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Revision 1.74 by root, Sat Dec 8 14:12:08 2007 UTC vs.
Revision 1.232 by root, Thu Apr 16 06:17:26 2009 UTC

…		…
2		2
3	libev - a high performance full-featured event loop written in C	3	libev - a high performance full-featured event loop written in C
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
8		8
9	=head1 EXAMPLE PROGRAM	9	=head2 EXAMPLE PROGRAM
10		10
		11	// a single header file is required
11	#include <ev.h>	12	#include <ev.h>
12		13
		14	#include <stdio.h> // for puts
		15
		16	// every watcher type has its own typedef'd struct
		17	// with the name ev_TYPE
13	ev_io stdin_watcher;	18	ev_io stdin_watcher;
14	ev_timer timeout_watcher;	19	ev_timer timeout_watcher;
15		20
16	/* called when data readable on stdin */	21	// all watcher callbacks have a similar signature
		22	// this callback is called when data is readable on stdin
17	static void	23	static void
18	stdin_cb (EV_P_ struct ev_io *w, int revents)	24	stdin_cb (EV_P_ ev_io *w, int revents)
19	{	25	{
20	/* puts ("stdin ready"); */	26	puts ("stdin ready");
21	ev_io_stop (EV_A_ w); /* just a syntax example */	27	// for one-shot events, one must manually stop the watcher
22	ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */	28	// with its corresponding stop function.
		29	ev_io_stop (EV_A_ w);
		30
		31	// this causes all nested ev_loop's to stop iterating
		32	ev_unloop (EV_A_ EVUNLOOP_ALL);
23	}	33	}
24		34
		35	// another callback, this time for a time-out
25	static void	36	static void
26	timeout_cb (EV_P_ struct ev_timer *w, int revents)	37	timeout_cb (EV_P_ ev_timer *w, int revents)
27	{	38	{
28	/* puts ("timeout"); */	39	puts ("timeout");
29	ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */	40	// this causes the innermost ev_loop to stop iterating
		41	ev_unloop (EV_A_ EVUNLOOP_ONE);
30	}	42	}
31		43
32	int	44	int
33	main (void)	45	main (void)
34	{	46	{
		47	// use the default event loop unless you have special needs
35	struct ev_loop *loop = ev_default_loop (0);	48	struct ev_loop *loop = ev_default_loop (0);
36		49
37	/* initialise an io watcher, then start it */	50	// initialise an io watcher, then start it
		51	// this one will watch for stdin to become readable
38	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);	52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
39	ev_io_start (loop, &stdin_watcher);	53	ev_io_start (loop, &stdin_watcher);
40		54
		55	// initialise a timer watcher, then start it
41	/* simple non-repeating 5.5 second timeout */	56	// simple non-repeating 5.5 second timeout
42	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);	57	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
43	ev_timer_start (loop, &timeout_watcher);	58	ev_timer_start (loop, &timeout_watcher);
44		59
45	/* loop till timeout or data ready */	60	// now wait for events to arrive
46	ev_loop (loop, 0);	61	ev_loop (loop, 0);
47		62
		63	// unloop was called, so exit
48	return 0;	64	return 0;
49	}	65	}
50		66
51	=head1 DESCRIPTION	67	=head1 DESCRIPTION
52		68
53	The newest version of this document is also available as a html-formatted	69	The newest version of this document is also available as an html-formatted
54	web page you might find easier to navigate when reading it for the first	70	web page you might find easier to navigate when reading it for the first
55	time: L<http://cvs.schmorp.de/libev/ev.html>.	71	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
56		72
57	Libev is an event loop: you register interest in certain events (such as a	73	Libev is an event loop: you register interest in certain events (such as a
58	file descriptor being readable or a timeout occuring), and it will manage	74	file descriptor being readable or a timeout occurring), and it will manage
59	these event sources and provide your program with events.	75	these event sources and provide your program with events.
60		76
61	To do this, it must take more or less complete control over your process	77	To do this, it must take more or less complete control over your process
62	(or thread) by executing the I<event loop> handler, and will then	78	(or thread) by executing the I<event loop> handler, and will then
63	communicate events via a callback mechanism.	79	communicate events via a callback mechanism.
…		…
65	You register interest in certain events by registering so-called I<event	81	You register interest in certain events by registering so-called I<event
66	watchers>, which are relatively small C structures you initialise with the	82	watchers>, which are relatively small C structures you initialise with the
67	details of the event, and then hand it over to libev by I<starting> the	83	details of the event, and then hand it over to libev by I<starting> the
68	watcher.	84	watcher.
69		85
70	=head1 FEATURES	86	=head2 FEATURES
71		87
72	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	88	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
73	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	89	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
74	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	90	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
75	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	91	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
…		…
82		98
83	It also is quite fast (see this	99	It also is quite fast (see this
84	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent	100	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
85	for example).	101	for example).
86		102
87	=head1 CONVENTIONS	103	=head2 CONVENTIONS
88		104
89	Libev is very configurable. In this manual the default configuration will	105	Libev is very configurable. In this manual the default (and most common)
90	be described, which supports multiple event loops. For more info about	106	configuration will be described, which supports multiple event loops. For
91	various configuration options please have a look at B<EMBED> section in	107	more info about various configuration options please have a look at
92	this manual. If libev was configured without support for multiple event	108	B<EMBED> section in this manual. If libev was configured without support
93	loops, then all functions taking an initial argument of name C<loop>	109	for multiple event loops, then all functions taking an initial argument of
94	(which is always of type C<struct ev_loop *>) will not have this argument.	110	name C<loop> (which is always of type C<ev_loop *>) will not have
		111	this argument.
95		112
96	=head1 TIME REPRESENTATION	113	=head2 TIME REPRESENTATION
97		114
98	Libev represents time as a single floating point number, representing the	115	Libev represents time as a single floating point number, representing the
99	(fractional) number of seconds since the (POSIX) epoch (somewhere near	116	(fractional) number of seconds since the (POSIX) epoch (somewhere near
100	the beginning of 1970, details are complicated, don't ask). This type is	117	the beginning of 1970, details are complicated, don't ask). This type is
101	called C<ev_tstamp>, which is what you should use too. It usually aliases	118	called C<ev_tstamp>, which is what you should use too. It usually aliases
102	to the C<double> type in C, and when you need to do any calculations on	119	to the C<double> type in C, and when you need to do any calculations on
103	it, you should treat it as such.	120	it, you should treat it as some floating point value. Unlike the name
		121	component C<stamp> might indicate, it is also used for time differences
		122	throughout libev.
		123
		124	=head1 ERROR HANDLING
		125
		126	Libev knows three classes of errors: operating system errors, usage errors
		127	and internal errors (bugs).
		128
		129	When libev catches an operating system error it cannot handle (for example
		130	a system call indicating a condition libev cannot fix), it calls the callback
		131	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		132	abort. The default is to print a diagnostic message and to call C<abort
		133	()>.
		134
		135	When libev detects a usage error such as a negative timer interval, then
		136	it will print a diagnostic message and abort (via the C<assert> mechanism,
		137	so C<NDEBUG> will disable this checking): these are programming errors in
		138	the libev caller and need to be fixed there.
		139
		140	Libev also has a few internal error-checking C<assert>ions, and also has
		141	extensive consistency checking code. These do not trigger under normal
		142	circumstances, as they indicate either a bug in libev or worse.
		143
104		144
105	=head1 GLOBAL FUNCTIONS	145	=head1 GLOBAL FUNCTIONS
106		146
107	These functions can be called anytime, even before initialising the	147	These functions can be called anytime, even before initialising the
108	library in any way.	148	library in any way.
…		…
113		153
114	Returns the current time as libev would use it. Please note that the	154	Returns the current time as libev would use it. Please note that the
115	C<ev_now> function is usually faster and also often returns the timestamp	155	C<ev_now> function is usually faster and also often returns the timestamp
116	you actually want to know.	156	you actually want to know.
117		157
		158	=item ev_sleep (ev_tstamp interval)
		159
		160	Sleep for the given interval: The current thread will be blocked until
		161	either it is interrupted or the given time interval has passed. Basically
		162	this is a sub-second-resolution C<sleep ()>.
		163
118	=item int ev_version_major ()	164	=item int ev_version_major ()
119		165
120	=item int ev_version_minor ()	166	=item int ev_version_minor ()
121		167
122	You can find out the major and minor version numbers of the library	168	You can find out the major and minor ABI version numbers of the library
123	you linked against by calling the functions C<ev_version_major> and	169	you linked against by calling the functions C<ev_version_major> and
124	C<ev_version_minor>. If you want, you can compare against the global	170	C<ev_version_minor>. If you want, you can compare against the global
125	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the	171	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
126	version of the library your program was compiled against.	172	version of the library your program was compiled against.
127		173
		174	These version numbers refer to the ABI version of the library, not the
		175	release version.
		176
128	Usually, it's a good idea to terminate if the major versions mismatch,	177	Usually, it's a good idea to terminate if the major versions mismatch,
129	as this indicates an incompatible change. Minor versions are usually	178	as this indicates an incompatible change. Minor versions are usually
130	compatible to older versions, so a larger minor version alone is usually	179	compatible to older versions, so a larger minor version alone is usually
131	not a problem.	180	not a problem.
132		181
133	Example: Make sure we haven't accidentally been linked against the wrong	182	Example: Make sure we haven't accidentally been linked against the wrong
134	version.	183	version.
135		184
136	assert (("libev version mismatch",	185	assert (("libev version mismatch",
137	ev_version_major () == EV_VERSION_MAJOR	186	ev_version_major () == EV_VERSION_MAJOR
138	&& ev_version_minor () >= EV_VERSION_MINOR));	187	&& ev_version_minor () >= EV_VERSION_MINOR));
139		188
140	=item unsigned int ev_supported_backends ()	189	=item unsigned int ev_supported_backends ()
141		190
142	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	191	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
143	value) compiled into this binary of libev (independent of their	192	value) compiled into this binary of libev (independent of their
…		…
145	a description of the set values.	194	a description of the set values.
146		195
147	Example: make sure we have the epoll method, because yeah this is cool and	196	Example: make sure we have the epoll method, because yeah this is cool and
148	a must have and can we have a torrent of it please!!!11	197	a must have and can we have a torrent of it please!!!11
149		198
150	assert (("sorry, no epoll, no sex",	199	assert (("sorry, no epoll, no sex",
151	ev_supported_backends () & EVBACKEND_EPOLL));	200	ev_supported_backends () & EVBACKEND_EPOLL));
152		201
153	=item unsigned int ev_recommended_backends ()	202	=item unsigned int ev_recommended_backends ()
154		203
155	Return the set of all backends compiled into this binary of libev and also	204	Return the set of all backends compiled into this binary of libev and also
156	recommended for this platform. This set is often smaller than the one	205	recommended for this platform. This set is often smaller than the one
157	returned by C<ev_supported_backends>, as for example kqueue is broken on	206	returned by C<ev_supported_backends>, as for example kqueue is broken on
158	most BSDs and will not be autodetected unless you explicitly request it	207	most BSDs and will not be auto-detected unless you explicitly request it
159	(assuming you know what you are doing). This is the set of backends that	208	(assuming you know what you are doing). This is the set of backends that
160	libev will probe for if you specify no backends explicitly.	209	libev will probe for if you specify no backends explicitly.
161		210
162	=item unsigned int ev_embeddable_backends ()	211	=item unsigned int ev_embeddable_backends ()
163		212
…		…
167	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	216	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
168	recommended ones.	217	recommended ones.
169		218
170	See the description of C<ev_embed> watchers for more info.	219	See the description of C<ev_embed> watchers for more info.
171		220
172	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	221	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
173		222
174	Sets the allocation function to use (the prototype is similar - the	223	Sets the allocation function to use (the prototype is similar - the
175	semantics is identical - to the realloc C function). It is used to	224	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
176	allocate and free memory (no surprises here). If it returns zero when	225	used to allocate and free memory (no surprises here). If it returns zero
177	memory needs to be allocated, the library might abort or take some	226	when memory needs to be allocated (C<size != 0>), the library might abort
178	potentially destructive action. The default is your system realloc	227	or take some potentially destructive action.
179	function.	228
		229	Since some systems (at least OpenBSD and Darwin) fail to implement
		230	correct C<realloc> semantics, libev will use a wrapper around the system
		231	C<realloc> and C<free> functions by default.
180		232
181	You could override this function in high-availability programs to, say,	233	You could override this function in high-availability programs to, say,
182	free some memory if it cannot allocate memory, to use a special allocator,	234	free some memory if it cannot allocate memory, to use a special allocator,
183	or even to sleep a while and retry until some memory is available.	235	or even to sleep a while and retry until some memory is available.
184		236
185	Example: Replace the libev allocator with one that waits a bit and then	237	Example: Replace the libev allocator with one that waits a bit and then
186	retries).	238	retries (example requires a standards-compliant C<realloc>).
187		239
188	static void *	240	static void *
189	persistent_realloc (void *ptr, size_t size)	241	persistent_realloc (void *ptr, size_t size)
190	{	242	{
191	for (;;)	243	for (;;)
…		…
200	}	252	}
201		253
202	...	254	...
203	ev_set_allocator (persistent_realloc);	255	ev_set_allocator (persistent_realloc);
204		256
205	=item ev_set_syserr_cb (void (*cb)(const char *msg));	257	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
206		258
207	Set the callback function to call on a retryable syscall error (such	259	Set the callback function to call on a retryable system call error (such
208	as failed select, poll, epoll_wait). The message is a printable string	260	as failed select, poll, epoll_wait). The message is a printable string
209	indicating the system call or subsystem causing the problem. If this	261	indicating the system call or subsystem causing the problem. If this
210	callback is set, then libev will expect it to remedy the sitution, no	262	callback is set, then libev will expect it to remedy the situation, no
211	matter what, when it returns. That is, libev will generally retry the	263	matter what, when it returns. That is, libev will generally retry the
212	requested operation, or, if the condition doesn't go away, do bad stuff	264	requested operation, or, if the condition doesn't go away, do bad stuff
213	(such as abort).	265	(such as abort).
214		266
215	Example: This is basically the same thing that libev does internally, too.	267	Example: This is basically the same thing that libev does internally, too.
…		…
226		278
227	=back	279	=back
228		280
229	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	281	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
230		282
231	An event loop is described by a C<struct ev_loop *>. The library knows two	283	An event loop is described by a C<struct ev_loop *> (the C<struct>
232	types of such loops, the I<default> loop, which supports signals and child	284	is I<not> optional in this case, as there is also an C<ev_loop>
233	events, and dynamically created loops which do not.	285	I<function>).
234		286
235	If you use threads, a common model is to run the default event loop	287	The library knows two types of such loops, the I<default> loop, which
236	in your main thread (or in a separate thread) and for each thread you	288	supports signals and child events, and dynamically created loops which do
237	create, you also create another event loop. Libev itself does no locking	289	not.
238	whatsoever, so if you mix calls to the same event loop in different
239	threads, make sure you lock (this is usually a bad idea, though, even if
240	done correctly, because it's hideous and inefficient).
241		290
242	=over 4	291	=over 4
243		292
244	=item struct ev_loop *ev_default_loop (unsigned int flags)	293	=item struct ev_loop *ev_default_loop (unsigned int flags)
245		294
…		…
249	flags. If that is troubling you, check C<ev_backend ()> afterwards).	298	flags. If that is troubling you, check C<ev_backend ()> afterwards).
250		299
251	If you don't know what event loop to use, use the one returned from this	300	If you don't know what event loop to use, use the one returned from this
252	function.	301	function.
253		302
		303	Note that this function is I<not> thread-safe, so if you want to use it
		304	from multiple threads, you have to lock (note also that this is unlikely,
		305	as loops cannot be shared easily between threads anyway).
		306
		307	The default loop is the only loop that can handle C<ev_signal> and
		308	C<ev_child> watchers, and to do this, it always registers a handler
		309	for C<SIGCHLD>. If this is a problem for your application you can either
		310	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
		311	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
		312	C<ev_default_init>.
		313
254	The flags argument can be used to specify special behaviour or specific	314	The flags argument can be used to specify special behaviour or specific
255	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	315	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
256		316
257	The following flags are supported:	317	The following flags are supported:
258		318
…		…
263	The default flags value. Use this if you have no clue (it's the right	323	The default flags value. Use this if you have no clue (it's the right
264	thing, believe me).	324	thing, believe me).
265		325
266	=item C<EVFLAG_NOENV>	326	=item C<EVFLAG_NOENV>
267		327
268	If this flag bit is ored into the flag value (or the program runs setuid	328	If this flag bit is or'ed into the flag value (or the program runs setuid
269	or setgid) then libev will I<not> look at the environment variable	329	or setgid) then libev will I<not> look at the environment variable
270	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	330	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
271	override the flags completely if it is found in the environment. This is	331	override the flags completely if it is found in the environment. This is
272	useful to try out specific backends to test their performance, or to work	332	useful to try out specific backends to test their performance, or to work
273	around bugs.	333	around bugs.
…		…
279	enabling this flag.	339	enabling this flag.
280		340
281	This works by calling C<getpid ()> on every iteration of the loop,	341	This works by calling C<getpid ()> on every iteration of the loop,
282	and thus this might slow down your event loop if you do a lot of loop	342	and thus this might slow down your event loop if you do a lot of loop
283	iterations and little real work, but is usually not noticeable (on my	343	iterations and little real work, but is usually not noticeable (on my
284	Linux system for example, C<getpid> is actually a simple 5-insn sequence	344	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
285	without a syscall and thus I<very> fast, but my Linux system also has	345	without a system call and thus I<very> fast, but my GNU/Linux system also has
286	C<pthread_atfork> which is even faster).	346	C<pthread_atfork> which is even faster).
287		347
288	The big advantage of this flag is that you can forget about fork (and	348	The big advantage of this flag is that you can forget about fork (and
289	forget about forgetting to tell libev about forking) when you use this	349	forget about forgetting to tell libev about forking) when you use this
290	flag.	350	flag.
291		351
292	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>	352	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
293	environment variable.	353	environment variable.
294		354
295	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	355	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
296		356
297	This is your standard select(2) backend. Not I<completely> standard, as	357	This is your standard select(2) backend. Not I<completely> standard, as
298	libev tries to roll its own fd_set with no limits on the number of fds,	358	libev tries to roll its own fd_set with no limits on the number of fds,
299	but if that fails, expect a fairly low limit on the number of fds when	359	but if that fails, expect a fairly low limit on the number of fds when
300	using this backend. It doesn't scale too well (O(highest_fd)), but its usually	360	using this backend. It doesn't scale too well (O(highest_fd)), but its
301	the fastest backend for a low number of fds.	361	usually the fastest backend for a low number of (low-numbered :) fds.
		362
		363	To get good performance out of this backend you need a high amount of
		364	parallelism (most of the file descriptors should be busy). If you are
		365	writing a server, you should C<accept ()> in a loop to accept as many
		366	connections as possible during one iteration. You might also want to have
		367	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		368	readiness notifications you get per iteration.
		369
		370	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		371	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		372	C<exceptfds> set on that platform).
302		373
303	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	374	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
304		375
305	And this is your standard poll(2) backend. It's more complicated than	376	And this is your standard poll(2) backend. It's more complicated
306	select, but handles sparse fds better and has no artificial limit on the	377	than select, but handles sparse fds better and has no artificial
307	number of fds you can use (except it will slow down considerably with a	378	limit on the number of fds you can use (except it will slow down
308	lot of inactive fds). It scales similarly to select, i.e. O(total_fds).	379	considerably with a lot of inactive fds). It scales similarly to select,
		380	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		381	performance tips.
		382
		383	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		384	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
309		385
310	=item C<EVBACKEND_EPOLL> (value 4, Linux)	386	=item C<EVBACKEND_EPOLL> (value 4, Linux)
311		387
312	For few fds, this backend is a bit little slower than poll and select,	388	For few fds, this backend is a bit little slower than poll and select,
313	but it scales phenomenally better. While poll and select usually scale like	389	but it scales phenomenally better. While poll and select usually scale
314	O(total_fds) where n is the total number of fds (or the highest fd), epoll scales	390	like O(total_fds) where n is the total number of fds (or the highest fd),
315	either O(1) or O(active_fds).	391	epoll scales either O(1) or O(active_fds).
316		392
		393	The epoll mechanism deserves honorable mention as the most misdesigned
		394	of the more advanced event mechanisms: mere annoyances include silently
		395	dropping file descriptors, requiring a system call per change per file
		396	descriptor (and unnecessary guessing of parameters), problems with dup and
		397	so on. The biggest issue is fork races, however - if a program forks then
		398	I<both> parent and child process have to recreate the epoll set, which can
		399	take considerable time (one syscall per file descriptor) and is of course
		400	hard to detect.
		401
		402	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		403	of course I<doesn't>, and epoll just loves to report events for totally
		404	I<different> file descriptors (even already closed ones, so one cannot
		405	even remove them from the set) than registered in the set (especially
		406	on SMP systems). Libev tries to counter these spurious notifications by
		407	employing an additional generation counter and comparing that against the
		408	events to filter out spurious ones, recreating the set when required.
		409
317	While stopping and starting an I/O watcher in the same iteration will	410	While stopping, setting and starting an I/O watcher in the same iteration
318	result in some caching, there is still a syscall per such incident	411	will result in some caching, there is still a system call per such
319	(because the fd could point to a different file description now), so its	412	incident (because the same I<file descriptor> could point to a different
320	best to avoid that. Also, dup()ed file descriptors might not work very	413	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
321	well if you register events for both fds.	414	file descriptors might not work very well if you register events for both
		415	file descriptors.
322		416
323	Please note that epoll sometimes generates spurious notifications, so you	417	Best performance from this backend is achieved by not unregistering all
324	need to use non-blocking I/O or other means to avoid blocking when no data	418	watchers for a file descriptor until it has been closed, if possible,
325	(or space) is available.	419	i.e. keep at least one watcher active per fd at all times. Stopping and
		420	starting a watcher (without re-setting it) also usually doesn't cause
		421	extra overhead. A fork can both result in spurious notifications as well
		422	as in libev having to destroy and recreate the epoll object, which can
		423	take considerable time and thus should be avoided.
		424
		425	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		426	faster than epoll for maybe up to a hundred file descriptors, depending on
		427	the usage. So sad.
		428
		429	While nominally embeddable in other event loops, this feature is broken in
		430	all kernel versions tested so far.
		431
		432	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		433	C<EVBACKEND_POLL>.
326		434
327	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	435	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
328		436
329	Kqueue deserves special mention, as at the time of this writing, it	437	Kqueue deserves special mention, as at the time of this writing, it
330	was broken on all BSDs except NetBSD (usually it doesn't work with	438	was broken on all BSDs except NetBSD (usually it doesn't work reliably
331	anything but sockets and pipes, except on Darwin, where of course its	439	with anything but sockets and pipes, except on Darwin, where of course
332	completely useless). For this reason its not being "autodetected"	440	it's completely useless). Unlike epoll, however, whose brokenness
		441	is by design, these kqueue bugs can (and eventually will) be fixed
		442	without API changes to existing programs. For this reason it's not being
333	unless you explicitly specify it explicitly in the flags (i.e. using	443	"auto-detected" unless you explicitly specify it in the flags (i.e. using
334	C<EVBACKEND_KQUEUE>).	444	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		445	system like NetBSD.
		446
		447	You still can embed kqueue into a normal poll or select backend and use it
		448	only for sockets (after having made sure that sockets work with kqueue on
		449	the target platform). See C<ev_embed> watchers for more info.
335		450
336	It scales in the same way as the epoll backend, but the interface to the	451	It scales in the same way as the epoll backend, but the interface to the
337	kernel is more efficient (which says nothing about its actual speed, of	452	kernel is more efficient (which says nothing about its actual speed, of
338	course). While starting and stopping an I/O watcher does not cause an	453	course). While stopping, setting and starting an I/O watcher does never
339	extra syscall as with epoll, it still adds up to four event changes per	454	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
340	incident, so its best to avoid that.	455	two event changes per incident. Support for C<fork ()> is very bad (but
		456	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		457	cases
		458
		459	This backend usually performs well under most conditions.
		460
		461	While nominally embeddable in other event loops, this doesn't work
		462	everywhere, so you might need to test for this. And since it is broken
		463	almost everywhere, you should only use it when you have a lot of sockets
		464	(for which it usually works), by embedding it into another event loop
		465	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
		466	also broken on OS X)) and, did I mention it, using it only for sockets.
