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Revision 1.66 by root, Mon Dec 3 13:41:25 2007 UTC vs.
Revision 1.205 by root, Mon Oct 27 12:20:32 2008 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	// every watcher type has its own typedef'd struct
		15	// with the name ev_TYPE
13	ev_io stdin_watcher;	16	ev_io stdin_watcher;
14	ev_timer timeout_watcher;	17	ev_timer timeout_watcher;
15		18
16	/* called when data readable on stdin */	19	// all watcher callbacks have a similar signature
		20	// this callback is called when data is readable on stdin
17	static void	21	static void
18	stdin_cb (EV_P_ struct ev_io *w, int revents)	22	stdin_cb (EV_P_ ev_io *w, int revents)
19	{	23	{
20	/* puts ("stdin ready"); */	24	puts ("stdin ready");
21	ev_io_stop (EV_A_ w); /* just a syntax example */	25	// for one-shot events, one must manually stop the watcher
22	ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */	26	// with its corresponding stop function.
		27	ev_io_stop (EV_A_ w);
		28
		29	// this causes all nested ev_loop's to stop iterating
		30	ev_unloop (EV_A_ EVUNLOOP_ALL);
23	}	31	}
24		32
		33	// another callback, this time for a time-out
25	static void	34	static void
26	timeout_cb (EV_P_ struct ev_timer *w, int revents)	35	timeout_cb (EV_P_ ev_timer *w, int revents)
27	{	36	{
28	/* puts ("timeout"); */	37	puts ("timeout");
29	ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */	38	// this causes the innermost ev_loop to stop iterating
		39	ev_unloop (EV_A_ EVUNLOOP_ONE);
30	}	40	}
31		41
32	int	42	int
33	main (void)	43	main (void)
34	{	44	{
		45	// use the default event loop unless you have special needs
35	struct ev_loop *loop = ev_default_loop (0);	46	ev_loop *loop = ev_default_loop (0);
36		47
37	/* initialise an io watcher, then start it */	48	// initialise an io watcher, then start it
		49	// this one will watch for stdin to become readable
38	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);	50	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
39	ev_io_start (loop, &stdin_watcher);	51	ev_io_start (loop, &stdin_watcher);
40		52
		53	// initialise a timer watcher, then start it
41	/* simple non-repeating 5.5 second timeout */	54	// simple non-repeating 5.5 second timeout
42	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);	55	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
43	ev_timer_start (loop, &timeout_watcher);	56	ev_timer_start (loop, &timeout_watcher);
44		57
45	/* loop till timeout or data ready */	58	// now wait for events to arrive
46	ev_loop (loop, 0);	59	ev_loop (loop, 0);
47		60
		61	// unloop was called, so exit
48	return 0;	62	return 0;
49	}	63	}
50		64
51	=head1 DESCRIPTION	65	=head1 DESCRIPTION
52		66
		67	The newest version of this document is also available as an html-formatted
		68	web page you might find easier to navigate when reading it for the first
		69	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		70
53	Libev is an event loop: you register interest in certain events (such as a	71	Libev is an event loop: you register interest in certain events (such as a
54	file descriptor being readable or a timeout occuring), and it will manage	72	file descriptor being readable or a timeout occurring), and it will manage
55	these event sources and provide your program with events.	73	these event sources and provide your program with events.
56		74
57	To do this, it must take more or less complete control over your process	75	To do this, it must take more or less complete control over your process
58	(or thread) by executing the I<event loop> handler, and will then	76	(or thread) by executing the I<event loop> handler, and will then
59	communicate events via a callback mechanism.	77	communicate events via a callback mechanism.
…		…
61	You register interest in certain events by registering so-called I<event	79	You register interest in certain events by registering so-called I<event
62	watchers>, which are relatively small C structures you initialise with the	80	watchers>, which are relatively small C structures you initialise with the
63	details of the event, and then hand it over to libev by I<starting> the	81	details of the event, and then hand it over to libev by I<starting> the
64	watcher.	82	watcher.
65		83
66	=head1 FEATURES	84	=head2 FEATURES
67		85
68	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	86	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
69	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	87	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
70	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	88	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
71	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	89	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
…		…
78		96
79	It also is quite fast (see this	97	It also is quite fast (see this
80	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent	98	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
81	for example).	99	for example).
82		100
83	=head1 CONVENTIONS	101	=head2 CONVENTIONS
84		102
85	Libev is very configurable. In this manual the default configuration will	103	Libev is very configurable. In this manual the default (and most common)
86	be described, which supports multiple event loops. For more info about	104	configuration will be described, which supports multiple event loops. For
87	various configuration options please have a look at B<EMBED> section in	105	more info about various configuration options please have a look at
88	this manual. If libev was configured without support for multiple event	106	B<EMBED> section in this manual. If libev was configured without support
89	loops, then all functions taking an initial argument of name C<loop>	107	for multiple event loops, then all functions taking an initial argument of
90	(which is always of type C<struct ev_loop *>) will not have this argument.	108	name C<loop> (which is always of type C<ev_loop *>) will not have
		109	this argument.
91		110
92	=head1 TIME REPRESENTATION	111	=head2 TIME REPRESENTATION
93		112
94	Libev represents time as a single floating point number, representing the	113	Libev represents time as a single floating point number, representing the
95	(fractional) number of seconds since the (POSIX) epoch (somewhere near	114	(fractional) number of seconds since the (POSIX) epoch (somewhere near
96	the beginning of 1970, details are complicated, don't ask). This type is	115	the beginning of 1970, details are complicated, don't ask). This type is
97	called C<ev_tstamp>, which is what you should use too. It usually aliases	116	called C<ev_tstamp>, which is what you should use too. It usually aliases
98	to the C<double> type in C, and when you need to do any calculations on	117	to the C<double> type in C, and when you need to do any calculations on
99	it, you should treat it as such.	118	it, you should treat it as some floating point value. Unlike the name
		119	component C<stamp> might indicate, it is also used for time differences
		120	throughout libev.
		121
		122	=head1 ERROR HANDLING
		123
		124	Libev knows three classes of errors: operating system errors, usage errors
		125	and internal errors (bugs).
		126
		127	When libev catches an operating system error it cannot handle (for example
		128	a system call indicating a condition libev cannot fix), it calls the callback
		129	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		130	abort. The default is to print a diagnostic message and to call C<abort
		131	()>.
		132
		133	When libev detects a usage error such as a negative timer interval, then
		134	it will print a diagnostic message and abort (via the C<assert> mechanism,
		135	so C<NDEBUG> will disable this checking): these are programming errors in
		136	the libev caller and need to be fixed there.
		137
		138	Libev also has a few internal error-checking C<assert>ions, and also has
		139	extensive consistency checking code. These do not trigger under normal
		140	circumstances, as they indicate either a bug in libev or worse.
		141
100		142
101	=head1 GLOBAL FUNCTIONS	143	=head1 GLOBAL FUNCTIONS
102		144
103	These functions can be called anytime, even before initialising the	145	These functions can be called anytime, even before initialising the
104	library in any way.	146	library in any way.
…		…
109		151
110	Returns the current time as libev would use it. Please note that the	152	Returns the current time as libev would use it. Please note that the
111	C<ev_now> function is usually faster and also often returns the timestamp	153	C<ev_now> function is usually faster and also often returns the timestamp
112	you actually want to know.	154	you actually want to know.
113		155
		156	=item ev_sleep (ev_tstamp interval)
		157
		158	Sleep for the given interval: The current thread will be blocked until
		159	either it is interrupted or the given time interval has passed. Basically
		160	this is a sub-second-resolution C<sleep ()>.
		161
114	=item int ev_version_major ()	162	=item int ev_version_major ()
115		163
116	=item int ev_version_minor ()	164	=item int ev_version_minor ()
117		165
118	You can find out the major and minor version numbers of the library	166	You can find out the major and minor ABI version numbers of the library
119	you linked against by calling the functions C<ev_version_major> and	167	you linked against by calling the functions C<ev_version_major> and
120	C<ev_version_minor>. If you want, you can compare against the global	168	C<ev_version_minor>. If you want, you can compare against the global
121	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the	169	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
122	version of the library your program was compiled against.	170	version of the library your program was compiled against.
123		171
		172	These version numbers refer to the ABI version of the library, not the
		173	release version.
		174
124	Usually, it's a good idea to terminate if the major versions mismatch,	175	Usually, it's a good idea to terminate if the major versions mismatch,
125	as this indicates an incompatible change. Minor versions are usually	176	as this indicates an incompatible change. Minor versions are usually
126	compatible to older versions, so a larger minor version alone is usually	177	compatible to older versions, so a larger minor version alone is usually
127	not a problem.	178	not a problem.
128		179
129	Example: Make sure we haven't accidentally been linked against the wrong	180	Example: Make sure we haven't accidentally been linked against the wrong
130	version.	181	version.
131		182
132	assert (("libev version mismatch",	183	assert (("libev version mismatch",
133	ev_version_major () == EV_VERSION_MAJOR	184	ev_version_major () == EV_VERSION_MAJOR
134	&& ev_version_minor () >= EV_VERSION_MINOR));	185	&& ev_version_minor () >= EV_VERSION_MINOR));
135		186
136	=item unsigned int ev_supported_backends ()	187	=item unsigned int ev_supported_backends ()
137		188
138	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	189	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
139	value) compiled into this binary of libev (independent of their	190	value) compiled into this binary of libev (independent of their
…		…
141	a description of the set values.	192	a description of the set values.
142		193
143	Example: make sure we have the epoll method, because yeah this is cool and	194	Example: make sure we have the epoll method, because yeah this is cool and
144	a must have and can we have a torrent of it please!!!11	195	a must have and can we have a torrent of it please!!!11
145		196
146	assert (("sorry, no epoll, no sex",	197	assert (("sorry, no epoll, no sex",
147	ev_supported_backends () & EVBACKEND_EPOLL));	198	ev_supported_backends () & EVBACKEND_EPOLL));
148		199
149	=item unsigned int ev_recommended_backends ()	200	=item unsigned int ev_recommended_backends ()
150		201
151	Return the set of all backends compiled into this binary of libev and also	202	Return the set of all backends compiled into this binary of libev and also
152	recommended for this platform. This set is often smaller than the one	203	recommended for this platform. This set is often smaller than the one
153	returned by C<ev_supported_backends>, as for example kqueue is broken on	204	returned by C<ev_supported_backends>, as for example kqueue is broken on
154	most BSDs and will not be autodetected unless you explicitly request it	205	most BSDs and will not be auto-detected unless you explicitly request it
155	(assuming you know what you are doing). This is the set of backends that	206	(assuming you know what you are doing). This is the set of backends that
156	libev will probe for if you specify no backends explicitly.	207	libev will probe for if you specify no backends explicitly.
157		208
158	=item unsigned int ev_embeddable_backends ()	209	=item unsigned int ev_embeddable_backends ()
159		210
…		…
163	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	214	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
164	recommended ones.	215	recommended ones.
165		216
166	See the description of C<ev_embed> watchers for more info.	217	See the description of C<ev_embed> watchers for more info.
167		218
168	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	219	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
169		220
170	Sets the allocation function to use (the prototype is similar - the	221	Sets the allocation function to use (the prototype is similar - the
171	semantics is identical - to the realloc C function). It is used to	222	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
172	allocate and free memory (no surprises here). If it returns zero when	223	used to allocate and free memory (no surprises here). If it returns zero
173	memory needs to be allocated, the library might abort or take some	224	when memory needs to be allocated (C<size != 0>), the library might abort
174	potentially destructive action. The default is your system realloc	225	or take some potentially destructive action.
175	function.	226
		227	Since some systems (at least OpenBSD and Darwin) fail to implement
		228	correct C<realloc> semantics, libev will use a wrapper around the system
		229	C<realloc> and C<free> functions by default.
176		230
177	You could override this function in high-availability programs to, say,	231	You could override this function in high-availability programs to, say,
178	free some memory if it cannot allocate memory, to use a special allocator,	232	free some memory if it cannot allocate memory, to use a special allocator,
179	or even to sleep a while and retry until some memory is available.	233	or even to sleep a while and retry until some memory is available.
180		234
181	Example: Replace the libev allocator with one that waits a bit and then	235	Example: Replace the libev allocator with one that waits a bit and then
182	retries).	236	retries (example requires a standards-compliant C<realloc>).
183		237
184	static void *	238	static void *
185	persistent_realloc (void *ptr, size_t size)	239	persistent_realloc (void *ptr, size_t size)
186	{	240	{
187	for (;;)	241	for (;;)
…		…
196	}	250	}
197		251
198	...	252	...
199	ev_set_allocator (persistent_realloc);	253	ev_set_allocator (persistent_realloc);
200		254
201	=item ev_set_syserr_cb (void (*cb)(const char *msg));	255	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
202		256
203	Set the callback function to call on a retryable syscall error (such	257	Set the callback function to call on a retryable system call error (such
204	as failed select, poll, epoll_wait). The message is a printable string	258	as failed select, poll, epoll_wait). The message is a printable string
205	indicating the system call or subsystem causing the problem. If this	259	indicating the system call or subsystem causing the problem. If this
206	callback is set, then libev will expect it to remedy the sitution, no	260	callback is set, then libev will expect it to remedy the situation, no
207	matter what, when it returns. That is, libev will generally retry the	261	matter what, when it returns. That is, libev will generally retry the
208	requested operation, or, if the condition doesn't go away, do bad stuff	262	requested operation, or, if the condition doesn't go away, do bad stuff
209	(such as abort).	263	(such as abort).
210		264
211	Example: This is basically the same thing that libev does internally, too.	265	Example: This is basically the same thing that libev does internally, too.
…		…
222		276
223	=back	277	=back
224		278
225	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	279	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
226		280
227	An event loop is described by a C<struct ev_loop *>. The library knows two	281	An event loop is described by a C<struct ev_loop *> (the C<struct>
228	types of such loops, the I<default> loop, which supports signals and child	282	is I<not> optional in this case, as there is also an C<ev_loop>
229	events, and dynamically created loops which do not.	283	I<function>).
230		284
231	If you use threads, a common model is to run the default event loop	285	The library knows two types of such loops, the I<default> loop, which
232	in your main thread (or in a separate thread) and for each thread you	286	supports signals and child events, and dynamically created loops which do
233	create, you also create another event loop. Libev itself does no locking	287	not.
234	whatsoever, so if you mix calls to the same event loop in different
235	threads, make sure you lock (this is usually a bad idea, though, even if
236	done correctly, because it's hideous and inefficient).
237		288
238	=over 4	289	=over 4
239		290
240	=item struct ev_loop *ev_default_loop (unsigned int flags)	291	=item struct ev_loop *ev_default_loop (unsigned int flags)
241		292
…		…
245	flags. If that is troubling you, check C<ev_backend ()> afterwards).	296	flags. If that is troubling you, check C<ev_backend ()> afterwards).
246		297
247	If you don't know what event loop to use, use the one returned from this	298	If you don't know what event loop to use, use the one returned from this
248	function.	299	function.
249		300
		301	Note that this function is I<not> thread-safe, so if you want to use it
		302	from multiple threads, you have to lock (note also that this is unlikely,
		303	as loops cannot bes hared easily between threads anyway).
		304
		305	The default loop is the only loop that can handle C<ev_signal> and
		306	C<ev_child> watchers, and to do this, it always registers a handler
		307	for C<SIGCHLD>. If this is a problem for your application you can either
		308	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
		309	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
		310	C<ev_default_init>.
		311
250	The flags argument can be used to specify special behaviour or specific	312	The flags argument can be used to specify special behaviour or specific
251	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	313	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
252		314
253	The following flags are supported:	315	The following flags are supported:
254		316
…		…
259	The default flags value. Use this if you have no clue (it's the right	321	The default flags value. Use this if you have no clue (it's the right
260	thing, believe me).	322	thing, believe me).
261		323
262	=item C<EVFLAG_NOENV>	324	=item C<EVFLAG_NOENV>
263		325
264	If this flag bit is ored into the flag value (or the program runs setuid	326	If this flag bit is or'ed into the flag value (or the program runs setuid
265	or setgid) then libev will I<not> look at the environment variable	327	or setgid) then libev will I<not> look at the environment variable
266	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	328	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
267	override the flags completely if it is found in the environment. This is	329	override the flags completely if it is found in the environment. This is
268	useful to try out specific backends to test their performance, or to work	330	useful to try out specific backends to test their performance, or to work
269	around bugs.	331	around bugs.
…		…
275	enabling this flag.	337	enabling this flag.
276		338
277	This works by calling C<getpid ()> on every iteration of the loop,	339	This works by calling C<getpid ()> on every iteration of the loop,
278	and thus this might slow down your event loop if you do a lot of loop	340	and thus this might slow down your event loop if you do a lot of loop
279	iterations and little real work, but is usually not noticeable (on my	341	iterations and little real work, but is usually not noticeable (on my
280	Linux system for example, C<getpid> is actually a simple 5-insn sequence	342	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
281	without a syscall and thus I<very> fast, but my Linux system also has	343	without a system call and thus I<very> fast, but my GNU/Linux system also has
282	C<pthread_atfork> which is even faster).	344	C<pthread_atfork> which is even faster).
283		345
284	The big advantage of this flag is that you can forget about fork (and	346	The big advantage of this flag is that you can forget about fork (and
285	forget about forgetting to tell libev about forking) when you use this	347	forget about forgetting to tell libev about forking) when you use this
286	flag.	348	flag.
287		349
288	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>	350	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
289	environment variable.	351	environment variable.
290		352
291	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	353	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
292		354
293	This is your standard select(2) backend. Not I<completely> standard, as	355	This is your standard select(2) backend. Not I<completely> standard, as
294	libev tries to roll its own fd_set with no limits on the number of fds,	356	libev tries to roll its own fd_set with no limits on the number of fds,
295	but if that fails, expect a fairly low limit on the number of fds when	357	but if that fails, expect a fairly low limit on the number of fds when
296	using this backend. It doesn't scale too well (O(highest_fd)), but its usually	358	using this backend. It doesn't scale too well (O(highest_fd)), but its
297	the fastest backend for a low number of fds.	359	usually the fastest backend for a low number of (low-numbered :) fds.
		360
		361	To get good performance out of this backend you need a high amount of
		362	parallelism (most of the file descriptors should be busy). If you are
		363	writing a server, you should C<accept ()> in a loop to accept as many
		364	connections as possible during one iteration. You might also want to have
		365	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		366	readiness notifications you get per iteration.
		367
		368	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		369	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		370	C<exceptfds> set on that platform).
298		371
299	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	372	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
300		373
301	And this is your standard poll(2) backend. It's more complicated than	374	And this is your standard poll(2) backend. It's more complicated
302	select, but handles sparse fds better and has no artificial limit on the	375	than select, but handles sparse fds better and has no artificial
303	number of fds you can use (except it will slow down considerably with a	376	limit on the number of fds you can use (except it will slow down
304	lot of inactive fds). It scales similarly to select, i.e. O(total_fds).	377	considerably with a lot of inactive fds). It scales similarly to select,
		378	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		379	performance tips.
		380
		381	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		382	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
305		383
306	=item C<EVBACKEND_EPOLL> (value 4, Linux)	384	=item C<EVBACKEND_EPOLL> (value 4, Linux)
307		385
308	For few fds, this backend is a bit little slower than poll and select,	386	For few fds, this backend is a bit little slower than poll and select,
309	but it scales phenomenally better. While poll and select usually scale like	387	but it scales phenomenally better. While poll and select usually scale
310	O(total_fds) where n is the total number of fds (or the highest fd), epoll scales	388	like O(total_fds) where n is the total number of fds (or the highest fd),
311	either O(1) or O(active_fds).	389	epoll scales either O(1) or O(active_fds).
312		390
		391	The epoll syscalls are the most misdesigned of the more advanced
		392	event mechanisms: probelsm include silently dropping events in some
		393	hard-to-detect cases, requiring a system call per fd change, no fork
		394	support, problems with dup and so on.
		395
		396	Epoll is also notoriously buggy - embedding epoll fds should work, but
		397	of course doesn't, and epoll just loves to report events for totally
		398	I<different> file descriptors (even already closed ones, so one cannot
		399	even remove them from the set) than registered in the set (especially
		400	on SMP systems). Libev tries to counter these spurious notifications by
		401	employing an additional generation counter and comparing that against the
		402	events to filter out spurious ones.
		403
313	While stopping and starting an I/O watcher in the same iteration will	404	While stopping, setting and starting an I/O watcher in the same iteration
314	result in some caching, there is still a syscall per such incident	405	will result in some caching, there is still a system call per such incident
315	(because the fd could point to a different file description now), so its	406	(because the fd could point to a different file description now), so its
316	best to avoid that. Also, dup()ed file descriptors might not work very	407	best to avoid that. Also, C<dup ()>'ed file descriptors might not work
317	well if you register events for both fds.	408	very well if you register events for both fds.
318		409
319	Please note that epoll sometimes generates spurious notifications, so you	410	Best performance from this backend is achieved by not unregistering all
320	need to use non-blocking I/O or other means to avoid blocking when no data	411	watchers for a file descriptor until it has been closed, if possible,
321	(or space) is available.	412	i.e. keep at least one watcher active per fd at all times. Stopping and
		413	starting a watcher (without re-setting it) also usually doesn't cause
		414	extra overhead.
		415
		416	While nominally embeddable in other event loops, this feature is broken in
		417	all kernel versions tested so far.
		418
		419	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		420	C<EVBACKEND_POLL>.
322		421
323	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	422	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
324		423
325	Kqueue deserves special mention, as at the time of this writing, it	424	Kqueue deserves special mention, as at the time of this writing, it was
326	was broken on all BSDs except NetBSD (usually it doesn't work with	425	broken on all BSDs except NetBSD (usually it doesn't work reliably with
327	anything but sockets and pipes, except on Darwin, where of course its	426	anything but sockets and pipes, except on Darwin, where of course it's
328	completely useless). For this reason its not being "autodetected"	427	completely useless). For this reason it's not being "auto-detected" unless
329	unless you explicitly specify it explicitly in the flags (i.e. using	428	you explicitly specify it in the flags (i.e. using C<EVBACKEND_KQUEUE>) or
330	C<EVBACKEND_KQUEUE>).	429	libev was compiled on a known-to-be-good (-enough) system like NetBSD.
		430
		431	You still can embed kqueue into a normal poll or select backend and use it
		432	only for sockets (after having made sure that sockets work with kqueue on
		433	the target platform). See C<ev_embed> watchers for more info.
331		434
332	It scales in the same way as the epoll backend, but the interface to the	435	It scales in the same way as the epoll backend, but the interface to the
333	kernel is more efficient (which says nothing about its actual speed, of	436	kernel is more efficient (which says nothing about its actual speed, of
334	course). While starting and stopping an I/O watcher does not cause an	437	course). While stopping, setting and starting an I/O watcher does never
335	extra syscall as with epoll, it still adds up to four event changes per	438	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
336	incident, so its best to avoid that.	439	two event changes per incident. Support for C<fork ()> is very bad and it
		440	drops fds silently in similarly hard-to-detect cases.
		441
		442	This backend usually performs well under most conditions.
		443
		444	While nominally embeddable in other event loops, this doesn't work
		445	everywhere, so you might need to test for this. And since it is broken
		446	almost everywhere, you should only use it when you have a lot of sockets
		447	(for which it usually works), by embedding it into another event loop
		448	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and, did I mention it,
		449	using it only for sockets.
		450
		451	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		452	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		453	C<NOTE_EOF>.
337		454
338	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	455	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
339		456
340	This is not implemented yet (and might never be).	457	This is not implemented yet (and might never be, unless you send me an
		458	implementation). According to reports, C</dev/poll> only supports sockets
		459	and is not embeddable, which would limit the usefulness of this backend
		460	immensely.
341		461
342	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	462	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
343		463
344	This uses the Solaris 10 port mechanism. As with everything on Solaris,	464	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
345	it's really slow, but it still scales very well (O(active_fds)).	465	it's really slow, but it still scales very well (O(active_fds)).
