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Revision 1.256 by root, Tue Jul 14 20:31:21 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 occuring), and it will manage	86	file descriptor being readable or a timeout occurring), and it will manage
59	these event sources and provide your program with events.	87	these event sources and provide your program with events.
60		88
61	To do this, it must take more or less complete control over your process	89	To do this, it must take more or less complete control over your process
62	(or thread) by executing the I<event loop> handler, and will then	90	(or thread) by executing the I<event loop> handler, and will then
63	communicate events via a callback mechanism.	91	communicate events via a callback mechanism.
…		…
65	You register interest in certain events by registering so-called I<event	93	You register interest in certain events by registering so-called I<event
66	watchers>, which are relatively small C structures you initialise with the	94	watchers>, which are relatively small C structures you initialise with the
67	details of the event, and then hand it over to libev by I<starting> the	95	details of the event, and then hand it over to libev by I<starting> the
68	watcher.	96	watcher.
69		97
70	=head1 FEATURES	98	=head2 FEATURES
71		99
72	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	100	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
73	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	101	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
74	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	102	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
75	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	103	(for C<ev_stat>), 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 such.	132	on it, you should treat it as some floating point value. Unlike the name
		133	component C<stamp> might indicate, it is also used for time differences
		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
104		156
105	=head1 GLOBAL FUNCTIONS	157	=head1 GLOBAL FUNCTIONS
106		158
107	These functions can be called anytime, even before initialising the	159	These functions can be called anytime, even before initialising the
108	library in any way.	160	library in any way.
…		…
112	=item ev_tstamp ev_time ()	164	=item ev_tstamp ev_time ()
113		165
114	Returns the current time as libev would use it. Please note that the	166	Returns the current time as libev would use it. Please note that the
115	C<ev_now> function is usually faster and also often returns the timestamp	167	C<ev_now> function is usually faster and also often returns the timestamp
116	you actually want to know.	168	you actually want to know.
		169
		170	=item ev_sleep (ev_tstamp interval)
		171
		172	Sleep for the given interval: The current thread will be blocked until
		173	either it is interrupted or the given time interval has passed. Basically
		174	this is a sub-second-resolution C<sleep ()>.
117		175
118	=item int ev_version_major ()	176	=item int ev_version_major ()
119		177
120	=item int ev_version_minor ()	178	=item int ev_version_minor ()
121		179
…		…
134	not a problem.	192	not a problem.
135		193
136	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
137	version.	195	version.
138		196
139	assert (("libev version mismatch",	197	assert (("libev version mismatch",
140	ev_version_major () == EV_VERSION_MAJOR	198	ev_version_major () == EV_VERSION_MAJOR
141	&& ev_version_minor () >= EV_VERSION_MINOR));	199	&& ev_version_minor () >= EV_VERSION_MINOR));
142		200
143	=item unsigned int ev_supported_backends ()	201	=item unsigned int ev_supported_backends ()
144		202
145	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_*>
146	value) compiled into this binary of libev (independent of their	204	value) compiled into this binary of libev (independent of their
…		…
148	a description of the set values.	206	a description of the set values.
149		207
150	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
151	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
152		210
153	assert (("sorry, no epoll, no sex",	211	assert (("sorry, no epoll, no sex",
154	ev_supported_backends () & EVBACKEND_EPOLL));	212	ev_supported_backends () & EVBACKEND_EPOLL));
155		213
156	=item unsigned int ev_recommended_backends ()	214	=item unsigned int ev_recommended_backends ()
157		215
158	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
159	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
160	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
161	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
162	(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
163	libev will probe for if you specify no backends explicitly.	221	libev will probe for if you specify no backends explicitly.
164		222
165	=item unsigned int ev_embeddable_backends ()	223	=item unsigned int ev_embeddable_backends ()
166		224
…		…
170	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	228	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
171	recommended ones.	229	recommended ones.
172		230
173	See the description of C<ev_embed> watchers for more info.	231	See the description of C<ev_embed> watchers for more info.
174		232
175	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	233	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
176		234
177	Sets the allocation function to use (the prototype is similar - the	235	Sets the allocation function to use (the prototype is similar - the
178	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
179	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
180	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
181	potentially destructive action. The default is your system realloc	239	or take some potentially destructive action.
182	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.
183		244
184	You could override this function in high-availability programs to, say,	245	You could override this function in high-availability programs to, say,
185	free some memory if it cannot allocate memory, to use a special allocator,	246	free some memory if it cannot allocate memory, to use a special allocator,
186	or even to sleep a while and retry until some memory is available.	247	or even to sleep a while and retry until some memory is available.
187		248
188	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
189	retries).	250	retries (example requires a standards-compliant C<realloc>).
190		251
191	static void *	252	static void *
192	persistent_realloc (void *ptr, size_t size)	253	persistent_realloc (void *ptr, size_t size)
193	{	254	{
194	for (;;)	255	for (;;)
…		…
203	}	264	}
204		265
205	...	266	...
206	ev_set_allocator (persistent_realloc);	267	ev_set_allocator (persistent_realloc);
207		268
208	=item ev_set_syserr_cb (void (*cb)(const char *msg));	269	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
209		270
210	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
211	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
212	indicating the system call or subsystem causing the problem. If this	273	indicating the system call or subsystem causing the problem. If this
213	callback is set, then libev will expect it to remedy the sitution, no	274	callback is set, then libev will expect it to remedy the situation, no
214	matter what, when it returns. That is, libev will generally retry the	275	matter what, when it returns. That is, libev will generally retry the
215	requested operation, or, if the condition doesn't go away, do bad stuff	276	requested operation, or, if the condition doesn't go away, do bad stuff
216	(such as abort).	277	(such as abort).
217		278
218	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.
…		…
229		290
230	=back	291	=back
231		292
232	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	293	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
233		294
234	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>
235	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>
236	events, and dynamically created loops which do not.	297	I<function>).
237		298
238	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
239	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
240	create, you also create another event loop. Libev itself does no locking	301	not.
241	whatsoever, so if you mix calls to the same event loop in different
242	threads, make sure you lock (this is usually a bad idea, though, even if
243	done correctly, because it's hideous and inefficient).
244		302
245	=over 4	303	=over 4
246		304
247	=item struct ev_loop *ev_default_loop (unsigned int flags)	305	=item struct ev_loop *ev_default_loop (unsigned int flags)
248		306
…		…
252	flags. If that is troubling you, check C<ev_backend ()> afterwards).	310	flags. If that is troubling you, check C<ev_backend ()> afterwards).
253		311
254	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
255	function.	313	function.
256		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
257	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
258	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>).
259		328
260	The following flags are supported:	329	The following flags are supported:
261		330
…		…
266	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
267	thing, believe me).	336	thing, believe me).
268		337
269	=item C<EVFLAG_NOENV>	338	=item C<EVFLAG_NOENV>
270		339
271	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
272	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
273	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	342	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
274	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
275	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
276	around bugs.	345	around bugs.
…		…
282	enabling this flag.	351	enabling this flag.
283		352
284	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,
285	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
286	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
287	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
288	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
289	C<pthread_atfork> which is even faster).	358	C<pthread_atfork> which is even faster).
290		359
291	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
292	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
293	flag.	362	flag.
294		363
295	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>
296	environment variable.	365	environment variable.
297		366
298	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	367	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
299		368
300	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
301	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,
302	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
303	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
304	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).
305		385
306	=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)
307		387
308	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
309	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
310	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
311	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>.
312		397
313	=item C<EVBACKEND_EPOLL> (value 4, Linux)	398	=item C<EVBACKEND_EPOLL> (value 4, Linux)
314		399
315	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,
316	but it scales phenomenally better. While poll and select usually scale like	401	but it scales phenomenally better. While poll and select usually scale
317	O(total_fds) where n is the total number of fds (or the highest fd), epoll scales	402	like O(total_fds) where n is the total number of fds (or the highest fd),
318	either O(1) or O(active_fds).	403	epoll scales either O(1) or O(active_fds).
319		404
		405	The epoll mechanism deserves honorable mention as the most misdesigned
		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.
		421
320	While stopping and starting an I/O watcher in the same iteration will	422	While stopping, setting and starting an I/O watcher in the same iteration
321	result in some caching, there is still a syscall per such incident	423	will result in some caching, there is still a system call per such
322	(because the fd could point to a different file description now), so its	424	incident (because the same I<file descriptor> could point to a different
323	best to avoid that. Also, dup()ed file descriptors might not work very	425	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
324	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.
325		428
326	Please note that epoll sometimes generates spurious notifications, so you	429	Best performance from this backend is achieved by not unregistering all
327	need to use non-blocking I/O or other means to avoid blocking when no data	430	watchers for a file descriptor until it has been closed, if possible,
328	(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>.
329		446
330	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	447	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
331		448
332	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
333	was broken on all BSDs except NetBSD (usually it doesn't work with	450	was broken on all BSDs except NetBSD (usually it doesn't work reliably
334	anything but sockets and pipes, except on Darwin, where of course its	451	with anything but sockets and pipes, except on Darwin, where of course
335	completely useless). For this reason its 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
336	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
337	C<EVBACKEND_KQUEUE>).	456	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		457	system like NetBSD.
		458
		459	You still can embed kqueue into a normal poll or select backend and use it
		460	only for sockets (after having made sure that sockets work with kqueue on
		461	the target platform). See C<ev_embed> watchers for more info.
338		462
339	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
340	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
341	course). While starting and stopping an I/O watcher does not cause an	465	course). While stopping, setting and starting an I/O watcher does never
342	extra syscall as with epoll, it still adds up to four event changes per	466	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
343	incident, so its best to avoid that.	467	two event changes per incident. Support for C<fork ()> is very bad (but
		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>.
344		483
345	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	484	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
346		485
347	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.
348		490
349	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	491	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
350		492
351	This uses the Solaris 10 port mechanism. As with everything on Solaris,	493	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
352	it's really slow, but it still scales very well (O(active_fds)).	494	it's really slow, but it still scales very well (O(active_fds)).
353		495
354	Please note that solaris ports can result in a lot of spurious	496	Please note that Solaris event ports can deliver a lot of spurious
355	notifications, so you need to use non-blocking I/O or other means to avoid	497	notifications, so you need to use non-blocking I/O or other means to avoid
356	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>.
357		512
358	=item C<EVBACKEND_ALL>	513	=item C<EVBACKEND_ALL>
359		514
360	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
361	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
362	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	517	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
363		518
		519	It is definitely not recommended to use this flag.
		520
364	=back	521	=back
365		522
366	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
367	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
368	specified, most compiled-in backend will be tried, usually in reverse	525	specified, all backends in C<ev_recommended_backends ()> will be tried.
369	order of their flag values :)
370		526
371	The most typical usage is like this:	527	Example: This is the most typical usage.
372		528
373	if (!ev_default_loop (0))	529	if (!ev_default_loop (0))
374	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	530	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
375		531
376	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
377	environment settings to be taken into account:	533	environment settings to be taken into account:
378		534
379	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	535	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
380		536
381	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
382	available (warning, breaks stuff, best use only with your own private	538	used if available (warning, breaks stuff, best use only with your own
383	event loop and only if you know the OS supports your types of fds):	539	private event loop and only if you know the OS supports your types of
		540	fds):
384		541
385	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	542	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
386		543
387	=item struct ev_loop *ev_loop_new (unsigned int flags)	544	=item struct ev_loop *ev_loop_new (unsigned int flags)
388		545
389	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
390	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
391	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
392	undefined behaviour (or a failed assertion if assertions are enabled).	549	undefined behaviour (or a failed assertion if assertions are enabled).
393		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
394	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.
395		556
396	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	557	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
397	if (!epoller)	558	if (!epoller)
398	fatal ("no epoll found here, maybe it hides under your chair");	559	fatal ("no epoll found here, maybe it hides under your chair");
399		560
400	=item ev_default_destroy ()	561	=item ev_default_destroy ()
401		562
402	Destroys the default loop again (frees all memory and kernel state	563	Destroys the default loop again (frees all memory and kernel state
403	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
404	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
405	responsibility to either stop all watchers cleanly yoursef I<before>	566	responsibility to either stop all watchers cleanly yourself I<before>
406	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
407	the easiest thing, youc na just ignore the watchers and/or C<free ()> them	568	the easiest thing, you can just ignore the watchers and/or C<free ()> them
408	for example).	569	for example).
		570
		571	Note that certain global state, such as signal state (and installed signal
		572	handlers), will not be freed by this function, and related watchers (such
		573	as signal and child watchers) would need to be stopped manually.
		574
		575	In general it is not advisable to call this function except in the
		576	rare occasion where you really need to free e.g. the signal handling
		577	pipe fds. If you need dynamically allocated loops it is better to use
		578	C<ev_loop_new> and C<ev_loop_destroy>).
409		579
410	=item ev_loop_destroy (loop)	580	=item ev_loop_destroy (loop)
411		581
412	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
413	earlier call to C<ev_loop_new>.	583	earlier call to C<ev_loop_new>.
414		584
415	=item ev_default_fork ()	585	=item ev_default_fork ()
416		586
		587	This function sets a flag that causes subsequent C<ev_loop> iterations
417	This function reinitialises the kernel state for backends that have	588	to reinitialise the kernel state for backends that have one. Despite the
418	one. Despite the name, you can call it anytime, but it makes most sense	589	name, you can call it anytime, but it makes most sense after forking, in
419	after forking, in either the parent or child process (or both, but that	590	the child process (or both child and parent, but that again makes little
420	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.
421		593
422	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
423	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
424	fork+exec, you don't have to call it.	596	you just fork+exec, you don't have to call it at all.
425		597
426	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
427	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
428	quite nicely into a call to C<pthread_atfork>:	600	quite nicely into a call to C<pthread_atfork>:
429		601
430	pthread_atfork (0, 0, ev_default_fork);	602	pthread_atfork (0, 0, ev_default_fork);
431		603
432	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
433	without calling this function, so if you force one of those backends you
434	do not need to care.
435
436	=item ev_loop_fork (loop)	604	=item ev_loop_fork (loop)
437		605
438	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
439	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
440	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.
441		615
442	=item unsigned int ev_loop_count (loop)	616	=item unsigned int ev_loop_count (loop)
443		617
444	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
445	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
446	happily wraps around with enough iterations.	620	happily wraps around with enough iterations.
447		621
448	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
449	"ticks" the number of loop iterations), as it roughly corresponds with	623	"ticks" the number of loop iterations), as it roughly corresponds with
450	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.
451		637
452	=item unsigned int ev_backend (loop)	638	=item unsigned int ev_backend (loop)
453		639
454	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
455	use.	641	use.
…		…
458		644
459	Returns the current "event loop time", which is the time the event loop	645	Returns the current "event loop time", which is the time the event loop
460	received events and started processing them. This timestamp does not	646	received events and started processing them. This timestamp does not
461	change as long as callbacks are being processed, and this is also the base	647	change as long as callbacks are being processed, and this is also the base
462	time used for relative timers. You can treat it as the timestamp of the	648	time used for relative timers. You can treat it as the timestamp of the
463	event occuring (or more correctly, libev finding out about it).	649	event occurring (or more correctly, libev finding out about it).
		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>).
464		688
465	=item ev_loop (loop, int flags)	689	=item ev_loop (loop, int flags)
466		690
467	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
468	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
…		…
471	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
472	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.
473		697
474	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
475	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
476	finished (especially in interactive programs), but having a program that	700	finished (especially in interactive programs), but having a program
477	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
478	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.
479		704
480	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
481	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
482	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.
483		709
484	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
485	neccessary) and will handle those and any outstanding ones. It will block	711	necessary) and will handle those and any already outstanding ones. It
486	your process until at least one new event arrives, and will return after	712	will block your process until at least one new event arrives (which could
487	one iteration of the loop. This is useful if you are waiting for some	713	be an event internal to libev itself, so there is no guarantee that a
488	external event in conjunction with something not expressible using other	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
489	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
490	usually a better approach for this kind of thing.	720	usually a better approach for this kind of thing.
491		721
492	Here are the gory details of what C<ev_loop> does:	722	Here are the gory details of what C<ev_loop> does:
493		723
494	- Before the first iteration, call any pending watchers.	724	- Before the first iteration, call any pending watchers.
495	* If there are no active watchers (reference count is zero), return.	725	* If EVFLAG_FORKCHECK was used, check for a fork.
496	- 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.
497	- 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.
498	- Update the kernel state with all outstanding changes.	730	- Update the kernel state with all outstanding changes.
499	- Update the "event loop time".	731	- Update the "event loop time" (ev_now ()).
500	- 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.
501	- Block the process, waiting for any events.	736	- Block the process, waiting for any events.
502	- Queue all outstanding I/O (fd) events.	737	- Queue all outstanding I/O (fd) events.
503	- Update the "event loop time" and do time jump handling.	738	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
504	- Queue all outstanding timers.	739	- Queue all expired timers.
505	- Queue all outstanding periodics.	740	- Queue all expired periodics.
506	- If no events are pending now, queue all idle watchers.	741	- Unless any events are pending now, queue all idle watchers.
507	- Queue all check watchers.	742	- Queue all check watchers.
508	- 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).
509	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
510	be handled here by queueing them when their watcher gets executed.	745	be handled here by queueing them when their watcher gets executed.
511	- 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
512	were used, return, otherwise continue with step *.	747	were used, or there are no active watchers, return, otherwise
		748	continue with step *.
513		749
514	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
515	anymore.	751	anymore.
516		752
517	... queue jobs here, make sure they register event watchers as long	753	... queue jobs here, make sure they register event watchers as long
518	... as they still have work to do (even an idle watcher will do..)	754	... as they still have work to do (even an idle watcher will do..)
519	ev_loop (my_loop, 0);	755	ev_loop (my_loop, 0);
520	... jobs done. yeah!	756	... jobs done or somebody called unloop. yeah!
521		757
522	=item ev_unloop (loop, how)	758	=item ev_unloop (loop, how)
523		759
524	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
525	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
526	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
527	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.
528		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
529	=item ev_ref (loop)	769	=item ev_ref (loop)
530		770
531	=item ev_unref (loop)	771	=item ev_unref (loop)
532		772
533	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
534	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
535	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
536	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>
537	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
538	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
539	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
540	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
541	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
542	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).
543		790
544	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>
545	running when nothing else is active.	792	running when nothing else is active.
546		793
547	struct ev_signal exitsig;	794	ev_signal exitsig;
548	ev_signal_init (&exitsig, sig_cb, SIGINT);	795	ev_signal_init (&exitsig, sig_cb, SIGINT);
549	ev_signal_start (loop, &exitsig);	796	ev_signal_start (loop, &exitsig);
550	evf_unref (loop);	797	evf_unref (loop);
551		798
552	Example: For some weird reason, unregister the above signal handler again.	799	Example: For some weird reason, unregister the above signal handler again.
553		800
554	ev_ref (loop);	801	ev_ref (loop);
555	ev_signal_stop (loop, &exitsig);	802	ev_signal_stop (loop, &exitsig);
		803
		804	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		805
		806	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		807
		808	These advanced functions influence the time that libev will spend waiting
		809	for events. Both time intervals are by default C<0>, meaning that libev
		810	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		811	latency.
		812
		813	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		814	allows libev to delay invocation of I/O and timer/periodic callbacks
		815	to increase efficiency of loop iterations (or to increase power-saving
		816	opportunities).
		817
		818	The idea is that sometimes your program runs just fast enough to handle
		819	one (or very few) event(s) per loop iteration. While this makes the
		820	program responsive, it also wastes a lot of CPU time to poll for new
		821	events, especially with backends like C<select ()> which have a high
		822	overhead for the actual polling but can deliver many events at once.
		823
		824	By setting a higher I<io collect interval> you allow libev to spend more
		825	time collecting I/O events, so you can handle more events per iteration,
		826	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		827	C<ev_timer>) will be not affected. Setting this to a non-null value will
		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.
		831
		832	Likewise, by setting a higher I<timeout collect interval> you allow libev
		833	to spend more time collecting timeouts, at the expense of increased
		834	latency/jitter/inexactness (the watcher callback will be called
		835	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		836	value will not introduce any overhead in libev.
		837
		838	Many (busy) programs can usually benefit by setting the I/O collect
		839	interval to a value near C<0.1> or so, which is often enough for
		840	interactive servers (of course not for games), likewise for timeouts. It
		841	usually doesn't make much sense to set it to a lower value than C<0.01>,
		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 int ev_pending_count (loop)
		868
		869	Returns the number of pending watchers - zero indicates that no watchers
		870	are pending.
		871
		872	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		873
		874	This overrides the invoke pending functionality of the loop: Instead of
		875	invoking all pending watchers when there are any, C<ev_loop> will call
		876	this callback instead. This is useful, for example, when you want to
		877	invoke the actual watchers inside another context (another thread etc.).
		878
		879	If you want to reset the callback, use C<ev_invoke_pending> as new
		880	callback.
		881
		882	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		883
		884	Sometimes you want to share the same loop between multiple threads. This
		885	can be done relatively simply by putting mutex_lock/unlock calls around
		886	each call to a libev function.
		887
		888	However, C<ev_loop> can run an indefinite time, so it is not feasible to
		889	wait for it to return. One way around this is to wake up the loop via
		890	C<ev_unloop> and C<av_async_send>, another way is to set these I<release>
		891	and I<acquire> callbacks on the loop.
		892
		893	When set, then C<release> will be called just before the thread is
		894	suspended waiting for new events, and C<acquire> is called just
		895	afterwards.
		896
		897	Ideally, C<release> will just call your mutex_unlock function, and
		898	C<acquire> will just call the mutex_lock function again.
		899
		900	While event loop modifications are allowed between invocations of
		901	C<release> and C<acquire> (that's their only purpose after all), no
		902	modifications done will affect the event loop, i.e. adding watchers will
		903	have no effect on the set of file descriptors being watched, or the time
		904	waited. USe an C<ev_async> watcher to wake up C<ev_loop> when you want it
		905	to take note of any changes you made.
		906
		907	In theory, threads executing C<ev_loop> will be async-cancel safe between
		908	invocations of C<release> and C<acquire>.
		909
		910	See also the locking example in the C<THREADS> section later in this
		911	document.
		912
		913	=item ev_set_userdata (loop, void *data)
		914
		915	=item ev_userdata (loop)
		916
		917	Set and retrieve a single C<void *> associated with a loop. When
		918	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		919	C<0.>
		920
		921	These two functions can be used to associate arbitrary data with a loop,
		922	and are intended solely for the C<invoke_pending_cb>, C<release> and
		923	C<acquire> callbacks described above, but of course can be (ab-)used for
		924	any other purpose as well.
		925
		926	=item ev_loop_verify (loop)
		927
		928	This function only does something when C<EV_VERIFY> support has been
		929	compiled in, which is the default for non-minimal builds. It tries to go
		930	through all internal structures and checks them for validity. If anything
		931	is found to be inconsistent, it will print an error message to standard
		932	error and call C<abort ()>.
		933
		934	This can be used to catch bugs inside libev itself: under normal
		935	circumstances, this function will never abort as of course libev keeps its
		936	data structures consistent.
556		937
557	=back	938	=back
558		939
559		940
560	=head1 ANATOMY OF A WATCHER	941	=head1 ANATOMY OF A WATCHER
		942
		943	In the following description, uppercase C<TYPE> in names stands for the
		944	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		945	watchers and C<ev_io_start> for I/O watchers.
