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Revision 1.71 by root, Fri Dec 7 20:13:09 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 occuring), 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
61	To do this, it must take more or less complete control over your process	77	To do this, it must take more or less complete control over your process
62	(or thread) by executing the I<event loop> handler, and will then	78	(or thread) by executing the I<event loop> handler, and will then
63	communicate events via a callback mechanism.	79	communicate events via a callback mechanism.
…		…
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 such.	120	it, you should treat it as some floating point value. Unlike the name
		121	component C<stamp> might indicate, it is also used for time differences
		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
104		144
105	=head1 GLOBAL FUNCTIONS	145	=head1 GLOBAL FUNCTIONS
106		146
107	These functions can be called anytime, even before initialising the	147	These functions can be called anytime, even before initialising the
108	library in any way.	148	library in any way.
…		…
113		153
114	Returns the current time as libev would use it. Please note that the	154	Returns the current time as libev would use it. Please note that the
115	C<ev_now> function is usually faster and also often returns the timestamp	155	C<ev_now> function is usually faster and also often returns the timestamp
116	you actually want to know.	156	you actually want to know.
117		157
		158	=item ev_sleep (ev_tstamp interval)
		159
		160	Sleep for the given interval: The current thread will be blocked until
		161	either it is interrupted or the given time interval has passed. Basically
		162	this is a sub-second-resolution C<sleep ()>.
		163
118	=item int ev_version_major ()	164	=item int ev_version_major ()
119		165
120	=item int ev_version_minor ()	166	=item int ev_version_minor ()
121		167
122	You can find out the major and minor version numbers of the library	168	You can find out the major and minor ABI version numbers of the library
123	you linked against by calling the functions C<ev_version_major> and	169	you linked against by calling the functions C<ev_version_major> and
124	C<ev_version_minor>. If you want, you can compare against the global	170	C<ev_version_minor>. If you want, you can compare against the global
125	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the	171	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
126	version of the library your program was compiled against.	172	version of the library your program was compiled against.
127		173
		174	These version numbers refer to the ABI version of the library, not the
		175	release version.
		176
128	Usually, it's a good idea to terminate if the major versions mismatch,	177	Usually, it's a good idea to terminate if the major versions mismatch,
129	as this indicates an incompatible change. Minor versions are usually	178	as this indicates an incompatible change. Minor versions are usually
130	compatible to older versions, so a larger minor version alone is usually	179	compatible to older versions, so a larger minor version alone is usually
131	not a problem.	180	not a problem.
132		181
133	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
134	version.	183	version.
135		184
136	assert (("libev version mismatch",	185	assert (("libev version mismatch",
137	ev_version_major () == EV_VERSION_MAJOR	186	ev_version_major () == EV_VERSION_MAJOR
138	&& ev_version_minor () >= EV_VERSION_MINOR));	187	&& ev_version_minor () >= EV_VERSION_MINOR));
139		188
140	=item unsigned int ev_supported_backends ()	189	=item unsigned int ev_supported_backends ()
141		190
142	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_*>
143	value) compiled into this binary of libev (independent of their	192	value) compiled into this binary of libev (independent of their
…		…
145	a description of the set values.	194	a description of the set values.
146		195
147	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
148	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
149		198
150	assert (("sorry, no epoll, no sex",	199	assert (("sorry, no epoll, no sex",
151	ev_supported_backends () & EVBACKEND_EPOLL));	200	ev_supported_backends () & EVBACKEND_EPOLL));
152		201
153	=item unsigned int ev_recommended_backends ()	202	=item unsigned int ev_recommended_backends ()
154		203
155	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
156	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
157	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
158	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
159	(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
160	libev will probe for if you specify no backends explicitly.	209	libev will probe for if you specify no backends explicitly.
161		210
162	=item unsigned int ev_embeddable_backends ()	211	=item unsigned int ev_embeddable_backends ()
163		212
…		…
167	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	216	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
168	recommended ones.	217	recommended ones.
169		218
170	See the description of C<ev_embed> watchers for more info.	219	See the description of C<ev_embed> watchers for more info.
171		220
172	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	221	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
173		222
174	Sets the allocation function to use (the prototype is similar - the	223	Sets the allocation function to use (the prototype is similar - the
175	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
176	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
177	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
178	potentially destructive action. The default is your system realloc	227	or take some potentially destructive action.
179	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.
180		232
181	You could override this function in high-availability programs to, say,	233	You could override this function in high-availability programs to, say,
182	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,
183	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.
184		236
185	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
186	retries).	238	retries (example requires a standards-compliant C<realloc>).
187		239
188	static void *	240	static void *
189	persistent_realloc (void *ptr, size_t size)	241	persistent_realloc (void *ptr, size_t size)
190	{	242	{
191	for (;;)	243	for (;;)
…		…
200	}	252	}
201		253
202	...	254	...
203	ev_set_allocator (persistent_realloc);	255	ev_set_allocator (persistent_realloc);
204		256
205	=item ev_set_syserr_cb (void (*cb)(const char *msg));	257	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
206		258
207	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
208	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
209	indicating the system call or subsystem causing the problem. If this	261	indicating the system call or subsystem causing the problem. If this
210	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
211	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
212	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
213	(such as abort).	265	(such as abort).
214		266
215	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.
…		…
226		278
227	=back	279	=back
228		280
229	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	281	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
230		282
231	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>
232	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>
233	events, and dynamically created loops which do not.	285	I<function>).
234		286
235	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
236	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
237	create, you also create another event loop. Libev itself does no locking	289	not.
238	whatsoever, so if you mix calls to the same event loop in different
239	threads, make sure you lock (this is usually a bad idea, though, even if
240	done correctly, because it's hideous and inefficient).
241		290
242	=over 4	291	=over 4
243		292
244	=item struct ev_loop *ev_default_loop (unsigned int flags)	293	=item struct ev_loop *ev_default_loop (unsigned int flags)
245		294
…		…
249	flags. If that is troubling you, check C<ev_backend ()> afterwards).	298	flags. If that is troubling you, check C<ev_backend ()> afterwards).
250		299
251	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
252	function.	301	function.
253		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
254	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
255	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>).
256		316
257	The following flags are supported:	317	The following flags are supported:
258		318
…		…
263	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
264	thing, believe me).	324	thing, believe me).
265		325
266	=item C<EVFLAG_NOENV>	326	=item C<EVFLAG_NOENV>
267		327
268	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
269	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
270	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	330	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
271	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
272	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
273	around bugs.	333	around bugs.
…		…
279	enabling this flag.	339	enabling this flag.
280		340
281	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,
282	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
283	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
284	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
285	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
286	C<pthread_atfork> which is even faster).	346	C<pthread_atfork> which is even faster).
287		347
288	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
289	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
290	flag.	350	flag.
291		351
292	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>
293	environment variable.	353	environment variable.
294		354
295	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	355	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
296		356
297	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
298	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,
299	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
300	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
301	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).
302		373
303	=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)
304		375
305	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
306	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
307	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
308	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>.
309		385
310	=item C<EVBACKEND_EPOLL> (value 4, Linux)	386	=item C<EVBACKEND_EPOLL> (value 4, Linux)
311		387
312	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,
313	but it scales phenomenally better. While poll and select usually scale like	389	but it scales phenomenally better. While poll and select usually scale
314	O(total_fds) where n is the total number of fds (or the highest fd), epoll scales	390	like O(total_fds) where n is the total number of fds (or the highest fd),
315	either O(1) or O(active_fds).	391	epoll scales either O(1) or O(active_fds).
316		392
		393	The epoll mechanism deserves honorable mention as the most misdesigned
		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.
		409
317	While stopping and starting an I/O watcher in the same iteration will	410	While stopping, setting and starting an I/O watcher in the same iteration
318	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
319	(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
320	best to avoid that. Also, dup()ed file descriptors might not work very	413	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
321	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.
322		416
323	Please note that epoll sometimes generates spurious notifications, so you	417	Best performance from this backend is achieved by not unregistering all
324	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,
325	(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>.
326		434
327	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	435	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
328		436
329	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
330	was broken on all BSDs except NetBSD (usually it doesn't work with	438	was broken on all BSDs except NetBSD (usually it doesn't work reliably
331	anything but sockets and pipes, except on Darwin, where of course its	439	with anything but sockets and pipes, except on Darwin, where of course
332	completely useless). For this reason its not being "autodetected"	440	it's completely useless). Unlike epoll, however, whose brokenness
		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
333	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
334	C<EVBACKEND_KQUEUE>).	444	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		445	system like NetBSD.
		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.
335		450
336	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
337	kernel is more efficient (which says nothing about its actual speed, of	452	kernel is more efficient (which says nothing about its actual speed, of
338	course). While starting and stopping an I/O watcher does not cause an	453	course). While stopping, setting and starting an I/O watcher does never
339	extra syscall as with epoll, it still adds up to four event changes per	454	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
340	incident, so its best to avoid that.	455	two event changes per incident. Support for C<fork ()> is very bad (but
		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>.
341		471
342	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	472	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
343		473
344	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.
345		478
346	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	479	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
347		480
348	This uses the Solaris 10 port mechanism. As with everything on Solaris,	481	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
349	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)).
350		483
351	Please note that solaris ports can result in a lot of spurious	484	Please note that Solaris event ports can deliver a lot of spurious
352	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
353	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>.
354		500
355	=item C<EVBACKEND_ALL>	501	=item C<EVBACKEND_ALL>
356		502
357	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
358	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
359	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	505	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
360		506
		507	It is definitely not recommended to use this flag.
		508
361	=back	509	=back
362		510
363	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
364	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
365	specified, most compiled-in backend will be tried, usually in reverse	513	specified, all backends in C<ev_recommended_backends ()> will be tried.
366	order of their flag values :)
367		514
368	The most typical usage is like this:	515	Example: This is the most typical usage.
369		516
370	if (!ev_default_loop (0))	517	if (!ev_default_loop (0))
371	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	518	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
372		519
373	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
374	environment settings to be taken into account:	521	environment settings to be taken into account:
375		522
376	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	523	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
377		524
378	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
379	available (warning, breaks stuff, best use only with your own private	526	used if available (warning, breaks stuff, best use only with your own
380	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):
381		529
382	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	530	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
383		531
384	=item struct ev_loop *ev_loop_new (unsigned int flags)	532	=item struct ev_loop *ev_loop_new (unsigned int flags)
385		533
386	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
387	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
388	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
389	undefined behaviour (or a failed assertion if assertions are enabled).	537	undefined behaviour (or a failed assertion if assertions are enabled).
390		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
391	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.
392		544
393	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	545	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
394	if (!epoller)	546	if (!epoller)
395	fatal ("no epoll found here, maybe it hides under your chair");	547	fatal ("no epoll found here, maybe it hides under your chair");
396		548
397	=item ev_default_destroy ()	549	=item ev_default_destroy ()
398		550
399	Destroys the default loop again (frees all memory and kernel state	551	Destroys the default loop again (frees all memory and kernel state
400	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
401	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
402	responsibility to either stop all watchers cleanly yoursef I<before>	554	responsibility to either stop all watchers cleanly yourself I<before>
403	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
404	the easiest thing, youc na just ignore the watchers and/or C<free ()> them	556	the easiest thing, you can just ignore the watchers and/or C<free ()> them
405	for example).	557	for example).