		467
		468	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		469	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		470	C<NOTE_EOF>.
341		471
342	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	472	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
343		473
344	This is not implemented yet (and might never be).	474	This is not implemented yet (and might never be, unless you send me an
		475	implementation). According to reports, C</dev/poll> only supports sockets
		476	and is not embeddable, which would limit the usefulness of this backend
		477	immensely.
345		478
346	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	479	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
347		480
348	This uses the Solaris 10 port mechanism. As with everything on Solaris,	481	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
349	it's really slow, but it still scales very well (O(active_fds)).	482	it's really slow, but it still scales very well (O(active_fds)).
350		483
351	Please note that solaris ports can result in a lot of spurious	484	Please note that Solaris event ports can deliver a lot of spurious
352	notifications, so you need to use non-blocking I/O or other means to avoid	485	notifications, so you need to use non-blocking I/O or other means to avoid
353	blocking when no data (or space) is available.	486	blocking when no data (or space) is available.
		487
		488	While this backend scales well, it requires one system call per active
		489	file descriptor per loop iteration. For small and medium numbers of file
		490	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		491	might perform better.
		492
		493	On the positive side, with the exception of the spurious readiness
		494	notifications, this backend actually performed fully to specification
		495	in all tests and is fully embeddable, which is a rare feat among the
		496	OS-specific backends (I vastly prefer correctness over speed hacks).
		497
		498	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		499	C<EVBACKEND_POLL>.
354		500
355	=item C<EVBACKEND_ALL>	501	=item C<EVBACKEND_ALL>
356		502
357	Try all backends (even potentially broken ones that wouldn't be tried	503	Try all backends (even potentially broken ones that wouldn't be tried
358	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	504	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
359	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	505	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
360		506
		507	It is definitely not recommended to use this flag.
		508
361	=back	509	=back
362		510
363	If one or more of these are ored into the flags value, then only these	511	If one or more of these are or'ed into the flags value, then only these
364	backends will be tried (in the reverse order as given here). If none are	512	backends will be tried (in the reverse order as listed here). If none are
365	specified, most compiled-in backend will be tried, usually in reverse	513	specified, all backends in C<ev_recommended_backends ()> will be tried.
366	order of their flag values :)
367		514
368	The most typical usage is like this:	515	Example: This is the most typical usage.
369		516
370	if (!ev_default_loop (0))	517	if (!ev_default_loop (0))
371	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	518	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
372		519
373	Restrict libev to the select and poll backends, and do not allow	520	Example: Restrict libev to the select and poll backends, and do not allow
374	environment settings to be taken into account:	521	environment settings to be taken into account:
375		522
376	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	523	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
377		524
378	Use whatever libev has to offer, but make sure that kqueue is used if	525	Example: Use whatever libev has to offer, but make sure that kqueue is
379	available (warning, breaks stuff, best use only with your own private	526	used if available (warning, breaks stuff, best use only with your own
380	event loop and only if you know the OS supports your types of fds):	527	private event loop and only if you know the OS supports your types of
		528	fds):
381		529
382	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	530	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
383		531
384	=item struct ev_loop *ev_loop_new (unsigned int flags)	532	=item struct ev_loop *ev_loop_new (unsigned int flags)
385		533
386	Similar to C<ev_default_loop>, but always creates a new event loop that is	534	Similar to C<ev_default_loop>, but always creates a new event loop that is
387	always distinct from the default loop. Unlike the default loop, it cannot	535	always distinct from the default loop. Unlike the default loop, it cannot
388	handle signal and child watchers, and attempts to do so will be greeted by	536	handle signal and child watchers, and attempts to do so will be greeted by
389	undefined behaviour (or a failed assertion if assertions are enabled).	537	undefined behaviour (or a failed assertion if assertions are enabled).
390		538
		539	Note that this function I<is> thread-safe, and the recommended way to use
		540	libev with threads is indeed to create one loop per thread, and using the
		541	default loop in the "main" or "initial" thread.
		542
391	Example: Try to create a event loop that uses epoll and nothing else.	543	Example: Try to create a event loop that uses epoll and nothing else.
392		544
393	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	545	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
394	if (!epoller)	546	if (!epoller)
395	fatal ("no epoll found here, maybe it hides under your chair");	547	fatal ("no epoll found here, maybe it hides under your chair");
396		548
397	=item ev_default_destroy ()	549	=item ev_default_destroy ()
398		550
399	Destroys the default loop again (frees all memory and kernel state	551	Destroys the default loop again (frees all memory and kernel state
400	etc.). None of the active event watchers will be stopped in the normal	552	etc.). None of the active event watchers will be stopped in the normal
401	sense, so e.g. C<ev_is_active> might still return true. It is your	553	sense, so e.g. C<ev_is_active> might still return true. It is your
402	responsibility to either stop all watchers cleanly yoursef I<before>	554	responsibility to either stop all watchers cleanly yourself I<before>
403	calling this function, or cope with the fact afterwards (which is usually	555	calling this function, or cope with the fact afterwards (which is usually
404	the easiest thing, youc na just ignore the watchers and/or C<free ()> them	556	the easiest thing, you can just ignore the watchers and/or C<free ()> them
405	for example).	557	for example).
		558
		559	Note that certain global state, such as signal state (and installed signal
		560	handlers), will not be freed by this function, and related watchers (such
		561	as signal and child watchers) would need to be stopped manually.
		562
		563	In general it is not advisable to call this function except in the
		564	rare occasion where you really need to free e.g. the signal handling
		565	pipe fds. If you need dynamically allocated loops it is better to use
		566	C<ev_loop_new> and C<ev_loop_destroy>).
406		567
407	=item ev_loop_destroy (loop)	568	=item ev_loop_destroy (loop)
408		569
409	Like C<ev_default_destroy>, but destroys an event loop created by an	570	Like C<ev_default_destroy>, but destroys an event loop created by an
410	earlier call to C<ev_loop_new>.	571	earlier call to C<ev_loop_new>.
411		572
412	=item ev_default_fork ()	573	=item ev_default_fork ()
413		574
		575	This function sets a flag that causes subsequent C<ev_loop> iterations
414	This function reinitialises the kernel state for backends that have	576	to reinitialise the kernel state for backends that have one. Despite the
415	one. Despite the name, you can call it anytime, but it makes most sense	577	name, you can call it anytime, but it makes most sense after forking, in
416	after forking, in either the parent or child process (or both, but that	578	the child process (or both child and parent, but that again makes little
417	again makes little sense).	579	sense). You I<must> call it in the child before using any of the libev
		580	functions, and it will only take effect at the next C<ev_loop> iteration.
418		581
419	You I<must> call this function in the child process after forking if and	582	On the other hand, you only need to call this function in the child
420	only if you want to use the event library in both processes. If you just	583	process if and only if you want to use the event library in the child. If
421	fork+exec, you don't have to call it.	584	you just fork+exec, you don't have to call it at all.
422		585
423	The function itself is quite fast and it's usually not a problem to call	586	The function itself is quite fast and it's usually not a problem to call
424	it just in case after a fork. To make this easy, the function will fit in	587	it just in case after a fork. To make this easy, the function will fit in
425	quite nicely into a call to C<pthread_atfork>:	588	quite nicely into a call to C<pthread_atfork>:
426		589
427	pthread_atfork (0, 0, ev_default_fork);	590	pthread_atfork (0, 0, ev_default_fork);
428		591
429	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
430	without calling this function, so if you force one of those backends you
431	do not need to care.
432
433	=item ev_loop_fork (loop)	592	=item ev_loop_fork (loop)
434		593
435	Like C<ev_default_fork>, but acts on an event loop created by	594	Like C<ev_default_fork>, but acts on an event loop created by
436	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	595	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
437	after fork, and how you do this is entirely your own problem.	596	after fork that you want to re-use in the child, and how you do this is
		597	entirely your own problem.
		598
		599	=item int ev_is_default_loop (loop)
		600
		601	Returns true when the given loop is, in fact, the default loop, and false
		602	otherwise.
438		603
439	=item unsigned int ev_loop_count (loop)	604	=item unsigned int ev_loop_count (loop)
440		605
441	Returns the count of loop iterations for the loop, which is identical to	606	Returns the count of loop iterations for the loop, which is identical to
442	the number of times libev did poll for new events. It starts at C<0> and	607	the number of times libev did poll for new events. It starts at C<0> and
…		…
455		620
456	Returns the current "event loop time", which is the time the event loop	621	Returns the current "event loop time", which is the time the event loop
457	received events and started processing them. This timestamp does not	622	received events and started processing them. This timestamp does not
458	change as long as callbacks are being processed, and this is also the base	623	change as long as callbacks are being processed, and this is also the base
459	time used for relative timers. You can treat it as the timestamp of the	624	time used for relative timers. You can treat it as the timestamp of the
460	event occuring (or more correctly, libev finding out about it).	625	event occurring (or more correctly, libev finding out about it).
		626
		627	=item ev_now_update (loop)
		628
		629	Establishes the current time by querying the kernel, updating the time
		630	returned by C<ev_now ()> in the progress. This is a costly operation and
		631	is usually done automatically within C<ev_loop ()>.
		632
		633	This function is rarely useful, but when some event callback runs for a
		634	very long time without entering the event loop, updating libev's idea of
		635	the current time is a good idea.
		636
		637	See also "The special problem of time updates" in the C<ev_timer> section.
		638
		639	=item ev_suspend (loop)
		640
		641	=item ev_resume (loop)
		642
		643	These two functions suspend and resume a loop, for use when the loop is
		644	not used for a while and timeouts should not be processed.
		645
		646	A typical use case would be an interactive program such as a game: When
		647	the user presses C<^Z> to suspend the game and resumes it an hour later it
		648	would be best to handle timeouts as if no time had actually passed while
		649	the program was suspended. This can be achieved by calling C<ev_suspend>
		650	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		651	C<ev_resume> directly afterwards to resume timer processing.
		652
		653	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		654	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		655	will be rescheduled (that is, they will lose any events that would have
		656	occured while suspended).
		657
		658	After calling C<ev_suspend> you B<must not> call I<any> function on the
		659	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		660	without a previous call to C<ev_suspend>.
		661
		662	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		663	event loop time (see C<ev_now_update>).
461		664
462	=item ev_loop (loop, int flags)	665	=item ev_loop (loop, int flags)
463		666
464	Finally, this is it, the event handler. This function usually is called	667	Finally, this is it, the event handler. This function usually is called
465	after you initialised all your watchers and you want to start handling	668	after you initialised all your watchers and you want to start handling
…		…
468	If the flags argument is specified as C<0>, it will not return until	671	If the flags argument is specified as C<0>, it will not return until
469	either no event watchers are active anymore or C<ev_unloop> was called.	672	either no event watchers are active anymore or C<ev_unloop> was called.
470		673
471	Please note that an explicit C<ev_unloop> is usually better than	674	Please note that an explicit C<ev_unloop> is usually better than
472	relying on all watchers to be stopped when deciding when a program has	675	relying on all watchers to be stopped when deciding when a program has
473	finished (especially in interactive programs), but having a program that	676	finished (especially in interactive programs), but having a program
474	automatically loops as long as it has to and no longer by virtue of	677	that automatically loops as long as it has to and no longer by virtue
475	relying on its watchers stopping correctly is a thing of beauty.	678	of relying on its watchers stopping correctly, that is truly a thing of
		679	beauty.
476		680
477	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	681	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
478	those events and any outstanding ones, but will not block your process in	682	those events and any already outstanding ones, but will not block your
479	case there are no events and will return after one iteration of the loop.	683	process in case there are no events and will return after one iteration of
		684	the loop.
480		685
481	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	686	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
482	neccessary) and will handle those and any outstanding ones. It will block	687	necessary) and will handle those and any already outstanding ones. It
483	your process until at least one new event arrives, and will return after	688	will block your process until at least one new event arrives (which could
484	one iteration of the loop. This is useful if you are waiting for some	689	be an event internal to libev itself, so there is no guarantee that a
485	external event in conjunction with something not expressible using other	690	user-registered callback will be called), and will return after one
		691	iteration of the loop.
		692
		693	This is useful if you are waiting for some external event in conjunction
		694	with something not expressible using other libev watchers (i.e. "roll your
486	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	695	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
487	usually a better approach for this kind of thing.	696	usually a better approach for this kind of thing.
488		697
489	Here are the gory details of what C<ev_loop> does:	698	Here are the gory details of what C<ev_loop> does:
490		699
491	* If there are no active watchers (reference count is zero), return.	700	- Before the first iteration, call any pending watchers.
492	- Queue prepare watchers and then call all outstanding watchers.	701	* If EVFLAG_FORKCHECK was used, check for a fork.
		702	- If a fork was detected (by any means), queue and call all fork watchers.
		703	- Queue and call all prepare watchers.
493	- If we have been forked, recreate the kernel state.	704	- If we have been forked, detach and recreate the kernel state
		705	as to not disturb the other process.
494	- Update the kernel state with all outstanding changes.	706	- Update the kernel state with all outstanding changes.
495	- Update the "event loop time".	707	- Update the "event loop time" (ev_now ()).
496	- Calculate for how long to block.	708	- Calculate for how long to sleep or block, if at all
		709	(active idle watchers, EVLOOP_NONBLOCK or not having
		710	any active watchers at all will result in not sleeping).
		711	- Sleep if the I/O and timer collect interval say so.
497	- Block the process, waiting for any events.	712	- Block the process, waiting for any events.
498	- Queue all outstanding I/O (fd) events.	713	- Queue all outstanding I/O (fd) events.
499	- Update the "event loop time" and do time jump handling.	714	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
500	- Queue all outstanding timers.	715	- Queue all expired timers.
501	- Queue all outstanding periodics.	716	- Queue all expired periodics.
502	- If no events are pending now, queue all idle watchers.	717	- Unless any events are pending now, queue all idle watchers.
503	- Queue all check watchers.	718	- Queue all check watchers.
504	- Call all queued watchers in reverse order (i.e. check watchers first).	719	- Call all queued watchers in reverse order (i.e. check watchers first).
505	Signals and child watchers are implemented as I/O watchers, and will	720	Signals and child watchers are implemented as I/O watchers, and will
506	be handled here by queueing them when their watcher gets executed.	721	be handled here by queueing them when their watcher gets executed.
507	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	722	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
508	were used, return, otherwise continue with step *.	723	were used, or there are no active watchers, return, otherwise
		724	continue with step *.
509		725
510	Example: Queue some jobs and then loop until no events are outsanding	726	Example: Queue some jobs and then loop until no events are outstanding
511	anymore.	727	anymore.
512		728
513	... queue jobs here, make sure they register event watchers as long	729	... queue jobs here, make sure they register event watchers as long
514	... as they still have work to do (even an idle watcher will do..)	730	... as they still have work to do (even an idle watcher will do..)
515	ev_loop (my_loop, 0);	731	ev_loop (my_loop, 0);
516	... jobs done. yeah!	732	... jobs done or somebody called unloop. yeah!
517		733
518	=item ev_unloop (loop, how)	734	=item ev_unloop (loop, how)
519		735
520	Can be used to make a call to C<ev_loop> return early (but only after it	736	Can be used to make a call to C<ev_loop> return early (but only after it
521	has processed all outstanding events). The C<how> argument must be either	737	has processed all outstanding events). The C<how> argument must be either
522	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	738	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
523	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	739	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
524		740
		741	This "unloop state" will be cleared when entering C<ev_loop> again.
		742
		743	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
		744
525	=item ev_ref (loop)	745	=item ev_ref (loop)
526		746
527	=item ev_unref (loop)	747	=item ev_unref (loop)
528		748
529	Ref/unref can be used to add or remove a reference count on the event	749	Ref/unref can be used to add or remove a reference count on the event
530	loop: Every watcher keeps one reference, and as long as the reference	750	loop: Every watcher keeps one reference, and as long as the reference
531	count is nonzero, C<ev_loop> will not return on its own. If you have	751	count is nonzero, C<ev_loop> will not return on its own.
		752
532	a watcher you never unregister that should not keep C<ev_loop> from	753	If you have a watcher you never unregister that should not keep C<ev_loop>
533	returning, ev_unref() after starting, and ev_ref() before stopping it. For	754	from returning, call ev_unref() after starting, and ev_ref() before
		755	stopping it.
		756
534	example, libev itself uses this for its internal signal pipe: It is not	757	As an example, libev itself uses this for its internal signal pipe: It
535	visible to the libev user and should not keep C<ev_loop> from exiting if	758	is not visible to the libev user and should not keep C<ev_loop> from
536	no event watchers registered by it are active. It is also an excellent	759	exiting if no event watchers registered by it are active. It is also an
537	way to do this for generic recurring timers or from within third-party	760	excellent way to do this for generic recurring timers or from within
538	libraries. Just remember to I<unref after start> and I<ref before stop>.	761	third-party libraries. Just remember to I<unref after start> and I<ref
		762	before stop> (but only if the watcher wasn't active before, or was active
		763	before, respectively. Note also that libev might stop watchers itself
		764	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		765	in the callback).
539		766
540	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	767	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
541	running when nothing else is active.	768	running when nothing else is active.
542		769
543	struct ev_signal exitsig;	770	ev_signal exitsig;
544	ev_signal_init (&exitsig, sig_cb, SIGINT);	771	ev_signal_init (&exitsig, sig_cb, SIGINT);
545	ev_signal_start (loop, &exitsig);	772	ev_signal_start (loop, &exitsig);
546	evf_unref (loop);	773	evf_unref (loop);
547		774
548	Example: For some weird reason, unregister the above signal handler again.	775	Example: For some weird reason, unregister the above signal handler again.
549		776
550	ev_ref (loop);	777	ev_ref (loop);
551	ev_signal_stop (loop, &exitsig);	778	ev_signal_stop (loop, &exitsig);
		779
		780	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		781
		782	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		783
		784	These advanced functions influence the time that libev will spend waiting
		785	for events. Both time intervals are by default C<0>, meaning that libev
		786	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		787	latency.
		788
		789	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		790	allows libev to delay invocation of I/O and timer/periodic callbacks
		791	to increase efficiency of loop iterations (or to increase power-saving
		792	opportunities).
		793
		794	The idea is that sometimes your program runs just fast enough to handle
		795	one (or very few) event(s) per loop iteration. While this makes the
		796	program responsive, it also wastes a lot of CPU time to poll for new
		797	events, especially with backends like C<select ()> which have a high
		798	overhead for the actual polling but can deliver many events at once.
		799
		800	By setting a higher I<io collect interval> you allow libev to spend more
		801	time collecting I/O events, so you can handle more events per iteration,
		802	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		803	C<ev_timer>) will be not affected. Setting this to a non-null value will
		804	introduce an additional C<ev_sleep ()> call into most loop iterations.
		805
		806	Likewise, by setting a higher I<timeout collect interval> you allow libev
		807	to spend more time collecting timeouts, at the expense of increased
		808	latency/jitter/inexactness (the watcher callback will be called
		809	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		810	value will not introduce any overhead in libev.
		811
		812	Many (busy) programs can usually benefit by setting the I/O collect
		813	interval to a value near C<0.1> or so, which is often enough for
		814	interactive servers (of course not for games), likewise for timeouts. It
		815	usually doesn't make much sense to set it to a lower value than C<0.01>,
		816	as this approaches the timing granularity of most systems.
		817
		818	Setting the I<timeout collect interval> can improve the opportunity for
		819	saving power, as the program will "bundle" timer callback invocations that
		820	are "near" in time together, by delaying some, thus reducing the number of
		821	times the process sleeps and wakes up again. Another useful technique to
		822	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		823	they fire on, say, one-second boundaries only.
		824
		825	=item ev_loop_verify (loop)
		826
		827	This function only does something when C<EV_VERIFY> support has been
		828	compiled in, which is the default for non-minimal builds. It tries to go
		829	through all internal structures and checks them for validity. If anything
		830	is found to be inconsistent, it will print an error message to standard
		831	error and call C<abort ()>.
		832
		833	This can be used to catch bugs inside libev itself: under normal
		834	circumstances, this function will never abort as of course libev keeps its
		835	data structures consistent.
552		836
553	=back	837	=back
554		838
555		839
556	=head1 ANATOMY OF A WATCHER	840	=head1 ANATOMY OF A WATCHER
		841
		842	In the following description, uppercase C<TYPE> in names stands for the
		843	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		844	watchers and C<ev_io_start> for I/O watchers.
557		845
558	A watcher is a structure that you create and register to record your	846	A watcher is a structure that you create and register to record your
559	interest in some event. For instance, if you want to wait for STDIN to	847	interest in some event. For instance, if you want to wait for STDIN to
560	become readable, you would create an C<ev_io> watcher for that:	848	become readable, you would create an C<ev_io> watcher for that:
561		849
562	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	850	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
563	{	851	{
564	ev_io_stop (w);	852	ev_io_stop (w);
565	ev_unloop (loop, EVUNLOOP_ALL);	853	ev_unloop (loop, EVUNLOOP_ALL);
566	}	854	}
567		855
568	struct ev_loop *loop = ev_default_loop (0);	856	struct ev_loop *loop = ev_default_loop (0);
		857
569	struct ev_io stdin_watcher;	858	ev_io stdin_watcher;
		859
570	ev_init (&stdin_watcher, my_cb);	860	ev_init (&stdin_watcher, my_cb);
571	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	861	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
572	ev_io_start (loop, &stdin_watcher);	862	ev_io_start (loop, &stdin_watcher);
		863
573	ev_loop (loop, 0);	864	ev_loop (loop, 0);
574		865
575	As you can see, you are responsible for allocating the memory for your	866	As you can see, you are responsible for allocating the memory for your
576	watcher structures (and it is usually a bad idea to do this on the stack,	867	watcher structures (and it is I<usually> a bad idea to do this on the
577	although this can sometimes be quite valid).	868	stack).
		869
		870	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		871	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
578		872
579	Each watcher structure must be initialised by a call to C<ev_init	873	Each watcher structure must be initialised by a call to C<ev_init
580	(watcher *, callback)>, which expects a callback to be provided. This	874	(watcher *, callback)>, which expects a callback to be provided. This
581	callback gets invoked each time the event occurs (or, in the case of io	875	callback gets invoked each time the event occurs (or, in the case of I/O
582	watchers, each time the event loop detects that the file descriptor given	876	watchers, each time the event loop detects that the file descriptor given
583	is readable and/or writable).	877	is readable and/or writable).
584		878
585	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	879	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
586	with arguments specific to this watcher type. There is also a macro	880	macro to configure it, with arguments specific to the watcher type. There
587	to combine initialisation and setting in one call: C<< ev_<type>_init	881	is also a macro to combine initialisation and setting in one call: C<<
588	(watcher *, callback, ...) >>.	882	ev_TYPE_init (watcher *, callback, ...) >>.
589		883
590	To make the watcher actually watch out for events, you have to start it	884	To make the watcher actually watch out for events, you have to start it
591	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	885	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
592	*) >>), and you can stop watching for events at any time by calling the	886	*) >>), and you can stop watching for events at any time by calling the
593	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	887	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
594		888
595	As long as your watcher is active (has been started but not stopped) you	889	As long as your watcher is active (has been started but not stopped) you
596	must not touch the values stored in it. Most specifically you must never	890	must not touch the values stored in it. Most specifically you must never
597	reinitialise it or call its C<set> macro.	891	reinitialise it or call its C<ev_TYPE_set> macro.
598		892
599	Each and every callback receives the event loop pointer as first, the	893	Each and every callback receives the event loop pointer as first, the
600	registered watcher structure as second, and a bitset of received events as	894	registered watcher structure as second, and a bitset of received events as
601	third argument.	895	third argument.
602		896
…		…
656	=item C<EV_FORK>	950	=item C<EV_FORK>
657		951
658	The event loop has been resumed in the child process after fork (see	952	The event loop has been resumed in the child process after fork (see
659	C<ev_fork>).	953	C<ev_fork>).
660		954
		955	=item C<EV_ASYNC>
		956
		957	The given async watcher has been asynchronously notified (see C<ev_async>).
		958
		959	=item C<EV_CUSTOM>
		960
		961	Not ever sent (or otherwise used) by libev itself, but can be freely used
		962	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		963
661	=item C<EV_ERROR>	964	=item C<EV_ERROR>
662		965
663	An unspecified error has occured, the watcher has been stopped. This might	966	An unspecified error has occurred, the watcher has been stopped. This might
664	happen because the watcher could not be properly started because libev	967	happen because the watcher could not be properly started because libev
665	ran out of memory, a file descriptor was found to be closed or any other	968	ran out of memory, a file descriptor was found to be closed or any other
		969	problem. Libev considers these application bugs.
