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Revision 1.68 by root, Fri Dec 7 18:09:43 2007 UTC vs.
Revision 1.226 by root, Wed Mar 4 12:51:37 2009 UTC

…		…
2		2
3	libev - a high performance full-featured event loop written in C	3	libev - a high performance full-featured event loop written in C
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
8		8
9	=head1 EXAMPLE PROGRAM	9	=head2 EXAMPLE PROGRAM
10		10
		11	// a single header file is required
11	#include <ev.h>	12	#include <ev.h>
12		13
		14	#include <stdio.h> // for puts
		15
		16	// every watcher type has its own typedef'd struct
		17	// with the name ev_TYPE
13	ev_io stdin_watcher;	18	ev_io stdin_watcher;
14	ev_timer timeout_watcher;	19	ev_timer timeout_watcher;
15		20
16	/* called when data readable on stdin */	21	// all watcher callbacks have a similar signature
		22	// this callback is called when data is readable on stdin
17	static void	23	static void
18	stdin_cb (EV_P_ struct ev_io *w, int revents)	24	stdin_cb (EV_P_ ev_io *w, int revents)
19	{	25	{
20	/* puts ("stdin ready"); */	26	puts ("stdin ready");
21	ev_io_stop (EV_A_ w); /* just a syntax example */	27	// for one-shot events, one must manually stop the watcher
22	ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */	28	// with its corresponding stop function.
		29	ev_io_stop (EV_A_ w);
		30
		31	// this causes all nested ev_loop's to stop iterating
		32	ev_unloop (EV_A_ EVUNLOOP_ALL);
23	}	33	}
24		34
		35	// another callback, this time for a time-out
25	static void	36	static void
26	timeout_cb (EV_P_ struct ev_timer *w, int revents)	37	timeout_cb (EV_P_ ev_timer *w, int revents)
27	{	38	{
28	/* puts ("timeout"); */	39	puts ("timeout");
29	ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */	40	// this causes the innermost ev_loop to stop iterating
		41	ev_unloop (EV_A_ EVUNLOOP_ONE);
30	}	42	}
31		43
32	int	44	int
33	main (void)	45	main (void)
34	{	46	{
		47	// use the default event loop unless you have special needs
35	struct ev_loop *loop = ev_default_loop (0);	48	struct ev_loop *loop = ev_default_loop (0);
36		49
37	/* initialise an io watcher, then start it */	50	// initialise an io watcher, then start it
		51	// this one will watch for stdin to become readable
38	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);	52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
39	ev_io_start (loop, &stdin_watcher);	53	ev_io_start (loop, &stdin_watcher);
40		54
		55	// initialise a timer watcher, then start it
41	/* simple non-repeating 5.5 second timeout */	56	// simple non-repeating 5.5 second timeout
42	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);	57	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
43	ev_timer_start (loop, &timeout_watcher);	58	ev_timer_start (loop, &timeout_watcher);
44		59
45	/* loop till timeout or data ready */	60	// now wait for events to arrive
46	ev_loop (loop, 0);	61	ev_loop (loop, 0);
47		62
		63	// unloop was called, so exit
48	return 0;	64	return 0;
49	}	65	}
50		66
51	=head1 DESCRIPTION	67	=head1 DESCRIPTION
52		68
		69	The newest version of this document is also available as an html-formatted
		70	web page you might find easier to navigate when reading it for the first
		71	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		72
53	Libev is an event loop: you register interest in certain events (such as a	73	Libev is an event loop: you register interest in certain events (such as a
54	file descriptor being readable or a timeout occuring), and it will manage	74	file descriptor being readable or a timeout occurring), and it will manage
55	these event sources and provide your program with events.	75	these event sources and provide your program with events.
56		76
57	To do this, it must take more or less complete control over your process	77	To do this, it must take more or less complete control over your process
58	(or thread) by executing the I<event loop> handler, and will then	78	(or thread) by executing the I<event loop> handler, and will then
59	communicate events via a callback mechanism.	79	communicate events via a callback mechanism.
…		…
61	You register interest in certain events by registering so-called I<event	81	You register interest in certain events by registering so-called I<event
62	watchers>, which are relatively small C structures you initialise with the	82	watchers>, which are relatively small C structures you initialise with the
63	details of the event, and then hand it over to libev by I<starting> the	83	details of the event, and then hand it over to libev by I<starting> the
64	watcher.	84	watcher.
65		85
66	=head1 FEATURES	86	=head2 FEATURES
67		87
68	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	88	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
69	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	89	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
70	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	90	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
71	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	91	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
…		…
78		98
79	It also is quite fast (see this	99	It also is quite fast (see this
80	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent	100	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
81	for example).	101	for example).
82		102
83	=head1 CONVENTIONS	103	=head2 CONVENTIONS
84		104
85	Libev is very configurable. In this manual the default configuration will	105	Libev is very configurable. In this manual the default (and most common)
86	be described, which supports multiple event loops. For more info about	106	configuration will be described, which supports multiple event loops. For
87	various configuration options please have a look at B<EMBED> section in	107	more info about various configuration options please have a look at
88	this manual. If libev was configured without support for multiple event	108	B<EMBED> section in this manual. If libev was configured without support
89	loops, then all functions taking an initial argument of name C<loop>	109	for multiple event loops, then all functions taking an initial argument of
90	(which is always of type C<struct ev_loop *>) will not have this argument.	110	name C<loop> (which is always of type C<ev_loop *>) will not have
		111	this argument.
91		112
92	=head1 TIME REPRESENTATION	113	=head2 TIME REPRESENTATION
93		114
94	Libev represents time as a single floating point number, representing the	115	Libev represents time as a single floating point number, representing the
95	(fractional) number of seconds since the (POSIX) epoch (somewhere near	116	(fractional) number of seconds since the (POSIX) epoch (somewhere near
96	the beginning of 1970, details are complicated, don't ask). This type is	117	the beginning of 1970, details are complicated, don't ask). This type is
97	called C<ev_tstamp>, which is what you should use too. It usually aliases	118	called C<ev_tstamp>, which is what you should use too. It usually aliases
98	to the C<double> type in C, and when you need to do any calculations on	119	to the C<double> type in C, and when you need to do any calculations on
99	it, you should treat it as such.	120	it, you should treat it as some floating point value. Unlike the name
		121	component C<stamp> might indicate, it is also used for time differences
		122	throughout libev.
		123
		124	=head1 ERROR HANDLING
		125
		126	Libev knows three classes of errors: operating system errors, usage errors
		127	and internal errors (bugs).
		128
		129	When libev catches an operating system error it cannot handle (for example
		130	a system call indicating a condition libev cannot fix), it calls the callback
		131	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		132	abort. The default is to print a diagnostic message and to call C<abort
		133	()>.
		134
		135	When libev detects a usage error such as a negative timer interval, then
		136	it will print a diagnostic message and abort (via the C<assert> mechanism,
		137	so C<NDEBUG> will disable this checking): these are programming errors in
		138	the libev caller and need to be fixed there.
		139
		140	Libev also has a few internal error-checking C<assert>ions, and also has
		141	extensive consistency checking code. These do not trigger under normal
		142	circumstances, as they indicate either a bug in libev or worse.
		143
100		144
101	=head1 GLOBAL FUNCTIONS	145	=head1 GLOBAL FUNCTIONS
102		146
103	These functions can be called anytime, even before initialising the	147	These functions can be called anytime, even before initialising the
104	library in any way.	148	library in any way.
…		…
109		153
110	Returns the current time as libev would use it. Please note that the	154	Returns the current time as libev would use it. Please note that the
111	C<ev_now> function is usually faster and also often returns the timestamp	155	C<ev_now> function is usually faster and also often returns the timestamp
112	you actually want to know.	156	you actually want to know.
113		157
		158	=item ev_sleep (ev_tstamp interval)
		159
		160	Sleep for the given interval: The current thread will be blocked until
		161	either it is interrupted or the given time interval has passed. Basically
		162	this is a sub-second-resolution C<sleep ()>.
		163
114	=item int ev_version_major ()	164	=item int ev_version_major ()
115		165
116	=item int ev_version_minor ()	166	=item int ev_version_minor ()
117		167
118	You can find out the major and minor version numbers of the library	168	You can find out the major and minor ABI version numbers of the library
119	you linked against by calling the functions C<ev_version_major> and	169	you linked against by calling the functions C<ev_version_major> and
120	C<ev_version_minor>. If you want, you can compare against the global	170	C<ev_version_minor>. If you want, you can compare against the global
121	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the	171	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
122	version of the library your program was compiled against.	172	version of the library your program was compiled against.
123		173
		174	These version numbers refer to the ABI version of the library, not the
		175	release version.
		176
124	Usually, it's a good idea to terminate if the major versions mismatch,	177	Usually, it's a good idea to terminate if the major versions mismatch,
125	as this indicates an incompatible change. Minor versions are usually	178	as this indicates an incompatible change. Minor versions are usually
126	compatible to older versions, so a larger minor version alone is usually	179	compatible to older versions, so a larger minor version alone is usually
127	not a problem.	180	not a problem.
128		181
129	Example: Make sure we haven't accidentally been linked against the wrong	182	Example: Make sure we haven't accidentally been linked against the wrong
130	version.	183	version.
131		184
132	assert (("libev version mismatch",	185	assert (("libev version mismatch",
133	ev_version_major () == EV_VERSION_MAJOR	186	ev_version_major () == EV_VERSION_MAJOR
134	&& ev_version_minor () >= EV_VERSION_MINOR));	187	&& ev_version_minor () >= EV_VERSION_MINOR));
135		188
136	=item unsigned int ev_supported_backends ()	189	=item unsigned int ev_supported_backends ()
137		190
138	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	191	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
139	value) compiled into this binary of libev (independent of their	192	value) compiled into this binary of libev (independent of their
…		…
141	a description of the set values.	194	a description of the set values.
142		195
143	Example: make sure we have the epoll method, because yeah this is cool and	196	Example: make sure we have the epoll method, because yeah this is cool and
144	a must have and can we have a torrent of it please!!!11	197	a must have and can we have a torrent of it please!!!11
145		198
146	assert (("sorry, no epoll, no sex",	199	assert (("sorry, no epoll, no sex",
147	ev_supported_backends () & EVBACKEND_EPOLL));	200	ev_supported_backends () & EVBACKEND_EPOLL));
148		201
149	=item unsigned int ev_recommended_backends ()	202	=item unsigned int ev_recommended_backends ()
150		203
151	Return the set of all backends compiled into this binary of libev and also	204	Return the set of all backends compiled into this binary of libev and also
152	recommended for this platform. This set is often smaller than the one	205	recommended for this platform. This set is often smaller than the one
153	returned by C<ev_supported_backends>, as for example kqueue is broken on	206	returned by C<ev_supported_backends>, as for example kqueue is broken on
154	most BSDs and will not be autodetected unless you explicitly request it	207	most BSDs and will not be auto-detected unless you explicitly request it
155	(assuming you know what you are doing). This is the set of backends that	208	(assuming you know what you are doing). This is the set of backends that
156	libev will probe for if you specify no backends explicitly.	209	libev will probe for if you specify no backends explicitly.
157		210
158	=item unsigned int ev_embeddable_backends ()	211	=item unsigned int ev_embeddable_backends ()
159		212
…		…
163	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	216	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
164	recommended ones.	217	recommended ones.
165		218
166	See the description of C<ev_embed> watchers for more info.	219	See the description of C<ev_embed> watchers for more info.
167		220
168	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	221	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
169		222
170	Sets the allocation function to use (the prototype is similar - the	223	Sets the allocation function to use (the prototype is similar - the
171	semantics is identical - to the realloc C function). It is used to	224	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
172	allocate and free memory (no surprises here). If it returns zero when	225	used to allocate and free memory (no surprises here). If it returns zero
173	memory needs to be allocated, the library might abort or take some	226	when memory needs to be allocated (C<size != 0>), the library might abort
174	potentially destructive action. The default is your system realloc	227	or take some potentially destructive action.
175	function.	228
		229	Since some systems (at least OpenBSD and Darwin) fail to implement
		230	correct C<realloc> semantics, libev will use a wrapper around the system
		231	C<realloc> and C<free> functions by default.
176		232
177	You could override this function in high-availability programs to, say,	233	You could override this function in high-availability programs to, say,
178	free some memory if it cannot allocate memory, to use a special allocator,	234	free some memory if it cannot allocate memory, to use a special allocator,
179	or even to sleep a while and retry until some memory is available.	235	or even to sleep a while and retry until some memory is available.
180		236
181	Example: Replace the libev allocator with one that waits a bit and then	237	Example: Replace the libev allocator with one that waits a bit and then
182	retries).	238	retries (example requires a standards-compliant C<realloc>).
183		239
184	static void *	240	static void *
185	persistent_realloc (void *ptr, size_t size)	241	persistent_realloc (void *ptr, size_t size)
186	{	242	{
187	for (;;)	243	for (;;)
…		…
196	}	252	}
197		253
198	...	254	...
199	ev_set_allocator (persistent_realloc);	255	ev_set_allocator (persistent_realloc);
200		256
201	=item ev_set_syserr_cb (void (*cb)(const char *msg));	257	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
202		258
203	Set the callback function to call on a retryable syscall error (such	259	Set the callback function to call on a retryable system call error (such
204	as failed select, poll, epoll_wait). The message is a printable string	260	as failed select, poll, epoll_wait). The message is a printable string
205	indicating the system call or subsystem causing the problem. If this	261	indicating the system call or subsystem causing the problem. If this
206	callback is set, then libev will expect it to remedy the sitution, no	262	callback is set, then libev will expect it to remedy the situation, no
207	matter what, when it returns. That is, libev will generally retry the	263	matter what, when it returns. That is, libev will generally retry the
208	requested operation, or, if the condition doesn't go away, do bad stuff	264	requested operation, or, if the condition doesn't go away, do bad stuff
209	(such as abort).	265	(such as abort).
210		266
211	Example: This is basically the same thing that libev does internally, too.	267	Example: This is basically the same thing that libev does internally, too.
…		…
222		278
223	=back	279	=back
224		280
225	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	281	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
226		282
227	An event loop is described by a C<struct ev_loop *>. The library knows two	283	An event loop is described by a C<struct ev_loop *> (the C<struct>
228	types of such loops, the I<default> loop, which supports signals and child	284	is I<not> optional in this case, as there is also an C<ev_loop>
229	events, and dynamically created loops which do not.	285	I<function>).