		558
		559	Note that certain global state, such as signal state (and installed signal
		560	handlers), will not be freed by this function, and related watchers (such
		561	as signal and child watchers) would need to be stopped manually.
		562
		563	In general it is not advisable to call this function except in the
		564	rare occasion where you really need to free e.g. the signal handling
		565	pipe fds. If you need dynamically allocated loops it is better to use
		566	C<ev_loop_new> and C<ev_loop_destroy>).
406		567
407	=item ev_loop_destroy (loop)	568	=item ev_loop_destroy (loop)
408		569
409	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
410	earlier call to C<ev_loop_new>.	571	earlier call to C<ev_loop_new>.
411		572
412	=item ev_default_fork ()	573	=item ev_default_fork ()
413		574
		575	This function sets a flag that causes subsequent C<ev_loop> iterations
414	This function reinitialises the kernel state for backends that have	576	to reinitialise the kernel state for backends that have one. Despite the
415	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
416	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
417	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.
418		581
419	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
420	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
421	fork+exec, you don't have to call it.	584	you just fork+exec, you don't have to call it at all.
422		585
423	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
424	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
425	quite nicely into a call to C<pthread_atfork>:	588	quite nicely into a call to C<pthread_atfork>:
426		589
427	pthread_atfork (0, 0, ev_default_fork);	590	pthread_atfork (0, 0, ev_default_fork);
428		591
429	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
430	without calling this function, so if you force one of those backends you
431	do not need to care.
432
433	=item ev_loop_fork (loop)	592	=item ev_loop_fork (loop)
434		593
435	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
436	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
437	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.
438		603
439	=item unsigned int ev_loop_count (loop)	604	=item unsigned int ev_loop_count (loop)
440		605
441	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
442	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
…		…
455		620
456	Returns the current "event loop time", which is the time the event loop	621	Returns the current "event loop time", which is the time the event loop
457	received events and started processing them. This timestamp does not	622	received events and started processing them. This timestamp does not
458	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
459	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
460	event occuring (or more correctly, libev finding out about it).	625	event occurring (or more correctly, libev finding out about it).
		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.
461		638
462	=item ev_loop (loop, int flags)	639	=item ev_loop (loop, int flags)
463		640
464	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
465	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
…		…
468	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
469	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.
470		647
471	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
472	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
473	finished (especially in interactive programs), but having a program that	650	finished (especially in interactive programs), but having a program
474	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
475	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.
476		654
477	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
478	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
479	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.
480		659
481	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
482	neccessary) and will handle those and any outstanding ones. It will block	661	necessary) and will handle those and any already outstanding ones. It
483	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
484	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
485	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
486	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
487	usually a better approach for this kind of thing.	670	usually a better approach for this kind of thing.
488		671
489	Here are the gory details of what C<ev_loop> does:	672	Here are the gory details of what C<ev_loop> does:
490		673
491	* If there are no active watchers (reference count is zero), return.	674	- Before the first iteration, call any pending watchers.
492	- Queue prepare watchers and then call all outstanding watchers.	675	* If EVFLAG_FORKCHECK was used, check for a fork.
		676	- If a fork was detected (by any means), queue and call all fork watchers.
		677	- Queue and call all prepare watchers.
493	- 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.
494	- Update the kernel state with all outstanding changes.	680	- Update the kernel state with all outstanding changes.
495	- Update the "event loop time".	681	- Update the "event loop time" (ev_now ()).
496	- 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.
497	- Block the process, waiting for any events.	686	- Block the process, waiting for any events.
498	- Queue all outstanding I/O (fd) events.	687	- Queue all outstanding I/O (fd) events.
499	- Update the "event loop time" and do time jump handling.	688	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
500	- Queue all outstanding timers.	689	- Queue all expired timers.
501	- Queue all outstanding periodics.	690	- Queue all expired periodics.
502	- If no events are pending now, queue all idle watchers.	691	- Unless any events are pending now, queue all idle watchers.
503	- Queue all check watchers.	692	- Queue all check watchers.
504	- 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).
505	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
506	be handled here by queueing them when their watcher gets executed.	695	be handled here by queueing them when their watcher gets executed.
507	- 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
508	were used, return, otherwise continue with step *.	697	were used, or there are no active watchers, return, otherwise
		698	continue with step *.
509		699
510	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
511	anymore.	701	anymore.
512		702
513	... queue jobs here, make sure they register event watchers as long	703	... queue jobs here, make sure they register event watchers as long
514	... 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..)
515	ev_loop (my_loop, 0);	705	ev_loop (my_loop, 0);
516	... jobs done. yeah!	706	... jobs done or somebody called unloop. yeah!
517		707
518	=item ev_unloop (loop, how)	708	=item ev_unloop (loop, how)
519		709
520	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
521	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
522	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
523	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.
524		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
525	=item ev_ref (loop)	719	=item ev_ref (loop)
526		720
527	=item ev_unref (loop)	721	=item ev_unref (loop)
528		722
529	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
530	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
531	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
532	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>
533	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
534	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
535	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
536	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
537	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
538	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).
539		738
540	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>
541	running when nothing else is active.	740	running when nothing else is active.
542		741
543	struct ev_signal exitsig;	742	ev_signal exitsig;
544	ev_signal_init (&exitsig, sig_cb, SIGINT);	743	ev_signal_init (&exitsig, sig_cb, SIGINT);
545	ev_signal_start (loop, &exitsig);	744	ev_signal_start (loop, &exitsig);
546	evf_unref (loop);	745	evf_unref (loop);
547		746
548	Example: For some weird reason, unregister the above signal handler again.	747	Example: For some weird reason, unregister the above signal handler again.
549		748
550	ev_ref (loop);	749	ev_ref (loop);
551	ev_signal_stop (loop, &exitsig);	750	ev_signal_stop (loop, &exitsig);
		751
		752	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		753
		754	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		755
		756	These advanced functions influence the time that libev will spend waiting
		757	for events. Both time intervals are by default C<0>, meaning that libev
		758	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		759	latency.
		760
		761	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		762	allows libev to delay invocation of I/O and timer/periodic callbacks
		763	to increase efficiency of loop iterations (or to increase power-saving
		764	opportunities).
		765
		766	The idea is that sometimes your program runs just fast enough to handle
		767	one (or very few) event(s) per loop iteration. While this makes the
		768	program responsive, it also wastes a lot of CPU time to poll for new
		769	events, especially with backends like C<select ()> which have a high
		770	overhead for the actual polling but can deliver many events at once.
		771
		772	By setting a higher I<io collect interval> you allow libev to spend more
		773	time collecting I/O events, so you can handle more events per iteration,
		774	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		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.
		777
		778	Likewise, by setting a higher I<timeout collect interval> you allow libev
		779	to spend more time collecting timeouts, at the expense of increased
		780	latency/jitter/inexactness (the watcher callback will be called
		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.
		783
		784	Many (busy) programs can usually benefit by setting the I/O collect
		785	interval to a value near C<0.1> or so, which is often enough for
		786	interactive servers (of course not for games), likewise for timeouts. It
		787	usually doesn't make much sense to set it to a lower value than C<0.01>,
		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.
552		808
553	=back	809	=back
554		810
555		811
556	=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.
557		817
558	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
559	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
560	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:
561		821
562	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)
563	{	823	{
564	ev_io_stop (w);	824	ev_io_stop (w);
565	ev_unloop (loop, EVUNLOOP_ALL);	825	ev_unloop (loop, EVUNLOOP_ALL);
566	}	826	}
567		827
568	struct ev_loop *loop = ev_default_loop (0);	828	struct ev_loop *loop = ev_default_loop (0);
		829
569	struct ev_io stdin_watcher;	830	ev_io stdin_watcher;
		831
570	ev_init (&stdin_watcher, my_cb);	832	ev_init (&stdin_watcher, my_cb);
571	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	833	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
572	ev_io_start (loop, &stdin_watcher);	834	ev_io_start (loop, &stdin_watcher);
		835
573	ev_loop (loop, 0);	836	ev_loop (loop, 0);
574		837
575	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
576	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
577	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).
578		844
579	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
580	(watcher *, callback)>, which expects a callback to be provided. This	846	(watcher *, callback)>, which expects a callback to be provided. This
581	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
582	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
583	is readable and/or writable).	849	is readable and/or writable).
584		850
585	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 *, ...) >>
586	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
587	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<<
588	(watcher *, callback, ...) >>.	854	ev_TYPE_init (watcher *, callback, ...) >>.
589		855
590	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
591	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
592	*) >>), 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
593	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	859	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
594		860
595	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
596	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
597	reinitialise it or call its C<set> macro.	863	reinitialise it or call its C<ev_TYPE_set> macro.
598		864
599	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
600	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
601	third argument.	867	third argument.
602		868
…		…
656	=item C<EV_FORK>	922	=item C<EV_FORK>
657		923
658	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
659	C<ev_fork>).	925	C<ev_fork>).
660		926
		927	=item C<EV_ASYNC>
		928
		929	The given async watcher has been asynchronously notified (see C<ev_async>).
		930
661	=item C<EV_ERROR>	931	=item C<EV_ERROR>
662		932
663	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
664	happen because the watcher could not be properly started because libev	934	happen because the watcher could not be properly started because libev
665	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
666	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
667	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.
668		942
669	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
670	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
671	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
672	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
673	programs, though, so beware.	947	programs, though, as the fd could already be closed and reused for another
		948	thing, so beware.
674		949
675	=back	950	=back
676		951
677	=head2 GENERIC WATCHER FUNCTIONS	952	=head2 GENERIC WATCHER FUNCTIONS
678
679	In the following description, C<TYPE> stands for the watcher type,
680	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
681		953
682	=over 4	954	=over 4
683		955
684	=item C<ev_init> (ev_TYPE *watcher, callback)	956	=item C<ev_init> (ev_TYPE *watcher, callback)
685		957
…		…
691	which rolls both calls into one.	963	which rolls both calls into one.
692		964
693	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
694	(or never started) and there are no pending events outstanding.	966	(or never started) and there are no pending events outstanding.
695		967
696	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,
697	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);
698		976
699	=item C<ev_TYPE_set> (ev_TYPE *, [args])	977	=item C<ev_TYPE_set> (ev_TYPE *, [args])
700		978
701	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
702	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
…		…
705	difference to the C<ev_init> macro).	983	difference to the C<ev_init> macro).
706		984
707	Although some watcher types do not have type-specific arguments	985	Although some watcher types do not have type-specific arguments
708	(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.
709		987
		988	See C<ev_init>, above, for an example.
		989
710	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	990	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
711		991
712	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
713	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
714	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);
715		999
716	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1000	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
717		1001
718	Starts (activates) the given watcher. Only active watchers will receive	1002	Starts (activates) the given watcher. Only active watchers will receive
719	events. If the watcher is already active nothing will happen.	1003	events. If the watcher is already active nothing will happen.
720		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
721	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1010	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
722		1011
723	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
724	status. It is possible that stopped watchers are pending (for example,	1015	It is possible that stopped watchers are pending - for example,
725	non-repeating timers are being stopped when they become pending), but	1016	non-repeating timers are being stopped when they become pending - but
726	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
727	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
728	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.
