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Revision 1.56 by root, Wed Nov 28 11:15:55 2007 UTC vs.
Revision 1.211 by root, Mon Nov 3 14:34:16 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>), relative timers (C<ev_timer>),	88	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
		89	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
71	absolute timers with customised rescheduling (C<ev_periodic>), synchronous	90	with customised rescheduling (C<ev_periodic>), synchronous signals
72	signals (C<ev_signal>), process status change events (C<ev_child>), and	91	(C<ev_signal>), process status change events (C<ev_child>), and event
73	event watchers dealing with the event loop mechanism itself (C<ev_idle>,	92	watchers dealing with the event loop mechanism itself (C<ev_idle>,
74	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as	93	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as
75	file watchers (C<ev_stat>) and even limited support for fork events	94	file watchers (C<ev_stat>) and even limited support for fork events
76	(C<ev_fork>).	95	(C<ev_fork>).
77		96
78	It also is quite fast (see this	97	It also is quite fast (see this
79	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
80	for example).	99	for example).
81		100
82	=head1 CONVENTIONS	101	=head2 CONVENTIONS
83		102
84	Libev is very configurable. In this manual the default configuration will	103	Libev is very configurable. In this manual the default (and most common)
85	be described, which supports multiple event loops. For more info about	104	configuration will be described, which supports multiple event loops. For
86	various configuration options please have a look at B<EMBED> section in	105	more info about various configuration options please have a look at
87	this manual. If libev was configured without support for multiple event	106	B<EMBED> section in this manual. If libev was configured without support
88	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
89	(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.
90		110
91	=head1 TIME REPRESENTATION	111	=head2 TIME REPRESENTATION
92		112
93	Libev represents time as a single floating point number, representing the	113	Libev represents time as a single floating point number, representing the
94	(fractional) number of seconds since the (POSIX) epoch (somewhere near	114	(fractional) number of seconds since the (POSIX) epoch (somewhere near
95	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
96	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
97	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
98	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
99		142
100	=head1 GLOBAL FUNCTIONS	143	=head1 GLOBAL FUNCTIONS
101		144
102	These functions can be called anytime, even before initialising the	145	These functions can be called anytime, even before initialising the
103	library in any way.	146	library in any way.
…		…
108		151
109	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
110	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
111	you actually want to know.	154	you actually want to know.
112		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
113	=item int ev_version_major ()	162	=item int ev_version_major ()
114		163
115	=item int ev_version_minor ()	164	=item int ev_version_minor ()
116		165
117	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
118	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
119	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
120	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
121	version of the library your program was compiled against.	170	version of the library your program was compiled against.
122		171
		172	These version numbers refer to the ABI version of the library, not the
		173	release version.
		174
123	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,
124	as this indicates an incompatible change. Minor versions are usually	176	as this indicates an incompatible change. Minor versions are usually
125	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
126	not a problem.	178	not a problem.
127		179
128	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
129	version.	181	version.
130		182
131	assert (("libev version mismatch",	183	assert (("libev version mismatch",
132	ev_version_major () == EV_VERSION_MAJOR	184	ev_version_major () == EV_VERSION_MAJOR
133	&& ev_version_minor () >= EV_VERSION_MINOR));	185	&& ev_version_minor () >= EV_VERSION_MINOR));
134		186
135	=item unsigned int ev_supported_backends ()	187	=item unsigned int ev_supported_backends ()
136		188
137	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_*>
138	value) compiled into this binary of libev (independent of their	190	value) compiled into this binary of libev (independent of their
…		…
140	a description of the set values.	192	a description of the set values.
141		193
142	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
143	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
144		196
145	assert (("sorry, no epoll, no sex",	197	assert (("sorry, no epoll, no sex",
146	ev_supported_backends () & EVBACKEND_EPOLL));	198	ev_supported_backends () & EVBACKEND_EPOLL));
147		199
148	=item unsigned int ev_recommended_backends ()	200	=item unsigned int ev_recommended_backends ()
149		201
150	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
151	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
152	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
153	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
154	(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
155	libev will probe for if you specify no backends explicitly.	207	libev will probe for if you specify no backends explicitly.
156		208
157	=item unsigned int ev_embeddable_backends ()	209	=item unsigned int ev_embeddable_backends ()
158		210
…		…
162	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	214	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
163	recommended ones.	215	recommended ones.
164		216
165	See the description of C<ev_embed> watchers for more info.	217	See the description of C<ev_embed> watchers for more info.
166		218
167	=item ev_set_allocator (void *(*cb)(void *ptr, size_t size))	219	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
168		220
169	Sets the allocation function to use (the prototype and semantics are	221	Sets the allocation function to use (the prototype is similar - the
170	identical to the realloc C function). It is used to allocate and free	222	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
171	memory (no surprises here). If it returns zero when memory needs to be	223	used to allocate and free memory (no surprises here). If it returns zero
172	allocated, the library might abort or take some potentially destructive	224	when memory needs to be allocated (C<size != 0>), the library might abort
173	action. The default is your system realloc function.	225	or take some potentially destructive action.
		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.
174		230
175	You could override this function in high-availability programs to, say,	231	You could override this function in high-availability programs to, say,
176	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,
177	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.
178		234
179	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
180	retries).	236	retries (example requires a standards-compliant C<realloc>).
181		237
182	static void *	238	static void *
183	persistent_realloc (void *ptr, size_t size)	239	persistent_realloc (void *ptr, size_t size)
184	{	240	{
185	for (;;)	241	for (;;)
…		…
194	}	250	}
195		251
196	...	252	...
197	ev_set_allocator (persistent_realloc);	253	ev_set_allocator (persistent_realloc);
198		254
199	=item ev_set_syserr_cb (void (*cb)(const char *msg));	255	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
200		256
201	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
202	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
203	indicating the system call or subsystem causing the problem. If this	259	indicating the system call or subsystem causing the problem. If this
204	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
205	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
206	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
207	(such as abort).	263	(such as abort).
208		264
209	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.
…		…
220		276
221	=back	277	=back
222		278
223	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	279	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
224		280
225	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>
226	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>
227	events, and dynamically created loops which do not.	283	I<function>).
228		284
229	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
230	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
231	create, you also create another event loop. Libev itself does no locking	287	not.
232	whatsoever, so if you mix calls to the same event loop in different
233	threads, make sure you lock (this is usually a bad idea, though, even if
234	done correctly, because it's hideous and inefficient).
235		288
236	=over 4	289	=over 4
237		290
238	=item struct ev_loop *ev_default_loop (unsigned int flags)	291	=item struct ev_loop *ev_default_loop (unsigned int flags)
239		292
…		…
243	flags. If that is troubling you, check C<ev_backend ()> afterwards).	296	flags. If that is troubling you, check C<ev_backend ()> afterwards).
244		297
245	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
246	function.	299	function.
247		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 be shared 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
248	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
249	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>).
250		314
251	The following flags are supported:	315	The following flags are supported:
252		316
…		…
257	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
258	thing, believe me).	322	thing, believe me).
259		323
260	=item C<EVFLAG_NOENV>	324	=item C<EVFLAG_NOENV>
261		325
262	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
263	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
264	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	328	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
265	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
266	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
267	around bugs.	331	around bugs.
268		332
		333	=item C<EVFLAG_FORKCHECK>
		334
		335	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after
		336	a fork, you can also make libev check for a fork in each iteration by
		337	enabling this flag.
		338
		339	This works by calling C<getpid ()> on every iteration of the loop,
		340	and thus this might slow down your event loop if you do a lot of loop
		341	iterations and little real work, but is usually not noticeable (on my
		342	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
		343	without a system call and thus I<very> fast, but my GNU/Linux system also has
		344	C<pthread_atfork> which is even faster).
		345
		346	The big advantage of this flag is that you can forget about fork (and
		347	forget about forgetting to tell libev about forking) when you use this
		348	flag.
		349
		350	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
		351	environment variable.
		352
269	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	353	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
270		354
271	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
272	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,
273	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
274	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
275	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).
276		371
277	=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)
278		373
279	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
280	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
281	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
282	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>.
283		383
284	=item C<EVBACKEND_EPOLL> (value 4, Linux)	384	=item C<EVBACKEND_EPOLL> (value 4, Linux)
285		385
286	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,
287	but it scales phenomenally better. While poll and select usually scale like	387	but it scales phenomenally better. While poll and select usually scale
288	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),
289	either O(1) or O(active_fds).	389	epoll scales either O(1) or O(active_fds).
290		390
		391	The epoll mechanism deserves honorable mention as the most misdesigned
		392	of the more advanced event mechanisms: mere annoyances include silently
		393	dropping file descriptors, requiring a system call per change per file
		394	descriptor (and unnecessary guessing of parameters), problems with dup and
		395	so on. The biggest issue is fork races, however - if a program forks then
		396	I<both> parent and child process have to recreate the epoll set, which can
		397	take considerable time (one syscall per file descriptor) and is of course
		398	hard to detect.
		399
		400	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		401	of course I<doesn't>, and epoll just loves to report events for totally
		402	I<different> file descriptors (even already closed ones, so one cannot
		403	even remove them from the set) than registered in the set (especially
		404	on SMP systems). Libev tries to counter these spurious notifications by
		405	employing an additional generation counter and comparing that against the
		406	events to filter out spurious ones, recreating the set when required.
		407
291	While stopping and starting an I/O watcher in the same iteration will	408	While stopping, setting and starting an I/O watcher in the same iteration
292	result in some caching, there is still a syscall per such incident	409	will result in some caching, there is still a system call per such
293	(because the fd could point to a different file description now), so its	410	incident (because the same I<file descriptor> could point to a different
294	best to avoid that. Also, dup()ed file descriptors might not work very	411	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
295	well if you register events for both fds.	412	file descriptors might not work very well if you register events for both
		413	file descriptors.
296		414
297	Please note that epoll sometimes generates spurious notifications, so you	415	Best performance from this backend is achieved by not unregistering all
298	need to use non-blocking I/O or other means to avoid blocking when no data	416	watchers for a file descriptor until it has been closed, if possible,
299	(or space) is available.	417	i.e. keep at least one watcher active per fd at all times. Stopping and
		418	starting a watcher (without re-setting it) also usually doesn't cause
		419	extra overhead. A fork can both result in spurious notifications as well
		420	as in libev having to destroy and recreate the epoll object, which can
		421	take considerable time and thus should be avoided.
		422
		423	While nominally embeddable in other event loops, this feature is broken in
		424	all kernel versions tested so far.
		425
		426	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		427	C<EVBACKEND_POLL>.
300		428
301	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	429	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
302		430
303	Kqueue deserves special mention, as at the time of this writing, it	431	Kqueue deserves special mention, as at the time of this writing, it
304	was broken on all BSDs except NetBSD (usually it doesn't work with	432	was broken on all BSDs except NetBSD (usually it doesn't work reliably
305	anything but sockets and pipes, except on Darwin, where of course its	433	with anything but sockets and pipes, except on Darwin, where of course
306	completely useless). For this reason its not being "autodetected"	434	it's completely useless). Unlike epoll, however, whose brokenness
		435	is by design, these kqueue bugs can (and eventually will) be fixed
		436	without API changes to existing programs. For this reason it's not being
307	unless you explicitly specify it explicitly in the flags (i.e. using	437	"auto-detected" unless you explicitly specify it in the flags (i.e. using
308	C<EVBACKEND_KQUEUE>).	438	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		439	system like NetBSD.
		440
		441	You still can embed kqueue into a normal poll or select backend and use it
		442	only for sockets (after having made sure that sockets work with kqueue on
		443	the target platform). See C<ev_embed> watchers for more info.
309		444
310	It scales in the same way as the epoll backend, but the interface to the	445	It scales in the same way as the epoll backend, but the interface to the
311	kernel is more efficient (which says nothing about its actual speed, of	446	kernel is more efficient (which says nothing about its actual speed, of
312	course). While starting and stopping an I/O watcher does not cause an	447	course). While stopping, setting and starting an I/O watcher does never
313	extra syscall as with epoll, it still adds up to four event changes per	448	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
314	incident, so its best to avoid that.	449	two event changes per incident. Support for C<fork ()> is very bad (but
		450	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		451	cases
		452
		453	This backend usually performs well under most conditions.
		454
		455	While nominally embeddable in other event loops, this doesn't work
		456	everywhere, so you might need to test for this. And since it is broken
		457	almost everywhere, you should only use it when you have a lot of sockets
		458	(for which it usually works), by embedding it into another event loop
		459	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and, did I mention it,
		460	using it only for sockets.
		461
		462	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		463	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		464	C<NOTE_EOF>.
315		465
316	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	466	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
317		467
318	This is not implemented yet (and might never be).	468	This is not implemented yet (and might never be, unless you send me an
		469	implementation). According to reports, C</dev/poll> only supports sockets
		470	and is not embeddable, which would limit the usefulness of this backend
		471	immensely.
319		472
320	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	473	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
321		474
322	This uses the Solaris 10 port mechanism. As with everything on Solaris,	475	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
323	it's really slow, but it still scales very well (O(active_fds)).	476	it's really slow, but it still scales very well (O(active_fds)).
324		477
325	Please note that solaris ports can result in a lot of spurious	478	Please note that Solaris event ports can deliver a lot of spurious
326	notifications, so you need to use non-blocking I/O or other means to avoid	479	notifications, so you need to use non-blocking I/O or other means to avoid
327	blocking when no data (or space) is available.	480	blocking when no data (or space) is available.
		481
		482	While this backend scales well, it requires one system call per active
		483	file descriptor per loop iteration. For small and medium numbers of file
		484	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		485	might perform better.
		486
		487	On the positive side, with the exception of the spurious readiness
		488	notifications, this backend actually performed fully to specification
		489	in all tests and is fully embeddable, which is a rare feat among the
		490	OS-specific backends (I vastly prefer correctness over speed hacks).
		491
		492	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		493	C<EVBACKEND_POLL>.
328		494
329	=item C<EVBACKEND_ALL>	495	=item C<EVBACKEND_ALL>
330		496
331	Try all backends (even potentially broken ones that wouldn't be tried	497	Try all backends (even potentially broken ones that wouldn't be tried
332	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	498	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
333	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	499	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
334		500
		501	It is definitely not recommended to use this flag.
		502
335	=back	503	=back
336		504
337	If one or more of these are ored into the flags value, then only these	505	If one or more of these are or'ed into the flags value, then only these
338	backends will be tried (in the reverse order as given here). If none are	506	backends will be tried (in the reverse order as listed here). If none are
339	specified, most compiled-in backend will be tried, usually in reverse	507	specified, all backends in C<ev_recommended_backends ()> will be tried.
340	order of their flag values :)
341		508
342	The most typical usage is like this:	509	Example: This is the most typical usage.
343		510
344	if (!ev_default_loop (0))	511	if (!ev_default_loop (0))
345	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	512	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
346		513
347	Restrict libev to the select and poll backends, and do not allow	514	Example: Restrict libev to the select and poll backends, and do not allow
348	environment settings to be taken into account:	515	environment settings to be taken into account:
349		516
350	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	517	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
351		518
352	Use whatever libev has to offer, but make sure that kqueue is used if	519	Example: Use whatever libev has to offer, but make sure that kqueue is
353	available (warning, breaks stuff, best use only with your own private	520	used if available (warning, breaks stuff, best use only with your own
354	event loop and only if you know the OS supports your types of fds):	521	private event loop and only if you know the OS supports your types of
		522	fds):
355		523
356	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	524	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
357		525
358	=item struct ev_loop *ev_loop_new (unsigned int flags)	526	=item struct ev_loop *ev_loop_new (unsigned int flags)
359		527
360	Similar to C<ev_default_loop>, but always creates a new event loop that is	528	Similar to C<ev_default_loop>, but always creates a new event loop that is
361	always distinct from the default loop. Unlike the default loop, it cannot	529	always distinct from the default loop. Unlike the default loop, it cannot
362	handle signal and child watchers, and attempts to do so will be greeted by	530	handle signal and child watchers, and attempts to do so will be greeted by
363	undefined behaviour (or a failed assertion if assertions are enabled).	531	undefined behaviour (or a failed assertion if assertions are enabled).
364		532
		533	Note that this function I<is> thread-safe, and the recommended way to use
		534	libev with threads is indeed to create one loop per thread, and using the
		535	default loop in the "main" or "initial" thread.
		536
365	Example: Try to create a event loop that uses epoll and nothing else.	537	Example: Try to create a event loop that uses epoll and nothing else.
366		538
367	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	539	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
368	if (!epoller)	540	if (!epoller)
369	fatal ("no epoll found here, maybe it hides under your chair");	541	fatal ("no epoll found here, maybe it hides under your chair");
370		542
371	=item ev_default_destroy ()	543	=item ev_default_destroy ()
372		544
373	Destroys the default loop again (frees all memory and kernel state	545	Destroys the default loop again (frees all memory and kernel state
374	etc.). None of the active event watchers will be stopped in the normal	546	etc.). None of the active event watchers will be stopped in the normal
375	sense, so e.g. C<ev_is_active> might still return true. It is your	547	sense, so e.g. C<ev_is_active> might still return true. It is your
376	responsibility to either stop all watchers cleanly yoursef I<before>	548	responsibility to either stop all watchers cleanly yourself I<before>
377	calling this function, or cope with the fact afterwards (which is usually	549	calling this function, or cope with the fact afterwards (which is usually
378	the easiest thing, youc na just ignore the watchers and/or C<free ()> them	550	the easiest thing, you can just ignore the watchers and/or C<free ()> them
379	for example).	551	for example).
		552
		553	Note that certain global state, such as signal state (and installed signal
		554	handlers), will not be freed by this function, and related watchers (such
		555	as signal and child watchers) would need to be stopped manually.
		556
		557	In general it is not advisable to call this function except in the
		558	rare occasion where you really need to free e.g. the signal handling
		559	pipe fds. If you need dynamically allocated loops it is better to use
		560	C<ev_loop_new> and C<ev_loop_destroy>).
380		561
381	=item ev_loop_destroy (loop)	562	=item ev_loop_destroy (loop)
382		563
383	Like C<ev_default_destroy>, but destroys an event loop created by an	564	Like C<ev_default_destroy>, but destroys an event loop created by an
384	earlier call to C<ev_loop_new>.	565	earlier call to C<ev_loop_new>.
385		566
386	=item ev_default_fork ()	567	=item ev_default_fork ()
387		568
		569	This function sets a flag that causes subsequent C<ev_loop> iterations
388	This function reinitialises the kernel state for backends that have	570	to reinitialise the kernel state for backends that have one. Despite the
389	one. Despite the name, you can call it anytime, but it makes most sense	571	name, you can call it anytime, but it makes most sense after forking, in
390	after forking, in either the parent or child process (or both, but that	572	the child process (or both child and parent, but that again makes little
391	again makes little sense).	573	sense). You I<must> call it in the child before using any of the libev
		574	functions, and it will only take effect at the next C<ev_loop> iteration.
392		575
393	You I<must> call this function in the child process after forking if and	576	On the other hand, you only need to call this function in the child
394	only if you want to use the event library in both processes. If you just	577	process if and only if you want to use the event library in the child. If
395	fork+exec, you don't have to call it.	578	you just fork+exec, you don't have to call it at all.
396		579
397	The function itself is quite fast and it's usually not a problem to call	580	The function itself is quite fast and it's usually not a problem to call
398	it just in case after a fork. To make this easy, the function will fit in	581	it just in case after a fork. To make this easy, the function will fit in
399	quite nicely into a call to C<pthread_atfork>:	582	quite nicely into a call to C<pthread_atfork>:
400		583
401	pthread_atfork (0, 0, ev_default_fork);	584	pthread_atfork (0, 0, ev_default_fork);
402		585
403	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
404	without calling this function, so if you force one of those backends you
405	do not need to care.
406
407	=item ev_loop_fork (loop)	586	=item ev_loop_fork (loop)
408		587
409	Like C<ev_default_fork>, but acts on an event loop created by	588	Like C<ev_default_fork>, but acts on an event loop created by
410	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	589	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
411	after fork, and how you do this is entirely your own problem.	590	after fork that you want to re-use in the child, and how you do this is
		591	entirely your own problem.
		592
		593	=item int ev_is_default_loop (loop)
		594
		595	Returns true when the given loop is, in fact, the default loop, and false
		596	otherwise.
		597
		598	=item unsigned int ev_loop_count (loop)
		599
		600	Returns the count of loop iterations for the loop, which is identical to
		601	the number of times libev did poll for new events. It starts at C<0> and
		602	happily wraps around with enough iterations.
		603
		604	This value can sometimes be useful as a generation counter of sorts (it
		605	"ticks" the number of loop iterations), as it roughly corresponds with
		606	C<ev_prepare> and C<ev_check> calls.
412		607
413	=item unsigned int ev_backend (loop)	608	=item unsigned int ev_backend (loop)
414		609
415	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	610	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
416	use.	611	use.
…		…
419		614
420	Returns the current "event loop time", which is the time the event loop	615	Returns the current "event loop time", which is the time the event loop
421	received events and started processing them. This timestamp does not	616	received events and started processing them. This timestamp does not
422	change as long as callbacks are being processed, and this is also the base	617	change as long as callbacks are being processed, and this is also the base
423	time used for relative timers. You can treat it as the timestamp of the	618	time used for relative timers. You can treat it as the timestamp of the
424	event occuring (or more correctly, libev finding out about it).	619	event occurring (or more correctly, libev finding out about it).
		620
		621	=item ev_now_update (loop)
		622
		623	Establishes the current time by querying the kernel, updating the time
		624	returned by C<ev_now ()> in the progress. This is a costly operation and
		625	is usually done automatically within C<ev_loop ()>.
		626
		627	This function is rarely useful, but when some event callback runs for a
		628	very long time without entering the event loop, updating libev's idea of
		629	the current time is a good idea.
		630
		631	See also "The special problem of time updates" in the C<ev_timer> section.
425		632
426	=item ev_loop (loop, int flags)	633	=item ev_loop (loop, int flags)
427		634
428	Finally, this is it, the event handler. This function usually is called	635	Finally, this is it, the event handler. This function usually is called
429	after you initialised all your watchers and you want to start handling	636	after you initialised all your watchers and you want to start handling
…		…
432	If the flags argument is specified as C<0>, it will not return until	639	If the flags argument is specified as C<0>, it will not return until
433	either no event watchers are active anymore or C<ev_unloop> was called.	640	either no event watchers are active anymore or C<ev_unloop> was called.
