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Revision 1.98 by root, Sat Dec 22 06:10:25 2007 UTC vs.
Revision 1.228 by root, Sat Mar 28 08:22:30 2009 UTC

…		…
2		2
3	libev - a high performance full-featured event loop written in C	3	libev - a high performance full-featured event loop written in C
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
8		8
9	=head1 EXAMPLE PROGRAM	9	=head2 EXAMPLE PROGRAM
10		10
		11	// a single header file is required
11	#include <ev.h>	12	#include <ev.h>
12		13
		14	#include <stdio.h> // for puts
		15
		16	// every watcher type has its own typedef'd struct
		17	// with the name ev_TYPE
13	ev_io stdin_watcher;	18	ev_io stdin_watcher;
14	ev_timer timeout_watcher;	19	ev_timer timeout_watcher;
15		20
16	/* called when data readable on stdin */	21	// all watcher callbacks have a similar signature
		22	// this callback is called when data is readable on stdin
17	static void	23	static void
18	stdin_cb (EV_P_ struct ev_io *w, int revents)	24	stdin_cb (EV_P_ ev_io *w, int revents)
19	{	25	{
20	/* puts ("stdin ready"); */	26	puts ("stdin ready");
21	ev_io_stop (EV_A_ w); /* just a syntax example */	27	// for one-shot events, one must manually stop the watcher
22	ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */	28	// with its corresponding stop function.
		29	ev_io_stop (EV_A_ w);
		30
		31	// this causes all nested ev_loop's to stop iterating
		32	ev_unloop (EV_A_ EVUNLOOP_ALL);
23	}	33	}
24		34
		35	// another callback, this time for a time-out
25	static void	36	static void
26	timeout_cb (EV_P_ struct ev_timer *w, int revents)	37	timeout_cb (EV_P_ ev_timer *w, int revents)
27	{	38	{
28	/* puts ("timeout"); */	39	puts ("timeout");
29	ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */	40	// this causes the innermost ev_loop to stop iterating
		41	ev_unloop (EV_A_ EVUNLOOP_ONE);
30	}	42	}
31		43
32	int	44	int
33	main (void)	45	main (void)
34	{	46	{
		47	// use the default event loop unless you have special needs
35	struct ev_loop *loop = ev_default_loop (0);	48	struct ev_loop *loop = ev_default_loop (0);
36		49
37	/* initialise an io watcher, then start it */	50	// initialise an io watcher, then start it
		51	// this one will watch for stdin to become readable
38	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);	52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
39	ev_io_start (loop, &stdin_watcher);	53	ev_io_start (loop, &stdin_watcher);
40		54
		55	// initialise a timer watcher, then start it
41	/* simple non-repeating 5.5 second timeout */	56	// simple non-repeating 5.5 second timeout
42	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);	57	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
43	ev_timer_start (loop, &timeout_watcher);	58	ev_timer_start (loop, &timeout_watcher);
44		59
45	/* loop till timeout or data ready */	60	// now wait for events to arrive
46	ev_loop (loop, 0);	61	ev_loop (loop, 0);
47		62
		63	// unloop was called, so exit
48	return 0;	64	return 0;
49	}	65	}
50		66
51	=head1 DESCRIPTION	67	=head1 DESCRIPTION
52		68
53	The newest version of this document is also available as a html-formatted	69	The newest version of this document is also available as an html-formatted
54	web page you might find easier to navigate when reading it for the first	70	web page you might find easier to navigate when reading it for the first
55	time: L<http://cvs.schmorp.de/libev/ev.html>.	71	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
56		72
57	Libev is an event loop: you register interest in certain events (such as a	73	Libev is an event loop: you register interest in certain events (such as a
58	file descriptor being readable or a timeout occurring), and it will manage	74	file descriptor being readable or a timeout occurring), and it will manage
59	these event sources and provide your program with events.	75	these event sources and provide your program with events.
60		76
…		…
65	You register interest in certain events by registering so-called I<event	81	You register interest in certain events by registering so-called I<event
66	watchers>, which are relatively small C structures you initialise with the	82	watchers>, which are relatively small C structures you initialise with the
67	details of the event, and then hand it over to libev by I<starting> the	83	details of the event, and then hand it over to libev by I<starting> the
68	watcher.	84	watcher.
69		85
70	=head1 FEATURES	86	=head2 FEATURES
71		87
72	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	88	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
73	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	89	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
74	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	90	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
75	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	91	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
…		…
82		98
83	It also is quite fast (see this	99	It also is quite fast (see this
84	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent	100	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
85	for example).	101	for example).
86		102
87	=head1 CONVENTIONS	103	=head2 CONVENTIONS
88		104
89	Libev is very configurable. In this manual the default configuration will	105	Libev is very configurable. In this manual the default (and most common)
90	be described, which supports multiple event loops. For more info about	106	configuration will be described, which supports multiple event loops. For
91	various configuration options please have a look at B<EMBED> section in	107	more info about various configuration options please have a look at
92	this manual. If libev was configured without support for multiple event	108	B<EMBED> section in this manual. If libev was configured without support
93	loops, then all functions taking an initial argument of name C<loop>	109	for multiple event loops, then all functions taking an initial argument of
94	(which is always of type C<struct ev_loop *>) will not have this argument.	110	name C<loop> (which is always of type C<ev_loop *>) will not have
		111	this argument.
95		112
96	=head1 TIME REPRESENTATION	113	=head2 TIME REPRESENTATION
97		114
98	Libev represents time as a single floating point number, representing the	115	Libev represents time as a single floating point number, representing the
99	(fractional) number of seconds since the (POSIX) epoch (somewhere near	116	(fractional) number of seconds since the (POSIX) epoch (somewhere near
100	the beginning of 1970, details are complicated, don't ask). This type is	117	the beginning of 1970, details are complicated, don't ask). This type is
101	called C<ev_tstamp>, which is what you should use too. It usually aliases	118	called C<ev_tstamp>, which is what you should use too. It usually aliases
102	to the C<double> type in C, and when you need to do any calculations on	119	to the C<double> type in C, and when you need to do any calculations on
103	it, you should treat it as some floatingpoint value. Unlike the name	120	it, you should treat it as some floating point value. Unlike the name
104	component C<stamp> might indicate, it is also used for time differences	121	component C<stamp> might indicate, it is also used for time differences
105	throughout libev.	122	throughout libev.
		123
		124	=head1 ERROR HANDLING
		125
		126	Libev knows three classes of errors: operating system errors, usage errors
		127	and internal errors (bugs).
		128
		129	When libev catches an operating system error it cannot handle (for example
		130	a system call indicating a condition libev cannot fix), it calls the callback
		131	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		132	abort. The default is to print a diagnostic message and to call C<abort
		133	()>.
		134
		135	When libev detects a usage error such as a negative timer interval, then
		136	it will print a diagnostic message and abort (via the C<assert> mechanism,
		137	so C<NDEBUG> will disable this checking): these are programming errors in
		138	the libev caller and need to be fixed there.
		139
		140	Libev also has a few internal error-checking C<assert>ions, and also has
		141	extensive consistency checking code. These do not trigger under normal
		142	circumstances, as they indicate either a bug in libev or worse.
		143
106		144
107	=head1 GLOBAL FUNCTIONS	145	=head1 GLOBAL FUNCTIONS
108		146
109	These functions can be called anytime, even before initialising the	147	These functions can be called anytime, even before initialising the
110	library in any way.	148	library in any way.
…		…
119		157
120	=item ev_sleep (ev_tstamp interval)	158	=item ev_sleep (ev_tstamp interval)
121		159
122	Sleep for the given interval: The current thread will be blocked until	160	Sleep for the given interval: The current thread will be blocked until
123	either it is interrupted or the given time interval has passed. Basically	161	either it is interrupted or the given time interval has passed. Basically
124	this is a subsecond-resolution C<sleep ()>.	162	this is a sub-second-resolution C<sleep ()>.
125		163
126	=item int ev_version_major ()	164	=item int ev_version_major ()
127		165
128	=item int ev_version_minor ()	166	=item int ev_version_minor ()
129		167
…		…
142	not a problem.	180	not a problem.
143		181
144	Example: Make sure we haven't accidentally been linked against the wrong	182	Example: Make sure we haven't accidentally been linked against the wrong
145	version.	183	version.
146		184
147	assert (("libev version mismatch",	185	assert (("libev version mismatch",
148	ev_version_major () == EV_VERSION_MAJOR	186	ev_version_major () == EV_VERSION_MAJOR
149	&& ev_version_minor () >= EV_VERSION_MINOR));	187	&& ev_version_minor () >= EV_VERSION_MINOR));
150		188
151	=item unsigned int ev_supported_backends ()	189	=item unsigned int ev_supported_backends ()
152		190
153	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	191	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
154	value) compiled into this binary of libev (independent of their	192	value) compiled into this binary of libev (independent of their
…		…
156	a description of the set values.	194	a description of the set values.
157		195
158	Example: make sure we have the epoll method, because yeah this is cool and	196	Example: make sure we have the epoll method, because yeah this is cool and
159	a must have and can we have a torrent of it please!!!11	197	a must have and can we have a torrent of it please!!!11
160		198
161	assert (("sorry, no epoll, no sex",	199	assert (("sorry, no epoll, no sex",
162	ev_supported_backends () & EVBACKEND_EPOLL));	200	ev_supported_backends () & EVBACKEND_EPOLL));
163		201
164	=item unsigned int ev_recommended_backends ()	202	=item unsigned int ev_recommended_backends ()
165		203
166	Return the set of all backends compiled into this binary of libev and also	204	Return the set of all backends compiled into this binary of libev and also
167	recommended for this platform. This set is often smaller than the one	205	recommended for this platform. This set is often smaller than the one
168	returned by C<ev_supported_backends>, as for example kqueue is broken on	206	returned by C<ev_supported_backends>, as for example kqueue is broken on
169	most BSDs and will not be autodetected unless you explicitly request it	207	most BSDs and will not be auto-detected unless you explicitly request it
170	(assuming you know what you are doing). This is the set of backends that	208	(assuming you know what you are doing). This is the set of backends that
171	libev will probe for if you specify no backends explicitly.	209	libev will probe for if you specify no backends explicitly.
172		210
173	=item unsigned int ev_embeddable_backends ()	211	=item unsigned int ev_embeddable_backends ()
174		212
…		…
178	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	216	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
179	recommended ones.	217	recommended ones.
180		218
181	See the description of C<ev_embed> watchers for more info.	219	See the description of C<ev_embed> watchers for more info.
182		220
183	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	221	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
184		222
185	Sets the allocation function to use (the prototype is similar - the	223	Sets the allocation function to use (the prototype is similar - the
186	semantics is identical - to the realloc C function). It is used to	224	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
187	allocate and free memory (no surprises here). If it returns zero when	225	used to allocate and free memory (no surprises here). If it returns zero
188	memory needs to be allocated, the library might abort or take some	226	when memory needs to be allocated (C<size != 0>), the library might abort
189	potentially destructive action. The default is your system realloc	227	or take some potentially destructive action.
190	function.	228
		229	Since some systems (at least OpenBSD and Darwin) fail to implement
		230	correct C<realloc> semantics, libev will use a wrapper around the system
		231	C<realloc> and C<free> functions by default.
191		232
192	You could override this function in high-availability programs to, say,	233	You could override this function in high-availability programs to, say,
193	free some memory if it cannot allocate memory, to use a special allocator,	234	free some memory if it cannot allocate memory, to use a special allocator,
194	or even to sleep a while and retry until some memory is available.	235	or even to sleep a while and retry until some memory is available.
195		236
196	Example: Replace the libev allocator with one that waits a bit and then	237	Example: Replace the libev allocator with one that waits a bit and then
197	retries).	238	retries (example requires a standards-compliant C<realloc>).
198		239
199	static void *	240	static void *
200	persistent_realloc (void *ptr, size_t size)	241	persistent_realloc (void *ptr, size_t size)
201	{	242	{
202	for (;;)	243	for (;;)
…		…
211	}	252	}
212		253
213	...	254	...
214	ev_set_allocator (persistent_realloc);	255	ev_set_allocator (persistent_realloc);
215		256
216	=item ev_set_syserr_cb (void (*cb)(const char *msg));	257	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
217		258
218	Set the callback function to call on a retryable syscall error (such	259	Set the callback function to call on a retryable system call error (such
219	as failed select, poll, epoll_wait). The message is a printable string	260	as failed select, poll, epoll_wait). The message is a printable string
220	indicating the system call or subsystem causing the problem. If this	261	indicating the system call or subsystem causing the problem. If this
221	callback is set, then libev will expect it to remedy the sitution, no	262	callback is set, then libev will expect it to remedy the situation, no
222	matter what, when it returns. That is, libev will generally retry the	263	matter what, when it returns. That is, libev will generally retry the
223	requested operation, or, if the condition doesn't go away, do bad stuff	264	requested operation, or, if the condition doesn't go away, do bad stuff
224	(such as abort).	265	(such as abort).
225		266
226	Example: This is basically the same thing that libev does internally, too.	267	Example: This is basically the same thing that libev does internally, too.
…		…
237		278
238	=back	279	=back
239		280
240	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	281	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
241		282
242	An event loop is described by a C<struct ev_loop *>. The library knows two	283	An event loop is described by a C<struct ev_loop *> (the C<struct>
243	types of such loops, the I<default> loop, which supports signals and child	284	is I<not> optional in this case, as there is also an C<ev_loop>
244	events, and dynamically created loops which do not.	285	I<function>).
245		286
246	If you use threads, a common model is to run the default event loop	287	The library knows two types of such loops, the I<default> loop, which
247	in your main thread (or in a separate thread) and for each thread you	288	supports signals and child events, and dynamically created loops which do
248	create, you also create another event loop. Libev itself does no locking	289	not.
249	whatsoever, so if you mix calls to the same event loop in different
250	threads, make sure you lock (this is usually a bad idea, though, even if
251	done correctly, because it's hideous and inefficient).
252		290
253	=over 4	291	=over 4
254		292
255	=item struct ev_loop *ev_default_loop (unsigned int flags)	293	=item struct ev_loop *ev_default_loop (unsigned int flags)
256		294
…		…
260	flags. If that is troubling you, check C<ev_backend ()> afterwards).	298	flags. If that is troubling you, check C<ev_backend ()> afterwards).
261		299
262	If you don't know what event loop to use, use the one returned from this	300	If you don't know what event loop to use, use the one returned from this
263	function.	301	function.
264		302
		303	Note that this function is I<not> thread-safe, so if you want to use it
		304	from multiple threads, you have to lock (note also that this is unlikely,
		305	as loops cannot be shared easily between threads anyway).
		306
		307	The default loop is the only loop that can handle C<ev_signal> and
		308	C<ev_child> watchers, and to do this, it always registers a handler
		309	for C<SIGCHLD>. If this is a problem for your application you can either
		310	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
		311	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
		312	C<ev_default_init>.
		313
265	The flags argument can be used to specify special behaviour or specific	314	The flags argument can be used to specify special behaviour or specific
266	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	315	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
267		316
268	The following flags are supported:	317	The following flags are supported:
269		318
…		…
274	The default flags value. Use this if you have no clue (it's the right	323	The default flags value. Use this if you have no clue (it's the right
275	thing, believe me).	324	thing, believe me).
276		325
277	=item C<EVFLAG_NOENV>	326	=item C<EVFLAG_NOENV>
278		327
279	If this flag bit is ored into the flag value (or the program runs setuid	328	If this flag bit is or'ed into the flag value (or the program runs setuid
280	or setgid) then libev will I<not> look at the environment variable	329	or setgid) then libev will I<not> look at the environment variable
281	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	330	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
282	override the flags completely if it is found in the environment. This is	331	override the flags completely if it is found in the environment. This is
283	useful to try out specific backends to test their performance, or to work	332	useful to try out specific backends to test their performance, or to work
284	around bugs.	333	around bugs.
…		…
290	enabling this flag.	339	enabling this flag.
291		340
292	This works by calling C<getpid ()> on every iteration of the loop,	341	This works by calling C<getpid ()> on every iteration of the loop,
293	and thus this might slow down your event loop if you do a lot of loop	342	and thus this might slow down your event loop if you do a lot of loop
294	iterations and little real work, but is usually not noticeable (on my	343	iterations and little real work, but is usually not noticeable (on my
295	Linux system for example, C<getpid> is actually a simple 5-insn sequence	344	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
296	without a syscall and thus I<very> fast, but my Linux system also has	345	without a system call and thus I<very> fast, but my GNU/Linux system also has
297	C<pthread_atfork> which is even faster).	346	C<pthread_atfork> which is even faster).
298		347
299	The big advantage of this flag is that you can forget about fork (and	348	The big advantage of this flag is that you can forget about fork (and
300	forget about forgetting to tell libev about forking) when you use this	349	forget about forgetting to tell libev about forking) when you use this
301	flag.	350	flag.
302		351
303	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>	352	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
304	environment variable.	353	environment variable.
305		354
306	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	355	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
307		356
308	This is your standard select(2) backend. Not I<completely> standard, as	357	This is your standard select(2) backend. Not I<completely> standard, as
309	libev tries to roll its own fd_set with no limits on the number of fds,	358	libev tries to roll its own fd_set with no limits on the number of fds,
310	but if that fails, expect a fairly low limit on the number of fds when	359	but if that fails, expect a fairly low limit on the number of fds when
311	using this backend. It doesn't scale too well (O(highest_fd)), but its usually	360	using this backend. It doesn't scale too well (O(highest_fd)), but its
312	the fastest backend for a low number of fds.	361	usually the fastest backend for a low number of (low-numbered :) fds.
		362
		363	To get good performance out of this backend you need a high amount of
		364	parallelism (most of the file descriptors should be busy). If you are
		365	writing a server, you should C<accept ()> in a loop to accept as many
		366	connections as possible during one iteration. You might also want to have
		367	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		368	readiness notifications you get per iteration.
		369
		370	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		371	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		372	C<exceptfds> set on that platform).
313		373
314	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	374	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
315		375
316	And this is your standard poll(2) backend. It's more complicated than	376	And this is your standard poll(2) backend. It's more complicated
317	select, but handles sparse fds better and has no artificial limit on the	377	than select, but handles sparse fds better and has no artificial
318	number of fds you can use (except it will slow down considerably with a	378	limit on the number of fds you can use (except it will slow down
319	lot of inactive fds). It scales similarly to select, i.e. O(total_fds).	379	considerably with a lot of inactive fds). It scales similarly to select,
		380	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		381	performance tips.
		382
		383	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		384	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
320		385
321	=item C<EVBACKEND_EPOLL> (value 4, Linux)	386	=item C<EVBACKEND_EPOLL> (value 4, Linux)
322		387
323	For few fds, this backend is a bit little slower than poll and select,	388	For few fds, this backend is a bit little slower than poll and select,
324	but it scales phenomenally better. While poll and select usually scale	389	but it scales phenomenally better. While poll and select usually scale
325	like O(total_fds) where n is the total number of fds (or the highest fd),	390	like O(total_fds) where n is the total number of fds (or the highest fd),
326	epoll scales either O(1) or O(active_fds). The epoll design has a number	391	epoll scales either O(1) or O(active_fds).
327	of shortcomings, such as silently dropping events in some hard-to-detect	392
328	cases and rewiring a syscall per fd change, no fork support and bad	393	The epoll mechanism deserves honorable mention as the most misdesigned
329	support for dup:	394	of the more advanced event mechanisms: mere annoyances include silently
		395	dropping file descriptors, requiring a system call per change per file
		396	descriptor (and unnecessary guessing of parameters), problems with dup and
		397	so on. The biggest issue is fork races, however - if a program forks then
		398	I<both> parent and child process have to recreate the epoll set, which can
		399	take considerable time (one syscall per file descriptor) and is of course
		400	hard to detect.
		401
		402	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		403	of course I<doesn't>, and epoll just loves to report events for totally
		404	I<different> file descriptors (even already closed ones, so one cannot
		405	even remove them from the set) than registered in the set (especially
		406	on SMP systems). Libev tries to counter these spurious notifications by
		407	employing an additional generation counter and comparing that against the
		408	events to filter out spurious ones, recreating the set when required.
330		409
331	While stopping, setting and starting an I/O watcher in the same iteration	410	While stopping, setting and starting an I/O watcher in the same iteration
332	will result in some caching, there is still a syscall per such incident	411	will result in some caching, there is still a system call per such
333	(because the fd could point to a different file description now), so its	412	incident (because the same I<file descriptor> could point to a different
334	best to avoid that. Also, C<dup ()>'ed file descriptors might not work	413	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
335	very well if you register events for both fds.	414	file descriptors might not work very well if you register events for both
		415	file descriptors.
336		416
337	Please note that epoll sometimes generates spurious notifications, so you	417	Best performance from this backend is achieved by not unregistering all
338	need to use non-blocking I/O or other means to avoid blocking when no data	418	watchers for a file descriptor until it has been closed, if possible,
339	(or space) is available.	419	i.e. keep at least one watcher active per fd at all times. Stopping and
		420	starting a watcher (without re-setting it) also usually doesn't cause
		421	extra overhead. A fork can both result in spurious notifications as well
		422	as in libev having to destroy and recreate the epoll object, which can
		423	take considerable time and thus should be avoided.
		424
		425	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		426	faster than epoll for maybe up to a hundred file descriptors, depending on
		427	the usage. So sad.
		428
		429	While nominally embeddable in other event loops, this feature is broken in
		430	all kernel versions tested so far.
		431
		432	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		433	C<EVBACKEND_POLL>.
340		434
341	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	435	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
342		436
343	Kqueue deserves special mention, as at the time of this writing, it	437	Kqueue deserves special mention, as at the time of this writing, it
344	was broken on I<all> BSDs (usually it doesn't work with anything but	438	was broken on all BSDs except NetBSD (usually it doesn't work reliably
345	sockets and pipes, except on Darwin, where of course it's completely	439	with anything but sockets and pipes, except on Darwin, where of course
346	useless. On NetBSD, it seems to work for all the FD types I tested, so it	440	it's completely useless). Unlike epoll, however, whose brokenness
347	is used by default there). For this reason it's not being "autodetected"	441	is by design, these kqueue bugs can (and eventually will) be fixed
		442	without API changes to existing programs. For this reason it's not being
348	unless you explicitly specify it explicitly in the flags (i.e. using	443	"auto-detected" unless you explicitly specify it in the flags (i.e. using
349	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)	444	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
350	system like NetBSD.	445	system like NetBSD.
351		446
		447	You still can embed kqueue into a normal poll or select backend and use it
		448	only for sockets (after having made sure that sockets work with kqueue on
		449	the target platform). See C<ev_embed> watchers for more info.
		450
352	It scales in the same way as the epoll backend, but the interface to the	451	It scales in the same way as the epoll backend, but the interface to the
353	kernel is more efficient (which says nothing about its actual speed,	452	kernel is more efficient (which says nothing about its actual speed, of
354	of course). While stopping, setting and starting an I/O watcher does	453	course). While stopping, setting and starting an I/O watcher does never
355	never cause an extra syscall as with epoll, it still adds up to two event	454	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
356	changes per incident, support for C<fork ()> is very bad and it drops fds	455	two event changes per incident. Support for C<fork ()> is very bad (but
357	silently in similarly hard-to-detetc cases.	456	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		457	cases
		458
		459	This backend usually performs well under most conditions.
		460
		461	While nominally embeddable in other event loops, this doesn't work
		462	everywhere, so you might need to test for this. And since it is broken
		463	almost everywhere, you should only use it when you have a lot of sockets
		464	(for which it usually works), by embedding it into another event loop
		465	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
		466	also broken on OS X)) and, did I mention it, using it only for sockets.
		467
		468	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		469	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		470	C<NOTE_EOF>.
358		471
359	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	472	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
360		473
361	This is not implemented yet (and might never be).	474	This is not implemented yet (and might never be, unless you send me an
		475	implementation). According to reports, C</dev/poll> only supports sockets
		476	and is not embeddable, which would limit the usefulness of this backend
		477	immensely.
362		478
363	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	479	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
364		480
365	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	481	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
366	it's really slow, but it still scales very well (O(active_fds)).	482	it's really slow, but it still scales very well (O(active_fds)).
367		483
368	Please note that solaris event ports can deliver a lot of spurious	484	Please note that Solaris event ports can deliver a lot of spurious
369	notifications, so you need to use non-blocking I/O or other means to avoid	485	notifications, so you need to use non-blocking I/O or other means to avoid
370	blocking when no data (or space) is available.	486	blocking when no data (or space) is available.
