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Revision 1.58 by root, Wed Nov 28 11:31:34 2007 UTC vs.
Revision 1.215 by root, Wed Nov 5 21:44:21 2008 UTC

…		…
2		2
3	libev - a high performance full-featured event loop written in C	3	libev - a high performance full-featured event loop written in C
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
8		8
9	=head1 EXAMPLE PROGRAM	9	=head2 EXAMPLE PROGRAM
10		10
		11	// a single header file is required
11	#include <ev.h>	12	#include <ev.h>
12		13
		14	// every watcher type has its own typedef'd struct
		15	// with the name ev_TYPE
13	ev_io stdin_watcher;	16	ev_io stdin_watcher;
14	ev_timer timeout_watcher;	17	ev_timer timeout_watcher;
15		18
16	/* called when data readable on stdin */	19	// all watcher callbacks have a similar signature
		20	// this callback is called when data is readable on stdin
17	static void	21	static void
18	stdin_cb (EV_P_ struct ev_io *w, int revents)	22	stdin_cb (EV_P_ ev_io *w, int revents)
19	{	23	{
20	/* puts ("stdin ready"); */	24	puts ("stdin ready");
21	ev_io_stop (EV_A_ w); /* just a syntax example */	25	// for one-shot events, one must manually stop the watcher
22	ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */	26	// with its corresponding stop function.
		27	ev_io_stop (EV_A_ w);
		28
		29	// this causes all nested ev_loop's to stop iterating
		30	ev_unloop (EV_A_ EVUNLOOP_ALL);
23	}	31	}
24		32
		33	// another callback, this time for a time-out
25	static void	34	static void
26	timeout_cb (EV_P_ struct ev_timer *w, int revents)	35	timeout_cb (EV_P_ ev_timer *w, int revents)
27	{	36	{
28	/* puts ("timeout"); */	37	puts ("timeout");
29	ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */	38	// this causes the innermost ev_loop to stop iterating
		39	ev_unloop (EV_A_ EVUNLOOP_ONE);
30	}	40	}
31		41
32	int	42	int
33	main (void)	43	main (void)
34	{	44	{
		45	// use the default event loop unless you have special needs
35	struct ev_loop *loop = ev_default_loop (0);	46	ev_loop *loop = ev_default_loop (0);
36		47
37	/* initialise an io watcher, then start it */	48	// initialise an io watcher, then start it
		49	// this one will watch for stdin to become readable
38	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);	50	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
39	ev_io_start (loop, &stdin_watcher);	51	ev_io_start (loop, &stdin_watcher);
40		52
		53	// initialise a timer watcher, then start it
41	/* simple non-repeating 5.5 second timeout */	54	// simple non-repeating 5.5 second timeout
42	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);	55	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
43	ev_timer_start (loop, &timeout_watcher);	56	ev_timer_start (loop, &timeout_watcher);
44		57
45	/* loop till timeout or data ready */	58	// now wait for events to arrive
46	ev_loop (loop, 0);	59	ev_loop (loop, 0);
47		60
		61	// unloop was called, so exit
48	return 0;	62	return 0;
49	}	63	}
50		64
51	=head1 DESCRIPTION	65	=head1 DESCRIPTION
52		66
		67	The newest version of this document is also available as an html-formatted
		68	web page you might find easier to navigate when reading it for the first
		69	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		70
53	Libev is an event loop: you register interest in certain events (such as a	71	Libev is an event loop: you register interest in certain events (such as a
54	file descriptor being readable or a timeout occuring), and it will manage	72	file descriptor being readable or a timeout occurring), and it will manage
55	these event sources and provide your program with events.	73	these event sources and provide your program with events.
56		74
57	To do this, it must take more or less complete control over your process	75	To do this, it must take more or less complete control over your process
58	(or thread) by executing the I<event loop> handler, and will then	76	(or thread) by executing the I<event loop> handler, and will then
59	communicate events via a callback mechanism.	77	communicate events via a callback mechanism.
…		…
61	You register interest in certain events by registering so-called I<event	79	You register interest in certain events by registering so-called I<event
62	watchers>, which are relatively small C structures you initialise with the	80	watchers>, which are relatively small C structures you initialise with the
63	details of the event, and then hand it over to libev by I<starting> the	81	details of the event, and then hand it over to libev by I<starting> the
64	watcher.	82	watcher.
65		83
66	=head1 FEATURES	84	=head2 FEATURES
67		85
68	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	86	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
69	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	87	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
70	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	88	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
71	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	89	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
…		…
78		96
79	It also is quite fast (see this	97	It also is quite fast (see this
80	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent	98	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
81	for example).	99	for example).
82		100
83	=head1 CONVENTIONS	101	=head2 CONVENTIONS
84		102
85	Libev is very configurable. In this manual the default configuration will	103	Libev is very configurable. In this manual the default (and most common)
86	be described, which supports multiple event loops. For more info about	104	configuration will be described, which supports multiple event loops. For
87	various configuration options please have a look at B<EMBED> section in	105	more info about various configuration options please have a look at
88	this manual. If libev was configured without support for multiple event	106	B<EMBED> section in this manual. If libev was configured without support
89	loops, then all functions taking an initial argument of name C<loop>	107	for multiple event loops, then all functions taking an initial argument of
90	(which is always of type C<struct ev_loop *>) will not have this argument.	108	name C<loop> (which is always of type C<ev_loop *>) will not have
		109	this argument.
91		110
92	=head1 TIME REPRESENTATION	111	=head2 TIME REPRESENTATION
93		112
94	Libev represents time as a single floating point number, representing the	113	Libev represents time as a single floating point number, representing the
95	(fractional) number of seconds since the (POSIX) epoch (somewhere near	114	(fractional) number of seconds since the (POSIX) epoch (somewhere near
96	the beginning of 1970, details are complicated, don't ask). This type is	115	the beginning of 1970, details are complicated, don't ask). This type is
97	called C<ev_tstamp>, which is what you should use too. It usually aliases	116	called C<ev_tstamp>, which is what you should use too. It usually aliases
98	to the C<double> type in C, and when you need to do any calculations on	117	to the C<double> type in C, and when you need to do any calculations on
99	it, you should treat it as such.	118	it, you should treat it as some floating point value. Unlike the name
		119	component C<stamp> might indicate, it is also used for time differences
		120	throughout libev.
		121
		122	=head1 ERROR HANDLING
		123
		124	Libev knows three classes of errors: operating system errors, usage errors
		125	and internal errors (bugs).
		126
		127	When libev catches an operating system error it cannot handle (for example
		128	a system call indicating a condition libev cannot fix), it calls the callback
		129	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		130	abort. The default is to print a diagnostic message and to call C<abort
		131	()>.
		132
		133	When libev detects a usage error such as a negative timer interval, then
		134	it will print a diagnostic message and abort (via the C<assert> mechanism,
		135	so C<NDEBUG> will disable this checking): these are programming errors in
		136	the libev caller and need to be fixed there.
		137
		138	Libev also has a few internal error-checking C<assert>ions, and also has
		139	extensive consistency checking code. These do not trigger under normal
		140	circumstances, as they indicate either a bug in libev or worse.
		141
100		142
101	=head1 GLOBAL FUNCTIONS	143	=head1 GLOBAL FUNCTIONS
102		144
103	These functions can be called anytime, even before initialising the	145	These functions can be called anytime, even before initialising the
104	library in any way.	146	library in any way.
…		…
109		151
110	Returns the current time as libev would use it. Please note that the	152	Returns the current time as libev would use it. Please note that the
111	C<ev_now> function is usually faster and also often returns the timestamp	153	C<ev_now> function is usually faster and also often returns the timestamp
112	you actually want to know.	154	you actually want to know.
113		155
		156	=item ev_sleep (ev_tstamp interval)
		157
		158	Sleep for the given interval: The current thread will be blocked until
		159	either it is interrupted or the given time interval has passed. Basically
		160	this is a sub-second-resolution C<sleep ()>.
		161
114	=item int ev_version_major ()	162	=item int ev_version_major ()
115		163
116	=item int ev_version_minor ()	164	=item int ev_version_minor ()
117		165
118	You can find out the major and minor version numbers of the library	166	You can find out the major and minor ABI version numbers of the library
119	you linked against by calling the functions C<ev_version_major> and	167	you linked against by calling the functions C<ev_version_major> and
120	C<ev_version_minor>. If you want, you can compare against the global	168	C<ev_version_minor>. If you want, you can compare against the global
121	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the	169	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
122	version of the library your program was compiled against.	170	version of the library your program was compiled against.
123		171
		172	These version numbers refer to the ABI version of the library, not the
		173	release version.
		174
124	Usually, it's a good idea to terminate if the major versions mismatch,	175	Usually, it's a good idea to terminate if the major versions mismatch,
125	as this indicates an incompatible change. Minor versions are usually	176	as this indicates an incompatible change. Minor versions are usually
126	compatible to older versions, so a larger minor version alone is usually	177	compatible to older versions, so a larger minor version alone is usually
127	not a problem.	178	not a problem.
128		179
129	Example: Make sure we haven't accidentally been linked against the wrong	180	Example: Make sure we haven't accidentally been linked against the wrong
130	version.	181	version.
131		182
132	assert (("libev version mismatch",	183	assert (("libev version mismatch",
133	ev_version_major () == EV_VERSION_MAJOR	184	ev_version_major () == EV_VERSION_MAJOR
134	&& ev_version_minor () >= EV_VERSION_MINOR));	185	&& ev_version_minor () >= EV_VERSION_MINOR));
135		186
136	=item unsigned int ev_supported_backends ()	187	=item unsigned int ev_supported_backends ()
137		188
138	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	189	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
139	value) compiled into this binary of libev (independent of their	190	value) compiled into this binary of libev (independent of their
…		…
141	a description of the set values.	192	a description of the set values.
142		193
143	Example: make sure we have the epoll method, because yeah this is cool and	194	Example: make sure we have the epoll method, because yeah this is cool and
144	a must have and can we have a torrent of it please!!!11	195	a must have and can we have a torrent of it please!!!11
145		196
146	assert (("sorry, no epoll, no sex",	197	assert (("sorry, no epoll, no sex",
147	ev_supported_backends () & EVBACKEND_EPOLL));	198	ev_supported_backends () & EVBACKEND_EPOLL));
148		199
149	=item unsigned int ev_recommended_backends ()	200	=item unsigned int ev_recommended_backends ()
150		201
151	Return the set of all backends compiled into this binary of libev and also	202	Return the set of all backends compiled into this binary of libev and also
152	recommended for this platform. This set is often smaller than the one	203	recommended for this platform. This set is often smaller than the one
153	returned by C<ev_supported_backends>, as for example kqueue is broken on	204	returned by C<ev_supported_backends>, as for example kqueue is broken on
154	most BSDs and will not be autodetected unless you explicitly request it	205	most BSDs and will not be auto-detected unless you explicitly request it
155	(assuming you know what you are doing). This is the set of backends that	206	(assuming you know what you are doing). This is the set of backends that
156	libev will probe for if you specify no backends explicitly.	207	libev will probe for if you specify no backends explicitly.
157		208
158	=item unsigned int ev_embeddable_backends ()	209	=item unsigned int ev_embeddable_backends ()
159		210
…		…
163	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	214	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
164	recommended ones.	215	recommended ones.
165		216
166	See the description of C<ev_embed> watchers for more info.	217	See the description of C<ev_embed> watchers for more info.
167		218
168	=item ev_set_allocator (void *(*cb)(void *ptr, size_t size))	219	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
169		220
170	Sets the allocation function to use (the prototype and semantics are	221	Sets the allocation function to use (the prototype is similar - the
171	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
172	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
173	allocated, the library might abort or take some potentially destructive	224	when memory needs to be allocated (C<size != 0>), the library might abort
174	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.
175		230
176	You could override this function in high-availability programs to, say,	231	You could override this function in high-availability programs to, say,
177	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,
178	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.
179		234
180	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
181	retries).	236	retries (example requires a standards-compliant C<realloc>).
182		237
183	static void *	238	static void *
184	persistent_realloc (void *ptr, size_t size)	239	persistent_realloc (void *ptr, size_t size)
185	{	240	{
186	for (;;)	241	for (;;)
…		…
195	}	250	}
196		251
197	...	252	...
198	ev_set_allocator (persistent_realloc);	253	ev_set_allocator (persistent_realloc);
199		254
200	=item ev_set_syserr_cb (void (*cb)(const char *msg));	255	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
201		256
202	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
203	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
204	indicating the system call or subsystem causing the problem. If this	259	indicating the system call or subsystem causing the problem. If this
205	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
206	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
207	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
208	(such as abort).	263	(such as abort).
209		264
210	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.
…		…
221		276
222	=back	277	=back
223		278
224	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	279	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
225		280
226	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>
227	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>
228	events, and dynamically created loops which do not.	283	I<function>).
229		284
230	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
231	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
232	create, you also create another event loop. Libev itself does no locking	287	not.
233	whatsoever, so if you mix calls to the same event loop in different
234	threads, make sure you lock (this is usually a bad idea, though, even if
235	done correctly, because it's hideous and inefficient).
236		288
237	=over 4	289	=over 4
238		290
239	=item struct ev_loop *ev_default_loop (unsigned int flags)	291	=item struct ev_loop *ev_default_loop (unsigned int flags)
240		292
…		…
244	flags. If that is troubling you, check C<ev_backend ()> afterwards).	296	flags. If that is troubling you, check C<ev_backend ()> afterwards).
245		297
246	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
247	function.	299	function.
248		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
249	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
250	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>).
251		314
252	The following flags are supported:	315	The following flags are supported:
253		316
…		…
258	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
259	thing, believe me).	322	thing, believe me).
260		323
261	=item C<EVFLAG_NOENV>	324	=item C<EVFLAG_NOENV>
262		325
263	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
264	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
265	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	328	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
266	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
267	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
268	around bugs.	331	around bugs.
269		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
270	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	353	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
271		354
272	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
273	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,
274	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
275	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
276	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).
277		371
278	=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)
279		373
280	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
281	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
282	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
283	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>.
284		383
285	=item C<EVBACKEND_EPOLL> (value 4, Linux)	384	=item C<EVBACKEND_EPOLL> (value 4, Linux)
286		385
287	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,
288	but it scales phenomenally better. While poll and select usually scale like	387	but it scales phenomenally better. While poll and select usually scale
289	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),
290	either O(1) or O(active_fds).	389	epoll scales either O(1) or O(active_fds).
291		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
292	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
293	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
294	(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
295	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
296	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.
297		414
298	Please note that epoll sometimes generates spurious notifications, so you	415	Best performance from this backend is achieved by not unregistering all
299	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,
300	(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	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		424	faster than epoll for maybe up to a hundred file descriptors, depending on
		425	the usage. So sad.
		426
		427	While nominally embeddable in other event loops, this feature is broken in
		428	all kernel versions tested so far.
		429
		430	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		431	C<EVBACKEND_POLL>.
301		432
302	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	433	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
303		434
304	Kqueue deserves special mention, as at the time of this writing, it	435	Kqueue deserves special mention, as at the time of this writing, it
305	was broken on all BSDs except NetBSD (usually it doesn't work with	436	was broken on all BSDs except NetBSD (usually it doesn't work reliably
306	anything but sockets and pipes, except on Darwin, where of course its	437	with anything but sockets and pipes, except on Darwin, where of course
307	completely useless). For this reason its not being "autodetected"	438	it's completely useless). Unlike epoll, however, whose brokenness
		439	is by design, these kqueue bugs can (and eventually will) be fixed
		440	without API changes to existing programs. For this reason it's not being
308	unless you explicitly specify it explicitly in the flags (i.e. using	441	"auto-detected" unless you explicitly specify it in the flags (i.e. using
309	C<EVBACKEND_KQUEUE>).	442	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		443	system like NetBSD.
		444
		445	You still can embed kqueue into a normal poll or select backend and use it
		446	only for sockets (after having made sure that sockets work with kqueue on
		447	the target platform). See C<ev_embed> watchers for more info.
310		448
311	It scales in the same way as the epoll backend, but the interface to the	449	It scales in the same way as the epoll backend, but the interface to the
312	kernel is more efficient (which says nothing about its actual speed, of	450	kernel is more efficient (which says nothing about its actual speed, of
313	course). While starting and stopping an I/O watcher does not cause an	451	course). While stopping, setting and starting an I/O watcher does never
314	extra syscall as with epoll, it still adds up to four event changes per	452	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
315	incident, so its best to avoid that.	453	two event changes per incident. Support for C<fork ()> is very bad (but
		454	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		455	cases
		456
		457	This backend usually performs well under most conditions.
		458
		459	While nominally embeddable in other event loops, this doesn't work
		460	everywhere, so you might need to test for this. And since it is broken
		461	almost everywhere, you should only use it when you have a lot of sockets
		462	(for which it usually works), by embedding it into another event loop
		463	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and, did I mention it,
		464	using it only for sockets.
		465
		466	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		467	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		468	C<NOTE_EOF>.
316		469
317	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	470	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
318		471
319	This is not implemented yet (and might never be).	472	This is not implemented yet (and might never be, unless you send me an
		473	implementation). According to reports, C</dev/poll> only supports sockets
		474	and is not embeddable, which would limit the usefulness of this backend
		475	immensely.
320		476
321	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	477	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
322		478
323	This uses the Solaris 10 port mechanism. As with everything on Solaris,	479	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
324	it's really slow, but it still scales very well (O(active_fds)).	480	it's really slow, but it still scales very well (O(active_fds)).
325		481
326	Please note that solaris ports can result in a lot of spurious	482	Please note that Solaris event ports can deliver a lot of spurious
327	notifications, so you need to use non-blocking I/O or other means to avoid	483	notifications, so you need to use non-blocking I/O or other means to avoid
328	blocking when no data (or space) is available.	484	blocking when no data (or space) is available.
		485
		486	While this backend scales well, it requires one system call per active
		487	file descriptor per loop iteration. For small and medium numbers of file
		488	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		489	might perform better.
		490
		491	On the positive side, with the exception of the spurious readiness
		492	notifications, this backend actually performed fully to specification
		493	in all tests and is fully embeddable, which is a rare feat among the
		494	OS-specific backends (I vastly prefer correctness over speed hacks).
		495
		496	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		497	C<EVBACKEND_POLL>.
329		498
330	=item C<EVBACKEND_ALL>	499	=item C<EVBACKEND_ALL>
331		500
332	Try all backends (even potentially broken ones that wouldn't be tried	501	Try all backends (even potentially broken ones that wouldn't be tried
333	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	502	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
334	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	503	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
335		504
		505	It is definitely not recommended to use this flag.
		506
336	=back	507	=back
337		508
338	If one or more of these are ored into the flags value, then only these	509	If one or more of these are or'ed into the flags value, then only these
339	backends will be tried (in the reverse order as given here). If none are	510	backends will be tried (in the reverse order as listed here). If none are
340	specified, most compiled-in backend will be tried, usually in reverse	511	specified, all backends in C<ev_recommended_backends ()> will be tried.
341	order of their flag values :)
342		512
343	The most typical usage is like this:	513	Example: This is the most typical usage.
344		514
345	if (!ev_default_loop (0))	515	if (!ev_default_loop (0))
346	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	516	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
347		517
348	Restrict libev to the select and poll backends, and do not allow	518	Example: Restrict libev to the select and poll backends, and do not allow
349	environment settings to be taken into account:	519	environment settings to be taken into account:
350		520
351	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	521	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
352		522
353	Use whatever libev has to offer, but make sure that kqueue is used if	523	Example: Use whatever libev has to offer, but make sure that kqueue is
354	available (warning, breaks stuff, best use only with your own private	524	used if available (warning, breaks stuff, best use only with your own
355	event loop and only if you know the OS supports your types of fds):	525	private event loop and only if you know the OS supports your types of
		526	fds):
356		527
357	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	528	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
358		529
359	=item struct ev_loop *ev_loop_new (unsigned int flags)	530	=item struct ev_loop *ev_loop_new (unsigned int flags)
360		531
361	Similar to C<ev_default_loop>, but always creates a new event loop that is	532	Similar to C<ev_default_loop>, but always creates a new event loop that is
362	always distinct from the default loop. Unlike the default loop, it cannot	533	always distinct from the default loop. Unlike the default loop, it cannot
363	handle signal and child watchers, and attempts to do so will be greeted by	534	handle signal and child watchers, and attempts to do so will be greeted by
364	undefined behaviour (or a failed assertion if assertions are enabled).	535	undefined behaviour (or a failed assertion if assertions are enabled).
365		536
		537	Note that this function I<is> thread-safe, and the recommended way to use
		538	libev with threads is indeed to create one loop per thread, and using the
		539	default loop in the "main" or "initial" thread.
		540
366	Example: Try to create a event loop that uses epoll and nothing else.	541	Example: Try to create a event loop that uses epoll and nothing else.
367		542
368	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	543	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
369	if (!epoller)	544	if (!epoller)
370	fatal ("no epoll found here, maybe it hides under your chair");	545	fatal ("no epoll found here, maybe it hides under your chair");
371		546
372	=item ev_default_destroy ()	547	=item ev_default_destroy ()
373		548
374	Destroys the default loop again (frees all memory and kernel state	549	Destroys the default loop again (frees all memory and kernel state
375	etc.). None of the active event watchers will be stopped in the normal	550	etc.). None of the active event watchers will be stopped in the normal
376	sense, so e.g. C<ev_is_active> might still return true. It is your	551	sense, so e.g. C<ev_is_active> might still return true. It is your
377	responsibility to either stop all watchers cleanly yoursef I<before>	552	responsibility to either stop all watchers cleanly yourself I<before>
378	calling this function, or cope with the fact afterwards (which is usually	553	calling this function, or cope with the fact afterwards (which is usually
379	the easiest thing, youc na just ignore the watchers and/or C<free ()> them	554	the easiest thing, you can just ignore the watchers and/or C<free ()> them
380	for example).	555	for example).
		556
		557	Note that certain global state, such as signal state (and installed signal
		558	handlers), will not be freed by this function, and related watchers (such
		559	as signal and child watchers) would need to be stopped manually.
		560
		561	In general it is not advisable to call this function except in the
		562	rare occasion where you really need to free e.g. the signal handling
		563	pipe fds. If you need dynamically allocated loops it is better to use
		564	C<ev_loop_new> and C<ev_loop_destroy>).
381		565
382	=item ev_loop_destroy (loop)	566	=item ev_loop_destroy (loop)
383		567
384	Like C<ev_default_destroy>, but destroys an event loop created by an	568	Like C<ev_default_destroy>, but destroys an event loop created by an
385	earlier call to C<ev_loop_new>.	569	earlier call to C<ev_loop_new>.
386		570
387	=item ev_default_fork ()	571	=item ev_default_fork ()
388		572
		573	This function sets a flag that causes subsequent C<ev_loop> iterations
389	This function reinitialises the kernel state for backends that have	574	to reinitialise the kernel state for backends that have one. Despite the
390	one. Despite the name, you can call it anytime, but it makes most sense	575	name, you can call it anytime, but it makes most sense after forking, in
391	after forking, in either the parent or child process (or both, but that	576	the child process (or both child and parent, but that again makes little
392	again makes little sense).	577	sense). You I<must> call it in the child before using any of the libev
		578	functions, and it will only take effect at the next C<ev_loop> iteration.
