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Revision 1.60 by root, Wed Nov 28 18:29:30 2007 UTC vs.
Revision 1.230 by root, Wed Apr 15 18:47:07 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
		69	The newest version of this document is also available as an html-formatted
		70	web page you might find easier to navigate when reading it for the first
		71	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		72
53	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
54	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
55	these event sources and provide your program with events.	75	these event sources and provide your program with events.
56		76
57	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
58	(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
59	communicate events via a callback mechanism.	79	communicate events via a callback mechanism.
…		…
61	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
62	watchers>, which are relatively small C structures you initialise with the	82	watchers>, which are relatively small C structures you initialise with the
63	details of the event, and then hand it over to libev by I<starting> the	83	details of the event, and then hand it over to libev by I<starting> the
64	watcher.	84	watcher.
65		85
66	=head1 FEATURES	86	=head2 FEATURES
67		87
68	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
69	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	89	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
70	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
71	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	91	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
…		…
78		98
79	It also is quite fast (see this	99	It also is quite fast (see this
80	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
81	for example).	101	for example).
82		102
83	=head1 CONVENTIONS	103	=head2 CONVENTIONS
84		104
85	Libev is very configurable. In this manual the default configuration will	105	Libev is very configurable. In this manual the default (and most common)
86	be described, which supports multiple event loops. For more info about	106	configuration will be described, which supports multiple event loops. For
87	various configuration options please have a look at B<EMBED> section in	107	more info about various configuration options please have a look at
88	this manual. If libev was configured without support for multiple event	108	B<EMBED> section in this manual. If libev was configured without support
89	loops, then all functions taking an initial argument of name C<loop>	109	for multiple event loops, then all functions taking an initial argument of
90	(which is always of type C<struct ev_loop *>) will not have this argument.	110	name C<loop> (which is always of type C<ev_loop *>) will not have
		111	this argument.
91		112
92	=head1 TIME REPRESENTATION	113	=head2 TIME REPRESENTATION
93		114
94	Libev represents time as a single floating point number, representing the	115	Libev represents time as a single floating point number, representing the
95	(fractional) number of seconds since the (POSIX) epoch (somewhere near	116	(fractional) number of seconds since the (POSIX) epoch (somewhere near
96	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
97	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
98	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
99	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
100		144
101	=head1 GLOBAL FUNCTIONS	145	=head1 GLOBAL FUNCTIONS
102		146
103	These functions can be called anytime, even before initialising the	147	These functions can be called anytime, even before initialising the
104	library in any way.	148	library in any way.
…		…
109		153
110	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
111	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
112	you actually want to know.	156	you actually want to know.
113		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
114	=item int ev_version_major ()	164	=item int ev_version_major ()
115		165
116	=item int ev_version_minor ()	166	=item int ev_version_minor ()
117		167
118	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
119	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
120	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
121	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
122	version of the library your program was compiled against.	172	version of the library your program was compiled against.
123		173
		174	These version numbers refer to the ABI version of the library, not the
		175	release version.
		176
124	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,
125	as this indicates an incompatible change. Minor versions are usually	178	as this indicates an incompatible change. Minor versions are usually
126	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
127	not a problem.	180	not a problem.
128		181
129	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
130	version.	183	version.
131		184
132	assert (("libev version mismatch",	185	assert (("libev version mismatch",
133	ev_version_major () == EV_VERSION_MAJOR	186	ev_version_major () == EV_VERSION_MAJOR
134	&& ev_version_minor () >= EV_VERSION_MINOR));	187	&& ev_version_minor () >= EV_VERSION_MINOR));
135		188
136	=item unsigned int ev_supported_backends ()	189	=item unsigned int ev_supported_backends ()
137		190
138	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_*>
139	value) compiled into this binary of libev (independent of their	192	value) compiled into this binary of libev (independent of their
…		…
141	a description of the set values.	194	a description of the set values.
142		195
143	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
144	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
145		198
146	assert (("sorry, no epoll, no sex",	199	assert (("sorry, no epoll, no sex",
147	ev_supported_backends () & EVBACKEND_EPOLL));	200	ev_supported_backends () & EVBACKEND_EPOLL));
148		201
149	=item unsigned int ev_recommended_backends ()	202	=item unsigned int ev_recommended_backends ()
150		203
151	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
152	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
153	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
154	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
155	(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
156	libev will probe for if you specify no backends explicitly.	209	libev will probe for if you specify no backends explicitly.
157		210
158	=item unsigned int ev_embeddable_backends ()	211	=item unsigned int ev_embeddable_backends ()
159		212
…		…
163	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	216	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
164	recommended ones.	217	recommended ones.
165		218
166	See the description of C<ev_embed> watchers for more info.	219	See the description of C<ev_embed> watchers for more info.
167		220
168	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	221	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
169		222
170	Sets the allocation function to use (the prototype is similar - the	223	Sets the allocation function to use (the prototype is similar - the
171	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
172	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
173	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
174	potentially destructive action. The default is your system realloc	227	or take some potentially destructive action.
175	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.
176		232
177	You could override this function in high-availability programs to, say,	233	You could override this function in high-availability programs to, say,
178	free some memory if it cannot allocate memory, to use a special allocator,	234	free some memory if it cannot allocate memory, to use a special allocator,
179	or even to sleep a while and retry until some memory is available.	235	or even to sleep a while and retry until some memory is available.
180		236
181	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
182	retries).	238	retries (example requires a standards-compliant C<realloc>).
183		239
184	static void *	240	static void *
185	persistent_realloc (void *ptr, size_t size)	241	persistent_realloc (void *ptr, size_t size)
186	{	242	{
187	for (;;)	243	for (;;)
…		…
196	}	252	}
197		253
198	...	254	...
199	ev_set_allocator (persistent_realloc);	255	ev_set_allocator (persistent_realloc);
200		256
201	=item ev_set_syserr_cb (void (*cb)(const char *msg));	257	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
202		258
203	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
204	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
205	indicating the system call or subsystem causing the problem. If this	261	indicating the system call or subsystem causing the problem. If this
206	callback is set, then libev will expect it to remedy the sitution, no	262	callback is set, then libev will expect it to remedy the situation, no
207	matter what, when it returns. That is, libev will generally retry the	263	matter what, when it returns. That is, libev will generally retry the
208	requested operation, or, if the condition doesn't go away, do bad stuff	264	requested operation, or, if the condition doesn't go away, do bad stuff
209	(such as abort).	265	(such as abort).
210		266
211	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.
…		…
222		278
223	=back	279	=back
224		280
225	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	281	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
226		282
227	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>
228	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>
229	events, and dynamically created loops which do not.	285	I<function>).
230		286
231	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
232	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
233	create, you also create another event loop. Libev itself does no locking	289	not.
234	whatsoever, so if you mix calls to the same event loop in different
235	threads, make sure you lock (this is usually a bad idea, though, even if
236	done correctly, because it's hideous and inefficient).
237		290
238	=over 4	291	=over 4
239		292
240	=item struct ev_loop *ev_default_loop (unsigned int flags)	293	=item struct ev_loop *ev_default_loop (unsigned int flags)
241		294
…		…
245	flags. If that is troubling you, check C<ev_backend ()> afterwards).	298	flags. If that is troubling you, check C<ev_backend ()> afterwards).
246		299
247	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
248	function.	301	function.
249		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
250	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
251	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>).
252		316
253	The following flags are supported:	317	The following flags are supported:
254		318
…		…
259	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
260	thing, believe me).	324	thing, believe me).
261		325
262	=item C<EVFLAG_NOENV>	326	=item C<EVFLAG_NOENV>
263		327
264	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
265	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
266	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	330	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
267	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
268	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
269	around bugs.	333	around bugs.
270		334
		335	=item C<EVFLAG_FORKCHECK>
		336
		337	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after
		338	a fork, you can also make libev check for a fork in each iteration by
		339	enabling this flag.
		340
		341	This works by calling C<getpid ()> on every iteration of the loop,
		342	and thus this might slow down your event loop if you do a lot of loop
		343	iterations and little real work, but is usually not noticeable (on my
		344	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
		345	without a system call and thus I<very> fast, but my GNU/Linux system also has
		346	C<pthread_atfork> which is even faster).
		347
		348	The big advantage of this flag is that you can forget about fork (and
		349	forget about forgetting to tell libev about forking) when you use this
		350	flag.
		351
		352	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
		353	environment variable.
		354
271	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	355	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
272		356
273	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
274	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,
275	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
276	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
277	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).
278		373
279	=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)
280		375
281	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
282	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
283	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
284	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>.
285		385
286	=item C<EVBACKEND_EPOLL> (value 4, Linux)	386	=item C<EVBACKEND_EPOLL> (value 4, Linux)
287		387
288	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,
289	but it scales phenomenally better. While poll and select usually scale like	389	but it scales phenomenally better. While poll and select usually scale
290	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),
291	either O(1) or O(active_fds).	391	epoll scales either O(1) or O(active_fds).
292		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
293	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
294	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
295	(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
296	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
297	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.
298		416
299	Please note that epoll sometimes generates spurious notifications, so you	417	Best performance from this backend is achieved by not unregistering all
300	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,
301	(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>.
302		434
303	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	435	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
304		436
305	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
306	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
307	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
308	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
309	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
310	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.
311		450
312	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
313	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
314	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
315	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
316	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>.
317		471
318	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	472	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
319		473
320	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.
321		478
322	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	479	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
323		480
324	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,
325	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)).
326		483
327	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
328	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
329	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>.
330		500
331	=item C<EVBACKEND_ALL>	501	=item C<EVBACKEND_ALL>
332		502
333	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
334	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
335	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	505	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
336		506
		507	It is definitely not recommended to use this flag.
		508
337	=back	509	=back
338		510
339	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
340	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
341	specified, most compiled-in backend will be tried, usually in reverse	513	specified, all backends in C<ev_recommended_backends ()> will be tried.
342	order of their flag values :)
343		514
344	The most typical usage is like this:	515	Example: This is the most typical usage.
345		516
346	if (!ev_default_loop (0))	517	if (!ev_default_loop (0))
347	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	518	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
348		519
349	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
350	environment settings to be taken into account:	521	environment settings to be taken into account:
351		522
352	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	523	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
353		524
354	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
355	available (warning, breaks stuff, best use only with your own private	526	used if available (warning, breaks stuff, best use only with your own
356	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):
357		529
358	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	530	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
359		531
360	=item struct ev_loop *ev_loop_new (unsigned int flags)	532	=item struct ev_loop *ev_loop_new (unsigned int flags)
361		533
362	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
363	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
364	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
365	undefined behaviour (or a failed assertion if assertions are enabled).	537	undefined behaviour (or a failed assertion if assertions are enabled).
366		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
367	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.
368		544
369	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	545	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
370	if (!epoller)	546	if (!epoller)
371	fatal ("no epoll found here, maybe it hides under your chair");	547	fatal ("no epoll found here, maybe it hides under your chair");
372		548
373	=item ev_default_destroy ()	549	=item ev_default_destroy ()
374		550
375	Destroys the default loop again (frees all memory and kernel state	551	Destroys the default loop again (frees all memory and kernel state
376	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
377	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
378	responsibility to either stop all watchers cleanly yoursef I<before>	554	responsibility to either stop all watchers cleanly yourself I<before>
379	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
380	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
381	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>).
382		567
383	=item ev_loop_destroy (loop)	568	=item ev_loop_destroy (loop)
384		569
385	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
386	earlier call to C<ev_loop_new>.	571	earlier call to C<ev_loop_new>.
387		572
388	=item ev_default_fork ()	573	=item ev_default_fork ()
389		574
		575	This function sets a flag that causes subsequent C<ev_loop> iterations
390	This function reinitialises the kernel state for backends that have	576	to reinitialise the kernel state for backends that have one. Despite the
391	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
392	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
393	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.
394		581
395	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
396	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
397	fork+exec, you don't have to call it.	584	you just fork+exec, you don't have to call it at all.
398		585
399	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
400	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
401	quite nicely into a call to C<pthread_atfork>:	588	quite nicely into a call to C<pthread_atfork>:
402		589
403	pthread_atfork (0, 0, ev_default_fork);	590	pthread_atfork (0, 0, ev_default_fork);
404		591
405	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
406	without calling this function, so if you force one of those backends you
407	do not need to care.
408
409	=item ev_loop_fork (loop)	592	=item ev_loop_fork (loop)
410		593
411	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
412	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
413	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.
		603
		604	=item unsigned int ev_loop_count (loop)
		605
		606	Returns the count of loop iterations for the loop, which is identical to
		607	the number of times libev did poll for new events. It starts at C<0> and
		608	happily wraps around with enough iterations.
		609
		610	This value can sometimes be useful as a generation counter of sorts (it
		611	"ticks" the number of loop iterations), as it roughly corresponds with
		612	C<ev_prepare> and C<ev_check> calls.
414		613
415	=item unsigned int ev_backend (loop)	614	=item unsigned int ev_backend (loop)
416		615
417	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	616	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
418	use.	617	use.
…		…
421		620
422	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
423	received events and started processing them. This timestamp does not	622	received events and started processing them. This timestamp does not
424	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
425	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
426	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.
427		638
428	=item ev_loop (loop, int flags)	639	=item ev_loop (loop, int flags)
429		640
430	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
431	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
…		…
434	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
435	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.
436		647
437	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
438	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
439	finished (especially in interactive programs), but having a program that	650	finished (especially in interactive programs), but having a program
440	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
441	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.
442		654
443	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
444	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
445	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.
446		659
447	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
448	neccessary) and will handle those and any outstanding ones. It will block	661	necessary) and will handle those and any already outstanding ones. It
449	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
450	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
451	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
452	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
453	usually a better approach for this kind of thing.	670	usually a better approach for this kind of thing.
454		671
455	Here are the gory details of what C<ev_loop> does:	672	Here are the gory details of what C<ev_loop> does:
456		673
457	* If there are no active watchers (reference count is zero), return.	674	- Before the first iteration, call any pending watchers.
458	- 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.
459	- 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.
460	- Update the kernel state with all outstanding changes.	680	- Update the kernel state with all outstanding changes.
461	- Update the "event loop time".	681	- Update the "event loop time" (ev_now ()).
462	- 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.
463	- Block the process, waiting for any events.	686	- Block the process, waiting for any events.
464	- Queue all outstanding I/O (fd) events.	687	- Queue all outstanding I/O (fd) events.
465	- Update the "event loop time" and do time jump handling.	688	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
466	- Queue all outstanding timers.	689	- Queue all expired timers.
467	- Queue all outstanding periodics.	690	- Queue all expired periodics.
468	- If no events are pending now, queue all idle watchers.	691	- Unless any events are pending now, queue all idle watchers.
469	- Queue all check watchers.	692	- Queue all check watchers.
470	- 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).
471	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
472	be handled here by queueing them when their watcher gets executed.	695	be handled here by queueing them when their watcher gets executed.
473	- 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
474	were used, return, otherwise continue with step *.	697	were used, or there are no active watchers, return, otherwise
		698	continue with step *.
475		699
476	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
477	anymore.	701	anymore.
478		702
479	... queue jobs here, make sure they register event watchers as long	703	... queue jobs here, make sure they register event watchers as long
480	... 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..)
481	ev_loop (my_loop, 0);	705	ev_loop (my_loop, 0);
482	... jobs done. yeah!	706	... jobs done or somebody called unloop. yeah!
483		707
484	=item ev_unloop (loop, how)	708	=item ev_unloop (loop, how)
485		709
486	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
487	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
488	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
489	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.
490		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
491	=item ev_ref (loop)	719	=item ev_ref (loop)
492		720
493	=item ev_unref (loop)	721	=item ev_unref (loop)
494		722
495	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
496	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
497	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
498	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>
499	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
500	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
501	visible to the libev user and should not keep C<ev_loop> from exiting if	732	is not visible to the libev user and should not keep C<ev_loop> from
502	no event watchers registered by it are active. It is also an excellent	733	exiting if no event watchers registered by it are active. It is also an
503	way to do this for generic recurring timers or from within third-party	734	excellent way to do this for generic recurring timers or from within
504	libraries. Just remember to I<unref after start> and I<ref before stop>.	735	third-party libraries. Just remember to I<unref after start> and I<ref
		736	before stop> (but only if the watcher wasn't active before, or was active
		737	before, respectively. Note also that libev might stop watchers itself
		738	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		739	in the callback).
505		740
506	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	741	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
507	running when nothing else is active.	742	running when nothing else is active.
508		743
509	struct ev_signal exitsig;	744	ev_signal exitsig;
510	ev_signal_init (&exitsig, sig_cb, SIGINT);	745	ev_signal_init (&exitsig, sig_cb, SIGINT);
511	ev_signal_start (loop, &exitsig);	746	ev_signal_start (loop, &exitsig);
512	evf_unref (loop);	747	evf_unref (loop);
513		748
514	Example: For some weird reason, unregister the above signal handler again.	749	Example: For some weird reason, unregister the above signal handler again.
515		750
516	ev_ref (loop);	751	ev_ref (loop);
517	ev_signal_stop (loop, &exitsig);	752	ev_signal_stop (loop, &exitsig);
		753
		754	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		755
		756	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		757
		758	These advanced functions influence the time that libev will spend waiting
		759	for events. Both time intervals are by default C<0>, meaning that libev
		760	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		761	latency.
		762
		763	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		764	allows libev to delay invocation of I/O and timer/periodic callbacks
		765	to increase efficiency of loop iterations (or to increase power-saving
		766	opportunities).
		767
		768	The idea is that sometimes your program runs just fast enough to handle
		769	one (or very few) event(s) per loop iteration. While this makes the
		770	program responsive, it also wastes a lot of CPU time to poll for new
		771	events, especially with backends like C<select ()> which have a high
		772	overhead for the actual polling but can deliver many events at once.
		773
		774	By setting a higher I<io collect interval> you allow libev to spend more
		775	time collecting I/O events, so you can handle more events per iteration,
		776	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		777	C<ev_timer>) will be not affected. Setting this to a non-null value will
		778	introduce an additional C<ev_sleep ()> call into most loop iterations.
		779
		780	Likewise, by setting a higher I<timeout collect interval> you allow libev
		781	to spend more time collecting timeouts, at the expense of increased
		782	latency/jitter/inexactness (the watcher callback will be called
		783	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		784	value will not introduce any overhead in libev.
		785
		786	Many (busy) programs can usually benefit by setting the I/O collect
		787	interval to a value near C<0.1> or so, which is often enough for
		788	interactive servers (of course not for games), likewise for timeouts. It
		789	usually doesn't make much sense to set it to a lower value than C<0.01>,
		790	as this approaches the timing granularity of most systems.
		791
		792	Setting the I<timeout collect interval> can improve the opportunity for
		793	saving power, as the program will "bundle" timer callback invocations that
		794	are "near" in time together, by delaying some, thus reducing the number of
		795	times the process sleeps and wakes up again. Another useful technique to
		796	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		797	they fire on, say, one-second boundaries only.
		798
		799	=item ev_loop_verify (loop)
		800
		801	This function only does something when C<EV_VERIFY> support has been
		802	compiled in, which is the default for non-minimal builds. It tries to go
		803	through all internal structures and checks them for validity. If anything
		804	is found to be inconsistent, it will print an error message to standard
		805	error and call C<abort ()>.
		806
		807	This can be used to catch bugs inside libev itself: under normal
		808	circumstances, this function will never abort as of course libev keeps its
		809	data structures consistent.
518		810
519	=back	811	=back
520		812
521		813
522	=head1 ANATOMY OF A WATCHER	814	=head1 ANATOMY OF A WATCHER
		815
		816	In the following description, uppercase C<TYPE> in names stands for the
		817	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		818	watchers and C<ev_io_start> for I/O watchers.
523		819
524	A watcher is a structure that you create and register to record your	820	A watcher is a structure that you create and register to record your
525	interest in some event. For instance, if you want to wait for STDIN to	821	interest in some event. For instance, if you want to wait for STDIN to
526	become readable, you would create an C<ev_io> watcher for that:	822	become readable, you would create an C<ev_io> watcher for that:
527		823
528	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	824	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
529	{	825	{
530	ev_io_stop (w);	826	ev_io_stop (w);
531	ev_unloop (loop, EVUNLOOP_ALL);	827	ev_unloop (loop, EVUNLOOP_ALL);
532	}	828	}
533		829
534	struct ev_loop *loop = ev_default_loop (0);	830	struct ev_loop *loop = ev_default_loop (0);
		831
535	struct ev_io stdin_watcher;	832	ev_io stdin_watcher;
		833
536	ev_init (&stdin_watcher, my_cb);	834	ev_init (&stdin_watcher, my_cb);
537	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	835	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
538	ev_io_start (loop, &stdin_watcher);	836	ev_io_start (loop, &stdin_watcher);
		837
539	ev_loop (loop, 0);	838	ev_loop (loop, 0);
540		839
541	As you can see, you are responsible for allocating the memory for your	840	As you can see, you are responsible for allocating the memory for your
542	watcher structures (and it is usually a bad idea to do this on the stack,	841	watcher structures (and it is I<usually> a bad idea to do this on the
543	although this can sometimes be quite valid).	842	stack).
		843
		844	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		845	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
544		846
545	Each watcher structure must be initialised by a call to C<ev_init	847	Each watcher structure must be initialised by a call to C<ev_init
546	(watcher *, callback)>, which expects a callback to be provided. This	848	(watcher *, callback)>, which expects a callback to be provided. This
547	callback gets invoked each time the event occurs (or, in the case of io	849	callback gets invoked each time the event occurs (or, in the case of I/O
548	watchers, each time the event loop detects that the file descriptor given	850	watchers, each time the event loop detects that the file descriptor given
549	is readable and/or writable).	851	is readable and/or writable).
