2291	the previous second to update file times but libev might already execute
		2292	the timer callback).
1465		2293
1466	=head3 Watcher-Specific Functions and Data Members	2294	=head3 Watcher-Specific Functions and Data Members
1467		2295
1468	=over 4	2296	=over 4
1469		2297
…		…
1475	C<path>. The C<interval> is a hint on how quickly a change is expected to	2303	C<path>. The C<interval> is a hint on how quickly a change is expected to
1476	be detected and should normally be specified as C<0> to let libev choose	2304	be detected and should normally be specified as C<0> to let libev choose
1477	a suitable value. The memory pointed to by C<path> must point to the same	2305	a suitable value. The memory pointed to by C<path> must point to the same
1478	path for as long as the watcher is active.	2306	path for as long as the watcher is active.
1479		2307
1480	The callback will be receive C<EV_STAT> when a change was detected,	2308	The callback will receive an C<EV_STAT> event when a change was detected,
1481	relative to the attributes at the time the watcher was started (or the	2309	relative to the attributes at the time the watcher was started (or the
1482	last change was detected).	2310	last change was detected).
1483		2311
1484	=item ev_stat_stat (ev_stat *)	2312	=item ev_stat_stat (loop, ev_stat *)
1485		2313
1486	Updates the stat buffer immediately with new values. If you change the	2314	Updates the stat buffer immediately with new values. If you change the
1487	watched path in your callback, you could call this fucntion to avoid	2315	watched path in your callback, you could call this function to avoid
1488	detecting this change (while introducing a race condition). Can also be	2316	detecting this change (while introducing a race condition if you are not
1489	useful simply to find out the new values.	2317	the only one changing the path). Can also be useful simply to find out the
		2318	new values.
1490		2319
1491	=item ev_statdata attr [read-only]	2320	=item ev_statdata attr [read-only]
1492		2321
1493	The most-recently detected attributes of the file. Although the type is of	2322	The most-recently detected attributes of the file. Although the type is
1494	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2323	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1495	suitable for your system. If the C<st_nlink> member is C<0>, then there	2324	suitable for your system, but you can only rely on the POSIX-standardised
		2325	members to be present. If the C<st_nlink> member is C<0>, then there was
1496	was some error while C<stat>ing the file.	2326	some error while C<stat>ing the file.
1497		2327
1498	=item ev_statdata prev [read-only]	2328	=item ev_statdata prev [read-only]
1499		2329
1500	The previous attributes of the file. The callback gets invoked whenever	2330	The previous attributes of the file. The callback gets invoked whenever
1501	C<prev> != C<attr>.	2331	C<prev> != C<attr>, or, more precisely, one or more of these members
		2332	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2333	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1502		2334
1503	=item ev_tstamp interval [read-only]	2335	=item ev_tstamp interval [read-only]
1504		2336
1505	The specified interval.	2337	The specified interval.
1506		2338
1507	=item const char *path [read-only]	2339	=item const char *path [read-only]
1508		2340
1509	The filesystem path that is being watched.	2341	The file system path that is being watched.
1510		2342
1511	=back	2343	=back
1512		2344
		2345	=head3 Examples
		2346
1513	Example: Watch C</etc/passwd> for attribute changes.	2347	Example: Watch C</etc/passwd> for attribute changes.
1514		2348
1515	static void	2349	static void
1516	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2350	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1517	{	2351	{
1518	/* /etc/passwd changed in some way */	2352	/* /etc/passwd changed in some way */
1519	if (w->attr.st_nlink)	2353	if (w->attr.st_nlink)
1520	{	2354	{
1521	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2355	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1522	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2356	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1523	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2357	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1524	}	2358	}
1525	else	2359	else
1526	/* you shalt not abuse printf for puts */	2360	/* you shalt not abuse printf for puts */
1527	puts ("wow, /etc/passwd is not there, expect problems. "	2361	puts ("wow, /etc/passwd is not there, expect problems. "
1528	"if this is windows, they already arrived\n");	2362	"if this is windows, they already arrived\n");
1529	}	2363	}
1530		2364
1531	...	2365	...
1532	ev_stat passwd;	2366	ev_stat passwd;
1533		2367
1534	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	2368	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1535	ev_stat_start (loop, &passwd);	2369	ev_stat_start (loop, &passwd);
		2370
		2371	Example: Like above, but additionally use a one-second delay so we do not
		2372	miss updates (however, frequent updates will delay processing, too, so
		2373	one might do the work both on C<ev_stat> callback invocation I<and> on
		2374	C<ev_timer> callback invocation).
		2375
		2376	static ev_stat passwd;
		2377	static ev_timer timer;
		2378
		2379	static void
		2380	timer_cb (EV_P_ ev_timer *w, int revents)
		2381	{
		2382	ev_timer_stop (EV_A_ w);
		2383
		2384	/* now it's one second after the most recent passwd change */
		2385	}
		2386
		2387	static void
		2388	stat_cb (EV_P_ ev_stat *w, int revents)
		2389	{
		2390	/* reset the one-second timer */
		2391	ev_timer_again (EV_A_ &timer);
		2392	}
		2393
		2394	...
		2395	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2396	ev_stat_start (loop, &passwd);
		2397	ev_timer_init (&timer, timer_cb, 0., 1.02);
1536		2398
1537		2399
1538	=head2 C<ev_idle> - when you've got nothing better to do...	2400	=head2 C<ev_idle> - when you've got nothing better to do...
1539		2401
1540	Idle watchers trigger events when no other events of the same or higher	2402	Idle watchers trigger events when no other events of the same or higher
1541	priority are pending (prepare, check and other idle watchers do not	2403	priority are pending (prepare, check and other idle watchers do not count
1542	count).	2404	as receiving "events").
1543		2405
1544	That is, as long as your process is busy handling sockets or timeouts	2406	That is, as long as your process is busy handling sockets or timeouts
1545	(or even signals, imagine) of the same or higher priority it will not be	2407	(or even signals, imagine) of the same or higher priority it will not be
1546	triggered. But when your process is idle (or only lower-priority watchers	2408	triggered. But when your process is idle (or only lower-priority watchers
1547	are pending), the idle watchers are being called once per event loop	2409	are pending), the idle watchers are being called once per event loop
…		…
1558		2420
1559	=head3 Watcher-Specific Functions and Data Members	2421	=head3 Watcher-Specific Functions and Data Members
1560		2422
1561	=over 4	2423	=over 4
1562		2424
1563	=item ev_idle_init (ev_signal *, callback)	2425	=item ev_idle_init (ev_idle *, callback)
1564		2426
1565	Initialises and configures the idle watcher - it has no parameters of any	2427	Initialises and configures the idle watcher - it has no parameters of any
1566	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2428	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1567	believe me.	2429	believe me.
1568		2430
1569	=back	2431	=back
1570		2432
		2433	=head3 Examples
		2434
1571	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2435	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1572	callback, free it. Also, use no error checking, as usual.	2436	callback, free it. Also, use no error checking, as usual.
1573		2437
1574	static void	2438	static void
1575	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2439	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1576	{	2440	{
1577	free (w);	2441	free (w);
1578	// now do something you wanted to do when the program has	2442	// now do something you wanted to do when the program has
1579	// no longer asnything immediate to do.	2443	// no longer anything immediate to do.
1580	}	2444	}
1581		2445
1582	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2446	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1583	ev_idle_init (idle_watcher, idle_cb);	2447	ev_idle_init (idle_watcher, idle_cb);
1584	ev_idle_start (loop, idle_cb);	2448	ev_idle_start (loop, idle_watcher);
1585		2449
1586		2450
1587	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2451	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1588		2452
1589	Prepare and check watchers are usually (but not always) used in tandem:	2453	Prepare and check watchers are usually (but not always) used in pairs:
1590	prepare watchers get invoked before the process blocks and check watchers	2454	prepare watchers get invoked before the process blocks and check watchers
1591	afterwards.	2455	afterwards.
1592		2456
1593	You I<must not> call C<ev_loop> or similar functions that enter	2457	You I<must not> call C<ev_loop> or similar functions that enter
1594	the current event loop from either C<ev_prepare> or C<ev_check>	2458	the current event loop from either C<ev_prepare> or C<ev_check>
…		…
1597	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2461	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1598	C<ev_check> so if you have one watcher of each kind they will always be	2462	C<ev_check> so if you have one watcher of each kind they will always be
1599	called in pairs bracketing the blocking call.	2463	called in pairs bracketing the blocking call.
1600		2464
1601	Their main purpose is to integrate other event mechanisms into libev and	2465	Their main purpose is to integrate other event mechanisms into libev and
1602	their use is somewhat advanced. This could be used, for example, to track	2466	their use is somewhat advanced. They could be used, for example, to track
1603	variable changes, implement your own watchers, integrate net-snmp or a	2467	variable changes, implement your own watchers, integrate net-snmp or a
1604	coroutine library and lots more. They are also occasionally useful if	2468	coroutine library and lots more. They are also occasionally useful if
1605	you cache some data and want to flush it before blocking (for example,	2469	you cache some data and want to flush it before blocking (for example,
1606	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2470	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1607	watcher).	2471	watcher).
1608		2472
1609	This is done by examining in each prepare call which file descriptors need	2473	This is done by examining in each prepare call which file descriptors
1610	to be watched by the other library, registering C<ev_io> watchers for	2474	need to be watched by the other library, registering C<ev_io> watchers
1611	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2475	for them and starting an C<ev_timer> watcher for any timeouts (many
1612	provide just this functionality). Then, in the check watcher you check for	2476	libraries provide exactly this functionality). Then, in the check watcher,
1613	any events that occured (by checking the pending status of all watchers	2477	you check for any events that occurred (by checking the pending status
1614	and stopping them) and call back into the library. The I/O and timer	2478	of all watchers and stopping them) and call back into the library. The
1615	callbacks will never actually be called (but must be valid nevertheless,	2479	I/O and timer callbacks will never actually be called (but must be valid
1616	because you never know, you know?).	2480	nevertheless, because you never know, you know?).
1617		2481
1618	As another example, the Perl Coro module uses these hooks to integrate	2482	As another example, the Perl Coro module uses these hooks to integrate
1619	coroutines into libev programs, by yielding to other active coroutines	2483	coroutines into libev programs, by yielding to other active coroutines
1620	during each prepare and only letting the process block if no coroutines	2484	during each prepare and only letting the process block if no coroutines
1621	are ready to run (it's actually more complicated: it only runs coroutines	2485	are ready to run (it's actually more complicated: it only runs coroutines
…		…
1624	loop from blocking if lower-priority coroutines are active, thus mapping	2488	loop from blocking if lower-priority coroutines are active, thus mapping
1625	low-priority coroutines to idle/background tasks).	2489	low-priority coroutines to idle/background tasks).
1626		2490
1627	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2491	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1628	priority, to ensure that they are being run before any other watchers	2492	priority, to ensure that they are being run before any other watchers
		2493	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2494
1629	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2495	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1630	too) should not activate ("feed") events into libev. While libev fully	2496	activate ("feed") events into libev. While libev fully supports this, they
1631	supports this, they will be called before other C<ev_check> watchers	2497	might get executed before other C<ev_check> watchers did their job. As
1632	did their job. As C<ev_check> watchers are often used to embed other	2498	C<ev_check> watchers are often used to embed other (non-libev) event
1633	(non-libev) event loops those other event loops might be in an unusable	2499	loops those other event loops might be in an unusable state until their
1634	state until their C<ev_check> watcher ran (always remind yourself to	2500	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1635	coexist peacefully with others).	2501	others).