393		579
394	You I<must> call this function in the child process after forking if and	580	On the other hand, you only need to call this function in the child
395	only if you want to use the event library in both processes. If you just	581	process if and only if you want to use the event library in the child. If
396	fork+exec, you don't have to call it.	582	you just fork+exec, you don't have to call it at all.
397		583
398	The function itself is quite fast and it's usually not a problem to call	584	The function itself is quite fast and it's usually not a problem to call
399	it just in case after a fork. To make this easy, the function will fit in	585	it just in case after a fork. To make this easy, the function will fit in
400	quite nicely into a call to C<pthread_atfork>:	586	quite nicely into a call to C<pthread_atfork>:
401		587
402	pthread_atfork (0, 0, ev_default_fork);	588	pthread_atfork (0, 0, ev_default_fork);
403		589
404	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
405	without calling this function, so if you force one of those backends you
406	do not need to care.
407
408	=item ev_loop_fork (loop)	590	=item ev_loop_fork (loop)
409		591
410	Like C<ev_default_fork>, but acts on an event loop created by	592	Like C<ev_default_fork>, but acts on an event loop created by
411	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	593	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
412	after fork, and how you do this is entirely your own problem.	594	after fork that you want to re-use in the child, and how you do this is
		595	entirely your own problem.
		596
		597	=item int ev_is_default_loop (loop)
		598
		599	Returns true when the given loop is, in fact, the default loop, and false
		600	otherwise.
		601
		602	=item unsigned int ev_loop_count (loop)
		603
		604	Returns the count of loop iterations for the loop, which is identical to
		605	the number of times libev did poll for new events. It starts at C<0> and
		606	happily wraps around with enough iterations.
		607
		608	This value can sometimes be useful as a generation counter of sorts (it
		609	"ticks" the number of loop iterations), as it roughly corresponds with
		610	C<ev_prepare> and C<ev_check> calls.
413		611
414	=item unsigned int ev_backend (loop)	612	=item unsigned int ev_backend (loop)
415		613
416	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	614	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
417	use.	615	use.
…		…
420		618
421	Returns the current "event loop time", which is the time the event loop	619	Returns the current "event loop time", which is the time the event loop
422	received events and started processing them. This timestamp does not	620	received events and started processing them. This timestamp does not
423	change as long as callbacks are being processed, and this is also the base	621	change as long as callbacks are being processed, and this is also the base
424	time used for relative timers. You can treat it as the timestamp of the	622	time used for relative timers. You can treat it as the timestamp of the
425	event occuring (or more correctly, libev finding out about it).	623	event occurring (or more correctly, libev finding out about it).
		624
		625	=item ev_now_update (loop)
		626
		627	Establishes the current time by querying the kernel, updating the time
		628	returned by C<ev_now ()> in the progress. This is a costly operation and
		629	is usually done automatically within C<ev_loop ()>.
		630
		631	This function is rarely useful, but when some event callback runs for a
		632	very long time without entering the event loop, updating libev's idea of
		633	the current time is a good idea.
		634
		635	See also "The special problem of time updates" in the C<ev_timer> section.
426		636
427	=item ev_loop (loop, int flags)	637	=item ev_loop (loop, int flags)
428		638
429	Finally, this is it, the event handler. This function usually is called	639	Finally, this is it, the event handler. This function usually is called
430	after you initialised all your watchers and you want to start handling	640	after you initialised all your watchers and you want to start handling
…		…
433	If the flags argument is specified as C<0>, it will not return until	643	If the flags argument is specified as C<0>, it will not return until
434	either no event watchers are active anymore or C<ev_unloop> was called.	644	either no event watchers are active anymore or C<ev_unloop> was called.
435		645
436	Please note that an explicit C<ev_unloop> is usually better than	646	Please note that an explicit C<ev_unloop> is usually better than
437	relying on all watchers to be stopped when deciding when a program has	647	relying on all watchers to be stopped when deciding when a program has
438	finished (especially in interactive programs), but having a program that	648	finished (especially in interactive programs), but having a program
439	automatically loops as long as it has to and no longer by virtue of	649	that automatically loops as long as it has to and no longer by virtue
440	relying on its watchers stopping correctly is a thing of beauty.	650	of relying on its watchers stopping correctly, that is truly a thing of
		651	beauty.
441		652
442	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	653	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
443	those events and any outstanding ones, but will not block your process in	654	those events and any already outstanding ones, but will not block your
444	case there are no events and will return after one iteration of the loop.	655	process in case there are no events and will return after one iteration of
		656	the loop.
445		657
446	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	658	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
447	neccessary) and will handle those and any outstanding ones. It will block	659	necessary) and will handle those and any already outstanding ones. It
448	your process until at least one new event arrives, and will return after	660	will block your process until at least one new event arrives (which could
449	one iteration of the loop. This is useful if you are waiting for some	661	be an event internal to libev itself, so there is no guarantee that a
450	external event in conjunction with something not expressible using other	662	user-registered callback will be called), and will return after one
		663	iteration of the loop.
		664
		665	This is useful if you are waiting for some external event in conjunction
		666	with something not expressible using other libev watchers (i.e. "roll your
451	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	667	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
452	usually a better approach for this kind of thing.	668	usually a better approach for this kind of thing.
453		669
454	Here are the gory details of what C<ev_loop> does:	670	Here are the gory details of what C<ev_loop> does:
455		671
456	* If there are no active watchers (reference count is zero), return.	672	- Before the first iteration, call any pending watchers.
457	- Queue prepare watchers and then call all outstanding watchers.	673	* If EVFLAG_FORKCHECK was used, check for a fork.
		674	- If a fork was detected (by any means), queue and call all fork watchers.
		675	- Queue and call all prepare watchers.
458	- If we have been forked, recreate the kernel state.	676	- If we have been forked, detach and recreate the kernel state
		677	as to not disturb the other process.
459	- Update the kernel state with all outstanding changes.	678	- Update the kernel state with all outstanding changes.
460	- Update the "event loop time".	679	- Update the "event loop time" (ev_now ()).
461	- Calculate for how long to block.	680	- Calculate for how long to sleep or block, if at all
		681	(active idle watchers, EVLOOP_NONBLOCK or not having
		682	any active watchers at all will result in not sleeping).
		683	- Sleep if the I/O and timer collect interval say so.
462	- Block the process, waiting for any events.	684	- Block the process, waiting for any events.
463	- Queue all outstanding I/O (fd) events.	685	- Queue all outstanding I/O (fd) events.
464	- Update the "event loop time" and do time jump handling.	686	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
465	- Queue all outstanding timers.	687	- Queue all expired timers.
466	- Queue all outstanding periodics.	688	- Queue all expired periodics.
467	- If no events are pending now, queue all idle watchers.	689	- Unless any events are pending now, queue all idle watchers.
468	- Queue all check watchers.	690	- Queue all check watchers.
469	- Call all queued watchers in reverse order (i.e. check watchers first).	691	- Call all queued watchers in reverse order (i.e. check watchers first).
470	Signals and child watchers are implemented as I/O watchers, and will	692	Signals and child watchers are implemented as I/O watchers, and will
471	be handled here by queueing them when their watcher gets executed.	693	be handled here by queueing them when their watcher gets executed.
472	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	694	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
473	were used, return, otherwise continue with step *.	695	were used, or there are no active watchers, return, otherwise
		696	continue with step *.
474		697
475	Example: Queue some jobs and then loop until no events are outsanding	698	Example: Queue some jobs and then loop until no events are outstanding
476	anymore.	699	anymore.
477		700
478	... queue jobs here, make sure they register event watchers as long	701	... queue jobs here, make sure they register event watchers as long
479	... as they still have work to do (even an idle watcher will do..)	702	... as they still have work to do (even an idle watcher will do..)
480	ev_loop (my_loop, 0);	703	ev_loop (my_loop, 0);
481	... jobs done. yeah!	704	... jobs done or somebody called unloop. yeah!
482		705
483	=item ev_unloop (loop, how)	706	=item ev_unloop (loop, how)
484		707
485	Can be used to make a call to C<ev_loop> return early (but only after it	708	Can be used to make a call to C<ev_loop> return early (but only after it
486	has processed all outstanding events). The C<how> argument must be either	709	has processed all outstanding events). The C<how> argument must be either
487	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	710	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
488	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	711	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
489		712
		713	This "unloop state" will be cleared when entering C<ev_loop> again.
		714
		715	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
		716
490	=item ev_ref (loop)	717	=item ev_ref (loop)
491		718
492	=item ev_unref (loop)	719	=item ev_unref (loop)
493		720
494	Ref/unref can be used to add or remove a reference count on the event	721	Ref/unref can be used to add or remove a reference count on the event
495	loop: Every watcher keeps one reference, and as long as the reference	722	loop: Every watcher keeps one reference, and as long as the reference
496	count is nonzero, C<ev_loop> will not return on its own. If you have	723	count is nonzero, C<ev_loop> will not return on its own.
		724
497	a watcher you never unregister that should not keep C<ev_loop> from	725	If you have a watcher you never unregister that should not keep C<ev_loop>
498	returning, ev_unref() after starting, and ev_ref() before stopping it. For	726	from returning, call ev_unref() after starting, and ev_ref() before
		727	stopping it.
		728
499	example, libev itself uses this for its internal signal pipe: It is not	729	As an example, libev itself uses this for its internal signal pipe: It is
500	visible to the libev user and should not keep C<ev_loop> from exiting if	730	not visible to the libev user and should not keep C<ev_loop> from exiting
501	no event watchers registered by it are active. It is also an excellent	731	if no event watchers registered by it are active. It is also an excellent
502	way to do this for generic recurring timers or from within third-party	732	way to do this for generic recurring timers or from within third-party
503	libraries. Just remember to I<unref after start> and I<ref before stop>.	733	libraries. Just remember to I<unref after start> and I<ref before stop>
		734	(but only if the watcher wasn't active before, or was active before,
		735	respectively).
504		736
505	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	737	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
506	running when nothing else is active.	738	running when nothing else is active.
507		739
508	struct ev_signal exitsig;	740	ev_signal exitsig;
509	ev_signal_init (&exitsig, sig_cb, SIGINT);	741	ev_signal_init (&exitsig, sig_cb, SIGINT);
510	ev_signal_start (loop, &exitsig);	742	ev_signal_start (loop, &exitsig);
511	evf_unref (loop);	743	evf_unref (loop);
512		744
513	Example: For some weird reason, unregister the above signal handler again.	745	Example: For some weird reason, unregister the above signal handler again.
514		746
515	ev_ref (loop);	747	ev_ref (loop);
516	ev_signal_stop (loop, &exitsig);	748	ev_signal_stop (loop, &exitsig);
		749
		750	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		751
		752	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		753
		754	These advanced functions influence the time that libev will spend waiting
		755	for events. Both time intervals are by default C<0>, meaning that libev
		756	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		757	latency.
		758
		759	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		760	allows libev to delay invocation of I/O and timer/periodic callbacks
		761	to increase efficiency of loop iterations (or to increase power-saving
		762	opportunities).
		763
		764	The idea is that sometimes your program runs just fast enough to handle
		765	one (or very few) event(s) per loop iteration. While this makes the
		766	program responsive, it also wastes a lot of CPU time to poll for new
		767	events, especially with backends like C<select ()> which have a high
		768	overhead for the actual polling but can deliver many events at once.
		769
		770	By setting a higher I<io collect interval> you allow libev to spend more
		771	time collecting I/O events, so you can handle more events per iteration,
		772	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		773	C<ev_timer>) will be not affected. Setting this to a non-null value will
		774	introduce an additional C<ev_sleep ()> call into most loop iterations.
		775
		776	Likewise, by setting a higher I<timeout collect interval> you allow libev
		777	to spend more time collecting timeouts, at the expense of increased
		778	latency/jitter/inexactness (the watcher callback will be called
		779	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		780	value will not introduce any overhead in libev.
		781
		782	Many (busy) programs can usually benefit by setting the I/O collect
		783	interval to a value near C<0.1> or so, which is often enough for
		784	interactive servers (of course not for games), likewise for timeouts. It
		785	usually doesn't make much sense to set it to a lower value than C<0.01>,
		786	as this approaches the timing granularity of most systems.
		787
		788	Setting the I<timeout collect interval> can improve the opportunity for
		789	saving power, as the program will "bundle" timer callback invocations that
		790	are "near" in time together, by delaying some, thus reducing the number of
		791	times the process sleeps and wakes up again. Another useful technique to
		792	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		793	they fire on, say, one-second boundaries only.
		794
		795	=item ev_loop_verify (loop)
		796
		797	This function only does something when C<EV_VERIFY> support has been
		798	compiled in, which is the default for non-minimal builds. It tries to go
		799	through all internal structures and checks them for validity. If anything
		800	is found to be inconsistent, it will print an error message to standard
		801	error and call C<abort ()>.
		802
		803	This can be used to catch bugs inside libev itself: under normal
		804	circumstances, this function will never abort as of course libev keeps its
		805	data structures consistent.
517		806
518	=back	807	=back
519		808
520		809
521	=head1 ANATOMY OF A WATCHER	810	=head1 ANATOMY OF A WATCHER
		811
		812	In the following description, uppercase C<TYPE> in names stands for the
		813	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		814	watchers and C<ev_io_start> for I/O watchers.
522		815
523	A watcher is a structure that you create and register to record your	816	A watcher is a structure that you create and register to record your
524	interest in some event. For instance, if you want to wait for STDIN to	817	interest in some event. For instance, if you want to wait for STDIN to
525	become readable, you would create an C<ev_io> watcher for that:	818	become readable, you would create an C<ev_io> watcher for that:
526		819
527	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	820	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
528	{	821	{
529	ev_io_stop (w);	822	ev_io_stop (w);
530	ev_unloop (loop, EVUNLOOP_ALL);	823	ev_unloop (loop, EVUNLOOP_ALL);
531	}	824	}
532		825
533	struct ev_loop *loop = ev_default_loop (0);	826	struct ev_loop *loop = ev_default_loop (0);
		827
534	struct ev_io stdin_watcher;	828	ev_io stdin_watcher;
		829
535	ev_init (&stdin_watcher, my_cb);	830	ev_init (&stdin_watcher, my_cb);
536	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	831	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
537	ev_io_start (loop, &stdin_watcher);	832	ev_io_start (loop, &stdin_watcher);
		833
538	ev_loop (loop, 0);	834	ev_loop (loop, 0);
539		835
540	As you can see, you are responsible for allocating the memory for your	836	As you can see, you are responsible for allocating the memory for your
541	watcher structures (and it is usually a bad idea to do this on the stack,	837	watcher structures (and it is I<usually> a bad idea to do this on the
542	although this can sometimes be quite valid).	838	stack).
		839
		840	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		841	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
543		842
544	Each watcher structure must be initialised by a call to C<ev_init	843	Each watcher structure must be initialised by a call to C<ev_init
545	(watcher *, callback)>, which expects a callback to be provided. This	844	(watcher *, callback)>, which expects a callback to be provided. This
546	callback gets invoked each time the event occurs (or, in the case of io	845	callback gets invoked each time the event occurs (or, in the case of I/O
547	watchers, each time the event loop detects that the file descriptor given	846	watchers, each time the event loop detects that the file descriptor given
548	is readable and/or writable).	847	is readable and/or writable).
549		848
550	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	849	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
551	with arguments specific to this watcher type. There is also a macro	850	macro to configure it, with arguments specific to the watcher type. There
552	to combine initialisation and setting in one call: C<< ev_<type>_init	851	is also a macro to combine initialisation and setting in one call: C<<
553	(watcher *, callback, ...) >>.	852	ev_TYPE_init (watcher *, callback, ...) >>.
554		853
555	To make the watcher actually watch out for events, you have to start it	854	To make the watcher actually watch out for events, you have to start it
556	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	855	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
557	*) >>), and you can stop watching for events at any time by calling the	856	*) >>), and you can stop watching for events at any time by calling the
558	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	857	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
559		858
560	As long as your watcher is active (has been started but not stopped) you	859	As long as your watcher is active (has been started but not stopped) you
561	must not touch the values stored in it. Most specifically you must never	860	must not touch the values stored in it. Most specifically you must never
562	reinitialise it or call its C<set> macro.	861	reinitialise it or call its C<ev_TYPE_set> macro.
563		862
564	Each and every callback receives the event loop pointer as first, the	863	Each and every callback receives the event loop pointer as first, the
565	registered watcher structure as second, and a bitset of received events as	864	registered watcher structure as second, and a bitset of received events as
566	third argument.	865	third argument.
567		866
…		…
621	=item C<EV_FORK>	920	=item C<EV_FORK>
622		921
623	The event loop has been resumed in the child process after fork (see	922	The event loop has been resumed in the child process after fork (see
624	C<ev_fork>).	923	C<ev_fork>).
625		924
		925	=item C<EV_ASYNC>
		926
		927	The given async watcher has been asynchronously notified (see C<ev_async>).
		928
626	=item C<EV_ERROR>	929	=item C<EV_ERROR>
627		930
628	An unspecified error has occured, the watcher has been stopped. This might	931	An unspecified error has occurred, the watcher has been stopped. This might
629	happen because the watcher could not be properly started because libev	932	happen because the watcher could not be properly started because libev
630	ran out of memory, a file descriptor was found to be closed or any other	933	ran out of memory, a file descriptor was found to be closed or any other
		934	problem. Libev considers these application bugs.
		935
631	problem. You best act on it by reporting the problem and somehow coping	936	You best act on it by reporting the problem and somehow coping with the
632	with the watcher being stopped.	937	watcher being stopped. Note that well-written programs should not receive
		938	an error ever, so when your watcher receives it, this usually indicates a
		939	bug in your program.
633		940
634	Libev will usually signal a few "dummy" events together with an error,	941	Libev will usually signal a few "dummy" events together with an error, for
635	for example it might indicate that a fd is readable or writable, and if	942	example it might indicate that a fd is readable or writable, and if your
636	your callbacks is well-written it can just attempt the operation and cope	943	callbacks is well-written it can just attempt the operation and cope with
637	with the error from read() or write(). This will not work in multithreaded	944	the error from read() or write(). This will not work in multi-threaded
638	programs, though, so beware.	945	programs, though, as the fd could already be closed and reused for another
		946	thing, so beware.
639		947
640	=back	948	=back
641		949
642	=head2 GENERIC WATCHER FUNCTIONS	950	=head2 GENERIC WATCHER FUNCTIONS
643
644	In the following description, C<TYPE> stands for the watcher type,
645	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
646		951
647	=over 4	952	=over 4
648		953
649	=item C<ev_init> (ev_TYPE *watcher, callback)	954	=item C<ev_init> (ev_TYPE *watcher, callback)
650		955
…		…
656	which rolls both calls into one.	961	which rolls both calls into one.
657		962
658	You can reinitialise a watcher at any time as long as it has been stopped	963	You can reinitialise a watcher at any time as long as it has been stopped
659	(or never started) and there are no pending events outstanding.	964	(or never started) and there are no pending events outstanding.
660		965
661	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	966	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
662	int revents)>.	967	int revents)>.
		968
		969	Example: Initialise an C<ev_io> watcher in two steps.
		970
		971	ev_io w;
		972	ev_init (&w, my_cb);
		973	ev_io_set (&w, STDIN_FILENO, EV_READ);
663		974
664	=item C<ev_TYPE_set> (ev_TYPE *, [args])	975	=item C<ev_TYPE_set> (ev_TYPE *, [args])
665		976
666	This macro initialises the type-specific parts of a watcher. You need to	977	This macro initialises the type-specific parts of a watcher. You need to
667	call C<ev_init> at least once before you call this macro, but you can	978	call C<ev_init> at least once before you call this macro, but you can
…		…
670	difference to the C<ev_init> macro).	981	difference to the C<ev_init> macro).
671		982
672	Although some watcher types do not have type-specific arguments	983	Although some watcher types do not have type-specific arguments
673	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	984	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
674		985
		986	See C<ev_init>, above, for an example.
		987
675	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	988	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
676		989
677	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	990	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
678	calls into a single call. This is the most convinient method to initialise	991	calls into a single call. This is the most convenient method to initialise
679	a watcher. The same limitations apply, of course.	992	a watcher. The same limitations apply, of course.
		993
		994	Example: Initialise and set an C<ev_io> watcher in one step.
		995
		996	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
680		997
681	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	998	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
682		999
683	Starts (activates) the given watcher. Only active watchers will receive	1000	Starts (activates) the given watcher. Only active watchers will receive
684	events. If the watcher is already active nothing will happen.	1001	events. If the watcher is already active nothing will happen.
685		1002
		1003	Example: Start the C<ev_io> watcher that is being abused as example in this
		1004	whole section.
		1005
		1006	ev_io_start (EV_DEFAULT_UC, &w);
		1007
686	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1008	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
687		1009
688	Stops the given watcher again (if active) and clears the pending	1010	Stops the given watcher if active, and clears the pending status (whether
		1011	the watcher was active or not).
		1012
689	status. It is possible that stopped watchers are pending (for example,	1013	It is possible that stopped watchers are pending - for example,
690	non-repeating timers are being stopped when they become pending), but	1014	non-repeating timers are being stopped when they become pending - but
691	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1015	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
692	you want to free or reuse the memory used by the watcher it is therefore a	1016	pending. If you want to free or reuse the memory used by the watcher it is
693	good idea to always call its C<ev_TYPE_stop> function.	1017	therefore a good idea to always call its C<ev_TYPE_stop> function.
694		1018
695	=item bool ev_is_active (ev_TYPE *watcher)	1019	=item bool ev_is_active (ev_TYPE *watcher)
696		1020
697	Returns a true value iff the watcher is active (i.e. it has been started	1021	Returns a true value iff the watcher is active (i.e. it has been started
698	and not yet been stopped). As long as a watcher is active you must not modify	1022	and not yet been stopped). As long as a watcher is active you must not modify
…		…
701	=item bool ev_is_pending (ev_TYPE *watcher)	1025	=item bool ev_is_pending (ev_TYPE *watcher)
702		1026
703	Returns a true value iff the watcher is pending, (i.e. it has outstanding	1027	Returns a true value iff the watcher is pending, (i.e. it has outstanding
704	events but its callback has not yet been invoked). As long as a watcher	1028	events but its callback has not yet been invoked). As long as a watcher
705	is pending (but not active) you must not call an init function on it (but	1029	is pending (but not active) you must not call an init function on it (but
706	C<ev_TYPE_set> is safe) and you must make sure the watcher is available to	1030	C<ev_TYPE_set> is safe), you must not change its priority, and you must
707	libev (e.g. you cnanot C<free ()> it).	1031	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1032	it).
708		1033
709	=item callback ev_cb (ev_TYPE *watcher)	1034	=item callback ev_cb (ev_TYPE *watcher)
710		1035
711	Returns the callback currently set on the watcher.	1036	Returns the callback currently set on the watcher.
712		1037
713	=item ev_cb_set (ev_TYPE *watcher, callback)	1038	=item ev_cb_set (ev_TYPE *watcher, callback)
714		1039
715	Change the callback. You can change the callback at virtually any time	1040	Change the callback. You can change the callback at virtually any time
716	(modulo threads).	1041	(modulo threads).