434		641
435	Please note that an explicit C<ev_unloop> is usually better than	642	Please note that an explicit C<ev_unloop> is usually better than
436	relying on all watchers to be stopped when deciding when a program has	643	relying on all watchers to be stopped when deciding when a program has
437	finished (especially in interactive programs), but having a program that	644	finished (especially in interactive programs), but having a program
438	automatically loops as long as it has to and no longer by virtue of	645	that automatically loops as long as it has to and no longer by virtue
439	relying on its watchers stopping correctly is a thing of beauty.	646	of relying on its watchers stopping correctly, that is truly a thing of
		647	beauty.
440		648
441	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	649	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
442	those events and any outstanding ones, but will not block your process in	650	those events and any already outstanding ones, but will not block your
443	case there are no events and will return after one iteration of the loop.	651	process in case there are no events and will return after one iteration of
		652	the loop.
444		653
445	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	654	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
446	neccessary) and will handle those and any outstanding ones. It will block	655	necessary) and will handle those and any already outstanding ones. It
447	your process until at least one new event arrives, and will return after	656	will block your process until at least one new event arrives (which could
448	one iteration of the loop. This is useful if you are waiting for some	657	be an event internal to libev itself, so there is no guarantee that a
449	external event in conjunction with something not expressible using other	658	user-registered callback will be called), and will return after one
		659	iteration of the loop.
		660
		661	This is useful if you are waiting for some external event in conjunction
		662	with something not expressible using other libev watchers (i.e. "roll your
450	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	663	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
451	usually a better approach for this kind of thing.	664	usually a better approach for this kind of thing.
452		665
453	Here are the gory details of what C<ev_loop> does:	666	Here are the gory details of what C<ev_loop> does:
454		667
455	* If there are no active watchers (reference count is zero), return.	668	- Before the first iteration, call any pending watchers.
456	- Queue prepare watchers and then call all outstanding watchers.	669	* If EVFLAG_FORKCHECK was used, check for a fork.
		670	- If a fork was detected (by any means), queue and call all fork watchers.
		671	- Queue and call all prepare watchers.
457	- If we have been forked, recreate the kernel state.	672	- If we have been forked, detach and recreate the kernel state
		673	as to not disturb the other process.
458	- Update the kernel state with all outstanding changes.	674	- Update the kernel state with all outstanding changes.
459	- Update the "event loop time".	675	- Update the "event loop time" (ev_now ()).
460	- Calculate for how long to block.	676	- Calculate for how long to sleep or block, if at all
		677	(active idle watchers, EVLOOP_NONBLOCK or not having
		678	any active watchers at all will result in not sleeping).
		679	- Sleep if the I/O and timer collect interval say so.
461	- Block the process, waiting for any events.	680	- Block the process, waiting for any events.
462	- Queue all outstanding I/O (fd) events.	681	- Queue all outstanding I/O (fd) events.
463	- Update the "event loop time" and do time jump handling.	682	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
464	- Queue all outstanding timers.	683	- Queue all expired timers.
465	- Queue all outstanding periodics.	684	- Queue all expired periodics.
466	- If no events are pending now, queue all idle watchers.	685	- Unless any events are pending now, queue all idle watchers.
467	- Queue all check watchers.	686	- Queue all check watchers.
468	- Call all queued watchers in reverse order (i.e. check watchers first).	687	- Call all queued watchers in reverse order (i.e. check watchers first).
469	Signals and child watchers are implemented as I/O watchers, and will	688	Signals and child watchers are implemented as I/O watchers, and will
470	be handled here by queueing them when their watcher gets executed.	689	be handled here by queueing them when their watcher gets executed.
471	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	690	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
472	were used, return, otherwise continue with step *.	691	were used, or there are no active watchers, return, otherwise
		692	continue with step *.
473		693
474	Example: Queue some jobs and then loop until no events are outsanding	694	Example: Queue some jobs and then loop until no events are outstanding
475	anymore.	695	anymore.
476		696
477	... queue jobs here, make sure they register event watchers as long	697	... queue jobs here, make sure they register event watchers as long
478	... as they still have work to do (even an idle watcher will do..)	698	... as they still have work to do (even an idle watcher will do..)
479	ev_loop (my_loop, 0);	699	ev_loop (my_loop, 0);
480	... jobs done. yeah!	700	... jobs done or somebody called unloop. yeah!
481		701
482	=item ev_unloop (loop, how)	702	=item ev_unloop (loop, how)
483		703
484	Can be used to make a call to C<ev_loop> return early (but only after it	704	Can be used to make a call to C<ev_loop> return early (but only after it
485	has processed all outstanding events). The C<how> argument must be either	705	has processed all outstanding events). The C<how> argument must be either
486	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	706	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
487	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	707	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
488		708
		709	This "unloop state" will be cleared when entering C<ev_loop> again.
		710
		711	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
		712
489	=item ev_ref (loop)	713	=item ev_ref (loop)
490		714
491	=item ev_unref (loop)	715	=item ev_unref (loop)
492		716
493	Ref/unref can be used to add or remove a reference count on the event	717	Ref/unref can be used to add or remove a reference count on the event
494	loop: Every watcher keeps one reference, and as long as the reference	718	loop: Every watcher keeps one reference, and as long as the reference
495	count is nonzero, C<ev_loop> will not return on its own. If you have	719	count is nonzero, C<ev_loop> will not return on its own.
		720
496	a watcher you never unregister that should not keep C<ev_loop> from	721	If you have a watcher you never unregister that should not keep C<ev_loop>
497	returning, ev_unref() after starting, and ev_ref() before stopping it. For	722	from returning, call ev_unref() after starting, and ev_ref() before
		723	stopping it.
		724
498	example, libev itself uses this for its internal signal pipe: It is not	725	As an example, libev itself uses this for its internal signal pipe: It is
499	visible to the libev user and should not keep C<ev_loop> from exiting if	726	not visible to the libev user and should not keep C<ev_loop> from exiting
500	no event watchers registered by it are active. It is also an excellent	727	if no event watchers registered by it are active. It is also an excellent
501	way to do this for generic recurring timers or from within third-party	728	way to do this for generic recurring timers or from within third-party
502	libraries. Just remember to I<unref after start> and I<ref before stop>.	729	libraries. Just remember to I<unref after start> and I<ref before stop>
		730	(but only if the watcher wasn't active before, or was active before,
		731	respectively).
503		732
504	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	733	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
505	running when nothing else is active.	734	running when nothing else is active.
506		735
507	struct ev_signal exitsig;	736	ev_signal exitsig;
508	ev_signal_init (&exitsig, sig_cb, SIGINT);	737	ev_signal_init (&exitsig, sig_cb, SIGINT);
509	ev_signal_start (loop, &exitsig);	738	ev_signal_start (loop, &exitsig);
510	evf_unref (loop);	739	evf_unref (loop);
511		740
512	Example: For some weird reason, unregister the above signal handler again.	741	Example: For some weird reason, unregister the above signal handler again.
513		742
514	ev_ref (loop);	743	ev_ref (loop);
515	ev_signal_stop (loop, &exitsig);	744	ev_signal_stop (loop, &exitsig);
		745
		746	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		747
		748	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		749
		750	These advanced functions influence the time that libev will spend waiting
		751	for events. Both time intervals are by default C<0>, meaning that libev
		752	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		753	latency.
		754
		755	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		756	allows libev to delay invocation of I/O and timer/periodic callbacks
		757	to increase efficiency of loop iterations (or to increase power-saving
		758	opportunities).
		759
		760	The idea is that sometimes your program runs just fast enough to handle
		761	one (or very few) event(s) per loop iteration. While this makes the
		762	program responsive, it also wastes a lot of CPU time to poll for new
		763	events, especially with backends like C<select ()> which have a high
		764	overhead for the actual polling but can deliver many events at once.
		765
		766	By setting a higher I<io collect interval> you allow libev to spend more
		767	time collecting I/O events, so you can handle more events per iteration,
		768	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		769	C<ev_timer>) will be not affected. Setting this to a non-null value will
		770	introduce an additional C<ev_sleep ()> call into most loop iterations.
		771
		772	Likewise, by setting a higher I<timeout collect interval> you allow libev
		773	to spend more time collecting timeouts, at the expense of increased
		774	latency/jitter/inexactness (the watcher callback will be called
		775	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		776	value will not introduce any overhead in libev.
		777
		778	Many (busy) programs can usually benefit by setting the I/O collect
		779	interval to a value near C<0.1> or so, which is often enough for
		780	interactive servers (of course not for games), likewise for timeouts. It
		781	usually doesn't make much sense to set it to a lower value than C<0.01>,
		782	as this approaches the timing granularity of most systems.
		783
		784	Setting the I<timeout collect interval> can improve the opportunity for
		785	saving power, as the program will "bundle" timer callback invocations that
		786	are "near" in time together, by delaying some, thus reducing the number of
		787	times the process sleeps and wakes up again. Another useful technique to
		788	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		789	they fire on, say, one-second boundaries only.
		790
		791	=item ev_loop_verify (loop)
		792
		793	This function only does something when C<EV_VERIFY> support has been
		794	compiled in, which is the default for non-minimal builds. It tries to go
		795	through all internal structures and checks them for validity. If anything
		796	is found to be inconsistent, it will print an error message to standard
		797	error and call C<abort ()>.
		798
		799	This can be used to catch bugs inside libev itself: under normal
		800	circumstances, this function will never abort as of course libev keeps its
		801	data structures consistent.
516		802
517	=back	803	=back
518		804
519		805
520	=head1 ANATOMY OF A WATCHER	806	=head1 ANATOMY OF A WATCHER
		807
		808	In the following description, uppercase C<TYPE> in names stands for the
		809	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		810	watchers and C<ev_io_start> for I/O watchers.
521		811
522	A watcher is a structure that you create and register to record your	812	A watcher is a structure that you create and register to record your
523	interest in some event. For instance, if you want to wait for STDIN to	813	interest in some event. For instance, if you want to wait for STDIN to
524	become readable, you would create an C<ev_io> watcher for that:	814	become readable, you would create an C<ev_io> watcher for that:
525		815
526	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	816	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
527	{	817	{
528	ev_io_stop (w);	818	ev_io_stop (w);
529	ev_unloop (loop, EVUNLOOP_ALL);	819	ev_unloop (loop, EVUNLOOP_ALL);
530	}	820	}
531		821
532	struct ev_loop *loop = ev_default_loop (0);	822	struct ev_loop *loop = ev_default_loop (0);
		823
533	struct ev_io stdin_watcher;	824	ev_io stdin_watcher;
		825
534	ev_init (&stdin_watcher, my_cb);	826	ev_init (&stdin_watcher, my_cb);
535	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	827	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
536	ev_io_start (loop, &stdin_watcher);	828	ev_io_start (loop, &stdin_watcher);
		829
537	ev_loop (loop, 0);	830	ev_loop (loop, 0);
538		831
539	As you can see, you are responsible for allocating the memory for your	832	As you can see, you are responsible for allocating the memory for your
540	watcher structures (and it is usually a bad idea to do this on the stack,	833	watcher structures (and it is I<usually> a bad idea to do this on the
541	although this can sometimes be quite valid).	834	stack).
		835
		836	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		837	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
542		838
543	Each watcher structure must be initialised by a call to C<ev_init	839	Each watcher structure must be initialised by a call to C<ev_init
544	(watcher *, callback)>, which expects a callback to be provided. This	840	(watcher *, callback)>, which expects a callback to be provided. This
545	callback gets invoked each time the event occurs (or, in the case of io	841	callback gets invoked each time the event occurs (or, in the case of I/O
546	watchers, each time the event loop detects that the file descriptor given	842	watchers, each time the event loop detects that the file descriptor given
547	is readable and/or writable).	843	is readable and/or writable).
548		844
549	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	845	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
550	with arguments specific to this watcher type. There is also a macro	846	macro to configure it, with arguments specific to the watcher type. There
551	to combine initialisation and setting in one call: C<< ev_<type>_init	847	is also a macro to combine initialisation and setting in one call: C<<
552	(watcher *, callback, ...) >>.	848	ev_TYPE_init (watcher *, callback, ...) >>.
553		849
554	To make the watcher actually watch out for events, you have to start it	850	To make the watcher actually watch out for events, you have to start it
555	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	851	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
556	*) >>), and you can stop watching for events at any time by calling the	852	*) >>), and you can stop watching for events at any time by calling the
557	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	853	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
558		854
559	As long as your watcher is active (has been started but not stopped) you	855	As long as your watcher is active (has been started but not stopped) you
560	must not touch the values stored in it. Most specifically you must never	856	must not touch the values stored in it. Most specifically you must never
561	reinitialise it or call its C<set> macro.	857	reinitialise it or call its C<ev_TYPE_set> macro.
562		858
563	Each and every callback receives the event loop pointer as first, the	859	Each and every callback receives the event loop pointer as first, the
564	registered watcher structure as second, and a bitset of received events as	860	registered watcher structure as second, and a bitset of received events as
565	third argument.	861	third argument.
566		862
…		…
620	=item C<EV_FORK>	916	=item C<EV_FORK>
621		917
622	The event loop has been resumed in the child process after fork (see	918	The event loop has been resumed in the child process after fork (see
623	C<ev_fork>).	919	C<ev_fork>).
624		920
		921	=item C<EV_ASYNC>
		922
		923	The given async watcher has been asynchronously notified (see C<ev_async>).
		924
625	=item C<EV_ERROR>	925	=item C<EV_ERROR>
626		926
627	An unspecified error has occured, the watcher has been stopped. This might	927	An unspecified error has occurred, the watcher has been stopped. This might
628	happen because the watcher could not be properly started because libev	928	happen because the watcher could not be properly started because libev
629	ran out of memory, a file descriptor was found to be closed or any other	929	ran out of memory, a file descriptor was found to be closed or any other
		930	problem. Libev considers these application bugs.
		931
630	problem. You best act on it by reporting the problem and somehow coping	932	You best act on it by reporting the problem and somehow coping with the
631	with the watcher being stopped.	933	watcher being stopped. Note that well-written programs should not receive
		934	an error ever, so when your watcher receives it, this usually indicates a
		935	bug in your program.
632		936
633	Libev will usually signal a few "dummy" events together with an error,	937	Libev will usually signal a few "dummy" events together with an error, for
634	for example it might indicate that a fd is readable or writable, and if	938	example it might indicate that a fd is readable or writable, and if your
635	your callbacks is well-written it can just attempt the operation and cope	939	callbacks is well-written it can just attempt the operation and cope with
636	with the error from read() or write(). This will not work in multithreaded	940	the error from read() or write(). This will not work in multi-threaded
637	programs, though, so beware.	941	programs, though, as the fd could already be closed and reused for another
		942	thing, so beware.
638		943
639	=back	944	=back
640		945
641	=head2 GENERIC WATCHER FUNCTIONS	946	=head2 GENERIC WATCHER FUNCTIONS
642
643	In the following description, C<TYPE> stands for the watcher type,
644	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
645		947
646	=over 4	948	=over 4
647		949
648	=item C<ev_init> (ev_TYPE *watcher, callback)	950	=item C<ev_init> (ev_TYPE *watcher, callback)
649		951
…		…
655	which rolls both calls into one.	957	which rolls both calls into one.
656		958
657	You can reinitialise a watcher at any time as long as it has been stopped	959	You can reinitialise a watcher at any time as long as it has been stopped
658	(or never started) and there are no pending events outstanding.	960	(or never started) and there are no pending events outstanding.
659		961
660	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	962	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
661	int revents)>.	963	int revents)>.
		964
		965	Example: Initialise an C<ev_io> watcher in two steps.
		966
		967	ev_io w;
		968	ev_init (&w, my_cb);
		969	ev_io_set (&w, STDIN_FILENO, EV_READ);
662		970
663	=item C<ev_TYPE_set> (ev_TYPE *, [args])	971	=item C<ev_TYPE_set> (ev_TYPE *, [args])
664		972
665	This macro initialises the type-specific parts of a watcher. You need to	973	This macro initialises the type-specific parts of a watcher. You need to
666	call C<ev_init> at least once before you call this macro, but you can	974	call C<ev_init> at least once before you call this macro, but you can
…		…
669	difference to the C<ev_init> macro).	977	difference to the C<ev_init> macro).
670		978
671	Although some watcher types do not have type-specific arguments	979	Although some watcher types do not have type-specific arguments
672	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	980	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
673		981
		982	See C<ev_init>, above, for an example.
		983
674	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	984	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
675		985
676	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	986	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
677	calls into a single call. This is the most convinient method to initialise	987	calls into a single call. This is the most convenient method to initialise
678	a watcher. The same limitations apply, of course.	988	a watcher. The same limitations apply, of course.
		989
		990	Example: Initialise and set an C<ev_io> watcher in one step.
		991
		992	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
679		993
680	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	994	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
681		995
682	Starts (activates) the given watcher. Only active watchers will receive	996	Starts (activates) the given watcher. Only active watchers will receive
683	events. If the watcher is already active nothing will happen.	997	events. If the watcher is already active nothing will happen.
684		998
		999	Example: Start the C<ev_io> watcher that is being abused as example in this
		1000	whole section.
		1001
		1002	ev_io_start (EV_DEFAULT_UC, &w);
		1003
685	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1004	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
686		1005
687	Stops the given watcher again (if active) and clears the pending	1006	Stops the given watcher if active, and clears the pending status (whether
		1007	the watcher was active or not).
		1008
688	status. It is possible that stopped watchers are pending (for example,	1009	It is possible that stopped watchers are pending - for example,
689	non-repeating timers are being stopped when they become pending), but	1010	non-repeating timers are being stopped when they become pending - but
690	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1011	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
691	you want to free or reuse the memory used by the watcher it is therefore a	1012	pending. If you want to free or reuse the memory used by the watcher it is
692	good idea to always call its C<ev_TYPE_stop> function.	1013	therefore a good idea to always call its C<ev_TYPE_stop> function.
693		1014
694	=item bool ev_is_active (ev_TYPE *watcher)	1015	=item bool ev_is_active (ev_TYPE *watcher)
695		1016
696	Returns a true value iff the watcher is active (i.e. it has been started	1017	Returns a true value iff the watcher is active (i.e. it has been started
697	and not yet been stopped). As long as a watcher is active you must not modify	1018	and not yet been stopped). As long as a watcher is active you must not modify
…		…
700	=item bool ev_is_pending (ev_TYPE *watcher)	1021	=item bool ev_is_pending (ev_TYPE *watcher)
701		1022
702	Returns a true value iff the watcher is pending, (i.e. it has outstanding	1023	Returns a true value iff the watcher is pending, (i.e. it has outstanding
703	events but its callback has not yet been invoked). As long as a watcher	1024	events but its callback has not yet been invoked). As long as a watcher
704	is pending (but not active) you must not call an init function on it (but	1025	is pending (but not active) you must not call an init function on it (but
705	C<ev_TYPE_set> is safe) and you must make sure the watcher is available to	1026	C<ev_TYPE_set> is safe), you must not change its priority, and you must
706	libev (e.g. you cnanot C<free ()> it).	1027	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1028	it).
707		1029
708	=item callback ev_cb (ev_TYPE *watcher)	1030	=item callback ev_cb (ev_TYPE *watcher)
709		1031
710	Returns the callback currently set on the watcher.	1032	Returns the callback currently set on the watcher.
711		1033
712	=item ev_cb_set (ev_TYPE *watcher, callback)	1034	=item ev_cb_set (ev_TYPE *watcher, callback)
713		1035
714	Change the callback. You can change the callback at virtually any time	1036	Change the callback. You can change the callback at virtually any time
715	(modulo threads).	1037	(modulo threads).
716		1038
		1039	=item ev_set_priority (ev_TYPE *watcher, priority)
		1040
		1041	=item int ev_priority (ev_TYPE *watcher)
		1042
		1043	Set and query the priority of the watcher. The priority is a small
		1044	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1045	(default: C<-2>). Pending watchers with higher priority will be invoked
		1046	before watchers with lower priority, but priority will not keep watchers
		1047	from being executed (except for C<ev_idle> watchers).
		1048
		1049	This means that priorities are I<only> used for ordering callback
		1050	invocation after new events have been received. This is useful, for
		1051	example, to reduce latency after idling, or more often, to bind two
		1052	watchers on the same event and make sure one is called first.
		1053
		1054	If you need to suppress invocation when higher priority events are pending
		1055	you need to look at C<ev_idle> watchers, which provide this functionality.
		1056
		1057	You I<must not> change the priority of a watcher as long as it is active or
		1058	pending.
		1059
		1060	The default priority used by watchers when no priority has been set is
		1061	always C<0>, which is supposed to not be too high and not be too low :).
		1062
		1063	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1064	fine, as long as you do not mind that the priority value you query might
		1065	or might not have been clamped to the valid range.
		1066
		1067	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1068
		1069	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1070	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1071	can deal with that fact, as both are simply passed through to the
		1072	callback.
		1073
		1074	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1075
		1076	If the watcher is pending, this function clears its pending status and
		1077	returns its C<revents> bitset (as if its callback was invoked). If the
		1078	watcher isn't pending it does nothing and returns C<0>.
		1079
		1080	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1081	callback to be invoked, which can be accomplished with this function.
		1082
717	=back	1083	=back
718		1084
719		1085
720	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1086	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
721		1087
722	Each watcher has, by default, a member C<void *data> that you can change	1088	Each watcher has, by default, a member C<void *data> that you can change
723	and read at any time, libev will completely ignore it. This can be used	1089	and read at any time: libev will completely ignore it. This can be used
724	to associate arbitrary data with your watcher. If you need more data and	1090	to associate arbitrary data with your watcher. If you need more data and
725	don't want to allocate memory and store a pointer to it in that data	1091	don't want to allocate memory and store a pointer to it in that data
726	member, you can also "subclass" the watcher type and provide your own	1092	member, you can also "subclass" the watcher type and provide your own
727	data:	1093	data:
728		1094
729	struct my_io	1095	struct my_io
730	{	1096	{
731	struct ev_io io;	1097	ev_io io;
732	int otherfd;	1098	int otherfd;
733	void *somedata;	1099	void *somedata;
734	struct whatever *mostinteresting;	1100	struct whatever *mostinteresting;
735	}	1101	};
		1102
		1103	...
		1104	struct my_io w;
		1105	ev_io_init (&w.io, my_cb, fd, EV_READ);
736		1106
737	And since your callback will be called with a pointer to the watcher, you	1107	And since your callback will be called with a pointer to the watcher, you
738	can cast it back to your own type:	1108	can cast it back to your own type:
739		1109
740	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1110	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
741	{	1111	{
742	struct my_io *w = (struct my_io *)w_;	1112	struct my_io *w = (struct my_io *)w_;
743	...	1113	...