1636		2502
1637	=head3 Watcher-Specific Functions and Data Members	2503	=head3 Watcher-Specific Functions and Data Members
1638		2504
1639	=over 4	2505	=over 4
1640		2506
…		…
1642		2508
1643	=item ev_check_init (ev_check *, callback)	2509	=item ev_check_init (ev_check *, callback)
1644		2510
1645	Initialises and configures the prepare or check watcher - they have no	2511	Initialises and configures the prepare or check watcher - they have no
1646	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2512	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1647	macros, but using them is utterly, utterly and completely pointless.	2513	macros, but using them is utterly, utterly, utterly and completely
		2514	pointless.
1648		2515
1649	=back	2516	=back
		2517
		2518	=head3 Examples
1650		2519
1651	There are a number of principal ways to embed other event loops or modules	2520	There are a number of principal ways to embed other event loops or modules
1652	into libev. Here are some ideas on how to include libadns into libev	2521	into libev. Here are some ideas on how to include libadns into libev
1653	(there is a Perl module named C<EV::ADNS> that does this, which you could	2522	(there is a Perl module named C<EV::ADNS> that does this, which you could
1654	use for an actually working example. Another Perl module named C<EV::Glib>	2523	use as a working example. Another Perl module named C<EV::Glib> embeds a
1655	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV	2524	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1656	into the Glib event loop).	2525	Glib event loop).
1657		2526
1658	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	2527	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1659	and in a check watcher, destroy them and call into libadns. What follows	2528	and in a check watcher, destroy them and call into libadns. What follows
1660	is pseudo-code only of course. This requires you to either use a low	2529	is pseudo-code only of course. This requires you to either use a low
1661	priority for the check watcher or use C<ev_clear_pending> explicitly, as	2530	priority for the check watcher or use C<ev_clear_pending> explicitly, as
1662	the callbacks for the IO/timeout watchers might not have been called yet.	2531	the callbacks for the IO/timeout watchers might not have been called yet.
1663		2532
1664	static ev_io iow [nfd];	2533	static ev_io iow [nfd];
1665	static ev_timer tw;	2534	static ev_timer tw;
1666		2535
1667	static void	2536	static void
1668	io_cb (ev_loop *loop, ev_io *w, int revents)	2537	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1669	{	2538	{
1670	}	2539	}
1671		2540
1672	// create io watchers for each fd and a timer before blocking	2541	// create io watchers for each fd and a timer before blocking
1673	static void	2542	static void
1674	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2543	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1675	{	2544	{
1676	int timeout = 3600000;	2545	int timeout = 3600000;
1677	struct pollfd fds [nfd];	2546	struct pollfd fds [nfd];
1678	// actual code will need to loop here and realloc etc.	2547	// actual code will need to loop here and realloc etc.
1679	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2548	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1680		2549
1681	/* the callback is illegal, but won't be called as we stop during check */	2550	/* the callback is illegal, but won't be called as we stop during check */
1682	ev_timer_init (&tw, 0, timeout * 1e-3);	2551	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1683	ev_timer_start (loop, &tw);	2552	ev_timer_start (loop, &tw);
1684		2553
1685	// create one ev_io per pollfd	2554	// create one ev_io per pollfd
1686	for (int i = 0; i < nfd; ++i)	2555	for (int i = 0; i < nfd; ++i)
1687	{	2556	{
1688	ev_io_init (iow + i, io_cb, fds [i].fd,	2557	ev_io_init (iow + i, io_cb, fds [i].fd,
1689	((fds [i].events & POLLIN ? EV_READ : 0)	2558	((fds [i].events & POLLIN ? EV_READ : 0)
1690	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2559	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1691		2560
1692	fds [i].revents = 0;	2561	fds [i].revents = 0;
1693	ev_io_start (loop, iow + i);	2562	ev_io_start (loop, iow + i);
1694	}	2563	}
1695	}	2564	}
1696		2565
1697	// stop all watchers after blocking	2566	// stop all watchers after blocking
1698	static void	2567	static void
1699	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2568	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1700	{	2569	{
1701	ev_timer_stop (loop, &tw);	2570	ev_timer_stop (loop, &tw);
1702		2571
1703	for (int i = 0; i < nfd; ++i)	2572	for (int i = 0; i < nfd; ++i)
1704	{	2573	{
1705	// set the relevant poll flags	2574	// set the relevant poll flags
1706	// could also call adns_processreadable etc. here	2575	// could also call adns_processreadable etc. here
1707	struct pollfd *fd = fds + i;	2576	struct pollfd *fd = fds + i;
1708	int revents = ev_clear_pending (iow + i);	2577	int revents = ev_clear_pending (iow + i);
1709	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;	2578	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1710	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;	2579	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1711		2580
1712	// now stop the watcher	2581	// now stop the watcher
1713	ev_io_stop (loop, iow + i);	2582	ev_io_stop (loop, iow + i);
1714	}	2583	}
1715		2584
1716	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2585	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1717	}	2586	}
1718		2587
1719	Method 2: This would be just like method 1, but you run C<adns_afterpoll>	2588	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
1720	in the prepare watcher and would dispose of the check watcher.	2589	in the prepare watcher and would dispose of the check watcher.
1721		2590
1722	Method 3: If the module to be embedded supports explicit event	2591	Method 3: If the module to be embedded supports explicit event
1723	notification (adns does), you can also make use of the actual watcher	2592	notification (libadns does), you can also make use of the actual watcher
1724	callbacks, and only destroy/create the watchers in the prepare watcher.	2593	callbacks, and only destroy/create the watchers in the prepare watcher.
1725		2594
1726	static void	2595	static void
1727	timer_cb (EV_P_ ev_timer *w, int revents)	2596	timer_cb (EV_P_ ev_timer *w, int revents)
1728	{	2597	{
1729	adns_state ads = (adns_state)w->data;	2598	adns_state ads = (adns_state)w->data;
1730	update_now (EV_A);	2599	update_now (EV_A);
1731		2600
1732	adns_processtimeouts (ads, &tv_now);	2601	adns_processtimeouts (ads, &tv_now);
1733	}	2602	}
1734		2603
1735	static void	2604	static void
1736	io_cb (EV_P_ ev_io *w, int revents)	2605	io_cb (EV_P_ ev_io *w, int revents)
1737	{	2606	{
1738	adns_state ads = (adns_state)w->data;	2607	adns_state ads = (adns_state)w->data;
1739	update_now (EV_A);	2608	update_now (EV_A);
1740		2609
1741	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);	2610	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
1742	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);	2611	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
1743	}	2612	}
1744		2613
1745	// do not ever call adns_afterpoll	2614	// do not ever call adns_afterpoll
1746		2615
1747	Method 4: Do not use a prepare or check watcher because the module you	2616	Method 4: Do not use a prepare or check watcher because the module you
1748	want to embed is too inflexible to support it. Instead, youc na override	2617	want to embed is not flexible enough to support it. Instead, you can
1749	their poll function. The drawback with this solution is that the main	2618	override their poll function. The drawback with this solution is that the
1750	loop is now no longer controllable by EV. The C<Glib::EV> module does	2619	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
1751	this.	2620	this approach, effectively embedding EV as a client into the horrible
		2621	libglib event loop.
1752		2622
1753	static gint	2623	static gint
1754	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	2624	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1755	{	2625	{
1756	int got_events = 0;	2626	int got_events = 0;
1757		2627
1758	for (n = 0; n < nfds; ++n)	2628	for (n = 0; n < nfds; ++n)
1759	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events	2629	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1760		2630
1761	if (timeout >= 0)	2631	if (timeout >= 0)
1762	// create/start timer	2632	// create/start timer
1763		2633
1764	// poll	2634	// poll
1765	ev_loop (EV_A_ 0);	2635	ev_loop (EV_A_ 0);
1766		2636
1767	// stop timer again	2637	// stop timer again
1768	if (timeout >= 0)	2638	if (timeout >= 0)
1769	ev_timer_stop (EV_A_ &to);	2639	ev_timer_stop (EV_A_ &to);
1770		2640
1771	// stop io watchers again - their callbacks should have set	2641	// stop io watchers again - their callbacks should have set
1772	for (n = 0; n < nfds; ++n)	2642	for (n = 0; n < nfds; ++n)
1773	ev_io_stop (EV_A_ iow [n]);	2643	ev_io_stop (EV_A_ iow [n]);
1774		2644
1775	return got_events;	2645	return got_events;
1776	}	2646	}
1777		2647
1778		2648
1779	=head2 C<ev_embed> - when one backend isn't enough...	2649	=head2 C<ev_embed> - when one backend isn't enough...
1780		2650
1781	This is a rather advanced watcher type that lets you embed one event loop	2651	This is a rather advanced watcher type that lets you embed one event loop
…		…
1787	prioritise I/O.	2657	prioritise I/O.
1788		2658
1789	As an example for a bug workaround, the kqueue backend might only support	2659	As an example for a bug workaround, the kqueue backend might only support
1790	sockets on some platform, so it is unusable as generic backend, but you	2660	sockets on some platform, so it is unusable as generic backend, but you
1791	still want to make use of it because you have many sockets and it scales	2661	still want to make use of it because you have many sockets and it scales
1792	so nicely. In this case, you would create a kqueue-based loop and embed it	2662	so nicely. In this case, you would create a kqueue-based loop and embed
1793	into your default loop (which might use e.g. poll). Overall operation will	2663	it into your default loop (which might use e.g. poll). Overall operation
1794	be a bit slower because first libev has to poll and then call kevent, but	2664	will be a bit slower because first libev has to call C<poll> and then
1795	at least you can use both at what they are best.	2665	C<kevent>, but at least you can use both mechanisms for what they are
		2666	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1796		2667
1797	As for prioritising I/O: rarely you have the case where some fds have	2668	As for prioritising I/O: under rare circumstances you have the case where
1798	to be watched and handled very quickly (with low latency), and even	2669	some fds have to be watched and handled very quickly (with low latency),
1799	priorities and idle watchers might have too much overhead. In this case	2670	and even priorities and idle watchers might have too much overhead. In
1800	you would put all the high priority stuff in one loop and all the rest in	2671	this case you would put all the high priority stuff in one loop and all
1801	a second one, and embed the second one in the first.	2672	the rest in a second one, and embed the second one in the first.
1802		2673
1803	As long as the watcher is active, the callback will be invoked every time	2674	As long as the watcher is active, the callback will be invoked every
1804	there might be events pending in the embedded loop. The callback must then	2675	time there might be events pending in the embedded loop. The callback
1805	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2676	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1806	their callbacks (you could also start an idle watcher to give the embedded	2677	sweep and invoke their callbacks (the callback doesn't need to invoke the
1807	loop strictly lower priority for example). You can also set the callback	2678	C<ev_embed_sweep> function directly, it could also start an idle watcher
1808	to C<0>, in which case the embed watcher will automatically execute the	2679	to give the embedded loop strictly lower priority for example).
1809	embedded loop sweep.
1810		2680
1811	As long as the watcher is started it will automatically handle events. The	2681	You can also set the callback to C<0>, in which case the embed watcher
1812	callback will be invoked whenever some events have been handled. You can	2682	will automatically execute the embedded loop sweep whenever necessary.
1813	set the callback to C<0> to avoid having to specify one if you are not
1814	interested in that.
1815		2683
1816	Also, there have not currently been made special provisions for forking:	2684	Fork detection will be handled transparently while the C<ev_embed> watcher
1817	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2685	is active, i.e., the embedded loop will automatically be forked when the
1818	but you will also have to stop and restart any C<ev_embed> watchers	2686	embedding loop forks. In other cases, the user is responsible for calling
1819	yourself.	2687	C<ev_loop_fork> on the embedded loop.
1820		2688
1821	Unfortunately, not all backends are embeddable, only the ones returned by	2689	Unfortunately, not all backends are embeddable: only the ones returned by
1822	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2690	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1823	portable one.	2691	portable one.