561		946
562	A watcher is a structure that you create and register to record your	947	A watcher is a structure that you create and register to record your
563	interest in some event. For instance, if you want to wait for STDIN to	948	interest in some event. For instance, if you want to wait for STDIN to
564	become readable, you would create an C<ev_io> watcher for that:	949	become readable, you would create an C<ev_io> watcher for that:
565		950
566	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	951	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
567	{	952	{
568	ev_io_stop (w);	953	ev_io_stop (w);
569	ev_unloop (loop, EVUNLOOP_ALL);	954	ev_unloop (loop, EVUNLOOP_ALL);
570	}	955	}
571		956
572	struct ev_loop *loop = ev_default_loop (0);	957	struct ev_loop *loop = ev_default_loop (0);
		958
573	struct ev_io stdin_watcher;	959	ev_io stdin_watcher;
		960
574	ev_init (&stdin_watcher, my_cb);	961	ev_init (&stdin_watcher, my_cb);
575	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	962	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
576	ev_io_start (loop, &stdin_watcher);	963	ev_io_start (loop, &stdin_watcher);
		964
577	ev_loop (loop, 0);	965	ev_loop (loop, 0);
578		966
579	As you can see, you are responsible for allocating the memory for your	967	As you can see, you are responsible for allocating the memory for your
580	watcher structures (and it is usually a bad idea to do this on the stack,	968	watcher structures (and it is I<usually> a bad idea to do this on the
581	although this can sometimes be quite valid).	969	stack).
		970
		971	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		972	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
582		973
583	Each watcher structure must be initialised by a call to C<ev_init	974	Each watcher structure must be initialised by a call to C<ev_init
584	(watcher *, callback)>, which expects a callback to be provided. This	975	(watcher *, callback)>, which expects a callback to be provided. This
585	callback gets invoked each time the event occurs (or, in the case of io	976	callback gets invoked each time the event occurs (or, in the case of I/O
586	watchers, each time the event loop detects that the file descriptor given	977	watchers, each time the event loop detects that the file descriptor given
587	is readable and/or writable).	978	is readable and/or writable).
588		979
589	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	980	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
590	with arguments specific to this watcher type. There is also a macro	981	macro to configure it, with arguments specific to the watcher type. There
591	to combine initialisation and setting in one call: C<< ev_<type>_init	982	is also a macro to combine initialisation and setting in one call: C<<
592	(watcher *, callback, ...) >>.	983	ev_TYPE_init (watcher *, callback, ...) >>.
593		984
594	To make the watcher actually watch out for events, you have to start it	985	To make the watcher actually watch out for events, you have to start it
595	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	986	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
596	*) >>), and you can stop watching for events at any time by calling the	987	*) >>), and you can stop watching for events at any time by calling the
597	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	988	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
598		989
599	As long as your watcher is active (has been started but not stopped) you	990	As long as your watcher is active (has been started but not stopped) you
600	must not touch the values stored in it. Most specifically you must never	991	must not touch the values stored in it. Most specifically you must never
601	reinitialise it or call its C<set> macro.	992	reinitialise it or call its C<ev_TYPE_set> macro.
602		993
603	Each and every callback receives the event loop pointer as first, the	994	Each and every callback receives the event loop pointer as first, the
604	registered watcher structure as second, and a bitset of received events as	995	registered watcher structure as second, and a bitset of received events as
605	third argument.	996	third argument.
606		997
…		…
660	=item C<EV_FORK>	1051	=item C<EV_FORK>
661		1052
662	The event loop has been resumed in the child process after fork (see	1053	The event loop has been resumed in the child process after fork (see
663	C<ev_fork>).	1054	C<ev_fork>).
664		1055
		1056	=item C<EV_ASYNC>
		1057
		1058	The given async watcher has been asynchronously notified (see C<ev_async>).
		1059
		1060	=item C<EV_CUSTOM>
		1061
		1062	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1063	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1064
665	=item C<EV_ERROR>	1065	=item C<EV_ERROR>
666		1066
667	An unspecified error has occured, the watcher has been stopped. This might	1067	An unspecified error has occurred, the watcher has been stopped. This might
668	happen because the watcher could not be properly started because libev	1068	happen because the watcher could not be properly started because libev
669	ran out of memory, a file descriptor was found to be closed or any other	1069	ran out of memory, a file descriptor was found to be closed or any other
		1070	problem. Libev considers these application bugs.
		1071
670	problem. You best act on it by reporting the problem and somehow coping	1072	You best act on it by reporting the problem and somehow coping with the
671	with the watcher being stopped.	1073	watcher being stopped. Note that well-written programs should not receive
		1074	an error ever, so when your watcher receives it, this usually indicates a
		1075	bug in your program.
672		1076
673	Libev will usually signal a few "dummy" events together with an error,	1077	Libev will usually signal a few "dummy" events together with an error, for
674	for example it might indicate that a fd is readable or writable, and if	1078	example it might indicate that a fd is readable or writable, and if your
675	your callbacks is well-written it can just attempt the operation and cope	1079	callbacks is well-written it can just attempt the operation and cope with
676	with the error from read() or write(). This will not work in multithreaded	1080	the error from read() or write(). This will not work in multi-threaded
677	programs, though, so beware.	1081	programs, though, as the fd could already be closed and reused for another
		1082	thing, so beware.
678		1083
679	=back	1084	=back
680		1085
681	=head2 GENERIC WATCHER FUNCTIONS	1086	=head2 GENERIC WATCHER FUNCTIONS
682
683	In the following description, C<TYPE> stands for the watcher type,
684	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
685		1087
686	=over 4	1088	=over 4
687		1089
688	=item C<ev_init> (ev_TYPE *watcher, callback)	1090	=item C<ev_init> (ev_TYPE *watcher, callback)
689		1091
…		…
695	which rolls both calls into one.	1097	which rolls both calls into one.
696		1098
697	You can reinitialise a watcher at any time as long as it has been stopped	1099	You can reinitialise a watcher at any time as long as it has been stopped
698	(or never started) and there are no pending events outstanding.	1100	(or never started) and there are no pending events outstanding.
699		1101
700	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1102	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
701	int revents)>.	1103	int revents)>.
		1104
		1105	Example: Initialise an C<ev_io> watcher in two steps.
		1106
		1107	ev_io w;
		1108	ev_init (&w, my_cb);
		1109	ev_io_set (&w, STDIN_FILENO, EV_READ);
702		1110
703	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1111	=item C<ev_TYPE_set> (ev_TYPE *, [args])
704		1112
705	This macro initialises the type-specific parts of a watcher. You need to	1113	This macro initialises the type-specific parts of a watcher. You need to
706	call C<ev_init> at least once before you call this macro, but you can	1114	call C<ev_init> at least once before you call this macro, but you can
…		…
709	difference to the C<ev_init> macro).	1117	difference to the C<ev_init> macro).
710		1118
711	Although some watcher types do not have type-specific arguments	1119	Although some watcher types do not have type-specific arguments
712	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1120	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
713		1121
		1122	See C<ev_init>, above, for an example.
		1123
714	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1124	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
715		1125
716	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1126	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
717	calls into a single call. This is the most convinient method to initialise	1127	calls into a single call. This is the most convenient method to initialise
718	a watcher. The same limitations apply, of course.	1128	a watcher. The same limitations apply, of course.
		1129
		1130	Example: Initialise and set an C<ev_io> watcher in one step.
		1131
		1132	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
719		1133
720	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1134	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
721		1135
722	Starts (activates) the given watcher. Only active watchers will receive	1136	Starts (activates) the given watcher. Only active watchers will receive
723	events. If the watcher is already active nothing will happen.	1137	events. If the watcher is already active nothing will happen.
724		1138
		1139	Example: Start the C<ev_io> watcher that is being abused as example in this
		1140	whole section.
		1141
		1142	ev_io_start (EV_DEFAULT_UC, &w);
		1143
725	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1144	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
726		1145
727	Stops the given watcher again (if active) and clears the pending	1146	Stops the given watcher if active, and clears the pending status (whether
		1147	the watcher was active or not).
		1148
728	status. It is possible that stopped watchers are pending (for example,	1149	It is possible that stopped watchers are pending - for example,
729	non-repeating timers are being stopped when they become pending), but	1150	non-repeating timers are being stopped when they become pending - but
730	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1151	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
731	you want to free or reuse the memory used by the watcher it is therefore a	1152	pending. If you want to free or reuse the memory used by the watcher it is
732	good idea to always call its C<ev_TYPE_stop> function.	1153	therefore a good idea to always call its C<ev_TYPE_stop> function.
733		1154
734	=item bool ev_is_active (ev_TYPE *watcher)	1155	=item bool ev_is_active (ev_TYPE *watcher)
735		1156
736	Returns a true value iff the watcher is active (i.e. it has been started	1157	Returns a true value iff the watcher is active (i.e. it has been started
737	and not yet been stopped). As long as a watcher is active you must not modify	1158	and not yet been stopped). As long as a watcher is active you must not modify
…		…
763	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1184	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
764	(default: C<-2>). Pending watchers with higher priority will be invoked	1185	(default: C<-2>). Pending watchers with higher priority will be invoked
765	before watchers with lower priority, but priority will not keep watchers	1186	before watchers with lower priority, but priority will not keep watchers
766	from being executed (except for C<ev_idle> watchers).	1187	from being executed (except for C<ev_idle> watchers).
767		1188
768	This means that priorities are I<only> used for ordering callback
769	invocation after new events have been received. This is useful, for
770	example, to reduce latency after idling, or more often, to bind two
771	watchers on the same event and make sure one is called first.
772
773	If you need to suppress invocation when higher priority events are pending	1189	If you need to suppress invocation when higher priority events are pending
774	you need to look at C<ev_idle> watchers, which provide this functionality.	1190	you need to look at C<ev_idle> watchers, which provide this functionality.
775		1191
776	You I<must not> change the priority of a watcher as long as it is active or	1192	You I<must not> change the priority of a watcher as long as it is active or
777	pending.	1193	pending.
778		1194
		1195	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1196	fine, as long as you do not mind that the priority value you query might
		1197	or might not have been clamped to the valid range.
		1198
779	The default priority used by watchers when no priority has been set is	1199	The default priority used by watchers when no priority has been set is
780	always C<0>, which is supposed to not be too high and not be too low :).	1200	always C<0>, which is supposed to not be too high and not be too low :).
781		1201
782	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1202	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
783	fine, as long as you do not mind that the priority value you query might	1203	priorities.
784	or might not have been adjusted to be within valid range.
785		1204
786	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1205	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
787		1206
788	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1207	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
789	C<loop> nor C<revents> need to be valid as long as the watcher callback	1208	C<loop> nor C<revents> need to be valid as long as the watcher callback
790	can deal with that fact.	1209	can deal with that fact, as both are simply passed through to the
		1210	callback.
791		1211
792	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1212	=item int ev_clear_pending (loop, ev_TYPE *watcher)
793		1213
794	If the watcher is pending, this function returns clears its pending status	1214	If the watcher is pending, this function clears its pending status and
795	and returns its C<revents> bitset (as if its callback was invoked). If the	1215	returns its C<revents> bitset (as if its callback was invoked). If the
796	watcher isn't pending it does nothing and returns C<0>.	1216	watcher isn't pending it does nothing and returns C<0>.
797		1217
		1218	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1219	callback to be invoked, which can be accomplished with this function.
		1220
798	=back	1221	=back
799		1222
800		1223
801	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1224	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
802		1225
803	Each watcher has, by default, a member C<void *data> that you can change	1226	Each watcher has, by default, a member C<void *data> that you can change
804	and read at any time, libev will completely ignore it. This can be used	1227	and read at any time: libev will completely ignore it. This can be used
805	to associate arbitrary data with your watcher. If you need more data and	1228	to associate arbitrary data with your watcher. If you need more data and
806	don't want to allocate memory and store a pointer to it in that data	1229	don't want to allocate memory and store a pointer to it in that data
807	member, you can also "subclass" the watcher type and provide your own	1230	member, you can also "subclass" the watcher type and provide your own
808	data:	1231	data:
809		1232
810	struct my_io	1233	struct my_io
811	{	1234	{
812	struct ev_io io;	1235	ev_io io;
813	int otherfd;	1236	int otherfd;
814	void *somedata;	1237	void *somedata;
815	struct whatever *mostinteresting;	1238	struct whatever *mostinteresting;
816	}	1239	};
		1240
		1241	...
		1242	struct my_io w;
		1243	ev_io_init (&w.io, my_cb, fd, EV_READ);
817		1244
818	And since your callback will be called with a pointer to the watcher, you	1245	And since your callback will be called with a pointer to the watcher, you
819	can cast it back to your own type:	1246	can cast it back to your own type:
820		1247
821	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1248	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
822	{	1249	{
823	struct my_io *w = (struct my_io *)w_;	1250	struct my_io *w = (struct my_io *)w_;
824	...	1251	...
825	}	1252	}
826		1253
827	More interesting and less C-conformant ways of casting your callback type	1254	More interesting and less C-conformant ways of casting your callback type
828	instead have been omitted.	1255	instead have been omitted.
829		1256
830	Another common scenario is having some data structure with multiple	1257	Another common scenario is to use some data structure with multiple
831	watchers:	1258	embedded watchers:
832		1259
833	struct my_biggy	1260	struct my_biggy
834	{	1261	{
835	int some_data;	1262	int some_data;
836	ev_timer t1;	1263	ev_timer t1;
837	ev_timer t2;	1264	ev_timer t2;
838	}	1265	}
839		1266
840	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1267	In this case getting the pointer to C<my_biggy> is a bit more
841	you need to use C<offsetof>:	1268	complicated: Either you store the address of your C<my_biggy> struct
		1269	in the C<data> member of the watcher (for woozies), or you need to use
		1270	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1271	programmers):
842		1272
843	#include <stddef.h>	1273	#include <stddef.h>
844		1274
845	static void	1275	static void
846	t1_cb (EV_P_ struct ev_timer *w, int revents)	1276	t1_cb (EV_P_ ev_timer *w, int revents)
847	{	1277	{
848	struct my_biggy big = (struct my_biggy *	1278	struct my_biggy big = (struct my_biggy *)
849	(((char *)w) - offsetof (struct my_biggy, t1));	1279	(((char *)w) - offsetof (struct my_biggy, t1));
850	}	1280	}
851		1281
852	static void	1282	static void
853	t2_cb (EV_P_ struct ev_timer *w, int revents)	1283	t2_cb (EV_P_ ev_timer *w, int revents)
854	{	1284	{
855	struct my_biggy big = (struct my_biggy *	1285	struct my_biggy big = (struct my_biggy *)
856	(((char *)w) - offsetof (struct my_biggy, t2));	1286	(((char *)w) - offsetof (struct my_biggy, t2));
857	}	1287	}
		1288
		1289	=head2 WATCHER PRIORITY MODELS
		1290
		1291	Many event loops support I<watcher priorities>, which are usually small
		1292	integers that influence the ordering of event callback invocation
		1293	between watchers in some way, all else being equal.
		1294
		1295	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1296	description for the more technical details such as the actual priority
		1297	range.
		1298
		1299	There are two common ways how these these priorities are being interpreted
		1300	by event loops:
		1301
		1302	In the more common lock-out model, higher priorities "lock out" invocation
		1303	of lower priority watchers, which means as long as higher priority
		1304	watchers receive events, lower priority watchers are not being invoked.
		1305
		1306	The less common only-for-ordering model uses priorities solely to order
		1307	callback invocation within a single event loop iteration: Higher priority
		1308	watchers are invoked before lower priority ones, but they all get invoked
		1309	before polling for new events.
		1310
		1311	Libev uses the second (only-for-ordering) model for all its watchers
		1312	except for idle watchers (which use the lock-out model).
		1313
		1314	The rationale behind this is that implementing the lock-out model for
		1315	watchers is not well supported by most kernel interfaces, and most event
		1316	libraries will just poll for the same events again and again as long as
		1317	their callbacks have not been executed, which is very inefficient in the
		1318	common case of one high-priority watcher locking out a mass of lower
		1319	priority ones.
		1320
		1321	Static (ordering) priorities are most useful when you have two or more
		1322	watchers handling the same resource: a typical usage example is having an
		1323	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1324	timeouts. Under load, data might be received while the program handles
		1325	other jobs, but since timers normally get invoked first, the timeout
		1326	handler will be executed before checking for data. In that case, giving
		1327	the timer a lower priority than the I/O watcher ensures that I/O will be
		1328	handled first even under adverse conditions (which is usually, but not
		1329	always, what you want).
		1330
		1331	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1332	will only be executed when no same or higher priority watchers have
		1333	received events, they can be used to implement the "lock-out" model when
		1334	required.
		1335
		1336	For example, to emulate how many other event libraries handle priorities,
		1337	you can associate an C<ev_idle> watcher to each such watcher, and in
		1338	the normal watcher callback, you just start the idle watcher. The real
		1339	processing is done in the idle watcher callback. This causes libev to
		1340	continously poll and process kernel event data for the watcher, but when
		1341	the lock-out case is known to be rare (which in turn is rare :), this is
		1342	workable.
		1343
		1344	Usually, however, the lock-out model implemented that way will perform
		1345	miserably under the type of load it was designed to handle. In that case,
		1346	it might be preferable to stop the real watcher before starting the
		1347	idle watcher, so the kernel will not have to process the event in case
		1348	the actual processing will be delayed for considerable time.
		1349
		1350	Here is an example of an I/O watcher that should run at a strictly lower
		1351	priority than the default, and which should only process data when no
		1352	other events are pending:
		1353
		1354	ev_idle idle; // actual processing watcher
		1355	ev_io io; // actual event watcher
		1356
		1357	static void
		1358	io_cb (EV_P_ ev_io *w, int revents)
		1359	{
		1360	// stop the I/O watcher, we received the event, but
		1361	// are not yet ready to handle it.
		1362	ev_io_stop (EV_A_ w);
		1363
		1364	// start the idle watcher to ahndle the actual event.
		1365	// it will not be executed as long as other watchers
		1366	// with the default priority are receiving events.
		1367	ev_idle_start (EV_A_ &idle);
		1368	}
		1369
		1370	static void
		1371	idle_cb (EV_P_ ev_idle *w, int revents)
		1372	{
		1373	// actual processing
		1374	read (STDIN_FILENO, ...);
		1375
		1376	// have to start the I/O watcher again, as
		1377	// we have handled the event
		1378	ev_io_start (EV_P_ &io);
		1379	}
		1380
		1381	// initialisation
		1382	ev_idle_init (&idle, idle_cb);
		1383	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1384	ev_io_start (EV_DEFAULT_ &io);
		1385
		1386	In the "real" world, it might also be beneficial to start a timer, so that
		1387	low-priority connections can not be locked out forever under load. This
		1388	enables your program to keep a lower latency for important connections
		1389	during short periods of high load, while not completely locking out less
		1390	important ones.
858		1391
859		1392
860	=head1 WATCHER TYPES	1393	=head1 WATCHER TYPES
861		1394
862	This section describes each watcher in detail, but will not repeat	1395	This section describes each watcher in detail, but will not repeat
…		…
886	In general you can register as many read and/or write event watchers per	1419	In general you can register as many read and/or write event watchers per
887	fd as you want (as long as you don't confuse yourself). Setting all file	1420	fd as you want (as long as you don't confuse yourself). Setting all file
888	descriptors to non-blocking mode is also usually a good idea (but not	1421	descriptors to non-blocking mode is also usually a good idea (but not
889	required if you know what you are doing).	1422	required if you know what you are doing).
890		1423
891	You have to be careful with dup'ed file descriptors, though. Some backends	1424	If you cannot use non-blocking mode, then force the use of a
892	(the linux epoll backend is a notable example) cannot handle dup'ed file	1425	known-to-be-good backend (at the time of this writing, this includes only
893	descriptors correctly if you register interest in two or more fds pointing	1426	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
894	to the same underlying file/socket/etc. description (that is, they share	1427	descriptors for which non-blocking operation makes no sense (such as
895	the same underlying "file open").	1428	files) - libev doesn't guarentee any specific behaviour in that case.
896
897	If you must do this, then force the use of a known-to-be-good backend
898	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
899	C<EVBACKEND_POLL>).
900		1429
901	Another thing you have to watch out for is that it is quite easy to	1430	Another thing you have to watch out for is that it is quite easy to
902	receive "spurious" readyness notifications, that is your callback might	1431	receive "spurious" readiness notifications, that is your callback might
903	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1432	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
904	because there is no data. Not only are some backends known to create a	1433	because there is no data. Not only are some backends known to create a
905	lot of those (for example solaris ports), it is very easy to get into	1434	lot of those (for example Solaris ports), it is very easy to get into
906	this situation even with a relatively standard program structure. Thus	1435	this situation even with a relatively standard program structure. Thus
907	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1436	it is best to always use non-blocking I/O: An extra C<read>(2) returning
908	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1437	C<EAGAIN> is far preferable to a program hanging until some data arrives.
909		1438
910	If you cannot run the fd in non-blocking mode (for example you should not	1439	If you cannot run the fd in non-blocking mode (for example you should
911	play around with an Xlib connection), then you have to seperately re-test	1440	not play around with an Xlib connection), then you have to separately
912	whether a file descriptor is really ready with a known-to-be good interface	1441	re-test whether a file descriptor is really ready with a known-to-be good
913	such as poll (fortunately in our Xlib example, Xlib already does this on	1442	interface such as poll (fortunately in our Xlib example, Xlib already
914	its own, so its quite safe to use).	1443	does this on its own, so its quite safe to use). Some people additionally
		1444	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1445	indefinitely.
		1446
		1447	But really, best use non-blocking mode.
915		1448
916	=head3 The special problem of disappearing file descriptors	1449	=head3 The special problem of disappearing file descriptors
917		1450
918	Some backends (e.g kqueue, epoll) need to be told about closing a file	1451	Some backends (e.g. kqueue, epoll) need to be told about closing a file
919	descriptor (either by calling C<close> explicitly or by any other means,	1452	descriptor (either due to calling C<close> explicitly or any other means,
920	such as C<dup>). The reason is that you register interest in some file	1453	such as C<dup2>). The reason is that you register interest in some file
921	descriptor, but when it goes away, the operating system will silently drop	1454	descriptor, but when it goes away, the operating system will silently drop
922	this interest. If another file descriptor with the same number then is	1455	this interest. If another file descriptor with the same number then is
923	registered with libev, there is no efficient way to see that this is, in	1456	registered with libev, there is no efficient way to see that this is, in
924	fact, a different file descriptor.	1457	fact, a different file descriptor.
925		1458
…		…
932		1465
933	This is how one would do it normally anyway, the important point is that	1466	This is how one would do it normally anyway, the important point is that
934	the libev application should not optimise around libev but should leave	1467	the libev application should not optimise around libev but should leave
935	optimisations to libev.	1468	optimisations to libev.
936		1469
		1470	=head3 The special problem of dup'ed file descriptors
		1471
		1472	Some backends (e.g. epoll), cannot register events for file descriptors,
		1473	but only events for the underlying file descriptions. That means when you
		1474	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1475	events for them, only one file descriptor might actually receive events.
		1476
		1477	There is no workaround possible except not registering events
		1478	for potentially C<dup ()>'ed file descriptors, or to resort to
		1479	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1480
		1481	=head3 The special problem of fork
		1482
		1483	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1484	useless behaviour. Libev fully supports fork, but needs to be told about
		1485	it in the child.
		1486
		1487	To support fork in your programs, you either have to call
		1488	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1489	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1490	C<EVBACKEND_POLL>.
		1491
		1492	=head3 The special problem of SIGPIPE
		1493
		1494	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1495	when writing to a pipe whose other end has been closed, your program gets
		1496	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1497	this is sensible behaviour, for daemons, this is usually undesirable.
		1498
		1499	So when you encounter spurious, unexplained daemon exits, make sure you
		1500	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1501	somewhere, as that would have given you a big clue).