230		286
231	If you use threads, a common model is to run the default event loop	287	The library knows two types of such loops, the I<default> loop, which
232	in your main thread (or in a separate thread) and for each thread you	288	supports signals and child events, and dynamically created loops which do
233	create, you also create another event loop. Libev itself does no locking	289	not.
234	whatsoever, so if you mix calls to the same event loop in different
235	threads, make sure you lock (this is usually a bad idea, though, even if
236	done correctly, because it's hideous and inefficient).
237		290
238	=over 4	291	=over 4
239		292
240	=item struct ev_loop *ev_default_loop (unsigned int flags)	293	=item struct ev_loop *ev_default_loop (unsigned int flags)
241		294
…		…
245	flags. If that is troubling you, check C<ev_backend ()> afterwards).	298	flags. If that is troubling you, check C<ev_backend ()> afterwards).
246		299
247	If you don't know what event loop to use, use the one returned from this	300	If you don't know what event loop to use, use the one returned from this
248	function.	301	function.
249		302
		303	Note that this function is I<not> thread-safe, so if you want to use it
		304	from multiple threads, you have to lock (note also that this is unlikely,
		305	as loops cannot be shared easily between threads anyway).
		306
		307	The default loop is the only loop that can handle C<ev_signal> and
		308	C<ev_child> watchers, and to do this, it always registers a handler
		309	for C<SIGCHLD>. If this is a problem for your application you can either
		310	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
		311	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
		312	C<ev_default_init>.
		313
250	The flags argument can be used to specify special behaviour or specific	314	The flags argument can be used to specify special behaviour or specific
251	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	315	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
252		316
253	The following flags are supported:	317	The following flags are supported:
254		318
…		…
259	The default flags value. Use this if you have no clue (it's the right	323	The default flags value. Use this if you have no clue (it's the right
260	thing, believe me).	324	thing, believe me).
261		325
262	=item C<EVFLAG_NOENV>	326	=item C<EVFLAG_NOENV>
263		327
264	If this flag bit is ored into the flag value (or the program runs setuid	328	If this flag bit is or'ed into the flag value (or the program runs setuid
265	or setgid) then libev will I<not> look at the environment variable	329	or setgid) then libev will I<not> look at the environment variable
266	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	330	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
267	override the flags completely if it is found in the environment. This is	331	override the flags completely if it is found in the environment. This is
268	useful to try out specific backends to test their performance, or to work	332	useful to try out specific backends to test their performance, or to work
269	around bugs.	333	around bugs.
…		…
275	enabling this flag.	339	enabling this flag.
276		340
277	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,
278	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
279	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
280	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
281	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
282	C<pthread_atfork> which is even faster).	346	C<pthread_atfork> which is even faster).
283		347
284	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
285	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
286	flag.	350	flag.
287		351
288	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>
289	environment variable.	353	environment variable.
290		354
291	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	355	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
292		356
293	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
294	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,
295	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
296	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
297	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).
298		373
299	=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)
300		375
301	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
302	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
303	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
304	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>.
305		385
306	=item C<EVBACKEND_EPOLL> (value 4, Linux)	386	=item C<EVBACKEND_EPOLL> (value 4, Linux)
307		387
308	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,
309	but it scales phenomenally better. While poll and select usually scale like	389	but it scales phenomenally better. While poll and select usually scale
310	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),
311	either O(1) or O(active_fds).	391	epoll scales either O(1) or O(active_fds).
312		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
313	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
314	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
315	(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
316	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
317	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.
318		416
319	Please note that epoll sometimes generates spurious notifications, so you	417	Best performance from this backend is achieved by not unregistering all
320	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,
321	(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>.
322		434
323	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	435	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
324		436
325	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
326	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
327	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
328	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
329	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
330	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.
331		450
332	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
333	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
334	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
335	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
336	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>.
337		471
338	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	472	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
339		473
340	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.
341		478
342	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	479	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
343		480
344	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,
345	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)).
346		483
347	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
348	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
349	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>.
350		500
351	=item C<EVBACKEND_ALL>	501	=item C<EVBACKEND_ALL>
352		502
353	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
354	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
355	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	505	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
356		506
		507	It is definitely not recommended to use this flag.
		508
357	=back	509	=back
358		510
359	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
360	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
361	specified, most compiled-in backend will be tried, usually in reverse	513	specified, all backends in C<ev_recommended_backends ()> will be tried.
362	order of their flag values :)
363		514
364	The most typical usage is like this:	515	Example: This is the most typical usage.
365		516
366	if (!ev_default_loop (0))	517	if (!ev_default_loop (0))
367	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	518	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
368		519
369	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
370	environment settings to be taken into account:	521	environment settings to be taken into account:
371		522
372	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	523	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
373		524
374	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
375	available (warning, breaks stuff, best use only with your own private	526	used if available (warning, breaks stuff, best use only with your own
376	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):
377		529
378	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	530	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
379		531
380	=item struct ev_loop *ev_loop_new (unsigned int flags)	532	=item struct ev_loop *ev_loop_new (unsigned int flags)
381		533
382	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
383	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
384	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
385	undefined behaviour (or a failed assertion if assertions are enabled).	537	undefined behaviour (or a failed assertion if assertions are enabled).
386		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
387	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.
388		544
389	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	545	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
390	if (!epoller)	546	if (!epoller)
391	fatal ("no epoll found here, maybe it hides under your chair");	547	fatal ("no epoll found here, maybe it hides under your chair");
392		548
393	=item ev_default_destroy ()	549	=item ev_default_destroy ()
394		550
395	Destroys the default loop again (frees all memory and kernel state	551	Destroys the default loop again (frees all memory and kernel state
396	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
397	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
398	responsibility to either stop all watchers cleanly yoursef I<before>	554	responsibility to either stop all watchers cleanly yourself I<before>
399	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
400	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
401	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>).
402		567
403	=item ev_loop_destroy (loop)	568	=item ev_loop_destroy (loop)
404		569
405	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
406	earlier call to C<ev_loop_new>.	571	earlier call to C<ev_loop_new>.
407		572
408	=item ev_default_fork ()	573	=item ev_default_fork ()
409		574
		575	This function sets a flag that causes subsequent C<ev_loop> iterations
410	This function reinitialises the kernel state for backends that have	576	to reinitialise the kernel state for backends that have one. Despite the
411	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
412	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
413	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.
414		581
415	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
416	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
417	fork+exec, you don't have to call it.	584	you just fork+exec, you don't have to call it at all.
418		585
419	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
420	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
421	quite nicely into a call to C<pthread_atfork>:	588	quite nicely into a call to C<pthread_atfork>:
422		589
423	pthread_atfork (0, 0, ev_default_fork);	590	pthread_atfork (0, 0, ev_default_fork);
424		591
425	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
426	without calling this function, so if you force one of those backends you
427	do not need to care.
428
429	=item ev_loop_fork (loop)	592	=item ev_loop_fork (loop)
430		593
431	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
432	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
433	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.
434		603
435	=item unsigned int ev_loop_count (loop)	604	=item unsigned int ev_loop_count (loop)
436		605
437	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
438	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
…		…
451		620
452	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
453	received events and started processing them. This timestamp does not	622	received events and started processing them. This timestamp does not
454	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
455	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
456	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.
457		638
458	=item ev_loop (loop, int flags)	639	=item ev_loop (loop, int flags)
459		640
460	Finally, this is it, the event handler. This function usually is called	641	Finally, this is it, the event handler. This function usually is called
461	after you initialised all your watchers and you want to start handling	642	after you initialised all your watchers and you want to start handling
…		…
464	If the flags argument is specified as C<0>, it will not return until	645	If the flags argument is specified as C<0>, it will not return until
465	either no event watchers are active anymore or C<ev_unloop> was called.	646	either no event watchers are active anymore or C<ev_unloop> was called.
466		647
467	Please note that an explicit C<ev_unloop> is usually better than	648	Please note that an explicit C<ev_unloop> is usually better than
468	relying on all watchers to be stopped when deciding when a program has	649	relying on all watchers to be stopped when deciding when a program has
469	finished (especially in interactive programs), but having a program that	650	finished (especially in interactive programs), but having a program
470	automatically loops as long as it has to and no longer by virtue of	651	that automatically loops as long as it has to and no longer by virtue
471	relying on its watchers stopping correctly is a thing of beauty.	652	of relying on its watchers stopping correctly, that is truly a thing of
		653	beauty.
472		654
473	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	655	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
474	those events and any outstanding ones, but will not block your process in	656	those events and any already outstanding ones, but will not block your
475	case there are no events and will return after one iteration of the loop.	657	process in case there are no events and will return after one iteration of
		658	the loop.
476		659
477	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	660	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
478	neccessary) and will handle those and any outstanding ones. It will block	661	necessary) and will handle those and any already outstanding ones. It
479	your process until at least one new event arrives, and will return after	662	will block your process until at least one new event arrives (which could
480	one iteration of the loop. This is useful if you are waiting for some	663	be an event internal to libev itself, so there is no guarantee that a
481	external event in conjunction with something not expressible using other	664	user-registered callback will be called), and will return after one
		665	iteration of the loop.
		666
		667	This is useful if you are waiting for some external event in conjunction
		668	with something not expressible using other libev watchers (i.e. "roll your
482	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	669	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
483	usually a better approach for this kind of thing.	670	usually a better approach for this kind of thing.
484		671
485	Here are the gory details of what C<ev_loop> does:	672	Here are the gory details of what C<ev_loop> does:
486		673
487	* If there are no active watchers (reference count is zero), return.	674	- Before the first iteration, call any pending watchers.
488	- Queue prepare watchers and then call all outstanding watchers.	675	* If EVFLAG_FORKCHECK was used, check for a fork.
		676	- If a fork was detected (by any means), queue and call all fork watchers.
		677	- Queue and call all prepare watchers.
489	- If we have been forked, recreate the kernel state.	678	- If we have been forked, detach and recreate the kernel state
		679	as to not disturb the other process.
490	- Update the kernel state with all outstanding changes.	680	- Update the kernel state with all outstanding changes.
491	- Update the "event loop time".	681	- Update the "event loop time" (ev_now ()).
492	- Calculate for how long to block.	682	- Calculate for how long to sleep or block, if at all
		683	(active idle watchers, EVLOOP_NONBLOCK or not having
		684	any active watchers at all will result in not sleeping).
		685	- Sleep if the I/O and timer collect interval say so.
493	- Block the process, waiting for any events.	686	- Block the process, waiting for any events.
494	- Queue all outstanding I/O (fd) events.	687	- Queue all outstanding I/O (fd) events.
495	- Update the "event loop time" and do time jump handling.	688	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
496	- Queue all outstanding timers.	689	- Queue all expired timers.
497	- Queue all outstanding periodics.	690	- Queue all expired periodics.
498	- If no events are pending now, queue all idle watchers.	691	- Unless any events are pending now, queue all idle watchers.
499	- Queue all check watchers.	692	- Queue all check watchers.
500	- Call all queued watchers in reverse order (i.e. check watchers first).	693	- Call all queued watchers in reverse order (i.e. check watchers first).
501	Signals and child watchers are implemented as I/O watchers, and will	694	Signals and child watchers are implemented as I/O watchers, and will
502	be handled here by queueing them when their watcher gets executed.	695	be handled here by queueing them when their watcher gets executed.
503	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	696	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
504	were used, return, otherwise continue with step *.	697	were used, or there are no active watchers, return, otherwise
		698	continue with step *.
505		699
506	Example: Queue some jobs and then loop until no events are outsanding	700	Example: Queue some jobs and then loop until no events are outstanding
507	anymore.	701	anymore.
508		702
509	... queue jobs here, make sure they register event watchers as long	703	... queue jobs here, make sure they register event watchers as long
510	... as they still have work to do (even an idle watcher will do..)	704	... as they still have work to do (even an idle watcher will do..)
511	ev_loop (my_loop, 0);	705	ev_loop (my_loop, 0);
512	... jobs done. yeah!	706	... jobs done or somebody called unloop. yeah!
513		707
514	=item ev_unloop (loop, how)	708	=item ev_unloop (loop, how)
515		709
516	Can be used to make a call to C<ev_loop> return early (but only after it	710	Can be used to make a call to C<ev_loop> return early (but only after it
517	has processed all outstanding events). The C<how> argument must be either	711	has processed all outstanding events). The C<how> argument must be either
518	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	712	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
519	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	713	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
520		714
		715	This "unloop state" will be cleared when entering C<ev_loop> again.
		716
		717	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
		718
521	=item ev_ref (loop)	719	=item ev_ref (loop)
522		720
523	=item ev_unref (loop)	721	=item ev_unref (loop)
524		722
525	Ref/unref can be used to add or remove a reference count on the event	723	Ref/unref can be used to add or remove a reference count on the event
526	loop: Every watcher keeps one reference, and as long as the reference	724	loop: Every watcher keeps one reference, and as long as the reference
527	count is nonzero, C<ev_loop> will not return on its own. If you have	725	count is nonzero, C<ev_loop> will not return on its own.
		726
528	a watcher you never unregister that should not keep C<ev_loop> from	727	If you have a watcher you never unregister that should not keep C<ev_loop>
529	returning, ev_unref() after starting, and ev_ref() before stopping it. For	728	from returning, call ev_unref() after starting, and ev_ref() before
		729	stopping it.
		730
530	example, libev itself uses this for its internal signal pipe: It is not	731	As an example, libev itself uses this for its internal signal pipe: It is
531	visible to the libev user and should not keep C<ev_loop> from exiting if	732	not visible to the libev user and should not keep C<ev_loop> from exiting
532	no event watchers registered by it are active. It is also an excellent	733	if no event watchers registered by it are active. It is also an excellent
533	way to do this for generic recurring timers or from within third-party	734	way to do this for generic recurring timers or from within third-party
534	libraries. Just remember to I<unref after start> and I<ref before stop>.	735	libraries. Just remember to I<unref after start> and I<ref before stop>
		736	(but only if the watcher wasn't active before, or was active before,
		737	respectively).
535		738
536	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	739	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
537	running when nothing else is active.	740	running when nothing else is active.