550		852
551	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	853	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
552	with arguments specific to this watcher type. There is also a macro	854	macro to configure it, with arguments specific to the watcher type. There
553	to combine initialisation and setting in one call: C<< ev_<type>_init	855	is also a macro to combine initialisation and setting in one call: C<<
554	(watcher *, callback, ...) >>.	856	ev_TYPE_init (watcher *, callback, ...) >>.
555		857
556	To make the watcher actually watch out for events, you have to start it	858	To make the watcher actually watch out for events, you have to start it
557	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	859	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
558	*) >>), and you can stop watching for events at any time by calling the	860	*) >>), and you can stop watching for events at any time by calling the
559	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	861	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
560		862
561	As long as your watcher is active (has been started but not stopped) you	863	As long as your watcher is active (has been started but not stopped) you
562	must not touch the values stored in it. Most specifically you must never	864	must not touch the values stored in it. Most specifically you must never
563	reinitialise it or call its C<set> macro.	865	reinitialise it or call its C<ev_TYPE_set> macro.
564		866
565	Each and every callback receives the event loop pointer as first, the	867	Each and every callback receives the event loop pointer as first, the
566	registered watcher structure as second, and a bitset of received events as	868	registered watcher structure as second, and a bitset of received events as
567	third argument.	869	third argument.
568		870
…		…
622	=item C<EV_FORK>	924	=item C<EV_FORK>
623		925
624	The event loop has been resumed in the child process after fork (see	926	The event loop has been resumed in the child process after fork (see
625	C<ev_fork>).	927	C<ev_fork>).
626		928
		929	=item C<EV_ASYNC>
		930
		931	The given async watcher has been asynchronously notified (see C<ev_async>).
		932
		933	=item C<EV_CUSTOM>
		934
		935	Not ever sent (or otherwise used) by libev itself, but can be freely used
		936	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		937
627	=item C<EV_ERROR>	938	=item C<EV_ERROR>
628		939
629	An unspecified error has occured, the watcher has been stopped. This might	940	An unspecified error has occurred, the watcher has been stopped. This might
630	happen because the watcher could not be properly started because libev	941	happen because the watcher could not be properly started because libev
631	ran out of memory, a file descriptor was found to be closed or any other	942	ran out of memory, a file descriptor was found to be closed or any other
		943	problem. Libev considers these application bugs.
		944
632	problem. You best act on it by reporting the problem and somehow coping	945	You best act on it by reporting the problem and somehow coping with the
633	with the watcher being stopped.	946	watcher being stopped. Note that well-written programs should not receive
		947	an error ever, so when your watcher receives it, this usually indicates a
		948	bug in your program.
634		949
635	Libev will usually signal a few "dummy" events together with an error,	950	Libev will usually signal a few "dummy" events together with an error, for
636	for example it might indicate that a fd is readable or writable, and if	951	example it might indicate that a fd is readable or writable, and if your
637	your callbacks is well-written it can just attempt the operation and cope	952	callbacks is well-written it can just attempt the operation and cope with
638	with the error from read() or write(). This will not work in multithreaded	953	the error from read() or write(). This will not work in multi-threaded
639	programs, though, so beware.	954	programs, though, as the fd could already be closed and reused for another
		955	thing, so beware.
640		956
641	=back	957	=back
642		958
643	=head2 GENERIC WATCHER FUNCTIONS	959	=head2 GENERIC WATCHER FUNCTIONS
644
645	In the following description, C<TYPE> stands for the watcher type,
646	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
647		960
648	=over 4	961	=over 4
649		962
650	=item C<ev_init> (ev_TYPE *watcher, callback)	963	=item C<ev_init> (ev_TYPE *watcher, callback)
651		964
…		…
657	which rolls both calls into one.	970	which rolls both calls into one.
658		971
659	You can reinitialise a watcher at any time as long as it has been stopped	972	You can reinitialise a watcher at any time as long as it has been stopped
660	(or never started) and there are no pending events outstanding.	973	(or never started) and there are no pending events outstanding.
661		974
662	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	975	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
663	int revents)>.	976	int revents)>.
		977
		978	Example: Initialise an C<ev_io> watcher in two steps.
		979
		980	ev_io w;
		981	ev_init (&w, my_cb);
		982	ev_io_set (&w, STDIN_FILENO, EV_READ);
664		983
665	=item C<ev_TYPE_set> (ev_TYPE *, [args])	984	=item C<ev_TYPE_set> (ev_TYPE *, [args])
666		985
667	This macro initialises the type-specific parts of a watcher. You need to	986	This macro initialises the type-specific parts of a watcher. You need to
668	call C<ev_init> at least once before you call this macro, but you can	987	call C<ev_init> at least once before you call this macro, but you can
…		…
671	difference to the C<ev_init> macro).	990	difference to the C<ev_init> macro).
672		991
673	Although some watcher types do not have type-specific arguments	992	Although some watcher types do not have type-specific arguments
674	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	993	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
675		994
		995	See C<ev_init>, above, for an example.
		996
676	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	997	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
677		998
678	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	999	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
679	calls into a single call. This is the most convinient method to initialise	1000	calls into a single call. This is the most convenient method to initialise
680	a watcher. The same limitations apply, of course.	1001	a watcher. The same limitations apply, of course.
		1002
		1003	Example: Initialise and set an C<ev_io> watcher in one step.
		1004
		1005	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
681		1006
682	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1007	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
683		1008
684	Starts (activates) the given watcher. Only active watchers will receive	1009	Starts (activates) the given watcher. Only active watchers will receive
685	events. If the watcher is already active nothing will happen.	1010	events. If the watcher is already active nothing will happen.
686		1011
		1012	Example: Start the C<ev_io> watcher that is being abused as example in this
		1013	whole section.
		1014
		1015	ev_io_start (EV_DEFAULT_UC, &w);
		1016
687	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1017	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
688		1018
689	Stops the given watcher again (if active) and clears the pending	1019	Stops the given watcher if active, and clears the pending status (whether
		1020	the watcher was active or not).
		1021
690	status. It is possible that stopped watchers are pending (for example,	1022	It is possible that stopped watchers are pending - for example,
691	non-repeating timers are being stopped when they become pending), but	1023	non-repeating timers are being stopped when they become pending - but
692	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1024	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
693	you want to free or reuse the memory used by the watcher it is therefore a	1025	pending. If you want to free or reuse the memory used by the watcher it is
694	good idea to always call its C<ev_TYPE_stop> function.	1026	therefore a good idea to always call its C<ev_TYPE_stop> function.
695		1027
696	=item bool ev_is_active (ev_TYPE *watcher)	1028	=item bool ev_is_active (ev_TYPE *watcher)
697		1029
698	Returns a true value iff the watcher is active (i.e. it has been started	1030	Returns a true value iff the watcher is active (i.e. it has been started
699	and not yet been stopped). As long as a watcher is active you must not modify	1031	and not yet been stopped). As long as a watcher is active you must not modify
…		…
702	=item bool ev_is_pending (ev_TYPE *watcher)	1034	=item bool ev_is_pending (ev_TYPE *watcher)
703		1035
704	Returns a true value iff the watcher is pending, (i.e. it has outstanding	1036	Returns a true value iff the watcher is pending, (i.e. it has outstanding
705	events but its callback has not yet been invoked). As long as a watcher	1037	events but its callback has not yet been invoked). As long as a watcher
706	is pending (but not active) you must not call an init function on it (but	1038	is pending (but not active) you must not call an init function on it (but
707	C<ev_TYPE_set> is safe) and you must make sure the watcher is available to	1039	C<ev_TYPE_set> is safe), you must not change its priority, and you must
708	libev (e.g. you cnanot C<free ()> it).	1040	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1041	it).
709		1042
710	=item callback ev_cb (ev_TYPE *watcher)	1043	=item callback ev_cb (ev_TYPE *watcher)
711		1044
712	Returns the callback currently set on the watcher.	1045	Returns the callback currently set on the watcher.
713		1046
714	=item ev_cb_set (ev_TYPE *watcher, callback)	1047	=item ev_cb_set (ev_TYPE *watcher, callback)
715		1048
716	Change the callback. You can change the callback at virtually any time	1049	Change the callback. You can change the callback at virtually any time
717	(modulo threads).	1050	(modulo threads).
718		1051
		1052	=item ev_set_priority (ev_TYPE *watcher, priority)
		1053
		1054	=item int ev_priority (ev_TYPE *watcher)
		1055
		1056	Set and query the priority of the watcher. The priority is a small
		1057	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1058	(default: C<-2>). Pending watchers with higher priority will be invoked
		1059	before watchers with lower priority, but priority will not keep watchers
		1060	from being executed (except for C<ev_idle> watchers).
		1061
		1062	This means that priorities are I<only> used for ordering callback
		1063	invocation after new events have been received. This is useful, for
		1064	example, to reduce latency after idling, or more often, to bind two
		1065	watchers on the same event and make sure one is called first.
		1066
		1067	If you need to suppress invocation when higher priority events are pending
		1068	you need to look at C<ev_idle> watchers, which provide this functionality.
		1069
		1070	You I<must not> change the priority of a watcher as long as it is active or
		1071	pending.
		1072
		1073	The default priority used by watchers when no priority has been set is
		1074	always C<0>, which is supposed to not be too high and not be too low :).
		1075
		1076	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1077	fine, as long as you do not mind that the priority value you query might
		1078	or might not have been clamped to the valid range.
		1079
		1080	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1081
		1082	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1083	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1084	can deal with that fact, as both are simply passed through to the
		1085	callback.
		1086
		1087	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1088
		1089	If the watcher is pending, this function clears its pending status and
		1090	returns its C<revents> bitset (as if its callback was invoked). If the
		1091	watcher isn't pending it does nothing and returns C<0>.
		1092
		1093	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1094	callback to be invoked, which can be accomplished with this function.
		1095
719	=back	1096	=back
720		1097
721		1098
722	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1099	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
723		1100
724	Each watcher has, by default, a member C<void *data> that you can change	1101	Each watcher has, by default, a member C<void *data> that you can change
725	and read at any time, libev will completely ignore it. This can be used	1102	and read at any time: libev will completely ignore it. This can be used
726	to associate arbitrary data with your watcher. If you need more data and	1103	to associate arbitrary data with your watcher. If you need more data and
727	don't want to allocate memory and store a pointer to it in that data	1104	don't want to allocate memory and store a pointer to it in that data
728	member, you can also "subclass" the watcher type and provide your own	1105	member, you can also "subclass" the watcher type and provide your own
729	data:	1106	data:
730		1107
731	struct my_io	1108	struct my_io
732	{	1109	{
733	struct ev_io io;	1110	ev_io io;
734	int otherfd;	1111	int otherfd;
735	void *somedata;	1112	void *somedata;
736	struct whatever *mostinteresting;	1113	struct whatever *mostinteresting;
737	}	1114	};
		1115
		1116	...
		1117	struct my_io w;
		1118	ev_io_init (&w.io, my_cb, fd, EV_READ);
738		1119
739	And since your callback will be called with a pointer to the watcher, you	1120	And since your callback will be called with a pointer to the watcher, you
740	can cast it back to your own type:	1121	can cast it back to your own type:
741		1122
742	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1123	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
743	{	1124	{
744	struct my_io *w = (struct my_io *)w_;	1125	struct my_io *w = (struct my_io *)w_;
745	...	1126	...
746	}	1127	}
747		1128
748	More interesting and less C-conformant ways of casting your callback type	1129	More interesting and less C-conformant ways of casting your callback type
749	instead have been omitted.	1130	instead have been omitted.
750		1131
751	Another common scenario is having some data structure with multiple	1132	Another common scenario is to use some data structure with multiple
752	watchers:	1133	embedded watchers:
753		1134
754	struct my_biggy	1135	struct my_biggy
755	{	1136	{
756	int some_data;	1137	int some_data;
757	ev_timer t1;	1138	ev_timer t1;
758	ev_timer t2;	1139	ev_timer t2;
759	}	1140	}
760		1141
761	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1142	In this case getting the pointer to C<my_biggy> is a bit more
762	you need to use C<offsetof>:	1143	complicated: Either you store the address of your C<my_biggy> struct
		1144	in the C<data> member of the watcher (for woozies), or you need to use
		1145	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1146	programmers):
763		1147
764	#include <stddef.h>	1148	#include <stddef.h>
765		1149
766	static void	1150	static void
767	t1_cb (EV_P_ struct ev_timer *w, int revents)	1151	t1_cb (EV_P_ ev_timer *w, int revents)
768	{	1152	{
769	struct my_biggy big = (struct my_biggy *	1153	struct my_biggy big = (struct my_biggy *
770	(((char *)w) - offsetof (struct my_biggy, t1));	1154	(((char *)w) - offsetof (struct my_biggy, t1));
771	}	1155	}
772		1156
773	static void	1157	static void
774	t2_cb (EV_P_ struct ev_timer *w, int revents)	1158	t2_cb (EV_P_ ev_timer *w, int revents)
775	{	1159	{
776	struct my_biggy big = (struct my_biggy *	1160	struct my_biggy big = (struct my_biggy *
777	(((char *)w) - offsetof (struct my_biggy, t2));	1161	(((char *)w) - offsetof (struct my_biggy, t2));
778	}	1162	}
779		1163
780		1164
781	=head1 WATCHER TYPES	1165	=head1 WATCHER TYPES
782		1166
783	This section describes each watcher in detail, but will not repeat	1167	This section describes each watcher in detail, but will not repeat
…		…
807	In general you can register as many read and/or write event watchers per	1191	In general you can register as many read and/or write event watchers per
808	fd as you want (as long as you don't confuse yourself). Setting all file	1192	fd as you want (as long as you don't confuse yourself). Setting all file
809	descriptors to non-blocking mode is also usually a good idea (but not	1193	descriptors to non-blocking mode is also usually a good idea (but not
810	required if you know what you are doing).	1194	required if you know what you are doing).
811		1195
812	You have to be careful with dup'ed file descriptors, though. Some backends	1196	If you cannot use non-blocking mode, then force the use of a
813	(the linux epoll backend is a notable example) cannot handle dup'ed file	1197	known-to-be-good backend (at the time of this writing, this includes only
814	descriptors correctly if you register interest in two or more fds pointing	1198	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>).
815	to the same underlying file/socket/etc. description (that is, they share
816	the same underlying "file open").
817
818	If you must do this, then force the use of a known-to-be-good backend
819	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
820	C<EVBACKEND_POLL>).
821		1199
822	Another thing you have to watch out for is that it is quite easy to	1200	Another thing you have to watch out for is that it is quite easy to
823	receive "spurious" readyness notifications, that is your callback might	1201	receive "spurious" readiness notifications, that is your callback might
824	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1202	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
825	because there is no data. Not only are some backends known to create a	1203	because there is no data. Not only are some backends known to create a
826	lot of those (for example solaris ports), it is very easy to get into	1204	lot of those (for example Solaris ports), it is very easy to get into
827	this situation even with a relatively standard program structure. Thus	1205	this situation even with a relatively standard program structure. Thus
828	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1206	it is best to always use non-blocking I/O: An extra C<read>(2) returning
829	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1207	C<EAGAIN> is far preferable to a program hanging until some data arrives.
830		1208
831	If you cannot run the fd in non-blocking mode (for example you should not	1209	If you cannot run the fd in non-blocking mode (for example you should
832	play around with an Xlib connection), then you have to seperately re-test	1210	not play around with an Xlib connection), then you have to separately
833	wether a file descriptor is really ready with a known-to-be good interface	1211	re-test whether a file descriptor is really ready with a known-to-be good
834	such as poll (fortunately in our Xlib example, Xlib already does this on	1212	interface such as poll (fortunately in our Xlib example, Xlib already
835	its own, so its quite safe to use).	1213	does this on its own, so its quite safe to use). Some people additionally
		1214	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1215	indefinitely.
		1216
		1217	But really, best use non-blocking mode.
		1218
		1219	=head3 The special problem of disappearing file descriptors
		1220
		1221	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1222	descriptor (either due to calling C<close> explicitly or any other means,
		1223	such as C<dup2>). The reason is that you register interest in some file
		1224	descriptor, but when it goes away, the operating system will silently drop
		1225	this interest. If another file descriptor with the same number then is
		1226	registered with libev, there is no efficient way to see that this is, in
		1227	fact, a different file descriptor.
		1228
		1229	To avoid having to explicitly tell libev about such cases, libev follows
		1230	the following policy: Each time C<ev_io_set> is being called, libev
		1231	will assume that this is potentially a new file descriptor, otherwise
		1232	it is assumed that the file descriptor stays the same. That means that
		1233	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1234	descriptor even if the file descriptor number itself did not change.
		1235
		1236	This is how one would do it normally anyway, the important point is that
		1237	the libev application should not optimise around libev but should leave
		1238	optimisations to libev.
		1239
		1240	=head3 The special problem of dup'ed file descriptors
		1241
		1242	Some backends (e.g. epoll), cannot register events for file descriptors,
		1243	but only events for the underlying file descriptions. That means when you
		1244	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1245	events for them, only one file descriptor might actually receive events.
		1246
		1247	There is no workaround possible except not registering events
		1248	for potentially C<dup ()>'ed file descriptors, or to resort to
		1249	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1250
		1251	=head3 The special problem of fork
		1252
		1253	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1254	useless behaviour. Libev fully supports fork, but needs to be told about
		1255	it in the child.
		1256
		1257	To support fork in your programs, you either have to call
		1258	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1259	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1260	C<EVBACKEND_POLL>.
		1261
		1262	=head3 The special problem of SIGPIPE
		1263
		1264	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1265	when writing to a pipe whose other end has been closed, your program gets
		1266	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1267	this is sensible behaviour, for daemons, this is usually undesirable.
		1268
		1269	So when you encounter spurious, unexplained daemon exits, make sure you
		1270	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1271	somewhere, as that would have given you a big clue).
		1272
		1273
		1274	=head3 Watcher-Specific Functions
836		1275
837	=over 4	1276	=over 4
838		1277
839	=item ev_io_init (ev_io *, callback, int fd, int events)	1278	=item ev_io_init (ev_io *, callback, int fd, int events)
840		1279
841	=item ev_io_set (ev_io *, int fd, int events)	1280	=item ev_io_set (ev_io *, int fd, int events)
842		1281
843	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1282	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
844	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1283	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
845	C<EV_READ | EV_WRITE> to receive the given events.	1284	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
846		1285
847	=item int fd [read-only]	1286	=item int fd [read-only]
848		1287
849	The file descriptor being watched.	1288	The file descriptor being watched.
850		1289
851	=item int events [read-only]	1290	=item int events [read-only]
852		1291
853	The events being watched.	1292	The events being watched.
854		1293
855	=back	1294	=back
		1295
		1296	=head3 Examples
856		1297
857	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1298	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
858	readable, but only once. Since it is likely line-buffered, you could	1299	readable, but only once. Since it is likely line-buffered, you could
859	attempt to read a whole line in the callback.	1300	attempt to read a whole line in the callback.
860		1301
861	static void	1302	static void
862	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1303	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
863	{	1304	{
864	ev_io_stop (loop, w);	1305	ev_io_stop (loop, w);
865	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1306	.. read from stdin here (or from w->fd) and handle any I/O errors
866	}	1307	}
867		1308
868	...	1309	...
869	struct ev_loop *loop = ev_default_init (0);	1310	struct ev_loop *loop = ev_default_init (0);
870	struct ev_io stdin_readable;	1311	ev_io stdin_readable;
871	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1312	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
872	ev_io_start (loop, &stdin_readable);	1313	ev_io_start (loop, &stdin_readable);
873	ev_loop (loop, 0);	1314	ev_loop (loop, 0);
874		1315
875		1316
876	=head2 C<ev_timer> - relative and optionally repeating timeouts	1317	=head2 C<ev_timer> - relative and optionally repeating timeouts
877		1318
878	Timer watchers are simple relative timers that generate an event after a	1319	Timer watchers are simple relative timers that generate an event after a
879	given time, and optionally repeating in regular intervals after that.	1320	given time, and optionally repeating in regular intervals after that.
880		1321
881	The timers are based on real time, that is, if you register an event that	1322	The timers are based on real time, that is, if you register an event that
882	times out after an hour and you reset your system clock to last years	1323	times out after an hour and you reset your system clock to January last
883	time, it will still time out after (roughly) and hour. "Roughly" because	1324	year, it will still time out after (roughly) one hour. "Roughly" because
884	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1325	detecting time jumps is hard, and some inaccuracies are unavoidable (the
885	monotonic clock option helps a lot here).	1326	monotonic clock option helps a lot here).
		1327
		1328	The callback is guaranteed to be invoked only I<after> its timeout has
		1329	passed. If multiple timers become ready during the same loop iteration
		1330	then the ones with earlier time-out values are invoked before ones with
		1331	later time-out values (but this is no longer true when a callback calls
		1332	C<ev_loop> recursively).
		1333
		1334	=head3 Be smart about timeouts
		1335
		1336	Many real-world problems involve some kind of timeout, usually for error
		1337	recovery. A typical example is an HTTP request - if the other side hangs,
		1338	you want to raise some error after a while.
		1339
		1340	What follows are some ways to handle this problem, from obvious and
		1341	inefficient to smart and efficient.
		1342
		1343	In the following, a 60 second activity timeout is assumed - a timeout that
		1344	gets reset to 60 seconds each time there is activity (e.g. each time some
		1345	data or other life sign was received).