		487
		488	While this backend scales well, it requires one system call per active
		489	file descriptor per loop iteration. For small and medium numbers of file
		490	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		491	might perform better.
		492
		493	On the positive side, with the exception of the spurious readiness
		494	notifications, this backend actually performed fully to specification
		495	in all tests and is fully embeddable, which is a rare feat among the
		496	OS-specific backends (I vastly prefer correctness over speed hacks).
		497
		498	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		499	C<EVBACKEND_POLL>.
371		500
372	=item C<EVBACKEND_ALL>	501	=item C<EVBACKEND_ALL>
373		502
374	Try all backends (even potentially broken ones that wouldn't be tried	503	Try all backends (even potentially broken ones that wouldn't be tried
375	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	504	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
376	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	505	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
377		506
		507	It is definitely not recommended to use this flag.
		508
378	=back	509	=back
379		510
380	If one or more of these are ored into the flags value, then only these	511	If one or more of these are or'ed into the flags value, then only these
381	backends will be tried (in the reverse order as given here). If none are	512	backends will be tried (in the reverse order as listed here). If none are
382	specified, most compiled-in backend will be tried, usually in reverse	513	specified, all backends in C<ev_recommended_backends ()> will be tried.
383	order of their flag values :)
384		514
385	The most typical usage is like this:	515	Example: This is the most typical usage.
386		516
387	if (!ev_default_loop (0))	517	if (!ev_default_loop (0))
388	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	518	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
389		519
390	Restrict libev to the select and poll backends, and do not allow	520	Example: Restrict libev to the select and poll backends, and do not allow
391	environment settings to be taken into account:	521	environment settings to be taken into account:
392		522
393	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	523	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
394		524
395	Use whatever libev has to offer, but make sure that kqueue is used if	525	Example: Use whatever libev has to offer, but make sure that kqueue is
396	available (warning, breaks stuff, best use only with your own private	526	used if available (warning, breaks stuff, best use only with your own
397	event loop and only if you know the OS supports your types of fds):	527	private event loop and only if you know the OS supports your types of
		528	fds):
398		529
399	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	530	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
400		531
401	=item struct ev_loop *ev_loop_new (unsigned int flags)	532	=item struct ev_loop *ev_loop_new (unsigned int flags)
402		533
403	Similar to C<ev_default_loop>, but always creates a new event loop that is	534	Similar to C<ev_default_loop>, but always creates a new event loop that is
404	always distinct from the default loop. Unlike the default loop, it cannot	535	always distinct from the default loop. Unlike the default loop, it cannot
405	handle signal and child watchers, and attempts to do so will be greeted by	536	handle signal and child watchers, and attempts to do so will be greeted by
406	undefined behaviour (or a failed assertion if assertions are enabled).	537	undefined behaviour (or a failed assertion if assertions are enabled).
407		538
		539	Note that this function I<is> thread-safe, and the recommended way to use
		540	libev with threads is indeed to create one loop per thread, and using the
		541	default loop in the "main" or "initial" thread.
		542
408	Example: Try to create a event loop that uses epoll and nothing else.	543	Example: Try to create a event loop that uses epoll and nothing else.
409		544
410	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	545	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
411	if (!epoller)	546	if (!epoller)
412	fatal ("no epoll found here, maybe it hides under your chair");	547	fatal ("no epoll found here, maybe it hides under your chair");
413		548
414	=item ev_default_destroy ()	549	=item ev_default_destroy ()
415		550
416	Destroys the default loop again (frees all memory and kernel state	551	Destroys the default loop again (frees all memory and kernel state
417	etc.). None of the active event watchers will be stopped in the normal	552	etc.). None of the active event watchers will be stopped in the normal
418	sense, so e.g. C<ev_is_active> might still return true. It is your	553	sense, so e.g. C<ev_is_active> might still return true. It is your
419	responsibility to either stop all watchers cleanly yoursef I<before>	554	responsibility to either stop all watchers cleanly yourself I<before>
420	calling this function, or cope with the fact afterwards (which is usually	555	calling this function, or cope with the fact afterwards (which is usually
421	the easiest thing, you can just ignore the watchers and/or C<free ()> them	556	the easiest thing, you can just ignore the watchers and/or C<free ()> them
422	for example).	557	for example).
423		558
424	Note that certain global state, such as signal state, will not be freed by	559	Note that certain global state, such as signal state (and installed signal
425	this function, and related watchers (such as signal and child watchers)	560	handlers), will not be freed by this function, and related watchers (such
426	would need to be stopped manually.	561	as signal and child watchers) would need to be stopped manually.
427		562
428	In general it is not advisable to call this function except in the	563	In general it is not advisable to call this function except in the
429	rare occasion where you really need to free e.g. the signal handling	564	rare occasion where you really need to free e.g. the signal handling
430	pipe fds. If you need dynamically allocated loops it is better to use	565	pipe fds. If you need dynamically allocated loops it is better to use
431	C<ev_loop_new> and C<ev_loop_destroy>).	566	C<ev_loop_new> and C<ev_loop_destroy>).
…		…
435	Like C<ev_default_destroy>, but destroys an event loop created by an	570	Like C<ev_default_destroy>, but destroys an event loop created by an
436	earlier call to C<ev_loop_new>.	571	earlier call to C<ev_loop_new>.
437		572
438	=item ev_default_fork ()	573	=item ev_default_fork ()
439		574
		575	This function sets a flag that causes subsequent C<ev_loop> iterations
440	This function reinitialises the kernel state for backends that have	576	to reinitialise the kernel state for backends that have one. Despite the
441	one. Despite the name, you can call it anytime, but it makes most sense	577	name, you can call it anytime, but it makes most sense after forking, in
442	after forking, in either the parent or child process (or both, but that	578	the child process (or both child and parent, but that again makes little
443	again makes little sense).	579	sense). You I<must> call it in the child before using any of the libev
		580	functions, and it will only take effect at the next C<ev_loop> iteration.
444		581
445	You I<must> call this function in the child process after forking if and	582	On the other hand, you only need to call this function in the child
446	only if you want to use the event library in both processes. If you just	583	process if and only if you want to use the event library in the child. If
447	fork+exec, you don't have to call it.	584	you just fork+exec, you don't have to call it at all.
448		585
449	The function itself is quite fast and it's usually not a problem to call	586	The function itself is quite fast and it's usually not a problem to call
450	it just in case after a fork. To make this easy, the function will fit in	587	it just in case after a fork. To make this easy, the function will fit in
451	quite nicely into a call to C<pthread_atfork>:	588	quite nicely into a call to C<pthread_atfork>:
452		589
453	pthread_atfork (0, 0, ev_default_fork);	590	pthread_atfork (0, 0, ev_default_fork);
454		591
455	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
456	without calling this function, so if you force one of those backends you
457	do not need to care.
458
459	=item ev_loop_fork (loop)	592	=item ev_loop_fork (loop)
460		593
461	Like C<ev_default_fork>, but acts on an event loop created by	594	Like C<ev_default_fork>, but acts on an event loop created by
462	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	595	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
463	after fork, and how you do this is entirely your own problem.	596	after fork that you want to re-use in the child, and how you do this is
		597	entirely your own problem.
		598
		599	=item int ev_is_default_loop (loop)
		600
		601	Returns true when the given loop is, in fact, the default loop, and false
		602	otherwise.
464		603
465	=item unsigned int ev_loop_count (loop)	604	=item unsigned int ev_loop_count (loop)
466		605
467	Returns the count of loop iterations for the loop, which is identical to	606	Returns the count of loop iterations for the loop, which is identical to
468	the number of times libev did poll for new events. It starts at C<0> and	607	the number of times libev did poll for new events. It starts at C<0> and
…		…
483	received events and started processing them. This timestamp does not	622	received events and started processing them. This timestamp does not
484	change as long as callbacks are being processed, and this is also the base	623	change as long as callbacks are being processed, and this is also the base
485	time used for relative timers. You can treat it as the timestamp of the	624	time used for relative timers. You can treat it as the timestamp of the
486	event occurring (or more correctly, libev finding out about it).	625	event occurring (or more correctly, libev finding out about it).
487		626
		627	=item ev_now_update (loop)
		628
		629	Establishes the current time by querying the kernel, updating the time
		630	returned by C<ev_now ()> in the progress. This is a costly operation and
		631	is usually done automatically within C<ev_loop ()>.
		632
		633	This function is rarely useful, but when some event callback runs for a
		634	very long time without entering the event loop, updating libev's idea of
		635	the current time is a good idea.
		636
		637	See also "The special problem of time updates" in the C<ev_timer> section.
		638
488	=item ev_loop (loop, int flags)	639	=item ev_loop (loop, int flags)
489		640
490	Finally, this is it, the event handler. This function usually is called	641	Finally, this is it, the event handler. This function usually is called
491	after you initialised all your watchers and you want to start handling	642	after you initialised all your watchers and you want to start handling
492	events.	643	events.
…		…
494	If the flags argument is specified as C<0>, it will not return until	645	If the flags argument is specified as C<0>, it will not return until
495	either no event watchers are active anymore or C<ev_unloop> was called.	646	either no event watchers are active anymore or C<ev_unloop> was called.
496		647
497	Please note that an explicit C<ev_unloop> is usually better than	648	Please note that an explicit C<ev_unloop> is usually better than
498	relying on all watchers to be stopped when deciding when a program has	649	relying on all watchers to be stopped when deciding when a program has
499	finished (especially in interactive programs), but having a program that	650	finished (especially in interactive programs), but having a program
500	automatically loops as long as it has to and no longer by virtue of	651	that automatically loops as long as it has to and no longer by virtue
501	relying on its watchers stopping correctly is a thing of beauty.	652	of relying on its watchers stopping correctly, that is truly a thing of
		653	beauty.
502		654
503	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	655	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
504	those events and any outstanding ones, but will not block your process in	656	those events and any already outstanding ones, but will not block your
505	case there are no events and will return after one iteration of the loop.	657	process in case there are no events and will return after one iteration of
		658	the loop.
506		659
507	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	660	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
508	neccessary) and will handle those and any outstanding ones. It will block	661	necessary) and will handle those and any already outstanding ones. It
509	your process until at least one new event arrives, and will return after	662	will block your process until at least one new event arrives (which could
510	one iteration of the loop. This is useful if you are waiting for some	663	be an event internal to libev itself, so there is no guarantee that a
511	external event in conjunction with something not expressible using other	664	user-registered callback will be called), and will return after one
		665	iteration of the loop.
		666
		667	This is useful if you are waiting for some external event in conjunction
		668	with something not expressible using other libev watchers (i.e. "roll your
512	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	669	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
513	usually a better approach for this kind of thing.	670	usually a better approach for this kind of thing.
514		671
515	Here are the gory details of what C<ev_loop> does:	672	Here are the gory details of what C<ev_loop> does:
516		673
517	- Before the first iteration, call any pending watchers.	674	- Before the first iteration, call any pending watchers.
518	* If there are no active watchers (reference count is zero), return.	675	* If EVFLAG_FORKCHECK was used, check for a fork.
519	- Queue all prepare watchers and then call all outstanding watchers.	676	- If a fork was detected (by any means), queue and call all fork watchers.
		677	- Queue and call all prepare watchers.
520	- If we have been forked, recreate the kernel state.	678	- If we have been forked, detach and recreate the kernel state
		679	as to not disturb the other process.
521	- Update the kernel state with all outstanding changes.	680	- Update the kernel state with all outstanding changes.
522	- Update the "event loop time".	681	- Update the "event loop time" (ev_now ()).
523	- Calculate for how long to block.	682	- Calculate for how long to sleep or block, if at all
		683	(active idle watchers, EVLOOP_NONBLOCK or not having
		684	any active watchers at all will result in not sleeping).
		685	- Sleep if the I/O and timer collect interval say so.
524	- Block the process, waiting for any events.	686	- Block the process, waiting for any events.
525	- Queue all outstanding I/O (fd) events.	687	- Queue all outstanding I/O (fd) events.
526	- Update the "event loop time" and do time jump handling.	688	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
527	- Queue all outstanding timers.	689	- Queue all expired timers.
528	- Queue all outstanding periodics.	690	- Queue all expired periodics.
529	- If no events are pending now, queue all idle watchers.	691	- Unless any events are pending now, queue all idle watchers.
530	- Queue all check watchers.	692	- Queue all check watchers.
531	- Call all queued watchers in reverse order (i.e. check watchers first).	693	- Call all queued watchers in reverse order (i.e. check watchers first).
532	Signals and child watchers are implemented as I/O watchers, and will	694	Signals and child watchers are implemented as I/O watchers, and will
533	be handled here by queueing them when their watcher gets executed.	695	be handled here by queueing them when their watcher gets executed.
534	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	696	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
535	were used, return, otherwise continue with step *.	697	were used, or there are no active watchers, return, otherwise
		698	continue with step *.
536		699
537	Example: Queue some jobs and then loop until no events are outsanding	700	Example: Queue some jobs and then loop until no events are outstanding
538	anymore.	701	anymore.
539		702
540	... queue jobs here, make sure they register event watchers as long	703	... queue jobs here, make sure they register event watchers as long
541	... as they still have work to do (even an idle watcher will do..)	704	... as they still have work to do (even an idle watcher will do..)
542	ev_loop (my_loop, 0);	705	ev_loop (my_loop, 0);
543	... jobs done. yeah!	706	... jobs done or somebody called unloop. yeah!
544		707
545	=item ev_unloop (loop, how)	708	=item ev_unloop (loop, how)
546		709
547	Can be used to make a call to C<ev_loop> return early (but only after it	710	Can be used to make a call to C<ev_loop> return early (but only after it
548	has processed all outstanding events). The C<how> argument must be either	711	has processed all outstanding events). The C<how> argument must be either
549	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	712	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
550	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	713	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
551		714
		715	This "unloop state" will be cleared when entering C<ev_loop> again.
		716
		717	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
		718
552	=item ev_ref (loop)	719	=item ev_ref (loop)
553		720
554	=item ev_unref (loop)	721	=item ev_unref (loop)
555		722
556	Ref/unref can be used to add or remove a reference count on the event	723	Ref/unref can be used to add or remove a reference count on the event
557	loop: Every watcher keeps one reference, and as long as the reference	724	loop: Every watcher keeps one reference, and as long as the reference
558	count is nonzero, C<ev_loop> will not return on its own. If you have	725	count is nonzero, C<ev_loop> will not return on its own.
		726
559	a watcher you never unregister that should not keep C<ev_loop> from	727	If you have a watcher you never unregister that should not keep C<ev_loop>
560	returning, ev_unref() after starting, and ev_ref() before stopping it. For	728	from returning, call ev_unref() after starting, and ev_ref() before
		729	stopping it.
		730
561	example, libev itself uses this for its internal signal pipe: It is not	731	As an example, libev itself uses this for its internal signal pipe: It is
562	visible to the libev user and should not keep C<ev_loop> from exiting if	732	not visible to the libev user and should not keep C<ev_loop> from exiting
563	no event watchers registered by it are active. It is also an excellent	733	if no event watchers registered by it are active. It is also an excellent
564	way to do this for generic recurring timers or from within third-party	734	way to do this for generic recurring timers or from within third-party
565	libraries. Just remember to I<unref after start> and I<ref before stop>.	735	libraries. Just remember to I<unref after start> and I<ref before stop>
		736	(but only if the watcher wasn't active before, or was active before,
		737	respectively).
566		738
567	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	739	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
568	running when nothing else is active.	740	running when nothing else is active.
569		741
570	struct ev_signal exitsig;	742	ev_signal exitsig;
571	ev_signal_init (&exitsig, sig_cb, SIGINT);	743	ev_signal_init (&exitsig, sig_cb, SIGINT);
572	ev_signal_start (loop, &exitsig);	744	ev_signal_start (loop, &exitsig);
573	evf_unref (loop);	745	evf_unref (loop);
574		746
575	Example: For some weird reason, unregister the above signal handler again.	747	Example: For some weird reason, unregister the above signal handler again.
576		748
577	ev_ref (loop);	749	ev_ref (loop);
578	ev_signal_stop (loop, &exitsig);	750	ev_signal_stop (loop, &exitsig);
579		751
580	=item ev_set_io_collect_interval (loop, ev_tstamp interval)	752	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
581		753
582	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)	754	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
583		755
584	These advanced functions influence the time that libev will spend waiting	756	These advanced functions influence the time that libev will spend waiting
585	for events. Both are by default C<0>, meaning that libev will try to	757	for events. Both time intervals are by default C<0>, meaning that libev
586	invoke timer/periodic callbacks and I/O callbacks with minimum latency.	758	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		759	latency.
587		760
588	Setting these to a higher value (the C<interval> I<must> be >= C<0>)	761	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
589	allows libev to delay invocation of I/O and timer/periodic callbacks to	762	allows libev to delay invocation of I/O and timer/periodic callbacks
590	increase efficiency of loop iterations.	763	to increase efficiency of loop iterations (or to increase power-saving
		764	opportunities).
591		765
592	The background is that sometimes your program runs just fast enough to	766	The idea is that sometimes your program runs just fast enough to handle
593	handle one (or very few) event(s) per loop iteration. While this makes	767	one (or very few) event(s) per loop iteration. While this makes the
594	the program responsive, it also wastes a lot of CPU time to poll for new	768	program responsive, it also wastes a lot of CPU time to poll for new
595	events, especially with backends like C<select ()> which have a high	769	events, especially with backends like C<select ()> which have a high
596	overhead for the actual polling but can deliver many events at once.	770	overhead for the actual polling but can deliver many events at once.
597		771
598	By setting a higher I<io collect interval> you allow libev to spend more	772	By setting a higher I<io collect interval> you allow libev to spend more
599	time collecting I/O events, so you can handle more events per iteration,	773	time collecting I/O events, so you can handle more events per iteration,
600	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	774	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
601	C<ev_timer>) will be not affected.	775	C<ev_timer>) will be not affected. Setting this to a non-null value will
		776	introduce an additional C<ev_sleep ()> call into most loop iterations.
602		777
603	Likewise, by setting a higher I<timeout collect interval> you allow libev	778	Likewise, by setting a higher I<timeout collect interval> you allow libev
604	to spend more time collecting timeouts, at the expense of increased	779	to spend more time collecting timeouts, at the expense of increased
605	latency (the watcher callback will be called later). C<ev_io> watchers	780	latency/jitter/inexactness (the watcher callback will be called
606	will not be affected.	781	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		782	value will not introduce any overhead in libev.
607		783
608	Many (busy) programs can usually benefit by setting the io collect	784	Many (busy) programs can usually benefit by setting the I/O collect
609	interval to a value near C<0.1> or so, which is often enough for	785	interval to a value near C<0.1> or so, which is often enough for
610	interactive servers (of course not for games), likewise for timeouts. It	786	interactive servers (of course not for games), likewise for timeouts. It
611	usually doesn't make much sense to set it to a lower value than C<0.01>,	787	usually doesn't make much sense to set it to a lower value than C<0.01>,
612	as this approsaches the timing granularity of most systems.	788	as this approaches the timing granularity of most systems.
		789
		790	Setting the I<timeout collect interval> can improve the opportunity for
		791	saving power, as the program will "bundle" timer callback invocations that
		792	are "near" in time together, by delaying some, thus reducing the number of
		793	times the process sleeps and wakes up again. Another useful technique to
		794	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		795	they fire on, say, one-second boundaries only.
		796
		797	=item ev_loop_verify (loop)
		798
		799	This function only does something when C<EV_VERIFY> support has been
		800	compiled in, which is the default for non-minimal builds. It tries to go
		801	through all internal structures and checks them for validity. If anything
		802	is found to be inconsistent, it will print an error message to standard
		803	error and call C<abort ()>.
		804
		805	This can be used to catch bugs inside libev itself: under normal
		806	circumstances, this function will never abort as of course libev keeps its
		807	data structures consistent.
613		808
614	=back	809	=back
615		810
616		811
617	=head1 ANATOMY OF A WATCHER	812	=head1 ANATOMY OF A WATCHER
		813
		814	In the following description, uppercase C<TYPE> in names stands for the
		815	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		816	watchers and C<ev_io_start> for I/O watchers.
618		817
619	A watcher is a structure that you create and register to record your	818	A watcher is a structure that you create and register to record your
620	interest in some event. For instance, if you want to wait for STDIN to	819	interest in some event. For instance, if you want to wait for STDIN to
621	become readable, you would create an C<ev_io> watcher for that:	820	become readable, you would create an C<ev_io> watcher for that:
622		821
623	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	822	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
624	{	823	{
625	ev_io_stop (w);	824	ev_io_stop (w);
626	ev_unloop (loop, EVUNLOOP_ALL);	825	ev_unloop (loop, EVUNLOOP_ALL);
627	}	826	}
628		827
629	struct ev_loop *loop = ev_default_loop (0);	828	struct ev_loop *loop = ev_default_loop (0);
		829
630	struct ev_io stdin_watcher;	830	ev_io stdin_watcher;
		831
631	ev_init (&stdin_watcher, my_cb);	832	ev_init (&stdin_watcher, my_cb);
632	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	833	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
633	ev_io_start (loop, &stdin_watcher);	834	ev_io_start (loop, &stdin_watcher);
		835
634	ev_loop (loop, 0);	836	ev_loop (loop, 0);
635		837
636	As you can see, you are responsible for allocating the memory for your	838	As you can see, you are responsible for allocating the memory for your
637	watcher structures (and it is usually a bad idea to do this on the stack,	839	watcher structures (and it is I<usually> a bad idea to do this on the
638	although this can sometimes be quite valid).	840	stack).
		841
		842	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		843	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
639		844
640	Each watcher structure must be initialised by a call to C<ev_init	845	Each watcher structure must be initialised by a call to C<ev_init
641	(watcher *, callback)>, which expects a callback to be provided. This	846	(watcher *, callback)>, which expects a callback to be provided. This
642	callback gets invoked each time the event occurs (or, in the case of io	847	callback gets invoked each time the event occurs (or, in the case of I/O
643	watchers, each time the event loop detects that the file descriptor given	848	watchers, each time the event loop detects that the file descriptor given
644	is readable and/or writable).	849	is readable and/or writable).
645		850
646	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	851	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
647	with arguments specific to this watcher type. There is also a macro	852	macro to configure it, with arguments specific to the watcher type. There
648	to combine initialisation and setting in one call: C<< ev_<type>_init	853	is also a macro to combine initialisation and setting in one call: C<<
649	(watcher *, callback, ...) >>.	854	ev_TYPE_init (watcher *, callback, ...) >>.
650		855
651	To make the watcher actually watch out for events, you have to start it	856	To make the watcher actually watch out for events, you have to start it
652	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	857	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
653	*) >>), and you can stop watching for events at any time by calling the	858	*) >>), and you can stop watching for events at any time by calling the
654	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	859	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
655		860
656	As long as your watcher is active (has been started but not stopped) you	861	As long as your watcher is active (has been started but not stopped) you
657	must not touch the values stored in it. Most specifically you must never	862	must not touch the values stored in it. Most specifically you must never
658	reinitialise it or call its C<set> macro.	863	reinitialise it or call its C<ev_TYPE_set> macro.
659		864
660	Each and every callback receives the event loop pointer as first, the	865	Each and every callback receives the event loop pointer as first, the
661	registered watcher structure as second, and a bitset of received events as	866	registered watcher structure as second, and a bitset of received events as
662	third argument.	867	third argument.
663		868
…		…
717	=item C<EV_FORK>	922	=item C<EV_FORK>
718		923
719	The event loop has been resumed in the child process after fork (see	924	The event loop has been resumed in the child process after fork (see
720	C<ev_fork>).	925	C<ev_fork>).
721		926
		927	=item C<EV_ASYNC>
		928
		929	The given async watcher has been asynchronously notified (see C<ev_async>).
		930
722	=item C<EV_ERROR>	931	=item C<EV_ERROR>
723		932
724	An unspecified error has occured, the watcher has been stopped. This might	933	An unspecified error has occurred, the watcher has been stopped. This might
725	happen because the watcher could not be properly started because libev	934	happen because the watcher could not be properly started because libev
726	ran out of memory, a file descriptor was found to be closed or any other	935	ran out of memory, a file descriptor was found to be closed or any other
		936	problem. Libev considers these application bugs.