		970
666	problem. You best act on it by reporting the problem and somehow coping	971	You best act on it by reporting the problem and somehow coping with the
667	with the watcher being stopped.	972	watcher being stopped. Note that well-written programs should not receive
		973	an error ever, so when your watcher receives it, this usually indicates a
		974	bug in your program.
668		975
669	Libev will usually signal a few "dummy" events together with an error,	976	Libev will usually signal a few "dummy" events together with an error, for
670	for example it might indicate that a fd is readable or writable, and if	977	example it might indicate that a fd is readable or writable, and if your
671	your callbacks is well-written it can just attempt the operation and cope	978	callbacks is well-written it can just attempt the operation and cope with
672	with the error from read() or write(). This will not work in multithreaded	979	the error from read() or write(). This will not work in multi-threaded
673	programs, though, so beware.	980	programs, though, as the fd could already be closed and reused for another
		981	thing, so beware.
674		982
675	=back	983	=back
676		984
677	=head2 GENERIC WATCHER FUNCTIONS	985	=head2 GENERIC WATCHER FUNCTIONS
678
679	In the following description, C<TYPE> stands for the watcher type,
680	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
681		986
682	=over 4	987	=over 4
683		988
684	=item C<ev_init> (ev_TYPE *watcher, callback)	989	=item C<ev_init> (ev_TYPE *watcher, callback)
685		990
…		…
691	which rolls both calls into one.	996	which rolls both calls into one.
692		997
693	You can reinitialise a watcher at any time as long as it has been stopped	998	You can reinitialise a watcher at any time as long as it has been stopped
694	(or never started) and there are no pending events outstanding.	999	(or never started) and there are no pending events outstanding.
695		1000
696	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1001	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
697	int revents)>.	1002	int revents)>.
		1003
		1004	Example: Initialise an C<ev_io> watcher in two steps.
		1005
		1006	ev_io w;
		1007	ev_init (&w, my_cb);
		1008	ev_io_set (&w, STDIN_FILENO, EV_READ);
698		1009
699	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1010	=item C<ev_TYPE_set> (ev_TYPE *, [args])
700		1011
701	This macro initialises the type-specific parts of a watcher. You need to	1012	This macro initialises the type-specific parts of a watcher. You need to
702	call C<ev_init> at least once before you call this macro, but you can	1013	call C<ev_init> at least once before you call this macro, but you can
…		…
705	difference to the C<ev_init> macro).	1016	difference to the C<ev_init> macro).
706		1017
707	Although some watcher types do not have type-specific arguments	1018	Although some watcher types do not have type-specific arguments
708	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1019	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
709		1020
		1021	See C<ev_init>, above, for an example.
		1022
710	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1023	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
711		1024
712	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1025	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
713	calls into a single call. This is the most convinient method to initialise	1026	calls into a single call. This is the most convenient method to initialise
714	a watcher. The same limitations apply, of course.	1027	a watcher. The same limitations apply, of course.
		1028
		1029	Example: Initialise and set an C<ev_io> watcher in one step.
		1030
		1031	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
715		1032
716	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1033	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
717		1034
718	Starts (activates) the given watcher. Only active watchers will receive	1035	Starts (activates) the given watcher. Only active watchers will receive
719	events. If the watcher is already active nothing will happen.	1036	events. If the watcher is already active nothing will happen.
720		1037
		1038	Example: Start the C<ev_io> watcher that is being abused as example in this
		1039	whole section.
		1040
		1041	ev_io_start (EV_DEFAULT_UC, &w);
		1042
721	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1043	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
722		1044
723	Stops the given watcher again (if active) and clears the pending	1045	Stops the given watcher if active, and clears the pending status (whether
		1046	the watcher was active or not).
		1047
724	status. It is possible that stopped watchers are pending (for example,	1048	It is possible that stopped watchers are pending - for example,
725	non-repeating timers are being stopped when they become pending), but	1049	non-repeating timers are being stopped when they become pending - but
726	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1050	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
727	you want to free or reuse the memory used by the watcher it is therefore a	1051	pending. If you want to free or reuse the memory used by the watcher it is
728	good idea to always call its C<ev_TYPE_stop> function.	1052	therefore a good idea to always call its C<ev_TYPE_stop> function.
729		1053
730	=item bool ev_is_active (ev_TYPE *watcher)	1054	=item bool ev_is_active (ev_TYPE *watcher)
731		1055
732	Returns a true value iff the watcher is active (i.e. it has been started	1056	Returns a true value iff the watcher is active (i.e. it has been started
733	and not yet been stopped). As long as a watcher is active you must not modify	1057	and not yet been stopped). As long as a watcher is active you must not modify
…		…
759	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1083	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
760	(default: C<-2>). Pending watchers with higher priority will be invoked	1084	(default: C<-2>). Pending watchers with higher priority will be invoked
761	before watchers with lower priority, but priority will not keep watchers	1085	before watchers with lower priority, but priority will not keep watchers
762	from being executed (except for C<ev_idle> watchers).	1086	from being executed (except for C<ev_idle> watchers).
763		1087
		1088	See L<
		1089
764	This means that priorities are I<only> used for ordering callback	1090	This means that priorities are I<only> used for ordering callback
765	invocation after new events have been received. This is useful, for	1091	invocation after new events have been received. This is useful, for
766	example, to reduce latency after idling, or more often, to bind two	1092	example, to reduce latency after idling, or more often, to bind two
767	watchers on the same event and make sure one is called first.	1093	watchers on the same event and make sure one is called first.
768		1094
…		…
775	The default priority used by watchers when no priority has been set is	1101	The default priority used by watchers when no priority has been set is
776	always C<0>, which is supposed to not be too high and not be too low :).	1102	always C<0>, which is supposed to not be too high and not be too low :).
777		1103
778	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1104	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
779	fine, as long as you do not mind that the priority value you query might	1105	fine, as long as you do not mind that the priority value you query might
780	or might not have been adjusted to be within valid range.	1106	or might not have been clamped to the valid range.
781		1107
782	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1108	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
783		1109
784	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1110	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
785	C<loop> nor C<revents> need to be valid as long as the watcher callback	1111	C<loop> nor C<revents> need to be valid as long as the watcher callback
786	can deal with that fact.	1112	can deal with that fact, as both are simply passed through to the
		1113	callback.
787		1114
788	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1115	=item int ev_clear_pending (loop, ev_TYPE *watcher)
789		1116
790	If the watcher is pending, this function returns clears its pending status	1117	If the watcher is pending, this function clears its pending status and
791	and returns its C<revents> bitset (as if its callback was invoked). If the	1118	returns its C<revents> bitset (as if its callback was invoked). If the
792	watcher isn't pending it does nothing and returns C<0>.	1119	watcher isn't pending it does nothing and returns C<0>.
793		1120
		1121	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1122	callback to be invoked, which can be accomplished with this function.
		1123
794	=back	1124	=back
795		1125
796		1126
797	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1127	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
798		1128
799	Each watcher has, by default, a member C<void *data> that you can change	1129	Each watcher has, by default, a member C<void *data> that you can change
800	and read at any time, libev will completely ignore it. This can be used	1130	and read at any time: libev will completely ignore it. This can be used
801	to associate arbitrary data with your watcher. If you need more data and	1131	to associate arbitrary data with your watcher. If you need more data and
802	don't want to allocate memory and store a pointer to it in that data	1132	don't want to allocate memory and store a pointer to it in that data
803	member, you can also "subclass" the watcher type and provide your own	1133	member, you can also "subclass" the watcher type and provide your own
804	data:	1134	data:
805		1135
806	struct my_io	1136	struct my_io
807	{	1137	{
808	struct ev_io io;	1138	ev_io io;
809	int otherfd;	1139	int otherfd;
810	void *somedata;	1140	void *somedata;
811	struct whatever *mostinteresting;	1141	struct whatever *mostinteresting;
812	}	1142	};
		1143
		1144	...
		1145	struct my_io w;
		1146	ev_io_init (&w.io, my_cb, fd, EV_READ);
813		1147
814	And since your callback will be called with a pointer to the watcher, you	1148	And since your callback will be called with a pointer to the watcher, you
815	can cast it back to your own type:	1149	can cast it back to your own type:
816		1150
817	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1151	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
818	{	1152	{
819	struct my_io *w = (struct my_io *)w_;	1153	struct my_io *w = (struct my_io *)w_;
820	...	1154	...
821	}	1155	}
822		1156
823	More interesting and less C-conformant ways of casting your callback type	1157	More interesting and less C-conformant ways of casting your callback type
824	instead have been omitted.	1158	instead have been omitted.
825		1159
826	Another common scenario is having some data structure with multiple	1160	Another common scenario is to use some data structure with multiple
827	watchers:	1161	embedded watchers:
828		1162
829	struct my_biggy	1163	struct my_biggy
830	{	1164	{
831	int some_data;	1165	int some_data;
832	ev_timer t1;	1166	ev_timer t1;
833	ev_timer t2;	1167	ev_timer t2;
834	}	1168	}
835		1169
836	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1170	In this case getting the pointer to C<my_biggy> is a bit more
837	you need to use C<offsetof>:	1171	complicated: Either you store the address of your C<my_biggy> struct
		1172	in the C<data> member of the watcher (for woozies), or you need to use
		1173	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1174	programmers):
838		1175
839	#include <stddef.h>	1176	#include <stddef.h>
840		1177
841	static void	1178	static void
842	t1_cb (EV_P_ struct ev_timer *w, int revents)	1179	t1_cb (EV_P_ ev_timer *w, int revents)
843	{	1180	{
844	struct my_biggy big = (struct my_biggy *	1181	struct my_biggy big = (struct my_biggy *
845	(((char *)w) - offsetof (struct my_biggy, t1));	1182	(((char *)w) - offsetof (struct my_biggy, t1));
846	}	1183	}
847		1184
848	static void	1185	static void
849	t2_cb (EV_P_ struct ev_timer *w, int revents)	1186	t2_cb (EV_P_ ev_timer *w, int revents)
850	{	1187	{
851	struct my_biggy big = (struct my_biggy *	1188	struct my_biggy big = (struct my_biggy *
852	(((char *)w) - offsetof (struct my_biggy, t2));	1189	(((char *)w) - offsetof (struct my_biggy, t2));
853	}	1190	}
854		1191
855		1192
856	=head1 WATCHER TYPES	1193	=head1 WATCHER TYPES
857		1194
858	This section describes each watcher in detail, but will not repeat	1195	This section describes each watcher in detail, but will not repeat
…		…
882	In general you can register as many read and/or write event watchers per	1219	In general you can register as many read and/or write event watchers per
883	fd as you want (as long as you don't confuse yourself). Setting all file	1220	fd as you want (as long as you don't confuse yourself). Setting all file
884	descriptors to non-blocking mode is also usually a good idea (but not	1221	descriptors to non-blocking mode is also usually a good idea (but not
885	required if you know what you are doing).	1222	required if you know what you are doing).
886		1223
887	You have to be careful with dup'ed file descriptors, though. Some backends	1224	If you cannot use non-blocking mode, then force the use of a
888	(the linux epoll backend is a notable example) cannot handle dup'ed file	1225	known-to-be-good backend (at the time of this writing, this includes only
889	descriptors correctly if you register interest in two or more fds pointing	1226	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>).
890	to the same underlying file/socket/etc. description (that is, they share
891	the same underlying "file open").
892
893	If you must do this, then force the use of a known-to-be-good backend
894	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
895	C<EVBACKEND_POLL>).
896		1227
897	Another thing you have to watch out for is that it is quite easy to	1228	Another thing you have to watch out for is that it is quite easy to
898	receive "spurious" readyness notifications, that is your callback might	1229	receive "spurious" readiness notifications, that is your callback might
899	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1230	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
900	because there is no data. Not only are some backends known to create a	1231	because there is no data. Not only are some backends known to create a
901	lot of those (for example solaris ports), it is very easy to get into	1232	lot of those (for example Solaris ports), it is very easy to get into
902	this situation even with a relatively standard program structure. Thus	1233	this situation even with a relatively standard program structure. Thus
903	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1234	it is best to always use non-blocking I/O: An extra C<read>(2) returning
904	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1235	C<EAGAIN> is far preferable to a program hanging until some data arrives.
905		1236
906	If you cannot run the fd in non-blocking mode (for example you should not	1237	If you cannot run the fd in non-blocking mode (for example you should
907	play around with an Xlib connection), then you have to seperately re-test	1238	not play around with an Xlib connection), then you have to separately
908	whether a file descriptor is really ready with a known-to-be good interface	1239	re-test whether a file descriptor is really ready with a known-to-be good
909	such as poll (fortunately in our Xlib example, Xlib already does this on	1240	interface such as poll (fortunately in our Xlib example, Xlib already
910	its own, so its quite safe to use).	1241	does this on its own, so its quite safe to use). Some people additionally
		1242	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1243	indefinitely.
		1244
		1245	But really, best use non-blocking mode.
		1246
		1247	=head3 The special problem of disappearing file descriptors
		1248
		1249	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1250	descriptor (either due to calling C<close> explicitly or any other means,
		1251	such as C<dup2>). The reason is that you register interest in some file
		1252	descriptor, but when it goes away, the operating system will silently drop
		1253	this interest. If another file descriptor with the same number then is
		1254	registered with libev, there is no efficient way to see that this is, in
		1255	fact, a different file descriptor.
		1256
		1257	To avoid having to explicitly tell libev about such cases, libev follows
		1258	the following policy: Each time C<ev_io_set> is being called, libev
		1259	will assume that this is potentially a new file descriptor, otherwise
		1260	it is assumed that the file descriptor stays the same. That means that
		1261	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1262	descriptor even if the file descriptor number itself did not change.
		1263
		1264	This is how one would do it normally anyway, the important point is that
		1265	the libev application should not optimise around libev but should leave
		1266	optimisations to libev.
		1267
		1268	=head3 The special problem of dup'ed file descriptors
		1269
		1270	Some backends (e.g. epoll), cannot register events for file descriptors,
		1271	but only events for the underlying file descriptions. That means when you
		1272	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1273	events for them, only one file descriptor might actually receive events.
		1274
		1275	There is no workaround possible except not registering events
		1276	for potentially C<dup ()>'ed file descriptors, or to resort to
		1277	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1278
		1279	=head3 The special problem of fork
		1280
		1281	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1282	useless behaviour. Libev fully supports fork, but needs to be told about
		1283	it in the child.
		1284
		1285	To support fork in your programs, you either have to call
		1286	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1287	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1288	C<EVBACKEND_POLL>.
		1289
		1290	=head3 The special problem of SIGPIPE
		1291
		1292	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1293	when writing to a pipe whose other end has been closed, your program gets
		1294	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1295	this is sensible behaviour, for daemons, this is usually undesirable.
		1296
		1297	So when you encounter spurious, unexplained daemon exits, make sure you
		1298	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1299	somewhere, as that would have given you a big clue).
		1300
		1301
		1302	=head3 Watcher-Specific Functions
911		1303
912	=over 4	1304	=over 4
913		1305
914	=item ev_io_init (ev_io *, callback, int fd, int events)	1306	=item ev_io_init (ev_io *, callback, int fd, int events)
915		1307
916	=item ev_io_set (ev_io *, int fd, int events)	1308	=item ev_io_set (ev_io *, int fd, int events)
917		1309
918	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1310	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
919	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1311	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
920	C<EV_READ | EV_WRITE> to receive the given events.	1312	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
921		1313
922	=item int fd [read-only]	1314	=item int fd [read-only]
923		1315
924	The file descriptor being watched.	1316	The file descriptor being watched.
925		1317
926	=item int events [read-only]	1318	=item int events [read-only]
927		1319
928	The events being watched.	1320	The events being watched.
929		1321
930	=back	1322	=back
		1323
		1324	=head3 Examples
931		1325
932	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1326	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
933	readable, but only once. Since it is likely line-buffered, you could	1327	readable, but only once. Since it is likely line-buffered, you could
934	attempt to read a whole line in the callback.	1328	attempt to read a whole line in the callback.
935		1329
936	static void	1330	static void
937	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1331	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
938	{	1332	{
939	ev_io_stop (loop, w);	1333	ev_io_stop (loop, w);
940	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1334	.. read from stdin here (or from w->fd) and handle any I/O errors
941	}	1335	}
942		1336
943	...	1337	...
944	struct ev_loop *loop = ev_default_init (0);	1338	struct ev_loop *loop = ev_default_init (0);
945	struct ev_io stdin_readable;	1339	ev_io stdin_readable;
946	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1340	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
947	ev_io_start (loop, &stdin_readable);	1341	ev_io_start (loop, &stdin_readable);
948	ev_loop (loop, 0);	1342	ev_loop (loop, 0);
949		1343
950		1344
951	=head2 C<ev_timer> - relative and optionally repeating timeouts	1345	=head2 C<ev_timer> - relative and optionally repeating timeouts
952		1346
953	Timer watchers are simple relative timers that generate an event after a	1347	Timer watchers are simple relative timers that generate an event after a
954	given time, and optionally repeating in regular intervals after that.	1348	given time, and optionally repeating in regular intervals after that.
955		1349
956	The timers are based on real time, that is, if you register an event that	1350	The timers are based on real time, that is, if you register an event that
957	times out after an hour and you reset your system clock to last years	1351	times out after an hour and you reset your system clock to January last
958	time, it will still time out after (roughly) and hour. "Roughly" because	1352	year, it will still time out after (roughly) one hour. "Roughly" because
959	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1353	detecting time jumps is hard, and some inaccuracies are unavoidable (the
960	monotonic clock option helps a lot here).	1354	monotonic clock option helps a lot here).
		1355
		1356	The callback is guaranteed to be invoked only I<after> its timeout has
		1357	passed. If multiple timers become ready during the same loop iteration
		1358	then the ones with earlier time-out values are invoked before ones with
		1359	later time-out values (but this is no longer true when a callback calls
		1360	C<ev_loop> recursively).
		1361
		1362	=head3 Be smart about timeouts
		1363
		1364	Many real-world problems involve some kind of timeout, usually for error
		1365	recovery. A typical example is an HTTP request - if the other side hangs,
		1366	you want to raise some error after a while.
		1367
		1368	What follows are some ways to handle this problem, from obvious and
		1369	inefficient to smart and efficient.
		1370
		1371	In the following, a 60 second activity timeout is assumed - a timeout that
		1372	gets reset to 60 seconds each time there is activity (e.g. each time some
		1373	data or other life sign was received).
		1374
		1375	=over 4
		1376
		1377	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1378
		1379	This is the most obvious, but not the most simple way: In the beginning,
		1380	start the watcher:
		1381
		1382	ev_timer_init (timer, callback, 60., 0.);
		1383	ev_timer_start (loop, timer);
		1384
		1385	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1386	and start it again:
		1387
		1388	ev_timer_stop (loop, timer);
		1389	ev_timer_set (timer, 60., 0.);
		1390	ev_timer_start (loop, timer);
		1391
		1392	This is relatively simple to implement, but means that each time there is
		1393	some activity, libev will first have to remove the timer from its internal
		1394	data structure and then add it again. Libev tries to be fast, but it's
		1395	still not a constant-time operation.
		1396
		1397	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1398
		1399	This is the easiest way, and involves using C<ev_timer_again> instead of
		1400	C<ev_timer_start>.
		1401
		1402	To implement this, configure an C<ev_timer> with a C<repeat> value
		1403	of C<60> and then call C<ev_timer_again> at start and each time you
		1404	successfully read or write some data. If you go into an idle state where
		1405	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1406	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1407
		1408	That means you can ignore both the C<ev_timer_start> function and the
		1409	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1410	member and C<ev_timer_again>.
		1411
		1412	At start:
		1413
		1414	ev_timer_init (timer, callback);
		1415	timer->repeat = 60.;
		1416	ev_timer_again (loop, timer);
		1417
		1418	Each time there is some activity:
		1419
		1420	ev_timer_again (loop, timer);
		1421
		1422	It is even possible to change the time-out on the fly, regardless of
		1423	whether the watcher is active or not:
		1424
		1425	timer->repeat = 30.;
		1426	ev_timer_again (loop, timer);
		1427
		1428	This is slightly more efficient then stopping/starting the timer each time
		1429	you want to modify its timeout value, as libev does not have to completely
		1430	remove and re-insert the timer from/into its internal data structure.
		1431
		1432	It is, however, even simpler than the "obvious" way to do it.
		1433
		1434	=item 3. Let the timer time out, but then re-arm it as required.
		1435
		1436	This method is more tricky, but usually most efficient: Most timeouts are
		1437	relatively long compared to the intervals between other activity - in
		1438	our example, within 60 seconds, there are usually many I/O events with
		1439	associated activity resets.
		1440
		1441	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1442	but remember the time of last activity, and check for a real timeout only
		1443	within the callback:
		1444
		1445	ev_tstamp last_activity; // time of last activity
		1446
		1447	static void
		1448	callback (EV_P_ ev_timer *w, int revents)
		1449	{
		1450	ev_tstamp now = ev_now (EV_A);
		1451	ev_tstamp timeout = last_activity + 60.;
		1452
		1453	// if last_activity + 60. is older than now, we did time out
		1454	if (timeout < now)
		1455	{
		1456	// timeout occured, take action
		1457	}
		1458	else
		1459	{
		1460	// callback was invoked, but there was some activity, re-arm
		1461	// the watcher to fire in last_activity + 60, which is
		1462	// guaranteed to be in the future, so "again" is positive:
		1463	w->repeat = timeout - now;
		1464	ev_timer_again (EV_A_ w);
		1465	}
		1466	}
		1467
		1468	To summarise the callback: first calculate the real timeout (defined
		1469	as "60 seconds after the last activity"), then check if that time has
		1470	been reached, which means something I<did>, in fact, time out. Otherwise
		1471	the callback was invoked too early (C<timeout> is in the future), so
		1472	re-schedule the timer to fire at that future time, to see if maybe we have
		1473	a timeout then.
		1474
		1475	Note how C<ev_timer_again> is used, taking advantage of the
		1476	C<ev_timer_again> optimisation when the timer is already running.
		1477
		1478	This scheme causes more callback invocations (about one every 60 seconds
		1479	minus half the average time between activity), but virtually no calls to
		1480	libev to change the timeout.
		1481
		1482	To start the timer, simply initialise the watcher and set C<last_activity>
		1483	to the current time (meaning we just have some activity :), then call the
		1484	callback, which will "do the right thing" and start the timer:
		1485
		1486	ev_timer_init (timer, callback);
		1487	last_activity = ev_now (loop);
		1488	callback (loop, timer, EV_TIMEOUT);
		1489
		1490	And when there is some activity, simply store the current time in
		1491	C<last_activity>, no libev calls at all:
		1492
		1493	last_actiivty = ev_now (loop);
		1494
		1495	This technique is slightly more complex, but in most cases where the
		1496	time-out is unlikely to be triggered, much more efficient.
		1497
		1498	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1499	callback :) - just change the timeout and invoke the callback, which will
		1500	fix things for you.
		1501
		1502	=item 4. Wee, just use a double-linked list for your timeouts.
		1503
		1504	If there is not one request, but many thousands (millions...), all
		1505	employing some kind of timeout with the same timeout value, then one can
		1506	do even better:
		1507
		1508	When starting the timeout, calculate the timeout value and put the timeout
		1509	at the I<end> of the list.
		1510
		1511	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1512	the list is expected to fire (for example, using the technique #3).
		1513
		1514	When there is some activity, remove the timer from the list, recalculate
		1515	the timeout, append it to the end of the list again, and make sure to
		1516	update the C<ev_timer> if it was taken from the beginning of the list.
		1517
		1518	This way, one can manage an unlimited number of timeouts in O(1) time for
		1519	starting, stopping and updating the timers, at the expense of a major
		1520	complication, and having to use a constant timeout. The constant timeout
		1521	ensures that the list stays sorted.
		1522
		1523	=back
		1524
		1525	So which method the best?
		1526
		1527	Method #2 is a simple no-brain-required solution that is adequate in most
		1528	situations. Method #3 requires a bit more thinking, but handles many cases
		1529	better, and isn't very complicated either. In most case, choosing either
		1530	one is fine, with #3 being better in typical situations.