1824		2692
1825	So when you want to use this feature you will always have to be prepared	2693	So when you want to use this feature you will always have to be prepared
1826	that you cannot get an embeddable loop. The recommended way to get around	2694	that you cannot get an embeddable loop. The recommended way to get around
1827	this is to have a separate variables for your embeddable loop, try to	2695	this is to have a separate variables for your embeddable loop, try to
1828	create it, and if that fails, use the normal loop for everything:	2696	create it, and if that fails, use the normal loop for everything.
1829		2697
1830	struct ev_loop *loop_hi = ev_default_init (0);	2698	=head3 C<ev_embed> and fork
1831	struct ev_loop *loop_lo = 0;
1832	struct ev_embed embed;
1833
1834	// see if there is a chance of getting one that works
1835	// (remember that a flags value of 0 means autodetection)
1836	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1837	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1838	: 0;
1839		2699
1840	// if we got one, then embed it, otherwise default to loop_hi	2700	While the C<ev_embed> watcher is running, forks in the embedding loop will
1841	if (loop_lo)	2701	automatically be applied to the embedded loop as well, so no special
1842	{	2702	fork handling is required in that case. When the watcher is not running,
1843	ev_embed_init (&embed, 0, loop_lo);	2703	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1844	ev_embed_start (loop_hi, &embed);	2704	as applicable.
1845	}
1846	else
1847	loop_lo = loop_hi;
1848		2705
1849	=head3 Watcher-Specific Functions and Data Members	2706	=head3 Watcher-Specific Functions and Data Members
1850		2707
1851	=over 4	2708	=over 4
1852		2709
…		…
1856		2713
1857	Configures the watcher to embed the given loop, which must be	2714	Configures the watcher to embed the given loop, which must be
1858	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	2715	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1859	invoked automatically, otherwise it is the responsibility of the callback	2716	invoked automatically, otherwise it is the responsibility of the callback
1860	to invoke it (it will continue to be called until the sweep has been done,	2717	to invoke it (it will continue to be called until the sweep has been done,
1861	if you do not want thta, you need to temporarily stop the embed watcher).	2718	if you do not want that, you need to temporarily stop the embed watcher).
1862		2719
1863	=item ev_embed_sweep (loop, ev_embed *)	2720	=item ev_embed_sweep (loop, ev_embed *)
1864		2721
1865	Make a single, non-blocking sweep over the embedded loop. This works	2722	Make a single, non-blocking sweep over the embedded loop. This works
1866	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	2723	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
1867	apropriate way for embedded loops.	2724	appropriate way for embedded loops.
1868		2725
1869	=item struct ev_loop *other [read-only]	2726	=item struct ev_loop *other [read-only]
1870		2727
1871	The embedded event loop.	2728	The embedded event loop.
1872		2729
1873	=back	2730	=back
		2731
		2732	=head3 Examples
		2733
		2734	Example: Try to get an embeddable event loop and embed it into the default
		2735	event loop. If that is not possible, use the default loop. The default
		2736	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2737	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2738	used).
		2739
		2740	struct ev_loop *loop_hi = ev_default_init (0);
		2741	struct ev_loop *loop_lo = 0;
		2742	ev_embed embed;
		2743
		2744	// see if there is a chance of getting one that works
		2745	// (remember that a flags value of 0 means autodetection)
		2746	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2747	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2748	: 0;
		2749
		2750	// if we got one, then embed it, otherwise default to loop_hi
		2751	if (loop_lo)
		2752	{
		2753	ev_embed_init (&embed, 0, loop_lo);
		2754	ev_embed_start (loop_hi, &embed);
		2755	}
		2756	else
		2757	loop_lo = loop_hi;
		2758
		2759	Example: Check if kqueue is available but not recommended and create
		2760	a kqueue backend for use with sockets (which usually work with any
		2761	kqueue implementation). Store the kqueue/socket-only event loop in
		2762	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2763
		2764	struct ev_loop *loop = ev_default_init (0);
		2765	struct ev_loop *loop_socket = 0;
		2766	ev_embed embed;
		2767
		2768	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2769	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2770	{
		2771	ev_embed_init (&embed, 0, loop_socket);
		2772	ev_embed_start (loop, &embed);
		2773	}
		2774
		2775	if (!loop_socket)
		2776	loop_socket = loop;
		2777
		2778	// now use loop_socket for all sockets, and loop for everything else
1874		2779
1875		2780
1876	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	2781	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
1877		2782
1878	Fork watchers are called when a C<fork ()> was detected (usually because	2783	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
1881	event loop blocks next and before C<ev_check> watchers are being called,	2786	event loop blocks next and before C<ev_check> watchers are being called,
1882	and only in the child after the fork. If whoever good citizen calling	2787	and only in the child after the fork. If whoever good citizen calling
1883	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2788	C<ev_default_fork> cheats and calls it in the wrong process, the fork
1884	handlers will be invoked, too, of course.	2789	handlers will be invoked, too, of course.
1885		2790
		2791	=head3 The special problem of life after fork - how is it possible?
		2792
		2793	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2794	up/change the process environment, followed by a call to C<exec()>. This
		2795	sequence should be handled by libev without any problems.
		2796
		2797	This changes when the application actually wants to do event handling
		2798	in the child, or both parent in child, in effect "continuing" after the
		2799	fork.
		2800
		2801	The default mode of operation (for libev, with application help to detect
		2802	forks) is to duplicate all the state in the child, as would be expected
		2803	when I<either> the parent I<or> the child process continues.
		2804
		2805	When both processes want to continue using libev, then this is usually the
		2806	wrong result. In that case, usually one process (typically the parent) is
		2807	supposed to continue with all watchers in place as before, while the other
		2808	process typically wants to start fresh, i.e. without any active watchers.
		2809
		2810	The cleanest and most efficient way to achieve that with libev is to
		2811	simply create a new event loop, which of course will be "empty", and
		2812	use that for new watchers. This has the advantage of not touching more
		2813	memory than necessary, and thus avoiding the copy-on-write, and the
		2814	disadvantage of having to use multiple event loops (which do not support
		2815	signal watchers).
		2816
		2817	When this is not possible, or you want to use the default loop for
		2818	other reasons, then in the process that wants to start "fresh", call
		2819	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2820	the default loop will "orphan" (not stop) all registered watchers, so you
		2821	have to be careful not to execute code that modifies those watchers. Note
		2822	also that in that case, you have to re-register any signal watchers.
		2823
1886	=head3 Watcher-Specific Functions and Data Members	2824	=head3 Watcher-Specific Functions and Data Members
1887		2825
1888	=over 4	2826	=over 4
1889		2827
1890	=item ev_fork_init (ev_signal *, callback)	2828	=item ev_fork_init (ev_signal *, callback)
…		…
1894	believe me.	2832	believe me.
1895		2833
1896	=back	2834	=back
1897		2835
1898		2836
		2837	=head2 C<ev_async> - how to wake up another event loop
		2838
		2839	In general, you cannot use an C<ev_loop> from multiple threads or other
		2840	asynchronous sources such as signal handlers (as opposed to multiple event
		2841	loops - those are of course safe to use in different threads).
		2842
		2843	Sometimes, however, you need to wake up another event loop you do not
		2844	control, for example because it belongs to another thread. This is what
		2845	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2846	can signal it by calling C<ev_async_send>, which is thread- and signal
		2847	safe.
		2848
		2849	This functionality is very similar to C<ev_signal> watchers, as signals,
		2850	too, are asynchronous in nature, and signals, too, will be compressed
		2851	(i.e. the number of callback invocations may be less than the number of
		2852	C<ev_async_sent> calls).
		2853
		2854	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2855	just the default loop.
		2856
		2857	=head3 Queueing
		2858
		2859	C<ev_async> does not support queueing of data in any way. The reason
		2860	is that the author does not know of a simple (or any) algorithm for a
		2861	multiple-writer-single-reader queue that works in all cases and doesn't
		2862	need elaborate support such as pthreads.
		2863
		2864	That means that if you want to queue data, you have to provide your own
		2865	queue. But at least I can tell you how to implement locking around your
		2866	queue:
		2867
		2868	=over 4
		2869
		2870	=item queueing from a signal handler context
		2871
		2872	To implement race-free queueing, you simply add to the queue in the signal
		2873	handler but you block the signal handler in the watcher callback. Here is
		2874	an example that does that for some fictitious SIGUSR1 handler:
		2875
		2876	static ev_async mysig;
		2877
		2878	static void
		2879	sigusr1_handler (void)
		2880	{
		2881	sometype data;
		2882
		2883	// no locking etc.
		2884	queue_put (data);
		2885	ev_async_send (EV_DEFAULT_ &mysig);
		2886	}
		2887
		2888	static void
		2889	mysig_cb (EV_P_ ev_async *w, int revents)
		2890	{
		2891	sometype data;
		2892	sigset_t block, prev;
		2893
		2894	sigemptyset (&block);
		2895	sigaddset (&block, SIGUSR1);
		2896	sigprocmask (SIG_BLOCK, &block, &prev);
		2897
		2898	while (queue_get (&data))
		2899	process (data);
		2900
		2901	if (sigismember (&prev, SIGUSR1)
		2902	sigprocmask (SIG_UNBLOCK, &block, 0);
		2903	}
		2904
		2905	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2906	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2907	either...).
		2908
		2909	=item queueing from a thread context
		2910
		2911	The strategy for threads is different, as you cannot (easily) block
		2912	threads but you can easily preempt them, so to queue safely you need to
		2913	employ a traditional mutex lock, such as in this pthread example:
		2914
		2915	static ev_async mysig;
		2916	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2917
		2918	static void
		2919	otherthread (void)
		2920	{
		2921	// only need to lock the actual queueing operation
		2922	pthread_mutex_lock (&mymutex);
		2923	queue_put (data);
		2924	pthread_mutex_unlock (&mymutex);
		2925
		2926	ev_async_send (EV_DEFAULT_ &mysig);
		2927	}
		2928
		2929	static void
		2930	mysig_cb (EV_P_ ev_async *w, int revents)
		2931	{
		2932	pthread_mutex_lock (&mymutex);
		2933
		2934	while (queue_get (&data))
		2935	process (data);
		2936
		2937	pthread_mutex_unlock (&mymutex);
		2938	}
		2939
		2940	=back
		2941
		2942
		2943	=head3 Watcher-Specific Functions and Data Members
		2944
		2945	=over 4
		2946
		2947	=item ev_async_init (ev_async *, callback)
		2948
		2949	Initialises and configures the async watcher - it has no parameters of any
		2950	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		2951	trust me.
		2952
		2953	=item ev_async_send (loop, ev_async *)
		2954
		2955	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2956	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2957	C<ev_feed_event>, this call is safe to do from other threads, signal or
		2958	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		2959	section below on what exactly this means).
		2960
		2961	Note that, as with other watchers in libev, multiple events might get
		2962	compressed into a single callback invocation (another way to look at this
		2963	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		2964	reset when the event loop detects that).
		2965
		2966	This call incurs the overhead of a system call only once per event loop
		2967	iteration, so while the overhead might be noticeable, it doesn't apply to
		2968	repeated calls to C<ev_async_send> for the same event loop.
		2969
		2970	=item bool = ev_async_pending (ev_async *)
		2971
		2972	Returns a non-zero value when C<ev_async_send> has been called on the
		2973	watcher but the event has not yet been processed (or even noted) by the
		2974	event loop.
		2975
		2976	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2977	the loop iterates next and checks for the watcher to have become active,
		2978	it will reset the flag again. C<ev_async_pending> can be used to very
		2979	quickly check whether invoking the loop might be a good idea.