		937
727	problem. You best act on it by reporting the problem and somehow coping	938	You best act on it by reporting the problem and somehow coping with the
728	with the watcher being stopped.	939	watcher being stopped. Note that well-written programs should not receive
		940	an error ever, so when your watcher receives it, this usually indicates a
		941	bug in your program.
729		942
730	Libev will usually signal a few "dummy" events together with an error,	943	Libev will usually signal a few "dummy" events together with an error, for
731	for example it might indicate that a fd is readable or writable, and if	944	example it might indicate that a fd is readable or writable, and if your
732	your callbacks is well-written it can just attempt the operation and cope	945	callbacks is well-written it can just attempt the operation and cope with
733	with the error from read() or write(). This will not work in multithreaded	946	the error from read() or write(). This will not work in multi-threaded
734	programs, though, so beware.	947	programs, though, as the fd could already be closed and reused for another
		948	thing, so beware.
735		949
736	=back	950	=back
737		951
738	=head2 GENERIC WATCHER FUNCTIONS	952	=head2 GENERIC WATCHER FUNCTIONS
739
740	In the following description, C<TYPE> stands for the watcher type,
741	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
742		953
743	=over 4	954	=over 4
744		955
745	=item C<ev_init> (ev_TYPE *watcher, callback)	956	=item C<ev_init> (ev_TYPE *watcher, callback)
746		957
…		…
752	which rolls both calls into one.	963	which rolls both calls into one.
753		964
754	You can reinitialise a watcher at any time as long as it has been stopped	965	You can reinitialise a watcher at any time as long as it has been stopped
755	(or never started) and there are no pending events outstanding.	966	(or never started) and there are no pending events outstanding.
756		967
757	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	968	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
758	int revents)>.	969	int revents)>.
		970
		971	Example: Initialise an C<ev_io> watcher in two steps.
		972
		973	ev_io w;
		974	ev_init (&w, my_cb);
		975	ev_io_set (&w, STDIN_FILENO, EV_READ);
759		976
760	=item C<ev_TYPE_set> (ev_TYPE *, [args])	977	=item C<ev_TYPE_set> (ev_TYPE *, [args])
761		978
762	This macro initialises the type-specific parts of a watcher. You need to	979	This macro initialises the type-specific parts of a watcher. You need to
763	call C<ev_init> at least once before you call this macro, but you can	980	call C<ev_init> at least once before you call this macro, but you can
…		…
766	difference to the C<ev_init> macro).	983	difference to the C<ev_init> macro).
767		984
768	Although some watcher types do not have type-specific arguments	985	Although some watcher types do not have type-specific arguments
769	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	986	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
770		987
		988	See C<ev_init>, above, for an example.
		989
771	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	990	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
772		991
773	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	992	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
774	calls into a single call. This is the most convinient method to initialise	993	calls into a single call. This is the most convenient method to initialise
775	a watcher. The same limitations apply, of course.	994	a watcher. The same limitations apply, of course.
		995
		996	Example: Initialise and set an C<ev_io> watcher in one step.
		997
		998	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
776		999
777	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1000	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
778		1001
779	Starts (activates) the given watcher. Only active watchers will receive	1002	Starts (activates) the given watcher. Only active watchers will receive
780	events. If the watcher is already active nothing will happen.	1003	events. If the watcher is already active nothing will happen.
781		1004
		1005	Example: Start the C<ev_io> watcher that is being abused as example in this
		1006	whole section.
		1007
		1008	ev_io_start (EV_DEFAULT_UC, &w);
		1009
782	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1010	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
783		1011
784	Stops the given watcher again (if active) and clears the pending	1012	Stops the given watcher if active, and clears the pending status (whether
		1013	the watcher was active or not).
		1014
785	status. It is possible that stopped watchers are pending (for example,	1015	It is possible that stopped watchers are pending - for example,
786	non-repeating timers are being stopped when they become pending), but	1016	non-repeating timers are being stopped when they become pending - but
787	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1017	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
788	you want to free or reuse the memory used by the watcher it is therefore a	1018	pending. If you want to free or reuse the memory used by the watcher it is
789	good idea to always call its C<ev_TYPE_stop> function.	1019	therefore a good idea to always call its C<ev_TYPE_stop> function.
790		1020
791	=item bool ev_is_active (ev_TYPE *watcher)	1021	=item bool ev_is_active (ev_TYPE *watcher)
792		1022
793	Returns a true value iff the watcher is active (i.e. it has been started	1023	Returns a true value iff the watcher is active (i.e. it has been started
794	and not yet been stopped). As long as a watcher is active you must not modify	1024	and not yet been stopped). As long as a watcher is active you must not modify
…		…
836	The default priority used by watchers when no priority has been set is	1066	The default priority used by watchers when no priority has been set is
837	always C<0>, which is supposed to not be too high and not be too low :).	1067	always C<0>, which is supposed to not be too high and not be too low :).
838		1068
839	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1069	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
840	fine, as long as you do not mind that the priority value you query might	1070	fine, as long as you do not mind that the priority value you query might
841	or might not have been adjusted to be within valid range.	1071	or might not have been clamped to the valid range.
842		1072
843	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1073	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
844		1074
845	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1075	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
846	C<loop> nor C<revents> need to be valid as long as the watcher callback	1076	C<loop> nor C<revents> need to be valid as long as the watcher callback
847	can deal with that fact.	1077	can deal with that fact, as both are simply passed through to the
		1078	callback.
848		1079
849	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1080	=item int ev_clear_pending (loop, ev_TYPE *watcher)
850		1081
851	If the watcher is pending, this function returns clears its pending status	1082	If the watcher is pending, this function clears its pending status and
852	and returns its C<revents> bitset (as if its callback was invoked). If the	1083	returns its C<revents> bitset (as if its callback was invoked). If the
853	watcher isn't pending it does nothing and returns C<0>.	1084	watcher isn't pending it does nothing and returns C<0>.
854		1085
		1086	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1087	callback to be invoked, which can be accomplished with this function.
		1088
855	=back	1089	=back
856		1090
857		1091
858	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1092	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
859		1093
860	Each watcher has, by default, a member C<void *data> that you can change	1094	Each watcher has, by default, a member C<void *data> that you can change
861	and read at any time, libev will completely ignore it. This can be used	1095	and read at any time: libev will completely ignore it. This can be used
862	to associate arbitrary data with your watcher. If you need more data and	1096	to associate arbitrary data with your watcher. If you need more data and
863	don't want to allocate memory and store a pointer to it in that data	1097	don't want to allocate memory and store a pointer to it in that data
864	member, you can also "subclass" the watcher type and provide your own	1098	member, you can also "subclass" the watcher type and provide your own
865	data:	1099	data:
866		1100
867	struct my_io	1101	struct my_io
868	{	1102	{
869	struct ev_io io;	1103	ev_io io;
870	int otherfd;	1104	int otherfd;
871	void *somedata;	1105	void *somedata;
872	struct whatever *mostinteresting;	1106	struct whatever *mostinteresting;
873	}	1107	};
		1108
		1109	...
		1110	struct my_io w;
		1111	ev_io_init (&w.io, my_cb, fd, EV_READ);
874		1112
875	And since your callback will be called with a pointer to the watcher, you	1113	And since your callback will be called with a pointer to the watcher, you
876	can cast it back to your own type:	1114	can cast it back to your own type:
877		1115
878	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1116	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
879	{	1117	{
880	struct my_io *w = (struct my_io *)w_;	1118	struct my_io *w = (struct my_io *)w_;
881	...	1119	...
882	}	1120	}
883		1121
884	More interesting and less C-conformant ways of casting your callback type	1122	More interesting and less C-conformant ways of casting your callback type
885	instead have been omitted.	1123	instead have been omitted.
886		1124
887	Another common scenario is having some data structure with multiple	1125	Another common scenario is to use some data structure with multiple
888	watchers:	1126	embedded watchers:
889		1127
890	struct my_biggy	1128	struct my_biggy
891	{	1129	{
892	int some_data;	1130	int some_data;
893	ev_timer t1;	1131	ev_timer t1;
894	ev_timer t2;	1132	ev_timer t2;
895	}	1133	}
896		1134
897	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1135	In this case getting the pointer to C<my_biggy> is a bit more
898	you need to use C<offsetof>:	1136	complicated: Either you store the address of your C<my_biggy> struct
		1137	in the C<data> member of the watcher (for woozies), or you need to use
		1138	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1139	programmers):
899		1140
900	#include <stddef.h>	1141	#include <stddef.h>
901		1142
902	static void	1143	static void
903	t1_cb (EV_P_ struct ev_timer *w, int revents)	1144	t1_cb (EV_P_ ev_timer *w, int revents)
904	{	1145	{
905	struct my_biggy big = (struct my_biggy *	1146	struct my_biggy big = (struct my_biggy *
906	(((char *)w) - offsetof (struct my_biggy, t1));	1147	(((char *)w) - offsetof (struct my_biggy, t1));
907	}	1148	}
908		1149
909	static void	1150	static void
910	t2_cb (EV_P_ struct ev_timer *w, int revents)	1151	t2_cb (EV_P_ ev_timer *w, int revents)
911	{	1152	{
912	struct my_biggy big = (struct my_biggy *	1153	struct my_biggy big = (struct my_biggy *
913	(((char *)w) - offsetof (struct my_biggy, t2));	1154	(((char *)w) - offsetof (struct my_biggy, t2));
914	}	1155	}
915		1156
916		1157
917	=head1 WATCHER TYPES	1158	=head1 WATCHER TYPES
918		1159
919	This section describes each watcher in detail, but will not repeat	1160	This section describes each watcher in detail, but will not repeat
…		…
943	In general you can register as many read and/or write event watchers per	1184	In general you can register as many read and/or write event watchers per
944	fd as you want (as long as you don't confuse yourself). Setting all file	1185	fd as you want (as long as you don't confuse yourself). Setting all file
945	descriptors to non-blocking mode is also usually a good idea (but not	1186	descriptors to non-blocking mode is also usually a good idea (but not
946	required if you know what you are doing).	1187	required if you know what you are doing).
947		1188
948	You have to be careful with dup'ed file descriptors, though. Some backends	1189	If you cannot use non-blocking mode, then force the use of a
949	(the linux epoll backend is a notable example) cannot handle dup'ed file	1190	known-to-be-good backend (at the time of this writing, this includes only
950	descriptors correctly if you register interest in two or more fds pointing	1191	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>).
951	to the same underlying file/socket/etc. description (that is, they share
952	the same underlying "file open").
953
954	If you must do this, then force the use of a known-to-be-good backend
955	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
956	C<EVBACKEND_POLL>).
957		1192
958	Another thing you have to watch out for is that it is quite easy to	1193	Another thing you have to watch out for is that it is quite easy to
959	receive "spurious" readyness notifications, that is your callback might	1194	receive "spurious" readiness notifications, that is your callback might
960	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1195	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
961	because there is no data. Not only are some backends known to create a	1196	because there is no data. Not only are some backends known to create a
962	lot of those (for example solaris ports), it is very easy to get into	1197	lot of those (for example Solaris ports), it is very easy to get into
963	this situation even with a relatively standard program structure. Thus	1198	this situation even with a relatively standard program structure. Thus
964	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1199	it is best to always use non-blocking I/O: An extra C<read>(2) returning
965	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1200	C<EAGAIN> is far preferable to a program hanging until some data arrives.
966		1201
967	If you cannot run the fd in non-blocking mode (for example you should not	1202	If you cannot run the fd in non-blocking mode (for example you should
968	play around with an Xlib connection), then you have to seperately re-test	1203	not play around with an Xlib connection), then you have to separately
969	whether a file descriptor is really ready with a known-to-be good interface	1204	re-test whether a file descriptor is really ready with a known-to-be good
970	such as poll (fortunately in our Xlib example, Xlib already does this on	1205	interface such as poll (fortunately in our Xlib example, Xlib already
971	its own, so its quite safe to use).	1206	does this on its own, so its quite safe to use). Some people additionally
		1207	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1208	indefinitely.
		1209
		1210	But really, best use non-blocking mode.
972		1211
973	=head3 The special problem of disappearing file descriptors	1212	=head3 The special problem of disappearing file descriptors
974		1213
975	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1214	Some backends (e.g. kqueue, epoll) need to be told about closing a file
976	descriptor (either by calling C<close> explicitly or by any other means,	1215	descriptor (either due to calling C<close> explicitly or any other means,
977	such as C<dup>). The reason is that you register interest in some file	1216	such as C<dup2>). The reason is that you register interest in some file
978	descriptor, but when it goes away, the operating system will silently drop	1217	descriptor, but when it goes away, the operating system will silently drop
979	this interest. If another file descriptor with the same number then is	1218	this interest. If another file descriptor with the same number then is
980	registered with libev, there is no efficient way to see that this is, in	1219	registered with libev, there is no efficient way to see that this is, in
981	fact, a different file descriptor.	1220	fact, a different file descriptor.
982		1221
…		…
992	optimisations to libev.	1231	optimisations to libev.
993		1232
994	=head3 The special problem of dup'ed file descriptors	1233	=head3 The special problem of dup'ed file descriptors
995		1234
996	Some backends (e.g. epoll), cannot register events for file descriptors,	1235	Some backends (e.g. epoll), cannot register events for file descriptors,
997	but only events for the underlying file descriptions. That menas when you	1236	but only events for the underlying file descriptions. That means when you
998	have C<dup ()>'ed file descriptors and register events for them, only one	1237	have C<dup ()>'ed file descriptors or weirder constellations, and register
999	file descriptor might actually receive events.	1238	events for them, only one file descriptor might actually receive events.
1000		1239
1001	There is no workaorund possible except not registering events	1240	There is no workaround possible except not registering events
1002	for potentially C<dup ()>'ed file descriptors or to resort to	1241	for potentially C<dup ()>'ed file descriptors, or to resort to
1003	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1242	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1004		1243
1005	=head3 The special problem of fork	1244	=head3 The special problem of fork
1006		1245
1007	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1246	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
…		…
1011	To support fork in your programs, you either have to call	1250	To support fork in your programs, you either have to call
1012	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1251	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
1013	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1252	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
1014	C<EVBACKEND_POLL>.	1253	C<EVBACKEND_POLL>.
1015		1254
		1255	=head3 The special problem of SIGPIPE
		1256
		1257	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1258	when writing to a pipe whose other end has been closed, your program gets
		1259	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1260	this is sensible behaviour, for daemons, this is usually undesirable.
		1261
		1262	So when you encounter spurious, unexplained daemon exits, make sure you
		1263	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1264	somewhere, as that would have given you a big clue).
		1265
1016		1266
1017	=head3 Watcher-Specific Functions	1267	=head3 Watcher-Specific Functions
1018		1268
1019	=over 4	1269	=over 4
1020		1270
1021	=item ev_io_init (ev_io *, callback, int fd, int events)	1271	=item ev_io_init (ev_io *, callback, int fd, int events)
1022		1272
1023	=item ev_io_set (ev_io *, int fd, int events)	1273	=item ev_io_set (ev_io *, int fd, int events)
1024		1274
1025	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1275	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
1026	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1276	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
1027	C<EV_READ | EV_WRITE> to receive the given events.	1277	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
1028		1278
1029	=item int fd [read-only]	1279	=item int fd [read-only]
1030		1280
1031	The file descriptor being watched.	1281	The file descriptor being watched.
1032		1282
1033	=item int events [read-only]	1283	=item int events [read-only]
1034		1284
1035	The events being watched.	1285	The events being watched.
1036		1286
1037	=back	1287	=back
		1288
		1289	=head3 Examples
1038		1290
1039	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1291	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1040	readable, but only once. Since it is likely line-buffered, you could	1292	readable, but only once. Since it is likely line-buffered, you could
1041	attempt to read a whole line in the callback.	1293	attempt to read a whole line in the callback.
1042		1294
1043	static void	1295	static void
1044	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1296	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1045	{	1297	{
1046	ev_io_stop (loop, w);	1298	ev_io_stop (loop, w);
1047	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1299	.. read from stdin here (or from w->fd) and handle any I/O errors
1048	}	1300	}
1049		1301
1050	...	1302	...
1051	struct ev_loop *loop = ev_default_init (0);	1303	struct ev_loop *loop = ev_default_init (0);
1052	struct ev_io stdin_readable;	1304	ev_io stdin_readable;
1053	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1305	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1054	ev_io_start (loop, &stdin_readable);	1306	ev_io_start (loop, &stdin_readable);
1055	ev_loop (loop, 0);	1307	ev_loop (loop, 0);
1056		1308
1057		1309
1058	=head2 C<ev_timer> - relative and optionally repeating timeouts	1310	=head2 C<ev_timer> - relative and optionally repeating timeouts
1059		1311
1060	Timer watchers are simple relative timers that generate an event after a	1312	Timer watchers are simple relative timers that generate an event after a
1061	given time, and optionally repeating in regular intervals after that.	1313	given time, and optionally repeating in regular intervals after that.
1062		1314
1063	The timers are based on real time, that is, if you register an event that	1315	The timers are based on real time, that is, if you register an event that
1064	times out after an hour and you reset your system clock to last years	1316	times out after an hour and you reset your system clock to January last
1065	time, it will still time out after (roughly) and hour. "Roughly" because	1317	year, it will still time out after (roughly) one hour. "Roughly" because
1066	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1318	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1067	monotonic clock option helps a lot here).	1319	monotonic clock option helps a lot here).
		1320
		1321	The callback is guaranteed to be invoked only I<after> its timeout has
		1322	passed, but if multiple timers become ready during the same loop iteration
		1323	then order of execution is undefined.
		1324
		1325	=head3 Be smart about timeouts
		1326
		1327	Many real-world problems involve some kind of timeout, usually for error
		1328	recovery. A typical example is an HTTP request - if the other side hangs,
		1329	you want to raise some error after a while.
		1330
		1331	What follows are some ways to handle this problem, from obvious and
		1332	inefficient to smart and efficient.
		1333
		1334	In the following, a 60 second activity timeout is assumed - a timeout that
		1335	gets reset to 60 seconds each time there is activity (e.g. each time some
		1336	data or other life sign was received).
		1337
		1338	=over 4
		1339
		1340	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1341
		1342	This is the most obvious, but not the most simple way: In the beginning,
		1343	start the watcher:
		1344
		1345	ev_timer_init (timer, callback, 60., 0.);
		1346	ev_timer_start (loop, timer);
		1347
		1348	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1349	and start it again:
		1350
		1351	ev_timer_stop (loop, timer);
		1352	ev_timer_set (timer, 60., 0.);
		1353	ev_timer_start (loop, timer);
		1354
		1355	This is relatively simple to implement, but means that each time there is
		1356	some activity, libev will first have to remove the timer from its internal
		1357	data structure and then add it again. Libev tries to be fast, but it's
		1358	still not a constant-time operation.
		1359
		1360	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1361
		1362	This is the easiest way, and involves using C<ev_timer_again> instead of
		1363	C<ev_timer_start>.
		1364
		1365	To implement this, configure an C<ev_timer> with a C<repeat> value
		1366	of C<60> and then call C<ev_timer_again> at start and each time you
		1367	successfully read or write some data. If you go into an idle state where
		1368	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1369	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1370
		1371	That means you can ignore both the C<ev_timer_start> function and the
		1372	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1373	member and C<ev_timer_again>.
		1374
		1375	At start:
		1376
		1377	ev_timer_init (timer, callback);
		1378	timer->repeat = 60.;
		1379	ev_timer_again (loop, timer);
		1380
		1381	Each time there is some activity:
		1382
		1383	ev_timer_again (loop, timer);
		1384
		1385	It is even possible to change the time-out on the fly, regardless of
		1386	whether the watcher is active or not:
		1387
		1388	timer->repeat = 30.;
		1389	ev_timer_again (loop, timer);
		1390
		1391	This is slightly more efficient then stopping/starting the timer each time
		1392	you want to modify its timeout value, as libev does not have to completely
		1393	remove and re-insert the timer from/into its internal data structure.
		1394
		1395	It is, however, even simpler than the "obvious" way to do it.
		1396
		1397	=item 3. Let the timer time out, but then re-arm it as required.
		1398
		1399	This method is more tricky, but usually most efficient: Most timeouts are
		1400	relatively long compared to the intervals between other activity - in
		1401	our example, within 60 seconds, there are usually many I/O events with
		1402	associated activity resets.
		1403
		1404	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1405	but remember the time of last activity, and check for a real timeout only
		1406	within the callback:
		1407
		1408	ev_tstamp last_activity; // time of last activity
		1409
		1410	static void
		1411	callback (EV_P_ ev_timer *w, int revents)
		1412	{
		1413	ev_tstamp now = ev_now (EV_A);
		1414	ev_tstamp timeout = last_activity + 60.;
		1415
		1416	// if last_activity + 60. is older than now, we did time out
		1417	if (timeout < now)
		1418	{
		1419	// timeout occured, take action
		1420	}
		1421	else
		1422	{
		1423	// callback was invoked, but there was some activity, re-arm
		1424	// the watcher to fire in last_activity + 60, which is
		1425	// guaranteed to be in the future, so "again" is positive:
		1426	w->repeat = timeout - now;
		1427	ev_timer_again (EV_A_ w);
		1428	}
		1429	}
		1430
		1431	To summarise the callback: first calculate the real timeout (defined
		1432	as "60 seconds after the last activity"), then check if that time has
		1433	been reached, which means something I<did>, in fact, time out. Otherwise
		1434	the callback was invoked too early (C<timeout> is in the future), so
		1435	re-schedule the timer to fire at that future time, to see if maybe we have
		1436	a timeout then.
		1437
		1438	Note how C<ev_timer_again> is used, taking advantage of the
		1439	C<ev_timer_again> optimisation when the timer is already running.
		1440
		1441	This scheme causes more callback invocations (about one every 60 seconds
		1442	minus half the average time between activity), but virtually no calls to
		1443	libev to change the timeout.
		1444
		1445	To start the timer, simply initialise the watcher and set C<last_activity>
		1446	to the current time (meaning we just have some activity :), then call the
		1447	callback, which will "do the right thing" and start the timer:
		1448
		1449	ev_timer_init (timer, callback);
		1450	last_activity = ev_now (loop);
		1451	callback (loop, timer, EV_TIMEOUT);
		1452
		1453	And when there is some activity, simply store the current time in
		1454	C<last_activity>, no libev calls at all:
		1455
		1456	last_actiivty = ev_now (loop);
		1457
		1458	This technique is slightly more complex, but in most cases where the
		1459	time-out is unlikely to be triggered, much more efficient.
		1460
		1461	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1462	callback :) - just change the timeout and invoke the callback, which will
		1463	fix things for you.
		1464
		1465	=item 4. Wee, just use a double-linked list for your timeouts.
		1466
		1467	If there is not one request, but many thousands (millions...), all
		1468	employing some kind of timeout with the same timeout value, then one can
		1469	do even better:
		1470
		1471	When starting the timeout, calculate the timeout value and put the timeout
		1472	at the I<end> of the list.
		1473
		1474	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1475	the list is expected to fire (for example, using the technique #3).
		1476
		1477	When there is some activity, remove the timer from the list, recalculate
		1478	the timeout, append it to the end of the list again, and make sure to
		1479	update the C<ev_timer> if it was taken from the beginning of the list.
		1480
		1481	This way, one can manage an unlimited number of timeouts in O(1) time for
		1482	starting, stopping and updating the timers, at the expense of a major
		1483	complication, and having to use a constant timeout. The constant timeout
		1484	ensures that the list stays sorted.
		1485
		1486	=back
		1487
		1488	So which method the best?
		1489
		1490	Method #2 is a simple no-brain-required solution that is adequate in most
		1491	situations. Method #3 requires a bit more thinking, but handles many cases
		1492	better, and isn't very complicated either. In most case, choosing either
		1493	one is fine, with #3 being better in typical situations.
		1494
		1495	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1496	rather complicated, but extremely efficient, something that really pays
		1497	off after the first million or so of active timers, i.e. it's usually
		1498	overkill :)
		1499
		1500	=head3 The special problem of time updates
		1501
		1502	Establishing the current time is a costly operation (it usually takes at
		1503	least two system calls): EV therefore updates its idea of the current
		1504	time only before and after C<ev_loop> collects new events, which causes a
		1505	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1506	lots of events in one iteration.