		1531
		1532	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1533	rather complicated, but extremely efficient, something that really pays
		1534	off after the first million or so of active timers, i.e. it's usually
		1535	overkill :)
		1536
		1537	=head3 The special problem of time updates
		1538
		1539	Establishing the current time is a costly operation (it usually takes at
		1540	least two system calls): EV therefore updates its idea of the current
		1541	time only before and after C<ev_loop> collects new events, which causes a
		1542	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1543	lots of events in one iteration.
961		1544
962	The relative timeouts are calculated relative to the C<ev_now ()>	1545	The relative timeouts are calculated relative to the C<ev_now ()>
963	time. This is usually the right thing as this timestamp refers to the time	1546	time. This is usually the right thing as this timestamp refers to the time
964	of the event triggering whatever timeout you are modifying/starting. If	1547	of the event triggering whatever timeout you are modifying/starting. If
965	you suspect event processing to be delayed and you I<need> to base the timeout	1548	you suspect event processing to be delayed and you I<need> to base the
966	on the current time, use something like this to adjust for this:	1549	timeout on the current time, use something like this to adjust for this:
967		1550
968	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1551	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
969		1552
970	The callback is guarenteed to be invoked only when its timeout has passed,	1553	If the event loop is suspended for a long time, you can also force an
971	but if multiple timers become ready during the same loop iteration then	1554	update of the time returned by C<ev_now ()> by calling C<ev_now_update
972	order of execution is undefined.	1555	()>.
		1556
		1557	=head3 Watcher-Specific Functions and Data Members
973		1558
974	=over 4	1559	=over 4
975		1560
976	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1561	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
977		1562
978	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1563	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
979		1564
980	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1565	Configure the timer to trigger after C<after> seconds. If C<repeat>
981	C<0.>, then it will automatically be stopped. If it is positive, then the	1566	is C<0.>, then it will automatically be stopped once the timeout is
982	timer will automatically be configured to trigger again C<repeat> seconds	1567	reached. If it is positive, then the timer will automatically be
983	later, again, and again, until stopped manually.	1568	configured to trigger again C<repeat> seconds later, again, and again,
		1569	until stopped manually.
984		1570
985	The timer itself will do a best-effort at avoiding drift, that is, if you	1571	The timer itself will do a best-effort at avoiding drift, that is, if
986	configure a timer to trigger every 10 seconds, then it will trigger at	1572	you configure a timer to trigger every 10 seconds, then it will normally
987	exactly 10 second intervals. If, however, your program cannot keep up with	1573	trigger at exactly 10 second intervals. If, however, your program cannot
988	the timer (because it takes longer than those 10 seconds to do stuff) the	1574	keep up with the timer (because it takes longer than those 10 seconds to
989	timer will not fire more than once per event loop iteration.	1575	do stuff) the timer will not fire more than once per event loop iteration.
990		1576
991	=item ev_timer_again (loop)	1577	=item ev_timer_again (loop, ev_timer *)
992		1578
993	This will act as if the timer timed out and restart it again if it is	1579	This will act as if the timer timed out and restart it again if it is
994	repeating. The exact semantics are:	1580	repeating. The exact semantics are:
995		1581
996	If the timer is pending, its pending status is cleared.	1582	If the timer is pending, its pending status is cleared.
997		1583
998	If the timer is started but nonrepeating, stop it (as if it timed out).	1584	If the timer is started but non-repeating, stop it (as if it timed out).
999		1585
1000	If the timer is repeating, either start it if necessary (with the	1586	If the timer is repeating, either start it if necessary (with the
1001	C<repeat> value), or reset the running timer to the C<repeat> value.	1587	C<repeat> value), or reset the running timer to the C<repeat> value.
1002		1588
1003	This sounds a bit complicated, but here is a useful and typical	1589	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1004	example: Imagine you have a tcp connection and you want a so-called idle	1590	usage example.
1005	timeout, that is, you want to be called when there have been, say, 60
1006	seconds of inactivity on the socket. The easiest way to do this is to
1007	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1008	C<ev_timer_again> each time you successfully read or write some data. If
1009	you go into an idle state where you do not expect data to travel on the
1010	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1011	automatically restart it if need be.
1012
1013	That means you can ignore the C<after> value and C<ev_timer_start>
1014	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1015
1016	ev_timer_init (timer, callback, 0., 5.);
1017	ev_timer_again (loop, timer);
1018	...
1019	timer->again = 17.;
1020	ev_timer_again (loop, timer);
1021	...
1022	timer->again = 10.;
1023	ev_timer_again (loop, timer);
1024
1025	This is more slightly efficient then stopping/starting the timer each time
1026	you want to modify its timeout value.
1027		1591
1028	=item ev_tstamp repeat [read-write]	1592	=item ev_tstamp repeat [read-write]
1029		1593
1030	The current C<repeat> value. Will be used each time the watcher times out	1594	The current C<repeat> value. Will be used each time the watcher times out
1031	or C<ev_timer_again> is called and determines the next timeout (if any),	1595	or C<ev_timer_again> is called, and determines the next timeout (if any),
1032	which is also when any modifications are taken into account.	1596	which is also when any modifications are taken into account.
1033		1597
1034	=back	1598	=back
1035		1599
		1600	=head3 Examples
		1601
1036	Example: Create a timer that fires after 60 seconds.	1602	Example: Create a timer that fires after 60 seconds.
1037		1603
1038	static void	1604	static void
1039	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1605	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1040	{	1606	{
1041	.. one minute over, w is actually stopped right here	1607	.. one minute over, w is actually stopped right here
1042	}	1608	}
1043		1609
1044	struct ev_timer mytimer;	1610	ev_timer mytimer;
1045	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1611	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1046	ev_timer_start (loop, &mytimer);	1612	ev_timer_start (loop, &mytimer);
1047		1613
1048	Example: Create a timeout timer that times out after 10 seconds of	1614	Example: Create a timeout timer that times out after 10 seconds of
1049	inactivity.	1615	inactivity.
1050		1616
1051	static void	1617	static void
1052	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1618	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1053	{	1619	{
1054	.. ten seconds without any activity	1620	.. ten seconds without any activity
1055	}	1621	}
1056		1622
1057	struct ev_timer mytimer;	1623	ev_timer mytimer;
1058	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1624	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1059	ev_timer_again (&mytimer); /* start timer */	1625	ev_timer_again (&mytimer); /* start timer */
1060	ev_loop (loop, 0);	1626	ev_loop (loop, 0);
1061		1627
1062	// and in some piece of code that gets executed on any "activity":	1628	// and in some piece of code that gets executed on any "activity":
1063	// reset the timeout to start ticking again at 10 seconds	1629	// reset the timeout to start ticking again at 10 seconds
1064	ev_timer_again (&mytimer);	1630	ev_timer_again (&mytimer);
1065		1631
1066		1632
1067	=head2 C<ev_periodic> - to cron or not to cron?	1633	=head2 C<ev_periodic> - to cron or not to cron?
1068		1634
1069	Periodic watchers are also timers of a kind, but they are very versatile	1635	Periodic watchers are also timers of a kind, but they are very versatile
1070	(and unfortunately a bit complex).	1636	(and unfortunately a bit complex).
1071		1637
1072	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1638	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1073	but on wallclock time (absolute time). You can tell a periodic watcher	1639	relative time, the physical time that passes) but on wall clock time
1074	to trigger "at" some specific point in time. For example, if you tell a	1640	(absolute time, the thing you can read on your calender or clock). The
1075	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	1641	difference is that wall clock time can run faster or slower than real
1076	+ 10.>) and then reset your system clock to the last year, then it will	1642	time, and time jumps are not uncommon (e.g. when you adjust your
1077	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1643	wrist-watch).
1078	roughly 10 seconds later and of course not if you reset your system time
1079	again).
1080		1644
1081	They can also be used to implement vastly more complex timers, such as	1645	You can tell a periodic watcher to trigger after some specific point
		1646	in time: for example, if you tell a periodic watcher to trigger "in 10
		1647	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1648	not a delay) and then reset your system clock to January of the previous
		1649	year, then it will take a year or more to trigger the event (unlike an
		1650	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1651	it, as it uses a relative timeout).
		1652
		1653	C<ev_periodic> watchers can also be used to implement vastly more complex
1082	triggering an event on eahc midnight, local time.	1654	timers, such as triggering an event on each "midnight, local time", or
		1655	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1656	those cannot react to time jumps.
1083		1657
1084	As with timers, the callback is guarenteed to be invoked only when the	1658	As with timers, the callback is guaranteed to be invoked only when the
1085	time (C<at>) has been passed, but if multiple periodic timers become ready	1659	point in time where it is supposed to trigger has passed. If multiple
1086	during the same loop iteration then order of execution is undefined.	1660	timers become ready during the same loop iteration then the ones with
		1661	earlier time-out values are invoked before ones with later time-out values
		1662	(but this is no longer true when a callback calls C<ev_loop> recursively).
		1663
		1664	=head3 Watcher-Specific Functions and Data Members
1087		1665
1088	=over 4	1666	=over 4
1089		1667
1090	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1668	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1091		1669
1092	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1670	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1093		1671
1094	Lots of arguments, lets sort it out... There are basically three modes of	1672	Lots of arguments, let's sort it out... There are basically three modes of
1095	operation, and we will explain them from simplest to complex:	1673	operation, and we will explain them from simplest to most complex:
1096		1674
1097	=over 4	1675	=over 4
1098		1676
1099	=item * absolute timer (interval = reschedule_cb = 0)	1677	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1100		1678
1101	In this configuration the watcher triggers an event at the wallclock time	1679	In this configuration the watcher triggers an event after the wall clock
1102	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1680	time C<offset> has passed. It will not repeat and will not adjust when a
1103	that is, if it is to be run at January 1st 2011 then it will run when the	1681	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1104	system time reaches or surpasses this time.	1682	will be stopped and invoked when the system clock reaches or surpasses
		1683	this point in time.
1105		1684
1106	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1685	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1107		1686
1108	In this mode the watcher will always be scheduled to time out at the next	1687	In this mode the watcher will always be scheduled to time out at the next
1109	C<at + N * interval> time (for some integer N) and then repeat, regardless	1688	C<offset + N * interval> time (for some integer N, which can also be
1110	of any time jumps.	1689	negative) and then repeat, regardless of any time jumps. The C<offset>
		1690	argument is merely an offset into the C<interval> periods.
1111		1691
1112	This can be used to create timers that do not drift with respect to system	1692	This can be used to create timers that do not drift with respect to the
1113	time:	1693	system clock, for example, here is an C<ev_periodic> that triggers each
		1694	hour, on the hour (with respect to UTC):
1114		1695
1115	ev_periodic_set (&periodic, 0., 3600., 0);	1696	ev_periodic_set (&periodic, 0., 3600., 0);
1116		1697
1117	This doesn't mean there will always be 3600 seconds in between triggers,	1698	This doesn't mean there will always be 3600 seconds in between triggers,
1118	but only that the the callback will be called when the system time shows a	1699	but only that the callback will be called when the system time shows a
1119	full hour (UTC), or more correctly, when the system time is evenly divisible	1700	full hour (UTC), or more correctly, when the system time is evenly divisible
1120	by 3600.	1701	by 3600.
1121		1702
1122	Another way to think about it (for the mathematically inclined) is that	1703	Another way to think about it (for the mathematically inclined) is that
1123	C<ev_periodic> will try to run the callback in this mode at the next possible	1704	C<ev_periodic> will try to run the callback in this mode at the next possible
1124	time where C<time = at (mod interval)>, regardless of any time jumps.	1705	time where C<time = offset (mod interval)>, regardless of any time jumps.
1125		1706
		1707	For numerical stability it is preferable that the C<offset> value is near
		1708	C<ev_now ()> (the current time), but there is no range requirement for
		1709	this value, and in fact is often specified as zero.
		1710
		1711	Note also that there is an upper limit to how often a timer can fire (CPU
		1712	speed for example), so if C<interval> is very small then timing stability
		1713	will of course deteriorate. Libev itself tries to be exact to be about one
		1714	millisecond (if the OS supports it and the machine is fast enough).
		1715
1126	=item * manual reschedule mode (reschedule_cb = callback)	1716	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1127		1717
1128	In this mode the values for C<interval> and C<at> are both being	1718	In this mode the values for C<interval> and C<offset> are both being
1129	ignored. Instead, each time the periodic watcher gets scheduled, the	1719	ignored. Instead, each time the periodic watcher gets scheduled, the
1130	reschedule callback will be called with the watcher as first, and the	1720	reschedule callback will be called with the watcher as first, and the
1131	current time as second argument.	1721	current time as second argument.
1132		1722
1133	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1723	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1134	ever, or make any event loop modifications>. If you need to stop it,	1724	or make ANY other event loop modifications whatsoever, unless explicitly
1135	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	1725	allowed by documentation here>.
1136	starting a prepare watcher).
1137		1726
		1727	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1728	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1729	only event loop modification you are allowed to do).
		1730
1138	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1731	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1139	ev_tstamp now)>, e.g.:	1732	*w, ev_tstamp now)>, e.g.:
1140		1733
		1734	static ev_tstamp
1141	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1735	my_rescheduler (ev_periodic *w, ev_tstamp now)
1142	{	1736	{
1143	return now + 60.;	1737	return now + 60.;
1144	}	1738	}
1145		1739
1146	It must return the next time to trigger, based on the passed time value	1740	It must return the next time to trigger, based on the passed time value
1147	(that is, the lowest time value larger than to the second argument). It	1741	(that is, the lowest time value larger than to the second argument). It
1148	will usually be called just before the callback will be triggered, but	1742	will usually be called just before the callback will be triggered, but
1149	might be called at other times, too.	1743	might be called at other times, too.
1150		1744
1151	NOTE: I<< This callback must always return a time that is later than the	1745	NOTE: I<< This callback must always return a time that is higher than or
1152	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	1746	equal to the passed C<now> value >>.
1153		1747
1154	This can be used to create very complex timers, such as a timer that	1748	This can be used to create very complex timers, such as a timer that
1155	triggers on each midnight, local time. To do this, you would calculate the	1749	triggers on "next midnight, local time". To do this, you would calculate the
1156	next midnight after C<now> and return the timestamp value for this. How	1750	next midnight after C<now> and return the timestamp value for this. How
1157	you do this is, again, up to you (but it is not trivial, which is the main	1751	you do this is, again, up to you (but it is not trivial, which is the main
1158	reason I omitted it as an example).	1752	reason I omitted it as an example).
1159		1753
1160	=back	1754	=back
…		…
1164	Simply stops and restarts the periodic watcher again. This is only useful	1758	Simply stops and restarts the periodic watcher again. This is only useful
1165	when you changed some parameters or the reschedule callback would return	1759	when you changed some parameters or the reschedule callback would return
1166	a different time than the last time it was called (e.g. in a crond like	1760	a different time than the last time it was called (e.g. in a crond like
1167	program when the crontabs have changed).	1761	program when the crontabs have changed).
1168		1762
		1763	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1764
		1765	When active, returns the absolute time that the watcher is supposed
		1766	to trigger next. This is not the same as the C<offset> argument to
		1767	C<ev_periodic_set>, but indeed works even in interval and manual
		1768	rescheduling modes.
		1769
		1770	=item ev_tstamp offset [read-write]
		1771
		1772	When repeating, this contains the offset value, otherwise this is the
		1773	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		1774	although libev might modify this value for better numerical stability).
		1775
		1776	Can be modified any time, but changes only take effect when the periodic
		1777	timer fires or C<ev_periodic_again> is being called.
		1778
1169	=item ev_tstamp interval [read-write]	1779	=item ev_tstamp interval [read-write]
1170		1780
1171	The current interval value. Can be modified any time, but changes only	1781	The current interval value. Can be modified any time, but changes only
1172	take effect when the periodic timer fires or C<ev_periodic_again> is being	1782	take effect when the periodic timer fires or C<ev_periodic_again> is being
1173	called.	1783	called.
1174		1784
1175	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	1785	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1176		1786
1177	The current reschedule callback, or C<0>, if this functionality is	1787	The current reschedule callback, or C<0>, if this functionality is
1178	switched off. Can be changed any time, but changes only take effect when	1788	switched off. Can be changed any time, but changes only take effect when
1179	the periodic timer fires or C<ev_periodic_again> is being called.	1789	the periodic timer fires or C<ev_periodic_again> is being called.
1180		1790
1181	=back	1791	=back
1182		1792
		1793	=head3 Examples
		1794
1183	Example: Call a callback every hour, or, more precisely, whenever the	1795	Example: Call a callback every hour, or, more precisely, whenever the
1184	system clock is divisible by 3600. The callback invocation times have	1796	system time is divisible by 3600. The callback invocation times have
1185	potentially a lot of jittering, but good long-term stability.	1797	potentially a lot of jitter, but good long-term stability.
1186		1798
1187	static void	1799	static void
1188	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1800	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1189	{	1801	{
1190	... its now a full hour (UTC, or TAI or whatever your clock follows)	1802	... its now a full hour (UTC, or TAI or whatever your clock follows)
1191	}	1803	}
1192		1804
1193	struct ev_periodic hourly_tick;	1805	ev_periodic hourly_tick;
1194	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	1806	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1195	ev_periodic_start (loop, &hourly_tick);	1807	ev_periodic_start (loop, &hourly_tick);
1196		1808
1197	Example: The same as above, but use a reschedule callback to do it:	1809	Example: The same as above, but use a reschedule callback to do it:
1198		1810
1199	#include <math.h>	1811	#include <math.h>
1200		1812
1201	static ev_tstamp	1813	static ev_tstamp
1202	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	1814	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1203	{	1815	{
1204	return fmod (now, 3600.) + 3600.;	1816	return now + (3600. - fmod (now, 3600.));
1205	}	1817	}
1206		1818
1207	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	1819	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1208		1820
1209	Example: Call a callback every hour, starting now:	1821	Example: Call a callback every hour, starting now:
1210		1822
1211	struct ev_periodic hourly_tick;	1823	ev_periodic hourly_tick;
1212	ev_periodic_init (&hourly_tick, clock_cb,	1824	ev_periodic_init (&hourly_tick, clock_cb,
1213	fmod (ev_now (loop), 3600.), 3600., 0);	1825	fmod (ev_now (loop), 3600.), 3600., 0);
1214	ev_periodic_start (loop, &hourly_tick);	1826	ev_periodic_start (loop, &hourly_tick);
1215		1827
1216		1828
1217	=head2 C<ev_signal> - signal me when a signal gets signalled!	1829	=head2 C<ev_signal> - signal me when a signal gets signalled!
1218		1830
1219	Signal watchers will trigger an event when the process receives a specific	1831	Signal watchers will trigger an event when the process receives a specific
1220	signal one or more times. Even though signals are very asynchronous, libev	1832	signal one or more times. Even though signals are very asynchronous, libev
1221	will try it's best to deliver signals synchronously, i.e. as part of the	1833	will try it's best to deliver signals synchronously, i.e. as part of the
1222	normal event processing, like any other event.	1834	normal event processing, like any other event.
1223		1835
		1836	If you want signals asynchronously, just use C<sigaction> as you would
		1837	do without libev and forget about sharing the signal. You can even use
		1838	C<ev_async> from a signal handler to synchronously wake up an event loop.
		1839
1224	You can configure as many watchers as you like per signal. Only when the	1840	You can configure as many watchers as you like per signal. Only when the
1225	first watcher gets started will libev actually register a signal watcher	1841	first watcher gets started will libev actually register a signal handler
1226	with the kernel (thus it coexists with your own signal handlers as long	1842	with the kernel (thus it coexists with your own signal handlers as long as
1227	as you don't register any with libev). Similarly, when the last signal	1843	you don't register any with libev for the same signal). Similarly, when
1228	watcher for a signal is stopped libev will reset the signal handler to	1844	the last signal watcher for a signal is stopped, libev will reset the
1229	SIG_DFL (regardless of what it was set to before).	1845	signal handler to SIG_DFL (regardless of what it was set to before).
		1846
		1847	If possible and supported, libev will install its handlers with
		1848	C<SA_RESTART> behaviour enabled, so system calls should not be unduly
		1849	interrupted. If you have a problem with system calls getting interrupted by
		1850	signals you can block all signals in an C<ev_check> watcher and unblock
		1851	them in an C<ev_prepare> watcher.
		1852
		1853	=head3 Watcher-Specific Functions and Data Members
1230		1854
1231	=over 4	1855	=over 4
1232		1856
1233	=item ev_signal_init (ev_signal *, callback, int signum)	1857	=item ev_signal_init (ev_signal *, callback, int signum)
1234		1858
…		…
1241		1865
1242	The signal the watcher watches out for.	1866	The signal the watcher watches out for.
1243		1867
1244	=back	1868	=back
1245		1869
		1870	=head3 Examples
		1871
		1872	Example: Try to exit cleanly on SIGINT.
		1873
		1874	static void
		1875	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		1876	{
		1877	ev_unloop (loop, EVUNLOOP_ALL);
		1878	}
		1879
		1880	ev_signal signal_watcher;
		1881	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1882	ev_signal_start (loop, &signal_watcher);
		1883
1246		1884
1247	=head2 C<ev_child> - watch out for process status changes	1885	=head2 C<ev_child> - watch out for process status changes
1248		1886
1249	Child watchers trigger when your process receives a SIGCHLD in response to	1887	Child watchers trigger when your process receives a SIGCHLD in response to
1250	some child status changes (most typically when a child of yours dies).	1888	some child status changes (most typically when a child of yours dies or
		1889	exits). It is permissible to install a child watcher I<after> the child
		1890	has been forked (which implies it might have already exited), as long
		1891	as the event loop isn't entered (or is continued from a watcher), i.e.,
		1892	forking and then immediately registering a watcher for the child is fine,
		1893	but forking and registering a watcher a few event loop iterations later is
		1894	not.
		1895
		1896	Only the default event loop is capable of handling signals, and therefore
		1897	you can only register child watchers in the default event loop.
		1898
		1899	=head3 Process Interaction
		1900
		1901	Libev grabs C<SIGCHLD> as soon as the default event loop is
		1902	initialised. This is necessary to guarantee proper behaviour even if
		1903	the first child watcher is started after the child exits. The occurrence
		1904	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		1905	synchronously as part of the event loop processing. Libev always reaps all
		1906	children, even ones not watched.
		1907
		1908	=head3 Overriding the Built-In Processing
		1909
		1910	Libev offers no special support for overriding the built-in child
		1911	processing, but if your application collides with libev's default child
		1912	handler, you can override it easily by installing your own handler for
		1913	C<SIGCHLD> after initialising the default loop, and making sure the
		1914	default loop never gets destroyed. You are encouraged, however, to use an
		1915	event-based approach to child reaping and thus use libev's support for
		1916	that, so other libev users can use C<ev_child> watchers freely.
		1917
		1918	=head3 Stopping the Child Watcher
		1919
		1920	Currently, the child watcher never gets stopped, even when the
		1921	child terminates, so normally one needs to stop the watcher in the
		1922	callback. Future versions of libev might stop the watcher automatically
		1923	when a child exit is detected.
		1924
		1925	=head3 Watcher-Specific Functions and Data Members
1251		1926
1252	=over 4	1927	=over 4
1253		1928
1254	=item ev_child_init (ev_child *, callback, int pid)	1929	=item ev_child_init (ev_child *, callback, int pid, int trace)
1255		1930
1256	=item ev_child_set (ev_child *, int pid)	1931	=item ev_child_set (ev_child *, int pid, int trace)
1257		1932
1258	Configures the watcher to wait for status changes of process C<pid> (or	1933	Configures the watcher to wait for status changes of process C<pid> (or
1259	I<any> process if C<pid> is specified as C<0>). The callback can look	1934	I<any> process if C<pid> is specified as C<0>). The callback can look
1260	at the C<rstatus> member of the C<ev_child> watcher structure to see	1935	at the C<rstatus> member of the C<ev_child> watcher structure to see
1261	the status word (use the macros from C<sys/wait.h> and see your systems	1936	the status word (use the macros from C<sys/wait.h> and see your systems
1262	C<waitpid> documentation). The C<rpid> member contains the pid of the	1937	C<waitpid> documentation). The C<rpid> member contains the pid of the
1263	process causing the status change.	1938	process causing the status change. C<trace> must be either C<0> (only
		1939	activate the watcher when the process terminates) or C<1> (additionally
		1940	activate the watcher when the process is stopped or continued).