		2980
		2981	Not that this does I<not> check whether the watcher itself is pending,
		2982	only whether it has been requested to make this watcher pending: there
		2983	is a time window between the event loop checking and resetting the async
		2984	notification, and the callback being invoked.
		2985
		2986	=back
		2987
		2988
1899	=head1 OTHER FUNCTIONS	2989	=head1 OTHER FUNCTIONS
1900		2990
1901	There are some other functions of possible interest. Described. Here. Now.	2991	There are some other functions of possible interest. Described. Here. Now.
1902		2992
1903	=over 4	2993	=over 4
1904		2994
1905	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	2995	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1906		2996
1907	This function combines a simple timer and an I/O watcher, calls your	2997	This function combines a simple timer and an I/O watcher, calls your
1908	callback on whichever event happens first and automatically stop both	2998	callback on whichever event happens first and automatically stops both
1909	watchers. This is useful if you want to wait for a single event on an fd	2999	watchers. This is useful if you want to wait for a single event on an fd
1910	or timeout without having to allocate/configure/start/stop/free one or	3000	or timeout without having to allocate/configure/start/stop/free one or
1911	more watchers yourself.	3001	more watchers yourself.
1912		3002
1913	If C<fd> is less than 0, then no I/O watcher will be started and events	3003	If C<fd> is less than 0, then no I/O watcher will be started and the
1914	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3004	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1915	C<events> set will be craeted and started.	3005	the given C<fd> and C<events> set will be created and started.
1916		3006
1917	If C<timeout> is less than 0, then no timeout watcher will be	3007	If C<timeout> is less than 0, then no timeout watcher will be
1918	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3008	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1919	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3009	repeat = 0) will be started. C<0> is a valid timeout.
1920	dubious value.
1921		3010
1922	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3011	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
1923	passed an C<revents> set like normal event callbacks (a combination of	3012	passed an C<revents> set like normal event callbacks (a combination of
1924	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3013	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
1925	value passed to C<ev_once>:	3014	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3015	a timeout and an io event at the same time - you probably should give io
		3016	events precedence.
1926		3017
		3018	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3019
1927	static void stdin_ready (int revents, void *arg)	3020	static void stdin_ready (int revents, void *arg)
1928	{	3021	{
1929	if (revents & EV_TIMEOUT)
1930	/* doh, nothing entered */;
1931	else if (revents & EV_READ)	3022	if (revents & EV_READ)
1932	/* stdin might have data for us, joy! */;	3023	/* stdin might have data for us, joy! */;
		3024	else if (revents & EV_TIMEOUT)
		3025	/* doh, nothing entered */;
1933	}	3026	}
1934		3027
1935	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3028	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1936		3029
1937	=item ev_feed_event (ev_loop *, watcher *, int revents)	3030	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
1938		3031
1939	Feeds the given event set into the event loop, as if the specified event	3032	Feeds the given event set into the event loop, as if the specified event
1940	had happened for the specified watcher (which must be a pointer to an	3033	had happened for the specified watcher (which must be a pointer to an
1941	initialised but not necessarily started event watcher).	3034	initialised but not necessarily started event watcher).
1942		3035
1943	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3036	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
1944		3037
1945	Feed an event on the given fd, as if a file descriptor backend detected	3038	Feed an event on the given fd, as if a file descriptor backend detected
1946	the given events it.	3039	the given events it.
1947		3040
1948	=item ev_feed_signal_event (ev_loop *loop, int signum)	3041	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
1949		3042
1950	Feed an event as if the given signal occured (C<loop> must be the default	3043	Feed an event as if the given signal occurred (C<loop> must be the default
1951	loop!).	3044	loop!).
1952		3045
1953	=back	3046	=back
1954		3047
1955		3048
…		…
1971		3064
1972	=item * Priorities are not currently supported. Initialising priorities	3065	=item * Priorities are not currently supported. Initialising priorities
1973	will fail and all watchers will have the same priority, even though there	3066	will fail and all watchers will have the same priority, even though there
1974	is an ev_pri field.	3067	is an ev_pri field.
1975		3068
		3069	=item * In libevent, the last base created gets the signals, in libev, the
		3070	first base created (== the default loop) gets the signals.
		3071
1976	=item * Other members are not supported.	3072	=item * Other members are not supported.
1977		3073
1978	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3074	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1979	to use the libev header file and library.	3075	to use the libev header file and library.
1980		3076
1981	=back	3077	=back
1982		3078
1983	=head1 C++ SUPPORT	3079	=head1 C++ SUPPORT
1984		3080
1985	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3081	Libev comes with some simplistic wrapper classes for C++ that mainly allow
1986	you to use some convinience methods to start/stop watchers and also change	3082	you to use some convenience methods to start/stop watchers and also change
1987	the callback model to a model using method callbacks on objects.	3083	the callback model to a model using method callbacks on objects.
1988		3084
1989	To use it,	3085	To use it,
1990		3086
1991	#include <ev++.h>	3087	#include <ev++.h>
1992		3088
1993	This automatically includes F<ev.h> and puts all of its definitions (many	3089	This automatically includes F<ev.h> and puts all of its definitions (many
1994	of them macros) into the global namespace. All C++ specific things are	3090	of them macros) into the global namespace. All C++ specific things are
1995	put into the C<ev> namespace. It should support all the same embedding	3091	put into the C<ev> namespace. It should support all the same embedding
1996	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	3092	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
2063	your compiler is good :), then the method will be fully inlined into the	3159	your compiler is good :), then the method will be fully inlined into the
2064	thunking function, making it as fast as a direct C callback.	3160	thunking function, making it as fast as a direct C callback.
2065		3161
2066	Example: simple class declaration and watcher initialisation	3162	Example: simple class declaration and watcher initialisation
2067		3163
2068	struct myclass	3164	struct myclass
2069	{	3165	{
2070	void io_cb (ev::io &w, int revents) { }	3166	void io_cb (ev::io &w, int revents) { }
2071	}	3167	}
2072		3168
2073	myclass obj;	3169	myclass obj;
2074	ev::io iow;	3170	ev::io iow;
2075	iow.set <myclass, &myclass::io_cb> (&obj);	3171	iow.set <myclass, &myclass::io_cb> (&obj);
		3172
		3173	=item w->set (object *)
		3174
		3175	This is an B<experimental> feature that might go away in a future version.
		3176
		3177	This is a variation of a method callback - leaving out the method to call
		3178	will default the method to C<operator ()>, which makes it possible to use
		3179	functor objects without having to manually specify the C<operator ()> all
		3180	the time. Incidentally, you can then also leave out the template argument
		3181	list.
		3182
		3183	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3184	int revents)>.
		3185
		3186	See the method-C<set> above for more details.
		3187
		3188	Example: use a functor object as callback.
		3189
		3190	struct myfunctor
		3191	{
		3192	void operator() (ev::io &w, int revents)
		3193	{
		3194	...
		3195	}
		3196	}
		3197
		3198	myfunctor f;
		3199
		3200	ev::io w;
		3201	w.set (&f);
2076		3202
2077	=item w->set<function> (void *data = 0)	3203	=item w->set<function> (void *data = 0)
2078		3204
2079	Also sets a callback, but uses a static method or plain function as	3205	Also sets a callback, but uses a static method or plain function as
2080	callback. The optional C<data> argument will be stored in the watcher's	3206	callback. The optional C<data> argument will be stored in the watcher's
…		…
2082		3208
2083	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	3209	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2084		3210
2085	See the method-C<set> above for more details.	3211	See the method-C<set> above for more details.
2086		3212
2087	Example:	3213	Example: Use a plain function as callback.
2088		3214
2089	static void io_cb (ev::io &w, int revents) { }	3215	static void io_cb (ev::io &w, int revents) { }
2090	iow.set <io_cb> ();	3216	iow.set <io_cb> ();
2091		3217
2092	=item w->set (struct ev_loop *)	3218	=item w->set (struct ev_loop *)
2093		3219
2094	Associates a different C<struct ev_loop> with this watcher. You can only	3220	Associates a different C<struct ev_loop> with this watcher. You can only
2095	do this when the watcher is inactive (and not pending either).	3221	do this when the watcher is inactive (and not pending either).
2096		3222
2097	=item w->set ([args])	3223	=item w->set ([arguments])
2098		3224
2099	Basically the same as C<ev_TYPE_set>, with the same args. Must be	3225	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
2100	called at least once. Unlike the C counterpart, an active watcher gets	3226	called at least once. Unlike the C counterpart, an active watcher gets
2101	automatically stopped and restarted when reconfiguring it with this	3227	automatically stopped and restarted when reconfiguring it with this
2102	method.	3228	method.
2103		3229
2104	=item w->start ()	3230	=item w->start ()
…		…
2128	=back	3254	=back
2129		3255
2130	Example: Define a class with an IO and idle watcher, start one of them in	3256	Example: Define a class with an IO and idle watcher, start one of them in
2131	the constructor.	3257	the constructor.
2132		3258
2133	class myclass	3259	class myclass
2134	{	3260	{
2135	ev_io io; void io_cb (ev::io &w, int revents);	3261	ev::io io ; void io_cb (ev::io &w, int revents);
2136	ev_idle idle void idle_cb (ev::idle &w, int revents);	3262	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2137		3263
2138	myclass ();	3264	myclass (int fd)
2139	}	3265	{
2140
2141	myclass::myclass (int fd)
2142	{
2143	io .set <myclass, &myclass::io_cb > (this);	3266	io .set <myclass, &myclass::io_cb > (this);
2144	idle.set <myclass, &myclass::idle_cb> (this);	3267	idle.set <myclass, &myclass::idle_cb> (this);
2145		3268
2146	io.start (fd, ev::READ);	3269	io.start (fd, ev::READ);
		3270	}
2147	}	3271	};
		3272
		3273
		3274	=head1 OTHER LANGUAGE BINDINGS
		3275
		3276	Libev does not offer other language bindings itself, but bindings for a
		3277	number of languages exist in the form of third-party packages. If you know
		3278	any interesting language binding in addition to the ones listed here, drop
		3279	me a note.
		3280
		3281	=over 4
		3282
		3283	=item Perl
		3284
		3285	The EV module implements the full libev API and is actually used to test
		3286	libev. EV is developed together with libev. Apart from the EV core module,
		3287	there are additional modules that implement libev-compatible interfaces
		3288	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3289	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3290	and C<EV::Glib>).
		3291
		3292	It can be found and installed via CPAN, its homepage is at
		3293	L<http://software.schmorp.de/pkg/EV>.
		3294
		3295	=item Python
		3296
		3297	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3298	seems to be quite complete and well-documented.
		3299
		3300	=item Ruby
		3301
		3302	Tony Arcieri has written a ruby extension that offers access to a subset
		3303	of the libev API and adds file handle abstractions, asynchronous DNS and
		3304	more on top of it. It can be found via gem servers. Its homepage is at
		3305	L<http://rev.rubyforge.org/>.
		3306
		3307	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3308	makes rev work even on mingw.
		3309
		3310	=item Haskell
		3311
		3312	A haskell binding to libev is available at
		3313	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3314
		3315	=item D
		3316
		3317	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3318	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3319
		3320	=item Ocaml
		3321
		3322	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3323	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3324
		3325	=back
2148		3326
2149		3327
2150	=head1 MACRO MAGIC	3328	=head1 MACRO MAGIC
2151		3329
2152	Libev can be compiled with a variety of options, the most fundamantal	3330	Libev can be compiled with a variety of options, the most fundamental
2153	of which is C<EV_MULTIPLICITY>. This option determines whether (most)	3331	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2154	functions and callbacks have an initial C<struct ev_loop *> argument.	3332	functions and callbacks have an initial C<struct ev_loop *> argument.