346		466
347	Please note that solaris ports can result in a lot of spurious	467	Please note that Solaris event ports can deliver a lot of spurious
348	notifications, so you need to use non-blocking I/O or other means to avoid	468	notifications, so you need to use non-blocking I/O or other means to avoid
349	blocking when no data (or space) is available.	469	blocking when no data (or space) is available.
		470
		471	While this backend scales well, it requires one system call per active
		472	file descriptor per loop iteration. For small and medium numbers of file
		473	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		474	might perform better.
		475
		476	On the positive side, with the exception of the spurious readiness
		477	notifications, this backend actually performed fully to specification
		478	in all tests and is fully embeddable, which is a rare feat among the
		479	OS-specific backends.
		480
		481	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		482	C<EVBACKEND_POLL>.
350		483
351	=item C<EVBACKEND_ALL>	484	=item C<EVBACKEND_ALL>
352		485
353	Try all backends (even potentially broken ones that wouldn't be tried	486	Try all backends (even potentially broken ones that wouldn't be tried
354	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	487	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
355	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	488	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
356		489
		490	It is definitely not recommended to use this flag.
		491
357	=back	492	=back
358		493
359	If one or more of these are ored into the flags value, then only these	494	If one or more of these are or'ed into the flags value, then only these
360	backends will be tried (in the reverse order as given here). If none are	495	backends will be tried (in the reverse order as listed here). If none are
361	specified, most compiled-in backend will be tried, usually in reverse	496	specified, all backends in C<ev_recommended_backends ()> will be tried.
362	order of their flag values :)
363		497
364	The most typical usage is like this:	498	Example: This is the most typical usage.
365		499
366	if (!ev_default_loop (0))	500	if (!ev_default_loop (0))
367	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	501	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
368		502
369	Restrict libev to the select and poll backends, and do not allow	503	Example: Restrict libev to the select and poll backends, and do not allow
370	environment settings to be taken into account:	504	environment settings to be taken into account:
371		505
372	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	506	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
373		507
374	Use whatever libev has to offer, but make sure that kqueue is used if	508	Example: Use whatever libev has to offer, but make sure that kqueue is
375	available (warning, breaks stuff, best use only with your own private	509	used if available (warning, breaks stuff, best use only with your own
376	event loop and only if you know the OS supports your types of fds):	510	private event loop and only if you know the OS supports your types of
		511	fds):
377		512
378	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	513	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
379		514
380	=item struct ev_loop *ev_loop_new (unsigned int flags)	515	=item struct ev_loop *ev_loop_new (unsigned int flags)
381		516
382	Similar to C<ev_default_loop>, but always creates a new event loop that is	517	Similar to C<ev_default_loop>, but always creates a new event loop that is
383	always distinct from the default loop. Unlike the default loop, it cannot	518	always distinct from the default loop. Unlike the default loop, it cannot
384	handle signal and child watchers, and attempts to do so will be greeted by	519	handle signal and child watchers, and attempts to do so will be greeted by
385	undefined behaviour (or a failed assertion if assertions are enabled).	520	undefined behaviour (or a failed assertion if assertions are enabled).
386		521
		522	Note that this function I<is> thread-safe, and the recommended way to use
		523	libev with threads is indeed to create one loop per thread, and using the
		524	default loop in the "main" or "initial" thread.
		525
387	Example: Try to create a event loop that uses epoll and nothing else.	526	Example: Try to create a event loop that uses epoll and nothing else.
388		527
389	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	528	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
390	if (!epoller)	529	if (!epoller)
391	fatal ("no epoll found here, maybe it hides under your chair");	530	fatal ("no epoll found here, maybe it hides under your chair");
392		531
393	=item ev_default_destroy ()	532	=item ev_default_destroy ()
394		533
395	Destroys the default loop again (frees all memory and kernel state	534	Destroys the default loop again (frees all memory and kernel state
396	etc.). None of the active event watchers will be stopped in the normal	535	etc.). None of the active event watchers will be stopped in the normal
397	sense, so e.g. C<ev_is_active> might still return true. It is your	536	sense, so e.g. C<ev_is_active> might still return true. It is your
398	responsibility to either stop all watchers cleanly yoursef I<before>	537	responsibility to either stop all watchers cleanly yourself I<before>
399	calling this function, or cope with the fact afterwards (which is usually	538	calling this function, or cope with the fact afterwards (which is usually
400	the easiest thing, youc na just ignore the watchers and/or C<free ()> them	539	the easiest thing, you can just ignore the watchers and/or C<free ()> them
401	for example).	540	for example).
		541
		542	Note that certain global state, such as signal state (and installed signal
		543	handlers), will not be freed by this function, and related watchers (such
		544	as signal and child watchers) would need to be stopped manually.
		545
		546	In general it is not advisable to call this function except in the
		547	rare occasion where you really need to free e.g. the signal handling
		548	pipe fds. If you need dynamically allocated loops it is better to use
		549	C<ev_loop_new> and C<ev_loop_destroy>).
402		550
403	=item ev_loop_destroy (loop)	551	=item ev_loop_destroy (loop)
404		552
405	Like C<ev_default_destroy>, but destroys an event loop created by an	553	Like C<ev_default_destroy>, but destroys an event loop created by an
406	earlier call to C<ev_loop_new>.	554	earlier call to C<ev_loop_new>.
407		555
408	=item ev_default_fork ()	556	=item ev_default_fork ()
409		557
		558	This function sets a flag that causes subsequent C<ev_loop> iterations
410	This function reinitialises the kernel state for backends that have	559	to reinitialise the kernel state for backends that have one. Despite the
411	one. Despite the name, you can call it anytime, but it makes most sense	560	name, you can call it anytime, but it makes most sense after forking, in
412	after forking, in either the parent or child process (or both, but that	561	the child process (or both child and parent, but that again makes little
413	again makes little sense).	562	sense). You I<must> call it in the child before using any of the libev
		563	functions, and it will only take effect at the next C<ev_loop> iteration.
414		564
415	You I<must> call this function in the child process after forking if and	565	On the other hand, you only need to call this function in the child
416	only if you want to use the event library in both processes. If you just	566	process if and only if you want to use the event library in the child. If
417	fork+exec, you don't have to call it.	567	you just fork+exec, you don't have to call it at all.
418		568
419	The function itself is quite fast and it's usually not a problem to call	569	The function itself is quite fast and it's usually not a problem to call
420	it just in case after a fork. To make this easy, the function will fit in	570	it just in case after a fork. To make this easy, the function will fit in
421	quite nicely into a call to C<pthread_atfork>:	571	quite nicely into a call to C<pthread_atfork>:
422		572
423	pthread_atfork (0, 0, ev_default_fork);	573	pthread_atfork (0, 0, ev_default_fork);
424		574
425	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
426	without calling this function, so if you force one of those backends you
427	do not need to care.
428
429	=item ev_loop_fork (loop)	575	=item ev_loop_fork (loop)
430		576
431	Like C<ev_default_fork>, but acts on an event loop created by	577	Like C<ev_default_fork>, but acts on an event loop created by
432	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	578	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
433	after fork, and how you do this is entirely your own problem.	579	after fork that you want to re-use in the child, and how you do this is
		580	entirely your own problem.
		581
		582	=item int ev_is_default_loop (loop)
		583
		584	Returns true when the given loop is, in fact, the default loop, and false
		585	otherwise.
434		586
435	=item unsigned int ev_loop_count (loop)	587	=item unsigned int ev_loop_count (loop)
436		588
437	Returns the count of loop iterations for the loop, which is identical to	589	Returns the count of loop iterations for the loop, which is identical to
438	the number of times libev did poll for new events. It starts at C<0> and	590	the number of times libev did poll for new events. It starts at C<0> and
…		…
451		603
452	Returns the current "event loop time", which is the time the event loop	604	Returns the current "event loop time", which is the time the event loop
453	received events and started processing them. This timestamp does not	605	received events and started processing them. This timestamp does not
454	change as long as callbacks are being processed, and this is also the base	606	change as long as callbacks are being processed, and this is also the base
455	time used for relative timers. You can treat it as the timestamp of the	607	time used for relative timers. You can treat it as the timestamp of the
456	event occuring (or more correctly, libev finding out about it).	608	event occurring (or more correctly, libev finding out about it).
		609
		610	=item ev_now_update (loop)
		611
		612	Establishes the current time by querying the kernel, updating the time
		613	returned by C<ev_now ()> in the progress. This is a costly operation and
		614	is usually done automatically within C<ev_loop ()>.
		615
		616	This function is rarely useful, but when some event callback runs for a
		617	very long time without entering the event loop, updating libev's idea of
		618	the current time is a good idea.
		619
		620	See also "The special problem of time updates" in the C<ev_timer> section.
457		621
458	=item ev_loop (loop, int flags)	622	=item ev_loop (loop, int flags)
459		623
460	Finally, this is it, the event handler. This function usually is called	624	Finally, this is it, the event handler. This function usually is called
461	after you initialised all your watchers and you want to start handling	625	after you initialised all your watchers and you want to start handling
…		…
464	If the flags argument is specified as C<0>, it will not return until	628	If the flags argument is specified as C<0>, it will not return until
465	either no event watchers are active anymore or C<ev_unloop> was called.	629	either no event watchers are active anymore or C<ev_unloop> was called.
466		630
467	Please note that an explicit C<ev_unloop> is usually better than	631	Please note that an explicit C<ev_unloop> is usually better than
468	relying on all watchers to be stopped when deciding when a program has	632	relying on all watchers to be stopped when deciding when a program has
469	finished (especially in interactive programs), but having a program that	633	finished (especially in interactive programs), but having a program
470	automatically loops as long as it has to and no longer by virtue of	634	that automatically loops as long as it has to and no longer by virtue
471	relying on its watchers stopping correctly is a thing of beauty.	635	of relying on its watchers stopping correctly, that is truly a thing of
		636	beauty.
472		637
473	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	638	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
474	those events and any outstanding ones, but will not block your process in	639	those events and any already outstanding ones, but will not block your
475	case there are no events and will return after one iteration of the loop.	640	process in case there are no events and will return after one iteration of
		641	the loop.
476		642
477	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	643	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
478	neccessary) and will handle those and any outstanding ones. It will block	644	necessary) and will handle those and any already outstanding ones. It
479	your process until at least one new event arrives, and will return after	645	will block your process until at least one new event arrives (which could
480	one iteration of the loop. This is useful if you are waiting for some	646	be an event internal to libev itself, so there is no guarentee that a
481	external event in conjunction with something not expressible using other	647	user-registered callback will be called), and will return after one
		648	iteration of the loop.
		649
		650	This is useful if you are waiting for some external event in conjunction
		651	with something not expressible using other libev watchers (i.e. "roll your
482	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	652	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
483	usually a better approach for this kind of thing.	653	usually a better approach for this kind of thing.
484		654
485	Here are the gory details of what C<ev_loop> does:	655	Here are the gory details of what C<ev_loop> does:
486		656
487	* If there are no active watchers (reference count is zero), return.	657	- Before the first iteration, call any pending watchers.
488	- Queue prepare watchers and then call all outstanding watchers.	658	* If EVFLAG_FORKCHECK was used, check for a fork.
		659	- If a fork was detected (by any means), queue and call all fork watchers.
		660	- Queue and call all prepare watchers.
489	- If we have been forked, recreate the kernel state.	661	- If we have been forked, detach and recreate the kernel state
		662	as to not disturb the other process.
490	- Update the kernel state with all outstanding changes.	663	- Update the kernel state with all outstanding changes.
491	- Update the "event loop time".	664	- Update the "event loop time" (ev_now ()).
492	- Calculate for how long to block.	665	- Calculate for how long to sleep or block, if at all
		666	(active idle watchers, EVLOOP_NONBLOCK or not having
		667	any active watchers at all will result in not sleeping).
		668	- Sleep if the I/O and timer collect interval say so.
493	- Block the process, waiting for any events.	669	- Block the process, waiting for any events.
494	- Queue all outstanding I/O (fd) events.	670	- Queue all outstanding I/O (fd) events.
495	- Update the "event loop time" and do time jump handling.	671	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
496	- Queue all outstanding timers.	672	- Queue all expired timers.
497	- Queue all outstanding periodics.	673	- Queue all expired periodics.
498	- If no events are pending now, queue all idle watchers.	674	- Unless any events are pending now, queue all idle watchers.
499	- Queue all check watchers.	675	- Queue all check watchers.
500	- Call all queued watchers in reverse order (i.e. check watchers first).	676	- Call all queued watchers in reverse order (i.e. check watchers first).
501	Signals and child watchers are implemented as I/O watchers, and will	677	Signals and child watchers are implemented as I/O watchers, and will
502	be handled here by queueing them when their watcher gets executed.	678	be handled here by queueing them when their watcher gets executed.
503	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	679	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
504	were used, return, otherwise continue with step *.	680	were used, or there are no active watchers, return, otherwise
		681	continue with step *.
505		682
506	Example: Queue some jobs and then loop until no events are outsanding	683	Example: Queue some jobs and then loop until no events are outstanding
507	anymore.	684	anymore.
508		685
509	... queue jobs here, make sure they register event watchers as long	686	... queue jobs here, make sure they register event watchers as long
510	... as they still have work to do (even an idle watcher will do..)	687	... as they still have work to do (even an idle watcher will do..)
511	ev_loop (my_loop, 0);	688	ev_loop (my_loop, 0);
512	... jobs done. yeah!	689	... jobs done or somebody called unloop. yeah!
513		690
514	=item ev_unloop (loop, how)	691	=item ev_unloop (loop, how)
515		692
516	Can be used to make a call to C<ev_loop> return early (but only after it	693	Can be used to make a call to C<ev_loop> return early (but only after it
517	has processed all outstanding events). The C<how> argument must be either	694	has processed all outstanding events). The C<how> argument must be either
518	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	695	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
519	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	696	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
520		697
		698	This "unloop state" will be cleared when entering C<ev_loop> again.
		699
		700	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
		701
521	=item ev_ref (loop)	702	=item ev_ref (loop)
522		703
523	=item ev_unref (loop)	704	=item ev_unref (loop)
524		705
525	Ref/unref can be used to add or remove a reference count on the event	706	Ref/unref can be used to add or remove a reference count on the event
526	loop: Every watcher keeps one reference, and as long as the reference	707	loop: Every watcher keeps one reference, and as long as the reference
527	count is nonzero, C<ev_loop> will not return on its own. If you have	708	count is nonzero, C<ev_loop> will not return on its own.
		709
528	a watcher you never unregister that should not keep C<ev_loop> from	710	If you have a watcher you never unregister that should not keep C<ev_loop>
529	returning, ev_unref() after starting, and ev_ref() before stopping it. For	711	from returning, call ev_unref() after starting, and ev_ref() before
		712	stopping it.
		713
530	example, libev itself uses this for its internal signal pipe: It is not	714	As an example, libev itself uses this for its internal signal pipe: It is
531	visible to the libev user and should not keep C<ev_loop> from exiting if	715	not visible to the libev user and should not keep C<ev_loop> from exiting
532	no event watchers registered by it are active. It is also an excellent	716	if no event watchers registered by it are active. It is also an excellent
533	way to do this for generic recurring timers or from within third-party	717	way to do this for generic recurring timers or from within third-party
534	libraries. Just remember to I<unref after start> and I<ref before stop>.	718	libraries. Just remember to I<unref after start> and I<ref before stop>
		719	(but only if the watcher wasn't active before, or was active before,
		720	respectively).
535		721
536	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	722	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
537	running when nothing else is active.	723	running when nothing else is active.
538		724
539	struct ev_signal exitsig;	725	ev_signal exitsig;
540	ev_signal_init (&exitsig, sig_cb, SIGINT);	726	ev_signal_init (&exitsig, sig_cb, SIGINT);
541	ev_signal_start (loop, &exitsig);	727	ev_signal_start (loop, &exitsig);
542	evf_unref (loop);	728	evf_unref (loop);
543		729
544	Example: For some weird reason, unregister the above signal handler again.	730	Example: For some weird reason, unregister the above signal handler again.
545		731
546	ev_ref (loop);	732	ev_ref (loop);
547	ev_signal_stop (loop, &exitsig);	733	ev_signal_stop (loop, &exitsig);
		734
		735	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		736
		737	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		738
		739	These advanced functions influence the time that libev will spend waiting
		740	for events. Both time intervals are by default C<0>, meaning that libev
		741	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		742	latency.
		743
		744	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		745	allows libev to delay invocation of I/O and timer/periodic callbacks
		746	to increase efficiency of loop iterations (or to increase power-saving
		747	opportunities).
		748
		749	The idea is that sometimes your program runs just fast enough to handle
		750	one (or very few) event(s) per loop iteration. While this makes the
		751	program responsive, it also wastes a lot of CPU time to poll for new
		752	events, especially with backends like C<select ()> which have a high
		753	overhead for the actual polling but can deliver many events at once.
		754
		755	By setting a higher I<io collect interval> you allow libev to spend more
		756	time collecting I/O events, so you can handle more events per iteration,
		757	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		758	C<ev_timer>) will be not affected. Setting this to a non-null value will
		759	introduce an additional C<ev_sleep ()> call into most loop iterations.
		760
		761	Likewise, by setting a higher I<timeout collect interval> you allow libev
		762	to spend more time collecting timeouts, at the expense of increased
		763	latency/jitter/inexactness (the watcher callback will be called
		764	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		765	value will not introduce any overhead in libev.
		766
		767	Many (busy) programs can usually benefit by setting the I/O collect
		768	interval to a value near C<0.1> or so, which is often enough for
		769	interactive servers (of course not for games), likewise for timeouts. It
		770	usually doesn't make much sense to set it to a lower value than C<0.01>,
		771	as this approaches the timing granularity of most systems.
		772
		773	Setting the I<timeout collect interval> can improve the opportunity for
		774	saving power, as the program will "bundle" timer callback invocations that
		775	are "near" in time together, by delaying some, thus reducing the number of
		776	times the process sleeps and wakes up again. Another useful technique to
		777	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		778	they fire on, say, one-second boundaries only.
		779
		780	=item ev_loop_verify (loop)
		781
		782	This function only does something when C<EV_VERIFY> support has been
		783	compiled in, which is the default for non-minimal builds. It tries to go
		784	through all internal structures and checks them for validity. If anything
		785	is found to be inconsistent, it will print an error message to standard
		786	error and call C<abort ()>.
		787
		788	This can be used to catch bugs inside libev itself: under normal
		789	circumstances, this function will never abort as of course libev keeps its
		790	data structures consistent.
548		791
549	=back	792	=back
550		793
551		794
552	=head1 ANATOMY OF A WATCHER	795	=head1 ANATOMY OF A WATCHER
		796
		797	In the following description, uppercase C<TYPE> in names stands for the
		798	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		799	watchers and C<ev_io_start> for I/O watchers.
553		800
554	A watcher is a structure that you create and register to record your	801	A watcher is a structure that you create and register to record your
555	interest in some event. For instance, if you want to wait for STDIN to	802	interest in some event. For instance, if you want to wait for STDIN to
556	become readable, you would create an C<ev_io> watcher for that:	803	become readable, you would create an C<ev_io> watcher for that:
557		804
558	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	805	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
559	{	806	{
560	ev_io_stop (w);	807	ev_io_stop (w);
561	ev_unloop (loop, EVUNLOOP_ALL);	808	ev_unloop (loop, EVUNLOOP_ALL);
562	}	809	}
563		810
564	struct ev_loop *loop = ev_default_loop (0);	811	struct ev_loop *loop = ev_default_loop (0);
		812
565	struct ev_io stdin_watcher;	813	ev_io stdin_watcher;
		814
566	ev_init (&stdin_watcher, my_cb);	815	ev_init (&stdin_watcher, my_cb);
567	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	816	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
568	ev_io_start (loop, &stdin_watcher);	817	ev_io_start (loop, &stdin_watcher);
		818
569	ev_loop (loop, 0);	819	ev_loop (loop, 0);
570		820
571	As you can see, you are responsible for allocating the memory for your	821	As you can see, you are responsible for allocating the memory for your
572	watcher structures (and it is usually a bad idea to do this on the stack,	822	watcher structures (and it is I<usually> a bad idea to do this on the
573	although this can sometimes be quite valid).	823	stack).
		824
		825	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		826	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
574		827
575	Each watcher structure must be initialised by a call to C<ev_init	828	Each watcher structure must be initialised by a call to C<ev_init
576	(watcher *, callback)>, which expects a callback to be provided. This	829	(watcher *, callback)>, which expects a callback to be provided. This
577	callback gets invoked each time the event occurs (or, in the case of io	830	callback gets invoked each time the event occurs (or, in the case of I/O
578	watchers, each time the event loop detects that the file descriptor given	831	watchers, each time the event loop detects that the file descriptor given
579	is readable and/or writable).	832	is readable and/or writable).
580		833
581	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	834	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
582	with arguments specific to this watcher type. There is also a macro	835	macro to configure it, with arguments specific to the watcher type. There
583	to combine initialisation and setting in one call: C<< ev_<type>_init	836	is also a macro to combine initialisation and setting in one call: C<<
584	(watcher *, callback, ...) >>.	837	ev_TYPE_init (watcher *, callback, ...) >>.
585		838
586	To make the watcher actually watch out for events, you have to start it	839	To make the watcher actually watch out for events, you have to start it
587	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	840	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
588	*) >>), and you can stop watching for events at any time by calling the	841	*) >>), and you can stop watching for events at any time by calling the
589	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	842	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
590		843
591	As long as your watcher is active (has been started but not stopped) you	844	As long as your watcher is active (has been started but not stopped) you
592	must not touch the values stored in it. Most specifically you must never	845	must not touch the values stored in it. Most specifically you must never
593	reinitialise it or call its C<set> macro.	846	reinitialise it or call its C<ev_TYPE_set> macro.
594		847
595	Each and every callback receives the event loop pointer as first, the	848	Each and every callback receives the event loop pointer as first, the
596	registered watcher structure as second, and a bitset of received events as	849	registered watcher structure as second, and a bitset of received events as
597	third argument.	850	third argument.
598		851
…		…
652	=item C<EV_FORK>	905	=item C<EV_FORK>
653		906
654	The event loop has been resumed in the child process after fork (see	907	The event loop has been resumed in the child process after fork (see
655	C<ev_fork>).	908	C<ev_fork>).
656		909
		910	=item C<EV_ASYNC>
		911
		912	The given async watcher has been asynchronously notified (see C<ev_async>).
		913
657	=item C<EV_ERROR>	914	=item C<EV_ERROR>
658		915
659	An unspecified error has occured, the watcher has been stopped. This might	916	An unspecified error has occurred, the watcher has been stopped. This might
660	happen because the watcher could not be properly started because libev	917	happen because the watcher could not be properly started because libev
661	ran out of memory, a file descriptor was found to be closed or any other	918	ran out of memory, a file descriptor was found to be closed or any other
		919	problem. Libev considers these application bugs.
		920
662	problem. You best act on it by reporting the problem and somehow coping	921	You best act on it by reporting the problem and somehow coping with the
663	with the watcher being stopped.	922	watcher being stopped. Note that well-written programs should not receive
		923	an error ever, so when your watcher receives it, this usually indicates a
		924	bug in your program.
664		925
665	Libev will usually signal a few "dummy" events together with an error,	926	Libev will usually signal a few "dummy" events together with an error, for
666	for example it might indicate that a fd is readable or writable, and if	927	example it might indicate that a fd is readable or writable, and if your
667	your callbacks is well-written it can just attempt the operation and cope	928	callbacks is well-written it can just attempt the operation and cope with
668	with the error from read() or write(). This will not work in multithreaded	929	the error from read() or write(). This will not work in multi-threaded
669	programs, though, so beware.	930	programs, though, as the fd could already be closed and reused for another
		931	thing, so beware.