1264		1941
1265	=item int pid [read-only]	1942	=item int pid [read-only]
1266		1943
1267	The process id this watcher watches out for, or C<0>, meaning any process id.	1944	The process id this watcher watches out for, or C<0>, meaning any process id.
1268		1945
…		…
1275	The process exit/trace status caused by C<rpid> (see your systems	1952	The process exit/trace status caused by C<rpid> (see your systems
1276	C<waitpid> and C<sys/wait.h> documentation for details).	1953	C<waitpid> and C<sys/wait.h> documentation for details).
1277		1954
1278	=back	1955	=back
1279		1956
1280	Example: Try to exit cleanly on SIGINT and SIGTERM.	1957	=head3 Examples
1281		1958
		1959	Example: C<fork()> a new process and install a child handler to wait for
		1960	its completion.
		1961
		1962	ev_child cw;
		1963
1282	static void	1964	static void
1283	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	1965	child_cb (EV_P_ ev_child *w, int revents)
1284	{	1966	{
1285	ev_unloop (loop, EVUNLOOP_ALL);	1967	ev_child_stop (EV_A_ w);
		1968	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1286	}	1969	}
1287		1970
1288	struct ev_signal signal_watcher;	1971	pid_t pid = fork ();
1289	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	1972
1290	ev_signal_start (loop, &sigint_cb);	1973	if (pid < 0)
		1974	// error
		1975	else if (pid == 0)
		1976	{
		1977	// the forked child executes here
		1978	exit (1);
		1979	}
		1980	else
		1981	{
		1982	ev_child_init (&cw, child_cb, pid, 0);
		1983	ev_child_start (EV_DEFAULT_ &cw);
		1984	}
1291		1985
1292		1986
1293	=head2 C<ev_stat> - did the file attributes just change?	1987	=head2 C<ev_stat> - did the file attributes just change?
1294		1988
1295	This watches a filesystem path for attribute changes. That is, it calls	1989	This watches a file system path for attribute changes. That is, it calls
1296	C<stat> regularly (or when the OS says it changed) and sees if it changed	1990	C<stat> on that path in regular intervals (or when the OS says it changed)
1297	compared to the last time, invoking the callback if it did.	1991	and sees if it changed compared to the last time, invoking the callback if
		1992	it did.
1298		1993
1299	The path does not need to exist: changing from "path exists" to "path does	1994	The path does not need to exist: changing from "path exists" to "path does
1300	not exist" is a status change like any other. The condition "path does	1995	not exist" is a status change like any other. The condition "path does not
1301	not exist" is signified by the C<st_nlink> field being zero (which is	1996	exist" (or more correctly "path cannot be stat'ed") is signified by the
1302	otherwise always forced to be at least one) and all the other fields of	1997	C<st_nlink> field being zero (which is otherwise always forced to be at
1303	the stat buffer having unspecified contents.	1998	least one) and all the other fields of the stat buffer having unspecified
		1999	contents.
1304		2000
1305	The path I<should> be absolute and I<must not> end in a slash. If it is	2001	The path I<must not> end in a slash or contain special components such as
		2002	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1306	relative and your working directory changes, the behaviour is undefined.	2003	your working directory changes, then the behaviour is undefined.
1307		2004
1308	Since there is no standard to do this, the portable implementation simply	2005	Since there is no portable change notification interface available, the
1309	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2006	portable implementation simply calls C<stat(2)> regularly on the path
1310	can specify a recommended polling interval for this case. If you specify	2007	to see if it changed somehow. You can specify a recommended polling
1311	a polling interval of C<0> (highly recommended!) then a I<suitable,	2008	interval for this case. If you specify a polling interval of C<0> (highly
1312	unspecified default> value will be used (which you can expect to be around	2009	recommended!) then a I<suitable, unspecified default> value will be used
1313	five seconds, although this might change dynamically). Libev will also	2010	(which you can expect to be around five seconds, although this might
1314	impose a minimum interval which is currently around C<0.1>, but thats	2011	change dynamically). Libev will also impose a minimum interval which is
1315	usually overkill.	2012	currently around C<0.1>, but that's usually overkill.
1316		2013
1317	This watcher type is not meant for massive numbers of stat watchers,	2014	This watcher type is not meant for massive numbers of stat watchers,
1318	as even with OS-supported change notifications, this can be	2015	as even with OS-supported change notifications, this can be
1319	resource-intensive.	2016	resource-intensive.
1320		2017
1321	At the time of this writing, only the Linux inotify interface is	2018	At the time of this writing, the only OS-specific interface implemented
1322	implemented (implementing kqueue support is left as an exercise for the	2019	is the Linux inotify interface (implementing kqueue support is left as an
1323	reader). Inotify will be used to give hints only and should not change the	2020	exercise for the reader. Note, however, that the author sees no way of
1324	semantics of C<ev_stat> watchers, which means that libev sometimes needs	2021	implementing C<ev_stat> semantics with kqueue, except as a hint).
1325	to fall back to regular polling again even with inotify, but changes are	2022
1326	usually detected immediately, and if the file exists there will be no	2023	=head3 ABI Issues (Largefile Support)
1327	polling.	2024
		2025	Libev by default (unless the user overrides this) uses the default
		2026	compilation environment, which means that on systems with large file
		2027	support disabled by default, you get the 32 bit version of the stat
		2028	structure. When using the library from programs that change the ABI to
		2029	use 64 bit file offsets the programs will fail. In that case you have to
		2030	compile libev with the same flags to get binary compatibility. This is
		2031	obviously the case with any flags that change the ABI, but the problem is
		2032	most noticeably displayed with ev_stat and large file support.
		2033
		2034	The solution for this is to lobby your distribution maker to make large
		2035	file interfaces available by default (as e.g. FreeBSD does) and not
		2036	optional. Libev cannot simply switch on large file support because it has
		2037	to exchange stat structures with application programs compiled using the
		2038	default compilation environment.
		2039
		2040	=head3 Inotify and Kqueue
		2041
		2042	When C<inotify (7)> support has been compiled into libev and present at
		2043	runtime, it will be used to speed up change detection where possible. The
		2044	inotify descriptor will be created lazily when the first C<ev_stat>
		2045	watcher is being started.
		2046
		2047	Inotify presence does not change the semantics of C<ev_stat> watchers
		2048	except that changes might be detected earlier, and in some cases, to avoid
		2049	making regular C<stat> calls. Even in the presence of inotify support
		2050	there are many cases where libev has to resort to regular C<stat> polling,
		2051	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2052	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2053	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2054	xfs are fully working) libev usually gets away without polling.
		2055
		2056	There is no support for kqueue, as apparently it cannot be used to
		2057	implement this functionality, due to the requirement of having a file
		2058	descriptor open on the object at all times, and detecting renames, unlinks
		2059	etc. is difficult.
		2060
		2061	=head3 C<stat ()> is a synchronous operation
		2062
		2063	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2064	the process. The exception are C<ev_stat> watchers - those call C<stat
		2065	()>, which is a synchronous operation.
		2066
		2067	For local paths, this usually doesn't matter: unless the system is very
		2068	busy or the intervals between stat's are large, a stat call will be fast,
		2069	as the path data is usually in memory already (except when starting the
		2070	watcher).
		2071
		2072	For networked file systems, calling C<stat ()> can block an indefinite
		2073	time due to network issues, and even under good conditions, a stat call
		2074	often takes multiple milliseconds.
		2075
		2076	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2077	paths, although this is fully supported by libev.
		2078
		2079	=head3 The special problem of stat time resolution
		2080
		2081	The C<stat ()> system call only supports full-second resolution portably,
		2082	and even on systems where the resolution is higher, most file systems
		2083	still only support whole seconds.
		2084
		2085	That means that, if the time is the only thing that changes, you can
		2086	easily miss updates: on the first update, C<ev_stat> detects a change and
		2087	calls your callback, which does something. When there is another update
		2088	within the same second, C<ev_stat> will be unable to detect unless the
		2089	stat data does change in other ways (e.g. file size).
		2090
		2091	The solution to this is to delay acting on a change for slightly more
		2092	than a second (or till slightly after the next full second boundary), using
		2093	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2094	ev_timer_again (loop, w)>).
		2095
		2096	The C<.02> offset is added to work around small timing inconsistencies
		2097	of some operating systems (where the second counter of the current time
		2098	might be be delayed. One such system is the Linux kernel, where a call to
		2099	C<gettimeofday> might return a timestamp with a full second later than
		2100	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2101	update file times then there will be a small window where the kernel uses
		2102	the previous second to update file times but libev might already execute
		2103	the timer callback).
		2104
		2105	=head3 Watcher-Specific Functions and Data Members
1328		2106
1329	=over 4	2107	=over 4
1330		2108
1331	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)	2109	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
1332		2110
…		…
1336	C<path>. The C<interval> is a hint on how quickly a change is expected to	2114	C<path>. The C<interval> is a hint on how quickly a change is expected to
1337	be detected and should normally be specified as C<0> to let libev choose	2115	be detected and should normally be specified as C<0> to let libev choose
1338	a suitable value. The memory pointed to by C<path> must point to the same	2116	a suitable value. The memory pointed to by C<path> must point to the same
1339	path for as long as the watcher is active.	2117	path for as long as the watcher is active.
1340		2118
1341	The callback will be receive C<EV_STAT> when a change was detected,	2119	The callback will receive an C<EV_STAT> event when a change was detected,
1342	relative to the attributes at the time the watcher was started (or the	2120	relative to the attributes at the time the watcher was started (or the
1343	last change was detected).	2121	last change was detected).
1344		2122
1345	=item ev_stat_stat (ev_stat *)	2123	=item ev_stat_stat (loop, ev_stat *)
1346		2124
1347	Updates the stat buffer immediately with new values. If you change the	2125	Updates the stat buffer immediately with new values. If you change the
1348	watched path in your callback, you could call this fucntion to avoid	2126	watched path in your callback, you could call this function to avoid
1349	detecting this change (while introducing a race condition). Can also be	2127	detecting this change (while introducing a race condition if you are not
1350	useful simply to find out the new values.	2128	the only one changing the path). Can also be useful simply to find out the
		2129	new values.
1351		2130
1352	=item ev_statdata attr [read-only]	2131	=item ev_statdata attr [read-only]
1353		2132
1354	The most-recently detected attributes of the file. Although the type is of	2133	The most-recently detected attributes of the file. Although the type is
1355	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2134	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1356	suitable for your system. If the C<st_nlink> member is C<0>, then there	2135	suitable for your system, but you can only rely on the POSIX-standardised
		2136	members to be present. If the C<st_nlink> member is C<0>, then there was
1357	was some error while C<stat>ing the file.	2137	some error while C<stat>ing the file.
1358		2138
1359	=item ev_statdata prev [read-only]	2139	=item ev_statdata prev [read-only]
1360		2140
1361	The previous attributes of the file. The callback gets invoked whenever	2141	The previous attributes of the file. The callback gets invoked whenever
1362	C<prev> != C<attr>.	2142	C<prev> != C<attr>, or, more precisely, one or more of these members
		2143	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2144	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1363		2145
1364	=item ev_tstamp interval [read-only]	2146	=item ev_tstamp interval [read-only]
1365		2147
1366	The specified interval.	2148	The specified interval.
1367		2149
1368	=item const char *path [read-only]	2150	=item const char *path [read-only]
1369		2151
1370	The filesystem path that is being watched.	2152	The file system path that is being watched.
1371		2153
1372	=back	2154	=back
1373		2155
		2156	=head3 Examples
		2157
1374	Example: Watch C</etc/passwd> for attribute changes.	2158	Example: Watch C</etc/passwd> for attribute changes.
1375		2159
1376	static void	2160	static void
1377	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2161	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1378	{	2162	{
1379	/* /etc/passwd changed in some way */	2163	/* /etc/passwd changed in some way */
1380	if (w->attr.st_nlink)	2164	if (w->attr.st_nlink)
1381	{	2165	{
1382	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2166	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1383	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2167	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1384	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2168	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1385	}	2169	}
1386	else	2170	else
1387	/* you shalt not abuse printf for puts */	2171	/* you shalt not abuse printf for puts */
1388	puts ("wow, /etc/passwd is not there, expect problems. "	2172	puts ("wow, /etc/passwd is not there, expect problems. "
1389	"if this is windows, they already arrived\n");	2173	"if this is windows, they already arrived\n");
1390	}	2174	}
1391		2175
1392	...	2176	...
1393	ev_stat passwd;	2177	ev_stat passwd;
1394		2178
1395	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	2179	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1396	ev_stat_start (loop, &passwd);	2180	ev_stat_start (loop, &passwd);
		2181
		2182	Example: Like above, but additionally use a one-second delay so we do not
		2183	miss updates (however, frequent updates will delay processing, too, so
		2184	one might do the work both on C<ev_stat> callback invocation I<and> on
		2185	C<ev_timer> callback invocation).
		2186
		2187	static ev_stat passwd;
		2188	static ev_timer timer;
		2189
		2190	static void
		2191	timer_cb (EV_P_ ev_timer *w, int revents)
		2192	{
		2193	ev_timer_stop (EV_A_ w);
		2194
		2195	/* now it's one second after the most recent passwd change */
		2196	}
		2197
		2198	static void
		2199	stat_cb (EV_P_ ev_stat *w, int revents)
		2200	{
		2201	/* reset the one-second timer */
		2202	ev_timer_again (EV_A_ &timer);
		2203	}
		2204
		2205	...
		2206	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2207	ev_stat_start (loop, &passwd);
		2208	ev_timer_init (&timer, timer_cb, 0., 1.02);
1397		2209
1398		2210
1399	=head2 C<ev_idle> - when you've got nothing better to do...	2211	=head2 C<ev_idle> - when you've got nothing better to do...
1400		2212
1401	Idle watchers trigger events when no other events of the same or higher	2213	Idle watchers trigger events when no other events of the same or higher
1402	priority are pending (prepare, check and other idle watchers do not	2214	priority are pending (prepare, check and other idle watchers do not count
1403	count).	2215	as receiving "events").
1404		2216
1405	That is, as long as your process is busy handling sockets or timeouts	2217	That is, as long as your process is busy handling sockets or timeouts
1406	(or even signals, imagine) of the same or higher priority it will not be	2218	(or even signals, imagine) of the same or higher priority it will not be
1407	triggered. But when your process is idle (or only lower-priority watchers	2219	triggered. But when your process is idle (or only lower-priority watchers
1408	are pending), the idle watchers are being called once per event loop	2220	are pending), the idle watchers are being called once per event loop
…		…
1415	Apart from keeping your process non-blocking (which is a useful	2227	Apart from keeping your process non-blocking (which is a useful
1416	effect on its own sometimes), idle watchers are a good place to do	2228	effect on its own sometimes), idle watchers are a good place to do
1417	"pseudo-background processing", or delay processing stuff to after the	2229	"pseudo-background processing", or delay processing stuff to after the
1418	event loop has handled all outstanding events.	2230	event loop has handled all outstanding events.
1419		2231
		2232	=head3 Watcher-Specific Functions and Data Members
		2233
1420	=over 4	2234	=over 4
1421		2235
1422	=item ev_idle_init (ev_signal *, callback)	2236	=item ev_idle_init (ev_idle *, callback)
1423		2237
1424	Initialises and configures the idle watcher - it has no parameters of any	2238	Initialises and configures the idle watcher - it has no parameters of any
1425	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2239	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1426	believe me.	2240	believe me.
1427		2241
1428	=back	2242	=back
1429		2243
		2244	=head3 Examples
		2245
1430	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2246	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1431	callback, free it. Also, use no error checking, as usual.	2247	callback, free it. Also, use no error checking, as usual.
1432		2248
1433	static void	2249	static void
1434	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2250	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1435	{	2251	{
1436	free (w);	2252	free (w);
1437	// now do something you wanted to do when the program has	2253	// now do something you wanted to do when the program has
1438	// no longer asnything immediate to do.	2254	// no longer anything immediate to do.
1439	}	2255	}
1440		2256
1441	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2257	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1442	ev_idle_init (idle_watcher, idle_cb);	2258	ev_idle_init (idle_watcher, idle_cb);
1443	ev_idle_start (loop, idle_cb);	2259	ev_idle_start (loop, idle_cb);
1444		2260
1445		2261
1446	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2262	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1447		2263
1448	Prepare and check watchers are usually (but not always) used in tandem:	2264	Prepare and check watchers are usually (but not always) used in pairs:
1449	prepare watchers get invoked before the process blocks and check watchers	2265	prepare watchers get invoked before the process blocks and check watchers
1450	afterwards.	2266	afterwards.
1451		2267
1452	You I<must not> call C<ev_loop> or similar functions that enter	2268	You I<must not> call C<ev_loop> or similar functions that enter
1453	the current event loop from either C<ev_prepare> or C<ev_check>	2269	the current event loop from either C<ev_prepare> or C<ev_check>
…		…
1456	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2272	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1457	C<ev_check> so if you have one watcher of each kind they will always be	2273	C<ev_check> so if you have one watcher of each kind they will always be
1458	called in pairs bracketing the blocking call.	2274	called in pairs bracketing the blocking call.
1459		2275
1460	Their main purpose is to integrate other event mechanisms into libev and	2276	Their main purpose is to integrate other event mechanisms into libev and
1461	their use is somewhat advanced. This could be used, for example, to track	2277	their use is somewhat advanced. They could be used, for example, to track
1462	variable changes, implement your own watchers, integrate net-snmp or a	2278	variable changes, implement your own watchers, integrate net-snmp or a
1463	coroutine library and lots more. They are also occasionally useful if	2279	coroutine library and lots more. They are also occasionally useful if
1464	you cache some data and want to flush it before blocking (for example,	2280	you cache some data and want to flush it before blocking (for example,
1465	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2281	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1466	watcher).	2282	watcher).
1467		2283
1468	This is done by examining in each prepare call which file descriptors need	2284	This is done by examining in each prepare call which file descriptors
1469	to be watched by the other library, registering C<ev_io> watchers for	2285	need to be watched by the other library, registering C<ev_io> watchers
1470	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2286	for them and starting an C<ev_timer> watcher for any timeouts (many
1471	provide just this functionality). Then, in the check watcher you check for	2287	libraries provide exactly this functionality). Then, in the check watcher,
1472	any events that occured (by checking the pending status of all watchers	2288	you check for any events that occurred (by checking the pending status
1473	and stopping them) and call back into the library. The I/O and timer	2289	of all watchers and stopping them) and call back into the library. The
1474	callbacks will never actually be called (but must be valid nevertheless,	2290	I/O and timer callbacks will never actually be called (but must be valid
1475	because you never know, you know?).	2291	nevertheless, because you never know, you know?).
1476		2292
1477	As another example, the Perl Coro module uses these hooks to integrate	2293	As another example, the Perl Coro module uses these hooks to integrate
1478	coroutines into libev programs, by yielding to other active coroutines	2294	coroutines into libev programs, by yielding to other active coroutines
1479	during each prepare and only letting the process block if no coroutines	2295	during each prepare and only letting the process block if no coroutines
1480	are ready to run (it's actually more complicated: it only runs coroutines	2296	are ready to run (it's actually more complicated: it only runs coroutines
1481	with priority higher than or equal to the event loop and one coroutine	2297	with priority higher than or equal to the event loop and one coroutine
1482	of lower priority, but only once, using idle watchers to keep the event	2298	of lower priority, but only once, using idle watchers to keep the event
1483	loop from blocking if lower-priority coroutines are active, thus mapping	2299	loop from blocking if lower-priority coroutines are active, thus mapping
1484	low-priority coroutines to idle/background tasks).	2300	low-priority coroutines to idle/background tasks).
1485		2301
		2302	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		2303	priority, to ensure that they are being run before any other watchers
		2304	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2305
		2306	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2307	activate ("feed") events into libev. While libev fully supports this, they
		2308	might get executed before other C<ev_check> watchers did their job. As
		2309	C<ev_check> watchers are often used to embed other (non-libev) event
		2310	loops those other event loops might be in an unusable state until their
		2311	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2312	others).
		2313
		2314	=head3 Watcher-Specific Functions and Data Members
		2315
1486	=over 4	2316	=over 4
1487		2317
1488	=item ev_prepare_init (ev_prepare *, callback)	2318	=item ev_prepare_init (ev_prepare *, callback)
1489		2319
1490	=item ev_check_init (ev_check *, callback)	2320	=item ev_check_init (ev_check *, callback)
1491		2321
1492	Initialises and configures the prepare or check watcher - they have no	2322	Initialises and configures the prepare or check watcher - they have no
1493	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2323	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1494	macros, but using them is utterly, utterly and completely pointless.	2324	macros, but using them is utterly, utterly, utterly and completely
		2325	pointless.
1495		2326
1496	=back	2327	=back
1497		2328
1498	Example: To include a library such as adns, you would add IO watchers	2329	=head3 Examples
1499	and a timeout watcher in a prepare handler, as required by libadns, and	2330
		2331	There are a number of principal ways to embed other event loops or modules
		2332	into libev. Here are some ideas on how to include libadns into libev
		2333	(there is a Perl module named C<EV::ADNS> that does this, which you could
		2334	use as a working example. Another Perl module named C<EV::Glib> embeds a
		2335	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		2336	Glib event loop).
		2337
		2338	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1500	in a check watcher, destroy them and call into libadns. What follows is	2339	and in a check watcher, destroy them and call into libadns. What follows
1501	pseudo-code only of course:	2340	is pseudo-code only of course. This requires you to either use a low
		2341	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		2342	the callbacks for the IO/timeout watchers might not have been called yet.
1502		2343
1503	static ev_io iow [nfd];	2344	static ev_io iow [nfd];
1504	static ev_timer tw;	2345	static ev_timer tw;
1505		2346
1506	static void	2347	static void
1507	io_cb (ev_loop *loop, ev_io *w, int revents)	2348	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1508	{	2349	{
1509	// set the relevant poll flags
1510	// could also call adns_processreadable etc. here
1511	struct pollfd *fd = (struct pollfd *)w->data;
1512	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1513	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1514	}	2350	}
1515		2351
1516	// create io watchers for each fd and a timer before blocking	2352	// create io watchers for each fd and a timer before blocking
1517	static void	2353	static void
1518	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2354	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1519	{	2355	{
1520	int timeout = 3600000;	2356	int timeout = 3600000;
1521	struct pollfd fds [nfd];	2357	struct pollfd fds [nfd];
1522	// actual code will need to loop here and realloc etc.	2358	// actual code will need to loop here and realloc etc.
1523	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2359	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1524		2360
1525	/* the callback is illegal, but won't be called as we stop during check */	2361	/* the callback is illegal, but won't be called as we stop during check */
1526	ev_timer_init (&tw, 0, timeout * 1e-3);	2362	ev_timer_init (&tw, 0, timeout * 1e-3);
1527	ev_timer_start (loop, &tw);	2363	ev_timer_start (loop, &tw);
1528		2364
1529	// create on ev_io per pollfd	2365	// create one ev_io per pollfd
1530	for (int i = 0; i < nfd; ++i)	2366	for (int i = 0; i < nfd; ++i)
1531	{	2367	{
1532	ev_io_init (iow + i, io_cb, fds [i].fd,	2368	ev_io_init (iow + i, io_cb, fds [i].fd,
1533	((fds [i].events & POLLIN ? EV_READ : 0)	2369	((fds [i].events & POLLIN ? EV_READ : 0)
1534	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2370	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1535		2371
1536	fds [i].revents = 0;	2372	fds [i].revents = 0;
1537	iow [i].data = fds + i;
1538	ev_io_start (loop, iow + i);	2373	ev_io_start (loop, iow + i);
1539	}	2374	}
1540	}	2375	}
1541		2376
1542	// stop all watchers after blocking	2377	// stop all watchers after blocking
1543	static void	2378	static void
1544	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2379	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1545	{	2380	{
1546	ev_timer_stop (loop, &tw);	2381	ev_timer_stop (loop, &tw);
1547		2382
1548	for (int i = 0; i < nfd; ++i)	2383	for (int i = 0; i < nfd; ++i)
		2384	{
		2385	// set the relevant poll flags
		2386	// could also call adns_processreadable etc. here
		2387	struct pollfd *fd = fds + i;
		2388	int revents = ev_clear_pending (iow + i);
		2389	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2390	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2391
		2392	// now stop the watcher
1549	ev_io_stop (loop, iow + i);	2393	ev_io_stop (loop, iow + i);
		2394	}
1550		2395
1551	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2396	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1552	}	2397	}
		2398
		2399	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2400	in the prepare watcher and would dispose of the check watcher.