717		1042
		1043	=item ev_set_priority (ev_TYPE *watcher, priority)
		1044
		1045	=item int ev_priority (ev_TYPE *watcher)
		1046
		1047	Set and query the priority of the watcher. The priority is a small
		1048	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1049	(default: C<-2>). Pending watchers with higher priority will be invoked
		1050	before watchers with lower priority, but priority will not keep watchers
		1051	from being executed (except for C<ev_idle> watchers).
		1052
		1053	This means that priorities are I<only> used for ordering callback
		1054	invocation after new events have been received. This is useful, for
		1055	example, to reduce latency after idling, or more often, to bind two
		1056	watchers on the same event and make sure one is called first.
		1057
		1058	If you need to suppress invocation when higher priority events are pending
		1059	you need to look at C<ev_idle> watchers, which provide this functionality.
		1060
		1061	You I<must not> change the priority of a watcher as long as it is active or
		1062	pending.
		1063
		1064	The default priority used by watchers when no priority has been set is
		1065	always C<0>, which is supposed to not be too high and not be too low :).
		1066
		1067	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1068	fine, as long as you do not mind that the priority value you query might
		1069	or might not have been clamped to the valid range.
		1070
		1071	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1072
		1073	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1074	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1075	can deal with that fact, as both are simply passed through to the
		1076	callback.
		1077
		1078	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1079
		1080	If the watcher is pending, this function clears its pending status and
		1081	returns its C<revents> bitset (as if its callback was invoked). If the
		1082	watcher isn't pending it does nothing and returns C<0>.
		1083
		1084	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1085	callback to be invoked, which can be accomplished with this function.
		1086
718	=back	1087	=back
719		1088
720		1089
721	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1090	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
722		1091
723	Each watcher has, by default, a member C<void *data> that you can change	1092	Each watcher has, by default, a member C<void *data> that you can change
724	and read at any time, libev will completely ignore it. This can be used	1093	and read at any time: libev will completely ignore it. This can be used
725	to associate arbitrary data with your watcher. If you need more data and	1094	to associate arbitrary data with your watcher. If you need more data and
726	don't want to allocate memory and store a pointer to it in that data	1095	don't want to allocate memory and store a pointer to it in that data
727	member, you can also "subclass" the watcher type and provide your own	1096	member, you can also "subclass" the watcher type and provide your own
728	data:	1097	data:
729		1098
730	struct my_io	1099	struct my_io
731	{	1100	{
732	struct ev_io io;	1101	ev_io io;
733	int otherfd;	1102	int otherfd;
734	void *somedata;	1103	void *somedata;
735	struct whatever *mostinteresting;	1104	struct whatever *mostinteresting;
736	}	1105	};
		1106
		1107	...
		1108	struct my_io w;
		1109	ev_io_init (&w.io, my_cb, fd, EV_READ);
737		1110
738	And since your callback will be called with a pointer to the watcher, you	1111	And since your callback will be called with a pointer to the watcher, you
739	can cast it back to your own type:	1112	can cast it back to your own type:
740		1113
741	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1114	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
742	{	1115	{
743	struct my_io *w = (struct my_io *)w_;	1116	struct my_io *w = (struct my_io *)w_;
744	...	1117	...
745	}	1118	}
746		1119
747	More interesting and less C-conformant ways of casting your callback type	1120	More interesting and less C-conformant ways of casting your callback type
748	instead have been omitted.	1121	instead have been omitted.
749		1122
750	Another common scenario is having some data structure with multiple	1123	Another common scenario is to use some data structure with multiple
751	watchers:	1124	embedded watchers:
752		1125
753	struct my_biggy	1126	struct my_biggy
754	{	1127	{
755	int some_data;	1128	int some_data;
756	ev_timer t1;	1129	ev_timer t1;
757	ev_timer t2;	1130	ev_timer t2;
758	}	1131	}
759		1132
760	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1133	In this case getting the pointer to C<my_biggy> is a bit more
761	you need to use C<offsetof>:	1134	complicated: Either you store the address of your C<my_biggy> struct
		1135	in the C<data> member of the watcher (for woozies), or you need to use
		1136	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1137	programmers):
762		1138
763	#include <stddef.h>	1139	#include <stddef.h>
764		1140
765	static void	1141	static void
766	t1_cb (EV_P_ struct ev_timer *w, int revents)	1142	t1_cb (EV_P_ ev_timer *w, int revents)
767	{	1143	{
768	struct my_biggy big = (struct my_biggy *	1144	struct my_biggy big = (struct my_biggy *
769	(((char *)w) - offsetof (struct my_biggy, t1));	1145	(((char *)w) - offsetof (struct my_biggy, t1));
770	}	1146	}
771		1147
772	static void	1148	static void
773	t2_cb (EV_P_ struct ev_timer *w, int revents)	1149	t2_cb (EV_P_ ev_timer *w, int revents)
774	{	1150	{
775	struct my_biggy big = (struct my_biggy *	1151	struct my_biggy big = (struct my_biggy *
776	(((char *)w) - offsetof (struct my_biggy, t2));	1152	(((char *)w) - offsetof (struct my_biggy, t2));
777	}	1153	}
778		1154
779		1155
780	=head1 WATCHER TYPES	1156	=head1 WATCHER TYPES
781		1157
782	This section describes each watcher in detail, but will not repeat	1158	This section describes each watcher in detail, but will not repeat
…		…
806	In general you can register as many read and/or write event watchers per	1182	In general you can register as many read and/or write event watchers per
807	fd as you want (as long as you don't confuse yourself). Setting all file	1183	fd as you want (as long as you don't confuse yourself). Setting all file
808	descriptors to non-blocking mode is also usually a good idea (but not	1184	descriptors to non-blocking mode is also usually a good idea (but not
809	required if you know what you are doing).	1185	required if you know what you are doing).
810		1186
811	You have to be careful with dup'ed file descriptors, though. Some backends	1187	If you cannot use non-blocking mode, then force the use of a
812	(the linux epoll backend is a notable example) cannot handle dup'ed file	1188	known-to-be-good backend (at the time of this writing, this includes only
813	descriptors correctly if you register interest in two or more fds pointing	1189	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>).
814	to the same underlying file/socket/etc. description (that is, they share
815	the same underlying "file open").
816
817	If you must do this, then force the use of a known-to-be-good backend
818	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
819	C<EVBACKEND_POLL>).
820		1190
821	Another thing you have to watch out for is that it is quite easy to	1191	Another thing you have to watch out for is that it is quite easy to
822	receive "spurious" readyness notifications, that is your callback might	1192	receive "spurious" readiness notifications, that is your callback might
823	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1193	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
824	because there is no data. Not only are some backends known to create a	1194	because there is no data. Not only are some backends known to create a
825	lot of those (for example solaris ports), it is very easy to get into	1195	lot of those (for example Solaris ports), it is very easy to get into
826	this situation even with a relatively standard program structure. Thus	1196	this situation even with a relatively standard program structure. Thus
827	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1197	it is best to always use non-blocking I/O: An extra C<read>(2) returning
828	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1198	C<EAGAIN> is far preferable to a program hanging until some data arrives.
829		1199
830	If you cannot run the fd in non-blocking mode (for example you should not	1200	If you cannot run the fd in non-blocking mode (for example you should
831	play around with an Xlib connection), then you have to seperately re-test	1201	not play around with an Xlib connection), then you have to separately
832	wether a file descriptor is really ready with a known-to-be good interface	1202	re-test whether a file descriptor is really ready with a known-to-be good
833	such as poll (fortunately in our Xlib example, Xlib already does this on	1203	interface such as poll (fortunately in our Xlib example, Xlib already
834	its own, so its quite safe to use).	1204	does this on its own, so its quite safe to use). Some people additionally
		1205	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1206	indefinitely.
		1207
		1208	But really, best use non-blocking mode.
		1209
		1210	=head3 The special problem of disappearing file descriptors
		1211
		1212	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1213	descriptor (either due to calling C<close> explicitly or any other means,
		1214	such as C<dup2>). The reason is that you register interest in some file
		1215	descriptor, but when it goes away, the operating system will silently drop
		1216	this interest. If another file descriptor with the same number then is
		1217	registered with libev, there is no efficient way to see that this is, in
		1218	fact, a different file descriptor.
		1219
		1220	To avoid having to explicitly tell libev about such cases, libev follows
		1221	the following policy: Each time C<ev_io_set> is being called, libev
		1222	will assume that this is potentially a new file descriptor, otherwise
		1223	it is assumed that the file descriptor stays the same. That means that
		1224	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1225	descriptor even if the file descriptor number itself did not change.
		1226
		1227	This is how one would do it normally anyway, the important point is that
		1228	the libev application should not optimise around libev but should leave
		1229	optimisations to libev.
		1230
		1231	=head3 The special problem of dup'ed file descriptors
		1232
		1233	Some backends (e.g. epoll), cannot register events for file descriptors,
		1234	but only events for the underlying file descriptions. That means when you
		1235	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1236	events for them, only one file descriptor might actually receive events.
		1237
		1238	There is no workaround possible except not registering events
		1239	for potentially C<dup ()>'ed file descriptors, or to resort to
		1240	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1241
		1242	=head3 The special problem of fork
		1243
		1244	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1245	useless behaviour. Libev fully supports fork, but needs to be told about
		1246	it in the child.
		1247
		1248	To support fork in your programs, you either have to call
		1249	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1250	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1251	C<EVBACKEND_POLL>.
		1252
		1253	=head3 The special problem of SIGPIPE
		1254
		1255	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1256	when writing to a pipe whose other end has been closed, your program gets
		1257	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1258	this is sensible behaviour, for daemons, this is usually undesirable.
		1259
		1260	So when you encounter spurious, unexplained daemon exits, make sure you
		1261	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1262	somewhere, as that would have given you a big clue).
		1263
		1264
		1265	=head3 Watcher-Specific Functions
835		1266
836	=over 4	1267	=over 4
837		1268
838	=item ev_io_init (ev_io *, callback, int fd, int events)	1269	=item ev_io_init (ev_io *, callback, int fd, int events)
839		1270
840	=item ev_io_set (ev_io *, int fd, int events)	1271	=item ev_io_set (ev_io *, int fd, int events)
841		1272
842	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1273	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
843	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1274	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
844	C<EV_READ | EV_WRITE> to receive the given events.	1275	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
845		1276
846	=item int fd [read-only]	1277	=item int fd [read-only]
847		1278
848	The file descriptor being watched.	1279	The file descriptor being watched.
849		1280
850	=item int events [read-only]	1281	=item int events [read-only]
851		1282
852	The events being watched.	1283	The events being watched.
853		1284
854	=back	1285	=back
		1286
		1287	=head3 Examples
855		1288
856	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1289	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
857	readable, but only once. Since it is likely line-buffered, you could	1290	readable, but only once. Since it is likely line-buffered, you could
858	attempt to read a whole line in the callback.	1291	attempt to read a whole line in the callback.
859		1292
860	static void	1293	static void
861	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1294	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
862	{	1295	{
863	ev_io_stop (loop, w);	1296	ev_io_stop (loop, w);
864	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1297	.. read from stdin here (or from w->fd) and handle any I/O errors
865	}	1298	}
866		1299
867	...	1300	...
868	struct ev_loop *loop = ev_default_init (0);	1301	struct ev_loop *loop = ev_default_init (0);
869	struct ev_io stdin_readable;	1302	ev_io stdin_readable;
870	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1303	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
871	ev_io_start (loop, &stdin_readable);	1304	ev_io_start (loop, &stdin_readable);
872	ev_loop (loop, 0);	1305	ev_loop (loop, 0);
873		1306
874		1307
875	=head2 C<ev_timer> - relative and optionally repeating timeouts	1308	=head2 C<ev_timer> - relative and optionally repeating timeouts
876		1309
877	Timer watchers are simple relative timers that generate an event after a	1310	Timer watchers are simple relative timers that generate an event after a
878	given time, and optionally repeating in regular intervals after that.	1311	given time, and optionally repeating in regular intervals after that.
879		1312
880	The timers are based on real time, that is, if you register an event that	1313	The timers are based on real time, that is, if you register an event that
881	times out after an hour and you reset your system clock to last years	1314	times out after an hour and you reset your system clock to January last
882	time, it will still time out after (roughly) and hour. "Roughly" because	1315	year, it will still time out after (roughly) one hour. "Roughly" because
883	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1316	detecting time jumps is hard, and some inaccuracies are unavoidable (the
884	monotonic clock option helps a lot here).	1317	monotonic clock option helps a lot here).
		1318
		1319	The callback is guaranteed to be invoked only I<after> its timeout has
		1320	passed, but if multiple timers become ready during the same loop iteration
		1321	then order of execution is undefined.
		1322
		1323	=head3 Be smart about timeouts
		1324
		1325	Many real-world problems involve some kind of timeout, usually for error
		1326	recovery. A typical example is an HTTP request - if the other side hangs,
		1327	you want to raise some error after a while.
		1328
		1329	What follows are some ways to handle this problem, from obvious and
		1330	inefficient to smart and efficient.
		1331
		1332	In the following, a 60 second activity timeout is assumed - a timeout that
		1333	gets reset to 60 seconds each time there is activity (e.g. each time some
		1334	data or other life sign was received).
		1335
		1336	=over 4
		1337
		1338	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1339
		1340	This is the most obvious, but not the most simple way: In the beginning,
		1341	start the watcher:
		1342
		1343	ev_timer_init (timer, callback, 60., 0.);
		1344	ev_timer_start (loop, timer);
		1345
		1346	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1347	and start it again:
		1348
		1349	ev_timer_stop (loop, timer);
		1350	ev_timer_set (timer, 60., 0.);
		1351	ev_timer_start (loop, timer);
		1352
		1353	This is relatively simple to implement, but means that each time there is
		1354	some activity, libev will first have to remove the timer from its internal
		1355	data structure and then add it again. Libev tries to be fast, but it's
		1356	still not a constant-time operation.
		1357
		1358	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1359
		1360	This is the easiest way, and involves using C<ev_timer_again> instead of
		1361	C<ev_timer_start>.
		1362
		1363	To implement this, configure an C<ev_timer> with a C<repeat> value
		1364	of C<60> and then call C<ev_timer_again> at start and each time you
		1365	successfully read or write some data. If you go into an idle state where
		1366	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1367	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1368
		1369	That means you can ignore both the C<ev_timer_start> function and the
		1370	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1371	member and C<ev_timer_again>.
		1372
		1373	At start:
		1374
		1375	ev_timer_init (timer, callback);
		1376	timer->repeat = 60.;
		1377	ev_timer_again (loop, timer);
		1378
		1379	Each time there is some activity:
		1380
		1381	ev_timer_again (loop, timer);
		1382
		1383	It is even possible to change the time-out on the fly, regardless of
		1384	whether the watcher is active or not:
		1385
		1386	timer->repeat = 30.;
		1387	ev_timer_again (loop, timer);
		1388
		1389	This is slightly more efficient then stopping/starting the timer each time
		1390	you want to modify its timeout value, as libev does not have to completely
		1391	remove and re-insert the timer from/into its internal data structure.
		1392
		1393	It is, however, even simpler than the "obvious" way to do it.
		1394
		1395	=item 3. Let the timer time out, but then re-arm it as required.
		1396
		1397	This method is more tricky, but usually most efficient: Most timeouts are
		1398	relatively long compared to the intervals between other activity - in
		1399	our example, within 60 seconds, there are usually many I/O events with
		1400	associated activity resets.
		1401
		1402	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1403	but remember the time of last activity, and check for a real timeout only
		1404	within the callback:
		1405
		1406	ev_tstamp last_activity; // time of last activity
		1407
		1408	static void
		1409	callback (EV_P_ ev_timer *w, int revents)
		1410	{
		1411	ev_tstamp now = ev_now (EV_A);
		1412	ev_tstamp timeout = last_activity + 60.;
		1413
		1414	// if last_activity + 60. is older than now, we did time out
		1415	if (timeout < now)
		1416	{
		1417	// timeout occured, take action
		1418	}
		1419	else
		1420	{
		1421	// callback was invoked, but there was some activity, re-arm
		1422	// the watcher to fire in last_activity + 60, which is
		1423	// guaranteed to be in the future, so "again" is positive:
		1424	w->again = timeout - now;
		1425	ev_timer_again (EV_A_ w);
		1426	}
		1427	}
		1428
		1429	To summarise the callback: first calculate the real timeout (defined
		1430	as "60 seconds after the last activity"), then check if that time has
		1431	been reached, which means something I<did>, in fact, time out. Otherwise
		1432	the callback was invoked too early (C<timeout> is in the future), so
		1433	re-schedule the timer to fire at that future time, to see if maybe we have
		1434	a timeout then.
		1435
		1436	Note how C<ev_timer_again> is used, taking advantage of the
		1437	C<ev_timer_again> optimisation when the timer is already running.
		1438
		1439	This scheme causes more callback invocations (about one every 60 seconds
		1440	minus half the average time between activity), but virtually no calls to
		1441	libev to change the timeout.
		1442
		1443	To start the timer, simply initialise the watcher and set C<last_activity>
		1444	to the current time (meaning we just have some activity :), then call the
		1445	callback, which will "do the right thing" and start the timer:
		1446
		1447	ev_timer_init (timer, callback);
		1448	last_activity = ev_now (loop);
		1449	callback (loop, timer, EV_TIMEOUT);
		1450
		1451	And when there is some activity, simply store the current time in
		1452	C<last_activity>, no libev calls at all:
		1453
		1454	last_actiivty = ev_now (loop);
		1455
		1456	This technique is slightly more complex, but in most cases where the
		1457	time-out is unlikely to be triggered, much more efficient.
		1458
		1459	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1460	callback :) - just change the timeout and invoke the callback, which will
		1461	fix things for you.
		1462
		1463	=item 4. Wee, just use a double-linked list for your timeouts.
		1464
		1465	If there is not one request, but many thousands (millions...), all
		1466	employing some kind of timeout with the same timeout value, then one can
		1467	do even better:
		1468
		1469	When starting the timeout, calculate the timeout value and put the timeout
		1470	at the I<end> of the list.
		1471
		1472	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1473	the list is expected to fire (for example, using the technique #3).
		1474
		1475	When there is some activity, remove the timer from the list, recalculate
		1476	the timeout, append it to the end of the list again, and make sure to
		1477	update the C<ev_timer> if it was taken from the beginning of the list.
		1478
		1479	This way, one can manage an unlimited number of timeouts in O(1) time for
		1480	starting, stopping and updating the timers, at the expense of a major
		1481	complication, and having to use a constant timeout. The constant timeout
		1482	ensures that the list stays sorted.
		1483
		1484	=back
		1485
		1486	So which method the best?
		1487
		1488	Method #2 is a simple no-brain-required solution that is adequate in most
		1489	situations. Method #3 requires a bit more thinking, but handles many cases
		1490	better, and isn't very complicated either. In most case, choosing either
		1491	one is fine, with #3 being better in typical situations.
		1492
		1493	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1494	rather complicated, but extremely efficient, something that really pays
		1495	off after the first million or so of active timers, i.e. it's usually
		1496	overkill :)
		1497
		1498	=head3 The special problem of time updates
		1499
		1500	Establishing the current time is a costly operation (it usually takes at
		1501	least two system calls): EV therefore updates its idea of the current
		1502	time only before and after C<ev_loop> collects new events, which causes a
		1503	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1504	lots of events in one iteration.
885		1505
886	The relative timeouts are calculated relative to the C<ev_now ()>	1506	The relative timeouts are calculated relative to the C<ev_now ()>
887	time. This is usually the right thing as this timestamp refers to the time	1507	time. This is usually the right thing as this timestamp refers to the time
888	of the event triggering whatever timeout you are modifying/starting. If	1508	of the event triggering whatever timeout you are modifying/starting. If
889	you suspect event processing to be delayed and you I<need> to base the timeout	1509	you suspect event processing to be delayed and you I<need> to base the
890	on the current time, use something like this to adjust for this:	1510	timeout on the current time, use something like this to adjust for this:
891		1511
892	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1512	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
893		1513
894	The callback is guarenteed to be invoked only when its timeout has passed,	1514	If the event loop is suspended for a long time, you can also force an
895	but if multiple timers become ready during the same loop iteration then	1515	update of the time returned by C<ev_now ()> by calling C<ev_now_update
896	order of execution is undefined.	1516	()>.
		1517
		1518	=head3 Watcher-Specific Functions and Data Members
897		1519
898	=over 4	1520	=over 4
899		1521
900	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1522	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
901		1523
902	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1524	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
903		1525
904	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1526	Configure the timer to trigger after C<after> seconds. If C<repeat>
905	C<0.>, then it will automatically be stopped. If it is positive, then the	1527	is C<0.>, then it will automatically be stopped once the timeout is
906	timer will automatically be configured to trigger again C<repeat> seconds	1528	reached. If it is positive, then the timer will automatically be
907	later, again, and again, until stopped manually.	1529	configured to trigger again C<repeat> seconds later, again, and again,
		1530	until stopped manually.
908		1531
909	The timer itself will do a best-effort at avoiding drift, that is, if you	1532	The timer itself will do a best-effort at avoiding drift, that is, if
910	configure a timer to trigger every 10 seconds, then it will trigger at	1533	you configure a timer to trigger every 10 seconds, then it will normally
911	exactly 10 second intervals. If, however, your program cannot keep up with	1534	trigger at exactly 10 second intervals. If, however, your program cannot
912	the timer (because it takes longer than those 10 seconds to do stuff) the	1535	keep up with the timer (because it takes longer than those 10 seconds to
913	timer will not fire more than once per event loop iteration.	1536	do stuff) the timer will not fire more than once per event loop iteration.
914		1537
915	=item ev_timer_again (loop)	1538	=item ev_timer_again (loop, ev_timer *)
916		1539
917	This will act as if the timer timed out and restart it again if it is	1540	This will act as if the timer timed out and restart it again if it is
918	repeating. The exact semantics are:	1541	repeating. The exact semantics are:
919		1542
		1543	If the timer is pending, its pending status is cleared.
		1544
920	If the timer is started but nonrepeating, stop it.	1545	If the timer is started but non-repeating, stop it (as if it timed out).
921		1546
922	If the timer is repeating, either start it if necessary (with the repeat	1547	If the timer is repeating, either start it if necessary (with the
923	value), or reset the running timer to the repeat value.	1548	C<repeat> value), or reset the running timer to the C<repeat> value.
924		1549
925	This sounds a bit complicated, but here is a useful and typical	1550	This sounds a bit complicated, see "Be smart about timeouts", above, for a
926	example: Imagine you have a tcp connection and you want a so-called	1551	usage example.
927	idle timeout, that is, you want to be called when there have been,
928	say, 60 seconds of inactivity on the socket. The easiest way to do
929	this is to configure an C<ev_timer> with C<after>=C<repeat>=C<60> and calling
930	C<ev_timer_again> each time you successfully read or write some data. If
931	you go into an idle state where you do not expect data to travel on the
932	socket, you can stop the timer, and again will automatically restart it if
933	need be.
934
935	You can also ignore the C<after> value and C<ev_timer_start> altogether
936	and only ever use the C<repeat> value:
937
938	ev_timer_init (timer, callback, 0., 5.);
939	ev_timer_again (loop, timer);
940	...