		1346
		1347	=over 4
		1348
		1349	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1350
		1351	This is the most obvious, but not the most simple way: In the beginning,
		1352	start the watcher:
		1353
		1354	ev_timer_init (timer, callback, 60., 0.);
		1355	ev_timer_start (loop, timer);
		1356
		1357	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1358	and start it again:
		1359
		1360	ev_timer_stop (loop, timer);
		1361	ev_timer_set (timer, 60., 0.);
		1362	ev_timer_start (loop, timer);
		1363
		1364	This is relatively simple to implement, but means that each time there is
		1365	some activity, libev will first have to remove the timer from its internal
		1366	data structure and then add it again. Libev tries to be fast, but it's
		1367	still not a constant-time operation.
		1368
		1369	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1370
		1371	This is the easiest way, and involves using C<ev_timer_again> instead of
		1372	C<ev_timer_start>.
		1373
		1374	To implement this, configure an C<ev_timer> with a C<repeat> value
		1375	of C<60> and then call C<ev_timer_again> at start and each time you
		1376	successfully read or write some data. If you go into an idle state where
		1377	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1378	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1379
		1380	That means you can ignore both the C<ev_timer_start> function and the
		1381	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1382	member and C<ev_timer_again>.
		1383
		1384	At start:
		1385
		1386	ev_timer_init (timer, callback);
		1387	timer->repeat = 60.;
		1388	ev_timer_again (loop, timer);
		1389
		1390	Each time there is some activity:
		1391
		1392	ev_timer_again (loop, timer);
		1393
		1394	It is even possible to change the time-out on the fly, regardless of
		1395	whether the watcher is active or not:
		1396
		1397	timer->repeat = 30.;
		1398	ev_timer_again (loop, timer);
		1399
		1400	This is slightly more efficient then stopping/starting the timer each time
		1401	you want to modify its timeout value, as libev does not have to completely
		1402	remove and re-insert the timer from/into its internal data structure.
		1403
		1404	It is, however, even simpler than the "obvious" way to do it.
		1405
		1406	=item 3. Let the timer time out, but then re-arm it as required.
		1407
		1408	This method is more tricky, but usually most efficient: Most timeouts are
		1409	relatively long compared to the intervals between other activity - in
		1410	our example, within 60 seconds, there are usually many I/O events with
		1411	associated activity resets.
		1412
		1413	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1414	but remember the time of last activity, and check for a real timeout only
		1415	within the callback:
		1416
		1417	ev_tstamp last_activity; // time of last activity
		1418
		1419	static void
		1420	callback (EV_P_ ev_timer *w, int revents)
		1421	{
		1422	ev_tstamp now = ev_now (EV_A);
		1423	ev_tstamp timeout = last_activity + 60.;
		1424
		1425	// if last_activity + 60. is older than now, we did time out
		1426	if (timeout < now)
		1427	{
		1428	// timeout occured, take action
		1429	}
		1430	else
		1431	{
		1432	// callback was invoked, but there was some activity, re-arm
		1433	// the watcher to fire in last_activity + 60, which is
		1434	// guaranteed to be in the future, so "again" is positive:
		1435	w->repeat = timeout - now;
		1436	ev_timer_again (EV_A_ w);
		1437	}
		1438	}
		1439
		1440	To summarise the callback: first calculate the real timeout (defined
		1441	as "60 seconds after the last activity"), then check if that time has
		1442	been reached, which means something I<did>, in fact, time out. Otherwise
		1443	the callback was invoked too early (C<timeout> is in the future), so
		1444	re-schedule the timer to fire at that future time, to see if maybe we have
		1445	a timeout then.
		1446
		1447	Note how C<ev_timer_again> is used, taking advantage of the
		1448	C<ev_timer_again> optimisation when the timer is already running.
		1449
		1450	This scheme causes more callback invocations (about one every 60 seconds
		1451	minus half the average time between activity), but virtually no calls to
		1452	libev to change the timeout.
		1453
		1454	To start the timer, simply initialise the watcher and set C<last_activity>
		1455	to the current time (meaning we just have some activity :), then call the
		1456	callback, which will "do the right thing" and start the timer:
		1457
		1458	ev_timer_init (timer, callback);
		1459	last_activity = ev_now (loop);
		1460	callback (loop, timer, EV_TIMEOUT);
		1461
		1462	And when there is some activity, simply store the current time in
		1463	C<last_activity>, no libev calls at all:
		1464
		1465	last_actiivty = ev_now (loop);
		1466
		1467	This technique is slightly more complex, but in most cases where the
		1468	time-out is unlikely to be triggered, much more efficient.
		1469
		1470	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1471	callback :) - just change the timeout and invoke the callback, which will
		1472	fix things for you.
		1473
		1474	=item 4. Wee, just use a double-linked list for your timeouts.
		1475
		1476	If there is not one request, but many thousands (millions...), all
		1477	employing some kind of timeout with the same timeout value, then one can
		1478	do even better:
		1479
		1480	When starting the timeout, calculate the timeout value and put the timeout
		1481	at the I<end> of the list.
		1482
		1483	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1484	the list is expected to fire (for example, using the technique #3).
		1485
		1486	When there is some activity, remove the timer from the list, recalculate
		1487	the timeout, append it to the end of the list again, and make sure to
		1488	update the C<ev_timer> if it was taken from the beginning of the list.
		1489
		1490	This way, one can manage an unlimited number of timeouts in O(1) time for
		1491	starting, stopping and updating the timers, at the expense of a major
		1492	complication, and having to use a constant timeout. The constant timeout
		1493	ensures that the list stays sorted.
		1494
		1495	=back
		1496
		1497	So which method the best?
		1498
		1499	Method #2 is a simple no-brain-required solution that is adequate in most
		1500	situations. Method #3 requires a bit more thinking, but handles many cases
		1501	better, and isn't very complicated either. In most case, choosing either
		1502	one is fine, with #3 being better in typical situations.
		1503
		1504	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1505	rather complicated, but extremely efficient, something that really pays
		1506	off after the first million or so of active timers, i.e. it's usually
		1507	overkill :)
		1508
		1509	=head3 The special problem of time updates
		1510
		1511	Establishing the current time is a costly operation (it usually takes at
		1512	least two system calls): EV therefore updates its idea of the current
		1513	time only before and after C<ev_loop> collects new events, which causes a
		1514	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1515	lots of events in one iteration.
886		1516
887	The relative timeouts are calculated relative to the C<ev_now ()>	1517	The relative timeouts are calculated relative to the C<ev_now ()>
888	time. This is usually the right thing as this timestamp refers to the time	1518	time. This is usually the right thing as this timestamp refers to the time
889	of the event triggering whatever timeout you are modifying/starting. If	1519	of the event triggering whatever timeout you are modifying/starting. If
890	you suspect event processing to be delayed and you I<need> to base the timeout	1520	you suspect event processing to be delayed and you I<need> to base the
891	on the current time, use something like this to adjust for this:	1521	timeout on the current time, use something like this to adjust for this:
892		1522
893	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1523	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
894		1524
895	The callback is guarenteed to be invoked only when its timeout has passed,	1525	If the event loop is suspended for a long time, you can also force an
896	but if multiple timers become ready during the same loop iteration then	1526	update of the time returned by C<ev_now ()> by calling C<ev_now_update
897	order of execution is undefined.	1527	()>.
		1528
		1529	=head3 Watcher-Specific Functions and Data Members
898		1530
899	=over 4	1531	=over 4
900		1532
901	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1533	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
902		1534
903	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1535	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
904		1536
905	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1537	Configure the timer to trigger after C<after> seconds. If C<repeat>
906	C<0.>, then it will automatically be stopped. If it is positive, then the	1538	is C<0.>, then it will automatically be stopped once the timeout is
907	timer will automatically be configured to trigger again C<repeat> seconds	1539	reached. If it is positive, then the timer will automatically be
908	later, again, and again, until stopped manually.	1540	configured to trigger again C<repeat> seconds later, again, and again,
		1541	until stopped manually.
909		1542
910	The timer itself will do a best-effort at avoiding drift, that is, if you	1543	The timer itself will do a best-effort at avoiding drift, that is, if
911	configure a timer to trigger every 10 seconds, then it will trigger at	1544	you configure a timer to trigger every 10 seconds, then it will normally
912	exactly 10 second intervals. If, however, your program cannot keep up with	1545	trigger at exactly 10 second intervals. If, however, your program cannot
913	the timer (because it takes longer than those 10 seconds to do stuff) the	1546	keep up with the timer (because it takes longer than those 10 seconds to
914	timer will not fire more than once per event loop iteration.	1547	do stuff) the timer will not fire more than once per event loop iteration.
915		1548
916	=item ev_timer_again (loop)	1549	=item ev_timer_again (loop, ev_timer *)
917		1550
918	This will act as if the timer timed out and restart it again if it is	1551	This will act as if the timer timed out and restart it again if it is
919	repeating. The exact semantics are:	1552	repeating. The exact semantics are:
920		1553
		1554	If the timer is pending, its pending status is cleared.
		1555
921	If the timer is started but nonrepeating, stop it.	1556	If the timer is started but non-repeating, stop it (as if it timed out).
922		1557
923	If the timer is repeating, either start it if necessary (with the repeat	1558	If the timer is repeating, either start it if necessary (with the
924	value), or reset the running timer to the repeat value.	1559	C<repeat> value), or reset the running timer to the C<repeat> value.
925		1560
926	This sounds a bit complicated, but here is a useful and typical	1561	This sounds a bit complicated, see "Be smart about timeouts", above, for a
927	example: Imagine you have a tcp connection and you want a so-called	1562	usage example.
928	idle timeout, that is, you want to be called when there have been,
929	say, 60 seconds of inactivity on the socket. The easiest way to do
930	this is to configure an C<ev_timer> with C<after>=C<repeat>=C<60> and calling
931	C<ev_timer_again> each time you successfully read or write some data. If
932	you go into an idle state where you do not expect data to travel on the
933	socket, you can stop the timer, and again will automatically restart it if
934	need be.
935
936	You can also ignore the C<after> value and C<ev_timer_start> altogether
937	and only ever use the C<repeat> value:
938
939	ev_timer_init (timer, callback, 0., 5.);
940	ev_timer_again (loop, timer);
941	...
942	timer->again = 17.;
943	ev_timer_again (loop, timer);
944	...
945	timer->again = 10.;
946	ev_timer_again (loop, timer);
947
948	This is more efficient then stopping/starting the timer eahc time you want
949	to modify its timeout value.
950		1563
951	=item ev_tstamp repeat [read-write]	1564	=item ev_tstamp repeat [read-write]
952		1565
953	The current C<repeat> value. Will be used each time the watcher times out	1566	The current C<repeat> value. Will be used each time the watcher times out
954	or C<ev_timer_again> is called and determines the next timeout (if any),	1567	or C<ev_timer_again> is called, and determines the next timeout (if any),
955	which is also when any modifications are taken into account.	1568	which is also when any modifications are taken into account.
956		1569
957	=back	1570	=back
958		1571
		1572	=head3 Examples
		1573
959	Example: Create a timer that fires after 60 seconds.	1574	Example: Create a timer that fires after 60 seconds.
960		1575
961	static void	1576	static void
962	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1577	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
963	{	1578	{
964	.. one minute over, w is actually stopped right here	1579	.. one minute over, w is actually stopped right here
965	}	1580	}
966		1581
967	struct ev_timer mytimer;	1582	ev_timer mytimer;
968	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1583	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
969	ev_timer_start (loop, &mytimer);	1584	ev_timer_start (loop, &mytimer);
970		1585
971	Example: Create a timeout timer that times out after 10 seconds of	1586	Example: Create a timeout timer that times out after 10 seconds of
972	inactivity.	1587	inactivity.
973		1588
974	static void	1589	static void
975	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1590	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
976	{	1591	{
977	.. ten seconds without any activity	1592	.. ten seconds without any activity
978	}	1593	}
979		1594
980	struct ev_timer mytimer;	1595	ev_timer mytimer;
981	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1596	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
982	ev_timer_again (&mytimer); /* start timer */	1597	ev_timer_again (&mytimer); /* start timer */
983	ev_loop (loop, 0);	1598	ev_loop (loop, 0);
984		1599
985	// and in some piece of code that gets executed on any "activity":	1600	// and in some piece of code that gets executed on any "activity":
986	// reset the timeout to start ticking again at 10 seconds	1601	// reset the timeout to start ticking again at 10 seconds
987	ev_timer_again (&mytimer);	1602	ev_timer_again (&mytimer);
988		1603
989		1604
990	=head2 C<ev_periodic> - to cron or not to cron?	1605	=head2 C<ev_periodic> - to cron or not to cron?
991		1606
992	Periodic watchers are also timers of a kind, but they are very versatile	1607	Periodic watchers are also timers of a kind, but they are very versatile
993	(and unfortunately a bit complex).	1608	(and unfortunately a bit complex).
994		1609
995	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1610	Unlike C<ev_timer>, periodic watchers are not based on real time (or
996	but on wallclock time (absolute time). You can tell a periodic watcher	1611	relative time, the physical time that passes) but on wall clock time
997	to trigger "at" some specific point in time. For example, if you tell a	1612	(absolute time, the thing you can read on your calender or clock). The
998	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	1613	difference is that wall clock time can run faster or slower than real
999	+ 10.>) and then reset your system clock to the last year, then it will	1614	time, and time jumps are not uncommon (e.g. when you adjust your
1000	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1615	wrist-watch).
1001	roughly 10 seconds later and of course not if you reset your system time
1002	again).
1003		1616
1004	They can also be used to implement vastly more complex timers, such as	1617	You can tell a periodic watcher to trigger after some specific point
		1618	in time: for example, if you tell a periodic watcher to trigger "in 10
		1619	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1620	not a delay) and then reset your system clock to January of the previous
		1621	year, then it will take a year or more to trigger the event (unlike an
		1622	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1623	it, as it uses a relative timeout).
		1624
		1625	C<ev_periodic> watchers can also be used to implement vastly more complex
1005	triggering an event on eahc midnight, local time.	1626	timers, such as triggering an event on each "midnight, local time", or
		1627	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1628	those cannot react to time jumps.
1006		1629
1007	As with timers, the callback is guarenteed to be invoked only when the	1630	As with timers, the callback is guaranteed to be invoked only when the
1008	time (C<at>) has been passed, but if multiple periodic timers become ready	1631	point in time where it is supposed to trigger has passed. If multiple
1009	during the same loop iteration then order of execution is undefined.	1632	timers become ready during the same loop iteration then the ones with
		1633	earlier time-out values are invoked before ones with later time-out values
		1634	(but this is no longer true when a callback calls C<ev_loop> recursively).
		1635
		1636	=head3 Watcher-Specific Functions and Data Members
1010		1637
1011	=over 4	1638	=over 4
1012		1639
1013	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1640	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1014		1641
1015	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1642	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1016		1643
1017	Lots of arguments, lets sort it out... There are basically three modes of	1644	Lots of arguments, let's sort it out... There are basically three modes of
1018	operation, and we will explain them from simplest to complex:	1645	operation, and we will explain them from simplest to most complex:
1019		1646
1020	=over 4	1647	=over 4
1021		1648
1022	=item * absolute timer (interval = reschedule_cb = 0)	1649	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1023		1650
1024	In this configuration the watcher triggers an event at the wallclock time	1651	In this configuration the watcher triggers an event after the wall clock
1025	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1652	time C<offset> has passed. It will not repeat and will not adjust when a
1026	that is, if it is to be run at January 1st 2011 then it will run when the	1653	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1027	system time reaches or surpasses this time.	1654	will be stopped and invoked when the system clock reaches or surpasses
		1655	this point in time.
1028		1656
1029	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1657	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1030		1658
1031	In this mode the watcher will always be scheduled to time out at the next	1659	In this mode the watcher will always be scheduled to time out at the next
1032	C<at + N * interval> time (for some integer N) and then repeat, regardless	1660	C<offset + N * interval> time (for some integer N, which can also be
1033	of any time jumps.	1661	negative) and then repeat, regardless of any time jumps. The C<offset>
		1662	argument is merely an offset into the C<interval> periods.
1034		1663
1035	This can be used to create timers that do not drift with respect to system	1664	This can be used to create timers that do not drift with respect to the
1036	time:	1665	system clock, for example, here is an C<ev_periodic> that triggers each
		1666	hour, on the hour (with respect to UTC):
1037		1667
1038	ev_periodic_set (&periodic, 0., 3600., 0);	1668	ev_periodic_set (&periodic, 0., 3600., 0);
1039		1669
1040	This doesn't mean there will always be 3600 seconds in between triggers,	1670	This doesn't mean there will always be 3600 seconds in between triggers,
1041	but only that the the callback will be called when the system time shows a	1671	but only that the callback will be called when the system time shows a
1042	full hour (UTC), or more correctly, when the system time is evenly divisible	1672	full hour (UTC), or more correctly, when the system time is evenly divisible
1043	by 3600.	1673	by 3600.
1044		1674
1045	Another way to think about it (for the mathematically inclined) is that	1675	Another way to think about it (for the mathematically inclined) is that
1046	C<ev_periodic> will try to run the callback in this mode at the next possible	1676	C<ev_periodic> will try to run the callback in this mode at the next possible
1047	time where C<time = at (mod interval)>, regardless of any time jumps.	1677	time where C<time = offset (mod interval)>, regardless of any time jumps.
1048		1678
		1679	For numerical stability it is preferable that the C<offset> value is near
		1680	C<ev_now ()> (the current time), but there is no range requirement for
		1681	this value, and in fact is often specified as zero.
		1682
		1683	Note also that there is an upper limit to how often a timer can fire (CPU
		1684	speed for example), so if C<interval> is very small then timing stability
		1685	will of course deteriorate. Libev itself tries to be exact to be about one
		1686	millisecond (if the OS supports it and the machine is fast enough).
		1687
1049	=item * manual reschedule mode (reschedule_cb = callback)	1688	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1050		1689
1051	In this mode the values for C<interval> and C<at> are both being	1690	In this mode the values for C<interval> and C<offset> are both being
1052	ignored. Instead, each time the periodic watcher gets scheduled, the	1691	ignored. Instead, each time the periodic watcher gets scheduled, the
1053	reschedule callback will be called with the watcher as first, and the	1692	reschedule callback will be called with the watcher as first, and the
1054	current time as second argument.	1693	current time as second argument.
1055		1694
1056	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1695	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1057	ever, or make any event loop modifications>. If you need to stop it,	1696	or make ANY other event loop modifications whatsoever, unless explicitly
1058	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	1697	allowed by documentation here>.
1059	starting a prepare watcher).
1060		1698
		1699	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1700	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1701	only event loop modification you are allowed to do).
		1702
1061	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1703	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1062	ev_tstamp now)>, e.g.:	1704	*w, ev_tstamp now)>, e.g.:
1063		1705
		1706	static ev_tstamp
1064	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1707	my_rescheduler (ev_periodic *w, ev_tstamp now)
1065	{	1708	{
1066	return now + 60.;	1709	return now + 60.;
1067	}	1710	}
1068		1711
1069	It must return the next time to trigger, based on the passed time value	1712	It must return the next time to trigger, based on the passed time value
1070	(that is, the lowest time value larger than to the second argument). It	1713	(that is, the lowest time value larger than to the second argument). It
1071	will usually be called just before the callback will be triggered, but	1714	will usually be called just before the callback will be triggered, but
1072	might be called at other times, too.	1715	might be called at other times, too.
1073		1716
1074	NOTE: I<< This callback must always return a time that is later than the	1717	NOTE: I<< This callback must always return a time that is higher than or
1075	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	1718	equal to the passed C<now> value >>.
1076		1719
1077	This can be used to create very complex timers, such as a timer that	1720	This can be used to create very complex timers, such as a timer that
1078	triggers on each midnight, local time. To do this, you would calculate the	1721	triggers on "next midnight, local time". To do this, you would calculate the
1079	next midnight after C<now> and return the timestamp value for this. How	1722	next midnight after C<now> and return the timestamp value for this. How
1080	you do this is, again, up to you (but it is not trivial, which is the main	1723	you do this is, again, up to you (but it is not trivial, which is the main
1081	reason I omitted it as an example).	1724	reason I omitted it as an example).
1082		1725
1083	=back	1726	=back
…		…
1087	Simply stops and restarts the periodic watcher again. This is only useful	1730	Simply stops and restarts the periodic watcher again. This is only useful
1088	when you changed some parameters or the reschedule callback would return	1731	when you changed some parameters or the reschedule callback would return
1089	a different time than the last time it was called (e.g. in a crond like	1732	a different time than the last time it was called (e.g. in a crond like
1090	program when the crontabs have changed).	1733	program when the crontabs have changed).
1091		1734
		1735	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1736
		1737	When active, returns the absolute time that the watcher is supposed
		1738	to trigger next. This is not the same as the C<offset> argument to
		1739	C<ev_periodic_set>, but indeed works even in interval and manual
		1740	rescheduling modes.
		1741
		1742	=item ev_tstamp offset [read-write]
		1743
		1744	When repeating, this contains the offset value, otherwise this is the
		1745	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		1746	although libev might modify this value for better numerical stability).
		1747
		1748	Can be modified any time, but changes only take effect when the periodic
		1749	timer fires or C<ev_periodic_again> is being called.
		1750
1092	=item ev_tstamp interval [read-write]	1751	=item ev_tstamp interval [read-write]
1093		1752
1094	The current interval value. Can be modified any time, but changes only	1753	The current interval value. Can be modified any time, but changes only
1095	take effect when the periodic timer fires or C<ev_periodic_again> is being	1754	take effect when the periodic timer fires or C<ev_periodic_again> is being
1096	called.	1755	called.