670		932
671	=back	933	=back
672		934
673	=head2 GENERIC WATCHER FUNCTIONS	935	=head2 GENERIC WATCHER FUNCTIONS
674
675	In the following description, C<TYPE> stands for the watcher type,
676	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
677		936
678	=over 4	937	=over 4
679		938
680	=item C<ev_init> (ev_TYPE *watcher, callback)	939	=item C<ev_init> (ev_TYPE *watcher, callback)
681		940
…		…
687	which rolls both calls into one.	946	which rolls both calls into one.
688		947
689	You can reinitialise a watcher at any time as long as it has been stopped	948	You can reinitialise a watcher at any time as long as it has been stopped
690	(or never started) and there are no pending events outstanding.	949	(or never started) and there are no pending events outstanding.
691		950
692	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	951	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
693	int revents)>.	952	int revents)>.
		953
		954	Example: Initialise an C<ev_io> watcher in two steps.
		955
		956	ev_io w;
		957	ev_init (&w, my_cb);
		958	ev_io_set (&w, STDIN_FILENO, EV_READ);
694		959
695	=item C<ev_TYPE_set> (ev_TYPE *, [args])	960	=item C<ev_TYPE_set> (ev_TYPE *, [args])
696		961
697	This macro initialises the type-specific parts of a watcher. You need to	962	This macro initialises the type-specific parts of a watcher. You need to
698	call C<ev_init> at least once before you call this macro, but you can	963	call C<ev_init> at least once before you call this macro, but you can
…		…
701	difference to the C<ev_init> macro).	966	difference to the C<ev_init> macro).
702		967
703	Although some watcher types do not have type-specific arguments	968	Although some watcher types do not have type-specific arguments
704	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	969	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
705		970
		971	See C<ev_init>, above, for an example.
		972
706	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	973	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
707		974
708	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	975	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
709	calls into a single call. This is the most convinient method to initialise	976	calls into a single call. This is the most convenient method to initialise
710	a watcher. The same limitations apply, of course.	977	a watcher. The same limitations apply, of course.
		978
		979	Example: Initialise and set an C<ev_io> watcher in one step.
		980
		981	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
711		982
712	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	983	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
713		984
714	Starts (activates) the given watcher. Only active watchers will receive	985	Starts (activates) the given watcher. Only active watchers will receive
715	events. If the watcher is already active nothing will happen.	986	events. If the watcher is already active nothing will happen.
716		987
		988	Example: Start the C<ev_io> watcher that is being abused as example in this
		989	whole section.
		990
		991	ev_io_start (EV_DEFAULT_UC, &w);
		992
717	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	993	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
718		994
719	Stops the given watcher again (if active) and clears the pending	995	Stops the given watcher if active, and clears the pending status (whether
		996	the watcher was active or not).
		997
720	status. It is possible that stopped watchers are pending (for example,	998	It is possible that stopped watchers are pending - for example,
721	non-repeating timers are being stopped when they become pending), but	999	non-repeating timers are being stopped when they become pending - but
722	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1000	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
723	you want to free or reuse the memory used by the watcher it is therefore a	1001	pending. If you want to free or reuse the memory used by the watcher it is
724	good idea to always call its C<ev_TYPE_stop> function.	1002	therefore a good idea to always call its C<ev_TYPE_stop> function.
725		1003
726	=item bool ev_is_active (ev_TYPE *watcher)	1004	=item bool ev_is_active (ev_TYPE *watcher)
727		1005
728	Returns a true value iff the watcher is active (i.e. it has been started	1006	Returns a true value iff the watcher is active (i.e. it has been started
729	and not yet been stopped). As long as a watcher is active you must not modify	1007	and not yet been stopped). As long as a watcher is active you must not modify
…		…
732	=item bool ev_is_pending (ev_TYPE *watcher)	1010	=item bool ev_is_pending (ev_TYPE *watcher)
733		1011
734	Returns a true value iff the watcher is pending, (i.e. it has outstanding	1012	Returns a true value iff the watcher is pending, (i.e. it has outstanding
735	events but its callback has not yet been invoked). As long as a watcher	1013	events but its callback has not yet been invoked). As long as a watcher
736	is pending (but not active) you must not call an init function on it (but	1014	is pending (but not active) you must not call an init function on it (but
737	C<ev_TYPE_set> is safe) and you must make sure the watcher is available to	1015	C<ev_TYPE_set> is safe), you must not change its priority, and you must
738	libev (e.g. you cnanot C<free ()> it).	1016	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1017	it).
739		1018
740	=item callback ev_cb (ev_TYPE *watcher)	1019	=item callback ev_cb (ev_TYPE *watcher)
741		1020
742	Returns the callback currently set on the watcher.	1021	Returns the callback currently set on the watcher.
743		1022
744	=item ev_cb_set (ev_TYPE *watcher, callback)	1023	=item ev_cb_set (ev_TYPE *watcher, callback)
745		1024
746	Change the callback. You can change the callback at virtually any time	1025	Change the callback. You can change the callback at virtually any time
747	(modulo threads).	1026	(modulo threads).
748		1027
		1028	=item ev_set_priority (ev_TYPE *watcher, priority)
		1029
		1030	=item int ev_priority (ev_TYPE *watcher)
		1031
		1032	Set and query the priority of the watcher. The priority is a small
		1033	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1034	(default: C<-2>). Pending watchers with higher priority will be invoked
		1035	before watchers with lower priority, but priority will not keep watchers
		1036	from being executed (except for C<ev_idle> watchers).
		1037
		1038	This means that priorities are I<only> used for ordering callback
		1039	invocation after new events have been received. This is useful, for
		1040	example, to reduce latency after idling, or more often, to bind two
		1041	watchers on the same event and make sure one is called first.
		1042
		1043	If you need to suppress invocation when higher priority events are pending
		1044	you need to look at C<ev_idle> watchers, which provide this functionality.
		1045
		1046	You I<must not> change the priority of a watcher as long as it is active or
		1047	pending.
		1048
		1049	The default priority used by watchers when no priority has been set is
		1050	always C<0>, which is supposed to not be too high and not be too low :).
		1051
		1052	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1053	fine, as long as you do not mind that the priority value you query might
		1054	or might not have been clamped to the valid range.
		1055
		1056	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1057
		1058	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1059	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1060	can deal with that fact, as both are simply passed through to the
		1061	callback.
		1062
		1063	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1064
		1065	If the watcher is pending, this function clears its pending status and
		1066	returns its C<revents> bitset (as if its callback was invoked). If the
		1067	watcher isn't pending it does nothing and returns C<0>.
		1068
		1069	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1070	callback to be invoked, which can be accomplished with this function.
		1071
749	=back	1072	=back
750		1073
751		1074
752	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1075	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
753		1076
754	Each watcher has, by default, a member C<void *data> that you can change	1077	Each watcher has, by default, a member C<void *data> that you can change
755	and read at any time, libev will completely ignore it. This can be used	1078	and read at any time: libev will completely ignore it. This can be used
756	to associate arbitrary data with your watcher. If you need more data and	1079	to associate arbitrary data with your watcher. If you need more data and
757	don't want to allocate memory and store a pointer to it in that data	1080	don't want to allocate memory and store a pointer to it in that data
758	member, you can also "subclass" the watcher type and provide your own	1081	member, you can also "subclass" the watcher type and provide your own
759	data:	1082	data:
760		1083
761	struct my_io	1084	struct my_io
762	{	1085	{
763	struct ev_io io;	1086	ev_io io;
764	int otherfd;	1087	int otherfd;
765	void *somedata;	1088	void *somedata;
766	struct whatever *mostinteresting;	1089	struct whatever *mostinteresting;
767	}	1090	};
		1091
		1092	...
		1093	struct my_io w;
		1094	ev_io_init (&w.io, my_cb, fd, EV_READ);
768		1095
769	And since your callback will be called with a pointer to the watcher, you	1096	And since your callback will be called with a pointer to the watcher, you
770	can cast it back to your own type:	1097	can cast it back to your own type:
771		1098
772	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1099	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
773	{	1100	{
774	struct my_io *w = (struct my_io *)w_;	1101	struct my_io *w = (struct my_io *)w_;
775	...	1102	...
776	}	1103	}
777		1104
778	More interesting and less C-conformant ways of casting your callback type	1105	More interesting and less C-conformant ways of casting your callback type
779	instead have been omitted.	1106	instead have been omitted.
780		1107
781	Another common scenario is having some data structure with multiple	1108	Another common scenario is to use some data structure with multiple
782	watchers:	1109	embedded watchers:
783		1110
784	struct my_biggy	1111	struct my_biggy
785	{	1112	{
786	int some_data;	1113	int some_data;
787	ev_timer t1;	1114	ev_timer t1;
788	ev_timer t2;	1115	ev_timer t2;
789	}	1116	}
790		1117
791	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1118	In this case getting the pointer to C<my_biggy> is a bit more
792	you need to use C<offsetof>:	1119	complicated: Either you store the address of your C<my_biggy> struct
		1120	in the C<data> member of the watcher (for woozies), or you need to use
		1121	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1122	programmers):
793		1123
794	#include <stddef.h>	1124	#include <stddef.h>
795		1125
796	static void	1126	static void
797	t1_cb (EV_P_ struct ev_timer *w, int revents)	1127	t1_cb (EV_P_ ev_timer *w, int revents)
798	{	1128	{
799	struct my_biggy big = (struct my_biggy *	1129	struct my_biggy big = (struct my_biggy *
800	(((char *)w) - offsetof (struct my_biggy, t1));	1130	(((char *)w) - offsetof (struct my_biggy, t1));
801	}	1131	}
802		1132
803	static void	1133	static void
804	t2_cb (EV_P_ struct ev_timer *w, int revents)	1134	t2_cb (EV_P_ ev_timer *w, int revents)
805	{	1135	{
806	struct my_biggy big = (struct my_biggy *	1136	struct my_biggy big = (struct my_biggy *
807	(((char *)w) - offsetof (struct my_biggy, t2));	1137	(((char *)w) - offsetof (struct my_biggy, t2));
808	}	1138	}
809		1139
810		1140
811	=head1 WATCHER TYPES	1141	=head1 WATCHER TYPES
812		1142
813	This section describes each watcher in detail, but will not repeat	1143	This section describes each watcher in detail, but will not repeat
…		…
837	In general you can register as many read and/or write event watchers per	1167	In general you can register as many read and/or write event watchers per
838	fd as you want (as long as you don't confuse yourself). Setting all file	1168	fd as you want (as long as you don't confuse yourself). Setting all file
839	descriptors to non-blocking mode is also usually a good idea (but not	1169	descriptors to non-blocking mode is also usually a good idea (but not
840	required if you know what you are doing).	1170	required if you know what you are doing).
841		1171
842	You have to be careful with dup'ed file descriptors, though. Some backends	1172	If you cannot use non-blocking mode, then force the use of a
843	(the linux epoll backend is a notable example) cannot handle dup'ed file	1173	known-to-be-good backend (at the time of this writing, this includes only
844	descriptors correctly if you register interest in two or more fds pointing	1174	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>).
845	to the same underlying file/socket/etc. description (that is, they share
846	the same underlying "file open").
847
848	If you must do this, then force the use of a known-to-be-good backend
849	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
850	C<EVBACKEND_POLL>).
851		1175
852	Another thing you have to watch out for is that it is quite easy to	1176	Another thing you have to watch out for is that it is quite easy to
853	receive "spurious" readyness notifications, that is your callback might	1177	receive "spurious" readiness notifications, that is your callback might
854	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1178	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
855	because there is no data. Not only are some backends known to create a	1179	because there is no data. Not only are some backends known to create a
856	lot of those (for example solaris ports), it is very easy to get into	1180	lot of those (for example Solaris ports), it is very easy to get into
857	this situation even with a relatively standard program structure. Thus	1181	this situation even with a relatively standard program structure. Thus
858	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1182	it is best to always use non-blocking I/O: An extra C<read>(2) returning
859	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1183	C<EAGAIN> is far preferable to a program hanging until some data arrives.
860		1184
861	If you cannot run the fd in non-blocking mode (for example you should not	1185	If you cannot run the fd in non-blocking mode (for example you should
862	play around with an Xlib connection), then you have to seperately re-test	1186	not play around with an Xlib connection), then you have to separately
863	wether a file descriptor is really ready with a known-to-be good interface	1187	re-test whether a file descriptor is really ready with a known-to-be good
864	such as poll (fortunately in our Xlib example, Xlib already does this on	1188	interface such as poll (fortunately in our Xlib example, Xlib already
865	its own, so its quite safe to use).	1189	does this on its own, so its quite safe to use). Some people additionally
		1190	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1191	indefinitely.
		1192
		1193	But really, best use non-blocking mode.
		1194
		1195	=head3 The special problem of disappearing file descriptors
		1196
		1197	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1198	descriptor (either due to calling C<close> explicitly or any other means,
		1199	such as C<dup2>). The reason is that you register interest in some file
		1200	descriptor, but when it goes away, the operating system will silently drop
		1201	this interest. If another file descriptor with the same number then is
		1202	registered with libev, there is no efficient way to see that this is, in
		1203	fact, a different file descriptor.
		1204
		1205	To avoid having to explicitly tell libev about such cases, libev follows
		1206	the following policy: Each time C<ev_io_set> is being called, libev
		1207	will assume that this is potentially a new file descriptor, otherwise
		1208	it is assumed that the file descriptor stays the same. That means that
		1209	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1210	descriptor even if the file descriptor number itself did not change.
		1211
		1212	This is how one would do it normally anyway, the important point is that
		1213	the libev application should not optimise around libev but should leave
		1214	optimisations to libev.
		1215
		1216	=head3 The special problem of dup'ed file descriptors
		1217
		1218	Some backends (e.g. epoll), cannot register events for file descriptors,
		1219	but only events for the underlying file descriptions. That means when you
		1220	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1221	events for them, only one file descriptor might actually receive events.
		1222
		1223	There is no workaround possible except not registering events
		1224	for potentially C<dup ()>'ed file descriptors, or to resort to
		1225	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1226
		1227	=head3 The special problem of fork
		1228
		1229	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1230	useless behaviour. Libev fully supports fork, but needs to be told about
		1231	it in the child.
		1232
		1233	To support fork in your programs, you either have to call
		1234	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1235	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1236	C<EVBACKEND_POLL>.
		1237
		1238	=head3 The special problem of SIGPIPE
		1239
		1240	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1241	when writing to a pipe whose other end has been closed, your program gets
		1242	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1243	this is sensible behaviour, for daemons, this is usually undesirable.
		1244
		1245	So when you encounter spurious, unexplained daemon exits, make sure you
		1246	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1247	somewhere, as that would have given you a big clue).
		1248
		1249
		1250	=head3 Watcher-Specific Functions
866		1251
867	=over 4	1252	=over 4
868		1253
869	=item ev_io_init (ev_io *, callback, int fd, int events)	1254	=item ev_io_init (ev_io *, callback, int fd, int events)
870		1255
871	=item ev_io_set (ev_io *, int fd, int events)	1256	=item ev_io_set (ev_io *, int fd, int events)
872		1257
873	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1258	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
874	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1259	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
875	C<EV_READ | EV_WRITE> to receive the given events.	1260	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
876		1261
877	=item int fd [read-only]	1262	=item int fd [read-only]
878		1263
879	The file descriptor being watched.	1264	The file descriptor being watched.
880		1265
881	=item int events [read-only]	1266	=item int events [read-only]
882		1267
883	The events being watched.	1268	The events being watched.
884		1269
885	=back	1270	=back
		1271
		1272	=head3 Examples
886		1273
887	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1274	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
888	readable, but only once. Since it is likely line-buffered, you could	1275	readable, but only once. Since it is likely line-buffered, you could
889	attempt to read a whole line in the callback.	1276	attempt to read a whole line in the callback.
890		1277
891	static void	1278	static void
892	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1279	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
893	{	1280	{
894	ev_io_stop (loop, w);	1281	ev_io_stop (loop, w);
895	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1282	.. read from stdin here (or from w->fd) and handle any I/O errors
896	}	1283	}
897		1284
898	...	1285	...
899	struct ev_loop *loop = ev_default_init (0);	1286	struct ev_loop *loop = ev_default_init (0);
900	struct ev_io stdin_readable;	1287	ev_io stdin_readable;
901	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1288	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
902	ev_io_start (loop, &stdin_readable);	1289	ev_io_start (loop, &stdin_readable);
903	ev_loop (loop, 0);	1290	ev_loop (loop, 0);
904		1291
905		1292
906	=head2 C<ev_timer> - relative and optionally repeating timeouts	1293	=head2 C<ev_timer> - relative and optionally repeating timeouts
907		1294
908	Timer watchers are simple relative timers that generate an event after a	1295	Timer watchers are simple relative timers that generate an event after a
909	given time, and optionally repeating in regular intervals after that.	1296	given time, and optionally repeating in regular intervals after that.
910		1297
911	The timers are based on real time, that is, if you register an event that	1298	The timers are based on real time, that is, if you register an event that
912	times out after an hour and you reset your system clock to last years	1299	times out after an hour and you reset your system clock to January last
913	time, it will still time out after (roughly) and hour. "Roughly" because	1300	year, it will still time out after (roughly) one hour. "Roughly" because
914	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1301	detecting time jumps is hard, and some inaccuracies are unavoidable (the
915	monotonic clock option helps a lot here).	1302	monotonic clock option helps a lot here).
		1303
		1304	The callback is guaranteed to be invoked only I<after> its timeout has
		1305	passed, but if multiple timers become ready during the same loop iteration
		1306	then order of execution is undefined.
		1307
		1308	=head3 Be smart about timeouts
		1309
		1310	Many real-world problems involve some kind of timeout, usually for error
		1311	recovery. A typical example is an HTTP request - if the other side hangs,
		1312	you want to raise some error after a while.
		1313
		1314	What follows are some ways to handle this problem, from obvious and
		1315	inefficient to smart and efficient.
		1316
		1317	In the following, a 60 second activity timeout is assumed - a timeout that
		1318	gets reset to 60 seconds each time there is activity (e.g. each time some
		1319	data or other life sign was received).
		1320
		1321	=over 4
		1322
		1323	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1324
		1325	This is the most obvious, but not the most simple way: In the beginning,
		1326	start the watcher:
		1327
		1328	ev_timer_init (timer, callback, 60., 0.);
		1329	ev_timer_start (loop, timer);
		1330
		1331	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1332	and start it again:
		1333
		1334	ev_timer_stop (loop, timer);
		1335	ev_timer_set (timer, 60., 0.);
		1336	ev_timer_start (loop, timer);
		1337
		1338	This is relatively simple to implement, but means that each time there is
		1339	some activity, libev will first have to remove the timer from its internal
		1340	data structure and then add it again. Libev tries to be fast, but it's
		1341	still not a constant-time operation.
		1342
		1343	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1344
		1345	This is the easiest way, and involves using C<ev_timer_again> instead of
		1346	C<ev_timer_start>.
		1347
		1348	To implement this, configure an C<ev_timer> with a C<repeat> value
		1349	of C<60> and then call C<ev_timer_again> at start and each time you
		1350	successfully read or write some data. If you go into an idle state where
		1351	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1352	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1353
		1354	That means you can ignore both the C<ev_timer_start> function and the
		1355	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1356	member and C<ev_timer_again>.
		1357
		1358	At start:
		1359
		1360	ev_timer_init (timer, callback);
		1361	timer->repeat = 60.;
		1362	ev_timer_again (loop, timer);
		1363
		1364	Each time there is some activity:
		1365
		1366	ev_timer_again (loop, timer);
		1367
		1368	It is even possible to change the time-out on the fly, regardless of
		1369	whether the watcher is active or not:
		1370
		1371	timer->repeat = 30.;
		1372	ev_timer_again (loop, timer);
		1373
		1374	This is slightly more efficient then stopping/starting the timer each time
		1375	you want to modify its timeout value, as libev does not have to completely
		1376	remove and re-insert the timer from/into its internal data structure.
		1377
		1378	It is, however, even simpler than the "obvious" way to do it.
		1379
		1380	=item 3. Let the timer time out, but then re-arm it as required.
		1381
		1382	This method is more tricky, but usually most efficient: Most timeouts are
		1383	relatively long compared to the intervals between other activity - in
		1384	our example, within 60 seconds, there are usually many I/O events with
		1385	associated activity resets.
		1386
		1387	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1388	but remember the time of last activity, and check for a real timeout only
		1389	within the callback:
		1390
		1391	ev_tstamp last_activity; // time of last activity
		1392
		1393	static void
		1394	callback (EV_P_ ev_timer *w, int revents)
		1395	{
		1396	ev_tstamp now = ev_now (EV_A);
		1397	ev_tstamp timeout = last_activity + 60.;
		1398
		1399	// if last_activity + 60. is older than now, we did time out
		1400	if (timeout < now)
		1401	{
		1402	// timeout occured, take action
		1403	}
		1404	else
		1405	{
		1406	// callback was invoked, but there was some activity, re-arm
		1407	// the watcher to fire in last_activity + 60, which is
		1408	// guaranteed to be in the future, so "again" is positive:
		1409	w->again = timeout - now;
		1410	ev_timer_again (EV_A_ w);
		1411	}
		1412	}
		1413
		1414	To summarise the callback: first calculate the real timeout (defined
		1415	as "60 seconds after the last activity"), then check if that time has
		1416	been reached, which means something I<did>, in fact, time out. Otherwise
		1417	the callback was invoked too early (C<timeout> is in the future), so
		1418	re-schedule the timer to fire at that future time, to see if maybe we have
		1419	a timeout then.
		1420
		1421	Note how C<ev_timer_again> is used, taking advantage of the
		1422	C<ev_timer_again> optimisation when the timer is already running.
		1423
		1424	This scheme causes more callback invocations (about one every 60 seconds
		1425	minus half the average time between activity), but virtually no calls to
		1426	libev to change the timeout.
		1427
		1428	To start the timer, simply initialise the watcher and set C<last_activity>
		1429	to the current time (meaning we just have some activity :), then call the
		1430	callback, which will "do the right thing" and start the timer:
		1431
		1432	ev_timer_init (timer, callback);
		1433	last_activity = ev_now (loop);
		1434	callback (loop, timer, EV_TIMEOUT);
		1435
		1436	And when there is some activity, simply store the current time in
		1437	C<last_activity>, no libev calls at all:
		1438
		1439	last_actiivty = ev_now (loop);
		1440
		1441	This technique is slightly more complex, but in most cases where the
		1442	time-out is unlikely to be triggered, much more efficient.
		1443
		1444	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1445	callback :) - just change the timeout and invoke the callback, which will
		1446	fix things for you.
		1447
		1448	=item 4. Wee, just use a double-linked list for your timeouts.
		1449
		1450	If there is not one request, but many thousands (millions...), all
		1451	employing some kind of timeout with the same timeout value, then one can
		1452	do even better:
		1453
		1454	When starting the timeout, calculate the timeout value and put the timeout
		1455	at the I<end> of the list.
		1456
		1457	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1458	the list is expected to fire (for example, using the technique #3).
		1459
		1460	When there is some activity, remove the timer from the list, recalculate
		1461	the timeout, append it to the end of the list again, and make sure to
		1462	update the C<ev_timer> if it was taken from the beginning of the list.
		1463
		1464	This way, one can manage an unlimited number of timeouts in O(1) time for
		1465	starting, stopping and updating the timers, at the expense of a major
		1466	complication, and having to use a constant timeout. The constant timeout
		1467	ensures that the list stays sorted.
		1468
		1469	=back
		1470
		1471	So which method the best?
		1472
		1473	Method #2 is a simple no-brain-required solution that is adequate in most
		1474	situations. Method #3 requires a bit more thinking, but handles many cases
		1475	better, and isn't very complicated either. In most case, choosing either
		1476	one is fine, with #3 being better in typical situations.