744	}	1114	}
745		1115
746	More interesting and less C-conformant ways of casting your callback type	1116	More interesting and less C-conformant ways of casting your callback type
747	instead have been omitted.	1117	instead have been omitted.
748		1118
749	Another common scenario is having some data structure with multiple	1119	Another common scenario is to use some data structure with multiple
750	watchers:	1120	embedded watchers:
751		1121
752	struct my_biggy	1122	struct my_biggy
753	{	1123	{
754	int some_data;	1124	int some_data;
755	ev_timer t1;	1125	ev_timer t1;
756	ev_timer t2;	1126	ev_timer t2;
757	}	1127	}
758		1128
759	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1129	In this case getting the pointer to C<my_biggy> is a bit more
760	you need to use C<offsetof>:	1130	complicated: Either you store the address of your C<my_biggy> struct
		1131	in the C<data> member of the watcher (for woozies), or you need to use
		1132	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1133	programmers):
761		1134
762	#include <stddef.h>	1135	#include <stddef.h>
763		1136
764	static void	1137	static void
765	t1_cb (EV_P_ struct ev_timer *w, int revents)	1138	t1_cb (EV_P_ ev_timer *w, int revents)
766	{	1139	{
767	struct my_biggy big = (struct my_biggy *	1140	struct my_biggy big = (struct my_biggy *
768	(((char *)w) - offsetof (struct my_biggy, t1));	1141	(((char *)w) - offsetof (struct my_biggy, t1));
769	}	1142	}
770		1143
771	static void	1144	static void
772	t2_cb (EV_P_ struct ev_timer *w, int revents)	1145	t2_cb (EV_P_ ev_timer *w, int revents)
773	{	1146	{
774	struct my_biggy big = (struct my_biggy *	1147	struct my_biggy big = (struct my_biggy *
775	(((char *)w) - offsetof (struct my_biggy, t2));	1148	(((char *)w) - offsetof (struct my_biggy, t2));
776	}	1149	}
777		1150
778		1151
779	=head1 WATCHER TYPES	1152	=head1 WATCHER TYPES
780		1153
781	This section describes each watcher in detail, but will not repeat	1154	This section describes each watcher in detail, but will not repeat
…		…
805	In general you can register as many read and/or write event watchers per	1178	In general you can register as many read and/or write event watchers per
806	fd as you want (as long as you don't confuse yourself). Setting all file	1179	fd as you want (as long as you don't confuse yourself). Setting all file
807	descriptors to non-blocking mode is also usually a good idea (but not	1180	descriptors to non-blocking mode is also usually a good idea (but not
808	required if you know what you are doing).	1181	required if you know what you are doing).
809		1182
810	You have to be careful with dup'ed file descriptors, though. Some backends	1183	If you cannot use non-blocking mode, then force the use of a
811	(the linux epoll backend is a notable example) cannot handle dup'ed file	1184	known-to-be-good backend (at the time of this writing, this includes only
812	descriptors correctly if you register interest in two or more fds pointing	1185	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>).
813	to the same underlying file/socket/etc. description (that is, they share
814	the same underlying "file open").
815
816	If you must do this, then force the use of a known-to-be-good backend
817	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
818	C<EVBACKEND_POLL>).
819		1186
820	Another thing you have to watch out for is that it is quite easy to	1187	Another thing you have to watch out for is that it is quite easy to
821	receive "spurious" readyness notifications, that is your callback might	1188	receive "spurious" readiness notifications, that is your callback might
822	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1189	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
823	because there is no data. Not only are some backends known to create a	1190	because there is no data. Not only are some backends known to create a
824	lot of those (for example solaris ports), it is very easy to get into	1191	lot of those (for example Solaris ports), it is very easy to get into
825	this situation even with a relatively standard program structure. Thus	1192	this situation even with a relatively standard program structure. Thus
826	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1193	it is best to always use non-blocking I/O: An extra C<read>(2) returning
827	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1194	C<EAGAIN> is far preferable to a program hanging until some data arrives.
828		1195
829	If you cannot run the fd in non-blocking mode (for example you should not	1196	If you cannot run the fd in non-blocking mode (for example you should
830	play around with an Xlib connection), then you have to seperately re-test	1197	not play around with an Xlib connection), then you have to separately
831	wether a file descriptor is really ready with a known-to-be good interface	1198	re-test whether a file descriptor is really ready with a known-to-be good
832	such as poll (fortunately in our Xlib example, Xlib already does this on	1199	interface such as poll (fortunately in our Xlib example, Xlib already
833	its own, so its quite safe to use).	1200	does this on its own, so its quite safe to use). Some people additionally
		1201	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1202	indefinitely.
		1203
		1204	But really, best use non-blocking mode.
		1205
		1206	=head3 The special problem of disappearing file descriptors
		1207
		1208	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1209	descriptor (either due to calling C<close> explicitly or any other means,
		1210	such as C<dup2>). The reason is that you register interest in some file
		1211	descriptor, but when it goes away, the operating system will silently drop
		1212	this interest. If another file descriptor with the same number then is
		1213	registered with libev, there is no efficient way to see that this is, in
		1214	fact, a different file descriptor.
		1215
		1216	To avoid having to explicitly tell libev about such cases, libev follows
		1217	the following policy: Each time C<ev_io_set> is being called, libev
		1218	will assume that this is potentially a new file descriptor, otherwise
		1219	it is assumed that the file descriptor stays the same. That means that
		1220	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1221	descriptor even if the file descriptor number itself did not change.
		1222
		1223	This is how one would do it normally anyway, the important point is that
		1224	the libev application should not optimise around libev but should leave
		1225	optimisations to libev.
		1226
		1227	=head3 The special problem of dup'ed file descriptors
		1228
		1229	Some backends (e.g. epoll), cannot register events for file descriptors,
		1230	but only events for the underlying file descriptions. That means when you
		1231	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1232	events for them, only one file descriptor might actually receive events.
		1233
		1234	There is no workaround possible except not registering events
		1235	for potentially C<dup ()>'ed file descriptors, or to resort to
		1236	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1237
		1238	=head3 The special problem of fork
		1239
		1240	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1241	useless behaviour. Libev fully supports fork, but needs to be told about
		1242	it in the child.
		1243
		1244	To support fork in your programs, you either have to call
		1245	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1246	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1247	C<EVBACKEND_POLL>.
		1248
		1249	=head3 The special problem of SIGPIPE
		1250
		1251	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1252	when writing to a pipe whose other end has been closed, your program gets
		1253	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1254	this is sensible behaviour, for daemons, this is usually undesirable.
		1255
		1256	So when you encounter spurious, unexplained daemon exits, make sure you
		1257	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1258	somewhere, as that would have given you a big clue).
		1259
		1260
		1261	=head3 Watcher-Specific Functions
834		1262
835	=over 4	1263	=over 4
836		1264
837	=item ev_io_init (ev_io *, callback, int fd, int events)	1265	=item ev_io_init (ev_io *, callback, int fd, int events)
838		1266
839	=item ev_io_set (ev_io *, int fd, int events)	1267	=item ev_io_set (ev_io *, int fd, int events)
840		1268
841	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1269	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
842	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1270	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
843	C<EV_READ | EV_WRITE> to receive the given events.	1271	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
844		1272
845	=item int fd [read-only]	1273	=item int fd [read-only]
846		1274
847	The file descriptor being watched.	1275	The file descriptor being watched.
848		1276
849	=item int events [read-only]	1277	=item int events [read-only]
850		1278
851	The events being watched.	1279	The events being watched.
852		1280
853	=back	1281	=back
		1282
		1283	=head3 Examples
854		1284
855	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1285	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
856	readable, but only once. Since it is likely line-buffered, you could	1286	readable, but only once. Since it is likely line-buffered, you could
857	attempt to read a whole line in the callback.	1287	attempt to read a whole line in the callback.
858		1288
859	static void	1289	static void
860	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1290	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
861	{	1291	{
862	ev_io_stop (loop, w);	1292	ev_io_stop (loop, w);
863	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1293	.. read from stdin here (or from w->fd) and handle any I/O errors
864	}	1294	}
865		1295
866	...	1296	...
867	struct ev_loop *loop = ev_default_init (0);	1297	struct ev_loop *loop = ev_default_init (0);
868	struct ev_io stdin_readable;	1298	ev_io stdin_readable;
869	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1299	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
870	ev_io_start (loop, &stdin_readable);	1300	ev_io_start (loop, &stdin_readable);
871	ev_loop (loop, 0);	1301	ev_loop (loop, 0);
872		1302
873		1303
874	=head2 C<ev_timer> - relative and optionally repeating timeouts	1304	=head2 C<ev_timer> - relative and optionally repeating timeouts
875		1305
876	Timer watchers are simple relative timers that generate an event after a	1306	Timer watchers are simple relative timers that generate an event after a
877	given time, and optionally repeating in regular intervals after that.	1307	given time, and optionally repeating in regular intervals after that.
878		1308
879	The timers are based on real time, that is, if you register an event that	1309	The timers are based on real time, that is, if you register an event that
880	times out after an hour and you reset your system clock to last years	1310	times out after an hour and you reset your system clock to January last
881	time, it will still time out after (roughly) and hour. "Roughly" because	1311	year, it will still time out after (roughly) one hour. "Roughly" because
882	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1312	detecting time jumps is hard, and some inaccuracies are unavoidable (the
883	monotonic clock option helps a lot here).	1313	monotonic clock option helps a lot here).
		1314
		1315	The callback is guaranteed to be invoked only I<after> its timeout has
		1316	passed, but if multiple timers become ready during the same loop iteration
		1317	then order of execution is undefined.
		1318
		1319	=head3 Be smart about timeouts
		1320
		1321	Many real-world problems involve some kind of timeout, usually for error
		1322	recovery. A typical example is an HTTP request - if the other side hangs,
		1323	you want to raise some error after a while.
		1324
		1325	What follows are some ways to handle this problem, from obvious and
		1326	inefficient to smart and efficient.
		1327
		1328	In the following, a 60 second activity timeout is assumed - a timeout that
		1329	gets reset to 60 seconds each time there is activity (e.g. each time some
		1330	data or other life sign was received).
		1331
		1332	=over 4
		1333
		1334	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1335
		1336	This is the most obvious, but not the most simple way: In the beginning,
		1337	start the watcher:
		1338
		1339	ev_timer_init (timer, callback, 60., 0.);
		1340	ev_timer_start (loop, timer);
		1341
		1342	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1343	and start it again:
		1344
		1345	ev_timer_stop (loop, timer);
		1346	ev_timer_set (timer, 60., 0.);
		1347	ev_timer_start (loop, timer);
		1348
		1349	This is relatively simple to implement, but means that each time there is
		1350	some activity, libev will first have to remove the timer from its internal
		1351	data structure and then add it again. Libev tries to be fast, but it's
		1352	still not a constant-time operation.
		1353
		1354	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1355
		1356	This is the easiest way, and involves using C<ev_timer_again> instead of
		1357	C<ev_timer_start>.
		1358
		1359	To implement this, configure an C<ev_timer> with a C<repeat> value
		1360	of C<60> and then call C<ev_timer_again> at start and each time you
		1361	successfully read or write some data. If you go into an idle state where
		1362	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1363	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1364
		1365	That means you can ignore both the C<ev_timer_start> function and the
		1366	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1367	member and C<ev_timer_again>.
		1368
		1369	At start:
		1370
		1371	ev_timer_init (timer, callback);
		1372	timer->repeat = 60.;
		1373	ev_timer_again (loop, timer);
		1374
		1375	Each time there is some activity:
		1376
		1377	ev_timer_again (loop, timer);
		1378
		1379	It is even possible to change the time-out on the fly, regardless of
		1380	whether the watcher is active or not:
		1381
		1382	timer->repeat = 30.;
		1383	ev_timer_again (loop, timer);
		1384
		1385	This is slightly more efficient then stopping/starting the timer each time
		1386	you want to modify its timeout value, as libev does not have to completely
		1387	remove and re-insert the timer from/into its internal data structure.
		1388
		1389	It is, however, even simpler than the "obvious" way to do it.
		1390
		1391	=item 3. Let the timer time out, but then re-arm it as required.
		1392
		1393	This method is more tricky, but usually most efficient: Most timeouts are
		1394	relatively long compared to the intervals between other activity - in
		1395	our example, within 60 seconds, there are usually many I/O events with
		1396	associated activity resets.
		1397
		1398	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1399	but remember the time of last activity, and check for a real timeout only
		1400	within the callback:
		1401
		1402	ev_tstamp last_activity; // time of last activity
		1403
		1404	static void
		1405	callback (EV_P_ ev_timer *w, int revents)
		1406	{
		1407	ev_tstamp now = ev_now (EV_A);
		1408	ev_tstamp timeout = last_activity + 60.;
		1409
		1410	// if last_activity + 60. is older than now, we did time out
		1411	if (timeout < now)
		1412	{
		1413	// timeout occured, take action
		1414	}
		1415	else
		1416	{
		1417	// callback was invoked, but there was some activity, re-arm
		1418	// the watcher to fire in last_activity + 60, which is
		1419	// guaranteed to be in the future, so "again" is positive:
		1420	w->again = timeout - now;
		1421	ev_timer_again (EV_A_ w);
		1422	}
		1423	}
		1424
		1425	To summarise the callback: first calculate the real timeout (defined
		1426	as "60 seconds after the last activity"), then check if that time has
		1427	been reached, which means something I<did>, in fact, time out. Otherwise
		1428	the callback was invoked too early (C<timeout> is in the future), so
		1429	re-schedule the timer to fire at that future time, to see if maybe we have
		1430	a timeout then.
		1431
		1432	Note how C<ev_timer_again> is used, taking advantage of the
		1433	C<ev_timer_again> optimisation when the timer is already running.
		1434
		1435	This scheme causes more callback invocations (about one every 60 seconds
		1436	minus half the average time between activity), but virtually no calls to
		1437	libev to change the timeout.
		1438
		1439	To start the timer, simply initialise the watcher and set C<last_activity>
		1440	to the current time (meaning we just have some activity :), then call the
		1441	callback, which will "do the right thing" and start the timer:
		1442
		1443	ev_timer_init (timer, callback);
		1444	last_activity = ev_now (loop);
		1445	callback (loop, timer, EV_TIMEOUT);
		1446
		1447	And when there is some activity, simply store the current time in
		1448	C<last_activity>, no libev calls at all:
		1449
		1450	last_actiivty = ev_now (loop);
		1451
		1452	This technique is slightly more complex, but in most cases where the
		1453	time-out is unlikely to be triggered, much more efficient.
		1454
		1455	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1456	callback :) - just change the timeout and invoke the callback, which will
		1457	fix things for you.
		1458
		1459	=item 4. Wee, just use a double-linked list for your timeouts.
		1460
		1461	If there is not one request, but many thousands (millions...), all
		1462	employing some kind of timeout with the same timeout value, then one can
		1463	do even better:
		1464
		1465	When starting the timeout, calculate the timeout value and put the timeout
		1466	at the I<end> of the list.
		1467
		1468	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1469	the list is expected to fire (for example, using the technique #3).
		1470
		1471	When there is some activity, remove the timer from the list, recalculate
		1472	the timeout, append it to the end of the list again, and make sure to
		1473	update the C<ev_timer> if it was taken from the beginning of the list.
		1474
		1475	This way, one can manage an unlimited number of timeouts in O(1) time for
		1476	starting, stopping and updating the timers, at the expense of a major
		1477	complication, and having to use a constant timeout. The constant timeout
		1478	ensures that the list stays sorted.
		1479
		1480	=back
		1481
		1482	So which method the best?
		1483
		1484	Method #2 is a simple no-brain-required solution that is adequate in most
		1485	situations. Method #3 requires a bit more thinking, but handles many cases
		1486	better, and isn't very complicated either. In most case, choosing either
		1487	one is fine, with #3 being better in typical situations.
		1488
		1489	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1490	rather complicated, but extremely efficient, something that really pays
		1491	off after the first million or so of active timers, i.e. it's usually
		1492	overkill :)
		1493
		1494	=head3 The special problem of time updates
		1495
		1496	Establishing the current time is a costly operation (it usually takes at
		1497	least two system calls): EV therefore updates its idea of the current
		1498	time only before and after C<ev_loop> collects new events, which causes a
		1499	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1500	lots of events in one iteration.
884		1501
885	The relative timeouts are calculated relative to the C<ev_now ()>	1502	The relative timeouts are calculated relative to the C<ev_now ()>
886	time. This is usually the right thing as this timestamp refers to the time	1503	time. This is usually the right thing as this timestamp refers to the time
887	of the event triggering whatever timeout you are modifying/starting. If	1504	of the event triggering whatever timeout you are modifying/starting. If
888	you suspect event processing to be delayed and you I<need> to base the timeout	1505	you suspect event processing to be delayed and you I<need> to base the
889	on the current time, use something like this to adjust for this:	1506	timeout on the current time, use something like this to adjust for this:
890		1507
891	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1508	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
892		1509
893	The callback is guarenteed to be invoked only when its timeout has passed,	1510	If the event loop is suspended for a long time, you can also force an
894	but if multiple timers become ready during the same loop iteration then	1511	update of the time returned by C<ev_now ()> by calling C<ev_now_update
895	order of execution is undefined.	1512	()>.
		1513
		1514	=head3 Watcher-Specific Functions and Data Members
896		1515
897	=over 4	1516	=over 4
898		1517
899	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1518	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
900		1519
901	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1520	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
902		1521
903	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1522	Configure the timer to trigger after C<after> seconds. If C<repeat>
904	C<0.>, then it will automatically be stopped. If it is positive, then the	1523	is C<0.>, then it will automatically be stopped once the timeout is
905	timer will automatically be configured to trigger again C<repeat> seconds	1524	reached. If it is positive, then the timer will automatically be
906	later, again, and again, until stopped manually.	1525	configured to trigger again C<repeat> seconds later, again, and again,
		1526	until stopped manually.
907		1527
908	The timer itself will do a best-effort at avoiding drift, that is, if you	1528	The timer itself will do a best-effort at avoiding drift, that is, if
909	configure a timer to trigger every 10 seconds, then it will trigger at	1529	you configure a timer to trigger every 10 seconds, then it will normally
910	exactly 10 second intervals. If, however, your program cannot keep up with	1530	trigger at exactly 10 second intervals. If, however, your program cannot
911	the timer (because it takes longer than those 10 seconds to do stuff) the	1531	keep up with the timer (because it takes longer than those 10 seconds to
912	timer will not fire more than once per event loop iteration.	1532	do stuff) the timer will not fire more than once per event loop iteration.
913		1533
914	=item ev_timer_again (loop)	1534	=item ev_timer_again (loop, ev_timer *)
915		1535
916	This will act as if the timer timed out and restart it again if it is	1536	This will act as if the timer timed out and restart it again if it is
917	repeating. The exact semantics are:	1537	repeating. The exact semantics are:
918		1538
		1539	If the timer is pending, its pending status is cleared.
		1540
919	If the timer is started but nonrepeating, stop it.	1541	If the timer is started but non-repeating, stop it (as if it timed out).
920		1542
921	If the timer is repeating, either start it if necessary (with the repeat	1543	If the timer is repeating, either start it if necessary (with the
922	value), or reset the running timer to the repeat value.	1544	C<repeat> value), or reset the running timer to the C<repeat> value.
923		1545
924	This sounds a bit complicated, but here is a useful and typical	1546	This sounds a bit complicated, see "Be smart about timeouts", above, for a
925	example: Imagine you have a tcp connection and you want a so-called	1547	usage example.
926	idle timeout, that is, you want to be called when there have been,
927	say, 60 seconds of inactivity on the socket. The easiest way to do
928	this is to configure an C<ev_timer> with C<after>=C<repeat>=C<60> and calling
929	C<ev_timer_again> each time you successfully read or write some data. If
930	you go into an idle state where you do not expect data to travel on the
931	socket, you can stop the timer, and again will automatically restart it if
932	need be.
933
934	You can also ignore the C<after> value and C<ev_timer_start> altogether
935	and only ever use the C<repeat> value:
936
937	ev_timer_init (timer, callback, 0., 5.);
938	ev_timer_again (loop, timer);
939	...
940	timer->again = 17.;
941	ev_timer_again (loop, timer);
942	...
943	timer->again = 10.;
944	ev_timer_again (loop, timer);
945
946	This is more efficient then stopping/starting the timer eahc time you want
947	to modify its timeout value.
948		1548
949	=item ev_tstamp repeat [read-write]	1549	=item ev_tstamp repeat [read-write]
950		1550
951	The current C<repeat> value. Will be used each time the watcher times out	1551	The current C<repeat> value. Will be used each time the watcher times out
952	or C<ev_timer_again> is called and determines the next timeout (if any),	1552	or C<ev_timer_again> is called, and determines the next timeout (if any),
953	which is also when any modifications are taken into account.	1553	which is also when any modifications are taken into account.
954		1554
955	=back	1555	=back
956		1556
		1557	=head3 Examples
		1558
957	Example: Create a timer that fires after 60 seconds.	1559	Example: Create a timer that fires after 60 seconds.
958		1560
959	static void	1561	static void
960	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1562	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
961	{	1563	{
962	.. one minute over, w is actually stopped right here	1564	.. one minute over, w is actually stopped right here
963	}	1565	}
964		1566
965	struct ev_timer mytimer;	1567	ev_timer mytimer;
966	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1568	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
967	ev_timer_start (loop, &mytimer);	1569	ev_timer_start (loop, &mytimer);
968		1570
969	Example: Create a timeout timer that times out after 10 seconds of	1571	Example: Create a timeout timer that times out after 10 seconds of
970	inactivity.	1572	inactivity.
971		1573
972	static void	1574	static void
973	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1575	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
974	{	1576	{
975	.. ten seconds without any activity	1577	.. ten seconds without any activity
976	}	1578	}
977		1579
978	struct ev_timer mytimer;	1580	ev_timer mytimer;
979	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1581	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
980	ev_timer_again (&mytimer); /* start timer */	1582	ev_timer_again (&mytimer); /* start timer */
981	ev_loop (loop, 0);	1583	ev_loop (loop, 0);
982		1584
983	// and in some piece of code that gets executed on any "activity":	1585	// and in some piece of code that gets executed on any "activity":
984	// reset the timeout to start ticking again at 10 seconds	1586	// reset the timeout to start ticking again at 10 seconds
985	ev_timer_again (&mytimer);	1587	ev_timer_again (&mytimer);
986		1588
987		1589
988	=head2 C<ev_periodic> - to cron or not to cron?	1590	=head2 C<ev_periodic> - to cron or not to cron?