1097		1756
1098	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	1757	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1099		1758
1100	The current reschedule callback, or C<0>, if this functionality is	1759	The current reschedule callback, or C<0>, if this functionality is
1101	switched off. Can be changed any time, but changes only take effect when	1760	switched off. Can be changed any time, but changes only take effect when
1102	the periodic timer fires or C<ev_periodic_again> is being called.	1761	the periodic timer fires or C<ev_periodic_again> is being called.
1103		1762
1104	=back	1763	=back
1105		1764
		1765	=head3 Examples
		1766
1106	Example: Call a callback every hour, or, more precisely, whenever the	1767	Example: Call a callback every hour, or, more precisely, whenever the
1107	system clock is divisible by 3600. The callback invocation times have	1768	system time is divisible by 3600. The callback invocation times have
1108	potentially a lot of jittering, but good long-term stability.	1769	potentially a lot of jitter, but good long-term stability.
1109		1770
1110	static void	1771	static void
1111	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1772	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1112	{	1773	{
1113	... its now a full hour (UTC, or TAI or whatever your clock follows)	1774	... its now a full hour (UTC, or TAI or whatever your clock follows)
1114	}	1775	}
1115		1776
1116	struct ev_periodic hourly_tick;	1777	ev_periodic hourly_tick;
1117	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	1778	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1118	ev_periodic_start (loop, &hourly_tick);	1779	ev_periodic_start (loop, &hourly_tick);
1119		1780
1120	Example: The same as above, but use a reschedule callback to do it:	1781	Example: The same as above, but use a reschedule callback to do it:
1121		1782
1122	#include <math.h>	1783	#include <math.h>
1123		1784
1124	static ev_tstamp	1785	static ev_tstamp
1125	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	1786	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1126	{	1787	{
1127	return fmod (now, 3600.) + 3600.;	1788	return now + (3600. - fmod (now, 3600.));
1128	}	1789	}
1129		1790
1130	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	1791	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1131		1792
1132	Example: Call a callback every hour, starting now:	1793	Example: Call a callback every hour, starting now:
1133		1794
1134	struct ev_periodic hourly_tick;	1795	ev_periodic hourly_tick;
1135	ev_periodic_init (&hourly_tick, clock_cb,	1796	ev_periodic_init (&hourly_tick, clock_cb,
1136	fmod (ev_now (loop), 3600.), 3600., 0);	1797	fmod (ev_now (loop), 3600.), 3600., 0);
1137	ev_periodic_start (loop, &hourly_tick);	1798	ev_periodic_start (loop, &hourly_tick);
1138		1799
1139		1800
1140	=head2 C<ev_signal> - signal me when a signal gets signalled!	1801	=head2 C<ev_signal> - signal me when a signal gets signalled!
1141		1802
1142	Signal watchers will trigger an event when the process receives a specific	1803	Signal watchers will trigger an event when the process receives a specific
1143	signal one or more times. Even though signals are very asynchronous, libev	1804	signal one or more times. Even though signals are very asynchronous, libev
1144	will try it's best to deliver signals synchronously, i.e. as part of the	1805	will try it's best to deliver signals synchronously, i.e. as part of the
1145	normal event processing, like any other event.	1806	normal event processing, like any other event.
1146		1807
		1808	If you want signals asynchronously, just use C<sigaction> as you would
		1809	do without libev and forget about sharing the signal. You can even use
		1810	C<ev_async> from a signal handler to synchronously wake up an event loop.
		1811
1147	You can configure as many watchers as you like per signal. Only when the	1812	You can configure as many watchers as you like per signal. Only when the
1148	first watcher gets started will libev actually register a signal watcher	1813	first watcher gets started will libev actually register a signal handler
1149	with the kernel (thus it coexists with your own signal handlers as long	1814	with the kernel (thus it coexists with your own signal handlers as long as
1150	as you don't register any with libev). Similarly, when the last signal	1815	you don't register any with libev for the same signal). Similarly, when
1151	watcher for a signal is stopped libev will reset the signal handler to	1816	the last signal watcher for a signal is stopped, libev will reset the
1152	SIG_DFL (regardless of what it was set to before).	1817	signal handler to SIG_DFL (regardless of what it was set to before).
		1818
		1819	If possible and supported, libev will install its handlers with
		1820	C<SA_RESTART> behaviour enabled, so system calls should not be unduly
		1821	interrupted. If you have a problem with system calls getting interrupted by
		1822	signals you can block all signals in an C<ev_check> watcher and unblock
		1823	them in an C<ev_prepare> watcher.
		1824
		1825	=head3 Watcher-Specific Functions and Data Members
1153		1826
1154	=over 4	1827	=over 4
1155		1828
1156	=item ev_signal_init (ev_signal *, callback, int signum)	1829	=item ev_signal_init (ev_signal *, callback, int signum)
1157		1830
…		…
1164		1837
1165	The signal the watcher watches out for.	1838	The signal the watcher watches out for.
1166		1839
1167	=back	1840	=back
1168		1841
		1842	=head3 Examples
		1843
		1844	Example: Try to exit cleanly on SIGINT.
		1845
		1846	static void
		1847	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		1848	{
		1849	ev_unloop (loop, EVUNLOOP_ALL);
		1850	}
		1851
		1852	ev_signal signal_watcher;
		1853	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1854	ev_signal_start (loop, &signal_watcher);
		1855
1169		1856
1170	=head2 C<ev_child> - watch out for process status changes	1857	=head2 C<ev_child> - watch out for process status changes
1171		1858
1172	Child watchers trigger when your process receives a SIGCHLD in response to	1859	Child watchers trigger when your process receives a SIGCHLD in response to
1173	some child status changes (most typically when a child of yours dies).	1860	some child status changes (most typically when a child of yours dies or
		1861	exits). It is permissible to install a child watcher I<after> the child
		1862	has been forked (which implies it might have already exited), as long
		1863	as the event loop isn't entered (or is continued from a watcher), i.e.,
		1864	forking and then immediately registering a watcher for the child is fine,
		1865	but forking and registering a watcher a few event loop iterations later is
		1866	not.
		1867
		1868	Only the default event loop is capable of handling signals, and therefore
		1869	you can only register child watchers in the default event loop.
		1870
		1871	=head3 Process Interaction
		1872
		1873	Libev grabs C<SIGCHLD> as soon as the default event loop is
		1874	initialised. This is necessary to guarantee proper behaviour even if
		1875	the first child watcher is started after the child exits. The occurrence
		1876	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		1877	synchronously as part of the event loop processing. Libev always reaps all
		1878	children, even ones not watched.
		1879
		1880	=head3 Overriding the Built-In Processing
		1881
		1882	Libev offers no special support for overriding the built-in child
		1883	processing, but if your application collides with libev's default child
		1884	handler, you can override it easily by installing your own handler for
		1885	C<SIGCHLD> after initialising the default loop, and making sure the
		1886	default loop never gets destroyed. You are encouraged, however, to use an
		1887	event-based approach to child reaping and thus use libev's support for
		1888	that, so other libev users can use C<ev_child> watchers freely.
		1889
		1890	=head3 Stopping the Child Watcher
		1891
		1892	Currently, the child watcher never gets stopped, even when the
		1893	child terminates, so normally one needs to stop the watcher in the
		1894	callback. Future versions of libev might stop the watcher automatically
		1895	when a child exit is detected.
		1896
		1897	=head3 Watcher-Specific Functions and Data Members
1174		1898
1175	=over 4	1899	=over 4
1176		1900
1177	=item ev_child_init (ev_child *, callback, int pid)	1901	=item ev_child_init (ev_child *, callback, int pid, int trace)
1178		1902
1179	=item ev_child_set (ev_child *, int pid)	1903	=item ev_child_set (ev_child *, int pid, int trace)
1180		1904
1181	Configures the watcher to wait for status changes of process C<pid> (or	1905	Configures the watcher to wait for status changes of process C<pid> (or
1182	I<any> process if C<pid> is specified as C<0>). The callback can look	1906	I<any> process if C<pid> is specified as C<0>). The callback can look
1183	at the C<rstatus> member of the C<ev_child> watcher structure to see	1907	at the C<rstatus> member of the C<ev_child> watcher structure to see
1184	the status word (use the macros from C<sys/wait.h> and see your systems	1908	the status word (use the macros from C<sys/wait.h> and see your systems
1185	C<waitpid> documentation). The C<rpid> member contains the pid of the	1909	C<waitpid> documentation). The C<rpid> member contains the pid of the
1186	process causing the status change.	1910	process causing the status change. C<trace> must be either C<0> (only
		1911	activate the watcher when the process terminates) or C<1> (additionally
		1912	activate the watcher when the process is stopped or continued).
1187		1913
1188	=item int pid [read-only]	1914	=item int pid [read-only]
1189		1915
1190	The process id this watcher watches out for, or C<0>, meaning any process id.	1916	The process id this watcher watches out for, or C<0>, meaning any process id.
1191		1917
…		…
1198	The process exit/trace status caused by C<rpid> (see your systems	1924	The process exit/trace status caused by C<rpid> (see your systems
1199	C<waitpid> and C<sys/wait.h> documentation for details).	1925	C<waitpid> and C<sys/wait.h> documentation for details).
1200		1926
1201	=back	1927	=back
1202		1928
1203	Example: Try to exit cleanly on SIGINT and SIGTERM.	1929	=head3 Examples
1204		1930
		1931	Example: C<fork()> a new process and install a child handler to wait for
		1932	its completion.
		1933
		1934	ev_child cw;
		1935
1205	static void	1936	static void
1206	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	1937	child_cb (EV_P_ ev_child *w, int revents)
1207	{	1938	{
1208	ev_unloop (loop, EVUNLOOP_ALL);	1939	ev_child_stop (EV_A_ w);
		1940	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1209	}	1941	}
1210		1942
1211	struct ev_signal signal_watcher;	1943	pid_t pid = fork ();
1212	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	1944
1213	ev_signal_start (loop, &sigint_cb);	1945	if (pid < 0)
		1946	// error
		1947	else if (pid == 0)
		1948	{
		1949	// the forked child executes here
		1950	exit (1);
		1951	}
		1952	else
		1953	{
		1954	ev_child_init (&cw, child_cb, pid, 0);
		1955	ev_child_start (EV_DEFAULT_ &cw);
		1956	}
1214		1957
1215		1958
1216	=head2 C<ev_stat> - did the file attributes just change?	1959	=head2 C<ev_stat> - did the file attributes just change?
1217		1960
1218	This watches a filesystem path for attribute changes. That is, it calls	1961	This watches a file system path for attribute changes. That is, it calls
1219	C<stat> regularly (or when the OS says it changed) and sees if it changed	1962	C<stat> on that path in regular intervals (or when the OS says it changed)
1220	compared to the last time, invoking the callback if it did.	1963	and sees if it changed compared to the last time, invoking the callback if
		1964	it did.
1221		1965
1222	The path does not need to exist: changing from "path exists" to "path does	1966	The path does not need to exist: changing from "path exists" to "path does
1223	not exist" is a status change like any other. The condition "path does	1967	not exist" is a status change like any other. The condition "path does not
1224	not exist" is signified by the C<st_nlink> field being zero (which is	1968	exist" (or more correctly "path cannot be stat'ed") is signified by the
1225	otherwise always forced to be at least one) and all the other fields of	1969	C<st_nlink> field being zero (which is otherwise always forced to be at
1226	the stat buffer having unspecified contents.	1970	least one) and all the other fields of the stat buffer having unspecified
		1971	contents.
1227		1972
1228	The path I<should> be absolute and I<must not> end in a slash. If it is	1973	The path I<must not> end in a slash or contain special components such as
		1974	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1229	relative and your working directory changes, the behaviour is undefined.	1975	your working directory changes, then the behaviour is undefined.
1230		1976
1231	Since there is no standard to do this, the portable implementation simply	1977	Since there is no portable change notification interface available, the
1232	calls C<stat (2)> regularly on the path to see if it changed somehow. You	1978	portable implementation simply calls C<stat(2)> regularly on the path
1233	can specify a recommended polling interval for this case. If you specify	1979	to see if it changed somehow. You can specify a recommended polling
1234	a polling interval of C<0> (highly recommended!) then a I<suitable,	1980	interval for this case. If you specify a polling interval of C<0> (highly
1235	unspecified default> value will be used (which you can expect to be around	1981	recommended!) then a I<suitable, unspecified default> value will be used
1236	five seconds, although this might change dynamically). Libev will also	1982	(which you can expect to be around five seconds, although this might
1237	impose a minimum interval which is currently around C<0.1>, but thats	1983	change dynamically). Libev will also impose a minimum interval which is
1238	usually overkill.	1984	currently around C<0.1>, but that's usually overkill.
1239		1985
1240	This watcher type is not meant for massive numbers of stat watchers,	1986	This watcher type is not meant for massive numbers of stat watchers,
1241	as even with OS-supported change notifications, this can be	1987	as even with OS-supported change notifications, this can be
1242	resource-intensive.	1988	resource-intensive.
1243		1989
1244	At the time of this writing, only the Linux inotify interface is	1990	At the time of this writing, the only OS-specific interface implemented
1245	implemented (implementing kqueue support is left as an exercise for the	1991	is the Linux inotify interface (implementing kqueue support is left as an
1246	reader). Inotify will be used to give hints only and should not change the	1992	exercise for the reader. Note, however, that the author sees no way of
1247	semantics of C<ev_stat> watchers, which means that libev sometimes needs	1993	implementing C<ev_stat> semantics with kqueue, except as a hint).
1248	to fall back to regular polling again even with inotify, but changes are	1994
1249	usually detected immediately, and if the file exists there will be no	1995	=head3 ABI Issues (Largefile Support)
1250	polling.	1996
		1997	Libev by default (unless the user overrides this) uses the default
		1998	compilation environment, which means that on systems with large file
		1999	support disabled by default, you get the 32 bit version of the stat
		2000	structure. When using the library from programs that change the ABI to
		2001	use 64 bit file offsets the programs will fail. In that case you have to
		2002	compile libev with the same flags to get binary compatibility. This is
		2003	obviously the case with any flags that change the ABI, but the problem is
		2004	most noticeably displayed with ev_stat and large file support.
		2005
		2006	The solution for this is to lobby your distribution maker to make large
		2007	file interfaces available by default (as e.g. FreeBSD does) and not
		2008	optional. Libev cannot simply switch on large file support because it has
		2009	to exchange stat structures with application programs compiled using the
		2010	default compilation environment.
		2011
		2012	=head3 Inotify and Kqueue
		2013
		2014	When C<inotify (7)> support has been compiled into libev and present at
		2015	runtime, it will be used to speed up change detection where possible. The
		2016	inotify descriptor will be created lazily when the first C<ev_stat>
		2017	watcher is being started.
		2018
		2019	Inotify presence does not change the semantics of C<ev_stat> watchers
		2020	except that changes might be detected earlier, and in some cases, to avoid
		2021	making regular C<stat> calls. Even in the presence of inotify support
		2022	there are many cases where libev has to resort to regular C<stat> polling,
		2023	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2024	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2025	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2026	xfs are fully working) libev usually gets away without polling.
		2027
		2028	There is no support for kqueue, as apparently it cannot be used to
		2029	implement this functionality, due to the requirement of having a file
		2030	descriptor open on the object at all times, and detecting renames, unlinks
		2031	etc. is difficult.
		2032
		2033	=head3 C<stat ()> is a synchronous operation
		2034
		2035	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2036	the process. The exception are C<ev_stat> watchers - those call C<stat
		2037	()>, which is a synchronous operation.
		2038
		2039	For local paths, this usually doesn't matter: unless the system is very
		2040	busy or the intervals between stat's are large, a stat call will be fast,
		2041	as the path data is usually in memory already (except when starting the
		2042	watcher).
		2043
		2044	For networked file systems, calling C<stat ()> can block an indefinite
		2045	time due to network issues, and even under good conditions, a stat call
		2046	often takes multiple milliseconds.
		2047
		2048	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2049	paths, although this is fully supported by libev.
		2050
		2051	=head3 The special problem of stat time resolution
		2052
		2053	The C<stat ()> system call only supports full-second resolution portably,
		2054	and even on systems where the resolution is higher, most file systems
		2055	still only support whole seconds.
		2056
		2057	That means that, if the time is the only thing that changes, you can
		2058	easily miss updates: on the first update, C<ev_stat> detects a change and
		2059	calls your callback, which does something. When there is another update
		2060	within the same second, C<ev_stat> will be unable to detect unless the
		2061	stat data does change in other ways (e.g. file size).
		2062
		2063	The solution to this is to delay acting on a change for slightly more
		2064	than a second (or till slightly after the next full second boundary), using
		2065	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2066	ev_timer_again (loop, w)>).
		2067
		2068	The C<.02> offset is added to work around small timing inconsistencies
		2069	of some operating systems (where the second counter of the current time
		2070	might be be delayed. One such system is the Linux kernel, where a call to
		2071	C<gettimeofday> might return a timestamp with a full second later than
		2072	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2073	update file times then there will be a small window where the kernel uses
		2074	the previous second to update file times but libev might already execute
		2075	the timer callback).
		2076
		2077	=head3 Watcher-Specific Functions and Data Members
1251		2078
1252	=over 4	2079	=over 4
1253		2080
1254	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)	2081	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
1255		2082
…		…
1259	C<path>. The C<interval> is a hint on how quickly a change is expected to	2086	C<path>. The C<interval> is a hint on how quickly a change is expected to
1260	be detected and should normally be specified as C<0> to let libev choose	2087	be detected and should normally be specified as C<0> to let libev choose
1261	a suitable value. The memory pointed to by C<path> must point to the same	2088	a suitable value. The memory pointed to by C<path> must point to the same
1262	path for as long as the watcher is active.	2089	path for as long as the watcher is active.
1263		2090
1264	The callback will be receive C<EV_STAT> when a change was detected,	2091	The callback will receive an C<EV_STAT> event when a change was detected,
1265	relative to the attributes at the time the watcher was started (or the	2092	relative to the attributes at the time the watcher was started (or the
1266	last change was detected).	2093	last change was detected).
1267		2094
1268	=item ev_stat_stat (ev_stat *)	2095	=item ev_stat_stat (loop, ev_stat *)
1269		2096
1270	Updates the stat buffer immediately with new values. If you change the	2097	Updates the stat buffer immediately with new values. If you change the
1271	watched path in your callback, you could call this fucntion to avoid	2098	watched path in your callback, you could call this function to avoid
1272	detecting this change (while introducing a race condition). Can also be	2099	detecting this change (while introducing a race condition if you are not
1273	useful simply to find out the new values.	2100	the only one changing the path). Can also be useful simply to find out the
		2101	new values.
1274		2102
1275	=item ev_statdata attr [read-only]	2103	=item ev_statdata attr [read-only]
1276		2104
1277	The most-recently detected attributes of the file. Although the type is of	2105	The most-recently detected attributes of the file. Although the type is
1278	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2106	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1279	suitable for your system. If the C<st_nlink> member is C<0>, then there	2107	suitable for your system, but you can only rely on the POSIX-standardised
		2108	members to be present. If the C<st_nlink> member is C<0>, then there was
1280	was some error while C<stat>ing the file.	2109	some error while C<stat>ing the file.
1281		2110
1282	=item ev_statdata prev [read-only]	2111	=item ev_statdata prev [read-only]
1283		2112
1284	The previous attributes of the file. The callback gets invoked whenever	2113	The previous attributes of the file. The callback gets invoked whenever
1285	C<prev> != C<attr>.	2114	C<prev> != C<attr>, or, more precisely, one or more of these members
		2115	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2116	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1286		2117
1287	=item ev_tstamp interval [read-only]	2118	=item ev_tstamp interval [read-only]
1288		2119
1289	The specified interval.	2120	The specified interval.
1290		2121
1291	=item const char *path [read-only]	2122	=item const char *path [read-only]
1292		2123
1293	The filesystem path that is being watched.	2124	The file system path that is being watched.
1294		2125
1295	=back	2126	=back
1296		2127
		2128	=head3 Examples
		2129
1297	Example: Watch C</etc/passwd> for attribute changes.	2130	Example: Watch C</etc/passwd> for attribute changes.
1298		2131
1299	static void	2132	static void
1300	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2133	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1301	{	2134	{
1302	/* /etc/passwd changed in some way */	2135	/* /etc/passwd changed in some way */
1303	if (w->attr.st_nlink)	2136	if (w->attr.st_nlink)
1304	{	2137	{
1305	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2138	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1306	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2139	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1307	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2140	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1308	}	2141	}
1309	else	2142	else
1310	/* you shalt not abuse printf for puts */	2143	/* you shalt not abuse printf for puts */
1311	puts ("wow, /etc/passwd is not there, expect problems. "	2144	puts ("wow, /etc/passwd is not there, expect problems. "
1312	"if this is windows, they already arrived\n");	2145	"if this is windows, they already arrived\n");
1313	}	2146	}
1314		2147
1315	...	2148	...
1316	ev_stat passwd;	2149	ev_stat passwd;
1317		2150
1318	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	2151	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1319	ev_stat_start (loop, &passwd);	2152	ev_stat_start (loop, &passwd);
		2153
		2154	Example: Like above, but additionally use a one-second delay so we do not
		2155	miss updates (however, frequent updates will delay processing, too, so
		2156	one might do the work both on C<ev_stat> callback invocation I<and> on
		2157	C<ev_timer> callback invocation).
		2158
		2159	static ev_stat passwd;
		2160	static ev_timer timer;
		2161
		2162	static void
		2163	timer_cb (EV_P_ ev_timer *w, int revents)
		2164	{
		2165	ev_timer_stop (EV_A_ w);
		2166
		2167	/* now it's one second after the most recent passwd change */
		2168	}
		2169
		2170	static void
		2171	stat_cb (EV_P_ ev_stat *w, int revents)
		2172	{
		2173	/* reset the one-second timer */
		2174	ev_timer_again (EV_A_ &timer);
		2175	}
		2176
		2177	...