		1502
		1503
		1504	=head3 Watcher-Specific Functions
937		1505
938	=over 4	1506	=over 4
939		1507
940	=item ev_io_init (ev_io *, callback, int fd, int events)	1508	=item ev_io_init (ev_io *, callback, int fd, int events)
941		1509
942	=item ev_io_set (ev_io *, int fd, int events)	1510	=item ev_io_set (ev_io *, int fd, int events)
943		1511
944	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1512	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
945	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1513	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
946	C<EV_READ | EV_WRITE> to receive the given events.	1514	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
947		1515
948	=item int fd [read-only]	1516	=item int fd [read-only]
949		1517
950	The file descriptor being watched.	1518	The file descriptor being watched.
951		1519
952	=item int events [read-only]	1520	=item int events [read-only]
953		1521
954	The events being watched.	1522	The events being watched.
955		1523
956	=back	1524	=back
		1525
		1526	=head3 Examples
957		1527
958	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1528	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
959	readable, but only once. Since it is likely line-buffered, you could	1529	readable, but only once. Since it is likely line-buffered, you could
960	attempt to read a whole line in the callback.	1530	attempt to read a whole line in the callback.
961		1531
962	static void	1532	static void
963	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1533	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
964	{	1534	{
965	ev_io_stop (loop, w);	1535	ev_io_stop (loop, w);
966	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1536	.. read from stdin here (or from w->fd) and handle any I/O errors
967	}	1537	}
968		1538
969	...	1539	...
970	struct ev_loop *loop = ev_default_init (0);	1540	struct ev_loop *loop = ev_default_init (0);
971	struct ev_io stdin_readable;	1541	ev_io stdin_readable;
972	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1542	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
973	ev_io_start (loop, &stdin_readable);	1543	ev_io_start (loop, &stdin_readable);
974	ev_loop (loop, 0);	1544	ev_loop (loop, 0);
975		1545
976		1546
977	=head2 C<ev_timer> - relative and optionally repeating timeouts	1547	=head2 C<ev_timer> - relative and optionally repeating timeouts
978		1548
979	Timer watchers are simple relative timers that generate an event after a	1549	Timer watchers are simple relative timers that generate an event after a
980	given time, and optionally repeating in regular intervals after that.	1550	given time, and optionally repeating in regular intervals after that.
981		1551
982	The timers are based on real time, that is, if you register an event that	1552	The timers are based on real time, that is, if you register an event that
983	times out after an hour and you reset your system clock to last years	1553	times out after an hour and you reset your system clock to January last
984	time, it will still time out after (roughly) and hour. "Roughly" because	1554	year, it will still time out after (roughly) one hour. "Roughly" because
985	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1555	detecting time jumps is hard, and some inaccuracies are unavoidable (the
986	monotonic clock option helps a lot here).	1556	monotonic clock option helps a lot here).
		1557
		1558	The callback is guaranteed to be invoked only I<after> its timeout has
		1559	passed (not I<at>, so on systems with very low-resolution clocks this
		1560	might introduce a small delay). If multiple timers become ready during the
		1561	same loop iteration then the ones with earlier time-out values are invoked
		1562	before ones of the same priority with later time-out values (but this is
		1563	no longer true when a callback calls C<ev_loop> recursively).
		1564
		1565	=head3 Be smart about timeouts
		1566
		1567	Many real-world problems involve some kind of timeout, usually for error
		1568	recovery. A typical example is an HTTP request - if the other side hangs,
		1569	you want to raise some error after a while.
		1570
		1571	What follows are some ways to handle this problem, from obvious and
		1572	inefficient to smart and efficient.
		1573
		1574	In the following, a 60 second activity timeout is assumed - a timeout that
		1575	gets reset to 60 seconds each time there is activity (e.g. each time some
		1576	data or other life sign was received).
		1577
		1578	=over 4
		1579
		1580	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1581
		1582	This is the most obvious, but not the most simple way: In the beginning,
		1583	start the watcher:
		1584
		1585	ev_timer_init (timer, callback, 60., 0.);
		1586	ev_timer_start (loop, timer);
		1587
		1588	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1589	and start it again:
		1590
		1591	ev_timer_stop (loop, timer);
		1592	ev_timer_set (timer, 60., 0.);
		1593	ev_timer_start (loop, timer);
		1594
		1595	This is relatively simple to implement, but means that each time there is
		1596	some activity, libev will first have to remove the timer from its internal
		1597	data structure and then add it again. Libev tries to be fast, but it's
		1598	still not a constant-time operation.
		1599
		1600	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1601
		1602	This is the easiest way, and involves using C<ev_timer_again> instead of
		1603	C<ev_timer_start>.
		1604
		1605	To implement this, configure an C<ev_timer> with a C<repeat> value
		1606	of C<60> and then call C<ev_timer_again> at start and each time you
		1607	successfully read or write some data. If you go into an idle state where
		1608	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1609	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1610
		1611	That means you can ignore both the C<ev_timer_start> function and the
		1612	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1613	member and C<ev_timer_again>.
		1614
		1615	At start:
		1616
		1617	ev_init (timer, callback);
		1618	timer->repeat = 60.;
		1619	ev_timer_again (loop, timer);
		1620
		1621	Each time there is some activity:
		1622
		1623	ev_timer_again (loop, timer);
		1624
		1625	It is even possible to change the time-out on the fly, regardless of
		1626	whether the watcher is active or not:
		1627
		1628	timer->repeat = 30.;
		1629	ev_timer_again (loop, timer);
		1630
		1631	This is slightly more efficient then stopping/starting the timer each time
		1632	you want to modify its timeout value, as libev does not have to completely
		1633	remove and re-insert the timer from/into its internal data structure.
		1634
		1635	It is, however, even simpler than the "obvious" way to do it.
		1636
		1637	=item 3. Let the timer time out, but then re-arm it as required.
		1638
		1639	This method is more tricky, but usually most efficient: Most timeouts are
		1640	relatively long compared to the intervals between other activity - in
		1641	our example, within 60 seconds, there are usually many I/O events with
		1642	associated activity resets.
		1643
		1644	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1645	but remember the time of last activity, and check for a real timeout only
		1646	within the callback:
		1647
		1648	ev_tstamp last_activity; // time of last activity
		1649
		1650	static void
		1651	callback (EV_P_ ev_timer *w, int revents)
		1652	{
		1653	ev_tstamp now = ev_now (EV_A);
		1654	ev_tstamp timeout = last_activity + 60.;
		1655
		1656	// if last_activity + 60. is older than now, we did time out
		1657	if (timeout < now)
		1658	{
		1659	// timeout occured, take action
		1660	}
		1661	else
		1662	{
		1663	// callback was invoked, but there was some activity, re-arm
		1664	// the watcher to fire in last_activity + 60, which is
		1665	// guaranteed to be in the future, so "again" is positive:
		1666	w->repeat = timeout - now;
		1667	ev_timer_again (EV_A_ w);
		1668	}
		1669	}
		1670
		1671	To summarise the callback: first calculate the real timeout (defined
		1672	as "60 seconds after the last activity"), then check if that time has
		1673	been reached, which means something I<did>, in fact, time out. Otherwise
		1674	the callback was invoked too early (C<timeout> is in the future), so
		1675	re-schedule the timer to fire at that future time, to see if maybe we have
		1676	a timeout then.
		1677
		1678	Note how C<ev_timer_again> is used, taking advantage of the
		1679	C<ev_timer_again> optimisation when the timer is already running.
		1680
		1681	This scheme causes more callback invocations (about one every 60 seconds
		1682	minus half the average time between activity), but virtually no calls to
		1683	libev to change the timeout.
		1684
		1685	To start the timer, simply initialise the watcher and set C<last_activity>
		1686	to the current time (meaning we just have some activity :), then call the
		1687	callback, which will "do the right thing" and start the timer:
		1688
		1689	ev_init (timer, callback);
		1690	last_activity = ev_now (loop);
		1691	callback (loop, timer, EV_TIMEOUT);
		1692
		1693	And when there is some activity, simply store the current time in
		1694	C<last_activity>, no libev calls at all:
		1695
		1696	last_actiivty = ev_now (loop);
		1697
		1698	This technique is slightly more complex, but in most cases where the
		1699	time-out is unlikely to be triggered, much more efficient.
		1700
		1701	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1702	callback :) - just change the timeout and invoke the callback, which will
		1703	fix things for you.
		1704
		1705	=item 4. Wee, just use a double-linked list for your timeouts.
		1706
		1707	If there is not one request, but many thousands (millions...), all
		1708	employing some kind of timeout with the same timeout value, then one can
		1709	do even better:
		1710
		1711	When starting the timeout, calculate the timeout value and put the timeout
		1712	at the I<end> of the list.
		1713
		1714	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1715	the list is expected to fire (for example, using the technique #3).
		1716
		1717	When there is some activity, remove the timer from the list, recalculate
		1718	the timeout, append it to the end of the list again, and make sure to
		1719	update the C<ev_timer> if it was taken from the beginning of the list.
		1720
		1721	This way, one can manage an unlimited number of timeouts in O(1) time for
		1722	starting, stopping and updating the timers, at the expense of a major
		1723	complication, and having to use a constant timeout. The constant timeout
		1724	ensures that the list stays sorted.
		1725
		1726	=back
		1727
		1728	So which method the best?
		1729
		1730	Method #2 is a simple no-brain-required solution that is adequate in most
		1731	situations. Method #3 requires a bit more thinking, but handles many cases
		1732	better, and isn't very complicated either. In most case, choosing either
		1733	one is fine, with #3 being better in typical situations.
		1734
		1735	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1736	rather complicated, but extremely efficient, something that really pays
		1737	off after the first million or so of active timers, i.e. it's usually
		1738	overkill :)
		1739
		1740	=head3 The special problem of time updates
		1741
		1742	Establishing the current time is a costly operation (it usually takes at
		1743	least two system calls): EV therefore updates its idea of the current
		1744	time only before and after C<ev_loop> collects new events, which causes a
		1745	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1746	lots of events in one iteration.
987		1747
988	The relative timeouts are calculated relative to the C<ev_now ()>	1748	The relative timeouts are calculated relative to the C<ev_now ()>
989	time. This is usually the right thing as this timestamp refers to the time	1749	time. This is usually the right thing as this timestamp refers to the time
990	of the event triggering whatever timeout you are modifying/starting. If	1750	of the event triggering whatever timeout you are modifying/starting. If
991	you suspect event processing to be delayed and you I<need> to base the timeout	1751	you suspect event processing to be delayed and you I<need> to base the
992	on the current time, use something like this to adjust for this:	1752	timeout on the current time, use something like this to adjust for this:
993		1753
994	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1754	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
995		1755
996	The callback is guarenteed to be invoked only when its timeout has passed,	1756	If the event loop is suspended for a long time, you can also force an
997	but if multiple timers become ready during the same loop iteration then	1757	update of the time returned by C<ev_now ()> by calling C<ev_now_update
998	order of execution is undefined.	1758	()>.
		1759
		1760	=head3 Watcher-Specific Functions and Data Members
999		1761
1000	=over 4	1762	=over 4
1001		1763
1002	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1764	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1003		1765
1004	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1766	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1005		1767
1006	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1768	Configure the timer to trigger after C<after> seconds. If C<repeat>
1007	C<0.>, then it will automatically be stopped. If it is positive, then the	1769	is C<0.>, then it will automatically be stopped once the timeout is
1008	timer will automatically be configured to trigger again C<repeat> seconds	1770	reached. If it is positive, then the timer will automatically be
1009	later, again, and again, until stopped manually.	1771	configured to trigger again C<repeat> seconds later, again, and again,
		1772	until stopped manually.
1010		1773
1011	The timer itself will do a best-effort at avoiding drift, that is, if you	1774	The timer itself will do a best-effort at avoiding drift, that is, if
1012	configure a timer to trigger every 10 seconds, then it will trigger at	1775	you configure a timer to trigger every 10 seconds, then it will normally
1013	exactly 10 second intervals. If, however, your program cannot keep up with	1776	trigger at exactly 10 second intervals. If, however, your program cannot
1014	the timer (because it takes longer than those 10 seconds to do stuff) the	1777	keep up with the timer (because it takes longer than those 10 seconds to
1015	timer will not fire more than once per event loop iteration.	1778	do stuff) the timer will not fire more than once per event loop iteration.
1016		1779
1017	=item ev_timer_again (loop)	1780	=item ev_timer_again (loop, ev_timer *)
1018		1781
1019	This will act as if the timer timed out and restart it again if it is	1782	This will act as if the timer timed out and restart it again if it is
1020	repeating. The exact semantics are:	1783	repeating. The exact semantics are:
1021		1784
1022	If the timer is pending, its pending status is cleared.	1785	If the timer is pending, its pending status is cleared.
1023		1786
1024	If the timer is started but nonrepeating, stop it (as if it timed out).	1787	If the timer is started but non-repeating, stop it (as if it timed out).
1025		1788
1026	If the timer is repeating, either start it if necessary (with the	1789	If the timer is repeating, either start it if necessary (with the
1027	C<repeat> value), or reset the running timer to the C<repeat> value.	1790	C<repeat> value), or reset the running timer to the C<repeat> value.
1028		1791
1029	This sounds a bit complicated, but here is a useful and typical	1792	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1030	example: Imagine you have a tcp connection and you want a so-called idle	1793	usage example.
1031	timeout, that is, you want to be called when there have been, say, 60
1032	seconds of inactivity on the socket. The easiest way to do this is to
1033	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1034	C<ev_timer_again> each time you successfully read or write some data. If
1035	you go into an idle state where you do not expect data to travel on the
1036	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1037	automatically restart it if need be.
1038
1039	That means you can ignore the C<after> value and C<ev_timer_start>
1040	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1041
1042	ev_timer_init (timer, callback, 0., 5.);
1043	ev_timer_again (loop, timer);
1044	...
1045	timer->again = 17.;
1046	ev_timer_again (loop, timer);
1047	...
1048	timer->again = 10.;
1049	ev_timer_again (loop, timer);
1050
1051	This is more slightly efficient then stopping/starting the timer each time
1052	you want to modify its timeout value.
1053		1794
1054	=item ev_tstamp repeat [read-write]	1795	=item ev_tstamp repeat [read-write]
1055		1796
1056	The current C<repeat> value. Will be used each time the watcher times out	1797	The current C<repeat> value. Will be used each time the watcher times out
1057	or C<ev_timer_again> is called and determines the next timeout (if any),	1798	or C<ev_timer_again> is called, and determines the next timeout (if any),
1058	which is also when any modifications are taken into account.	1799	which is also when any modifications are taken into account.
1059		1800
1060	=back	1801	=back
1061		1802
		1803	=head3 Examples
		1804
1062	Example: Create a timer that fires after 60 seconds.	1805	Example: Create a timer that fires after 60 seconds.
1063		1806
1064	static void	1807	static void
1065	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1808	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1066	{	1809	{
1067	.. one minute over, w is actually stopped right here	1810	.. one minute over, w is actually stopped right here
1068	}	1811	}
1069		1812
1070	struct ev_timer mytimer;	1813	ev_timer mytimer;
1071	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1814	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1072	ev_timer_start (loop, &mytimer);	1815	ev_timer_start (loop, &mytimer);
1073		1816
1074	Example: Create a timeout timer that times out after 10 seconds of	1817	Example: Create a timeout timer that times out after 10 seconds of
1075	inactivity.	1818	inactivity.
1076		1819
1077	static void	1820	static void
1078	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1821	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1079	{	1822	{
1080	.. ten seconds without any activity	1823	.. ten seconds without any activity
1081	}	1824	}
1082		1825
1083	struct ev_timer mytimer;	1826	ev_timer mytimer;
1084	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1827	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1085	ev_timer_again (&mytimer); /* start timer */	1828	ev_timer_again (&mytimer); /* start timer */
1086	ev_loop (loop, 0);	1829	ev_loop (loop, 0);
1087		1830
1088	// and in some piece of code that gets executed on any "activity":	1831	// and in some piece of code that gets executed on any "activity":
1089	// reset the timeout to start ticking again at 10 seconds	1832	// reset the timeout to start ticking again at 10 seconds
1090	ev_timer_again (&mytimer);	1833	ev_timer_again (&mytimer);
1091		1834
1092		1835
1093	=head2 C<ev_periodic> - to cron or not to cron?	1836	=head2 C<ev_periodic> - to cron or not to cron?
1094		1837
1095	Periodic watchers are also timers of a kind, but they are very versatile	1838	Periodic watchers are also timers of a kind, but they are very versatile
1096	(and unfortunately a bit complex).	1839	(and unfortunately a bit complex).
1097		1840
1098	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1841	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1099	but on wallclock time (absolute time). You can tell a periodic watcher	1842	relative time, the physical time that passes) but on wall clock time
1100	to trigger "at" some specific point in time. For example, if you tell a	1843	(absolute time, the thing you can read on your calender or clock). The
1101	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	1844	difference is that wall clock time can run faster or slower than real
1102	+ 10.>) and then reset your system clock to the last year, then it will	1845	time, and time jumps are not uncommon (e.g. when you adjust your
1103	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1846	wrist-watch).
1104	roughly 10 seconds later).
1105		1847
1106	They can also be used to implement vastly more complex timers, such as	1848	You can tell a periodic watcher to trigger after some specific point
1107	triggering an event on each midnight, local time or other, complicated,	1849	in time: for example, if you tell a periodic watcher to trigger "in 10
1108	rules.	1850	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1851	not a delay) and then reset your system clock to January of the previous
		1852	year, then it will take a year or more to trigger the event (unlike an
		1853	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1854	it, as it uses a relative timeout).
1109		1855
		1856	C<ev_periodic> watchers can also be used to implement vastly more complex
		1857	timers, such as triggering an event on each "midnight, local time", or
		1858	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1859	those cannot react to time jumps.
		1860
1110	As with timers, the callback is guarenteed to be invoked only when the	1861	As with timers, the callback is guaranteed to be invoked only when the
1111	time (C<at>) has been passed, but if multiple periodic timers become ready	1862	point in time where it is supposed to trigger has passed. If multiple
1112	during the same loop iteration then order of execution is undefined.	1863	timers become ready during the same loop iteration then the ones with
		1864	earlier time-out values are invoked before ones with later time-out values
		1865	(but this is no longer true when a callback calls C<ev_loop> recursively).
		1866
		1867	=head3 Watcher-Specific Functions and Data Members
1113		1868
1114	=over 4	1869	=over 4
1115		1870
1116	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1871	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1117		1872
1118	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1873	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1119		1874
1120	Lots of arguments, lets sort it out... There are basically three modes of	1875	Lots of arguments, let's sort it out... There are basically three modes of
1121	operation, and we will explain them from simplest to complex:	1876	operation, and we will explain them from simplest to most complex:
1122		1877
1123	=over 4	1878	=over 4
1124		1879
1125	=item * absolute timer (at = time, interval = reschedule_cb = 0)	1880	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1126		1881
1127	In this configuration the watcher triggers an event at the wallclock time	1882	In this configuration the watcher triggers an event after the wall clock
1128	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1883	time C<offset> has passed. It will not repeat and will not adjust when a
1129	that is, if it is to be run at January 1st 2011 then it will run when the	1884	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1130	system time reaches or surpasses this time.	1885	will be stopped and invoked when the system clock reaches or surpasses
		1886	this point in time.
1131		1887
1132	=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	1888	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1133		1889
1134	In this mode the watcher will always be scheduled to time out at the next	1890	In this mode the watcher will always be scheduled to time out at the next
1135	C<at + N * interval> time (for some integer N, which can also be negative)	1891	C<offset + N * interval> time (for some integer N, which can also be
1136	and then repeat, regardless of any time jumps.	1892	negative) and then repeat, regardless of any time jumps. The C<offset>
		1893	argument is merely an offset into the C<interval> periods.
1137		1894
1138	This can be used to create timers that do not drift with respect to system	1895	This can be used to create timers that do not drift with respect to the
1139	time:	1896	system clock, for example, here is an C<ev_periodic> that triggers each
		1897	hour, on the hour (with respect to UTC):
1140		1898
1141	ev_periodic_set (&periodic, 0., 3600., 0);	1899	ev_periodic_set (&periodic, 0., 3600., 0);
1142		1900
1143	This doesn't mean there will always be 3600 seconds in between triggers,	1901	This doesn't mean there will always be 3600 seconds in between triggers,
1144	but only that the the callback will be called when the system time shows a	1902	but only that the callback will be called when the system time shows a
1145	full hour (UTC), or more correctly, when the system time is evenly divisible	1903	full hour (UTC), or more correctly, when the system time is evenly divisible
1146	by 3600.	1904	by 3600.
1147		1905
1148	Another way to think about it (for the mathematically inclined) is that	1906	Another way to think about it (for the mathematically inclined) is that
1149	C<ev_periodic> will try to run the callback in this mode at the next possible	1907	C<ev_periodic> will try to run the callback in this mode at the next possible
1150	time where C<time = at (mod interval)>, regardless of any time jumps.	1908	time where C<time = offset (mod interval)>, regardless of any time jumps.
1151		1909
1152	For numerical stability it is preferable that the C<at> value is near	1910	For numerical stability it is preferable that the C<offset> value is near
1153	C<ev_now ()> (the current time), but there is no range requirement for	1911	C<ev_now ()> (the current time), but there is no range requirement for
1154	this value.	1912	this value, and in fact is often specified as zero.
1155		1913
		1914	Note also that there is an upper limit to how often a timer can fire (CPU
		1915	speed for example), so if C<interval> is very small then timing stability
		1916	will of course deteriorate. Libev itself tries to be exact to be about one
		1917	millisecond (if the OS supports it and the machine is fast enough).
		1918
1156	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	1919	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1157		1920
1158	In this mode the values for C<interval> and C<at> are both being	1921	In this mode the values for C<interval> and C<offset> are both being
1159	ignored. Instead, each time the periodic watcher gets scheduled, the	1922	ignored. Instead, each time the periodic watcher gets scheduled, the
1160	reschedule callback will be called with the watcher as first, and the	1923	reschedule callback will be called with the watcher as first, and the
1161	current time as second argument.	1924	current time as second argument.
1162		1925
1163	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1926	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1164	ever, or make any event loop modifications>. If you need to stop it,	1927	or make ANY other event loop modifications whatsoever, unless explicitly
1165	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	1928	allowed by documentation here>.
1166	starting an C<ev_prepare> watcher, which is legal).
1167		1929
		1930	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1931	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1932	only event loop modification you are allowed to do).
		1933
1168	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1934	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1169	ev_tstamp now)>, e.g.:	1935	*w, ev_tstamp now)>, e.g.:
1170		1936
		1937	static ev_tstamp
1171	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1938	my_rescheduler (ev_periodic *w, ev_tstamp now)
1172	{	1939	{
1173	return now + 60.;	1940	return now + 60.;
1174	}	1941	}
1175		1942
1176	It must return the next time to trigger, based on the passed time value	1943	It must return the next time to trigger, based on the passed time value
1177	(that is, the lowest time value larger than to the second argument). It	1944	(that is, the lowest time value larger than to the second argument). It
1178	will usually be called just before the callback will be triggered, but	1945	will usually be called just before the callback will be triggered, but
1179	might be called at other times, too.	1946	might be called at other times, too.
1180		1947
1181	NOTE: I<< This callback must always return a time that is later than the	1948	NOTE: I<< This callback must always return a time that is higher than or
1182	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	1949	equal to the passed C<now> value >>.