1068		1507
1069	The relative timeouts are calculated relative to the C<ev_now ()>	1508	The relative timeouts are calculated relative to the C<ev_now ()>
1070	time. This is usually the right thing as this timestamp refers to the time	1509	time. This is usually the right thing as this timestamp refers to the time
1071	of the event triggering whatever timeout you are modifying/starting. If	1510	of the event triggering whatever timeout you are modifying/starting. If
1072	you suspect event processing to be delayed and you I<need> to base the timeout	1511	you suspect event processing to be delayed and you I<need> to base the
1073	on the current time, use something like this to adjust for this:	1512	timeout on the current time, use something like this to adjust for this:
1074		1513
1075	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1514	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1076		1515
1077	The callback is guarenteed to be invoked only when its timeout has passed,	1516	If the event loop is suspended for a long time, you can also force an
1078	but if multiple timers become ready during the same loop iteration then	1517	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1079	order of execution is undefined.	1518	()>.
1080		1519
1081	=head3 Watcher-Specific Functions and Data Members	1520	=head3 Watcher-Specific Functions and Data Members
1082		1521
1083	=over 4	1522	=over 4
1084		1523
1085	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1524	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1086		1525
1087	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1526	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1088		1527
1089	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1528	Configure the timer to trigger after C<after> seconds. If C<repeat>
1090	C<0.>, then it will automatically be stopped. If it is positive, then the	1529	is C<0.>, then it will automatically be stopped once the timeout is
1091	timer will automatically be configured to trigger again C<repeat> seconds	1530	reached. If it is positive, then the timer will automatically be
1092	later, again, and again, until stopped manually.	1531	configured to trigger again C<repeat> seconds later, again, and again,
		1532	until stopped manually.
1093		1533
1094	The timer itself will do a best-effort at avoiding drift, that is, if you	1534	The timer itself will do a best-effort at avoiding drift, that is, if
1095	configure a timer to trigger every 10 seconds, then it will trigger at	1535	you configure a timer to trigger every 10 seconds, then it will normally
1096	exactly 10 second intervals. If, however, your program cannot keep up with	1536	trigger at exactly 10 second intervals. If, however, your program cannot
1097	the timer (because it takes longer than those 10 seconds to do stuff) the	1537	keep up with the timer (because it takes longer than those 10 seconds to
1098	timer will not fire more than once per event loop iteration.	1538	do stuff) the timer will not fire more than once per event loop iteration.
1099		1539
1100	=item ev_timer_again (loop)	1540	=item ev_timer_again (loop, ev_timer *)
1101		1541
1102	This will act as if the timer timed out and restart it again if it is	1542	This will act as if the timer timed out and restart it again if it is
1103	repeating. The exact semantics are:	1543	repeating. The exact semantics are:
1104		1544
1105	If the timer is pending, its pending status is cleared.	1545	If the timer is pending, its pending status is cleared.
1106		1546
1107	If the timer is started but nonrepeating, stop it (as if it timed out).	1547	If the timer is started but non-repeating, stop it (as if it timed out).
1108		1548
1109	If the timer is repeating, either start it if necessary (with the	1549	If the timer is repeating, either start it if necessary (with the
1110	C<repeat> value), or reset the running timer to the C<repeat> value.	1550	C<repeat> value), or reset the running timer to the C<repeat> value.
1111		1551
1112	This sounds a bit complicated, but here is a useful and typical	1552	This sounds a bit complicated, see "Be smart about timeouts", above, for a
1113	example: Imagine you have a tcp connection and you want a so-called idle	1553	usage example.
1114	timeout, that is, you want to be called when there have been, say, 60
1115	seconds of inactivity on the socket. The easiest way to do this is to
1116	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1117	C<ev_timer_again> each time you successfully read or write some data. If
1118	you go into an idle state where you do not expect data to travel on the
1119	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1120	automatically restart it if need be.
1121
1122	That means you can ignore the C<after> value and C<ev_timer_start>
1123	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1124
1125	ev_timer_init (timer, callback, 0., 5.);
1126	ev_timer_again (loop, timer);
1127	...
1128	timer->again = 17.;
1129	ev_timer_again (loop, timer);
1130	...
1131	timer->again = 10.;
1132	ev_timer_again (loop, timer);
1133
1134	This is more slightly efficient then stopping/starting the timer each time
1135	you want to modify its timeout value.
1136		1554
1137	=item ev_tstamp repeat [read-write]	1555	=item ev_tstamp repeat [read-write]
1138		1556
1139	The current C<repeat> value. Will be used each time the watcher times out	1557	The current C<repeat> value. Will be used each time the watcher times out
1140	or C<ev_timer_again> is called and determines the next timeout (if any),	1558	or C<ev_timer_again> is called, and determines the next timeout (if any),
1141	which is also when any modifications are taken into account.	1559	which is also when any modifications are taken into account.
1142		1560
1143	=back	1561	=back
1144		1562
		1563	=head3 Examples
		1564
1145	Example: Create a timer that fires after 60 seconds.	1565	Example: Create a timer that fires after 60 seconds.
1146		1566
1147	static void	1567	static void
1148	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1568	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1149	{	1569	{
1150	.. one minute over, w is actually stopped right here	1570	.. one minute over, w is actually stopped right here
1151	}	1571	}
1152		1572
1153	struct ev_timer mytimer;	1573	ev_timer mytimer;
1154	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1574	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1155	ev_timer_start (loop, &mytimer);	1575	ev_timer_start (loop, &mytimer);
1156		1576
1157	Example: Create a timeout timer that times out after 10 seconds of	1577	Example: Create a timeout timer that times out after 10 seconds of
1158	inactivity.	1578	inactivity.
1159		1579
1160	static void	1580	static void
1161	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1581	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1162	{	1582	{
1163	.. ten seconds without any activity	1583	.. ten seconds without any activity
1164	}	1584	}
1165		1585
1166	struct ev_timer mytimer;	1586	ev_timer mytimer;
1167	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1587	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1168	ev_timer_again (&mytimer); /* start timer */	1588	ev_timer_again (&mytimer); /* start timer */
1169	ev_loop (loop, 0);	1589	ev_loop (loop, 0);
1170		1590
1171	// and in some piece of code that gets executed on any "activity":	1591	// and in some piece of code that gets executed on any "activity":
1172	// reset the timeout to start ticking again at 10 seconds	1592	// reset the timeout to start ticking again at 10 seconds
1173	ev_timer_again (&mytimer);	1593	ev_timer_again (&mytimer);
1174		1594
1175		1595
1176	=head2 C<ev_periodic> - to cron or not to cron?	1596	=head2 C<ev_periodic> - to cron or not to cron?
1177		1597
1178	Periodic watchers are also timers of a kind, but they are very versatile	1598	Periodic watchers are also timers of a kind, but they are very versatile
1179	(and unfortunately a bit complex).	1599	(and unfortunately a bit complex).
1180		1600
1181	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1601	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1182	but on wallclock time (absolute time). You can tell a periodic watcher	1602	relative time, the physical time that passes) but on wall clock time
1183	to trigger "at" some specific point in time. For example, if you tell a	1603	(absolute time, the thing you can read on your calender or clock). The
1184	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	1604	difference is that wall clock time can run faster or slower than real
1185	+ 10.>) and then reset your system clock to the last year, then it will	1605	time, and time jumps are not uncommon (e.g. when you adjust your
1186	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1606	wrist-watch).
1187	roughly 10 seconds later).
1188		1607
1189	They can also be used to implement vastly more complex timers, such as	1608	You can tell a periodic watcher to trigger after some specific point
1190	triggering an event on each midnight, local time or other, complicated,	1609	in time: for example, if you tell a periodic watcher to trigger "in 10
1191	rules.	1610	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1611	not a delay) and then reset your system clock to January of the previous
		1612	year, then it will take a year or more to trigger the event (unlike an
		1613	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1614	it, as it uses a relative timeout).
1192		1615
		1616	C<ev_periodic> watchers can also be used to implement vastly more complex
		1617	timers, such as triggering an event on each "midnight, local time", or
		1618	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1619	those cannot react to time jumps.
		1620
1193	As with timers, the callback is guarenteed to be invoked only when the	1621	As with timers, the callback is guaranteed to be invoked only when the
1194	time (C<at>) has been passed, but if multiple periodic timers become ready	1622	point in time where it is supposed to trigger has passed, but if multiple
1195	during the same loop iteration then order of execution is undefined.	1623	periodic timers become ready during the same loop iteration, then order of
		1624	execution is undefined.
1196		1625
1197	=head3 Watcher-Specific Functions and Data Members	1626	=head3 Watcher-Specific Functions and Data Members
1198		1627
1199	=over 4	1628	=over 4
1200		1629
1201	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1630	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1202		1631
1203	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1632	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1204		1633
1205	Lots of arguments, lets sort it out... There are basically three modes of	1634	Lots of arguments, let's sort it out... There are basically three modes of
1206	operation, and we will explain them from simplest to complex:	1635	operation, and we will explain them from simplest to most complex:
1207		1636
1208	=over 4	1637	=over 4
1209		1638
1210	=item * absolute timer (at = time, interval = reschedule_cb = 0)	1639	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1211		1640
1212	In this configuration the watcher triggers an event at the wallclock time	1641	In this configuration the watcher triggers an event after the wall clock
1213	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1642	time C<offset> has passed. It will not repeat and will not adjust when a
1214	that is, if it is to be run at January 1st 2011 then it will run when the	1643	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1215	system time reaches or surpasses this time.	1644	will be stopped and invoked when the system clock reaches or surpasses
		1645	this point in time.
1216		1646
1217	=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	1647	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1218		1648
1219	In this mode the watcher will always be scheduled to time out at the next	1649	In this mode the watcher will always be scheduled to time out at the next
1220	C<at + N * interval> time (for some integer N, which can also be negative)	1650	C<offset + N * interval> time (for some integer N, which can also be
1221	and then repeat, regardless of any time jumps.	1651	negative) and then repeat, regardless of any time jumps. The C<offset>
		1652	argument is merely an offset into the C<interval> periods.
1222		1653
1223	This can be used to create timers that do not drift with respect to system	1654	This can be used to create timers that do not drift with respect to the
1224	time:	1655	system clock, for example, here is an C<ev_periodic> that triggers each
		1656	hour, on the hour (with respect to UTC):
1225		1657
1226	ev_periodic_set (&periodic, 0., 3600., 0);	1658	ev_periodic_set (&periodic, 0., 3600., 0);
1227		1659
1228	This doesn't mean there will always be 3600 seconds in between triggers,	1660	This doesn't mean there will always be 3600 seconds in between triggers,
1229	but only that the the callback will be called when the system time shows a	1661	but only that the callback will be called when the system time shows a
1230	full hour (UTC), or more correctly, when the system time is evenly divisible	1662	full hour (UTC), or more correctly, when the system time is evenly divisible
1231	by 3600.	1663	by 3600.
1232		1664
1233	Another way to think about it (for the mathematically inclined) is that	1665	Another way to think about it (for the mathematically inclined) is that
1234	C<ev_periodic> will try to run the callback in this mode at the next possible	1666	C<ev_periodic> will try to run the callback in this mode at the next possible
1235	time where C<time = at (mod interval)>, regardless of any time jumps.	1667	time where C<time = offset (mod interval)>, regardless of any time jumps.
1236		1668
1237	For numerical stability it is preferable that the C<at> value is near	1669	For numerical stability it is preferable that the C<offset> value is near
1238	C<ev_now ()> (the current time), but there is no range requirement for	1670	C<ev_now ()> (the current time), but there is no range requirement for
1239	this value.	1671	this value, and in fact is often specified as zero.
1240		1672
		1673	Note also that there is an upper limit to how often a timer can fire (CPU
		1674	speed for example), so if C<interval> is very small then timing stability
		1675	will of course deteriorate. Libev itself tries to be exact to be about one
		1676	millisecond (if the OS supports it and the machine is fast enough).
		1677
1241	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	1678	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1242		1679
1243	In this mode the values for C<interval> and C<at> are both being	1680	In this mode the values for C<interval> and C<offset> are both being
1244	ignored. Instead, each time the periodic watcher gets scheduled, the	1681	ignored. Instead, each time the periodic watcher gets scheduled, the
1245	reschedule callback will be called with the watcher as first, and the	1682	reschedule callback will be called with the watcher as first, and the
1246	current time as second argument.	1683	current time as second argument.
1247		1684
1248	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1685	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1249	ever, or make any event loop modifications>. If you need to stop it,	1686	or make ANY other event loop modifications whatsoever, unless explicitly
1250	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	1687	allowed by documentation here>.
1251	starting an C<ev_prepare> watcher, which is legal).
1252		1688
		1689	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1690	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1691	only event loop modification you are allowed to do).
		1692
1253	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1693	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1254	ev_tstamp now)>, e.g.:	1694	*w, ev_tstamp now)>, e.g.:
1255		1695
		1696	static ev_tstamp
1256	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1697	my_rescheduler (ev_periodic *w, ev_tstamp now)
1257	{	1698	{
1258	return now + 60.;	1699	return now + 60.;
1259	}	1700	}
1260		1701
1261	It must return the next time to trigger, based on the passed time value	1702	It must return the next time to trigger, based on the passed time value
1262	(that is, the lowest time value larger than to the second argument). It	1703	(that is, the lowest time value larger than to the second argument). It
1263	will usually be called just before the callback will be triggered, but	1704	will usually be called just before the callback will be triggered, but
1264	might be called at other times, too.	1705	might be called at other times, too.
1265		1706
1266	NOTE: I<< This callback must always return a time that is later than the	1707	NOTE: I<< This callback must always return a time that is higher than or
1267	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	1708	equal to the passed C<now> value >>.
1268		1709
1269	This can be used to create very complex timers, such as a timer that	1710	This can be used to create very complex timers, such as a timer that
1270	triggers on each midnight, local time. To do this, you would calculate the	1711	triggers on "next midnight, local time". To do this, you would calculate the
1271	next midnight after C<now> and return the timestamp value for this. How	1712	next midnight after C<now> and return the timestamp value for this. How
1272	you do this is, again, up to you (but it is not trivial, which is the main	1713	you do this is, again, up to you (but it is not trivial, which is the main
1273	reason I omitted it as an example).	1714	reason I omitted it as an example).
1274		1715
1275	=back	1716	=back
…		…
1279	Simply stops and restarts the periodic watcher again. This is only useful	1720	Simply stops and restarts the periodic watcher again. This is only useful
1280	when you changed some parameters or the reschedule callback would return	1721	when you changed some parameters or the reschedule callback would return
1281	a different time than the last time it was called (e.g. in a crond like	1722	a different time than the last time it was called (e.g. in a crond like
1282	program when the crontabs have changed).	1723	program when the crontabs have changed).
1283		1724
		1725	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1726
		1727	When active, returns the absolute time that the watcher is supposed
		1728	to trigger next. This is not the same as the C<offset> argument to
		1729	C<ev_periodic_set>, but indeed works even in interval and manual
		1730	rescheduling modes.
		1731
1284	=item ev_tstamp offset [read-write]	1732	=item ev_tstamp offset [read-write]
1285		1733
1286	When repeating, this contains the offset value, otherwise this is the	1734	When repeating, this contains the offset value, otherwise this is the
1287	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	1735	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		1736	although libev might modify this value for better numerical stability).
1288		1737
1289	Can be modified any time, but changes only take effect when the periodic	1738	Can be modified any time, but changes only take effect when the periodic
1290	timer fires or C<ev_periodic_again> is being called.	1739	timer fires or C<ev_periodic_again> is being called.
1291		1740
1292	=item ev_tstamp interval [read-write]	1741	=item ev_tstamp interval [read-write]
1293		1742
1294	The current interval value. Can be modified any time, but changes only	1743	The current interval value. Can be modified any time, but changes only
1295	take effect when the periodic timer fires or C<ev_periodic_again> is being	1744	take effect when the periodic timer fires or C<ev_periodic_again> is being
1296	called.	1745	called.
1297		1746
1298	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	1747	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1299		1748
1300	The current reschedule callback, or C<0>, if this functionality is	1749	The current reschedule callback, or C<0>, if this functionality is
1301	switched off. Can be changed any time, but changes only take effect when	1750	switched off. Can be changed any time, but changes only take effect when
1302	the periodic timer fires or C<ev_periodic_again> is being called.	1751	the periodic timer fires or C<ev_periodic_again> is being called.
1303		1752
1304	=item ev_tstamp at [read-only]
1305
1306	When active, contains the absolute time that the watcher is supposed to
1307	trigger next.
1308
1309	=back	1753	=back
1310		1754
		1755	=head3 Examples
		1756
1311	Example: Call a callback every hour, or, more precisely, whenever the	1757	Example: Call a callback every hour, or, more precisely, whenever the
1312	system clock is divisible by 3600. The callback invocation times have	1758	system time is divisible by 3600. The callback invocation times have
1313	potentially a lot of jittering, but good long-term stability.	1759	potentially a lot of jitter, but good long-term stability.
1314		1760
1315	static void	1761	static void
1316	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1762	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1317	{	1763	{
1318	... its now a full hour (UTC, or TAI or whatever your clock follows)	1764	... its now a full hour (UTC, or TAI or whatever your clock follows)
1319	}	1765	}
1320		1766
1321	struct ev_periodic hourly_tick;	1767	ev_periodic hourly_tick;
1322	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	1768	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1323	ev_periodic_start (loop, &hourly_tick);	1769	ev_periodic_start (loop, &hourly_tick);
1324		1770
1325	Example: The same as above, but use a reschedule callback to do it:	1771	Example: The same as above, but use a reschedule callback to do it:
1326		1772
1327	#include <math.h>	1773	#include <math.h>
1328		1774
1329	static ev_tstamp	1775	static ev_tstamp
1330	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	1776	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1331	{	1777	{
1332	return fmod (now, 3600.) + 3600.;	1778	return now + (3600. - fmod (now, 3600.));
1333	}	1779	}
1334		1780
1335	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	1781	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1336		1782
1337	Example: Call a callback every hour, starting now:	1783	Example: Call a callback every hour, starting now:
1338		1784
1339	struct ev_periodic hourly_tick;	1785	ev_periodic hourly_tick;
1340	ev_periodic_init (&hourly_tick, clock_cb,	1786	ev_periodic_init (&hourly_tick, clock_cb,
1341	fmod (ev_now (loop), 3600.), 3600., 0);	1787	fmod (ev_now (loop), 3600.), 3600., 0);
1342	ev_periodic_start (loop, &hourly_tick);	1788	ev_periodic_start (loop, &hourly_tick);
1343		1789
1344		1790
1345	=head2 C<ev_signal> - signal me when a signal gets signalled!	1791	=head2 C<ev_signal> - signal me when a signal gets signalled!
1346		1792
1347	Signal watchers will trigger an event when the process receives a specific	1793	Signal watchers will trigger an event when the process receives a specific
1348	signal one or more times. Even though signals are very asynchronous, libev	1794	signal one or more times. Even though signals are very asynchronous, libev
1349	will try it's best to deliver signals synchronously, i.e. as part of the	1795	will try it's best to deliver signals synchronously, i.e. as part of the
1350	normal event processing, like any other event.	1796	normal event processing, like any other event.
1351		1797
		1798	If you want signals asynchronously, just use C<sigaction> as you would
		1799	do without libev and forget about sharing the signal. You can even use
		1800	C<ev_async> from a signal handler to synchronously wake up an event loop.
		1801
1352	You can configure as many watchers as you like per signal. Only when the	1802	You can configure as many watchers as you like per signal. Only when the
1353	first watcher gets started will libev actually register a signal watcher	1803	first watcher gets started will libev actually register a signal handler
1354	with the kernel (thus it coexists with your own signal handlers as long	1804	with the kernel (thus it coexists with your own signal handlers as long as
1355	as you don't register any with libev). Similarly, when the last signal	1805	you don't register any with libev for the same signal). Similarly, when
1356	watcher for a signal is stopped libev will reset the signal handler to	1806	the last signal watcher for a signal is stopped, libev will reset the
1357	SIG_DFL (regardless of what it was set to before).	1807	signal handler to SIG_DFL (regardless of what it was set to before).
		1808
		1809	If possible and supported, libev will install its handlers with
		1810	C<SA_RESTART> behaviour enabled, so system calls should not be unduly
		1811	interrupted. If you have a problem with system calls getting interrupted by
		1812	signals you can block all signals in an C<ev_check> watcher and unblock
		1813	them in an C<ev_prepare> watcher.
1358		1814
1359	=head3 Watcher-Specific Functions and Data Members	1815	=head3 Watcher-Specific Functions and Data Members
1360		1816
1361	=over 4	1817	=over 4
1362		1818
…		…
1371		1827
1372	The signal the watcher watches out for.	1828	The signal the watcher watches out for.
1373		1829
1374	=back	1830	=back
1375		1831
		1832	=head3 Examples
		1833
		1834	Example: Try to exit cleanly on SIGINT.
		1835
		1836	static void
		1837	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		1838	{
		1839	ev_unloop (loop, EVUNLOOP_ALL);
		1840	}
		1841
		1842	ev_signal signal_watcher;
		1843	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1844	ev_signal_start (loop, &signal_watcher);
		1845
1376		1846
1377	=head2 C<ev_child> - watch out for process status changes	1847	=head2 C<ev_child> - watch out for process status changes
1378		1848
1379	Child watchers trigger when your process receives a SIGCHLD in response to	1849	Child watchers trigger when your process receives a SIGCHLD in response to
1380	some child status changes (most typically when a child of yours dies).	1850	some child status changes (most typically when a child of yours dies or
		1851	exits). It is permissible to install a child watcher I<after> the child
		1852	has been forked (which implies it might have already exited), as long
		1853	as the event loop isn't entered (or is continued from a watcher), i.e.,
		1854	forking and then immediately registering a watcher for the child is fine,
		1855	but forking and registering a watcher a few event loop iterations later is
		1856	not.
		1857
		1858	Only the default event loop is capable of handling signals, and therefore
		1859	you can only register child watchers in the default event loop.
		1860
		1861	=head3 Process Interaction
		1862
		1863	Libev grabs C<SIGCHLD> as soon as the default event loop is
		1864	initialised. This is necessary to guarantee proper behaviour even if
		1865	the first child watcher is started after the child exits. The occurrence
		1866	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		1867	synchronously as part of the event loop processing. Libev always reaps all
		1868	children, even ones not watched.
		1869
		1870	=head3 Overriding the Built-In Processing
		1871
		1872	Libev offers no special support for overriding the built-in child
		1873	processing, but if your application collides with libev's default child
		1874	handler, you can override it easily by installing your own handler for
		1875	C<SIGCHLD> after initialising the default loop, and making sure the
		1876	default loop never gets destroyed. You are encouraged, however, to use an
		1877	event-based approach to child reaping and thus use libev's support for
		1878	that, so other libev users can use C<ev_child> watchers freely.
		1879
		1880	=head3 Stopping the Child Watcher
		1881
		1882	Currently, the child watcher never gets stopped, even when the
		1883	child terminates, so normally one needs to stop the watcher in the
		1884	callback. Future versions of libev might stop the watcher automatically
		1885	when a child exit is detected.
1381		1886
1382	=head3 Watcher-Specific Functions and Data Members	1887	=head3 Watcher-Specific Functions and Data Members
1383		1888
1384	=over 4	1889	=over 4
1385		1890
1386	=item ev_child_init (ev_child *, callback, int pid)	1891	=item ev_child_init (ev_child *, callback, int pid, int trace)
1387		1892
1388	=item ev_child_set (ev_child *, int pid)	1893	=item ev_child_set (ev_child *, int pid, int trace)
1389		1894
1390	Configures the watcher to wait for status changes of process C<pid> (or	1895	Configures the watcher to wait for status changes of process C<pid> (or
1391	I<any> process if C<pid> is specified as C<0>). The callback can look	1896	I<any> process if C<pid> is specified as C<0>). The callback can look
1392	at the C<rstatus> member of the C<ev_child> watcher structure to see	1897	at the C<rstatus> member of the C<ev_child> watcher structure to see
1393	the status word (use the macros from C<sys/wait.h> and see your systems	1898	the status word (use the macros from C<sys/wait.h> and see your systems
1394	C<waitpid> documentation). The C<rpid> member contains the pid of the	1899	C<waitpid> documentation). The C<rpid> member contains the pid of the
1395	process causing the status change.	1900	process causing the status change. C<trace> must be either C<0> (only
		1901	activate the watcher when the process terminates) or C<1> (additionally
		1902	activate the watcher when the process is stopped or continued).