		1477
		1478	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1479	rather complicated, but extremely efficient, something that really pays
		1480	off after the first million or so of active timers, i.e. it's usually
		1481	overkill :)
		1482
		1483	=head3 The special problem of time updates
		1484
		1485	Establishing the current time is a costly operation (it usually takes at
		1486	least two system calls): EV therefore updates its idea of the current
		1487	time only before and after C<ev_loop> collects new events, which causes a
		1488	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1489	lots of events in one iteration.
916		1490
917	The relative timeouts are calculated relative to the C<ev_now ()>	1491	The relative timeouts are calculated relative to the C<ev_now ()>
918	time. This is usually the right thing as this timestamp refers to the time	1492	time. This is usually the right thing as this timestamp refers to the time
919	of the event triggering whatever timeout you are modifying/starting. If	1493	of the event triggering whatever timeout you are modifying/starting. If
920	you suspect event processing to be delayed and you I<need> to base the timeout	1494	you suspect event processing to be delayed and you I<need> to base the
921	on the current time, use something like this to adjust for this:	1495	timeout on the current time, use something like this to adjust for this:
922		1496
923	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1497	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
924		1498
925	The callback is guarenteed to be invoked only when its timeout has passed,	1499	If the event loop is suspended for a long time, you can also force an
926	but if multiple timers become ready during the same loop iteration then	1500	update of the time returned by C<ev_now ()> by calling C<ev_now_update
927	order of execution is undefined.	1501	()>.
		1502
		1503	=head3 Watcher-Specific Functions and Data Members
928		1504
929	=over 4	1505	=over 4
930		1506
931	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1507	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
932		1508
933	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1509	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
934		1510
935	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1511	Configure the timer to trigger after C<after> seconds. If C<repeat>
936	C<0.>, then it will automatically be stopped. If it is positive, then the	1512	is C<0.>, then it will automatically be stopped once the timeout is
937	timer will automatically be configured to trigger again C<repeat> seconds	1513	reached. If it is positive, then the timer will automatically be
938	later, again, and again, until stopped manually.	1514	configured to trigger again C<repeat> seconds later, again, and again,
		1515	until stopped manually.
939		1516
940	The timer itself will do a best-effort at avoiding drift, that is, if you	1517	The timer itself will do a best-effort at avoiding drift, that is, if
941	configure a timer to trigger every 10 seconds, then it will trigger at	1518	you configure a timer to trigger every 10 seconds, then it will normally
942	exactly 10 second intervals. If, however, your program cannot keep up with	1519	trigger at exactly 10 second intervals. If, however, your program cannot
943	the timer (because it takes longer than those 10 seconds to do stuff) the	1520	keep up with the timer (because it takes longer than those 10 seconds to
944	timer will not fire more than once per event loop iteration.	1521	do stuff) the timer will not fire more than once per event loop iteration.
945		1522
946	=item ev_timer_again (loop)	1523	=item ev_timer_again (loop, ev_timer *)
947		1524
948	This will act as if the timer timed out and restart it again if it is	1525	This will act as if the timer timed out and restart it again if it is
949	repeating. The exact semantics are:	1526	repeating. The exact semantics are:
950		1527
951	If the timer is pending, its pending status is cleared.	1528	If the timer is pending, its pending status is cleared.
952		1529
953	If the timer is started but nonrepeating, stop it (as if it timed out).	1530	If the timer is started but non-repeating, stop it (as if it timed out).
954		1531
955	If the timer is repeating, either start it if necessary (with the	1532	If the timer is repeating, either start it if necessary (with the
956	C<repeat> value), or reset the running timer to the C<repeat> value.	1533	C<repeat> value), or reset the running timer to the C<repeat> value.
957		1534
958	This sounds a bit complicated, but here is a useful and typical	1535	This sounds a bit complicated, see "Be smart about timeouts", above, for a
959	example: Imagine you have a tcp connection and you want a so-called idle	1536	usage example.
960	timeout, that is, you want to be called when there have been, say, 60
961	seconds of inactivity on the socket. The easiest way to do this is to
962	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
963	C<ev_timer_again> each time you successfully read or write some data. If
964	you go into an idle state where you do not expect data to travel on the
965	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
966	automatically restart it if need be.
967
968	That means you can ignore the C<after> value and C<ev_timer_start>
969	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
970
971	ev_timer_init (timer, callback, 0., 5.);
972	ev_timer_again (loop, timer);
973	...
974	timer->again = 17.;
975	ev_timer_again (loop, timer);
976	...
977	timer->again = 10.;
978	ev_timer_again (loop, timer);
979
980	This is more slightly efficient then stopping/starting the timer each time
981	you want to modify its timeout value.
982		1537
983	=item ev_tstamp repeat [read-write]	1538	=item ev_tstamp repeat [read-write]
984		1539
985	The current C<repeat> value. Will be used each time the watcher times out	1540	The current C<repeat> value. Will be used each time the watcher times out
986	or C<ev_timer_again> is called and determines the next timeout (if any),	1541	or C<ev_timer_again> is called, and determines the next timeout (if any),
987	which is also when any modifications are taken into account.	1542	which is also when any modifications are taken into account.
988		1543
989	=back	1544	=back
990		1545
		1546	=head3 Examples
		1547
991	Example: Create a timer that fires after 60 seconds.	1548	Example: Create a timer that fires after 60 seconds.
992		1549
993	static void	1550	static void
994	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1551	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
995	{	1552	{
996	.. one minute over, w is actually stopped right here	1553	.. one minute over, w is actually stopped right here
997	}	1554	}
998		1555
999	struct ev_timer mytimer;	1556	ev_timer mytimer;
1000	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1557	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1001	ev_timer_start (loop, &mytimer);	1558	ev_timer_start (loop, &mytimer);
1002		1559
1003	Example: Create a timeout timer that times out after 10 seconds of	1560	Example: Create a timeout timer that times out after 10 seconds of
1004	inactivity.	1561	inactivity.
1005		1562
1006	static void	1563	static void
1007	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1564	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1008	{	1565	{
1009	.. ten seconds without any activity	1566	.. ten seconds without any activity
1010	}	1567	}
1011		1568
1012	struct ev_timer mytimer;	1569	ev_timer mytimer;
1013	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1570	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1014	ev_timer_again (&mytimer); /* start timer */	1571	ev_timer_again (&mytimer); /* start timer */
1015	ev_loop (loop, 0);	1572	ev_loop (loop, 0);
1016		1573
1017	// and in some piece of code that gets executed on any "activity":	1574	// and in some piece of code that gets executed on any "activity":
1018	// reset the timeout to start ticking again at 10 seconds	1575	// reset the timeout to start ticking again at 10 seconds
1019	ev_timer_again (&mytimer);	1576	ev_timer_again (&mytimer);
1020		1577
1021		1578
1022	=head2 C<ev_periodic> - to cron or not to cron?	1579	=head2 C<ev_periodic> - to cron or not to cron?
1023		1580
1024	Periodic watchers are also timers of a kind, but they are very versatile	1581	Periodic watchers are also timers of a kind, but they are very versatile
1025	(and unfortunately a bit complex).	1582	(and unfortunately a bit complex).
1026		1583
1027	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1584	Unlike C<ev_timer>'s, they are not based on real time (or relative time)
1028	but on wallclock time (absolute time). You can tell a periodic watcher	1585	but on wall clock time (absolute time). You can tell a periodic watcher
1029	to trigger "at" some specific point in time. For example, if you tell a	1586	to trigger after some specific point in time. For example, if you tell a
1030	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	1587	periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now ()
1031	+ 10.>) and then reset your system clock to the last year, then it will	1588	+ 10.>, that is, an absolute time not a delay) and then reset your system
		1589	clock to January of the previous year, then it will take more than year
1032	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1590	to trigger the event (unlike an C<ev_timer>, which would still trigger
1033	roughly 10 seconds later and of course not if you reset your system time	1591	roughly 10 seconds later as it uses a relative timeout).
1034	again).
1035		1592
1036	They can also be used to implement vastly more complex timers, such as	1593	C<ev_periodic>s can also be used to implement vastly more complex timers,
1037	triggering an event on eahc midnight, local time.	1594	such as triggering an event on each "midnight, local time", or other
		1595	complicated rules.
1038		1596
1039	As with timers, the callback is guarenteed to be invoked only when the	1597	As with timers, the callback is guaranteed to be invoked only when the
1040	time (C<at>) has been passed, but if multiple periodic timers become ready	1598	time (C<at>) has passed, but if multiple periodic timers become ready
1041	during the same loop iteration then order of execution is undefined.	1599	during the same loop iteration, then order of execution is undefined.
		1600
		1601	=head3 Watcher-Specific Functions and Data Members
1042		1602
1043	=over 4	1603	=over 4
1044		1604
1045	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1605	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
1046		1606
1047	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1607	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)
1048		1608
1049	Lots of arguments, lets sort it out... There are basically three modes of	1609	Lots of arguments, lets sort it out... There are basically three modes of
1050	operation, and we will explain them from simplest to complex:	1610	operation, and we will explain them from simplest to most complex:
1051		1611
1052	=over 4	1612	=over 4
1053		1613
1054	=item * absolute timer (interval = reschedule_cb = 0)	1614	=item * absolute timer (at = time, interval = reschedule_cb = 0)
1055		1615
1056	In this configuration the watcher triggers an event at the wallclock time	1616	In this configuration the watcher triggers an event after the wall clock
1057	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1617	time C<at> has passed. It will not repeat and will not adjust when a time
1058	that is, if it is to be run at January 1st 2011 then it will run when the	1618	jump occurs, that is, if it is to be run at January 1st 2011 then it will
1059	system time reaches or surpasses this time.	1619	only run when the system clock reaches or surpasses this time.
1060		1620
1061	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1621	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
1062		1622
1063	In this mode the watcher will always be scheduled to time out at the next	1623	In this mode the watcher will always be scheduled to time out at the next
1064	C<at + N * interval> time (for some integer N) and then repeat, regardless	1624	C<at + N * interval> time (for some integer N, which can also be negative)
1065	of any time jumps.	1625	and then repeat, regardless of any time jumps.
1066		1626
1067	This can be used to create timers that do not drift with respect to system	1627	This can be used to create timers that do not drift with respect to the
1068	time:	1628	system clock, for example, here is a C<ev_periodic> that triggers each
		1629	hour, on the hour:
1069		1630
1070	ev_periodic_set (&periodic, 0., 3600., 0);	1631	ev_periodic_set (&periodic, 0., 3600., 0);
1071		1632
1072	This doesn't mean there will always be 3600 seconds in between triggers,	1633	This doesn't mean there will always be 3600 seconds in between triggers,
1073	but only that the the callback will be called when the system time shows a	1634	but only that the callback will be called when the system time shows a
1074	full hour (UTC), or more correctly, when the system time is evenly divisible	1635	full hour (UTC), or more correctly, when the system time is evenly divisible
1075	by 3600.	1636	by 3600.
1076		1637
1077	Another way to think about it (for the mathematically inclined) is that	1638	Another way to think about it (for the mathematically inclined) is that
1078	C<ev_periodic> will try to run the callback in this mode at the next possible	1639	C<ev_periodic> will try to run the callback in this mode at the next possible
1079	time where C<time = at (mod interval)>, regardless of any time jumps.	1640	time where C<time = at (mod interval)>, regardless of any time jumps.
1080		1641
		1642	For numerical stability it is preferable that the C<at> value is near
		1643	C<ev_now ()> (the current time), but there is no range requirement for
		1644	this value, and in fact is often specified as zero.
		1645
		1646	Note also that there is an upper limit to how often a timer can fire (CPU
		1647	speed for example), so if C<interval> is very small then timing stability
		1648	will of course deteriorate. Libev itself tries to be exact to be about one
		1649	millisecond (if the OS supports it and the machine is fast enough).
		1650
1081	=item * manual reschedule mode (reschedule_cb = callback)	1651	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
1082		1652
1083	In this mode the values for C<interval> and C<at> are both being	1653	In this mode the values for C<interval> and C<at> are both being
1084	ignored. Instead, each time the periodic watcher gets scheduled, the	1654	ignored. Instead, each time the periodic watcher gets scheduled, the
1085	reschedule callback will be called with the watcher as first, and the	1655	reschedule callback will be called with the watcher as first, and the
1086	current time as second argument.	1656	current time as second argument.
1087		1657
1088	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1658	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,
1089	ever, or make any event loop modifications>. If you need to stop it,	1659	ever, or make ANY event loop modifications whatsoever>.
1090	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by
1091	starting a prepare watcher).
1092		1660
		1661	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1662	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1663	only event loop modification you are allowed to do).
		1664
1093	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1665	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1094	ev_tstamp now)>, e.g.:	1666	*w, ev_tstamp now)>, e.g.:
1095		1667
		1668	static ev_tstamp
1096	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1669	my_rescheduler (ev_periodic *w, ev_tstamp now)
1097	{	1670	{
1098	return now + 60.;	1671	return now + 60.;
1099	}	1672	}
1100		1673
1101	It must return the next time to trigger, based on the passed time value	1674	It must return the next time to trigger, based on the passed time value
1102	(that is, the lowest time value larger than to the second argument). It	1675	(that is, the lowest time value larger than to the second argument). It
1103	will usually be called just before the callback will be triggered, but	1676	will usually be called just before the callback will be triggered, but
1104	might be called at other times, too.	1677	might be called at other times, too.
1105		1678
1106	NOTE: I<< This callback must always return a time that is later than the	1679	NOTE: I<< This callback must always return a time that is higher than or
1107	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	1680	equal to the passed C<now> value >>.
1108		1681
1109	This can be used to create very complex timers, such as a timer that	1682	This can be used to create very complex timers, such as a timer that
1110	triggers on each midnight, local time. To do this, you would calculate the	1683	triggers on "next midnight, local time". To do this, you would calculate the
1111	next midnight after C<now> and return the timestamp value for this. How	1684	next midnight after C<now> and return the timestamp value for this. How
1112	you do this is, again, up to you (but it is not trivial, which is the main	1685	you do this is, again, up to you (but it is not trivial, which is the main
1113	reason I omitted it as an example).	1686	reason I omitted it as an example).
1114		1687
1115	=back	1688	=back
…		…
1119	Simply stops and restarts the periodic watcher again. This is only useful	1692	Simply stops and restarts the periodic watcher again. This is only useful
1120	when you changed some parameters or the reschedule callback would return	1693	when you changed some parameters or the reschedule callback would return
1121	a different time than the last time it was called (e.g. in a crond like	1694	a different time than the last time it was called (e.g. in a crond like
1122	program when the crontabs have changed).	1695	program when the crontabs have changed).
1123		1696
		1697	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1698
		1699	When active, returns the absolute time that the watcher is supposed to
		1700	trigger next.
		1701
		1702	=item ev_tstamp offset [read-write]
		1703
		1704	When repeating, this contains the offset value, otherwise this is the
		1705	absolute point in time (the C<at> value passed to C<ev_periodic_set>).
		1706
		1707	Can be modified any time, but changes only take effect when the periodic
		1708	timer fires or C<ev_periodic_again> is being called.
		1709
1124	=item ev_tstamp interval [read-write]	1710	=item ev_tstamp interval [read-write]
1125		1711
1126	The current interval value. Can be modified any time, but changes only	1712	The current interval value. Can be modified any time, but changes only
1127	take effect when the periodic timer fires or C<ev_periodic_again> is being	1713	take effect when the periodic timer fires or C<ev_periodic_again> is being
1128	called.	1714	called.
1129		1715
1130	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	1716	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1131		1717
1132	The current reschedule callback, or C<0>, if this functionality is	1718	The current reschedule callback, or C<0>, if this functionality is
1133	switched off. Can be changed any time, but changes only take effect when	1719	switched off. Can be changed any time, but changes only take effect when
1134	the periodic timer fires or C<ev_periodic_again> is being called.	1720	the periodic timer fires or C<ev_periodic_again> is being called.
1135		1721
1136	=back	1722	=back
1137		1723
		1724	=head3 Examples
		1725
1138	Example: Call a callback every hour, or, more precisely, whenever the	1726	Example: Call a callback every hour, or, more precisely, whenever the
1139	system clock is divisible by 3600. The callback invocation times have	1727	system time is divisible by 3600. The callback invocation times have
1140	potentially a lot of jittering, but good long-term stability.	1728	potentially a lot of jitter, but good long-term stability.
1141		1729
1142	static void	1730	static void
1143	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1731	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1144	{	1732	{
1145	... its now a full hour (UTC, or TAI or whatever your clock follows)	1733	... its now a full hour (UTC, or TAI or whatever your clock follows)
1146	}	1734	}
1147		1735
1148	struct ev_periodic hourly_tick;	1736	ev_periodic hourly_tick;
1149	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	1737	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1150	ev_periodic_start (loop, &hourly_tick);	1738	ev_periodic_start (loop, &hourly_tick);
1151		1739
1152	Example: The same as above, but use a reschedule callback to do it:	1740	Example: The same as above, but use a reschedule callback to do it:
1153		1741
1154	#include <math.h>	1742	#include <math.h>
1155		1743
1156	static ev_tstamp	1744	static ev_tstamp
1157	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	1745	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1158	{	1746	{
1159	return fmod (now, 3600.) + 3600.;	1747	return now + (3600. - fmod (now, 3600.));
1160	}	1748	}
1161		1749
1162	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	1750	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1163		1751
1164	Example: Call a callback every hour, starting now:	1752	Example: Call a callback every hour, starting now:
1165		1753
1166	struct ev_periodic hourly_tick;	1754	ev_periodic hourly_tick;
1167	ev_periodic_init (&hourly_tick, clock_cb,	1755	ev_periodic_init (&hourly_tick, clock_cb,
1168	fmod (ev_now (loop), 3600.), 3600., 0);	1756	fmod (ev_now (loop), 3600.), 3600., 0);
1169	ev_periodic_start (loop, &hourly_tick);	1757	ev_periodic_start (loop, &hourly_tick);
1170		1758
1171		1759
1172	=head2 C<ev_signal> - signal me when a signal gets signalled!	1760	=head2 C<ev_signal> - signal me when a signal gets signalled!
1173		1761
1174	Signal watchers will trigger an event when the process receives a specific	1762	Signal watchers will trigger an event when the process receives a specific
1175	signal one or more times. Even though signals are very asynchronous, libev	1763	signal one or more times. Even though signals are very asynchronous, libev
1176	will try it's best to deliver signals synchronously, i.e. as part of the	1764	will try it's best to deliver signals synchronously, i.e. as part of the
1177	normal event processing, like any other event.	1765	normal event processing, like any other event.
1178		1766
		1767	If you want signals asynchronously, just use C<sigaction> as you would
		1768	do without libev and forget about sharing the signal. You can even use
		1769	C<ev_async> from a signal handler to synchronously wake up an event loop.
		1770
1179	You can configure as many watchers as you like per signal. Only when the	1771	You can configure as many watchers as you like per signal. Only when the
1180	first watcher gets started will libev actually register a signal watcher	1772	first watcher gets started will libev actually register a signal handler
1181	with the kernel (thus it coexists with your own signal handlers as long	1773	with the kernel (thus it coexists with your own signal handlers as long as
1182	as you don't register any with libev). Similarly, when the last signal	1774	you don't register any with libev for the same signal). Similarly, when
1183	watcher for a signal is stopped libev will reset the signal handler to	1775	the last signal watcher for a signal is stopped, libev will reset the
1184	SIG_DFL (regardless of what it was set to before).	1776	signal handler to SIG_DFL (regardless of what it was set to before).
		1777
		1778	If possible and supported, libev will install its handlers with
		1779	C<SA_RESTART> behaviour enabled, so system calls should not be unduly
		1780	interrupted. If you have a problem with system calls getting interrupted by
		1781	signals you can block all signals in an C<ev_check> watcher and unblock
		1782	them in an C<ev_prepare> watcher.
		1783
		1784	=head3 Watcher-Specific Functions and Data Members
1185		1785
1186	=over 4	1786	=over 4
1187		1787
1188	=item ev_signal_init (ev_signal *, callback, int signum)	1788	=item ev_signal_init (ev_signal *, callback, int signum)
1189		1789
…		…
1196		1796
1197	The signal the watcher watches out for.	1797	The signal the watcher watches out for.
1198		1798
1199	=back	1799	=back
1200		1800
		1801	=head3 Examples
		1802
		1803	Example: Try to exit cleanly on SIGINT.
		1804
		1805	static void
		1806	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		1807	{
		1808	ev_unloop (loop, EVUNLOOP_ALL);
		1809	}
		1810
		1811	ev_signal signal_watcher;
		1812	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1813	ev_signal_start (loop, &signal_watcher);
		1814
1201		1815
1202	=head2 C<ev_child> - watch out for process status changes	1816	=head2 C<ev_child> - watch out for process status changes
1203		1817
1204	Child watchers trigger when your process receives a SIGCHLD in response to	1818	Child watchers trigger when your process receives a SIGCHLD in response to
1205	some child status changes (most typically when a child of yours dies).	1819	some child status changes (most typically when a child of yours dies or
		1820	exits). It is permissible to install a child watcher I<after> the child
		1821	has been forked (which implies it might have already exited), as long
		1822	as the event loop isn't entered (or is continued from a watcher), i.e.,
		1823	forking and then immediately registering a watcher for the child is fine,
		1824	but forking and registering a watcher a few event loop iterations later is
		1825	not.
		1826
		1827	Only the default event loop is capable of handling signals, and therefore
		1828	you can only register child watchers in the default event loop.
		1829
		1830	=head3 Process Interaction
		1831
		1832	Libev grabs C<SIGCHLD> as soon as the default event loop is
		1833	initialised. This is necessary to guarantee proper behaviour even if
		1834	the first child watcher is started after the child exits. The occurrence
		1835	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		1836	synchronously as part of the event loop processing. Libev always reaps all
		1837	children, even ones not watched.
		1838
		1839	=head3 Overriding the Built-In Processing
		1840
		1841	Libev offers no special support for overriding the built-in child
		1842	processing, but if your application collides with libev's default child
		1843	handler, you can override it easily by installing your own handler for
		1844	C<SIGCHLD> after initialising the default loop, and making sure the
		1845	default loop never gets destroyed. You are encouraged, however, to use an
		1846	event-based approach to child reaping and thus use libev's support for
		1847	that, so other libev users can use C<ev_child> watchers freely.
		1848
		1849	=head3 Stopping the Child Watcher
		1850
		1851	Currently, the child watcher never gets stopped, even when the
		1852	child terminates, so normally one needs to stop the watcher in the
		1853	callback. Future versions of libev might stop the watcher automatically
		1854	when a child exit is detected.
		1855
		1856	=head3 Watcher-Specific Functions and Data Members
1206		1857
1207	=over 4	1858	=over 4
1208		1859
1209	=item ev_child_init (ev_child *, callback, int pid)	1860	=item ev_child_init (ev_child *, callback, int pid, int trace)
1210		1861
1211	=item ev_child_set (ev_child *, int pid)	1862	=item ev_child_set (ev_child *, int pid, int trace)
1212		1863
1213	Configures the watcher to wait for status changes of process C<pid> (or	1864	Configures the watcher to wait for status changes of process C<pid> (or
1214	I<any> process if C<pid> is specified as C<0>). The callback can look	1865	I<any> process if C<pid> is specified as C<0>). The callback can look
1215	at the C<rstatus> member of the C<ev_child> watcher structure to see	1866	at the C<rstatus> member of the C<ev_child> watcher structure to see
1216	the status word (use the macros from C<sys/wait.h> and see your systems	1867	the status word (use the macros from C<sys/wait.h> and see your systems
1217	C<waitpid> documentation). The C<rpid> member contains the pid of the	1868	C<waitpid> documentation). The C<rpid> member contains the pid of the
1218	process causing the status change.	1869	process causing the status change. C<trace> must be either C<0> (only
		1870	activate the watcher when the process terminates) or C<1> (additionally
		1871	activate the watcher when the process is stopped or continued).