729		1020
730	=item bool ev_is_active (ev_TYPE *watcher)	1021	=item bool ev_is_active (ev_TYPE *watcher)
731		1022
732	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
733	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
…		…
736	=item bool ev_is_pending (ev_TYPE *watcher)	1027	=item bool ev_is_pending (ev_TYPE *watcher)
737		1028
738	Returns a true value iff the watcher is pending, (i.e. it has outstanding	1029	Returns a true value iff the watcher is pending, (i.e. it has outstanding
739	events but its callback has not yet been invoked). As long as a watcher	1030	events but its callback has not yet been invoked). As long as a watcher
740	is pending (but not active) you must not call an init function on it (but	1031	is pending (but not active) you must not call an init function on it (but
741	C<ev_TYPE_set> is safe) and you must make sure the watcher is available to	1032	C<ev_TYPE_set> is safe), you must not change its priority, and you must
742	libev (e.g. you cnanot C<free ()> it).	1033	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1034	it).
743		1035
744	=item callback ev_cb (ev_TYPE *watcher)	1036	=item callback ev_cb (ev_TYPE *watcher)
745		1037
746	Returns the callback currently set on the watcher.	1038	Returns the callback currently set on the watcher.
747		1039
…		…
766	watchers on the same event and make sure one is called first.	1058	watchers on the same event and make sure one is called first.
767		1059
768	If you need to suppress invocation when higher priority events are pending	1060	If you need to suppress invocation when higher priority events are pending
769	you need to look at C<ev_idle> watchers, which provide this functionality.	1061	you need to look at C<ev_idle> watchers, which provide this functionality.
770		1062
		1063	You I<must not> change the priority of a watcher as long as it is active or
		1064	pending.
		1065
771	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
772	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 :).
773		1068
774	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
775	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
776	or might not have been adjusted to be within valid range.	1071	or might not have been clamped to the valid range.
		1072
		1073	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1074
		1075	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1076	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1077	can deal with that fact, as both are simply passed through to the
		1078	callback.
		1079
		1080	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1081
		1082	If the watcher is pending, this function clears its pending status and
		1083	returns its C<revents> bitset (as if its callback was invoked). If the
		1084	watcher isn't pending it does nothing and returns C<0>.
		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.
777		1088
778	=back	1089	=back
779		1090
780		1091
781	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1092	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
782		1093
783	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
784	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
785	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
786	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
787	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
788	data:	1099	data:
789		1100
790	struct my_io	1101	struct my_io
791	{	1102	{
792	struct ev_io io;	1103	ev_io io;
793	int otherfd;	1104	int otherfd;
794	void *somedata;	1105	void *somedata;
795	struct whatever *mostinteresting;	1106	struct whatever *mostinteresting;
796	}	1107	};
		1108
		1109	...
		1110	struct my_io w;
		1111	ev_io_init (&w.io, my_cb, fd, EV_READ);
797		1112
798	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
799	can cast it back to your own type:	1114	can cast it back to your own type:
800		1115
801	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)
802	{	1117	{
803	struct my_io *w = (struct my_io *)w_;	1118	struct my_io *w = (struct my_io *)w_;
804	...	1119	...
805	}	1120	}
806		1121
807	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
808	instead have been omitted.	1123	instead have been omitted.
809		1124
810	Another common scenario is having some data structure with multiple	1125	Another common scenario is to use some data structure with multiple
811	watchers:	1126	embedded watchers:
812		1127
813	struct my_biggy	1128	struct my_biggy
814	{	1129	{
815	int some_data;	1130	int some_data;
816	ev_timer t1;	1131	ev_timer t1;
817	ev_timer t2;	1132	ev_timer t2;
818	}	1133	}
819		1134
820	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
821	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):
822		1140
823	#include <stddef.h>	1141	#include <stddef.h>
824		1142
825	static void	1143	static void
826	t1_cb (EV_P_ struct ev_timer *w, int revents)	1144	t1_cb (EV_P_ ev_timer *w, int revents)
827	{	1145	{
828	struct my_biggy big = (struct my_biggy *	1146	struct my_biggy big = (struct my_biggy *
829	(((char *)w) - offsetof (struct my_biggy, t1));	1147	(((char *)w) - offsetof (struct my_biggy, t1));
830	}	1148	}
831		1149
832	static void	1150	static void
833	t2_cb (EV_P_ struct ev_timer *w, int revents)	1151	t2_cb (EV_P_ ev_timer *w, int revents)
834	{	1152	{
835	struct my_biggy big = (struct my_biggy *	1153	struct my_biggy big = (struct my_biggy *
836	(((char *)w) - offsetof (struct my_biggy, t2));	1154	(((char *)w) - offsetof (struct my_biggy, t2));
837	}	1155	}
838		1156
839		1157
840	=head1 WATCHER TYPES	1158	=head1 WATCHER TYPES
841		1159
842	This section describes each watcher in detail, but will not repeat	1160	This section describes each watcher in detail, but will not repeat
…		…
866	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
867	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
868	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
869	required if you know what you are doing).	1187	required if you know what you are doing).
870		1188
871	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
872	(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
873	descriptors correctly if you register interest in two or more fds pointing	1191	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>).
874	to the same underlying file/socket/etc. description (that is, they share
875	the same underlying "file open").
876
877	If you must do this, then force the use of a known-to-be-good backend
878	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
879	C<EVBACKEND_POLL>).
880		1192
881	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
882	receive "spurious" readyness notifications, that is your callback might	1194	receive "spurious" readiness notifications, that is your callback might
883	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
884	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
885	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
886	this situation even with a relatively standard program structure. Thus	1198	this situation even with a relatively standard program structure. Thus
887	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
888	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.
889		1201
890	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
891	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
892	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
893	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
894	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.
		1211
		1212	=head3 The special problem of disappearing file descriptors
		1213
		1214	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1215	descriptor (either due to calling C<close> explicitly or any other means,
		1216	such as C<dup2>). The reason is that you register interest in some file
		1217	descriptor, but when it goes away, the operating system will silently drop
		1218	this interest. If another file descriptor with the same number then is
		1219	registered with libev, there is no efficient way to see that this is, in
		1220	fact, a different file descriptor.
		1221
		1222	To avoid having to explicitly tell libev about such cases, libev follows
		1223	the following policy: Each time C<ev_io_set> is being called, libev
		1224	will assume that this is potentially a new file descriptor, otherwise
		1225	it is assumed that the file descriptor stays the same. That means that
		1226	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1227	descriptor even if the file descriptor number itself did not change.
		1228
		1229	This is how one would do it normally anyway, the important point is that
		1230	the libev application should not optimise around libev but should leave
		1231	optimisations to libev.
		1232
		1233	=head3 The special problem of dup'ed file descriptors
		1234
		1235	Some backends (e.g. epoll), cannot register events for file descriptors,
		1236	but only events for the underlying file descriptions. That means when you
		1237	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1238	events for them, only one file descriptor might actually receive events.
		1239
		1240	There is no workaround possible except not registering events
		1241	for potentially C<dup ()>'ed file descriptors, or to resort to
		1242	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1243
		1244	=head3 The special problem of fork
		1245
		1246	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1247	useless behaviour. Libev fully supports fork, but needs to be told about
		1248	it in the child.
		1249
		1250	To support fork in your programs, you either have to call
		1251	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1252	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1253	C<EVBACKEND_POLL>.
		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
		1266
		1267	=head3 Watcher-Specific Functions
895		1268
896	=over 4	1269	=over 4
897		1270
898	=item ev_io_init (ev_io *, callback, int fd, int events)	1271	=item ev_io_init (ev_io *, callback, int fd, int events)
899		1272
900	=item ev_io_set (ev_io *, int fd, int events)	1273	=item ev_io_set (ev_io *, int fd, int events)
901		1274
902	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
903	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
904	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.
905		1278
906	=item int fd [read-only]	1279	=item int fd [read-only]
907		1280
908	The file descriptor being watched.	1281	The file descriptor being watched.
909		1282
910	=item int events [read-only]	1283	=item int events [read-only]
911		1284
912	The events being watched.	1285	The events being watched.
913		1286
914	=back	1287	=back
		1288
		1289	=head3 Examples
915		1290
916	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
917	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
918	attempt to read a whole line in the callback.	1293	attempt to read a whole line in the callback.
919		1294
920	static void	1295	static void
921	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)
922	{	1297	{
923	ev_io_stop (loop, w);	1298	ev_io_stop (loop, w);
924	.. 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
925	}	1300	}
926		1301
927	...	1302	...
928	struct ev_loop *loop = ev_default_init (0);	1303	struct ev_loop *loop = ev_default_init (0);
929	struct ev_io stdin_readable;	1304	ev_io stdin_readable;
930	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);
931	ev_io_start (loop, &stdin_readable);	1306	ev_io_start (loop, &stdin_readable);
932	ev_loop (loop, 0);	1307	ev_loop (loop, 0);
933		1308
934		1309
935	=head2 C<ev_timer> - relative and optionally repeating timeouts	1310	=head2 C<ev_timer> - relative and optionally repeating timeouts
936		1311
937	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
938	given time, and optionally repeating in regular intervals after that.	1313	given time, and optionally repeating in regular intervals after that.
939		1314
940	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
941	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
942	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
943	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1318	detecting time jumps is hard, and some inaccuracies are unavoidable (the
944	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.
945		1507
946	The relative timeouts are calculated relative to the C<ev_now ()>	1508	The relative timeouts are calculated relative to the C<ev_now ()>
947	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
948	of the event triggering whatever timeout you are modifying/starting. If	1510	of the event triggering whatever timeout you are modifying/starting. If
949	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
950	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:
951		1513
952	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1514	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
953		1515
954	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
955	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
956	order of execution is undefined.	1518	()>.
		1519
		1520	=head3 Watcher-Specific Functions and Data Members
957		1521
958	=over 4	1522	=over 4
959		1523
960	=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)
961		1525
962	=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)
963		1527
964	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>
965	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
966	timer will automatically be configured to trigger again C<repeat> seconds	1530	reached. If it is positive, then the timer will automatically be
967	later, again, and again, until stopped manually.	1531	configured to trigger again C<repeat> seconds later, again, and again,
		1532	until stopped manually.
968		1533
969	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
970	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
971	exactly 10 second intervals. If, however, your program cannot keep up with	1536	trigger at exactly 10 second intervals. If, however, your program cannot
972	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
973	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.
974		1539
975	=item ev_timer_again (loop)	1540	=item ev_timer_again (loop, ev_timer *)
976		1541
977	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
978	repeating. The exact semantics are:	1543	repeating. The exact semantics are:
979		1544
980	If the timer is pending, its pending status is cleared.	1545	If the timer is pending, its pending status is cleared.
981		1546
982	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).
983		1548
984	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
985	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.
986		1551
987	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
988	example: Imagine you have a tcp connection and you want a so-called idle	1553	usage example.
989	timeout, that is, you want to be called when there have been, say, 60
990	seconds of inactivity on the socket. The easiest way to do this is to
991	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
992	C<ev_timer_again> each time you successfully read or write some data. If
993	you go into an idle state where you do not expect data to travel on the
994	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
995	automatically restart it if need be.
996
997	That means you can ignore the C<after> value and C<ev_timer_start>
998	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
999
1000	ev_timer_init (timer, callback, 0., 5.);
1001	ev_timer_again (loop, timer);
1002	...