1396		1903
1397	=item int pid [read-only]	1904	=item int pid [read-only]
1398		1905
1399	The process id this watcher watches out for, or C<0>, meaning any process id.	1906	The process id this watcher watches out for, or C<0>, meaning any process id.
1400		1907
…		…
1407	The process exit/trace status caused by C<rpid> (see your systems	1914	The process exit/trace status caused by C<rpid> (see your systems
1408	C<waitpid> and C<sys/wait.h> documentation for details).	1915	C<waitpid> and C<sys/wait.h> documentation for details).
1409		1916
1410	=back	1917	=back
1411		1918
1412	Example: Try to exit cleanly on SIGINT and SIGTERM.	1919	=head3 Examples
1413		1920
		1921	Example: C<fork()> a new process and install a child handler to wait for
		1922	its completion.
		1923
		1924	ev_child cw;
		1925
1414	static void	1926	static void
1415	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	1927	child_cb (EV_P_ ev_child *w, int revents)
1416	{	1928	{
1417	ev_unloop (loop, EVUNLOOP_ALL);	1929	ev_child_stop (EV_A_ w);
		1930	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1418	}	1931	}
1419		1932
1420	struct ev_signal signal_watcher;	1933	pid_t pid = fork ();
1421	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	1934
1422	ev_signal_start (loop, &sigint_cb);	1935	if (pid < 0)
		1936	// error
		1937	else if (pid == 0)
		1938	{
		1939	// the forked child executes here
		1940	exit (1);
		1941	}
		1942	else
		1943	{
		1944	ev_child_init (&cw, child_cb, pid, 0);
		1945	ev_child_start (EV_DEFAULT_ &cw);
		1946	}
1423		1947
1424		1948
1425	=head2 C<ev_stat> - did the file attributes just change?	1949	=head2 C<ev_stat> - did the file attributes just change?
1426		1950
1427	This watches a filesystem path for attribute changes. That is, it calls	1951	This watches a file system path for attribute changes. That is, it calls
1428	C<stat> regularly (or when the OS says it changed) and sees if it changed	1952	C<stat> on that path in regular intervals (or when the OS says it changed)
1429	compared to the last time, invoking the callback if it did.	1953	and sees if it changed compared to the last time, invoking the callback if
		1954	it did.
1430		1955
1431	The path does not need to exist: changing from "path exists" to "path does	1956	The path does not need to exist: changing from "path exists" to "path does
1432	not exist" is a status change like any other. The condition "path does	1957	not exist" is a status change like any other. The condition "path does not
1433	not exist" is signified by the C<st_nlink> field being zero (which is	1958	exist" (or more correctly "path cannot be stat'ed") is signified by the
1434	otherwise always forced to be at least one) and all the other fields of	1959	C<st_nlink> field being zero (which is otherwise always forced to be at
1435	the stat buffer having unspecified contents.	1960	least one) and all the other fields of the stat buffer having unspecified
		1961	contents.
1436		1962
1437	The path I<should> be absolute and I<must not> end in a slash. If it is	1963	The path I<must not> end in a slash or contain special components such as
		1964	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1438	relative and your working directory changes, the behaviour is undefined.	1965	your working directory changes, then the behaviour is undefined.
1439		1966
1440	Since there is no standard to do this, the portable implementation simply	1967	Since there is no portable change notification interface available, the
1441	calls C<stat (2)> regularly on the path to see if it changed somehow. You	1968	portable implementation simply calls C<stat(2)> regularly on the path
1442	can specify a recommended polling interval for this case. If you specify	1969	to see if it changed somehow. You can specify a recommended polling
1443	a polling interval of C<0> (highly recommended!) then a I<suitable,	1970	interval for this case. If you specify a polling interval of C<0> (highly
1444	unspecified default> value will be used (which you can expect to be around	1971	recommended!) then a I<suitable, unspecified default> value will be used
1445	five seconds, although this might change dynamically). Libev will also	1972	(which you can expect to be around five seconds, although this might
1446	impose a minimum interval which is currently around C<0.1>, but thats	1973	change dynamically). Libev will also impose a minimum interval which is
1447	usually overkill.	1974	currently around C<0.1>, but that's usually overkill.
1448		1975
1449	This watcher type is not meant for massive numbers of stat watchers,	1976	This watcher type is not meant for massive numbers of stat watchers,
1450	as even with OS-supported change notifications, this can be	1977	as even with OS-supported change notifications, this can be
1451	resource-intensive.	1978	resource-intensive.
1452		1979
1453	At the time of this writing, only the Linux inotify interface is	1980	At the time of this writing, the only OS-specific interface implemented
1454	implemented (implementing kqueue support is left as an exercise for the	1981	is the Linux inotify interface (implementing kqueue support is left as an
1455	reader). Inotify will be used to give hints only and should not change the	1982	exercise for the reader. Note, however, that the author sees no way of
1456	semantics of C<ev_stat> watchers, which means that libev sometimes needs	1983	implementing C<ev_stat> semantics with kqueue, except as a hint).
1457	to fall back to regular polling again even with inotify, but changes are	1984
1458	usually detected immediately, and if the file exists there will be no	1985	=head3 ABI Issues (Largefile Support)
1459	polling.	1986
		1987	Libev by default (unless the user overrides this) uses the default
		1988	compilation environment, which means that on systems with large file
		1989	support disabled by default, you get the 32 bit version of the stat
		1990	structure. When using the library from programs that change the ABI to
		1991	use 64 bit file offsets the programs will fail. In that case you have to
		1992	compile libev with the same flags to get binary compatibility. This is
		1993	obviously the case with any flags that change the ABI, but the problem is
		1994	most noticeably displayed with ev_stat and large file support.
		1995
		1996	The solution for this is to lobby your distribution maker to make large
		1997	file interfaces available by default (as e.g. FreeBSD does) and not
		1998	optional. Libev cannot simply switch on large file support because it has
		1999	to exchange stat structures with application programs compiled using the
		2000	default compilation environment.
		2001
		2002	=head3 Inotify and Kqueue
		2003
		2004	When C<inotify (7)> support has been compiled into libev and present at
		2005	runtime, it will be used to speed up change detection where possible. The
		2006	inotify descriptor will be created lazily when the first C<ev_stat>
		2007	watcher is being started.
		2008
		2009	Inotify presence does not change the semantics of C<ev_stat> watchers
		2010	except that changes might be detected earlier, and in some cases, to avoid
		2011	making regular C<stat> calls. Even in the presence of inotify support
		2012	there are many cases where libev has to resort to regular C<stat> polling,
		2013	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2014	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2015	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2016	xfs are fully working) libev usually gets away without polling.
		2017
		2018	There is no support for kqueue, as apparently it cannot be used to
		2019	implement this functionality, due to the requirement of having a file
		2020	descriptor open on the object at all times, and detecting renames, unlinks
		2021	etc. is difficult.
		2022
		2023	=head3 C<stat ()> is a synchronous operation
		2024
		2025	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2026	the process. The exception are C<ev_stat> watchers - those call C<stat
		2027	()>, which is a synchronous operation.
		2028
		2029	For local paths, this usually doesn't matter: unless the system is very
		2030	busy or the intervals between stat's are large, a stat call will be fast,
		2031	as the path data is usually in memory already (except when starting the
		2032	watcher).
		2033
		2034	For networked file systems, calling C<stat ()> can block an indefinite
		2035	time due to network issues, and even under good conditions, a stat call
		2036	often takes multiple milliseconds.
		2037
		2038	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2039	paths, although this is fully supported by libev.
		2040
		2041	=head3 The special problem of stat time resolution
		2042
		2043	The C<stat ()> system call only supports full-second resolution portably,
		2044	and even on systems where the resolution is higher, most file systems
		2045	still only support whole seconds.
		2046
		2047	That means that, if the time is the only thing that changes, you can
		2048	easily miss updates: on the first update, C<ev_stat> detects a change and
		2049	calls your callback, which does something. When there is another update
		2050	within the same second, C<ev_stat> will be unable to detect unless the
		2051	stat data does change in other ways (e.g. file size).
		2052
		2053	The solution to this is to delay acting on a change for slightly more
		2054	than a second (or till slightly after the next full second boundary), using
		2055	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2056	ev_timer_again (loop, w)>).
		2057
		2058	The C<.02> offset is added to work around small timing inconsistencies
		2059	of some operating systems (where the second counter of the current time
		2060	might be be delayed. One such system is the Linux kernel, where a call to
		2061	C<gettimeofday> might return a timestamp with a full second later than
		2062	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2063	update file times then there will be a small window where the kernel uses
		2064	the previous second to update file times but libev might already execute
		2065	the timer callback).
1460		2066
1461	=head3 Watcher-Specific Functions and Data Members	2067	=head3 Watcher-Specific Functions and Data Members
1462		2068
1463	=over 4	2069	=over 4
1464		2070
…		…
1470	C<path>. The C<interval> is a hint on how quickly a change is expected to	2076	C<path>. The C<interval> is a hint on how quickly a change is expected to
1471	be detected and should normally be specified as C<0> to let libev choose	2077	be detected and should normally be specified as C<0> to let libev choose
1472	a suitable value. The memory pointed to by C<path> must point to the same	2078	a suitable value. The memory pointed to by C<path> must point to the same
1473	path for as long as the watcher is active.	2079	path for as long as the watcher is active.
1474		2080
1475	The callback will be receive C<EV_STAT> when a change was detected,	2081	The callback will receive an C<EV_STAT> event when a change was detected,
1476	relative to the attributes at the time the watcher was started (or the	2082	relative to the attributes at the time the watcher was started (or the
1477	last change was detected).	2083	last change was detected).
1478		2084
1479	=item ev_stat_stat (ev_stat *)	2085	=item ev_stat_stat (loop, ev_stat *)
1480		2086
1481	Updates the stat buffer immediately with new values. If you change the	2087	Updates the stat buffer immediately with new values. If you change the
1482	watched path in your callback, you could call this fucntion to avoid	2088	watched path in your callback, you could call this function to avoid
1483	detecting this change (while introducing a race condition). Can also be	2089	detecting this change (while introducing a race condition if you are not
1484	useful simply to find out the new values.	2090	the only one changing the path). Can also be useful simply to find out the
		2091	new values.
1485		2092
1486	=item ev_statdata attr [read-only]	2093	=item ev_statdata attr [read-only]
1487		2094
1488	The most-recently detected attributes of the file. Although the type is of	2095	The most-recently detected attributes of the file. Although the type is
1489	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2096	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1490	suitable for your system. If the C<st_nlink> member is C<0>, then there	2097	suitable for your system, but you can only rely on the POSIX-standardised
		2098	members to be present. If the C<st_nlink> member is C<0>, then there was
1491	was some error while C<stat>ing the file.	2099	some error while C<stat>ing the file.
1492		2100
1493	=item ev_statdata prev [read-only]	2101	=item ev_statdata prev [read-only]
1494		2102
1495	The previous attributes of the file. The callback gets invoked whenever	2103	The previous attributes of the file. The callback gets invoked whenever
1496	C<prev> != C<attr>.	2104	C<prev> != C<attr>, or, more precisely, one or more of these members
		2105	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2106	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1497		2107
1498	=item ev_tstamp interval [read-only]	2108	=item ev_tstamp interval [read-only]
1499		2109
1500	The specified interval.	2110	The specified interval.
1501		2111
1502	=item const char *path [read-only]	2112	=item const char *path [read-only]
1503		2113
1504	The filesystem path that is being watched.	2114	The file system path that is being watched.
1505		2115
1506	=back	2116	=back
1507		2117
		2118	=head3 Examples
		2119
1508	Example: Watch C</etc/passwd> for attribute changes.	2120	Example: Watch C</etc/passwd> for attribute changes.
1509		2121
1510	static void	2122	static void
1511	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2123	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1512	{	2124	{
1513	/* /etc/passwd changed in some way */	2125	/* /etc/passwd changed in some way */
1514	if (w->attr.st_nlink)	2126	if (w->attr.st_nlink)
1515	{	2127	{
1516	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2128	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1517	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2129	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1518	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2130	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1519	}	2131	}
1520	else	2132	else
1521	/* you shalt not abuse printf for puts */	2133	/* you shalt not abuse printf for puts */
1522	puts ("wow, /etc/passwd is not there, expect problems. "	2134	puts ("wow, /etc/passwd is not there, expect problems. "
1523	"if this is windows, they already arrived\n");	2135	"if this is windows, they already arrived\n");
1524	}	2136	}
1525		2137
1526	...	2138	...
1527	ev_stat passwd;	2139	ev_stat passwd;
1528		2140
1529	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	2141	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1530	ev_stat_start (loop, &passwd);	2142	ev_stat_start (loop, &passwd);
		2143
		2144	Example: Like above, but additionally use a one-second delay so we do not
		2145	miss updates (however, frequent updates will delay processing, too, so
		2146	one might do the work both on C<ev_stat> callback invocation I<and> on
		2147	C<ev_timer> callback invocation).
		2148
		2149	static ev_stat passwd;
		2150	static ev_timer timer;
		2151
		2152	static void
		2153	timer_cb (EV_P_ ev_timer *w, int revents)
		2154	{
		2155	ev_timer_stop (EV_A_ w);
		2156
		2157	/* now it's one second after the most recent passwd change */
		2158	}
		2159
		2160	static void
		2161	stat_cb (EV_P_ ev_stat *w, int revents)
		2162	{
		2163	/* reset the one-second timer */
		2164	ev_timer_again (EV_A_ &timer);
		2165	}
		2166
		2167	...
		2168	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2169	ev_stat_start (loop, &passwd);
		2170	ev_timer_init (&timer, timer_cb, 0., 1.02);
1531		2171
1532		2172
1533	=head2 C<ev_idle> - when you've got nothing better to do...	2173	=head2 C<ev_idle> - when you've got nothing better to do...
1534		2174
1535	Idle watchers trigger events when no other events of the same or higher	2175	Idle watchers trigger events when no other events of the same or higher
1536	priority are pending (prepare, check and other idle watchers do not	2176	priority are pending (prepare, check and other idle watchers do not count
1537	count).	2177	as receiving "events").
1538		2178
1539	That is, as long as your process is busy handling sockets or timeouts	2179	That is, as long as your process is busy handling sockets or timeouts
1540	(or even signals, imagine) of the same or higher priority it will not be	2180	(or even signals, imagine) of the same or higher priority it will not be
1541	triggered. But when your process is idle (or only lower-priority watchers	2181	triggered. But when your process is idle (or only lower-priority watchers
1542	are pending), the idle watchers are being called once per event loop	2182	are pending), the idle watchers are being called once per event loop
…		…
1553		2193
1554	=head3 Watcher-Specific Functions and Data Members	2194	=head3 Watcher-Specific Functions and Data Members
1555		2195
1556	=over 4	2196	=over 4
1557		2197
1558	=item ev_idle_init (ev_signal *, callback)	2198	=item ev_idle_init (ev_idle *, callback)
1559		2199
1560	Initialises and configures the idle watcher - it has no parameters of any	2200	Initialises and configures the idle watcher - it has no parameters of any
1561	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2201	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1562	believe me.	2202	believe me.
1563		2203
1564	=back	2204	=back
1565		2205
		2206	=head3 Examples
		2207
1566	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2208	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1567	callback, free it. Also, use no error checking, as usual.	2209	callback, free it. Also, use no error checking, as usual.
1568		2210
1569	static void	2211	static void
1570	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2212	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1571	{	2213	{
1572	free (w);	2214	free (w);
1573	// now do something you wanted to do when the program has	2215	// now do something you wanted to do when the program has
1574	// no longer asnything immediate to do.	2216	// no longer anything immediate to do.
1575	}	2217	}
1576		2218
1577	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2219	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1578	ev_idle_init (idle_watcher, idle_cb);	2220	ev_idle_init (idle_watcher, idle_cb);
1579	ev_idle_start (loop, idle_cb);	2221	ev_idle_start (loop, idle_cb);
1580		2222
1581		2223
1582	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2224	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1583		2225
1584	Prepare and check watchers are usually (but not always) used in tandem:	2226	Prepare and check watchers are usually (but not always) used in pairs:
1585	prepare watchers get invoked before the process blocks and check watchers	2227	prepare watchers get invoked before the process blocks and check watchers
1586	afterwards.	2228	afterwards.
1587		2229
1588	You I<must not> call C<ev_loop> or similar functions that enter	2230	You I<must not> call C<ev_loop> or similar functions that enter
1589	the current event loop from either C<ev_prepare> or C<ev_check>	2231	the current event loop from either C<ev_prepare> or C<ev_check>
…		…
1592	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2234	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1593	C<ev_check> so if you have one watcher of each kind they will always be	2235	C<ev_check> so if you have one watcher of each kind they will always be
1594	called in pairs bracketing the blocking call.	2236	called in pairs bracketing the blocking call.
1595		2237
1596	Their main purpose is to integrate other event mechanisms into libev and	2238	Their main purpose is to integrate other event mechanisms into libev and
1597	their use is somewhat advanced. This could be used, for example, to track	2239	their use is somewhat advanced. They could be used, for example, to track
1598	variable changes, implement your own watchers, integrate net-snmp or a	2240	variable changes, implement your own watchers, integrate net-snmp or a
1599	coroutine library and lots more. They are also occasionally useful if	2241	coroutine library and lots more. They are also occasionally useful if
1600	you cache some data and want to flush it before blocking (for example,	2242	you cache some data and want to flush it before blocking (for example,
1601	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2243	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1602	watcher).	2244	watcher).
1603		2245
1604	This is done by examining in each prepare call which file descriptors need	2246	This is done by examining in each prepare call which file descriptors
1605	to be watched by the other library, registering C<ev_io> watchers for	2247	need to be watched by the other library, registering C<ev_io> watchers
1606	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2248	for them and starting an C<ev_timer> watcher for any timeouts (many
1607	provide just this functionality). Then, in the check watcher you check for	2249	libraries provide exactly this functionality). Then, in the check watcher,
1608	any events that occured (by checking the pending status of all watchers	2250	you check for any events that occurred (by checking the pending status
1609	and stopping them) and call back into the library. The I/O and timer	2251	of all watchers and stopping them) and call back into the library. The
1610	callbacks will never actually be called (but must be valid nevertheless,	2252	I/O and timer callbacks will never actually be called (but must be valid
1611	because you never know, you know?).	2253	nevertheless, because you never know, you know?).
1612		2254
1613	As another example, the Perl Coro module uses these hooks to integrate	2255	As another example, the Perl Coro module uses these hooks to integrate
1614	coroutines into libev programs, by yielding to other active coroutines	2256	coroutines into libev programs, by yielding to other active coroutines
1615	during each prepare and only letting the process block if no coroutines	2257	during each prepare and only letting the process block if no coroutines
1616	are ready to run (it's actually more complicated: it only runs coroutines	2258	are ready to run (it's actually more complicated: it only runs coroutines
…		…
1619	loop from blocking if lower-priority coroutines are active, thus mapping	2261	loop from blocking if lower-priority coroutines are active, thus mapping
1620	low-priority coroutines to idle/background tasks).	2262	low-priority coroutines to idle/background tasks).
1621		2263
1622	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2264	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1623	priority, to ensure that they are being run before any other watchers	2265	priority, to ensure that they are being run before any other watchers
		2266	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2267
1624	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2268	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1625	too) should not activate ("feed") events into libev. While libev fully	2269	activate ("feed") events into libev. While libev fully supports this, they
1626	supports this, they will be called before other C<ev_check> watchers did	2270	might get executed before other C<ev_check> watchers did their job. As
1627	their job. As C<ev_check> watchers are often used to embed other event	2271	C<ev_check> watchers are often used to embed other (non-libev) event
1628	loops those other event loops might be in an unusable state until their	2272	loops those other event loops might be in an unusable state until their
1629	C<ev_check> watcher ran (always remind yourself to coexist peacefully with	2273	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1630	others).	2274	others).
1631		2275
1632	=head3 Watcher-Specific Functions and Data Members	2276	=head3 Watcher-Specific Functions and Data Members
…		…
1637		2281
1638	=item ev_check_init (ev_check *, callback)	2282	=item ev_check_init (ev_check *, callback)
1639		2283
1640	Initialises and configures the prepare or check watcher - they have no	2284	Initialises and configures the prepare or check watcher - they have no
1641	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2285	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1642	macros, but using them is utterly, utterly and completely pointless.	2286	macros, but using them is utterly, utterly, utterly and completely
		2287	pointless.
1643		2288
1644	=back	2289	=back
		2290
		2291	=head3 Examples
1645		2292
1646	There are a number of principal ways to embed other event loops or modules	2293	There are a number of principal ways to embed other event loops or modules
1647	into libev. Here are some ideas on how to include libadns into libev	2294	into libev. Here are some ideas on how to include libadns into libev
1648	(there is a Perl module named C<EV::ADNS> that does this, which you could	2295	(there is a Perl module named C<EV::ADNS> that does this, which you could
1649	use for an actually working example. Another Perl module named C<EV::Glib>	2296	use as a working example. Another Perl module named C<EV::Glib> embeds a
1650	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV	2297	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1651	into the Glib event loop).	2298	Glib event loop).
1652		2299
1653	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	2300	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1654	and in a check watcher, destroy them and call into libadns. What follows	2301	and in a check watcher, destroy them and call into libadns. What follows
1655	is pseudo-code only of course. This requires you to either use a low	2302	is pseudo-code only of course. This requires you to either use a low
1656	priority for the check watcher or use C<ev_clear_pending> explicitly, as	2303	priority for the check watcher or use C<ev_clear_pending> explicitly, as
1657	the callbacks for the IO/timeout watchers might not have been called yet.	2304	the callbacks for the IO/timeout watchers might not have been called yet.
1658		2305
1659	static ev_io iow [nfd];	2306	static ev_io iow [nfd];
1660	static ev_timer tw;	2307	static ev_timer tw;
1661		2308
1662	static void	2309	static void
1663	io_cb (ev_loop *loop, ev_io *w, int revents)	2310	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1664	{	2311	{
1665	}	2312	}
1666		2313
1667	// create io watchers for each fd and a timer before blocking	2314	// create io watchers for each fd and a timer before blocking
1668	static void	2315	static void
1669	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2316	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1670	{	2317	{
1671	int timeout = 3600000;	2318	int timeout = 3600000;
1672	struct pollfd fds [nfd];	2319	struct pollfd fds [nfd];
1673	// actual code will need to loop here and realloc etc.	2320	// actual code will need to loop here and realloc etc.
1674	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2321	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1675		2322
1676	/* the callback is illegal, but won't be called as we stop during check */	2323	/* the callback is illegal, but won't be called as we stop during check */
1677	ev_timer_init (&tw, 0, timeout * 1e-3);	2324	ev_timer_init (&tw, 0, timeout * 1e-3);
1678	ev_timer_start (loop, &tw);	2325	ev_timer_start (loop, &tw);
1679		2326
1680	// create one ev_io per pollfd	2327	// create one ev_io per pollfd
1681	for (int i = 0; i < nfd; ++i)	2328	for (int i = 0; i < nfd; ++i)
1682	{	2329	{
1683	ev_io_init (iow + i, io_cb, fds [i].fd,	2330	ev_io_init (iow + i, io_cb, fds [i].fd,
1684	((fds [i].events & POLLIN ? EV_READ : 0)	2331	((fds [i].events & POLLIN ? EV_READ : 0)
1685	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2332	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1686		2333
1687	fds [i].revents = 0;	2334	fds [i].revents = 0;
1688	ev_io_start (loop, iow + i);	2335	ev_io_start (loop, iow + i);
1689	}	2336	}
1690	}	2337	}
1691		2338
1692	// stop all watchers after blocking	2339	// stop all watchers after blocking
1693	static void	2340	static void
1694	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2341	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1695	{	2342	{
1696	ev_timer_stop (loop, &tw);	2343	ev_timer_stop (loop, &tw);
1697		2344
1698	for (int i = 0; i < nfd; ++i)	2345	for (int i = 0; i < nfd; ++i)
1699	{	2346	{
1700	// set the relevant poll flags	2347	// set the relevant poll flags
1701	// could also call adns_processreadable etc. here	2348	// could also call adns_processreadable etc. here
1702	struct pollfd *fd = fds + i;	2349	struct pollfd *fd = fds + i;
1703	int revents = ev_clear_pending (iow + i);	2350	int revents = ev_clear_pending (iow + i);
1704	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;	2351	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1705	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;	2352	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1706		2353
1707	// now stop the watcher	2354	// now stop the watcher
1708	ev_io_stop (loop, iow + i);	2355	ev_io_stop (loop, iow + i);
1709	}	2356	}
1710		2357
1711	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2358	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1712	}	2359	}
1713		2360
1714	Method 2: This would be just like method 1, but you run C<adns_afterpoll>	2361	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
1715	in the prepare watcher and would dispose of the check watcher.	2362	in the prepare watcher and would dispose of the check watcher.