2155		3333
2156	To make it easier to write programs that cope with either variant, the	3334	To make it easier to write programs that cope with either variant, the
2157	following macros are defined:	3335	following macros are defined:
…		…
2162		3340
2163	This provides the loop I<argument> for functions, if one is required ("ev	3341	This provides the loop I<argument> for functions, if one is required ("ev
2164	loop argument"). The C<EV_A> form is used when this is the sole argument,	3342	loop argument"). The C<EV_A> form is used when this is the sole argument,
2165	C<EV_A_> is used when other arguments are following. Example:	3343	C<EV_A_> is used when other arguments are following. Example:
2166		3344
2167	ev_unref (EV_A);	3345	ev_unref (EV_A);
2168	ev_timer_add (EV_A_ watcher);	3346	ev_timer_add (EV_A_ watcher);
2169	ev_loop (EV_A_ 0);	3347	ev_loop (EV_A_ 0);
2170		3348
2171	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	3349	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2172	which is often provided by the following macro.	3350	which is often provided by the following macro.
2173		3351
2174	=item C<EV_P>, C<EV_P_>	3352	=item C<EV_P>, C<EV_P_>
2175		3353
2176	This provides the loop I<parameter> for functions, if one is required ("ev	3354	This provides the loop I<parameter> for functions, if one is required ("ev
2177	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	3355	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
2178	C<EV_P_> is used when other parameters are following. Example:	3356	C<EV_P_> is used when other parameters are following. Example:
2179		3357
2180	// this is how ev_unref is being declared	3358	// this is how ev_unref is being declared
2181	static void ev_unref (EV_P);	3359	static void ev_unref (EV_P);
2182		3360
2183	// this is how you can declare your typical callback	3361	// this is how you can declare your typical callback
2184	static void cb (EV_P_ ev_timer *w, int revents)	3362	static void cb (EV_P_ ev_timer *w, int revents)
2185		3363
2186	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	3364	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
2187	suitable for use with C<EV_A>.	3365	suitable for use with C<EV_A>.
2188		3366
2189	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3367	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2190		3368
2191	Similar to the other two macros, this gives you the value of the default	3369	Similar to the other two macros, this gives you the value of the default
2192	loop, if multiple loops are supported ("ev loop default").	3370	loop, if multiple loops are supported ("ev loop default").
		3371
		3372	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3373
		3374	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3375	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3376	is undefined when the default loop has not been initialised by a previous
		3377	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3378
		3379	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3380	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
2193		3381
2194	=back	3382	=back
2195		3383
2196	Example: Declare and initialise a check watcher, utilising the above	3384	Example: Declare and initialise a check watcher, utilising the above
2197	macros so it will work regardless of whether multiple loops are supported	3385	macros so it will work regardless of whether multiple loops are supported
2198	or not.	3386	or not.
2199		3387
2200	static void	3388	static void
2201	check_cb (EV_P_ ev_timer *w, int revents)	3389	check_cb (EV_P_ ev_timer *w, int revents)
2202	{	3390	{
2203	ev_check_stop (EV_A_ w);	3391	ev_check_stop (EV_A_ w);
2204	}	3392	}
2205		3393
2206	ev_check check;	3394	ev_check check;
2207	ev_check_init (&check, check_cb);	3395	ev_check_init (&check, check_cb);
2208	ev_check_start (EV_DEFAULT_ &check);	3396	ev_check_start (EV_DEFAULT_ &check);
2209	ev_loop (EV_DEFAULT_ 0);	3397	ev_loop (EV_DEFAULT_ 0);
2210		3398
2211	=head1 EMBEDDING	3399	=head1 EMBEDDING
2212		3400
2213	Libev can (and often is) directly embedded into host	3401	Libev can (and often is) directly embedded into host
2214	applications. Examples of applications that embed it include the Deliantra	3402	applications. Examples of applications that embed it include the Deliantra
…		…
2221	libev somewhere in your source tree).	3409	libev somewhere in your source tree).
2222		3410
2223	=head2 FILESETS	3411	=head2 FILESETS
2224		3412
2225	Depending on what features you need you need to include one or more sets of files	3413	Depending on what features you need you need to include one or more sets of files
2226	in your app.	3414	in your application.
2227		3415
2228	=head3 CORE EVENT LOOP	3416	=head3 CORE EVENT LOOP
2229		3417
2230	To include only the libev core (all the C<ev_*> functions), with manual	3418	To include only the libev core (all the C<ev_*> functions), with manual
2231	configuration (no autoconf):	3419	configuration (no autoconf):
2232		3420
2233	#define EV_STANDALONE 1	3421	#define EV_STANDALONE 1
2234	#include "ev.c"	3422	#include "ev.c"
2235		3423
2236	This will automatically include F<ev.h>, too, and should be done in a	3424	This will automatically include F<ev.h>, too, and should be done in a
2237	single C source file only to provide the function implementations. To use	3425	single C source file only to provide the function implementations. To use
2238	it, do the same for F<ev.h> in all files wishing to use this API (best	3426	it, do the same for F<ev.h> in all files wishing to use this API (best
2239	done by writing a wrapper around F<ev.h> that you can include instead and	3427	done by writing a wrapper around F<ev.h> that you can include instead and
2240	where you can put other configuration options):	3428	where you can put other configuration options):
2241		3429
2242	#define EV_STANDALONE 1	3430	#define EV_STANDALONE 1
2243	#include "ev.h"	3431	#include "ev.h"
2244		3432
2245	Both header files and implementation files can be compiled with a C++	3433	Both header files and implementation files can be compiled with a C++
2246	compiler (at least, thats a stated goal, and breakage will be treated	3434	compiler (at least, that's a stated goal, and breakage will be treated
2247	as a bug).	3435	as a bug).
2248		3436
2249	You need the following files in your source tree, or in a directory	3437	You need the following files in your source tree, or in a directory
2250	in your include path (e.g. in libev/ when using -Ilibev):	3438	in your include path (e.g. in libev/ when using -Ilibev):
2251		3439
2252	ev.h	3440	ev.h
2253	ev.c	3441	ev.c
2254	ev_vars.h	3442	ev_vars.h
2255	ev_wrap.h	3443	ev_wrap.h
2256		3444
2257	ev_win32.c required on win32 platforms only	3445	ev_win32.c required on win32 platforms only
2258		3446
2259	ev_select.c only when select backend is enabled (which is enabled by default)	3447	ev_select.c only when select backend is enabled (which is enabled by default)
2260	ev_poll.c only when poll backend is enabled (disabled by default)	3448	ev_poll.c only when poll backend is enabled (disabled by default)
2261	ev_epoll.c only when the epoll backend is enabled (disabled by default)	3449	ev_epoll.c only when the epoll backend is enabled (disabled by default)
2262	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	3450	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2263	ev_port.c only when the solaris port backend is enabled (disabled by default)	3451	ev_port.c only when the solaris port backend is enabled (disabled by default)
2264		3452
2265	F<ev.c> includes the backend files directly when enabled, so you only need	3453	F<ev.c> includes the backend files directly when enabled, so you only need
2266	to compile this single file.	3454	to compile this single file.
2267		3455
2268	=head3 LIBEVENT COMPATIBILITY API	3456	=head3 LIBEVENT COMPATIBILITY API
2269		3457
2270	To include the libevent compatibility API, also include:	3458	To include the libevent compatibility API, also include:
2271		3459
2272	#include "event.c"	3460	#include "event.c"
2273		3461
2274	in the file including F<ev.c>, and:	3462	in the file including F<ev.c>, and:
2275		3463
2276	#include "event.h"	3464	#include "event.h"
2277		3465
2278	in the files that want to use the libevent API. This also includes F<ev.h>.	3466	in the files that want to use the libevent API. This also includes F<ev.h>.
2279		3467
2280	You need the following additional files for this:	3468	You need the following additional files for this:
2281		3469
2282	event.h	3470	event.h
2283	event.c	3471	event.c
2284		3472
2285	=head3 AUTOCONF SUPPORT	3473	=head3 AUTOCONF SUPPORT
2286		3474
2287	Instead of using C<EV_STANDALONE=1> and providing your config in	3475	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2288	whatever way you want, you can also C<m4_include([libev.m4])> in your	3476	whatever way you want, you can also C<m4_include([libev.m4])> in your
2289	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	3477	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2290	include F<config.h> and configure itself accordingly.	3478	include F<config.h> and configure itself accordingly.
2291		3479
2292	For this of course you need the m4 file:	3480	For this of course you need the m4 file:
2293		3481
2294	libev.m4	3482	libev.m4
2295		3483
2296	=head2 PREPROCESSOR SYMBOLS/MACROS	3484	=head2 PREPROCESSOR SYMBOLS/MACROS
2297		3485
2298	Libev can be configured via a variety of preprocessor symbols you have to define	3486	Libev can be configured via a variety of preprocessor symbols you have to
2299	before including any of its files. The default is not to build for multiplicity	3487	define before including any of its files. The default in the absence of
2300	and only include the select backend.	3488	autoconf is documented for every option.
2301		3489
2302	=over 4	3490	=over 4
2303		3491
2304	=item EV_STANDALONE	3492	=item EV_STANDALONE
2305		3493
…		…
2307	keeps libev from including F<config.h>, and it also defines dummy	3495	keeps libev from including F<config.h>, and it also defines dummy
2308	implementations for some libevent functions (such as logging, which is not	3496	implementations for some libevent functions (such as logging, which is not
2309	supported). It will also not define any of the structs usually found in	3497	supported). It will also not define any of the structs usually found in
2310	F<event.h> that are not directly supported by the libev core alone.	3498	F<event.h> that are not directly supported by the libev core alone.
2311		3499
		3500	In stanbdalone mode, libev will still try to automatically deduce the
		3501	configuration, but has to be more conservative.
		3502
2312	=item EV_USE_MONOTONIC	3503	=item EV_USE_MONOTONIC
2313		3504
2314	If defined to be C<1>, libev will try to detect the availability of the	3505	If defined to be C<1>, libev will try to detect the availability of the
2315	monotonic clock option at both compiletime and runtime. Otherwise no use	3506	monotonic clock option at both compile time and runtime. Otherwise no
2316	of the monotonic clock option will be attempted. If you enable this, you	3507	use of the monotonic clock option will be attempted. If you enable this,
2317	usually have to link against librt or something similar. Enabling it when	3508	you usually have to link against librt or something similar. Enabling it
2318	the functionality isn't available is safe, though, although you have	3509	when the functionality isn't available is safe, though, although you have
2319	to make sure you link against any libraries where the C<clock_gettime>	3510	to make sure you link against any libraries where the C<clock_gettime>
2320	function is hiding in (often F<-lrt>).	3511	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2321		3512
2322	=item EV_USE_REALTIME	3513	=item EV_USE_REALTIME
2323		3514
2324	If defined to be C<1>, libev will try to detect the availability of the	3515	If defined to be C<1>, libev will try to detect the availability of the
2325	realtime clock option at compiletime (and assume its availability at	3516	real-time clock option at compile time (and assume its availability
2326	runtime if successful). Otherwise no use of the realtime clock option will	3517	at runtime if successful). Otherwise no use of the real-time clock
2327	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3518	option will be attempted. This effectively replaces C<gettimeofday>
2328	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	3519	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2329	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	3520	correctness. See the note about libraries in the description of
		3521	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3522	C<EV_USE_CLOCK_SYSCALL>.
		3523
		3524	=item EV_USE_CLOCK_SYSCALL
		3525
		3526	If defined to be C<1>, libev will try to use a direct syscall instead
		3527	of calling the system-provided C<clock_gettime> function. This option
		3528	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3529	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3530	programs needlessly. Using a direct syscall is slightly slower (in
		3531	theory), because no optimised vdso implementation can be used, but avoids
		3532	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3533	higher, as it simplifies linking (no need for C<-lrt>).