		2401
		2402	Method 3: If the module to be embedded supports explicit event
		2403	notification (libadns does), you can also make use of the actual watcher
		2404	callbacks, and only destroy/create the watchers in the prepare watcher.
		2405
		2406	static void
		2407	timer_cb (EV_P_ ev_timer *w, int revents)
		2408	{
		2409	adns_state ads = (adns_state)w->data;
		2410	update_now (EV_A);
		2411
		2412	adns_processtimeouts (ads, &tv_now);
		2413	}
		2414
		2415	static void
		2416	io_cb (EV_P_ ev_io *w, int revents)
		2417	{
		2418	adns_state ads = (adns_state)w->data;
		2419	update_now (EV_A);
		2420
		2421	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2422	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2423	}
		2424
		2425	// do not ever call adns_afterpoll
		2426
		2427	Method 4: Do not use a prepare or check watcher because the module you
		2428	want to embed is not flexible enough to support it. Instead, you can
		2429	override their poll function. The drawback with this solution is that the
		2430	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		2431	this approach, effectively embedding EV as a client into the horrible
		2432	libglib event loop.
		2433
		2434	static gint
		2435	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2436	{
		2437	int got_events = 0;
		2438
		2439	for (n = 0; n < nfds; ++n)
		2440	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2441
		2442	if (timeout >= 0)
		2443	// create/start timer
		2444
		2445	// poll
		2446	ev_loop (EV_A_ 0);
		2447
		2448	// stop timer again
		2449	if (timeout >= 0)
		2450	ev_timer_stop (EV_A_ &to);
		2451
		2452	// stop io watchers again - their callbacks should have set
		2453	for (n = 0; n < nfds; ++n)
		2454	ev_io_stop (EV_A_ iow [n]);
		2455
		2456	return got_events;
		2457	}
1553		2458
1554		2459
1555	=head2 C<ev_embed> - when one backend isn't enough...	2460	=head2 C<ev_embed> - when one backend isn't enough...
1556		2461
1557	This is a rather advanced watcher type that lets you embed one event loop	2462	This is a rather advanced watcher type that lets you embed one event loop
…		…
1563	prioritise I/O.	2468	prioritise I/O.
1564		2469
1565	As an example for a bug workaround, the kqueue backend might only support	2470	As an example for a bug workaround, the kqueue backend might only support
1566	sockets on some platform, so it is unusable as generic backend, but you	2471	sockets on some platform, so it is unusable as generic backend, but you
1567	still want to make use of it because you have many sockets and it scales	2472	still want to make use of it because you have many sockets and it scales
1568	so nicely. In this case, you would create a kqueue-based loop and embed it	2473	so nicely. In this case, you would create a kqueue-based loop and embed
1569	into your default loop (which might use e.g. poll). Overall operation will	2474	it into your default loop (which might use e.g. poll). Overall operation
1570	be a bit slower because first libev has to poll and then call kevent, but	2475	will be a bit slower because first libev has to call C<poll> and then
1571	at least you can use both at what they are best.	2476	C<kevent>, but at least you can use both mechanisms for what they are
		2477	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1572		2478
1573	As for prioritising I/O: rarely you have the case where some fds have	2479	As for prioritising I/O: under rare circumstances you have the case where
1574	to be watched and handled very quickly (with low latency), and even	2480	some fds have to be watched and handled very quickly (with low latency),
1575	priorities and idle watchers might have too much overhead. In this case	2481	and even priorities and idle watchers might have too much overhead. In
1576	you would put all the high priority stuff in one loop and all the rest in	2482	this case you would put all the high priority stuff in one loop and all
1577	a second one, and embed the second one in the first.	2483	the rest in a second one, and embed the second one in the first.
1578		2484
1579	As long as the watcher is active, the callback will be invoked every time	2485	As long as the watcher is active, the callback will be invoked every
1580	there might be events pending in the embedded loop. The callback must then	2486	time there might be events pending in the embedded loop. The callback
1581	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2487	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1582	their callbacks (you could also start an idle watcher to give the embedded	2488	sweep and invoke their callbacks (the callback doesn't need to invoke the
1583	loop strictly lower priority for example). You can also set the callback	2489	C<ev_embed_sweep> function directly, it could also start an idle watcher
1584	to C<0>, in which case the embed watcher will automatically execute the	2490	to give the embedded loop strictly lower priority for example).
1585	embedded loop sweep.
1586		2491
1587	As long as the watcher is started it will automatically handle events. The	2492	You can also set the callback to C<0>, in which case the embed watcher
1588	callback will be invoked whenever some events have been handled. You can	2493	will automatically execute the embedded loop sweep whenever necessary.
1589	set the callback to C<0> to avoid having to specify one if you are not
1590	interested in that.
1591		2494
1592	Also, there have not currently been made special provisions for forking:	2495	Fork detection will be handled transparently while the C<ev_embed> watcher
1593	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2496	is active, i.e., the embedded loop will automatically be forked when the
1594	but you will also have to stop and restart any C<ev_embed> watchers	2497	embedding loop forks. In other cases, the user is responsible for calling
1595	yourself.	2498	C<ev_loop_fork> on the embedded loop.
1596		2499
1597	Unfortunately, not all backends are embeddable, only the ones returned by	2500	Unfortunately, not all backends are embeddable: only the ones returned by
1598	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2501	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1599	portable one.	2502	portable one.
1600		2503
1601	So when you want to use this feature you will always have to be prepared	2504	So when you want to use this feature you will always have to be prepared
1602	that you cannot get an embeddable loop. The recommended way to get around	2505	that you cannot get an embeddable loop. The recommended way to get around
1603	this is to have a separate variables for your embeddable loop, try to	2506	this is to have a separate variables for your embeddable loop, try to
1604	create it, and if that fails, use the normal loop for everything:	2507	create it, and if that fails, use the normal loop for everything.
1605		2508
1606	struct ev_loop *loop_hi = ev_default_init (0);	2509	=head3 C<ev_embed> and fork
1607	struct ev_loop *loop_lo = 0;
1608	struct ev_embed embed;
1609
1610	// see if there is a chance of getting one that works
1611	// (remember that a flags value of 0 means autodetection)
1612	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1613	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1614	: 0;
1615		2510
1616	// if we got one, then embed it, otherwise default to loop_hi	2511	While the C<ev_embed> watcher is running, forks in the embedding loop will
1617	if (loop_lo)	2512	automatically be applied to the embedded loop as well, so no special
1618	{	2513	fork handling is required in that case. When the watcher is not running,
1619	ev_embed_init (&embed, 0, loop_lo);	2514	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1620	ev_embed_start (loop_hi, &embed);	2515	as applicable.
1621	}	2516
1622	else	2517	=head3 Watcher-Specific Functions and Data Members
1623	loop_lo = loop_hi;
1624		2518
1625	=over 4	2519	=over 4
1626		2520
1627	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	2521	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
1628		2522
…		…
1630		2524
1631	Configures the watcher to embed the given loop, which must be	2525	Configures the watcher to embed the given loop, which must be
1632	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	2526	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1633	invoked automatically, otherwise it is the responsibility of the callback	2527	invoked automatically, otherwise it is the responsibility of the callback
1634	to invoke it (it will continue to be called until the sweep has been done,	2528	to invoke it (it will continue to be called until the sweep has been done,
1635	if you do not want thta, you need to temporarily stop the embed watcher).	2529	if you do not want that, you need to temporarily stop the embed watcher).
1636		2530
1637	=item ev_embed_sweep (loop, ev_embed *)	2531	=item ev_embed_sweep (loop, ev_embed *)
1638		2532
1639	Make a single, non-blocking sweep over the embedded loop. This works	2533	Make a single, non-blocking sweep over the embedded loop. This works
1640	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	2534	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
1641	apropriate way for embedded loops.	2535	appropriate way for embedded loops.
1642		2536
1643	=item struct ev_loop *loop [read-only]	2537	=item struct ev_loop *other [read-only]
1644		2538
1645	The embedded event loop.	2539	The embedded event loop.
1646		2540
1647	=back	2541	=back
		2542
		2543	=head3 Examples
		2544
		2545	Example: Try to get an embeddable event loop and embed it into the default
		2546	event loop. If that is not possible, use the default loop. The default
		2547	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2548	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2549	used).
		2550
		2551	struct ev_loop *loop_hi = ev_default_init (0);
		2552	struct ev_loop *loop_lo = 0;
		2553	ev_embed embed;
		2554
		2555	// see if there is a chance of getting one that works
		2556	// (remember that a flags value of 0 means autodetection)
		2557	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2558	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2559	: 0;
		2560
		2561	// if we got one, then embed it, otherwise default to loop_hi
		2562	if (loop_lo)
		2563	{
		2564	ev_embed_init (&embed, 0, loop_lo);
		2565	ev_embed_start (loop_hi, &embed);
		2566	}
		2567	else
		2568	loop_lo = loop_hi;
		2569
		2570	Example: Check if kqueue is available but not recommended and create
		2571	a kqueue backend for use with sockets (which usually work with any
		2572	kqueue implementation). Store the kqueue/socket-only event loop in
		2573	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2574
		2575	struct ev_loop *loop = ev_default_init (0);
		2576	struct ev_loop *loop_socket = 0;
		2577	ev_embed embed;
		2578
		2579	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2580	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2581	{
		2582	ev_embed_init (&embed, 0, loop_socket);
		2583	ev_embed_start (loop, &embed);
		2584	}
		2585
		2586	if (!loop_socket)
		2587	loop_socket = loop;
		2588
		2589	// now use loop_socket for all sockets, and loop for everything else
1648		2590
1649		2591
1650	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	2592	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
1651		2593
1652	Fork watchers are called when a C<fork ()> was detected (usually because	2594	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
1655	event loop blocks next and before C<ev_check> watchers are being called,	2597	event loop blocks next and before C<ev_check> watchers are being called,
1656	and only in the child after the fork. If whoever good citizen calling	2598	and only in the child after the fork. If whoever good citizen calling
1657	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2599	C<ev_default_fork> cheats and calls it in the wrong process, the fork
1658	handlers will be invoked, too, of course.	2600	handlers will be invoked, too, of course.
1659		2601
		2602	=head3 Watcher-Specific Functions and Data Members
		2603
1660	=over 4	2604	=over 4
1661		2605
1662	=item ev_fork_init (ev_signal *, callback)	2606	=item ev_fork_init (ev_signal *, callback)
1663		2607
1664	Initialises and configures the fork watcher - it has no parameters of any	2608	Initialises and configures the fork watcher - it has no parameters of any
…		…
1666	believe me.	2610	believe me.
1667		2611
1668	=back	2612	=back
1669		2613
1670		2614
		2615	=head2 C<ev_async> - how to wake up another event loop
		2616
		2617	In general, you cannot use an C<ev_loop> from multiple threads or other
		2618	asynchronous sources such as signal handlers (as opposed to multiple event
		2619	loops - those are of course safe to use in different threads).
		2620
		2621	Sometimes, however, you need to wake up another event loop you do not
		2622	control, for example because it belongs to another thread. This is what
		2623	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2624	can signal it by calling C<ev_async_send>, which is thread- and signal
		2625	safe.
		2626
		2627	This functionality is very similar to C<ev_signal> watchers, as signals,
		2628	too, are asynchronous in nature, and signals, too, will be compressed
		2629	(i.e. the number of callback invocations may be less than the number of
		2630	C<ev_async_sent> calls).
		2631
		2632	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2633	just the default loop.
		2634
		2635	=head3 Queueing
		2636
		2637	C<ev_async> does not support queueing of data in any way. The reason
		2638	is that the author does not know of a simple (or any) algorithm for a
		2639	multiple-writer-single-reader queue that works in all cases and doesn't
		2640	need elaborate support such as pthreads.
		2641
		2642	That means that if you want to queue data, you have to provide your own
		2643	queue. But at least I can tell you how to implement locking around your
		2644	queue:
		2645
		2646	=over 4
		2647
		2648	=item queueing from a signal handler context
		2649
		2650	To implement race-free queueing, you simply add to the queue in the signal
		2651	handler but you block the signal handler in the watcher callback. Here is
		2652	an example that does that for some fictitious SIGUSR1 handler:
		2653
		2654	static ev_async mysig;
		2655
		2656	static void
		2657	sigusr1_handler (void)
		2658	{
		2659	sometype data;
		2660
		2661	// no locking etc.
		2662	queue_put (data);
		2663	ev_async_send (EV_DEFAULT_ &mysig);
		2664	}
		2665
		2666	static void
		2667	mysig_cb (EV_P_ ev_async *w, int revents)
		2668	{
		2669	sometype data;
		2670	sigset_t block, prev;
		2671
		2672	sigemptyset (&block);
		2673	sigaddset (&block, SIGUSR1);
		2674	sigprocmask (SIG_BLOCK, &block, &prev);
		2675
		2676	while (queue_get (&data))
		2677	process (data);
		2678
		2679	if (sigismember (&prev, SIGUSR1)
		2680	sigprocmask (SIG_UNBLOCK, &block, 0);
		2681	}
		2682
		2683	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2684	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2685	either...).
		2686
		2687	=item queueing from a thread context
		2688
		2689	The strategy for threads is different, as you cannot (easily) block
		2690	threads but you can easily preempt them, so to queue safely you need to
		2691	employ a traditional mutex lock, such as in this pthread example:
		2692
		2693	static ev_async mysig;
		2694	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2695
		2696	static void
		2697	otherthread (void)
		2698	{
		2699	// only need to lock the actual queueing operation
		2700	pthread_mutex_lock (&mymutex);
		2701	queue_put (data);
		2702	pthread_mutex_unlock (&mymutex);
		2703
		2704	ev_async_send (EV_DEFAULT_ &mysig);
		2705	}
		2706
		2707	static void
		2708	mysig_cb (EV_P_ ev_async *w, int revents)
		2709	{
		2710	pthread_mutex_lock (&mymutex);
		2711
		2712	while (queue_get (&data))
		2713	process (data);
		2714
		2715	pthread_mutex_unlock (&mymutex);
		2716	}
		2717
		2718	=back
		2719
		2720
		2721	=head3 Watcher-Specific Functions and Data Members
		2722
		2723	=over 4
		2724
		2725	=item ev_async_init (ev_async *, callback)
		2726
		2727	Initialises and configures the async watcher - it has no parameters of any
		2728	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		2729	trust me.
		2730
		2731	=item ev_async_send (loop, ev_async *)
		2732
		2733	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2734	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2735	C<ev_feed_event>, this call is safe to do from other threads, signal or
		2736	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		2737	section below on what exactly this means).
		2738
		2739	Note that, as with other watchers in libev, multiple events might get
		2740	compressed into a single callback invocation (another way to look at this
		2741	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		2742	reset when the event loop detects that).
		2743
		2744	This call incurs the overhead of a system call only once per event loop
		2745	iteration, so while the overhead might be noticeable, it doesn't apply to
		2746	repeated calls to C<ev_async_send> for the same event loop.
		2747
		2748	=item bool = ev_async_pending (ev_async *)
		2749
		2750	Returns a non-zero value when C<ev_async_send> has been called on the
		2751	watcher but the event has not yet been processed (or even noted) by the
		2752	event loop.
		2753
		2754	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2755	the loop iterates next and checks for the watcher to have become active,
		2756	it will reset the flag again. C<ev_async_pending> can be used to very
		2757	quickly check whether invoking the loop might be a good idea.
		2758
		2759	Not that this does I<not> check whether the watcher itself is pending,
		2760	only whether it has been requested to make this watcher pending: there
		2761	is a time window between the event loop checking and resetting the async
		2762	notification, and the callback being invoked.
		2763
		2764	=back
		2765
		2766
1671	=head1 OTHER FUNCTIONS	2767	=head1 OTHER FUNCTIONS
1672		2768
1673	There are some other functions of possible interest. Described. Here. Now.	2769	There are some other functions of possible interest. Described. Here. Now.
1674		2770
1675	=over 4	2771	=over 4
1676		2772
1677	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	2773	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1678		2774
1679	This function combines a simple timer and an I/O watcher, calls your	2775	This function combines a simple timer and an I/O watcher, calls your
1680	callback on whichever event happens first and automatically stop both	2776	callback on whichever event happens first and automatically stops both
1681	watchers. This is useful if you want to wait for a single event on an fd	2777	watchers. This is useful if you want to wait for a single event on an fd
1682	or timeout without having to allocate/configure/start/stop/free one or	2778	or timeout without having to allocate/configure/start/stop/free one or
1683	more watchers yourself.	2779	more watchers yourself.
1684		2780
1685	If C<fd> is less than 0, then no I/O watcher will be started and events	2781	If C<fd> is less than 0, then no I/O watcher will be started and the
1686	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	2782	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1687	C<events> set will be craeted and started.	2783	the given C<fd> and C<events> set will be created and started.
1688		2784
1689	If C<timeout> is less than 0, then no timeout watcher will be	2785	If C<timeout> is less than 0, then no timeout watcher will be
1690	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	2786	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1691	repeat = 0) will be started. While C<0> is a valid timeout, it is of	2787	repeat = 0) will be started. C<0> is a valid timeout.
1692	dubious value.
1693		2788
1694	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	2789	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
1695	passed an C<revents> set like normal event callbacks (a combination of	2790	passed an C<revents> set like normal event callbacks (a combination of
1696	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	2791	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
1697	value passed to C<ev_once>:	2792	value passed to C<ev_once>. Note that it is possible to receive I<both>
		2793	a timeout and an io event at the same time - you probably should give io
		2794	events precedence.
1698		2795
		2796	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		2797
1699	static void stdin_ready (int revents, void *arg)	2798	static void stdin_ready (int revents, void *arg)
1700	{	2799	{
1701	if (revents & EV_TIMEOUT)
1702	/* doh, nothing entered */;
1703	else if (revents & EV_READ)	2800	if (revents & EV_READ)
1704	/* stdin might have data for us, joy! */;	2801	/* stdin might have data for us, joy! */;
		2802	else if (revents & EV_TIMEOUT)
		2803	/* doh, nothing entered */;
1705	}	2804	}
1706		2805
1707	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2806	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1708		2807
1709	=item ev_feed_event (ev_loop *, watcher *, int revents)	2808	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
1710		2809
1711	Feeds the given event set into the event loop, as if the specified event	2810	Feeds the given event set into the event loop, as if the specified event
1712	had happened for the specified watcher (which must be a pointer to an	2811	had happened for the specified watcher (which must be a pointer to an
1713	initialised but not necessarily started event watcher).	2812	initialised but not necessarily started event watcher).
1714		2813
1715	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	2814	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
1716		2815
1717	Feed an event on the given fd, as if a file descriptor backend detected	2816	Feed an event on the given fd, as if a file descriptor backend detected
1718	the given events it.	2817	the given events it.
1719		2818
1720	=item ev_feed_signal_event (ev_loop *loop, int signum)	2819	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
1721		2820
1722	Feed an event as if the given signal occured (C<loop> must be the default	2821	Feed an event as if the given signal occurred (C<loop> must be the default
1723	loop!).	2822	loop!).
1724		2823
1725	=back	2824	=back
1726		2825
1727		2826
…		…
1743		2842
1744	=item * Priorities are not currently supported. Initialising priorities	2843	=item * Priorities are not currently supported. Initialising priorities
1745	will fail and all watchers will have the same priority, even though there	2844	will fail and all watchers will have the same priority, even though there
1746	is an ev_pri field.	2845	is an ev_pri field.
1747		2846
		2847	=item * In libevent, the last base created gets the signals, in libev, the
		2848	first base created (== the default loop) gets the signals.
		2849
1748	=item * Other members are not supported.	2850	=item * Other members are not supported.
1749		2851
1750	=item * The libev emulation is I<not> ABI compatible to libevent, you need	2852	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1751	to use the libev header file and library.	2853	to use the libev header file and library.
1752		2854
1753	=back	2855	=back
1754		2856
1755	=head1 C++ SUPPORT	2857	=head1 C++ SUPPORT
1756		2858
1757	Libev comes with some simplistic wrapper classes for C++ that mainly allow	2859	Libev comes with some simplistic wrapper classes for C++ that mainly allow
1758	you to use some convinience methods to start/stop watchers and also change	2860	you to use some convenience methods to start/stop watchers and also change
1759	the callback model to a model using method callbacks on objects.	2861	the callback model to a model using method callbacks on objects.
1760		2862
1761	To use it,	2863	To use it,
1762		2864
1763	#include <ev++.h>	2865	#include <ev++.h>
1764		2866
1765	This automatically includes F<ev.h> and puts all of its definitions (many	2867	This automatically includes F<ev.h> and puts all of its definitions (many
1766	of them macros) into the global namespace. All C++ specific things are	2868	of them macros) into the global namespace. All C++ specific things are
1767	put into the C<ev> namespace. It should support all the same embedding	2869	put into the C<ev> namespace. It should support all the same embedding
1768	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	2870	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
1835	your compiler is good :), then the method will be fully inlined into the	2937	your compiler is good :), then the method will be fully inlined into the
1836	thunking function, making it as fast as a direct C callback.	2938	thunking function, making it as fast as a direct C callback.
1837		2939
1838	Example: simple class declaration and watcher initialisation	2940	Example: simple class declaration and watcher initialisation
1839		2941
1840	struct myclass	2942	struct myclass
1841	{	2943	{
1842	void io_cb (ev::io &w, int revents) { }	2944	void io_cb (ev::io &w, int revents) { }
1843	}	2945	}
1844		2946
1845	myclass obj;	2947	myclass obj;
1846	ev::io iow;	2948	ev::io iow;
1847	iow.set <myclass, &myclass::io_cb> (&obj);	2949	iow.set <myclass, &myclass::io_cb> (&obj);
1848		2950
1849	=item w->set (void (*function)(watcher &w, int), void *data = 0)	2951	=item w->set (object *)
		2952
		2953	This is an B<experimental> feature that might go away in a future version.
		2954
		2955	This is a variation of a method callback - leaving out the method to call
		2956	will default the method to C<operator ()>, which makes it possible to use
		2957	functor objects without having to manually specify the C<operator ()> all
		2958	the time. Incidentally, you can then also leave out the template argument
		2959	list.
		2960
		2961	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		2962	int revents)>.
		2963
		2964	See the method-C<set> above for more details.
		2965
		2966	Example: use a functor object as callback.
		2967
		2968	struct myfunctor
		2969	{
		2970	void operator() (ev::io &w, int revents)
		2971	{
		2972	...
		2973	}
		2974	}
		2975
		2976	myfunctor f;
		2977
		2978	ev::io w;
		2979	w.set (&f);
		2980
		2981	=item w->set<function> (void *data = 0)
1850		2982
1851	Also sets a callback, but uses a static method or plain function as	2983	Also sets a callback, but uses a static method or plain function as
1852	callback. The optional C<data> argument will be stored in the watcher's	2984	callback. The optional C<data> argument will be stored in the watcher's
1853	C<data> member and is free for you to use.	2985	C<data> member and is free for you to use.
1854		2986
		2987	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		2988
1855	See the method-C<set> above for more details.	2989	See the method-C<set> above for more details.
		2990
		2991	Example: Use a plain function as callback.
		2992
		2993	static void io_cb (ev::io &w, int revents) { }
		2994	iow.set <io_cb> ();
1856		2995
1857	=item w->set (struct ev_loop *)	2996	=item w->set (struct ev_loop *)
1858		2997
1859	Associates a different C<struct ev_loop> with this watcher. You can only	2998	Associates a different C<struct ev_loop> with this watcher. You can only
1860	do this when the watcher is inactive (and not pending either).	2999	do this when the watcher is inactive (and not pending either).
1861		3000
1862	=item w->set ([args])	3001	=item w->set ([arguments])
1863		3002
1864	Basically the same as C<ev_TYPE_set>, with the same args. Must be	3003	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
1865	called at least once. Unlike the C counterpart, an active watcher gets	3004	called at least once. Unlike the C counterpart, an active watcher gets
1866	automatically stopped and restarted when reconfiguring it with this	3005	automatically stopped and restarted when reconfiguring it with this
1867	method.	3006	method.