1183		1950
1184	This can be used to create very complex timers, such as a timer that	1951	This can be used to create very complex timers, such as a timer that
1185	triggers on each midnight, local time. To do this, you would calculate the	1952	triggers on "next midnight, local time". To do this, you would calculate the
1186	next midnight after C<now> and return the timestamp value for this. How	1953	next midnight after C<now> and return the timestamp value for this. How
1187	you do this is, again, up to you (but it is not trivial, which is the main	1954	you do this is, again, up to you (but it is not trivial, which is the main
1188	reason I omitted it as an example).	1955	reason I omitted it as an example).
1189		1956
1190	=back	1957	=back
…		…
1194	Simply stops and restarts the periodic watcher again. This is only useful	1961	Simply stops and restarts the periodic watcher again. This is only useful
1195	when you changed some parameters or the reschedule callback would return	1962	when you changed some parameters or the reschedule callback would return
1196	a different time than the last time it was called (e.g. in a crond like	1963	a different time than the last time it was called (e.g. in a crond like
1197	program when the crontabs have changed).	1964	program when the crontabs have changed).
1198		1965
		1966	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1967
		1968	When active, returns the absolute time that the watcher is supposed
		1969	to trigger next. This is not the same as the C<offset> argument to
		1970	C<ev_periodic_set>, but indeed works even in interval and manual
		1971	rescheduling modes.
		1972
1199	=item ev_tstamp offset [read-write]	1973	=item ev_tstamp offset [read-write]
1200		1974
1201	When repeating, this contains the offset value, otherwise this is the	1975	When repeating, this contains the offset value, otherwise this is the
1202	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	1976	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		1977	although libev might modify this value for better numerical stability).
1203		1978
1204	Can be modified any time, but changes only take effect when the periodic	1979	Can be modified any time, but changes only take effect when the periodic
1205	timer fires or C<ev_periodic_again> is being called.	1980	timer fires or C<ev_periodic_again> is being called.
1206		1981
1207	=item ev_tstamp interval [read-write]	1982	=item ev_tstamp interval [read-write]
1208		1983
1209	The current interval value. Can be modified any time, but changes only	1984	The current interval value. Can be modified any time, but changes only
1210	take effect when the periodic timer fires or C<ev_periodic_again> is being	1985	take effect when the periodic timer fires or C<ev_periodic_again> is being
1211	called.	1986	called.
1212		1987
1213	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	1988	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1214		1989
1215	The current reschedule callback, or C<0>, if this functionality is	1990	The current reschedule callback, or C<0>, if this functionality is
1216	switched off. Can be changed any time, but changes only take effect when	1991	switched off. Can be changed any time, but changes only take effect when
1217	the periodic timer fires or C<ev_periodic_again> is being called.	1992	the periodic timer fires or C<ev_periodic_again> is being called.
1218		1993
1219	=back	1994	=back
1220		1995
		1996	=head3 Examples
		1997
1221	Example: Call a callback every hour, or, more precisely, whenever the	1998	Example: Call a callback every hour, or, more precisely, whenever the
1222	system clock is divisible by 3600. The callback invocation times have	1999	system time is divisible by 3600. The callback invocation times have
1223	potentially a lot of jittering, but good long-term stability.	2000	potentially a lot of jitter, but good long-term stability.
1224		2001
1225	static void	2002	static void
1226	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2003	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1227	{	2004	{
1228	... its now a full hour (UTC, or TAI or whatever your clock follows)	2005	... its now a full hour (UTC, or TAI or whatever your clock follows)
1229	}	2006	}
1230		2007
1231	struct ev_periodic hourly_tick;	2008	ev_periodic hourly_tick;
1232	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2009	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1233	ev_periodic_start (loop, &hourly_tick);	2010	ev_periodic_start (loop, &hourly_tick);
1234		2011
1235	Example: The same as above, but use a reschedule callback to do it:	2012	Example: The same as above, but use a reschedule callback to do it:
1236		2013
1237	#include <math.h>	2014	#include <math.h>
1238		2015
1239	static ev_tstamp	2016	static ev_tstamp
1240	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2017	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1241	{	2018	{
1242	return fmod (now, 3600.) + 3600.;	2019	return now + (3600. - fmod (now, 3600.));
1243	}	2020	}
1244		2021
1245	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2022	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1246		2023
1247	Example: Call a callback every hour, starting now:	2024	Example: Call a callback every hour, starting now:
1248		2025
1249	struct ev_periodic hourly_tick;	2026	ev_periodic hourly_tick;
1250	ev_periodic_init (&hourly_tick, clock_cb,	2027	ev_periodic_init (&hourly_tick, clock_cb,
1251	fmod (ev_now (loop), 3600.), 3600., 0);	2028	fmod (ev_now (loop), 3600.), 3600., 0);
1252	ev_periodic_start (loop, &hourly_tick);	2029	ev_periodic_start (loop, &hourly_tick);
1253		2030
1254		2031
1255	=head2 C<ev_signal> - signal me when a signal gets signalled!	2032	=head2 C<ev_signal> - signal me when a signal gets signalled!
1256		2033
1257	Signal watchers will trigger an event when the process receives a specific	2034	Signal watchers will trigger an event when the process receives a specific
1258	signal one or more times. Even though signals are very asynchronous, libev	2035	signal one or more times. Even though signals are very asynchronous, libev
1259	will try it's best to deliver signals synchronously, i.e. as part of the	2036	will try it's best to deliver signals synchronously, i.e. as part of the
1260	normal event processing, like any other event.	2037	normal event processing, like any other event.
1261		2038
		2039	If you want signals asynchronously, just use C<sigaction> as you would
		2040	do without libev and forget about sharing the signal. You can even use
		2041	C<ev_async> from a signal handler to synchronously wake up an event loop.
		2042
1262	You can configure as many watchers as you like per signal. Only when the	2043	You can configure as many watchers as you like per signal. Only when the
1263	first watcher gets started will libev actually register a signal watcher	2044	first watcher gets started will libev actually register a signal handler
1264	with the kernel (thus it coexists with your own signal handlers as long	2045	with the kernel (thus it coexists with your own signal handlers as long as
1265	as you don't register any with libev). Similarly, when the last signal	2046	you don't register any with libev for the same signal). Similarly, when
1266	watcher for a signal is stopped libev will reset the signal handler to	2047	the last signal watcher for a signal is stopped, libev will reset the
1267	SIG_DFL (regardless of what it was set to before).	2048	signal handler to SIG_DFL (regardless of what it was set to before).
		2049
		2050	If possible and supported, libev will install its handlers with
		2051	C<SA_RESTART> behaviour enabled, so system calls should not be unduly
		2052	interrupted. If you have a problem with system calls getting interrupted by
		2053	signals you can block all signals in an C<ev_check> watcher and unblock
		2054	them in an C<ev_prepare> watcher.
		2055
		2056	=head3 Watcher-Specific Functions and Data Members
1268		2057
1269	=over 4	2058	=over 4
1270		2059
1271	=item ev_signal_init (ev_signal *, callback, int signum)	2060	=item ev_signal_init (ev_signal *, callback, int signum)
1272		2061
…		…
1279		2068
1280	The signal the watcher watches out for.	2069	The signal the watcher watches out for.
1281		2070
1282	=back	2071	=back
1283		2072
		2073	=head3 Examples
		2074
		2075	Example: Try to exit cleanly on SIGINT.
		2076
		2077	static void
		2078	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2079	{
		2080	ev_unloop (loop, EVUNLOOP_ALL);
		2081	}
		2082
		2083	ev_signal signal_watcher;
		2084	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2085	ev_signal_start (loop, &signal_watcher);
		2086
1284		2087
1285	=head2 C<ev_child> - watch out for process status changes	2088	=head2 C<ev_child> - watch out for process status changes
1286		2089
1287	Child watchers trigger when your process receives a SIGCHLD in response to	2090	Child watchers trigger when your process receives a SIGCHLD in response to
1288	some child status changes (most typically when a child of yours dies).	2091	some child status changes (most typically when a child of yours dies or
		2092	exits). It is permissible to install a child watcher I<after> the child
		2093	has been forked (which implies it might have already exited), as long
		2094	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2095	forking and then immediately registering a watcher for the child is fine,
		2096	but forking and registering a watcher a few event loop iterations later or
		2097	in the next callback invocation is not.
		2098
		2099	Only the default event loop is capable of handling signals, and therefore
		2100	you can only register child watchers in the default event loop.
		2101
		2102	Due to some design glitches inside libev, child watchers will always be
		2103	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2104	libev)
		2105
		2106	=head3 Process Interaction
		2107
		2108	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2109	initialised. This is necessary to guarantee proper behaviour even if
		2110	the first child watcher is started after the child exits. The occurrence
		2111	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2112	synchronously as part of the event loop processing. Libev always reaps all
		2113	children, even ones not watched.
		2114
		2115	=head3 Overriding the Built-In Processing
		2116
		2117	Libev offers no special support for overriding the built-in child
		2118	processing, but if your application collides with libev's default child
		2119	handler, you can override it easily by installing your own handler for
		2120	C<SIGCHLD> after initialising the default loop, and making sure the
		2121	default loop never gets destroyed. You are encouraged, however, to use an
		2122	event-based approach to child reaping and thus use libev's support for
		2123	that, so other libev users can use C<ev_child> watchers freely.
		2124
		2125	=head3 Stopping the Child Watcher
		2126
		2127	Currently, the child watcher never gets stopped, even when the
		2128	child terminates, so normally one needs to stop the watcher in the
		2129	callback. Future versions of libev might stop the watcher automatically
		2130	when a child exit is detected.
		2131
		2132	=head3 Watcher-Specific Functions and Data Members
1289		2133
1290	=over 4	2134	=over 4
1291		2135
1292	=item ev_child_init (ev_child *, callback, int pid)	2136	=item ev_child_init (ev_child *, callback, int pid, int trace)
1293		2137
1294	=item ev_child_set (ev_child *, int pid)	2138	=item ev_child_set (ev_child *, int pid, int trace)
1295		2139
1296	Configures the watcher to wait for status changes of process C<pid> (or	2140	Configures the watcher to wait for status changes of process C<pid> (or
1297	I<any> process if C<pid> is specified as C<0>). The callback can look	2141	I<any> process if C<pid> is specified as C<0>). The callback can look
1298	at the C<rstatus> member of the C<ev_child> watcher structure to see	2142	at the C<rstatus> member of the C<ev_child> watcher structure to see
1299	the status word (use the macros from C<sys/wait.h> and see your systems	2143	the status word (use the macros from C<sys/wait.h> and see your systems
1300	C<waitpid> documentation). The C<rpid> member contains the pid of the	2144	C<waitpid> documentation). The C<rpid> member contains the pid of the
1301	process causing the status change.	2145	process causing the status change. C<trace> must be either C<0> (only
		2146	activate the watcher when the process terminates) or C<1> (additionally
		2147	activate the watcher when the process is stopped or continued).
1302		2148
1303	=item int pid [read-only]	2149	=item int pid [read-only]
1304		2150
1305	The process id this watcher watches out for, or C<0>, meaning any process id.	2151	The process id this watcher watches out for, or C<0>, meaning any process id.
1306		2152
…		…
1313	The process exit/trace status caused by C<rpid> (see your systems	2159	The process exit/trace status caused by C<rpid> (see your systems
1314	C<waitpid> and C<sys/wait.h> documentation for details).	2160	C<waitpid> and C<sys/wait.h> documentation for details).
1315		2161
1316	=back	2162	=back
1317		2163
1318	Example: Try to exit cleanly on SIGINT and SIGTERM.	2164	=head3 Examples
1319		2165
		2166	Example: C<fork()> a new process and install a child handler to wait for
		2167	its completion.
		2168
		2169	ev_child cw;
		2170
1320	static void	2171	static void
1321	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2172	child_cb (EV_P_ ev_child *w, int revents)
1322	{	2173	{
1323	ev_unloop (loop, EVUNLOOP_ALL);	2174	ev_child_stop (EV_A_ w);
		2175	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1324	}	2176	}
1325		2177
1326	struct ev_signal signal_watcher;	2178	pid_t pid = fork ();
1327	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2179
1328	ev_signal_start (loop, &sigint_cb);	2180	if (pid < 0)
		2181	// error
		2182	else if (pid == 0)
		2183	{
		2184	// the forked child executes here
		2185	exit (1);
		2186	}
		2187	else
		2188	{
		2189	ev_child_init (&cw, child_cb, pid, 0);
		2190	ev_child_start (EV_DEFAULT_ &cw);
		2191	}
1329		2192
1330		2193
1331	=head2 C<ev_stat> - did the file attributes just change?	2194	=head2 C<ev_stat> - did the file attributes just change?
1332		2195
1333	This watches a filesystem path for attribute changes. That is, it calls	2196	This watches a file system path for attribute changes. That is, it calls
1334	C<stat> regularly (or when the OS says it changed) and sees if it changed	2197	C<stat> on that path in regular intervals (or when the OS says it changed)
1335	compared to the last time, invoking the callback if it did.	2198	and sees if it changed compared to the last time, invoking the callback if
		2199	it did.
1336		2200
1337	The path does not need to exist: changing from "path exists" to "path does	2201	The path does not need to exist: changing from "path exists" to "path does
1338	not exist" is a status change like any other. The condition "path does	2202	not exist" is a status change like any other. The condition "path does not
1339	not exist" is signified by the C<st_nlink> field being zero (which is	2203	exist" (or more correctly "path cannot be stat'ed") is signified by the
1340	otherwise always forced to be at least one) and all the other fields of	2204	C<st_nlink> field being zero (which is otherwise always forced to be at
1341	the stat buffer having unspecified contents.	2205	least one) and all the other fields of the stat buffer having unspecified
		2206	contents.
1342		2207
1343	The path I<should> be absolute and I<must not> end in a slash. If it is	2208	The path I<must not> end in a slash or contain special components such as
		2209	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1344	relative and your working directory changes, the behaviour is undefined.	2210	your working directory changes, then the behaviour is undefined.
1345		2211
1346	Since there is no standard to do this, the portable implementation simply	2212	Since there is no portable change notification interface available, the
1347	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2213	portable implementation simply calls C<stat(2)> regularly on the path
1348	can specify a recommended polling interval for this case. If you specify	2214	to see if it changed somehow. You can specify a recommended polling
1349	a polling interval of C<0> (highly recommended!) then a I<suitable,	2215	interval for this case. If you specify a polling interval of C<0> (highly
1350	unspecified default> value will be used (which you can expect to be around	2216	recommended!) then a I<suitable, unspecified default> value will be used
1351	five seconds, although this might change dynamically). Libev will also	2217	(which you can expect to be around five seconds, although this might
1352	impose a minimum interval which is currently around C<0.1>, but thats	2218	change dynamically). Libev will also impose a minimum interval which is
1353	usually overkill.	2219	currently around C<0.1>, but that's usually overkill.
1354		2220
1355	This watcher type is not meant for massive numbers of stat watchers,	2221	This watcher type is not meant for massive numbers of stat watchers,
1356	as even with OS-supported change notifications, this can be	2222	as even with OS-supported change notifications, this can be
1357	resource-intensive.	2223	resource-intensive.
1358		2224
1359	At the time of this writing, only the Linux inotify interface is	2225	At the time of this writing, the only OS-specific interface implemented
1360	implemented (implementing kqueue support is left as an exercise for the	2226	is the Linux inotify interface (implementing kqueue support is left as an
1361	reader). Inotify will be used to give hints only and should not change the	2227	exercise for the reader. Note, however, that the author sees no way of
1362	semantics of C<ev_stat> watchers, which means that libev sometimes needs	2228	implementing C<ev_stat> semantics with kqueue, except as a hint).
1363	to fall back to regular polling again even with inotify, but changes are	2229
1364	usually detected immediately, and if the file exists there will be no	2230	=head3 ABI Issues (Largefile Support)
1365	polling.	2231
		2232	Libev by default (unless the user overrides this) uses the default
		2233	compilation environment, which means that on systems with large file
		2234	support disabled by default, you get the 32 bit version of the stat
		2235	structure. When using the library from programs that change the ABI to
		2236	use 64 bit file offsets the programs will fail. In that case you have to
		2237	compile libev with the same flags to get binary compatibility. This is
		2238	obviously the case with any flags that change the ABI, but the problem is
		2239	most noticeably displayed with ev_stat and large file support.
		2240
		2241	The solution for this is to lobby your distribution maker to make large
		2242	file interfaces available by default (as e.g. FreeBSD does) and not
		2243	optional. Libev cannot simply switch on large file support because it has
		2244	to exchange stat structures with application programs compiled using the
		2245	default compilation environment.
		2246
		2247	=head3 Inotify and Kqueue
		2248
		2249	When C<inotify (7)> support has been compiled into libev and present at
		2250	runtime, it will be used to speed up change detection where possible. The
		2251	inotify descriptor will be created lazily when the first C<ev_stat>
		2252	watcher is being started.
		2253
		2254	Inotify presence does not change the semantics of C<ev_stat> watchers
		2255	except that changes might be detected earlier, and in some cases, to avoid
		2256	making regular C<stat> calls. Even in the presence of inotify support
		2257	there are many cases where libev has to resort to regular C<stat> polling,
		2258	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2259	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2260	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2261	xfs are fully working) libev usually gets away without polling.
		2262
		2263	There is no support for kqueue, as apparently it cannot be used to
		2264	implement this functionality, due to the requirement of having a file
		2265	descriptor open on the object at all times, and detecting renames, unlinks
		2266	etc. is difficult.
		2267
		2268	=head3 C<stat ()> is a synchronous operation
		2269
		2270	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2271	the process. The exception are C<ev_stat> watchers - those call C<stat
		2272	()>, which is a synchronous operation.
		2273
		2274	For local paths, this usually doesn't matter: unless the system is very
		2275	busy or the intervals between stat's are large, a stat call will be fast,
		2276	as the path data is usually in memory already (except when starting the
		2277	watcher).
		2278
		2279	For networked file systems, calling C<stat ()> can block an indefinite
		2280	time due to network issues, and even under good conditions, a stat call
		2281	often takes multiple milliseconds.
		2282
		2283	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2284	paths, although this is fully supported by libev.
		2285
		2286	=head3 The special problem of stat time resolution
		2287
		2288	The C<stat ()> system call only supports full-second resolution portably,
		2289	and even on systems where the resolution is higher, most file systems
		2290	still only support whole seconds.
		2291
		2292	That means that, if the time is the only thing that changes, you can
		2293	easily miss updates: on the first update, C<ev_stat> detects a change and
		2294	calls your callback, which does something. When there is another update
		2295	within the same second, C<ev_stat> will be unable to detect unless the
		2296	stat data does change in other ways (e.g. file size).
		2297
		2298	The solution to this is to delay acting on a change for slightly more
		2299	than a second (or till slightly after the next full second boundary), using
		2300	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2301	ev_timer_again (loop, w)>).
		2302
		2303	The C<.02> offset is added to work around small timing inconsistencies
		2304	of some operating systems (where the second counter of the current time
		2305	might be be delayed. One such system is the Linux kernel, where a call to
		2306	C<gettimeofday> might return a timestamp with a full second later than
		2307	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2308	update file times then there will be a small window where the kernel uses
		2309	the previous second to update file times but libev might already execute
		2310	the timer callback).
		2311
		2312	=head3 Watcher-Specific Functions and Data Members
1366		2313
1367	=over 4	2314	=over 4
1368		2315
1369	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)	2316	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
1370		2317
…		…
1374	C<path>. The C<interval> is a hint on how quickly a change is expected to	2321	C<path>. The C<interval> is a hint on how quickly a change is expected to
1375	be detected and should normally be specified as C<0> to let libev choose	2322	be detected and should normally be specified as C<0> to let libev choose
1376	a suitable value. The memory pointed to by C<path> must point to the same	2323	a suitable value. The memory pointed to by C<path> must point to the same
1377	path for as long as the watcher is active.	2324	path for as long as the watcher is active.
1378		2325
1379	The callback will be receive C<EV_STAT> when a change was detected,	2326	The callback will receive an C<EV_STAT> event when a change was detected,
1380	relative to the attributes at the time the watcher was started (or the	2327	relative to the attributes at the time the watcher was started (or the
1381	last change was detected).	2328	last change was detected).
1382		2329
1383	=item ev_stat_stat (ev_stat *)	2330	=item ev_stat_stat (loop, ev_stat *)
1384		2331
1385	Updates the stat buffer immediately with new values. If you change the	2332	Updates the stat buffer immediately with new values. If you change the
1386	watched path in your callback, you could call this fucntion to avoid	2333	watched path in your callback, you could call this function to avoid
1387	detecting this change (while introducing a race condition). Can also be	2334	detecting this change (while introducing a race condition if you are not
1388	useful simply to find out the new values.	2335	the only one changing the path). Can also be useful simply to find out the
		2336	new values.
1389		2337
1390	=item ev_statdata attr [read-only]	2338	=item ev_statdata attr [read-only]
1391		2339
1392	The most-recently detected attributes of the file. Although the type is of	2340	The most-recently detected attributes of the file. Although the type is
1393	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2341	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1394	suitable for your system. If the C<st_nlink> member is C<0>, then there	2342	suitable for your system, but you can only rely on the POSIX-standardised
		2343	members to be present. If the C<st_nlink> member is C<0>, then there was
1395	was some error while C<stat>ing the file.	2344	some error while C<stat>ing the file.
1396		2345
1397	=item ev_statdata prev [read-only]	2346	=item ev_statdata prev [read-only]
1398		2347
1399	The previous attributes of the file. The callback gets invoked whenever	2348	The previous attributes of the file. The callback gets invoked whenever
1400	C<prev> != C<attr>.	2349	C<prev> != C<attr>, or, more precisely, one or more of these members
		2350	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2351	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1401		2352
1402	=item ev_tstamp interval [read-only]	2353	=item ev_tstamp interval [read-only]
1403		2354
1404	The specified interval.	2355	The specified interval.
1405		2356
1406	=item const char *path [read-only]	2357	=item const char *path [read-only]
1407		2358
1408	The filesystem path that is being watched.	2359	The file system path that is being watched.
1409		2360
1410	=back	2361	=back
1411		2362
		2363	=head3 Examples
		2364
1412	Example: Watch C</etc/passwd> for attribute changes.	2365	Example: Watch C</etc/passwd> for attribute changes.
1413		2366
1414	static void	2367	static void
1415	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2368	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1416	{	2369	{
1417	/* /etc/passwd changed in some way */	2370	/* /etc/passwd changed in some way */
1418	if (w->attr.st_nlink)	2371	if (w->attr.st_nlink)
1419	{	2372	{
1420	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2373	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1421	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2374	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1422	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2375	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1423	}	2376	}
1424	else	2377	else
1425	/* you shalt not abuse printf for puts */	2378	/* you shalt not abuse printf for puts */
1426	puts ("wow, /etc/passwd is not there, expect problems. "	2379	puts ("wow, /etc/passwd is not there, expect problems. "
1427	"if this is windows, they already arrived\n");	2380	"if this is windows, they already arrived\n");
1428	}	2381	}
1429		2382
1430	...	2383	...
1431	ev_stat passwd;	2384	ev_stat passwd;
1432		2385
1433	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	2386	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1434	ev_stat_start (loop, &passwd);	2387	ev_stat_start (loop, &passwd);
		2388
		2389	Example: Like above, but additionally use a one-second delay so we do not
		2390	miss updates (however, frequent updates will delay processing, too, so
		2391	one might do the work both on C<ev_stat> callback invocation I<and> on
		2392	C<ev_timer> callback invocation).
		2393
		2394	static ev_stat passwd;
		2395	static ev_timer timer;
		2396
		2397	static void
		2398	timer_cb (EV_P_ ev_timer *w, int revents)
		2399	{
		2400	ev_timer_stop (EV_A_ w);
		2401
		2402	/* now it's one second after the most recent passwd change */
		2403	}
		2404
		2405	static void
		2406	stat_cb (EV_P_ ev_stat *w, int revents)
		2407	{
		2408	/* reset the one-second timer */
		2409	ev_timer_again (EV_A_ &timer);
		2410	}
		2411
		2412	...