941	timer->again = 17.;
942	ev_timer_again (loop, timer);
943	...
944	timer->again = 10.;
945	ev_timer_again (loop, timer);
946
947	This is more efficient then stopping/starting the timer eahc time you want
948	to modify its timeout value.
949		1552
950	=item ev_tstamp repeat [read-write]	1553	=item ev_tstamp repeat [read-write]
951		1554
952	The current C<repeat> value. Will be used each time the watcher times out	1555	The current C<repeat> value. Will be used each time the watcher times out
953	or C<ev_timer_again> is called and determines the next timeout (if any),	1556	or C<ev_timer_again> is called, and determines the next timeout (if any),
954	which is also when any modifications are taken into account.	1557	which is also when any modifications are taken into account.
955		1558
956	=back	1559	=back
957		1560
		1561	=head3 Examples
		1562
958	Example: Create a timer that fires after 60 seconds.	1563	Example: Create a timer that fires after 60 seconds.
959		1564
960	static void	1565	static void
961	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1566	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
962	{	1567	{
963	.. one minute over, w is actually stopped right here	1568	.. one minute over, w is actually stopped right here
964	}	1569	}
965		1570
966	struct ev_timer mytimer;	1571	ev_timer mytimer;
967	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1572	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
968	ev_timer_start (loop, &mytimer);	1573	ev_timer_start (loop, &mytimer);
969		1574
970	Example: Create a timeout timer that times out after 10 seconds of	1575	Example: Create a timeout timer that times out after 10 seconds of
971	inactivity.	1576	inactivity.
972		1577
973	static void	1578	static void
974	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1579	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
975	{	1580	{
976	.. ten seconds without any activity	1581	.. ten seconds without any activity
977	}	1582	}
978		1583
979	struct ev_timer mytimer;	1584	ev_timer mytimer;
980	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1585	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
981	ev_timer_again (&mytimer); /* start timer */	1586	ev_timer_again (&mytimer); /* start timer */
982	ev_loop (loop, 0);	1587	ev_loop (loop, 0);
983		1588
984	// and in some piece of code that gets executed on any "activity":	1589	// and in some piece of code that gets executed on any "activity":
985	// reset the timeout to start ticking again at 10 seconds	1590	// reset the timeout to start ticking again at 10 seconds
986	ev_timer_again (&mytimer);	1591	ev_timer_again (&mytimer);
987		1592
988		1593
989	=head2 C<ev_periodic> - to cron or not to cron?	1594	=head2 C<ev_periodic> - to cron or not to cron?
990		1595
991	Periodic watchers are also timers of a kind, but they are very versatile	1596	Periodic watchers are also timers of a kind, but they are very versatile
992	(and unfortunately a bit complex).	1597	(and unfortunately a bit complex).
993		1598
994	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1599	Unlike C<ev_timer>'s, they are not based on real time (or relative time)
995	but on wallclock time (absolute time). You can tell a periodic watcher	1600	but on wall clock time (absolute time). You can tell a periodic watcher
996	to trigger "at" some specific point in time. For example, if you tell a	1601	to trigger after some specific point in time. For example, if you tell a
997	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	1602	periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now ()
998	+ 10.>) and then reset your system clock to the last year, then it will	1603	+ 10.>, that is, an absolute time not a delay) and then reset your system
		1604	clock to January of the previous year, then it will take more than year
999	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1605	to trigger the event (unlike an C<ev_timer>, which would still trigger
1000	roughly 10 seconds later and of course not if you reset your system time	1606	roughly 10 seconds later as it uses a relative timeout).
1001	again).
1002		1607
1003	They can also be used to implement vastly more complex timers, such as	1608	C<ev_periodic>s can also be used to implement vastly more complex timers,
1004	triggering an event on eahc midnight, local time.	1609	such as triggering an event on each "midnight, local time", or other
		1610	complicated rules.
1005		1611
1006	As with timers, the callback is guarenteed to be invoked only when the	1612	As with timers, the callback is guaranteed to be invoked only when the
1007	time (C<at>) has been passed, but if multiple periodic timers become ready	1613	time (C<at>) has passed, but if multiple periodic timers become ready
1008	during the same loop iteration then order of execution is undefined.	1614	during the same loop iteration, then order of execution is undefined.
		1615
		1616	=head3 Watcher-Specific Functions and Data Members
1009		1617
1010	=over 4	1618	=over 4
1011		1619
1012	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1620	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
1013		1621
1014	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1622	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)
1015		1623
1016	Lots of arguments, lets sort it out... There are basically three modes of	1624	Lots of arguments, lets sort it out... There are basically three modes of
1017	operation, and we will explain them from simplest to complex:	1625	operation, and we will explain them from simplest to most complex:
1018		1626
1019	=over 4	1627	=over 4
1020		1628
1021	=item * absolute timer (interval = reschedule_cb = 0)	1629	=item * absolute timer (at = time, interval = reschedule_cb = 0)
1022		1630
1023	In this configuration the watcher triggers an event at the wallclock time	1631	In this configuration the watcher triggers an event after the wall clock
1024	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1632	time C<at> has passed. It will not repeat and will not adjust when a time
1025	that is, if it is to be run at January 1st 2011 then it will run when the	1633	jump occurs, that is, if it is to be run at January 1st 2011 then it will
1026	system time reaches or surpasses this time.	1634	only run when the system clock reaches or surpasses this time.
1027		1635
1028	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1636	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
1029		1637
1030	In this mode the watcher will always be scheduled to time out at the next	1638	In this mode the watcher will always be scheduled to time out at the next
1031	C<at + N * interval> time (for some integer N) and then repeat, regardless	1639	C<at + N * interval> time (for some integer N, which can also be negative)
1032	of any time jumps.	1640	and then repeat, regardless of any time jumps.
1033		1641
1034	This can be used to create timers that do not drift with respect to system	1642	This can be used to create timers that do not drift with respect to the
1035	time:	1643	system clock, for example, here is a C<ev_periodic> that triggers each
		1644	hour, on the hour:
1036		1645
1037	ev_periodic_set (&periodic, 0., 3600., 0);	1646	ev_periodic_set (&periodic, 0., 3600., 0);
1038		1647
1039	This doesn't mean there will always be 3600 seconds in between triggers,	1648	This doesn't mean there will always be 3600 seconds in between triggers,
1040	but only that the the callback will be called when the system time shows a	1649	but only that the callback will be called when the system time shows a
1041	full hour (UTC), or more correctly, when the system time is evenly divisible	1650	full hour (UTC), or more correctly, when the system time is evenly divisible
1042	by 3600.	1651	by 3600.
1043		1652
1044	Another way to think about it (for the mathematically inclined) is that	1653	Another way to think about it (for the mathematically inclined) is that
1045	C<ev_periodic> will try to run the callback in this mode at the next possible	1654	C<ev_periodic> will try to run the callback in this mode at the next possible
1046	time where C<time = at (mod interval)>, regardless of any time jumps.	1655	time where C<time = at (mod interval)>, regardless of any time jumps.
1047		1656
		1657	For numerical stability it is preferable that the C<at> value is near
		1658	C<ev_now ()> (the current time), but there is no range requirement for
		1659	this value, and in fact is often specified as zero.
		1660
		1661	Note also that there is an upper limit to how often a timer can fire (CPU
		1662	speed for example), so if C<interval> is very small then timing stability
		1663	will of course deteriorate. Libev itself tries to be exact to be about one
		1664	millisecond (if the OS supports it and the machine is fast enough).
		1665
1048	=item * manual reschedule mode (reschedule_cb = callback)	1666	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
1049		1667
1050	In this mode the values for C<interval> and C<at> are both being	1668	In this mode the values for C<interval> and C<at> are both being
1051	ignored. Instead, each time the periodic watcher gets scheduled, the	1669	ignored. Instead, each time the periodic watcher gets scheduled, the
1052	reschedule callback will be called with the watcher as first, and the	1670	reschedule callback will be called with the watcher as first, and the
1053	current time as second argument.	1671	current time as second argument.
1054		1672
1055	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1673	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,
1056	ever, or make any event loop modifications>. If you need to stop it,	1674	ever, or make ANY event loop modifications whatsoever>.
1057	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by
1058	starting a prepare watcher).
1059		1675
		1676	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1677	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1678	only event loop modification you are allowed to do).
		1679
1060	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1680	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1061	ev_tstamp now)>, e.g.:	1681	*w, ev_tstamp now)>, e.g.:
1062		1682
		1683	static ev_tstamp
1063	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1684	my_rescheduler (ev_periodic *w, ev_tstamp now)
1064	{	1685	{
1065	return now + 60.;	1686	return now + 60.;
1066	}	1687	}
1067		1688
1068	It must return the next time to trigger, based on the passed time value	1689	It must return the next time to trigger, based on the passed time value
1069	(that is, the lowest time value larger than to the second argument). It	1690	(that is, the lowest time value larger than to the second argument). It
1070	will usually be called just before the callback will be triggered, but	1691	will usually be called just before the callback will be triggered, but
1071	might be called at other times, too.	1692	might be called at other times, too.
1072		1693
1073	NOTE: I<< This callback must always return a time that is later than the	1694	NOTE: I<< This callback must always return a time that is higher than or
1074	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	1695	equal to the passed C<now> value >>.
1075		1696
1076	This can be used to create very complex timers, such as a timer that	1697	This can be used to create very complex timers, such as a timer that
1077	triggers on each midnight, local time. To do this, you would calculate the	1698	triggers on "next midnight, local time". To do this, you would calculate the
1078	next midnight after C<now> and return the timestamp value for this. How	1699	next midnight after C<now> and return the timestamp value for this. How
1079	you do this is, again, up to you (but it is not trivial, which is the main	1700	you do this is, again, up to you (but it is not trivial, which is the main
1080	reason I omitted it as an example).	1701	reason I omitted it as an example).
1081		1702
1082	=back	1703	=back
…		…
1086	Simply stops and restarts the periodic watcher again. This is only useful	1707	Simply stops and restarts the periodic watcher again. This is only useful
1087	when you changed some parameters or the reschedule callback would return	1708	when you changed some parameters or the reschedule callback would return
1088	a different time than the last time it was called (e.g. in a crond like	1709	a different time than the last time it was called (e.g. in a crond like
1089	program when the crontabs have changed).	1710	program when the crontabs have changed).
1090		1711
		1712	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1713
		1714	When active, returns the absolute time that the watcher is supposed to
		1715	trigger next.
		1716
		1717	=item ev_tstamp offset [read-write]
		1718
		1719	When repeating, this contains the offset value, otherwise this is the
		1720	absolute point in time (the C<at> value passed to C<ev_periodic_set>).
		1721
		1722	Can be modified any time, but changes only take effect when the periodic
		1723	timer fires or C<ev_periodic_again> is being called.
		1724
1091	=item ev_tstamp interval [read-write]	1725	=item ev_tstamp interval [read-write]
1092		1726
1093	The current interval value. Can be modified any time, but changes only	1727	The current interval value. Can be modified any time, but changes only
1094	take effect when the periodic timer fires or C<ev_periodic_again> is being	1728	take effect when the periodic timer fires or C<ev_periodic_again> is being
1095	called.	1729	called.
1096		1730
1097	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	1731	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1098		1732
1099	The current reschedule callback, or C<0>, if this functionality is	1733	The current reschedule callback, or C<0>, if this functionality is
1100	switched off. Can be changed any time, but changes only take effect when	1734	switched off. Can be changed any time, but changes only take effect when
1101	the periodic timer fires or C<ev_periodic_again> is being called.	1735	the periodic timer fires or C<ev_periodic_again> is being called.
1102		1736
1103	=back	1737	=back
1104		1738
		1739	=head3 Examples
		1740
1105	Example: Call a callback every hour, or, more precisely, whenever the	1741	Example: Call a callback every hour, or, more precisely, whenever the
1106	system clock is divisible by 3600. The callback invocation times have	1742	system time is divisible by 3600. The callback invocation times have
1107	potentially a lot of jittering, but good long-term stability.	1743	potentially a lot of jitter, but good long-term stability.
1108		1744
1109	static void	1745	static void
1110	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1746	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1111	{	1747	{
1112	... its now a full hour (UTC, or TAI or whatever your clock follows)	1748	... its now a full hour (UTC, or TAI or whatever your clock follows)
1113	}	1749	}
1114		1750
1115	struct ev_periodic hourly_tick;	1751	ev_periodic hourly_tick;
1116	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	1752	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1117	ev_periodic_start (loop, &hourly_tick);	1753	ev_periodic_start (loop, &hourly_tick);
1118		1754
1119	Example: The same as above, but use a reschedule callback to do it:	1755	Example: The same as above, but use a reschedule callback to do it:
1120		1756
1121	#include <math.h>	1757	#include <math.h>
1122		1758
1123	static ev_tstamp	1759	static ev_tstamp
1124	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	1760	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1125	{	1761	{
1126	return fmod (now, 3600.) + 3600.;	1762	return now + (3600. - fmod (now, 3600.));
1127	}	1763	}
1128		1764
1129	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	1765	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1130		1766
1131	Example: Call a callback every hour, starting now:	1767	Example: Call a callback every hour, starting now:
1132		1768
1133	struct ev_periodic hourly_tick;	1769	ev_periodic hourly_tick;
1134	ev_periodic_init (&hourly_tick, clock_cb,	1770	ev_periodic_init (&hourly_tick, clock_cb,
1135	fmod (ev_now (loop), 3600.), 3600., 0);	1771	fmod (ev_now (loop), 3600.), 3600., 0);
1136	ev_periodic_start (loop, &hourly_tick);	1772	ev_periodic_start (loop, &hourly_tick);
1137		1773
1138		1774
1139	=head2 C<ev_signal> - signal me when a signal gets signalled!	1775	=head2 C<ev_signal> - signal me when a signal gets signalled!
1140		1776
1141	Signal watchers will trigger an event when the process receives a specific	1777	Signal watchers will trigger an event when the process receives a specific
1142	signal one or more times. Even though signals are very asynchronous, libev	1778	signal one or more times. Even though signals are very asynchronous, libev
1143	will try it's best to deliver signals synchronously, i.e. as part of the	1779	will try it's best to deliver signals synchronously, i.e. as part of the
1144	normal event processing, like any other event.	1780	normal event processing, like any other event.
1145		1781
		1782	If you want signals asynchronously, just use C<sigaction> as you would
		1783	do without libev and forget about sharing the signal. You can even use
		1784	C<ev_async> from a signal handler to synchronously wake up an event loop.
		1785
1146	You can configure as many watchers as you like per signal. Only when the	1786	You can configure as many watchers as you like per signal. Only when the
1147	first watcher gets started will libev actually register a signal watcher	1787	first watcher gets started will libev actually register a signal handler
1148	with the kernel (thus it coexists with your own signal handlers as long	1788	with the kernel (thus it coexists with your own signal handlers as long as
1149	as you don't register any with libev). Similarly, when the last signal	1789	you don't register any with libev for the same signal). Similarly, when
1150	watcher for a signal is stopped libev will reset the signal handler to	1790	the last signal watcher for a signal is stopped, libev will reset the
1151	SIG_DFL (regardless of what it was set to before).	1791	signal handler to SIG_DFL (regardless of what it was set to before).
		1792
		1793	If possible and supported, libev will install its handlers with
		1794	C<SA_RESTART> behaviour enabled, so system calls should not be unduly
		1795	interrupted. If you have a problem with system calls getting interrupted by
		1796	signals you can block all signals in an C<ev_check> watcher and unblock
		1797	them in an C<ev_prepare> watcher.
		1798
		1799	=head3 Watcher-Specific Functions and Data Members
1152		1800
1153	=over 4	1801	=over 4
1154		1802
1155	=item ev_signal_init (ev_signal *, callback, int signum)	1803	=item ev_signal_init (ev_signal *, callback, int signum)
1156		1804
…		…
1163		1811
1164	The signal the watcher watches out for.	1812	The signal the watcher watches out for.
1165		1813
1166	=back	1814	=back
1167		1815
		1816	=head3 Examples
		1817
		1818	Example: Try to exit cleanly on SIGINT.
		1819
		1820	static void
		1821	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		1822	{
		1823	ev_unloop (loop, EVUNLOOP_ALL);
		1824	}
		1825
		1826	ev_signal signal_watcher;
		1827	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1828	ev_signal_start (loop, &signal_watcher);
		1829
1168		1830
1169	=head2 C<ev_child> - watch out for process status changes	1831	=head2 C<ev_child> - watch out for process status changes
1170		1832
1171	Child watchers trigger when your process receives a SIGCHLD in response to	1833	Child watchers trigger when your process receives a SIGCHLD in response to
1172	some child status changes (most typically when a child of yours dies).	1834	some child status changes (most typically when a child of yours dies or
		1835	exits). It is permissible to install a child watcher I<after> the child
		1836	has been forked (which implies it might have already exited), as long
		1837	as the event loop isn't entered (or is continued from a watcher), i.e.,
		1838	forking and then immediately registering a watcher for the child is fine,
		1839	but forking and registering a watcher a few event loop iterations later is
		1840	not.
		1841
		1842	Only the default event loop is capable of handling signals, and therefore
		1843	you can only register child watchers in the default event loop.
		1844
		1845	=head3 Process Interaction
		1846
		1847	Libev grabs C<SIGCHLD> as soon as the default event loop is
		1848	initialised. This is necessary to guarantee proper behaviour even if
		1849	the first child watcher is started after the child exits. The occurrence
		1850	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		1851	synchronously as part of the event loop processing. Libev always reaps all
		1852	children, even ones not watched.
		1853
		1854	=head3 Overriding the Built-In Processing
		1855
		1856	Libev offers no special support for overriding the built-in child
		1857	processing, but if your application collides with libev's default child
		1858	handler, you can override it easily by installing your own handler for
		1859	C<SIGCHLD> after initialising the default loop, and making sure the
		1860	default loop never gets destroyed. You are encouraged, however, to use an
		1861	event-based approach to child reaping and thus use libev's support for
		1862	that, so other libev users can use C<ev_child> watchers freely.
		1863
		1864	=head3 Stopping the Child Watcher
		1865
		1866	Currently, the child watcher never gets stopped, even when the
		1867	child terminates, so normally one needs to stop the watcher in the
		1868	callback. Future versions of libev might stop the watcher automatically
		1869	when a child exit is detected.
		1870
		1871	=head3 Watcher-Specific Functions and Data Members
1173		1872
1174	=over 4	1873	=over 4
1175		1874
1176	=item ev_child_init (ev_child *, callback, int pid)	1875	=item ev_child_init (ev_child *, callback, int pid, int trace)
1177		1876
1178	=item ev_child_set (ev_child *, int pid)	1877	=item ev_child_set (ev_child *, int pid, int trace)
1179		1878
1180	Configures the watcher to wait for status changes of process C<pid> (or	1879	Configures the watcher to wait for status changes of process C<pid> (or
1181	I<any> process if C<pid> is specified as C<0>). The callback can look	1880	I<any> process if C<pid> is specified as C<0>). The callback can look
1182	at the C<rstatus> member of the C<ev_child> watcher structure to see	1881	at the C<rstatus> member of the C<ev_child> watcher structure to see
1183	the status word (use the macros from C<sys/wait.h> and see your systems	1882	the status word (use the macros from C<sys/wait.h> and see your systems
1184	C<waitpid> documentation). The C<rpid> member contains the pid of the	1883	C<waitpid> documentation). The C<rpid> member contains the pid of the
1185	process causing the status change.	1884	process causing the status change. C<trace> must be either C<0> (only
		1885	activate the watcher when the process terminates) or C<1> (additionally
		1886	activate the watcher when the process is stopped or continued).
1186		1887
1187	=item int pid [read-only]	1888	=item int pid [read-only]
1188		1889
1189	The process id this watcher watches out for, or C<0>, meaning any process id.	1890	The process id this watcher watches out for, or C<0>, meaning any process id.
1190		1891
…		…
1197	The process exit/trace status caused by C<rpid> (see your systems	1898	The process exit/trace status caused by C<rpid> (see your systems
1198	C<waitpid> and C<sys/wait.h> documentation for details).	1899	C<waitpid> and C<sys/wait.h> documentation for details).
1199		1900
1200	=back	1901	=back
1201		1902
1202	Example: Try to exit cleanly on SIGINT and SIGTERM.	1903	=head3 Examples
1203		1904
		1905	Example: C<fork()> a new process and install a child handler to wait for
		1906	its completion.
		1907
		1908	ev_child cw;
		1909
1204	static void	1910	static void
1205	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	1911	child_cb (EV_P_ ev_child *w, int revents)
1206	{	1912	{
1207	ev_unloop (loop, EVUNLOOP_ALL);	1913	ev_child_stop (EV_A_ w);
		1914	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1208	}	1915	}
1209		1916
1210	struct ev_signal signal_watcher;	1917	pid_t pid = fork ();
1211	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	1918
1212	ev_signal_start (loop, &sigint_cb);	1919	if (pid < 0)
		1920	// error
		1921	else if (pid == 0)
		1922	{
		1923	// the forked child executes here
		1924	exit (1);
		1925	}
		1926	else
		1927	{
		1928	ev_child_init (&cw, child_cb, pid, 0);
		1929	ev_child_start (EV_DEFAULT_ &cw);
		1930	}
1213		1931
1214		1932
1215	=head2 C<ev_stat> - did the file attributes just change?	1933	=head2 C<ev_stat> - did the file attributes just change?
1216		1934
1217	This watches a filesystem path for attribute changes. That is, it calls	1935	This watches a file system path for attribute changes. That is, it calls
1218	C<stat> regularly (or when the OS says it changed) and sees if it changed	1936	C<stat> on that path in regular intervals (or when the OS says it changed)
1219	compared to the last time, invoking the callback if it did.	1937	and sees if it changed compared to the last time, invoking the callback if
		1938	it did.
1220		1939
1221	The path does not need to exist: changing from "path exists" to "path does	1940	The path does not need to exist: changing from "path exists" to "path does
1222	not exist" is a status change like any other. The condition "path does	1941	not exist" is a status change like any other. The condition "path does not
1223	not exist" is signified by the C<st_nlink> field being zero (which is	1942	exist" (or more correctly "path cannot be stat'ed") is signified by the
1224	otherwise always forced to be at least one) and all the other fields of	1943	C<st_nlink> field being zero (which is otherwise always forced to be at
1225	the stat buffer having unspecified contents.	1944	least one) and all the other fields of the stat buffer having unspecified
		1945	contents.
1226		1946
1227	Since there is no standard to do this, the portable implementation simply	1947	The path I<must not> end in a slash or contain special components such as
1228	calls C<stat (2)> regularly on the path to see if it changed somehow. You	1948	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1229	can specify a recommended polling interval for this case. If you specify	1949	your working directory changes, then the behaviour is undefined.
1230	a polling interval of C<0> (highly recommended!) then a I<suitable,	1950
1231	unspecified default> value will be used (which you can expect to be around	1951	Since there is no portable change notification interface available, the
1232	five seconds, although this might change dynamically). Libev will also	1952	portable implementation simply calls C<stat(2)> regularly on the path
1233	impose a minimum interval which is currently around C<0.1>, but thats	1953	to see if it changed somehow. You can specify a recommended polling
1234	usually overkill.	1954	interval for this case. If you specify a polling interval of C<0> (highly
		1955	recommended!) then a I<suitable, unspecified default> value will be used
		1956	(which you can expect to be around five seconds, although this might
		1957	change dynamically). Libev will also impose a minimum interval which is
		1958	currently around C<0.1>, but that's usually overkill.