1219		1872
1220	=item int pid [read-only]	1873	=item int pid [read-only]
1221		1874
1222	The process id this watcher watches out for, or C<0>, meaning any process id.	1875	The process id this watcher watches out for, or C<0>, meaning any process id.
1223		1876
…		…
1230	The process exit/trace status caused by C<rpid> (see your systems	1883	The process exit/trace status caused by C<rpid> (see your systems
1231	C<waitpid> and C<sys/wait.h> documentation for details).	1884	C<waitpid> and C<sys/wait.h> documentation for details).
1232		1885
1233	=back	1886	=back
1234		1887
1235	Example: Try to exit cleanly on SIGINT and SIGTERM.	1888	=head3 Examples
1236		1889
		1890	Example: C<fork()> a new process and install a child handler to wait for
		1891	its completion.
		1892
		1893	ev_child cw;
		1894
1237	static void	1895	static void
1238	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	1896	child_cb (EV_P_ ev_child *w, int revents)
1239	{	1897	{
1240	ev_unloop (loop, EVUNLOOP_ALL);	1898	ev_child_stop (EV_A_ w);
		1899	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1241	}	1900	}
1242		1901
1243	struct ev_signal signal_watcher;	1902	pid_t pid = fork ();
1244	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	1903
1245	ev_signal_start (loop, &sigint_cb);	1904	if (pid < 0)
		1905	// error
		1906	else if (pid == 0)
		1907	{
		1908	// the forked child executes here
		1909	exit (1);
		1910	}
		1911	else
		1912	{
		1913	ev_child_init (&cw, child_cb, pid, 0);
		1914	ev_child_start (EV_DEFAULT_ &cw);
		1915	}
1246		1916
1247		1917
1248	=head2 C<ev_stat> - did the file attributes just change?	1918	=head2 C<ev_stat> - did the file attributes just change?
1249		1919
1250	This watches a filesystem path for attribute changes. That is, it calls	1920	This watches a file system path for attribute changes. That is, it calls
1251	C<stat> regularly (or when the OS says it changed) and sees if it changed	1921	C<stat> regularly (or when the OS says it changed) and sees if it changed
1252	compared to the last time, invoking the callback if it did.	1922	compared to the last time, invoking the callback if it did.
1253		1923
1254	The path does not need to exist: changing from "path exists" to "path does	1924	The path does not need to exist: changing from "path exists" to "path does
1255	not exist" is a status change like any other. The condition "path does	1925	not exist" is a status change like any other. The condition "path does
…		…
1258	the stat buffer having unspecified contents.	1928	the stat buffer having unspecified contents.
1259		1929
1260	The path I<should> be absolute and I<must not> end in a slash. If it is	1930	The path I<should> be absolute and I<must not> end in a slash. If it is
1261	relative and your working directory changes, the behaviour is undefined.	1931	relative and your working directory changes, the behaviour is undefined.
1262		1932
1263	Since there is no standard to do this, the portable implementation simply	1933	Since there is no standard kernel interface to do this, the portable
1264	calls C<stat (2)> regularly on the path to see if it changed somehow. You	1934	implementation simply calls C<stat (2)> regularly on the path to see if
1265	can specify a recommended polling interval for this case. If you specify	1935	it changed somehow. You can specify a recommended polling interval for
1266	a polling interval of C<0> (highly recommended!) then a I<suitable,	1936	this case. If you specify a polling interval of C<0> (highly recommended!)
1267	unspecified default> value will be used (which you can expect to be around	1937	then a I<suitable, unspecified default> value will be used (which
1268	five seconds, although this might change dynamically). Libev will also	1938	you can expect to be around five seconds, although this might change
1269	impose a minimum interval which is currently around C<0.1>, but thats	1939	dynamically). Libev will also impose a minimum interval which is currently
1270	usually overkill.	1940	around C<0.1>, but thats usually overkill.
1271		1941
1272	This watcher type is not meant for massive numbers of stat watchers,	1942	This watcher type is not meant for massive numbers of stat watchers,
1273	as even with OS-supported change notifications, this can be	1943	as even with OS-supported change notifications, this can be
1274	resource-intensive.	1944	resource-intensive.
1275		1945
1276	At the time of this writing, only the Linux inotify interface is	1946	At the time of this writing, the only OS-specific interface implemented
1277	implemented (implementing kqueue support is left as an exercise for the	1947	is the Linux inotify interface (implementing kqueue support is left as
1278	reader). Inotify will be used to give hints only and should not change the	1948	an exercise for the reader. Note, however, that the author sees no way
1279	semantics of C<ev_stat> watchers, which means that libev sometimes needs	1949	of implementing C<ev_stat> semantics with kqueue).
1280	to fall back to regular polling again even with inotify, but changes are	1950
1281	usually detected immediately, and if the file exists there will be no	1951	=head3 ABI Issues (Largefile Support)
1282	polling.	1952
		1953	Libev by default (unless the user overrides this) uses the default
		1954	compilation environment, which means that on systems with large file
		1955	support disabled by default, you get the 32 bit version of the stat
		1956	structure. When using the library from programs that change the ABI to
		1957	use 64 bit file offsets the programs will fail. In that case you have to
		1958	compile libev with the same flags to get binary compatibility. This is
		1959	obviously the case with any flags that change the ABI, but the problem is
		1960	most noticeably disabled with ev_stat and large file support.
		1961
		1962	The solution for this is to lobby your distribution maker to make large
		1963	file interfaces available by default (as e.g. FreeBSD does) and not
		1964	optional. Libev cannot simply switch on large file support because it has
		1965	to exchange stat structures with application programs compiled using the
		1966	default compilation environment.
		1967
		1968	=head3 Inotify and Kqueue
		1969
		1970	When C<inotify (7)> support has been compiled into libev (generally
		1971	only available with Linux 2.6.25 or above due to bugs in earlier
		1972	implementations) and present at runtime, it will be used to speed up
		1973	change detection where possible. The inotify descriptor will be created
		1974	lazily when the first C<ev_stat> watcher is being started.
		1975
		1976	Inotify presence does not change the semantics of C<ev_stat> watchers
		1977	except that changes might be detected earlier, and in some cases, to avoid
		1978	making regular C<stat> calls. Even in the presence of inotify support
		1979	there are many cases where libev has to resort to regular C<stat> polling,
		1980	but as long as the path exists, libev usually gets away without polling.
		1981
		1982	There is no support for kqueue, as apparently it cannot be used to
		1983	implement this functionality, due to the requirement of having a file
		1984	descriptor open on the object at all times, and detecting renames, unlinks
		1985	etc. is difficult.
		1986
		1987	=head3 The special problem of stat time resolution
		1988
		1989	The C<stat ()> system call only supports full-second resolution portably, and
		1990	even on systems where the resolution is higher, most file systems still
		1991	only support whole seconds.
		1992
		1993	That means that, if the time is the only thing that changes, you can
		1994	easily miss updates: on the first update, C<ev_stat> detects a change and
		1995	calls your callback, which does something. When there is another update
		1996	within the same second, C<ev_stat> will be unable to detect unless the
		1997	stat data does change in other ways (e.g. file size).
		1998
		1999	The solution to this is to delay acting on a change for slightly more
		2000	than a second (or till slightly after the next full second boundary), using
		2001	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2002	ev_timer_again (loop, w)>).
		2003
		2004	The C<.02> offset is added to work around small timing inconsistencies
		2005	of some operating systems (where the second counter of the current time
		2006	might be be delayed. One such system is the Linux kernel, where a call to
		2007	C<gettimeofday> might return a timestamp with a full second later than
		2008	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2009	update file times then there will be a small window where the kernel uses
		2010	the previous second to update file times but libev might already execute
		2011	the timer callback).
		2012
		2013	=head3 Watcher-Specific Functions and Data Members
1283		2014
1284	=over 4	2015	=over 4
1285		2016
1286	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)	2017	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
1287		2018
…		…
1291	C<path>. The C<interval> is a hint on how quickly a change is expected to	2022	C<path>. The C<interval> is a hint on how quickly a change is expected to
1292	be detected and should normally be specified as C<0> to let libev choose	2023	be detected and should normally be specified as C<0> to let libev choose
1293	a suitable value. The memory pointed to by C<path> must point to the same	2024	a suitable value. The memory pointed to by C<path> must point to the same
1294	path for as long as the watcher is active.	2025	path for as long as the watcher is active.
1295		2026
1296	The callback will be receive C<EV_STAT> when a change was detected,	2027	The callback will receive an C<EV_STAT> event when a change was detected,
1297	relative to the attributes at the time the watcher was started (or the	2028	relative to the attributes at the time the watcher was started (or the
1298	last change was detected).	2029	last change was detected).
1299		2030
1300	=item ev_stat_stat (ev_stat *)	2031	=item ev_stat_stat (loop, ev_stat *)
1301		2032
1302	Updates the stat buffer immediately with new values. If you change the	2033	Updates the stat buffer immediately with new values. If you change the
1303	watched path in your callback, you could call this fucntion to avoid	2034	watched path in your callback, you could call this function to avoid
1304	detecting this change (while introducing a race condition). Can also be	2035	detecting this change (while introducing a race condition if you are not
1305	useful simply to find out the new values.	2036	the only one changing the path). Can also be useful simply to find out the
		2037	new values.
1306		2038
1307	=item ev_statdata attr [read-only]	2039	=item ev_statdata attr [read-only]
1308		2040
1309	The most-recently detected attributes of the file. Although the type is of	2041	The most-recently detected attributes of the file. Although the type is
1310	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2042	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1311	suitable for your system. If the C<st_nlink> member is C<0>, then there	2043	suitable for your system, but you can only rely on the POSIX-standardised
		2044	members to be present. If the C<st_nlink> member is C<0>, then there was
1312	was some error while C<stat>ing the file.	2045	some error while C<stat>ing the file.
1313		2046
1314	=item ev_statdata prev [read-only]	2047	=item ev_statdata prev [read-only]
1315		2048
1316	The previous attributes of the file. The callback gets invoked whenever	2049	The previous attributes of the file. The callback gets invoked whenever
1317	C<prev> != C<attr>.	2050	C<prev> != C<attr>, or, more precisely, one or more of these members
		2051	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2052	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1318		2053
1319	=item ev_tstamp interval [read-only]	2054	=item ev_tstamp interval [read-only]
1320		2055
1321	The specified interval.	2056	The specified interval.
1322		2057
1323	=item const char *path [read-only]	2058	=item const char *path [read-only]
1324		2059
1325	The filesystem path that is being watched.	2060	The file system path that is being watched.
1326		2061
1327	=back	2062	=back
1328		2063
		2064	=head3 Examples
		2065
1329	Example: Watch C</etc/passwd> for attribute changes.	2066	Example: Watch C</etc/passwd> for attribute changes.
1330		2067
1331	static void	2068	static void
1332	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2069	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1333	{	2070	{
1334	/* /etc/passwd changed in some way */	2071	/* /etc/passwd changed in some way */
1335	if (w->attr.st_nlink)	2072	if (w->attr.st_nlink)
1336	{	2073	{
1337	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2074	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1338	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2075	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1339	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2076	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1340	}	2077	}
1341	else	2078	else
1342	/* you shalt not abuse printf for puts */	2079	/* you shalt not abuse printf for puts */
1343	puts ("wow, /etc/passwd is not there, expect problems. "	2080	puts ("wow, /etc/passwd is not there, expect problems. "
1344	"if this is windows, they already arrived\n");	2081	"if this is windows, they already arrived\n");
1345	}	2082	}
1346		2083
1347	...	2084	...
1348	ev_stat passwd;	2085	ev_stat passwd;
1349		2086
1350	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	2087	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1351	ev_stat_start (loop, &passwd);	2088	ev_stat_start (loop, &passwd);
		2089
		2090	Example: Like above, but additionally use a one-second delay so we do not
		2091	miss updates (however, frequent updates will delay processing, too, so
		2092	one might do the work both on C<ev_stat> callback invocation I<and> on
		2093	C<ev_timer> callback invocation).
		2094
		2095	static ev_stat passwd;
		2096	static ev_timer timer;
		2097
		2098	static void
		2099	timer_cb (EV_P_ ev_timer *w, int revents)
		2100	{
		2101	ev_timer_stop (EV_A_ w);
		2102
		2103	/* now it's one second after the most recent passwd change */
		2104	}
		2105
		2106	static void
		2107	stat_cb (EV_P_ ev_stat *w, int revents)
		2108	{
		2109	/* reset the one-second timer */
		2110	ev_timer_again (EV_A_ &timer);
		2111	}
		2112
		2113	...
		2114	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2115	ev_stat_start (loop, &passwd);
		2116	ev_timer_init (&timer, timer_cb, 0., 1.02);
1352		2117
1353		2118
1354	=head2 C<ev_idle> - when you've got nothing better to do...	2119	=head2 C<ev_idle> - when you've got nothing better to do...
1355		2120
1356	Idle watchers trigger events when there are no other events are pending	2121	Idle watchers trigger events when no other events of the same or higher
1357	(prepare, check and other idle watchers do not count). That is, as long	2122	priority are pending (prepare, check and other idle watchers do not count
1358	as your process is busy handling sockets or timeouts (or even signals,	2123	as receiving "events").
1359	imagine) it will not be triggered. But when your process is idle all idle	2124
1360	watchers are being called again and again, once per event loop iteration -	2125	That is, as long as your process is busy handling sockets or timeouts
		2126	(or even signals, imagine) of the same or higher priority it will not be
		2127	triggered. But when your process is idle (or only lower-priority watchers
		2128	are pending), the idle watchers are being called once per event loop
1361	until stopped, that is, or your process receives more events and becomes	2129	iteration - until stopped, that is, or your process receives more events
1362	busy.	2130	and becomes busy again with higher priority stuff.
1363		2131
1364	The most noteworthy effect is that as long as any idle watchers are	2132	The most noteworthy effect is that as long as any idle watchers are
1365	active, the process will not block when waiting for new events.	2133	active, the process will not block when waiting for new events.
1366		2134
1367	Apart from keeping your process non-blocking (which is a useful	2135	Apart from keeping your process non-blocking (which is a useful
1368	effect on its own sometimes), idle watchers are a good place to do	2136	effect on its own sometimes), idle watchers are a good place to do
1369	"pseudo-background processing", or delay processing stuff to after the	2137	"pseudo-background processing", or delay processing stuff to after the
1370	event loop has handled all outstanding events.	2138	event loop has handled all outstanding events.
1371		2139
		2140	=head3 Watcher-Specific Functions and Data Members
		2141
1372	=over 4	2142	=over 4
1373		2143
1374	=item ev_idle_init (ev_signal *, callback)	2144	=item ev_idle_init (ev_signal *, callback)
1375		2145
1376	Initialises and configures the idle watcher - it has no parameters of any	2146	Initialises and configures the idle watcher - it has no parameters of any
1377	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2147	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1378	believe me.	2148	believe me.
1379		2149
1380	=back	2150	=back
1381		2151
		2152	=head3 Examples
		2153
1382	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2154	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1383	callback, free it. Also, use no error checking, as usual.	2155	callback, free it. Also, use no error checking, as usual.
1384		2156
1385	static void	2157	static void
1386	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2158	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1387	{	2159	{
1388	free (w);	2160	free (w);
1389	// now do something you wanted to do when the program has	2161	// now do something you wanted to do when the program has
1390	// no longer asnything immediate to do.	2162	// no longer anything immediate to do.
1391	}	2163	}
1392		2164
1393	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2165	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1394	ev_idle_init (idle_watcher, idle_cb);	2166	ev_idle_init (idle_watcher, idle_cb);
1395	ev_idle_start (loop, idle_cb);	2167	ev_idle_start (loop, idle_cb);
1396		2168
1397		2169
1398	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2170	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1399		2171
1400	Prepare and check watchers are usually (but not always) used in tandem:	2172	Prepare and check watchers are usually (but not always) used in pairs:
1401	prepare watchers get invoked before the process blocks and check watchers	2173	prepare watchers get invoked before the process blocks and check watchers
1402	afterwards.	2174	afterwards.
1403		2175
1404	You I<must not> call C<ev_loop> or similar functions that enter	2176	You I<must not> call C<ev_loop> or similar functions that enter
1405	the current event loop from either C<ev_prepare> or C<ev_check>	2177	the current event loop from either C<ev_prepare> or C<ev_check>
…		…
1408	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2180	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1409	C<ev_check> so if you have one watcher of each kind they will always be	2181	C<ev_check> so if you have one watcher of each kind they will always be
1410	called in pairs bracketing the blocking call.	2182	called in pairs bracketing the blocking call.
1411		2183
1412	Their main purpose is to integrate other event mechanisms into libev and	2184	Their main purpose is to integrate other event mechanisms into libev and
1413	their use is somewhat advanced. This could be used, for example, to track	2185	their use is somewhat advanced. They could be used, for example, to track
1414	variable changes, implement your own watchers, integrate net-snmp or a	2186	variable changes, implement your own watchers, integrate net-snmp or a
1415	coroutine library and lots more. They are also occasionally useful if	2187	coroutine library and lots more. They are also occasionally useful if
1416	you cache some data and want to flush it before blocking (for example,	2188	you cache some data and want to flush it before blocking (for example,
1417	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2189	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1418	watcher).	2190	watcher).
1419		2191
1420	This is done by examining in each prepare call which file descriptors need	2192	This is done by examining in each prepare call which file descriptors
1421	to be watched by the other library, registering C<ev_io> watchers for	2193	need to be watched by the other library, registering C<ev_io> watchers
1422	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2194	for them and starting an C<ev_timer> watcher for any timeouts (many
1423	provide just this functionality). Then, in the check watcher you check for	2195	libraries provide exactly this functionality). Then, in the check watcher,
1424	any events that occured (by checking the pending status of all watchers	2196	you check for any events that occurred (by checking the pending status
1425	and stopping them) and call back into the library. The I/O and timer	2197	of all watchers and stopping them) and call back into the library. The
1426	callbacks will never actually be called (but must be valid nevertheless,	2198	I/O and timer callbacks will never actually be called (but must be valid
1427	because you never know, you know?).	2199	nevertheless, because you never know, you know?).
1428		2200
1429	As another example, the Perl Coro module uses these hooks to integrate	2201	As another example, the Perl Coro module uses these hooks to integrate
1430	coroutines into libev programs, by yielding to other active coroutines	2202	coroutines into libev programs, by yielding to other active coroutines
1431	during each prepare and only letting the process block if no coroutines	2203	during each prepare and only letting the process block if no coroutines
1432	are ready to run (it's actually more complicated: it only runs coroutines	2204	are ready to run (it's actually more complicated: it only runs coroutines
1433	with priority higher than or equal to the event loop and one coroutine	2205	with priority higher than or equal to the event loop and one coroutine
1434	of lower priority, but only once, using idle watchers to keep the event	2206	of lower priority, but only once, using idle watchers to keep the event
1435	loop from blocking if lower-priority coroutines are active, thus mapping	2207	loop from blocking if lower-priority coroutines are active, thus mapping
1436	low-priority coroutines to idle/background tasks).	2208	low-priority coroutines to idle/background tasks).
1437		2209
		2210	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		2211	priority, to ensure that they are being run before any other watchers
		2212	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2213
		2214	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2215	activate ("feed") events into libev. While libev fully supports this, they
		2216	might get executed before other C<ev_check> watchers did their job. As
		2217	C<ev_check> watchers are often used to embed other (non-libev) event
		2218	loops those other event loops might be in an unusable state until their
		2219	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2220	others).
		2221
		2222	=head3 Watcher-Specific Functions and Data Members
		2223
1438	=over 4	2224	=over 4
1439		2225
1440	=item ev_prepare_init (ev_prepare *, callback)	2226	=item ev_prepare_init (ev_prepare *, callback)
1441		2227
1442	=item ev_check_init (ev_check *, callback)	2228	=item ev_check_init (ev_check *, callback)
1443		2229
1444	Initialises and configures the prepare or check watcher - they have no	2230	Initialises and configures the prepare or check watcher - they have no
1445	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2231	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1446	macros, but using them is utterly, utterly and completely pointless.	2232	macros, but using them is utterly, utterly, utterly and completely
		2233	pointless.
1447		2234
1448	=back	2235	=back
1449		2236
1450	Example: To include a library such as adns, you would add IO watchers	2237	=head3 Examples
1451	and a timeout watcher in a prepare handler, as required by libadns, and	2238
		2239	There are a number of principal ways to embed other event loops or modules
		2240	into libev. Here are some ideas on how to include libadns into libev
		2241	(there is a Perl module named C<EV::ADNS> that does this, which you could
		2242	use as a working example. Another Perl module named C<EV::Glib> embeds a
		2243	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		2244	Glib event loop).
		2245
		2246	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1452	in a check watcher, destroy them and call into libadns. What follows is	2247	and in a check watcher, destroy them and call into libadns. What follows
1453	pseudo-code only of course:	2248	is pseudo-code only of course. This requires you to either use a low
		2249	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		2250	the callbacks for the IO/timeout watchers might not have been called yet.
1454		2251
1455	static ev_io iow [nfd];	2252	static ev_io iow [nfd];
1456	static ev_timer tw;	2253	static ev_timer tw;
1457		2254
1458	static void	2255	static void
1459	io_cb (ev_loop *loop, ev_io *w, int revents)	2256	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1460	{	2257	{
1461	// set the relevant poll flags
1462	// could also call adns_processreadable etc. here
1463	struct pollfd *fd = (struct pollfd *)w->data;
1464	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1465	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1466	}	2258	}
1467		2259
1468	// create io watchers for each fd and a timer before blocking	2260	// create io watchers for each fd and a timer before blocking
1469	static void	2261	static void
1470	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2262	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1471	{	2263	{
1472	int timeout = 3600000;	2264	int timeout = 3600000;
1473	struct pollfd fds [nfd];	2265	struct pollfd fds [nfd];
1474	// actual code will need to loop here and realloc etc.	2266	// actual code will need to loop here and realloc etc.
1475	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2267	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1476		2268
1477	/* the callback is illegal, but won't be called as we stop during check */	2269	/* the callback is illegal, but won't be called as we stop during check */
1478	ev_timer_init (&tw, 0, timeout * 1e-3);	2270	ev_timer_init (&tw, 0, timeout * 1e-3);
1479	ev_timer_start (loop, &tw);	2271	ev_timer_start (loop, &tw);
1480		2272
1481	// create on ev_io per pollfd	2273	// create one ev_io per pollfd
1482	for (int i = 0; i < nfd; ++i)	2274	for (int i = 0; i < nfd; ++i)
1483	{	2275	{
1484	ev_io_init (iow + i, io_cb, fds [i].fd,	2276	ev_io_init (iow + i, io_cb, fds [i].fd,
1485	((fds [i].events & POLLIN ? EV_READ : 0)	2277	((fds [i].events & POLLIN ? EV_READ : 0)
1486	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2278	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1487		2279
1488	fds [i].revents = 0;	2280	fds [i].revents = 0;
1489	iow [i].data = fds + i;
1490	ev_io_start (loop, iow + i);	2281	ev_io_start (loop, iow + i);
1491	}	2282	}
1492	}	2283	}
1493		2284
1494	// stop all watchers after blocking	2285	// stop all watchers after blocking
1495	static void	2286	static void
1496	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2287	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1497	{	2288	{
1498	ev_timer_stop (loop, &tw);	2289	ev_timer_stop (loop, &tw);
1499		2290
1500	for (int i = 0; i < nfd; ++i)	2291	for (int i = 0; i < nfd; ++i)
		2292	{
		2293	// set the relevant poll flags
		2294	// could also call adns_processreadable etc. here
		2295	struct pollfd *fd = fds + i;
		2296	int revents = ev_clear_pending (iow + i);
		2297	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2298	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2299
		2300	// now stop the watcher
1501	ev_io_stop (loop, iow + i);	2301	ev_io_stop (loop, iow + i);
		2302	}
1502		2303
1503	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2304	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1504	}	2305	}
		2306
		2307	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2308	in the prepare watcher and would dispose of the check watcher.