538		741
539	struct ev_signal exitsig;	742	ev_signal exitsig;
540	ev_signal_init (&exitsig, sig_cb, SIGINT);	743	ev_signal_init (&exitsig, sig_cb, SIGINT);
541	ev_signal_start (loop, &exitsig);	744	ev_signal_start (loop, &exitsig);
542	evf_unref (loop);	745	evf_unref (loop);
543		746
544	Example: For some weird reason, unregister the above signal handler again.	747	Example: For some weird reason, unregister the above signal handler again.
545		748
546	ev_ref (loop);	749	ev_ref (loop);
547	ev_signal_stop (loop, &exitsig);	750	ev_signal_stop (loop, &exitsig);
		751
		752	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		753
		754	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		755
		756	These advanced functions influence the time that libev will spend waiting
		757	for events. Both time intervals are by default C<0>, meaning that libev
		758	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		759	latency.
		760
		761	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		762	allows libev to delay invocation of I/O and timer/periodic callbacks
		763	to increase efficiency of loop iterations (or to increase power-saving
		764	opportunities).
		765
		766	The idea is that sometimes your program runs just fast enough to handle
		767	one (or very few) event(s) per loop iteration. While this makes the
		768	program responsive, it also wastes a lot of CPU time to poll for new
		769	events, especially with backends like C<select ()> which have a high
		770	overhead for the actual polling but can deliver many events at once.
		771
		772	By setting a higher I<io collect interval> you allow libev to spend more
		773	time collecting I/O events, so you can handle more events per iteration,
		774	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		775	C<ev_timer>) will be not affected. Setting this to a non-null value will
		776	introduce an additional C<ev_sleep ()> call into most loop iterations.
		777
		778	Likewise, by setting a higher I<timeout collect interval> you allow libev
		779	to spend more time collecting timeouts, at the expense of increased
		780	latency/jitter/inexactness (the watcher callback will be called
		781	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		782	value will not introduce any overhead in libev.
		783
		784	Many (busy) programs can usually benefit by setting the I/O collect
		785	interval to a value near C<0.1> or so, which is often enough for
		786	interactive servers (of course not for games), likewise for timeouts. It
		787	usually doesn't make much sense to set it to a lower value than C<0.01>,
		788	as this approaches the timing granularity of most systems.
		789
		790	Setting the I<timeout collect interval> can improve the opportunity for
		791	saving power, as the program will "bundle" timer callback invocations that
		792	are "near" in time together, by delaying some, thus reducing the number of
		793	times the process sleeps and wakes up again. Another useful technique to
		794	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		795	they fire on, say, one-second boundaries only.
		796
		797	=item ev_loop_verify (loop)
		798
		799	This function only does something when C<EV_VERIFY> support has been
		800	compiled in, which is the default for non-minimal builds. It tries to go
		801	through all internal structures and checks them for validity. If anything
		802	is found to be inconsistent, it will print an error message to standard
		803	error and call C<abort ()>.
		804
		805	This can be used to catch bugs inside libev itself: under normal
		806	circumstances, this function will never abort as of course libev keeps its
		807	data structures consistent.
548		808
549	=back	809	=back
550		810
551		811
552	=head1 ANATOMY OF A WATCHER	812	=head1 ANATOMY OF A WATCHER
		813
		814	In the following description, uppercase C<TYPE> in names stands for the
		815	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		816	watchers and C<ev_io_start> for I/O watchers.
553		817
554	A watcher is a structure that you create and register to record your	818	A watcher is a structure that you create and register to record your
555	interest in some event. For instance, if you want to wait for STDIN to	819	interest in some event. For instance, if you want to wait for STDIN to
556	become readable, you would create an C<ev_io> watcher for that:	820	become readable, you would create an C<ev_io> watcher for that:
557		821
558	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	822	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
559	{	823	{
560	ev_io_stop (w);	824	ev_io_stop (w);
561	ev_unloop (loop, EVUNLOOP_ALL);	825	ev_unloop (loop, EVUNLOOP_ALL);
562	}	826	}
563		827
564	struct ev_loop *loop = ev_default_loop (0);	828	struct ev_loop *loop = ev_default_loop (0);
		829
565	struct ev_io stdin_watcher;	830	ev_io stdin_watcher;
		831
566	ev_init (&stdin_watcher, my_cb);	832	ev_init (&stdin_watcher, my_cb);
567	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	833	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
568	ev_io_start (loop, &stdin_watcher);	834	ev_io_start (loop, &stdin_watcher);
		835
569	ev_loop (loop, 0);	836	ev_loop (loop, 0);
570		837
571	As you can see, you are responsible for allocating the memory for your	838	As you can see, you are responsible for allocating the memory for your
572	watcher structures (and it is usually a bad idea to do this on the stack,	839	watcher structures (and it is I<usually> a bad idea to do this on the
573	although this can sometimes be quite valid).	840	stack).
		841
		842	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		843	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
574		844
575	Each watcher structure must be initialised by a call to C<ev_init	845	Each watcher structure must be initialised by a call to C<ev_init
576	(watcher *, callback)>, which expects a callback to be provided. This	846	(watcher *, callback)>, which expects a callback to be provided. This
577	callback gets invoked each time the event occurs (or, in the case of io	847	callback gets invoked each time the event occurs (or, in the case of I/O
578	watchers, each time the event loop detects that the file descriptor given	848	watchers, each time the event loop detects that the file descriptor given
579	is readable and/or writable).	849	is readable and/or writable).
580		850
581	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	851	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
582	with arguments specific to this watcher type. There is also a macro	852	macro to configure it, with arguments specific to the watcher type. There
583	to combine initialisation and setting in one call: C<< ev_<type>_init	853	is also a macro to combine initialisation and setting in one call: C<<
584	(watcher *, callback, ...) >>.	854	ev_TYPE_init (watcher *, callback, ...) >>.
585		855
586	To make the watcher actually watch out for events, you have to start it	856	To make the watcher actually watch out for events, you have to start it
587	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	857	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
588	*) >>), and you can stop watching for events at any time by calling the	858	*) >>), and you can stop watching for events at any time by calling the
589	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	859	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
590		860
591	As long as your watcher is active (has been started but not stopped) you	861	As long as your watcher is active (has been started but not stopped) you
592	must not touch the values stored in it. Most specifically you must never	862	must not touch the values stored in it. Most specifically you must never
593	reinitialise it or call its C<set> macro.	863	reinitialise it or call its C<ev_TYPE_set> macro.
594		864
595	Each and every callback receives the event loop pointer as first, the	865	Each and every callback receives the event loop pointer as first, the
596	registered watcher structure as second, and a bitset of received events as	866	registered watcher structure as second, and a bitset of received events as
597	third argument.	867	third argument.
598		868
…		…
652	=item C<EV_FORK>	922	=item C<EV_FORK>
653		923
654	The event loop has been resumed in the child process after fork (see	924	The event loop has been resumed in the child process after fork (see
655	C<ev_fork>).	925	C<ev_fork>).
656		926
		927	=item C<EV_ASYNC>
		928
		929	The given async watcher has been asynchronously notified (see C<ev_async>).
		930
657	=item C<EV_ERROR>	931	=item C<EV_ERROR>
658		932
659	An unspecified error has occured, the watcher has been stopped. This might	933	An unspecified error has occurred, the watcher has been stopped. This might
660	happen because the watcher could not be properly started because libev	934	happen because the watcher could not be properly started because libev
661	ran out of memory, a file descriptor was found to be closed or any other	935	ran out of memory, a file descriptor was found to be closed or any other
		936	problem. Libev considers these application bugs.
		937
662	problem. You best act on it by reporting the problem and somehow coping	938	You best act on it by reporting the problem and somehow coping with the
663	with the watcher being stopped.	939	watcher being stopped. Note that well-written programs should not receive
		940	an error ever, so when your watcher receives it, this usually indicates a
		941	bug in your program.
664		942
665	Libev will usually signal a few "dummy" events together with an error,	943	Libev will usually signal a few "dummy" events together with an error, for
666	for example it might indicate that a fd is readable or writable, and if	944	example it might indicate that a fd is readable or writable, and if your
667	your callbacks is well-written it can just attempt the operation and cope	945	callbacks is well-written it can just attempt the operation and cope with
668	with the error from read() or write(). This will not work in multithreaded	946	the error from read() or write(). This will not work in multi-threaded
669	programs, though, so beware.	947	programs, though, as the fd could already be closed and reused for another
		948	thing, so beware.
670		949
671	=back	950	=back
672		951
673	=head2 GENERIC WATCHER FUNCTIONS	952	=head2 GENERIC WATCHER FUNCTIONS
674
675	In the following description, C<TYPE> stands for the watcher type,
676	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
677		953
678	=over 4	954	=over 4
679		955
680	=item C<ev_init> (ev_TYPE *watcher, callback)	956	=item C<ev_init> (ev_TYPE *watcher, callback)
681		957
…		…
687	which rolls both calls into one.	963	which rolls both calls into one.
688		964
689	You can reinitialise a watcher at any time as long as it has been stopped	965	You can reinitialise a watcher at any time as long as it has been stopped
690	(or never started) and there are no pending events outstanding.	966	(or never started) and there are no pending events outstanding.
691		967
692	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	968	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
693	int revents)>.	969	int revents)>.
		970
		971	Example: Initialise an C<ev_io> watcher in two steps.
		972
		973	ev_io w;
		974	ev_init (&w, my_cb);
		975	ev_io_set (&w, STDIN_FILENO, EV_READ);
694		976
695	=item C<ev_TYPE_set> (ev_TYPE *, [args])	977	=item C<ev_TYPE_set> (ev_TYPE *, [args])
696		978
697	This macro initialises the type-specific parts of a watcher. You need to	979	This macro initialises the type-specific parts of a watcher. You need to
698	call C<ev_init> at least once before you call this macro, but you can	980	call C<ev_init> at least once before you call this macro, but you can
…		…
701	difference to the C<ev_init> macro).	983	difference to the C<ev_init> macro).
702		984
703	Although some watcher types do not have type-specific arguments	985	Although some watcher types do not have type-specific arguments
704	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	986	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
705		987
		988	See C<ev_init>, above, for an example.
		989
706	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	990	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
707		991
708	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	992	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
709	calls into a single call. This is the most convinient method to initialise	993	calls into a single call. This is the most convenient method to initialise
710	a watcher. The same limitations apply, of course.	994	a watcher. The same limitations apply, of course.
		995
		996	Example: Initialise and set an C<ev_io> watcher in one step.
		997
		998	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
711		999
712	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1000	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
713		1001
714	Starts (activates) the given watcher. Only active watchers will receive	1002	Starts (activates) the given watcher. Only active watchers will receive
715	events. If the watcher is already active nothing will happen.	1003	events. If the watcher is already active nothing will happen.
716		1004
		1005	Example: Start the C<ev_io> watcher that is being abused as example in this
		1006	whole section.
		1007
		1008	ev_io_start (EV_DEFAULT_UC, &w);
		1009
717	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1010	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
718		1011
719	Stops the given watcher again (if active) and clears the pending	1012	Stops the given watcher if active, and clears the pending status (whether
		1013	the watcher was active or not).
		1014
720	status. It is possible that stopped watchers are pending (for example,	1015	It is possible that stopped watchers are pending - for example,
721	non-repeating timers are being stopped when they become pending), but	1016	non-repeating timers are being stopped when they become pending - but
722	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1017	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
723	you want to free or reuse the memory used by the watcher it is therefore a	1018	pending. If you want to free or reuse the memory used by the watcher it is
724	good idea to always call its C<ev_TYPE_stop> function.	1019	therefore a good idea to always call its C<ev_TYPE_stop> function.
725		1020
726	=item bool ev_is_active (ev_TYPE *watcher)	1021	=item bool ev_is_active (ev_TYPE *watcher)
727		1022
728	Returns a true value iff the watcher is active (i.e. it has been started	1023	Returns a true value iff the watcher is active (i.e. it has been started
729	and not yet been stopped). As long as a watcher is active you must not modify	1024	and not yet been stopped). As long as a watcher is active you must not modify
…		…
732	=item bool ev_is_pending (ev_TYPE *watcher)	1027	=item bool ev_is_pending (ev_TYPE *watcher)
733		1028
734	Returns a true value iff the watcher is pending, (i.e. it has outstanding	1029	Returns a true value iff the watcher is pending, (i.e. it has outstanding
735	events but its callback has not yet been invoked). As long as a watcher	1030	events but its callback has not yet been invoked). As long as a watcher
736	is pending (but not active) you must not call an init function on it (but	1031	is pending (but not active) you must not call an init function on it (but
737	C<ev_TYPE_set> is safe) and you must make sure the watcher is available to	1032	C<ev_TYPE_set> is safe), you must not change its priority, and you must
738	libev (e.g. you cnanot C<free ()> it).	1033	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1034	it).
739		1035
740	=item callback ev_cb (ev_TYPE *watcher)	1036	=item callback ev_cb (ev_TYPE *watcher)
741		1037
742	Returns the callback currently set on the watcher.	1038	Returns the callback currently set on the watcher.
743		1039
…		…
762	watchers on the same event and make sure one is called first.	1058	watchers on the same event and make sure one is called first.
763		1059
764	If you need to suppress invocation when higher priority events are pending	1060	If you need to suppress invocation when higher priority events are pending
765	you need to look at C<ev_idle> watchers, which provide this functionality.	1061	you need to look at C<ev_idle> watchers, which provide this functionality.
766		1062
		1063	You I<must not> change the priority of a watcher as long as it is active or
		1064	pending.
		1065
767	The default priority used by watchers when no priority has been set is	1066	The default priority used by watchers when no priority has been set is
768	always C<0>, which is supposed to not be too high and not be too low :).	1067	always C<0>, which is supposed to not be too high and not be too low :).
769		1068
770	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1069	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
771	fine, as long as you do not mind that the priority value you query might	1070	fine, as long as you do not mind that the priority value you query might
772	or might not have been adjusted to be within valid range.	1071	or might not have been clamped to the valid range.
		1072
		1073	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1074
		1075	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1076	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1077	can deal with that fact, as both are simply passed through to the
		1078	callback.
		1079
		1080	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1081
		1082	If the watcher is pending, this function clears its pending status and
		1083	returns its C<revents> bitset (as if its callback was invoked). If the
		1084	watcher isn't pending it does nothing and returns C<0>.