1235		1959
1236	This watcher type is not meant for massive numbers of stat watchers,	1960	This watcher type is not meant for massive numbers of stat watchers,
1237	as even with OS-supported change notifications, this can be	1961	as even with OS-supported change notifications, this can be
1238	resource-intensive.	1962	resource-intensive.
1239		1963
1240	At the time of this writing, only the Linux inotify interface is	1964	At the time of this writing, the only OS-specific interface implemented
1241	implemented (implementing kqueue support is left as an exercise for the	1965	is the Linux inotify interface (implementing kqueue support is left as an
1242	reader). Inotify will be used to give hints only and should not change the	1966	exercise for the reader. Note, however, that the author sees no way of
1243	semantics of C<ev_stat> watchers, which means that libev sometimes needs	1967	implementing C<ev_stat> semantics with kqueue, except as a hint).
1244	to fall back to regular polling again even with inotify, but changes are	1968
1245	usually detected immediately, and if the file exists there will be no	1969	=head3 ABI Issues (Largefile Support)
1246	polling.	1970
		1971	Libev by default (unless the user overrides this) uses the default
		1972	compilation environment, which means that on systems with large file
		1973	support disabled by default, you get the 32 bit version of the stat
		1974	structure. When using the library from programs that change the ABI to
		1975	use 64 bit file offsets the programs will fail. In that case you have to
		1976	compile libev with the same flags to get binary compatibility. This is
		1977	obviously the case with any flags that change the ABI, but the problem is
		1978	most noticeably displayed with ev_stat and large file support.
		1979
		1980	The solution for this is to lobby your distribution maker to make large
		1981	file interfaces available by default (as e.g. FreeBSD does) and not
		1982	optional. Libev cannot simply switch on large file support because it has
		1983	to exchange stat structures with application programs compiled using the
		1984	default compilation environment.
		1985
		1986	=head3 Inotify and Kqueue
		1987
		1988	When C<inotify (7)> support has been compiled into libev and present at
		1989	runtime, it will be used to speed up change detection where possible. The
		1990	inotify descriptor will be created lazily when the first C<ev_stat>
		1991	watcher is being started.
		1992
		1993	Inotify presence does not change the semantics of C<ev_stat> watchers
		1994	except that changes might be detected earlier, and in some cases, to avoid
		1995	making regular C<stat> calls. Even in the presence of inotify support
		1996	there are many cases where libev has to resort to regular C<stat> polling,
		1997	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		1998	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		1999	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2000	xfs are fully working) libev usually gets away without polling.
		2001
		2002	There is no support for kqueue, as apparently it cannot be used to
		2003	implement this functionality, due to the requirement of having a file
		2004	descriptor open on the object at all times, and detecting renames, unlinks
		2005	etc. is difficult.
		2006
		2007	=head3 C<stat ()> is a synchronous operation
		2008
		2009	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2010	the process. The exception are C<ev_stat> watchers - those call C<stat
		2011	()>, which is a synchronous operation.
		2012
		2013	For local paths, this usually doesn't matter: unless the system is very
		2014	busy or the intervals between stat's are large, a stat call will be fast,
		2015	as the path data is suually in memory already (except when starting the
		2016	watcher).
		2017
		2018	For networked file systems, calling C<stat ()> can block an indefinite
		2019	time due to network issues, and even under good conditions, a stat call
		2020	often takes multiple milliseconds.
		2021
		2022	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2023	paths, although this is fully supported by libev.
		2024
		2025	=head3 The special problem of stat time resolution
		2026
		2027	The C<stat ()> system call only supports full-second resolution portably,
		2028	and even on systems where the resolution is higher, most file systems
		2029	still only support whole seconds.
		2030
		2031	That means that, if the time is the only thing that changes, you can
		2032	easily miss updates: on the first update, C<ev_stat> detects a change and
		2033	calls your callback, which does something. When there is another update
		2034	within the same second, C<ev_stat> will be unable to detect unless the
		2035	stat data does change in other ways (e.g. file size).
		2036
		2037	The solution to this is to delay acting on a change for slightly more
		2038	than a second (or till slightly after the next full second boundary), using
		2039	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2040	ev_timer_again (loop, w)>).
		2041
		2042	The C<.02> offset is added to work around small timing inconsistencies
		2043	of some operating systems (where the second counter of the current time
		2044	might be be delayed. One such system is the Linux kernel, where a call to
		2045	C<gettimeofday> might return a timestamp with a full second later than
		2046	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2047	update file times then there will be a small window where the kernel uses
		2048	the previous second to update file times but libev might already execute
		2049	the timer callback).
		2050
		2051	=head3 Watcher-Specific Functions and Data Members
1247		2052
1248	=over 4	2053	=over 4
1249		2054
1250	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)	2055	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
1251		2056
…		…
1255	C<path>. The C<interval> is a hint on how quickly a change is expected to	2060	C<path>. The C<interval> is a hint on how quickly a change is expected to
1256	be detected and should normally be specified as C<0> to let libev choose	2061	be detected and should normally be specified as C<0> to let libev choose
1257	a suitable value. The memory pointed to by C<path> must point to the same	2062	a suitable value. The memory pointed to by C<path> must point to the same
1258	path for as long as the watcher is active.	2063	path for as long as the watcher is active.
1259		2064
1260	The callback will be receive C<EV_STAT> when a change was detected,	2065	The callback will receive an C<EV_STAT> event when a change was detected,
1261	relative to the attributes at the time the watcher was started (or the	2066	relative to the attributes at the time the watcher was started (or the
1262	last change was detected).	2067	last change was detected).
1263		2068
1264	=item ev_stat_stat (ev_stat *)	2069	=item ev_stat_stat (loop, ev_stat *)
1265		2070
1266	Updates the stat buffer immediately with new values. If you change the	2071	Updates the stat buffer immediately with new values. If you change the
1267	watched path in your callback, you could call this fucntion to avoid	2072	watched path in your callback, you could call this function to avoid
1268	detecting this change (while introducing a race condition). Can also be	2073	detecting this change (while introducing a race condition if you are not
1269	useful simply to find out the new values.	2074	the only one changing the path). Can also be useful simply to find out the
		2075	new values.
1270		2076
1271	=item ev_statdata attr [read-only]	2077	=item ev_statdata attr [read-only]
1272		2078
1273	The most-recently detected attributes of the file. Although the type is of	2079	The most-recently detected attributes of the file. Although the type is
1274	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2080	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1275	suitable for your system. If the C<st_nlink> member is C<0>, then there	2081	suitable for your system, but you can only rely on the POSIX-standardised
		2082	members to be present. If the C<st_nlink> member is C<0>, then there was
1276	was some error while C<stat>ing the file.	2083	some error while C<stat>ing the file.
1277		2084
1278	=item ev_statdata prev [read-only]	2085	=item ev_statdata prev [read-only]
1279		2086
1280	The previous attributes of the file. The callback gets invoked whenever	2087	The previous attributes of the file. The callback gets invoked whenever
1281	C<prev> != C<attr>.	2088	C<prev> != C<attr>, or, more precisely, one or more of these members
		2089	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2090	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1282		2091
1283	=item ev_tstamp interval [read-only]	2092	=item ev_tstamp interval [read-only]
1284		2093
1285	The specified interval.	2094	The specified interval.
1286		2095
1287	=item const char *path [read-only]	2096	=item const char *path [read-only]
1288		2097
1289	The filesystem path that is being watched.	2098	The file system path that is being watched.
1290		2099
1291	=back	2100	=back
1292		2101
		2102	=head3 Examples
		2103
1293	Example: Watch C</etc/passwd> for attribute changes.	2104	Example: Watch C</etc/passwd> for attribute changes.
1294		2105
1295	static void	2106	static void
1296	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2107	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1297	{	2108	{
1298	/* /etc/passwd changed in some way */	2109	/* /etc/passwd changed in some way */
1299	if (w->attr.st_nlink)	2110	if (w->attr.st_nlink)
1300	{	2111	{
1301	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2112	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1302	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2113	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1303	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2114	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1304	}	2115	}
1305	else	2116	else
1306	/* you shalt not abuse printf for puts */	2117	/* you shalt not abuse printf for puts */
1307	puts ("wow, /etc/passwd is not there, expect problems. "	2118	puts ("wow, /etc/passwd is not there, expect problems. "
1308	"if this is windows, they already arrived\n");	2119	"if this is windows, they already arrived\n");
1309	}	2120	}
1310		2121
1311	...	2122	...
1312	ev_stat passwd;	2123	ev_stat passwd;
1313		2124
1314	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	2125	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1315	ev_stat_start (loop, &passwd);	2126	ev_stat_start (loop, &passwd);
		2127
		2128	Example: Like above, but additionally use a one-second delay so we do not
		2129	miss updates (however, frequent updates will delay processing, too, so
		2130	one might do the work both on C<ev_stat> callback invocation I<and> on
		2131	C<ev_timer> callback invocation).
		2132
		2133	static ev_stat passwd;
		2134	static ev_timer timer;
		2135
		2136	static void
		2137	timer_cb (EV_P_ ev_timer *w, int revents)
		2138	{
		2139	ev_timer_stop (EV_A_ w);
		2140
		2141	/* now it's one second after the most recent passwd change */
		2142	}
		2143
		2144	static void
		2145	stat_cb (EV_P_ ev_stat *w, int revents)
		2146	{
		2147	/* reset the one-second timer */
		2148	ev_timer_again (EV_A_ &timer);
		2149	}
		2150
		2151	...
		2152	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2153	ev_stat_start (loop, &passwd);
		2154	ev_timer_init (&timer, timer_cb, 0., 1.02);
1316		2155
1317		2156
1318	=head2 C<ev_idle> - when you've got nothing better to do...	2157	=head2 C<ev_idle> - when you've got nothing better to do...
1319		2158
1320	Idle watchers trigger events when there are no other events are pending	2159	Idle watchers trigger events when no other events of the same or higher
1321	(prepare, check and other idle watchers do not count). That is, as long	2160	priority are pending (prepare, check and other idle watchers do not count
1322	as your process is busy handling sockets or timeouts (or even signals,	2161	as receiving "events").
1323	imagine) it will not be triggered. But when your process is idle all idle	2162
1324	watchers are being called again and again, once per event loop iteration -	2163	That is, as long as your process is busy handling sockets or timeouts
		2164	(or even signals, imagine) of the same or higher priority it will not be
		2165	triggered. But when your process is idle (or only lower-priority watchers
		2166	are pending), the idle watchers are being called once per event loop
1325	until stopped, that is, or your process receives more events and becomes	2167	iteration - until stopped, that is, or your process receives more events
1326	busy.	2168	and becomes busy again with higher priority stuff.
1327		2169
1328	The most noteworthy effect is that as long as any idle watchers are	2170	The most noteworthy effect is that as long as any idle watchers are
1329	active, the process will not block when waiting for new events.	2171	active, the process will not block when waiting for new events.
1330		2172
1331	Apart from keeping your process non-blocking (which is a useful	2173	Apart from keeping your process non-blocking (which is a useful
1332	effect on its own sometimes), idle watchers are a good place to do	2174	effect on its own sometimes), idle watchers are a good place to do
1333	"pseudo-background processing", or delay processing stuff to after the	2175	"pseudo-background processing", or delay processing stuff to after the
1334	event loop has handled all outstanding events.	2176	event loop has handled all outstanding events.
1335		2177
		2178	=head3 Watcher-Specific Functions and Data Members
		2179
1336	=over 4	2180	=over 4
1337		2181
1338	=item ev_idle_init (ev_signal *, callback)	2182	=item ev_idle_init (ev_signal *, callback)
1339		2183
1340	Initialises and configures the idle watcher - it has no parameters of any	2184	Initialises and configures the idle watcher - it has no parameters of any
1341	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2185	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1342	believe me.	2186	believe me.
1343		2187
1344	=back	2188	=back
1345		2189
		2190	=head3 Examples
		2191
1346	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2192	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1347	callback, free it. Also, use no error checking, as usual.	2193	callback, free it. Also, use no error checking, as usual.
1348		2194
1349	static void	2195	static void
1350	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2196	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1351	{	2197	{
1352	free (w);	2198	free (w);
1353	// now do something you wanted to do when the program has	2199	// now do something you wanted to do when the program has
1354	// no longer asnything immediate to do.	2200	// no longer anything immediate to do.
1355	}	2201	}
1356		2202
1357	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2203	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1358	ev_idle_init (idle_watcher, idle_cb);	2204	ev_idle_init (idle_watcher, idle_cb);
1359	ev_idle_start (loop, idle_cb);	2205	ev_idle_start (loop, idle_cb);
1360		2206
1361		2207
1362	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2208	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1363		2209
1364	Prepare and check watchers are usually (but not always) used in tandem:	2210	Prepare and check watchers are usually (but not always) used in pairs:
1365	prepare watchers get invoked before the process blocks and check watchers	2211	prepare watchers get invoked before the process blocks and check watchers
1366	afterwards.	2212	afterwards.
1367		2213
1368	You I<must not> call C<ev_loop> or similar functions that enter	2214	You I<must not> call C<ev_loop> or similar functions that enter
1369	the current event loop from either C<ev_prepare> or C<ev_check>	2215	the current event loop from either C<ev_prepare> or C<ev_check>
…		…
1372	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2218	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1373	C<ev_check> so if you have one watcher of each kind they will always be	2219	C<ev_check> so if you have one watcher of each kind they will always be
1374	called in pairs bracketing the blocking call.	2220	called in pairs bracketing the blocking call.
1375		2221
1376	Their main purpose is to integrate other event mechanisms into libev and	2222	Their main purpose is to integrate other event mechanisms into libev and
1377	their use is somewhat advanced. This could be used, for example, to track	2223	their use is somewhat advanced. They could be used, for example, to track
1378	variable changes, implement your own watchers, integrate net-snmp or a	2224	variable changes, implement your own watchers, integrate net-snmp or a
1379	coroutine library and lots more. They are also occasionally useful if	2225	coroutine library and lots more. They are also occasionally useful if
1380	you cache some data and want to flush it before blocking (for example,	2226	you cache some data and want to flush it before blocking (for example,
1381	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2227	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1382	watcher).	2228	watcher).
1383		2229
1384	This is done by examining in each prepare call which file descriptors need	2230	This is done by examining in each prepare call which file descriptors
1385	to be watched by the other library, registering C<ev_io> watchers for	2231	need to be watched by the other library, registering C<ev_io> watchers
1386	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2232	for them and starting an C<ev_timer> watcher for any timeouts (many
1387	provide just this functionality). Then, in the check watcher you check for	2233	libraries provide exactly this functionality). Then, in the check watcher,
1388	any events that occured (by checking the pending status of all watchers	2234	you check for any events that occurred (by checking the pending status
1389	and stopping them) and call back into the library. The I/O and timer	2235	of all watchers and stopping them) and call back into the library. The
1390	callbacks will never actually be called (but must be valid nevertheless,	2236	I/O and timer callbacks will never actually be called (but must be valid
1391	because you never know, you know?).	2237	nevertheless, because you never know, you know?).
1392		2238
1393	As another example, the Perl Coro module uses these hooks to integrate	2239	As another example, the Perl Coro module uses these hooks to integrate
1394	coroutines into libev programs, by yielding to other active coroutines	2240	coroutines into libev programs, by yielding to other active coroutines
1395	during each prepare and only letting the process block if no coroutines	2241	during each prepare and only letting the process block if no coroutines
1396	are ready to run (it's actually more complicated: it only runs coroutines	2242	are ready to run (it's actually more complicated: it only runs coroutines
1397	with priority higher than or equal to the event loop and one coroutine	2243	with priority higher than or equal to the event loop and one coroutine
1398	of lower priority, but only once, using idle watchers to keep the event	2244	of lower priority, but only once, using idle watchers to keep the event
1399	loop from blocking if lower-priority coroutines are active, thus mapping	2245	loop from blocking if lower-priority coroutines are active, thus mapping
1400	low-priority coroutines to idle/background tasks).	2246	low-priority coroutines to idle/background tasks).
1401		2247
		2248	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		2249	priority, to ensure that they are being run before any other watchers
		2250	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2251
		2252	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2253	activate ("feed") events into libev. While libev fully supports this, they
		2254	might get executed before other C<ev_check> watchers did their job. As
		2255	C<ev_check> watchers are often used to embed other (non-libev) event
		2256	loops those other event loops might be in an unusable state until their
		2257	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2258	others).
		2259
		2260	=head3 Watcher-Specific Functions and Data Members
		2261
1402	=over 4	2262	=over 4
1403		2263
1404	=item ev_prepare_init (ev_prepare *, callback)	2264	=item ev_prepare_init (ev_prepare *, callback)
1405		2265
1406	=item ev_check_init (ev_check *, callback)	2266	=item ev_check_init (ev_check *, callback)
1407		2267
1408	Initialises and configures the prepare or check watcher - they have no	2268	Initialises and configures the prepare or check watcher - they have no
1409	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2269	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1410	macros, but using them is utterly, utterly and completely pointless.	2270	macros, but using them is utterly, utterly, utterly and completely
		2271	pointless.
1411		2272
1412	=back	2273	=back
1413		2274
1414	Example: To include a library such as adns, you would add IO watchers	2275	=head3 Examples
1415	and a timeout watcher in a prepare handler, as required by libadns, and	2276
		2277	There are a number of principal ways to embed other event loops or modules
		2278	into libev. Here are some ideas on how to include libadns into libev
		2279	(there is a Perl module named C<EV::ADNS> that does this, which you could
		2280	use as a working example. Another Perl module named C<EV::Glib> embeds a
		2281	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		2282	Glib event loop).
		2283
		2284	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1416	in a check watcher, destroy them and call into libadns. What follows is	2285	and in a check watcher, destroy them and call into libadns. What follows
1417	pseudo-code only of course:	2286	is pseudo-code only of course. This requires you to either use a low
		2287	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		2288	the callbacks for the IO/timeout watchers might not have been called yet.
1418		2289
1419	static ev_io iow [nfd];	2290	static ev_io iow [nfd];
1420	static ev_timer tw;	2291	static ev_timer tw;
1421		2292
1422	static void	2293	static void
1423	io_cb (ev_loop *loop, ev_io *w, int revents)	2294	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1424	{	2295	{
1425	// set the relevant poll flags
1426	// could also call adns_processreadable etc. here
1427	struct pollfd *fd = (struct pollfd *)w->data;
1428	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1429	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1430	}	2296	}
1431		2297
1432	// create io watchers for each fd and a timer before blocking	2298	// create io watchers for each fd and a timer before blocking
1433	static void	2299	static void
1434	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2300	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1435	{	2301	{
1436	int timeout = 3600000;truct pollfd fds [nfd];	2302	int timeout = 3600000;
		2303	struct pollfd fds [nfd];
1437	// actual code will need to loop here and realloc etc.	2304	// actual code will need to loop here and realloc etc.
1438	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2305	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1439		2306
1440	/* the callback is illegal, but won't be called as we stop during check */	2307	/* the callback is illegal, but won't be called as we stop during check */
1441	ev_timer_init (&tw, 0, timeout * 1e-3);	2308	ev_timer_init (&tw, 0, timeout * 1e-3);
1442	ev_timer_start (loop, &tw);	2309	ev_timer_start (loop, &tw);
1443		2310
1444	// create on ev_io per pollfd	2311	// create one ev_io per pollfd
1445	for (int i = 0; i < nfd; ++i)	2312	for (int i = 0; i < nfd; ++i)
1446	{	2313	{
1447	ev_io_init (iow + i, io_cb, fds [i].fd,	2314	ev_io_init (iow + i, io_cb, fds [i].fd,
1448	((fds [i].events & POLLIN ? EV_READ : 0)	2315	((fds [i].events & POLLIN ? EV_READ : 0)
1449	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2316	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1450		2317
1451	fds [i].revents = 0;	2318	fds [i].revents = 0;
1452	iow [i].data = fds + i;
1453	ev_io_start (loop, iow + i);	2319	ev_io_start (loop, iow + i);
1454	}	2320	}
1455	}	2321	}
1456		2322
1457	// stop all watchers after blocking	2323	// stop all watchers after blocking
1458	static void	2324	static void
1459	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2325	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1460	{	2326	{
1461	ev_timer_stop (loop, &tw);	2327	ev_timer_stop (loop, &tw);
1462		2328
1463	for (int i = 0; i < nfd; ++i)	2329	for (int i = 0; i < nfd; ++i)
		2330	{
		2331	// set the relevant poll flags
		2332	// could also call adns_processreadable etc. here
		2333	struct pollfd *fd = fds + i;
		2334	int revents = ev_clear_pending (iow + i);
		2335	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2336	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2337
		2338	// now stop the watcher
1464	ev_io_stop (loop, iow + i);	2339	ev_io_stop (loop, iow + i);
		2340	}
1465		2341
1466	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2342	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1467	}	2343	}
		2344
		2345	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2346	in the prepare watcher and would dispose of the check watcher.
		2347
		2348	Method 3: If the module to be embedded supports explicit event
		2349	notification (libadns does), you can also make use of the actual watcher
		2350	callbacks, and only destroy/create the watchers in the prepare watcher.
		2351
		2352	static void
		2353	timer_cb (EV_P_ ev_timer *w, int revents)
		2354	{
		2355	adns_state ads = (adns_state)w->data;
		2356	update_now (EV_A);
		2357
		2358	adns_processtimeouts (ads, &tv_now);
		2359	}
		2360
		2361	static void
		2362	io_cb (EV_P_ ev_io *w, int revents)
		2363	{
		2364	adns_state ads = (adns_state)w->data;
		2365	update_now (EV_A);
		2366
		2367	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2368	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2369	}
		2370
		2371	// do not ever call adns_afterpoll
		2372
		2373	Method 4: Do not use a prepare or check watcher because the module you
		2374	want to embed is not flexible enough to support it. Instead, you can
		2375	override their poll function. The drawback with this solution is that the
		2376	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		2377	this approach, effectively embedding EV as a client into the horrible
		2378	libglib event loop.
		2379
		2380	static gint
		2381	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2382	{
		2383	int got_events = 0;
		2384
		2385	for (n = 0; n < nfds; ++n)
		2386	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2387
		2388	if (timeout >= 0)
		2389	// create/start timer
		2390
		2391	// poll
		2392	ev_loop (EV_A_ 0);
		2393
		2394	// stop timer again
		2395	if (timeout >= 0)
		2396	ev_timer_stop (EV_A_ &to);
		2397
		2398	// stop io watchers again - their callbacks should have set
		2399	for (n = 0; n < nfds; ++n)
		2400	ev_io_stop (EV_A_ iow [n]);
		2401
		2402	return got_events;
		2403	}
1468		2404
1469		2405
1470	=head2 C<ev_embed> - when one backend isn't enough...	2406	=head2 C<ev_embed> - when one backend isn't enough...