1716		2363
1717	Method 3: If the module to be embedded supports explicit event	2364	Method 3: If the module to be embedded supports explicit event
1718	notification (adns does), you can also make use of the actual watcher	2365	notification (libadns does), you can also make use of the actual watcher
1719	callbacks, and only destroy/create the watchers in the prepare watcher.	2366	callbacks, and only destroy/create the watchers in the prepare watcher.
1720		2367
1721	static void	2368	static void
1722	timer_cb (EV_P_ ev_timer *w, int revents)	2369	timer_cb (EV_P_ ev_timer *w, int revents)
1723	{	2370	{
1724	adns_state ads = (adns_state)w->data;	2371	adns_state ads = (adns_state)w->data;
1725	update_now (EV_A);	2372	update_now (EV_A);
1726		2373
1727	adns_processtimeouts (ads, &tv_now);	2374	adns_processtimeouts (ads, &tv_now);
1728	}	2375	}
1729		2376
1730	static void	2377	static void
1731	io_cb (EV_P_ ev_io *w, int revents)	2378	io_cb (EV_P_ ev_io *w, int revents)
1732	{	2379	{
1733	adns_state ads = (adns_state)w->data;	2380	adns_state ads = (adns_state)w->data;
1734	update_now (EV_A);	2381	update_now (EV_A);
1735		2382
1736	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);	2383	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
1737	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);	2384	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
1738	}	2385	}
1739		2386
1740	// do not ever call adns_afterpoll	2387	// do not ever call adns_afterpoll
1741		2388
1742	Method 4: Do not use a prepare or check watcher because the module you	2389	Method 4: Do not use a prepare or check watcher because the module you
1743	want to embed is too inflexible to support it. Instead, youc na override	2390	want to embed is not flexible enough to support it. Instead, you can
1744	their poll function. The drawback with this solution is that the main	2391	override their poll function. The drawback with this solution is that the
1745	loop is now no longer controllable by EV. The C<Glib::EV> module does	2392	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
1746	this.	2393	this approach, effectively embedding EV as a client into the horrible
		2394	libglib event loop.
1747		2395
1748	static gint	2396	static gint
1749	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	2397	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1750	{	2398	{
1751	int got_events = 0;	2399	int got_events = 0;
1752		2400
1753	for (n = 0; n < nfds; ++n)	2401	for (n = 0; n < nfds; ++n)
1754	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events	2402	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1755		2403
1756	if (timeout >= 0)	2404	if (timeout >= 0)
1757	// create/start timer	2405	// create/start timer
1758		2406
1759	// poll	2407	// poll
1760	ev_loop (EV_A_ 0);	2408	ev_loop (EV_A_ 0);
1761		2409
1762	// stop timer again	2410	// stop timer again
1763	if (timeout >= 0)	2411	if (timeout >= 0)
1764	ev_timer_stop (EV_A_ &to);	2412	ev_timer_stop (EV_A_ &to);
1765		2413
1766	// stop io watchers again - their callbacks should have set	2414	// stop io watchers again - their callbacks should have set
1767	for (n = 0; n < nfds; ++n)	2415	for (n = 0; n < nfds; ++n)
1768	ev_io_stop (EV_A_ iow [n]);	2416	ev_io_stop (EV_A_ iow [n]);
1769		2417
1770	return got_events;	2418	return got_events;
1771	}	2419	}
1772		2420
1773		2421
1774	=head2 C<ev_embed> - when one backend isn't enough...	2422	=head2 C<ev_embed> - when one backend isn't enough...
1775		2423
1776	This is a rather advanced watcher type that lets you embed one event loop	2424	This is a rather advanced watcher type that lets you embed one event loop
1777	into another (currently only C<ev_io> events are supported in the embedded	2425	into another (currently only C<ev_io> events are supported in the embedded
1778	loop, other types of watchers might be handled in a delayed or incorrect	2426	loop, other types of watchers might be handled in a delayed or incorrect
1779	fashion and must not be used). (See portability notes, below).	2427	fashion and must not be used).
1780		2428
1781	There are primarily two reasons you would want that: work around bugs and	2429	There are primarily two reasons you would want that: work around bugs and
1782	prioritise I/O.	2430	prioritise I/O.
1783		2431
1784	As an example for a bug workaround, the kqueue backend might only support	2432	As an example for a bug workaround, the kqueue backend might only support
1785	sockets on some platform, so it is unusable as generic backend, but you	2433	sockets on some platform, so it is unusable as generic backend, but you
1786	still want to make use of it because you have many sockets and it scales	2434	still want to make use of it because you have many sockets and it scales
1787	so nicely. In this case, you would create a kqueue-based loop and embed it	2435	so nicely. In this case, you would create a kqueue-based loop and embed
1788	into your default loop (which might use e.g. poll). Overall operation will	2436	it into your default loop (which might use e.g. poll). Overall operation
1789	be a bit slower because first libev has to poll and then call kevent, but	2437	will be a bit slower because first libev has to call C<poll> and then
1790	at least you can use both at what they are best.	2438	C<kevent>, but at least you can use both mechanisms for what they are
		2439	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1791		2440
1792	As for prioritising I/O: rarely you have the case where some fds have	2441	As for prioritising I/O: under rare circumstances you have the case where
1793	to be watched and handled very quickly (with low latency), and even	2442	some fds have to be watched and handled very quickly (with low latency),
1794	priorities and idle watchers might have too much overhead. In this case	2443	and even priorities and idle watchers might have too much overhead. In
1795	you would put all the high priority stuff in one loop and all the rest in	2444	this case you would put all the high priority stuff in one loop and all
1796	a second one, and embed the second one in the first.	2445	the rest in a second one, and embed the second one in the first.
1797		2446
1798	As long as the watcher is active, the callback will be invoked every time	2447	As long as the watcher is active, the callback will be invoked every
1799	there might be events pending in the embedded loop. The callback must then	2448	time there might be events pending in the embedded loop. The callback
1800	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2449	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1801	their callbacks (you could also start an idle watcher to give the embedded	2450	sweep and invoke their callbacks (the callback doesn't need to invoke the
1802	loop strictly lower priority for example). You can also set the callback	2451	C<ev_embed_sweep> function directly, it could also start an idle watcher
1803	to C<0>, in which case the embed watcher will automatically execute the	2452	to give the embedded loop strictly lower priority for example).
1804	embedded loop sweep.
1805		2453
1806	As long as the watcher is started it will automatically handle events. The	2454	You can also set the callback to C<0>, in which case the embed watcher
1807	callback will be invoked whenever some events have been handled. You can	2455	will automatically execute the embedded loop sweep whenever necessary.
1808	set the callback to C<0> to avoid having to specify one if you are not
1809	interested in that.
1810		2456
1811	Also, there have not currently been made special provisions for forking:	2457	Fork detection will be handled transparently while the C<ev_embed> watcher
1812	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2458	is active, i.e., the embedded loop will automatically be forked when the
1813	but you will also have to stop and restart any C<ev_embed> watchers	2459	embedding loop forks. In other cases, the user is responsible for calling
1814	yourself.	2460	C<ev_loop_fork> on the embedded loop.
1815		2461
1816	Unfortunately, not all backends are embeddable, only the ones returned by	2462	Unfortunately, not all backends are embeddable: only the ones returned by
1817	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2463	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1818	portable one.	2464	portable one.
1819		2465
1820	So when you want to use this feature you will always have to be prepared	2466	So when you want to use this feature you will always have to be prepared
1821	that you cannot get an embeddable loop. The recommended way to get around	2467	that you cannot get an embeddable loop. The recommended way to get around
1822	this is to have a separate variables for your embeddable loop, try to	2468	this is to have a separate variables for your embeddable loop, try to
1823	create it, and if that fails, use the normal loop for everything:	2469	create it, and if that fails, use the normal loop for everything.
1824		2470
1825	struct ev_loop *loop_hi = ev_default_init (0);	2471	=head3 C<ev_embed> and fork
1826	struct ev_loop *loop_lo = 0;
1827	struct ev_embed embed;
1828
1829	// see if there is a chance of getting one that works
1830	// (remember that a flags value of 0 means autodetection)
1831	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1832	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1833	: 0;
1834		2472
1835	// if we got one, then embed it, otherwise default to loop_hi	2473	While the C<ev_embed> watcher is running, forks in the embedding loop will
1836	if (loop_lo)	2474	automatically be applied to the embedded loop as well, so no special
1837	{	2475	fork handling is required in that case. When the watcher is not running,
1838	ev_embed_init (&embed, 0, loop_lo);	2476	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1839	ev_embed_start (loop_hi, &embed);	2477	as applicable.
1840	}
1841	else
1842	loop_lo = loop_hi;
1843
1844	=head2 Portability notes
1845
1846	Kqueue is nominally embeddable, but this is broken on all BSDs that I
1847	tried, in various ways. Usually the embedded event loop will simply never
1848	receive events, sometimes it will only trigger a few times, sometimes in a
1849	loop. Epoll is also nominally embeddable, but many Linux kernel versions
1850	will always eport the epoll fd as ready, even when no events are pending.
1851
1852	While libev allows embedding these backends (they are contained in
1853	C<ev_embeddable_backends ()>), take extreme care that it will actually
1854	work.
1855
1856	When in doubt, create a dynamic event loop forced to use sockets (this
1857	usually works) and possibly another thread and a pipe or so to report to
1858	your main event loop.
1859		2478
1860	=head3 Watcher-Specific Functions and Data Members	2479	=head3 Watcher-Specific Functions and Data Members
1861		2480
1862	=over 4	2481	=over 4
1863		2482
…		…
1867		2486
1868	Configures the watcher to embed the given loop, which must be	2487	Configures the watcher to embed the given loop, which must be
1869	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	2488	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1870	invoked automatically, otherwise it is the responsibility of the callback	2489	invoked automatically, otherwise it is the responsibility of the callback
1871	to invoke it (it will continue to be called until the sweep has been done,	2490	to invoke it (it will continue to be called until the sweep has been done,
1872	if you do not want thta, you need to temporarily stop the embed watcher).	2491	if you do not want that, you need to temporarily stop the embed watcher).
1873		2492
1874	=item ev_embed_sweep (loop, ev_embed *)	2493	=item ev_embed_sweep (loop, ev_embed *)
1875		2494
1876	Make a single, non-blocking sweep over the embedded loop. This works	2495	Make a single, non-blocking sweep over the embedded loop. This works
1877	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	2496	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
1878	apropriate way for embedded loops.	2497	appropriate way for embedded loops.
1879		2498
1880	=item struct ev_loop *other [read-only]	2499	=item struct ev_loop *other [read-only]
1881		2500
1882	The embedded event loop.	2501	The embedded event loop.
1883		2502
1884	=back	2503	=back
		2504
		2505	=head3 Examples
		2506
		2507	Example: Try to get an embeddable event loop and embed it into the default
		2508	event loop. If that is not possible, use the default loop. The default
		2509	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2510	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2511	used).
		2512
		2513	struct ev_loop *loop_hi = ev_default_init (0);
		2514	struct ev_loop *loop_lo = 0;
		2515	ev_embed embed;
		2516
		2517	// see if there is a chance of getting one that works
		2518	// (remember that a flags value of 0 means autodetection)
		2519	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2520	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2521	: 0;
		2522
		2523	// if we got one, then embed it, otherwise default to loop_hi
		2524	if (loop_lo)
		2525	{
		2526	ev_embed_init (&embed, 0, loop_lo);
		2527	ev_embed_start (loop_hi, &embed);
		2528	}
		2529	else
		2530	loop_lo = loop_hi;
		2531
		2532	Example: Check if kqueue is available but not recommended and create
		2533	a kqueue backend for use with sockets (which usually work with any
		2534	kqueue implementation). Store the kqueue/socket-only event loop in
		2535	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2536
		2537	struct ev_loop *loop = ev_default_init (0);
		2538	struct ev_loop *loop_socket = 0;
		2539	ev_embed embed;
		2540
		2541	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2542	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2543	{
		2544	ev_embed_init (&embed, 0, loop_socket);
		2545	ev_embed_start (loop, &embed);
		2546	}
		2547
		2548	if (!loop_socket)
		2549	loop_socket = loop;
		2550
		2551	// now use loop_socket for all sockets, and loop for everything else
1885		2552
1886		2553
1887	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	2554	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
1888		2555
1889	Fork watchers are called when a C<fork ()> was detected (usually because	2556	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
1905	believe me.	2572	believe me.
1906		2573
1907	=back	2574	=back
1908		2575
1909		2576
		2577	=head2 C<ev_async> - how to wake up another event loop
		2578
		2579	In general, you cannot use an C<ev_loop> from multiple threads or other
		2580	asynchronous sources such as signal handlers (as opposed to multiple event
		2581	loops - those are of course safe to use in different threads).
		2582
		2583	Sometimes, however, you need to wake up another event loop you do not
		2584	control, for example because it belongs to another thread. This is what
		2585	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2586	can signal it by calling C<ev_async_send>, which is thread- and signal
		2587	safe.
		2588
		2589	This functionality is very similar to C<ev_signal> watchers, as signals,
		2590	too, are asynchronous in nature, and signals, too, will be compressed
		2591	(i.e. the number of callback invocations may be less than the number of
		2592	C<ev_async_sent> calls).
		2593
		2594	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2595	just the default loop.
		2596
		2597	=head3 Queueing
		2598
		2599	C<ev_async> does not support queueing of data in any way. The reason
		2600	is that the author does not know of a simple (or any) algorithm for a
		2601	multiple-writer-single-reader queue that works in all cases and doesn't
		2602	need elaborate support such as pthreads.
		2603
		2604	That means that if you want to queue data, you have to provide your own
		2605	queue. But at least I can tell you how to implement locking around your
		2606	queue:
		2607
		2608	=over 4
		2609
		2610	=item queueing from a signal handler context
		2611
		2612	To implement race-free queueing, you simply add to the queue in the signal
		2613	handler but you block the signal handler in the watcher callback. Here is
		2614	an example that does that for some fictitious SIGUSR1 handler:
		2615
		2616	static ev_async mysig;
		2617
		2618	static void
		2619	sigusr1_handler (void)
		2620	{
		2621	sometype data;
		2622
		2623	// no locking etc.
		2624	queue_put (data);
		2625	ev_async_send (EV_DEFAULT_ &mysig);
		2626	}
		2627
		2628	static void
		2629	mysig_cb (EV_P_ ev_async *w, int revents)
		2630	{
		2631	sometype data;
		2632	sigset_t block, prev;
		2633
		2634	sigemptyset (&block);
		2635	sigaddset (&block, SIGUSR1);
		2636	sigprocmask (SIG_BLOCK, &block, &prev);
		2637
		2638	while (queue_get (&data))
		2639	process (data);
		2640
		2641	if (sigismember (&prev, SIGUSR1)
		2642	sigprocmask (SIG_UNBLOCK, &block, 0);
		2643	}
		2644
		2645	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2646	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2647	either...).
		2648
		2649	=item queueing from a thread context
		2650
		2651	The strategy for threads is different, as you cannot (easily) block
		2652	threads but you can easily preempt them, so to queue safely you need to
		2653	employ a traditional mutex lock, such as in this pthread example:
		2654
		2655	static ev_async mysig;
		2656	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2657
		2658	static void
		2659	otherthread (void)
		2660	{
		2661	// only need to lock the actual queueing operation
		2662	pthread_mutex_lock (&mymutex);
		2663	queue_put (data);
		2664	pthread_mutex_unlock (&mymutex);
		2665
		2666	ev_async_send (EV_DEFAULT_ &mysig);
		2667	}
		2668
		2669	static void
		2670	mysig_cb (EV_P_ ev_async *w, int revents)
		2671	{
		2672	pthread_mutex_lock (&mymutex);
		2673
		2674	while (queue_get (&data))
		2675	process (data);
		2676
		2677	pthread_mutex_unlock (&mymutex);
		2678	}
		2679
		2680	=back
		2681
		2682
		2683	=head3 Watcher-Specific Functions and Data Members
		2684
		2685	=over 4
		2686
		2687	=item ev_async_init (ev_async *, callback)
		2688
		2689	Initialises and configures the async watcher - it has no parameters of any
		2690	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		2691	trust me.
		2692
		2693	=item ev_async_send (loop, ev_async *)
		2694
		2695	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2696	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2697	C<ev_feed_event>, this call is safe to do from other threads, signal or
		2698	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		2699	section below on what exactly this means).
		2700
		2701	Note that, as with other watchers in libev, multiple events might get
		2702	compressed into a single callback invocation (another way to look at this
		2703	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		2704	reset when the event loop detects that).
		2705
		2706	This call incurs the overhead of a system call only once per event loop
		2707	iteration, so while the overhead might be noticeable, it doesn't apply to
		2708	repeated calls to C<ev_async_send> for the same event loop.
		2709
		2710	=item bool = ev_async_pending (ev_async *)
		2711
		2712	Returns a non-zero value when C<ev_async_send> has been called on the
		2713	watcher but the event has not yet been processed (or even noted) by the
		2714	event loop.
		2715
		2716	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2717	the loop iterates next and checks for the watcher to have become active,
		2718	it will reset the flag again. C<ev_async_pending> can be used to very
		2719	quickly check whether invoking the loop might be a good idea.
		2720
		2721	Not that this does I<not> check whether the watcher itself is pending,
		2722	only whether it has been requested to make this watcher pending: there
		2723	is a time window between the event loop checking and resetting the async
		2724	notification, and the callback being invoked.
		2725
		2726	=back
		2727
		2728
1910	=head1 OTHER FUNCTIONS	2729	=head1 OTHER FUNCTIONS
1911		2730
1912	There are some other functions of possible interest. Described. Here. Now.	2731	There are some other functions of possible interest. Described. Here. Now.
1913		2732
1914	=over 4	2733	=over 4
1915		2734
1916	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	2735	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1917		2736
1918	This function combines a simple timer and an I/O watcher, calls your	2737	This function combines a simple timer and an I/O watcher, calls your
1919	callback on whichever event happens first and automatically stop both	2738	callback on whichever event happens first and automatically stops both
1920	watchers. This is useful if you want to wait for a single event on an fd	2739	watchers. This is useful if you want to wait for a single event on an fd
1921	or timeout without having to allocate/configure/start/stop/free one or	2740	or timeout without having to allocate/configure/start/stop/free one or
1922	more watchers yourself.	2741	more watchers yourself.
1923		2742
1924	If C<fd> is less than 0, then no I/O watcher will be started and events	2743	If C<fd> is less than 0, then no I/O watcher will be started and the
1925	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	2744	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1926	C<events> set will be craeted and started.	2745	the given C<fd> and C<events> set will be created and started.
1927		2746
1928	If C<timeout> is less than 0, then no timeout watcher will be	2747	If C<timeout> is less than 0, then no timeout watcher will be
1929	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	2748	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1930	repeat = 0) will be started. While C<0> is a valid timeout, it is of	2749	repeat = 0) will be started. C<0> is a valid timeout.
1931	dubious value.
1932		2750
1933	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	2751	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
1934	passed an C<revents> set like normal event callbacks (a combination of	2752	passed an C<revents> set like normal event callbacks (a combination of
1935	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	2753	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
1936	value passed to C<ev_once>:	2754	value passed to C<ev_once>. Note that it is possible to receive I<both>
		2755	a timeout and an io event at the same time - you probably should give io
		2756	events precedence.
1937		2757
		2758	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		2759
1938	static void stdin_ready (int revents, void *arg)	2760	static void stdin_ready (int revents, void *arg)
1939	{	2761	{
1940	if (revents & EV_TIMEOUT)
1941	/* doh, nothing entered */;
1942	else if (revents & EV_READ)	2762	if (revents & EV_READ)
1943	/* stdin might have data for us, joy! */;	2763	/* stdin might have data for us, joy! */;
		2764	else if (revents & EV_TIMEOUT)
		2765	/* doh, nothing entered */;
1944	}	2766	}
1945		2767
1946	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2768	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1947		2769
1948	=item ev_feed_event (ev_loop *, watcher *, int revents)	2770	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
1949		2771
1950	Feeds the given event set into the event loop, as if the specified event	2772	Feeds the given event set into the event loop, as if the specified event
1951	had happened for the specified watcher (which must be a pointer to an	2773	had happened for the specified watcher (which must be a pointer to an
1952	initialised but not necessarily started event watcher).	2774	initialised but not necessarily started event watcher).
1953		2775
1954	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	2776	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
1955		2777
1956	Feed an event on the given fd, as if a file descriptor backend detected	2778	Feed an event on the given fd, as if a file descriptor backend detected
1957	the given events it.	2779	the given events it.
1958		2780
1959	=item ev_feed_signal_event (ev_loop *loop, int signum)	2781	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
1960		2782
1961	Feed an event as if the given signal occured (C<loop> must be the default	2783	Feed an event as if the given signal occurred (C<loop> must be the default
1962	loop!).	2784	loop!).
1963		2785
1964	=back	2786	=back
1965		2787
1966		2788
…		…
1982		2804
1983	=item * Priorities are not currently supported. Initialising priorities	2805	=item * Priorities are not currently supported. Initialising priorities
1984	will fail and all watchers will have the same priority, even though there	2806	will fail and all watchers will have the same priority, even though there
1985	is an ev_pri field.	2807	is an ev_pri field.
1986		2808
		2809	=item * In libevent, the last base created gets the signals, in libev, the
		2810	first base created (== the default loop) gets the signals.
		2811
1987	=item * Other members are not supported.	2812	=item * Other members are not supported.
1988		2813
1989	=item * The libev emulation is I<not> ABI compatible to libevent, you need	2814	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1990	to use the libev header file and library.	2815	to use the libev header file and library.
1991		2816
1992	=back	2817	=back
1993		2818
1994	=head1 C++ SUPPORT	2819	=head1 C++ SUPPORT
1995		2820
1996	Libev comes with some simplistic wrapper classes for C++ that mainly allow	2821	Libev comes with some simplistic wrapper classes for C++ that mainly allow
1997	you to use some convinience methods to start/stop watchers and also change	2822	you to use some convenience methods to start/stop watchers and also change
1998	the callback model to a model using method callbacks on objects.	2823	the callback model to a model using method callbacks on objects.
1999		2824
2000	To use it,	2825	To use it,
2001		2826
2002	#include <ev++.h>	2827	#include <ev++.h>
2003		2828
2004	This automatically includes F<ev.h> and puts all of its definitions (many	2829	This automatically includes F<ev.h> and puts all of its definitions (many
2005	of them macros) into the global namespace. All C++ specific things are	2830	of them macros) into the global namespace. All C++ specific things are
2006	put into the C<ev> namespace. It should support all the same embedding	2831	put into the C<ev> namespace. It should support all the same embedding
2007	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	2832	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
2074	your compiler is good :), then the method will be fully inlined into the	2899	your compiler is good :), then the method will be fully inlined into the
2075	thunking function, making it as fast as a direct C callback.	2900	thunking function, making it as fast as a direct C callback.
2076		2901
2077	Example: simple class declaration and watcher initialisation	2902	Example: simple class declaration and watcher initialisation
2078		2903
2079	struct myclass	2904	struct myclass
2080	{	2905	{
2081	void io_cb (ev::io &w, int revents) { }	2906	void io_cb (ev::io &w, int revents) { }
2082	}	2907	}
2083		2908
2084	myclass obj;	2909	myclass obj;
2085	ev::io iow;	2910	ev::io iow;
2086	iow.set <myclass, &myclass::io_cb> (&obj);	2911	iow.set <myclass, &myclass::io_cb> (&obj);
		2912
		2913	=item w->set (object *)
		2914
		2915	This is an B<experimental> feature that might go away in a future version.
		2916
		2917	This is a variation of a method callback - leaving out the method to call
		2918	will default the method to C<operator ()>, which makes it possible to use
		2919	functor objects without having to manually specify the C<operator ()> all
		2920	the time. Incidentally, you can then also leave out the template argument
		2921	list.