2330		3534
2331	=item EV_USE_NANOSLEEP	3535	=item EV_USE_NANOSLEEP
2332		3536
2333	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	3537	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2334	and will use it for delays. Otherwise it will use C<select ()>.	3538	and will use it for delays. Otherwise it will use C<select ()>.
2335		3539
		3540	=item EV_USE_EVENTFD
		3541
		3542	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3543	available and will probe for kernel support at runtime. This will improve
		3544	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3545	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3546	2.7 or newer, otherwise disabled.
		3547
2336	=item EV_USE_SELECT	3548	=item EV_USE_SELECT
2337		3549
2338	If undefined or defined to be C<1>, libev will compile in support for the	3550	If undefined or defined to be C<1>, libev will compile in support for the
2339	C<select>(2) backend. No attempt at autodetection will be done: if no	3551	C<select>(2) backend. No attempt at auto-detection will be done: if no
2340	other method takes over, select will be it. Otherwise the select backend	3552	other method takes over, select will be it. Otherwise the select backend
2341	will not be compiled in.	3553	will not be compiled in.
2342		3554
2343	=item EV_SELECT_USE_FD_SET	3555	=item EV_SELECT_USE_FD_SET
2344		3556
2345	If defined to C<1>, then the select backend will use the system C<fd_set>	3557	If defined to C<1>, then the select backend will use the system C<fd_set>
2346	structure. This is useful if libev doesn't compile due to a missing	3558	structure. This is useful if libev doesn't compile due to a missing
2347	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	3559	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2348	exotic systems. This usually limits the range of file descriptors to some	3560	on exotic systems. This usually limits the range of file descriptors to
2349	low limit such as 1024 or might have other limitations (winsocket only	3561	some low limit such as 1024 or might have other limitations (winsocket
2350	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3562	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2351	influence the size of the C<fd_set> used.	3563	configures the maximum size of the C<fd_set>.
2352		3564
2353	=item EV_SELECT_IS_WINSOCKET	3565	=item EV_SELECT_IS_WINSOCKET
2354		3566
2355	When defined to C<1>, the select backend will assume that	3567	When defined to C<1>, the select backend will assume that
2356	select/socket/connect etc. don't understand file descriptors but	3568	select/socket/connect etc. don't understand file descriptors but
…		…
2358	be used is the winsock select). This means that it will call	3570	be used is the winsock select). This means that it will call
2359	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3571	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2360	it is assumed that all these functions actually work on fds, even	3572	it is assumed that all these functions actually work on fds, even
2361	on win32. Should not be defined on non-win32 platforms.	3573	on win32. Should not be defined on non-win32 platforms.
2362		3574
		3575	=item EV_FD_TO_WIN32_HANDLE
		3576
		3577	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3578	file descriptors to socket handles. When not defining this symbol (the
		3579	default), then libev will call C<_get_osfhandle>, which is usually
		3580	correct. In some cases, programs use their own file descriptor management,
		3581	in which case they can provide this function to map fds to socket handles.
		3582
2363	=item EV_USE_POLL	3583	=item EV_USE_POLL
2364		3584
2365	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3585	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2366	backend. Otherwise it will be enabled on non-win32 platforms. It	3586	backend. Otherwise it will be enabled on non-win32 platforms. It
2367	takes precedence over select.	3587	takes precedence over select.
2368		3588
2369	=item EV_USE_EPOLL	3589	=item EV_USE_EPOLL
2370		3590
2371	If defined to be C<1>, libev will compile in support for the Linux	3591	If defined to be C<1>, libev will compile in support for the Linux
2372	C<epoll>(7) backend. Its availability will be detected at runtime,	3592	C<epoll>(7) backend. Its availability will be detected at runtime,
2373	otherwise another method will be used as fallback. This is the	3593	otherwise another method will be used as fallback. This is the preferred
2374	preferred backend for GNU/Linux systems.	3594	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3595	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2375		3596
2376	=item EV_USE_KQUEUE	3597	=item EV_USE_KQUEUE
2377		3598
2378	If defined to be C<1>, libev will compile in support for the BSD style	3599	If defined to be C<1>, libev will compile in support for the BSD style
2379	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	3600	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2392	otherwise another method will be used as fallback. This is the preferred	3613	otherwise another method will be used as fallback. This is the preferred
2393	backend for Solaris 10 systems.	3614	backend for Solaris 10 systems.
2394		3615
2395	=item EV_USE_DEVPOLL	3616	=item EV_USE_DEVPOLL
2396		3617
2397	reserved for future expansion, works like the USE symbols above.	3618	Reserved for future expansion, works like the USE symbols above.
2398		3619
2399	=item EV_USE_INOTIFY	3620	=item EV_USE_INOTIFY
2400		3621
2401	If defined to be C<1>, libev will compile in support for the Linux inotify	3622	If defined to be C<1>, libev will compile in support for the Linux inotify
2402	interface to speed up C<ev_stat> watchers. Its actual availability will	3623	interface to speed up C<ev_stat> watchers. Its actual availability will
2403	be detected at runtime.	3624	be detected at runtime. If undefined, it will be enabled if the headers
		3625	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3626
		3627	=item EV_ATOMIC_T
		3628
		3629	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3630	access is atomic with respect to other threads or signal contexts. No such
		3631	type is easily found in the C language, so you can provide your own type
		3632	that you know is safe for your purposes. It is used both for signal handler "locking"
		3633	as well as for signal and thread safety in C<ev_async> watchers.
		3634
		3635	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3636	(from F<signal.h>), which is usually good enough on most platforms.
2404		3637
2405	=item EV_H	3638	=item EV_H
2406		3639
2407	The name of the F<ev.h> header file used to include it. The default if	3640	The name of the F<ev.h> header file used to include it. The default if
2408	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This	3641	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2409	can be used to virtually rename the F<ev.h> header file in case of conflicts.	3642	used to virtually rename the F<ev.h> header file in case of conflicts.
2410		3643
2411	=item EV_CONFIG_H	3644	=item EV_CONFIG_H
2412		3645
2413	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	3646	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2414	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	3647	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2415	C<EV_H>, above.	3648	C<EV_H>, above.
2416		3649
2417	=item EV_EVENT_H	3650	=item EV_EVENT_H
2418		3651
2419	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	3652	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2420	of how the F<event.h> header can be found.	3653	of how the F<event.h> header can be found, the default is C<"event.h">.
2421		3654
2422	=item EV_PROTOTYPES	3655	=item EV_PROTOTYPES
2423		3656
2424	If defined to be C<0>, then F<ev.h> will not define any function	3657	If defined to be C<0>, then F<ev.h> will not define any function
2425	prototypes, but still define all the structs and other symbols. This is	3658	prototypes, but still define all the structs and other symbols. This is
…		…
2446	When doing priority-based operations, libev usually has to linearly search	3679	When doing priority-based operations, libev usually has to linearly search
2447	all the priorities, so having many of them (hundreds) uses a lot of space	3680	all the priorities, so having many of them (hundreds) uses a lot of space
2448	and time, so using the defaults of five priorities (-2 .. +2) is usually	3681	and time, so using the defaults of five priorities (-2 .. +2) is usually
2449	fine.	3682	fine.
2450		3683
2451	If your embedding app does not need any priorities, defining these both to	3684	If your embedding application does not need any priorities, defining these
2452	C<0> will save some memory and cpu.	3685	both to C<0> will save some memory and CPU.
2453		3686
2454	=item EV_PERIODIC_ENABLE	3687	=item EV_PERIODIC_ENABLE
2455		3688
2456	If undefined or defined to be C<1>, then periodic timers are supported. If	3689	If undefined or defined to be C<1>, then periodic timers are supported. If
2457	defined to be C<0>, then they are not. Disabling them saves a few kB of	3690	defined to be C<0>, then they are not. Disabling them saves a few kB of
…		…
2464	code.	3697	code.
2465		3698
2466	=item EV_EMBED_ENABLE	3699	=item EV_EMBED_ENABLE
2467		3700
2468	If undefined or defined to be C<1>, then embed watchers are supported. If	3701	If undefined or defined to be C<1>, then embed watchers are supported. If
2469	defined to be C<0>, then they are not.	3702	defined to be C<0>, then they are not. Embed watchers rely on most other
		3703	watcher types, which therefore must not be disabled.
2470		3704
2471	=item EV_STAT_ENABLE	3705	=item EV_STAT_ENABLE
2472		3706
2473	If undefined or defined to be C<1>, then stat watchers are supported. If	3707	If undefined or defined to be C<1>, then stat watchers are supported. If
2474	defined to be C<0>, then they are not.	3708	defined to be C<0>, then they are not.
…		…
2476	=item EV_FORK_ENABLE	3710	=item EV_FORK_ENABLE
2477		3711
2478	If undefined or defined to be C<1>, then fork watchers are supported. If	3712	If undefined or defined to be C<1>, then fork watchers are supported. If
2479	defined to be C<0>, then they are not.	3713	defined to be C<0>, then they are not.
2480		3714
		3715	=item EV_ASYNC_ENABLE
		3716
		3717	If undefined or defined to be C<1>, then async watchers are supported. If
		3718	defined to be C<0>, then they are not.
		3719
2481	=item EV_MINIMAL	3720	=item EV_MINIMAL
2482		3721
2483	If you need to shave off some kilobytes of code at the expense of some	3722	If you need to shave off some kilobytes of code at the expense of some
2484	speed, define this symbol to C<1>. Currently only used for gcc to override	3723	speed (but with the full API), define this symbol to C<1>. Currently this
2485	some inlining decisions, saves roughly 30% codesize of amd64.	3724	is used to override some inlining decisions, saves roughly 30% code size
		3725	on amd64. It also selects a much smaller 2-heap for timer management over
		3726	the default 4-heap.
		3727
		3728	You can save even more by disabling watcher types you do not need
		3729	and setting C<EV_MAXPRI> == C<EV_MINPRI>. Also, disabling C<assert>
		3730	(C<-DNDEBUG>) will usually reduce code size a lot.
		3731
		3732	Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to
		3733	provide a bare-bones event library. See C<ev.h> for details on what parts
		3734	of the API are still available, and do not complain if this subset changes
		3735	over time.
2486		3736
2487	=item EV_PID_HASHSIZE	3737	=item EV_PID_HASHSIZE
2488		3738
2489	C<ev_child> watchers use a small hash table to distribute workload by	3739	C<ev_child> watchers use a small hash table to distribute workload by
2490	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3740	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
2491	than enough. If you need to manage thousands of children you might want to	3741	than enough. If you need to manage thousands of children you might want to
2492	increase this value (I<must> be a power of two).	3742	increase this value (I<must> be a power of two).
2493		3743
2494	=item EV_INOTIFY_HASHSIZE	3744	=item EV_INOTIFY_HASHSIZE
2495		3745
2496	C<ev_staz> watchers use a small hash table to distribute workload by	3746	C<ev_stat> watchers use a small hash table to distribute workload by
2497	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	3747	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
2498	usually more than enough. If you need to manage thousands of C<ev_stat>	3748	usually more than enough. If you need to manage thousands of C<ev_stat>
2499	watchers you might want to increase this value (I<must> be a power of	3749	watchers you might want to increase this value (I<must> be a power of
2500	two).	3750	two).
2501		3751
		3752	=item EV_USE_4HEAP
		3753
		3754	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3755	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		3756	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		3757	faster performance with many (thousands) of watchers.
		3758
		3759	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3760	(disabled).
		3761
		3762	=item EV_HEAP_CACHE_AT
		3763
		3764	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3765	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		3766	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3767	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3768	but avoids random read accesses on heap changes. This improves performance
		3769	noticeably with many (hundreds) of watchers.