1471		2407
1472	This is a rather advanced watcher type that lets you embed one event loop	2408	This is a rather advanced watcher type that lets you embed one event loop
…		…
1478	prioritise I/O.	2414	prioritise I/O.
1479		2415
1480	As an example for a bug workaround, the kqueue backend might only support	2416	As an example for a bug workaround, the kqueue backend might only support
1481	sockets on some platform, so it is unusable as generic backend, but you	2417	sockets on some platform, so it is unusable as generic backend, but you
1482	still want to make use of it because you have many sockets and it scales	2418	still want to make use of it because you have many sockets and it scales
1483	so nicely. In this case, you would create a kqueue-based loop and embed it	2419	so nicely. In this case, you would create a kqueue-based loop and embed
1484	into your default loop (which might use e.g. poll). Overall operation will	2420	it into your default loop (which might use e.g. poll). Overall operation
1485	be a bit slower because first libev has to poll and then call kevent, but	2421	will be a bit slower because first libev has to call C<poll> and then
1486	at least you can use both at what they are best.	2422	C<kevent>, but at least you can use both mechanisms for what they are
		2423	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1487		2424
1488	As for prioritising I/O: rarely you have the case where some fds have	2425	As for prioritising I/O: under rare circumstances you have the case where
1489	to be watched and handled very quickly (with low latency), and even	2426	some fds have to be watched and handled very quickly (with low latency),
1490	priorities and idle watchers might have too much overhead. In this case	2427	and even priorities and idle watchers might have too much overhead. In
1491	you would put all the high priority stuff in one loop and all the rest in	2428	this case you would put all the high priority stuff in one loop and all
1492	a second one, and embed the second one in the first.	2429	the rest in a second one, and embed the second one in the first.
1493		2430
1494	As long as the watcher is active, the callback will be invoked every time	2431	As long as the watcher is active, the callback will be invoked every time
1495	there might be events pending in the embedded loop. The callback must then	2432	there might be events pending in the embedded loop. The callback must then
1496	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2433	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke
1497	their callbacks (you could also start an idle watcher to give the embedded	2434	their callbacks (you could also start an idle watcher to give the embedded
…		…
1505	interested in that.	2442	interested in that.
1506		2443
1507	Also, there have not currently been made special provisions for forking:	2444	Also, there have not currently been made special provisions for forking:
1508	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2445	when you fork, you not only have to call C<ev_loop_fork> on both loops,
1509	but you will also have to stop and restart any C<ev_embed> watchers	2446	but you will also have to stop and restart any C<ev_embed> watchers
1510	yourself.	2447	yourself - but you can use a fork watcher to handle this automatically,
		2448	and future versions of libev might do just that.
1511		2449
1512	Unfortunately, not all backends are embeddable, only the ones returned by	2450	Unfortunately, not all backends are embeddable: only the ones returned by
1513	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2451	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1514	portable one.	2452	portable one.
1515		2453
1516	So when you want to use this feature you will always have to be prepared	2454	So when you want to use this feature you will always have to be prepared
1517	that you cannot get an embeddable loop. The recommended way to get around	2455	that you cannot get an embeddable loop. The recommended way to get around
1518	this is to have a separate variables for your embeddable loop, try to	2456	this is to have a separate variables for your embeddable loop, try to
1519	create it, and if that fails, use the normal loop for everything:	2457	create it, and if that fails, use the normal loop for everything.
1520		2458
1521	struct ev_loop *loop_hi = ev_default_init (0);	2459	=head3 C<ev_embed> and fork
1522	struct ev_loop *loop_lo = 0;
1523	struct ev_embed embed;
1524
1525	// see if there is a chance of getting one that works
1526	// (remember that a flags value of 0 means autodetection)
1527	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1528	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1529	: 0;
1530		2460
1531	// if we got one, then embed it, otherwise default to loop_hi	2461	While the C<ev_embed> watcher is running, forks in the embedding loop will
1532	if (loop_lo)	2462	automatically be applied to the embedded loop as well, so no special
1533	{	2463	fork handling is required in that case. When the watcher is not running,
1534	ev_embed_init (&embed, 0, loop_lo);	2464	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1535	ev_embed_start (loop_hi, &embed);	2465	as applicable.
1536	}	2466
1537	else	2467	=head3 Watcher-Specific Functions and Data Members
1538	loop_lo = loop_hi;
1539		2468
1540	=over 4	2469	=over 4
1541		2470
1542	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	2471	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
1543		2472
…		…
1545		2474
1546	Configures the watcher to embed the given loop, which must be	2475	Configures the watcher to embed the given loop, which must be
1547	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	2476	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1548	invoked automatically, otherwise it is the responsibility of the callback	2477	invoked automatically, otherwise it is the responsibility of the callback
1549	to invoke it (it will continue to be called until the sweep has been done,	2478	to invoke it (it will continue to be called until the sweep has been done,
1550	if you do not want thta, you need to temporarily stop the embed watcher).	2479	if you do not want that, you need to temporarily stop the embed watcher).
1551		2480
1552	=item ev_embed_sweep (loop, ev_embed *)	2481	=item ev_embed_sweep (loop, ev_embed *)
1553		2482
1554	Make a single, non-blocking sweep over the embedded loop. This works	2483	Make a single, non-blocking sweep over the embedded loop. This works
1555	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	2484	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
1556	apropriate way for embedded loops.	2485	appropriate way for embedded loops.
1557		2486
1558	=item struct ev_loop *loop [read-only]	2487	=item struct ev_loop *other [read-only]
1559		2488
1560	The embedded event loop.	2489	The embedded event loop.
1561		2490
1562	=back	2491	=back
		2492
		2493	=head3 Examples
		2494
		2495	Example: Try to get an embeddable event loop and embed it into the default
		2496	event loop. If that is not possible, use the default loop. The default
		2497	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2498	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2499	used).
		2500
		2501	struct ev_loop *loop_hi = ev_default_init (0);
		2502	struct ev_loop *loop_lo = 0;
		2503	ev_embed embed;
		2504
		2505	// see if there is a chance of getting one that works
		2506	// (remember that a flags value of 0 means autodetection)
		2507	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2508	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2509	: 0;
		2510
		2511	// if we got one, then embed it, otherwise default to loop_hi
		2512	if (loop_lo)
		2513	{
		2514	ev_embed_init (&embed, 0, loop_lo);
		2515	ev_embed_start (loop_hi, &embed);
		2516	}
		2517	else
		2518	loop_lo = loop_hi;
		2519
		2520	Example: Check if kqueue is available but not recommended and create
		2521	a kqueue backend for use with sockets (which usually work with any
		2522	kqueue implementation). Store the kqueue/socket-only event loop in
		2523	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2524
		2525	struct ev_loop *loop = ev_default_init (0);
		2526	struct ev_loop *loop_socket = 0;
		2527	ev_embed embed;
		2528
		2529	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2530	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2531	{
		2532	ev_embed_init (&embed, 0, loop_socket);
		2533	ev_embed_start (loop, &embed);
		2534	}
		2535
		2536	if (!loop_socket)
		2537	loop_socket = loop;
		2538
		2539	// now use loop_socket for all sockets, and loop for everything else
1563		2540
1564		2541
1565	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	2542	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
1566		2543
1567	Fork watchers are called when a C<fork ()> was detected (usually because	2544	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
1570	event loop blocks next and before C<ev_check> watchers are being called,	2547	event loop blocks next and before C<ev_check> watchers are being called,
1571	and only in the child after the fork. If whoever good citizen calling	2548	and only in the child after the fork. If whoever good citizen calling
1572	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2549	C<ev_default_fork> cheats and calls it in the wrong process, the fork
1573	handlers will be invoked, too, of course.	2550	handlers will be invoked, too, of course.
1574		2551
		2552	=head3 Watcher-Specific Functions and Data Members
		2553
1575	=over 4	2554	=over 4
1576		2555
1577	=item ev_fork_init (ev_signal *, callback)	2556	=item ev_fork_init (ev_signal *, callback)
1578		2557
1579	Initialises and configures the fork watcher - it has no parameters of any	2558	Initialises and configures the fork watcher - it has no parameters of any
…		…
1581	believe me.	2560	believe me.
1582		2561
1583	=back	2562	=back
1584		2563
1585		2564
		2565	=head2 C<ev_async> - how to wake up another event loop
		2566
		2567	In general, you cannot use an C<ev_loop> from multiple threads or other
		2568	asynchronous sources such as signal handlers (as opposed to multiple event
		2569	loops - those are of course safe to use in different threads).
		2570
		2571	Sometimes, however, you need to wake up another event loop you do not
		2572	control, for example because it belongs to another thread. This is what
		2573	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2574	can signal it by calling C<ev_async_send>, which is thread- and signal
		2575	safe.
		2576
		2577	This functionality is very similar to C<ev_signal> watchers, as signals,
		2578	too, are asynchronous in nature, and signals, too, will be compressed
		2579	(i.e. the number of callback invocations may be less than the number of
		2580	C<ev_async_sent> calls).
		2581
		2582	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2583	just the default loop.
		2584
		2585	=head3 Queueing
		2586
		2587	C<ev_async> does not support queueing of data in any way. The reason
		2588	is that the author does not know of a simple (or any) algorithm for a
		2589	multiple-writer-single-reader queue that works in all cases and doesn't
		2590	need elaborate support such as pthreads.
		2591
		2592	That means that if you want to queue data, you have to provide your own
		2593	queue. But at least I can tell you how to implement locking around your
		2594	queue:
		2595
		2596	=over 4
		2597
		2598	=item queueing from a signal handler context
		2599
		2600	To implement race-free queueing, you simply add to the queue in the signal
		2601	handler but you block the signal handler in the watcher callback. Here is
		2602	an example that does that for some fictitious SIGUSR1 handler:
		2603
		2604	static ev_async mysig;
		2605
		2606	static void
		2607	sigusr1_handler (void)
		2608	{
		2609	sometype data;
		2610
		2611	// no locking etc.
		2612	queue_put (data);
		2613	ev_async_send (EV_DEFAULT_ &mysig);
		2614	}
		2615
		2616	static void
		2617	mysig_cb (EV_P_ ev_async *w, int revents)
		2618	{
		2619	sometype data;
		2620	sigset_t block, prev;
		2621
		2622	sigemptyset (&block);
		2623	sigaddset (&block, SIGUSR1);
		2624	sigprocmask (SIG_BLOCK, &block, &prev);
		2625
		2626	while (queue_get (&data))
		2627	process (data);
		2628
		2629	if (sigismember (&prev, SIGUSR1)
		2630	sigprocmask (SIG_UNBLOCK, &block, 0);
		2631	}
		2632
		2633	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2634	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2635	either...).
		2636
		2637	=item queueing from a thread context
		2638
		2639	The strategy for threads is different, as you cannot (easily) block
		2640	threads but you can easily preempt them, so to queue safely you need to
		2641	employ a traditional mutex lock, such as in this pthread example:
		2642
		2643	static ev_async mysig;
		2644	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2645
		2646	static void
		2647	otherthread (void)
		2648	{
		2649	// only need to lock the actual queueing operation
		2650	pthread_mutex_lock (&mymutex);
		2651	queue_put (data);
		2652	pthread_mutex_unlock (&mymutex);
		2653
		2654	ev_async_send (EV_DEFAULT_ &mysig);
		2655	}
		2656
		2657	static void
		2658	mysig_cb (EV_P_ ev_async *w, int revents)
		2659	{
		2660	pthread_mutex_lock (&mymutex);
		2661
		2662	while (queue_get (&data))
		2663	process (data);
		2664
		2665	pthread_mutex_unlock (&mymutex);
		2666	}
		2667
		2668	=back
		2669
		2670
		2671	=head3 Watcher-Specific Functions and Data Members
		2672
		2673	=over 4
		2674
		2675	=item ev_async_init (ev_async *, callback)
		2676
		2677	Initialises and configures the async watcher - it has no parameters of any
		2678	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		2679	trust me.
		2680
		2681	=item ev_async_send (loop, ev_async *)
		2682
		2683	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2684	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2685	C<ev_feed_event>, this call is safe to do from other threads, signal or
		2686	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		2687	section below on what exactly this means).
		2688
		2689	This call incurs the overhead of a system call only once per loop iteration,
		2690	so while the overhead might be noticeable, it doesn't apply to repeated
		2691	calls to C<ev_async_send>.
		2692
		2693	=item bool = ev_async_pending (ev_async *)
		2694
		2695	Returns a non-zero value when C<ev_async_send> has been called on the
		2696	watcher but the event has not yet been processed (or even noted) by the
		2697	event loop.
		2698
		2699	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2700	the loop iterates next and checks for the watcher to have become active,
		2701	it will reset the flag again. C<ev_async_pending> can be used to very
		2702	quickly check whether invoking the loop might be a good idea.
		2703
		2704	Not that this does I<not> check whether the watcher itself is pending, only
		2705	whether it has been requested to make this watcher pending.
		2706
		2707	=back
		2708
		2709
1586	=head1 OTHER FUNCTIONS	2710	=head1 OTHER FUNCTIONS
1587		2711
1588	There are some other functions of possible interest. Described. Here. Now.	2712	There are some other functions of possible interest. Described. Here. Now.
1589		2713
1590	=over 4	2714	=over 4
1591		2715
1592	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	2716	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1593		2717
1594	This function combines a simple timer and an I/O watcher, calls your	2718	This function combines a simple timer and an I/O watcher, calls your
1595	callback on whichever event happens first and automatically stop both	2719	callback on whichever event happens first and automatically stops both
1596	watchers. This is useful if you want to wait for a single event on an fd	2720	watchers. This is useful if you want to wait for a single event on an fd
1597	or timeout without having to allocate/configure/start/stop/free one or	2721	or timeout without having to allocate/configure/start/stop/free one or
1598	more watchers yourself.	2722	more watchers yourself.
1599		2723
1600	If C<fd> is less than 0, then no I/O watcher will be started and events	2724	If C<fd> is less than 0, then no I/O watcher will be started and the
1601	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	2725	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1602	C<events> set will be craeted and started.	2726	the given C<fd> and C<events> set will be created and started.
1603		2727
1604	If C<timeout> is less than 0, then no timeout watcher will be	2728	If C<timeout> is less than 0, then no timeout watcher will be
1605	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	2729	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1606	repeat = 0) will be started. While C<0> is a valid timeout, it is of	2730	repeat = 0) will be started. C<0> is a valid timeout.
1607	dubious value.
1608		2731
1609	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	2732	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
1610	passed an C<revents> set like normal event callbacks (a combination of	2733	passed an C<revents> set like normal event callbacks (a combination of
1611	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	2734	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
1612	value passed to C<ev_once>:	2735	value passed to C<ev_once>. Note that it is possible to receive I<both>
		2736	a timeout and an io event at the same time - you probably should give io
		2737	events precedence.
1613		2738
		2739	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		2740
1614	static void stdin_ready (int revents, void *arg)	2741	static void stdin_ready (int revents, void *arg)
1615	{	2742	{
1616	if (revents & EV_TIMEOUT)
1617	/* doh, nothing entered */;
1618	else if (revents & EV_READ)	2743	if (revents & EV_READ)
1619	/* stdin might have data for us, joy! */;	2744	/* stdin might have data for us, joy! */;
		2745	else if (revents & EV_TIMEOUT)
		2746	/* doh, nothing entered */;
1620	}	2747	}
1621		2748
1622	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2749	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1623		2750
1624	=item ev_feed_event (ev_loop *, watcher *, int revents)	2751	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
1625		2752
1626	Feeds the given event set into the event loop, as if the specified event	2753	Feeds the given event set into the event loop, as if the specified event
1627	had happened for the specified watcher (which must be a pointer to an	2754	had happened for the specified watcher (which must be a pointer to an
1628	initialised but not necessarily started event watcher).	2755	initialised but not necessarily started event watcher).
1629		2756
1630	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	2757	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
1631		2758
1632	Feed an event on the given fd, as if a file descriptor backend detected	2759	Feed an event on the given fd, as if a file descriptor backend detected
1633	the given events it.	2760	the given events it.
1634		2761
1635	=item ev_feed_signal_event (ev_loop *loop, int signum)	2762	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
1636		2763
1637	Feed an event as if the given signal occured (C<loop> must be the default	2764	Feed an event as if the given signal occurred (C<loop> must be the default
1638	loop!).	2765	loop!).
1639		2766
1640	=back	2767	=back
1641		2768
1642		2769
…		…
1658		2785
1659	=item * Priorities are not currently supported. Initialising priorities	2786	=item * Priorities are not currently supported. Initialising priorities
1660	will fail and all watchers will have the same priority, even though there	2787	will fail and all watchers will have the same priority, even though there
1661	is an ev_pri field.	2788	is an ev_pri field.
1662		2789
		2790	=item * In libevent, the last base created gets the signals, in libev, the
		2791	first base created (== the default loop) gets the signals.
		2792
1663	=item * Other members are not supported.	2793	=item * Other members are not supported.
1664		2794
1665	=item * The libev emulation is I<not> ABI compatible to libevent, you need	2795	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1666	to use the libev header file and library.	2796	to use the libev header file and library.
1667		2797
1668	=back	2798	=back
1669		2799
1670	=head1 C++ SUPPORT	2800	=head1 C++ SUPPORT
1671		2801
1672	Libev comes with some simplistic wrapper classes for C++ that mainly allow	2802	Libev comes with some simplistic wrapper classes for C++ that mainly allow
1673	you to use some convinience methods to start/stop watchers and also change	2803	you to use some convenience methods to start/stop watchers and also change
1674	the callback model to a model using method callbacks on objects.	2804	the callback model to a model using method callbacks on objects.
1675		2805
1676	To use it,	2806	To use it,
1677		2807
1678	#include <ev++.h>	2808	#include <ev++.h>
1679		2809
1680	(it is not installed by default). This automatically includes F<ev.h>	2810	This automatically includes F<ev.h> and puts all of its definitions (many
1681	and puts all of its definitions (many of them macros) into the global	2811	of them macros) into the global namespace. All C++ specific things are
1682	namespace. All C++ specific things are put into the C<ev> namespace.	2812	put into the C<ev> namespace. It should support all the same embedding
		2813	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
1683		2814
1684	It should support all the same embedding options as F<ev.h>, most notably	2815	Care has been taken to keep the overhead low. The only data member the C++
1685	C<EV_MULTIPLICITY>.	2816	classes add (compared to plain C-style watchers) is the event loop pointer
		2817	that the watcher is associated with (or no additional members at all if
		2818	you disable C<EV_MULTIPLICITY> when embedding libev).
		2819
		2820	Currently, functions, and static and non-static member functions can be
		2821	used as callbacks. Other types should be easy to add as long as they only
		2822	need one additional pointer for context. If you need support for other
		2823	types of functors please contact the author (preferably after implementing
		2824	it).
1686		2825
1687	Here is a list of things available in the C<ev> namespace:	2826	Here is a list of things available in the C<ev> namespace:
1688		2827
1689	=over 4	2828	=over 4
1690		2829
…		…
1706		2845
1707	All of those classes have these methods:	2846	All of those classes have these methods:
1708		2847
1709	=over 4	2848	=over 4
1710		2849
1711	=item ev::TYPE::TYPE (object *, object::method *)	2850	=item ev::TYPE::TYPE ()
1712		2851
1713	=item ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)	2852	=item ev::TYPE::TYPE (struct ev_loop *)
1714		2853
1715	=item ev::TYPE::~TYPE	2854	=item ev::TYPE::~TYPE
1716		2855
1717	The constructor takes a pointer to an object and a method pointer to	2856	The constructor (optionally) takes an event loop to associate the watcher
1718	the event handler callback to call in this class. The constructor calls	2857	with. If it is omitted, it will use C<EV_DEFAULT>.
1719	C<ev_init> for you, which means you have to call the C<set> method	2858
1720	before starting it. If you do not specify a loop then the constructor	2859	The constructor calls C<ev_init> for you, which means you have to call the
1721	automatically associates the default loop with this watcher.	2860	C<set> method before starting it.
		2861
		2862	It will not set a callback, however: You have to call the templated C<set>
		2863	method to set a callback before you can start the watcher.
		2864
		2865	(The reason why you have to use a method is a limitation in C++ which does
		2866	not allow explicit template arguments for constructors).
1722		2867
1723	The destructor automatically stops the watcher if it is active.	2868	The destructor automatically stops the watcher if it is active.
		2869
		2870	=item w->set<class, &class::method> (object *)
		2871
		2872	This method sets the callback method to call. The method has to have a
		2873	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		2874	first argument and the C<revents> as second. The object must be given as
		2875	parameter and is stored in the C<data> member of the watcher.
		2876
		2877	This method synthesizes efficient thunking code to call your method from
		2878	the C callback that libev requires. If your compiler can inline your
		2879	callback (i.e. it is visible to it at the place of the C<set> call and
		2880	your compiler is good :), then the method will be fully inlined into the
		2881	thunking function, making it as fast as a direct C callback.
		2882
		2883	Example: simple class declaration and watcher initialisation
		2884
		2885	struct myclass
		2886	{
		2887	void io_cb (ev::io &w, int revents) { }
		2888	}
		2889
		2890	myclass obj;
		2891	ev::io iow;
		2892	iow.set <myclass, &myclass::io_cb> (&obj);
		2893
		2894	=item w->set<function> (void *data = 0)
		2895
		2896	Also sets a callback, but uses a static method or plain function as
		2897	callback. The optional C<data> argument will be stored in the watcher's
		2898	C<data> member and is free for you to use.
		2899
		2900	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		2901
		2902	See the method-C<set> above for more details.
		2903
		2904	Example: Use a plain function as callback.
		2905
		2906	static void io_cb (ev::io &w, int revents) { }
		2907	iow.set <io_cb> ();
1724		2908
1725	=item w->set (struct ev_loop *)	2909	=item w->set (struct ev_loop *)
1726		2910
1727	Associates a different C<struct ev_loop> with this watcher. You can only	2911	Associates a different C<struct ev_loop> with this watcher. You can only
1728	do this when the watcher is inactive (and not pending either).	2912	do this when the watcher is inactive (and not pending either).
1729		2913
1730	=item w->set ([args])	2914	=item w->set ([arguments])
1731		2915
1732	Basically the same as C<ev_TYPE_set>, with the same args. Must be	2916	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
1733	called at least once. Unlike the C counterpart, an active watcher gets	2917	called at least once. Unlike the C counterpart, an active watcher gets
1734	automatically stopped and restarted.	2918	automatically stopped and restarted when reconfiguring it with this
		2919	method.
1735		2920
1736	=item w->start ()	2921	=item w->start ()
1737		2922
1738	Starts the watcher. Note that there is no C<loop> argument as the	2923	Starts the watcher. Note that there is no C<loop> argument, as the
1739	constructor already takes the loop.	2924	constructor already stores the event loop.
1740		2925
1741	=item w->stop ()	2926	=item w->stop ()
1742		2927
1743	Stops the watcher if it is active. Again, no C<loop> argument.	2928	Stops the watcher if it is active. Again, no C<loop> argument.