1003	timer->again = 17.;
1004	ev_timer_again (loop, timer);
1005	...
1006	timer->again = 10.;
1007	ev_timer_again (loop, timer);
1008
1009	This is more slightly efficient then stopping/starting the timer each time
1010	you want to modify its timeout value.
1011		1554
1012	=item ev_tstamp repeat [read-write]	1555	=item ev_tstamp repeat [read-write]
1013		1556
1014	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
1015	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),
1016	which is also when any modifications are taken into account.	1559	which is also when any modifications are taken into account.
1017		1560
1018	=back	1561	=back
1019		1562
		1563	=head3 Examples
		1564
1020	Example: Create a timer that fires after 60 seconds.	1565	Example: Create a timer that fires after 60 seconds.
1021		1566
1022	static void	1567	static void
1023	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)
1024	{	1569	{
1025	.. one minute over, w is actually stopped right here	1570	.. one minute over, w is actually stopped right here
1026	}	1571	}
1027		1572
1028	struct ev_timer mytimer;	1573	ev_timer mytimer;
1029	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1574	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1030	ev_timer_start (loop, &mytimer);	1575	ev_timer_start (loop, &mytimer);
1031		1576
1032	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
1033	inactivity.	1578	inactivity.
1034		1579
1035	static void	1580	static void
1036	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1581	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1037	{	1582	{
1038	.. ten seconds without any activity	1583	.. ten seconds without any activity
1039	}	1584	}
1040		1585
1041	struct ev_timer mytimer;	1586	ev_timer mytimer;
1042	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 */
1043	ev_timer_again (&mytimer); /* start timer */	1588	ev_timer_again (&mytimer); /* start timer */
1044	ev_loop (loop, 0);	1589	ev_loop (loop, 0);
1045		1590
1046	// 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":
1047	// reset the timeout to start ticking again at 10 seconds	1592	// reset the timeout to start ticking again at 10 seconds
1048	ev_timer_again (&mytimer);	1593	ev_timer_again (&mytimer);
1049		1594
1050		1595
1051	=head2 C<ev_periodic> - to cron or not to cron?	1596	=head2 C<ev_periodic> - to cron or not to cron?
1052		1597
1053	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
1054	(and unfortunately a bit complex).	1599	(and unfortunately a bit complex).
1055		1600
1056	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
1057	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
1058	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
1059	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
1060	+ 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
1061	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1606	wrist-watch).
1062	roughly 10 seconds later and of course not if you reset your system time
1063	again).
1064		1607
1065	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
		1609	in time: for example, if you tell a periodic watcher to trigger "in 10
		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).
		1615
		1616	C<ev_periodic> watchers can also be used to implement vastly more complex
1066	triggering an event on eahc midnight, local time.	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.
1067		1620
1068	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
1069	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
1070	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.
		1625
		1626	=head3 Watcher-Specific Functions and Data Members
1071		1627
1072	=over 4	1628	=over 4
1073		1629
1074	=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)
1075		1631
1076	=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)
1077		1633
1078	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
1079	operation, and we will explain them from simplest to complex:	1635	operation, and we will explain them from simplest to most complex:
1080		1636
1081	=over 4	1637	=over 4
1082		1638
1083	=item * absolute timer (interval = reschedule_cb = 0)	1639	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1084		1640
1085	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
1086	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
1087	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
1088	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.
1089		1646
1090	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1647	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1091		1648
1092	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
1093	C<at + N * interval> time (for some integer N) and then repeat, regardless	1650	C<offset + N * interval> time (for some integer N, which can also be
1094	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.
1095		1653
1096	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
1097	time:	1655	system clock, for example, here is an C<ev_periodic> that triggers each
		1656	hour, on the hour (with respect to UTC):
1098		1657
1099	ev_periodic_set (&periodic, 0., 3600., 0);	1658	ev_periodic_set (&periodic, 0., 3600., 0);
1100		1659
1101	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,
1102	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
1103	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
1104	by 3600.	1663	by 3600.
1105		1664
1106	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
1107	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
1108	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.
1109		1668
		1669	For numerical stability it is preferable that the C<offset> value is near
		1670	C<ev_now ()> (the current time), but there is no range requirement for
		1671	this value, and in fact is often specified as zero.
		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
1110	=item * manual reschedule mode (reschedule_cb = callback)	1678	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1111		1679
1112	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
1113	ignored. Instead, each time the periodic watcher gets scheduled, the	1681	ignored. Instead, each time the periodic watcher gets scheduled, the
1114	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
1115	current time as second argument.	1683	current time as second argument.
1116		1684
1117	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,
1118	ever, or make any event loop modifications>. If you need to stop it,	1686	or make ANY other event loop modifications whatsoever, unless explicitly
1119	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	1687	allowed by documentation here>.
1120	starting a prepare watcher).
1121		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
1122	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1693	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1123	ev_tstamp now)>, e.g.:	1694	*w, ev_tstamp now)>, e.g.:
1124		1695
		1696	static ev_tstamp
1125	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1697	my_rescheduler (ev_periodic *w, ev_tstamp now)
1126	{	1698	{
1127	return now + 60.;	1699	return now + 60.;
1128	}	1700	}
1129		1701
1130	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
1131	(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
1132	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
1133	might be called at other times, too.	1705	might be called at other times, too.
1134		1706
1135	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
1136	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	1708	equal to the passed C<now> value >>.
1137		1709
1138	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
1139	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
1140	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
1141	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
1142	reason I omitted it as an example).	1714	reason I omitted it as an example).
1143		1715
1144	=back	1716	=back
…		…
1148	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
1149	when you changed some parameters or the reschedule callback would return	1721	when you changed some parameters or the reschedule callback would return
1150	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
1151	program when the crontabs have changed).	1723	program when the crontabs have changed).
1152		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
		1732	=item ev_tstamp offset [read-write]
		1733
		1734	When repeating, this contains the offset value, otherwise this is the
		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).
		1737
		1738	Can be modified any time, but changes only take effect when the periodic
		1739	timer fires or C<ev_periodic_again> is being called.
		1740
1153	=item ev_tstamp interval [read-write]	1741	=item ev_tstamp interval [read-write]
1154		1742
1155	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
1156	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
1157	called.	1745	called.
1158		1746
1159	=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]
1160		1748
1161	The current reschedule callback, or C<0>, if this functionality is	1749	The current reschedule callback, or C<0>, if this functionality is
1162	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
1163	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.
1164		1752
1165	=back	1753	=back
1166		1754
		1755	=head3 Examples
		1756
1167	Example: Call a callback every hour, or, more precisely, whenever the	1757	Example: Call a callback every hour, or, more precisely, whenever the
1168	system clock is divisible by 3600. The callback invocation times have	1758	system time is divisible by 3600. The callback invocation times have
1169	potentially a lot of jittering, but good long-term stability.	1759	potentially a lot of jitter, but good long-term stability.
1170		1760
1171	static void	1761	static void
1172	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1762	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1173	{	1763	{
1174	... 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)
1175	}	1765	}
1176		1766
1177	struct ev_periodic hourly_tick;	1767	ev_periodic hourly_tick;
1178	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	1768	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1179	ev_periodic_start (loop, &hourly_tick);	1769	ev_periodic_start (loop, &hourly_tick);
1180		1770
1181	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:
1182		1772
1183	#include <math.h>	1773	#include <math.h>
1184		1774
1185	static ev_tstamp	1775	static ev_tstamp
1186	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	1776	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1187	{	1777	{
1188	return fmod (now, 3600.) + 3600.;	1778	return now + (3600. - fmod (now, 3600.));
1189	}	1779	}
1190		1780
1191	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);
1192		1782
1193	Example: Call a callback every hour, starting now:	1783	Example: Call a callback every hour, starting now:
1194		1784
1195	struct ev_periodic hourly_tick;	1785	ev_periodic hourly_tick;
1196	ev_periodic_init (&hourly_tick, clock_cb,	1786	ev_periodic_init (&hourly_tick, clock_cb,
1197	fmod (ev_now (loop), 3600.), 3600., 0);	1787	fmod (ev_now (loop), 3600.), 3600., 0);
1198	ev_periodic_start (loop, &hourly_tick);	1788	ev_periodic_start (loop, &hourly_tick);
1199		1789
1200		1790
1201	=head2 C<ev_signal> - signal me when a signal gets signalled!	1791	=head2 C<ev_signal> - signal me when a signal gets signalled!
1202		1792
1203	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
1204	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
1205	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
1206	normal event processing, like any other event.	1796	normal event processing, like any other event.
1207		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
1208	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
1209	first watcher gets started will libev actually register a signal watcher	1803	first watcher gets started will libev actually register a signal handler
1210	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
1211	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
1212	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
1213	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.
		1814
		1815	=head3 Watcher-Specific Functions and Data Members
1214		1816
1215	=over 4	1817	=over 4
1216		1818
1217	=item ev_signal_init (ev_signal *, callback, int signum)	1819	=item ev_signal_init (ev_signal *, callback, int signum)
1218		1820
…		…
1225		1827
1226	The signal the watcher watches out for.	1828	The signal the watcher watches out for.
1227		1829
1228	=back	1830	=back
1229		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
1230		1846
1231	=head2 C<ev_child> - watch out for process status changes	1847	=head2 C<ev_child> - watch out for process status changes
1232		1848
1233	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
1234	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.
		1886
		1887	=head3 Watcher-Specific Functions and Data Members
1235		1888
1236	=over 4	1889	=over 4
1237		1890
1238	=item ev_child_init (ev_child *, callback, int pid)	1891	=item ev_child_init (ev_child *, callback, int pid, int trace)
1239		1892
1240	=item ev_child_set (ev_child *, int pid)	1893	=item ev_child_set (ev_child *, int pid, int trace)
1241		1894
1242	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
1243	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
1244	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
1245	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
1246	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
1247	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).
1248		1903
1249	=item int pid [read-only]	1904	=item int pid [read-only]
1250		1905
1251	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.
1252		1907
…		…
1259	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
1260	C<waitpid> and C<sys/wait.h> documentation for details).	1915	C<waitpid> and C<sys/wait.h> documentation for details).
1261		1916
1262	=back	1917	=back
1263		1918
1264	Example: Try to exit cleanly on SIGINT and SIGTERM.	1919	=head3 Examples
1265		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
1266	static void	1926	static void
1267	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	1927	child_cb (EV_P_ ev_child *w, int revents)
1268	{	1928	{
1269	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);
1270	}	1931	}
1271		1932
1272	struct ev_signal signal_watcher;	1933	pid_t pid = fork ();
1273	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	1934
1274	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	}
1275		1947
1276		1948
1277	=head2 C<ev_stat> - did the file attributes just change?	1949	=head2 C<ev_stat> - did the file attributes just change?
1278		1950
1279	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
1280	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)
1281	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.
1282		1955
1283	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
1284	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
1285	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
1286	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
1287	the stat buffer having unspecified contents.	1960	least one) and all the other fields of the stat buffer having unspecified
		1961	contents.
1288		1962
1289	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
1290	relative and your working directory changes, the behaviour is undefined.	1965	your working directory changes, then the behaviour is undefined.