		3770
		3771	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3772	(disabled).
		3773
		3774	=item EV_VERIFY
		3775
		3776	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3777	be done: If set to C<0>, no internal verification code will be compiled
		3778	in. If set to C<1>, then verification code will be compiled in, but not
		3779	called. If set to C<2>, then the internal verification code will be
		3780	called once per loop, which can slow down libev. If set to C<3>, then the
		3781	verification code will be called very frequently, which will slow down
		3782	libev considerably.
		3783
		3784	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3785	C<0>.
		3786
2502	=item EV_COMMON	3787	=item EV_COMMON
2503		3788
2504	By default, all watchers have a C<void *data> member. By redefining	3789	By default, all watchers have a C<void *data> member. By redefining
2505	this macro to a something else you can include more and other types of	3790	this macro to a something else you can include more and other types of
2506	members. You have to define it each time you include one of the files,	3791	members. You have to define it each time you include one of the files,
2507	though, and it must be identical each time.	3792	though, and it must be identical each time.
2508		3793
2509	For example, the perl EV module uses something like this:	3794	For example, the perl EV module uses something like this:
2510		3795
2511	#define EV_COMMON \	3796	#define EV_COMMON \
2512	SV *self; /* contains this struct */ \	3797	SV *self; /* contains this struct */ \
2513	SV *cb_sv, *fh /* note no trailing ";" */	3798	SV *cb_sv, *fh /* note no trailing ";" */
2514		3799
2515	=item EV_CB_DECLARE (type)	3800	=item EV_CB_DECLARE (type)
2516		3801
2517	=item EV_CB_INVOKE (watcher, revents)	3802	=item EV_CB_INVOKE (watcher, revents)
2518		3803
…		…
2523	definition and a statement, respectively. See the F<ev.h> header file for	3808	definition and a statement, respectively. See the F<ev.h> header file for
2524	their default definitions. One possible use for overriding these is to	3809	their default definitions. One possible use for overriding these is to
2525	avoid the C<struct ev_loop *> as first argument in all cases, or to use	3810	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2526	method calls instead of plain function calls in C++.	3811	method calls instead of plain function calls in C++.
2527		3812
		3813	=back
		3814
2528	=head2 EXPORTED API SYMBOLS	3815	=head2 EXPORTED API SYMBOLS
2529		3816
2530	If you need to re-export the API (e.g. via a dll) and you need a list of	3817	If you need to re-export the API (e.g. via a DLL) and you need a list of
2531	exported symbols, you can use the provided F<Symbol.*> files which list	3818	exported symbols, you can use the provided F<Symbol.*> files which list
2532	all public symbols, one per line:	3819	all public symbols, one per line:
2533		3820
2534	Symbols.ev for libev proper	3821	Symbols.ev for libev proper
2535	Symbols.event for the libevent emulation	3822	Symbols.event for the libevent emulation
2536		3823
2537	This can also be used to rename all public symbols to avoid clashes with	3824	This can also be used to rename all public symbols to avoid clashes with
2538	multiple versions of libev linked together (which is obviously bad in	3825	multiple versions of libev linked together (which is obviously bad in
2539	itself, but sometimes it is inconvinient to avoid this).	3826	itself, but sometimes it is inconvenient to avoid this).
2540		3827
2541	A sed command like this will create wrapper C<#define>'s that you need to	3828	A sed command like this will create wrapper C<#define>'s that you need to
2542	include before including F<ev.h>:	3829	include before including F<ev.h>:
2543		3830
2544	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h	3831	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
…		…
2561	file.	3848	file.
2562		3849
2563	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	3850	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2564	that everybody includes and which overrides some configure choices:	3851	that everybody includes and which overrides some configure choices:
2565		3852
2566	#define EV_MINIMAL 1	3853	#define EV_MINIMAL 1
2567	#define EV_USE_POLL 0	3854	#define EV_USE_POLL 0
2568	#define EV_MULTIPLICITY 0	3855	#define EV_MULTIPLICITY 0
2569	#define EV_PERIODIC_ENABLE 0	3856	#define EV_PERIODIC_ENABLE 0
2570	#define EV_STAT_ENABLE 0	3857	#define EV_STAT_ENABLE 0
2571	#define EV_FORK_ENABLE 0	3858	#define EV_FORK_ENABLE 0
2572	#define EV_CONFIG_H <config.h>	3859	#define EV_CONFIG_H <config.h>
2573	#define EV_MINPRI 0	3860	#define EV_MINPRI 0
2574	#define EV_MAXPRI 0	3861	#define EV_MAXPRI 0
2575		3862
2576	#include "ev++.h"	3863	#include "ev++.h"
2577		3864
2578	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	3865	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2579		3866
2580	#include "ev_cpp.h"	3867	#include "ev_cpp.h"
2581	#include "ev.c"	3868	#include "ev.c"
2582		3869
		3870	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
2583		3871
		3872	=head2 THREADS AND COROUTINES
		3873
		3874	=head3 THREADS
		3875
		3876	All libev functions are reentrant and thread-safe unless explicitly
		3877	documented otherwise, but libev implements no locking itself. This means
		3878	that you can use as many loops as you want in parallel, as long as there
		3879	are no concurrent calls into any libev function with the same loop
		3880	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		3881	of course): libev guarantees that different event loops share no data
		3882	structures that need any locking.
		3883
		3884	Or to put it differently: calls with different loop parameters can be done
		3885	concurrently from multiple threads, calls with the same loop parameter
		3886	must be done serially (but can be done from different threads, as long as
		3887	only one thread ever is inside a call at any point in time, e.g. by using
		3888	a mutex per loop).
		3889
		3890	Specifically to support threads (and signal handlers), libev implements
		3891	so-called C<ev_async> watchers, which allow some limited form of
		3892	concurrency on the same event loop, namely waking it up "from the
		3893	outside".
		3894
		3895	If you want to know which design (one loop, locking, or multiple loops
		3896	without or something else still) is best for your problem, then I cannot
		3897	help you, but here is some generic advice:
		3898
		3899	=over 4
		3900
		3901	=item * most applications have a main thread: use the default libev loop
		3902	in that thread, or create a separate thread running only the default loop.
		3903
		3904	This helps integrating other libraries or software modules that use libev
		3905	themselves and don't care/know about threading.
		3906
		3907	=item * one loop per thread is usually a good model.
		3908
		3909	Doing this is almost never wrong, sometimes a better-performance model
		3910	exists, but it is always a good start.
		3911
		3912	=item * other models exist, such as the leader/follower pattern, where one
		3913	loop is handed through multiple threads in a kind of round-robin fashion.
		3914
		3915	Choosing a model is hard - look around, learn, know that usually you can do
		3916	better than you currently do :-)
		3917
		3918	=item * often you need to talk to some other thread which blocks in the
		3919	event loop.
		3920
		3921	C<ev_async> watchers can be used to wake them up from other threads safely
		3922	(or from signal contexts...).
		3923
		3924	An example use would be to communicate signals or other events that only
		3925	work in the default loop by registering the signal watcher with the
		3926	default loop and triggering an C<ev_async> watcher from the default loop
		3927	watcher callback into the event loop interested in the signal.
		3928
		3929	=back
		3930
		3931	=head4 THREAD LOCKING EXAMPLE
		3932
		3933	=head3 COROUTINES
		3934
		3935	Libev is very accommodating to coroutines ("cooperative threads"):
		3936	libev fully supports nesting calls to its functions from different
		3937	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3938	different coroutines, and switch freely between both coroutines running the
		3939	loop, as long as you don't confuse yourself). The only exception is that
		3940	you must not do this from C<ev_periodic> reschedule callbacks.
		3941
		3942	Care has been taken to ensure that libev does not keep local state inside
		3943	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		3944	they do not call any callbacks.
		3945
		3946	=head2 COMPILER WARNINGS
		3947
		3948	Depending on your compiler and compiler settings, you might get no or a
		3949	lot of warnings when compiling libev code. Some people are apparently
		3950	scared by this.
		3951
		3952	However, these are unavoidable for many reasons. For one, each compiler
		3953	has different warnings, and each user has different tastes regarding
		3954	warning options. "Warn-free" code therefore cannot be a goal except when
		3955	targeting a specific compiler and compiler-version.
		3956
		3957	Another reason is that some compiler warnings require elaborate
		3958	workarounds, or other changes to the code that make it less clear and less
		3959	maintainable.
		3960
		3961	And of course, some compiler warnings are just plain stupid, or simply
		3962	wrong (because they don't actually warn about the condition their message
		3963	seems to warn about). For example, certain older gcc versions had some
		3964	warnings that resulted an extreme number of false positives. These have
		3965	been fixed, but some people still insist on making code warn-free with
		3966	such buggy versions.
		3967
		3968	While libev is written to generate as few warnings as possible,
		3969	"warn-free" code is not a goal, and it is recommended not to build libev
		3970	with any compiler warnings enabled unless you are prepared to cope with
		3971	them (e.g. by ignoring them). Remember that warnings are just that:
		3972	warnings, not errors, or proof of bugs.
		3973
		3974
		3975	=head2 VALGRIND
		3976
		3977	Valgrind has a special section here because it is a popular tool that is
		3978	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		3979
		3980	If you think you found a bug (memory leak, uninitialised data access etc.)
		3981	in libev, then check twice: If valgrind reports something like:
		3982
		3983	==2274== definitely lost: 0 bytes in 0 blocks.
		3984	==2274== possibly lost: 0 bytes in 0 blocks.
		3985	==2274== still reachable: 256 bytes in 1 blocks.
		3986
		3987	Then there is no memory leak, just as memory accounted to global variables
		3988	is not a memleak - the memory is still being referenced, and didn't leak.
		3989
		3990	Similarly, under some circumstances, valgrind might report kernel bugs
		3991	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		3992	although an acceptable workaround has been found here), or it might be
		3993	confused.
		3994
		3995	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		3996	make it into some kind of religion.
		3997
		3998	If you are unsure about something, feel free to contact the mailing list
		3999	with the full valgrind report and an explanation on why you think this
		4000	is a bug in libev (best check the archives, too :). However, don't be
		4001	annoyed when you get a brisk "this is no bug" answer and take the chance
		4002	of learning how to interpret valgrind properly.
		4003
		4004	If you need, for some reason, empty reports from valgrind for your project
		4005	I suggest using suppression lists.
		4006
		4007
		4008	=head1 PORTABILITY NOTES
		4009
		4010	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		4011
		4012	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		4013	requires, and its I/O model is fundamentally incompatible with the POSIX
		4014	model. Libev still offers limited functionality on this platform in
		4015	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		4016	descriptors. This only applies when using Win32 natively, not when using
		4017	e.g. cygwin.
		4018
		4019	Lifting these limitations would basically require the full
		4020	re-implementation of the I/O system. If you are into these kinds of
		4021	things, then note that glib does exactly that for you in a very portable
		4022	way (note also that glib is the slowest event library known to man).
		4023
		4024	There is no supported compilation method available on windows except
		4025	embedding it into other applications.
		4026
		4027	Sensible signal handling is officially unsupported by Microsoft - libev
		4028	tries its best, but under most conditions, signals will simply not work.
		4029
		4030	Not a libev limitation but worth mentioning: windows apparently doesn't
		4031	accept large writes: instead of resulting in a partial write, windows will
		4032	either accept everything or return C<ENOBUFS> if the buffer is too large,
		4033	so make sure you only write small amounts into your sockets (less than a
		4034	megabyte seems safe, but this apparently depends on the amount of memory
		4035	available).