		2178	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2179	ev_stat_start (loop, &passwd);
		2180	ev_timer_init (&timer, timer_cb, 0., 1.02);
1320		2181
1321		2182
1322	=head2 C<ev_idle> - when you've got nothing better to do...	2183	=head2 C<ev_idle> - when you've got nothing better to do...
1323		2184
1324	Idle watchers trigger events when there are no other events are pending	2185	Idle watchers trigger events when no other events of the same or higher
1325	(prepare, check and other idle watchers do not count). That is, as long	2186	priority are pending (prepare, check and other idle watchers do not count
1326	as your process is busy handling sockets or timeouts (or even signals,	2187	as receiving "events").
1327	imagine) it will not be triggered. But when your process is idle all idle	2188
1328	watchers are being called again and again, once per event loop iteration -	2189	That is, as long as your process is busy handling sockets or timeouts
		2190	(or even signals, imagine) of the same or higher priority it will not be
		2191	triggered. But when your process is idle (or only lower-priority watchers
		2192	are pending), the idle watchers are being called once per event loop
1329	until stopped, that is, or your process receives more events and becomes	2193	iteration - until stopped, that is, or your process receives more events
1330	busy.	2194	and becomes busy again with higher priority stuff.
1331		2195
1332	The most noteworthy effect is that as long as any idle watchers are	2196	The most noteworthy effect is that as long as any idle watchers are
1333	active, the process will not block when waiting for new events.	2197	active, the process will not block when waiting for new events.
1334		2198
1335	Apart from keeping your process non-blocking (which is a useful	2199	Apart from keeping your process non-blocking (which is a useful
1336	effect on its own sometimes), idle watchers are a good place to do	2200	effect on its own sometimes), idle watchers are a good place to do
1337	"pseudo-background processing", or delay processing stuff to after the	2201	"pseudo-background processing", or delay processing stuff to after the
1338	event loop has handled all outstanding events.	2202	event loop has handled all outstanding events.
1339		2203
		2204	=head3 Watcher-Specific Functions and Data Members
		2205
1340	=over 4	2206	=over 4
1341		2207
1342	=item ev_idle_init (ev_signal *, callback)	2208	=item ev_idle_init (ev_idle *, callback)
1343		2209
1344	Initialises and configures the idle watcher - it has no parameters of any	2210	Initialises and configures the idle watcher - it has no parameters of any
1345	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2211	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1346	believe me.	2212	believe me.
1347		2213
1348	=back	2214	=back
1349		2215
		2216	=head3 Examples
		2217
1350	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2218	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1351	callback, free it. Also, use no error checking, as usual.	2219	callback, free it. Also, use no error checking, as usual.
1352		2220
1353	static void	2221	static void
1354	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2222	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1355	{	2223	{
1356	free (w);	2224	free (w);
1357	// now do something you wanted to do when the program has	2225	// now do something you wanted to do when the program has
1358	// no longer asnything immediate to do.	2226	// no longer anything immediate to do.
1359	}	2227	}
1360		2228
1361	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2229	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1362	ev_idle_init (idle_watcher, idle_cb);	2230	ev_idle_init (idle_watcher, idle_cb);
1363	ev_idle_start (loop, idle_cb);	2231	ev_idle_start (loop, idle_cb);
1364		2232
1365		2233
1366	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2234	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1367		2235
1368	Prepare and check watchers are usually (but not always) used in tandem:	2236	Prepare and check watchers are usually (but not always) used in pairs:
1369	prepare watchers get invoked before the process blocks and check watchers	2237	prepare watchers get invoked before the process blocks and check watchers
1370	afterwards.	2238	afterwards.
1371		2239
1372	You I<must not> call C<ev_loop> or similar functions that enter	2240	You I<must not> call C<ev_loop> or similar functions that enter
1373	the current event loop from either C<ev_prepare> or C<ev_check>	2241	the current event loop from either C<ev_prepare> or C<ev_check>
…		…
1376	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2244	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1377	C<ev_check> so if you have one watcher of each kind they will always be	2245	C<ev_check> so if you have one watcher of each kind they will always be
1378	called in pairs bracketing the blocking call.	2246	called in pairs bracketing the blocking call.
1379		2247
1380	Their main purpose is to integrate other event mechanisms into libev and	2248	Their main purpose is to integrate other event mechanisms into libev and
1381	their use is somewhat advanced. This could be used, for example, to track	2249	their use is somewhat advanced. They could be used, for example, to track
1382	variable changes, implement your own watchers, integrate net-snmp or a	2250	variable changes, implement your own watchers, integrate net-snmp or a
1383	coroutine library and lots more. They are also occasionally useful if	2251	coroutine library and lots more. They are also occasionally useful if
1384	you cache some data and want to flush it before blocking (for example,	2252	you cache some data and want to flush it before blocking (for example,
1385	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2253	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1386	watcher).	2254	watcher).
1387		2255
1388	This is done by examining in each prepare call which file descriptors need	2256	This is done by examining in each prepare call which file descriptors
1389	to be watched by the other library, registering C<ev_io> watchers for	2257	need to be watched by the other library, registering C<ev_io> watchers
1390	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2258	for them and starting an C<ev_timer> watcher for any timeouts (many
1391	provide just this functionality). Then, in the check watcher you check for	2259	libraries provide exactly this functionality). Then, in the check watcher,
1392	any events that occured (by checking the pending status of all watchers	2260	you check for any events that occurred (by checking the pending status
1393	and stopping them) and call back into the library. The I/O and timer	2261	of all watchers and stopping them) and call back into the library. The
1394	callbacks will never actually be called (but must be valid nevertheless,	2262	I/O and timer callbacks will never actually be called (but must be valid
1395	because you never know, you know?).	2263	nevertheless, because you never know, you know?).
1396		2264
1397	As another example, the Perl Coro module uses these hooks to integrate	2265	As another example, the Perl Coro module uses these hooks to integrate
1398	coroutines into libev programs, by yielding to other active coroutines	2266	coroutines into libev programs, by yielding to other active coroutines
1399	during each prepare and only letting the process block if no coroutines	2267	during each prepare and only letting the process block if no coroutines
1400	are ready to run (it's actually more complicated: it only runs coroutines	2268	are ready to run (it's actually more complicated: it only runs coroutines
1401	with priority higher than or equal to the event loop and one coroutine	2269	with priority higher than or equal to the event loop and one coroutine
1402	of lower priority, but only once, using idle watchers to keep the event	2270	of lower priority, but only once, using idle watchers to keep the event
1403	loop from blocking if lower-priority coroutines are active, thus mapping	2271	loop from blocking if lower-priority coroutines are active, thus mapping
1404	low-priority coroutines to idle/background tasks).	2272	low-priority coroutines to idle/background tasks).
1405		2273
		2274	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		2275	priority, to ensure that they are being run before any other watchers
		2276	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2277
		2278	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2279	activate ("feed") events into libev. While libev fully supports this, they
		2280	might get executed before other C<ev_check> watchers did their job. As
		2281	C<ev_check> watchers are often used to embed other (non-libev) event
		2282	loops those other event loops might be in an unusable state until their
		2283	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2284	others).
		2285
		2286	=head3 Watcher-Specific Functions and Data Members
		2287
1406	=over 4	2288	=over 4
1407		2289
1408	=item ev_prepare_init (ev_prepare *, callback)	2290	=item ev_prepare_init (ev_prepare *, callback)
1409		2291
1410	=item ev_check_init (ev_check *, callback)	2292	=item ev_check_init (ev_check *, callback)
1411		2293
1412	Initialises and configures the prepare or check watcher - they have no	2294	Initialises and configures the prepare or check watcher - they have no
1413	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2295	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1414	macros, but using them is utterly, utterly and completely pointless.	2296	macros, but using them is utterly, utterly, utterly and completely
		2297	pointless.
1415		2298
1416	=back	2299	=back
1417		2300
1418	Example: To include a library such as adns, you would add IO watchers	2301	=head3 Examples
1419	and a timeout watcher in a prepare handler, as required by libadns, and	2302
		2303	There are a number of principal ways to embed other event loops or modules
		2304	into libev. Here are some ideas on how to include libadns into libev
		2305	(there is a Perl module named C<EV::ADNS> that does this, which you could
		2306	use as a working example. Another Perl module named C<EV::Glib> embeds a
		2307	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		2308	Glib event loop).
		2309
		2310	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1420	in a check watcher, destroy them and call into libadns. What follows is	2311	and in a check watcher, destroy them and call into libadns. What follows
1421	pseudo-code only of course:	2312	is pseudo-code only of course. This requires you to either use a low
		2313	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		2314	the callbacks for the IO/timeout watchers might not have been called yet.
1422		2315
1423	static ev_io iow [nfd];	2316	static ev_io iow [nfd];
1424	static ev_timer tw;	2317	static ev_timer tw;
1425		2318
1426	static void	2319	static void
1427	io_cb (ev_loop *loop, ev_io *w, int revents)	2320	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1428	{	2321	{
1429	// set the relevant poll flags
1430	// could also call adns_processreadable etc. here
1431	struct pollfd *fd = (struct pollfd *)w->data;
1432	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1433	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1434	}	2322	}
1435		2323
1436	// create io watchers for each fd and a timer before blocking	2324	// create io watchers for each fd and a timer before blocking
1437	static void	2325	static void
1438	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2326	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1439	{	2327	{
1440	int timeout = 3600000;truct pollfd fds [nfd];	2328	int timeout = 3600000;
		2329	struct pollfd fds [nfd];
1441	// actual code will need to loop here and realloc etc.	2330	// actual code will need to loop here and realloc etc.
1442	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2331	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1443		2332
1444	/* the callback is illegal, but won't be called as we stop during check */	2333	/* the callback is illegal, but won't be called as we stop during check */
1445	ev_timer_init (&tw, 0, timeout * 1e-3);	2334	ev_timer_init (&tw, 0, timeout * 1e-3);
1446	ev_timer_start (loop, &tw);	2335	ev_timer_start (loop, &tw);
1447		2336
1448	// create on ev_io per pollfd	2337	// create one ev_io per pollfd
1449	for (int i = 0; i < nfd; ++i)	2338	for (int i = 0; i < nfd; ++i)
1450	{	2339	{
1451	ev_io_init (iow + i, io_cb, fds [i].fd,	2340	ev_io_init (iow + i, io_cb, fds [i].fd,
1452	((fds [i].events & POLLIN ? EV_READ : 0)	2341	((fds [i].events & POLLIN ? EV_READ : 0)
1453	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2342	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1454		2343
1455	fds [i].revents = 0;	2344	fds [i].revents = 0;
1456	iow [i].data = fds + i;
1457	ev_io_start (loop, iow + i);	2345	ev_io_start (loop, iow + i);
1458	}	2346	}
1459	}	2347	}
1460		2348
1461	// stop all watchers after blocking	2349	// stop all watchers after blocking
1462	static void	2350	static void
1463	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2351	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1464	{	2352	{
1465	ev_timer_stop (loop, &tw);	2353	ev_timer_stop (loop, &tw);
1466		2354
1467	for (int i = 0; i < nfd; ++i)	2355	for (int i = 0; i < nfd; ++i)
		2356	{
		2357	// set the relevant poll flags
		2358	// could also call adns_processreadable etc. here
		2359	struct pollfd *fd = fds + i;
		2360	int revents = ev_clear_pending (iow + i);
		2361	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2362	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2363
		2364	// now stop the watcher
1468	ev_io_stop (loop, iow + i);	2365	ev_io_stop (loop, iow + i);
		2366	}
1469		2367
1470	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2368	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1471	}	2369	}
		2370
		2371	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2372	in the prepare watcher and would dispose of the check watcher.
		2373
		2374	Method 3: If the module to be embedded supports explicit event
		2375	notification (libadns does), you can also make use of the actual watcher
		2376	callbacks, and only destroy/create the watchers in the prepare watcher.
		2377
		2378	static void
		2379	timer_cb (EV_P_ ev_timer *w, int revents)
		2380	{
		2381	adns_state ads = (adns_state)w->data;
		2382	update_now (EV_A);
		2383
		2384	adns_processtimeouts (ads, &tv_now);
		2385	}
		2386
		2387	static void
		2388	io_cb (EV_P_ ev_io *w, int revents)
		2389	{
		2390	adns_state ads = (adns_state)w->data;
		2391	update_now (EV_A);
		2392
		2393	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2394	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2395	}
		2396
		2397	// do not ever call adns_afterpoll
		2398
		2399	Method 4: Do not use a prepare or check watcher because the module you
		2400	want to embed is not flexible enough to support it. Instead, you can
		2401	override their poll function. The drawback with this solution is that the
		2402	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		2403	this approach, effectively embedding EV as a client into the horrible
		2404	libglib event loop.
		2405
		2406	static gint
		2407	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2408	{
		2409	int got_events = 0;
		2410
		2411	for (n = 0; n < nfds; ++n)
		2412	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2413
		2414	if (timeout >= 0)
		2415	// create/start timer
		2416
		2417	// poll
		2418	ev_loop (EV_A_ 0);
		2419
		2420	// stop timer again
		2421	if (timeout >= 0)
		2422	ev_timer_stop (EV_A_ &to);
		2423
		2424	// stop io watchers again - their callbacks should have set
		2425	for (n = 0; n < nfds; ++n)
		2426	ev_io_stop (EV_A_ iow [n]);
		2427
		2428	return got_events;
		2429	}
1472		2430
1473		2431
1474	=head2 C<ev_embed> - when one backend isn't enough...	2432	=head2 C<ev_embed> - when one backend isn't enough...
1475		2433
1476	This is a rather advanced watcher type that lets you embed one event loop	2434	This is a rather advanced watcher type that lets you embed one event loop
…		…
1482	prioritise I/O.	2440	prioritise I/O.
1483		2441
1484	As an example for a bug workaround, the kqueue backend might only support	2442	As an example for a bug workaround, the kqueue backend might only support
1485	sockets on some platform, so it is unusable as generic backend, but you	2443	sockets on some platform, so it is unusable as generic backend, but you
1486	still want to make use of it because you have many sockets and it scales	2444	still want to make use of it because you have many sockets and it scales
1487	so nicely. In this case, you would create a kqueue-based loop and embed it	2445	so nicely. In this case, you would create a kqueue-based loop and embed
1488	into your default loop (which might use e.g. poll). Overall operation will	2446	it into your default loop (which might use e.g. poll). Overall operation
1489	be a bit slower because first libev has to poll and then call kevent, but	2447	will be a bit slower because first libev has to call C<poll> and then
1490	at least you can use both at what they are best.	2448	C<kevent>, but at least you can use both mechanisms for what they are
		2449	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1491		2450
1492	As for prioritising I/O: rarely you have the case where some fds have	2451	As for prioritising I/O: under rare circumstances you have the case where
1493	to be watched and handled very quickly (with low latency), and even	2452	some fds have to be watched and handled very quickly (with low latency),
1494	priorities and idle watchers might have too much overhead. In this case	2453	and even priorities and idle watchers might have too much overhead. In
1495	you would put all the high priority stuff in one loop and all the rest in	2454	this case you would put all the high priority stuff in one loop and all
1496	a second one, and embed the second one in the first.	2455	the rest in a second one, and embed the second one in the first.
1497		2456
1498	As long as the watcher is active, the callback will be invoked every time	2457	As long as the watcher is active, the callback will be invoked every
1499	there might be events pending in the embedded loop. The callback must then	2458	time there might be events pending in the embedded loop. The callback
1500	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2459	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1501	their callbacks (you could also start an idle watcher to give the embedded	2460	sweep and invoke their callbacks (the callback doesn't need to invoke the
1502	loop strictly lower priority for example). You can also set the callback	2461	C<ev_embed_sweep> function directly, it could also start an idle watcher
1503	to C<0>, in which case the embed watcher will automatically execute the	2462	to give the embedded loop strictly lower priority for example).
1504	embedded loop sweep.
1505		2463
1506	As long as the watcher is started it will automatically handle events. The	2464	You can also set the callback to C<0>, in which case the embed watcher
1507	callback will be invoked whenever some events have been handled. You can	2465	will automatically execute the embedded loop sweep whenever necessary.
1508	set the callback to C<0> to avoid having to specify one if you are not
1509	interested in that.
1510		2466
1511	Also, there have not currently been made special provisions for forking:	2467	Fork detection will be handled transparently while the C<ev_embed> watcher
1512	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2468	is active, i.e., the embedded loop will automatically be forked when the
1513	but you will also have to stop and restart any C<ev_embed> watchers	2469	embedding loop forks. In other cases, the user is responsible for calling
1514	yourself.	2470	C<ev_loop_fork> on the embedded loop.
1515		2471
1516	Unfortunately, not all backends are embeddable, only the ones returned by	2472	Unfortunately, not all backends are embeddable: only the ones returned by
1517	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2473	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1518	portable one.	2474	portable one.
1519		2475
1520	So when you want to use this feature you will always have to be prepared	2476	So when you want to use this feature you will always have to be prepared
1521	that you cannot get an embeddable loop. The recommended way to get around	2477	that you cannot get an embeddable loop. The recommended way to get around
1522	this is to have a separate variables for your embeddable loop, try to	2478	this is to have a separate variables for your embeddable loop, try to
1523	create it, and if that fails, use the normal loop for everything:	2479	create it, and if that fails, use the normal loop for everything.
1524		2480
1525	struct ev_loop *loop_hi = ev_default_init (0);	2481	=head3 C<ev_embed> and fork
1526	struct ev_loop *loop_lo = 0;
1527	struct ev_embed embed;
1528
1529	// see if there is a chance of getting one that works
1530	// (remember that a flags value of 0 means autodetection)
1531	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1532	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1533	: 0;
1534		2482
1535	// if we got one, then embed it, otherwise default to loop_hi	2483	While the C<ev_embed> watcher is running, forks in the embedding loop will
1536	if (loop_lo)	2484	automatically be applied to the embedded loop as well, so no special
1537	{	2485	fork handling is required in that case. When the watcher is not running,
1538	ev_embed_init (&embed, 0, loop_lo);	2486	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1539	ev_embed_start (loop_hi, &embed);	2487	as applicable.
1540	}	2488
1541	else	2489	=head3 Watcher-Specific Functions and Data Members
1542	loop_lo = loop_hi;
1543		2490
1544	=over 4	2491	=over 4
1545		2492
1546	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	2493	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
1547		2494
…		…
1549		2496
1550	Configures the watcher to embed the given loop, which must be	2497	Configures the watcher to embed the given loop, which must be
1551	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	2498	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1552	invoked automatically, otherwise it is the responsibility of the callback	2499	invoked automatically, otherwise it is the responsibility of the callback
1553	to invoke it (it will continue to be called until the sweep has been done,	2500	to invoke it (it will continue to be called until the sweep has been done,
1554	if you do not want thta, you need to temporarily stop the embed watcher).	2501	if you do not want that, you need to temporarily stop the embed watcher).
1555		2502
1556	=item ev_embed_sweep (loop, ev_embed *)	2503	=item ev_embed_sweep (loop, ev_embed *)
1557		2504
1558	Make a single, non-blocking sweep over the embedded loop. This works	2505	Make a single, non-blocking sweep over the embedded loop. This works
1559	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	2506	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
1560	apropriate way for embedded loops.	2507	appropriate way for embedded loops.
1561		2508
1562	=item struct ev_loop *loop [read-only]	2509	=item struct ev_loop *other [read-only]
1563		2510
1564	The embedded event loop.	2511	The embedded event loop.
1565		2512
1566	=back	2513	=back
		2514
		2515	=head3 Examples
		2516
		2517	Example: Try to get an embeddable event loop and embed it into the default
		2518	event loop. If that is not possible, use the default loop. The default
		2519	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2520	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2521	used).
		2522
		2523	struct ev_loop *loop_hi = ev_default_init (0);
		2524	struct ev_loop *loop_lo = 0;
		2525	ev_embed embed;
		2526
		2527	// see if there is a chance of getting one that works
		2528	// (remember that a flags value of 0 means autodetection)
		2529	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2530	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2531	: 0;
		2532
		2533	// if we got one, then embed it, otherwise default to loop_hi
		2534	if (loop_lo)
		2535	{
		2536	ev_embed_init (&embed, 0, loop_lo);
		2537	ev_embed_start (loop_hi, &embed);
		2538	}
		2539	else
		2540	loop_lo = loop_hi;
		2541
		2542	Example: Check if kqueue is available but not recommended and create
		2543	a kqueue backend for use with sockets (which usually work with any
		2544	kqueue implementation). Store the kqueue/socket-only event loop in
		2545	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2546
		2547	struct ev_loop *loop = ev_default_init (0);
		2548	struct ev_loop *loop_socket = 0;
		2549	ev_embed embed;
		2550
		2551	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2552	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2553	{
		2554	ev_embed_init (&embed, 0, loop_socket);
		2555	ev_embed_start (loop, &embed);
		2556	}
		2557
		2558	if (!loop_socket)
		2559	loop_socket = loop;
		2560
		2561	// now use loop_socket for all sockets, and loop for everything else
1567		2562
1568		2563
1569	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	2564	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
1570		2565
1571	Fork watchers are called when a C<fork ()> was detected (usually because	2566	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
1574	event loop blocks next and before C<ev_check> watchers are being called,	2569	event loop blocks next and before C<ev_check> watchers are being called,
1575	and only in the child after the fork. If whoever good citizen calling	2570	and only in the child after the fork. If whoever good citizen calling
1576	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2571	C<ev_default_fork> cheats and calls it in the wrong process, the fork
1577	handlers will be invoked, too, of course.	2572	handlers will be invoked, too, of course.