1291		1966
1292	Since there is no standard to do this, the portable implementation simply	1967	Since there is no portable change notification interface available, the
1293	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
1294	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
1295	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
1296	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
1297	five seconds, although this might change dynamically). Libev will also	1972	(which you can expect to be around five seconds, although this might
1298	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
1299	usually overkill.	1974	currently around C<0.1>, but that's usually overkill.
1300		1975
1301	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,
1302	as even with OS-supported change notifications, this can be	1977	as even with OS-supported change notifications, this can be
1303	resource-intensive.	1978	resource-intensive.
1304		1979
1305	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
1306	implemented (implementing kqueue support is left as an exercise for the	1981	is the Linux inotify interface (implementing kqueue support is left as an
1307	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
1308	semantics of C<ev_stat> watchers, which means that libev sometimes needs	1983	implementing C<ev_stat> semantics with kqueue, except as a hint).
1309	to fall back to regular polling again even with inotify, but changes are	1984
1310	usually detected immediately, and if the file exists there will be no	1985	=head3 ABI Issues (Largefile Support)
1311	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).
		2066
		2067	=head3 Watcher-Specific Functions and Data Members
1312		2068
1313	=over 4	2069	=over 4
1314		2070
1315	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)	2071	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
1316		2072
…		…
1320	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
1321	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
1322	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
1323	path for as long as the watcher is active.	2079	path for as long as the watcher is active.
1324		2080
1325	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,
1326	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
1327	last change was detected).	2083	last change was detected).
1328		2084
1329	=item ev_stat_stat (ev_stat *)	2085	=item ev_stat_stat (loop, ev_stat *)
1330		2086
1331	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
1332	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
1333	detecting this change (while introducing a race condition). Can also be	2089	detecting this change (while introducing a race condition if you are not
1334	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.
1335		2092
1336	=item ev_statdata attr [read-only]	2093	=item ev_statdata attr [read-only]
1337		2094
1338	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
1339	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
1340	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
1341	was some error while C<stat>ing the file.	2099	some error while C<stat>ing the file.
1342		2100
1343	=item ev_statdata prev [read-only]	2101	=item ev_statdata prev [read-only]
1344		2102
1345	The previous attributes of the file. The callback gets invoked whenever	2103	The previous attributes of the file. The callback gets invoked whenever
1346	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>.
1347		2107
1348	=item ev_tstamp interval [read-only]	2108	=item ev_tstamp interval [read-only]
1349		2109
1350	The specified interval.	2110	The specified interval.
1351		2111
1352	=item const char *path [read-only]	2112	=item const char *path [read-only]
1353		2113
1354	The filesystem path that is being watched.	2114	The file system path that is being watched.
1355		2115
1356	=back	2116	=back
1357		2117
		2118	=head3 Examples
		2119
1358	Example: Watch C</etc/passwd> for attribute changes.	2120	Example: Watch C</etc/passwd> for attribute changes.
1359		2121
1360	static void	2122	static void
1361	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2123	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1362	{	2124	{
1363	/* /etc/passwd changed in some way */	2125	/* /etc/passwd changed in some way */
1364	if (w->attr.st_nlink)	2126	if (w->attr.st_nlink)
1365	{	2127	{
1366	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2128	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1367	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2129	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1368	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2130	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1369	}	2131	}
1370	else	2132	else
1371	/* you shalt not abuse printf for puts */	2133	/* you shalt not abuse printf for puts */
1372	puts ("wow, /etc/passwd is not there, expect problems. "	2134	puts ("wow, /etc/passwd is not there, expect problems. "
1373	"if this is windows, they already arrived\n");	2135	"if this is windows, they already arrived\n");
1374	}	2136	}
1375		2137
1376	...	2138	...
1377	ev_stat passwd;	2139	ev_stat passwd;
1378		2140
1379	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	2141	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1380	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);
1381		2171
1382		2172
1383	=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...
1384		2174
1385	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
1386	priority are pending (prepare, check and other idle watchers do not	2176	priority are pending (prepare, check and other idle watchers do not count
1387	count).	2177	as receiving "events").
1388		2178
1389	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
1390	(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
1391	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
1392	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
…		…
1399	Apart from keeping your process non-blocking (which is a useful	2189	Apart from keeping your process non-blocking (which is a useful
1400	effect on its own sometimes), idle watchers are a good place to do	2190	effect on its own sometimes), idle watchers are a good place to do
1401	"pseudo-background processing", or delay processing stuff to after the	2191	"pseudo-background processing", or delay processing stuff to after the
1402	event loop has handled all outstanding events.	2192	event loop has handled all outstanding events.
1403		2193
		2194	=head3 Watcher-Specific Functions and Data Members
		2195
1404	=over 4	2196	=over 4
1405		2197
1406	=item ev_idle_init (ev_signal *, callback)	2198	=item ev_idle_init (ev_idle *, callback)
1407		2199
1408	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
1409	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,
1410	believe me.	2202	believe me.
1411		2203
1412	=back	2204	=back
1413		2205
		2206	=head3 Examples
		2207
1414	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
1415	callback, free it. Also, use no error checking, as usual.	2209	callback, free it. Also, use no error checking, as usual.
1416		2210
1417	static void	2211	static void
1418	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2212	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1419	{	2213	{
1420	free (w);	2214	free (w);
1421	// now do something you wanted to do when the program has	2215	// now do something you wanted to do when the program has
1422	// no longer asnything immediate to do.	2216	// no longer anything immediate to do.
1423	}	2217	}
1424		2218
1425	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2219	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1426	ev_idle_init (idle_watcher, idle_cb);	2220	ev_idle_init (idle_watcher, idle_cb);
1427	ev_idle_start (loop, idle_cb);	2221	ev_idle_start (loop, idle_cb);
1428		2222
1429		2223
1430	=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!
1431		2225
1432	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:
1433	prepare watchers get invoked before the process blocks and check watchers	2227	prepare watchers get invoked before the process blocks and check watchers
1434	afterwards.	2228	afterwards.
1435		2229
1436	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
1437	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>
…		…
1440	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,
1441	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
1442	called in pairs bracketing the blocking call.	2236	called in pairs bracketing the blocking call.
1443		2237
1444	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
1445	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
1446	variable changes, implement your own watchers, integrate net-snmp or a	2240	variable changes, implement your own watchers, integrate net-snmp or a
1447	coroutine library and lots more. They are also occasionally useful if	2241	coroutine library and lots more. They are also occasionally useful if
1448	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,
1449	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>
1450	watcher).	2244	watcher).
1451		2245
1452	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
1453	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
1454	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
1455	provide just this functionality). Then, in the check watcher you check for	2249	libraries provide exactly this functionality). Then, in the check watcher,
1456	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
1457	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
1458	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
1459	because you never know, you know?).	2253	nevertheless, because you never know, you know?).
1460		2254
1461	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
1462	coroutines into libev programs, by yielding to other active coroutines	2256	coroutines into libev programs, by yielding to other active coroutines
1463	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
1464	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
1465	with priority higher than or equal to the event loop and one coroutine	2259	with priority higher than or equal to the event loop and one coroutine
1466	of lower priority, but only once, using idle watchers to keep the event	2260	of lower priority, but only once, using idle watchers to keep the event
1467	loop from blocking if lower-priority coroutines are active, thus mapping	2261	loop from blocking if lower-priority coroutines are active, thus mapping
1468	low-priority coroutines to idle/background tasks).	2262	low-priority coroutines to idle/background tasks).
1469		2263
		2264	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		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
		2268	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2269	activate ("feed") events into libev. While libev fully supports this, they
		2270	might get executed before other C<ev_check> watchers did their job. As
		2271	C<ev_check> watchers are often used to embed other (non-libev) event
		2272	loops those other event loops might be in an unusable state until their
		2273	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2274	others).
		2275
		2276	=head3 Watcher-Specific Functions and Data Members
		2277
1470	=over 4	2278	=over 4
1471		2279
1472	=item ev_prepare_init (ev_prepare *, callback)	2280	=item ev_prepare_init (ev_prepare *, callback)
1473		2281
1474	=item ev_check_init (ev_check *, callback)	2282	=item ev_check_init (ev_check *, callback)
1475		2283
1476	Initialises and configures the prepare or check watcher - they have no	2284	Initialises and configures the prepare or check watcher - they have no
1477	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>
1478	macros, but using them is utterly, utterly and completely pointless.	2286	macros, but using them is utterly, utterly, utterly and completely
		2287	pointless.
1479		2288
1480	=back	2289	=back
1481		2290
1482	Example: To include a library such as adns, you would add IO watchers	2291	=head3 Examples
1483	and a timeout watcher in a prepare handler, as required by libadns, and	2292
		2293	There are a number of principal ways to embed other event loops or modules
		2294	into libev. Here are some ideas on how to include libadns into libev
		2295	(there is a Perl module named C<EV::ADNS> that does this, which you could
		2296	use as a working example. Another Perl module named C<EV::Glib> embeds a
		2297	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		2298	Glib event loop).
		2299
		2300	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1484	in a check watcher, destroy them and call into libadns. What follows is	2301	and in a check watcher, destroy them and call into libadns. What follows
1485	pseudo-code only of course:	2302	is pseudo-code only of course. This requires you to either use a low
		2303	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		2304	the callbacks for the IO/timeout watchers might not have been called yet.
1486		2305
1487	static ev_io iow [nfd];	2306	static ev_io iow [nfd];
1488	static ev_timer tw;	2307	static ev_timer tw;
1489		2308
1490	static void	2309	static void
1491	io_cb (ev_loop *loop, ev_io *w, int revents)	2310	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1492	{	2311	{
1493	// set the relevant poll flags
1494	// could also call adns_processreadable etc. here
1495	struct pollfd *fd = (struct pollfd *)w->data;
1496	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1497	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1498	}	2312	}
1499		2313
1500	// create io watchers for each fd and a timer before blocking	2314	// create io watchers for each fd and a timer before blocking
1501	static void	2315	static void
1502	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2316	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1503	{	2317	{
1504	int timeout = 3600000;	2318	int timeout = 3600000;
1505	struct pollfd fds [nfd];	2319	struct pollfd fds [nfd];
1506	// actual code will need to loop here and realloc etc.	2320	// actual code will need to loop here and realloc etc.
1507	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2321	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1508		2322
1509	/* 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 */
1510	ev_timer_init (&tw, 0, timeout * 1e-3);	2324	ev_timer_init (&tw, 0, timeout * 1e-3);
1511	ev_timer_start (loop, &tw);	2325	ev_timer_start (loop, &tw);
1512		2326
1513	// create on ev_io per pollfd	2327	// create one ev_io per pollfd
1514	for (int i = 0; i < nfd; ++i)	2328	for (int i = 0; i < nfd; ++i)
1515	{	2329	{
1516	ev_io_init (iow + i, io_cb, fds [i].fd,	2330	ev_io_init (iow + i, io_cb, fds [i].fd,
1517	((fds [i].events & POLLIN ? EV_READ : 0)	2331	((fds [i].events & POLLIN ? EV_READ : 0)
1518	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2332	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1519		2333
1520	fds [i].revents = 0;	2334	fds [i].revents = 0;
1521	iow [i].data = fds + i;
1522	ev_io_start (loop, iow + i);	2335	ev_io_start (loop, iow + i);
1523	}	2336	}
1524	}	2337	}
1525		2338
1526	// stop all watchers after blocking	2339	// stop all watchers after blocking
1527	static void	2340	static void
1528	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2341	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1529	{	2342	{
1530	ev_timer_stop (loop, &tw);	2343	ev_timer_stop (loop, &tw);
1531		2344
1532	for (int i = 0; i < nfd; ++i)	2345	for (int i = 0; i < nfd; ++i)
		2346	{
		2347	// set the relevant poll flags
		2348	// could also call adns_processreadable etc. here
		2349	struct pollfd *fd = fds + i;
		2350	int revents = ev_clear_pending (iow + i);
		2351	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2352	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2353
		2354	// now stop the watcher
1533	ev_io_stop (loop, iow + i);	2355	ev_io_stop (loop, iow + i);
		2356	}
1534		2357
1535	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2358	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1536	}	2359	}
		2360
		2361	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2362	in the prepare watcher and would dispose of the check watcher.