		2922
		2923	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		2924	int revents)>.
		2925
		2926	See the method-C<set> above for more details.
		2927
		2928	Example: use a functor object as callback.
		2929
		2930	struct myfunctor
		2931	{
		2932	void operator() (ev::io &w, int revents)
		2933	{
		2934	...
		2935	}
		2936	}
		2937
		2938	myfunctor f;
		2939
		2940	ev::io w;
		2941	w.set (&f);
2087		2942
2088	=item w->set<function> (void *data = 0)	2943	=item w->set<function> (void *data = 0)
2089		2944
2090	Also sets a callback, but uses a static method or plain function as	2945	Also sets a callback, but uses a static method or plain function as
2091	callback. The optional C<data> argument will be stored in the watcher's	2946	callback. The optional C<data> argument will be stored in the watcher's
…		…
2093		2948
2094	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	2949	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2095		2950
2096	See the method-C<set> above for more details.	2951	See the method-C<set> above for more details.
2097		2952
2098	Example:	2953	Example: Use a plain function as callback.
2099		2954
2100	static void io_cb (ev::io &w, int revents) { }	2955	static void io_cb (ev::io &w, int revents) { }
2101	iow.set <io_cb> ();	2956	iow.set <io_cb> ();
2102		2957
2103	=item w->set (struct ev_loop *)	2958	=item w->set (struct ev_loop *)
2104		2959
2105	Associates a different C<struct ev_loop> with this watcher. You can only	2960	Associates a different C<struct ev_loop> with this watcher. You can only
2106	do this when the watcher is inactive (and not pending either).	2961	do this when the watcher is inactive (and not pending either).
2107		2962
2108	=item w->set ([args])	2963	=item w->set ([arguments])
2109		2964
2110	Basically the same as C<ev_TYPE_set>, with the same args. Must be	2965	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
2111	called at least once. Unlike the C counterpart, an active watcher gets	2966	called at least once. Unlike the C counterpart, an active watcher gets
2112	automatically stopped and restarted when reconfiguring it with this	2967	automatically stopped and restarted when reconfiguring it with this
2113	method.	2968	method.
2114		2969
2115	=item w->start ()	2970	=item w->start ()
…		…
2139	=back	2994	=back
2140		2995
2141	Example: Define a class with an IO and idle watcher, start one of them in	2996	Example: Define a class with an IO and idle watcher, start one of them in
2142	the constructor.	2997	the constructor.
2143		2998
2144	class myclass	2999	class myclass
2145	{	3000	{
2146	ev_io io; void io_cb (ev::io &w, int revents);	3001	ev::io io ; void io_cb (ev::io &w, int revents);
2147	ev_idle idle void idle_cb (ev::idle &w, int revents);	3002	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2148		3003
2149	myclass ();	3004	myclass (int fd)
2150	}	3005	{
2151
2152	myclass::myclass (int fd)
2153	{
2154	io .set <myclass, &myclass::io_cb > (this);	3006	io .set <myclass, &myclass::io_cb > (this);
2155	idle.set <myclass, &myclass::idle_cb> (this);	3007	idle.set <myclass, &myclass::idle_cb> (this);
2156		3008
2157	io.start (fd, ev::READ);	3009	io.start (fd, ev::READ);
		3010	}
2158	}	3011	};
		3012
		3013
		3014	=head1 OTHER LANGUAGE BINDINGS
		3015
		3016	Libev does not offer other language bindings itself, but bindings for a
		3017	number of languages exist in the form of third-party packages. If you know
		3018	any interesting language binding in addition to the ones listed here, drop
		3019	me a note.
		3020
		3021	=over 4
		3022
		3023	=item Perl
		3024
		3025	The EV module implements the full libev API and is actually used to test
		3026	libev. EV is developed together with libev. Apart from the EV core module,
		3027	there are additional modules that implement libev-compatible interfaces
		3028	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3029	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3030	and C<EV::Glib>).
		3031
		3032	It can be found and installed via CPAN, its homepage is at
		3033	L<http://software.schmorp.de/pkg/EV>.
		3034
		3035	=item Python
		3036
		3037	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3038	seems to be quite complete and well-documented.
		3039
		3040	=item Ruby
		3041
		3042	Tony Arcieri has written a ruby extension that offers access to a subset
		3043	of the libev API and adds file handle abstractions, asynchronous DNS and
		3044	more on top of it. It can be found via gem servers. Its homepage is at
		3045	L<http://rev.rubyforge.org/>.
		3046
		3047	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3048	makes rev work even on mingw.
		3049
		3050	=item Haskell
		3051
		3052	A haskell binding to libev is available at
		3053	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3054
		3055	=item D
		3056
		3057	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3058	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3059
		3060	=item Ocaml
		3061
		3062	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3063	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3064
		3065	=back
2159		3066
2160		3067
2161	=head1 MACRO MAGIC	3068	=head1 MACRO MAGIC
2162		3069
2163	Libev can be compiled with a variety of options, the most fundamantal	3070	Libev can be compiled with a variety of options, the most fundamental
2164	of which is C<EV_MULTIPLICITY>. This option determines whether (most)	3071	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2165	functions and callbacks have an initial C<struct ev_loop *> argument.	3072	functions and callbacks have an initial C<struct ev_loop *> argument.
2166		3073
2167	To make it easier to write programs that cope with either variant, the	3074	To make it easier to write programs that cope with either variant, the
2168	following macros are defined:	3075	following macros are defined:
…		…
2173		3080
2174	This provides the loop I<argument> for functions, if one is required ("ev	3081	This provides the loop I<argument> for functions, if one is required ("ev
2175	loop argument"). The C<EV_A> form is used when this is the sole argument,	3082	loop argument"). The C<EV_A> form is used when this is the sole argument,
2176	C<EV_A_> is used when other arguments are following. Example:	3083	C<EV_A_> is used when other arguments are following. Example:
2177		3084
2178	ev_unref (EV_A);	3085	ev_unref (EV_A);
2179	ev_timer_add (EV_A_ watcher);	3086	ev_timer_add (EV_A_ watcher);
2180	ev_loop (EV_A_ 0);	3087	ev_loop (EV_A_ 0);
2181		3088
2182	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	3089	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2183	which is often provided by the following macro.	3090	which is often provided by the following macro.
2184		3091
2185	=item C<EV_P>, C<EV_P_>	3092	=item C<EV_P>, C<EV_P_>
2186		3093
2187	This provides the loop I<parameter> for functions, if one is required ("ev	3094	This provides the loop I<parameter> for functions, if one is required ("ev
2188	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	3095	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
2189	C<EV_P_> is used when other parameters are following. Example:	3096	C<EV_P_> is used when other parameters are following. Example:
2190		3097
2191	// this is how ev_unref is being declared	3098	// this is how ev_unref is being declared
2192	static void ev_unref (EV_P);	3099	static void ev_unref (EV_P);
2193		3100
2194	// this is how you can declare your typical callback	3101	// this is how you can declare your typical callback
2195	static void cb (EV_P_ ev_timer *w, int revents)	3102	static void cb (EV_P_ ev_timer *w, int revents)
2196		3103
2197	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	3104	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
2198	suitable for use with C<EV_A>.	3105	suitable for use with C<EV_A>.
2199		3106
2200	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3107	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2201		3108
2202	Similar to the other two macros, this gives you the value of the default	3109	Similar to the other two macros, this gives you the value of the default
2203	loop, if multiple loops are supported ("ev loop default").	3110	loop, if multiple loops are supported ("ev loop default").
		3111
		3112	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3113
		3114	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3115	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3116	is undefined when the default loop has not been initialised by a previous
		3117	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3118
		3119	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3120	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
2204		3121
2205	=back	3122	=back
2206		3123
2207	Example: Declare and initialise a check watcher, utilising the above	3124	Example: Declare and initialise a check watcher, utilising the above
2208	macros so it will work regardless of whether multiple loops are supported	3125	macros so it will work regardless of whether multiple loops are supported
2209	or not.	3126	or not.
2210		3127
2211	static void	3128	static void
2212	check_cb (EV_P_ ev_timer *w, int revents)	3129	check_cb (EV_P_ ev_timer *w, int revents)
2213	{	3130	{
2214	ev_check_stop (EV_A_ w);	3131	ev_check_stop (EV_A_ w);
2215	}	3132	}
2216		3133
2217	ev_check check;	3134	ev_check check;
2218	ev_check_init (&check, check_cb);	3135	ev_check_init (&check, check_cb);
2219	ev_check_start (EV_DEFAULT_ &check);	3136	ev_check_start (EV_DEFAULT_ &check);
2220	ev_loop (EV_DEFAULT_ 0);	3137	ev_loop (EV_DEFAULT_ 0);
2221		3138
2222	=head1 EMBEDDING	3139	=head1 EMBEDDING
2223		3140
2224	Libev can (and often is) directly embedded into host	3141	Libev can (and often is) directly embedded into host
2225	applications. Examples of applications that embed it include the Deliantra	3142	applications. Examples of applications that embed it include the Deliantra
…		…
2232	libev somewhere in your source tree).	3149	libev somewhere in your source tree).
2233		3150
2234	=head2 FILESETS	3151	=head2 FILESETS
2235		3152
2236	Depending on what features you need you need to include one or more sets of files	3153	Depending on what features you need you need to include one or more sets of files
2237	in your app.	3154	in your application.
2238		3155
2239	=head3 CORE EVENT LOOP	3156	=head3 CORE EVENT LOOP
2240		3157
2241	To include only the libev core (all the C<ev_*> functions), with manual	3158	To include only the libev core (all the C<ev_*> functions), with manual
2242	configuration (no autoconf):	3159	configuration (no autoconf):
2243		3160
2244	#define EV_STANDALONE 1	3161	#define EV_STANDALONE 1
2245	#include "ev.c"	3162	#include "ev.c"
2246		3163
2247	This will automatically include F<ev.h>, too, and should be done in a	3164	This will automatically include F<ev.h>, too, and should be done in a
2248	single C source file only to provide the function implementations. To use	3165	single C source file only to provide the function implementations. To use
2249	it, do the same for F<ev.h> in all files wishing to use this API (best	3166	it, do the same for F<ev.h> in all files wishing to use this API (best
2250	done by writing a wrapper around F<ev.h> that you can include instead and	3167	done by writing a wrapper around F<ev.h> that you can include instead and
2251	where you can put other configuration options):	3168	where you can put other configuration options):
2252		3169
2253	#define EV_STANDALONE 1	3170	#define EV_STANDALONE 1
2254	#include "ev.h"	3171	#include "ev.h"
2255		3172
2256	Both header files and implementation files can be compiled with a C++	3173	Both header files and implementation files can be compiled with a C++
2257	compiler (at least, thats a stated goal, and breakage will be treated	3174	compiler (at least, that's a stated goal, and breakage will be treated
2258	as a bug).	3175	as a bug).
2259		3176
2260	You need the following files in your source tree, or in a directory	3177	You need the following files in your source tree, or in a directory
2261	in your include path (e.g. in libev/ when using -Ilibev):	3178	in your include path (e.g. in libev/ when using -Ilibev):
2262		3179
2263	ev.h	3180	ev.h
2264	ev.c	3181	ev.c
2265	ev_vars.h	3182	ev_vars.h
2266	ev_wrap.h	3183	ev_wrap.h
2267		3184
2268	ev_win32.c required on win32 platforms only	3185	ev_win32.c required on win32 platforms only
2269		3186
2270	ev_select.c only when select backend is enabled (which is enabled by default)	3187	ev_select.c only when select backend is enabled (which is enabled by default)
2271	ev_poll.c only when poll backend is enabled (disabled by default)	3188	ev_poll.c only when poll backend is enabled (disabled by default)
2272	ev_epoll.c only when the epoll backend is enabled (disabled by default)	3189	ev_epoll.c only when the epoll backend is enabled (disabled by default)
2273	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	3190	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2274	ev_port.c only when the solaris port backend is enabled (disabled by default)	3191	ev_port.c only when the solaris port backend is enabled (disabled by default)
2275		3192
2276	F<ev.c> includes the backend files directly when enabled, so you only need	3193	F<ev.c> includes the backend files directly when enabled, so you only need
2277	to compile this single file.	3194	to compile this single file.
2278		3195
2279	=head3 LIBEVENT COMPATIBILITY API	3196	=head3 LIBEVENT COMPATIBILITY API
2280		3197
2281	To include the libevent compatibility API, also include:	3198	To include the libevent compatibility API, also include:
2282		3199
2283	#include "event.c"	3200	#include "event.c"
2284		3201
2285	in the file including F<ev.c>, and:	3202	in the file including F<ev.c>, and:
2286		3203
2287	#include "event.h"	3204	#include "event.h"
2288		3205
2289	in the files that want to use the libevent API. This also includes F<ev.h>.	3206	in the files that want to use the libevent API. This also includes F<ev.h>.
2290		3207
2291	You need the following additional files for this:	3208	You need the following additional files for this:
2292		3209
2293	event.h	3210	event.h
2294	event.c	3211	event.c
2295		3212
2296	=head3 AUTOCONF SUPPORT	3213	=head3 AUTOCONF SUPPORT
2297		3214
2298	Instead of using C<EV_STANDALONE=1> and providing your config in	3215	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2299	whatever way you want, you can also C<m4_include([libev.m4])> in your	3216	whatever way you want, you can also C<m4_include([libev.m4])> in your
2300	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	3217	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2301	include F<config.h> and configure itself accordingly.	3218	include F<config.h> and configure itself accordingly.
2302		3219
2303	For this of course you need the m4 file:	3220	For this of course you need the m4 file:
2304		3221
2305	libev.m4	3222	libev.m4
2306		3223
2307	=head2 PREPROCESSOR SYMBOLS/MACROS	3224	=head2 PREPROCESSOR SYMBOLS/MACROS
2308		3225
2309	Libev can be configured via a variety of preprocessor symbols you have to define	3226	Libev can be configured via a variety of preprocessor symbols you have to
2310	before including any of its files. The default is not to build for multiplicity	3227	define before including any of its files. The default in the absence of
2311	and only include the select backend.	3228	autoconf is documented for every option.
2312		3229
2313	=over 4	3230	=over 4
2314		3231
2315	=item EV_STANDALONE	3232	=item EV_STANDALONE
2316		3233
…		…
2318	keeps libev from including F<config.h>, and it also defines dummy	3235	keeps libev from including F<config.h>, and it also defines dummy
2319	implementations for some libevent functions (such as logging, which is not	3236	implementations for some libevent functions (such as logging, which is not
2320	supported). It will also not define any of the structs usually found in	3237	supported). It will also not define any of the structs usually found in
2321	F<event.h> that are not directly supported by the libev core alone.	3238	F<event.h> that are not directly supported by the libev core alone.
2322		3239
		3240	In stanbdalone mode, libev will still try to automatically deduce the
		3241	configuration, but has to be more conservative.
		3242
2323	=item EV_USE_MONOTONIC	3243	=item EV_USE_MONOTONIC
2324		3244
2325	If defined to be C<1>, libev will try to detect the availability of the	3245	If defined to be C<1>, libev will try to detect the availability of the
2326	monotonic clock option at both compiletime and runtime. Otherwise no use	3246	monotonic clock option at both compile time and runtime. Otherwise no
2327	of the monotonic clock option will be attempted. If you enable this, you	3247	use of the monotonic clock option will be attempted. If you enable this,
2328	usually have to link against librt or something similar. Enabling it when	3248	you usually have to link against librt or something similar. Enabling it
2329	the functionality isn't available is safe, though, although you have	3249	when the functionality isn't available is safe, though, although you have
2330	to make sure you link against any libraries where the C<clock_gettime>	3250	to make sure you link against any libraries where the C<clock_gettime>
2331	function is hiding in (often F<-lrt>).	3251	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2332		3252
2333	=item EV_USE_REALTIME	3253	=item EV_USE_REALTIME
2334		3254
2335	If defined to be C<1>, libev will try to detect the availability of the	3255	If defined to be C<1>, libev will try to detect the availability of the
2336	realtime clock option at compiletime (and assume its availability at	3256	real-time clock option at compile time (and assume its availability
2337	runtime if successful). Otherwise no use of the realtime clock option will	3257	at runtime if successful). Otherwise no use of the real-time clock
2338	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3258	option will be attempted. This effectively replaces C<gettimeofday>
2339	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	3259	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2340	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	3260	correctness. See the note about libraries in the description of
		3261	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3262	C<EV_USE_CLOCK_SYSCALL>.
		3263
		3264	=item EV_USE_CLOCK_SYSCALL
		3265
		3266	If defined to be C<1>, libev will try to use a direct syscall instead
		3267	of calling the system-provided C<clock_gettime> function. This option
		3268	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3269	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3270	programs needlessly. Using a direct syscall is slightly slower (in
		3271	theory), because no optimised vdso implementation can be used, but avoids
		3272	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3273	higher, as it simplifies linking (no need for C<-lrt>).
2341		3274
2342	=item EV_USE_NANOSLEEP	3275	=item EV_USE_NANOSLEEP
2343		3276
2344	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	3277	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2345	and will use it for delays. Otherwise it will use C<select ()>.	3278	and will use it for delays. Otherwise it will use C<select ()>.
2346		3279
		3280	=item EV_USE_EVENTFD
		3281
		3282	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3283	available and will probe for kernel support at runtime. This will improve
		3284	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3285	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3286	2.7 or newer, otherwise disabled.
		3287
2347	=item EV_USE_SELECT	3288	=item EV_USE_SELECT
2348		3289
2349	If undefined or defined to be C<1>, libev will compile in support for the	3290	If undefined or defined to be C<1>, libev will compile in support for the
2350	C<select>(2) backend. No attempt at autodetection will be done: if no	3291	C<select>(2) backend. No attempt at auto-detection will be done: if no
2351	other method takes over, select will be it. Otherwise the select backend	3292	other method takes over, select will be it. Otherwise the select backend
2352	will not be compiled in.	3293	will not be compiled in.
2353		3294
2354	=item EV_SELECT_USE_FD_SET	3295	=item EV_SELECT_USE_FD_SET
2355		3296
2356	If defined to C<1>, then the select backend will use the system C<fd_set>	3297	If defined to C<1>, then the select backend will use the system C<fd_set>
2357	structure. This is useful if libev doesn't compile due to a missing	3298	structure. This is useful if libev doesn't compile due to a missing
2358	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	3299	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2359	exotic systems. This usually limits the range of file descriptors to some	3300	on exotic systems. This usually limits the range of file descriptors to
2360	low limit such as 1024 or might have other limitations (winsocket only	3301	some low limit such as 1024 or might have other limitations (winsocket
2361	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3302	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2362	influence the size of the C<fd_set> used.	3303	configures the maximum size of the C<fd_set>.
2363		3304
2364	=item EV_SELECT_IS_WINSOCKET	3305	=item EV_SELECT_IS_WINSOCKET
2365		3306
2366	When defined to C<1>, the select backend will assume that	3307	When defined to C<1>, the select backend will assume that
2367	select/socket/connect etc. don't understand file descriptors but	3308	select/socket/connect etc. don't understand file descriptors but
…		…
2369	be used is the winsock select). This means that it will call	3310	be used is the winsock select). This means that it will call
2370	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3311	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2371	it is assumed that all these functions actually work on fds, even	3312	it is assumed that all these functions actually work on fds, even
2372	on win32. Should not be defined on non-win32 platforms.	3313	on win32. Should not be defined on non-win32 platforms.
2373		3314
		3315	=item EV_FD_TO_WIN32_HANDLE
		3316
		3317	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3318	file descriptors to socket handles. When not defining this symbol (the
		3319	default), then libev will call C<_get_osfhandle>, which is usually
		3320	correct. In some cases, programs use their own file descriptor management,
		3321	in which case they can provide this function to map fds to socket handles.
		3322
2374	=item EV_USE_POLL	3323	=item EV_USE_POLL
2375		3324
2376	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3325	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2377	backend. Otherwise it will be enabled on non-win32 platforms. It	3326	backend. Otherwise it will be enabled on non-win32 platforms. It
2378	takes precedence over select.	3327	takes precedence over select.
2379		3328
2380	=item EV_USE_EPOLL	3329	=item EV_USE_EPOLL
2381		3330
2382	If defined to be C<1>, libev will compile in support for the Linux	3331	If defined to be C<1>, libev will compile in support for the Linux
2383	C<epoll>(7) backend. Its availability will be detected at runtime,	3332	C<epoll>(7) backend. Its availability will be detected at runtime,
2384	otherwise another method will be used as fallback. This is the	3333	otherwise another method will be used as fallback. This is the preferred
2385	preferred backend for GNU/Linux systems.	3334	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3335	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2386		3336
2387	=item EV_USE_KQUEUE	3337	=item EV_USE_KQUEUE
2388		3338
2389	If defined to be C<1>, libev will compile in support for the BSD style	3339	If defined to be C<1>, libev will compile in support for the BSD style
2390	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	3340	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2403	otherwise another method will be used as fallback. This is the preferred	3353	otherwise another method will be used as fallback. This is the preferred
2404	backend for Solaris 10 systems.	3354	backend for Solaris 10 systems.
2405		3355
2406	=item EV_USE_DEVPOLL	3356	=item EV_USE_DEVPOLL
2407		3357
2408	reserved for future expansion, works like the USE symbols above.	3358	Reserved for future expansion, works like the USE symbols above.
2409		3359
2410	=item EV_USE_INOTIFY	3360	=item EV_USE_INOTIFY
2411		3361
2412	If defined to be C<1>, libev will compile in support for the Linux inotify	3362	If defined to be C<1>, libev will compile in support for the Linux inotify
2413	interface to speed up C<ev_stat> watchers. Its actual availability will	3363	interface to speed up C<ev_stat> watchers. Its actual availability will
2414	be detected at runtime.	3364	be detected at runtime. If undefined, it will be enabled if the headers
		3365	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3366
		3367	=item EV_ATOMIC_T
		3368
		3369	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3370	access is atomic with respect to other threads or signal contexts. No such
		3371	type is easily found in the C language, so you can provide your own type
		3372	that you know is safe for your purposes. It is used both for signal handler "locking"
		3373	as well as for signal and thread safety in C<ev_async> watchers.
		3374
		3375	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3376	(from F<signal.h>), which is usually good enough on most platforms.
2415		3377
2416	=item EV_H	3378	=item EV_H
2417		3379
2418	The name of the F<ev.h> header file used to include it. The default if	3380	The name of the F<ev.h> header file used to include it. The default if
2419	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This	3381	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2420	can be used to virtually rename the F<ev.h> header file in case of conflicts.	3382	used to virtually rename the F<ev.h> header file in case of conflicts.
2421		3383
2422	=item EV_CONFIG_H	3384	=item EV_CONFIG_H
2423		3385
2424	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	3386	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2425	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	3387	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2426	C<EV_H>, above.	3388	C<EV_H>, above.
2427		3389
2428	=item EV_EVENT_H	3390	=item EV_EVENT_H
2429		3391
2430	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	3392	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2431	of how the F<event.h> header can be found.	3393	of how the F<event.h> header can be found, the default is C<"event.h">.
2432		3394
2433	=item EV_PROTOTYPES	3395	=item EV_PROTOTYPES
2434		3396
2435	If defined to be C<0>, then F<ev.h> will not define any function	3397	If defined to be C<0>, then F<ev.h> will not define any function
2436	prototypes, but still define all the structs and other symbols. This is	3398	prototypes, but still define all the structs and other symbols. This is
…		…
2457	When doing priority-based operations, libev usually has to linearly search	3419	When doing priority-based operations, libev usually has to linearly search
2458	all the priorities, so having many of them (hundreds) uses a lot of space	3420	all the priorities, so having many of them (hundreds) uses a lot of space
2459	and time, so using the defaults of five priorities (-2 .. +2) is usually	3421	and time, so using the defaults of five priorities (-2 .. +2) is usually
2460	fine.	3422	fine.
2461		3423
2462	If your embedding app does not need any priorities, defining these both to	3424	If your embedding application does not need any priorities, defining these
2463	C<0> will save some memory and cpu.	3425	both to C<0> will save some memory and CPU.
2464		3426
2465	=item EV_PERIODIC_ENABLE	3427	=item EV_PERIODIC_ENABLE
2466		3428
2467	If undefined or defined to be C<1>, then periodic timers are supported. If	3429	If undefined or defined to be C<1>, then periodic timers are supported. If
2468	defined to be C<0>, then they are not. Disabling them saves a few kB of	3430	defined to be C<0>, then they are not. Disabling them saves a few kB of
…		…
2475	code.	3437	code.