		1085
		1086	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1087	callback to be invoked, which can be accomplished with this function.
773		1088
774	=back	1089	=back
775		1090
776		1091
777	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1092	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
778		1093
779	Each watcher has, by default, a member C<void *data> that you can change	1094	Each watcher has, by default, a member C<void *data> that you can change
780	and read at any time, libev will completely ignore it. This can be used	1095	and read at any time: libev will completely ignore it. This can be used
781	to associate arbitrary data with your watcher. If you need more data and	1096	to associate arbitrary data with your watcher. If you need more data and
782	don't want to allocate memory and store a pointer to it in that data	1097	don't want to allocate memory and store a pointer to it in that data
783	member, you can also "subclass" the watcher type and provide your own	1098	member, you can also "subclass" the watcher type and provide your own
784	data:	1099	data:
785		1100
786	struct my_io	1101	struct my_io
787	{	1102	{
788	struct ev_io io;	1103	ev_io io;
789	int otherfd;	1104	int otherfd;
790	void *somedata;	1105	void *somedata;
791	struct whatever *mostinteresting;	1106	struct whatever *mostinteresting;
792	}	1107	};
		1108
		1109	...
		1110	struct my_io w;
		1111	ev_io_init (&w.io, my_cb, fd, EV_READ);
793		1112
794	And since your callback will be called with a pointer to the watcher, you	1113	And since your callback will be called with a pointer to the watcher, you
795	can cast it back to your own type:	1114	can cast it back to your own type:
796		1115
797	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1116	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
798	{	1117	{
799	struct my_io *w = (struct my_io *)w_;	1118	struct my_io *w = (struct my_io *)w_;
800	...	1119	...
801	}	1120	}
802		1121
803	More interesting and less C-conformant ways of casting your callback type	1122	More interesting and less C-conformant ways of casting your callback type
804	instead have been omitted.	1123	instead have been omitted.
805		1124
806	Another common scenario is having some data structure with multiple	1125	Another common scenario is to use some data structure with multiple
807	watchers:	1126	embedded watchers:
808		1127
809	struct my_biggy	1128	struct my_biggy
810	{	1129	{
811	int some_data;	1130	int some_data;
812	ev_timer t1;	1131	ev_timer t1;
813	ev_timer t2;	1132	ev_timer t2;
814	}	1133	}
815		1134
816	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1135	In this case getting the pointer to C<my_biggy> is a bit more
817	you need to use C<offsetof>:	1136	complicated: Either you store the address of your C<my_biggy> struct
		1137	in the C<data> member of the watcher (for woozies), or you need to use
		1138	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1139	programmers):
818		1140
819	#include <stddef.h>	1141	#include <stddef.h>
820		1142
821	static void	1143	static void
822	t1_cb (EV_P_ struct ev_timer *w, int revents)	1144	t1_cb (EV_P_ ev_timer *w, int revents)
823	{	1145	{
824	struct my_biggy big = (struct my_biggy *	1146	struct my_biggy big = (struct my_biggy *
825	(((char *)w) - offsetof (struct my_biggy, t1));	1147	(((char *)w) - offsetof (struct my_biggy, t1));
826	}	1148	}
827		1149
828	static void	1150	static void
829	t2_cb (EV_P_ struct ev_timer *w, int revents)	1151	t2_cb (EV_P_ ev_timer *w, int revents)
830	{	1152	{
831	struct my_biggy big = (struct my_biggy *	1153	struct my_biggy big = (struct my_biggy *
832	(((char *)w) - offsetof (struct my_biggy, t2));	1154	(((char *)w) - offsetof (struct my_biggy, t2));
833	}	1155	}
834		1156
835		1157
836	=head1 WATCHER TYPES	1158	=head1 WATCHER TYPES
837		1159
838	This section describes each watcher in detail, but will not repeat	1160	This section describes each watcher in detail, but will not repeat
…		…
862	In general you can register as many read and/or write event watchers per	1184	In general you can register as many read and/or write event watchers per
863	fd as you want (as long as you don't confuse yourself). Setting all file	1185	fd as you want (as long as you don't confuse yourself). Setting all file
864	descriptors to non-blocking mode is also usually a good idea (but not	1186	descriptors to non-blocking mode is also usually a good idea (but not
865	required if you know what you are doing).	1187	required if you know what you are doing).
866		1188
867	You have to be careful with dup'ed file descriptors, though. Some backends	1189	If you cannot use non-blocking mode, then force the use of a
868	(the linux epoll backend is a notable example) cannot handle dup'ed file	1190	known-to-be-good backend (at the time of this writing, this includes only
869	descriptors correctly if you register interest in two or more fds pointing	1191	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>).
870	to the same underlying file/socket/etc. description (that is, they share
871	the same underlying "file open").
872
873	If you must do this, then force the use of a known-to-be-good backend
874	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
875	C<EVBACKEND_POLL>).
876		1192
877	Another thing you have to watch out for is that it is quite easy to	1193	Another thing you have to watch out for is that it is quite easy to
878	receive "spurious" readyness notifications, that is your callback might	1194	receive "spurious" readiness notifications, that is your callback might
879	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1195	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
880	because there is no data. Not only are some backends known to create a	1196	because there is no data. Not only are some backends known to create a
881	lot of those (for example solaris ports), it is very easy to get into	1197	lot of those (for example Solaris ports), it is very easy to get into
882	this situation even with a relatively standard program structure. Thus	1198	this situation even with a relatively standard program structure. Thus
883	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1199	it is best to always use non-blocking I/O: An extra C<read>(2) returning
884	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1200	C<EAGAIN> is far preferable to a program hanging until some data arrives.
885		1201
886	If you cannot run the fd in non-blocking mode (for example you should not	1202	If you cannot run the fd in non-blocking mode (for example you should
887	play around with an Xlib connection), then you have to seperately re-test	1203	not play around with an Xlib connection), then you have to separately
888	whether a file descriptor is really ready with a known-to-be good interface	1204	re-test whether a file descriptor is really ready with a known-to-be good
889	such as poll (fortunately in our Xlib example, Xlib already does this on	1205	interface such as poll (fortunately in our Xlib example, Xlib already
890	its own, so its quite safe to use).	1206	does this on its own, so its quite safe to use). Some people additionally
		1207	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1208	indefinitely.
		1209
		1210	But really, best use non-blocking mode.
		1211
		1212	=head3 The special problem of disappearing file descriptors
		1213
		1214	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1215	descriptor (either due to calling C<close> explicitly or any other means,
		1216	such as C<dup2>). The reason is that you register interest in some file
		1217	descriptor, but when it goes away, the operating system will silently drop
		1218	this interest. If another file descriptor with the same number then is
		1219	registered with libev, there is no efficient way to see that this is, in
		1220	fact, a different file descriptor.
		1221
		1222	To avoid having to explicitly tell libev about such cases, libev follows
		1223	the following policy: Each time C<ev_io_set> is being called, libev
		1224	will assume that this is potentially a new file descriptor, otherwise
		1225	it is assumed that the file descriptor stays the same. That means that
		1226	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1227	descriptor even if the file descriptor number itself did not change.
		1228
		1229	This is how one would do it normally anyway, the important point is that
		1230	the libev application should not optimise around libev but should leave
		1231	optimisations to libev.
		1232
		1233	=head3 The special problem of dup'ed file descriptors
		1234
		1235	Some backends (e.g. epoll), cannot register events for file descriptors,
		1236	but only events for the underlying file descriptions. That means when you
		1237	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1238	events for them, only one file descriptor might actually receive events.
		1239
		1240	There is no workaround possible except not registering events
		1241	for potentially C<dup ()>'ed file descriptors, or to resort to
		1242	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1243
		1244	=head3 The special problem of fork
		1245
		1246	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1247	useless behaviour. Libev fully supports fork, but needs to be told about
		1248	it in the child.
		1249
		1250	To support fork in your programs, you either have to call
		1251	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1252	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1253	C<EVBACKEND_POLL>.
		1254
		1255	=head3 The special problem of SIGPIPE
		1256
		1257	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1258	when writing to a pipe whose other end has been closed, your program gets
		1259	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1260	this is sensible behaviour, for daemons, this is usually undesirable.
		1261
		1262	So when you encounter spurious, unexplained daemon exits, make sure you
		1263	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1264	somewhere, as that would have given you a big clue).
		1265
		1266
		1267	=head3 Watcher-Specific Functions
891		1268
892	=over 4	1269	=over 4
893		1270
894	=item ev_io_init (ev_io *, callback, int fd, int events)	1271	=item ev_io_init (ev_io *, callback, int fd, int events)
895		1272
896	=item ev_io_set (ev_io *, int fd, int events)	1273	=item ev_io_set (ev_io *, int fd, int events)
897		1274
898	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1275	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
899	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1276	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
900	C<EV_READ | EV_WRITE> to receive the given events.	1277	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
901		1278
902	=item int fd [read-only]	1279	=item int fd [read-only]
903		1280
904	The file descriptor being watched.	1281	The file descriptor being watched.
905		1282
906	=item int events [read-only]	1283	=item int events [read-only]
907		1284
908	The events being watched.	1285	The events being watched.
909		1286
910	=back	1287	=back
		1288
		1289	=head3 Examples
911		1290
912	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1291	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
913	readable, but only once. Since it is likely line-buffered, you could	1292	readable, but only once. Since it is likely line-buffered, you could
914	attempt to read a whole line in the callback.	1293	attempt to read a whole line in the callback.
915		1294
916	static void	1295	static void
917	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1296	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
918	{	1297	{
919	ev_io_stop (loop, w);	1298	ev_io_stop (loop, w);
920	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1299	.. read from stdin here (or from w->fd) and handle any I/O errors
921	}	1300	}
922		1301
923	...	1302	...
924	struct ev_loop *loop = ev_default_init (0);	1303	struct ev_loop *loop = ev_default_init (0);
925	struct ev_io stdin_readable;	1304	ev_io stdin_readable;
926	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1305	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
927	ev_io_start (loop, &stdin_readable);	1306	ev_io_start (loop, &stdin_readable);
928	ev_loop (loop, 0);	1307	ev_loop (loop, 0);
929		1308
930		1309
931	=head2 C<ev_timer> - relative and optionally repeating timeouts	1310	=head2 C<ev_timer> - relative and optionally repeating timeouts
932		1311
933	Timer watchers are simple relative timers that generate an event after a	1312	Timer watchers are simple relative timers that generate an event after a
934	given time, and optionally repeating in regular intervals after that.	1313	given time, and optionally repeating in regular intervals after that.
935		1314
936	The timers are based on real time, that is, if you register an event that	1315	The timers are based on real time, that is, if you register an event that
937	times out after an hour and you reset your system clock to last years	1316	times out after an hour and you reset your system clock to January last
938	time, it will still time out after (roughly) and hour. "Roughly" because	1317	year, it will still time out after (roughly) one hour. "Roughly" because
939	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1318	detecting time jumps is hard, and some inaccuracies are unavoidable (the
940	monotonic clock option helps a lot here).	1319	monotonic clock option helps a lot here).
		1320
		1321	The callback is guaranteed to be invoked only I<after> its timeout has
		1322	passed, but if multiple timers become ready during the same loop iteration
		1323	then order of execution is undefined.
		1324
		1325	=head3 Be smart about timeouts
		1326
		1327	Many real-world problems involve some kind of timeout, usually for error
		1328	recovery. A typical example is an HTTP request - if the other side hangs,
		1329	you want to raise some error after a while.
		1330
		1331	What follows are some ways to handle this problem, from obvious and
		1332	inefficient to smart and efficient.
		1333
		1334	In the following, a 60 second activity timeout is assumed - a timeout that
		1335	gets reset to 60 seconds each time there is activity (e.g. each time some
		1336	data or other life sign was received).
		1337
		1338	=over 4
		1339
		1340	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1341
		1342	This is the most obvious, but not the most simple way: In the beginning,
		1343	start the watcher:
		1344
		1345	ev_timer_init (timer, callback, 60., 0.);
		1346	ev_timer_start (loop, timer);
		1347
		1348	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1349	and start it again:
		1350
		1351	ev_timer_stop (loop, timer);
		1352	ev_timer_set (timer, 60., 0.);
		1353	ev_timer_start (loop, timer);
		1354
		1355	This is relatively simple to implement, but means that each time there is
		1356	some activity, libev will first have to remove the timer from its internal
		1357	data structure and then add it again. Libev tries to be fast, but it's
		1358	still not a constant-time operation.
		1359
		1360	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1361
		1362	This is the easiest way, and involves using C<ev_timer_again> instead of
		1363	C<ev_timer_start>.
		1364
		1365	To implement this, configure an C<ev_timer> with a C<repeat> value
		1366	of C<60> and then call C<ev_timer_again> at start and each time you
		1367	successfully read or write some data. If you go into an idle state where
		1368	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1369	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1370
		1371	That means you can ignore both the C<ev_timer_start> function and the
		1372	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1373	member and C<ev_timer_again>.
		1374
		1375	At start:
		1376
		1377	ev_timer_init (timer, callback);
		1378	timer->repeat = 60.;
		1379	ev_timer_again (loop, timer);
		1380
		1381	Each time there is some activity:
		1382
		1383	ev_timer_again (loop, timer);
		1384
		1385	It is even possible to change the time-out on the fly, regardless of
		1386	whether the watcher is active or not:
		1387
		1388	timer->repeat = 30.;
		1389	ev_timer_again (loop, timer);
		1390
		1391	This is slightly more efficient then stopping/starting the timer each time
		1392	you want to modify its timeout value, as libev does not have to completely
		1393	remove and re-insert the timer from/into its internal data structure.
		1394
		1395	It is, however, even simpler than the "obvious" way to do it.
		1396
		1397	=item 3. Let the timer time out, but then re-arm it as required.
		1398
		1399	This method is more tricky, but usually most efficient: Most timeouts are
		1400	relatively long compared to the intervals between other activity - in
		1401	our example, within 60 seconds, there are usually many I/O events with
		1402	associated activity resets.