1868		3007
1869	=item w->start ()	3008	=item w->start ()
…		…
1873		3012
1874	=item w->stop ()	3013	=item w->stop ()
1875		3014
1876	Stops the watcher if it is active. Again, no C<loop> argument.	3015	Stops the watcher if it is active. Again, no C<loop> argument.
1877		3016
1878	=item w->again () C<ev::timer>, C<ev::periodic> only	3017	=item w->again () (C<ev::timer>, C<ev::periodic> only)
1879		3018
1880	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding	3019	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
1881	C<ev_TYPE_again> function.	3020	C<ev_TYPE_again> function.
1882		3021
1883	=item w->sweep () C<ev::embed> only	3022	=item w->sweep () (C<ev::embed> only)
1884		3023
1885	Invokes C<ev_embed_sweep>.	3024	Invokes C<ev_embed_sweep>.
1886		3025
1887	=item w->update () C<ev::stat> only	3026	=item w->update () (C<ev::stat> only)
1888		3027
1889	Invokes C<ev_stat_stat>.	3028	Invokes C<ev_stat_stat>.
1890		3029
1891	=back	3030	=back
1892		3031
1893	=back	3032	=back
1894		3033
1895	Example: Define a class with an IO and idle watcher, start one of them in	3034	Example: Define a class with an IO and idle watcher, start one of them in
1896	the constructor.	3035	the constructor.
1897		3036
1898	class myclass	3037	class myclass
1899	{	3038	{
1900	ev_io io; void io_cb (ev::io &w, int revents);	3039	ev::io io ; void io_cb (ev::io &w, int revents);
1901	ev_idle idle void idle_cb (ev::idle &w, int revents);	3040	ev::idle idle; void idle_cb (ev::idle &w, int revents);
1902		3041
1903	myclass ();	3042	myclass (int fd)
1904	}	3043	{
1905
1906	myclass::myclass (int fd)
1907	{
1908	io .set <myclass, &myclass::io_cb > (this);	3044	io .set <myclass, &myclass::io_cb > (this);
1909	idle.set <myclass, &myclass::idle_cb> (this);	3045	idle.set <myclass, &myclass::idle_cb> (this);
1910		3046
1911	io.start (fd, ev::READ);	3047	io.start (fd, ev::READ);
		3048	}
1912	}	3049	};
		3050
		3051
		3052	=head1 OTHER LANGUAGE BINDINGS
		3053
		3054	Libev does not offer other language bindings itself, but bindings for a
		3055	number of languages exist in the form of third-party packages. If you know
		3056	any interesting language binding in addition to the ones listed here, drop
		3057	me a note.
		3058
		3059	=over 4
		3060
		3061	=item Perl
		3062
		3063	The EV module implements the full libev API and is actually used to test
		3064	libev. EV is developed together with libev. Apart from the EV core module,
		3065	there are additional modules that implement libev-compatible interfaces
		3066	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3067	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3068	and C<EV::Glib>).
		3069
		3070	It can be found and installed via CPAN, its homepage is at
		3071	L<http://software.schmorp.de/pkg/EV>.
		3072
		3073	=item Python
		3074
		3075	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3076	seems to be quite complete and well-documented.
		3077
		3078	=item Ruby
		3079
		3080	Tony Arcieri has written a ruby extension that offers access to a subset
		3081	of the libev API and adds file handle abstractions, asynchronous DNS and
		3082	more on top of it. It can be found via gem servers. Its homepage is at
		3083	L<http://rev.rubyforge.org/>.
		3084
		3085	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3086	makes rev work even on mingw.
		3087
		3088	=item Haskell
		3089
		3090	A haskell binding to libev is available at
		3091	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3092
		3093	=item D
		3094
		3095	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3096	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3097
		3098	=item Ocaml
		3099
		3100	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3101	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3102
		3103	=back
1913		3104
1914		3105
1915	=head1 MACRO MAGIC	3106	=head1 MACRO MAGIC
1916		3107
1917	Libev can be compiled with a variety of options, the most fundemantal is	3108	Libev can be compiled with a variety of options, the most fundamental
1918	C<EV_MULTIPLICITY>. This option determines whether (most) functions and	3109	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
1919	callbacks have an initial C<struct ev_loop *> argument.	3110	functions and callbacks have an initial C<struct ev_loop *> argument.
1920		3111
1921	To make it easier to write programs that cope with either variant, the	3112	To make it easier to write programs that cope with either variant, the
1922	following macros are defined:	3113	following macros are defined:
1923		3114
1924	=over 4	3115	=over 4
…		…
1927		3118
1928	This provides the loop I<argument> for functions, if one is required ("ev	3119	This provides the loop I<argument> for functions, if one is required ("ev
1929	loop argument"). The C<EV_A> form is used when this is the sole argument,	3120	loop argument"). The C<EV_A> form is used when this is the sole argument,
1930	C<EV_A_> is used when other arguments are following. Example:	3121	C<EV_A_> is used when other arguments are following. Example:
1931		3122
1932	ev_unref (EV_A);	3123	ev_unref (EV_A);
1933	ev_timer_add (EV_A_ watcher);	3124	ev_timer_add (EV_A_ watcher);
1934	ev_loop (EV_A_ 0);	3125	ev_loop (EV_A_ 0);
1935		3126
1936	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	3127	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
1937	which is often provided by the following macro.	3128	which is often provided by the following macro.
1938		3129
1939	=item C<EV_P>, C<EV_P_>	3130	=item C<EV_P>, C<EV_P_>
1940		3131
1941	This provides the loop I<parameter> for functions, if one is required ("ev	3132	This provides the loop I<parameter> for functions, if one is required ("ev
1942	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	3133	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
1943	C<EV_P_> is used when other parameters are following. Example:	3134	C<EV_P_> is used when other parameters are following. Example:
1944		3135
1945	// this is how ev_unref is being declared	3136	// this is how ev_unref is being declared
1946	static void ev_unref (EV_P);	3137	static void ev_unref (EV_P);
1947		3138
1948	// this is how you can declare your typical callback	3139	// this is how you can declare your typical callback
1949	static void cb (EV_P_ ev_timer *w, int revents)	3140	static void cb (EV_P_ ev_timer *w, int revents)
1950		3141
1951	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	3142	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
1952	suitable for use with C<EV_A>.	3143	suitable for use with C<EV_A>.
1953		3144
1954	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3145	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
1955		3146
1956	Similar to the other two macros, this gives you the value of the default	3147	Similar to the other two macros, this gives you the value of the default
1957	loop, if multiple loops are supported ("ev loop default").	3148	loop, if multiple loops are supported ("ev loop default").
		3149
		3150	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3151
		3152	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3153	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3154	is undefined when the default loop has not been initialised by a previous
		3155	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3156
		3157	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3158	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
1958		3159
1959	=back	3160	=back
1960		3161
1961	Example: Declare and initialise a check watcher, utilising the above	3162	Example: Declare and initialise a check watcher, utilising the above
1962	macros so it will work regardless of whether multiple loops are supported	3163	macros so it will work regardless of whether multiple loops are supported
1963	or not.	3164	or not.
1964		3165
1965	static void	3166	static void
1966	check_cb (EV_P_ ev_timer *w, int revents)	3167	check_cb (EV_P_ ev_timer *w, int revents)
1967	{	3168	{
1968	ev_check_stop (EV_A_ w);	3169	ev_check_stop (EV_A_ w);
1969	}	3170	}
1970		3171
1971	ev_check check;	3172	ev_check check;
1972	ev_check_init (&check, check_cb);	3173	ev_check_init (&check, check_cb);
1973	ev_check_start (EV_DEFAULT_ &check);	3174	ev_check_start (EV_DEFAULT_ &check);
1974	ev_loop (EV_DEFAULT_ 0);	3175	ev_loop (EV_DEFAULT_ 0);
1975		3176
1976	=head1 EMBEDDING	3177	=head1 EMBEDDING
1977		3178
1978	Libev can (and often is) directly embedded into host	3179	Libev can (and often is) directly embedded into host
1979	applications. Examples of applications that embed it include the Deliantra	3180	applications. Examples of applications that embed it include the Deliantra
1980	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)	3181	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
1981	and rxvt-unicode.	3182	and rxvt-unicode.
1982		3183
1983	The goal is to enable you to just copy the neecssary files into your	3184	The goal is to enable you to just copy the necessary files into your
1984	source directory without having to change even a single line in them, so	3185	source directory without having to change even a single line in them, so
1985	you can easily upgrade by simply copying (or having a checked-out copy of	3186	you can easily upgrade by simply copying (or having a checked-out copy of
1986	libev somewhere in your source tree).	3187	libev somewhere in your source tree).
1987		3188
1988	=head2 FILESETS	3189	=head2 FILESETS
1989		3190
1990	Depending on what features you need you need to include one or more sets of files	3191	Depending on what features you need you need to include one or more sets of files
1991	in your app.	3192	in your application.
1992		3193
1993	=head3 CORE EVENT LOOP	3194	=head3 CORE EVENT LOOP
1994		3195
1995	To include only the libev core (all the C<ev_*> functions), with manual	3196	To include only the libev core (all the C<ev_*> functions), with manual
1996	configuration (no autoconf):	3197	configuration (no autoconf):
1997		3198
1998	#define EV_STANDALONE 1	3199	#define EV_STANDALONE 1
1999	#include "ev.c"	3200	#include "ev.c"
2000		3201
2001	This will automatically include F<ev.h>, too, and should be done in a	3202	This will automatically include F<ev.h>, too, and should be done in a
2002	single C source file only to provide the function implementations. To use	3203	single C source file only to provide the function implementations. To use
2003	it, do the same for F<ev.h> in all files wishing to use this API (best	3204	it, do the same for F<ev.h> in all files wishing to use this API (best
2004	done by writing a wrapper around F<ev.h> that you can include instead and	3205	done by writing a wrapper around F<ev.h> that you can include instead and
2005	where you can put other configuration options):	3206	where you can put other configuration options):
2006		3207
2007	#define EV_STANDALONE 1	3208	#define EV_STANDALONE 1
2008	#include "ev.h"	3209	#include "ev.h"
2009		3210
2010	Both header files and implementation files can be compiled with a C++	3211	Both header files and implementation files can be compiled with a C++
2011	compiler (at least, thats a stated goal, and breakage will be treated	3212	compiler (at least, that's a stated goal, and breakage will be treated
2012	as a bug).	3213	as a bug).
2013		3214
2014	You need the following files in your source tree, or in a directory	3215	You need the following files in your source tree, or in a directory
2015	in your include path (e.g. in libev/ when using -Ilibev):	3216	in your include path (e.g. in libev/ when using -Ilibev):
2016		3217
2017	ev.h	3218	ev.h
2018	ev.c	3219	ev.c
2019	ev_vars.h	3220	ev_vars.h
2020	ev_wrap.h	3221	ev_wrap.h
2021		3222
2022	ev_win32.c required on win32 platforms only	3223	ev_win32.c required on win32 platforms only
2023		3224
2024	ev_select.c only when select backend is enabled (which is enabled by default)	3225	ev_select.c only when select backend is enabled (which is enabled by default)
2025	ev_poll.c only when poll backend is enabled (disabled by default)	3226	ev_poll.c only when poll backend is enabled (disabled by default)
2026	ev_epoll.c only when the epoll backend is enabled (disabled by default)	3227	ev_epoll.c only when the epoll backend is enabled (disabled by default)
2027	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	3228	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2028	ev_port.c only when the solaris port backend is enabled (disabled by default)	3229	ev_port.c only when the solaris port backend is enabled (disabled by default)
2029		3230
2030	F<ev.c> includes the backend files directly when enabled, so you only need	3231	F<ev.c> includes the backend files directly when enabled, so you only need
2031	to compile this single file.	3232	to compile this single file.
2032		3233
2033	=head3 LIBEVENT COMPATIBILITY API	3234	=head3 LIBEVENT COMPATIBILITY API
2034		3235
2035	To include the libevent compatibility API, also include:	3236	To include the libevent compatibility API, also include:
2036		3237
2037	#include "event.c"	3238	#include "event.c"
2038		3239
2039	in the file including F<ev.c>, and:	3240	in the file including F<ev.c>, and:
2040		3241
2041	#include "event.h"	3242	#include "event.h"
2042		3243
2043	in the files that want to use the libevent API. This also includes F<ev.h>.	3244	in the files that want to use the libevent API. This also includes F<ev.h>.
2044		3245
2045	You need the following additional files for this:	3246	You need the following additional files for this:
2046		3247
2047	event.h	3248	event.h
2048	event.c	3249	event.c
2049		3250
2050	=head3 AUTOCONF SUPPORT	3251	=head3 AUTOCONF SUPPORT
2051		3252
2052	Instead of using C<EV_STANDALONE=1> and providing your config in	3253	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2053	whatever way you want, you can also C<m4_include([libev.m4])> in your	3254	whatever way you want, you can also C<m4_include([libev.m4])> in your
2054	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	3255	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2055	include F<config.h> and configure itself accordingly.	3256	include F<config.h> and configure itself accordingly.
2056		3257
2057	For this of course you need the m4 file:	3258	For this of course you need the m4 file:
2058		3259
2059	libev.m4	3260	libev.m4
2060		3261
2061	=head2 PREPROCESSOR SYMBOLS/MACROS	3262	=head2 PREPROCESSOR SYMBOLS/MACROS
2062		3263
2063	Libev can be configured via a variety of preprocessor symbols you have to define	3264	Libev can be configured via a variety of preprocessor symbols you have to
2064	before including any of its files. The default is not to build for multiplicity	3265	define before including any of its files. The default in the absence of
2065	and only include the select backend.	3266	autoconf is documented for every option.
2066		3267
2067	=over 4	3268	=over 4
2068		3269
2069	=item EV_STANDALONE	3270	=item EV_STANDALONE
2070		3271
…		…
2072	keeps libev from including F<config.h>, and it also defines dummy	3273	keeps libev from including F<config.h>, and it also defines dummy
2073	implementations for some libevent functions (such as logging, which is not	3274	implementations for some libevent functions (such as logging, which is not
2074	supported). It will also not define any of the structs usually found in	3275	supported). It will also not define any of the structs usually found in
2075	F<event.h> that are not directly supported by the libev core alone.	3276	F<event.h> that are not directly supported by the libev core alone.
2076		3277
		3278	In stanbdalone mode, libev will still try to automatically deduce the
		3279	configuration, but has to be more conservative.
		3280
2077	=item EV_USE_MONOTONIC	3281	=item EV_USE_MONOTONIC
2078		3282
2079	If defined to be C<1>, libev will try to detect the availability of the	3283	If defined to be C<1>, libev will try to detect the availability of the
2080	monotonic clock option at both compiletime and runtime. Otherwise no use	3284	monotonic clock option at both compile time and runtime. Otherwise no
2081	of the monotonic clock option will be attempted. If you enable this, you	3285	use of the monotonic clock option will be attempted. If you enable this,
2082	usually have to link against librt or something similar. Enabling it when	3286	you usually have to link against librt or something similar. Enabling it
2083	the functionality isn't available is safe, though, althoguh you have	3287	when the functionality isn't available is safe, though, although you have
2084	to make sure you link against any libraries where the C<clock_gettime>	3288	to make sure you link against any libraries where the C<clock_gettime>
2085	function is hiding in (often F<-lrt>).	3289	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2086		3290
2087	=item EV_USE_REALTIME	3291	=item EV_USE_REALTIME
2088		3292
2089	If defined to be C<1>, libev will try to detect the availability of the	3293	If defined to be C<1>, libev will try to detect the availability of the
2090	realtime clock option at compiletime (and assume its availability at	3294	real-time clock option at compile time (and assume its availability
2091	runtime if successful). Otherwise no use of the realtime clock option will	3295	at runtime if successful). Otherwise no use of the real-time clock
2092	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3296	option will be attempted. This effectively replaces C<gettimeofday>
2093	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See tzhe note about libraries	3297	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2094	in the description of C<EV_USE_MONOTONIC>, though.	3298	correctness. See the note about libraries in the description of
		3299	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3300	C<EV_USE_CLOCK_SYSCALL>.
		3301
		3302	=item EV_USE_CLOCK_SYSCALL
		3303
		3304	If defined to be C<1>, libev will try to use a direct syscall instead
		3305	of calling the system-provided C<clock_gettime> function. This option
		3306	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3307	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3308	programs needlessly. Using a direct syscall is slightly slower (in
		3309	theory), because no optimised vdso implementation can be used, but avoids
		3310	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3311	higher, as it simplifies linking (no need for C<-lrt>).
		3312
		3313	=item EV_USE_NANOSLEEP
		3314
		3315	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		3316	and will use it for delays. Otherwise it will use C<select ()>.
		3317
		3318	=item EV_USE_EVENTFD
		3319
		3320	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3321	available and will probe for kernel support at runtime. This will improve
		3322	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3323	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3324	2.7 or newer, otherwise disabled.
2095		3325
2096	=item EV_USE_SELECT	3326	=item EV_USE_SELECT
2097		3327
2098	If undefined or defined to be C<1>, libev will compile in support for the	3328	If undefined or defined to be C<1>, libev will compile in support for the
2099	C<select>(2) backend. No attempt at autodetection will be done: if no	3329	C<select>(2) backend. No attempt at auto-detection will be done: if no
2100	other method takes over, select will be it. Otherwise the select backend	3330	other method takes over, select will be it. Otherwise the select backend
2101	will not be compiled in.	3331	will not be compiled in.
2102		3332
2103	=item EV_SELECT_USE_FD_SET	3333	=item EV_SELECT_USE_FD_SET
2104		3334
2105	If defined to C<1>, then the select backend will use the system C<fd_set>	3335	If defined to C<1>, then the select backend will use the system C<fd_set>
2106	structure. This is useful if libev doesn't compile due to a missing	3336	structure. This is useful if libev doesn't compile due to a missing
2107	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	3337	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2108	exotic systems. This usually limits the range of file descriptors to some	3338	on exotic systems. This usually limits the range of file descriptors to
2109	low limit such as 1024 or might have other limitations (winsocket only	3339	some low limit such as 1024 or might have other limitations (winsocket
2110	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3340	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2111	influence the size of the C<fd_set> used.	3341	configures the maximum size of the C<fd_set>.
2112		3342
2113	=item EV_SELECT_IS_WINSOCKET	3343	=item EV_SELECT_IS_WINSOCKET
2114		3344
2115	When defined to C<1>, the select backend will assume that	3345	When defined to C<1>, the select backend will assume that
2116	select/socket/connect etc. don't understand file descriptors but	3346	select/socket/connect etc. don't understand file descriptors but
…		…
2118	be used is the winsock select). This means that it will call	3348	be used is the winsock select). This means that it will call
2119	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3349	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2120	it is assumed that all these functions actually work on fds, even	3350	it is assumed that all these functions actually work on fds, even
2121	on win32. Should not be defined on non-win32 platforms.	3351	on win32. Should not be defined on non-win32 platforms.
2122		3352
		3353	=item EV_FD_TO_WIN32_HANDLE
		3354
		3355	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3356	file descriptors to socket handles. When not defining this symbol (the
		3357	default), then libev will call C<_get_osfhandle>, which is usually
		3358	correct. In some cases, programs use their own file descriptor management,
		3359	in which case they can provide this function to map fds to socket handles.
		3360
2123	=item EV_USE_POLL	3361	=item EV_USE_POLL
2124		3362
2125	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3363	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2126	backend. Otherwise it will be enabled on non-win32 platforms. It	3364	backend. Otherwise it will be enabled on non-win32 platforms. It
2127	takes precedence over select.	3365	takes precedence over select.
2128		3366
2129	=item EV_USE_EPOLL	3367	=item EV_USE_EPOLL
2130		3368
2131	If defined to be C<1>, libev will compile in support for the Linux	3369	If defined to be C<1>, libev will compile in support for the Linux
2132	C<epoll>(7) backend. Its availability will be detected at runtime,	3370	C<epoll>(7) backend. Its availability will be detected at runtime,
2133	otherwise another method will be used as fallback. This is the	3371	otherwise another method will be used as fallback. This is the preferred
2134	preferred backend for GNU/Linux systems.	3372	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3373	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2135		3374
2136	=item EV_USE_KQUEUE	3375	=item EV_USE_KQUEUE
2137		3376
2138	If defined to be C<1>, libev will compile in support for the BSD style	3377	If defined to be C<1>, libev will compile in support for the BSD style
2139	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	3378	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2152	otherwise another method will be used as fallback. This is the preferred	3391	otherwise another method will be used as fallback. This is the preferred
2153	backend for Solaris 10 systems.	3392	backend for Solaris 10 systems.
2154		3393
2155	=item EV_USE_DEVPOLL	3394	=item EV_USE_DEVPOLL
2156		3395
2157	reserved for future expansion, works like the USE symbols above.	3396	Reserved for future expansion, works like the USE symbols above.
2158		3397
2159	=item EV_USE_INOTIFY	3398	=item EV_USE_INOTIFY
2160		3399
2161	If defined to be C<1>, libev will compile in support for the Linux inotify	3400	If defined to be C<1>, libev will compile in support for the Linux inotify
2162	interface to speed up C<ev_stat> watchers. Its actual availability will	3401	interface to speed up C<ev_stat> watchers. Its actual availability will
2163	be detected at runtime.	3402	be detected at runtime. If undefined, it will be enabled if the headers
		3403	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3404
		3405	=item EV_ATOMIC_T
		3406
		3407	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3408	access is atomic with respect to other threads or signal contexts. No such
		3409	type is easily found in the C language, so you can provide your own type
		3410	that you know is safe for your purposes. It is used both for signal handler "locking"
		3411	as well as for signal and thread safety in C<ev_async> watchers.
		3412
		3413	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3414	(from F<signal.h>), which is usually good enough on most platforms.
2164		3415
2165	=item EV_H	3416	=item EV_H
2166		3417
2167	The name of the F<ev.h> header file used to include it. The default if	3418	The name of the F<ev.h> header file used to include it. The default if
2168	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This	3419	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2169	can be used to virtually rename the F<ev.h> header file in case of conflicts.	3420	used to virtually rename the F<ev.h> header file in case of conflicts.
2170		3421
2171	=item EV_CONFIG_H	3422	=item EV_CONFIG_H
2172		3423
2173	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	3424	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2174	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	3425	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2175	C<EV_H>, above.	3426	C<EV_H>, above.
2176		3427
2177	=item EV_EVENT_H	3428	=item EV_EVENT_H
2178		3429
2179	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	3430	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2180	of how the F<event.h> header can be found.	3431	of how the F<event.h> header can be found, the default is C<"event.h">.
2181		3432
2182	=item EV_PROTOTYPES	3433	=item EV_PROTOTYPES
2183		3434
2184	If defined to be C<0>, then F<ev.h> will not define any function	3435	If defined to be C<0>, then F<ev.h> will not define any function
2185	prototypes, but still define all the structs and other symbols. This is	3436	prototypes, but still define all the structs and other symbols. This is
…		…
2206	When doing priority-based operations, libev usually has to linearly search	3457	When doing priority-based operations, libev usually has to linearly search
2207	all the priorities, so having many of them (hundreds) uses a lot of space	3458	all the priorities, so having many of them (hundreds) uses a lot of space
2208	and time, so using the defaults of five priorities (-2 .. +2) is usually	3459	and time, so using the defaults of five priorities (-2 .. +2) is usually
2209	fine.	3460	fine.
2210		3461
2211	If your embedding app does not need any priorities, defining these both to	3462	If your embedding application does not need any priorities, defining these
2212	C<0> will save some memory and cpu.	3463	both to C<0> will save some memory and CPU.
2213		3464
2214	=item EV_PERIODIC_ENABLE	3465	=item EV_PERIODIC_ENABLE
2215		3466
2216	If undefined or defined to be C<1>, then periodic timers are supported. If	3467	If undefined or defined to be C<1>, then periodic timers are supported. If
2217	defined to be C<0>, then they are not. Disabling them saves a few kB of	3468	defined to be C<0>, then they are not. Disabling them saves a few kB of
…		…
2224	code.	3475	code.
2225		3476
2226	=item EV_EMBED_ENABLE	3477	=item EV_EMBED_ENABLE
2227		3478
2228	If undefined or defined to be C<1>, then embed watchers are supported. If	3479	If undefined or defined to be C<1>, then embed watchers are supported. If
2229	defined to be C<0>, then they are not.	3480	defined to be C<0>, then they are not. Embed watchers rely on most other
		3481	watcher types, which therefore must not be disabled.