		2309
		2310	Method 3: If the module to be embedded supports explicit event
		2311	notification (libadns does), you can also make use of the actual watcher
		2312	callbacks, and only destroy/create the watchers in the prepare watcher.
		2313
		2314	static void
		2315	timer_cb (EV_P_ ev_timer *w, int revents)
		2316	{
		2317	adns_state ads = (adns_state)w->data;
		2318	update_now (EV_A);
		2319
		2320	adns_processtimeouts (ads, &tv_now);
		2321	}
		2322
		2323	static void
		2324	io_cb (EV_P_ ev_io *w, int revents)
		2325	{
		2326	adns_state ads = (adns_state)w->data;
		2327	update_now (EV_A);
		2328
		2329	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2330	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2331	}
		2332
		2333	// do not ever call adns_afterpoll
		2334
		2335	Method 4: Do not use a prepare or check watcher because the module you
		2336	want to embed is not flexible enough to support it. Instead, you can
		2337	override their poll function. The drawback with this solution is that the
		2338	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		2339	this approach, effectively embedding EV as a client into the horrible
		2340	libglib event loop.
		2341
		2342	static gint
		2343	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2344	{
		2345	int got_events = 0;
		2346
		2347	for (n = 0; n < nfds; ++n)
		2348	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2349
		2350	if (timeout >= 0)
		2351	// create/start timer
		2352
		2353	// poll
		2354	ev_loop (EV_A_ 0);
		2355
		2356	// stop timer again
		2357	if (timeout >= 0)
		2358	ev_timer_stop (EV_A_ &to);
		2359
		2360	// stop io watchers again - their callbacks should have set
		2361	for (n = 0; n < nfds; ++n)
		2362	ev_io_stop (EV_A_ iow [n]);
		2363
		2364	return got_events;
		2365	}
1505		2366
1506		2367
1507	=head2 C<ev_embed> - when one backend isn't enough...	2368	=head2 C<ev_embed> - when one backend isn't enough...
1508		2369
1509	This is a rather advanced watcher type that lets you embed one event loop	2370	This is a rather advanced watcher type that lets you embed one event loop
…		…
1515	prioritise I/O.	2376	prioritise I/O.
1516		2377
1517	As an example for a bug workaround, the kqueue backend might only support	2378	As an example for a bug workaround, the kqueue backend might only support
1518	sockets on some platform, so it is unusable as generic backend, but you	2379	sockets on some platform, so it is unusable as generic backend, but you
1519	still want to make use of it because you have many sockets and it scales	2380	still want to make use of it because you have many sockets and it scales
1520	so nicely. In this case, you would create a kqueue-based loop and embed it	2381	so nicely. In this case, you would create a kqueue-based loop and embed
1521	into your default loop (which might use e.g. poll). Overall operation will	2382	it into your default loop (which might use e.g. poll). Overall operation
1522	be a bit slower because first libev has to poll and then call kevent, but	2383	will be a bit slower because first libev has to call C<poll> and then
1523	at least you can use both at what they are best.	2384	C<kevent>, but at least you can use both mechanisms for what they are
		2385	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1524		2386
1525	As for prioritising I/O: rarely you have the case where some fds have	2387	As for prioritising I/O: under rare circumstances you have the case where
1526	to be watched and handled very quickly (with low latency), and even	2388	some fds have to be watched and handled very quickly (with low latency),
1527	priorities and idle watchers might have too much overhead. In this case	2389	and even priorities and idle watchers might have too much overhead. In
1528	you would put all the high priority stuff in one loop and all the rest in	2390	this case you would put all the high priority stuff in one loop and all
1529	a second one, and embed the second one in the first.	2391	the rest in a second one, and embed the second one in the first.
1530		2392
1531	As long as the watcher is active, the callback will be invoked every time	2393	As long as the watcher is active, the callback will be invoked every time
1532	there might be events pending in the embedded loop. The callback must then	2394	there might be events pending in the embedded loop. The callback must then
1533	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2395	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke
1534	their callbacks (you could also start an idle watcher to give the embedded	2396	their callbacks (you could also start an idle watcher to give the embedded
…		…
1542	interested in that.	2404	interested in that.
1543		2405
1544	Also, there have not currently been made special provisions for forking:	2406	Also, there have not currently been made special provisions for forking:
1545	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2407	when you fork, you not only have to call C<ev_loop_fork> on both loops,
1546	but you will also have to stop and restart any C<ev_embed> watchers	2408	but you will also have to stop and restart any C<ev_embed> watchers
1547	yourself.	2409	yourself - but you can use a fork watcher to handle this automatically,
		2410	and future versions of libev might do just that.
1548		2411
1549	Unfortunately, not all backends are embeddable, only the ones returned by	2412	Unfortunately, not all backends are embeddable: only the ones returned by
1550	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2413	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1551	portable one.	2414	portable one.
1552		2415
1553	So when you want to use this feature you will always have to be prepared	2416	So when you want to use this feature you will always have to be prepared
1554	that you cannot get an embeddable loop. The recommended way to get around	2417	that you cannot get an embeddable loop. The recommended way to get around
1555	this is to have a separate variables for your embeddable loop, try to	2418	this is to have a separate variables for your embeddable loop, try to
1556	create it, and if that fails, use the normal loop for everything:	2419	create it, and if that fails, use the normal loop for everything.
1557		2420
1558	struct ev_loop *loop_hi = ev_default_init (0);	2421	=head3 C<ev_embed> and fork
1559	struct ev_loop *loop_lo = 0;
1560	struct ev_embed embed;
1561
1562	// see if there is a chance of getting one that works
1563	// (remember that a flags value of 0 means autodetection)
1564	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1565	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1566	: 0;
1567		2422
1568	// if we got one, then embed it, otherwise default to loop_hi	2423	While the C<ev_embed> watcher is running, forks in the embedding loop will
1569	if (loop_lo)	2424	automatically be applied to the embedded loop as well, so no special
1570	{	2425	fork handling is required in that case. When the watcher is not running,
1571	ev_embed_init (&embed, 0, loop_lo);	2426	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1572	ev_embed_start (loop_hi, &embed);	2427	as applicable.
1573	}	2428
1574	else	2429	=head3 Watcher-Specific Functions and Data Members
1575	loop_lo = loop_hi;
1576		2430
1577	=over 4	2431	=over 4
1578		2432
1579	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	2433	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
1580		2434
…		…
1582		2436
1583	Configures the watcher to embed the given loop, which must be	2437	Configures the watcher to embed the given loop, which must be
1584	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	2438	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1585	invoked automatically, otherwise it is the responsibility of the callback	2439	invoked automatically, otherwise it is the responsibility of the callback
1586	to invoke it (it will continue to be called until the sweep has been done,	2440	to invoke it (it will continue to be called until the sweep has been done,
1587	if you do not want thta, you need to temporarily stop the embed watcher).	2441	if you do not want that, you need to temporarily stop the embed watcher).
1588		2442
1589	=item ev_embed_sweep (loop, ev_embed *)	2443	=item ev_embed_sweep (loop, ev_embed *)
1590		2444
1591	Make a single, non-blocking sweep over the embedded loop. This works	2445	Make a single, non-blocking sweep over the embedded loop. This works
1592	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	2446	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
1593	apropriate way for embedded loops.	2447	appropriate way for embedded loops.
1594		2448
1595	=item struct ev_loop *loop [read-only]	2449	=item struct ev_loop *other [read-only]
1596		2450
1597	The embedded event loop.	2451	The embedded event loop.
1598		2452
1599	=back	2453	=back
		2454
		2455	=head3 Examples
		2456
		2457	Example: Try to get an embeddable event loop and embed it into the default
		2458	event loop. If that is not possible, use the default loop. The default
		2459	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2460	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2461	used).
		2462
		2463	struct ev_loop *loop_hi = ev_default_init (0);
		2464	struct ev_loop *loop_lo = 0;
		2465	ev_embed embed;
		2466
		2467	// see if there is a chance of getting one that works
		2468	// (remember that a flags value of 0 means autodetection)
		2469	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2470	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2471	: 0;
		2472
		2473	// if we got one, then embed it, otherwise default to loop_hi
		2474	if (loop_lo)
		2475	{
		2476	ev_embed_init (&embed, 0, loop_lo);
		2477	ev_embed_start (loop_hi, &embed);
		2478	}
		2479	else
		2480	loop_lo = loop_hi;
		2481
		2482	Example: Check if kqueue is available but not recommended and create
		2483	a kqueue backend for use with sockets (which usually work with any
		2484	kqueue implementation). Store the kqueue/socket-only event loop in
		2485	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2486
		2487	struct ev_loop *loop = ev_default_init (0);
		2488	struct ev_loop *loop_socket = 0;
		2489	ev_embed embed;
		2490
		2491	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2492	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2493	{
		2494	ev_embed_init (&embed, 0, loop_socket);
		2495	ev_embed_start (loop, &embed);
		2496	}
		2497
		2498	if (!loop_socket)
		2499	loop_socket = loop;
		2500
		2501	// now use loop_socket for all sockets, and loop for everything else
1600		2502
1601		2503
1602	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	2504	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
1603		2505
1604	Fork watchers are called when a C<fork ()> was detected (usually because	2506	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
1607	event loop blocks next and before C<ev_check> watchers are being called,	2509	event loop blocks next and before C<ev_check> watchers are being called,
1608	and only in the child after the fork. If whoever good citizen calling	2510	and only in the child after the fork. If whoever good citizen calling
1609	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2511	C<ev_default_fork> cheats and calls it in the wrong process, the fork
1610	handlers will be invoked, too, of course.	2512	handlers will be invoked, too, of course.
1611		2513
		2514	=head3 Watcher-Specific Functions and Data Members
		2515
1612	=over 4	2516	=over 4
1613		2517
1614	=item ev_fork_init (ev_signal *, callback)	2518	=item ev_fork_init (ev_signal *, callback)
1615		2519
1616	Initialises and configures the fork watcher - it has no parameters of any	2520	Initialises and configures the fork watcher - it has no parameters of any
…		…
1618	believe me.	2522	believe me.
1619		2523
1620	=back	2524	=back
1621		2525
1622		2526
		2527	=head2 C<ev_async> - how to wake up another event loop
		2528
		2529	In general, you cannot use an C<ev_loop> from multiple threads or other
		2530	asynchronous sources such as signal handlers (as opposed to multiple event
		2531	loops - those are of course safe to use in different threads).
		2532
		2533	Sometimes, however, you need to wake up another event loop you do not
		2534	control, for example because it belongs to another thread. This is what
		2535	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2536	can signal it by calling C<ev_async_send>, which is thread- and signal
		2537	safe.
		2538
		2539	This functionality is very similar to C<ev_signal> watchers, as signals,
		2540	too, are asynchronous in nature, and signals, too, will be compressed
		2541	(i.e. the number of callback invocations may be less than the number of
		2542	C<ev_async_sent> calls).
		2543
		2544	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2545	just the default loop.
		2546
		2547	=head3 Queueing
		2548
		2549	C<ev_async> does not support queueing of data in any way. The reason
		2550	is that the author does not know of a simple (or any) algorithm for a
		2551	multiple-writer-single-reader queue that works in all cases and doesn't
		2552	need elaborate support such as pthreads.
		2553
		2554	That means that if you want to queue data, you have to provide your own
		2555	queue. But at least I can tell you how to implement locking around your
		2556	queue:
		2557
		2558	=over 4
		2559
		2560	=item queueing from a signal handler context
		2561
		2562	To implement race-free queueing, you simply add to the queue in the signal
		2563	handler but you block the signal handler in the watcher callback. Here is
		2564	an example that does that for some fictitious SIGUSR1 handler:
		2565
		2566	static ev_async mysig;
		2567
		2568	static void
		2569	sigusr1_handler (void)
		2570	{
		2571	sometype data;
		2572
		2573	// no locking etc.
		2574	queue_put (data);
		2575	ev_async_send (EV_DEFAULT_ &mysig);
		2576	}
		2577
		2578	static void
		2579	mysig_cb (EV_P_ ev_async *w, int revents)
		2580	{
		2581	sometype data;
		2582	sigset_t block, prev;
		2583
		2584	sigemptyset (&block);
		2585	sigaddset (&block, SIGUSR1);
		2586	sigprocmask (SIG_BLOCK, &block, &prev);
		2587
		2588	while (queue_get (&data))
		2589	process (data);
		2590
		2591	if (sigismember (&prev, SIGUSR1)
		2592	sigprocmask (SIG_UNBLOCK, &block, 0);
		2593	}
		2594
		2595	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2596	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2597	either...).
		2598
		2599	=item queueing from a thread context
		2600
		2601	The strategy for threads is different, as you cannot (easily) block
		2602	threads but you can easily preempt them, so to queue safely you need to
		2603	employ a traditional mutex lock, such as in this pthread example:
		2604
		2605	static ev_async mysig;
		2606	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2607
		2608	static void
		2609	otherthread (void)
		2610	{
		2611	// only need to lock the actual queueing operation
		2612	pthread_mutex_lock (&mymutex);
		2613	queue_put (data);
		2614	pthread_mutex_unlock (&mymutex);
		2615
		2616	ev_async_send (EV_DEFAULT_ &mysig);
		2617	}
		2618
		2619	static void
		2620	mysig_cb (EV_P_ ev_async *w, int revents)
		2621	{
		2622	pthread_mutex_lock (&mymutex);
		2623
		2624	while (queue_get (&data))
		2625	process (data);
		2626
		2627	pthread_mutex_unlock (&mymutex);
		2628	}
		2629
		2630	=back
		2631
		2632
		2633	=head3 Watcher-Specific Functions and Data Members
		2634
		2635	=over 4
		2636
		2637	=item ev_async_init (ev_async *, callback)
		2638
		2639	Initialises and configures the async watcher - it has no parameters of any
		2640	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,
		2641	trust me.
		2642
		2643	=item ev_async_send (loop, ev_async *)
		2644
		2645	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2646	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2647	C<ev_feed_event>, this call is safe to do from other threads, signal or
		2648	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		2649	section below on what exactly this means).
		2650
		2651	This call incurs the overhead of a system call only once per loop iteration,
		2652	so while the overhead might be noticeable, it doesn't apply to repeated
		2653	calls to C<ev_async_send>.
		2654
		2655	=item bool = ev_async_pending (ev_async *)
		2656
		2657	Returns a non-zero value when C<ev_async_send> has been called on the
		2658	watcher but the event has not yet been processed (or even noted) by the
		2659	event loop.
		2660
		2661	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2662	the loop iterates next and checks for the watcher to have become active,
		2663	it will reset the flag again. C<ev_async_pending> can be used to very
		2664	quickly check whether invoking the loop might be a good idea.
		2665
		2666	Not that this does I<not> check whether the watcher itself is pending, only
		2667	whether it has been requested to make this watcher pending.
		2668
		2669	=back
		2670
		2671
1623	=head1 OTHER FUNCTIONS	2672	=head1 OTHER FUNCTIONS
1624		2673
1625	There are some other functions of possible interest. Described. Here. Now.	2674	There are some other functions of possible interest. Described. Here. Now.
1626		2675
1627	=over 4	2676	=over 4
1628		2677
1629	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	2678	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1630		2679
1631	This function combines a simple timer and an I/O watcher, calls your	2680	This function combines a simple timer and an I/O watcher, calls your
1632	callback on whichever event happens first and automatically stop both	2681	callback on whichever event happens first and automatically stops both
1633	watchers. This is useful if you want to wait for a single event on an fd	2682	watchers. This is useful if you want to wait for a single event on an fd
1634	or timeout without having to allocate/configure/start/stop/free one or	2683	or timeout without having to allocate/configure/start/stop/free one or
1635	more watchers yourself.	2684	more watchers yourself.
1636		2685
1637	If C<fd> is less than 0, then no I/O watcher will be started and events	2686	If C<fd> is less than 0, then no I/O watcher will be started and the
1638	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	2687	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1639	C<events> set will be craeted and started.	2688	the given C<fd> and C<events> set will be created and started.
1640		2689
1641	If C<timeout> is less than 0, then no timeout watcher will be	2690	If C<timeout> is less than 0, then no timeout watcher will be
1642	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	2691	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1643	repeat = 0) will be started. While C<0> is a valid timeout, it is of	2692	repeat = 0) will be started. C<0> is a valid timeout.
1644	dubious value.
1645		2693
1646	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	2694	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
1647	passed an C<revents> set like normal event callbacks (a combination of	2695	passed an C<revents> set like normal event callbacks (a combination of
1648	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	2696	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
1649	value passed to C<ev_once>:	2697	value passed to C<ev_once>. Note that it is possible to receive I<both>
		2698	a timeout and an io event at the same time - you probably should give io
		2699	events precedence.
1650		2700
		2701	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		2702
1651	static void stdin_ready (int revents, void *arg)	2703	static void stdin_ready (int revents, void *arg)
1652	{	2704	{
1653	if (revents & EV_TIMEOUT)
1654	/* doh, nothing entered */;
1655	else if (revents & EV_READ)	2705	if (revents & EV_READ)
1656	/* stdin might have data for us, joy! */;	2706	/* stdin might have data for us, joy! */;
		2707	else if (revents & EV_TIMEOUT)
		2708	/* doh, nothing entered */;
1657	}	2709	}
1658		2710
1659	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2711	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1660		2712
1661	=item ev_feed_event (ev_loop *, watcher *, int revents)	2713	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
1662		2714
1663	Feeds the given event set into the event loop, as if the specified event	2715	Feeds the given event set into the event loop, as if the specified event
1664	had happened for the specified watcher (which must be a pointer to an	2716	had happened for the specified watcher (which must be a pointer to an
1665	initialised but not necessarily started event watcher).	2717	initialised but not necessarily started event watcher).
1666		2718
1667	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	2719	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
1668		2720
1669	Feed an event on the given fd, as if a file descriptor backend detected	2721	Feed an event on the given fd, as if a file descriptor backend detected
1670	the given events it.	2722	the given events it.
1671		2723
1672	=item ev_feed_signal_event (ev_loop *loop, int signum)	2724	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
1673		2725
1674	Feed an event as if the given signal occured (C<loop> must be the default	2726	Feed an event as if the given signal occurred (C<loop> must be the default
1675	loop!).	2727	loop!).
1676		2728
1677	=back	2729	=back
1678		2730
1679		2731
…		…
1695		2747
1696	=item * Priorities are not currently supported. Initialising priorities	2748	=item * Priorities are not currently supported. Initialising priorities
1697	will fail and all watchers will have the same priority, even though there	2749	will fail and all watchers will have the same priority, even though there
1698	is an ev_pri field.	2750	is an ev_pri field.
1699		2751
		2752	=item * In libevent, the last base created gets the signals, in libev, the
		2753	first base created (== the default loop) gets the signals.
		2754
1700	=item * Other members are not supported.	2755	=item * Other members are not supported.
1701		2756
1702	=item * The libev emulation is I<not> ABI compatible to libevent, you need	2757	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1703	to use the libev header file and library.	2758	to use the libev header file and library.
1704		2759
1705	=back	2760	=back
1706		2761
1707	=head1 C++ SUPPORT	2762	=head1 C++ SUPPORT
1708		2763
1709	Libev comes with some simplistic wrapper classes for C++ that mainly allow	2764	Libev comes with some simplistic wrapper classes for C++ that mainly allow
1710	you to use some convinience methods to start/stop watchers and also change	2765	you to use some convenience methods to start/stop watchers and also change
1711	the callback model to a model using method callbacks on objects.	2766	the callback model to a model using method callbacks on objects.
1712		2767
1713	To use it,	2768	To use it,
1714		2769
1715	#include <ev++.h>	2770	#include <ev++.h>
1716		2771
1717	(it is not installed by default). This automatically includes F<ev.h>	2772	This automatically includes F<ev.h> and puts all of its definitions (many
1718	and puts all of its definitions (many of them macros) into the global	2773	of them macros) into the global namespace. All C++ specific things are
1719	namespace. All C++ specific things are put into the C<ev> namespace.	2774	put into the C<ev> namespace. It should support all the same embedding
		2775	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
1720		2776
1721	It should support all the same embedding options as F<ev.h>, most notably	2777	Care has been taken to keep the overhead low. The only data member the C++
1722	C<EV_MULTIPLICITY>.	2778	classes add (compared to plain C-style watchers) is the event loop pointer
		2779	that the watcher is associated with (or no additional members at all if
		2780	you disable C<EV_MULTIPLICITY> when embedding libev).
		2781
		2782	Currently, functions, and static and non-static member functions can be
		2783	used as callbacks. Other types should be easy to add as long as they only
		2784	need one additional pointer for context. If you need support for other
		2785	types of functors please contact the author (preferably after implementing
		2786	it).
1723		2787
1724	Here is a list of things available in the C<ev> namespace:	2788	Here is a list of things available in the C<ev> namespace:
1725		2789
1726	=over 4	2790	=over 4
1727		2791
…		…
1743		2807
1744	All of those classes have these methods:	2808	All of those classes have these methods:
1745		2809
1746	=over 4	2810	=over 4
1747		2811
1748	=item ev::TYPE::TYPE (object *, object::method *)	2812	=item ev::TYPE::TYPE ()
1749		2813
1750	=item ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)	2814	=item ev::TYPE::TYPE (struct ev_loop *)
1751		2815
1752	=item ev::TYPE::~TYPE	2816	=item ev::TYPE::~TYPE
1753		2817
1754	The constructor takes a pointer to an object and a method pointer to	2818	The constructor (optionally) takes an event loop to associate the watcher
1755	the event handler callback to call in this class. The constructor calls	2819	with. If it is omitted, it will use C<EV_DEFAULT>.
1756	C<ev_init> for you, which means you have to call the C<set> method	2820
1757	before starting it. If you do not specify a loop then the constructor	2821	The constructor calls C<ev_init> for you, which means you have to call the
1758	automatically associates the default loop with this watcher.	2822	C<set> method before starting it.
		2823
		2824	It will not set a callback, however: You have to call the templated C<set>
		2825	method to set a callback before you can start the watcher.
		2826
		2827	(The reason why you have to use a method is a limitation in C++ which does
		2828	not allow explicit template arguments for constructors).
1759		2829
1760	The destructor automatically stops the watcher if it is active.	2830	The destructor automatically stops the watcher if it is active.
		2831
		2832	=item w->set<class, &class::method> (object *)
		2833
		2834	This method sets the callback method to call. The method has to have a
		2835	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		2836	first argument and the C<revents> as second. The object must be given as
		2837	parameter and is stored in the C<data> member of the watcher.
		2838
		2839	This method synthesizes efficient thunking code to call your method from
		2840	the C callback that libev requires. If your compiler can inline your
		2841	callback (i.e. it is visible to it at the place of the C<set> call and
		2842	your compiler is good :), then the method will be fully inlined into the
		2843	thunking function, making it as fast as a direct C callback.
		2844
		2845	Example: simple class declaration and watcher initialisation
		2846
		2847	struct myclass
		2848	{
		2849	void io_cb (ev::io &w, int revents) { }
		2850	}
		2851
		2852	myclass obj;
		2853	ev::io iow;
		2854	iow.set <myclass, &myclass::io_cb> (&obj);
		2855
		2856	=item w->set<function> (void *data = 0)
		2857
		2858	Also sets a callback, but uses a static method or plain function as
		2859	callback. The optional C<data> argument will be stored in the watcher's
		2860	C<data> member and is free for you to use.
		2861
		2862	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		2863
		2864	See the method-C<set> above for more details.
		2865
		2866	Example: Use a plain function as callback.
		2867
		2868	static void io_cb (ev::io &w, int revents) { }
		2869	iow.set <io_cb> ();
1761		2870
1762	=item w->set (struct ev_loop *)	2871	=item w->set (struct ev_loop *)
1763		2872
1764	Associates a different C<struct ev_loop> with this watcher. You can only	2873	Associates a different C<struct ev_loop> with this watcher. You can only
1765	do this when the watcher is inactive (and not pending either).	2874	do this when the watcher is inactive (and not pending either).