989		1591
990	Periodic watchers are also timers of a kind, but they are very versatile	1592	Periodic watchers are also timers of a kind, but they are very versatile
991	(and unfortunately a bit complex).	1593	(and unfortunately a bit complex).
992		1594
993	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1595	Unlike C<ev_timer>'s, they are not based on real time (or relative time)
994	but on wallclock time (absolute time). You can tell a periodic watcher	1596	but on wall clock time (absolute time). You can tell a periodic watcher
995	to trigger "at" some specific point in time. For example, if you tell a	1597	to trigger after some specific point in time. For example, if you tell a
996	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	1598	periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now ()
997	+ 10.>) and then reset your system clock to the last year, then it will	1599	+ 10.>, that is, an absolute time not a delay) and then reset your system
		1600	clock to January of the previous year, then it will take more than year
998	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1601	to trigger the event (unlike an C<ev_timer>, which would still trigger
999	roughly 10 seconds later and of course not if you reset your system time	1602	roughly 10 seconds later as it uses a relative timeout).
1000	again).
1001		1603
1002	They can also be used to implement vastly more complex timers, such as	1604	C<ev_periodic>s can also be used to implement vastly more complex timers,
1003	triggering an event on eahc midnight, local time.	1605	such as triggering an event on each "midnight, local time", or other
		1606	complicated rules.
1004		1607
1005	As with timers, the callback is guarenteed to be invoked only when the	1608	As with timers, the callback is guaranteed to be invoked only when the
1006	time (C<at>) has been passed, but if multiple periodic timers become ready	1609	time (C<at>) has passed, but if multiple periodic timers become ready
1007	during the same loop iteration then order of execution is undefined.	1610	during the same loop iteration, then order of execution is undefined.
		1611
		1612	=head3 Watcher-Specific Functions and Data Members
1008		1613
1009	=over 4	1614	=over 4
1010		1615
1011	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1616	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
1012		1617
1013	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1618	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)
1014		1619
1015	Lots of arguments, lets sort it out... There are basically three modes of	1620	Lots of arguments, lets sort it out... There are basically three modes of
1016	operation, and we will explain them from simplest to complex:	1621	operation, and we will explain them from simplest to most complex:
1017		1622
1018	=over 4	1623	=over 4
1019		1624
1020	=item * absolute timer (interval = reschedule_cb = 0)	1625	=item * absolute timer (at = time, interval = reschedule_cb = 0)
1021		1626
1022	In this configuration the watcher triggers an event at the wallclock time	1627	In this configuration the watcher triggers an event after the wall clock
1023	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1628	time C<at> has passed. It will not repeat and will not adjust when a time
1024	that is, if it is to be run at January 1st 2011 then it will run when the	1629	jump occurs, that is, if it is to be run at January 1st 2011 then it will
1025	system time reaches or surpasses this time.	1630	only run when the system clock reaches or surpasses this time.
1026		1631
1027	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1632	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
1028		1633
1029	In this mode the watcher will always be scheduled to time out at the next	1634	In this mode the watcher will always be scheduled to time out at the next
1030	C<at + N * interval> time (for some integer N) and then repeat, regardless	1635	C<at + N * interval> time (for some integer N, which can also be negative)
1031	of any time jumps.	1636	and then repeat, regardless of any time jumps.
1032		1637
1033	This can be used to create timers that do not drift with respect to system	1638	This can be used to create timers that do not drift with respect to the
1034	time:	1639	system clock, for example, here is a C<ev_periodic> that triggers each
		1640	hour, on the hour:
1035		1641
1036	ev_periodic_set (&periodic, 0., 3600., 0);	1642	ev_periodic_set (&periodic, 0., 3600., 0);
1037		1643
1038	This doesn't mean there will always be 3600 seconds in between triggers,	1644	This doesn't mean there will always be 3600 seconds in between triggers,
1039	but only that the the callback will be called when the system time shows a	1645	but only that the callback will be called when the system time shows a
1040	full hour (UTC), or more correctly, when the system time is evenly divisible	1646	full hour (UTC), or more correctly, when the system time is evenly divisible
1041	by 3600.	1647	by 3600.
1042		1648
1043	Another way to think about it (for the mathematically inclined) is that	1649	Another way to think about it (for the mathematically inclined) is that
1044	C<ev_periodic> will try to run the callback in this mode at the next possible	1650	C<ev_periodic> will try to run the callback in this mode at the next possible
1045	time where C<time = at (mod interval)>, regardless of any time jumps.	1651	time where C<time = at (mod interval)>, regardless of any time jumps.
1046		1652
		1653	For numerical stability it is preferable that the C<at> value is near
		1654	C<ev_now ()> (the current time), but there is no range requirement for
		1655	this value, and in fact is often specified as zero.
		1656
		1657	Note also that there is an upper limit to how often a timer can fire (CPU
		1658	speed for example), so if C<interval> is very small then timing stability
		1659	will of course deteriorate. Libev itself tries to be exact to be about one
		1660	millisecond (if the OS supports it and the machine is fast enough).
		1661
1047	=item * manual reschedule mode (reschedule_cb = callback)	1662	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
1048		1663
1049	In this mode the values for C<interval> and C<at> are both being	1664	In this mode the values for C<interval> and C<at> are both being
1050	ignored. Instead, each time the periodic watcher gets scheduled, the	1665	ignored. Instead, each time the periodic watcher gets scheduled, the
1051	reschedule callback will be called with the watcher as first, and the	1666	reschedule callback will be called with the watcher as first, and the
1052	current time as second argument.	1667	current time as second argument.
1053		1668
1054	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1669	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,
1055	ever, or make any event loop modifications>. If you need to stop it,	1670	ever, or make ANY event loop modifications whatsoever>.
1056	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by
1057	starting a prepare watcher).
1058		1671
		1672	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1673	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1674	only event loop modification you are allowed to do).
		1675
1059	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1676	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1060	ev_tstamp now)>, e.g.:	1677	*w, ev_tstamp now)>, e.g.:
1061		1678
		1679	static ev_tstamp
1062	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1680	my_rescheduler (ev_periodic *w, ev_tstamp now)
1063	{	1681	{
1064	return now + 60.;	1682	return now + 60.;
1065	}	1683	}
1066		1684
1067	It must return the next time to trigger, based on the passed time value	1685	It must return the next time to trigger, based on the passed time value
1068	(that is, the lowest time value larger than to the second argument). It	1686	(that is, the lowest time value larger than to the second argument). It
1069	will usually be called just before the callback will be triggered, but	1687	will usually be called just before the callback will be triggered, but
1070	might be called at other times, too.	1688	might be called at other times, too.
1071		1689
1072	NOTE: I<< This callback must always return a time that is later than the	1690	NOTE: I<< This callback must always return a time that is higher than or
1073	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	1691	equal to the passed C<now> value >>.
1074		1692
1075	This can be used to create very complex timers, such as a timer that	1693	This can be used to create very complex timers, such as a timer that
1076	triggers on each midnight, local time. To do this, you would calculate the	1694	triggers on "next midnight, local time". To do this, you would calculate the
1077	next midnight after C<now> and return the timestamp value for this. How	1695	next midnight after C<now> and return the timestamp value for this. How
1078	you do this is, again, up to you (but it is not trivial, which is the main	1696	you do this is, again, up to you (but it is not trivial, which is the main
1079	reason I omitted it as an example).	1697	reason I omitted it as an example).
1080		1698
1081	=back	1699	=back
…		…
1085	Simply stops and restarts the periodic watcher again. This is only useful	1703	Simply stops and restarts the periodic watcher again. This is only useful
1086	when you changed some parameters or the reschedule callback would return	1704	when you changed some parameters or the reschedule callback would return
1087	a different time than the last time it was called (e.g. in a crond like	1705	a different time than the last time it was called (e.g. in a crond like
1088	program when the crontabs have changed).	1706	program when the crontabs have changed).
1089		1707
		1708	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1709
		1710	When active, returns the absolute time that the watcher is supposed to
		1711	trigger next.
		1712
		1713	=item ev_tstamp offset [read-write]
		1714
		1715	When repeating, this contains the offset value, otherwise this is the
		1716	absolute point in time (the C<at> value passed to C<ev_periodic_set>).
		1717
		1718	Can be modified any time, but changes only take effect when the periodic
		1719	timer fires or C<ev_periodic_again> is being called.
		1720
1090	=item ev_tstamp interval [read-write]	1721	=item ev_tstamp interval [read-write]
1091		1722
1092	The current interval value. Can be modified any time, but changes only	1723	The current interval value. Can be modified any time, but changes only
1093	take effect when the periodic timer fires or C<ev_periodic_again> is being	1724	take effect when the periodic timer fires or C<ev_periodic_again> is being
1094	called.	1725	called.
1095		1726
1096	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	1727	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1097		1728
1098	The current reschedule callback, or C<0>, if this functionality is	1729	The current reschedule callback, or C<0>, if this functionality is
1099	switched off. Can be changed any time, but changes only take effect when	1730	switched off. Can be changed any time, but changes only take effect when
1100	the periodic timer fires or C<ev_periodic_again> is being called.	1731	the periodic timer fires or C<ev_periodic_again> is being called.
1101		1732
1102	=back	1733	=back
1103		1734
		1735	=head3 Examples
		1736
1104	Example: Call a callback every hour, or, more precisely, whenever the	1737	Example: Call a callback every hour, or, more precisely, whenever the
1105	system clock is divisible by 3600. The callback invocation times have	1738	system time is divisible by 3600. The callback invocation times have
1106	potentially a lot of jittering, but good long-term stability.	1739	potentially a lot of jitter, but good long-term stability.
1107		1740
1108	static void	1741	static void
1109	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1742	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1110	{	1743	{
1111	... its now a full hour (UTC, or TAI or whatever your clock follows)	1744	... its now a full hour (UTC, or TAI or whatever your clock follows)
1112	}	1745	}
1113		1746
1114	struct ev_periodic hourly_tick;	1747	ev_periodic hourly_tick;
1115	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	1748	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1116	ev_periodic_start (loop, &hourly_tick);	1749	ev_periodic_start (loop, &hourly_tick);
1117		1750
1118	Example: The same as above, but use a reschedule callback to do it:	1751	Example: The same as above, but use a reschedule callback to do it:
1119		1752
1120	#include <math.h>	1753	#include <math.h>
1121		1754
1122	static ev_tstamp	1755	static ev_tstamp
1123	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	1756	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1124	{	1757	{
1125	return fmod (now, 3600.) + 3600.;	1758	return now + (3600. - fmod (now, 3600.));
1126	}	1759	}
1127		1760
1128	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	1761	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1129		1762
1130	Example: Call a callback every hour, starting now:	1763	Example: Call a callback every hour, starting now:
1131		1764
1132	struct ev_periodic hourly_tick;	1765	ev_periodic hourly_tick;
1133	ev_periodic_init (&hourly_tick, clock_cb,	1766	ev_periodic_init (&hourly_tick, clock_cb,
1134	fmod (ev_now (loop), 3600.), 3600., 0);	1767	fmod (ev_now (loop), 3600.), 3600., 0);
1135	ev_periodic_start (loop, &hourly_tick);	1768	ev_periodic_start (loop, &hourly_tick);
1136		1769
1137		1770
1138	=head2 C<ev_signal> - signal me when a signal gets signalled!	1771	=head2 C<ev_signal> - signal me when a signal gets signalled!
1139		1772
1140	Signal watchers will trigger an event when the process receives a specific	1773	Signal watchers will trigger an event when the process receives a specific
1141	signal one or more times. Even though signals are very asynchronous, libev	1774	signal one or more times. Even though signals are very asynchronous, libev
1142	will try it's best to deliver signals synchronously, i.e. as part of the	1775	will try it's best to deliver signals synchronously, i.e. as part of the
1143	normal event processing, like any other event.	1776	normal event processing, like any other event.
1144		1777
		1778	If you want signals asynchronously, just use C<sigaction> as you would
		1779	do without libev and forget about sharing the signal. You can even use
		1780	C<ev_async> from a signal handler to synchronously wake up an event loop.
		1781
1145	You can configure as many watchers as you like per signal. Only when the	1782	You can configure as many watchers as you like per signal. Only when the
1146	first watcher gets started will libev actually register a signal watcher	1783	first watcher gets started will libev actually register a signal handler
1147	with the kernel (thus it coexists with your own signal handlers as long	1784	with the kernel (thus it coexists with your own signal handlers as long as
1148	as you don't register any with libev). Similarly, when the last signal	1785	you don't register any with libev for the same signal). Similarly, when
1149	watcher for a signal is stopped libev will reset the signal handler to	1786	the last signal watcher for a signal is stopped, libev will reset the
1150	SIG_DFL (regardless of what it was set to before).	1787	signal handler to SIG_DFL (regardless of what it was set to before).
		1788
		1789	If possible and supported, libev will install its handlers with
		1790	C<SA_RESTART> behaviour enabled, so system calls should not be unduly
		1791	interrupted. If you have a problem with system calls getting interrupted by
		1792	signals you can block all signals in an C<ev_check> watcher and unblock
		1793	them in an C<ev_prepare> watcher.
		1794
		1795	=head3 Watcher-Specific Functions and Data Members
1151		1796
1152	=over 4	1797	=over 4
1153		1798
1154	=item ev_signal_init (ev_signal *, callback, int signum)	1799	=item ev_signal_init (ev_signal *, callback, int signum)
1155		1800
…		…
1162		1807
1163	The signal the watcher watches out for.	1808	The signal the watcher watches out for.
1164		1809
1165	=back	1810	=back
1166		1811
		1812	=head3 Examples
		1813
		1814	Example: Try to exit cleanly on SIGINT.
		1815
		1816	static void
		1817	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		1818	{
		1819	ev_unloop (loop, EVUNLOOP_ALL);
		1820	}
		1821
		1822	ev_signal signal_watcher;
		1823	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1824	ev_signal_start (loop, &signal_watcher);
		1825
1167		1826
1168	=head2 C<ev_child> - watch out for process status changes	1827	=head2 C<ev_child> - watch out for process status changes
1169		1828
1170	Child watchers trigger when your process receives a SIGCHLD in response to	1829	Child watchers trigger when your process receives a SIGCHLD in response to
1171	some child status changes (most typically when a child of yours dies).	1830	some child status changes (most typically when a child of yours dies or
		1831	exits). It is permissible to install a child watcher I<after> the child
		1832	has been forked (which implies it might have already exited), as long
		1833	as the event loop isn't entered (or is continued from a watcher), i.e.,
		1834	forking and then immediately registering a watcher for the child is fine,
		1835	but forking and registering a watcher a few event loop iterations later is
		1836	not.
		1837
		1838	Only the default event loop is capable of handling signals, and therefore
		1839	you can only register child watchers in the default event loop.
		1840
		1841	=head3 Process Interaction
		1842
		1843	Libev grabs C<SIGCHLD> as soon as the default event loop is
		1844	initialised. This is necessary to guarantee proper behaviour even if
		1845	the first child watcher is started after the child exits. The occurrence
		1846	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		1847	synchronously as part of the event loop processing. Libev always reaps all
		1848	children, even ones not watched.
		1849
		1850	=head3 Overriding the Built-In Processing
		1851
		1852	Libev offers no special support for overriding the built-in child
		1853	processing, but if your application collides with libev's default child
		1854	handler, you can override it easily by installing your own handler for
		1855	C<SIGCHLD> after initialising the default loop, and making sure the
		1856	default loop never gets destroyed. You are encouraged, however, to use an
		1857	event-based approach to child reaping and thus use libev's support for
		1858	that, so other libev users can use C<ev_child> watchers freely.
		1859
		1860	=head3 Stopping the Child Watcher
		1861
		1862	Currently, the child watcher never gets stopped, even when the
		1863	child terminates, so normally one needs to stop the watcher in the
		1864	callback. Future versions of libev might stop the watcher automatically
		1865	when a child exit is detected.
		1866
		1867	=head3 Watcher-Specific Functions and Data Members
1172		1868
1173	=over 4	1869	=over 4
1174		1870
1175	=item ev_child_init (ev_child *, callback, int pid)	1871	=item ev_child_init (ev_child *, callback, int pid, int trace)
1176		1872
1177	=item ev_child_set (ev_child *, int pid)	1873	=item ev_child_set (ev_child *, int pid, int trace)
1178		1874
1179	Configures the watcher to wait for status changes of process C<pid> (or	1875	Configures the watcher to wait for status changes of process C<pid> (or
1180	I<any> process if C<pid> is specified as C<0>). The callback can look	1876	I<any> process if C<pid> is specified as C<0>). The callback can look
1181	at the C<rstatus> member of the C<ev_child> watcher structure to see	1877	at the C<rstatus> member of the C<ev_child> watcher structure to see
1182	the status word (use the macros from C<sys/wait.h> and see your systems	1878	the status word (use the macros from C<sys/wait.h> and see your systems
1183	C<waitpid> documentation). The C<rpid> member contains the pid of the	1879	C<waitpid> documentation). The C<rpid> member contains the pid of the
1184	process causing the status change.	1880	process causing the status change. C<trace> must be either C<0> (only
		1881	activate the watcher when the process terminates) or C<1> (additionally
		1882	activate the watcher when the process is stopped or continued).
1185		1883
1186	=item int pid [read-only]	1884	=item int pid [read-only]
1187		1885
1188	The process id this watcher watches out for, or C<0>, meaning any process id.	1886	The process id this watcher watches out for, or C<0>, meaning any process id.
1189		1887
…		…
1196	The process exit/trace status caused by C<rpid> (see your systems	1894	The process exit/trace status caused by C<rpid> (see your systems
1197	C<waitpid> and C<sys/wait.h> documentation for details).	1895	C<waitpid> and C<sys/wait.h> documentation for details).
1198		1896
1199	=back	1897	=back
1200		1898
1201	Example: Try to exit cleanly on SIGINT and SIGTERM.	1899	=head3 Examples
1202		1900
		1901	Example: C<fork()> a new process and install a child handler to wait for
		1902	its completion.
		1903
		1904	ev_child cw;
		1905
1203	static void	1906	static void
1204	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	1907	child_cb (EV_P_ ev_child *w, int revents)
1205	{	1908	{
1206	ev_unloop (loop, EVUNLOOP_ALL);	1909	ev_child_stop (EV_A_ w);
		1910	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1207	}	1911	}
1208		1912
1209	struct ev_signal signal_watcher;	1913	pid_t pid = fork ();
1210	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	1914
1211	ev_signal_start (loop, &sigint_cb);	1915	if (pid < 0)
		1916	// error
		1917	else if (pid == 0)
		1918	{
		1919	// the forked child executes here
		1920	exit (1);
		1921	}
		1922	else
		1923	{
		1924	ev_child_init (&cw, child_cb, pid, 0);
		1925	ev_child_start (EV_DEFAULT_ &cw);
		1926	}
1212		1927
1213		1928
1214	=head2 C<ev_stat> - did the file attributes just change?	1929	=head2 C<ev_stat> - did the file attributes just change?
1215		1930
1216	This watches a filesystem path for attribute changes. That is, it calls	1931	This watches a file system path for attribute changes. That is, it calls
1217	C<stat> regularly (or when the OS says it changed) and sees if it changed	1932	C<stat> on that path in regular intervals (or when the OS says it changed)
1218	compared to the last time, invoking the callback if it did.	1933	and sees if it changed compared to the last time, invoking the callback if
		1934	it did.
1219		1935
1220	The path does not need to exist: changing from "path exists" to "path does	1936	The path does not need to exist: changing from "path exists" to "path does
1221	not exist" is a status change like any other. The condition "path does	1937	not exist" is a status change like any other. The condition "path does not
1222	not exist" is signified by the C<st_nlink> field being zero (which is	1938	exist" (or more correctly "path cannot be stat'ed") is signified by the
1223	otherwise always forced to be at least one) and all the other fields of	1939	C<st_nlink> field being zero (which is otherwise always forced to be at
1224	the stat buffer having unspecified contents.	1940	least one) and all the other fields of the stat buffer having unspecified
		1941	contents.
1225		1942
1226	Since there is no standard to do this, the portable implementation simply	1943	The path I<must not> end in a slash or contain special components such as
1227	calls C<stat (2)> regulalry on the path to see if it changed somehow. You	1944	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1228	can specify a recommended polling interval for this case. If you specify	1945	your working directory changes, then the behaviour is undefined.
1229	a polling interval of C<0> (highly recommended!) then a I<suitable,	1946
1230	unspecified default> value will be used (which you can expect to be around	1947	Since there is no portable change notification interface available, the
1231	five seconds, although this might change dynamically). Libev will also	1948	portable implementation simply calls C<stat(2)> regularly on the path
1232	impose a minimum interval which is currently around C<0.1>, but thats	1949	to see if it changed somehow. You can specify a recommended polling
1233	usually overkill.	1950	interval for this case. If you specify a polling interval of C<0> (highly
		1951	recommended!) then a I<suitable, unspecified default> value will be used
		1952	(which you can expect to be around five seconds, although this might
		1953	change dynamically). Libev will also impose a minimum interval which is
		1954	currently around C<0.1>, but that's usually overkill.
1234		1955
1235	This watcher type is not meant for massive numbers of stat watchers,	1956	This watcher type is not meant for massive numbers of stat watchers,
1236	as even with OS-supported change notifications, this can be	1957	as even with OS-supported change notifications, this can be
1237	resource-intensive.	1958	resource-intensive.
1238		1959
1239	At the time of this writing, no specific OS backends are implemented, but	1960	At the time of this writing, the only OS-specific interface implemented
1240	if demand increases, at least a kqueue and inotify backend will be added.	1961	is the Linux inotify interface (implementing kqueue support is left as an
		1962	exercise for the reader. Note, however, that the author sees no way of
		1963	implementing C<ev_stat> semantics with kqueue, except as a hint).
		1964
		1965	=head3 ABI Issues (Largefile Support)
		1966
		1967	Libev by default (unless the user overrides this) uses the default
		1968	compilation environment, which means that on systems with large file
		1969	support disabled by default, you get the 32 bit version of the stat
		1970	structure. When using the library from programs that change the ABI to
		1971	use 64 bit file offsets the programs will fail. In that case you have to
		1972	compile libev with the same flags to get binary compatibility. This is
		1973	obviously the case with any flags that change the ABI, but the problem is
		1974	most noticeably displayed with ev_stat and large file support.
		1975
		1976	The solution for this is to lobby your distribution maker to make large
		1977	file interfaces available by default (as e.g. FreeBSD does) and not
		1978	optional. Libev cannot simply switch on large file support because it has
		1979	to exchange stat structures with application programs compiled using the
		1980	default compilation environment.