		2413	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2414	ev_stat_start (loop, &passwd);
		2415	ev_timer_init (&timer, timer_cb, 0., 1.02);
1435		2416
1436		2417
1437	=head2 C<ev_idle> - when you've got nothing better to do...	2418	=head2 C<ev_idle> - when you've got nothing better to do...
1438		2419
1439	Idle watchers trigger events when no other events of the same or higher	2420	Idle watchers trigger events when no other events of the same or higher
1440	priority are pending (prepare, check and other idle watchers do not	2421	priority are pending (prepare, check and other idle watchers do not count
1441	count).	2422	as receiving "events").
1442		2423
1443	That is, as long as your process is busy handling sockets or timeouts	2424	That is, as long as your process is busy handling sockets or timeouts
1444	(or even signals, imagine) of the same or higher priority it will not be	2425	(or even signals, imagine) of the same or higher priority it will not be
1445	triggered. But when your process is idle (or only lower-priority watchers	2426	triggered. But when your process is idle (or only lower-priority watchers
1446	are pending), the idle watchers are being called once per event loop	2427	are pending), the idle watchers are being called once per event loop
…		…
1453	Apart from keeping your process non-blocking (which is a useful	2434	Apart from keeping your process non-blocking (which is a useful
1454	effect on its own sometimes), idle watchers are a good place to do	2435	effect on its own sometimes), idle watchers are a good place to do
1455	"pseudo-background processing", or delay processing stuff to after the	2436	"pseudo-background processing", or delay processing stuff to after the
1456	event loop has handled all outstanding events.	2437	event loop has handled all outstanding events.
1457		2438
		2439	=head3 Watcher-Specific Functions and Data Members
		2440
1458	=over 4	2441	=over 4
1459		2442
1460	=item ev_idle_init (ev_signal *, callback)	2443	=item ev_idle_init (ev_idle *, callback)
1461		2444
1462	Initialises and configures the idle watcher - it has no parameters of any	2445	Initialises and configures the idle watcher - it has no parameters of any
1463	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2446	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1464	believe me.	2447	believe me.
1465		2448
1466	=back	2449	=back
1467		2450
		2451	=head3 Examples
		2452
1468	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2453	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1469	callback, free it. Also, use no error checking, as usual.	2454	callback, free it. Also, use no error checking, as usual.
1470		2455
1471	static void	2456	static void
1472	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2457	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1473	{	2458	{
1474	free (w);	2459	free (w);
1475	// now do something you wanted to do when the program has	2460	// now do something you wanted to do when the program has
1476	// no longer asnything immediate to do.	2461	// no longer anything immediate to do.
1477	}	2462	}
1478		2463
1479	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2464	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1480	ev_idle_init (idle_watcher, idle_cb);	2465	ev_idle_init (idle_watcher, idle_cb);
1481	ev_idle_start (loop, idle_cb);	2466	ev_idle_start (loop, idle_watcher);
1482		2467
1483		2468
1484	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2469	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1485		2470
1486	Prepare and check watchers are usually (but not always) used in tandem:	2471	Prepare and check watchers are usually (but not always) used in pairs:
1487	prepare watchers get invoked before the process blocks and check watchers	2472	prepare watchers get invoked before the process blocks and check watchers
1488	afterwards.	2473	afterwards.
1489		2474
1490	You I<must not> call C<ev_loop> or similar functions that enter	2475	You I<must not> call C<ev_loop> or similar functions that enter
1491	the current event loop from either C<ev_prepare> or C<ev_check>	2476	the current event loop from either C<ev_prepare> or C<ev_check>
…		…
1494	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2479	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1495	C<ev_check> so if you have one watcher of each kind they will always be	2480	C<ev_check> so if you have one watcher of each kind they will always be
1496	called in pairs bracketing the blocking call.	2481	called in pairs bracketing the blocking call.
1497		2482
1498	Their main purpose is to integrate other event mechanisms into libev and	2483	Their main purpose is to integrate other event mechanisms into libev and
1499	their use is somewhat advanced. This could be used, for example, to track	2484	their use is somewhat advanced. They could be used, for example, to track
1500	variable changes, implement your own watchers, integrate net-snmp or a	2485	variable changes, implement your own watchers, integrate net-snmp or a
1501	coroutine library and lots more. They are also occasionally useful if	2486	coroutine library and lots more. They are also occasionally useful if
1502	you cache some data and want to flush it before blocking (for example,	2487	you cache some data and want to flush it before blocking (for example,
1503	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2488	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1504	watcher).	2489	watcher).
1505		2490
1506	This is done by examining in each prepare call which file descriptors need	2491	This is done by examining in each prepare call which file descriptors
1507	to be watched by the other library, registering C<ev_io> watchers for	2492	need to be watched by the other library, registering C<ev_io> watchers
1508	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2493	for them and starting an C<ev_timer> watcher for any timeouts (many
1509	provide just this functionality). Then, in the check watcher you check for	2494	libraries provide exactly this functionality). Then, in the check watcher,
1510	any events that occured (by checking the pending status of all watchers	2495	you check for any events that occurred (by checking the pending status
1511	and stopping them) and call back into the library. The I/O and timer	2496	of all watchers and stopping them) and call back into the library. The
1512	callbacks will never actually be called (but must be valid nevertheless,	2497	I/O and timer callbacks will never actually be called (but must be valid
1513	because you never know, you know?).	2498	nevertheless, because you never know, you know?).
1514		2499
1515	As another example, the Perl Coro module uses these hooks to integrate	2500	As another example, the Perl Coro module uses these hooks to integrate
1516	coroutines into libev programs, by yielding to other active coroutines	2501	coroutines into libev programs, by yielding to other active coroutines
1517	during each prepare and only letting the process block if no coroutines	2502	during each prepare and only letting the process block if no coroutines
1518	are ready to run (it's actually more complicated: it only runs coroutines	2503	are ready to run (it's actually more complicated: it only runs coroutines
…		…
1521	loop from blocking if lower-priority coroutines are active, thus mapping	2506	loop from blocking if lower-priority coroutines are active, thus mapping
1522	low-priority coroutines to idle/background tasks).	2507	low-priority coroutines to idle/background tasks).
1523		2508
1524	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2509	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1525	priority, to ensure that they are being run before any other watchers	2510	priority, to ensure that they are being run before any other watchers
		2511	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2512
1526	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2513	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1527	too) should not activate ("feed") events into libev. While libev fully	2514	activate ("feed") events into libev. While libev fully supports this, they
1528	supports this, they will be called before other C<ev_check> watchers did	2515	might get executed before other C<ev_check> watchers did their job. As
1529	their job. As C<ev_check> watchers are often used to embed other event	2516	C<ev_check> watchers are often used to embed other (non-libev) event
1530	loops those other event loops might be in an unusable state until their	2517	loops those other event loops might be in an unusable state until their
1531	C<ev_check> watcher ran (always remind yourself to coexist peacefully with	2518	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1532	others).	2519	others).
1533		2520
		2521	=head3 Watcher-Specific Functions and Data Members
		2522
1534	=over 4	2523	=over 4
1535		2524
1536	=item ev_prepare_init (ev_prepare *, callback)	2525	=item ev_prepare_init (ev_prepare *, callback)
1537		2526
1538	=item ev_check_init (ev_check *, callback)	2527	=item ev_check_init (ev_check *, callback)
1539		2528
1540	Initialises and configures the prepare or check watcher - they have no	2529	Initialises and configures the prepare or check watcher - they have no
1541	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2530	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1542	macros, but using them is utterly, utterly and completely pointless.	2531	macros, but using them is utterly, utterly, utterly and completely
		2532	pointless.
1543		2533
1544	=back	2534	=back
		2535
		2536	=head3 Examples
1545		2537
1546	There are a number of principal ways to embed other event loops or modules	2538	There are a number of principal ways to embed other event loops or modules
1547	into libev. Here are some ideas on how to include libadns into libev	2539	into libev. Here are some ideas on how to include libadns into libev
1548	(there is a Perl module named C<EV::ADNS> that does this, which you could	2540	(there is a Perl module named C<EV::ADNS> that does this, which you could
1549	use for an actually working example. Another Perl module named C<EV::Glib>	2541	use as a working example. Another Perl module named C<EV::Glib> embeds a
1550	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV	2542	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1551	into the Glib event loop).	2543	Glib event loop).
1552		2544
1553	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	2545	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1554	and in a check watcher, destroy them and call into libadns. What follows	2546	and in a check watcher, destroy them and call into libadns. What follows
1555	is pseudo-code only of course. This requires you to either use a low	2547	is pseudo-code only of course. This requires you to either use a low
1556	priority for the check watcher or use C<ev_clear_pending> explicitly, as	2548	priority for the check watcher or use C<ev_clear_pending> explicitly, as
1557	the callbacks for the IO/timeout watchers might not have been called yet.	2549	the callbacks for the IO/timeout watchers might not have been called yet.
1558		2550
1559	static ev_io iow [nfd];	2551	static ev_io iow [nfd];
1560	static ev_timer tw;	2552	static ev_timer tw;
1561		2553
1562	static void	2554	static void
1563	io_cb (ev_loop *loop, ev_io *w, int revents)	2555	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1564	{	2556	{
1565	}	2557	}
1566		2558
1567	// create io watchers for each fd and a timer before blocking	2559	// create io watchers for each fd and a timer before blocking
1568	static void	2560	static void
1569	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2561	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1570	{	2562	{
1571	int timeout = 3600000;	2563	int timeout = 3600000;
1572	struct pollfd fds [nfd];	2564	struct pollfd fds [nfd];
1573	// actual code will need to loop here and realloc etc.	2565	// actual code will need to loop here and realloc etc.
1574	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2566	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1575		2567
1576	/* the callback is illegal, but won't be called as we stop during check */	2568	/* the callback is illegal, but won't be called as we stop during check */
1577	ev_timer_init (&tw, 0, timeout * 1e-3);	2569	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1578	ev_timer_start (loop, &tw);	2570	ev_timer_start (loop, &tw);
1579		2571
1580	// create one ev_io per pollfd	2572	// create one ev_io per pollfd
1581	for (int i = 0; i < nfd; ++i)	2573	for (int i = 0; i < nfd; ++i)
1582	{	2574	{
1583	ev_io_init (iow + i, io_cb, fds [i].fd,	2575	ev_io_init (iow + i, io_cb, fds [i].fd,
1584	((fds [i].events & POLLIN ? EV_READ : 0)	2576	((fds [i].events & POLLIN ? EV_READ : 0)
1585	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2577	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1586		2578
1587	fds [i].revents = 0;	2579	fds [i].revents = 0;
1588	ev_io_start (loop, iow + i);	2580	ev_io_start (loop, iow + i);
1589	}	2581	}
1590	}	2582	}
1591		2583
1592	// stop all watchers after blocking	2584	// stop all watchers after blocking
1593	static void	2585	static void
1594	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2586	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1595	{	2587	{
1596	ev_timer_stop (loop, &tw);	2588	ev_timer_stop (loop, &tw);
1597		2589
1598	for (int i = 0; i < nfd; ++i)	2590	for (int i = 0; i < nfd; ++i)
1599	{	2591	{
1600	// set the relevant poll flags	2592	// set the relevant poll flags
1601	// could also call adns_processreadable etc. here	2593	// could also call adns_processreadable etc. here
1602	struct pollfd *fd = fds + i;	2594	struct pollfd *fd = fds + i;
1603	int revents = ev_clear_pending (iow + i);	2595	int revents = ev_clear_pending (iow + i);
1604	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;	2596	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1605	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;	2597	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1606		2598
1607	// now stop the watcher	2599	// now stop the watcher
1608	ev_io_stop (loop, iow + i);	2600	ev_io_stop (loop, iow + i);
1609	}	2601	}
1610		2602
1611	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2603	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1612	}	2604	}
1613		2605
1614	Method 2: This would be just like method 1, but you run C<adns_afterpoll>	2606	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
1615	in the prepare watcher and would dispose of the check watcher.	2607	in the prepare watcher and would dispose of the check watcher.
1616		2608
1617	Method 3: If the module to be embedded supports explicit event	2609	Method 3: If the module to be embedded supports explicit event
1618	notification (adns does), you can also make use of the actual watcher	2610	notification (libadns does), you can also make use of the actual watcher
1619	callbacks, and only destroy/create the watchers in the prepare watcher.	2611	callbacks, and only destroy/create the watchers in the prepare watcher.
1620		2612
1621	static void	2613	static void
1622	timer_cb (EV_P_ ev_timer *w, int revents)	2614	timer_cb (EV_P_ ev_timer *w, int revents)
1623	{	2615	{
1624	adns_state ads = (adns_state)w->data;	2616	adns_state ads = (adns_state)w->data;
1625	update_now (EV_A);	2617	update_now (EV_A);
1626		2618
1627	adns_processtimeouts (ads, &tv_now);	2619	adns_processtimeouts (ads, &tv_now);
1628	}	2620	}
1629		2621
1630	static void	2622	static void
1631	io_cb (EV_P_ ev_io *w, int revents)	2623	io_cb (EV_P_ ev_io *w, int revents)
1632	{	2624	{
1633	adns_state ads = (adns_state)w->data;	2625	adns_state ads = (adns_state)w->data;
1634	update_now (EV_A);	2626	update_now (EV_A);
1635		2627
1636	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);	2628	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
1637	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);	2629	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
1638	}	2630	}
1639		2631
1640	// do not ever call adns_afterpoll	2632	// do not ever call adns_afterpoll
1641		2633
1642	Method 4: Do not use a prepare or check watcher because the module you	2634	Method 4: Do not use a prepare or check watcher because the module you
1643	want to embed is too inflexible to support it. Instead, youc na override	2635	want to embed is not flexible enough to support it. Instead, you can
1644	their poll function. The drawback with this solution is that the main	2636	override their poll function. The drawback with this solution is that the
1645	loop is now no longer controllable by EV. The C<Glib::EV> module does	2637	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
1646	this.	2638	this approach, effectively embedding EV as a client into the horrible
		2639	libglib event loop.
1647		2640
1648	static gint	2641	static gint
1649	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	2642	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1650	{	2643	{
1651	int got_events = 0;	2644	int got_events = 0;
1652		2645
1653	for (n = 0; n < nfds; ++n)	2646	for (n = 0; n < nfds; ++n)
1654	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events	2647	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1655		2648
1656	if (timeout >= 0)	2649	if (timeout >= 0)
1657	// create/start timer	2650	// create/start timer
1658		2651
1659	// poll	2652	// poll
1660	ev_loop (EV_A_ 0);	2653	ev_loop (EV_A_ 0);
1661		2654
1662	// stop timer again	2655	// stop timer again
1663	if (timeout >= 0)	2656	if (timeout >= 0)
1664	ev_timer_stop (EV_A_ &to);	2657	ev_timer_stop (EV_A_ &to);
1665		2658
1666	// stop io watchers again - their callbacks should have set	2659	// stop io watchers again - their callbacks should have set
1667	for (n = 0; n < nfds; ++n)	2660	for (n = 0; n < nfds; ++n)
1668	ev_io_stop (EV_A_ iow [n]);	2661	ev_io_stop (EV_A_ iow [n]);
1669		2662
1670	return got_events;	2663	return got_events;
1671	}	2664	}
1672		2665
1673		2666
1674	=head2 C<ev_embed> - when one backend isn't enough...	2667	=head2 C<ev_embed> - when one backend isn't enough...
1675		2668
1676	This is a rather advanced watcher type that lets you embed one event loop	2669	This is a rather advanced watcher type that lets you embed one event loop
…		…
1682	prioritise I/O.	2675	prioritise I/O.
1683		2676
1684	As an example for a bug workaround, the kqueue backend might only support	2677	As an example for a bug workaround, the kqueue backend might only support
1685	sockets on some platform, so it is unusable as generic backend, but you	2678	sockets on some platform, so it is unusable as generic backend, but you
1686	still want to make use of it because you have many sockets and it scales	2679	still want to make use of it because you have many sockets and it scales
1687	so nicely. In this case, you would create a kqueue-based loop and embed it	2680	so nicely. In this case, you would create a kqueue-based loop and embed
1688	into your default loop (which might use e.g. poll). Overall operation will	2681	it into your default loop (which might use e.g. poll). Overall operation
1689	be a bit slower because first libev has to poll and then call kevent, but	2682	will be a bit slower because first libev has to call C<poll> and then
1690	at least you can use both at what they are best.	2683	C<kevent>, but at least you can use both mechanisms for what they are
		2684	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1691		2685
1692	As for prioritising I/O: rarely you have the case where some fds have	2686	As for prioritising I/O: under rare circumstances you have the case where
1693	to be watched and handled very quickly (with low latency), and even	2687	some fds have to be watched and handled very quickly (with low latency),
1694	priorities and idle watchers might have too much overhead. In this case	2688	and even priorities and idle watchers might have too much overhead. In
1695	you would put all the high priority stuff in one loop and all the rest in	2689	this case you would put all the high priority stuff in one loop and all
1696	a second one, and embed the second one in the first.	2690	the rest in a second one, and embed the second one in the first.
1697		2691
1698	As long as the watcher is active, the callback will be invoked every time	2692	As long as the watcher is active, the callback will be invoked every
1699	there might be events pending in the embedded loop. The callback must then	2693	time there might be events pending in the embedded loop. The callback
1700	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2694	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1701	their callbacks (you could also start an idle watcher to give the embedded	2695	sweep and invoke their callbacks (the callback doesn't need to invoke the
1702	loop strictly lower priority for example). You can also set the callback	2696	C<ev_embed_sweep> function directly, it could also start an idle watcher
1703	to C<0>, in which case the embed watcher will automatically execute the	2697	to give the embedded loop strictly lower priority for example).
1704	embedded loop sweep.
1705		2698
1706	As long as the watcher is started it will automatically handle events. The	2699	You can also set the callback to C<0>, in which case the embed watcher
1707	callback will be invoked whenever some events have been handled. You can	2700	will automatically execute the embedded loop sweep whenever necessary.
1708	set the callback to C<0> to avoid having to specify one if you are not
1709	interested in that.
1710		2701
1711	Also, there have not currently been made special provisions for forking:	2702	Fork detection will be handled transparently while the C<ev_embed> watcher
1712	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2703	is active, i.e., the embedded loop will automatically be forked when the
1713	but you will also have to stop and restart any C<ev_embed> watchers	2704	embedding loop forks. In other cases, the user is responsible for calling
1714	yourself.	2705	C<ev_loop_fork> on the embedded loop.
1715		2706
1716	Unfortunately, not all backends are embeddable, only the ones returned by	2707	Unfortunately, not all backends are embeddable: only the ones returned by
1717	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2708	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1718	portable one.	2709	portable one.
1719		2710
1720	So when you want to use this feature you will always have to be prepared	2711	So when you want to use this feature you will always have to be prepared
1721	that you cannot get an embeddable loop. The recommended way to get around	2712	that you cannot get an embeddable loop. The recommended way to get around
1722	this is to have a separate variables for your embeddable loop, try to	2713	this is to have a separate variables for your embeddable loop, try to
1723	create it, and if that fails, use the normal loop for everything:	2714	create it, and if that fails, use the normal loop for everything.
1724		2715
1725	struct ev_loop *loop_hi = ev_default_init (0);	2716	=head3 C<ev_embed> and fork
1726	struct ev_loop *loop_lo = 0;
1727	struct ev_embed embed;
1728
1729	// see if there is a chance of getting one that works
1730	// (remember that a flags value of 0 means autodetection)
1731	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1732	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1733	: 0;
1734		2717
1735	// if we got one, then embed it, otherwise default to loop_hi	2718	While the C<ev_embed> watcher is running, forks in the embedding loop will
1736	if (loop_lo)	2719	automatically be applied to the embedded loop as well, so no special
1737	{	2720	fork handling is required in that case. When the watcher is not running,
1738	ev_embed_init (&embed, 0, loop_lo);	2721	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1739	ev_embed_start (loop_hi, &embed);	2722	as applicable.
1740	}	2723
1741	else	2724	=head3 Watcher-Specific Functions and Data Members
1742	loop_lo = loop_hi;
1743		2725
1744	=over 4	2726	=over 4
1745		2727
1746	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	2728	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
1747		2729
…		…
1749		2731
1750	Configures the watcher to embed the given loop, which must be	2732	Configures the watcher to embed the given loop, which must be
1751	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	2733	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1752	invoked automatically, otherwise it is the responsibility of the callback	2734	invoked automatically, otherwise it is the responsibility of the callback
1753	to invoke it (it will continue to be called until the sweep has been done,	2735	to invoke it (it will continue to be called until the sweep has been done,
1754	if you do not want thta, you need to temporarily stop the embed watcher).	2736	if you do not want that, you need to temporarily stop the embed watcher).
1755		2737
1756	=item ev_embed_sweep (loop, ev_embed *)	2738	=item ev_embed_sweep (loop, ev_embed *)
1757		2739
1758	Make a single, non-blocking sweep over the embedded loop. This works	2740	Make a single, non-blocking sweep over the embedded loop. This works
1759	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	2741	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
1760	apropriate way for embedded loops.	2742	appropriate way for embedded loops.
1761		2743
1762	=item struct ev_loop *loop [read-only]	2744	=item struct ev_loop *other [read-only]
1763		2745
1764	The embedded event loop.	2746	The embedded event loop.
1765		2747
1766	=back	2748	=back
		2749
		2750	=head3 Examples
		2751
		2752	Example: Try to get an embeddable event loop and embed it into the default
		2753	event loop. If that is not possible, use the default loop. The default
		2754	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2755	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2756	used).
		2757
		2758	struct ev_loop *loop_hi = ev_default_init (0);
		2759	struct ev_loop *loop_lo = 0;
		2760	ev_embed embed;
		2761
		2762	// see if there is a chance of getting one that works
		2763	// (remember that a flags value of 0 means autodetection)
		2764	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2765	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2766	: 0;
		2767
		2768	// if we got one, then embed it, otherwise default to loop_hi
		2769	if (loop_lo)
		2770	{
		2771	ev_embed_init (&embed, 0, loop_lo);
		2772	ev_embed_start (loop_hi, &embed);
		2773	}
		2774	else
		2775	loop_lo = loop_hi;
		2776
		2777	Example: Check if kqueue is available but not recommended and create
		2778	a kqueue backend for use with sockets (which usually work with any
		2779	kqueue implementation). Store the kqueue/socket-only event loop in
		2780	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2781
		2782	struct ev_loop *loop = ev_default_init (0);
		2783	struct ev_loop *loop_socket = 0;
		2784	ev_embed embed;
		2785
		2786	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2787	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2788	{
		2789	ev_embed_init (&embed, 0, loop_socket);
		2790	ev_embed_start (loop, &embed);
		2791	}
		2792
		2793	if (!loop_socket)
		2794	loop_socket = loop;
		2795
		2796	// now use loop_socket for all sockets, and loop for everything else
1767		2797
1768		2798
1769	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	2799	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
1770		2800
1771	Fork watchers are called when a C<fork ()> was detected (usually because	2801	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
1774	event loop blocks next and before C<ev_check> watchers are being called,	2804	event loop blocks next and before C<ev_check> watchers are being called,
1775	and only in the child after the fork. If whoever good citizen calling	2805	and only in the child after the fork. If whoever good citizen calling
1776	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2806	C<ev_default_fork> cheats and calls it in the wrong process, the fork
1777	handlers will be invoked, too, of course.	2807	handlers will be invoked, too, of course.