		1403
		1404	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1405	but remember the time of last activity, and check for a real timeout only
		1406	within the callback:
		1407
		1408	ev_tstamp last_activity; // time of last activity
		1409
		1410	static void
		1411	callback (EV_P_ ev_timer *w, int revents)
		1412	{
		1413	ev_tstamp now = ev_now (EV_A);
		1414	ev_tstamp timeout = last_activity + 60.;
		1415
		1416	// if last_activity + 60. is older than now, we did time out
		1417	if (timeout < now)
		1418	{
		1419	// timeout occured, take action
		1420	}
		1421	else
		1422	{
		1423	// callback was invoked, but there was some activity, re-arm
		1424	// the watcher to fire in last_activity + 60, which is
		1425	// guaranteed to be in the future, so "again" is positive:
		1426	w->repeat = timeout - now;
		1427	ev_timer_again (EV_A_ w);
		1428	}
		1429	}
		1430
		1431	To summarise the callback: first calculate the real timeout (defined
		1432	as "60 seconds after the last activity"), then check if that time has
		1433	been reached, which means something I<did>, in fact, time out. Otherwise
		1434	the callback was invoked too early (C<timeout> is in the future), so
		1435	re-schedule the timer to fire at that future time, to see if maybe we have
		1436	a timeout then.
		1437
		1438	Note how C<ev_timer_again> is used, taking advantage of the
		1439	C<ev_timer_again> optimisation when the timer is already running.
		1440
		1441	This scheme causes more callback invocations (about one every 60 seconds
		1442	minus half the average time between activity), but virtually no calls to
		1443	libev to change the timeout.
		1444
		1445	To start the timer, simply initialise the watcher and set C<last_activity>
		1446	to the current time (meaning we just have some activity :), then call the
		1447	callback, which will "do the right thing" and start the timer:
		1448
		1449	ev_timer_init (timer, callback);
		1450	last_activity = ev_now (loop);
		1451	callback (loop, timer, EV_TIMEOUT);
		1452
		1453	And when there is some activity, simply store the current time in
		1454	C<last_activity>, no libev calls at all:
		1455
		1456	last_actiivty = ev_now (loop);
		1457
		1458	This technique is slightly more complex, but in most cases where the
		1459	time-out is unlikely to be triggered, much more efficient.
		1460
		1461	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1462	callback :) - just change the timeout and invoke the callback, which will
		1463	fix things for you.
		1464
		1465	=item 4. Wee, just use a double-linked list for your timeouts.
		1466
		1467	If there is not one request, but many thousands (millions...), all
		1468	employing some kind of timeout with the same timeout value, then one can
		1469	do even better:
		1470
		1471	When starting the timeout, calculate the timeout value and put the timeout
		1472	at the I<end> of the list.
		1473
		1474	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1475	the list is expected to fire (for example, using the technique #3).
		1476
		1477	When there is some activity, remove the timer from the list, recalculate
		1478	the timeout, append it to the end of the list again, and make sure to
		1479	update the C<ev_timer> if it was taken from the beginning of the list.
		1480
		1481	This way, one can manage an unlimited number of timeouts in O(1) time for
		1482	starting, stopping and updating the timers, at the expense of a major
		1483	complication, and having to use a constant timeout. The constant timeout
		1484	ensures that the list stays sorted.
		1485
		1486	=back
		1487
		1488	So which method the best?
		1489
		1490	Method #2 is a simple no-brain-required solution that is adequate in most
		1491	situations. Method #3 requires a bit more thinking, but handles many cases
		1492	better, and isn't very complicated either. In most case, choosing either
		1493	one is fine, with #3 being better in typical situations.
		1494
		1495	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1496	rather complicated, but extremely efficient, something that really pays
		1497	off after the first million or so of active timers, i.e. it's usually
		1498	overkill :)
		1499
		1500	=head3 The special problem of time updates
		1501
		1502	Establishing the current time is a costly operation (it usually takes at
		1503	least two system calls): EV therefore updates its idea of the current
		1504	time only before and after C<ev_loop> collects new events, which causes a
		1505	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1506	lots of events in one iteration.
941		1507
942	The relative timeouts are calculated relative to the C<ev_now ()>	1508	The relative timeouts are calculated relative to the C<ev_now ()>
943	time. This is usually the right thing as this timestamp refers to the time	1509	time. This is usually the right thing as this timestamp refers to the time
944	of the event triggering whatever timeout you are modifying/starting. If	1510	of the event triggering whatever timeout you are modifying/starting. If
945	you suspect event processing to be delayed and you I<need> to base the timeout	1511	you suspect event processing to be delayed and you I<need> to base the
946	on the current time, use something like this to adjust for this:	1512	timeout on the current time, use something like this to adjust for this:
947		1513
948	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1514	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
949		1515
950	The callback is guarenteed to be invoked only when its timeout has passed,	1516	If the event loop is suspended for a long time, you can also force an
951	but if multiple timers become ready during the same loop iteration then	1517	update of the time returned by C<ev_now ()> by calling C<ev_now_update
952	order of execution is undefined.	1518	()>.
		1519
		1520	=head3 Watcher-Specific Functions and Data Members
953		1521
954	=over 4	1522	=over 4
955		1523
956	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1524	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
957		1525
958	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1526	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
959		1527
960	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1528	Configure the timer to trigger after C<after> seconds. If C<repeat>
961	C<0.>, then it will automatically be stopped. If it is positive, then the	1529	is C<0.>, then it will automatically be stopped once the timeout is
962	timer will automatically be configured to trigger again C<repeat> seconds	1530	reached. If it is positive, then the timer will automatically be
963	later, again, and again, until stopped manually.	1531	configured to trigger again C<repeat> seconds later, again, and again,
		1532	until stopped manually.
964		1533
965	The timer itself will do a best-effort at avoiding drift, that is, if you	1534	The timer itself will do a best-effort at avoiding drift, that is, if
966	configure a timer to trigger every 10 seconds, then it will trigger at	1535	you configure a timer to trigger every 10 seconds, then it will normally
967	exactly 10 second intervals. If, however, your program cannot keep up with	1536	trigger at exactly 10 second intervals. If, however, your program cannot
968	the timer (because it takes longer than those 10 seconds to do stuff) the	1537	keep up with the timer (because it takes longer than those 10 seconds to
969	timer will not fire more than once per event loop iteration.	1538	do stuff) the timer will not fire more than once per event loop iteration.
970		1539
971	=item ev_timer_again (loop)	1540	=item ev_timer_again (loop, ev_timer *)
972		1541
973	This will act as if the timer timed out and restart it again if it is	1542	This will act as if the timer timed out and restart it again if it is
974	repeating. The exact semantics are:	1543	repeating. The exact semantics are:
975		1544
976	If the timer is pending, its pending status is cleared.	1545	If the timer is pending, its pending status is cleared.
977		1546
978	If the timer is started but nonrepeating, stop it (as if it timed out).	1547	If the timer is started but non-repeating, stop it (as if it timed out).
979		1548
980	If the timer is repeating, either start it if necessary (with the	1549	If the timer is repeating, either start it if necessary (with the
981	C<repeat> value), or reset the running timer to the C<repeat> value.	1550	C<repeat> value), or reset the running timer to the C<repeat> value.
982		1551
983	This sounds a bit complicated, but here is a useful and typical	1552	This sounds a bit complicated, see "Be smart about timeouts", above, for a
984	example: Imagine you have a tcp connection and you want a so-called idle	1553	usage example.
985	timeout, that is, you want to be called when there have been, say, 60
986	seconds of inactivity on the socket. The easiest way to do this is to
987	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
988	C<ev_timer_again> each time you successfully read or write some data. If
989	you go into an idle state where you do not expect data to travel on the
990	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
991	automatically restart it if need be.
992
993	That means you can ignore the C<after> value and C<ev_timer_start>
994	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
995
996	ev_timer_init (timer, callback, 0., 5.);
997	ev_timer_again (loop, timer);
998	...
999	timer->again = 17.;
1000	ev_timer_again (loop, timer);
1001	...
1002	timer->again = 10.;
1003	ev_timer_again (loop, timer);
1004
1005	This is more slightly efficient then stopping/starting the timer each time
1006	you want to modify its timeout value.
1007		1554
1008	=item ev_tstamp repeat [read-write]	1555	=item ev_tstamp repeat [read-write]
1009		1556
1010	The current C<repeat> value. Will be used each time the watcher times out	1557	The current C<repeat> value. Will be used each time the watcher times out
1011	or C<ev_timer_again> is called and determines the next timeout (if any),	1558	or C<ev_timer_again> is called, and determines the next timeout (if any),
1012	which is also when any modifications are taken into account.	1559	which is also when any modifications are taken into account.
1013		1560
1014	=back	1561	=back
1015		1562
		1563	=head3 Examples
		1564
1016	Example: Create a timer that fires after 60 seconds.	1565	Example: Create a timer that fires after 60 seconds.
1017		1566
1018	static void	1567	static void
1019	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1568	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1020	{	1569	{
1021	.. one minute over, w is actually stopped right here	1570	.. one minute over, w is actually stopped right here
1022	}	1571	}
1023		1572
1024	struct ev_timer mytimer;	1573	ev_timer mytimer;
1025	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1574	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1026	ev_timer_start (loop, &mytimer);	1575	ev_timer_start (loop, &mytimer);
1027		1576
1028	Example: Create a timeout timer that times out after 10 seconds of	1577	Example: Create a timeout timer that times out after 10 seconds of
1029	inactivity.	1578	inactivity.
1030		1579
1031	static void	1580	static void
1032	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1581	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1033	{	1582	{
1034	.. ten seconds without any activity	1583	.. ten seconds without any activity
1035	}	1584	}
1036		1585
1037	struct ev_timer mytimer;	1586	ev_timer mytimer;
1038	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1587	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1039	ev_timer_again (&mytimer); /* start timer */	1588	ev_timer_again (&mytimer); /* start timer */
1040	ev_loop (loop, 0);	1589	ev_loop (loop, 0);
1041		1590
1042	// and in some piece of code that gets executed on any "activity":	1591	// and in some piece of code that gets executed on any "activity":
1043	// reset the timeout to start ticking again at 10 seconds	1592	// reset the timeout to start ticking again at 10 seconds
1044	ev_timer_again (&mytimer);	1593	ev_timer_again (&mytimer);
1045		1594
1046		1595
1047	=head2 C<ev_periodic> - to cron or not to cron?	1596	=head2 C<ev_periodic> - to cron or not to cron?
1048		1597
1049	Periodic watchers are also timers of a kind, but they are very versatile	1598	Periodic watchers are also timers of a kind, but they are very versatile
1050	(and unfortunately a bit complex).	1599	(and unfortunately a bit complex).
1051		1600
1052	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1601	Unlike C<ev_timer>'s, they are not based on real time (or relative time)
1053	but on wallclock time (absolute time). You can tell a periodic watcher	1602	but on wall clock time (absolute time). You can tell a periodic watcher
1054	to trigger "at" some specific point in time. For example, if you tell a	1603	to trigger after some specific point in time. For example, if you tell a
1055	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	1604	periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now ()
1056	+ 10.>) and then reset your system clock to the last year, then it will	1605	+ 10.>, that is, an absolute time not a delay) and then reset your system
		1606	clock to January of the previous year, then it will take more than year
1057	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1607	to trigger the event (unlike an C<ev_timer>, which would still trigger
1058	roughly 10 seconds later and of course not if you reset your system time	1608	roughly 10 seconds later as it uses a relative timeout).
1059	again).
1060		1609
1061	They can also be used to implement vastly more complex timers, such as	1610	C<ev_periodic>s can also be used to implement vastly more complex timers,
1062	triggering an event on eahc midnight, local time.	1611	such as triggering an event on each "midnight, local time", or other
		1612	complicated rules.
1063		1613
1064	As with timers, the callback is guarenteed to be invoked only when the	1614	As with timers, the callback is guaranteed to be invoked only when the
1065	time (C<at>) has been passed, but if multiple periodic timers become ready	1615	time (C<at>) has passed, but if multiple periodic timers become ready
1066	during the same loop iteration then order of execution is undefined.	1616	during the same loop iteration, then order of execution is undefined.
		1617
		1618	=head3 Watcher-Specific Functions and Data Members
1067		1619
1068	=over 4	1620	=over 4
1069		1621
1070	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1622	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
1071		1623
1072	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1624	=item ev_periodic_set (ev_periodic *, ev_tstamp at, ev_tstamp interval, reschedule_cb)
1073		1625
1074	Lots of arguments, lets sort it out... There are basically three modes of	1626	Lots of arguments, lets sort it out... There are basically three modes of
1075	operation, and we will explain them from simplest to complex:	1627	operation, and we will explain them from simplest to most complex:
1076		1628
1077	=over 4	1629	=over 4
1078		1630
1079	=item * absolute timer (interval = reschedule_cb = 0)	1631	=item * absolute timer (at = time, interval = reschedule_cb = 0)
1080		1632
1081	In this configuration the watcher triggers an event at the wallclock time	1633	In this configuration the watcher triggers an event after the wall clock
1082	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1634	time C<at> has passed. It will not repeat and will not adjust when a time
1083	that is, if it is to be run at January 1st 2011 then it will run when the	1635	jump occurs, that is, if it is to be run at January 1st 2011 then it will
1084	system time reaches or surpasses this time.	1636	only run when the system clock reaches or surpasses this time.
1085		1637
1086	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1638	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
1087		1639
1088	In this mode the watcher will always be scheduled to time out at the next	1640	In this mode the watcher will always be scheduled to time out at the next
1089	C<at + N * interval> time (for some integer N) and then repeat, regardless	1641	C<at + N * interval> time (for some integer N, which can also be negative)
1090	of any time jumps.	1642	and then repeat, regardless of any time jumps.
1091		1643
1092	This can be used to create timers that do not drift with respect to system	1644	This can be used to create timers that do not drift with respect to the
1093	time:	1645	system clock, for example, here is a C<ev_periodic> that triggers each
		1646	hour, on the hour:
1094		1647
1095	ev_periodic_set (&periodic, 0., 3600., 0);	1648	ev_periodic_set (&periodic, 0., 3600., 0);
1096		1649
1097	This doesn't mean there will always be 3600 seconds in between triggers,	1650	This doesn't mean there will always be 3600 seconds in between triggers,
1098	but only that the the callback will be called when the system time shows a	1651	but only that the callback will be called when the system time shows a
1099	full hour (UTC), or more correctly, when the system time is evenly divisible	1652	full hour (UTC), or more correctly, when the system time is evenly divisible
1100	by 3600.	1653	by 3600.