		4036
		4037	Due to the many, low, and arbitrary limits on the win32 platform and
		4038	the abysmal performance of winsockets, using a large number of sockets
		4039	is not recommended (and not reasonable). If your program needs to use
		4040	more than a hundred or so sockets, then likely it needs to use a totally
		4041	different implementation for windows, as libev offers the POSIX readiness
		4042	notification model, which cannot be implemented efficiently on windows
		4043	(due to Microsoft monopoly games).
		4044
		4045	A typical way to use libev under windows is to embed it (see the embedding
		4046	section for details) and use the following F<evwrap.h> header file instead
		4047	of F<ev.h>:
		4048
		4049	#define EV_STANDALONE /* keeps ev from requiring config.h */
		4050	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		4051
		4052	#include "ev.h"
		4053
		4054	And compile the following F<evwrap.c> file into your project (make sure
		4055	you do I<not> compile the F<ev.c> or any other embedded source files!):
		4056
		4057	#include "evwrap.h"
		4058	#include "ev.c"
		4059
		4060	=over 4
		4061
		4062	=item The winsocket select function
		4063
		4064	The winsocket C<select> function doesn't follow POSIX in that it
		4065	requires socket I<handles> and not socket I<file descriptors> (it is
		4066	also extremely buggy). This makes select very inefficient, and also
		4067	requires a mapping from file descriptors to socket handles (the Microsoft
		4068	C runtime provides the function C<_open_osfhandle> for this). See the
		4069	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		4070	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		4071
		4072	The configuration for a "naked" win32 using the Microsoft runtime
		4073	libraries and raw winsocket select is:
		4074
		4075	#define EV_USE_SELECT 1
		4076	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		4077
		4078	Note that winsockets handling of fd sets is O(n), so you can easily get a
		4079	complexity in the O(n²) range when using win32.
		4080
		4081	=item Limited number of file descriptors
		4082
		4083	Windows has numerous arbitrary (and low) limits on things.
		4084
		4085	Early versions of winsocket's select only supported waiting for a maximum
		4086	of C<64> handles (probably owning to the fact that all windows kernels
		4087	can only wait for C<64> things at the same time internally; Microsoft
		4088	recommends spawning a chain of threads and wait for 63 handles and the
		4089	previous thread in each. Sounds great!).
		4090
		4091	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		4092	to some high number (e.g. C<2048>) before compiling the winsocket select
		4093	call (which might be in libev or elsewhere, for example, perl and many
		4094	other interpreters do their own select emulation on windows).
		4095
		4096	Another limit is the number of file descriptors in the Microsoft runtime
		4097	libraries, which by default is C<64> (there must be a hidden I<64>
		4098	fetish or something like this inside Microsoft). You can increase this
		4099	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		4100	(another arbitrary limit), but is broken in many versions of the Microsoft
		4101	runtime libraries. This might get you to about C<512> or C<2048> sockets
		4102	(depending on windows version and/or the phase of the moon). To get more,
		4103	you need to wrap all I/O functions and provide your own fd management, but
		4104	the cost of calling select (O(n²)) will likely make this unworkable.
		4105
		4106	=back
		4107
		4108	=head2 PORTABILITY REQUIREMENTS
		4109
		4110	In addition to a working ISO-C implementation and of course the
		4111	backend-specific APIs, libev relies on a few additional extensions:
		4112
		4113	=over 4
		4114
		4115	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4116	calling conventions regardless of C<ev_watcher_type *>.
		4117
		4118	Libev assumes not only that all watcher pointers have the same internal
		4119	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4120	assumes that the same (machine) code can be used to call any watcher
		4121	callback: The watcher callbacks have different type signatures, but libev
		4122	calls them using an C<ev_watcher *> internally.
		4123
		4124	=item C<sig_atomic_t volatile> must be thread-atomic as well
		4125
		4126	The type C<sig_atomic_t volatile> (or whatever is defined as
		4127	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		4128	threads. This is not part of the specification for C<sig_atomic_t>, but is
		4129	believed to be sufficiently portable.
		4130
		4131	=item C<sigprocmask> must work in a threaded environment
		4132
		4133	Libev uses C<sigprocmask> to temporarily block signals. This is not
		4134	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		4135	pthread implementations will either allow C<sigprocmask> in the "main
		4136	thread" or will block signals process-wide, both behaviours would
		4137	be compatible with libev. Interaction between C<sigprocmask> and
		4138	C<pthread_sigmask> could complicate things, however.
		4139
		4140	The most portable way to handle signals is to block signals in all threads
		4141	except the initial one, and run the default loop in the initial thread as
		4142	well.
		4143
		4144	=item C<long> must be large enough for common memory allocation sizes
		4145
		4146	To improve portability and simplify its API, libev uses C<long> internally
		4147	instead of C<size_t> when allocating its data structures. On non-POSIX
		4148	systems (Microsoft...) this might be unexpectedly low, but is still at
		4149	least 31 bits everywhere, which is enough for hundreds of millions of
		4150	watchers.
		4151
		4152	=item C<double> must hold a time value in seconds with enough accuracy
		4153
		4154	The type C<double> is used to represent timestamps. It is required to
		4155	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		4156	enough for at least into the year 4000. This requirement is fulfilled by
		4157	implementations implementing IEEE 754, which is basically all existing
		4158	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4159	2200.
		4160
		4161	=back
		4162
		4163	If you know of other additional requirements drop me a note.
		4164
		4165
2584	=head1 COMPLEXITIES	4166	=head1 ALGORITHMIC COMPLEXITIES
2585		4167
2586	In this section the complexities of (many of) the algorithms used inside	4168	In this section the complexities of (many of) the algorithms used inside
2587	libev will be explained. For complexity discussions about backends see the	4169	libev will be documented. For complexity discussions about backends see
2588	documentation for C<ev_default_init>.	4170	the documentation for C<ev_default_init>.
2589		4171
2590	All of the following are about amortised time: If an array needs to be	4172	All of the following are about amortised time: If an array needs to be
2591	extended, libev needs to realloc and move the whole array, but this	4173	extended, libev needs to realloc and move the whole array, but this
2592	happens asymptotically never with higher number of elements, so O(1) might	4174	happens asymptotically rarer with higher number of elements, so O(1) might
2593	mean it might do a lengthy realloc operation in rare cases, but on average	4175	mean that libev does a lengthy realloc operation in rare cases, but on
2594	it is much faster and asymptotically approaches constant time.	4176	average it is much faster and asymptotically approaches constant time.
2595		4177
2596	=over 4	4178	=over 4
2597		4179
2598	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4180	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2599		4181
2600	This means that, when you have a watcher that triggers in one hour and	4182	This means that, when you have a watcher that triggers in one hour and
2601	there are 100 watchers that would trigger before that then inserting will	4183	there are 100 watchers that would trigger before that, then inserting will
2602	have to skip those 100 watchers.	4184	have to skip roughly seven (C<ld 100>) of these watchers.
2603		4185
2604	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	4186	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2605		4187
2606	That means that for changing a timer costs less than removing/adding them	4188	That means that changing a timer costs less than removing/adding them,
2607	as only the relative motion in the event queue has to be paid for.	4189	as only the relative motion in the event queue has to be paid for.
2608		4190
2609	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	4191	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
2610		4192
2611	These just add the watcher into an array or at the head of a list.	4193	These just add the watcher into an array or at the head of a list.
		4194
2612	=item Stopping check/prepare/idle watchers: O(1)	4195	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2613		4196
2614	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	4197	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2615		4198
2616	These watchers are stored in lists then need to be walked to find the	4199	These watchers are stored in lists, so they need to be walked to find the
2617	correct watcher to remove. The lists are usually short (you don't usually	4200	correct watcher to remove. The lists are usually short (you don't usually
2618	have many watchers waiting for the same fd or signal).	4201	have many watchers waiting for the same fd or signal: one is typical, two
		4202	is rare).
2619		4203
2620	=item Finding the next timer per loop iteration: O(1)	4204	=item Finding the next timer in each loop iteration: O(1)
		4205
		4206	By virtue of using a binary or 4-heap, the next timer is always found at a
		4207	fixed position in the storage array.
2621		4208
2622	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	4209	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2623		4210
2624	A change means an I/O watcher gets started or stopped, which requires	4211	A change means an I/O watcher gets started or stopped, which requires
2625	libev to recalculate its status (and possibly tell the kernel).	4212	libev to recalculate its status (and possibly tell the kernel, depending
		4213	on backend and whether C<ev_io_set> was used).
2626		4214
2627	=item Activating one watcher: O(1)	4215	=item Activating one watcher (putting it into the pending state): O(1)
2628		4216
2629	=item Priority handling: O(number_of_priorities)	4217	=item Priority handling: O(number_of_priorities)
2630		4218
2631	Priorities are implemented by allocating some space for each	4219	Priorities are implemented by allocating some space for each
2632	priority. When doing priority-based operations, libev usually has to	4220	priority. When doing priority-based operations, libev usually has to
2633	linearly search all the priorities.	4221	linearly search all the priorities, but starting/stopping and activating
		4222	watchers becomes O(1) with respect to priority handling.
		4223
		4224	=item Sending an ev_async: O(1)
		4225
		4226	=item Processing ev_async_send: O(number_of_async_watchers)
		4227
		4228	=item Processing signals: O(max_signal_number)
		4229
		4230	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4231	calls in the current loop iteration. Checking for async and signal events
		4232	involves iterating over all running async watchers or all signal numbers.
2634		4233
2635	=back	4234	=back
2636		4235
2637		4236
		4237	=head1 GLOSSARY
		4238
		4239	=over 4
		4240
		4241	=item active
		4242
		4243	A watcher is active as long as it has been started (has been attached to
		4244	an event loop) but not yet stopped (disassociated from the event loop).
		4245
		4246	=item application
		4247
		4248	In this document, an application is whatever is using libev.
		4249
		4250	=item callback
		4251
		4252	The address of a function that is called when some event has been
		4253	detected. Callbacks are being passed the event loop, the watcher that
		4254	received the event, and the actual event bitset.
		4255
		4256	=item callback invocation
		4257
		4258	The act of calling the callback associated with a watcher.
		4259
		4260	=item event
		4261
		4262	A change of state of some external event, such as data now being available
		4263	for reading on a file descriptor, time having passed or simply not having
		4264	any other events happening anymore.
		4265
		4266	In libev, events are represented as single bits (such as C<EV_READ> or
		4267	C<EV_TIMEOUT>).
		4268
		4269	=item event library
		4270
		4271	A software package implementing an event model and loop.
		4272
		4273	=item event loop
		4274
		4275	An entity that handles and processes external events and converts them
		4276	into callback invocations.
		4277
		4278	=item event model
		4279
		4280	The model used to describe how an event loop handles and processes
		4281	watchers and events.
		4282
		4283	=item pending
		4284
		4285	A watcher is pending as soon as the corresponding event has been detected,
		4286	and stops being pending as soon as the watcher will be invoked or its
		4287	pending status is explicitly cleared by the application.
		4288
		4289	A watcher can be pending, but not active. Stopping a watcher also clears
		4290	its pending status.
		4291
		4292	=item real time
		4293
		4294	The physical time that is observed. It is apparently strictly monotonic :)
		4295
		4296	=item wall-clock time
		4297
		4298	The time and date as shown on clocks. Unlike real time, it can actually
		4299	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4300	clock.
		4301
		4302	=item watcher
		4303
		4304	A data structure that describes interest in certain events. Watchers need
		4305	to be started (attached to an event loop) before they can receive events.
		4306
		4307	=item watcher invocation
		4308
		4309	The act of calling the callback associated with a watcher.
		4310
		4311	=back
		4312
2638	=head1 AUTHOR	4313	=head1 AUTHOR
2639		4314
2640	Marc Lehmann <libev@schmorp.de>.	4315	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
2641		4316

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