1766		2875
1767	=item w->set ([args])	2876	=item w->set ([arguments])
1768		2877
1769	Basically the same as C<ev_TYPE_set>, with the same args. Must be	2878	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
1770	called at least once. Unlike the C counterpart, an active watcher gets	2879	called at least once. Unlike the C counterpart, an active watcher gets
1771	automatically stopped and restarted.	2880	automatically stopped and restarted when reconfiguring it with this
		2881	method.
1772		2882
1773	=item w->start ()	2883	=item w->start ()
1774		2884
1775	Starts the watcher. Note that there is no C<loop> argument as the	2885	Starts the watcher. Note that there is no C<loop> argument, as the
1776	constructor already takes the loop.	2886	constructor already stores the event loop.
1777		2887
1778	=item w->stop ()	2888	=item w->stop ()
1779		2889
1780	Stops the watcher if it is active. Again, no C<loop> argument.	2890	Stops the watcher if it is active. Again, no C<loop> argument.
1781		2891
1782	=item w->again () C<ev::timer>, C<ev::periodic> only	2892	=item w->again () (C<ev::timer>, C<ev::periodic> only)
1783		2893
1784	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding	2894	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
1785	C<ev_TYPE_again> function.	2895	C<ev_TYPE_again> function.
1786		2896
1787	=item w->sweep () C<ev::embed> only	2897	=item w->sweep () (C<ev::embed> only)
1788		2898
1789	Invokes C<ev_embed_sweep>.	2899	Invokes C<ev_embed_sweep>.
1790		2900
1791	=item w->update () C<ev::stat> only	2901	=item w->update () (C<ev::stat> only)
1792		2902
1793	Invokes C<ev_stat_stat>.	2903	Invokes C<ev_stat_stat>.
1794		2904
1795	=back	2905	=back
1796		2906
1797	=back	2907	=back
1798		2908
1799	Example: Define a class with an IO and idle watcher, start one of them in	2909	Example: Define a class with an IO and idle watcher, start one of them in
1800	the constructor.	2910	the constructor.
1801		2911
1802	class myclass	2912	class myclass
1803	{	2913	{
1804	ev_io io; void io_cb (ev::io &w, int revents);	2914	ev::io io ; void io_cb (ev::io &w, int revents);
1805	ev_idle idle void idle_cb (ev::idle &w, int revents);	2915	ev::idle idle; void idle_cb (ev::idle &w, int revents);
1806		2916
1807	myclass ();	2917	myclass (int fd)
1808	}	2918	{
		2919	io .set <myclass, &myclass::io_cb > (this);
		2920	idle.set <myclass, &myclass::idle_cb> (this);
1809		2921
1810	myclass::myclass (int fd)
1811	: io (this, &myclass::io_cb),
1812	idle (this, &myclass::idle_cb)
1813	{
1814	io.start (fd, ev::READ);	2922	io.start (fd, ev::READ);
		2923	}
1815	}	2924	};
		2925
		2926
		2927	=head1 OTHER LANGUAGE BINDINGS
		2928
		2929	Libev does not offer other language bindings itself, but bindings for a
		2930	number of languages exist in the form of third-party packages. If you know
		2931	any interesting language binding in addition to the ones listed here, drop
		2932	me a note.
		2933
		2934	=over 4
		2935
		2936	=item Perl
		2937
		2938	The EV module implements the full libev API and is actually used to test
		2939	libev. EV is developed together with libev. Apart from the EV core module,
		2940	there are additional modules that implement libev-compatible interfaces
		2941	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		2942	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		2943	and C<EV::Glib>).
		2944
		2945	It can be found and installed via CPAN, its homepage is at
		2946	L<http://software.schmorp.de/pkg/EV>.
		2947
		2948	=item Python
		2949
		2950	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		2951	seems to be quite complete and well-documented. Note, however, that the
		2952	patch they require for libev is outright dangerous as it breaks the ABI
		2953	for everybody else, and therefore, should never be applied in an installed
		2954	libev (if python requires an incompatible ABI then it needs to embed
		2955	libev).
		2956
		2957	=item Ruby
		2958
		2959	Tony Arcieri has written a ruby extension that offers access to a subset
		2960	of the libev API and adds file handle abstractions, asynchronous DNS and
		2961	more on top of it. It can be found via gem servers. Its homepage is at
		2962	L<http://rev.rubyforge.org/>.
		2963
		2964	=item D
		2965
		2966	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		2967	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		2968
		2969	=item Ocaml
		2970
		2971	Erkki Seppala has written Ocaml bindings for libev, to be found at
		2972	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		2973
		2974	=back
1816		2975
1817		2976
1818	=head1 MACRO MAGIC	2977	=head1 MACRO MAGIC
1819		2978
1820	Libev can be compiled with a variety of options, the most fundemantal is	2979	Libev can be compiled with a variety of options, the most fundamental
1821	C<EV_MULTIPLICITY>. This option determines wether (most) functions and	2980	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
1822	callbacks have an initial C<struct ev_loop *> argument.	2981	functions and callbacks have an initial C<struct ev_loop *> argument.
1823		2982
1824	To make it easier to write programs that cope with either variant, the	2983	To make it easier to write programs that cope with either variant, the
1825	following macros are defined:	2984	following macros are defined:
1826		2985
1827	=over 4	2986	=over 4
…		…
1830		2989
1831	This provides the loop I<argument> for functions, if one is required ("ev	2990	This provides the loop I<argument> for functions, if one is required ("ev
1832	loop argument"). The C<EV_A> form is used when this is the sole argument,	2991	loop argument"). The C<EV_A> form is used when this is the sole argument,
1833	C<EV_A_> is used when other arguments are following. Example:	2992	C<EV_A_> is used when other arguments are following. Example:
1834		2993
1835	ev_unref (EV_A);	2994	ev_unref (EV_A);
1836	ev_timer_add (EV_A_ watcher);	2995	ev_timer_add (EV_A_ watcher);
1837	ev_loop (EV_A_ 0);	2996	ev_loop (EV_A_ 0);
1838		2997
1839	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	2998	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
1840	which is often provided by the following macro.	2999	which is often provided by the following macro.
1841		3000
1842	=item C<EV_P>, C<EV_P_>	3001	=item C<EV_P>, C<EV_P_>
1843		3002
1844	This provides the loop I<parameter> for functions, if one is required ("ev	3003	This provides the loop I<parameter> for functions, if one is required ("ev
1845	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	3004	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
1846	C<EV_P_> is used when other parameters are following. Example:	3005	C<EV_P_> is used when other parameters are following. Example:
1847		3006
1848	// this is how ev_unref is being declared	3007	// this is how ev_unref is being declared
1849	static void ev_unref (EV_P);	3008	static void ev_unref (EV_P);
1850		3009
1851	// this is how you can declare your typical callback	3010	// this is how you can declare your typical callback
1852	static void cb (EV_P_ ev_timer *w, int revents)	3011	static void cb (EV_P_ ev_timer *w, int revents)
1853		3012
1854	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	3013	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
1855	suitable for use with C<EV_A>.	3014	suitable for use with C<EV_A>.
1856		3015
1857	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3016	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
1858		3017
1859	Similar to the other two macros, this gives you the value of the default	3018	Similar to the other two macros, this gives you the value of the default
1860	loop, if multiple loops are supported ("ev loop default").	3019	loop, if multiple loops are supported ("ev loop default").
1861		3020
		3021	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3022
		3023	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3024	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3025	is undefined when the default loop has not been initialised by a previous
		3026	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3027
		3028	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3029	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		3030
1862	=back	3031	=back
1863		3032
1864	Example: Declare and initialise a check watcher, utilising the above	3033	Example: Declare and initialise a check watcher, utilising the above
1865	macros so it will work regardless of wether multiple loops are supported	3034	macros so it will work regardless of whether multiple loops are supported
1866	or not.	3035	or not.
1867		3036
1868	static void	3037	static void
1869	check_cb (EV_P_ ev_timer *w, int revents)	3038	check_cb (EV_P_ ev_timer *w, int revents)
1870	{	3039	{
1871	ev_check_stop (EV_A_ w);	3040	ev_check_stop (EV_A_ w);
1872	}	3041	}
1873		3042
1874	ev_check check;	3043	ev_check check;
1875	ev_check_init (&check, check_cb);	3044	ev_check_init (&check, check_cb);
1876	ev_check_start (EV_DEFAULT_ &check);	3045	ev_check_start (EV_DEFAULT_ &check);
1877	ev_loop (EV_DEFAULT_ 0);	3046	ev_loop (EV_DEFAULT_ 0);
1878		3047
1879	=head1 EMBEDDING	3048	=head1 EMBEDDING
1880		3049
1881	Libev can (and often is) directly embedded into host	3050	Libev can (and often is) directly embedded into host
1882	applications. Examples of applications that embed it include the Deliantra	3051	applications. Examples of applications that embed it include the Deliantra
1883	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)	3052	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
1884	and rxvt-unicode.	3053	and rxvt-unicode.
1885		3054
1886	The goal is to enable you to just copy the neecssary files into your	3055	The goal is to enable you to just copy the necessary files into your
1887	source directory without having to change even a single line in them, so	3056	source directory without having to change even a single line in them, so
1888	you can easily upgrade by simply copying (or having a checked-out copy of	3057	you can easily upgrade by simply copying (or having a checked-out copy of
1889	libev somewhere in your source tree).	3058	libev somewhere in your source tree).
1890		3059
1891	=head2 FILESETS	3060	=head2 FILESETS
1892		3061
1893	Depending on what features you need you need to include one or more sets of files	3062	Depending on what features you need you need to include one or more sets of files
1894	in your app.	3063	in your application.
1895		3064
1896	=head3 CORE EVENT LOOP	3065	=head3 CORE EVENT LOOP
1897		3066
1898	To include only the libev core (all the C<ev_*> functions), with manual	3067	To include only the libev core (all the C<ev_*> functions), with manual
1899	configuration (no autoconf):	3068	configuration (no autoconf):
1900		3069
1901	#define EV_STANDALONE 1	3070	#define EV_STANDALONE 1
1902	#include "ev.c"	3071	#include "ev.c"
1903		3072
1904	This will automatically include F<ev.h>, too, and should be done in a	3073	This will automatically include F<ev.h>, too, and should be done in a
1905	single C source file only to provide the function implementations. To use	3074	single C source file only to provide the function implementations. To use
1906	it, do the same for F<ev.h> in all files wishing to use this API (best	3075	it, do the same for F<ev.h> in all files wishing to use this API (best
1907	done by writing a wrapper around F<ev.h> that you can include instead and	3076	done by writing a wrapper around F<ev.h> that you can include instead and
1908	where you can put other configuration options):	3077	where you can put other configuration options):
1909		3078
1910	#define EV_STANDALONE 1	3079	#define EV_STANDALONE 1
1911	#include "ev.h"	3080	#include "ev.h"
1912		3081
1913	Both header files and implementation files can be compiled with a C++	3082	Both header files and implementation files can be compiled with a C++
1914	compiler (at least, thats a stated goal, and breakage will be treated	3083	compiler (at least, thats a stated goal, and breakage will be treated
1915	as a bug).	3084	as a bug).
1916		3085
1917	You need the following files in your source tree, or in a directory	3086	You need the following files in your source tree, or in a directory
1918	in your include path (e.g. in libev/ when using -Ilibev):	3087	in your include path (e.g. in libev/ when using -Ilibev):
1919		3088
1920	ev.h	3089	ev.h
1921	ev.c	3090	ev.c
1922	ev_vars.h	3091	ev_vars.h
1923	ev_wrap.h	3092	ev_wrap.h
1924		3093
1925	ev_win32.c required on win32 platforms only	3094	ev_win32.c required on win32 platforms only
1926		3095
1927	ev_select.c only when select backend is enabled (which is enabled by default)	3096	ev_select.c only when select backend is enabled (which is enabled by default)
1928	ev_poll.c only when poll backend is enabled (disabled by default)	3097	ev_poll.c only when poll backend is enabled (disabled by default)
1929	ev_epoll.c only when the epoll backend is enabled (disabled by default)	3098	ev_epoll.c only when the epoll backend is enabled (disabled by default)
1930	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	3099	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
1931	ev_port.c only when the solaris port backend is enabled (disabled by default)	3100	ev_port.c only when the solaris port backend is enabled (disabled by default)
1932		3101
1933	F<ev.c> includes the backend files directly when enabled, so you only need	3102	F<ev.c> includes the backend files directly when enabled, so you only need
1934	to compile this single file.	3103	to compile this single file.
1935		3104
1936	=head3 LIBEVENT COMPATIBILITY API	3105	=head3 LIBEVENT COMPATIBILITY API
1937		3106
1938	To include the libevent compatibility API, also include:	3107	To include the libevent compatibility API, also include:
1939		3108
1940	#include "event.c"	3109	#include "event.c"
1941		3110
1942	in the file including F<ev.c>, and:	3111	in the file including F<ev.c>, and:
1943		3112
1944	#include "event.h"	3113	#include "event.h"
1945		3114
1946	in the files that want to use the libevent API. This also includes F<ev.h>.	3115	in the files that want to use the libevent API. This also includes F<ev.h>.
1947		3116
1948	You need the following additional files for this:	3117	You need the following additional files for this:
1949		3118
1950	event.h	3119	event.h
1951	event.c	3120	event.c
1952		3121
1953	=head3 AUTOCONF SUPPORT	3122	=head3 AUTOCONF SUPPORT
1954		3123
1955	Instead of using C<EV_STANDALONE=1> and providing your config in	3124	Instead of using C<EV_STANDALONE=1> and providing your configuration in
1956	whatever way you want, you can also C<m4_include([libev.m4])> in your	3125	whatever way you want, you can also C<m4_include([libev.m4])> in your
1957	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	3126	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
1958	include F<config.h> and configure itself accordingly.	3127	include F<config.h> and configure itself accordingly.
1959		3128
1960	For this of course you need the m4 file:	3129	For this of course you need the m4 file:
1961		3130
1962	libev.m4	3131	libev.m4
1963		3132
1964	=head2 PREPROCESSOR SYMBOLS/MACROS	3133	=head2 PREPROCESSOR SYMBOLS/MACROS
1965		3134
1966	Libev can be configured via a variety of preprocessor symbols you have to define	3135	Libev can be configured via a variety of preprocessor symbols you have to
1967	before including any of its files. The default is not to build for multiplicity	3136	define before including any of its files. The default in the absence of
1968	and only include the select backend.	3137	autoconf is documented for every option.
1969		3138
1970	=over 4	3139	=over 4
1971		3140
1972	=item EV_STANDALONE	3141	=item EV_STANDALONE
1973		3142
…		…
1978	F<event.h> that are not directly supported by the libev core alone.	3147	F<event.h> that are not directly supported by the libev core alone.
1979		3148
1980	=item EV_USE_MONOTONIC	3149	=item EV_USE_MONOTONIC
1981		3150
1982	If defined to be C<1>, libev will try to detect the availability of the	3151	If defined to be C<1>, libev will try to detect the availability of the
1983	monotonic clock option at both compiletime and runtime. Otherwise no use	3152	monotonic clock option at both compile time and runtime. Otherwise no use
1984	of the monotonic clock option will be attempted. If you enable this, you	3153	of the monotonic clock option will be attempted. If you enable this, you
1985	usually have to link against librt or something similar. Enabling it when	3154	usually have to link against librt or something similar. Enabling it when
1986	the functionality isn't available is safe, though, althoguh you have	3155	the functionality isn't available is safe, though, although you have
1987	to make sure you link against any libraries where the C<clock_gettime>	3156	to make sure you link against any libraries where the C<clock_gettime>
1988	function is hiding in (often F<-lrt>).	3157	function is hiding in (often F<-lrt>).
1989		3158
1990	=item EV_USE_REALTIME	3159	=item EV_USE_REALTIME
1991		3160
1992	If defined to be C<1>, libev will try to detect the availability of the	3161	If defined to be C<1>, libev will try to detect the availability of the
1993	realtime clock option at compiletime (and assume its availability at	3162	real-time clock option at compile time (and assume its availability at
1994	runtime if successful). Otherwise no use of the realtime clock option will	3163	runtime if successful). Otherwise no use of the real-time clock option will
1995	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3164	be attempted. This effectively replaces C<gettimeofday> by C<clock_get
1996	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See tzhe note about libraries	3165	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the
1997	in the description of C<EV_USE_MONOTONIC>, though.	3166	note about libraries in the description of C<EV_USE_MONOTONIC>, though.
		3167
		3168	=item EV_USE_NANOSLEEP
		3169
		3170	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		3171	and will use it for delays. Otherwise it will use C<select ()>.
		3172
		3173	=item EV_USE_EVENTFD
		3174
		3175	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3176	available and will probe for kernel support at runtime. This will improve
		3177	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3178	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3179	2.7 or newer, otherwise disabled.
1998		3180
1999	=item EV_USE_SELECT	3181	=item EV_USE_SELECT
2000		3182
2001	If undefined or defined to be C<1>, libev will compile in support for the	3183	If undefined or defined to be C<1>, libev will compile in support for the
2002	C<select>(2) backend. No attempt at autodetection will be done: if no	3184	C<select>(2) backend. No attempt at auto-detection will be done: if no
2003	other method takes over, select will be it. Otherwise the select backend	3185	other method takes over, select will be it. Otherwise the select backend
2004	will not be compiled in.	3186	will not be compiled in.
2005		3187
2006	=item EV_SELECT_USE_FD_SET	3188	=item EV_SELECT_USE_FD_SET
2007		3189
2008	If defined to C<1>, then the select backend will use the system C<fd_set>	3190	If defined to C<1>, then the select backend will use the system C<fd_set>
2009	structure. This is useful if libev doesn't compile due to a missing	3191	structure. This is useful if libev doesn't compile due to a missing
2010	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	3192	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout on
2011	exotic systems. This usually limits the range of file descriptors to some	3193	exotic systems. This usually limits the range of file descriptors to some
2012	low limit such as 1024 or might have other limitations (winsocket only	3194	low limit such as 1024 or might have other limitations (winsocket only
2013	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3195	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might
2014	influence the size of the C<fd_set> used.	3196	influence the size of the C<fd_set> used.
2015		3197
…		…
2021	be used is the winsock select). This means that it will call	3203	be used is the winsock select). This means that it will call
2022	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3204	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2023	it is assumed that all these functions actually work on fds, even	3205	it is assumed that all these functions actually work on fds, even
2024	on win32. Should not be defined on non-win32 platforms.	3206	on win32. Should not be defined on non-win32 platforms.
2025		3207
		3208	=item EV_FD_TO_WIN32_HANDLE
		3209
		3210	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3211	file descriptors to socket handles. When not defining this symbol (the
		3212	default), then libev will call C<_get_osfhandle>, which is usually
		3213	correct. In some cases, programs use their own file descriptor management,
		3214	in which case they can provide this function to map fds to socket handles.
		3215
2026	=item EV_USE_POLL	3216	=item EV_USE_POLL
2027		3217
2028	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3218	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2029	backend. Otherwise it will be enabled on non-win32 platforms. It	3219	backend. Otherwise it will be enabled on non-win32 platforms. It
2030	takes precedence over select.	3220	takes precedence over select.
2031		3221
2032	=item EV_USE_EPOLL	3222	=item EV_USE_EPOLL
2033		3223
2034	If defined to be C<1>, libev will compile in support for the Linux	3224	If defined to be C<1>, libev will compile in support for the Linux
2035	C<epoll>(7) backend. Its availability will be detected at runtime,	3225	C<epoll>(7) backend. Its availability will be detected at runtime,
2036	otherwise another method will be used as fallback. This is the	3226	otherwise another method will be used as fallback. This is the preferred
2037	preferred backend for GNU/Linux systems.	3227	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3228	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2038		3229
2039	=item EV_USE_KQUEUE	3230	=item EV_USE_KQUEUE
2040		3231
2041	If defined to be C<1>, libev will compile in support for the BSD style	3232	If defined to be C<1>, libev will compile in support for the BSD style
2042	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	3233	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2055	otherwise another method will be used as fallback. This is the preferred	3246	otherwise another method will be used as fallback. This is the preferred
2056	backend for Solaris 10 systems.	3247	backend for Solaris 10 systems.
2057		3248
2058	=item EV_USE_DEVPOLL	3249	=item EV_USE_DEVPOLL
2059		3250
2060	reserved for future expansion, works like the USE symbols above.	3251	Reserved for future expansion, works like the USE symbols above.
2061		3252
2062	=item EV_USE_INOTIFY	3253	=item EV_USE_INOTIFY
2063		3254
2064	If defined to be C<1>, libev will compile in support for the Linux inotify	3255	If defined to be C<1>, libev will compile in support for the Linux inotify
2065	interface to speed up C<ev_stat> watchers. Its actual availability will	3256	interface to speed up C<ev_stat> watchers. Its actual availability will
2066	be detected at runtime.	3257	be detected at runtime. If undefined, it will be enabled if the headers
		3258	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3259
		3260	=item EV_ATOMIC_T
		3261
		3262	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3263	access is atomic with respect to other threads or signal contexts. No such
		3264	type is easily found in the C language, so you can provide your own type
		3265	that you know is safe for your purposes. It is used both for signal handler "locking"
		3266	as well as for signal and thread safety in C<ev_async> watchers.
		3267
		3268	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3269	(from F<signal.h>), which is usually good enough on most platforms.
2067		3270
2068	=item EV_H	3271	=item EV_H
2069		3272
2070	The name of the F<ev.h> header file used to include it. The default if	3273	The name of the F<ev.h> header file used to include it. The default if
2071	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This	3274	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2072	can be used to virtually rename the F<ev.h> header file in case of conflicts.	3275	used to virtually rename the F<ev.h> header file in case of conflicts.
2073		3276
2074	=item EV_CONFIG_H	3277	=item EV_CONFIG_H
2075		3278
2076	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	3279	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2077	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	3280	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2078	C<EV_H>, above.	3281	C<EV_H>, above.
2079		3282
2080	=item EV_EVENT_H	3283	=item EV_EVENT_H
2081		3284
2082	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	3285	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2083	of how the F<event.h> header can be found.	3286	of how the F<event.h> header can be found, the default is C<"event.h">.
2084		3287
2085	=item EV_PROTOTYPES	3288	=item EV_PROTOTYPES
2086		3289
2087	If defined to be C<0>, then F<ev.h> will not define any function	3290	If defined to be C<0>, then F<ev.h> will not define any function
2088	prototypes, but still define all the structs and other symbols. This is	3291	prototypes, but still define all the structs and other symbols. This is
…		…
2095	will have the C<struct ev_loop *> as first argument, and you can create	3298	will have the C<struct ev_loop *> as first argument, and you can create
2096	additional independent event loops. Otherwise there will be no support	3299	additional independent event loops. Otherwise there will be no support
2097	for multiple event loops and there is no first event loop pointer	3300	for multiple event loops and there is no first event loop pointer
2098	argument. Instead, all functions act on the single default loop.	3301	argument. Instead, all functions act on the single default loop.
2099		3302
		3303	=item EV_MINPRI
		3304
		3305	=item EV_MAXPRI
		3306
		3307	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		3308	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		3309	provide for more priorities by overriding those symbols (usually defined
		3310	to be C<-2> and C<2>, respectively).
		3311
		3312	When doing priority-based operations, libev usually has to linearly search
		3313	all the priorities, so having many of them (hundreds) uses a lot of space
		3314	and time, so using the defaults of five priorities (-2 .. +2) is usually
		3315	fine.
		3316
		3317	If your embedding application does not need any priorities, defining these
		3318	both to C<0> will save some memory and CPU.