1101		1654
1102	Another way to think about it (for the mathematically inclined) is that	1655	Another way to think about it (for the mathematically inclined) is that
1103	C<ev_periodic> will try to run the callback in this mode at the next possible	1656	C<ev_periodic> will try to run the callback in this mode at the next possible
1104	time where C<time = at (mod interval)>, regardless of any time jumps.	1657	time where C<time = at (mod interval)>, regardless of any time jumps.
1105		1658
		1659	For numerical stability it is preferable that the C<at> value is near
		1660	C<ev_now ()> (the current time), but there is no range requirement for
		1661	this value, and in fact is often specified as zero.
		1662
		1663	Note also that there is an upper limit to how often a timer can fire (CPU
		1664	speed for example), so if C<interval> is very small then timing stability
		1665	will of course deteriorate. Libev itself tries to be exact to be about one
		1666	millisecond (if the OS supports it and the machine is fast enough).
		1667
1106	=item * manual reschedule mode (reschedule_cb = callback)	1668	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
1107		1669
1108	In this mode the values for C<interval> and C<at> are both being	1670	In this mode the values for C<interval> and C<at> are both being
1109	ignored. Instead, each time the periodic watcher gets scheduled, the	1671	ignored. Instead, each time the periodic watcher gets scheduled, the
1110	reschedule callback will be called with the watcher as first, and the	1672	reschedule callback will be called with the watcher as first, and the
1111	current time as second argument.	1673	current time as second argument.
1112		1674
1113	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1675	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,
1114	ever, or make any event loop modifications>. If you need to stop it,	1676	ever, or make ANY other event loop modifications whatsoever>.
1115	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by
1116	starting a prepare watcher).
1117		1677
		1678	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1679	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1680	only event loop modification you are allowed to do).
		1681
1118	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1682	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1119	ev_tstamp now)>, e.g.:	1683	*w, ev_tstamp now)>, e.g.:
1120		1684
		1685	static ev_tstamp
1121	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1686	my_rescheduler (ev_periodic *w, ev_tstamp now)
1122	{	1687	{
1123	return now + 60.;	1688	return now + 60.;
1124	}	1689	}
1125		1690
1126	It must return the next time to trigger, based on the passed time value	1691	It must return the next time to trigger, based on the passed time value
1127	(that is, the lowest time value larger than to the second argument). It	1692	(that is, the lowest time value larger than to the second argument). It
1128	will usually be called just before the callback will be triggered, but	1693	will usually be called just before the callback will be triggered, but
1129	might be called at other times, too.	1694	might be called at other times, too.
1130		1695
1131	NOTE: I<< This callback must always return a time that is later than the	1696	NOTE: I<< This callback must always return a time that is higher than or
1132	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	1697	equal to the passed C<now> value >>.
1133		1698
1134	This can be used to create very complex timers, such as a timer that	1699	This can be used to create very complex timers, such as a timer that
1135	triggers on each midnight, local time. To do this, you would calculate the	1700	triggers on "next midnight, local time". To do this, you would calculate the
1136	next midnight after C<now> and return the timestamp value for this. How	1701	next midnight after C<now> and return the timestamp value for this. How
1137	you do this is, again, up to you (but it is not trivial, which is the main	1702	you do this is, again, up to you (but it is not trivial, which is the main
1138	reason I omitted it as an example).	1703	reason I omitted it as an example).
1139		1704
1140	=back	1705	=back
…		…
1144	Simply stops and restarts the periodic watcher again. This is only useful	1709	Simply stops and restarts the periodic watcher again. This is only useful
1145	when you changed some parameters or the reschedule callback would return	1710	when you changed some parameters or the reschedule callback would return
1146	a different time than the last time it was called (e.g. in a crond like	1711	a different time than the last time it was called (e.g. in a crond like
1147	program when the crontabs have changed).	1712	program when the crontabs have changed).
1148		1713
		1714	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1715
		1716	When active, returns the absolute time that the watcher is supposed to
		1717	trigger next.
		1718
		1719	=item ev_tstamp offset [read-write]
		1720
		1721	When repeating, this contains the offset value, otherwise this is the
		1722	absolute point in time (the C<at> value passed to C<ev_periodic_set>).
		1723
		1724	Can be modified any time, but changes only take effect when the periodic
		1725	timer fires or C<ev_periodic_again> is being called.
		1726
1149	=item ev_tstamp interval [read-write]	1727	=item ev_tstamp interval [read-write]
1150		1728
1151	The current interval value. Can be modified any time, but changes only	1729	The current interval value. Can be modified any time, but changes only
1152	take effect when the periodic timer fires or C<ev_periodic_again> is being	1730	take effect when the periodic timer fires or C<ev_periodic_again> is being
1153	called.	1731	called.
1154		1732
1155	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	1733	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1156		1734
1157	The current reschedule callback, or C<0>, if this functionality is	1735	The current reschedule callback, or C<0>, if this functionality is
1158	switched off. Can be changed any time, but changes only take effect when	1736	switched off. Can be changed any time, but changes only take effect when
1159	the periodic timer fires or C<ev_periodic_again> is being called.	1737	the periodic timer fires or C<ev_periodic_again> is being called.
1160		1738
1161	=back	1739	=back
1162		1740
		1741	=head3 Examples
		1742
1163	Example: Call a callback every hour, or, more precisely, whenever the	1743	Example: Call a callback every hour, or, more precisely, whenever the
1164	system clock is divisible by 3600. The callback invocation times have	1744	system time is divisible by 3600. The callback invocation times have
1165	potentially a lot of jittering, but good long-term stability.	1745	potentially a lot of jitter, but good long-term stability.
1166		1746
1167	static void	1747	static void
1168	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1748	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1169	{	1749	{
1170	... its now a full hour (UTC, or TAI or whatever your clock follows)	1750	... its now a full hour (UTC, or TAI or whatever your clock follows)
1171	}	1751	}
1172		1752
1173	struct ev_periodic hourly_tick;	1753	ev_periodic hourly_tick;
1174	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	1754	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1175	ev_periodic_start (loop, &hourly_tick);	1755	ev_periodic_start (loop, &hourly_tick);
1176		1756
1177	Example: The same as above, but use a reschedule callback to do it:	1757	Example: The same as above, but use a reschedule callback to do it:
1178		1758
1179	#include <math.h>	1759	#include <math.h>
1180		1760
1181	static ev_tstamp	1761	static ev_tstamp
1182	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	1762	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1183	{	1763	{
1184	return fmod (now, 3600.) + 3600.;	1764	return now + (3600. - fmod (now, 3600.));
1185	}	1765	}
1186		1766
1187	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	1767	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1188		1768
1189	Example: Call a callback every hour, starting now:	1769	Example: Call a callback every hour, starting now:
1190		1770
1191	struct ev_periodic hourly_tick;	1771	ev_periodic hourly_tick;
1192	ev_periodic_init (&hourly_tick, clock_cb,	1772	ev_periodic_init (&hourly_tick, clock_cb,
1193	fmod (ev_now (loop), 3600.), 3600., 0);	1773	fmod (ev_now (loop), 3600.), 3600., 0);
1194	ev_periodic_start (loop, &hourly_tick);	1774	ev_periodic_start (loop, &hourly_tick);
1195		1775
1196		1776
1197	=head2 C<ev_signal> - signal me when a signal gets signalled!	1777	=head2 C<ev_signal> - signal me when a signal gets signalled!
1198		1778
1199	Signal watchers will trigger an event when the process receives a specific	1779	Signal watchers will trigger an event when the process receives a specific
1200	signal one or more times. Even though signals are very asynchronous, libev	1780	signal one or more times. Even though signals are very asynchronous, libev
1201	will try it's best to deliver signals synchronously, i.e. as part of the	1781	will try it's best to deliver signals synchronously, i.e. as part of the
1202	normal event processing, like any other event.	1782	normal event processing, like any other event.
1203		1783
		1784	If you want signals asynchronously, just use C<sigaction> as you would
		1785	do without libev and forget about sharing the signal. You can even use
		1786	C<ev_async> from a signal handler to synchronously wake up an event loop.
		1787
1204	You can configure as many watchers as you like per signal. Only when the	1788	You can configure as many watchers as you like per signal. Only when the
1205	first watcher gets started will libev actually register a signal watcher	1789	first watcher gets started will libev actually register a signal handler
1206	with the kernel (thus it coexists with your own signal handlers as long	1790	with the kernel (thus it coexists with your own signal handlers as long as
1207	as you don't register any with libev). Similarly, when the last signal	1791	you don't register any with libev for the same signal). Similarly, when
1208	watcher for a signal is stopped libev will reset the signal handler to	1792	the last signal watcher for a signal is stopped, libev will reset the
1209	SIG_DFL (regardless of what it was set to before).	1793	signal handler to SIG_DFL (regardless of what it was set to before).
		1794
		1795	If possible and supported, libev will install its handlers with
		1796	C<SA_RESTART> behaviour enabled, so system calls should not be unduly
		1797	interrupted. If you have a problem with system calls getting interrupted by
		1798	signals you can block all signals in an C<ev_check> watcher and unblock
		1799	them in an C<ev_prepare> watcher.
		1800
		1801	=head3 Watcher-Specific Functions and Data Members
1210		1802
1211	=over 4	1803	=over 4
1212		1804
1213	=item ev_signal_init (ev_signal *, callback, int signum)	1805	=item ev_signal_init (ev_signal *, callback, int signum)
1214		1806
…		…
1221		1813
1222	The signal the watcher watches out for.	1814	The signal the watcher watches out for.
1223		1815
1224	=back	1816	=back
1225		1817
		1818	=head3 Examples
		1819
		1820	Example: Try to exit cleanly on SIGINT.
		1821
		1822	static void
		1823	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		1824	{
		1825	ev_unloop (loop, EVUNLOOP_ALL);
		1826	}
		1827
		1828	ev_signal signal_watcher;
		1829	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1830	ev_signal_start (loop, &signal_watcher);
		1831
1226		1832
1227	=head2 C<ev_child> - watch out for process status changes	1833	=head2 C<ev_child> - watch out for process status changes
1228		1834
1229	Child watchers trigger when your process receives a SIGCHLD in response to	1835	Child watchers trigger when your process receives a SIGCHLD in response to
1230	some child status changes (most typically when a child of yours dies).	1836	some child status changes (most typically when a child of yours dies or
		1837	exits). It is permissible to install a child watcher I<after> the child
		1838	has been forked (which implies it might have already exited), as long
		1839	as the event loop isn't entered (or is continued from a watcher), i.e.,
		1840	forking and then immediately registering a watcher for the child is fine,
		1841	but forking and registering a watcher a few event loop iterations later is
		1842	not.
		1843
		1844	Only the default event loop is capable of handling signals, and therefore
		1845	you can only register child watchers in the default event loop.
		1846
		1847	=head3 Process Interaction
		1848
		1849	Libev grabs C<SIGCHLD> as soon as the default event loop is
		1850	initialised. This is necessary to guarantee proper behaviour even if
		1851	the first child watcher is started after the child exits. The occurrence
		1852	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		1853	synchronously as part of the event loop processing. Libev always reaps all
		1854	children, even ones not watched.
		1855
		1856	=head3 Overriding the Built-In Processing
		1857
		1858	Libev offers no special support for overriding the built-in child
		1859	processing, but if your application collides with libev's default child
		1860	handler, you can override it easily by installing your own handler for
		1861	C<SIGCHLD> after initialising the default loop, and making sure the
		1862	default loop never gets destroyed. You are encouraged, however, to use an
		1863	event-based approach to child reaping and thus use libev's support for
		1864	that, so other libev users can use C<ev_child> watchers freely.
		1865
		1866	=head3 Stopping the Child Watcher
		1867
		1868	Currently, the child watcher never gets stopped, even when the
		1869	child terminates, so normally one needs to stop the watcher in the
		1870	callback. Future versions of libev might stop the watcher automatically
		1871	when a child exit is detected.
		1872
		1873	=head3 Watcher-Specific Functions and Data Members
1231		1874
1232	=over 4	1875	=over 4
1233		1876
1234	=item ev_child_init (ev_child *, callback, int pid)	1877	=item ev_child_init (ev_child *, callback, int pid, int trace)
1235		1878
1236	=item ev_child_set (ev_child *, int pid)	1879	=item ev_child_set (ev_child *, int pid, int trace)
1237		1880
1238	Configures the watcher to wait for status changes of process C<pid> (or	1881	Configures the watcher to wait for status changes of process C<pid> (or
1239	I<any> process if C<pid> is specified as C<0>). The callback can look	1882	I<any> process if C<pid> is specified as C<0>). The callback can look
1240	at the C<rstatus> member of the C<ev_child> watcher structure to see	1883	at the C<rstatus> member of the C<ev_child> watcher structure to see
1241	the status word (use the macros from C<sys/wait.h> and see your systems	1884	the status word (use the macros from C<sys/wait.h> and see your systems
1242	C<waitpid> documentation). The C<rpid> member contains the pid of the	1885	C<waitpid> documentation). The C<rpid> member contains the pid of the
1243	process causing the status change.	1886	process causing the status change. C<trace> must be either C<0> (only
		1887	activate the watcher when the process terminates) or C<1> (additionally
		1888	activate the watcher when the process is stopped or continued).
1244		1889
1245	=item int pid [read-only]	1890	=item int pid [read-only]
1246		1891
1247	The process id this watcher watches out for, or C<0>, meaning any process id.	1892	The process id this watcher watches out for, or C<0>, meaning any process id.
1248		1893
…		…
1255	The process exit/trace status caused by C<rpid> (see your systems	1900	The process exit/trace status caused by C<rpid> (see your systems
1256	C<waitpid> and C<sys/wait.h> documentation for details).	1901	C<waitpid> and C<sys/wait.h> documentation for details).
1257		1902
1258	=back	1903	=back
1259		1904
1260	Example: Try to exit cleanly on SIGINT and SIGTERM.	1905	=head3 Examples
1261		1906
		1907	Example: C<fork()> a new process and install a child handler to wait for
		1908	its completion.