1744		2929
1745	=item w->again () C<ev::timer>, C<ev::periodic> only	2930	=item w->again () (C<ev::timer>, C<ev::periodic> only)
1746		2931
1747	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding	2932	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
1748	C<ev_TYPE_again> function.	2933	C<ev_TYPE_again> function.
1749		2934
1750	=item w->sweep () C<ev::embed> only	2935	=item w->sweep () (C<ev::embed> only)
1751		2936
1752	Invokes C<ev_embed_sweep>.	2937	Invokes C<ev_embed_sweep>.
1753		2938
1754	=item w->update () C<ev::stat> only	2939	=item w->update () (C<ev::stat> only)
1755		2940
1756	Invokes C<ev_stat_stat>.	2941	Invokes C<ev_stat_stat>.
1757		2942
1758	=back	2943	=back
1759		2944
1760	=back	2945	=back
1761		2946
1762	Example: Define a class with an IO and idle watcher, start one of them in	2947	Example: Define a class with an IO and idle watcher, start one of them in
1763	the constructor.	2948	the constructor.
1764		2949
1765	class myclass	2950	class myclass
1766	{	2951	{
1767	ev_io io; void io_cb (ev::io &w, int revents);	2952	ev::io io ; void io_cb (ev::io &w, int revents);
1768	ev_idle idle void idle_cb (ev::idle &w, int revents);	2953	ev::idle idle; void idle_cb (ev::idle &w, int revents);
1769		2954
1770	myclass ();	2955	myclass (int fd)
1771	}	2956	{
		2957	io .set <myclass, &myclass::io_cb > (this);
		2958	idle.set <myclass, &myclass::idle_cb> (this);
1772		2959
1773	myclass::myclass (int fd)
1774	: io (this, &myclass::io_cb),
1775	idle (this, &myclass::idle_cb)
1776	{
1777	io.start (fd, ev::READ);	2960	io.start (fd, ev::READ);
		2961	}
1778	}	2962	};
		2963
		2964
		2965	=head1 OTHER LANGUAGE BINDINGS
		2966
		2967	Libev does not offer other language bindings itself, but bindings for a
		2968	number of languages exist in the form of third-party packages. If you know
		2969	any interesting language binding in addition to the ones listed here, drop
		2970	me a note.
		2971
		2972	=over 4
		2973
		2974	=item Perl
		2975
		2976	The EV module implements the full libev API and is actually used to test
		2977	libev. EV is developed together with libev. Apart from the EV core module,
		2978	there are additional modules that implement libev-compatible interfaces
		2979	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		2980	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		2981	and C<EV::Glib>).
		2982
		2983	It can be found and installed via CPAN, its homepage is at
		2984	L<http://software.schmorp.de/pkg/EV>.
		2985
		2986	=item Python
		2987
		2988	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		2989	seems to be quite complete and well-documented. Note, however, that the
		2990	patch they require for libev is outright dangerous as it breaks the ABI
		2991	for everybody else, and therefore, should never be applied in an installed
		2992	libev (if python requires an incompatible ABI then it needs to embed
		2993	libev).
		2994
		2995	=item Ruby
		2996
		2997	Tony Arcieri has written a ruby extension that offers access to a subset
		2998	of the libev API and adds file handle abstractions, asynchronous DNS and
		2999	more on top of it. It can be found via gem servers. Its homepage is at
		3000	L<http://rev.rubyforge.org/>.
		3001
		3002	=item D
		3003
		3004	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3005	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3006
		3007	=item Ocaml
		3008
		3009	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3010	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3011
		3012	=back
1779		3013
1780		3014
1781	=head1 MACRO MAGIC	3015	=head1 MACRO MAGIC
1782		3016
1783	Libev can be compiled with a variety of options, the most fundemantal is	3017	Libev can be compiled with a variety of options, the most fundamental
1784	C<EV_MULTIPLICITY>. This option determines wether (most) functions and	3018	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
1785	callbacks have an initial C<struct ev_loop *> argument.	3019	functions and callbacks have an initial C<struct ev_loop *> argument.
1786		3020
1787	To make it easier to write programs that cope with either variant, the	3021	To make it easier to write programs that cope with either variant, the
1788	following macros are defined:	3022	following macros are defined:
1789		3023
1790	=over 4	3024	=over 4
…		…
1793		3027
1794	This provides the loop I<argument> for functions, if one is required ("ev	3028	This provides the loop I<argument> for functions, if one is required ("ev
1795	loop argument"). The C<EV_A> form is used when this is the sole argument,	3029	loop argument"). The C<EV_A> form is used when this is the sole argument,
1796	C<EV_A_> is used when other arguments are following. Example:	3030	C<EV_A_> is used when other arguments are following. Example:
1797		3031
1798	ev_unref (EV_A);	3032	ev_unref (EV_A);
1799	ev_timer_add (EV_A_ watcher);	3033	ev_timer_add (EV_A_ watcher);
1800	ev_loop (EV_A_ 0);	3034	ev_loop (EV_A_ 0);
1801		3035
1802	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	3036	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
1803	which is often provided by the following macro.	3037	which is often provided by the following macro.
1804		3038
1805	=item C<EV_P>, C<EV_P_>	3039	=item C<EV_P>, C<EV_P_>
1806		3040
1807	This provides the loop I<parameter> for functions, if one is required ("ev	3041	This provides the loop I<parameter> for functions, if one is required ("ev
1808	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	3042	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
1809	C<EV_P_> is used when other parameters are following. Example:	3043	C<EV_P_> is used when other parameters are following. Example:
1810		3044
1811	// this is how ev_unref is being declared	3045	// this is how ev_unref is being declared
1812	static void ev_unref (EV_P);	3046	static void ev_unref (EV_P);
1813		3047
1814	// this is how you can declare your typical callback	3048	// this is how you can declare your typical callback
1815	static void cb (EV_P_ ev_timer *w, int revents)	3049	static void cb (EV_P_ ev_timer *w, int revents)
1816		3050
1817	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	3051	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
1818	suitable for use with C<EV_A>.	3052	suitable for use with C<EV_A>.
1819		3053
1820	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3054	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
1821		3055
1822	Similar to the other two macros, this gives you the value of the default	3056	Similar to the other two macros, this gives you the value of the default
1823	loop, if multiple loops are supported ("ev loop default").	3057	loop, if multiple loops are supported ("ev loop default").
1824		3058
		3059	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3060
		3061	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3062	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3063	is undefined when the default loop has not been initialised by a previous
		3064	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3065
		3066	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3067	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		3068
1825	=back	3069	=back
1826		3070
1827	Example: Declare and initialise a check watcher, working regardless of	3071	Example: Declare and initialise a check watcher, utilising the above
1828	wether multiple loops are supported or not.	3072	macros so it will work regardless of whether multiple loops are supported
		3073	or not.
1829		3074
1830	static void	3075	static void
1831	check_cb (EV_P_ ev_timer *w, int revents)	3076	check_cb (EV_P_ ev_timer *w, int revents)
1832	{	3077	{
1833	ev_check_stop (EV_A_ w);	3078	ev_check_stop (EV_A_ w);
1834	}	3079	}
1835		3080
1836	ev_check check;	3081	ev_check check;
1837	ev_check_init (&check, check_cb);	3082	ev_check_init (&check, check_cb);
1838	ev_check_start (EV_DEFAULT_ &check);	3083	ev_check_start (EV_DEFAULT_ &check);
1839	ev_loop (EV_DEFAULT_ 0);	3084	ev_loop (EV_DEFAULT_ 0);
1840
1841		3085
1842	=head1 EMBEDDING	3086	=head1 EMBEDDING
1843		3087
1844	Libev can (and often is) directly embedded into host	3088	Libev can (and often is) directly embedded into host
1845	applications. Examples of applications that embed it include the Deliantra	3089	applications. Examples of applications that embed it include the Deliantra
1846	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)	3090	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
1847	and rxvt-unicode.	3091	and rxvt-unicode.
1848		3092
1849	The goal is to enable you to just copy the neecssary files into your	3093	The goal is to enable you to just copy the necessary files into your
1850	source directory without having to change even a single line in them, so	3094	source directory without having to change even a single line in them, so
1851	you can easily upgrade by simply copying (or having a checked-out copy of	3095	you can easily upgrade by simply copying (or having a checked-out copy of
1852	libev somewhere in your source tree).	3096	libev somewhere in your source tree).
1853		3097
1854	=head2 FILESETS	3098	=head2 FILESETS
1855		3099
1856	Depending on what features you need you need to include one or more sets of files	3100	Depending on what features you need you need to include one or more sets of files
1857	in your app.	3101	in your application.
1858		3102
1859	=head3 CORE EVENT LOOP	3103	=head3 CORE EVENT LOOP
1860		3104
1861	To include only the libev core (all the C<ev_*> functions), with manual	3105	To include only the libev core (all the C<ev_*> functions), with manual
1862	configuration (no autoconf):	3106	configuration (no autoconf):
1863		3107
1864	#define EV_STANDALONE 1	3108	#define EV_STANDALONE 1
1865	#include "ev.c"	3109	#include "ev.c"
1866		3110
1867	This will automatically include F<ev.h>, too, and should be done in a	3111	This will automatically include F<ev.h>, too, and should be done in a
1868	single C source file only to provide the function implementations. To use	3112	single C source file only to provide the function implementations. To use
1869	it, do the same for F<ev.h> in all files wishing to use this API (best	3113	it, do the same for F<ev.h> in all files wishing to use this API (best
1870	done by writing a wrapper around F<ev.h> that you can include instead and	3114	done by writing a wrapper around F<ev.h> that you can include instead and
1871	where you can put other configuration options):	3115	where you can put other configuration options):
1872		3116
1873	#define EV_STANDALONE 1	3117	#define EV_STANDALONE 1
1874	#include "ev.h"	3118	#include "ev.h"
1875		3119
1876	Both header files and implementation files can be compiled with a C++	3120	Both header files and implementation files can be compiled with a C++
1877	compiler (at least, thats a stated goal, and breakage will be treated	3121	compiler (at least, that's a stated goal, and breakage will be treated
1878	as a bug).	3122	as a bug).
1879		3123
1880	You need the following files in your source tree, or in a directory	3124	You need the following files in your source tree, or in a directory
1881	in your include path (e.g. in libev/ when using -Ilibev):	3125	in your include path (e.g. in libev/ when using -Ilibev):
1882		3126
1883	ev.h	3127	ev.h
1884	ev.c	3128	ev.c
1885	ev_vars.h	3129	ev_vars.h
1886	ev_wrap.h	3130	ev_wrap.h
1887		3131
1888	ev_win32.c required on win32 platforms only	3132	ev_win32.c required on win32 platforms only
1889		3133
1890	ev_select.c only when select backend is enabled (which is by default)	3134	ev_select.c only when select backend is enabled (which is enabled by default)
1891	ev_poll.c only when poll backend is enabled (disabled by default)	3135	ev_poll.c only when poll backend is enabled (disabled by default)
1892	ev_epoll.c only when the epoll backend is enabled (disabled by default)	3136	ev_epoll.c only when the epoll backend is enabled (disabled by default)
1893	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	3137	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
1894	ev_port.c only when the solaris port backend is enabled (disabled by default)	3138	ev_port.c only when the solaris port backend is enabled (disabled by default)
1895		3139
1896	F<ev.c> includes the backend files directly when enabled, so you only need	3140	F<ev.c> includes the backend files directly when enabled, so you only need
1897	to compile this single file.	3141	to compile this single file.
1898		3142
1899	=head3 LIBEVENT COMPATIBILITY API	3143	=head3 LIBEVENT COMPATIBILITY API
1900		3144
1901	To include the libevent compatibility API, also include:	3145	To include the libevent compatibility API, also include:
1902		3146
1903	#include "event.c"	3147	#include "event.c"
1904		3148
1905	in the file including F<ev.c>, and:	3149	in the file including F<ev.c>, and:
1906		3150
1907	#include "event.h"	3151	#include "event.h"
1908		3152
1909	in the files that want to use the libevent API. This also includes F<ev.h>.	3153	in the files that want to use the libevent API. This also includes F<ev.h>.
1910		3154
1911	You need the following additional files for this:	3155	You need the following additional files for this:
1912		3156
1913	event.h	3157	event.h
1914	event.c	3158	event.c
1915		3159
1916	=head3 AUTOCONF SUPPORT	3160	=head3 AUTOCONF SUPPORT
1917		3161
1918	Instead of using C<EV_STANDALONE=1> and providing your config in	3162	Instead of using C<EV_STANDALONE=1> and providing your configuration in
1919	whatever way you want, you can also C<m4_include([libev.m4])> in your	3163	whatever way you want, you can also C<m4_include([libev.m4])> in your
1920	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	3164	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
1921	include F<config.h> and configure itself accordingly.	3165	include F<config.h> and configure itself accordingly.
1922		3166
1923	For this of course you need the m4 file:	3167	For this of course you need the m4 file:
1924		3168
1925	libev.m4	3169	libev.m4
1926		3170
1927	=head2 PREPROCESSOR SYMBOLS/MACROS	3171	=head2 PREPROCESSOR SYMBOLS/MACROS
1928		3172
1929	Libev can be configured via a variety of preprocessor symbols you have to define	3173	Libev can be configured via a variety of preprocessor symbols you have to
1930	before including any of its files. The default is not to build for multiplicity	3174	define before including any of its files. The default in the absence of
1931	and only include the select backend.	3175	autoconf is documented for every option.
1932		3176
1933	=over 4	3177	=over 4
1934		3178
1935	=item EV_STANDALONE	3179	=item EV_STANDALONE
1936		3180
…		…
1941	F<event.h> that are not directly supported by the libev core alone.	3185	F<event.h> that are not directly supported by the libev core alone.
1942		3186
1943	=item EV_USE_MONOTONIC	3187	=item EV_USE_MONOTONIC
1944		3188
1945	If defined to be C<1>, libev will try to detect the availability of the	3189	If defined to be C<1>, libev will try to detect the availability of the
1946	monotonic clock option at both compiletime and runtime. Otherwise no use	3190	monotonic clock option at both compile time and runtime. Otherwise no use
1947	of the monotonic clock option will be attempted. If you enable this, you	3191	of the monotonic clock option will be attempted. If you enable this, you
1948	usually have to link against librt or something similar. Enabling it when	3192	usually have to link against librt or something similar. Enabling it when
1949	the functionality isn't available is safe, though, althoguh you have	3193	the functionality isn't available is safe, though, although you have
1950	to make sure you link against any libraries where the C<clock_gettime>	3194	to make sure you link against any libraries where the C<clock_gettime>
1951	function is hiding in (often F<-lrt>).	3195	function is hiding in (often F<-lrt>).
1952		3196
1953	=item EV_USE_REALTIME	3197	=item EV_USE_REALTIME
1954		3198
1955	If defined to be C<1>, libev will try to detect the availability of the	3199	If defined to be C<1>, libev will try to detect the availability of the
1956	realtime clock option at compiletime (and assume its availability at	3200	real-time clock option at compile time (and assume its availability at
1957	runtime if successful). Otherwise no use of the realtime clock option will	3201	runtime if successful). Otherwise no use of the real-time clock option will
1958	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3202	be attempted. This effectively replaces C<gettimeofday> by C<clock_get
1959	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See tzhe note about libraries	3203	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the
1960	in the description of C<EV_USE_MONOTONIC>, though.	3204	note about libraries in the description of C<EV_USE_MONOTONIC>, though.
		3205
		3206	=item EV_USE_NANOSLEEP
		3207
		3208	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		3209	and will use it for delays. Otherwise it will use C<select ()>.
		3210
		3211	=item EV_USE_EVENTFD
		3212
		3213	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3214	available and will probe for kernel support at runtime. This will improve
		3215	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3216	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3217	2.7 or newer, otherwise disabled.
1961		3218
1962	=item EV_USE_SELECT	3219	=item EV_USE_SELECT
1963		3220
1964	If undefined or defined to be C<1>, libev will compile in support for the	3221	If undefined or defined to be C<1>, libev will compile in support for the
1965	C<select>(2) backend. No attempt at autodetection will be done: if no	3222	C<select>(2) backend. No attempt at auto-detection will be done: if no
1966	other method takes over, select will be it. Otherwise the select backend	3223	other method takes over, select will be it. Otherwise the select backend
1967	will not be compiled in.	3224	will not be compiled in.
1968		3225
1969	=item EV_SELECT_USE_FD_SET	3226	=item EV_SELECT_USE_FD_SET
1970		3227
1971	If defined to C<1>, then the select backend will use the system C<fd_set>	3228	If defined to C<1>, then the select backend will use the system C<fd_set>
1972	structure. This is useful if libev doesn't compile due to a missing	3229	structure. This is useful if libev doesn't compile due to a missing
1973	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	3230	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout on
1974	exotic systems. This usually limits the range of file descriptors to some	3231	exotic systems. This usually limits the range of file descriptors to some
1975	low limit such as 1024 or might have other limitations (winsocket only	3232	low limit such as 1024 or might have other limitations (winsocket only
1976	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3233	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might
1977	influence the size of the C<fd_set> used.	3234	influence the size of the C<fd_set> used.
1978		3235
…		…
1984	be used is the winsock select). This means that it will call	3241	be used is the winsock select). This means that it will call
1985	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3242	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
1986	it is assumed that all these functions actually work on fds, even	3243	it is assumed that all these functions actually work on fds, even
1987	on win32. Should not be defined on non-win32 platforms.	3244	on win32. Should not be defined on non-win32 platforms.
1988		3245
		3246	=item EV_FD_TO_WIN32_HANDLE
		3247
		3248	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3249	file descriptors to socket handles. When not defining this symbol (the
		3250	default), then libev will call C<_get_osfhandle>, which is usually
		3251	correct. In some cases, programs use their own file descriptor management,
		3252	in which case they can provide this function to map fds to socket handles.
		3253
1989	=item EV_USE_POLL	3254	=item EV_USE_POLL
1990		3255
1991	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3256	If defined to be C<1>, libev will compile in support for the C<poll>(2)
1992	backend. Otherwise it will be enabled on non-win32 platforms. It	3257	backend. Otherwise it will be enabled on non-win32 platforms. It
1993	takes precedence over select.	3258	takes precedence over select.
1994		3259
1995	=item EV_USE_EPOLL	3260	=item EV_USE_EPOLL
1996		3261
1997	If defined to be C<1>, libev will compile in support for the Linux	3262	If defined to be C<1>, libev will compile in support for the Linux
1998	C<epoll>(7) backend. Its availability will be detected at runtime,	3263	C<epoll>(7) backend. Its availability will be detected at runtime,
1999	otherwise another method will be used as fallback. This is the	3264	otherwise another method will be used as fallback. This is the preferred
2000	preferred backend for GNU/Linux systems.	3265	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3266	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2001		3267
2002	=item EV_USE_KQUEUE	3268	=item EV_USE_KQUEUE
2003		3269
2004	If defined to be C<1>, libev will compile in support for the BSD style	3270	If defined to be C<1>, libev will compile in support for the BSD style
2005	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	3271	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2018	otherwise another method will be used as fallback. This is the preferred	3284	otherwise another method will be used as fallback. This is the preferred
2019	backend for Solaris 10 systems.	3285	backend for Solaris 10 systems.
2020		3286
2021	=item EV_USE_DEVPOLL	3287	=item EV_USE_DEVPOLL
2022		3288
2023	reserved for future expansion, works like the USE symbols above.	3289	Reserved for future expansion, works like the USE symbols above.
2024		3290
2025	=item EV_USE_INOTIFY	3291	=item EV_USE_INOTIFY
2026		3292
2027	If defined to be C<1>, libev will compile in support for the Linux inotify	3293	If defined to be C<1>, libev will compile in support for the Linux inotify
2028	interface to speed up C<ev_stat> watchers. Its actual availability will	3294	interface to speed up C<ev_stat> watchers. Its actual availability will
2029	be detected at runtime.	3295	be detected at runtime. If undefined, it will be enabled if the headers
		3296	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3297
		3298	=item EV_ATOMIC_T
		3299
		3300	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3301	access is atomic with respect to other threads or signal contexts. No such
		3302	type is easily found in the C language, so you can provide your own type
		3303	that you know is safe for your purposes. It is used both for signal handler "locking"
		3304	as well as for signal and thread safety in C<ev_async> watchers.
		3305
		3306	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3307	(from F<signal.h>), which is usually good enough on most platforms.
2030		3308
2031	=item EV_H	3309	=item EV_H
2032		3310
2033	The name of the F<ev.h> header file used to include it. The default if	3311	The name of the F<ev.h> header file used to include it. The default if
2034	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This	3312	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2035	can be used to virtually rename the F<ev.h> header file in case of conflicts.	3313	used to virtually rename the F<ev.h> header file in case of conflicts.
2036		3314
2037	=item EV_CONFIG_H	3315	=item EV_CONFIG_H
2038		3316
2039	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	3317	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2040	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	3318	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2041	C<EV_H>, above.	3319	C<EV_H>, above.
2042		3320
2043	=item EV_EVENT_H	3321	=item EV_EVENT_H
2044		3322
2045	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	3323	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2046	of how the F<event.h> header can be found.	3324	of how the F<event.h> header can be found, the default is C<"event.h">.
2047		3325
2048	=item EV_PROTOTYPES	3326	=item EV_PROTOTYPES
2049		3327
2050	If defined to be C<0>, then F<ev.h> will not define any function	3328	If defined to be C<0>, then F<ev.h> will not define any function
2051	prototypes, but still define all the structs and other symbols. This is	3329	prototypes, but still define all the structs and other symbols. This is
…		…
2058	will have the C<struct ev_loop *> as first argument, and you can create	3336	will have the C<struct ev_loop *> as first argument, and you can create
2059	additional independent event loops. Otherwise there will be no support	3337	additional independent event loops. Otherwise there will be no support
2060	for multiple event loops and there is no first event loop pointer	3338	for multiple event loops and there is no first event loop pointer
2061	argument. Instead, all functions act on the single default loop.	3339	argument. Instead, all functions act on the single default loop.
2062		3340
		3341	=item EV_MINPRI
		3342
		3343	=item EV_MAXPRI
		3344
		3345	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		3346	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		3347	provide for more priorities by overriding those symbols (usually defined
		3348	to be C<-2> and C<2>, respectively).
		3349
		3350	When doing priority-based operations, libev usually has to linearly search
		3351	all the priorities, so having many of them (hundreds) uses a lot of space
		3352	and time, so using the defaults of five priorities (-2 .. +2) is usually
		3353	fine.
		3354
		3355	If your embedding application does not need any priorities, defining these
		3356	both to C<0> will save some memory and CPU.
		3357
2063	=item EV_PERIODIC_ENABLE	3358	=item EV_PERIODIC_ENABLE
2064		3359
2065	If undefined or defined to be C<1>, then periodic timers are supported. If	3360	If undefined or defined to be C<1>, then periodic timers are supported. If
2066	defined to be C<0>, then they are not. Disabling them saves a few kB of	3361	defined to be C<0>, then they are not. Disabling them saves a few kB of
2067	code.	3362	code.
2068		3363
		3364	=item EV_IDLE_ENABLE
		3365
		3366	If undefined or defined to be C<1>, then idle watchers are supported. If
		3367	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3368	code.