2230		3482
2231	=item EV_STAT_ENABLE	3483	=item EV_STAT_ENABLE
2232		3484
2233	If undefined or defined to be C<1>, then stat watchers are supported. If	3485	If undefined or defined to be C<1>, then stat watchers are supported. If
2234	defined to be C<0>, then they are not.	3486	defined to be C<0>, then they are not.
…		…
2236	=item EV_FORK_ENABLE	3488	=item EV_FORK_ENABLE
2237		3489
2238	If undefined or defined to be C<1>, then fork watchers are supported. If	3490	If undefined or defined to be C<1>, then fork watchers are supported. If
2239	defined to be C<0>, then they are not.	3491	defined to be C<0>, then they are not.
2240		3492
		3493	=item EV_ASYNC_ENABLE
		3494
		3495	If undefined or defined to be C<1>, then async watchers are supported. If
		3496	defined to be C<0>, then they are not.
		3497
2241	=item EV_MINIMAL	3498	=item EV_MINIMAL
2242		3499
2243	If you need to shave off some kilobytes of code at the expense of some	3500	If you need to shave off some kilobytes of code at the expense of some
2244	speed, define this symbol to C<1>. Currently only used for gcc to override	3501	speed, define this symbol to C<1>. Currently this is used to override some
2245	some inlining decisions, saves roughly 30% codesize of amd64.	3502	inlining decisions, saves roughly 30% code size on amd64. It also selects a
		3503	much smaller 2-heap for timer management over the default 4-heap.
2246		3504
2247	=item EV_PID_HASHSIZE	3505	=item EV_PID_HASHSIZE
2248		3506
2249	C<ev_child> watchers use a small hash table to distribute workload by	3507	C<ev_child> watchers use a small hash table to distribute workload by
2250	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3508	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
2251	than enough. If you need to manage thousands of children you might want to	3509	than enough. If you need to manage thousands of children you might want to
2252	increase this value (I<must> be a power of two).	3510	increase this value (I<must> be a power of two).
2253		3511
2254	=item EV_INOTIFY_HASHSIZE	3512	=item EV_INOTIFY_HASHSIZE
2255		3513
2256	C<ev_staz> watchers use a small hash table to distribute workload by	3514	C<ev_stat> watchers use a small hash table to distribute workload by
2257	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	3515	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
2258	usually more than enough. If you need to manage thousands of C<ev_stat>	3516	usually more than enough. If you need to manage thousands of C<ev_stat>
2259	watchers you might want to increase this value (I<must> be a power of	3517	watchers you might want to increase this value (I<must> be a power of
2260	two).	3518	two).
2261		3519
		3520	=item EV_USE_4HEAP
		3521
		3522	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3523	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		3524	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		3525	faster performance with many (thousands) of watchers.
		3526
		3527	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3528	(disabled).
		3529
		3530	=item EV_HEAP_CACHE_AT
		3531
		3532	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3533	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		3534	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3535	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3536	but avoids random read accesses on heap changes. This improves performance
		3537	noticeably with many (hundreds) of watchers.
		3538
		3539	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3540	(disabled).
		3541
		3542	=item EV_VERIFY
		3543
		3544	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3545	be done: If set to C<0>, no internal verification code will be compiled
		3546	in. If set to C<1>, then verification code will be compiled in, but not
		3547	called. If set to C<2>, then the internal verification code will be
		3548	called once per loop, which can slow down libev. If set to C<3>, then the
		3549	verification code will be called very frequently, which will slow down
		3550	libev considerably.
		3551
		3552	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3553	C<0>.
		3554
2262	=item EV_COMMON	3555	=item EV_COMMON
2263		3556
2264	By default, all watchers have a C<void *data> member. By redefining	3557	By default, all watchers have a C<void *data> member. By redefining
2265	this macro to a something else you can include more and other types of	3558	this macro to a something else you can include more and other types of
2266	members. You have to define it each time you include one of the files,	3559	members. You have to define it each time you include one of the files,
2267	though, and it must be identical each time.	3560	though, and it must be identical each time.
2268		3561
2269	For example, the perl EV module uses something like this:	3562	For example, the perl EV module uses something like this:
2270		3563
2271	#define EV_COMMON \	3564	#define EV_COMMON \
2272	SV *self; /* contains this struct */ \	3565	SV *self; /* contains this struct */ \
2273	SV *cb_sv, *fh /* note no trailing ";" */	3566	SV *cb_sv, *fh /* note no trailing ";" */
2274		3567
2275	=item EV_CB_DECLARE (type)	3568	=item EV_CB_DECLARE (type)
2276		3569
2277	=item EV_CB_INVOKE (watcher, revents)	3570	=item EV_CB_INVOKE (watcher, revents)
2278		3571
2279	=item ev_set_cb (ev, cb)	3572	=item ev_set_cb (ev, cb)
2280		3573
2281	Can be used to change the callback member declaration in each watcher,	3574	Can be used to change the callback member declaration in each watcher,
2282	and the way callbacks are invoked and set. Must expand to a struct member	3575	and the way callbacks are invoked and set. Must expand to a struct member
2283	definition and a statement, respectively. See the F<ev.v> header file for	3576	definition and a statement, respectively. See the F<ev.h> header file for
2284	their default definitions. One possible use for overriding these is to	3577	their default definitions. One possible use for overriding these is to
2285	avoid the C<struct ev_loop *> as first argument in all cases, or to use	3578	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2286	method calls instead of plain function calls in C++.	3579	method calls instead of plain function calls in C++.
		3580
		3581	=back
		3582
		3583	=head2 EXPORTED API SYMBOLS
		3584
		3585	If you need to re-export the API (e.g. via a DLL) and you need a list of
		3586	exported symbols, you can use the provided F<Symbol.*> files which list
		3587	all public symbols, one per line:
		3588
		3589	Symbols.ev for libev proper
		3590	Symbols.event for the libevent emulation
		3591
		3592	This can also be used to rename all public symbols to avoid clashes with
		3593	multiple versions of libev linked together (which is obviously bad in
		3594	itself, but sometimes it is inconvenient to avoid this).
		3595
		3596	A sed command like this will create wrapper C<#define>'s that you need to
		3597	include before including F<ev.h>:
		3598
		3599	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		3600
		3601	This would create a file F<wrap.h> which essentially looks like this:
		3602
		3603	#define ev_backend myprefix_ev_backend
		3604	#define ev_check_start myprefix_ev_check_start
		3605	#define ev_check_stop myprefix_ev_check_stop
		3606	...
2287		3607
2288	=head2 EXAMPLES	3608	=head2 EXAMPLES
2289		3609
2290	For a real-world example of a program the includes libev	3610	For a real-world example of a program the includes libev
2291	verbatim, you can have a look at the EV perl module	3611	verbatim, you can have a look at the EV perl module
…		…
2296	file.	3616	file.
2297		3617
2298	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	3618	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2299	that everybody includes and which overrides some configure choices:	3619	that everybody includes and which overrides some configure choices:
2300		3620
2301	#define EV_MINIMAL 1	3621	#define EV_MINIMAL 1
2302	#define EV_USE_POLL 0	3622	#define EV_USE_POLL 0
2303	#define EV_MULTIPLICITY 0	3623	#define EV_MULTIPLICITY 0
2304	#define EV_PERIODIC_ENABLE 0	3624	#define EV_PERIODIC_ENABLE 0
2305	#define EV_STAT_ENABLE 0	3625	#define EV_STAT_ENABLE 0
2306	#define EV_FORK_ENABLE 0	3626	#define EV_FORK_ENABLE 0
2307	#define EV_CONFIG_H <config.h>	3627	#define EV_CONFIG_H <config.h>
2308	#define EV_MINPRI 0	3628	#define EV_MINPRI 0
2309	#define EV_MAXPRI 0	3629	#define EV_MAXPRI 0
2310		3630
2311	#include "ev++.h"	3631	#include "ev++.h"
2312		3632
2313	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	3633	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2314		3634
2315	#include "ev_cpp.h"	3635	#include "ev_cpp.h"
2316	#include "ev.c"	3636	#include "ev.c"
2317		3637
		3638	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
2318		3639
		3640	=head2 THREADS AND COROUTINES
		3641
		3642	=head3 THREADS
		3643
		3644	All libev functions are reentrant and thread-safe unless explicitly
		3645	documented otherwise, but libev implements no locking itself. This means
		3646	that you can use as many loops as you want in parallel, as long as there
		3647	are no concurrent calls into any libev function with the same loop
		3648	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		3649	of course): libev guarantees that different event loops share no data
		3650	structures that need any locking.
		3651
		3652	Or to put it differently: calls with different loop parameters can be done
		3653	concurrently from multiple threads, calls with the same loop parameter
		3654	must be done serially (but can be done from different threads, as long as
		3655	only one thread ever is inside a call at any point in time, e.g. by using
		3656	a mutex per loop).
		3657
		3658	Specifically to support threads (and signal handlers), libev implements
		3659	so-called C<ev_async> watchers, which allow some limited form of
		3660	concurrency on the same event loop, namely waking it up "from the
		3661	outside".
		3662
		3663	If you want to know which design (one loop, locking, or multiple loops
		3664	without or something else still) is best for your problem, then I cannot
		3665	help you, but here is some generic advice:
		3666
		3667	=over 4
		3668
		3669	=item * most applications have a main thread: use the default libev loop
		3670	in that thread, or create a separate thread running only the default loop.
		3671
		3672	This helps integrating other libraries or software modules that use libev
		3673	themselves and don't care/know about threading.
		3674
		3675	=item * one loop per thread is usually a good model.
		3676
		3677	Doing this is almost never wrong, sometimes a better-performance model
		3678	exists, but it is always a good start.
		3679
		3680	=item * other models exist, such as the leader/follower pattern, where one
		3681	loop is handed through multiple threads in a kind of round-robin fashion.
		3682
		3683	Choosing a model is hard - look around, learn, know that usually you can do
		3684	better than you currently do :-)
		3685
		3686	=item * often you need to talk to some other thread which blocks in the
		3687	event loop.
		3688
		3689	C<ev_async> watchers can be used to wake them up from other threads safely
		3690	(or from signal contexts...).
		3691
		3692	An example use would be to communicate signals or other events that only
		3693	work in the default loop by registering the signal watcher with the
		3694	default loop and triggering an C<ev_async> watcher from the default loop
		3695	watcher callback into the event loop interested in the signal.
		3696
		3697	=back
		3698
		3699	=head3 COROUTINES
		3700
		3701	Libev is very accommodating to coroutines ("cooperative threads"):
		3702	libev fully supports nesting calls to its functions from different
		3703	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3704	different coroutines, and switch freely between both coroutines running the
		3705	loop, as long as you don't confuse yourself). The only exception is that
		3706	you must not do this from C<ev_periodic> reschedule callbacks.
		3707
		3708	Care has been taken to ensure that libev does not keep local state inside
		3709	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		3710	they do not call any callbacks.
		3711
		3712	=head2 COMPILER WARNINGS
		3713
		3714	Depending on your compiler and compiler settings, you might get no or a
		3715	lot of warnings when compiling libev code. Some people are apparently
		3716	scared by this.
		3717
		3718	However, these are unavoidable for many reasons. For one, each compiler
		3719	has different warnings, and each user has different tastes regarding
		3720	warning options. "Warn-free" code therefore cannot be a goal except when
		3721	targeting a specific compiler and compiler-version.
		3722
		3723	Another reason is that some compiler warnings require elaborate
		3724	workarounds, or other changes to the code that make it less clear and less
		3725	maintainable.
		3726
		3727	And of course, some compiler warnings are just plain stupid, or simply
		3728	wrong (because they don't actually warn about the condition their message
		3729	seems to warn about). For example, certain older gcc versions had some
		3730	warnings that resulted an extreme number of false positives. These have
		3731	been fixed, but some people still insist on making code warn-free with
		3732	such buggy versions.
		3733
		3734	While libev is written to generate as few warnings as possible,
		3735	"warn-free" code is not a goal, and it is recommended not to build libev
		3736	with any compiler warnings enabled unless you are prepared to cope with
		3737	them (e.g. by ignoring them). Remember that warnings are just that:
		3738	warnings, not errors, or proof of bugs.
		3739
		3740
		3741	=head2 VALGRIND
		3742
		3743	Valgrind has a special section here because it is a popular tool that is
		3744	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		3745
		3746	If you think you found a bug (memory leak, uninitialised data access etc.)
		3747	in libev, then check twice: If valgrind reports something like:
		3748
		3749	==2274== definitely lost: 0 bytes in 0 blocks.
		3750	==2274== possibly lost: 0 bytes in 0 blocks.
		3751	==2274== still reachable: 256 bytes in 1 blocks.
		3752
		3753	Then there is no memory leak, just as memory accounted to global variables
		3754	is not a memleak - the memory is still being referenced, and didn't leak.
		3755
		3756	Similarly, under some circumstances, valgrind might report kernel bugs
		3757	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		3758	although an acceptable workaround has been found here), or it might be
		3759	confused.
		3760
		3761	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		3762	make it into some kind of religion.
		3763
		3764	If you are unsure about something, feel free to contact the mailing list
		3765	with the full valgrind report and an explanation on why you think this
		3766	is a bug in libev (best check the archives, too :). However, don't be
		3767	annoyed when you get a brisk "this is no bug" answer and take the chance
		3768	of learning how to interpret valgrind properly.
		3769
		3770	If you need, for some reason, empty reports from valgrind for your project
		3771	I suggest using suppression lists.
		3772
		3773
		3774	=head1 PORTABILITY NOTES
		3775
		3776	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		3777
		3778	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		3779	requires, and its I/O model is fundamentally incompatible with the POSIX
		3780	model. Libev still offers limited functionality on this platform in
		3781	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		3782	descriptors. This only applies when using Win32 natively, not when using
		3783	e.g. cygwin.
		3784
		3785	Lifting these limitations would basically require the full
		3786	re-implementation of the I/O system. If you are into these kinds of
		3787	things, then note that glib does exactly that for you in a very portable
		3788	way (note also that glib is the slowest event library known to man).
		3789
		3790	There is no supported compilation method available on windows except
		3791	embedding it into other applications.
		3792
		3793	Not a libev limitation but worth mentioning: windows apparently doesn't
		3794	accept large writes: instead of resulting in a partial write, windows will
		3795	either accept everything or return C<ENOBUFS> if the buffer is too large,
		3796	so make sure you only write small amounts into your sockets (less than a
		3797	megabyte seems safe, but this apparently depends on the amount of memory
		3798	available).
		3799
		3800	Due to the many, low, and arbitrary limits on the win32 platform and
		3801	the abysmal performance of winsockets, using a large number of sockets
		3802	is not recommended (and not reasonable). If your program needs to use
		3803	more than a hundred or so sockets, then likely it needs to use a totally
		3804	different implementation for windows, as libev offers the POSIX readiness
		3805	notification model, which cannot be implemented efficiently on windows
		3806	(Microsoft monopoly games).
		3807
		3808	A typical way to use libev under windows is to embed it (see the embedding
		3809	section for details) and use the following F<evwrap.h> header file instead
		3810	of F<ev.h>:
		3811
		3812	#define EV_STANDALONE /* keeps ev from requiring config.h */
		3813	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		3814
		3815	#include "ev.h"
		3816
		3817	And compile the following F<evwrap.c> file into your project (make sure
		3818	you do I<not> compile the F<ev.c> or any other embedded source files!):
		3819
		3820	#include "evwrap.h"
		3821	#include "ev.c"
		3822
		3823	=over 4
		3824
		3825	=item The winsocket select function
		3826
		3827	The winsocket C<select> function doesn't follow POSIX in that it
		3828	requires socket I<handles> and not socket I<file descriptors> (it is
		3829	also extremely buggy). This makes select very inefficient, and also
		3830	requires a mapping from file descriptors to socket handles (the Microsoft
		3831	C runtime provides the function C<_open_osfhandle> for this). See the
		3832	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		3833	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		3834
		3835	The configuration for a "naked" win32 using the Microsoft runtime
		3836	libraries and raw winsocket select is:
		3837
		3838	#define EV_USE_SELECT 1
		3839	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		3840
		3841	Note that winsockets handling of fd sets is O(n), so you can easily get a
		3842	complexity in the O(n²) range when using win32.
		3843
		3844	=item Limited number of file descriptors
		3845
		3846	Windows has numerous arbitrary (and low) limits on things.
		3847
		3848	Early versions of winsocket's select only supported waiting for a maximum
		3849	of C<64> handles (probably owning to the fact that all windows kernels
		3850	can only wait for C<64> things at the same time internally; Microsoft
		3851	recommends spawning a chain of threads and wait for 63 handles and the
		3852	previous thread in each. Great).
		3853
		3854	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		3855	to some high number (e.g. C<2048>) before compiling the winsocket select
		3856	call (which might be in libev or elsewhere, for example, perl does its own
		3857	select emulation on windows).
		3858
		3859	Another limit is the number of file descriptors in the Microsoft runtime
		3860	libraries, which by default is C<64> (there must be a hidden I<64> fetish
		3861	or something like this inside Microsoft). You can increase this by calling
		3862	C<_setmaxstdio>, which can increase this limit to C<2048> (another
		3863	arbitrary limit), but is broken in many versions of the Microsoft runtime
		3864	libraries.
		3865
		3866	This might get you to about C<512> or C<2048> sockets (depending on
		3867	windows version and/or the phase of the moon). To get more, you need to
		3868	wrap all I/O functions and provide your own fd management, but the cost of
		3869	calling select (O(n²)) will likely make this unworkable.
		3870
		3871	=back
		3872
		3873	=head2 PORTABILITY REQUIREMENTS
		3874
		3875	In addition to a working ISO-C implementation and of course the
		3876	backend-specific APIs, libev relies on a few additional extensions:
		3877
		3878	=over 4
		3879
		3880	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		3881	calling conventions regardless of C<ev_watcher_type *>.
		3882
		3883	Libev assumes not only that all watcher pointers have the same internal
		3884	structure (guaranteed by POSIX but not by ISO C for example), but it also
		3885	assumes that the same (machine) code can be used to call any watcher
		3886	callback: The watcher callbacks have different type signatures, but libev
		3887	calls them using an C<ev_watcher *> internally.
		3888
		3889	=item C<sig_atomic_t volatile> must be thread-atomic as well
		3890
		3891	The type C<sig_atomic_t volatile> (or whatever is defined as
		3892	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		3893	threads. This is not part of the specification for C<sig_atomic_t>, but is
		3894	believed to be sufficiently portable.
		3895
		3896	=item C<sigprocmask> must work in a threaded environment
		3897
		3898	Libev uses C<sigprocmask> to temporarily block signals. This is not
		3899	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		3900	pthread implementations will either allow C<sigprocmask> in the "main
		3901	thread" or will block signals process-wide, both behaviours would
		3902	be compatible with libev. Interaction between C<sigprocmask> and
		3903	C<pthread_sigmask> could complicate things, however.
		3904
		3905	The most portable way to handle signals is to block signals in all threads
		3906	except the initial one, and run the default loop in the initial thread as
		3907	well.
		3908
		3909	=item C<long> must be large enough for common memory allocation sizes
		3910
		3911	To improve portability and simplify its API, libev uses C<long> internally
		3912	instead of C<size_t> when allocating its data structures. On non-POSIX
		3913	systems (Microsoft...) this might be unexpectedly low, but is still at
		3914	least 31 bits everywhere, which is enough for hundreds of millions of
		3915	watchers.
		3916
		3917	=item C<double> must hold a time value in seconds with enough accuracy
		3918
		3919	The type C<double> is used to represent timestamps. It is required to
		3920	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		3921	enough for at least into the year 4000. This requirement is fulfilled by
		3922	implementations implementing IEEE 754 (basically all existing ones).
		3923
		3924	=back
		3925
		3926	If you know of other additional requirements drop me a note.
		3927
		3928
2319	=head1 COMPLEXITIES	3929	=head1 ALGORITHMIC COMPLEXITIES
2320		3930
2321	In this section the complexities of (many of) the algorithms used inside	3931	In this section the complexities of (many of) the algorithms used inside
2322	libev will be explained. For complexity discussions about backends see the	3932	libev will be documented. For complexity discussions about backends see
2323	documentation for C<ev_default_init>.	3933	the documentation for C<ev_default_init>.
2324		3934
2325	All of the following are about amortised time: If an array needs to be	3935	All of the following are about amortised time: If an array needs to be
2326	extended, libev needs to realloc and move the whole array, but this	3936	extended, libev needs to realloc and move the whole array, but this
2327	happens asymptotically never with higher number of elements, so O(1) might	3937	happens asymptotically rarer with higher number of elements, so O(1) might
2328	mean it might do a lengthy realloc operation in rare cases, but on average	3938	mean that libev does a lengthy realloc operation in rare cases, but on
2329	it is much faster and asymptotically approaches constant time.	3939	average it is much faster and asymptotically approaches constant time.
2330		3940
2331	=over 4	3941	=over 4
2332		3942
2333	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	3943	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2334		3944
2335	This means that, when you have a watcher that triggers in one hour and	3945	This means that, when you have a watcher that triggers in one hour and
2336	there are 100 watchers that would trigger before that then inserting will	3946	there are 100 watchers that would trigger before that, then inserting will
2337	have to skip those 100 watchers.	3947	have to skip roughly seven (C<ld 100>) of these watchers.
2338		3948
2339	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	3949	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2340		3950
2341	That means that for changing a timer costs less than removing/adding them	3951	That means that changing a timer costs less than removing/adding them,
2342	as only the relative motion in the event queue has to be paid for.	3952	as only the relative motion in the event queue has to be paid for.
2343		3953
2344	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	3954	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
2345		3955
2346	These just add the watcher into an array or at the head of a list.	3956	These just add the watcher into an array or at the head of a list.
		3957
2347	=item Stopping check/prepare/idle watchers: O(1)	3958	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2348		3959
2349	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	3960	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2350		3961
2351	These watchers are stored in lists then need to be walked to find the	3962	These watchers are stored in lists, so they need to be walked to find the
2352	correct watcher to remove. The lists are usually short (you don't usually	3963	correct watcher to remove. The lists are usually short (you don't usually
2353	have many watchers waiting for the same fd or signal).	3964	have many watchers waiting for the same fd or signal: one is typical, two
		3965	is rare).
2354		3966
2355	=item Finding the next timer per loop iteration: O(1)	3967	=item Finding the next timer in each loop iteration: O(1)
		3968
		3969	By virtue of using a binary or 4-heap, the next timer is always found at a
		3970	fixed position in the storage array.
2356		3971
2357	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	3972	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2358		3973
2359	A change means an I/O watcher gets started or stopped, which requires	3974	A change means an I/O watcher gets started or stopped, which requires
2360	libev to recalculate its status (and possibly tell the kernel).	3975	libev to recalculate its status (and possibly tell the kernel, depending
		3976	on backend and whether C<ev_io_set> was used).
2361		3977
2362	=item Activating one watcher: O(1)	3978	=item Activating one watcher (putting it into the pending state): O(1)
2363		3979
2364	=item Priority handling: O(number_of_priorities)	3980	=item Priority handling: O(number_of_priorities)
2365		3981
2366	Priorities are implemented by allocating some space for each	3982	Priorities are implemented by allocating some space for each
2367	priority. When doing priority-based operations, libev usually has to	3983	priority. When doing priority-based operations, libev usually has to
2368	linearly search all the priorities.	3984	linearly search all the priorities, but starting/stopping and activating
		3985	watchers becomes O(1) with respect to priority handling.
		3986
		3987	=item Sending an ev_async: O(1)
		3988
		3989	=item Processing ev_async_send: O(number_of_async_watchers)
		3990
		3991	=item Processing signals: O(max_signal_number)
		3992
		3993	Sending involves a system call I<iff> there were no other C<ev_async_send>
		3994	calls in the current loop iteration. Checking for async and signal events
		3995	involves iterating over all running async watchers or all signal numbers.
2369		3996
2370	=back	3997	=back
2371		3998
2372		3999
2373	=head1 AUTHOR	4000	=head1 AUTHOR
2374		4001
2375	Marc Lehmann <libev@schmorp.de>.	4002	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
2376		4003

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