		1909
		1910	ev_child cw;
		1911
1262	static void	1912	static void
1263	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	1913	child_cb (EV_P_ ev_child *w, int revents)
1264	{	1914	{
1265	ev_unloop (loop, EVUNLOOP_ALL);	1915	ev_child_stop (EV_A_ w);
		1916	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1266	}	1917	}
1267		1918
1268	struct ev_signal signal_watcher;	1919	pid_t pid = fork ();
1269	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	1920
1270	ev_signal_start (loop, &sigint_cb);	1921	if (pid < 0)
		1922	// error
		1923	else if (pid == 0)
		1924	{
		1925	// the forked child executes here
		1926	exit (1);
		1927	}
		1928	else
		1929	{
		1930	ev_child_init (&cw, child_cb, pid, 0);
		1931	ev_child_start (EV_DEFAULT_ &cw);
		1932	}
1271		1933
1272		1934
1273	=head2 C<ev_stat> - did the file attributes just change?	1935	=head2 C<ev_stat> - did the file attributes just change?
1274		1936
1275	This watches a filesystem path for attribute changes. That is, it calls	1937	This watches a file system path for attribute changes. That is, it calls
1276	C<stat> regularly (or when the OS says it changed) and sees if it changed	1938	C<stat> on that path in regular intervals (or when the OS says it changed)
1277	compared to the last time, invoking the callback if it did.	1939	and sees if it changed compared to the last time, invoking the callback if
		1940	it did.
1278		1941
1279	The path does not need to exist: changing from "path exists" to "path does	1942	The path does not need to exist: changing from "path exists" to "path does
1280	not exist" is a status change like any other. The condition "path does	1943	not exist" is a status change like any other. The condition "path does not
1281	not exist" is signified by the C<st_nlink> field being zero (which is	1944	exist" (or more correctly "path cannot be stat'ed") is signified by the
1282	otherwise always forced to be at least one) and all the other fields of	1945	C<st_nlink> field being zero (which is otherwise always forced to be at
1283	the stat buffer having unspecified contents.	1946	least one) and all the other fields of the stat buffer having unspecified
		1947	contents.
1284		1948
1285	The path I<should> be absolute and I<must not> end in a slash. If it is	1949	The path I<must not> end in a slash or contain special components such as
		1950	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1286	relative and your working directory changes, the behaviour is undefined.	1951	your working directory changes, then the behaviour is undefined.
1287		1952
1288	Since there is no standard to do this, the portable implementation simply	1953	Since there is no portable change notification interface available, the
1289	calls C<stat (2)> regularly on the path to see if it changed somehow. You	1954	portable implementation simply calls C<stat(2)> regularly on the path
1290	can specify a recommended polling interval for this case. If you specify	1955	to see if it changed somehow. You can specify a recommended polling
1291	a polling interval of C<0> (highly recommended!) then a I<suitable,	1956	interval for this case. If you specify a polling interval of C<0> (highly
1292	unspecified default> value will be used (which you can expect to be around	1957	recommended!) then a I<suitable, unspecified default> value will be used
1293	five seconds, although this might change dynamically). Libev will also	1958	(which you can expect to be around five seconds, although this might
1294	impose a minimum interval which is currently around C<0.1>, but thats	1959	change dynamically). Libev will also impose a minimum interval which is
1295	usually overkill.	1960	currently around C<0.1>, but that's usually overkill.
1296		1961
1297	This watcher type is not meant for massive numbers of stat watchers,	1962	This watcher type is not meant for massive numbers of stat watchers,
1298	as even with OS-supported change notifications, this can be	1963	as even with OS-supported change notifications, this can be
1299	resource-intensive.	1964	resource-intensive.
1300		1965
1301	At the time of this writing, only the Linux inotify interface is	1966	At the time of this writing, the only OS-specific interface implemented
1302	implemented (implementing kqueue support is left as an exercise for the	1967	is the Linux inotify interface (implementing kqueue support is left as an
1303	reader). Inotify will be used to give hints only and should not change the	1968	exercise for the reader. Note, however, that the author sees no way of
1304	semantics of C<ev_stat> watchers, which means that libev sometimes needs	1969	implementing C<ev_stat> semantics with kqueue, except as a hint).
1305	to fall back to regular polling again even with inotify, but changes are	1970
1306	usually detected immediately, and if the file exists there will be no	1971	=head3 ABI Issues (Largefile Support)
1307	polling.	1972
		1973	Libev by default (unless the user overrides this) uses the default
		1974	compilation environment, which means that on systems with large file
		1975	support disabled by default, you get the 32 bit version of the stat
		1976	structure. When using the library from programs that change the ABI to
		1977	use 64 bit file offsets the programs will fail. In that case you have to
		1978	compile libev with the same flags to get binary compatibility. This is
		1979	obviously the case with any flags that change the ABI, but the problem is
		1980	most noticeably displayed with ev_stat and large file support.
		1981
		1982	The solution for this is to lobby your distribution maker to make large
		1983	file interfaces available by default (as e.g. FreeBSD does) and not
		1984	optional. Libev cannot simply switch on large file support because it has
		1985	to exchange stat structures with application programs compiled using the
		1986	default compilation environment.
		1987
		1988	=head3 Inotify and Kqueue
		1989
		1990	When C<inotify (7)> support has been compiled into libev and present at
		1991	runtime, it will be used to speed up change detection where possible. The
		1992	inotify descriptor will be created lazily when the first C<ev_stat>
		1993	watcher is being started.
		1994
		1995	Inotify presence does not change the semantics of C<ev_stat> watchers
		1996	except that changes might be detected earlier, and in some cases, to avoid
		1997	making regular C<stat> calls. Even in the presence of inotify support
		1998	there are many cases where libev has to resort to regular C<stat> polling,
		1999	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2000	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2001	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2002	xfs are fully working) libev usually gets away without polling.
		2003
		2004	There is no support for kqueue, as apparently it cannot be used to
		2005	implement this functionality, due to the requirement of having a file
		2006	descriptor open on the object at all times, and detecting renames, unlinks
		2007	etc. is difficult.
		2008
		2009	=head3 C<stat ()> is a synchronous operation
		2010
		2011	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2012	the process. The exception are C<ev_stat> watchers - those call C<stat
		2013	()>, which is a synchronous operation.
		2014
		2015	For local paths, this usually doesn't matter: unless the system is very
		2016	busy or the intervals between stat's are large, a stat call will be fast,
		2017	as the path data is usually in memory already (except when starting the
		2018	watcher).
		2019
		2020	For networked file systems, calling C<stat ()> can block an indefinite
		2021	time due to network issues, and even under good conditions, a stat call
		2022	often takes multiple milliseconds.
		2023
		2024	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2025	paths, although this is fully supported by libev.
		2026
		2027	=head3 The special problem of stat time resolution
		2028
		2029	The C<stat ()> system call only supports full-second resolution portably,
		2030	and even on systems where the resolution is higher, most file systems
		2031	still only support whole seconds.
		2032
		2033	That means that, if the time is the only thing that changes, you can
		2034	easily miss updates: on the first update, C<ev_stat> detects a change and
		2035	calls your callback, which does something. When there is another update
		2036	within the same second, C<ev_stat> will be unable to detect unless the
		2037	stat data does change in other ways (e.g. file size).
		2038
		2039	The solution to this is to delay acting on a change for slightly more
		2040	than a second (or till slightly after the next full second boundary), using
		2041	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2042	ev_timer_again (loop, w)>).
		2043
		2044	The C<.02> offset is added to work around small timing inconsistencies
		2045	of some operating systems (where the second counter of the current time
		2046	might be be delayed. One such system is the Linux kernel, where a call to
		2047	C<gettimeofday> might return a timestamp with a full second later than
		2048	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2049	update file times then there will be a small window where the kernel uses
		2050	the previous second to update file times but libev might already execute
		2051	the timer callback).
		2052
		2053	=head3 Watcher-Specific Functions and Data Members
1308		2054
1309	=over 4	2055	=over 4
1310		2056
1311	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)	2057	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
1312		2058
…		…
1316	C<path>. The C<interval> is a hint on how quickly a change is expected to	2062	C<path>. The C<interval> is a hint on how quickly a change is expected to
1317	be detected and should normally be specified as C<0> to let libev choose	2063	be detected and should normally be specified as C<0> to let libev choose
1318	a suitable value. The memory pointed to by C<path> must point to the same	2064	a suitable value. The memory pointed to by C<path> must point to the same
1319	path for as long as the watcher is active.	2065	path for as long as the watcher is active.
1320		2066
1321	The callback will be receive C<EV_STAT> when a change was detected,	2067	The callback will receive an C<EV_STAT> event when a change was detected,
1322	relative to the attributes at the time the watcher was started (or the	2068	relative to the attributes at the time the watcher was started (or the
1323	last change was detected).	2069	last change was detected).
1324		2070
1325	=item ev_stat_stat (ev_stat *)	2071	=item ev_stat_stat (loop, ev_stat *)
1326		2072
1327	Updates the stat buffer immediately with new values. If you change the	2073	Updates the stat buffer immediately with new values. If you change the
1328	watched path in your callback, you could call this fucntion to avoid	2074	watched path in your callback, you could call this function to avoid
1329	detecting this change (while introducing a race condition). Can also be	2075	detecting this change (while introducing a race condition if you are not
1330	useful simply to find out the new values.	2076	the only one changing the path). Can also be useful simply to find out the
		2077	new values.
1331		2078
1332	=item ev_statdata attr [read-only]	2079	=item ev_statdata attr [read-only]
1333		2080
1334	The most-recently detected attributes of the file. Although the type is of	2081	The most-recently detected attributes of the file. Although the type is
1335	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2082	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1336	suitable for your system. If the C<st_nlink> member is C<0>, then there	2083	suitable for your system, but you can only rely on the POSIX-standardised
		2084	members to be present. If the C<st_nlink> member is C<0>, then there was
1337	was some error while C<stat>ing the file.	2085	some error while C<stat>ing the file.
1338		2086
1339	=item ev_statdata prev [read-only]	2087	=item ev_statdata prev [read-only]
1340		2088
1341	The previous attributes of the file. The callback gets invoked whenever	2089	The previous attributes of the file. The callback gets invoked whenever
1342	C<prev> != C<attr>.	2090	C<prev> != C<attr>, or, more precisely, one or more of these members
		2091	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2092	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1343		2093
1344	=item ev_tstamp interval [read-only]	2094	=item ev_tstamp interval [read-only]
1345		2095
1346	The specified interval.	2096	The specified interval.
1347		2097
1348	=item const char *path [read-only]	2098	=item const char *path [read-only]
1349		2099
1350	The filesystem path that is being watched.	2100	The file system path that is being watched.
1351		2101
1352	=back	2102	=back
1353		2103
		2104	=head3 Examples
		2105
1354	Example: Watch C</etc/passwd> for attribute changes.	2106	Example: Watch C</etc/passwd> for attribute changes.
1355		2107
1356	static void	2108	static void
1357	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2109	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1358	{	2110	{
1359	/* /etc/passwd changed in some way */	2111	/* /etc/passwd changed in some way */
1360	if (w->attr.st_nlink)	2112	if (w->attr.st_nlink)
1361	{	2113	{
1362	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2114	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1363	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2115	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1364	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2116	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1365	}	2117	}
1366	else	2118	else
1367	/* you shalt not abuse printf for puts */	2119	/* you shalt not abuse printf for puts */
1368	puts ("wow, /etc/passwd is not there, expect problems. "	2120	puts ("wow, /etc/passwd is not there, expect problems. "
1369	"if this is windows, they already arrived\n");	2121	"if this is windows, they already arrived\n");
1370	}	2122	}
1371		2123
1372	...	2124	...
1373	ev_stat passwd;	2125	ev_stat passwd;
1374		2126
1375	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	2127	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1376	ev_stat_start (loop, &passwd);	2128	ev_stat_start (loop, &passwd);
		2129
		2130	Example: Like above, but additionally use a one-second delay so we do not
		2131	miss updates (however, frequent updates will delay processing, too, so
		2132	one might do the work both on C<ev_stat> callback invocation I<and> on
		2133	C<ev_timer> callback invocation).
		2134
		2135	static ev_stat passwd;
		2136	static ev_timer timer;
		2137
		2138	static void
		2139	timer_cb (EV_P_ ev_timer *w, int revents)
		2140	{
		2141	ev_timer_stop (EV_A_ w);
		2142
		2143	/* now it's one second after the most recent passwd change */
		2144	}
		2145
		2146	static void
		2147	stat_cb (EV_P_ ev_stat *w, int revents)
		2148	{
		2149	/* reset the one-second timer */
		2150	ev_timer_again (EV_A_ &timer);
		2151	}
		2152
		2153	...
		2154	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2155	ev_stat_start (loop, &passwd);
		2156	ev_timer_init (&timer, timer_cb, 0., 1.02);
1377		2157
1378		2158
1379	=head2 C<ev_idle> - when you've got nothing better to do...	2159	=head2 C<ev_idle> - when you've got nothing better to do...
1380		2160
1381	Idle watchers trigger events when no other events of the same or higher	2161	Idle watchers trigger events when no other events of the same or higher
1382	priority are pending (prepare, check and other idle watchers do not	2162	priority are pending (prepare, check and other idle watchers do not count
1383	count).	2163	as receiving "events").
1384		2164
1385	That is, as long as your process is busy handling sockets or timeouts	2165	That is, as long as your process is busy handling sockets or timeouts
1386	(or even signals, imagine) of the same or higher priority it will not be	2166	(or even signals, imagine) of the same or higher priority it will not be
1387	triggered. But when your process is idle (or only lower-priority watchers	2167	triggered. But when your process is idle (or only lower-priority watchers
1388	are pending), the idle watchers are being called once per event loop	2168	are pending), the idle watchers are being called once per event loop
…		…
1395	Apart from keeping your process non-blocking (which is a useful	2175	Apart from keeping your process non-blocking (which is a useful
1396	effect on its own sometimes), idle watchers are a good place to do	2176	effect on its own sometimes), idle watchers are a good place to do
1397	"pseudo-background processing", or delay processing stuff to after the	2177	"pseudo-background processing", or delay processing stuff to after the
1398	event loop has handled all outstanding events.	2178	event loop has handled all outstanding events.
1399		2179
		2180	=head3 Watcher-Specific Functions and Data Members
		2181
1400	=over 4	2182	=over 4
1401		2183
1402	=item ev_idle_init (ev_signal *, callback)	2184	=item ev_idle_init (ev_idle *, callback)
1403		2185
1404	Initialises and configures the idle watcher - it has no parameters of any	2186	Initialises and configures the idle watcher - it has no parameters of any
1405	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2187	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1406	believe me.	2188	believe me.