2476		3438
2477	=item EV_EMBED_ENABLE	3439	=item EV_EMBED_ENABLE
2478		3440
2479	If undefined or defined to be C<1>, then embed watchers are supported. If	3441	If undefined or defined to be C<1>, then embed watchers are supported. If
2480	defined to be C<0>, then they are not.	3442	defined to be C<0>, then they are not. Embed watchers rely on most other
		3443	watcher types, which therefore must not be disabled.
2481		3444
2482	=item EV_STAT_ENABLE	3445	=item EV_STAT_ENABLE
2483		3446
2484	If undefined or defined to be C<1>, then stat watchers are supported. If	3447	If undefined or defined to be C<1>, then stat watchers are supported. If
2485	defined to be C<0>, then they are not.	3448	defined to be C<0>, then they are not.
…		…
2487	=item EV_FORK_ENABLE	3450	=item EV_FORK_ENABLE
2488		3451
2489	If undefined or defined to be C<1>, then fork watchers are supported. If	3452	If undefined or defined to be C<1>, then fork watchers are supported. If
2490	defined to be C<0>, then they are not.	3453	defined to be C<0>, then they are not.
2491		3454
		3455	=item EV_ASYNC_ENABLE
		3456
		3457	If undefined or defined to be C<1>, then async watchers are supported. If
		3458	defined to be C<0>, then they are not.
		3459
2492	=item EV_MINIMAL	3460	=item EV_MINIMAL
2493		3461
2494	If you need to shave off some kilobytes of code at the expense of some	3462	If you need to shave off some kilobytes of code at the expense of some
2495	speed, define this symbol to C<1>. Currently only used for gcc to override	3463	speed, define this symbol to C<1>. Currently this is used to override some
2496	some inlining decisions, saves roughly 30% codesize of amd64.	3464	inlining decisions, saves roughly 30% code size on amd64. It also selects a
		3465	much smaller 2-heap for timer management over the default 4-heap.
2497		3466
2498	=item EV_PID_HASHSIZE	3467	=item EV_PID_HASHSIZE
2499		3468
2500	C<ev_child> watchers use a small hash table to distribute workload by	3469	C<ev_child> watchers use a small hash table to distribute workload by
2501	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3470	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
2502	than enough. If you need to manage thousands of children you might want to	3471	than enough. If you need to manage thousands of children you might want to
2503	increase this value (I<must> be a power of two).	3472	increase this value (I<must> be a power of two).
2504		3473
2505	=item EV_INOTIFY_HASHSIZE	3474	=item EV_INOTIFY_HASHSIZE
2506		3475
2507	C<ev_staz> watchers use a small hash table to distribute workload by	3476	C<ev_stat> watchers use a small hash table to distribute workload by
2508	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	3477	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
2509	usually more than enough. If you need to manage thousands of C<ev_stat>	3478	usually more than enough. If you need to manage thousands of C<ev_stat>
2510	watchers you might want to increase this value (I<must> be a power of	3479	watchers you might want to increase this value (I<must> be a power of
2511	two).	3480	two).
2512		3481
		3482	=item EV_USE_4HEAP
		3483
		3484	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3485	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		3486	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		3487	faster performance with many (thousands) of watchers.
		3488
		3489	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3490	(disabled).
		3491
		3492	=item EV_HEAP_CACHE_AT
		3493
		3494	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3495	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		3496	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3497	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3498	but avoids random read accesses on heap changes. This improves performance
		3499	noticeably with many (hundreds) of watchers.
		3500
		3501	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3502	(disabled).
		3503
		3504	=item EV_VERIFY
		3505
		3506	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3507	be done: If set to C<0>, no internal verification code will be compiled
		3508	in. If set to C<1>, then verification code will be compiled in, but not
		3509	called. If set to C<2>, then the internal verification code will be
		3510	called once per loop, which can slow down libev. If set to C<3>, then the
		3511	verification code will be called very frequently, which will slow down
		3512	libev considerably.
		3513
		3514	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3515	C<0>.
		3516
2513	=item EV_COMMON	3517	=item EV_COMMON
2514		3518
2515	By default, all watchers have a C<void *data> member. By redefining	3519	By default, all watchers have a C<void *data> member. By redefining
2516	this macro to a something else you can include more and other types of	3520	this macro to a something else you can include more and other types of
2517	members. You have to define it each time you include one of the files,	3521	members. You have to define it each time you include one of the files,
2518	though, and it must be identical each time.	3522	though, and it must be identical each time.
2519		3523
2520	For example, the perl EV module uses something like this:	3524	For example, the perl EV module uses something like this:
2521		3525
2522	#define EV_COMMON \	3526	#define EV_COMMON \
2523	SV *self; /* contains this struct */ \	3527	SV *self; /* contains this struct */ \
2524	SV *cb_sv, *fh /* note no trailing ";" */	3528	SV *cb_sv, *fh /* note no trailing ";" */
2525		3529
2526	=item EV_CB_DECLARE (type)	3530	=item EV_CB_DECLARE (type)
2527		3531
2528	=item EV_CB_INVOKE (watcher, revents)	3532	=item EV_CB_INVOKE (watcher, revents)
2529		3533
…		…
2534	definition and a statement, respectively. See the F<ev.h> header file for	3538	definition and a statement, respectively. See the F<ev.h> header file for
2535	their default definitions. One possible use for overriding these is to	3539	their default definitions. One possible use for overriding these is to
2536	avoid the C<struct ev_loop *> as first argument in all cases, or to use	3540	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2537	method calls instead of plain function calls in C++.	3541	method calls instead of plain function calls in C++.
2538		3542
		3543	=back
		3544
2539	=head2 EXPORTED API SYMBOLS	3545	=head2 EXPORTED API SYMBOLS
2540		3546
2541	If you need to re-export the API (e.g. via a dll) and you need a list of	3547	If you need to re-export the API (e.g. via a DLL) and you need a list of
2542	exported symbols, you can use the provided F<Symbol.*> files which list	3548	exported symbols, you can use the provided F<Symbol.*> files which list
2543	all public symbols, one per line:	3549	all public symbols, one per line:
2544		3550
2545	Symbols.ev for libev proper	3551	Symbols.ev for libev proper
2546	Symbols.event for the libevent emulation	3552	Symbols.event for the libevent emulation
2547		3553
2548	This can also be used to rename all public symbols to avoid clashes with	3554	This can also be used to rename all public symbols to avoid clashes with
2549	multiple versions of libev linked together (which is obviously bad in	3555	multiple versions of libev linked together (which is obviously bad in
2550	itself, but sometimes it is inconvinient to avoid this).	3556	itself, but sometimes it is inconvenient to avoid this).
2551		3557
2552	A sed command like this will create wrapper C<#define>'s that you need to	3558	A sed command like this will create wrapper C<#define>'s that you need to
2553	include before including F<ev.h>:	3559	include before including F<ev.h>:
2554		3560
2555	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h	3561	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
…		…
2572	file.	3578	file.
2573		3579
2574	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	3580	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2575	that everybody includes and which overrides some configure choices:	3581	that everybody includes and which overrides some configure choices:
2576		3582
2577	#define EV_MINIMAL 1	3583	#define EV_MINIMAL 1
2578	#define EV_USE_POLL 0	3584	#define EV_USE_POLL 0
2579	#define EV_MULTIPLICITY 0	3585	#define EV_MULTIPLICITY 0
2580	#define EV_PERIODIC_ENABLE 0	3586	#define EV_PERIODIC_ENABLE 0
2581	#define EV_STAT_ENABLE 0	3587	#define EV_STAT_ENABLE 0
2582	#define EV_FORK_ENABLE 0	3588	#define EV_FORK_ENABLE 0
2583	#define EV_CONFIG_H <config.h>	3589	#define EV_CONFIG_H <config.h>
2584	#define EV_MINPRI 0	3590	#define EV_MINPRI 0
2585	#define EV_MAXPRI 0	3591	#define EV_MAXPRI 0
2586		3592
2587	#include "ev++.h"	3593	#include "ev++.h"
2588		3594
2589	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	3595	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2590		3596
2591	#include "ev_cpp.h"	3597	#include "ev_cpp.h"
2592	#include "ev.c"	3598	#include "ev.c"
2593		3599
		3600	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
2594		3601
		3602	=head2 THREADS AND COROUTINES
		3603
		3604	=head3 THREADS
		3605
		3606	All libev functions are reentrant and thread-safe unless explicitly
		3607	documented otherwise, but libev implements no locking itself. This means
		3608	that you can use as many loops as you want in parallel, as long as there
		3609	are no concurrent calls into any libev function with the same loop
		3610	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		3611	of course): libev guarantees that different event loops share no data
		3612	structures that need any locking.
		3613
		3614	Or to put it differently: calls with different loop parameters can be done
		3615	concurrently from multiple threads, calls with the same loop parameter
		3616	must be done serially (but can be done from different threads, as long as
		3617	only one thread ever is inside a call at any point in time, e.g. by using
		3618	a mutex per loop).
		3619
		3620	Specifically to support threads (and signal handlers), libev implements
		3621	so-called C<ev_async> watchers, which allow some limited form of
		3622	concurrency on the same event loop, namely waking it up "from the
		3623	outside".
		3624
		3625	If you want to know which design (one loop, locking, or multiple loops
		3626	without or something else still) is best for your problem, then I cannot
		3627	help you, but here is some generic advice:
		3628
		3629	=over 4
		3630
		3631	=item * most applications have a main thread: use the default libev loop
		3632	in that thread, or create a separate thread running only the default loop.
		3633
		3634	This helps integrating other libraries or software modules that use libev
		3635	themselves and don't care/know about threading.
		3636
		3637	=item * one loop per thread is usually a good model.
		3638
		3639	Doing this is almost never wrong, sometimes a better-performance model
		3640	exists, but it is always a good start.
		3641
		3642	=item * other models exist, such as the leader/follower pattern, where one
		3643	loop is handed through multiple threads in a kind of round-robin fashion.
		3644
		3645	Choosing a model is hard - look around, learn, know that usually you can do
		3646	better than you currently do :-)
		3647
		3648	=item * often you need to talk to some other thread which blocks in the
		3649	event loop.
		3650
		3651	C<ev_async> watchers can be used to wake them up from other threads safely
		3652	(or from signal contexts...).
		3653
		3654	An example use would be to communicate signals or other events that only
		3655	work in the default loop by registering the signal watcher with the
		3656	default loop and triggering an C<ev_async> watcher from the default loop
		3657	watcher callback into the event loop interested in the signal.
		3658
		3659	=back
		3660
		3661	=head3 COROUTINES
		3662
		3663	Libev is very accommodating to coroutines ("cooperative threads"):
		3664	libev fully supports nesting calls to its functions from different
		3665	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3666	different coroutines, and switch freely between both coroutines running the
		3667	loop, as long as you don't confuse yourself). The only exception is that
		3668	you must not do this from C<ev_periodic> reschedule callbacks.
		3669
		3670	Care has been taken to ensure that libev does not keep local state inside
		3671	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		3672	they do not call any callbacks.
		3673
		3674	=head2 COMPILER WARNINGS
		3675
		3676	Depending on your compiler and compiler settings, you might get no or a
		3677	lot of warnings when compiling libev code. Some people are apparently
		3678	scared by this.
		3679
		3680	However, these are unavoidable for many reasons. For one, each compiler
		3681	has different warnings, and each user has different tastes regarding
		3682	warning options. "Warn-free" code therefore cannot be a goal except when
		3683	targeting a specific compiler and compiler-version.
		3684
		3685	Another reason is that some compiler warnings require elaborate
		3686	workarounds, or other changes to the code that make it less clear and less
		3687	maintainable.
		3688
		3689	And of course, some compiler warnings are just plain stupid, or simply
		3690	wrong (because they don't actually warn about the condition their message
		3691	seems to warn about). For example, certain older gcc versions had some
		3692	warnings that resulted an extreme number of false positives. These have
		3693	been fixed, but some people still insist on making code warn-free with
		3694	such buggy versions.
		3695
		3696	While libev is written to generate as few warnings as possible,
		3697	"warn-free" code is not a goal, and it is recommended not to build libev
		3698	with any compiler warnings enabled unless you are prepared to cope with
		3699	them (e.g. by ignoring them). Remember that warnings are just that:
		3700	warnings, not errors, or proof of bugs.
		3701
		3702
		3703	=head2 VALGRIND
		3704
		3705	Valgrind has a special section here because it is a popular tool that is
		3706	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		3707
		3708	If you think you found a bug (memory leak, uninitialised data access etc.)
		3709	in libev, then check twice: If valgrind reports something like:
		3710
		3711	==2274== definitely lost: 0 bytes in 0 blocks.
		3712	==2274== possibly lost: 0 bytes in 0 blocks.
		3713	==2274== still reachable: 256 bytes in 1 blocks.
		3714
		3715	Then there is no memory leak, just as memory accounted to global variables
		3716	is not a memleak - the memory is still being referenced, and didn't leak.
		3717
		3718	Similarly, under some circumstances, valgrind might report kernel bugs
		3719	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		3720	although an acceptable workaround has been found here), or it might be
		3721	confused.
		3722
		3723	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		3724	make it into some kind of religion.
		3725
		3726	If you are unsure about something, feel free to contact the mailing list
		3727	with the full valgrind report and an explanation on why you think this
		3728	is a bug in libev (best check the archives, too :). However, don't be
		3729	annoyed when you get a brisk "this is no bug" answer and take the chance
		3730	of learning how to interpret valgrind properly.
		3731
		3732	If you need, for some reason, empty reports from valgrind for your project
		3733	I suggest using suppression lists.
		3734
		3735
		3736	=head1 PORTABILITY NOTES
		3737
		3738	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		3739
		3740	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		3741	requires, and its I/O model is fundamentally incompatible with the POSIX
		3742	model. Libev still offers limited functionality on this platform in
		3743	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		3744	descriptors. This only applies when using Win32 natively, not when using
		3745	e.g. cygwin.
		3746
		3747	Lifting these limitations would basically require the full
		3748	re-implementation of the I/O system. If you are into these kinds of
		3749	things, then note that glib does exactly that for you in a very portable
		3750	way (note also that glib is the slowest event library known to man).
		3751
		3752	There is no supported compilation method available on windows except
		3753	embedding it into other applications.
		3754
		3755	Not a libev limitation but worth mentioning: windows apparently doesn't
		3756	accept large writes: instead of resulting in a partial write, windows will
		3757	either accept everything or return C<ENOBUFS> if the buffer is too large,
		3758	so make sure you only write small amounts into your sockets (less than a
		3759	megabyte seems safe, but this apparently depends on the amount of memory
		3760	available).
		3761
		3762	Due to the many, low, and arbitrary limits on the win32 platform and
		3763	the abysmal performance of winsockets, using a large number of sockets
		3764	is not recommended (and not reasonable). If your program needs to use
		3765	more than a hundred or so sockets, then likely it needs to use a totally
		3766	different implementation for windows, as libev offers the POSIX readiness
		3767	notification model, which cannot be implemented efficiently on windows
		3768	(Microsoft monopoly games).
		3769
		3770	A typical way to use libev under windows is to embed it (see the embedding
		3771	section for details) and use the following F<evwrap.h> header file instead
		3772	of F<ev.h>:
		3773
		3774	#define EV_STANDALONE /* keeps ev from requiring config.h */
		3775	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		3776
		3777	#include "ev.h"
		3778
		3779	And compile the following F<evwrap.c> file into your project (make sure
		3780	you do I<not> compile the F<ev.c> or any other embedded source files!):
		3781
		3782	#include "evwrap.h"
		3783	#include "ev.c"
		3784
		3785	=over 4
		3786
		3787	=item The winsocket select function
		3788
		3789	The winsocket C<select> function doesn't follow POSIX in that it
		3790	requires socket I<handles> and not socket I<file descriptors> (it is
		3791	also extremely buggy). This makes select very inefficient, and also
		3792	requires a mapping from file descriptors to socket handles (the Microsoft
		3793	C runtime provides the function C<_open_osfhandle> for this). See the
		3794	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		3795	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		3796
		3797	The configuration for a "naked" win32 using the Microsoft runtime
		3798	libraries and raw winsocket select is:
		3799
		3800	#define EV_USE_SELECT 1
		3801	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		3802
		3803	Note that winsockets handling of fd sets is O(n), so you can easily get a
		3804	complexity in the O(n²) range when using win32.
		3805
		3806	=item Limited number of file descriptors
		3807
		3808	Windows has numerous arbitrary (and low) limits on things.
		3809
		3810	Early versions of winsocket's select only supported waiting for a maximum
		3811	of C<64> handles (probably owning to the fact that all windows kernels
		3812	can only wait for C<64> things at the same time internally; Microsoft
		3813	recommends spawning a chain of threads and wait for 63 handles and the
		3814	previous thread in each. Great).
		3815
		3816	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		3817	to some high number (e.g. C<2048>) before compiling the winsocket select
		3818	call (which might be in libev or elsewhere, for example, perl does its own
		3819	select emulation on windows).
		3820
		3821	Another limit is the number of file descriptors in the Microsoft runtime
		3822	libraries, which by default is C<64> (there must be a hidden I<64> fetish
		3823	or something like this inside Microsoft). You can increase this by calling
		3824	C<_setmaxstdio>, which can increase this limit to C<2048> (another
		3825	arbitrary limit), but is broken in many versions of the Microsoft runtime
		3826	libraries.
		3827
		3828	This might get you to about C<512> or C<2048> sockets (depending on
		3829	windows version and/or the phase of the moon). To get more, you need to
		3830	wrap all I/O functions and provide your own fd management, but the cost of
		3831	calling select (O(n²)) will likely make this unworkable.
		3832
		3833	=back
		3834
		3835	=head2 PORTABILITY REQUIREMENTS
		3836
		3837	In addition to a working ISO-C implementation and of course the
		3838	backend-specific APIs, libev relies on a few additional extensions:
		3839
		3840	=over 4
		3841
		3842	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		3843	calling conventions regardless of C<ev_watcher_type *>.
		3844
		3845	Libev assumes not only that all watcher pointers have the same internal
		3846	structure (guaranteed by POSIX but not by ISO C for example), but it also
		3847	assumes that the same (machine) code can be used to call any watcher
		3848	callback: The watcher callbacks have different type signatures, but libev
		3849	calls them using an C<ev_watcher *> internally.
		3850
		3851	=item C<sig_atomic_t volatile> must be thread-atomic as well
		3852
		3853	The type C<sig_atomic_t volatile> (or whatever is defined as
		3854	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		3855	threads. This is not part of the specification for C<sig_atomic_t>, but is
		3856	believed to be sufficiently portable.
		3857
		3858	=item C<sigprocmask> must work in a threaded environment
		3859
		3860	Libev uses C<sigprocmask> to temporarily block signals. This is not
		3861	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		3862	pthread implementations will either allow C<sigprocmask> in the "main
		3863	thread" or will block signals process-wide, both behaviours would
		3864	be compatible with libev. Interaction between C<sigprocmask> and
		3865	C<pthread_sigmask> could complicate things, however.
		3866
		3867	The most portable way to handle signals is to block signals in all threads
		3868	except the initial one, and run the default loop in the initial thread as
		3869	well.
		3870
		3871	=item C<long> must be large enough for common memory allocation sizes
		3872
		3873	To improve portability and simplify its API, libev uses C<long> internally
		3874	instead of C<size_t> when allocating its data structures. On non-POSIX
		3875	systems (Microsoft...) this might be unexpectedly low, but is still at
		3876	least 31 bits everywhere, which is enough for hundreds of millions of
		3877	watchers.
		3878
		3879	=item C<double> must hold a time value in seconds with enough accuracy
		3880
		3881	The type C<double> is used to represent timestamps. It is required to
		3882	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		3883	enough for at least into the year 4000. This requirement is fulfilled by
		3884	implementations implementing IEEE 754 (basically all existing ones).
		3885
		3886	=back
		3887
		3888	If you know of other additional requirements drop me a note.
		3889
		3890
2595	=head1 COMPLEXITIES	3891	=head1 ALGORITHMIC COMPLEXITIES
2596		3892
2597	In this section the complexities of (many of) the algorithms used inside	3893	In this section the complexities of (many of) the algorithms used inside
2598	libev will be explained. For complexity discussions about backends see the	3894	libev will be documented. For complexity discussions about backends see
2599	documentation for C<ev_default_init>.	3895	the documentation for C<ev_default_init>.
2600		3896
2601	All of the following are about amortised time: If an array needs to be	3897	All of the following are about amortised time: If an array needs to be
2602	extended, libev needs to realloc and move the whole array, but this	3898	extended, libev needs to realloc and move the whole array, but this
2603	happens asymptotically never with higher number of elements, so O(1) might	3899	happens asymptotically rarer with higher number of elements, so O(1) might
2604	mean it might do a lengthy realloc operation in rare cases, but on average	3900	mean that libev does a lengthy realloc operation in rare cases, but on
2605	it is much faster and asymptotically approaches constant time.	3901	average it is much faster and asymptotically approaches constant time.
2606		3902
2607	=over 4	3903	=over 4
2608		3904
2609	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	3905	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2610		3906
2611	This means that, when you have a watcher that triggers in one hour and	3907	This means that, when you have a watcher that triggers in one hour and
2612	there are 100 watchers that would trigger before that then inserting will	3908	there are 100 watchers that would trigger before that, then inserting will
2613	have to skip those 100 watchers.	3909	have to skip roughly seven (C<ld 100>) of these watchers.
2614		3910
2615	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	3911	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2616		3912
2617	That means that for changing a timer costs less than removing/adding them	3913	That means that changing a timer costs less than removing/adding them,
2618	as only the relative motion in the event queue has to be paid for.	3914	as only the relative motion in the event queue has to be paid for.
2619		3915
2620	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	3916	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
2621		3917
2622	These just add the watcher into an array or at the head of a list.	3918	These just add the watcher into an array or at the head of a list.
		3919
2623	=item Stopping check/prepare/idle watchers: O(1)	3920	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2624		3921
2625	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	3922	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2626		3923
2627	These watchers are stored in lists then need to be walked to find the	3924	These watchers are stored in lists, so they need to be walked to find the
2628	correct watcher to remove. The lists are usually short (you don't usually	3925	correct watcher to remove. The lists are usually short (you don't usually
2629	have many watchers waiting for the same fd or signal).	3926	have many watchers waiting for the same fd or signal: one is typical, two
		3927	is rare).
2630		3928
2631	=item Finding the next timer per loop iteration: O(1)	3929	=item Finding the next timer in each loop iteration: O(1)
		3930
		3931	By virtue of using a binary or 4-heap, the next timer is always found at a
		3932	fixed position in the storage array.
2632		3933
2633	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	3934	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2634		3935
2635	A change means an I/O watcher gets started or stopped, which requires	3936	A change means an I/O watcher gets started or stopped, which requires
2636	libev to recalculate its status (and possibly tell the kernel).	3937	libev to recalculate its status (and possibly tell the kernel, depending
		3938	on backend and whether C<ev_io_set> was used).
2637		3939
2638	=item Activating one watcher: O(1)	3940	=item Activating one watcher (putting it into the pending state): O(1)
2639		3941
2640	=item Priority handling: O(number_of_priorities)	3942	=item Priority handling: O(number_of_priorities)
2641		3943
2642	Priorities are implemented by allocating some space for each	3944	Priorities are implemented by allocating some space for each
2643	priority. When doing priority-based operations, libev usually has to	3945	priority. When doing priority-based operations, libev usually has to
2644	linearly search all the priorities.	3946	linearly search all the priorities, but starting/stopping and activating
		3947	watchers becomes O(1) with respect to priority handling.
		3948
		3949	=item Sending an ev_async: O(1)
		3950
		3951	=item Processing ev_async_send: O(number_of_async_watchers)
		3952
		3953	=item Processing signals: O(max_signal_number)
		3954
		3955	Sending involves a system call I<iff> there were no other C<ev_async_send>
		3956	calls in the current loop iteration. Checking for async and signal events
		3957	involves iterating over all running async watchers or all signal numbers.
2645		3958
2646	=back	3959	=back
2647		3960
2648		3961
2649	=head1 AUTHOR	3962	=head1 AUTHOR
2650		3963
2651	Marc Lehmann <libev@schmorp.de>.	3964	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
2652		3965

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