		1981
		1982	=head3 Inotify and Kqueue
		1983
		1984	When C<inotify (7)> support has been compiled into libev and present at
		1985	runtime, it will be used to speed up change detection where possible. The
		1986	inotify descriptor will be created lazily when the first C<ev_stat>
		1987	watcher is being started.
		1988
		1989	Inotify presence does not change the semantics of C<ev_stat> watchers
		1990	except that changes might be detected earlier, and in some cases, to avoid
		1991	making regular C<stat> calls. Even in the presence of inotify support
		1992	there are many cases where libev has to resort to regular C<stat> polling,
		1993	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		1994	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		1995	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		1996	xfs are fully working) libev usually gets away without polling.
		1997
		1998	There is no support for kqueue, as apparently it cannot be used to
		1999	implement this functionality, due to the requirement of having a file
		2000	descriptor open on the object at all times, and detecting renames, unlinks
		2001	etc. is difficult.
		2002
		2003	=head3 The special problem of stat time resolution
		2004
		2005	The C<stat ()> system call only supports full-second resolution portably,
		2006	and even on systems where the resolution is higher, most file systems
		2007	still only support whole seconds.
		2008
		2009	That means that, if the time is the only thing that changes, you can
		2010	easily miss updates: on the first update, C<ev_stat> detects a change and
		2011	calls your callback, which does something. When there is another update
		2012	within the same second, C<ev_stat> will be unable to detect unless the
		2013	stat data does change in other ways (e.g. file size).
		2014
		2015	The solution to this is to delay acting on a change for slightly more
		2016	than a second (or till slightly after the next full second boundary), using
		2017	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2018	ev_timer_again (loop, w)>).
		2019
		2020	The C<.02> offset is added to work around small timing inconsistencies
		2021	of some operating systems (where the second counter of the current time
		2022	might be be delayed. One such system is the Linux kernel, where a call to
		2023	C<gettimeofday> might return a timestamp with a full second later than
		2024	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2025	update file times then there will be a small window where the kernel uses
		2026	the previous second to update file times but libev might already execute
		2027	the timer callback).
		2028
		2029	=head3 Watcher-Specific Functions and Data Members
1241		2030
1242	=over 4	2031	=over 4
1243		2032
1244	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)	2033	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
1245		2034
…		…
1249	C<path>. The C<interval> is a hint on how quickly a change is expected to	2038	C<path>. The C<interval> is a hint on how quickly a change is expected to
1250	be detected and should normally be specified as C<0> to let libev choose	2039	be detected and should normally be specified as C<0> to let libev choose
1251	a suitable value. The memory pointed to by C<path> must point to the same	2040	a suitable value. The memory pointed to by C<path> must point to the same
1252	path for as long as the watcher is active.	2041	path for as long as the watcher is active.
1253		2042
1254	The callback will be receive C<EV_STAT> when a change was detected,	2043	The callback will receive an C<EV_STAT> event when a change was detected,
1255	relative to the attributes at the time the watcher was started (or the	2044	relative to the attributes at the time the watcher was started (or the
1256	last change was detected).	2045	last change was detected).
1257		2046
1258	=item ev_stat_stat (ev_stat *)	2047	=item ev_stat_stat (loop, ev_stat *)
1259		2048
1260	Updates the stat buffer immediately with new values. If you change the	2049	Updates the stat buffer immediately with new values. If you change the
1261	watched path in your callback, you could call this fucntion to avoid	2050	watched path in your callback, you could call this function to avoid
1262	detecting this change (while introducing a race condition). Can also be	2051	detecting this change (while introducing a race condition if you are not
1263	useful simply to find out the new values.	2052	the only one changing the path). Can also be useful simply to find out the
		2053	new values.
1264		2054
1265	=item ev_statdata attr [read-only]	2055	=item ev_statdata attr [read-only]
1266		2056
1267	The most-recently detected attributes of the file. Although the type is of	2057	The most-recently detected attributes of the file. Although the type is
1268	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2058	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1269	suitable for your system. If the C<st_nlink> member is C<0>, then there	2059	suitable for your system, but you can only rely on the POSIX-standardised
		2060	members to be present. If the C<st_nlink> member is C<0>, then there was
1270	was some error while C<stat>ing the file.	2061	some error while C<stat>ing the file.
1271		2062
1272	=item ev_statdata prev [read-only]	2063	=item ev_statdata prev [read-only]
1273		2064
1274	The previous attributes of the file. The callback gets invoked whenever	2065	The previous attributes of the file. The callback gets invoked whenever
1275	C<prev> != C<attr>.	2066	C<prev> != C<attr>, or, more precisely, one or more of these members
		2067	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2068	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1276		2069
1277	=item ev_tstamp interval [read-only]	2070	=item ev_tstamp interval [read-only]
1278		2071
1279	The specified interval.	2072	The specified interval.
1280		2073
1281	=item const char *path [read-only]	2074	=item const char *path [read-only]
1282		2075
1283	The filesystem path that is being watched.	2076	The file system path that is being watched.
1284		2077
1285	=back	2078	=back
1286		2079
		2080	=head3 Examples
		2081
1287	Example: Watch C</etc/passwd> for attribute changes.	2082	Example: Watch C</etc/passwd> for attribute changes.
1288		2083
1289	static void	2084	static void
1290	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2085	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1291	{	2086	{
1292	/* /etc/passwd changed in some way */	2087	/* /etc/passwd changed in some way */
1293	if (w->attr.st_nlink)	2088	if (w->attr.st_nlink)
1294	{	2089	{
1295	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2090	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1296	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2091	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1297	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2092	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1298	}	2093	}
1299	else	2094	else
1300	/* you shalt not abuse printf for puts */	2095	/* you shalt not abuse printf for puts */
1301	puts ("wow, /etc/passwd is not there, expect problems. "	2096	puts ("wow, /etc/passwd is not there, expect problems. "
1302	"if this is windows, they already arrived\n");	2097	"if this is windows, they already arrived\n");
1303	}	2098	}
1304		2099
1305	...	2100	...
1306	ev_stat passwd;	2101	ev_stat passwd;
1307		2102
1308	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	2103	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1309	ev_stat_start (loop, &passwd);	2104	ev_stat_start (loop, &passwd);
		2105
		2106	Example: Like above, but additionally use a one-second delay so we do not
		2107	miss updates (however, frequent updates will delay processing, too, so
		2108	one might do the work both on C<ev_stat> callback invocation I<and> on
		2109	C<ev_timer> callback invocation).
		2110
		2111	static ev_stat passwd;
		2112	static ev_timer timer;
		2113
		2114	static void
		2115	timer_cb (EV_P_ ev_timer *w, int revents)
		2116	{
		2117	ev_timer_stop (EV_A_ w);
		2118
		2119	/* now it's one second after the most recent passwd change */
		2120	}
		2121
		2122	static void
		2123	stat_cb (EV_P_ ev_stat *w, int revents)
		2124	{
		2125	/* reset the one-second timer */
		2126	ev_timer_again (EV_A_ &timer);
		2127	}
		2128
		2129	...
		2130	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2131	ev_stat_start (loop, &passwd);
		2132	ev_timer_init (&timer, timer_cb, 0., 1.02);
1310		2133
1311		2134
1312	=head2 C<ev_idle> - when you've got nothing better to do...	2135	=head2 C<ev_idle> - when you've got nothing better to do...
1313		2136
1314	Idle watchers trigger events when there are no other events are pending	2137	Idle watchers trigger events when no other events of the same or higher
1315	(prepare, check and other idle watchers do not count). That is, as long	2138	priority are pending (prepare, check and other idle watchers do not count
1316	as your process is busy handling sockets or timeouts (or even signals,	2139	as receiving "events").
1317	imagine) it will not be triggered. But when your process is idle all idle	2140
1318	watchers are being called again and again, once per event loop iteration -	2141	That is, as long as your process is busy handling sockets or timeouts
		2142	(or even signals, imagine) of the same or higher priority it will not be
		2143	triggered. But when your process is idle (or only lower-priority watchers
		2144	are pending), the idle watchers are being called once per event loop
1319	until stopped, that is, or your process receives more events and becomes	2145	iteration - until stopped, that is, or your process receives more events
1320	busy.	2146	and becomes busy again with higher priority stuff.
1321		2147
1322	The most noteworthy effect is that as long as any idle watchers are	2148	The most noteworthy effect is that as long as any idle watchers are
1323	active, the process will not block when waiting for new events.	2149	active, the process will not block when waiting for new events.
1324		2150
1325	Apart from keeping your process non-blocking (which is a useful	2151	Apart from keeping your process non-blocking (which is a useful
1326	effect on its own sometimes), idle watchers are a good place to do	2152	effect on its own sometimes), idle watchers are a good place to do
1327	"pseudo-background processing", or delay processing stuff to after the	2153	"pseudo-background processing", or delay processing stuff to after the
1328	event loop has handled all outstanding events.	2154	event loop has handled all outstanding events.
1329		2155
		2156	=head3 Watcher-Specific Functions and Data Members
		2157
1330	=over 4	2158	=over 4
1331		2159
1332	=item ev_idle_init (ev_signal *, callback)	2160	=item ev_idle_init (ev_signal *, callback)
1333		2161
1334	Initialises and configures the idle watcher - it has no parameters of any	2162	Initialises and configures the idle watcher - it has no parameters of any
1335	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2163	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1336	believe me.	2164	believe me.
1337		2165
1338	=back	2166	=back
1339		2167
		2168	=head3 Examples
		2169
1340	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2170	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1341	callback, free it. Also, use no error checking, as usual.	2171	callback, free it. Also, use no error checking, as usual.
1342		2172
1343	static void	2173	static void
1344	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2174	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1345	{	2175	{
1346	free (w);	2176	free (w);
1347	// now do something you wanted to do when the program has	2177	// now do something you wanted to do when the program has
1348	// no longer asnything immediate to do.	2178	// no longer anything immediate to do.
1349	}	2179	}
1350		2180
1351	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2181	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1352	ev_idle_init (idle_watcher, idle_cb);	2182	ev_idle_init (idle_watcher, idle_cb);
1353	ev_idle_start (loop, idle_cb);	2183	ev_idle_start (loop, idle_cb);
1354		2184
1355		2185
1356	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2186	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1357		2187
1358	Prepare and check watchers are usually (but not always) used in tandem:	2188	Prepare and check watchers are usually (but not always) used in pairs:
1359	prepare watchers get invoked before the process blocks and check watchers	2189	prepare watchers get invoked before the process blocks and check watchers
1360	afterwards.	2190	afterwards.
1361		2191
1362	You I<must not> call C<ev_loop> or similar functions that enter	2192	You I<must not> call C<ev_loop> or similar functions that enter
1363	the current event loop from either C<ev_prepare> or C<ev_check>	2193	the current event loop from either C<ev_prepare> or C<ev_check>
…		…
1366	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2196	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1367	C<ev_check> so if you have one watcher of each kind they will always be	2197	C<ev_check> so if you have one watcher of each kind they will always be
1368	called in pairs bracketing the blocking call.	2198	called in pairs bracketing the blocking call.
1369		2199
1370	Their main purpose is to integrate other event mechanisms into libev and	2200	Their main purpose is to integrate other event mechanisms into libev and
1371	their use is somewhat advanced. This could be used, for example, to track	2201	their use is somewhat advanced. They could be used, for example, to track
1372	variable changes, implement your own watchers, integrate net-snmp or a	2202	variable changes, implement your own watchers, integrate net-snmp or a
1373	coroutine library and lots more. They are also occasionally useful if	2203	coroutine library and lots more. They are also occasionally useful if
1374	you cache some data and want to flush it before blocking (for example,	2204	you cache some data and want to flush it before blocking (for example,
1375	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2205	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1376	watcher).	2206	watcher).
1377		2207
1378	This is done by examining in each prepare call which file descriptors need	2208	This is done by examining in each prepare call which file descriptors
1379	to be watched by the other library, registering C<ev_io> watchers for	2209	need to be watched by the other library, registering C<ev_io> watchers
1380	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2210	for them and starting an C<ev_timer> watcher for any timeouts (many
1381	provide just this functionality). Then, in the check watcher you check for	2211	libraries provide exactly this functionality). Then, in the check watcher,
1382	any events that occured (by checking the pending status of all watchers	2212	you check for any events that occurred (by checking the pending status
1383	and stopping them) and call back into the library. The I/O and timer	2213	of all watchers and stopping them) and call back into the library. The
1384	callbacks will never actually be called (but must be valid nevertheless,	2214	I/O and timer callbacks will never actually be called (but must be valid
1385	because you never know, you know?).	2215	nevertheless, because you never know, you know?).
1386		2216
1387	As another example, the Perl Coro module uses these hooks to integrate	2217	As another example, the Perl Coro module uses these hooks to integrate
1388	coroutines into libev programs, by yielding to other active coroutines	2218	coroutines into libev programs, by yielding to other active coroutines
1389	during each prepare and only letting the process block if no coroutines	2219	during each prepare and only letting the process block if no coroutines
1390	are ready to run (it's actually more complicated: it only runs coroutines	2220	are ready to run (it's actually more complicated: it only runs coroutines
1391	with priority higher than or equal to the event loop and one coroutine	2221	with priority higher than or equal to the event loop and one coroutine
1392	of lower priority, but only once, using idle watchers to keep the event	2222	of lower priority, but only once, using idle watchers to keep the event
1393	loop from blocking if lower-priority coroutines are active, thus mapping	2223	loop from blocking if lower-priority coroutines are active, thus mapping
1394	low-priority coroutines to idle/background tasks).	2224	low-priority coroutines to idle/background tasks).
1395		2225
		2226	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		2227	priority, to ensure that they are being run before any other watchers
		2228	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2229
		2230	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2231	activate ("feed") events into libev. While libev fully supports this, they
		2232	might get executed before other C<ev_check> watchers did their job. As
		2233	C<ev_check> watchers are often used to embed other (non-libev) event
		2234	loops those other event loops might be in an unusable state until their
		2235	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2236	others).
		2237
		2238	=head3 Watcher-Specific Functions and Data Members
		2239
1396	=over 4	2240	=over 4
1397		2241
1398	=item ev_prepare_init (ev_prepare *, callback)	2242	=item ev_prepare_init (ev_prepare *, callback)
1399		2243
1400	=item ev_check_init (ev_check *, callback)	2244	=item ev_check_init (ev_check *, callback)
1401		2245
1402	Initialises and configures the prepare or check watcher - they have no	2246	Initialises and configures the prepare or check watcher - they have no
1403	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2247	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1404	macros, but using them is utterly, utterly and completely pointless.	2248	macros, but using them is utterly, utterly, utterly and completely
		2249	pointless.
1405		2250
1406	=back	2251	=back
1407		2252
1408	Example: To include a library such as adns, you would add IO watchers	2253	=head3 Examples
1409	and a timeout watcher in a prepare handler, as required by libadns, and	2254
		2255	There are a number of principal ways to embed other event loops or modules
		2256	into libev. Here are some ideas on how to include libadns into libev
		2257	(there is a Perl module named C<EV::ADNS> that does this, which you could
		2258	use as a working example. Another Perl module named C<EV::Glib> embeds a
		2259	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		2260	Glib event loop).
		2261
		2262	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1410	in a check watcher, destroy them and call into libadns. What follows is	2263	and in a check watcher, destroy them and call into libadns. What follows
1411	pseudo-code only of course:	2264	is pseudo-code only of course. This requires you to either use a low
		2265	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		2266	the callbacks for the IO/timeout watchers might not have been called yet.
1412		2267
1413	static ev_io iow [nfd];	2268	static ev_io iow [nfd];
1414	static ev_timer tw;	2269	static ev_timer tw;
1415		2270
1416	static void	2271	static void
1417	io_cb (ev_loop *loop, ev_io *w, int revents)	2272	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1418	{	2273	{
1419	// set the relevant poll flags
1420	// could also call adns_processreadable etc. here
1421	struct pollfd *fd = (struct pollfd *)w->data;
1422	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1423	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1424	}	2274	}
1425		2275
1426	// create io watchers for each fd and a timer before blocking	2276	// create io watchers for each fd and a timer before blocking
1427	static void	2277	static void
1428	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2278	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1429	{	2279	{
1430	int timeout = 3600000;truct pollfd fds [nfd];	2280	int timeout = 3600000;
		2281	struct pollfd fds [nfd];
1431	// actual code will need to loop here and realloc etc.	2282	// actual code will need to loop here and realloc etc.
1432	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2283	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1433		2284
1434	/* the callback is illegal, but won't be called as we stop during check */	2285	/* the callback is illegal, but won't be called as we stop during check */
1435	ev_timer_init (&tw, 0, timeout * 1e-3);	2286	ev_timer_init (&tw, 0, timeout * 1e-3);
1436	ev_timer_start (loop, &tw);	2287	ev_timer_start (loop, &tw);
1437		2288
1438	// create on ev_io per pollfd	2289	// create one ev_io per pollfd
1439	for (int i = 0; i < nfd; ++i)	2290	for (int i = 0; i < nfd; ++i)
1440	{	2291	{
1441	ev_io_init (iow + i, io_cb, fds [i].fd,	2292	ev_io_init (iow + i, io_cb, fds [i].fd,
1442	((fds [i].events & POLLIN ? EV_READ : 0)	2293	((fds [i].events & POLLIN ? EV_READ : 0)
1443	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2294	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1444		2295
1445	fds [i].revents = 0;	2296	fds [i].revents = 0;
1446	iow [i].data = fds + i;
1447	ev_io_start (loop, iow + i);	2297	ev_io_start (loop, iow + i);
1448	}	2298	}
1449	}	2299	}
1450		2300
1451	// stop all watchers after blocking	2301	// stop all watchers after blocking
1452	static void	2302	static void
1453	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2303	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1454	{	2304	{
1455	ev_timer_stop (loop, &tw);	2305	ev_timer_stop (loop, &tw);
1456		2306
1457	for (int i = 0; i < nfd; ++i)	2307	for (int i = 0; i < nfd; ++i)
		2308	{
		2309	// set the relevant poll flags
		2310	// could also call adns_processreadable etc. here
		2311	struct pollfd *fd = fds + i;
		2312	int revents = ev_clear_pending (iow + i);
		2313	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2314	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2315
		2316	// now stop the watcher
1458	ev_io_stop (loop, iow + i);	2317	ev_io_stop (loop, iow + i);
		2318	}
1459		2319
1460	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2320	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1461	}	2321	}
		2322
		2323	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2324	in the prepare watcher and would dispose of the check watcher.
		2325
		2326	Method 3: If the module to be embedded supports explicit event
		2327	notification (libadns does), you can also make use of the actual watcher
		2328	callbacks, and only destroy/create the watchers in the prepare watcher.
		2329
		2330	static void
		2331	timer_cb (EV_P_ ev_timer *w, int revents)
		2332	{
		2333	adns_state ads = (adns_state)w->data;
		2334	update_now (EV_A);
		2335
		2336	adns_processtimeouts (ads, &tv_now);
		2337	}
		2338
		2339	static void
		2340	io_cb (EV_P_ ev_io *w, int revents)
		2341	{
		2342	adns_state ads = (adns_state)w->data;
		2343	update_now (EV_A);
		2344
		2345	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2346	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2347	}
		2348
		2349	// do not ever call adns_afterpoll
		2350
		2351	Method 4: Do not use a prepare or check watcher because the module you
		2352	want to embed is not flexible enough to support it. Instead, you can
		2353	override their poll function. The drawback with this solution is that the
		2354	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		2355	this approach, effectively embedding EV as a client into the horrible
		2356	libglib event loop.
		2357
		2358	static gint
		2359	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2360	{
		2361	int got_events = 0;
		2362
		2363	for (n = 0; n < nfds; ++n)
		2364	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2365
		2366	if (timeout >= 0)
		2367	// create/start timer
		2368
		2369	// poll
		2370	ev_loop (EV_A_ 0);
		2371
		2372	// stop timer again
		2373	if (timeout >= 0)
		2374	ev_timer_stop (EV_A_ &to);
		2375
		2376	// stop io watchers again - their callbacks should have set
		2377	for (n = 0; n < nfds; ++n)
		2378	ev_io_stop (EV_A_ iow [n]);
		2379
		2380	return got_events;
		2381	}
1462		2382
1463		2383
1464	=head2 C<ev_embed> - when one backend isn't enough...	2384	=head2 C<ev_embed> - when one backend isn't enough...
1465		2385
1466	This is a rather advanced watcher type that lets you embed one event loop	2386	This is a rather advanced watcher type that lets you embed one event loop
…		…
1472	prioritise I/O.	2392	prioritise I/O.
1473		2393
1474	As an example for a bug workaround, the kqueue backend might only support	2394	As an example for a bug workaround, the kqueue backend might only support
1475	sockets on some platform, so it is unusable as generic backend, but you	2395	sockets on some platform, so it is unusable as generic backend, but you
1476	still want to make use of it because you have many sockets and it scales	2396	still want to make use of it because you have many sockets and it scales
1477	so nicely. In this case, you would create a kqueue-based loop and embed it	2397	so nicely. In this case, you would create a kqueue-based loop and embed
1478	into your default loop (which might use e.g. poll). Overall operation will	2398	it into your default loop (which might use e.g. poll). Overall operation
1479	be a bit slower because first libev has to poll and then call kevent, but	2399	will be a bit slower because first libev has to call C<poll> and then
1480	at least you can use both at what they are best.	2400	C<kevent>, but at least you can use both mechanisms for what they are
		2401	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1481		2402
1482	As for prioritising I/O: rarely you have the case where some fds have	2403	As for prioritising I/O: under rare circumstances you have the case where
1483	to be watched and handled very quickly (with low latency), and even	2404	some fds have to be watched and handled very quickly (with low latency),
1484	priorities and idle watchers might have too much overhead. In this case	2405	and even priorities and idle watchers might have too much overhead. In
1485	you would put all the high priority stuff in one loop and all the rest in	2406	this case you would put all the high priority stuff in one loop and all
1486	a second one, and embed the second one in the first.	2407	the rest in a second one, and embed the second one in the first.
1487		2408
1488	As long as the watcher is active, the callback will be invoked every time	2409	As long as the watcher is active, the callback will be invoked every time
1489	there might be events pending in the embedded loop. The callback must then	2410	there might be events pending in the embedded loop. The callback must then
1490	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2411	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke
1491	their callbacks (you could also start an idle watcher to give the embedded	2412	their callbacks (you could also start an idle watcher to give the embedded
…		…
1499	interested in that.	2420	interested in that.