1778		2808
		2809	=head3 The special problem of life after fork - how is it possible?
		2810
		2811	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2812	up/change the process environment, followed by a call to C<exec()>. This
		2813	sequence should be handled by libev without any problems.
		2814
		2815	This changes when the application actually wants to do event handling
		2816	in the child, or both parent in child, in effect "continuing" after the
		2817	fork.
		2818
		2819	The default mode of operation (for libev, with application help to detect
		2820	forks) is to duplicate all the state in the child, as would be expected
		2821	when I<either> the parent I<or> the child process continues.
		2822
		2823	When both processes want to continue using libev, then this is usually the
		2824	wrong result. In that case, usually one process (typically the parent) is
		2825	supposed to continue with all watchers in place as before, while the other
		2826	process typically wants to start fresh, i.e. without any active watchers.
		2827
		2828	The cleanest and most efficient way to achieve that with libev is to
		2829	simply create a new event loop, which of course will be "empty", and
		2830	use that for new watchers. This has the advantage of not touching more
		2831	memory than necessary, and thus avoiding the copy-on-write, and the
		2832	disadvantage of having to use multiple event loops (which do not support
		2833	signal watchers).
		2834
		2835	When this is not possible, or you want to use the default loop for
		2836	other reasons, then in the process that wants to start "fresh", call
		2837	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2838	the default loop will "orphan" (not stop) all registered watchers, so you
		2839	have to be careful not to execute code that modifies those watchers. Note
		2840	also that in that case, you have to re-register any signal watchers.
		2841
		2842	=head3 Watcher-Specific Functions and Data Members
		2843
1779	=over 4	2844	=over 4
1780		2845
1781	=item ev_fork_init (ev_signal *, callback)	2846	=item ev_fork_init (ev_signal *, callback)
1782		2847
1783	Initialises and configures the fork watcher - it has no parameters of any	2848	Initialises and configures the fork watcher - it has no parameters of any
…		…
1785	believe me.	2850	believe me.
1786		2851
1787	=back	2852	=back
1788		2853
1789		2854
		2855	=head2 C<ev_async> - how to wake up another event loop
		2856
		2857	In general, you cannot use an C<ev_loop> from multiple threads or other
		2858	asynchronous sources such as signal handlers (as opposed to multiple event
		2859	loops - those are of course safe to use in different threads).
		2860
		2861	Sometimes, however, you need to wake up another event loop you do not
		2862	control, for example because it belongs to another thread. This is what
		2863	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2864	can signal it by calling C<ev_async_send>, which is thread- and signal
		2865	safe.
		2866
		2867	This functionality is very similar to C<ev_signal> watchers, as signals,
		2868	too, are asynchronous in nature, and signals, too, will be compressed
		2869	(i.e. the number of callback invocations may be less than the number of
		2870	C<ev_async_sent> calls).
		2871
		2872	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2873	just the default loop.
		2874
		2875	=head3 Queueing
		2876
		2877	C<ev_async> does not support queueing of data in any way. The reason
		2878	is that the author does not know of a simple (or any) algorithm for a
		2879	multiple-writer-single-reader queue that works in all cases and doesn't
		2880	need elaborate support such as pthreads.
		2881
		2882	That means that if you want to queue data, you have to provide your own
		2883	queue. But at least I can tell you how to implement locking around your
		2884	queue:
		2885
		2886	=over 4
		2887
		2888	=item queueing from a signal handler context
		2889
		2890	To implement race-free queueing, you simply add to the queue in the signal
		2891	handler but you block the signal handler in the watcher callback. Here is
		2892	an example that does that for some fictitious SIGUSR1 handler:
		2893
		2894	static ev_async mysig;
		2895
		2896	static void
		2897	sigusr1_handler (void)
		2898	{
		2899	sometype data;
		2900
		2901	// no locking etc.
		2902	queue_put (data);
		2903	ev_async_send (EV_DEFAULT_ &mysig);
		2904	}
		2905
		2906	static void
		2907	mysig_cb (EV_P_ ev_async *w, int revents)
		2908	{
		2909	sometype data;
		2910	sigset_t block, prev;
		2911
		2912	sigemptyset (&block);
		2913	sigaddset (&block, SIGUSR1);
		2914	sigprocmask (SIG_BLOCK, &block, &prev);
		2915
		2916	while (queue_get (&data))
		2917	process (data);
		2918
		2919	if (sigismember (&prev, SIGUSR1)
		2920	sigprocmask (SIG_UNBLOCK, &block, 0);
		2921	}
		2922
		2923	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2924	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2925	either...).
		2926
		2927	=item queueing from a thread context
		2928
		2929	The strategy for threads is different, as you cannot (easily) block
		2930	threads but you can easily preempt them, so to queue safely you need to
		2931	employ a traditional mutex lock, such as in this pthread example:
		2932
		2933	static ev_async mysig;
		2934	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2935
		2936	static void
		2937	otherthread (void)
		2938	{
		2939	// only need to lock the actual queueing operation
		2940	pthread_mutex_lock (&mymutex);
		2941	queue_put (data);
		2942	pthread_mutex_unlock (&mymutex);
		2943
		2944	ev_async_send (EV_DEFAULT_ &mysig);
		2945	}
		2946
		2947	static void
		2948	mysig_cb (EV_P_ ev_async *w, int revents)
		2949	{
		2950	pthread_mutex_lock (&mymutex);
		2951
		2952	while (queue_get (&data))
		2953	process (data);
		2954
		2955	pthread_mutex_unlock (&mymutex);
		2956	}
		2957
		2958	=back
		2959
		2960
		2961	=head3 Watcher-Specific Functions and Data Members
		2962
		2963	=over 4
		2964
		2965	=item ev_async_init (ev_async *, callback)
		2966
		2967	Initialises and configures the async watcher - it has no parameters of any
		2968	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		2969	trust me.
		2970
		2971	=item ev_async_send (loop, ev_async *)
		2972
		2973	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2974	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2975	C<ev_feed_event>, this call is safe to do from other threads, signal or
		2976	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		2977	section below on what exactly this means).
		2978
		2979	Note that, as with other watchers in libev, multiple events might get
		2980	compressed into a single callback invocation (another way to look at this
		2981	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		2982	reset when the event loop detects that).
		2983
		2984	This call incurs the overhead of a system call only once per event loop
		2985	iteration, so while the overhead might be noticeable, it doesn't apply to
		2986	repeated calls to C<ev_async_send> for the same event loop.
		2987
		2988	=item bool = ev_async_pending (ev_async *)
		2989
		2990	Returns a non-zero value when C<ev_async_send> has been called on the
		2991	watcher but the event has not yet been processed (or even noted) by the
		2992	event loop.
		2993
		2994	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2995	the loop iterates next and checks for the watcher to have become active,
		2996	it will reset the flag again. C<ev_async_pending> can be used to very
		2997	quickly check whether invoking the loop might be a good idea.
		2998
		2999	Not that this does I<not> check whether the watcher itself is pending,
		3000	only whether it has been requested to make this watcher pending: there
		3001	is a time window between the event loop checking and resetting the async
		3002	notification, and the callback being invoked.
		3003
		3004	=back
		3005
		3006
1790	=head1 OTHER FUNCTIONS	3007	=head1 OTHER FUNCTIONS
1791		3008
1792	There are some other functions of possible interest. Described. Here. Now.	3009	There are some other functions of possible interest. Described. Here. Now.
1793		3010
1794	=over 4	3011	=over 4
1795		3012
1796	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3013	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1797		3014
1798	This function combines a simple timer and an I/O watcher, calls your	3015	This function combines a simple timer and an I/O watcher, calls your
1799	callback on whichever event happens first and automatically stop both	3016	callback on whichever event happens first and automatically stops both
1800	watchers. This is useful if you want to wait for a single event on an fd	3017	watchers. This is useful if you want to wait for a single event on an fd
1801	or timeout without having to allocate/configure/start/stop/free one or	3018	or timeout without having to allocate/configure/start/stop/free one or
1802	more watchers yourself.	3019	more watchers yourself.
1803		3020
1804	If C<fd> is less than 0, then no I/O watcher will be started and events	3021	If C<fd> is less than 0, then no I/O watcher will be started and the
1805	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3022	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1806	C<events> set will be craeted and started.	3023	the given C<fd> and C<events> set will be created and started.
1807		3024
1808	If C<timeout> is less than 0, then no timeout watcher will be	3025	If C<timeout> is less than 0, then no timeout watcher will be
1809	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3026	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1810	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3027	repeat = 0) will be started. C<0> is a valid timeout.
1811	dubious value.
1812		3028
1813	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3029	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
1814	passed an C<revents> set like normal event callbacks (a combination of	3030	passed an C<revents> set like normal event callbacks (a combination of
1815	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3031	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
1816	value passed to C<ev_once>:	3032	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3033	a timeout and an io event at the same time - you probably should give io
		3034	events precedence.
1817		3035
		3036	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3037
1818	static void stdin_ready (int revents, void *arg)	3038	static void stdin_ready (int revents, void *arg)
1819	{	3039	{
1820	if (revents & EV_TIMEOUT)
1821	/* doh, nothing entered */;
1822	else if (revents & EV_READ)	3040	if (revents & EV_READ)
1823	/* stdin might have data for us, joy! */;	3041	/* stdin might have data for us, joy! */;
		3042	else if (revents & EV_TIMEOUT)
		3043	/* doh, nothing entered */;
1824	}	3044	}
1825		3045
1826	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3046	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1827		3047
1828	=item ev_feed_event (ev_loop *, watcher *, int revents)	3048	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
1829		3049
1830	Feeds the given event set into the event loop, as if the specified event	3050	Feeds the given event set into the event loop, as if the specified event
1831	had happened for the specified watcher (which must be a pointer to an	3051	had happened for the specified watcher (which must be a pointer to an
1832	initialised but not necessarily started event watcher).	3052	initialised but not necessarily started event watcher).
1833		3053
1834	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3054	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
1835		3055
1836	Feed an event on the given fd, as if a file descriptor backend detected	3056	Feed an event on the given fd, as if a file descriptor backend detected
1837	the given events it.	3057	the given events it.
1838		3058
1839	=item ev_feed_signal_event (ev_loop *loop, int signum)	3059	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
1840		3060
1841	Feed an event as if the given signal occured (C<loop> must be the default	3061	Feed an event as if the given signal occurred (C<loop> must be the default
1842	loop!).	3062	loop!).
1843		3063
1844	=back	3064	=back
1845		3065
1846		3066
…		…
1862		3082
1863	=item * Priorities are not currently supported. Initialising priorities	3083	=item * Priorities are not currently supported. Initialising priorities
1864	will fail and all watchers will have the same priority, even though there	3084	will fail and all watchers will have the same priority, even though there
1865	is an ev_pri field.	3085	is an ev_pri field.
1866		3086
		3087	=item * In libevent, the last base created gets the signals, in libev, the
		3088	first base created (== the default loop) gets the signals.
		3089
1867	=item * Other members are not supported.	3090	=item * Other members are not supported.
1868		3091
1869	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3092	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1870	to use the libev header file and library.	3093	to use the libev header file and library.
1871		3094
1872	=back	3095	=back
1873		3096
1874	=head1 C++ SUPPORT	3097	=head1 C++ SUPPORT
1875		3098
1876	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3099	Libev comes with some simplistic wrapper classes for C++ that mainly allow
1877	you to use some convinience methods to start/stop watchers and also change	3100	you to use some convenience methods to start/stop watchers and also change
1878	the callback model to a model using method callbacks on objects.	3101	the callback model to a model using method callbacks on objects.
1879		3102
1880	To use it,	3103	To use it,
1881		3104
1882	#include <ev++.h>	3105	#include <ev++.h>
1883		3106
1884	This automatically includes F<ev.h> and puts all of its definitions (many	3107	This automatically includes F<ev.h> and puts all of its definitions (many
1885	of them macros) into the global namespace. All C++ specific things are	3108	of them macros) into the global namespace. All C++ specific things are
1886	put into the C<ev> namespace. It should support all the same embedding	3109	put into the C<ev> namespace. It should support all the same embedding
1887	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	3110	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
1954	your compiler is good :), then the method will be fully inlined into the	3177	your compiler is good :), then the method will be fully inlined into the
1955	thunking function, making it as fast as a direct C callback.	3178	thunking function, making it as fast as a direct C callback.
1956		3179
1957	Example: simple class declaration and watcher initialisation	3180	Example: simple class declaration and watcher initialisation
1958		3181
1959	struct myclass	3182	struct myclass
1960	{	3183	{
1961	void io_cb (ev::io &w, int revents) { }	3184	void io_cb (ev::io &w, int revents) { }
1962	}	3185	}
1963		3186
1964	myclass obj;	3187	myclass obj;
1965	ev::io iow;	3188	ev::io iow;
1966	iow.set <myclass, &myclass::io_cb> (&obj);	3189	iow.set <myclass, &myclass::io_cb> (&obj);
		3190
		3191	=item w->set (object *)
		3192
		3193	This is an B<experimental> feature that might go away in a future version.
		3194
		3195	This is a variation of a method callback - leaving out the method to call
		3196	will default the method to C<operator ()>, which makes it possible to use
		3197	functor objects without having to manually specify the C<operator ()> all
		3198	the time. Incidentally, you can then also leave out the template argument
		3199	list.
		3200
		3201	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3202	int revents)>.
		3203
		3204	See the method-C<set> above for more details.
		3205
		3206	Example: use a functor object as callback.
		3207
		3208	struct myfunctor
		3209	{
		3210	void operator() (ev::io &w, int revents)
		3211	{
		3212	...
		3213	}
		3214	}
		3215
		3216	myfunctor f;
		3217
		3218	ev::io w;
		3219	w.set (&f);
1967		3220
1968	=item w->set<function> (void *data = 0)	3221	=item w->set<function> (void *data = 0)
1969		3222
1970	Also sets a callback, but uses a static method or plain function as	3223	Also sets a callback, but uses a static method or plain function as
1971	callback. The optional C<data> argument will be stored in the watcher's	3224	callback. The optional C<data> argument will be stored in the watcher's
…		…
1973		3226
1974	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	3227	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
1975		3228
1976	See the method-C<set> above for more details.	3229	See the method-C<set> above for more details.
1977		3230
1978	Example:	3231	Example: Use a plain function as callback.
1979		3232
1980	static void io_cb (ev::io &w, int revents) { }	3233	static void io_cb (ev::io &w, int revents) { }
1981	iow.set <io_cb> ();	3234	iow.set <io_cb> ();
1982		3235
1983	=item w->set (struct ev_loop *)	3236	=item w->set (struct ev_loop *)
1984		3237
1985	Associates a different C<struct ev_loop> with this watcher. You can only	3238	Associates a different C<struct ev_loop> with this watcher. You can only
1986	do this when the watcher is inactive (and not pending either).	3239	do this when the watcher is inactive (and not pending either).
1987		3240
1988	=item w->set ([args])	3241	=item w->set ([arguments])
1989		3242
1990	Basically the same as C<ev_TYPE_set>, with the same args. Must be	3243	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
1991	called at least once. Unlike the C counterpart, an active watcher gets	3244	called at least once. Unlike the C counterpart, an active watcher gets
1992	automatically stopped and restarted when reconfiguring it with this	3245	automatically stopped and restarted when reconfiguring it with this
1993	method.	3246	method.
1994		3247
1995	=item w->start ()	3248	=item w->start ()
…		…
1999		3252
2000	=item w->stop ()	3253	=item w->stop ()
2001		3254
2002	Stops the watcher if it is active. Again, no C<loop> argument.	3255	Stops the watcher if it is active. Again, no C<loop> argument.
2003		3256
2004	=item w->again () C<ev::timer>, C<ev::periodic> only	3257	=item w->again () (C<ev::timer>, C<ev::periodic> only)
2005		3258
2006	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding	3259	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
2007	C<ev_TYPE_again> function.	3260	C<ev_TYPE_again> function.
2008		3261
2009	=item w->sweep () C<ev::embed> only	3262	=item w->sweep () (C<ev::embed> only)
2010		3263
2011	Invokes C<ev_embed_sweep>.	3264	Invokes C<ev_embed_sweep>.
2012		3265
2013	=item w->update () C<ev::stat> only	3266	=item w->update () (C<ev::stat> only)
2014		3267
2015	Invokes C<ev_stat_stat>.	3268	Invokes C<ev_stat_stat>.
2016		3269
2017	=back	3270	=back
2018		3271
2019	=back	3272	=back
2020		3273
2021	Example: Define a class with an IO and idle watcher, start one of them in	3274	Example: Define a class with an IO and idle watcher, start one of them in
2022	the constructor.	3275	the constructor.
2023		3276
2024	class myclass	3277	class myclass
2025	{	3278	{
2026	ev_io io; void io_cb (ev::io &w, int revents);	3279	ev::io io ; void io_cb (ev::io &w, int revents);
2027	ev_idle idle void idle_cb (ev::idle &w, int revents);	3280	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2028		3281
2029	myclass ();	3282	myclass (int fd)
2030	}	3283	{
2031
2032	myclass::myclass (int fd)
2033	{
2034	io .set <myclass, &myclass::io_cb > (this);	3284	io .set <myclass, &myclass::io_cb > (this);
2035	idle.set <myclass, &myclass::idle_cb> (this);	3285	idle.set <myclass, &myclass::idle_cb> (this);
2036		3286
2037	io.start (fd, ev::READ);	3287	io.start (fd, ev::READ);
		3288	}
2038	}	3289	};
		3290
		3291
		3292	=head1 OTHER LANGUAGE BINDINGS
		3293
		3294	Libev does not offer other language bindings itself, but bindings for a
		3295	number of languages exist in the form of third-party packages. If you know
		3296	any interesting language binding in addition to the ones listed here, drop
		3297	me a note.
		3298
		3299	=over 4
		3300
		3301	=item Perl
		3302
		3303	The EV module implements the full libev API and is actually used to test
		3304	libev. EV is developed together with libev. Apart from the EV core module,
		3305	there are additional modules that implement libev-compatible interfaces
		3306	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3307	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3308	and C<EV::Glib>).
		3309
		3310	It can be found and installed via CPAN, its homepage is at
		3311	L<http://software.schmorp.de/pkg/EV>.
		3312
		3313	=item Python
		3314
		3315	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3316	seems to be quite complete and well-documented.
		3317
		3318	=item Ruby
		3319
		3320	Tony Arcieri has written a ruby extension that offers access to a subset
		3321	of the libev API and adds file handle abstractions, asynchronous DNS and
		3322	more on top of it. It can be found via gem servers. Its homepage is at
		3323	L<http://rev.rubyforge.org/>.
		3324
		3325	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3326	makes rev work even on mingw.
		3327
		3328	=item Haskell
		3329
		3330	A haskell binding to libev is available at
		3331	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3332
		3333	=item D
		3334
		3335	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3336	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3337
		3338	=item Ocaml
		3339
		3340	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3341	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3342
		3343	=back
2039		3344
2040		3345
2041	=head1 MACRO MAGIC	3346	=head1 MACRO MAGIC
2042		3347
2043	Libev can be compiled with a variety of options, the most fundemantal is	3348	Libev can be compiled with a variety of options, the most fundamental
2044	C<EV_MULTIPLICITY>. This option determines whether (most) functions and	3349	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2045	callbacks have an initial C<struct ev_loop *> argument.	3350	functions and callbacks have an initial C<struct ev_loop *> argument.
2046		3351
2047	To make it easier to write programs that cope with either variant, the	3352	To make it easier to write programs that cope with either variant, the
2048	following macros are defined:	3353	following macros are defined:
2049		3354
2050	=over 4	3355	=over 4
…		…
2053		3358
2054	This provides the loop I<argument> for functions, if one is required ("ev	3359	This provides the loop I<argument> for functions, if one is required ("ev
2055	loop argument"). The C<EV_A> form is used when this is the sole argument,	3360	loop argument"). The C<EV_A> form is used when this is the sole argument,
2056	C<EV_A_> is used when other arguments are following. Example:	3361	C<EV_A_> is used when other arguments are following. Example:
2057		3362
2058	ev_unref (EV_A);	3363	ev_unref (EV_A);
2059	ev_timer_add (EV_A_ watcher);	3364	ev_timer_add (EV_A_ watcher);
2060	ev_loop (EV_A_ 0);	3365	ev_loop (EV_A_ 0);
2061		3366
2062	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	3367	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2063	which is often provided by the following macro.	3368	which is often provided by the following macro.
2064		3369
2065	=item C<EV_P>, C<EV_P_>	3370	=item C<EV_P>, C<EV_P_>
2066		3371
2067	This provides the loop I<parameter> for functions, if one is required ("ev	3372	This provides the loop I<parameter> for functions, if one is required ("ev
2068	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	3373	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
2069	C<EV_P_> is used when other parameters are following. Example:	3374	C<EV_P_> is used when other parameters are following. Example:
2070		3375
2071	// this is how ev_unref is being declared	3376	// this is how ev_unref is being declared
2072	static void ev_unref (EV_P);	3377	static void ev_unref (EV_P);
2073		3378
2074	// this is how you can declare your typical callback	3379	// this is how you can declare your typical callback
2075	static void cb (EV_P_ ev_timer *w, int revents)	3380	static void cb (EV_P_ ev_timer *w, int revents)
2076		3381
2077	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	3382	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
2078	suitable for use with C<EV_A>.	3383	suitable for use with C<EV_A>.
2079		3384
2080	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3385	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2081		3386
2082	Similar to the other two macros, this gives you the value of the default	3387	Similar to the other two macros, this gives you the value of the default
2083	loop, if multiple loops are supported ("ev loop default").	3388	loop, if multiple loops are supported ("ev loop default").
		3389
		3390	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3391
		3392	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3393	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3394	is undefined when the default loop has not been initialised by a previous
		3395	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3396
		3397	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3398	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
2084		3399
2085	=back	3400	=back
2086		3401
2087	Example: Declare and initialise a check watcher, utilising the above	3402	Example: Declare and initialise a check watcher, utilising the above
2088	macros so it will work regardless of whether multiple loops are supported	3403	macros so it will work regardless of whether multiple loops are supported
2089	or not.	3404	or not.
2090		3405
2091	static void	3406	static void
2092	check_cb (EV_P_ ev_timer *w, int revents)	3407	check_cb (EV_P_ ev_timer *w, int revents)
2093	{	3408	{
2094	ev_check_stop (EV_A_ w);	3409	ev_check_stop (EV_A_ w);
2095	}	3410	}
2096		3411
2097	ev_check check;	3412	ev_check check;
2098	ev_check_init (&check, check_cb);	3413	ev_check_init (&check, check_cb);
2099	ev_check_start (EV_DEFAULT_ &check);	3414	ev_check_start (EV_DEFAULT_ &check);
2100	ev_loop (EV_DEFAULT_ 0);	3415	ev_loop (EV_DEFAULT_ 0);
2101		3416
2102	=head1 EMBEDDING	3417	=head1 EMBEDDING
2103		3418
2104	Libev can (and often is) directly embedded into host	3419	Libev can (and often is) directly embedded into host
2105	applications. Examples of applications that embed it include the Deliantra	3420	applications. Examples of applications that embed it include the Deliantra
2106	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)	3421	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
2107	and rxvt-unicode.	3422	and rxvt-unicode.
2108		3423
2109	The goal is to enable you to just copy the neecssary files into your	3424	The goal is to enable you to just copy the necessary files into your
2110	source directory without having to change even a single line in them, so	3425	source directory without having to change even a single line in them, so
2111	you can easily upgrade by simply copying (or having a checked-out copy of	3426	you can easily upgrade by simply copying (or having a checked-out copy of
2112	libev somewhere in your source tree).	3427	libev somewhere in your source tree).