		2363
		2364	Method 3: If the module to be embedded supports explicit event
		2365	notification (libadns does), you can also make use of the actual watcher
		2366	callbacks, and only destroy/create the watchers in the prepare watcher.
		2367
		2368	static void
		2369	timer_cb (EV_P_ ev_timer *w, int revents)
		2370	{
		2371	adns_state ads = (adns_state)w->data;
		2372	update_now (EV_A);
		2373
		2374	adns_processtimeouts (ads, &tv_now);
		2375	}
		2376
		2377	static void
		2378	io_cb (EV_P_ ev_io *w, int revents)
		2379	{
		2380	adns_state ads = (adns_state)w->data;
		2381	update_now (EV_A);
		2382
		2383	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2384	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2385	}
		2386
		2387	// do not ever call adns_afterpoll
		2388
		2389	Method 4: Do not use a prepare or check watcher because the module you
		2390	want to embed is not flexible enough to support it. Instead, you can
		2391	override their poll function. The drawback with this solution is that the
		2392	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		2393	this approach, effectively embedding EV as a client into the horrible
		2394	libglib event loop.
		2395
		2396	static gint
		2397	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2398	{
		2399	int got_events = 0;
		2400
		2401	for (n = 0; n < nfds; ++n)
		2402	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2403
		2404	if (timeout >= 0)
		2405	// create/start timer
		2406
		2407	// poll
		2408	ev_loop (EV_A_ 0);
		2409
		2410	// stop timer again
		2411	if (timeout >= 0)
		2412	ev_timer_stop (EV_A_ &to);
		2413
		2414	// stop io watchers again - their callbacks should have set
		2415	for (n = 0; n < nfds; ++n)
		2416	ev_io_stop (EV_A_ iow [n]);
		2417
		2418	return got_events;
		2419	}
1537		2420
1538		2421
1539	=head2 C<ev_embed> - when one backend isn't enough...	2422	=head2 C<ev_embed> - when one backend isn't enough...
1540		2423
1541	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
…		…
1547	prioritise I/O.	2430	prioritise I/O.
1548		2431
1549	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
1550	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
1551	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
1552	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
1553	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
1554	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
1555	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 :)
1556		2440
1557	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
1558	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),
1559	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
1560	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
1561	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.
1562		2446
1563	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
1564	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
1565	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
1566	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
1567	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
1568	to C<0>, in which case the embed watcher will automatically execute the	2452	to give the embedded loop strictly lower priority for example).
1569	embedded loop sweep.
1570		2453
1571	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
1572	callback will be invoked whenever some events have been handled. You can	2455	will automatically execute the embedded loop sweep whenever necessary.
1573	set the callback to C<0> to avoid having to specify one if you are not
1574	interested in that.
1575		2456
1576	Also, there have not currently been made special provisions for forking:	2457	Fork detection will be handled transparently while the C<ev_embed> watcher
1577	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
1578	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
1579	yourself.	2460	C<ev_loop_fork> on the embedded loop.
1580		2461
1581	Unfortunately, not all backends are embeddable, only the ones returned by	2462	Unfortunately, not all backends are embeddable: only the ones returned by
1582	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2463	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1583	portable one.	2464	portable one.
1584		2465
1585	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
1586	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
1587	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
1588	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.
1589		2470
1590	struct ev_loop *loop_hi = ev_default_init (0);	2471	=head3 C<ev_embed> and fork
1591	struct ev_loop *loop_lo = 0;
1592	struct ev_embed embed;
1593
1594	// see if there is a chance of getting one that works
1595	// (remember that a flags value of 0 means autodetection)
1596	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1597	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1598	: 0;
1599		2472
1600	// 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
1601	if (loop_lo)	2474	automatically be applied to the embedded loop as well, so no special
1602	{	2475	fork handling is required in that case. When the watcher is not running,
1603	ev_embed_init (&embed, 0, loop_lo);	2476	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1604	ev_embed_start (loop_hi, &embed);	2477	as applicable.
1605	}	2478
1606	else	2479	=head3 Watcher-Specific Functions and Data Members
1607	loop_lo = loop_hi;
1608		2480
1609	=over 4	2481	=over 4
1610		2482
1611	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	2483	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
1612		2484
…		…
1614		2486
1615	Configures the watcher to embed the given loop, which must be	2487	Configures the watcher to embed the given loop, which must be
1616	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
1617	invoked automatically, otherwise it is the responsibility of the callback	2489	invoked automatically, otherwise it is the responsibility of the callback
1618	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,
1619	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).
1620		2492
1621	=item ev_embed_sweep (loop, ev_embed *)	2493	=item ev_embed_sweep (loop, ev_embed *)
1622		2494
1623	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
1624	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
1625	apropriate way for embedded loops.	2497	appropriate way for embedded loops.
1626		2498
1627	=item struct ev_loop *loop [read-only]	2499	=item struct ev_loop *other [read-only]
1628		2500
1629	The embedded event loop.	2501	The embedded event loop.
1630		2502
1631	=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
1632		2552
1633		2553
1634	=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
1635		2555
1636	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
…		…
1639	event loop blocks next and before C<ev_check> watchers are being called,	2559	event loop blocks next and before C<ev_check> watchers are being called,
1640	and only in the child after the fork. If whoever good citizen calling	2560	and only in the child after the fork. If whoever good citizen calling
1641	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2561	C<ev_default_fork> cheats and calls it in the wrong process, the fork
1642	handlers will be invoked, too, of course.	2562	handlers will be invoked, too, of course.
1643		2563
		2564	=head3 Watcher-Specific Functions and Data Members
		2565
1644	=over 4	2566	=over 4
1645		2567
1646	=item ev_fork_init (ev_signal *, callback)	2568	=item ev_fork_init (ev_signal *, callback)
1647		2569
1648	Initialises and configures the fork watcher - it has no parameters of any	2570	Initialises and configures the fork watcher - it has no parameters of any
…		…
1650	believe me.	2572	believe me.
1651		2573
1652	=back	2574	=back
1653		2575
1654		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
1655	=head1 OTHER FUNCTIONS	2729	=head1 OTHER FUNCTIONS
1656		2730
1657	There are some other functions of possible interest. Described. Here. Now.	2731	There are some other functions of possible interest. Described. Here. Now.
1658		2732
1659	=over 4	2733	=over 4
1660		2734
1661	=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)
1662		2736
1663	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
1664	callback on whichever event happens first and automatically stop both	2738	callback on whichever event happens first and automatically stops both
1665	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
1666	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
1667	more watchers yourself.	2741	more watchers yourself.
1668		2742
1669	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
1670	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
1671	C<events> set will be craeted and started.	2745	the given C<fd> and C<events> set will be created and started.
1672		2746
1673	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
1674	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
1675	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.
1676	dubious value.
1677		2750
1678	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
1679	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
1680	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>
1681	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.
1682		2757
		2758	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		2759
1683	static void stdin_ready (int revents, void *arg)	2760	static void stdin_ready (int revents, void *arg)
1684	{	2761	{
1685	if (revents & EV_TIMEOUT)
1686	/* doh, nothing entered */;
1687	else if (revents & EV_READ)	2762	if (revents & EV_READ)
1688	/* 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 */;
1689	}	2766	}
1690		2767
1691	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2768	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1692		2769
1693	=item ev_feed_event (ev_loop *, watcher *, int revents)	2770	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
1694		2771
1695	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
1696	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
1697	initialised but not necessarily started event watcher).	2774	initialised but not necessarily started event watcher).
1698		2775
1699	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	2776	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
1700		2777
1701	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
1702	the given events it.	2779	the given events it.
1703		2780
1704	=item ev_feed_signal_event (ev_loop *loop, int signum)	2781	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
1705		2782
1706	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
1707	loop!).	2784	loop!).
1708		2785
1709	=back	2786	=back
1710		2787
1711		2788
…		…
1727		2804
1728	=item * Priorities are not currently supported. Initialising priorities	2805	=item * Priorities are not currently supported. Initialising priorities
1729	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
1730	is an ev_pri field.	2807	is an ev_pri field.
1731		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
1732	=item * Other members are not supported.	2812	=item * Other members are not supported.
1733		2813
1734	=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
1735	to use the libev header file and library.	2815	to use the libev header file and library.
1736		2816
1737	=back	2817	=back
1738		2818
1739	=head1 C++ SUPPORT	2819	=head1 C++ SUPPORT
1740		2820
1741	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
1742	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
1743	the callback model to a model using method callbacks on objects.	2823	the callback model to a model using method callbacks on objects.
1744		2824
1745	To use it,	2825	To use it,
1746		2826
1747	#include <ev++.h>	2827	#include <ev++.h>
1748		2828
1749	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
1750	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
1751	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
1752	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	2832	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
1753		2833
1754	Care has been taken to keep the overhead low. The only data member added	2834	Care has been taken to keep the overhead low. The only data member the C++
1755	to the C-style watchers is the event loop the watcher is associated with	2835	classes add (compared to plain C-style watchers) is the event loop pointer
1756	(or no additional members at all if you disable C<EV_MULTIPLICITY> when	2836	that the watcher is associated with (or no additional members at all if
1757	embedding libev).	2837	you disable C<EV_MULTIPLICITY> when embedding libev).
1758		2838
1759	Currently, functions and static and non-static member functions can be	2839	Currently, functions, and static and non-static member functions can be
1760	used as callbacks. Other types should be easy to add as long as they only	2840	used as callbacks. Other types should be easy to add as long as they only
1761	need one additional pointer for context. If you need support for other	2841	need one additional pointer for context. If you need support for other
1762	types of functors please contact the author (preferably after implementing	2842	types of functors please contact the author (preferably after implementing
1763	it).	2843	it).
1764		2844
…		…
1819	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
1820	thunking function, making it as fast as a direct C callback.	2900	thunking function, making it as fast as a direct C callback.