1500		2421
1501	Also, there have not currently been made special provisions for forking:	2422	Also, there have not currently been made special provisions for forking:
1502	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2423	when you fork, you not only have to call C<ev_loop_fork> on both loops,
1503	but you will also have to stop and restart any C<ev_embed> watchers	2424	but you will also have to stop and restart any C<ev_embed> watchers
1504	yourself.	2425	yourself - but you can use a fork watcher to handle this automatically,
		2426	and future versions of libev might do just that.
1505		2427
1506	Unfortunately, not all backends are embeddable, only the ones returned by	2428	Unfortunately, not all backends are embeddable: only the ones returned by
1507	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2429	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1508	portable one.	2430	portable one.
1509		2431
1510	So when you want to use this feature you will always have to be prepared	2432	So when you want to use this feature you will always have to be prepared
1511	that you cannot get an embeddable loop. The recommended way to get around	2433	that you cannot get an embeddable loop. The recommended way to get around
1512	this is to have a separate variables for your embeddable loop, try to	2434	this is to have a separate variables for your embeddable loop, try to
1513	create it, and if that fails, use the normal loop for everything:	2435	create it, and if that fails, use the normal loop for everything.
1514		2436
1515	struct ev_loop *loop_hi = ev_default_init (0);	2437	=head3 C<ev_embed> and fork
1516	struct ev_loop *loop_lo = 0;
1517	struct ev_embed embed;
1518
1519	// see if there is a chance of getting one that works
1520	// (remember that a flags value of 0 means autodetection)
1521	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1522	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1523	: 0;
1524		2438
1525	// if we got one, then embed it, otherwise default to loop_hi	2439	While the C<ev_embed> watcher is running, forks in the embedding loop will
1526	if (loop_lo)	2440	automatically be applied to the embedded loop as well, so no special
1527	{	2441	fork handling is required in that case. When the watcher is not running,
1528	ev_embed_init (&embed, 0, loop_lo);	2442	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1529	ev_embed_start (loop_hi, &embed);	2443	as applicable.
1530	}	2444
1531	else	2445	=head3 Watcher-Specific Functions and Data Members
1532	loop_lo = loop_hi;
1533		2446
1534	=over 4	2447	=over 4
1535		2448
1536	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	2449	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
1537		2450
…		…
1539		2452
1540	Configures the watcher to embed the given loop, which must be	2453	Configures the watcher to embed the given loop, which must be
1541	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	2454	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1542	invoked automatically, otherwise it is the responsibility of the callback	2455	invoked automatically, otherwise it is the responsibility of the callback
1543	to invoke it (it will continue to be called until the sweep has been done,	2456	to invoke it (it will continue to be called until the sweep has been done,
1544	if you do not want thta, you need to temporarily stop the embed watcher).	2457	if you do not want that, you need to temporarily stop the embed watcher).
1545		2458
1546	=item ev_embed_sweep (loop, ev_embed *)	2459	=item ev_embed_sweep (loop, ev_embed *)
1547		2460
1548	Make a single, non-blocking sweep over the embedded loop. This works	2461	Make a single, non-blocking sweep over the embedded loop. This works
1549	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	2462	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
1550	apropriate way for embedded loops.	2463	appropriate way for embedded loops.
1551		2464
1552	=item struct ev_loop *loop [read-only]	2465	=item struct ev_loop *other [read-only]
1553		2466
1554	The embedded event loop.	2467	The embedded event loop.
1555		2468
1556	=back	2469	=back
		2470
		2471	=head3 Examples
		2472
		2473	Example: Try to get an embeddable event loop and embed it into the default
		2474	event loop. If that is not possible, use the default loop. The default
		2475	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2476	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2477	used).
		2478
		2479	struct ev_loop *loop_hi = ev_default_init (0);
		2480	struct ev_loop *loop_lo = 0;
		2481	ev_embed embed;
		2482
		2483	// see if there is a chance of getting one that works
		2484	// (remember that a flags value of 0 means autodetection)
		2485	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2486	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2487	: 0;
		2488
		2489	// if we got one, then embed it, otherwise default to loop_hi
		2490	if (loop_lo)
		2491	{
		2492	ev_embed_init (&embed, 0, loop_lo);
		2493	ev_embed_start (loop_hi, &embed);
		2494	}
		2495	else
		2496	loop_lo = loop_hi;
		2497
		2498	Example: Check if kqueue is available but not recommended and create
		2499	a kqueue backend for use with sockets (which usually work with any
		2500	kqueue implementation). Store the kqueue/socket-only event loop in
		2501	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2502
		2503	struct ev_loop *loop = ev_default_init (0);
		2504	struct ev_loop *loop_socket = 0;
		2505	ev_embed embed;
		2506
		2507	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2508	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2509	{
		2510	ev_embed_init (&embed, 0, loop_socket);
		2511	ev_embed_start (loop, &embed);
		2512	}
		2513
		2514	if (!loop_socket)
		2515	loop_socket = loop;
		2516
		2517	// now use loop_socket for all sockets, and loop for everything else
1557		2518
1558		2519
1559	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	2520	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
1560		2521
1561	Fork watchers are called when a C<fork ()> was detected (usually because	2522	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
1564	event loop blocks next and before C<ev_check> watchers are being called,	2525	event loop blocks next and before C<ev_check> watchers are being called,
1565	and only in the child after the fork. If whoever good citizen calling	2526	and only in the child after the fork. If whoever good citizen calling
1566	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2527	C<ev_default_fork> cheats and calls it in the wrong process, the fork
1567	handlers will be invoked, too, of course.	2528	handlers will be invoked, too, of course.
1568		2529
		2530	=head3 Watcher-Specific Functions and Data Members
		2531
1569	=over 4	2532	=over 4
1570		2533
1571	=item ev_fork_init (ev_signal *, callback)	2534	=item ev_fork_init (ev_signal *, callback)
1572		2535
1573	Initialises and configures the fork watcher - it has no parameters of any	2536	Initialises and configures the fork watcher - it has no parameters of any
…		…
1575	believe me.	2538	believe me.
1576		2539
1577	=back	2540	=back
1578		2541
1579		2542
		2543	=head2 C<ev_async> - how to wake up another event loop
		2544
		2545	In general, you cannot use an C<ev_loop> from multiple threads or other
		2546	asynchronous sources such as signal handlers (as opposed to multiple event
		2547	loops - those are of course safe to use in different threads).
		2548
		2549	Sometimes, however, you need to wake up another event loop you do not
		2550	control, for example because it belongs to another thread. This is what
		2551	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2552	can signal it by calling C<ev_async_send>, which is thread- and signal
		2553	safe.
		2554
		2555	This functionality is very similar to C<ev_signal> watchers, as signals,
		2556	too, are asynchronous in nature, and signals, too, will be compressed
		2557	(i.e. the number of callback invocations may be less than the number of
		2558	C<ev_async_sent> calls).
		2559
		2560	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2561	just the default loop.
		2562
		2563	=head3 Queueing
		2564
		2565	C<ev_async> does not support queueing of data in any way. The reason
		2566	is that the author does not know of a simple (or any) algorithm for a
		2567	multiple-writer-single-reader queue that works in all cases and doesn't
		2568	need elaborate support such as pthreads.
		2569
		2570	That means that if you want to queue data, you have to provide your own
		2571	queue. But at least I can tell you how to implement locking around your
		2572	queue:
		2573
		2574	=over 4
		2575
		2576	=item queueing from a signal handler context
		2577
		2578	To implement race-free queueing, you simply add to the queue in the signal
		2579	handler but you block the signal handler in the watcher callback. Here is
		2580	an example that does that for some fictitious SIGUSR1 handler:
		2581
		2582	static ev_async mysig;
		2583
		2584	static void
		2585	sigusr1_handler (void)
		2586	{
		2587	sometype data;
		2588
		2589	// no locking etc.
		2590	queue_put (data);
		2591	ev_async_send (EV_DEFAULT_ &mysig);
		2592	}
		2593
		2594	static void
		2595	mysig_cb (EV_P_ ev_async *w, int revents)
		2596	{
		2597	sometype data;
		2598	sigset_t block, prev;
		2599
		2600	sigemptyset (&block);
		2601	sigaddset (&block, SIGUSR1);
		2602	sigprocmask (SIG_BLOCK, &block, &prev);
		2603
		2604	while (queue_get (&data))
		2605	process (data);
		2606
		2607	if (sigismember (&prev, SIGUSR1)
		2608	sigprocmask (SIG_UNBLOCK, &block, 0);
		2609	}
		2610
		2611	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2612	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2613	either...).
		2614
		2615	=item queueing from a thread context
		2616
		2617	The strategy for threads is different, as you cannot (easily) block
		2618	threads but you can easily preempt them, so to queue safely you need to
		2619	employ a traditional mutex lock, such as in this pthread example:
		2620
		2621	static ev_async mysig;
		2622	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2623
		2624	static void
		2625	otherthread (void)
		2626	{
		2627	// only need to lock the actual queueing operation
		2628	pthread_mutex_lock (&mymutex);
		2629	queue_put (data);
		2630	pthread_mutex_unlock (&mymutex);
		2631
		2632	ev_async_send (EV_DEFAULT_ &mysig);
		2633	}
		2634
		2635	static void
		2636	mysig_cb (EV_P_ ev_async *w, int revents)
		2637	{
		2638	pthread_mutex_lock (&mymutex);
		2639
		2640	while (queue_get (&data))
		2641	process (data);
		2642
		2643	pthread_mutex_unlock (&mymutex);
		2644	}
		2645
		2646	=back
		2647
		2648
		2649	=head3 Watcher-Specific Functions and Data Members
		2650
		2651	=over 4
		2652
		2653	=item ev_async_init (ev_async *, callback)
		2654
		2655	Initialises and configures the async watcher - it has no parameters of any
		2656	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		2657	trust me.
		2658
		2659	=item ev_async_send (loop, ev_async *)
		2660
		2661	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2662	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2663	C<ev_feed_event>, this call is safe to do from other threads, signal or
		2664	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		2665	section below on what exactly this means).
		2666
		2667	This call incurs the overhead of a system call only once per loop iteration,
		2668	so while the overhead might be noticeable, it doesn't apply to repeated
		2669	calls to C<ev_async_send>.
		2670
		2671	=item bool = ev_async_pending (ev_async *)
		2672
		2673	Returns a non-zero value when C<ev_async_send> has been called on the
		2674	watcher but the event has not yet been processed (or even noted) by the
		2675	event loop.
		2676
		2677	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2678	the loop iterates next and checks for the watcher to have become active,
		2679	it will reset the flag again. C<ev_async_pending> can be used to very
		2680	quickly check whether invoking the loop might be a good idea.
		2681
		2682	Not that this does I<not> check whether the watcher itself is pending, only
		2683	whether it has been requested to make this watcher pending.
		2684
		2685	=back
		2686
		2687
1580	=head1 OTHER FUNCTIONS	2688	=head1 OTHER FUNCTIONS
1581		2689
1582	There are some other functions of possible interest. Described. Here. Now.	2690	There are some other functions of possible interest. Described. Here. Now.
1583		2691
1584	=over 4	2692	=over 4
1585		2693
1586	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	2694	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1587		2695
1588	This function combines a simple timer and an I/O watcher, calls your	2696	This function combines a simple timer and an I/O watcher, calls your
1589	callback on whichever event happens first and automatically stop both	2697	callback on whichever event happens first and automatically stops both
1590	watchers. This is useful if you want to wait for a single event on an fd	2698	watchers. This is useful if you want to wait for a single event on an fd
1591	or timeout without having to allocate/configure/start/stop/free one or	2699	or timeout without having to allocate/configure/start/stop/free one or
1592	more watchers yourself.	2700	more watchers yourself.
1593		2701
1594	If C<fd> is less than 0, then no I/O watcher will be started and events	2702	If C<fd> is less than 0, then no I/O watcher will be started and the
1595	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	2703	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1596	C<events> set will be craeted and started.	2704	the given C<fd> and C<events> set will be created and started.
1597		2705
1598	If C<timeout> is less than 0, then no timeout watcher will be	2706	If C<timeout> is less than 0, then no timeout watcher will be
1599	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	2707	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1600	repeat = 0) will be started. While C<0> is a valid timeout, it is of	2708	repeat = 0) will be started. C<0> is a valid timeout.
1601	dubious value.
1602		2709
1603	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	2710	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
1604	passed an C<revents> set like normal event callbacks (a combination of	2711	passed an C<revents> set like normal event callbacks (a combination of
1605	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	2712	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
1606	value passed to C<ev_once>:	2713	value passed to C<ev_once>. Note that it is possible to receive I<both>
		2714	a timeout and an io event at the same time - you probably should give io
		2715	events precedence.
1607		2716
		2717	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		2718
1608	static void stdin_ready (int revents, void *arg)	2719	static void stdin_ready (int revents, void *arg)
1609	{	2720	{
1610	if (revents & EV_TIMEOUT)
1611	/* doh, nothing entered */;
1612	else if (revents & EV_READ)	2721	if (revents & EV_READ)
1613	/* stdin might have data for us, joy! */;	2722	/* stdin might have data for us, joy! */;
		2723	else if (revents & EV_TIMEOUT)
		2724	/* doh, nothing entered */;
1614	}	2725	}
1615		2726
1616	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2727	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1617		2728
1618	=item ev_feed_event (ev_loop *, watcher *, int revents)	2729	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
1619		2730
1620	Feeds the given event set into the event loop, as if the specified event	2731	Feeds the given event set into the event loop, as if the specified event
1621	had happened for the specified watcher (which must be a pointer to an	2732	had happened for the specified watcher (which must be a pointer to an
1622	initialised but not necessarily started event watcher).	2733	initialised but not necessarily started event watcher).
1623		2734
1624	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	2735	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
1625		2736
1626	Feed an event on the given fd, as if a file descriptor backend detected	2737	Feed an event on the given fd, as if a file descriptor backend detected
1627	the given events it.	2738	the given events it.
1628		2739
1629	=item ev_feed_signal_event (ev_loop *loop, int signum)	2740	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
1630		2741
1631	Feed an event as if the given signal occured (C<loop> must be the default	2742	Feed an event as if the given signal occurred (C<loop> must be the default
1632	loop!).	2743	loop!).
1633		2744
1634	=back	2745	=back
1635		2746
1636		2747
…		…
1652		2763
1653	=item * Priorities are not currently supported. Initialising priorities	2764	=item * Priorities are not currently supported. Initialising priorities
1654	will fail and all watchers will have the same priority, even though there	2765	will fail and all watchers will have the same priority, even though there
1655	is an ev_pri field.	2766	is an ev_pri field.
1656		2767
		2768	=item * In libevent, the last base created gets the signals, in libev, the
		2769	first base created (== the default loop) gets the signals.
		2770
1657	=item * Other members are not supported.	2771	=item * Other members are not supported.
1658		2772
1659	=item * The libev emulation is I<not> ABI compatible to libevent, you need	2773	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1660	to use the libev header file and library.	2774	to use the libev header file and library.
1661		2775
1662	=back	2776	=back
1663		2777
1664	=head1 C++ SUPPORT	2778	=head1 C++ SUPPORT
1665		2779
1666	Libev comes with some simplistic wrapper classes for C++ that mainly allow	2780	Libev comes with some simplistic wrapper classes for C++ that mainly allow
1667	you to use some convinience methods to start/stop watchers and also change	2781	you to use some convenience methods to start/stop watchers and also change
1668	the callback model to a model using method callbacks on objects.	2782	the callback model to a model using method callbacks on objects.
1669		2783
1670	To use it,	2784	To use it,
1671		2785
1672	#include <ev++.h>	2786	#include <ev++.h>
1673		2787
1674	(it is not installed by default). This automatically includes F<ev.h>	2788	This automatically includes F<ev.h> and puts all of its definitions (many
1675	and puts all of its definitions (many of them macros) into the global	2789	of them macros) into the global namespace. All C++ specific things are
1676	namespace. All C++ specific things are put into the C<ev> namespace.	2790	put into the C<ev> namespace. It should support all the same embedding
		2791	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
1677		2792
1678	It should support all the same embedding options as F<ev.h>, most notably	2793	Care has been taken to keep the overhead low. The only data member the C++
1679	C<EV_MULTIPLICITY>.	2794	classes add (compared to plain C-style watchers) is the event loop pointer
		2795	that the watcher is associated with (or no additional members at all if
		2796	you disable C<EV_MULTIPLICITY> when embedding libev).
		2797
		2798	Currently, functions, and static and non-static member functions can be
		2799	used as callbacks. Other types should be easy to add as long as they only
		2800	need one additional pointer for context. If you need support for other
		2801	types of functors please contact the author (preferably after implementing
		2802	it).
1680		2803
1681	Here is a list of things available in the C<ev> namespace:	2804	Here is a list of things available in the C<ev> namespace:
1682		2805
1683	=over 4	2806	=over 4
1684		2807
…		…
1700		2823
1701	All of those classes have these methods:	2824	All of those classes have these methods:
1702		2825
1703	=over 4	2826	=over 4
1704		2827
1705	=item ev::TYPE::TYPE (object *, object::method *)	2828	=item ev::TYPE::TYPE ()
1706		2829
1707	=item ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)	2830	=item ev::TYPE::TYPE (struct ev_loop *)
1708		2831
1709	=item ev::TYPE::~TYPE	2832	=item ev::TYPE::~TYPE
1710		2833
1711	The constructor takes a pointer to an object and a method pointer to	2834	The constructor (optionally) takes an event loop to associate the watcher
1712	the event handler callback to call in this class. The constructor calls	2835	with. If it is omitted, it will use C<EV_DEFAULT>.
1713	C<ev_init> for you, which means you have to call the C<set> method	2836
1714	before starting it. If you do not specify a loop then the constructor	2837	The constructor calls C<ev_init> for you, which means you have to call the
1715	automatically associates the default loop with this watcher.	2838	C<set> method before starting it.
		2839
		2840	It will not set a callback, however: You have to call the templated C<set>
		2841	method to set a callback before you can start the watcher.
		2842
		2843	(The reason why you have to use a method is a limitation in C++ which does
		2844	not allow explicit template arguments for constructors).
1716		2845
1717	The destructor automatically stops the watcher if it is active.	2846	The destructor automatically stops the watcher if it is active.
		2847
		2848	=item w->set<class, &class::method> (object *)
		2849
		2850	This method sets the callback method to call. The method has to have a
		2851	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		2852	first argument and the C<revents> as second. The object must be given as
		2853	parameter and is stored in the C<data> member of the watcher.
		2854
		2855	This method synthesizes efficient thunking code to call your method from
		2856	the C callback that libev requires. If your compiler can inline your
		2857	callback (i.e. it is visible to it at the place of the C<set> call and
		2858	your compiler is good :), then the method will be fully inlined into the
		2859	thunking function, making it as fast as a direct C callback.
		2860
		2861	Example: simple class declaration and watcher initialisation
		2862
		2863	struct myclass
		2864	{
		2865	void io_cb (ev::io &w, int revents) { }
		2866	}
		2867
		2868	myclass obj;
		2869	ev::io iow;
		2870	iow.set <myclass, &myclass::io_cb> (&obj);
		2871
		2872	=item w->set<function> (void *data = 0)
		2873
		2874	Also sets a callback, but uses a static method or plain function as
		2875	callback. The optional C<data> argument will be stored in the watcher's
		2876	C<data> member and is free for you to use.
		2877
		2878	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		2879
		2880	See the method-C<set> above for more details.
		2881
		2882	Example: Use a plain function as callback.
		2883
		2884	static void io_cb (ev::io &w, int revents) { }
		2885	iow.set <io_cb> ();
1718		2886
1719	=item w->set (struct ev_loop *)	2887	=item w->set (struct ev_loop *)
1720		2888
1721	Associates a different C<struct ev_loop> with this watcher. You can only	2889	Associates a different C<struct ev_loop> with this watcher. You can only
1722	do this when the watcher is inactive (and not pending either).	2890	do this when the watcher is inactive (and not pending either).
1723		2891
1724	=item w->set ([args])	2892	=item w->set ([arguments])
1725		2893
1726	Basically the same as C<ev_TYPE_set>, with the same args. Must be	2894	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
1727	called at least once. Unlike the C counterpart, an active watcher gets	2895	called at least once. Unlike the C counterpart, an active watcher gets
1728	automatically stopped and restarted.	2896	automatically stopped and restarted when reconfiguring it with this
		2897	method.
1729		2898
1730	=item w->start ()	2899	=item w->start ()
1731		2900
1732	Starts the watcher. Note that there is no C<loop> argument as the	2901	Starts the watcher. Note that there is no C<loop> argument, as the
1733	constructor already takes the loop.	2902	constructor already stores the event loop.
1734		2903
1735	=item w->stop ()	2904	=item w->stop ()
1736		2905
1737	Stops the watcher if it is active. Again, no C<loop> argument.	2906	Stops the watcher if it is active. Again, no C<loop> argument.
1738		2907
1739	=item w->again () C<ev::timer>, C<ev::periodic> only	2908	=item w->again () (C<ev::timer>, C<ev::periodic> only)
1740		2909
1741	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding	2910	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
1742	C<ev_TYPE_again> function.	2911	C<ev_TYPE_again> function.
1743		2912
1744	=item w->sweep () C<ev::embed> only	2913	=item w->sweep () (C<ev::embed> only)
1745		2914
1746	Invokes C<ev_embed_sweep>.	2915	Invokes C<ev_embed_sweep>.
1747		2916
1748	=item w->update () C<ev::stat> only	2917	=item w->update () (C<ev::stat> only)
1749		2918
1750	Invokes C<ev_stat_stat>.	2919	Invokes C<ev_stat_stat>.
1751		2920
1752	=back	2921	=back
1753		2922
1754	=back	2923	=back
1755		2924
1756	Example: Define a class with an IO and idle watcher, start one of them in	2925	Example: Define a class with an IO and idle watcher, start one of them in
1757	the constructor.	2926	the constructor.
1758		2927
1759	class myclass	2928	class myclass
1760	{	2929	{
1761	ev_io io; void io_cb (ev::io &w, int revents);	2930	ev::io io ; void io_cb (ev::io &w, int revents);
1762	ev_idle idle void idle_cb (ev::idle &w, int revents);	2931	ev::idle idle; void idle_cb (ev::idle &w, int revents);
1763		2932
1764	myclass ();	2933	myclass (int fd)
1765	}	2934	{
		2935	io .set <myclass, &myclass::io_cb > (this);
		2936	idle.set <myclass, &myclass::idle_cb> (this);
1766		2937
1767	myclass::myclass (int fd)
1768	: io (this, &myclass::io_cb),
1769	idle (this, &myclass::idle_cb)
1770	{
1771	io.start (fd, ev::READ);	2938	io.start (fd, ev::READ);
		2939	}
1772	}	2940	};
		2941
		2942
		2943	=head1 OTHER LANGUAGE BINDINGS
		2944
		2945	Libev does not offer other language bindings itself, but bindings for a
		2946	number of languages exist in the form of third-party packages. If you know
		2947	any interesting language binding in addition to the ones listed here, drop
		2948	me a note.