1578		2573
		2574	=head3 Watcher-Specific Functions and Data Members
		2575
1579	=over 4	2576	=over 4
1580		2577
1581	=item ev_fork_init (ev_signal *, callback)	2578	=item ev_fork_init (ev_signal *, callback)
1582		2579
1583	Initialises and configures the fork watcher - it has no parameters of any	2580	Initialises and configures the fork watcher - it has no parameters of any
…		…
1585	believe me.	2582	believe me.
1586		2583
1587	=back	2584	=back
1588		2585
1589		2586
		2587	=head2 C<ev_async> - how to wake up another event loop
		2588
		2589	In general, you cannot use an C<ev_loop> from multiple threads or other
		2590	asynchronous sources such as signal handlers (as opposed to multiple event
		2591	loops - those are of course safe to use in different threads).
		2592
		2593	Sometimes, however, you need to wake up another event loop you do not
		2594	control, for example because it belongs to another thread. This is what
		2595	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2596	can signal it by calling C<ev_async_send>, which is thread- and signal
		2597	safe.
		2598
		2599	This functionality is very similar to C<ev_signal> watchers, as signals,
		2600	too, are asynchronous in nature, and signals, too, will be compressed
		2601	(i.e. the number of callback invocations may be less than the number of
		2602	C<ev_async_sent> calls).
		2603
		2604	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2605	just the default loop.
		2606
		2607	=head3 Queueing
		2608
		2609	C<ev_async> does not support queueing of data in any way. The reason
		2610	is that the author does not know of a simple (or any) algorithm for a
		2611	multiple-writer-single-reader queue that works in all cases and doesn't
		2612	need elaborate support such as pthreads.
		2613
		2614	That means that if you want to queue data, you have to provide your own
		2615	queue. But at least I can tell you how to implement locking around your
		2616	queue:
		2617
		2618	=over 4
		2619
		2620	=item queueing from a signal handler context
		2621
		2622	To implement race-free queueing, you simply add to the queue in the signal
		2623	handler but you block the signal handler in the watcher callback. Here is
		2624	an example that does that for some fictitious SIGUSR1 handler:
		2625
		2626	static ev_async mysig;
		2627
		2628	static void
		2629	sigusr1_handler (void)
		2630	{
		2631	sometype data;
		2632
		2633	// no locking etc.
		2634	queue_put (data);
		2635	ev_async_send (EV_DEFAULT_ &mysig);
		2636	}
		2637
		2638	static void
		2639	mysig_cb (EV_P_ ev_async *w, int revents)
		2640	{
		2641	sometype data;
		2642	sigset_t block, prev;
		2643
		2644	sigemptyset (&block);
		2645	sigaddset (&block, SIGUSR1);
		2646	sigprocmask (SIG_BLOCK, &block, &prev);
		2647
		2648	while (queue_get (&data))
		2649	process (data);
		2650
		2651	if (sigismember (&prev, SIGUSR1)
		2652	sigprocmask (SIG_UNBLOCK, &block, 0);
		2653	}
		2654
		2655	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2656	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2657	either...).
		2658
		2659	=item queueing from a thread context
		2660
		2661	The strategy for threads is different, as you cannot (easily) block
		2662	threads but you can easily preempt them, so to queue safely you need to
		2663	employ a traditional mutex lock, such as in this pthread example:
		2664
		2665	static ev_async mysig;
		2666	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2667
		2668	static void
		2669	otherthread (void)
		2670	{
		2671	// only need to lock the actual queueing operation
		2672	pthread_mutex_lock (&mymutex);
		2673	queue_put (data);
		2674	pthread_mutex_unlock (&mymutex);
		2675
		2676	ev_async_send (EV_DEFAULT_ &mysig);
		2677	}
		2678
		2679	static void
		2680	mysig_cb (EV_P_ ev_async *w, int revents)
		2681	{
		2682	pthread_mutex_lock (&mymutex);
		2683
		2684	while (queue_get (&data))
		2685	process (data);
		2686
		2687	pthread_mutex_unlock (&mymutex);
		2688	}
		2689
		2690	=back
		2691
		2692
		2693	=head3 Watcher-Specific Functions and Data Members
		2694
		2695	=over 4
		2696
		2697	=item ev_async_init (ev_async *, callback)
		2698
		2699	Initialises and configures the async watcher - it has no parameters of any
		2700	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		2701	trust me.
		2702
		2703	=item ev_async_send (loop, ev_async *)
		2704
		2705	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2706	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2707	C<ev_feed_event>, this call is safe to do from other threads, signal or
		2708	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		2709	section below on what exactly this means).
		2710
		2711	Note that, as with other watchers in libev, multiple events might get
		2712	compressed into a single callback invocation (another way to look at this
		2713	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		2714	reset when the event loop detects that).
		2715
		2716	This call incurs the overhead of a system call only once per event loop
		2717	iteration, so while the overhead might be noticeable, it doesn't apply to
		2718	repeated calls to C<ev_async_send> for the same event loop.
		2719
		2720	=item bool = ev_async_pending (ev_async *)
		2721
		2722	Returns a non-zero value when C<ev_async_send> has been called on the
		2723	watcher but the event has not yet been processed (or even noted) by the
		2724	event loop.
		2725
		2726	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2727	the loop iterates next and checks for the watcher to have become active,
		2728	it will reset the flag again. C<ev_async_pending> can be used to very
		2729	quickly check whether invoking the loop might be a good idea.
		2730
		2731	Not that this does I<not> check whether the watcher itself is pending,
		2732	only whether it has been requested to make this watcher pending: there
		2733	is a time window between the event loop checking and resetting the async
		2734	notification, and the callback being invoked.
		2735
		2736	=back
		2737
		2738
1590	=head1 OTHER FUNCTIONS	2739	=head1 OTHER FUNCTIONS
1591		2740
1592	There are some other functions of possible interest. Described. Here. Now.	2741	There are some other functions of possible interest. Described. Here. Now.
1593		2742
1594	=over 4	2743	=over 4
1595		2744
1596	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	2745	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1597		2746
1598	This function combines a simple timer and an I/O watcher, calls your	2747	This function combines a simple timer and an I/O watcher, calls your
1599	callback on whichever event happens first and automatically stop both	2748	callback on whichever event happens first and automatically stops both
1600	watchers. This is useful if you want to wait for a single event on an fd	2749	watchers. This is useful if you want to wait for a single event on an fd
1601	or timeout without having to allocate/configure/start/stop/free one or	2750	or timeout without having to allocate/configure/start/stop/free one or
1602	more watchers yourself.	2751	more watchers yourself.
1603		2752
1604	If C<fd> is less than 0, then no I/O watcher will be started and events	2753	If C<fd> is less than 0, then no I/O watcher will be started and the
1605	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	2754	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1606	C<events> set will be craeted and started.	2755	the given C<fd> and C<events> set will be created and started.
1607		2756
1608	If C<timeout> is less than 0, then no timeout watcher will be	2757	If C<timeout> is less than 0, then no timeout watcher will be
1609	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	2758	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1610	repeat = 0) will be started. While C<0> is a valid timeout, it is of	2759	repeat = 0) will be started. C<0> is a valid timeout.
1611	dubious value.
1612		2760
1613	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	2761	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
1614	passed an C<revents> set like normal event callbacks (a combination of	2762	passed an C<revents> set like normal event callbacks (a combination of
1615	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	2763	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
1616	value passed to C<ev_once>:	2764	value passed to C<ev_once>. Note that it is possible to receive I<both>
		2765	a timeout and an io event at the same time - you probably should give io
		2766	events precedence.
1617		2767
		2768	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		2769
1618	static void stdin_ready (int revents, void *arg)	2770	static void stdin_ready (int revents, void *arg)
1619	{	2771	{
1620	if (revents & EV_TIMEOUT)
1621	/* doh, nothing entered */;
1622	else if (revents & EV_READ)	2772	if (revents & EV_READ)
1623	/* stdin might have data for us, joy! */;	2773	/* stdin might have data for us, joy! */;
		2774	else if (revents & EV_TIMEOUT)
		2775	/* doh, nothing entered */;
1624	}	2776	}
1625		2777
1626	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2778	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1627		2779
1628	=item ev_feed_event (ev_loop *, watcher *, int revents)	2780	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
1629		2781
1630	Feeds the given event set into the event loop, as if the specified event	2782	Feeds the given event set into the event loop, as if the specified event
1631	had happened for the specified watcher (which must be a pointer to an	2783	had happened for the specified watcher (which must be a pointer to an
1632	initialised but not necessarily started event watcher).	2784	initialised but not necessarily started event watcher).
1633		2785
1634	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	2786	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
1635		2787
1636	Feed an event on the given fd, as if a file descriptor backend detected	2788	Feed an event on the given fd, as if a file descriptor backend detected
1637	the given events it.	2789	the given events it.
1638		2790
1639	=item ev_feed_signal_event (ev_loop *loop, int signum)	2791	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
1640		2792
1641	Feed an event as if the given signal occured (C<loop> must be the default	2793	Feed an event as if the given signal occurred (C<loop> must be the default
1642	loop!).	2794	loop!).
1643		2795
1644	=back	2796	=back
1645		2797
1646		2798
…		…
1662		2814
1663	=item * Priorities are not currently supported. Initialising priorities	2815	=item * Priorities are not currently supported. Initialising priorities
1664	will fail and all watchers will have the same priority, even though there	2816	will fail and all watchers will have the same priority, even though there
1665	is an ev_pri field.	2817	is an ev_pri field.
1666		2818
		2819	=item * In libevent, the last base created gets the signals, in libev, the
		2820	first base created (== the default loop) gets the signals.
		2821
1667	=item * Other members are not supported.	2822	=item * Other members are not supported.
1668		2823
1669	=item * The libev emulation is I<not> ABI compatible to libevent, you need	2824	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1670	to use the libev header file and library.	2825	to use the libev header file and library.
1671		2826
1672	=back	2827	=back
1673		2828
1674	=head1 C++ SUPPORT	2829	=head1 C++ SUPPORT
1675		2830
1676	Libev comes with some simplistic wrapper classes for C++ that mainly allow	2831	Libev comes with some simplistic wrapper classes for C++ that mainly allow
1677	you to use some convinience methods to start/stop watchers and also change	2832	you to use some convenience methods to start/stop watchers and also change
1678	the callback model to a model using method callbacks on objects.	2833	the callback model to a model using method callbacks on objects.
1679		2834
1680	To use it,	2835	To use it,
1681		2836
1682	#include <ev++.h>	2837	#include <ev++.h>
1683		2838
1684	(it is not installed by default). This automatically includes F<ev.h>	2839	This automatically includes F<ev.h> and puts all of its definitions (many
1685	and puts all of its definitions (many of them macros) into the global	2840	of them macros) into the global namespace. All C++ specific things are
1686	namespace. All C++ specific things are put into the C<ev> namespace.	2841	put into the C<ev> namespace. It should support all the same embedding
		2842	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
1687		2843
1688	It should support all the same embedding options as F<ev.h>, most notably	2844	Care has been taken to keep the overhead low. The only data member the C++
1689	C<EV_MULTIPLICITY>.	2845	classes add (compared to plain C-style watchers) is the event loop pointer
		2846	that the watcher is associated with (or no additional members at all if
		2847	you disable C<EV_MULTIPLICITY> when embedding libev).
		2848
		2849	Currently, functions, and static and non-static member functions can be
		2850	used as callbacks. Other types should be easy to add as long as they only
		2851	need one additional pointer for context. If you need support for other
		2852	types of functors please contact the author (preferably after implementing
		2853	it).
1690		2854
1691	Here is a list of things available in the C<ev> namespace:	2855	Here is a list of things available in the C<ev> namespace:
1692		2856
1693	=over 4	2857	=over 4
1694		2858
…		…
1710		2874
1711	All of those classes have these methods:	2875	All of those classes have these methods:
1712		2876
1713	=over 4	2877	=over 4
1714		2878
1715	=item ev::TYPE::TYPE (object *, object::method *)	2879	=item ev::TYPE::TYPE ()
1716		2880
1717	=item ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)	2881	=item ev::TYPE::TYPE (struct ev_loop *)
1718		2882
1719	=item ev::TYPE::~TYPE	2883	=item ev::TYPE::~TYPE
1720		2884
1721	The constructor takes a pointer to an object and a method pointer to	2885	The constructor (optionally) takes an event loop to associate the watcher
1722	the event handler callback to call in this class. The constructor calls	2886	with. If it is omitted, it will use C<EV_DEFAULT>.
1723	C<ev_init> for you, which means you have to call the C<set> method	2887
1724	before starting it. If you do not specify a loop then the constructor	2888	The constructor calls C<ev_init> for you, which means you have to call the
1725	automatically associates the default loop with this watcher.	2889	C<set> method before starting it.
		2890
		2891	It will not set a callback, however: You have to call the templated C<set>
		2892	method to set a callback before you can start the watcher.
		2893
		2894	(The reason why you have to use a method is a limitation in C++ which does
		2895	not allow explicit template arguments for constructors).
1726		2896
1727	The destructor automatically stops the watcher if it is active.	2897	The destructor automatically stops the watcher if it is active.
		2898
		2899	=item w->set<class, &class::method> (object *)
		2900
		2901	This method sets the callback method to call. The method has to have a
		2902	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		2903	first argument and the C<revents> as second. The object must be given as
		2904	parameter and is stored in the C<data> member of the watcher.
		2905
		2906	This method synthesizes efficient thunking code to call your method from
		2907	the C callback that libev requires. If your compiler can inline your
		2908	callback (i.e. it is visible to it at the place of the C<set> call and
		2909	your compiler is good :), then the method will be fully inlined into the
		2910	thunking function, making it as fast as a direct C callback.
		2911
		2912	Example: simple class declaration and watcher initialisation
		2913
		2914	struct myclass
		2915	{
		2916	void io_cb (ev::io &w, int revents) { }
		2917	}
		2918
		2919	myclass obj;
		2920	ev::io iow;
		2921	iow.set <myclass, &myclass::io_cb> (&obj);
		2922
		2923	=item w->set (object *)
		2924
		2925	This is an B<experimental> feature that might go away in a future version.
		2926
		2927	This is a variation of a method callback - leaving out the method to call
		2928	will default the method to C<operator ()>, which makes it possible to use
		2929	functor objects without having to manually specify the C<operator ()> all
		2930	the time. Incidentally, you can then also leave out the template argument
		2931	list.
		2932
		2933	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		2934	int revents)>.
		2935
		2936	See the method-C<set> above for more details.
		2937
		2938	Example: use a functor object as callback.
		2939
		2940	struct myfunctor
		2941	{
		2942	void operator() (ev::io &w, int revents)
		2943	{
		2944	...
		2945	}
		2946	}
		2947
		2948	myfunctor f;
		2949
		2950	ev::io w;
		2951	w.set (&f);
		2952
		2953	=item w->set<function> (void *data = 0)
		2954
		2955	Also sets a callback, but uses a static method or plain function as
		2956	callback. The optional C<data> argument will be stored in the watcher's
		2957	C<data> member and is free for you to use.
		2958
		2959	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		2960
		2961	See the method-C<set> above for more details.
		2962
		2963	Example: Use a plain function as callback.
		2964
		2965	static void io_cb (ev::io &w, int revents) { }
		2966	iow.set <io_cb> ();
1728		2967
1729	=item w->set (struct ev_loop *)	2968	=item w->set (struct ev_loop *)
1730		2969
1731	Associates a different C<struct ev_loop> with this watcher. You can only	2970	Associates a different C<struct ev_loop> with this watcher. You can only
1732	do this when the watcher is inactive (and not pending either).	2971	do this when the watcher is inactive (and not pending either).
1733		2972
1734	=item w->set ([args])	2973	=item w->set ([arguments])
1735		2974
1736	Basically the same as C<ev_TYPE_set>, with the same args. Must be	2975	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
1737	called at least once. Unlike the C counterpart, an active watcher gets	2976	called at least once. Unlike the C counterpart, an active watcher gets
1738	automatically stopped and restarted.	2977	automatically stopped and restarted when reconfiguring it with this
		2978	method.
1739		2979
1740	=item w->start ()	2980	=item w->start ()
1741		2981
1742	Starts the watcher. Note that there is no C<loop> argument as the	2982	Starts the watcher. Note that there is no C<loop> argument, as the
1743	constructor already takes the loop.	2983	constructor already stores the event loop.
1744		2984
1745	=item w->stop ()	2985	=item w->stop ()
1746		2986
1747	Stops the watcher if it is active. Again, no C<loop> argument.	2987	Stops the watcher if it is active. Again, no C<loop> argument.
1748		2988
1749	=item w->again () C<ev::timer>, C<ev::periodic> only	2989	=item w->again () (C<ev::timer>, C<ev::periodic> only)
1750		2990
1751	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding	2991	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
1752	C<ev_TYPE_again> function.	2992	C<ev_TYPE_again> function.
1753		2993
1754	=item w->sweep () C<ev::embed> only	2994	=item w->sweep () (C<ev::embed> only)
1755		2995
1756	Invokes C<ev_embed_sweep>.	2996	Invokes C<ev_embed_sweep>.
1757		2997
1758	=item w->update () C<ev::stat> only	2998	=item w->update () (C<ev::stat> only)
1759		2999
1760	Invokes C<ev_stat_stat>.	3000	Invokes C<ev_stat_stat>.
1761		3001
1762	=back	3002	=back
1763		3003
1764	=back	3004	=back
1765		3005
1766	Example: Define a class with an IO and idle watcher, start one of them in	3006	Example: Define a class with an IO and idle watcher, start one of them in
1767	the constructor.	3007	the constructor.
1768		3008
1769	class myclass	3009	class myclass
1770	{	3010	{
1771	ev_io io; void io_cb (ev::io &w, int revents);	3011	ev::io io ; void io_cb (ev::io &w, int revents);
1772	ev_idle idle void idle_cb (ev::idle &w, int revents);	3012	ev::idle idle; void idle_cb (ev::idle &w, int revents);
1773		3013
1774	myclass ();	3014	myclass (int fd)
1775	}	3015	{
		3016	io .set <myclass, &myclass::io_cb > (this);
		3017	idle.set <myclass, &myclass::idle_cb> (this);
1776		3018
1777	myclass::myclass (int fd)
1778	: io (this, &myclass::io_cb),
1779	idle (this, &myclass::idle_cb)
1780	{
1781	io.start (fd, ev::READ);	3019	io.start (fd, ev::READ);
		3020	}
1782	}	3021	};
		3022
		3023
		3024	=head1 OTHER LANGUAGE BINDINGS
		3025
		3026	Libev does not offer other language bindings itself, but bindings for a
		3027	number of languages exist in the form of third-party packages. If you know
		3028	any interesting language binding in addition to the ones listed here, drop
		3029	me a note.
		3030
		3031	=over 4
		3032
		3033	=item Perl
		3034
		3035	The EV module implements the full libev API and is actually used to test
		3036	libev. EV is developed together with libev. Apart from the EV core module,
		3037	there are additional modules that implement libev-compatible interfaces
		3038	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3039	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3040	and C<EV::Glib>).
		3041
		3042	It can be found and installed via CPAN, its homepage is at
		3043	L<http://software.schmorp.de/pkg/EV>.
		3044
		3045	=item Python
		3046
		3047	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3048	seems to be quite complete and well-documented.
		3049
		3050	=item Ruby
		3051
		3052	Tony Arcieri has written a ruby extension that offers access to a subset
		3053	of the libev API and adds file handle abstractions, asynchronous DNS and
		3054	more on top of it. It can be found via gem servers. Its homepage is at
		3055	L<http://rev.rubyforge.org/>.
		3056
		3057	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3058	makes rev work even on mingw.
		3059
		3060	=item Haskell
		3061
		3062	A haskell binding to libev is available at
		3063	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3064
		3065	=item D
		3066
		3067	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3068	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3069
		3070	=item Ocaml
		3071
		3072	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3073	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3074
		3075	=back
1783		3076
1784		3077
1785	=head1 MACRO MAGIC	3078	=head1 MACRO MAGIC
1786		3079
1787	Libev can be compiled with a variety of options, the most fundemantal is	3080	Libev can be compiled with a variety of options, the most fundamental
1788	C<EV_MULTIPLICITY>. This option determines wether (most) functions and	3081	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
1789	callbacks have an initial C<struct ev_loop *> argument.	3082	functions and callbacks have an initial C<struct ev_loop *> argument.
1790		3083
1791	To make it easier to write programs that cope with either variant, the	3084	To make it easier to write programs that cope with either variant, the
1792	following macros are defined:	3085	following macros are defined:
1793		3086
1794	=over 4	3087	=over 4
…		…
1797		3090
1798	This provides the loop I<argument> for functions, if one is required ("ev	3091	This provides the loop I<argument> for functions, if one is required ("ev
1799	loop argument"). The C<EV_A> form is used when this is the sole argument,	3092	loop argument"). The C<EV_A> form is used when this is the sole argument,
1800	C<EV_A_> is used when other arguments are following. Example:	3093	C<EV_A_> is used when other arguments are following. Example:
1801		3094
1802	ev_unref (EV_A);	3095	ev_unref (EV_A);
1803	ev_timer_add (EV_A_ watcher);	3096	ev_timer_add (EV_A_ watcher);
1804	ev_loop (EV_A_ 0);	3097	ev_loop (EV_A_ 0);
1805		3098
1806	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	3099	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
1807	which is often provided by the following macro.	3100	which is often provided by the following macro.