1821		2901
1822	Example: simple class declaration and watcher initialisation	2902	Example: simple class declaration and watcher initialisation
1823		2903
1824	struct myclass	2904	struct myclass
1825	{	2905	{
1826	void io_cb (ev::io &w, int revents) { }	2906	void io_cb (ev::io &w, int revents) { }
1827	}	2907	}
1828		2908
1829	myclass obj;	2909	myclass obj;
1830	ev::io iow;	2910	ev::io iow;
1831	iow.set <myclass, &myclass::io_cb> (&obj);	2911	iow.set <myclass, &myclass::io_cb> (&obj);
1832		2912
1833	=item w->set (void (*function)(watcher &w, int), void *data = 0)	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);
		2942
		2943	=item w->set<function> (void *data = 0)
1834		2944
1835	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
1836	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
1837	C<data> member and is free for you to use.	2947	C<data> member and is free for you to use.
1838		2948
		2949	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		2950
1839	See the method-C<set> above for more details.	2951	See the method-C<set> above for more details.
		2952
		2953	Example: Use a plain function as callback.
		2954
		2955	static void io_cb (ev::io &w, int revents) { }
		2956	iow.set <io_cb> ();
1840		2957
1841	=item w->set (struct ev_loop *)	2958	=item w->set (struct ev_loop *)
1842		2959
1843	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
1844	do this when the watcher is inactive (and not pending either).	2961	do this when the watcher is inactive (and not pending either).
1845		2962
1846	=item w->set ([args])	2963	=item w->set ([arguments])
1847		2964
1848	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
1849	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
1850	automatically stopped and restarted when reconfiguring it with this	2967	automatically stopped and restarted when reconfiguring it with this
1851	method.	2968	method.
1852		2969
1853	=item w->start ()	2970	=item w->start ()
…		…
1857		2974
1858	=item w->stop ()	2975	=item w->stop ()
1859		2976
1860	Stops the watcher if it is active. Again, no C<loop> argument.	2977	Stops the watcher if it is active. Again, no C<loop> argument.
1861		2978
1862	=item w->again () C<ev::timer>, C<ev::periodic> only	2979	=item w->again () (C<ev::timer>, C<ev::periodic> only)
1863		2980
1864	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding	2981	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
1865	C<ev_TYPE_again> function.	2982	C<ev_TYPE_again> function.
1866		2983
1867	=item w->sweep () C<ev::embed> only	2984	=item w->sweep () (C<ev::embed> only)
1868		2985
1869	Invokes C<ev_embed_sweep>.	2986	Invokes C<ev_embed_sweep>.
1870		2987
1871	=item w->update () C<ev::stat> only	2988	=item w->update () (C<ev::stat> only)
1872		2989
1873	Invokes C<ev_stat_stat>.	2990	Invokes C<ev_stat_stat>.
1874		2991
1875	=back	2992	=back
1876		2993
1877	=back	2994	=back
1878		2995
1879	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
1880	the constructor.	2997	the constructor.
1881		2998
1882	class myclass	2999	class myclass
1883	{	3000	{
1884	ev_io io; void io_cb (ev::io &w, int revents);	3001	ev::io io ; void io_cb (ev::io &w, int revents);
1885	ev_idle idle void idle_cb (ev::idle &w, int revents);	3002	ev::idle idle; void idle_cb (ev::idle &w, int revents);
1886		3003
1887	myclass ();	3004	myclass (int fd)
1888	}	3005	{
1889
1890	myclass::myclass (int fd)
1891	{
1892	io .set <myclass, &myclass::io_cb > (this);	3006	io .set <myclass, &myclass::io_cb > (this);
1893	idle.set <myclass, &myclass::idle_cb> (this);	3007	idle.set <myclass, &myclass::idle_cb> (this);
1894		3008
1895	io.start (fd, ev::READ);	3009	io.start (fd, ev::READ);
		3010	}
1896	}	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
1897		3066
1898		3067
1899	=head1 MACRO MAGIC	3068	=head1 MACRO MAGIC
1900		3069
1901	Libev can be compiled with a variety of options, the most fundemantal is	3070	Libev can be compiled with a variety of options, the most fundamental
1902	C<EV_MULTIPLICITY>. This option determines whether (most) functions and	3071	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
1903	callbacks have an initial C<struct ev_loop *> argument.	3072	functions and callbacks have an initial C<struct ev_loop *> argument.
1904		3073
1905	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
1906	following macros are defined:	3075	following macros are defined:
1907		3076
1908	=over 4	3077	=over 4
…		…
1911		3080
1912	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
1913	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,
1914	C<EV_A_> is used when other arguments are following. Example:	3083	C<EV_A_> is used when other arguments are following. Example:
1915		3084
1916	ev_unref (EV_A);	3085	ev_unref (EV_A);
1917	ev_timer_add (EV_A_ watcher);	3086	ev_timer_add (EV_A_ watcher);
1918	ev_loop (EV_A_ 0);	3087	ev_loop (EV_A_ 0);
1919		3088
1920	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,
1921	which is often provided by the following macro.	3090	which is often provided by the following macro.
1922		3091
1923	=item C<EV_P>, C<EV_P_>	3092	=item C<EV_P>, C<EV_P_>
1924		3093
1925	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
1926	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,
1927	C<EV_P_> is used when other parameters are following. Example:	3096	C<EV_P_> is used when other parameters are following. Example:
1928		3097
1929	// this is how ev_unref is being declared	3098	// this is how ev_unref is being declared
1930	static void ev_unref (EV_P);	3099	static void ev_unref (EV_P);
1931		3100
1932	// this is how you can declare your typical callback	3101	// this is how you can declare your typical callback
1933	static void cb (EV_P_ ev_timer *w, int revents)	3102	static void cb (EV_P_ ev_timer *w, int revents)
1934		3103
1935	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
1936	suitable for use with C<EV_A>.	3105	suitable for use with C<EV_A>.
1937		3106
1938	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3107	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
1939		3108
1940	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
1941	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.
1942		3121
1943	=back	3122	=back
1944		3123
1945	Example: Declare and initialise a check watcher, utilising the above	3124	Example: Declare and initialise a check watcher, utilising the above
1946	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
1947	or not.	3126	or not.
1948		3127
1949	static void	3128	static void
1950	check_cb (EV_P_ ev_timer *w, int revents)	3129	check_cb (EV_P_ ev_timer *w, int revents)
1951	{	3130	{
1952	ev_check_stop (EV_A_ w);	3131	ev_check_stop (EV_A_ w);
1953	}	3132	}
1954		3133
1955	ev_check check;	3134	ev_check check;
1956	ev_check_init (&check, check_cb);	3135	ev_check_init (&check, check_cb);
1957	ev_check_start (EV_DEFAULT_ &check);	3136	ev_check_start (EV_DEFAULT_ &check);
1958	ev_loop (EV_DEFAULT_ 0);	3137	ev_loop (EV_DEFAULT_ 0);
1959		3138
1960	=head1 EMBEDDING	3139	=head1 EMBEDDING
1961		3140
1962	Libev can (and often is) directly embedded into host	3141	Libev can (and often is) directly embedded into host
1963	applications. Examples of applications that embed it include the Deliantra	3142	applications. Examples of applications that embed it include the Deliantra
1964	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)	3143	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
1965	and rxvt-unicode.	3144	and rxvt-unicode.
1966		3145
1967	The goal is to enable you to just copy the neecssary files into your	3146	The goal is to enable you to just copy the necessary files into your
1968	source directory without having to change even a single line in them, so	3147	source directory without having to change even a single line in them, so
1969	you can easily upgrade by simply copying (or having a checked-out copy of	3148	you can easily upgrade by simply copying (or having a checked-out copy of
1970	libev somewhere in your source tree).	3149	libev somewhere in your source tree).
1971		3150
1972	=head2 FILESETS	3151	=head2 FILESETS
1973		3152
1974	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
1975	in your app.	3154	in your application.
1976		3155
1977	=head3 CORE EVENT LOOP	3156	=head3 CORE EVENT LOOP
1978		3157
1979	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
1980	configuration (no autoconf):	3159	configuration (no autoconf):
1981		3160
1982	#define EV_STANDALONE 1	3161	#define EV_STANDALONE 1
1983	#include "ev.c"	3162	#include "ev.c"
1984		3163
1985	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
1986	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
1987	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
1988	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
1989	where you can put other configuration options):	3168	where you can put other configuration options):
1990		3169
1991	#define EV_STANDALONE 1	3170	#define EV_STANDALONE 1
1992	#include "ev.h"	3171	#include "ev.h"
1993		3172
1994	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++
1995	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
1996	as a bug).	3175	as a bug).
1997		3176
1998	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
1999	in your include path (e.g. in libev/ when using -Ilibev):	3178	in your include path (e.g. in libev/ when using -Ilibev):
2000		3179
2001	ev.h	3180	ev.h
2002	ev.c	3181	ev.c
2003	ev_vars.h	3182	ev_vars.h
2004	ev_wrap.h	3183	ev_wrap.h
2005		3184
2006	ev_win32.c required on win32 platforms only	3185	ev_win32.c required on win32 platforms only
2007		3186
2008	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)
2009	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)
2010	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)
2011	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)
2012	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)
2013		3192
2014	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
2015	to compile this single file.	3194	to compile this single file.
2016		3195
2017	=head3 LIBEVENT COMPATIBILITY API	3196	=head3 LIBEVENT COMPATIBILITY API
2018		3197
2019	To include the libevent compatibility API, also include:	3198	To include the libevent compatibility API, also include:
2020		3199
2021	#include "event.c"	3200	#include "event.c"
2022		3201
2023	in the file including F<ev.c>, and:	3202	in the file including F<ev.c>, and:
2024		3203
2025	#include "event.h"	3204	#include "event.h"
2026		3205
2027	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>.
2028		3207
2029	You need the following additional files for this:	3208	You need the following additional files for this:
2030		3209
2031	event.h	3210	event.h
2032	event.c	3211	event.c
2033		3212
2034	=head3 AUTOCONF SUPPORT	3213	=head3 AUTOCONF SUPPORT
2035		3214
2036	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
2037	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
2038	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
2039	include F<config.h> and configure itself accordingly.	3218	include F<config.h> and configure itself accordingly.
2040		3219
2041	For this of course you need the m4 file:	3220	For this of course you need the m4 file:
2042		3221
2043	libev.m4	3222	libev.m4
2044		3223
2045	=head2 PREPROCESSOR SYMBOLS/MACROS	3224	=head2 PREPROCESSOR SYMBOLS/MACROS
2046		3225
2047	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
2048	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
2049	and only include the select backend.	3228	autoconf is documented for every option.
2050		3229
2051	=over 4	3230	=over 4
2052		3231
2053	=item EV_STANDALONE	3232	=item EV_STANDALONE
2054		3233
…		…
2056	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
2057	implementations for some libevent functions (such as logging, which is not	3236	implementations for some libevent functions (such as logging, which is not
2058	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
2059	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.
2060		3239
		3240	In stanbdalone mode, libev will still try to automatically deduce the
		3241	configuration, but has to be more conservative.
		3242
2061	=item EV_USE_MONOTONIC	3243	=item EV_USE_MONOTONIC
2062		3244
2063	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
2064	monotonic clock option at both compiletime and runtime. Otherwise no use	3246	monotonic clock option at both compile time and runtime. Otherwise no
2065	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,
2066	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
2067	the functionality isn't available is safe, though, althoguh you have	3249	when the functionality isn't available is safe, though, although you have
2068	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>
2069	function is hiding in (often F<-lrt>).	3251	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2070		3252
2071	=item EV_USE_REALTIME	3253	=item EV_USE_REALTIME
2072		3254
2073	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
2074	realtime clock option at compiletime (and assume its availability at	3256	real-time clock option at compile time (and assume its availability
2075	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
2076	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3258	option will be attempted. This effectively replaces C<gettimeofday>
2077	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See tzhe note about libraries	3259	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2078	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>).