		2949
		2950	=over 4
		2951
		2952	=item Perl
		2953
		2954	The EV module implements the full libev API and is actually used to test
		2955	libev. EV is developed together with libev. Apart from the EV core module,
		2956	there are additional modules that implement libev-compatible interfaces
		2957	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		2958	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		2959	and C<EV::Glib>).
		2960
		2961	It can be found and installed via CPAN, its homepage is at
		2962	L<http://software.schmorp.de/pkg/EV>.
		2963
		2964	=item Python
		2965
		2966	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		2967	seems to be quite complete and well-documented. Note, however, that the
		2968	patch they require for libev is outright dangerous as it breaks the ABI
		2969	for everybody else, and therefore, should never be applied in an installed
		2970	libev (if python requires an incompatible ABI then it needs to embed
		2971	libev).
		2972
		2973	=item Ruby
		2974
		2975	Tony Arcieri has written a ruby extension that offers access to a subset
		2976	of the libev API and adds file handle abstractions, asynchronous DNS and
		2977	more on top of it. It can be found via gem servers. Its homepage is at
		2978	L<http://rev.rubyforge.org/>.
		2979
		2980	=item D
		2981
		2982	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		2983	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		2984
		2985	=item Ocaml
		2986
		2987	Erkki Seppala has written Ocaml bindings for libev, to be found at
		2988	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		2989
		2990	=back
1773		2991
1774		2992
1775	=head1 MACRO MAGIC	2993	=head1 MACRO MAGIC
1776		2994
1777	Libev can be compiled with a variety of options, the most fundemantal is	2995	Libev can be compiled with a variety of options, the most fundamental
1778	C<EV_MULTIPLICITY>. This option determines wether (most) functions and	2996	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
1779	callbacks have an initial C<struct ev_loop *> argument.	2997	functions and callbacks have an initial C<struct ev_loop *> argument.
1780		2998
1781	To make it easier to write programs that cope with either variant, the	2999	To make it easier to write programs that cope with either variant, the
1782	following macros are defined:	3000	following macros are defined:
1783		3001
1784	=over 4	3002	=over 4
…		…
1787		3005
1788	This provides the loop I<argument> for functions, if one is required ("ev	3006	This provides the loop I<argument> for functions, if one is required ("ev
1789	loop argument"). The C<EV_A> form is used when this is the sole argument,	3007	loop argument"). The C<EV_A> form is used when this is the sole argument,
1790	C<EV_A_> is used when other arguments are following. Example:	3008	C<EV_A_> is used when other arguments are following. Example:
1791		3009
1792	ev_unref (EV_A);	3010	ev_unref (EV_A);
1793	ev_timer_add (EV_A_ watcher);	3011	ev_timer_add (EV_A_ watcher);
1794	ev_loop (EV_A_ 0);	3012	ev_loop (EV_A_ 0);
1795		3013
1796	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	3014	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
1797	which is often provided by the following macro.	3015	which is often provided by the following macro.
1798		3016
1799	=item C<EV_P>, C<EV_P_>	3017	=item C<EV_P>, C<EV_P_>
1800		3018
1801	This provides the loop I<parameter> for functions, if one is required ("ev	3019	This provides the loop I<parameter> for functions, if one is required ("ev
1802	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	3020	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
1803	C<EV_P_> is used when other parameters are following. Example:	3021	C<EV_P_> is used when other parameters are following. Example:
1804		3022
1805	// this is how ev_unref is being declared	3023	// this is how ev_unref is being declared
1806	static void ev_unref (EV_P);	3024	static void ev_unref (EV_P);
1807		3025
1808	// this is how you can declare your typical callback	3026	// this is how you can declare your typical callback
1809	static void cb (EV_P_ ev_timer *w, int revents)	3027	static void cb (EV_P_ ev_timer *w, int revents)
1810		3028
1811	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	3029	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
1812	suitable for use with C<EV_A>.	3030	suitable for use with C<EV_A>.
1813		3031
1814	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3032	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
1815		3033
1816	Similar to the other two macros, this gives you the value of the default	3034	Similar to the other two macros, this gives you the value of the default
1817	loop, if multiple loops are supported ("ev loop default").	3035	loop, if multiple loops are supported ("ev loop default").
1818		3036
		3037	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3038
		3039	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3040	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3041	is undefined when the default loop has not been initialised by a previous
		3042	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3043
		3044	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3045	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		3046
1819	=back	3047	=back
1820		3048
1821	Example: Declare and initialise a check watcher, working regardless of	3049	Example: Declare and initialise a check watcher, utilising the above
1822	wether multiple loops are supported or not.	3050	macros so it will work regardless of whether multiple loops are supported
		3051	or not.
1823		3052
1824	static void	3053	static void
1825	check_cb (EV_P_ ev_timer *w, int revents)	3054	check_cb (EV_P_ ev_timer *w, int revents)
1826	{	3055	{
1827	ev_check_stop (EV_A_ w);	3056	ev_check_stop (EV_A_ w);
1828	}	3057	}
1829		3058
1830	ev_check check;	3059	ev_check check;
1831	ev_check_init (&check, check_cb);	3060	ev_check_init (&check, check_cb);
1832	ev_check_start (EV_DEFAULT_ &check);	3061	ev_check_start (EV_DEFAULT_ &check);
1833	ev_loop (EV_DEFAULT_ 0);	3062	ev_loop (EV_DEFAULT_ 0);
1834
1835		3063
1836	=head1 EMBEDDING	3064	=head1 EMBEDDING
1837		3065
1838	Libev can (and often is) directly embedded into host	3066	Libev can (and often is) directly embedded into host
1839	applications. Examples of applications that embed it include the Deliantra	3067	applications. Examples of applications that embed it include the Deliantra
1840	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)	3068	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
1841	and rxvt-unicode.	3069	and rxvt-unicode.
1842		3070
1843	The goal is to enable you to just copy the neecssary files into your	3071	The goal is to enable you to just copy the necessary files into your
1844	source directory without having to change even a single line in them, so	3072	source directory without having to change even a single line in them, so
1845	you can easily upgrade by simply copying (or having a checked-out copy of	3073	you can easily upgrade by simply copying (or having a checked-out copy of
1846	libev somewhere in your source tree).	3074	libev somewhere in your source tree).
1847		3075
1848	=head2 FILESETS	3076	=head2 FILESETS
1849		3077
1850	Depending on what features you need you need to include one or more sets of files	3078	Depending on what features you need you need to include one or more sets of files
1851	in your app.	3079	in your application.
1852		3080
1853	=head3 CORE EVENT LOOP	3081	=head3 CORE EVENT LOOP
1854		3082
1855	To include only the libev core (all the C<ev_*> functions), with manual	3083	To include only the libev core (all the C<ev_*> functions), with manual
1856	configuration (no autoconf):	3084	configuration (no autoconf):
1857		3085
1858	#define EV_STANDALONE 1	3086	#define EV_STANDALONE 1
1859	#include "ev.c"	3087	#include "ev.c"
1860		3088
1861	This will automatically include F<ev.h>, too, and should be done in a	3089	This will automatically include F<ev.h>, too, and should be done in a
1862	single C source file only to provide the function implementations. To use	3090	single C source file only to provide the function implementations. To use
1863	it, do the same for F<ev.h> in all files wishing to use this API (best	3091	it, do the same for F<ev.h> in all files wishing to use this API (best
1864	done by writing a wrapper around F<ev.h> that you can include instead and	3092	done by writing a wrapper around F<ev.h> that you can include instead and
1865	where you can put other configuration options):	3093	where you can put other configuration options):
1866		3094
1867	#define EV_STANDALONE 1	3095	#define EV_STANDALONE 1
1868	#include "ev.h"	3096	#include "ev.h"
1869		3097
1870	Both header files and implementation files can be compiled with a C++	3098	Both header files and implementation files can be compiled with a C++
1871	compiler (at least, thats a stated goal, and breakage will be treated	3099	compiler (at least, that's a stated goal, and breakage will be treated
1872	as a bug).	3100	as a bug).
1873		3101
1874	You need the following files in your source tree, or in a directory	3102	You need the following files in your source tree, or in a directory
1875	in your include path (e.g. in libev/ when using -Ilibev):	3103	in your include path (e.g. in libev/ when using -Ilibev):
1876		3104
1877	ev.h	3105	ev.h
1878	ev.c	3106	ev.c
1879	ev_vars.h	3107	ev_vars.h
1880	ev_wrap.h	3108	ev_wrap.h
1881		3109
1882	ev_win32.c required on win32 platforms only	3110	ev_win32.c required on win32 platforms only
1883		3111
1884	ev_select.c only when select backend is enabled (which is by default)	3112	ev_select.c only when select backend is enabled (which is enabled by default)
1885	ev_poll.c only when poll backend is enabled (disabled by default)	3113	ev_poll.c only when poll backend is enabled (disabled by default)
1886	ev_epoll.c only when the epoll backend is enabled (disabled by default)	3114	ev_epoll.c only when the epoll backend is enabled (disabled by default)
1887	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	3115	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
1888	ev_port.c only when the solaris port backend is enabled (disabled by default)	3116	ev_port.c only when the solaris port backend is enabled (disabled by default)
1889		3117
1890	F<ev.c> includes the backend files directly when enabled, so you only need	3118	F<ev.c> includes the backend files directly when enabled, so you only need
1891	to compile this single file.	3119	to compile this single file.
1892		3120
1893	=head3 LIBEVENT COMPATIBILITY API	3121	=head3 LIBEVENT COMPATIBILITY API
1894		3122
1895	To include the libevent compatibility API, also include:	3123	To include the libevent compatibility API, also include:
1896		3124
1897	#include "event.c"	3125	#include "event.c"
1898		3126
1899	in the file including F<ev.c>, and:	3127	in the file including F<ev.c>, and:
1900		3128
1901	#include "event.h"	3129	#include "event.h"
1902		3130
1903	in the files that want to use the libevent API. This also includes F<ev.h>.	3131	in the files that want to use the libevent API. This also includes F<ev.h>.
1904		3132
1905	You need the following additional files for this:	3133	You need the following additional files for this:
1906		3134
1907	event.h	3135	event.h
1908	event.c	3136	event.c
1909		3137
1910	=head3 AUTOCONF SUPPORT	3138	=head3 AUTOCONF SUPPORT
1911		3139
1912	Instead of using C<EV_STANDALONE=1> and providing your config in	3140	Instead of using C<EV_STANDALONE=1> and providing your configuration in
1913	whatever way you want, you can also C<m4_include([libev.m4])> in your	3141	whatever way you want, you can also C<m4_include([libev.m4])> in your
1914	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	3142	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
1915	include F<config.h> and configure itself accordingly.	3143	include F<config.h> and configure itself accordingly.
1916		3144
1917	For this of course you need the m4 file:	3145	For this of course you need the m4 file:
1918		3146
1919	libev.m4	3147	libev.m4
1920		3148
1921	=head2 PREPROCESSOR SYMBOLS/MACROS	3149	=head2 PREPROCESSOR SYMBOLS/MACROS
1922		3150
1923	Libev can be configured via a variety of preprocessor symbols you have to define	3151	Libev can be configured via a variety of preprocessor symbols you have to
1924	before including any of its files. The default is not to build for multiplicity	3152	define before including any of its files. The default in the absence of
1925	and only include the select backend.	3153	autoconf is documented for every option.
1926		3154
1927	=over 4	3155	=over 4
1928		3156
1929	=item EV_STANDALONE	3157	=item EV_STANDALONE
1930		3158
…		…
1935	F<event.h> that are not directly supported by the libev core alone.	3163	F<event.h> that are not directly supported by the libev core alone.
1936		3164
1937	=item EV_USE_MONOTONIC	3165	=item EV_USE_MONOTONIC
1938		3166
1939	If defined to be C<1>, libev will try to detect the availability of the	3167	If defined to be C<1>, libev will try to detect the availability of the
1940	monotonic clock option at both compiletime and runtime. Otherwise no use	3168	monotonic clock option at both compile time and runtime. Otherwise no use
1941	of the monotonic clock option will be attempted. If you enable this, you	3169	of the monotonic clock option will be attempted. If you enable this, you
1942	usually have to link against librt or something similar. Enabling it when	3170	usually have to link against librt or something similar. Enabling it when
1943	the functionality isn't available is safe, though, althoguh you have	3171	the functionality isn't available is safe, though, although you have
1944	to make sure you link against any libraries where the C<clock_gettime>	3172	to make sure you link against any libraries where the C<clock_gettime>
1945	function is hiding in (often F<-lrt>).	3173	function is hiding in (often F<-lrt>).
1946		3174
1947	=item EV_USE_REALTIME	3175	=item EV_USE_REALTIME
1948		3176
1949	If defined to be C<1>, libev will try to detect the availability of the	3177	If defined to be C<1>, libev will try to detect the availability of the
1950	realtime clock option at compiletime (and assume its availability at	3178	real-time clock option at compile time (and assume its availability at
1951	runtime if successful). Otherwise no use of the realtime clock option will	3179	runtime if successful). Otherwise no use of the real-time clock option will
1952	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3180	be attempted. This effectively replaces C<gettimeofday> by C<clock_get
1953	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See tzhe note about libraries	3181	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the
1954	in the description of C<EV_USE_MONOTONIC>, though.	3182	note about libraries in the description of C<EV_USE_MONOTONIC>, though.
		3183
		3184	=item EV_USE_NANOSLEEP
		3185
		3186	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		3187	and will use it for delays. Otherwise it will use C<select ()>.
		3188
		3189	=item EV_USE_EVENTFD
		3190
		3191	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3192	available and will probe for kernel support at runtime. This will improve
		3193	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3194	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3195	2.7 or newer, otherwise disabled.
1955		3196
1956	=item EV_USE_SELECT	3197	=item EV_USE_SELECT
1957		3198
1958	If undefined or defined to be C<1>, libev will compile in support for the	3199	If undefined or defined to be C<1>, libev will compile in support for the
1959	C<select>(2) backend. No attempt at autodetection will be done: if no	3200	C<select>(2) backend. No attempt at auto-detection will be done: if no
1960	other method takes over, select will be it. Otherwise the select backend	3201	other method takes over, select will be it. Otherwise the select backend
1961	will not be compiled in.	3202	will not be compiled in.
1962		3203
1963	=item EV_SELECT_USE_FD_SET	3204	=item EV_SELECT_USE_FD_SET
1964		3205
1965	If defined to C<1>, then the select backend will use the system C<fd_set>	3206	If defined to C<1>, then the select backend will use the system C<fd_set>
1966	structure. This is useful if libev doesn't compile due to a missing	3207	structure. This is useful if libev doesn't compile due to a missing
1967	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	3208	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout on
1968	exotic systems. This usually limits the range of file descriptors to some	3209	exotic systems. This usually limits the range of file descriptors to some
1969	low limit such as 1024 or might have other limitations (winsocket only	3210	low limit such as 1024 or might have other limitations (winsocket only
1970	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3211	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might
1971	influence the size of the C<fd_set> used.	3212	influence the size of the C<fd_set> used.
1972		3213
…		…
1978	be used is the winsock select). This means that it will call	3219	be used is the winsock select). This means that it will call
1979	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3220	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
1980	it is assumed that all these functions actually work on fds, even	3221	it is assumed that all these functions actually work on fds, even
1981	on win32. Should not be defined on non-win32 platforms.	3222	on win32. Should not be defined on non-win32 platforms.
1982		3223
		3224	=item EV_FD_TO_WIN32_HANDLE
		3225
		3226	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3227	file descriptors to socket handles. When not defining this symbol (the
		3228	default), then libev will call C<_get_osfhandle>, which is usually
		3229	correct. In some cases, programs use their own file descriptor management,
		3230	in which case they can provide this function to map fds to socket handles.
		3231
1983	=item EV_USE_POLL	3232	=item EV_USE_POLL
1984		3233
1985	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3234	If defined to be C<1>, libev will compile in support for the C<poll>(2)
1986	backend. Otherwise it will be enabled on non-win32 platforms. It	3235	backend. Otherwise it will be enabled on non-win32 platforms. It
1987	takes precedence over select.	3236	takes precedence over select.
1988		3237
1989	=item EV_USE_EPOLL	3238	=item EV_USE_EPOLL
1990		3239
1991	If defined to be C<1>, libev will compile in support for the Linux	3240	If defined to be C<1>, libev will compile in support for the Linux
1992	C<epoll>(7) backend. Its availability will be detected at runtime,	3241	C<epoll>(7) backend. Its availability will be detected at runtime,
1993	otherwise another method will be used as fallback. This is the	3242	otherwise another method will be used as fallback. This is the preferred
1994	preferred backend for GNU/Linux systems.	3243	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3244	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
1995		3245
1996	=item EV_USE_KQUEUE	3246	=item EV_USE_KQUEUE
1997		3247
1998	If defined to be C<1>, libev will compile in support for the BSD style	3248	If defined to be C<1>, libev will compile in support for the BSD style
1999	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	3249	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2012	otherwise another method will be used as fallback. This is the preferred	3262	otherwise another method will be used as fallback. This is the preferred
2013	backend for Solaris 10 systems.	3263	backend for Solaris 10 systems.
2014		3264
2015	=item EV_USE_DEVPOLL	3265	=item EV_USE_DEVPOLL
2016		3266
2017	reserved for future expansion, works like the USE symbols above.	3267	Reserved for future expansion, works like the USE symbols above.
2018		3268
2019	=item EV_USE_INOTIFY	3269	=item EV_USE_INOTIFY
2020		3270
2021	If defined to be C<1>, libev will compile in support for the Linux inotify	3271	If defined to be C<1>, libev will compile in support for the Linux inotify
2022	interface to speed up C<ev_stat> watchers. Its actual availability will	3272	interface to speed up C<ev_stat> watchers. Its actual availability will
2023	be detected at runtime.	3273	be detected at runtime. If undefined, it will be enabled if the headers
		3274	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3275
		3276	=item EV_ATOMIC_T
		3277
		3278	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3279	access is atomic with respect to other threads or signal contexts. No such
		3280	type is easily found in the C language, so you can provide your own type
		3281	that you know is safe for your purposes. It is used both for signal handler "locking"
		3282	as well as for signal and thread safety in C<ev_async> watchers.
		3283
		3284	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3285	(from F<signal.h>), which is usually good enough on most platforms.
2024		3286
2025	=item EV_H	3287	=item EV_H
2026		3288
2027	The name of the F<ev.h> header file used to include it. The default if	3289	The name of the F<ev.h> header file used to include it. The default if
2028	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This	3290	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2029	can be used to virtually rename the F<ev.h> header file in case of conflicts.	3291	used to virtually rename the F<ev.h> header file in case of conflicts.
2030		3292
2031	=item EV_CONFIG_H	3293	=item EV_CONFIG_H
2032		3294
2033	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	3295	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2034	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	3296	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2035	C<EV_H>, above.	3297	C<EV_H>, above.
2036		3298
2037	=item EV_EVENT_H	3299	=item EV_EVENT_H
2038		3300
2039	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	3301	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2040	of how the F<event.h> header can be found.	3302	of how the F<event.h> header can be found, the default is C<"event.h">.
2041		3303
2042	=item EV_PROTOTYPES	3304	=item EV_PROTOTYPES
2043		3305
2044	If defined to be C<0>, then F<ev.h> will not define any function	3306	If defined to be C<0>, then F<ev.h> will not define any function
2045	prototypes, but still define all the structs and other symbols. This is	3307	prototypes, but still define all the structs and other symbols. This is
…		…
2052	will have the C<struct ev_loop *> as first argument, and you can create	3314	will have the C<struct ev_loop *> as first argument, and you can create
2053	additional independent event loops. Otherwise there will be no support	3315	additional independent event loops. Otherwise there will be no support
2054	for multiple event loops and there is no first event loop pointer	3316	for multiple event loops and there is no first event loop pointer
2055	argument. Instead, all functions act on the single default loop.	3317	argument. Instead, all functions act on the single default loop.
2056		3318
		3319	=item EV_MINPRI
		3320
		3321	=item EV_MAXPRI
		3322
		3323	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		3324	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		3325	provide for more priorities by overriding those symbols (usually defined
		3326	to be C<-2> and C<2>, respectively).
		3327
		3328	When doing priority-based operations, libev usually has to linearly search
		3329	all the priorities, so having many of them (hundreds) uses a lot of space
		3330	and time, so using the defaults of five priorities (-2 .. +2) is usually
		3331	fine.
		3332
		3333	If your embedding application does not need any priorities, defining these
		3334	both to C<0> will save some memory and CPU.
		3335
2057	=item EV_PERIODIC_ENABLE	3336	=item EV_PERIODIC_ENABLE
2058		3337
2059	If undefined or defined to be C<1>, then periodic timers are supported. If	3338	If undefined or defined to be C<1>, then periodic timers are supported. If
2060	defined to be C<0>, then they are not. Disabling them saves a few kB of	3339	defined to be C<0>, then they are not. Disabling them saves a few kB of
2061	code.	3340	code.
2062		3341
		3342	=item EV_IDLE_ENABLE
		3343
		3344	If undefined or defined to be C<1>, then idle watchers are supported. If
		3345	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3346	code.
		3347
2063	=item EV_EMBED_ENABLE	3348	=item EV_EMBED_ENABLE
2064		3349
2065	If undefined or defined to be C<1>, then embed watchers are supported. If	3350	If undefined or defined to be C<1>, then embed watchers are supported. If
2066	defined to be C<0>, then they are not.	3351	defined to be C<0>, then they are not. Embed watchers rely on most other
		3352	watcher types, which therefore must not be disabled.
2067		3353
2068	=item EV_STAT_ENABLE	3354	=item EV_STAT_ENABLE
2069		3355
2070	If undefined or defined to be C<1>, then stat watchers are supported. If	3356	If undefined or defined to be C<1>, then stat watchers are supported. If
2071	defined to be C<0>, then they are not.	3357	defined to be C<0>, then they are not.