2113		3428
2114	=head2 FILESETS	3429	=head2 FILESETS
2115		3430
2116	Depending on what features you need you need to include one or more sets of files	3431	Depending on what features you need you need to include one or more sets of files
2117	in your app.	3432	in your application.
2118		3433
2119	=head3 CORE EVENT LOOP	3434	=head3 CORE EVENT LOOP
2120		3435
2121	To include only the libev core (all the C<ev_*> functions), with manual	3436	To include only the libev core (all the C<ev_*> functions), with manual
2122	configuration (no autoconf):	3437	configuration (no autoconf):
2123		3438
2124	#define EV_STANDALONE 1	3439	#define EV_STANDALONE 1
2125	#include "ev.c"	3440	#include "ev.c"
2126		3441
2127	This will automatically include F<ev.h>, too, and should be done in a	3442	This will automatically include F<ev.h>, too, and should be done in a
2128	single C source file only to provide the function implementations. To use	3443	single C source file only to provide the function implementations. To use
2129	it, do the same for F<ev.h> in all files wishing to use this API (best	3444	it, do the same for F<ev.h> in all files wishing to use this API (best
2130	done by writing a wrapper around F<ev.h> that you can include instead and	3445	done by writing a wrapper around F<ev.h> that you can include instead and
2131	where you can put other configuration options):	3446	where you can put other configuration options):
2132		3447
2133	#define EV_STANDALONE 1	3448	#define EV_STANDALONE 1
2134	#include "ev.h"	3449	#include "ev.h"
2135		3450
2136	Both header files and implementation files can be compiled with a C++	3451	Both header files and implementation files can be compiled with a C++
2137	compiler (at least, thats a stated goal, and breakage will be treated	3452	compiler (at least, that's a stated goal, and breakage will be treated
2138	as a bug).	3453	as a bug).
2139		3454
2140	You need the following files in your source tree, or in a directory	3455	You need the following files in your source tree, or in a directory
2141	in your include path (e.g. in libev/ when using -Ilibev):	3456	in your include path (e.g. in libev/ when using -Ilibev):
2142		3457
2143	ev.h	3458	ev.h
2144	ev.c	3459	ev.c
2145	ev_vars.h	3460	ev_vars.h
2146	ev_wrap.h	3461	ev_wrap.h
2147		3462
2148	ev_win32.c required on win32 platforms only	3463	ev_win32.c required on win32 platforms only
2149		3464
2150	ev_select.c only when select backend is enabled (which is enabled by default)	3465	ev_select.c only when select backend is enabled (which is enabled by default)
2151	ev_poll.c only when poll backend is enabled (disabled by default)	3466	ev_poll.c only when poll backend is enabled (disabled by default)
2152	ev_epoll.c only when the epoll backend is enabled (disabled by default)	3467	ev_epoll.c only when the epoll backend is enabled (disabled by default)
2153	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	3468	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2154	ev_port.c only when the solaris port backend is enabled (disabled by default)	3469	ev_port.c only when the solaris port backend is enabled (disabled by default)
2155		3470
2156	F<ev.c> includes the backend files directly when enabled, so you only need	3471	F<ev.c> includes the backend files directly when enabled, so you only need
2157	to compile this single file.	3472	to compile this single file.
2158		3473
2159	=head3 LIBEVENT COMPATIBILITY API	3474	=head3 LIBEVENT COMPATIBILITY API
2160		3475
2161	To include the libevent compatibility API, also include:	3476	To include the libevent compatibility API, also include:
2162		3477
2163	#include "event.c"	3478	#include "event.c"
2164		3479
2165	in the file including F<ev.c>, and:	3480	in the file including F<ev.c>, and:
2166		3481
2167	#include "event.h"	3482	#include "event.h"
2168		3483
2169	in the files that want to use the libevent API. This also includes F<ev.h>.	3484	in the files that want to use the libevent API. This also includes F<ev.h>.
2170		3485
2171	You need the following additional files for this:	3486	You need the following additional files for this:
2172		3487
2173	event.h	3488	event.h
2174	event.c	3489	event.c
2175		3490
2176	=head3 AUTOCONF SUPPORT	3491	=head3 AUTOCONF SUPPORT
2177		3492
2178	Instead of using C<EV_STANDALONE=1> and providing your config in	3493	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2179	whatever way you want, you can also C<m4_include([libev.m4])> in your	3494	whatever way you want, you can also C<m4_include([libev.m4])> in your
2180	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	3495	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2181	include F<config.h> and configure itself accordingly.	3496	include F<config.h> and configure itself accordingly.
2182		3497
2183	For this of course you need the m4 file:	3498	For this of course you need the m4 file:
2184		3499
2185	libev.m4	3500	libev.m4
2186		3501
2187	=head2 PREPROCESSOR SYMBOLS/MACROS	3502	=head2 PREPROCESSOR SYMBOLS/MACROS
2188		3503
2189	Libev can be configured via a variety of preprocessor symbols you have to define	3504	Libev can be configured via a variety of preprocessor symbols you have to
2190	before including any of its files. The default is not to build for multiplicity	3505	define before including any of its files. The default in the absence of
2191	and only include the select backend.	3506	autoconf is documented for every option.
2192		3507
2193	=over 4	3508	=over 4
2194		3509
2195	=item EV_STANDALONE	3510	=item EV_STANDALONE
2196		3511
…		…
2198	keeps libev from including F<config.h>, and it also defines dummy	3513	keeps libev from including F<config.h>, and it also defines dummy
2199	implementations for some libevent functions (such as logging, which is not	3514	implementations for some libevent functions (such as logging, which is not
2200	supported). It will also not define any of the structs usually found in	3515	supported). It will also not define any of the structs usually found in
2201	F<event.h> that are not directly supported by the libev core alone.	3516	F<event.h> that are not directly supported by the libev core alone.
2202		3517
		3518	In stanbdalone mode, libev will still try to automatically deduce the
		3519	configuration, but has to be more conservative.
		3520
2203	=item EV_USE_MONOTONIC	3521	=item EV_USE_MONOTONIC
2204		3522
2205	If defined to be C<1>, libev will try to detect the availability of the	3523	If defined to be C<1>, libev will try to detect the availability of the
2206	monotonic clock option at both compiletime and runtime. Otherwise no use	3524	monotonic clock option at both compile time and runtime. Otherwise no
2207	of the monotonic clock option will be attempted. If you enable this, you	3525	use of the monotonic clock option will be attempted. If you enable this,
2208	usually have to link against librt or something similar. Enabling it when	3526	you usually have to link against librt or something similar. Enabling it
2209	the functionality isn't available is safe, though, althoguh you have	3527	when the functionality isn't available is safe, though, although you have
2210	to make sure you link against any libraries where the C<clock_gettime>	3528	to make sure you link against any libraries where the C<clock_gettime>
2211	function is hiding in (often F<-lrt>).	3529	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2212		3530
2213	=item EV_USE_REALTIME	3531	=item EV_USE_REALTIME
2214		3532
2215	If defined to be C<1>, libev will try to detect the availability of the	3533	If defined to be C<1>, libev will try to detect the availability of the
2216	realtime clock option at compiletime (and assume its availability at	3534	real-time clock option at compile time (and assume its availability
2217	runtime if successful). Otherwise no use of the realtime clock option will	3535	at runtime if successful). Otherwise no use of the real-time clock
2218	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3536	option will be attempted. This effectively replaces C<gettimeofday>
2219	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See tzhe note about libraries	3537	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2220	in the description of C<EV_USE_MONOTONIC>, though.	3538	correctness. See the note about libraries in the description of
		3539	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3540	C<EV_USE_CLOCK_SYSCALL>.
		3541
		3542	=item EV_USE_CLOCK_SYSCALL
		3543
		3544	If defined to be C<1>, libev will try to use a direct syscall instead
		3545	of calling the system-provided C<clock_gettime> function. This option
		3546	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3547	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3548	programs needlessly. Using a direct syscall is slightly slower (in
		3549	theory), because no optimised vdso implementation can be used, but avoids
		3550	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3551	higher, as it simplifies linking (no need for C<-lrt>).
		3552
		3553	=item EV_USE_NANOSLEEP
		3554
		3555	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		3556	and will use it for delays. Otherwise it will use C<select ()>.
		3557
		3558	=item EV_USE_EVENTFD
		3559
		3560	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3561	available and will probe for kernel support at runtime. This will improve
		3562	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3563	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3564	2.7 or newer, otherwise disabled.
2221		3565
2222	=item EV_USE_SELECT	3566	=item EV_USE_SELECT
2223		3567
2224	If undefined or defined to be C<1>, libev will compile in support for the	3568	If undefined or defined to be C<1>, libev will compile in support for the
2225	C<select>(2) backend. No attempt at autodetection will be done: if no	3569	C<select>(2) backend. No attempt at auto-detection will be done: if no
2226	other method takes over, select will be it. Otherwise the select backend	3570	other method takes over, select will be it. Otherwise the select backend
2227	will not be compiled in.	3571	will not be compiled in.
2228		3572
2229	=item EV_SELECT_USE_FD_SET	3573	=item EV_SELECT_USE_FD_SET
2230		3574
2231	If defined to C<1>, then the select backend will use the system C<fd_set>	3575	If defined to C<1>, then the select backend will use the system C<fd_set>
2232	structure. This is useful if libev doesn't compile due to a missing	3576	structure. This is useful if libev doesn't compile due to a missing
2233	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	3577	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2234	exotic systems. This usually limits the range of file descriptors to some	3578	on exotic systems. This usually limits the range of file descriptors to
2235	low limit such as 1024 or might have other limitations (winsocket only	3579	some low limit such as 1024 or might have other limitations (winsocket
2236	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3580	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2237	influence the size of the C<fd_set> used.	3581	configures the maximum size of the C<fd_set>.
2238		3582
2239	=item EV_SELECT_IS_WINSOCKET	3583	=item EV_SELECT_IS_WINSOCKET
2240		3584
2241	When defined to C<1>, the select backend will assume that	3585	When defined to C<1>, the select backend will assume that
2242	select/socket/connect etc. don't understand file descriptors but	3586	select/socket/connect etc. don't understand file descriptors but
…		…
2244	be used is the winsock select). This means that it will call	3588	be used is the winsock select). This means that it will call
2245	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3589	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2246	it is assumed that all these functions actually work on fds, even	3590	it is assumed that all these functions actually work on fds, even
2247	on win32. Should not be defined on non-win32 platforms.	3591	on win32. Should not be defined on non-win32 platforms.
2248		3592
		3593	=item EV_FD_TO_WIN32_HANDLE
		3594
		3595	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3596	file descriptors to socket handles. When not defining this symbol (the
		3597	default), then libev will call C<_get_osfhandle>, which is usually
		3598	correct. In some cases, programs use their own file descriptor management,
		3599	in which case they can provide this function to map fds to socket handles.
		3600
2249	=item EV_USE_POLL	3601	=item EV_USE_POLL
2250		3602
2251	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3603	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2252	backend. Otherwise it will be enabled on non-win32 platforms. It	3604	backend. Otherwise it will be enabled on non-win32 platforms. It
2253	takes precedence over select.	3605	takes precedence over select.
2254		3606
2255	=item EV_USE_EPOLL	3607	=item EV_USE_EPOLL
2256		3608
2257	If defined to be C<1>, libev will compile in support for the Linux	3609	If defined to be C<1>, libev will compile in support for the Linux
2258	C<epoll>(7) backend. Its availability will be detected at runtime,	3610	C<epoll>(7) backend. Its availability will be detected at runtime,
2259	otherwise another method will be used as fallback. This is the	3611	otherwise another method will be used as fallback. This is the preferred
2260	preferred backend for GNU/Linux systems.	3612	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3613	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2261		3614
2262	=item EV_USE_KQUEUE	3615	=item EV_USE_KQUEUE
2263		3616
2264	If defined to be C<1>, libev will compile in support for the BSD style	3617	If defined to be C<1>, libev will compile in support for the BSD style
2265	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	3618	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2278	otherwise another method will be used as fallback. This is the preferred	3631	otherwise another method will be used as fallback. This is the preferred
2279	backend for Solaris 10 systems.	3632	backend for Solaris 10 systems.
2280		3633
2281	=item EV_USE_DEVPOLL	3634	=item EV_USE_DEVPOLL
2282		3635
2283	reserved for future expansion, works like the USE symbols above.	3636	Reserved for future expansion, works like the USE symbols above.
2284		3637
2285	=item EV_USE_INOTIFY	3638	=item EV_USE_INOTIFY
2286		3639
2287	If defined to be C<1>, libev will compile in support for the Linux inotify	3640	If defined to be C<1>, libev will compile in support for the Linux inotify
2288	interface to speed up C<ev_stat> watchers. Its actual availability will	3641	interface to speed up C<ev_stat> watchers. Its actual availability will
2289	be detected at runtime.	3642	be detected at runtime. If undefined, it will be enabled if the headers
		3643	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3644
		3645	=item EV_ATOMIC_T
		3646
		3647	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3648	access is atomic with respect to other threads or signal contexts. No such
		3649	type is easily found in the C language, so you can provide your own type
		3650	that you know is safe for your purposes. It is used both for signal handler "locking"
		3651	as well as for signal and thread safety in C<ev_async> watchers.
		3652
		3653	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3654	(from F<signal.h>), which is usually good enough on most platforms.
2290		3655
2291	=item EV_H	3656	=item EV_H
2292		3657
2293	The name of the F<ev.h> header file used to include it. The default if	3658	The name of the F<ev.h> header file used to include it. The default if
2294	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This	3659	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2295	can be used to virtually rename the F<ev.h> header file in case of conflicts.	3660	used to virtually rename the F<ev.h> header file in case of conflicts.
2296		3661
2297	=item EV_CONFIG_H	3662	=item EV_CONFIG_H
2298		3663
2299	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	3664	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2300	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	3665	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2301	C<EV_H>, above.	3666	C<EV_H>, above.
2302		3667
2303	=item EV_EVENT_H	3668	=item EV_EVENT_H
2304		3669
2305	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	3670	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2306	of how the F<event.h> header can be found.	3671	of how the F<event.h> header can be found, the default is C<"event.h">.
2307		3672
2308	=item EV_PROTOTYPES	3673	=item EV_PROTOTYPES
2309		3674
2310	If defined to be C<0>, then F<ev.h> will not define any function	3675	If defined to be C<0>, then F<ev.h> will not define any function
2311	prototypes, but still define all the structs and other symbols. This is	3676	prototypes, but still define all the structs and other symbols. This is
…		…
2332	When doing priority-based operations, libev usually has to linearly search	3697	When doing priority-based operations, libev usually has to linearly search
2333	all the priorities, so having many of them (hundreds) uses a lot of space	3698	all the priorities, so having many of them (hundreds) uses a lot of space
2334	and time, so using the defaults of five priorities (-2 .. +2) is usually	3699	and time, so using the defaults of five priorities (-2 .. +2) is usually
2335	fine.	3700	fine.
2336		3701
2337	If your embedding app does not need any priorities, defining these both to	3702	If your embedding application does not need any priorities, defining these
2338	C<0> will save some memory and cpu.	3703	both to C<0> will save some memory and CPU.
2339		3704
2340	=item EV_PERIODIC_ENABLE	3705	=item EV_PERIODIC_ENABLE
2341		3706
2342	If undefined or defined to be C<1>, then periodic timers are supported. If	3707	If undefined or defined to be C<1>, then periodic timers are supported. If
2343	defined to be C<0>, then they are not. Disabling them saves a few kB of	3708	defined to be C<0>, then they are not. Disabling them saves a few kB of
…		…
2350	code.	3715	code.
2351		3716
2352	=item EV_EMBED_ENABLE	3717	=item EV_EMBED_ENABLE
2353		3718
2354	If undefined or defined to be C<1>, then embed watchers are supported. If	3719	If undefined or defined to be C<1>, then embed watchers are supported. If
2355	defined to be C<0>, then they are not.	3720	defined to be C<0>, then they are not. Embed watchers rely on most other
		3721	watcher types, which therefore must not be disabled.
2356		3722
2357	=item EV_STAT_ENABLE	3723	=item EV_STAT_ENABLE
2358		3724
2359	If undefined or defined to be C<1>, then stat watchers are supported. If	3725	If undefined or defined to be C<1>, then stat watchers are supported. If
2360	defined to be C<0>, then they are not.	3726	defined to be C<0>, then they are not.
…		…
2362	=item EV_FORK_ENABLE	3728	=item EV_FORK_ENABLE
2363		3729
2364	If undefined or defined to be C<1>, then fork watchers are supported. If	3730	If undefined or defined to be C<1>, then fork watchers are supported. If
2365	defined to be C<0>, then they are not.	3731	defined to be C<0>, then they are not.
2366		3732
		3733	=item EV_ASYNC_ENABLE
		3734
		3735	If undefined or defined to be C<1>, then async watchers are supported. If
		3736	defined to be C<0>, then they are not.
		3737
2367	=item EV_MINIMAL	3738	=item EV_MINIMAL
2368		3739
2369	If you need to shave off some kilobytes of code at the expense of some	3740	If you need to shave off some kilobytes of code at the expense of some
2370	speed, define this symbol to C<1>. Currently only used for gcc to override	3741	speed (but with the full API), define this symbol to C<1>. Currently this
2371	some inlining decisions, saves roughly 30% codesize of amd64.	3742	is used to override some inlining decisions, saves roughly 30% code size
		3743	on amd64. It also selects a much smaller 2-heap for timer management over
		3744	the default 4-heap.
		3745
		3746	You can save even more by disabling watcher types you do not need
		3747	and setting C<EV_MAXPRI> == C<EV_MINPRI>. Also, disabling C<assert>
		3748	(C<-DNDEBUG>) will usually reduce code size a lot.
		3749
		3750	Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to
		3751	provide a bare-bones event library. See C<ev.h> for details on what parts
		3752	of the API are still available, and do not complain if this subset changes
		3753	over time.
2372		3754
2373	=item EV_PID_HASHSIZE	3755	=item EV_PID_HASHSIZE
2374		3756
2375	C<ev_child> watchers use a small hash table to distribute workload by	3757	C<ev_child> watchers use a small hash table to distribute workload by
2376	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3758	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
2377	than enough. If you need to manage thousands of children you might want to	3759	than enough. If you need to manage thousands of children you might want to
2378	increase this value (I<must> be a power of two).	3760	increase this value (I<must> be a power of two).
2379		3761
2380	=item EV_INOTIFY_HASHSIZE	3762	=item EV_INOTIFY_HASHSIZE
2381		3763
2382	C<ev_staz> watchers use a small hash table to distribute workload by	3764	C<ev_stat> watchers use a small hash table to distribute workload by
2383	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	3765	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
2384	usually more than enough. If you need to manage thousands of C<ev_stat>	3766	usually more than enough. If you need to manage thousands of C<ev_stat>
2385	watchers you might want to increase this value (I<must> be a power of	3767	watchers you might want to increase this value (I<must> be a power of
2386	two).	3768	two).
2387		3769
		3770	=item EV_USE_4HEAP
		3771
		3772	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3773	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		3774	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		3775	faster performance with many (thousands) of watchers.
		3776
		3777	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3778	(disabled).
		3779
		3780	=item EV_HEAP_CACHE_AT
		3781
		3782	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3783	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		3784	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3785	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3786	but avoids random read accesses on heap changes. This improves performance
		3787	noticeably with many (hundreds) of watchers.
		3788
		3789	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3790	(disabled).
		3791
		3792	=item EV_VERIFY
		3793
		3794	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3795	be done: If set to C<0>, no internal verification code will be compiled
		3796	in. If set to C<1>, then verification code will be compiled in, but not
		3797	called. If set to C<2>, then the internal verification code will be
		3798	called once per loop, which can slow down libev. If set to C<3>, then the
		3799	verification code will be called very frequently, which will slow down
		3800	libev considerably.
		3801
		3802	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3803	C<0>.
		3804
2388	=item EV_COMMON	3805	=item EV_COMMON
2389		3806
2390	By default, all watchers have a C<void *data> member. By redefining	3807	By default, all watchers have a C<void *data> member. By redefining
2391	this macro to a something else you can include more and other types of	3808	this macro to a something else you can include more and other types of
2392	members. You have to define it each time you include one of the files,	3809	members. You have to define it each time you include one of the files,
2393	though, and it must be identical each time.	3810	though, and it must be identical each time.
2394		3811
2395	For example, the perl EV module uses something like this:	3812	For example, the perl EV module uses something like this:
2396		3813
2397	#define EV_COMMON \	3814	#define EV_COMMON \
2398	SV *self; /* contains this struct */ \	3815	SV *self; /* contains this struct */ \
2399	SV *cb_sv, *fh /* note no trailing ";" */	3816	SV *cb_sv, *fh /* note no trailing ";" */
2400		3817
2401	=item EV_CB_DECLARE (type)	3818	=item EV_CB_DECLARE (type)
2402		3819
2403	=item EV_CB_INVOKE (watcher, revents)	3820	=item EV_CB_INVOKE (watcher, revents)
2404		3821
2405	=item ev_set_cb (ev, cb)	3822	=item ev_set_cb (ev, cb)
2406		3823
2407	Can be used to change the callback member declaration in each watcher,	3824	Can be used to change the callback member declaration in each watcher,
2408	and the way callbacks are invoked and set. Must expand to a struct member	3825	and the way callbacks are invoked and set. Must expand to a struct member
2409	definition and a statement, respectively. See the F<ev.v> header file for	3826	definition and a statement, respectively. See the F<ev.h> header file for
2410	their default definitions. One possible use for overriding these is to	3827	their default definitions. One possible use for overriding these is to
2411	avoid the C<struct ev_loop *> as first argument in all cases, or to use	3828	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2412	method calls instead of plain function calls in C++.	3829	method calls instead of plain function calls in C++.
		3830
		3831	=back
		3832
		3833	=head2 EXPORTED API SYMBOLS
		3834
		3835	If you need to re-export the API (e.g. via a DLL) and you need a list of
		3836	exported symbols, you can use the provided F<Symbol.*> files which list
		3837	all public symbols, one per line:
		3838
		3839	Symbols.ev for libev proper
		3840	Symbols.event for the libevent emulation
		3841
		3842	This can also be used to rename all public symbols to avoid clashes with
		3843	multiple versions of libev linked together (which is obviously bad in
		3844	itself, but sometimes it is inconvenient to avoid this).
		3845
		3846	A sed command like this will create wrapper C<#define>'s that you need to
		3847	include before including F<ev.h>:
		3848
		3849	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		3850
		3851	This would create a file F<wrap.h> which essentially looks like this:
		3852
		3853	#define ev_backend myprefix_ev_backend
		3854	#define ev_check_start myprefix_ev_check_start
		3855	#define ev_check_stop myprefix_ev_check_stop
		3856	...
2413		3857
2414	=head2 EXAMPLES	3858	=head2 EXAMPLES
2415		3859
2416	For a real-world example of a program the includes libev	3860	For a real-world example of a program the includes libev
2417	verbatim, you can have a look at the EV perl module	3861	verbatim, you can have a look at the EV perl module
…		…
2422	file.	3866	file.