1808		3101
1809	=item C<EV_P>, C<EV_P_>	3102	=item C<EV_P>, C<EV_P_>
1810		3103
1811	This provides the loop I<parameter> for functions, if one is required ("ev	3104	This provides the loop I<parameter> for functions, if one is required ("ev
1812	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	3105	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
1813	C<EV_P_> is used when other parameters are following. Example:	3106	C<EV_P_> is used when other parameters are following. Example:
1814		3107
1815	// this is how ev_unref is being declared	3108	// this is how ev_unref is being declared
1816	static void ev_unref (EV_P);	3109	static void ev_unref (EV_P);
1817		3110
1818	// this is how you can declare your typical callback	3111	// this is how you can declare your typical callback
1819	static void cb (EV_P_ ev_timer *w, int revents)	3112	static void cb (EV_P_ ev_timer *w, int revents)
1820		3113
1821	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	3114	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
1822	suitable for use with C<EV_A>.	3115	suitable for use with C<EV_A>.
1823		3116
1824	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3117	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
1825		3118
1826	Similar to the other two macros, this gives you the value of the default	3119	Similar to the other two macros, this gives you the value of the default
1827	loop, if multiple loops are supported ("ev loop default").	3120	loop, if multiple loops are supported ("ev loop default").
1828		3121
		3122	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3123
		3124	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3125	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3126	is undefined when the default loop has not been initialised by a previous
		3127	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3128
		3129	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3130	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		3131
1829	=back	3132	=back
1830		3133
1831	Example: Declare and initialise a check watcher, working regardless of	3134	Example: Declare and initialise a check watcher, utilising the above
1832	wether multiple loops are supported or not.	3135	macros so it will work regardless of whether multiple loops are supported
		3136	or not.
1833		3137
1834	static void	3138	static void
1835	check_cb (EV_P_ ev_timer *w, int revents)	3139	check_cb (EV_P_ ev_timer *w, int revents)
1836	{	3140	{
1837	ev_check_stop (EV_A_ w);	3141	ev_check_stop (EV_A_ w);
1838	}	3142	}
1839		3143
1840	ev_check check;	3144	ev_check check;
1841	ev_check_init (&check, check_cb);	3145	ev_check_init (&check, check_cb);
1842	ev_check_start (EV_DEFAULT_ &check);	3146	ev_check_start (EV_DEFAULT_ &check);
1843	ev_loop (EV_DEFAULT_ 0);	3147	ev_loop (EV_DEFAULT_ 0);
1844
1845		3148
1846	=head1 EMBEDDING	3149	=head1 EMBEDDING
1847		3150
1848	Libev can (and often is) directly embedded into host	3151	Libev can (and often is) directly embedded into host
1849	applications. Examples of applications that embed it include the Deliantra	3152	applications. Examples of applications that embed it include the Deliantra
1850	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)	3153	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
1851	and rxvt-unicode.	3154	and rxvt-unicode.
1852		3155
1853	The goal is to enable you to just copy the neecssary files into your	3156	The goal is to enable you to just copy the necessary files into your
1854	source directory without having to change even a single line in them, so	3157	source directory without having to change even a single line in them, so
1855	you can easily upgrade by simply copying (or having a checked-out copy of	3158	you can easily upgrade by simply copying (or having a checked-out copy of
1856	libev somewhere in your source tree).	3159	libev somewhere in your source tree).
1857		3160
1858	=head2 FILESETS	3161	=head2 FILESETS
1859		3162
1860	Depending on what features you need you need to include one or more sets of files	3163	Depending on what features you need you need to include one or more sets of files
1861	in your app.	3164	in your application.
1862		3165
1863	=head3 CORE EVENT LOOP	3166	=head3 CORE EVENT LOOP
1864		3167
1865	To include only the libev core (all the C<ev_*> functions), with manual	3168	To include only the libev core (all the C<ev_*> functions), with manual
1866	configuration (no autoconf):	3169	configuration (no autoconf):
1867		3170
1868	#define EV_STANDALONE 1	3171	#define EV_STANDALONE 1
1869	#include "ev.c"	3172	#include "ev.c"
1870		3173
1871	This will automatically include F<ev.h>, too, and should be done in a	3174	This will automatically include F<ev.h>, too, and should be done in a
1872	single C source file only to provide the function implementations. To use	3175	single C source file only to provide the function implementations. To use
1873	it, do the same for F<ev.h> in all files wishing to use this API (best	3176	it, do the same for F<ev.h> in all files wishing to use this API (best
1874	done by writing a wrapper around F<ev.h> that you can include instead and	3177	done by writing a wrapper around F<ev.h> that you can include instead and
1875	where you can put other configuration options):	3178	where you can put other configuration options):
1876		3179
1877	#define EV_STANDALONE 1	3180	#define EV_STANDALONE 1
1878	#include "ev.h"	3181	#include "ev.h"
1879		3182
1880	Both header files and implementation files can be compiled with a C++	3183	Both header files and implementation files can be compiled with a C++
1881	compiler (at least, thats a stated goal, and breakage will be treated	3184	compiler (at least, that's a stated goal, and breakage will be treated
1882	as a bug).	3185	as a bug).
1883		3186
1884	You need the following files in your source tree, or in a directory	3187	You need the following files in your source tree, or in a directory
1885	in your include path (e.g. in libev/ when using -Ilibev):	3188	in your include path (e.g. in libev/ when using -Ilibev):
1886		3189
1887	ev.h	3190	ev.h
1888	ev.c	3191	ev.c
1889	ev_vars.h	3192	ev_vars.h
1890	ev_wrap.h	3193	ev_wrap.h
1891		3194
1892	ev_win32.c required on win32 platforms only	3195	ev_win32.c required on win32 platforms only
1893		3196
1894	ev_select.c only when select backend is enabled (which is by default)	3197	ev_select.c only when select backend is enabled (which is enabled by default)
1895	ev_poll.c only when poll backend is enabled (disabled by default)	3198	ev_poll.c only when poll backend is enabled (disabled by default)
1896	ev_epoll.c only when the epoll backend is enabled (disabled by default)	3199	ev_epoll.c only when the epoll backend is enabled (disabled by default)
1897	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	3200	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
1898	ev_port.c only when the solaris port backend is enabled (disabled by default)	3201	ev_port.c only when the solaris port backend is enabled (disabled by default)
1899		3202
1900	F<ev.c> includes the backend files directly when enabled, so you only need	3203	F<ev.c> includes the backend files directly when enabled, so you only need
1901	to compile this single file.	3204	to compile this single file.
1902		3205
1903	=head3 LIBEVENT COMPATIBILITY API	3206	=head3 LIBEVENT COMPATIBILITY API
1904		3207
1905	To include the libevent compatibility API, also include:	3208	To include the libevent compatibility API, also include:
1906		3209
1907	#include "event.c"	3210	#include "event.c"
1908		3211
1909	in the file including F<ev.c>, and:	3212	in the file including F<ev.c>, and:
1910		3213
1911	#include "event.h"	3214	#include "event.h"
1912		3215
1913	in the files that want to use the libevent API. This also includes F<ev.h>.	3216	in the files that want to use the libevent API. This also includes F<ev.h>.
1914		3217
1915	You need the following additional files for this:	3218	You need the following additional files for this:
1916		3219
1917	event.h	3220	event.h
1918	event.c	3221	event.c
1919		3222
1920	=head3 AUTOCONF SUPPORT	3223	=head3 AUTOCONF SUPPORT
1921		3224
1922	Instead of using C<EV_STANDALONE=1> and providing your config in	3225	Instead of using C<EV_STANDALONE=1> and providing your configuration in
1923	whatever way you want, you can also C<m4_include([libev.m4])> in your	3226	whatever way you want, you can also C<m4_include([libev.m4])> in your
1924	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	3227	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
1925	include F<config.h> and configure itself accordingly.	3228	include F<config.h> and configure itself accordingly.
1926		3229
1927	For this of course you need the m4 file:	3230	For this of course you need the m4 file:
1928		3231
1929	libev.m4	3232	libev.m4
1930		3233
1931	=head2 PREPROCESSOR SYMBOLS/MACROS	3234	=head2 PREPROCESSOR SYMBOLS/MACROS
1932		3235
1933	Libev can be configured via a variety of preprocessor symbols you have to define	3236	Libev can be configured via a variety of preprocessor symbols you have to
1934	before including any of its files. The default is not to build for multiplicity	3237	define before including any of its files. The default in the absence of
1935	and only include the select backend.	3238	autoconf is documented for every option.
1936		3239
1937	=over 4	3240	=over 4
1938		3241
1939	=item EV_STANDALONE	3242	=item EV_STANDALONE
1940		3243
…		…
1942	keeps libev from including F<config.h>, and it also defines dummy	3245	keeps libev from including F<config.h>, and it also defines dummy
1943	implementations for some libevent functions (such as logging, which is not	3246	implementations for some libevent functions (such as logging, which is not
1944	supported). It will also not define any of the structs usually found in	3247	supported). It will also not define any of the structs usually found in
1945	F<event.h> that are not directly supported by the libev core alone.	3248	F<event.h> that are not directly supported by the libev core alone.
1946		3249
		3250	In stanbdalone mode, libev will still try to automatically deduce the
		3251	configuration, but has to be more conservative.
		3252
1947	=item EV_USE_MONOTONIC	3253	=item EV_USE_MONOTONIC
1948		3254
1949	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
1950	monotonic clock option at both compiletime and runtime. Otherwise no use	3256	monotonic clock option at both compile time and runtime. Otherwise no
1951	of the monotonic clock option will be attempted. If you enable this, you	3257	use of the monotonic clock option will be attempted. If you enable this,
1952	usually have to link against librt or something similar. Enabling it when	3258	you usually have to link against librt or something similar. Enabling it
1953	the functionality isn't available is safe, though, althoguh you have	3259	when the functionality isn't available is safe, though, although you have
1954	to make sure you link against any libraries where the C<clock_gettime>	3260	to make sure you link against any libraries where the C<clock_gettime>
1955	function is hiding in (often F<-lrt>).	3261	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
1956		3262
1957	=item EV_USE_REALTIME	3263	=item EV_USE_REALTIME
1958		3264
1959	If defined to be C<1>, libev will try to detect the availability of the	3265	If defined to be C<1>, libev will try to detect the availability of the
1960	realtime clock option at compiletime (and assume its availability at	3266	real-time clock option at compile time (and assume its availability
1961	runtime if successful). Otherwise no use of the realtime clock option will	3267	at runtime if successful). Otherwise no use of the real-time clock
1962	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3268	option will be attempted. This effectively replaces C<gettimeofday>
1963	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See tzhe note about libraries	3269	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
1964	in the description of C<EV_USE_MONOTONIC>, though.	3270	correctness. See the note about libraries in the description of
		3271	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3272	C<EV_USE_CLOCK_SYSCALL>.
		3273
		3274	=item EV_USE_CLOCK_SYSCALL
		3275
		3276	If defined to be C<1>, libev will try to use a direct syscall instead
		3277	of calling the system-provided C<clock_gettime> function. This option
		3278	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3279	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3280	programs needlessly. Using a direct syscall is slightly slower (in
		3281	theory), because no optimised vdso implementation can be used, but avoids
		3282	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3283	higher, as it simplifies linking (no need for C<-lrt>).
		3284
		3285	=item EV_USE_NANOSLEEP
		3286
		3287	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		3288	and will use it for delays. Otherwise it will use C<select ()>.
		3289
		3290	=item EV_USE_EVENTFD
		3291
		3292	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3293	available and will probe for kernel support at runtime. This will improve
		3294	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3295	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3296	2.7 or newer, otherwise disabled.
1965		3297
1966	=item EV_USE_SELECT	3298	=item EV_USE_SELECT
1967		3299
1968	If undefined or defined to be C<1>, libev will compile in support for the	3300	If undefined or defined to be C<1>, libev will compile in support for the
1969	C<select>(2) backend. No attempt at autodetection will be done: if no	3301	C<select>(2) backend. No attempt at auto-detection will be done: if no
1970	other method takes over, select will be it. Otherwise the select backend	3302	other method takes over, select will be it. Otherwise the select backend
1971	will not be compiled in.	3303	will not be compiled in.
1972		3304
1973	=item EV_SELECT_USE_FD_SET	3305	=item EV_SELECT_USE_FD_SET
1974		3306
1975	If defined to C<1>, then the select backend will use the system C<fd_set>	3307	If defined to C<1>, then the select backend will use the system C<fd_set>
1976	structure. This is useful if libev doesn't compile due to a missing	3308	structure. This is useful if libev doesn't compile due to a missing
1977	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	3309	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
1978	exotic systems. This usually limits the range of file descriptors to some	3310	on exotic systems. This usually limits the range of file descriptors to
1979	low limit such as 1024 or might have other limitations (winsocket only	3311	some low limit such as 1024 or might have other limitations (winsocket
1980	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3312	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
1981	influence the size of the C<fd_set> used.	3313	configures the maximum size of the C<fd_set>.
1982		3314
1983	=item EV_SELECT_IS_WINSOCKET	3315	=item EV_SELECT_IS_WINSOCKET
1984		3316
1985	When defined to C<1>, the select backend will assume that	3317	When defined to C<1>, the select backend will assume that
1986	select/socket/connect etc. don't understand file descriptors but	3318	select/socket/connect etc. don't understand file descriptors but
…		…
1988	be used is the winsock select). This means that it will call	3320	be used is the winsock select). This means that it will call
1989	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3321	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
1990	it is assumed that all these functions actually work on fds, even	3322	it is assumed that all these functions actually work on fds, even
1991	on win32. Should not be defined on non-win32 platforms.	3323	on win32. Should not be defined on non-win32 platforms.
1992		3324
		3325	=item EV_FD_TO_WIN32_HANDLE
		3326
		3327	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3328	file descriptors to socket handles. When not defining this symbol (the
		3329	default), then libev will call C<_get_osfhandle>, which is usually
		3330	correct. In some cases, programs use their own file descriptor management,
		3331	in which case they can provide this function to map fds to socket handles.
		3332
1993	=item EV_USE_POLL	3333	=item EV_USE_POLL
1994		3334
1995	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3335	If defined to be C<1>, libev will compile in support for the C<poll>(2)
1996	backend. Otherwise it will be enabled on non-win32 platforms. It	3336	backend. Otherwise it will be enabled on non-win32 platforms. It
1997	takes precedence over select.	3337	takes precedence over select.
1998		3338
1999	=item EV_USE_EPOLL	3339	=item EV_USE_EPOLL
2000		3340
2001	If defined to be C<1>, libev will compile in support for the Linux	3341	If defined to be C<1>, libev will compile in support for the Linux
2002	C<epoll>(7) backend. Its availability will be detected at runtime,	3342	C<epoll>(7) backend. Its availability will be detected at runtime,
2003	otherwise another method will be used as fallback. This is the	3343	otherwise another method will be used as fallback. This is the preferred
2004	preferred backend for GNU/Linux systems.	3344	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3345	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2005		3346
2006	=item EV_USE_KQUEUE	3347	=item EV_USE_KQUEUE
2007		3348
2008	If defined to be C<1>, libev will compile in support for the BSD style	3349	If defined to be C<1>, libev will compile in support for the BSD style
2009	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	3350	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2022	otherwise another method will be used as fallback. This is the preferred	3363	otherwise another method will be used as fallback. This is the preferred
2023	backend for Solaris 10 systems.	3364	backend for Solaris 10 systems.
2024		3365
2025	=item EV_USE_DEVPOLL	3366	=item EV_USE_DEVPOLL
2026		3367
2027	reserved for future expansion, works like the USE symbols above.	3368	Reserved for future expansion, works like the USE symbols above.
2028		3369
2029	=item EV_USE_INOTIFY	3370	=item EV_USE_INOTIFY
2030		3371
2031	If defined to be C<1>, libev will compile in support for the Linux inotify	3372	If defined to be C<1>, libev will compile in support for the Linux inotify
2032	interface to speed up C<ev_stat> watchers. Its actual availability will	3373	interface to speed up C<ev_stat> watchers. Its actual availability will
2033	be detected at runtime.	3374	be detected at runtime. If undefined, it will be enabled if the headers
		3375	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3376
		3377	=item EV_ATOMIC_T
		3378
		3379	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3380	access is atomic with respect to other threads or signal contexts. No such
		3381	type is easily found in the C language, so you can provide your own type
		3382	that you know is safe for your purposes. It is used both for signal handler "locking"
		3383	as well as for signal and thread safety in C<ev_async> watchers.
		3384
		3385	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3386	(from F<signal.h>), which is usually good enough on most platforms.
2034		3387
2035	=item EV_H	3388	=item EV_H
2036		3389
2037	The name of the F<ev.h> header file used to include it. The default if	3390	The name of the F<ev.h> header file used to include it. The default if
2038	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This	3391	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2039	can be used to virtually rename the F<ev.h> header file in case of conflicts.	3392	used to virtually rename the F<ev.h> header file in case of conflicts.
2040		3393
2041	=item EV_CONFIG_H	3394	=item EV_CONFIG_H
2042		3395
2043	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	3396	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2044	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	3397	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2045	C<EV_H>, above.	3398	C<EV_H>, above.
2046		3399
2047	=item EV_EVENT_H	3400	=item EV_EVENT_H
2048		3401
2049	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	3402	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2050	of how the F<event.h> header can be found.	3403	of how the F<event.h> header can be found, the default is C<"event.h">.
2051		3404
2052	=item EV_PROTOTYPES	3405	=item EV_PROTOTYPES
2053		3406
2054	If defined to be C<0>, then F<ev.h> will not define any function	3407	If defined to be C<0>, then F<ev.h> will not define any function
2055	prototypes, but still define all the structs and other symbols. This is	3408	prototypes, but still define all the structs and other symbols. This is
…		…
2062	will have the C<struct ev_loop *> as first argument, and you can create	3415	will have the C<struct ev_loop *> as first argument, and you can create
2063	additional independent event loops. Otherwise there will be no support	3416	additional independent event loops. Otherwise there will be no support
2064	for multiple event loops and there is no first event loop pointer	3417	for multiple event loops and there is no first event loop pointer
2065	argument. Instead, all functions act on the single default loop.	3418	argument. Instead, all functions act on the single default loop.
2066		3419
		3420	=item EV_MINPRI
		3421
		3422	=item EV_MAXPRI
		3423
		3424	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		3425	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		3426	provide for more priorities by overriding those symbols (usually defined
		3427	to be C<-2> and C<2>, respectively).
		3428
		3429	When doing priority-based operations, libev usually has to linearly search
		3430	all the priorities, so having many of them (hundreds) uses a lot of space
		3431	and time, so using the defaults of five priorities (-2 .. +2) is usually
		3432	fine.
		3433
		3434	If your embedding application does not need any priorities, defining these
		3435	both to C<0> will save some memory and CPU.
		3436
2067	=item EV_PERIODIC_ENABLE	3437	=item EV_PERIODIC_ENABLE
2068		3438
2069	If undefined or defined to be C<1>, then periodic timers are supported. If	3439	If undefined or defined to be C<1>, then periodic timers are supported. If
2070	defined to be C<0>, then they are not. Disabling them saves a few kB of	3440	defined to be C<0>, then they are not. Disabling them saves a few kB of
2071	code.	3441	code.
2072		3442
		3443	=item EV_IDLE_ENABLE
		3444
		3445	If undefined or defined to be C<1>, then idle watchers are supported. If
		3446	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3447	code.
		3448
2073	=item EV_EMBED_ENABLE	3449	=item EV_EMBED_ENABLE
2074		3450
2075	If undefined or defined to be C<1>, then embed watchers are supported. If	3451	If undefined or defined to be C<1>, then embed watchers are supported. If
2076	defined to be C<0>, then they are not.	3452	defined to be C<0>, then they are not. Embed watchers rely on most other
		3453	watcher types, which therefore must not be disabled.
2077		3454
2078	=item EV_STAT_ENABLE	3455	=item EV_STAT_ENABLE
2079		3456
2080	If undefined or defined to be C<1>, then stat watchers are supported. If	3457	If undefined or defined to be C<1>, then stat watchers are supported. If
2081	defined to be C<0>, then they are not.	3458	defined to be C<0>, then they are not.
…		…
2083	=item EV_FORK_ENABLE	3460	=item EV_FORK_ENABLE
2084		3461
2085	If undefined or defined to be C<1>, then fork watchers are supported. If	3462	If undefined or defined to be C<1>, then fork watchers are supported. If
2086	defined to be C<0>, then they are not.	3463	defined to be C<0>, then they are not.
2087		3464
		3465	=item EV_ASYNC_ENABLE
		3466
		3467	If undefined or defined to be C<1>, then async watchers are supported. If
		3468	defined to be C<0>, then they are not.
		3469
2088	=item EV_MINIMAL	3470	=item EV_MINIMAL
2089		3471
2090	If you need to shave off some kilobytes of code at the expense of some	3472	If you need to shave off some kilobytes of code at the expense of some
2091	speed, define this symbol to C<1>. Currently only used for gcc to override	3473	speed, define this symbol to C<1>. Currently this is used to override some
2092	some inlining decisions, saves roughly 30% codesize of amd64.	3474	inlining decisions, saves roughly 30% code size on amd64. It also selects a
		3475	much smaller 2-heap for timer management over the default 4-heap.