…		…
2073	=item EV_FORK_ENABLE	3359	=item EV_FORK_ENABLE
2074		3360
2075	If undefined or defined to be C<1>, then fork watchers are supported. If	3361	If undefined or defined to be C<1>, then fork watchers are supported. If
2076	defined to be C<0>, then they are not.	3362	defined to be C<0>, then they are not.
2077		3363
		3364	=item EV_ASYNC_ENABLE
		3365
		3366	If undefined or defined to be C<1>, then async watchers are supported. If
		3367	defined to be C<0>, then they are not.
		3368
2078	=item EV_MINIMAL	3369	=item EV_MINIMAL
2079		3370
2080	If you need to shave off some kilobytes of code at the expense of some	3371	If you need to shave off some kilobytes of code at the expense of some
2081	speed, define this symbol to C<1>. Currently only used for gcc to override	3372	speed, define this symbol to C<1>. Currently this is used to override some
2082	some inlining decisions, saves roughly 30% codesize of amd64.	3373	inlining decisions, saves roughly 30% code size on amd64. It also selects a
		3374	much smaller 2-heap for timer management over the default 4-heap.
2083		3375
2084	=item EV_PID_HASHSIZE	3376	=item EV_PID_HASHSIZE
2085		3377
2086	C<ev_child> watchers use a small hash table to distribute workload by	3378	C<ev_child> watchers use a small hash table to distribute workload by
2087	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3379	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
2088	than enough. If you need to manage thousands of children you might want to	3380	than enough. If you need to manage thousands of children you might want to
2089	increase this value (I<must> be a power of two).	3381	increase this value (I<must> be a power of two).
2090		3382
2091	=item EV_INOTIFY_HASHSIZE	3383	=item EV_INOTIFY_HASHSIZE
2092		3384
2093	C<ev_staz> watchers use a small hash table to distribute workload by	3385	C<ev_stat> watchers use a small hash table to distribute workload by
2094	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	3386	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
2095	usually more than enough. If you need to manage thousands of C<ev_stat>	3387	usually more than enough. If you need to manage thousands of C<ev_stat>
2096	watchers you might want to increase this value (I<must> be a power of	3388	watchers you might want to increase this value (I<must> be a power of
2097	two).	3389	two).
2098		3390
		3391	=item EV_USE_4HEAP
		3392
		3393	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3394	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		3395	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		3396	faster performance with many (thousands) of watchers.
		3397
		3398	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3399	(disabled).
		3400
		3401	=item EV_HEAP_CACHE_AT
		3402
		3403	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3404	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		3405	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3406	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3407	but avoids random read accesses on heap changes. This improves performance
		3408	noticeably with many (hundreds) of watchers.
		3409
		3410	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3411	(disabled).
		3412
		3413	=item EV_VERIFY
		3414
		3415	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3416	be done: If set to C<0>, no internal verification code will be compiled
		3417	in. If set to C<1>, then verification code will be compiled in, but not
		3418	called. If set to C<2>, then the internal verification code will be
		3419	called once per loop, which can slow down libev. If set to C<3>, then the
		3420	verification code will be called very frequently, which will slow down
		3421	libev considerably.
		3422
		3423	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3424	C<0>.
		3425
2099	=item EV_COMMON	3426	=item EV_COMMON
2100		3427
2101	By default, all watchers have a C<void *data> member. By redefining	3428	By default, all watchers have a C<void *data> member. By redefining
2102	this macro to a something else you can include more and other types of	3429	this macro to a something else you can include more and other types of
2103	members. You have to define it each time you include one of the files,	3430	members. You have to define it each time you include one of the files,
2104	though, and it must be identical each time.	3431	though, and it must be identical each time.
2105		3432
2106	For example, the perl EV module uses something like this:	3433	For example, the perl EV module uses something like this:
2107		3434
2108	#define EV_COMMON \	3435	#define EV_COMMON \
2109	SV *self; /* contains this struct */ \	3436	SV *self; /* contains this struct */ \
2110	SV *cb_sv, *fh /* note no trailing ";" */	3437	SV *cb_sv, *fh /* note no trailing ";" */
2111		3438
2112	=item EV_CB_DECLARE (type)	3439	=item EV_CB_DECLARE (type)
2113		3440
2114	=item EV_CB_INVOKE (watcher, revents)	3441	=item EV_CB_INVOKE (watcher, revents)
2115		3442
2116	=item ev_set_cb (ev, cb)	3443	=item ev_set_cb (ev, cb)
2117		3444
2118	Can be used to change the callback member declaration in each watcher,	3445	Can be used to change the callback member declaration in each watcher,
2119	and the way callbacks are invoked and set. Must expand to a struct member	3446	and the way callbacks are invoked and set. Must expand to a struct member
2120	definition and a statement, respectively. See the F<ev.v> header file for	3447	definition and a statement, respectively. See the F<ev.h> header file for
2121	their default definitions. One possible use for overriding these is to	3448	their default definitions. One possible use for overriding these is to
2122	avoid the C<struct ev_loop *> as first argument in all cases, or to use	3449	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2123	method calls instead of plain function calls in C++.	3450	method calls instead of plain function calls in C++.
		3451
		3452	=back
		3453
		3454	=head2 EXPORTED API SYMBOLS
		3455
		3456	If you need to re-export the API (e.g. via a DLL) and you need a list of
		3457	exported symbols, you can use the provided F<Symbol.*> files which list
		3458	all public symbols, one per line:
		3459
		3460	Symbols.ev for libev proper
		3461	Symbols.event for the libevent emulation
		3462
		3463	This can also be used to rename all public symbols to avoid clashes with
		3464	multiple versions of libev linked together (which is obviously bad in
		3465	itself, but sometimes it is inconvenient to avoid this).
		3466
		3467	A sed command like this will create wrapper C<#define>'s that you need to
		3468	include before including F<ev.h>:
		3469
		3470	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		3471
		3472	This would create a file F<wrap.h> which essentially looks like this:
		3473
		3474	#define ev_backend myprefix_ev_backend
		3475	#define ev_check_start myprefix_ev_check_start
		3476	#define ev_check_stop myprefix_ev_check_stop
		3477	...
2124		3478
2125	=head2 EXAMPLES	3479	=head2 EXAMPLES
2126		3480
2127	For a real-world example of a program the includes libev	3481	For a real-world example of a program the includes libev
2128	verbatim, you can have a look at the EV perl module	3482	verbatim, you can have a look at the EV perl module
…		…
2131	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file	3485	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
2132	will be compiled. It is pretty complex because it provides its own header	3486	will be compiled. It is pretty complex because it provides its own header
2133	file.	3487	file.
2134		3488
2135	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	3489	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2136	that everybody includes and which overrides some autoconf choices:	3490	that everybody includes and which overrides some configure choices:
2137		3491
		3492	#define EV_MINIMAL 1
2138	#define EV_USE_POLL 0	3493	#define EV_USE_POLL 0
2139	#define EV_MULTIPLICITY 0	3494	#define EV_MULTIPLICITY 0
2140	#define EV_PERIODICS 0	3495	#define EV_PERIODIC_ENABLE 0
		3496	#define EV_STAT_ENABLE 0
		3497	#define EV_FORK_ENABLE 0
2141	#define EV_CONFIG_H <config.h>	3498	#define EV_CONFIG_H <config.h>
		3499	#define EV_MINPRI 0
		3500	#define EV_MAXPRI 0
2142		3501
2143	#include "ev++.h"	3502	#include "ev++.h"
2144		3503
2145	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	3504	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2146		3505
2147	#include "ev_cpp.h"	3506	#include "ev_cpp.h"
2148	#include "ev.c"	3507	#include "ev.c"
2149		3508
		3509	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
2150		3510
		3511	=head2 THREADS AND COROUTINES
		3512
		3513	=head3 THREADS
		3514
		3515	All libev functions are reentrant and thread-safe unless explicitly
		3516	documented otherwise, but libev implements no locking itself. This means
		3517	that you can use as many loops as you want in parallel, as long as there
		3518	are no concurrent calls into any libev function with the same loop
		3519	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		3520	of course): libev guarantees that different event loops share no data
		3521	structures that need any locking.
		3522
		3523	Or to put it differently: calls with different loop parameters can be done
		3524	concurrently from multiple threads, calls with the same loop parameter
		3525	must be done serially (but can be done from different threads, as long as
		3526	only one thread ever is inside a call at any point in time, e.g. by using
		3527	a mutex per loop).
		3528
		3529	Specifically to support threads (and signal handlers), libev implements
		3530	so-called C<ev_async> watchers, which allow some limited form of
		3531	concurrency on the same event loop, namely waking it up "from the
		3532	outside".
		3533
		3534	If you want to know which design (one loop, locking, or multiple loops
		3535	without or something else still) is best for your problem, then I cannot
		3536	help you, but here is some generic advice:
		3537
		3538	=over 4
		3539
		3540	=item * most applications have a main thread: use the default libev loop
		3541	in that thread, or create a separate thread running only the default loop.
		3542
		3543	This helps integrating other libraries or software modules that use libev
		3544	themselves and don't care/know about threading.
		3545
		3546	=item * one loop per thread is usually a good model.
		3547
		3548	Doing this is almost never wrong, sometimes a better-performance model
		3549	exists, but it is always a good start.
		3550
		3551	=item * other models exist, such as the leader/follower pattern, where one
		3552	loop is handed through multiple threads in a kind of round-robin fashion.
		3553
		3554	Choosing a model is hard - look around, learn, know that usually you can do
		3555	better than you currently do :-)
		3556
		3557	=item * often you need to talk to some other thread which blocks in the
		3558	event loop.
		3559
		3560	C<ev_async> watchers can be used to wake them up from other threads safely
		3561	(or from signal contexts...).
		3562
		3563	An example use would be to communicate signals or other events that only
		3564	work in the default loop by registering the signal watcher with the
		3565	default loop and triggering an C<ev_async> watcher from the default loop
		3566	watcher callback into the event loop interested in the signal.
		3567
		3568	=back
		3569
		3570	=head3 COROUTINES
		3571
		3572	Libev is very accommodating to coroutines ("cooperative threads"):
		3573	libev fully supports nesting calls to its functions from different
		3574	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3575	different coroutines, and switch freely between both coroutines running the
		3576	loop, as long as you don't confuse yourself). The only exception is that
		3577	you must not do this from C<ev_periodic> reschedule callbacks.
		3578
		3579	Care has been taken to ensure that libev does not keep local state inside
		3580	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		3581	they do not call any callbacks.
		3582
		3583	=head2 COMPILER WARNINGS
		3584
		3585	Depending on your compiler and compiler settings, you might get no or a
		3586	lot of warnings when compiling libev code. Some people are apparently
		3587	scared by this.
		3588
		3589	However, these are unavoidable for many reasons. For one, each compiler
		3590	has different warnings, and each user has different tastes regarding
		3591	warning options. "Warn-free" code therefore cannot be a goal except when
		3592	targeting a specific compiler and compiler-version.
		3593
		3594	Another reason is that some compiler warnings require elaborate
		3595	workarounds, or other changes to the code that make it less clear and less
		3596	maintainable.
		3597
		3598	And of course, some compiler warnings are just plain stupid, or simply
		3599	wrong (because they don't actually warn about the condition their message
		3600	seems to warn about). For example, certain older gcc versions had some
		3601	warnings that resulted an extreme number of false positives. These have
		3602	been fixed, but some people still insist on making code warn-free with
		3603	such buggy versions.
		3604
		3605	While libev is written to generate as few warnings as possible,
		3606	"warn-free" code is not a goal, and it is recommended not to build libev
		3607	with any compiler warnings enabled unless you are prepared to cope with
		3608	them (e.g. by ignoring them). Remember that warnings are just that:
		3609	warnings, not errors, or proof of bugs.
		3610
		3611
		3612	=head2 VALGRIND
		3613
		3614	Valgrind has a special section here because it is a popular tool that is
		3615	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		3616
		3617	If you think you found a bug (memory leak, uninitialised data access etc.)
		3618	in libev, then check twice: If valgrind reports something like:
		3619
		3620	==2274== definitely lost: 0 bytes in 0 blocks.
		3621	==2274== possibly lost: 0 bytes in 0 blocks.
		3622	==2274== still reachable: 256 bytes in 1 blocks.
		3623
		3624	Then there is no memory leak, just as memory accounted to global variables
		3625	is not a memleak - the memory is still being referenced, and didn't leak.
		3626
		3627	Similarly, under some circumstances, valgrind might report kernel bugs
		3628	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		3629	although an acceptable workaround has been found here), or it might be
		3630	confused.
		3631
		3632	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		3633	make it into some kind of religion.
		3634
		3635	If you are unsure about something, feel free to contact the mailing list
		3636	with the full valgrind report and an explanation on why you think this
		3637	is a bug in libev (best check the archives, too :). However, don't be
		3638	annoyed when you get a brisk "this is no bug" answer and take the chance
		3639	of learning how to interpret valgrind properly.
		3640
		3641	If you need, for some reason, empty reports from valgrind for your project
		3642	I suggest using suppression lists.
		3643
		3644
		3645	=head1 PORTABILITY NOTES
		3646
		3647	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		3648
		3649	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		3650	requires, and its I/O model is fundamentally incompatible with the POSIX
		3651	model. Libev still offers limited functionality on this platform in
		3652	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		3653	descriptors. This only applies when using Win32 natively, not when using
		3654	e.g. cygwin.
		3655
		3656	Lifting these limitations would basically require the full
		3657	re-implementation of the I/O system. If you are into these kinds of
		3658	things, then note that glib does exactly that for you in a very portable
		3659	way (note also that glib is the slowest event library known to man).
		3660
		3661	There is no supported compilation method available on windows except
		3662	embedding it into other applications.
		3663
		3664	Not a libev limitation but worth mentioning: windows apparently doesn't
		3665	accept large writes: instead of resulting in a partial write, windows will
		3666	either accept everything or return C<ENOBUFS> if the buffer is too large,
		3667	so make sure you only write small amounts into your sockets (less than a
		3668	megabyte seems safe, but this apparently depends on the amount of memory
		3669	available).
		3670
		3671	Due to the many, low, and arbitrary limits on the win32 platform and
		3672	the abysmal performance of winsockets, using a large number of sockets
		3673	is not recommended (and not reasonable). If your program needs to use
		3674	more than a hundred or so sockets, then likely it needs to use a totally
		3675	different implementation for windows, as libev offers the POSIX readiness
		3676	notification model, which cannot be implemented efficiently on windows
		3677	(Microsoft monopoly games).
		3678
		3679	A typical way to use libev under windows is to embed it (see the embedding
		3680	section for details) and use the following F<evwrap.h> header file instead
		3681	of F<ev.h>:
		3682
		3683	#define EV_STANDALONE /* keeps ev from requiring config.h */
		3684	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		3685
		3686	#include "ev.h"
		3687
		3688	And compile the following F<evwrap.c> file into your project (make sure
		3689	you do I<not> compile the F<ev.c> or any other embedded source files!):
		3690
		3691	#include "evwrap.h"
		3692	#include "ev.c"
		3693
		3694	=over 4
		3695
		3696	=item The winsocket select function
		3697
		3698	The winsocket C<select> function doesn't follow POSIX in that it
		3699	requires socket I<handles> and not socket I<file descriptors> (it is
		3700	also extremely buggy). This makes select very inefficient, and also
		3701	requires a mapping from file descriptors to socket handles (the Microsoft
		3702	C runtime provides the function C<_open_osfhandle> for this). See the
		3703	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		3704	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		3705
		3706	The configuration for a "naked" win32 using the Microsoft runtime
		3707	libraries and raw winsocket select is:
		3708
		3709	#define EV_USE_SELECT 1
		3710	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		3711
		3712	Note that winsockets handling of fd sets is O(n), so you can easily get a
		3713	complexity in the O(n²) range when using win32.
		3714
		3715	=item Limited number of file descriptors
		3716
		3717	Windows has numerous arbitrary (and low) limits on things.
		3718
		3719	Early versions of winsocket's select only supported waiting for a maximum
		3720	of C<64> handles (probably owning to the fact that all windows kernels
		3721	can only wait for C<64> things at the same time internally; Microsoft
		3722	recommends spawning a chain of threads and wait for 63 handles and the
		3723	previous thread in each. Great).
		3724
		3725	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		3726	to some high number (e.g. C<2048>) before compiling the winsocket select
		3727	call (which might be in libev or elsewhere, for example, perl does its own
		3728	select emulation on windows).
		3729
		3730	Another limit is the number of file descriptors in the Microsoft runtime
		3731	libraries, which by default is C<64> (there must be a hidden I<64> fetish
		3732	or something like this inside Microsoft). You can increase this by calling
		3733	C<_setmaxstdio>, which can increase this limit to C<2048> (another
		3734	arbitrary limit), but is broken in many versions of the Microsoft runtime
		3735	libraries.
		3736
		3737	This might get you to about C<512> or C<2048> sockets (depending on
		3738	windows version and/or the phase of the moon). To get more, you need to
		3739	wrap all I/O functions and provide your own fd management, but the cost of
		3740	calling select (O(n²)) will likely make this unworkable.
		3741
		3742	=back
		3743
		3744	=head2 PORTABILITY REQUIREMENTS
		3745
		3746	In addition to a working ISO-C implementation and of course the
		3747	backend-specific APIs, libev relies on a few additional extensions:
		3748
		3749	=over 4
		3750
		3751	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		3752	calling conventions regardless of C<ev_watcher_type *>.
		3753
		3754	Libev assumes not only that all watcher pointers have the same internal
		3755	structure (guaranteed by POSIX but not by ISO C for example), but it also
		3756	assumes that the same (machine) code can be used to call any watcher
		3757	callback: The watcher callbacks have different type signatures, but libev
		3758	calls them using an C<ev_watcher *> internally.
		3759
		3760	=item C<sig_atomic_t volatile> must be thread-atomic as well
		3761
		3762	The type C<sig_atomic_t volatile> (or whatever is defined as
		3763	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		3764	threads. This is not part of the specification for C<sig_atomic_t>, but is
		3765	believed to be sufficiently portable.
		3766
		3767	=item C<sigprocmask> must work in a threaded environment
		3768
		3769	Libev uses C<sigprocmask> to temporarily block signals. This is not
		3770	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		3771	pthread implementations will either allow C<sigprocmask> in the "main
		3772	thread" or will block signals process-wide, both behaviours would
		3773	be compatible with libev. Interaction between C<sigprocmask> and
		3774	C<pthread_sigmask> could complicate things, however.
		3775
		3776	The most portable way to handle signals is to block signals in all threads
		3777	except the initial one, and run the default loop in the initial thread as
		3778	well.
		3779
		3780	=item C<long> must be large enough for common memory allocation sizes
		3781
		3782	To improve portability and simplify its API, libev uses C<long> internally
		3783	instead of C<size_t> when allocating its data structures. On non-POSIX
		3784	systems (Microsoft...) this might be unexpectedly low, but is still at
		3785	least 31 bits everywhere, which is enough for hundreds of millions of
		3786	watchers.
		3787
		3788	=item C<double> must hold a time value in seconds with enough accuracy
		3789
		3790	The type C<double> is used to represent timestamps. It is required to
		3791	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		3792	enough for at least into the year 4000. This requirement is fulfilled by
		3793	implementations implementing IEEE 754 (basically all existing ones).
		3794
		3795	=back
		3796
		3797	If you know of other additional requirements drop me a note.
		3798
		3799
2151	=head1 COMPLEXITIES	3800	=head1 ALGORITHMIC COMPLEXITIES
2152		3801
2153	In this section the complexities of (many of) the algorithms used inside	3802	In this section the complexities of (many of) the algorithms used inside
2154	libev will be explained. For complexity discussions about backends see the	3803	libev will be documented. For complexity discussions about backends see
2155	documentation for C<ev_default_init>.	3804	the documentation for C<ev_default_init>.
		3805
		3806	All of the following are about amortised time: If an array needs to be
		3807	extended, libev needs to realloc and move the whole array, but this
		3808	happens asymptotically rarer with higher number of elements, so O(1) might
		3809	mean that libev does a lengthy realloc operation in rare cases, but on
		3810	average it is much faster and asymptotically approaches constant time.
2156		3811
2157	=over 4	3812	=over 4
2158		3813
2159	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	3814	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2160		3815
		3816	This means that, when you have a watcher that triggers in one hour and
		3817	there are 100 watchers that would trigger before that, then inserting will
		3818	have to skip roughly seven (C<ld 100>) of these watchers.
		3819
2161	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	3820	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2162		3821
		3822	That means that changing a timer costs less than removing/adding them,
		3823	as only the relative motion in the event queue has to be paid for.
		3824
2163	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	3825	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
2164		3826
		3827	These just add the watcher into an array or at the head of a list.
		3828
2165	=item Stopping check/prepare/idle watchers: O(1)	3829	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2166		3830
2167	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	3831	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2168		3832
		3833	These watchers are stored in lists, so they need to be walked to find the
		3834	correct watcher to remove. The lists are usually short (you don't usually
		3835	have many watchers waiting for the same fd or signal: one is typical, two
		3836	is rare).
		3837
2169	=item Finding the next timer per loop iteration: O(1)	3838	=item Finding the next timer in each loop iteration: O(1)
		3839
		3840	By virtue of using a binary or 4-heap, the next timer is always found at a
		3841	fixed position in the storage array.
2170		3842
2171	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	3843	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2172		3844
2173	=item Activating one watcher: O(1)	3845	A change means an I/O watcher gets started or stopped, which requires
		3846	libev to recalculate its status (and possibly tell the kernel, depending
		3847	on backend and whether C<ev_io_set> was used).
		3848
		3849	=item Activating one watcher (putting it into the pending state): O(1)
		3850
		3851	=item Priority handling: O(number_of_priorities)
		3852
		3853	Priorities are implemented by allocating some space for each
		3854	priority. When doing priority-based operations, libev usually has to
		3855	linearly search all the priorities, but starting/stopping and activating
		3856	watchers becomes O(1) with respect to priority handling.
		3857
		3858	=item Sending an ev_async: O(1)
		3859
		3860	=item Processing ev_async_send: O(number_of_async_watchers)
		3861
		3862	=item Processing signals: O(max_signal_number)
		3863
		3864	Sending involves a system call I<iff> there were no other C<ev_async_send>
		3865	calls in the current loop iteration. Checking for async and signal events
		3866	involves iterating over all running async watchers or all signal numbers.
2174		3867
2175	=back	3868	=back
2176		3869
2177		3870
2178	=head1 AUTHOR	3871	=head1 AUTHOR
2179		3872
2180	Marc Lehmann <libev@schmorp.de>.	3873	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
2181		3874

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