2423		3867
2424	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	3868	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2425	that everybody includes and which overrides some configure choices:	3869	that everybody includes and which overrides some configure choices:
2426		3870
2427	#define EV_MINIMAL 1	3871	#define EV_MINIMAL 1
2428	#define EV_USE_POLL 0	3872	#define EV_USE_POLL 0
2429	#define EV_MULTIPLICITY 0	3873	#define EV_MULTIPLICITY 0
2430	#define EV_PERIODIC_ENABLE 0	3874	#define EV_PERIODIC_ENABLE 0
2431	#define EV_STAT_ENABLE 0	3875	#define EV_STAT_ENABLE 0
2432	#define EV_FORK_ENABLE 0	3876	#define EV_FORK_ENABLE 0
2433	#define EV_CONFIG_H <config.h>	3877	#define EV_CONFIG_H <config.h>
2434	#define EV_MINPRI 0	3878	#define EV_MINPRI 0
2435	#define EV_MAXPRI 0	3879	#define EV_MAXPRI 0
2436		3880
2437	#include "ev++.h"	3881	#include "ev++.h"
2438		3882
2439	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	3883	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2440		3884
2441	#include "ev_cpp.h"	3885	#include "ev_cpp.h"
2442	#include "ev.c"	3886	#include "ev.c"
2443		3887
		3888	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
2444		3889
		3890	=head2 THREADS AND COROUTINES
		3891
		3892	=head3 THREADS
		3893
		3894	All libev functions are reentrant and thread-safe unless explicitly
		3895	documented otherwise, but libev implements no locking itself. This means
		3896	that you can use as many loops as you want in parallel, as long as there
		3897	are no concurrent calls into any libev function with the same loop
		3898	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		3899	of course): libev guarantees that different event loops share no data
		3900	structures that need any locking.
		3901
		3902	Or to put it differently: calls with different loop parameters can be done
		3903	concurrently from multiple threads, calls with the same loop parameter
		3904	must be done serially (but can be done from different threads, as long as
		3905	only one thread ever is inside a call at any point in time, e.g. by using
		3906	a mutex per loop).
		3907
		3908	Specifically to support threads (and signal handlers), libev implements
		3909	so-called C<ev_async> watchers, which allow some limited form of
		3910	concurrency on the same event loop, namely waking it up "from the
		3911	outside".
		3912
		3913	If you want to know which design (one loop, locking, or multiple loops
		3914	without or something else still) is best for your problem, then I cannot
		3915	help you, but here is some generic advice:
		3916
		3917	=over 4
		3918
		3919	=item * most applications have a main thread: use the default libev loop
		3920	in that thread, or create a separate thread running only the default loop.
		3921
		3922	This helps integrating other libraries or software modules that use libev
		3923	themselves and don't care/know about threading.
		3924
		3925	=item * one loop per thread is usually a good model.
		3926
		3927	Doing this is almost never wrong, sometimes a better-performance model
		3928	exists, but it is always a good start.
		3929
		3930	=item * other models exist, such as the leader/follower pattern, where one
		3931	loop is handed through multiple threads in a kind of round-robin fashion.
		3932
		3933	Choosing a model is hard - look around, learn, know that usually you can do
		3934	better than you currently do :-)
		3935
		3936	=item * often you need to talk to some other thread which blocks in the
		3937	event loop.
		3938
		3939	C<ev_async> watchers can be used to wake them up from other threads safely
		3940	(or from signal contexts...).
		3941
		3942	An example use would be to communicate signals or other events that only
		3943	work in the default loop by registering the signal watcher with the
		3944	default loop and triggering an C<ev_async> watcher from the default loop
		3945	watcher callback into the event loop interested in the signal.
		3946
		3947	=back
		3948
		3949	=head4 THREAD LOCKING EXAMPLE
		3950
		3951	Here is a fictitious example of how to run an event loop in a different
		3952	thread than where callbacks are being invoked and watchers are
		3953	created/added/removed.
		3954
		3955	For a real-world example, see the C<EV::Loop::Async> perl module,
		3956	which uses exactly this technique (which is suited for many high-level
		3957	languages).
		3958
		3959	The example uses a pthread mutex to protect the loop data, a condition
		3960	variable to wait for callback invocations, an async watcher to notify the
		3961	event loop thread and an unspecified mechanism to wake up the main thread.
		3962
		3963	First, you need to associate some data with the event loop:
		3964
		3965	typedef struct {
		3966	mutex_t lock; /* global loop lock */
		3967	ev_async async_w;
		3968	thread_t tid;
		3969	cond_t invoke_cv;
		3970	} userdata;
		3971
		3972	void prepare_loop (EV_P)
		3973	{
		3974	// for simplicity, we use a static userdata struct.
		3975	static userdata u;
		3976
		3977	ev_async_init (&u->async_w, async_cb);
		3978	ev_async_start (EV_A_ &u->async_w);
		3979
		3980	pthread_mutex_init (&u->lock, 0);
		3981	pthread_cond_init (&u->invoke_cv, 0);
		3982
		3983	// now associate this with the loop
		3984	ev_set_userdata (EV_A_ u);
		3985	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3986	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3987
		3988	// then create the thread running ev_loop
		3989	pthread_create (&u->tid, 0, l_run, EV_A);
		3990	}
		3991
		3992	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3993	solely to wake up the event loop so it takes notice of any new watchers
		3994	that might have been added:
		3995
		3996	static void
		3997	async_cb (EV_P_ ev_async *w, int revents)
		3998	{
		3999	// just used for the side effects
		4000	}
		4001
		4002	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4003	protecting the loop data, respectively.
		4004
		4005	static void
		4006	l_release (EV_P)
		4007	{
		4008	userdata *u = ev_userdata (EV_A);
		4009	pthread_mutex_unlock (&u->lock);
		4010	}
		4011
		4012	static void
		4013	l_acquire (EV_P)
		4014	{
		4015	userdata *u = ev_userdata (EV_A);
		4016	pthread_mutex_lock (&u->lock);
		4017	}
		4018
		4019	The event loop thread first acquires the mutex, and then jumps straight
		4020	into C<ev_loop>:
		4021
		4022	void *
		4023	l_run (void *thr_arg)
		4024	{
		4025	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		4026
		4027	l_acquire (EV_A);
		4028	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4029	ev_loop (EV_A_ 0);
		4030	l_release (EV_A);
		4031
		4032	return 0;
		4033	}
		4034
		4035	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4036	signal the main thread via some unspecified mechanism (signals? pipe
		4037	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4038	have been called (in a while loop because a) spurious wakeups are possible
		4039	and b) skipping inter-thread-communication when there are no pending
		4040	watchers is very beneficial):
		4041
		4042	static void
		4043	l_invoke (EV_P)
		4044	{
		4045	userdata *u = ev_userdata (EV_A);
		4046
		4047	while (ev_pending_count (EV_A))
		4048	{
		4049	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4050	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4051	}
		4052	}
		4053
		4054	Now, whenever the main thread gets told to invoke pending watchers, it
		4055	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4056	thread to continue:
		4057
		4058	static void
		4059	real_invoke_pending (EV_P)
		4060	{
		4061	userdata *u = ev_userdata (EV_A);
		4062
		4063	pthread_mutex_lock (&u->lock);
		4064	ev_invoke_pending (EV_A);
		4065	pthread_cond_signal (&u->invoke_cv);
		4066	pthread_mutex_unlock (&u->lock);
		4067	}
		4068
		4069	Whenever you want to start/stop a watcher or do other modifications to an
		4070	event loop, you will now have to lock:
		4071
		4072	ev_timer timeout_watcher;
		4073	userdata *u = ev_userdata (EV_A);
		4074
		4075	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4076
		4077	pthread_mutex_lock (&u->lock);
		4078	ev_timer_start (EV_A_ &timeout_watcher);
		4079	ev_async_send (EV_A_ &u->async_w);
		4080	pthread_mutex_unlock (&u->lock);
		4081
		4082	Note that sending the C<ev_async> watcher is required because otherwise
		4083	an event loop currently blocking in the kernel will have no knowledge
		4084	about the newly added timer. By waking up the loop it will pick up any new
		4085	watchers in the next event loop iteration.
		4086
		4087	=head3 COROUTINES
		4088
		4089	Libev is very accommodating to coroutines ("cooperative threads"):
		4090	libev fully supports nesting calls to its functions from different
		4091	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		4092	different coroutines, and switch freely between both coroutines running
		4093	the loop, as long as you don't confuse yourself). The only exception is
		4094	that you must not do this from C<ev_periodic> reschedule callbacks.
		4095
		4096	Care has been taken to ensure that libev does not keep local state inside
		4097	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		4098	they do not call any callbacks.
		4099
		4100	=head2 COMPILER WARNINGS
		4101
		4102	Depending on your compiler and compiler settings, you might get no or a
		4103	lot of warnings when compiling libev code. Some people are apparently
		4104	scared by this.
		4105
		4106	However, these are unavoidable for many reasons. For one, each compiler
		4107	has different warnings, and each user has different tastes regarding
		4108	warning options. "Warn-free" code therefore cannot be a goal except when
		4109	targeting a specific compiler and compiler-version.
		4110
		4111	Another reason is that some compiler warnings require elaborate
		4112	workarounds, or other changes to the code that make it less clear and less
		4113	maintainable.
		4114
		4115	And of course, some compiler warnings are just plain stupid, or simply
		4116	wrong (because they don't actually warn about the condition their message
		4117	seems to warn about). For example, certain older gcc versions had some
		4118	warnings that resulted an extreme number of false positives. These have
		4119	been fixed, but some people still insist on making code warn-free with
		4120	such buggy versions.
		4121
		4122	While libev is written to generate as few warnings as possible,
		4123	"warn-free" code is not a goal, and it is recommended not to build libev
		4124	with any compiler warnings enabled unless you are prepared to cope with
		4125	them (e.g. by ignoring them). Remember that warnings are just that:
		4126	warnings, not errors, or proof of bugs.
		4127
		4128
		4129	=head2 VALGRIND
		4130
		4131	Valgrind has a special section here because it is a popular tool that is
		4132	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		4133
		4134	If you think you found a bug (memory leak, uninitialised data access etc.)
		4135	in libev, then check twice: If valgrind reports something like:
		4136
		4137	==2274== definitely lost: 0 bytes in 0 blocks.
		4138	==2274== possibly lost: 0 bytes in 0 blocks.
		4139	==2274== still reachable: 256 bytes in 1 blocks.
		4140
		4141	Then there is no memory leak, just as memory accounted to global variables
		4142	is not a memleak - the memory is still being referenced, and didn't leak.
		4143
		4144	Similarly, under some circumstances, valgrind might report kernel bugs
		4145	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4146	although an acceptable workaround has been found here), or it might be
		4147	confused.
		4148
		4149	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		4150	make it into some kind of religion.
		4151
		4152	If you are unsure about something, feel free to contact the mailing list
		4153	with the full valgrind report and an explanation on why you think this
		4154	is a bug in libev (best check the archives, too :). However, don't be
		4155	annoyed when you get a brisk "this is no bug" answer and take the chance
		4156	of learning how to interpret valgrind properly.
		4157
		4158	If you need, for some reason, empty reports from valgrind for your project
		4159	I suggest using suppression lists.
		4160
		4161
		4162	=head1 PORTABILITY NOTES
		4163
		4164	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		4165
		4166	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		4167	requires, and its I/O model is fundamentally incompatible with the POSIX
		4168	model. Libev still offers limited functionality on this platform in
		4169	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		4170	descriptors. This only applies when using Win32 natively, not when using
		4171	e.g. cygwin.
		4172
		4173	Lifting these limitations would basically require the full
		4174	re-implementation of the I/O system. If you are into these kinds of
		4175	things, then note that glib does exactly that for you in a very portable
		4176	way (note also that glib is the slowest event library known to man).
		4177
		4178	There is no supported compilation method available on windows except
		4179	embedding it into other applications.
		4180
		4181	Sensible signal handling is officially unsupported by Microsoft - libev
		4182	tries its best, but under most conditions, signals will simply not work.
		4183
		4184	Not a libev limitation but worth mentioning: windows apparently doesn't
		4185	accept large writes: instead of resulting in a partial write, windows will
		4186	either accept everything or return C<ENOBUFS> if the buffer is too large,
		4187	so make sure you only write small amounts into your sockets (less than a
		4188	megabyte seems safe, but this apparently depends on the amount of memory
		4189	available).
		4190
		4191	Due to the many, low, and arbitrary limits on the win32 platform and
		4192	the abysmal performance of winsockets, using a large number of sockets
		4193	is not recommended (and not reasonable). If your program needs to use
		4194	more than a hundred or so sockets, then likely it needs to use a totally
		4195	different implementation for windows, as libev offers the POSIX readiness
		4196	notification model, which cannot be implemented efficiently on windows
		4197	(due to Microsoft monopoly games).
		4198
		4199	A typical way to use libev under windows is to embed it (see the embedding
		4200	section for details) and use the following F<evwrap.h> header file instead
		4201	of F<ev.h>:
		4202
		4203	#define EV_STANDALONE /* keeps ev from requiring config.h */
		4204	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		4205
		4206	#include "ev.h"
		4207
		4208	And compile the following F<evwrap.c> file into your project (make sure
		4209	you do I<not> compile the F<ev.c> or any other embedded source files!):
		4210
		4211	#include "evwrap.h"
		4212	#include "ev.c"
		4213
		4214	=over 4
		4215
		4216	=item The winsocket select function
		4217
		4218	The winsocket C<select> function doesn't follow POSIX in that it
		4219	requires socket I<handles> and not socket I<file descriptors> (it is
		4220	also extremely buggy). This makes select very inefficient, and also
		4221	requires a mapping from file descriptors to socket handles (the Microsoft
		4222	C runtime provides the function C<_open_osfhandle> for this). See the
		4223	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		4224	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		4225
		4226	The configuration for a "naked" win32 using the Microsoft runtime
		4227	libraries and raw winsocket select is:
		4228
		4229	#define EV_USE_SELECT 1
		4230	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		4231
		4232	Note that winsockets handling of fd sets is O(n), so you can easily get a
		4233	complexity in the O(n²) range when using win32.
		4234
		4235	=item Limited number of file descriptors
		4236
		4237	Windows has numerous arbitrary (and low) limits on things.
		4238
		4239	Early versions of winsocket's select only supported waiting for a maximum
		4240	of C<64> handles (probably owning to the fact that all windows kernels
		4241	can only wait for C<64> things at the same time internally; Microsoft
		4242	recommends spawning a chain of threads and wait for 63 handles and the
		4243	previous thread in each. Sounds great!).
		4244
		4245	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		4246	to some high number (e.g. C<2048>) before compiling the winsocket select
		4247	call (which might be in libev or elsewhere, for example, perl and many
		4248	other interpreters do their own select emulation on windows).
		4249
		4250	Another limit is the number of file descriptors in the Microsoft runtime
		4251	libraries, which by default is C<64> (there must be a hidden I<64>
		4252	fetish or something like this inside Microsoft). You can increase this
		4253	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		4254	(another arbitrary limit), but is broken in many versions of the Microsoft
		4255	runtime libraries. This might get you to about C<512> or C<2048> sockets
		4256	(depending on windows version and/or the phase of the moon). To get more,
		4257	you need to wrap all I/O functions and provide your own fd management, but
		4258	the cost of calling select (O(n²)) will likely make this unworkable.
		4259
		4260	=back
		4261
		4262	=head2 PORTABILITY REQUIREMENTS
		4263
		4264	In addition to a working ISO-C implementation and of course the
		4265	backend-specific APIs, libev relies on a few additional extensions:
		4266
		4267	=over 4
		4268
		4269	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4270	calling conventions regardless of C<ev_watcher_type *>.
		4271
		4272	Libev assumes not only that all watcher pointers have the same internal
		4273	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4274	assumes that the same (machine) code can be used to call any watcher
		4275	callback: The watcher callbacks have different type signatures, but libev
		4276	calls them using an C<ev_watcher *> internally.
		4277
		4278	=item C<sig_atomic_t volatile> must be thread-atomic as well
		4279
		4280	The type C<sig_atomic_t volatile> (or whatever is defined as
		4281	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		4282	threads. This is not part of the specification for C<sig_atomic_t>, but is
		4283	believed to be sufficiently portable.
		4284
		4285	=item C<sigprocmask> must work in a threaded environment
		4286
		4287	Libev uses C<sigprocmask> to temporarily block signals. This is not
		4288	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		4289	pthread implementations will either allow C<sigprocmask> in the "main
		4290	thread" or will block signals process-wide, both behaviours would
		4291	be compatible with libev. Interaction between C<sigprocmask> and
		4292	C<pthread_sigmask> could complicate things, however.
		4293
		4294	The most portable way to handle signals is to block signals in all threads
		4295	except the initial one, and run the default loop in the initial thread as
		4296	well.
		4297
		4298	=item C<long> must be large enough for common memory allocation sizes
		4299
		4300	To improve portability and simplify its API, libev uses C<long> internally
		4301	instead of C<size_t> when allocating its data structures. On non-POSIX
		4302	systems (Microsoft...) this might be unexpectedly low, but is still at
		4303	least 31 bits everywhere, which is enough for hundreds of millions of
		4304	watchers.
		4305
		4306	=item C<double> must hold a time value in seconds with enough accuracy
		4307
		4308	The type C<double> is used to represent timestamps. It is required to
		4309	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		4310	enough for at least into the year 4000. This requirement is fulfilled by
		4311	implementations implementing IEEE 754, which is basically all existing
		4312	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4313	2200.
		4314
		4315	=back
		4316
		4317	If you know of other additional requirements drop me a note.
		4318
		4319
2445	=head1 COMPLEXITIES	4320	=head1 ALGORITHMIC COMPLEXITIES
2446		4321
2447	In this section the complexities of (many of) the algorithms used inside	4322	In this section the complexities of (many of) the algorithms used inside
2448	libev will be explained. For complexity discussions about backends see the	4323	libev will be documented. For complexity discussions about backends see
2449	documentation for C<ev_default_init>.	4324	the documentation for C<ev_default_init>.
2450		4325
2451	All of the following are about amortised time: If an array needs to be	4326	All of the following are about amortised time: If an array needs to be
2452	extended, libev needs to realloc and move the whole array, but this	4327	extended, libev needs to realloc and move the whole array, but this
2453	happens asymptotically never with higher number of elements, so O(1) might	4328	happens asymptotically rarer with higher number of elements, so O(1) might
2454	mean it might do a lengthy realloc operation in rare cases, but on average	4329	mean that libev does a lengthy realloc operation in rare cases, but on
2455	it is much faster and asymptotically approaches constant time.	4330	average it is much faster and asymptotically approaches constant time.
2456		4331
2457	=over 4	4332	=over 4
2458		4333
2459	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4334	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2460		4335
2461	This means that, when you have a watcher that triggers in one hour and	4336	This means that, when you have a watcher that triggers in one hour and
2462	there are 100 watchers that would trigger before that then inserting will	4337	there are 100 watchers that would trigger before that, then inserting will
2463	have to skip those 100 watchers.	4338	have to skip roughly seven (C<ld 100>) of these watchers.
2464		4339
2465	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	4340	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2466		4341
2467	That means that for changing a timer costs less than removing/adding them	4342	That means that changing a timer costs less than removing/adding them,
2468	as only the relative motion in the event queue has to be paid for.	4343	as only the relative motion in the event queue has to be paid for.
2469		4344
2470	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	4345	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
2471		4346
2472	These just add the watcher into an array or at the head of a list.	4347	These just add the watcher into an array or at the head of a list.
		4348
2473	=item Stopping check/prepare/idle watchers: O(1)	4349	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2474		4350
2475	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	4351	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2476		4352
2477	These watchers are stored in lists then need to be walked to find the	4353	These watchers are stored in lists, so they need to be walked to find the
2478	correct watcher to remove. The lists are usually short (you don't usually	4354	correct watcher to remove. The lists are usually short (you don't usually
2479	have many watchers waiting for the same fd or signal).	4355	have many watchers waiting for the same fd or signal: one is typical, two
		4356	is rare).
2480		4357
2481	=item Finding the next timer per loop iteration: O(1)	4358	=item Finding the next timer in each loop iteration: O(1)
		4359
		4360	By virtue of using a binary or 4-heap, the next timer is always found at a
		4361	fixed position in the storage array.
2482		4362
2483	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	4363	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2484		4364
2485	A change means an I/O watcher gets started or stopped, which requires	4365	A change means an I/O watcher gets started or stopped, which requires
2486	libev to recalculate its status (and possibly tell the kernel).	4366	libev to recalculate its status (and possibly tell the kernel, depending
		4367	on backend and whether C<ev_io_set> was used).
2487		4368
2488	=item Activating one watcher: O(1)	4369	=item Activating one watcher (putting it into the pending state): O(1)
2489		4370
2490	=item Priority handling: O(number_of_priorities)	4371	=item Priority handling: O(number_of_priorities)
2491		4372
2492	Priorities are implemented by allocating some space for each	4373	Priorities are implemented by allocating some space for each
2493	priority. When doing priority-based operations, libev usually has to	4374	priority. When doing priority-based operations, libev usually has to
2494	linearly search all the priorities.	4375	linearly search all the priorities, but starting/stopping and activating
		4376	watchers becomes O(1) with respect to priority handling.
		4377
		4378	=item Sending an ev_async: O(1)
		4379
		4380	=item Processing ev_async_send: O(number_of_async_watchers)
		4381
		4382	=item Processing signals: O(max_signal_number)
		4383
		4384	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4385	calls in the current loop iteration. Checking for async and signal events
		4386	involves iterating over all running async watchers or all signal numbers.
2495		4387
2496	=back	4388	=back
2497		4389
2498		4390
		4391	=head1 GLOSSARY
		4392
		4393	=over 4
		4394
		4395	=item active
		4396
		4397	A watcher is active as long as it has been started (has been attached to
		4398	an event loop) but not yet stopped (disassociated from the event loop).
		4399
		4400	=item application
		4401
		4402	In this document, an application is whatever is using libev.
		4403
		4404	=item callback
		4405
		4406	The address of a function that is called when some event has been
		4407	detected. Callbacks are being passed the event loop, the watcher that
		4408	received the event, and the actual event bitset.
		4409
		4410	=item callback invocation
		4411
		4412	The act of calling the callback associated with a watcher.
		4413
		4414	=item event
		4415
		4416	A change of state of some external event, such as data now being available
		4417	for reading on a file descriptor, time having passed or simply not having
		4418	any other events happening anymore.
		4419
		4420	In libev, events are represented as single bits (such as C<EV_READ> or
		4421	C<EV_TIMEOUT>).
		4422
		4423	=item event library
		4424
		4425	A software package implementing an event model and loop.
		4426
		4427	=item event loop
		4428
		4429	An entity that handles and processes external events and converts them
		4430	into callback invocations.
		4431
		4432	=item event model
		4433
		4434	The model used to describe how an event loop handles and processes
		4435	watchers and events.
		4436
		4437	=item pending
		4438
		4439	A watcher is pending as soon as the corresponding event has been detected,
		4440	and stops being pending as soon as the watcher will be invoked or its
		4441	pending status is explicitly cleared by the application.
		4442
		4443	A watcher can be pending, but not active. Stopping a watcher also clears
		4444	its pending status.
		4445
		4446	=item real time
		4447
		4448	The physical time that is observed. It is apparently strictly monotonic :)
		4449
		4450	=item wall-clock time
		4451
		4452	The time and date as shown on clocks. Unlike real time, it can actually
		4453	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4454	clock.
		4455
		4456	=item watcher
		4457
		4458	A data structure that describes interest in certain events. Watchers need
		4459	to be started (attached to an event loop) before they can receive events.
		4460
		4461	=item watcher invocation
		4462
		4463	The act of calling the callback associated with a watcher.
		4464
		4465	=back
		4466
2499	=head1 AUTHOR	4467	=head1 AUTHOR
2500		4468
2501	Marc Lehmann <libev@schmorp.de>.	4469	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
2502		4470

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