		3319
2100	=item EV_PERIODIC_ENABLE	3320	=item EV_PERIODIC_ENABLE
2101		3321
2102	If undefined or defined to be C<1>, then periodic timers are supported. If	3322	If undefined or defined to be C<1>, then periodic timers are supported. If
2103	defined to be C<0>, then they are not. Disabling them saves a few kB of	3323	defined to be C<0>, then they are not. Disabling them saves a few kB of
2104	code.	3324	code.
2105		3325
		3326	=item EV_IDLE_ENABLE
		3327
		3328	If undefined or defined to be C<1>, then idle watchers are supported. If
		3329	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3330	code.
		3331
2106	=item EV_EMBED_ENABLE	3332	=item EV_EMBED_ENABLE
2107		3333
2108	If undefined or defined to be C<1>, then embed watchers are supported. If	3334	If undefined or defined to be C<1>, then embed watchers are supported. If
2109	defined to be C<0>, then they are not.	3335	defined to be C<0>, then they are not. Embed watchers rely on most other
		3336	watcher types, which therefore must not be disabled.
2110		3337
2111	=item EV_STAT_ENABLE	3338	=item EV_STAT_ENABLE
2112		3339
2113	If undefined or defined to be C<1>, then stat watchers are supported. If	3340	If undefined or defined to be C<1>, then stat watchers are supported. If
2114	defined to be C<0>, then they are not.	3341	defined to be C<0>, then they are not.
…		…
2116	=item EV_FORK_ENABLE	3343	=item EV_FORK_ENABLE
2117		3344
2118	If undefined or defined to be C<1>, then fork watchers are supported. If	3345	If undefined or defined to be C<1>, then fork watchers are supported. If
2119	defined to be C<0>, then they are not.	3346	defined to be C<0>, then they are not.
2120		3347
		3348	=item EV_ASYNC_ENABLE
		3349
		3350	If undefined or defined to be C<1>, then async watchers are supported. If
		3351	defined to be C<0>, then they are not.
		3352
2121	=item EV_MINIMAL	3353	=item EV_MINIMAL
2122		3354
2123	If you need to shave off some kilobytes of code at the expense of some	3355	If you need to shave off some kilobytes of code at the expense of some
2124	speed, define this symbol to C<1>. Currently only used for gcc to override	3356	speed, define this symbol to C<1>. Currently this is used to override some
2125	some inlining decisions, saves roughly 30% codesize of amd64.	3357	inlining decisions, saves roughly 30% code size on amd64. It also selects a
		3358	much smaller 2-heap for timer management over the default 4-heap.
2126		3359
2127	=item EV_PID_HASHSIZE	3360	=item EV_PID_HASHSIZE
2128		3361
2129	C<ev_child> watchers use a small hash table to distribute workload by	3362	C<ev_child> watchers use a small hash table to distribute workload by
2130	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3363	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
2131	than enough. If you need to manage thousands of children you might want to	3364	than enough. If you need to manage thousands of children you might want to
2132	increase this value (I<must> be a power of two).	3365	increase this value (I<must> be a power of two).
2133		3366
2134	=item EV_INOTIFY_HASHSIZE	3367	=item EV_INOTIFY_HASHSIZE
2135		3368
2136	C<ev_staz> watchers use a small hash table to distribute workload by	3369	C<ev_stat> watchers use a small hash table to distribute workload by
2137	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	3370	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
2138	usually more than enough. If you need to manage thousands of C<ev_stat>	3371	usually more than enough. If you need to manage thousands of C<ev_stat>
2139	watchers you might want to increase this value (I<must> be a power of	3372	watchers you might want to increase this value (I<must> be a power of
2140	two).	3373	two).
2141		3374
		3375	=item EV_USE_4HEAP
		3376
		3377	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3378	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		3379	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		3380	faster performance with many (thousands) of watchers.
		3381
		3382	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3383	(disabled).
		3384
		3385	=item EV_HEAP_CACHE_AT
		3386
		3387	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3388	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		3389	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3390	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3391	but avoids random read accesses on heap changes. This improves performance
		3392	noticeably with many (hundreds) of watchers.
		3393
		3394	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3395	(disabled).
		3396
		3397	=item EV_VERIFY
		3398
		3399	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3400	be done: If set to C<0>, no internal verification code will be compiled
		3401	in. If set to C<1>, then verification code will be compiled in, but not
		3402	called. If set to C<2>, then the internal verification code will be
		3403	called once per loop, which can slow down libev. If set to C<3>, then the
		3404	verification code will be called very frequently, which will slow down
		3405	libev considerably.
		3406
		3407	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3408	C<0>.
		3409
2142	=item EV_COMMON	3410	=item EV_COMMON
2143		3411
2144	By default, all watchers have a C<void *data> member. By redefining	3412	By default, all watchers have a C<void *data> member. By redefining
2145	this macro to a something else you can include more and other types of	3413	this macro to a something else you can include more and other types of
2146	members. You have to define it each time you include one of the files,	3414	members. You have to define it each time you include one of the files,
2147	though, and it must be identical each time.	3415	though, and it must be identical each time.
2148		3416
2149	For example, the perl EV module uses something like this:	3417	For example, the perl EV module uses something like this:
2150		3418
2151	#define EV_COMMON \	3419	#define EV_COMMON \
2152	SV *self; /* contains this struct */ \	3420	SV *self; /* contains this struct */ \
2153	SV *cb_sv, *fh /* note no trailing ";" */	3421	SV *cb_sv, *fh /* note no trailing ";" */
2154		3422
2155	=item EV_CB_DECLARE (type)	3423	=item EV_CB_DECLARE (type)
2156		3424
2157	=item EV_CB_INVOKE (watcher, revents)	3425	=item EV_CB_INVOKE (watcher, revents)
2158		3426
2159	=item ev_set_cb (ev, cb)	3427	=item ev_set_cb (ev, cb)
2160		3428
2161	Can be used to change the callback member declaration in each watcher,	3429	Can be used to change the callback member declaration in each watcher,
2162	and the way callbacks are invoked and set. Must expand to a struct member	3430	and the way callbacks are invoked and set. Must expand to a struct member
2163	definition and a statement, respectively. See the F<ev.v> header file for	3431	definition and a statement, respectively. See the F<ev.h> header file for
2164	their default definitions. One possible use for overriding these is to	3432	their default definitions. One possible use for overriding these is to
2165	avoid the C<struct ev_loop *> as first argument in all cases, or to use	3433	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2166	method calls instead of plain function calls in C++.	3434	method calls instead of plain function calls in C++.
		3435
		3436	=back
		3437
		3438	=head2 EXPORTED API SYMBOLS
		3439
		3440	If you need to re-export the API (e.g. via a DLL) and you need a list of
		3441	exported symbols, you can use the provided F<Symbol.*> files which list
		3442	all public symbols, one per line:
		3443
		3444	Symbols.ev for libev proper
		3445	Symbols.event for the libevent emulation
		3446
		3447	This can also be used to rename all public symbols to avoid clashes with
		3448	multiple versions of libev linked together (which is obviously bad in
		3449	itself, but sometimes it is inconvenient to avoid this).
		3450
		3451	A sed command like this will create wrapper C<#define>'s that you need to
		3452	include before including F<ev.h>:
		3453
		3454	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		3455
		3456	This would create a file F<wrap.h> which essentially looks like this:
		3457
		3458	#define ev_backend myprefix_ev_backend
		3459	#define ev_check_start myprefix_ev_check_start
		3460	#define ev_check_stop myprefix_ev_check_stop
		3461	...
2167		3462
2168	=head2 EXAMPLES	3463	=head2 EXAMPLES
2169		3464
2170	For a real-world example of a program the includes libev	3465	For a real-world example of a program the includes libev
2171	verbatim, you can have a look at the EV perl module	3466	verbatim, you can have a look at the EV perl module
…		…
2176	file.	3471	file.
2177		3472
2178	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	3473	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2179	that everybody includes and which overrides some configure choices:	3474	that everybody includes and which overrides some configure choices:
2180		3475
2181	#define EV_MINIMAL 1	3476	#define EV_MINIMAL 1
2182	#define EV_USE_POLL 0	3477	#define EV_USE_POLL 0
2183	#define EV_MULTIPLICITY 0	3478	#define EV_MULTIPLICITY 0
2184	#define EV_PERIODIC_ENABLE 0	3479	#define EV_PERIODIC_ENABLE 0
2185	#define EV_STAT_ENABLE 0	3480	#define EV_STAT_ENABLE 0
2186	#define EV_FORK_ENABLE 0	3481	#define EV_FORK_ENABLE 0
2187	#define EV_CONFIG_H <config.h>	3482	#define EV_CONFIG_H <config.h>
2188	#define EV_MINPRI 0	3483	#define EV_MINPRI 0
2189	#define EV_MAXPRI 0	3484	#define EV_MAXPRI 0
2190		3485
2191	#include "ev++.h"	3486	#include "ev++.h"
2192		3487
2193	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	3488	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2194		3489
2195	#include "ev_cpp.h"	3490	#include "ev_cpp.h"
2196	#include "ev.c"	3491	#include "ev.c"
2197		3492
		3493	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
2198		3494
		3495	=head2 THREADS AND COROUTINES
		3496
		3497	=head3 THREADS
		3498
		3499	All libev functions are reentrant and thread-safe unless explicitly
		3500	documented otherwise, but libev implements no locking itself. This means
		3501	that you can use as many loops as you want in parallel, as long as there
		3502	are no concurrent calls into any libev function with the same loop
		3503	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		3504	of course): libev guarantees that different event loops share no data
		3505	structures that need any locking.
		3506
		3507	Or to put it differently: calls with different loop parameters can be done
		3508	concurrently from multiple threads, calls with the same loop parameter
		3509	must be done serially (but can be done from different threads, as long as
		3510	only one thread ever is inside a call at any point in time, e.g. by using
		3511	a mutex per loop).
		3512
		3513	Specifically to support threads (and signal handlers), libev implements
		3514	so-called C<ev_async> watchers, which allow some limited form of
		3515	concurrency on the same event loop, namely waking it up "from the
		3516	outside".
		3517
		3518	If you want to know which design (one loop, locking, or multiple loops
		3519	without or something else still) is best for your problem, then I cannot
		3520	help you, but here is some generic advice:
		3521
		3522	=over 4
		3523
		3524	=item * most applications have a main thread: use the default libev loop
		3525	in that thread, or create a separate thread running only the default loop.
		3526
		3527	This helps integrating other libraries or software modules that use libev
		3528	themselves and don't care/know about threading.
		3529
		3530	=item * one loop per thread is usually a good model.
		3531
		3532	Doing this is almost never wrong, sometimes a better-performance model
		3533	exists, but it is always a good start.
		3534
		3535	=item * other models exist, such as the leader/follower pattern, where one
		3536	loop is handed through multiple threads in a kind of round-robin fashion.
		3537
		3538	Choosing a model is hard - look around, learn, know that usually you can do
		3539	better than you currently do :-)
		3540
		3541	=item * often you need to talk to some other thread which blocks in the
		3542	event loop.
		3543
		3544	C<ev_async> watchers can be used to wake them up from other threads safely
		3545	(or from signal contexts...).
		3546
		3547	An example use would be to communicate signals or other events that only
		3548	work in the default loop by registering the signal watcher with the
		3549	default loop and triggering an C<ev_async> watcher from the default loop
		3550	watcher callback into the event loop interested in the signal.
		3551
		3552	=back
		3553
		3554	=head3 COROUTINES
		3555
		3556	Libev is very accommodating to coroutines ("cooperative threads"):
		3557	libev fully supports nesting calls to its functions from different
		3558	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3559	different coroutines, and switch freely between both coroutines running the
		3560	loop, as long as you don't confuse yourself). The only exception is that
		3561	you must not do this from C<ev_periodic> reschedule callbacks.
		3562
		3563	Care has been taken to ensure that libev does not keep local state inside
		3564	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		3565	they do not clal any callbacks.
		3566
		3567	=head2 COMPILER WARNINGS
		3568
		3569	Depending on your compiler and compiler settings, you might get no or a
		3570	lot of warnings when compiling libev code. Some people are apparently
		3571	scared by this.
		3572
		3573	However, these are unavoidable for many reasons. For one, each compiler
		3574	has different warnings, and each user has different tastes regarding
		3575	warning options. "Warn-free" code therefore cannot be a goal except when
		3576	targeting a specific compiler and compiler-version.
		3577
		3578	Another reason is that some compiler warnings require elaborate
		3579	workarounds, or other changes to the code that make it less clear and less
		3580	maintainable.
		3581
		3582	And of course, some compiler warnings are just plain stupid, or simply
		3583	wrong (because they don't actually warn about the condition their message
		3584	seems to warn about). For example, certain older gcc versions had some
		3585	warnings that resulted an extreme number of false positives. These have
		3586	been fixed, but some people still insist on making code warn-free with
		3587	such buggy versions.
		3588
		3589	While libev is written to generate as few warnings as possible,
		3590	"warn-free" code is not a goal, and it is recommended not to build libev
		3591	with any compiler warnings enabled unless you are prepared to cope with
		3592	them (e.g. by ignoring them). Remember that warnings are just that:
		3593	warnings, not errors, or proof of bugs.
		3594
		3595
		3596	=head2 VALGRIND
		3597
		3598	Valgrind has a special section here because it is a popular tool that is
		3599	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		3600
		3601	If you think you found a bug (memory leak, uninitialised data access etc.)
		3602	in libev, then check twice: If valgrind reports something like:
		3603
		3604	==2274== definitely lost: 0 bytes in 0 blocks.
		3605	==2274== possibly lost: 0 bytes in 0 blocks.
		3606	==2274== still reachable: 256 bytes in 1 blocks.
		3607
		3608	Then there is no memory leak, just as memory accounted to global variables
		3609	is not a memleak - the memory is still being refernced, and didn't leak.
		3610
		3611	Similarly, under some circumstances, valgrind might report kernel bugs
		3612	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		3613	although an acceptable workaround has been found here), or it might be
		3614	confused.
		3615
		3616	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		3617	make it into some kind of religion.
		3618
		3619	If you are unsure about something, feel free to contact the mailing list
		3620	with the full valgrind report and an explanation on why you think this
		3621	is a bug in libev (best check the archives, too :). However, don't be
		3622	annoyed when you get a brisk "this is no bug" answer and take the chance
		3623	of learning how to interpret valgrind properly.
		3624
		3625	If you need, for some reason, empty reports from valgrind for your project
		3626	I suggest using suppression lists.
		3627
		3628
		3629	=head1 PORTABILITY NOTES
		3630
		3631	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		3632
		3633	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		3634	requires, and its I/O model is fundamentally incompatible with the POSIX
		3635	model. Libev still offers limited functionality on this platform in
		3636	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		3637	descriptors. This only applies when using Win32 natively, not when using
		3638	e.g. cygwin.
		3639
		3640	Lifting these limitations would basically require the full
		3641	re-implementation of the I/O system. If you are into these kinds of
		3642	things, then note that glib does exactly that for you in a very portable
		3643	way (note also that glib is the slowest event library known to man).
		3644
		3645	There is no supported compilation method available on windows except
		3646	embedding it into other applications.
		3647
		3648	Not a libev limitation but worth mentioning: windows apparently doesn't
		3649	accept large writes: instead of resulting in a partial write, windows will
		3650	either accept everything or return C<ENOBUFS> if the buffer is too large,
		3651	so make sure you only write small amounts into your sockets (less than a
		3652	megabyte seems safe, but this apparently depends on the amount of memory
		3653	available).
		3654
		3655	Due to the many, low, and arbitrary limits on the win32 platform and
		3656	the abysmal performance of winsockets, using a large number of sockets
		3657	is not recommended (and not reasonable). If your program needs to use
		3658	more than a hundred or so sockets, then likely it needs to use a totally
		3659	different implementation for windows, as libev offers the POSIX readiness
		3660	notification model, which cannot be implemented efficiently on windows
		3661	(Microsoft monopoly games).
		3662
		3663	A typical way to use libev under windows is to embed it (see the embedding
		3664	section for details) and use the following F<evwrap.h> header file instead
		3665	of F<ev.h>:
		3666
		3667	#define EV_STANDALONE /* keeps ev from requiring config.h */
		3668	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		3669
		3670	#include "ev.h"
		3671
		3672	And compile the following F<evwrap.c> file into your project (make sure
		3673	you do I<not> compile the F<ev.c> or any other embedded source files!):
		3674
		3675	#include "evwrap.h"
		3676	#include "ev.c"
		3677
		3678	=over 4
		3679
		3680	=item The winsocket select function
		3681
		3682	The winsocket C<select> function doesn't follow POSIX in that it
		3683	requires socket I<handles> and not socket I<file descriptors> (it is
		3684	also extremely buggy). This makes select very inefficient, and also
		3685	requires a mapping from file descriptors to socket handles (the Microsoft
		3686	C runtime provides the function C<_open_osfhandle> for this). See the
		3687	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		3688	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		3689
		3690	The configuration for a "naked" win32 using the Microsoft runtime
		3691	libraries and raw winsocket select is:
		3692
		3693	#define EV_USE_SELECT 1
		3694	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		3695
		3696	Note that winsockets handling of fd sets is O(n), so you can easily get a
		3697	complexity in the O(n²) range when using win32.
		3698
		3699	=item Limited number of file descriptors
		3700
		3701	Windows has numerous arbitrary (and low) limits on things.
		3702
		3703	Early versions of winsocket's select only supported waiting for a maximum
		3704	of C<64> handles (probably owning to the fact that all windows kernels
		3705	can only wait for C<64> things at the same time internally; Microsoft
		3706	recommends spawning a chain of threads and wait for 63 handles and the
		3707	previous thread in each. Great).
		3708
		3709	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		3710	to some high number (e.g. C<2048>) before compiling the winsocket select
		3711	call (which might be in libev or elsewhere, for example, perl does its own
		3712	select emulation on windows).
		3713
		3714	Another limit is the number of file descriptors in the Microsoft runtime
		3715	libraries, which by default is C<64> (there must be a hidden I<64> fetish
		3716	or something like this inside Microsoft). You can increase this by calling
		3717	C<_setmaxstdio>, which can increase this limit to C<2048> (another
		3718	arbitrary limit), but is broken in many versions of the Microsoft runtime
		3719	libraries.
		3720
		3721	This might get you to about C<512> or C<2048> sockets (depending on
		3722	windows version and/or the phase of the moon). To get more, you need to
		3723	wrap all I/O functions and provide your own fd management, but the cost of
		3724	calling select (O(n²)) will likely make this unworkable.
		3725
		3726	=back
		3727
		3728	=head2 PORTABILITY REQUIREMENTS
		3729
		3730	In addition to a working ISO-C implementation and of course the
		3731	backend-specific APIs, libev relies on a few additional extensions:
		3732
		3733	=over 4
		3734
		3735	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		3736	calling conventions regardless of C<ev_watcher_type *>.
		3737
		3738	Libev assumes not only that all watcher pointers have the same internal
		3739	structure (guaranteed by POSIX but not by ISO C for example), but it also
		3740	assumes that the same (machine) code can be used to call any watcher
		3741	callback: The watcher callbacks have different type signatures, but libev
		3742	calls them using an C<ev_watcher *> internally.
		3743
		3744	=item C<sig_atomic_t volatile> must be thread-atomic as well
		3745
		3746	The type C<sig_atomic_t volatile> (or whatever is defined as
		3747	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		3748	threads. This is not part of the specification for C<sig_atomic_t>, but is
		3749	believed to be sufficiently portable.
		3750
		3751	=item C<sigprocmask> must work in a threaded environment
		3752
		3753	Libev uses C<sigprocmask> to temporarily block signals. This is not
		3754	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		3755	pthread implementations will either allow C<sigprocmask> in the "main
		3756	thread" or will block signals process-wide, both behaviours would
		3757	be compatible with libev. Interaction between C<sigprocmask> and
		3758	C<pthread_sigmask> could complicate things, however.
		3759
		3760	The most portable way to handle signals is to block signals in all threads
		3761	except the initial one, and run the default loop in the initial thread as
		3762	well.
		3763
		3764	=item C<long> must be large enough for common memory allocation sizes
		3765
		3766	To improve portability and simplify its API, libev uses C<long> internally
		3767	instead of C<size_t> when allocating its data structures. On non-POSIX
		3768	systems (Microsoft...) this might be unexpectedly low, but is still at
		3769	least 31 bits everywhere, which is enough for hundreds of millions of
		3770	watchers.
		3771
		3772	=item C<double> must hold a time value in seconds with enough accuracy
		3773
		3774	The type C<double> is used to represent timestamps. It is required to
		3775	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		3776	enough for at least into the year 4000. This requirement is fulfilled by
		3777	implementations implementing IEEE 754 (basically all existing ones).
		3778
		3779	=back
		3780
		3781	If you know of other additional requirements drop me a note.
		3782
		3783
2199	=head1 COMPLEXITIES	3784	=head1 ALGORITHMIC COMPLEXITIES
2200		3785
2201	In this section the complexities of (many of) the algorithms used inside	3786	In this section the complexities of (many of) the algorithms used inside
2202	libev will be explained. For complexity discussions about backends see the	3787	libev will be documented. For complexity discussions about backends see
2203	documentation for C<ev_default_init>.	3788	the documentation for C<ev_default_init>.
		3789
		3790	All of the following are about amortised time: If an array needs to be
		3791	extended, libev needs to realloc and move the whole array, but this
		3792	happens asymptotically rarer with higher number of elements, so O(1) might
		3793	mean that libev does a lengthy realloc operation in rare cases, but on
		3794	average it is much faster and asymptotically approaches constant time.
2204		3795
2205	=over 4	3796	=over 4
2206		3797
2207	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	3798	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2208		3799
		3800	This means that, when you have a watcher that triggers in one hour and
		3801	there are 100 watchers that would trigger before that, then inserting will
		3802	have to skip roughly seven (C<ld 100>) of these watchers.
		3803
2209	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	3804	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2210		3805
		3806	That means that changing a timer costs less than removing/adding them,
		3807	as only the relative motion in the event queue has to be paid for.
		3808
2211	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	3809	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
2212		3810
		3811	These just add the watcher into an array or at the head of a list.
		3812
2213	=item Stopping check/prepare/idle watchers: O(1)	3813	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2214		3814
2215	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	3815	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2216		3816
		3817	These watchers are stored in lists, so they need to be walked to find the
		3818	correct watcher to remove. The lists are usually short (you don't usually
		3819	have many watchers waiting for the same fd or signal: one is typical, two
		3820	is rare).
		3821
2217	=item Finding the next timer per loop iteration: O(1)	3822	=item Finding the next timer in each loop iteration: O(1)
		3823
		3824	By virtue of using a binary or 4-heap, the next timer is always found at a
		3825	fixed position in the storage array.
2218		3826
2219	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	3827	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2220		3828
2221	=item Activating one watcher: O(1)	3829	A change means an I/O watcher gets started or stopped, which requires
		3830	libev to recalculate its status (and possibly tell the kernel, depending
		3831	on backend and whether C<ev_io_set> was used).
		3832
		3833	=item Activating one watcher (putting it into the pending state): O(1)
		3834
		3835	=item Priority handling: O(number_of_priorities)
		3836
		3837	Priorities are implemented by allocating some space for each
		3838	priority. When doing priority-based operations, libev usually has to
		3839	linearly search all the priorities, but starting/stopping and activating
		3840	watchers becomes O(1) with respect to priority handling.
		3841
		3842	=item Sending an ev_async: O(1)
		3843
		3844	=item Processing ev_async_send: O(number_of_async_watchers)
		3845
		3846	=item Processing signals: O(max_signal_number)
		3847
		3848	Sending involves a system call I<iff> there were no other C<ev_async_send>
		3849	calls in the current loop iteration. Checking for async and signal events
		3850	involves iterating over all running async watchers or all signal numbers.
2222		3851
2223	=back	3852	=back
2224		3853
2225		3854
2226	=head1 AUTHOR	3855	=head1 AUTHOR

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