		3274
		3275	=item EV_USE_NANOSLEEP
		3276
		3277	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		3278	and will use it for delays. Otherwise it will use C<select ()>.
		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.
2079		3287
2080	=item EV_USE_SELECT	3288	=item EV_USE_SELECT
2081		3289
2082	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
2083	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
2084	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
2085	will not be compiled in.	3293	will not be compiled in.
2086		3294
2087	=item EV_SELECT_USE_FD_SET	3295	=item EV_SELECT_USE_FD_SET
2088		3296
2089	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>
2090	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
2091	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
2092	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
2093	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
2094	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,
2095	influence the size of the C<fd_set> used.	3303	configures the maximum size of the C<fd_set>.
2096		3304
2097	=item EV_SELECT_IS_WINSOCKET	3305	=item EV_SELECT_IS_WINSOCKET
2098		3306
2099	When defined to C<1>, the select backend will assume that	3307	When defined to C<1>, the select backend will assume that
2100	select/socket/connect etc. don't understand file descriptors but	3308	select/socket/connect etc. don't understand file descriptors but
…		…
2102	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
2103	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,
2104	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
2105	on win32. Should not be defined on non-win32 platforms.	3313	on win32. Should not be defined on non-win32 platforms.
2106		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
2107	=item EV_USE_POLL	3323	=item EV_USE_POLL
2108		3324
2109	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)
2110	backend. Otherwise it will be enabled on non-win32 platforms. It	3326	backend. Otherwise it will be enabled on non-win32 platforms. It
2111	takes precedence over select.	3327	takes precedence over select.
2112		3328
2113	=item EV_USE_EPOLL	3329	=item EV_USE_EPOLL
2114		3330
2115	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
2116	C<epoll>(7) backend. Its availability will be detected at runtime,	3332	C<epoll>(7) backend. Its availability will be detected at runtime,
2117	otherwise another method will be used as fallback. This is the	3333	otherwise another method will be used as fallback. This is the preferred
2118	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.
2119		3336
2120	=item EV_USE_KQUEUE	3337	=item EV_USE_KQUEUE
2121		3338
2122	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
2123	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,
…		…
2136	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
2137	backend for Solaris 10 systems.	3354	backend for Solaris 10 systems.
2138		3355
2139	=item EV_USE_DEVPOLL	3356	=item EV_USE_DEVPOLL
2140		3357
2141	reserved for future expansion, works like the USE symbols above.	3358	Reserved for future expansion, works like the USE symbols above.
2142		3359
2143	=item EV_USE_INOTIFY	3360	=item EV_USE_INOTIFY
2144		3361
2145	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
2146	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
2147	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.
2148		3377
2149	=item EV_H	3378	=item EV_H
2150		3379
2151	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
2152	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
2153	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.
2154		3383
2155	=item EV_CONFIG_H	3384	=item EV_CONFIG_H
2156		3385
2157	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
2158	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
2159	C<EV_H>, above.	3388	C<EV_H>, above.
2160		3389
2161	=item EV_EVENT_H	3390	=item EV_EVENT_H
2162		3391
2163	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
2164	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">.
2165		3394
2166	=item EV_PROTOTYPES	3395	=item EV_PROTOTYPES
2167		3396
2168	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
2169	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
…		…
2190	When doing priority-based operations, libev usually has to linearly search	3419	When doing priority-based operations, libev usually has to linearly search
2191	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
2192	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
2193	fine.	3422	fine.
2194		3423
2195	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
2196	C<0> will save some memory and cpu.	3425	both to C<0> will save some memory and CPU.
2197		3426
2198	=item EV_PERIODIC_ENABLE	3427	=item EV_PERIODIC_ENABLE
2199		3428
2200	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
2201	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
…		…
2208	code.	3437	code.
2209		3438
2210	=item EV_EMBED_ENABLE	3439	=item EV_EMBED_ENABLE
2211		3440
2212	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
2213	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.
2214		3444
2215	=item EV_STAT_ENABLE	3445	=item EV_STAT_ENABLE
2216		3446
2217	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
2218	defined to be C<0>, then they are not.	3448	defined to be C<0>, then they are not.
…		…
2220	=item EV_FORK_ENABLE	3450	=item EV_FORK_ENABLE
2221		3451
2222	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
2223	defined to be C<0>, then they are not.	3453	defined to be C<0>, then they are not.
2224		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
2225	=item EV_MINIMAL	3460	=item EV_MINIMAL
2226		3461
2227	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
2228	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
2229	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.
2230		3466
2231	=item EV_PID_HASHSIZE	3467	=item EV_PID_HASHSIZE
2232		3468
2233	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
2234	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
2235	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
2236	increase this value (I<must> be a power of two).	3472	increase this value (I<must> be a power of two).
2237		3473
2238	=item EV_INOTIFY_HASHSIZE	3474	=item EV_INOTIFY_HASHSIZE
2239		3475
2240	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
2241	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>),
2242	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>
2243	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
2244	two).	3480	two).
2245		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
2246	=item EV_COMMON	3517	=item EV_COMMON
2247		3518
2248	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
2249	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
2250	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,
2251	though, and it must be identical each time.	3522	though, and it must be identical each time.
2252		3523
2253	For example, the perl EV module uses something like this:	3524	For example, the perl EV module uses something like this:
2254		3525
2255	#define EV_COMMON \	3526	#define EV_COMMON \
2256	SV *self; /* contains this struct */ \	3527	SV *self; /* contains this struct */ \
2257	SV *cb_sv, *fh /* note no trailing ";" */	3528	SV *cb_sv, *fh /* note no trailing ";" */
2258		3529
2259	=item EV_CB_DECLARE (type)	3530	=item EV_CB_DECLARE (type)
2260		3531
2261	=item EV_CB_INVOKE (watcher, revents)	3532	=item EV_CB_INVOKE (watcher, revents)
2262		3533
2263	=item ev_set_cb (ev, cb)	3534	=item ev_set_cb (ev, cb)
2264		3535
2265	Can be used to change the callback member declaration in each watcher,	3536	Can be used to change the callback member declaration in each watcher,
2266	and the way callbacks are invoked and set. Must expand to a struct member	3537	and the way callbacks are invoked and set. Must expand to a struct member
2267	definition and a statement, respectively. See the F<ev.v> header file for	3538	definition and a statement, respectively. See the F<ev.h> header file for
2268	their default definitions. One possible use for overriding these is to	3539	their default definitions. One possible use for overriding these is to
2269	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
2270	method calls instead of plain function calls in C++.	3541	method calls instead of plain function calls in C++.
		3542
		3543	=back
		3544
		3545	=head2 EXPORTED API SYMBOLS
		3546
		3547	If you need to re-export the API (e.g. via a DLL) and you need a list of
		3548	exported symbols, you can use the provided F<Symbol.*> files which list
		3549	all public symbols, one per line:
		3550
		3551	Symbols.ev for libev proper
		3552	Symbols.event for the libevent emulation
		3553
		3554	This can also be used to rename all public symbols to avoid clashes with
		3555	multiple versions of libev linked together (which is obviously bad in
		3556	itself, but sometimes it is inconvenient to avoid this).
		3557
		3558	A sed command like this will create wrapper C<#define>'s that you need to
		3559	include before including F<ev.h>:
		3560
		3561	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		3562
		3563	This would create a file F<wrap.h> which essentially looks like this:
		3564
		3565	#define ev_backend myprefix_ev_backend
		3566	#define ev_check_start myprefix_ev_check_start
		3567	#define ev_check_stop myprefix_ev_check_stop
		3568	...
2271		3569
2272	=head2 EXAMPLES	3570	=head2 EXAMPLES
2273		3571
2274	For a real-world example of a program the includes libev	3572	For a real-world example of a program the includes libev
2275	verbatim, you can have a look at the EV perl module	3573	verbatim, you can have a look at the EV perl module
…		…
2280	file.	3578	file.
2281		3579
2282	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
2283	that everybody includes and which overrides some configure choices:	3581	that everybody includes and which overrides some configure choices:
2284		3582
2285	#define EV_MINIMAL 1	3583	#define EV_MINIMAL 1
2286	#define EV_USE_POLL 0	3584	#define EV_USE_POLL 0
2287	#define EV_MULTIPLICITY 0	3585	#define EV_MULTIPLICITY 0
2288	#define EV_PERIODIC_ENABLE 0	3586	#define EV_PERIODIC_ENABLE 0
2289	#define EV_STAT_ENABLE 0	3587	#define EV_STAT_ENABLE 0
2290	#define EV_FORK_ENABLE 0	3588	#define EV_FORK_ENABLE 0
2291	#define EV_CONFIG_H <config.h>	3589	#define EV_CONFIG_H <config.h>
2292	#define EV_MINPRI 0	3590	#define EV_MINPRI 0
2293	#define EV_MAXPRI 0	3591	#define EV_MAXPRI 0
2294		3592
2295	#include "ev++.h"	3593	#include "ev++.h"
2296		3594
2297	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:
2298		3596
2299	#include "ev_cpp.h"	3597	#include "ev_cpp.h"
2300	#include "ev.c"	3598	#include "ev.c"
2301		3599
		3600	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
2302		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
2303	=head1 COMPLEXITIES	3891	=head1 ALGORITHMIC COMPLEXITIES
2304		3892
2305	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
2306	libev will be explained. For complexity discussions about backends see the	3894	libev will be documented. For complexity discussions about backends see
2307	documentation for C<ev_default_init>.	3895	the documentation for C<ev_default_init>.
2308		3896
2309	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
2310	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
2311	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
2312	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
2313	it is much faster and asymptotically approaches constant time.	3901	average it is much faster and asymptotically approaches constant time.
2314		3902
2315	=over 4	3903	=over 4
2316		3904
2317	=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)
2318		3906
2319	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
2320	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
2321	have to skip those 100 watchers.	3909	have to skip roughly seven (C<ld 100>) of these watchers.
2322		3910
2323	=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)
2324		3912
2325	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,
2326	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.
2327		3915
2328	=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)
2329		3917
2330	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
2331	=item Stopping check/prepare/idle watchers: O(1)	3920	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2332		3921
2333	=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))
2334		3923
2335	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
2336	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
2337	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).
2338		3928
2339	=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.
2340		3933
2341	=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)
2342		3935
2343	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
2344	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).
2345		3939
2346	=item Activating one watcher: O(1)	3940	=item Activating one watcher (putting it into the pending state): O(1)
2347		3941
2348	=item Priority handling: O(number_of_priorities)	3942	=item Priority handling: O(number_of_priorities)
2349		3943
2350	Priorities are implemented by allocating some space for each	3944	Priorities are implemented by allocating some space for each
2351	priority. When doing priority-based operations, libev usually has to	3945	priority. When doing priority-based operations, libev usually has to
2352	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.
2353		3958
2354	=back	3959	=back
2355		3960
2356		3961
2357	=head1 AUTHOR	3962	=head1 AUTHOR
2358		3963
2359	Marc Lehmann <libev@schmorp.de>.	3964	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
2360		3965

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