2093		3476
2094	=item EV_PID_HASHSIZE	3477	=item EV_PID_HASHSIZE
2095		3478
2096	C<ev_child> watchers use a small hash table to distribute workload by	3479	C<ev_child> watchers use a small hash table to distribute workload by
2097	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3480	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
2098	than enough. If you need to manage thousands of children you might want to	3481	than enough. If you need to manage thousands of children you might want to
2099	increase this value (I<must> be a power of two).	3482	increase this value (I<must> be a power of two).
2100		3483
2101	=item EV_INOTIFY_HASHSIZE	3484	=item EV_INOTIFY_HASHSIZE
2102		3485
2103	C<ev_staz> watchers use a small hash table to distribute workload by	3486	C<ev_stat> watchers use a small hash table to distribute workload by
2104	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	3487	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
2105	usually more than enough. If you need to manage thousands of C<ev_stat>	3488	usually more than enough. If you need to manage thousands of C<ev_stat>
2106	watchers you might want to increase this value (I<must> be a power of	3489	watchers you might want to increase this value (I<must> be a power of
2107	two).	3490	two).
2108		3491
		3492	=item EV_USE_4HEAP
		3493
		3494	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3495	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		3496	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		3497	faster performance with many (thousands) of watchers.
		3498
		3499	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3500	(disabled).
		3501
		3502	=item EV_HEAP_CACHE_AT
		3503
		3504	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3505	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		3506	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3507	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3508	but avoids random read accesses on heap changes. This improves performance
		3509	noticeably with many (hundreds) of watchers.
		3510
		3511	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3512	(disabled).
		3513
		3514	=item EV_VERIFY
		3515
		3516	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3517	be done: If set to C<0>, no internal verification code will be compiled
		3518	in. If set to C<1>, then verification code will be compiled in, but not
		3519	called. If set to C<2>, then the internal verification code will be
		3520	called once per loop, which can slow down libev. If set to C<3>, then the
		3521	verification code will be called very frequently, which will slow down
		3522	libev considerably.
		3523
		3524	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3525	C<0>.
		3526
2109	=item EV_COMMON	3527	=item EV_COMMON
2110		3528
2111	By default, all watchers have a C<void *data> member. By redefining	3529	By default, all watchers have a C<void *data> member. By redefining
2112	this macro to a something else you can include more and other types of	3530	this macro to a something else you can include more and other types of
2113	members. You have to define it each time you include one of the files,	3531	members. You have to define it each time you include one of the files,
2114	though, and it must be identical each time.	3532	though, and it must be identical each time.
2115		3533
2116	For example, the perl EV module uses something like this:	3534	For example, the perl EV module uses something like this:
2117		3535
2118	#define EV_COMMON \	3536	#define EV_COMMON \
2119	SV *self; /* contains this struct */ \	3537	SV *self; /* contains this struct */ \
2120	SV *cb_sv, *fh /* note no trailing ";" */	3538	SV *cb_sv, *fh /* note no trailing ";" */
2121		3539
2122	=item EV_CB_DECLARE (type)	3540	=item EV_CB_DECLARE (type)
2123		3541
2124	=item EV_CB_INVOKE (watcher, revents)	3542	=item EV_CB_INVOKE (watcher, revents)
2125		3543
2126	=item ev_set_cb (ev, cb)	3544	=item ev_set_cb (ev, cb)
2127		3545
2128	Can be used to change the callback member declaration in each watcher,	3546	Can be used to change the callback member declaration in each watcher,
2129	and the way callbacks are invoked and set. Must expand to a struct member	3547	and the way callbacks are invoked and set. Must expand to a struct member
2130	definition and a statement, respectively. See the F<ev.v> header file for	3548	definition and a statement, respectively. See the F<ev.h> header file for
2131	their default definitions. One possible use for overriding these is to	3549	their default definitions. One possible use for overriding these is to
2132	avoid the C<struct ev_loop *> as first argument in all cases, or to use	3550	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2133	method calls instead of plain function calls in C++.	3551	method calls instead of plain function calls in C++.
		3552
		3553	=back
		3554
		3555	=head2 EXPORTED API SYMBOLS
		3556
		3557	If you need to re-export the API (e.g. via a DLL) and you need a list of
		3558	exported symbols, you can use the provided F<Symbol.*> files which list
		3559	all public symbols, one per line:
		3560
		3561	Symbols.ev for libev proper
		3562	Symbols.event for the libevent emulation
		3563
		3564	This can also be used to rename all public symbols to avoid clashes with
		3565	multiple versions of libev linked together (which is obviously bad in
		3566	itself, but sometimes it is inconvenient to avoid this).
		3567
		3568	A sed command like this will create wrapper C<#define>'s that you need to
		3569	include before including F<ev.h>:
		3570
		3571	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		3572
		3573	This would create a file F<wrap.h> which essentially looks like this:
		3574
		3575	#define ev_backend myprefix_ev_backend
		3576	#define ev_check_start myprefix_ev_check_start
		3577	#define ev_check_stop myprefix_ev_check_stop
		3578	...
2134		3579
2135	=head2 EXAMPLES	3580	=head2 EXAMPLES
2136		3581
2137	For a real-world example of a program the includes libev	3582	For a real-world example of a program the includes libev
2138	verbatim, you can have a look at the EV perl module	3583	verbatim, you can have a look at the EV perl module
…		…
2141	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file	3586	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
2142	will be compiled. It is pretty complex because it provides its own header	3587	will be compiled. It is pretty complex because it provides its own header
2143	file.	3588	file.
2144		3589
2145	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	3590	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2146	that everybody includes and which overrides some autoconf choices:	3591	that everybody includes and which overrides some configure choices:
2147		3592
		3593	#define EV_MINIMAL 1
2148	#define EV_USE_POLL 0	3594	#define EV_USE_POLL 0
2149	#define EV_MULTIPLICITY 0	3595	#define EV_MULTIPLICITY 0
2150	#define EV_PERIODICS 0	3596	#define EV_PERIODIC_ENABLE 0
		3597	#define EV_STAT_ENABLE 0
		3598	#define EV_FORK_ENABLE 0
2151	#define EV_CONFIG_H <config.h>	3599	#define EV_CONFIG_H <config.h>
		3600	#define EV_MINPRI 0
		3601	#define EV_MAXPRI 0
2152		3602
2153	#include "ev++.h"	3603	#include "ev++.h"
2154		3604
2155	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	3605	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2156		3606
2157	#include "ev_cpp.h"	3607	#include "ev_cpp.h"
2158	#include "ev.c"	3608	#include "ev.c"
2159		3609
		3610	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
2160		3611
		3612	=head2 THREADS AND COROUTINES
		3613
		3614	=head3 THREADS
		3615
		3616	All libev functions are reentrant and thread-safe unless explicitly
		3617	documented otherwise, but libev implements no locking itself. This means
		3618	that you can use as many loops as you want in parallel, as long as there
		3619	are no concurrent calls into any libev function with the same loop
		3620	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		3621	of course): libev guarantees that different event loops share no data
		3622	structures that need any locking.
		3623
		3624	Or to put it differently: calls with different loop parameters can be done
		3625	concurrently from multiple threads, calls with the same loop parameter
		3626	must be done serially (but can be done from different threads, as long as
		3627	only one thread ever is inside a call at any point in time, e.g. by using
		3628	a mutex per loop).
		3629
		3630	Specifically to support threads (and signal handlers), libev implements
		3631	so-called C<ev_async> watchers, which allow some limited form of
		3632	concurrency on the same event loop, namely waking it up "from the
		3633	outside".
		3634
		3635	If you want to know which design (one loop, locking, or multiple loops
		3636	without or something else still) is best for your problem, then I cannot
		3637	help you, but here is some generic advice:
		3638
		3639	=over 4
		3640
		3641	=item * most applications have a main thread: use the default libev loop
		3642	in that thread, or create a separate thread running only the default loop.
		3643
		3644	This helps integrating other libraries or software modules that use libev
		3645	themselves and don't care/know about threading.
		3646
		3647	=item * one loop per thread is usually a good model.
		3648
		3649	Doing this is almost never wrong, sometimes a better-performance model
		3650	exists, but it is always a good start.
		3651
		3652	=item * other models exist, such as the leader/follower pattern, where one
		3653	loop is handed through multiple threads in a kind of round-robin fashion.
		3654
		3655	Choosing a model is hard - look around, learn, know that usually you can do
		3656	better than you currently do :-)
		3657
		3658	=item * often you need to talk to some other thread which blocks in the
		3659	event loop.
		3660
		3661	C<ev_async> watchers can be used to wake them up from other threads safely
		3662	(or from signal contexts...).
		3663
		3664	An example use would be to communicate signals or other events that only
		3665	work in the default loop by registering the signal watcher with the
		3666	default loop and triggering an C<ev_async> watcher from the default loop
		3667	watcher callback into the event loop interested in the signal.
		3668
		3669	=back
		3670
		3671	=head3 COROUTINES
		3672
		3673	Libev is very accommodating to coroutines ("cooperative threads"):
		3674	libev fully supports nesting calls to its functions from different
		3675	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3676	different coroutines, and switch freely between both coroutines running the
		3677	loop, as long as you don't confuse yourself). The only exception is that
		3678	you must not do this from C<ev_periodic> reschedule callbacks.
		3679
		3680	Care has been taken to ensure that libev does not keep local state inside
		3681	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		3682	they do not call any callbacks.
		3683
		3684	=head2 COMPILER WARNINGS
		3685
		3686	Depending on your compiler and compiler settings, you might get no or a
		3687	lot of warnings when compiling libev code. Some people are apparently
		3688	scared by this.
		3689
		3690	However, these are unavoidable for many reasons. For one, each compiler
		3691	has different warnings, and each user has different tastes regarding
		3692	warning options. "Warn-free" code therefore cannot be a goal except when
		3693	targeting a specific compiler and compiler-version.
		3694
		3695	Another reason is that some compiler warnings require elaborate
		3696	workarounds, or other changes to the code that make it less clear and less
		3697	maintainable.
		3698
		3699	And of course, some compiler warnings are just plain stupid, or simply
		3700	wrong (because they don't actually warn about the condition their message
		3701	seems to warn about). For example, certain older gcc versions had some
		3702	warnings that resulted an extreme number of false positives. These have
		3703	been fixed, but some people still insist on making code warn-free with
		3704	such buggy versions.
		3705
		3706	While libev is written to generate as few warnings as possible,
		3707	"warn-free" code is not a goal, and it is recommended not to build libev
		3708	with any compiler warnings enabled unless you are prepared to cope with
		3709	them (e.g. by ignoring them). Remember that warnings are just that:
		3710	warnings, not errors, or proof of bugs.
		3711
		3712
		3713	=head2 VALGRIND
		3714
		3715	Valgrind has a special section here because it is a popular tool that is
		3716	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		3717
		3718	If you think you found a bug (memory leak, uninitialised data access etc.)
		3719	in libev, then check twice: If valgrind reports something like:
		3720
		3721	==2274== definitely lost: 0 bytes in 0 blocks.
		3722	==2274== possibly lost: 0 bytes in 0 blocks.
		3723	==2274== still reachable: 256 bytes in 1 blocks.
		3724
		3725	Then there is no memory leak, just as memory accounted to global variables
		3726	is not a memleak - the memory is still being referenced, and didn't leak.
		3727
		3728	Similarly, under some circumstances, valgrind might report kernel bugs
		3729	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		3730	although an acceptable workaround has been found here), or it might be
		3731	confused.
		3732
		3733	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		3734	make it into some kind of religion.
		3735
		3736	If you are unsure about something, feel free to contact the mailing list
		3737	with the full valgrind report and an explanation on why you think this
		3738	is a bug in libev (best check the archives, too :). However, don't be
		3739	annoyed when you get a brisk "this is no bug" answer and take the chance
		3740	of learning how to interpret valgrind properly.
		3741
		3742	If you need, for some reason, empty reports from valgrind for your project
		3743	I suggest using suppression lists.
		3744
		3745
		3746	=head1 PORTABILITY NOTES
		3747
		3748	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		3749
		3750	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		3751	requires, and its I/O model is fundamentally incompatible with the POSIX
		3752	model. Libev still offers limited functionality on this platform in
		3753	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		3754	descriptors. This only applies when using Win32 natively, not when using
		3755	e.g. cygwin.
		3756
		3757	Lifting these limitations would basically require the full
		3758	re-implementation of the I/O system. If you are into these kinds of
		3759	things, then note that glib does exactly that for you in a very portable
		3760	way (note also that glib is the slowest event library known to man).
		3761
		3762	There is no supported compilation method available on windows except
		3763	embedding it into other applications.
		3764
		3765	Not a libev limitation but worth mentioning: windows apparently doesn't
		3766	accept large writes: instead of resulting in a partial write, windows will
		3767	either accept everything or return C<ENOBUFS> if the buffer is too large,
		3768	so make sure you only write small amounts into your sockets (less than a
		3769	megabyte seems safe, but this apparently depends on the amount of memory
		3770	available).
		3771
		3772	Due to the many, low, and arbitrary limits on the win32 platform and
		3773	the abysmal performance of winsockets, using a large number of sockets
		3774	is not recommended (and not reasonable). If your program needs to use
		3775	more than a hundred or so sockets, then likely it needs to use a totally
		3776	different implementation for windows, as libev offers the POSIX readiness
		3777	notification model, which cannot be implemented efficiently on windows
		3778	(Microsoft monopoly games).
		3779
		3780	A typical way to use libev under windows is to embed it (see the embedding
		3781	section for details) and use the following F<evwrap.h> header file instead
		3782	of F<ev.h>:
		3783
		3784	#define EV_STANDALONE /* keeps ev from requiring config.h */
		3785	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		3786
		3787	#include "ev.h"
		3788
		3789	And compile the following F<evwrap.c> file into your project (make sure
		3790	you do I<not> compile the F<ev.c> or any other embedded source files!):
		3791
		3792	#include "evwrap.h"
		3793	#include "ev.c"
		3794
		3795	=over 4
		3796
		3797	=item The winsocket select function
		3798
		3799	The winsocket C<select> function doesn't follow POSIX in that it
		3800	requires socket I<handles> and not socket I<file descriptors> (it is
		3801	also extremely buggy). This makes select very inefficient, and also
		3802	requires a mapping from file descriptors to socket handles (the Microsoft
		3803	C runtime provides the function C<_open_osfhandle> for this). See the
		3804	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		3805	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		3806
		3807	The configuration for a "naked" win32 using the Microsoft runtime
		3808	libraries and raw winsocket select is:
		3809
		3810	#define EV_USE_SELECT 1
		3811	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		3812
		3813	Note that winsockets handling of fd sets is O(n), so you can easily get a
		3814	complexity in the O(n²) range when using win32.
		3815
		3816	=item Limited number of file descriptors
		3817
		3818	Windows has numerous arbitrary (and low) limits on things.
		3819
		3820	Early versions of winsocket's select only supported waiting for a maximum
		3821	of C<64> handles (probably owning to the fact that all windows kernels
		3822	can only wait for C<64> things at the same time internally; Microsoft
		3823	recommends spawning a chain of threads and wait for 63 handles and the
		3824	previous thread in each. Great).
		3825
		3826	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		3827	to some high number (e.g. C<2048>) before compiling the winsocket select
		3828	call (which might be in libev or elsewhere, for example, perl does its own
		3829	select emulation on windows).
		3830
		3831	Another limit is the number of file descriptors in the Microsoft runtime
		3832	libraries, which by default is C<64> (there must be a hidden I<64> fetish
		3833	or something like this inside Microsoft). You can increase this by calling
		3834	C<_setmaxstdio>, which can increase this limit to C<2048> (another
		3835	arbitrary limit), but is broken in many versions of the Microsoft runtime
		3836	libraries.
		3837
		3838	This might get you to about C<512> or C<2048> sockets (depending on
		3839	windows version and/or the phase of the moon). To get more, you need to
		3840	wrap all I/O functions and provide your own fd management, but the cost of
		3841	calling select (O(n²)) will likely make this unworkable.
		3842
		3843	=back
		3844
		3845	=head2 PORTABILITY REQUIREMENTS
		3846
		3847	In addition to a working ISO-C implementation and of course the
		3848	backend-specific APIs, libev relies on a few additional extensions:
		3849
		3850	=over 4
		3851
		3852	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		3853	calling conventions regardless of C<ev_watcher_type *>.
		3854
		3855	Libev assumes not only that all watcher pointers have the same internal
		3856	structure (guaranteed by POSIX but not by ISO C for example), but it also
		3857	assumes that the same (machine) code can be used to call any watcher
		3858	callback: The watcher callbacks have different type signatures, but libev
		3859	calls them using an C<ev_watcher *> internally.
		3860
		3861	=item C<sig_atomic_t volatile> must be thread-atomic as well
		3862
		3863	The type C<sig_atomic_t volatile> (or whatever is defined as
		3864	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		3865	threads. This is not part of the specification for C<sig_atomic_t>, but is
		3866	believed to be sufficiently portable.
		3867
		3868	=item C<sigprocmask> must work in a threaded environment
		3869
		3870	Libev uses C<sigprocmask> to temporarily block signals. This is not
		3871	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		3872	pthread implementations will either allow C<sigprocmask> in the "main
		3873	thread" or will block signals process-wide, both behaviours would
		3874	be compatible with libev. Interaction between C<sigprocmask> and
		3875	C<pthread_sigmask> could complicate things, however.
		3876
		3877	The most portable way to handle signals is to block signals in all threads
		3878	except the initial one, and run the default loop in the initial thread as
		3879	well.
		3880
		3881	=item C<long> must be large enough for common memory allocation sizes
		3882
		3883	To improve portability and simplify its API, libev uses C<long> internally
		3884	instead of C<size_t> when allocating its data structures. On non-POSIX
		3885	systems (Microsoft...) this might be unexpectedly low, but is still at
		3886	least 31 bits everywhere, which is enough for hundreds of millions of
		3887	watchers.
		3888
		3889	=item C<double> must hold a time value in seconds with enough accuracy
		3890
		3891	The type C<double> is used to represent timestamps. It is required to
		3892	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		3893	enough for at least into the year 4000. This requirement is fulfilled by
		3894	implementations implementing IEEE 754 (basically all existing ones).
		3895
		3896	=back
		3897
		3898	If you know of other additional requirements drop me a note.
		3899
		3900
2161	=head1 COMPLEXITIES	3901	=head1 ALGORITHMIC COMPLEXITIES
2162		3902
2163	In this section the complexities of (many of) the algorithms used inside	3903	In this section the complexities of (many of) the algorithms used inside
2164	libev will be explained. For complexity discussions about backends see the	3904	libev will be documented. For complexity discussions about backends see
2165	documentation for C<ev_default_init>.	3905	the documentation for C<ev_default_init>.
		3906
		3907	All of the following are about amortised time: If an array needs to be
		3908	extended, libev needs to realloc and move the whole array, but this
		3909	happens asymptotically rarer with higher number of elements, so O(1) might
		3910	mean that libev does a lengthy realloc operation in rare cases, but on
		3911	average it is much faster and asymptotically approaches constant time.
2166		3912
2167	=over 4	3913	=over 4
2168		3914
2169	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	3915	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2170		3916
		3917	This means that, when you have a watcher that triggers in one hour and
		3918	there are 100 watchers that would trigger before that, then inserting will
		3919	have to skip roughly seven (C<ld 100>) of these watchers.
		3920
2171	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	3921	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2172		3922
		3923	That means that changing a timer costs less than removing/adding them,
		3924	as only the relative motion in the event queue has to be paid for.
		3925
2173	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	3926	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
2174		3927
		3928	These just add the watcher into an array or at the head of a list.
		3929
2175	=item Stopping check/prepare/idle watchers: O(1)	3930	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2176		3931
2177	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	3932	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2178		3933
		3934	These watchers are stored in lists, so they need to be walked to find the
		3935	correct watcher to remove. The lists are usually short (you don't usually
		3936	have many watchers waiting for the same fd or signal: one is typical, two
		3937	is rare).
		3938
2179	=item Finding the next timer per loop iteration: O(1)	3939	=item Finding the next timer in each loop iteration: O(1)
		3940
		3941	By virtue of using a binary or 4-heap, the next timer is always found at a
		3942	fixed position in the storage array.
2180		3943
2181	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	3944	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2182		3945
2183	=item Activating one watcher: O(1)	3946	A change means an I/O watcher gets started or stopped, which requires
		3947	libev to recalculate its status (and possibly tell the kernel, depending
		3948	on backend and whether C<ev_io_set> was used).
		3949
		3950	=item Activating one watcher (putting it into the pending state): O(1)
		3951
		3952	=item Priority handling: O(number_of_priorities)
		3953
		3954	Priorities are implemented by allocating some space for each
		3955	priority. When doing priority-based operations, libev usually has to
		3956	linearly search all the priorities, but starting/stopping and activating
		3957	watchers becomes O(1) with respect to priority handling.
		3958
		3959	=item Sending an ev_async: O(1)
		3960
		3961	=item Processing ev_async_send: O(number_of_async_watchers)
		3962
		3963	=item Processing signals: O(max_signal_number)
		3964
		3965	Sending involves a system call I<iff> there were no other C<ev_async_send>
		3966	calls in the current loop iteration. Checking for async and signal events
		3967	involves iterating over all running async watchers or all signal numbers.
2184		3968
2185	=back	3969	=back
2186		3970
2187		3971
2188	=head1 AUTHOR	3972	=head1 AUTHOR
2189		3973
2190	Marc Lehmann <libev@schmorp.de>.	3974	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
2191		3975

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