		3369
2069	=item EV_EMBED_ENABLE	3370	=item EV_EMBED_ENABLE
2070		3371
2071	If undefined or defined to be C<1>, then embed watchers are supported. If	3372	If undefined or defined to be C<1>, then embed watchers are supported. If
2072	defined to be C<0>, then they are not.	3373	defined to be C<0>, then they are not. Embed watchers rely on most other
		3374	watcher types, which therefore must not be disabled.
2073		3375
2074	=item EV_STAT_ENABLE	3376	=item EV_STAT_ENABLE
2075		3377
2076	If undefined or defined to be C<1>, then stat watchers are supported. If	3378	If undefined or defined to be C<1>, then stat watchers are supported. If
2077	defined to be C<0>, then they are not.	3379	defined to be C<0>, then they are not.
…		…
2079	=item EV_FORK_ENABLE	3381	=item EV_FORK_ENABLE
2080		3382
2081	If undefined or defined to be C<1>, then fork watchers are supported. If	3383	If undefined or defined to be C<1>, then fork watchers are supported. If
2082	defined to be C<0>, then they are not.	3384	defined to be C<0>, then they are not.
2083		3385
		3386	=item EV_ASYNC_ENABLE
		3387
		3388	If undefined or defined to be C<1>, then async watchers are supported. If
		3389	defined to be C<0>, then they are not.
		3390
2084	=item EV_MINIMAL	3391	=item EV_MINIMAL
2085		3392
2086	If you need to shave off some kilobytes of code at the expense of some	3393	If you need to shave off some kilobytes of code at the expense of some
2087	speed, define this symbol to C<1>. Currently only used for gcc to override	3394	speed, define this symbol to C<1>. Currently this is used to override some
2088	some inlining decisions, saves roughly 30% codesize of amd64.	3395	inlining decisions, saves roughly 30% code size on amd64. It also selects a
		3396	much smaller 2-heap for timer management over the default 4-heap.
2089		3397
2090	=item EV_PID_HASHSIZE	3398	=item EV_PID_HASHSIZE
2091		3399
2092	C<ev_child> watchers use a small hash table to distribute workload by	3400	C<ev_child> watchers use a small hash table to distribute workload by
2093	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3401	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
2094	than enough. If you need to manage thousands of children you might want to	3402	than enough. If you need to manage thousands of children you might want to
2095	increase this value (I<must> be a power of two).	3403	increase this value (I<must> be a power of two).
2096		3404
2097	=item EV_INOTIFY_HASHSIZE	3405	=item EV_INOTIFY_HASHSIZE
2098		3406
2099	C<ev_staz> watchers use a small hash table to distribute workload by	3407	C<ev_stat> watchers use a small hash table to distribute workload by
2100	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	3408	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
2101	usually more than enough. If you need to manage thousands of C<ev_stat>	3409	usually more than enough. If you need to manage thousands of C<ev_stat>
2102	watchers you might want to increase this value (I<must> be a power of	3410	watchers you might want to increase this value (I<must> be a power of
2103	two).	3411	two).
2104		3412
		3413	=item EV_USE_4HEAP
		3414
		3415	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3416	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		3417	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		3418	faster performance with many (thousands) of watchers.
		3419
		3420	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3421	(disabled).
		3422
		3423	=item EV_HEAP_CACHE_AT
		3424
		3425	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3426	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		3427	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3428	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3429	but avoids random read accesses on heap changes. This improves performance
		3430	noticeably with many (hundreds) of watchers.
		3431
		3432	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3433	(disabled).
		3434
		3435	=item EV_VERIFY
		3436
		3437	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3438	be done: If set to C<0>, no internal verification code will be compiled
		3439	in. If set to C<1>, then verification code will be compiled in, but not
		3440	called. If set to C<2>, then the internal verification code will be
		3441	called once per loop, which can slow down libev. If set to C<3>, then the
		3442	verification code will be called very frequently, which will slow down
		3443	libev considerably.
		3444
		3445	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3446	C<0>.
		3447
2105	=item EV_COMMON	3448	=item EV_COMMON
2106		3449
2107	By default, all watchers have a C<void *data> member. By redefining	3450	By default, all watchers have a C<void *data> member. By redefining
2108	this macro to a something else you can include more and other types of	3451	this macro to a something else you can include more and other types of
2109	members. You have to define it each time you include one of the files,	3452	members. You have to define it each time you include one of the files,
2110	though, and it must be identical each time.	3453	though, and it must be identical each time.
2111		3454
2112	For example, the perl EV module uses something like this:	3455	For example, the perl EV module uses something like this:
2113		3456
2114	#define EV_COMMON \	3457	#define EV_COMMON \
2115	SV *self; /* contains this struct */ \	3458	SV *self; /* contains this struct */ \
2116	SV *cb_sv, *fh /* note no trailing ";" */	3459	SV *cb_sv, *fh /* note no trailing ";" */
2117		3460
2118	=item EV_CB_DECLARE (type)	3461	=item EV_CB_DECLARE (type)
2119		3462
2120	=item EV_CB_INVOKE (watcher, revents)	3463	=item EV_CB_INVOKE (watcher, revents)
2121		3464
2122	=item ev_set_cb (ev, cb)	3465	=item ev_set_cb (ev, cb)
2123		3466
2124	Can be used to change the callback member declaration in each watcher,	3467	Can be used to change the callback member declaration in each watcher,
2125	and the way callbacks are invoked and set. Must expand to a struct member	3468	and the way callbacks are invoked and set. Must expand to a struct member
2126	definition and a statement, respectively. See the F<ev.v> header file for	3469	definition and a statement, respectively. See the F<ev.h> header file for
2127	their default definitions. One possible use for overriding these is to	3470	their default definitions. One possible use for overriding these is to
2128	avoid the C<struct ev_loop *> as first argument in all cases, or to use	3471	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2129	method calls instead of plain function calls in C++.	3472	method calls instead of plain function calls in C++.
		3473
		3474	=back
		3475
		3476	=head2 EXPORTED API SYMBOLS
		3477
		3478	If you need to re-export the API (e.g. via a DLL) and you need a list of
		3479	exported symbols, you can use the provided F<Symbol.*> files which list
		3480	all public symbols, one per line:
		3481
		3482	Symbols.ev for libev proper
		3483	Symbols.event for the libevent emulation
		3484
		3485	This can also be used to rename all public symbols to avoid clashes with
		3486	multiple versions of libev linked together (which is obviously bad in
		3487	itself, but sometimes it is inconvenient to avoid this).
		3488
		3489	A sed command like this will create wrapper C<#define>'s that you need to
		3490	include before including F<ev.h>:
		3491
		3492	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		3493
		3494	This would create a file F<wrap.h> which essentially looks like this:
		3495
		3496	#define ev_backend myprefix_ev_backend
		3497	#define ev_check_start myprefix_ev_check_start
		3498	#define ev_check_stop myprefix_ev_check_stop
		3499	...
2130		3500
2131	=head2 EXAMPLES	3501	=head2 EXAMPLES
2132		3502
2133	For a real-world example of a program the includes libev	3503	For a real-world example of a program the includes libev
2134	verbatim, you can have a look at the EV perl module	3504	verbatim, you can have a look at the EV perl module
…		…
2137	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file	3507	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
2138	will be compiled. It is pretty complex because it provides its own header	3508	will be compiled. It is pretty complex because it provides its own header
2139	file.	3509	file.
2140		3510
2141	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	3511	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2142	that everybody includes and which overrides some autoconf choices:	3512	that everybody includes and which overrides some configure choices:
2143		3513
		3514	#define EV_MINIMAL 1
2144	#define EV_USE_POLL 0	3515	#define EV_USE_POLL 0
2145	#define EV_MULTIPLICITY 0	3516	#define EV_MULTIPLICITY 0
2146	#define EV_PERIODICS 0	3517	#define EV_PERIODIC_ENABLE 0
		3518	#define EV_STAT_ENABLE 0
		3519	#define EV_FORK_ENABLE 0
2147	#define EV_CONFIG_H <config.h>	3520	#define EV_CONFIG_H <config.h>
		3521	#define EV_MINPRI 0
		3522	#define EV_MAXPRI 0
2148		3523
2149	#include "ev++.h"	3524	#include "ev++.h"
2150		3525
2151	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	3526	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2152		3527
2153	#include "ev_cpp.h"	3528	#include "ev_cpp.h"
2154	#include "ev.c"	3529	#include "ev.c"
2155		3530
		3531	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
2156		3532
		3533	=head2 THREADS AND COROUTINES
		3534
		3535	=head3 THREADS
		3536
		3537	All libev functions are reentrant and thread-safe unless explicitly
		3538	documented otherwise, but libev implements no locking itself. This means
		3539	that you can use as many loops as you want in parallel, as long as there
		3540	are no concurrent calls into any libev function with the same loop
		3541	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		3542	of course): libev guarantees that different event loops share no data
		3543	structures that need any locking.
		3544
		3545	Or to put it differently: calls with different loop parameters can be done
		3546	concurrently from multiple threads, calls with the same loop parameter
		3547	must be done serially (but can be done from different threads, as long as
		3548	only one thread ever is inside a call at any point in time, e.g. by using
		3549	a mutex per loop).
		3550
		3551	Specifically to support threads (and signal handlers), libev implements
		3552	so-called C<ev_async> watchers, which allow some limited form of
		3553	concurrency on the same event loop, namely waking it up "from the
		3554	outside".
		3555
		3556	If you want to know which design (one loop, locking, or multiple loops
		3557	without or something else still) is best for your problem, then I cannot
		3558	help you, but here is some generic advice:
		3559
		3560	=over 4
		3561
		3562	=item * most applications have a main thread: use the default libev loop
		3563	in that thread, or create a separate thread running only the default loop.
		3564
		3565	This helps integrating other libraries or software modules that use libev
		3566	themselves and don't care/know about threading.
		3567
		3568	=item * one loop per thread is usually a good model.
		3569
		3570	Doing this is almost never wrong, sometimes a better-performance model
		3571	exists, but it is always a good start.
		3572
		3573	=item * other models exist, such as the leader/follower pattern, where one
		3574	loop is handed through multiple threads in a kind of round-robin fashion.
		3575
		3576	Choosing a model is hard - look around, learn, know that usually you can do
		3577	better than you currently do :-)
		3578
		3579	=item * often you need to talk to some other thread which blocks in the
		3580	event loop.
		3581
		3582	C<ev_async> watchers can be used to wake them up from other threads safely
		3583	(or from signal contexts...).
		3584
		3585	An example use would be to communicate signals or other events that only
		3586	work in the default loop by registering the signal watcher with the
		3587	default loop and triggering an C<ev_async> watcher from the default loop
		3588	watcher callback into the event loop interested in the signal.
		3589
		3590	=back
		3591
		3592	=head3 COROUTINES
		3593
		3594	Libev is very accommodating to coroutines ("cooperative threads"):
		3595	libev fully supports nesting calls to its functions from different
		3596	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3597	different coroutines, and switch freely between both coroutines running the
		3598	loop, as long as you don't confuse yourself). The only exception is that
		3599	you must not do this from C<ev_periodic> reschedule callbacks.
		3600
		3601	Care has been taken to ensure that libev does not keep local state inside
		3602	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		3603	they do not call any callbacks.
		3604
		3605	=head2 COMPILER WARNINGS
		3606
		3607	Depending on your compiler and compiler settings, you might get no or a
		3608	lot of warnings when compiling libev code. Some people are apparently
		3609	scared by this.
		3610
		3611	However, these are unavoidable for many reasons. For one, each compiler
		3612	has different warnings, and each user has different tastes regarding
		3613	warning options. "Warn-free" code therefore cannot be a goal except when
		3614	targeting a specific compiler and compiler-version.
		3615
		3616	Another reason is that some compiler warnings require elaborate
		3617	workarounds, or other changes to the code that make it less clear and less
		3618	maintainable.
		3619
		3620	And of course, some compiler warnings are just plain stupid, or simply
		3621	wrong (because they don't actually warn about the condition their message
		3622	seems to warn about). For example, certain older gcc versions had some
		3623	warnings that resulted an extreme number of false positives. These have
		3624	been fixed, but some people still insist on making code warn-free with
		3625	such buggy versions.
		3626
		3627	While libev is written to generate as few warnings as possible,
		3628	"warn-free" code is not a goal, and it is recommended not to build libev
		3629	with any compiler warnings enabled unless you are prepared to cope with
		3630	them (e.g. by ignoring them). Remember that warnings are just that:
		3631	warnings, not errors, or proof of bugs.
		3632
		3633
		3634	=head2 VALGRIND
		3635
		3636	Valgrind has a special section here because it is a popular tool that is
		3637	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		3638
		3639	If you think you found a bug (memory leak, uninitialised data access etc.)
		3640	in libev, then check twice: If valgrind reports something like:
		3641
		3642	==2274== definitely lost: 0 bytes in 0 blocks.
		3643	==2274== possibly lost: 0 bytes in 0 blocks.
		3644	==2274== still reachable: 256 bytes in 1 blocks.
		3645
		3646	Then there is no memory leak, just as memory accounted to global variables
		3647	is not a memleak - the memory is still being referenced, and didn't leak.
		3648
		3649	Similarly, under some circumstances, valgrind might report kernel bugs
		3650	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		3651	although an acceptable workaround has been found here), or it might be
		3652	confused.
		3653
		3654	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		3655	make it into some kind of religion.
		3656
		3657	If you are unsure about something, feel free to contact the mailing list
		3658	with the full valgrind report and an explanation on why you think this
		3659	is a bug in libev (best check the archives, too :). However, don't be
		3660	annoyed when you get a brisk "this is no bug" answer and take the chance
		3661	of learning how to interpret valgrind properly.
		3662
		3663	If you need, for some reason, empty reports from valgrind for your project
		3664	I suggest using suppression lists.
		3665
		3666
		3667	=head1 PORTABILITY NOTES
		3668
		3669	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		3670
		3671	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		3672	requires, and its I/O model is fundamentally incompatible with the POSIX
		3673	model. Libev still offers limited functionality on this platform in
		3674	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		3675	descriptors. This only applies when using Win32 natively, not when using
		3676	e.g. cygwin.
		3677
		3678	Lifting these limitations would basically require the full
		3679	re-implementation of the I/O system. If you are into these kinds of
		3680	things, then note that glib does exactly that for you in a very portable
		3681	way (note also that glib is the slowest event library known to man).
		3682
		3683	There is no supported compilation method available on windows except
		3684	embedding it into other applications.
		3685
		3686	Not a libev limitation but worth mentioning: windows apparently doesn't
		3687	accept large writes: instead of resulting in a partial write, windows will
		3688	either accept everything or return C<ENOBUFS> if the buffer is too large,
		3689	so make sure you only write small amounts into your sockets (less than a
		3690	megabyte seems safe, but this apparently depends on the amount of memory
		3691	available).
		3692
		3693	Due to the many, low, and arbitrary limits on the win32 platform and
		3694	the abysmal performance of winsockets, using a large number of sockets
		3695	is not recommended (and not reasonable). If your program needs to use
		3696	more than a hundred or so sockets, then likely it needs to use a totally
		3697	different implementation for windows, as libev offers the POSIX readiness
		3698	notification model, which cannot be implemented efficiently on windows
		3699	(Microsoft monopoly games).
		3700
		3701	A typical way to use libev under windows is to embed it (see the embedding
		3702	section for details) and use the following F<evwrap.h> header file instead
		3703	of F<ev.h>:
		3704
		3705	#define EV_STANDALONE /* keeps ev from requiring config.h */
		3706	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		3707
		3708	#include "ev.h"
		3709
		3710	And compile the following F<evwrap.c> file into your project (make sure
		3711	you do I<not> compile the F<ev.c> or any other embedded source files!):
		3712
		3713	#include "evwrap.h"
		3714	#include "ev.c"
		3715
		3716	=over 4
		3717
		3718	=item The winsocket select function
		3719
		3720	The winsocket C<select> function doesn't follow POSIX in that it
		3721	requires socket I<handles> and not socket I<file descriptors> (it is
		3722	also extremely buggy). This makes select very inefficient, and also
		3723	requires a mapping from file descriptors to socket handles (the Microsoft
		3724	C runtime provides the function C<_open_osfhandle> for this). See the
		3725	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		3726	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		3727
		3728	The configuration for a "naked" win32 using the Microsoft runtime
		3729	libraries and raw winsocket select is:
		3730
		3731	#define EV_USE_SELECT 1
		3732	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		3733
		3734	Note that winsockets handling of fd sets is O(n), so you can easily get a
		3735	complexity in the O(n²) range when using win32.
		3736
		3737	=item Limited number of file descriptors
		3738
		3739	Windows has numerous arbitrary (and low) limits on things.
		3740
		3741	Early versions of winsocket's select only supported waiting for a maximum
		3742	of C<64> handles (probably owning to the fact that all windows kernels
		3743	can only wait for C<64> things at the same time internally; Microsoft
		3744	recommends spawning a chain of threads and wait for 63 handles and the
		3745	previous thread in each. Great).
		3746
		3747	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		3748	to some high number (e.g. C<2048>) before compiling the winsocket select
		3749	call (which might be in libev or elsewhere, for example, perl does its own
		3750	select emulation on windows).
		3751
		3752	Another limit is the number of file descriptors in the Microsoft runtime
		3753	libraries, which by default is C<64> (there must be a hidden I<64> fetish
		3754	or something like this inside Microsoft). You can increase this by calling
		3755	C<_setmaxstdio>, which can increase this limit to C<2048> (another
		3756	arbitrary limit), but is broken in many versions of the Microsoft runtime
		3757	libraries.
		3758
		3759	This might get you to about C<512> or C<2048> sockets (depending on
		3760	windows version and/or the phase of the moon). To get more, you need to
		3761	wrap all I/O functions and provide your own fd management, but the cost of
		3762	calling select (O(n²)) will likely make this unworkable.
		3763
		3764	=back
		3765
		3766	=head2 PORTABILITY REQUIREMENTS
		3767
		3768	In addition to a working ISO-C implementation and of course the
		3769	backend-specific APIs, libev relies on a few additional extensions:
		3770
		3771	=over 4
		3772
		3773	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		3774	calling conventions regardless of C<ev_watcher_type *>.
		3775
		3776	Libev assumes not only that all watcher pointers have the same internal
		3777	structure (guaranteed by POSIX but not by ISO C for example), but it also
		3778	assumes that the same (machine) code can be used to call any watcher
		3779	callback: The watcher callbacks have different type signatures, but libev
		3780	calls them using an C<ev_watcher *> internally.
		3781
		3782	=item C<sig_atomic_t volatile> must be thread-atomic as well
		3783
		3784	The type C<sig_atomic_t volatile> (or whatever is defined as
		3785	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		3786	threads. This is not part of the specification for C<sig_atomic_t>, but is
		3787	believed to be sufficiently portable.
		3788
		3789	=item C<sigprocmask> must work in a threaded environment
		3790
		3791	Libev uses C<sigprocmask> to temporarily block signals. This is not
		3792	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		3793	pthread implementations will either allow C<sigprocmask> in the "main
		3794	thread" or will block signals process-wide, both behaviours would
		3795	be compatible with libev. Interaction between C<sigprocmask> and
		3796	C<pthread_sigmask> could complicate things, however.
		3797
		3798	The most portable way to handle signals is to block signals in all threads
		3799	except the initial one, and run the default loop in the initial thread as
		3800	well.
		3801
		3802	=item C<long> must be large enough for common memory allocation sizes
		3803
		3804	To improve portability and simplify its API, libev uses C<long> internally
		3805	instead of C<size_t> when allocating its data structures. On non-POSIX
		3806	systems (Microsoft...) this might be unexpectedly low, but is still at
		3807	least 31 bits everywhere, which is enough for hundreds of millions of
		3808	watchers.
		3809
		3810	=item C<double> must hold a time value in seconds with enough accuracy
		3811
		3812	The type C<double> is used to represent timestamps. It is required to
		3813	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		3814	enough for at least into the year 4000. This requirement is fulfilled by
		3815	implementations implementing IEEE 754 (basically all existing ones).
		3816
		3817	=back
		3818
		3819	If you know of other additional requirements drop me a note.
		3820
		3821
2157	=head1 COMPLEXITIES	3822	=head1 ALGORITHMIC COMPLEXITIES
2158		3823
2159	In this section the complexities of (many of) the algorithms used inside	3824	In this section the complexities of (many of) the algorithms used inside
2160	libev will be explained. For complexity discussions about backends see the	3825	libev will be documented. For complexity discussions about backends see
2161	documentation for C<ev_default_init>.	3826	the documentation for C<ev_default_init>.
		3827
		3828	All of the following are about amortised time: If an array needs to be
		3829	extended, libev needs to realloc and move the whole array, but this
		3830	happens asymptotically rarer with higher number of elements, so O(1) might
		3831	mean that libev does a lengthy realloc operation in rare cases, but on
		3832	average it is much faster and asymptotically approaches constant time.
2162		3833
2163	=over 4	3834	=over 4
2164		3835
2165	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	3836	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2166		3837
		3838	This means that, when you have a watcher that triggers in one hour and
		3839	there are 100 watchers that would trigger before that, then inserting will
		3840	have to skip roughly seven (C<ld 100>) of these watchers.
		3841
2167	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	3842	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2168		3843
		3844	That means that changing a timer costs less than removing/adding them,
		3845	as only the relative motion in the event queue has to be paid for.
		3846
2169	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	3847	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
2170		3848
		3849	These just add the watcher into an array or at the head of a list.
		3850
2171	=item Stopping check/prepare/idle watchers: O(1)	3851	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2172		3852
2173	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	3853	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2174		3854
		3855	These watchers are stored in lists, so they need to be walked to find the
		3856	correct watcher to remove. The lists are usually short (you don't usually
		3857	have many watchers waiting for the same fd or signal: one is typical, two
		3858	is rare).
		3859
2175	=item Finding the next timer per loop iteration: O(1)	3860	=item Finding the next timer in each loop iteration: O(1)
		3861
		3862	By virtue of using a binary or 4-heap, the next timer is always found at a
		3863	fixed position in the storage array.
2176		3864
2177	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	3865	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2178		3866
2179	=item Activating one watcher: O(1)	3867	A change means an I/O watcher gets started or stopped, which requires
		3868	libev to recalculate its status (and possibly tell the kernel, depending
		3869	on backend and whether C<ev_io_set> was used).
		3870
		3871	=item Activating one watcher (putting it into the pending state): O(1)
		3872
		3873	=item Priority handling: O(number_of_priorities)
		3874
		3875	Priorities are implemented by allocating some space for each
		3876	priority. When doing priority-based operations, libev usually has to
		3877	linearly search all the priorities, but starting/stopping and activating
		3878	watchers becomes O(1) with respect to priority handling.
		3879
		3880	=item Sending an ev_async: O(1)
		3881
		3882	=item Processing ev_async_send: O(number_of_async_watchers)
		3883
		3884	=item Processing signals: O(max_signal_number)
		3885
		3886	Sending involves a system call I<iff> there were no other C<ev_async_send>
		3887	calls in the current loop iteration. Checking for async and signal events
		3888	involves iterating over all running async watchers or all signal numbers.
2180		3889
2181	=back	3890	=back
2182		3891
2183		3892
2184	=head1 AUTHOR	3893	=head1 AUTHOR
2185		3894
2186	Marc Lehmann <libev@schmorp.de>.	3895	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
2187		3896

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