1407		2189
1408	=back	2190	=back
1409		2191
		2192	=head3 Examples
		2193
1410	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2194	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1411	callback, free it. Also, use no error checking, as usual.	2195	callback, free it. Also, use no error checking, as usual.
1412		2196
1413	static void	2197	static void
1414	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2198	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1415	{	2199	{
1416	free (w);	2200	free (w);
1417	// now do something you wanted to do when the program has	2201	// now do something you wanted to do when the program has
1418	// no longer asnything immediate to do.	2202	// no longer anything immediate to do.
1419	}	2203	}
1420		2204
1421	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2205	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1422	ev_idle_init (idle_watcher, idle_cb);	2206	ev_idle_init (idle_watcher, idle_cb);
1423	ev_idle_start (loop, idle_cb);	2207	ev_idle_start (loop, idle_cb);
1424		2208
1425		2209
1426	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2210	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1427		2211
1428	Prepare and check watchers are usually (but not always) used in tandem:	2212	Prepare and check watchers are usually (but not always) used in pairs:
1429	prepare watchers get invoked before the process blocks and check watchers	2213	prepare watchers get invoked before the process blocks and check watchers
1430	afterwards.	2214	afterwards.
1431		2215
1432	You I<must not> call C<ev_loop> or similar functions that enter	2216	You I<must not> call C<ev_loop> or similar functions that enter
1433	the current event loop from either C<ev_prepare> or C<ev_check>	2217	the current event loop from either C<ev_prepare> or C<ev_check>
…		…
1436	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2220	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1437	C<ev_check> so if you have one watcher of each kind they will always be	2221	C<ev_check> so if you have one watcher of each kind they will always be
1438	called in pairs bracketing the blocking call.	2222	called in pairs bracketing the blocking call.
1439		2223
1440	Their main purpose is to integrate other event mechanisms into libev and	2224	Their main purpose is to integrate other event mechanisms into libev and
1441	their use is somewhat advanced. This could be used, for example, to track	2225	their use is somewhat advanced. They could be used, for example, to track
1442	variable changes, implement your own watchers, integrate net-snmp or a	2226	variable changes, implement your own watchers, integrate net-snmp or a
1443	coroutine library and lots more. They are also occasionally useful if	2227	coroutine library and lots more. They are also occasionally useful if
1444	you cache some data and want to flush it before blocking (for example,	2228	you cache some data and want to flush it before blocking (for example,
1445	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2229	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1446	watcher).	2230	watcher).
1447		2231
1448	This is done by examining in each prepare call which file descriptors need	2232	This is done by examining in each prepare call which file descriptors
1449	to be watched by the other library, registering C<ev_io> watchers for	2233	need to be watched by the other library, registering C<ev_io> watchers
1450	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2234	for them and starting an C<ev_timer> watcher for any timeouts (many
1451	provide just this functionality). Then, in the check watcher you check for	2235	libraries provide exactly this functionality). Then, in the check watcher,
1452	any events that occured (by checking the pending status of all watchers	2236	you check for any events that occurred (by checking the pending status
1453	and stopping them) and call back into the library. The I/O and timer	2237	of all watchers and stopping them) and call back into the library. The
1454	callbacks will never actually be called (but must be valid nevertheless,	2238	I/O and timer callbacks will never actually be called (but must be valid
1455	because you never know, you know?).	2239	nevertheless, because you never know, you know?).
1456		2240
1457	As another example, the Perl Coro module uses these hooks to integrate	2241	As another example, the Perl Coro module uses these hooks to integrate
1458	coroutines into libev programs, by yielding to other active coroutines	2242	coroutines into libev programs, by yielding to other active coroutines
1459	during each prepare and only letting the process block if no coroutines	2243	during each prepare and only letting the process block if no coroutines
1460	are ready to run (it's actually more complicated: it only runs coroutines	2244	are ready to run (it's actually more complicated: it only runs coroutines
1461	with priority higher than or equal to the event loop and one coroutine	2245	with priority higher than or equal to the event loop and one coroutine
1462	of lower priority, but only once, using idle watchers to keep the event	2246	of lower priority, but only once, using idle watchers to keep the event
1463	loop from blocking if lower-priority coroutines are active, thus mapping	2247	loop from blocking if lower-priority coroutines are active, thus mapping
1464	low-priority coroutines to idle/background tasks).	2248	low-priority coroutines to idle/background tasks).
1465		2249
		2250	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		2251	priority, to ensure that they are being run before any other watchers
		2252	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2253
		2254	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2255	activate ("feed") events into libev. While libev fully supports this, they
		2256	might get executed before other C<ev_check> watchers did their job. As
		2257	C<ev_check> watchers are often used to embed other (non-libev) event
		2258	loops those other event loops might be in an unusable state until their
		2259	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2260	others).
		2261
		2262	=head3 Watcher-Specific Functions and Data Members
		2263
1466	=over 4	2264	=over 4
1467		2265
1468	=item ev_prepare_init (ev_prepare *, callback)	2266	=item ev_prepare_init (ev_prepare *, callback)
1469		2267
1470	=item ev_check_init (ev_check *, callback)	2268	=item ev_check_init (ev_check *, callback)
1471		2269
1472	Initialises and configures the prepare or check watcher - they have no	2270	Initialises and configures the prepare or check watcher - they have no
1473	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2271	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1474	macros, but using them is utterly, utterly and completely pointless.	2272	macros, but using them is utterly, utterly, utterly and completely
		2273	pointless.
1475		2274
1476	=back	2275	=back
1477		2276
1478	Example: To include a library such as adns, you would add IO watchers	2277	=head3 Examples
1479	and a timeout watcher in a prepare handler, as required by libadns, and	2278
		2279	There are a number of principal ways to embed other event loops or modules
		2280	into libev. Here are some ideas on how to include libadns into libev
		2281	(there is a Perl module named C<EV::ADNS> that does this, which you could
		2282	use as a working example. Another Perl module named C<EV::Glib> embeds a
		2283	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		2284	Glib event loop).
		2285
		2286	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1480	in a check watcher, destroy them and call into libadns. What follows is	2287	and in a check watcher, destroy them and call into libadns. What follows
1481	pseudo-code only of course:	2288	is pseudo-code only of course. This requires you to either use a low
		2289	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		2290	the callbacks for the IO/timeout watchers might not have been called yet.
1482		2291
1483	static ev_io iow [nfd];	2292	static ev_io iow [nfd];
1484	static ev_timer tw;	2293	static ev_timer tw;
1485		2294
1486	static void	2295	static void
1487	io_cb (ev_loop *loop, ev_io *w, int revents)	2296	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1488	{	2297	{
1489	// set the relevant poll flags
1490	// could also call adns_processreadable etc. here
1491	struct pollfd *fd = (struct pollfd *)w->data;
1492	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1493	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1494	}	2298	}
1495		2299
1496	// create io watchers for each fd and a timer before blocking	2300	// create io watchers for each fd and a timer before blocking
1497	static void	2301	static void
1498	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2302	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1499	{	2303	{
1500	int timeout = 3600000;	2304	int timeout = 3600000;
1501	struct pollfd fds [nfd];	2305	struct pollfd fds [nfd];
1502	// actual code will need to loop here and realloc etc.	2306	// actual code will need to loop here and realloc etc.
1503	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2307	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1504		2308
1505	/* the callback is illegal, but won't be called as we stop during check */	2309	/* the callback is illegal, but won't be called as we stop during check */
1506	ev_timer_init (&tw, 0, timeout * 1e-3);	2310	ev_timer_init (&tw, 0, timeout * 1e-3);
1507	ev_timer_start (loop, &tw);	2311	ev_timer_start (loop, &tw);
1508		2312
1509	// create on ev_io per pollfd	2313	// create one ev_io per pollfd
1510	for (int i = 0; i < nfd; ++i)	2314	for (int i = 0; i < nfd; ++i)
1511	{	2315	{
1512	ev_io_init (iow + i, io_cb, fds [i].fd,	2316	ev_io_init (iow + i, io_cb, fds [i].fd,
1513	((fds [i].events & POLLIN ? EV_READ : 0)	2317	((fds [i].events & POLLIN ? EV_READ : 0)
1514	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2318	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1515		2319
1516	fds [i].revents = 0;	2320	fds [i].revents = 0;
1517	iow [i].data = fds + i;
1518	ev_io_start (loop, iow + i);	2321	ev_io_start (loop, iow + i);
1519	}	2322	}
1520	}	2323	}
1521		2324
1522	// stop all watchers after blocking	2325	// stop all watchers after blocking
1523	static void	2326	static void
1524	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2327	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1525	{	2328	{
1526	ev_timer_stop (loop, &tw);	2329	ev_timer_stop (loop, &tw);
1527		2330
1528	for (int i = 0; i < nfd; ++i)	2331	for (int i = 0; i < nfd; ++i)
		2332	{
		2333	// set the relevant poll flags
		2334	// could also call adns_processreadable etc. here
		2335	struct pollfd *fd = fds + i;
		2336	int revents = ev_clear_pending (iow + i);
		2337	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2338	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2339
		2340	// now stop the watcher
1529	ev_io_stop (loop, iow + i);	2341	ev_io_stop (loop, iow + i);
		2342	}
1530		2343
1531	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2344	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1532	}	2345	}
		2346
		2347	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2348	in the prepare watcher and would dispose of the check watcher.
		2349
		2350	Method 3: If the module to be embedded supports explicit event
		2351	notification (libadns does), you can also make use of the actual watcher
		2352	callbacks, and only destroy/create the watchers in the prepare watcher.
		2353
		2354	static void
		2355	timer_cb (EV_P_ ev_timer *w, int revents)
		2356	{
		2357	adns_state ads = (adns_state)w->data;
		2358	update_now (EV_A);
		2359
		2360	adns_processtimeouts (ads, &tv_now);
		2361	}
		2362
		2363	static void
		2364	io_cb (EV_P_ ev_io *w, int revents)
		2365	{
		2366	adns_state ads = (adns_state)w->data;
		2367	update_now (EV_A);
		2368
		2369	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2370	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2371	}
		2372
		2373	// do not ever call adns_afterpoll
		2374
		2375	Method 4: Do not use a prepare or check watcher because the module you
		2376	want to embed is not flexible enough to support it. Instead, you can
		2377	override their poll function. The drawback with this solution is that the
		2378	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		2379	this approach, effectively embedding EV as a client into the horrible
		2380	libglib event loop.
		2381
		2382	static gint
		2383	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2384	{
		2385	int got_events = 0;
		2386
		2387	for (n = 0; n < nfds; ++n)
		2388	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2389
		2390	if (timeout >= 0)
		2391	// create/start timer
		2392
		2393	// poll
		2394	ev_loop (EV_A_ 0);
		2395
		2396	// stop timer again
		2397	if (timeout >= 0)
		2398	ev_timer_stop (EV_A_ &to);
		2399
		2400	// stop io watchers again - their callbacks should have set
		2401	for (n = 0; n < nfds; ++n)
		2402	ev_io_stop (EV_A_ iow [n]);
		2403
		2404	return got_events;
		2405	}
1533		2406
1534		2407
1535	=head2 C<ev_embed> - when one backend isn't enough...	2408	=head2 C<ev_embed> - when one backend isn't enough...
1536		2409
1537	This is a rather advanced watcher type that lets you embed one event loop	2410	This is a rather advanced watcher type that lets you embed one event loop
…		…
1543	prioritise I/O.	2416	prioritise I/O.
1544		2417
1545	As an example for a bug workaround, the kqueue backend might only support	2418	As an example for a bug workaround, the kqueue backend might only support
1546	sockets on some platform, so it is unusable as generic backend, but you	2419	sockets on some platform, so it is unusable as generic backend, but you
1547	still want to make use of it because you have many sockets and it scales	2420	still want to make use of it because you have many sockets and it scales
1548	so nicely. In this case, you would create a kqueue-based loop and embed it	2421	so nicely. In this case, you would create a kqueue-based loop and embed
1549	into your default loop (which might use e.g. poll). Overall operation will	2422	it into your default loop (which might use e.g. poll). Overall operation
1550	be a bit slower because first libev has to poll and then call kevent, but	2423	will be a bit slower because first libev has to call C<poll> and then
1551	at least you can use both at what they are best.	2424	C<kevent>, but at least you can use both mechanisms for what they are
		2425	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1552		2426
1553	As for prioritising I/O: rarely you have the case where some fds have	2427	As for prioritising I/O: under rare circumstances you have the case where
1554	to be watched and handled very quickly (with low latency), and even	2428	some fds have to be watched and handled very quickly (with low latency),
1555	priorities and idle watchers might have too much overhead. In this case	2429	and even priorities and idle watchers might have too much overhead. In
1556	you would put all the high priority stuff in one loop and all the rest in	2430	this case you would put all the high priority stuff in one loop and all
1557	a second one, and embed the second one in the first.	2431	the rest in a second one, and embed the second one in the first.
1558		2432
1559	As long as the watcher is active, the callback will be invoked every time	2433	As long as the watcher is active, the callback will be invoked every
1560	there might be events pending in the embedded loop. The callback must then	2434	time there might be events pending in the embedded loop. The callback
1561	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2435	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1562	their callbacks (you could also start an idle watcher to give the embedded	2436	sweep and invoke their callbacks (the callback doesn't need to invoke the
1563	loop strictly lower priority for example). You can also set the callback	2437	C<ev_embed_sweep> function directly, it could also start an idle watcher
1564	to C<0>, in which case the embed watcher will automatically execute the	2438	to give the embedded loop strictly lower priority for example).
1565	embedded loop sweep.
1566		2439
1567	As long as the watcher is started it will automatically handle events. The	2440	You can also set the callback to C<0>, in which case the embed watcher
1568	callback will be invoked whenever some events have been handled. You can	2441	will automatically execute the embedded loop sweep whenever necessary.
1569	set the callback to C<0> to avoid having to specify one if you are not
1570	interested in that.
1571		2442
1572	Also, there have not currently been made special provisions for forking:	2443	Fork detection will be handled transparently while the C<ev_embed> watcher
1573	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2444	is active, i.e., the embedded loop will automatically be forked when the
1574	but you will also have to stop and restart any C<ev_embed> watchers	2445	embedding loop forks. In other cases, the user is responsible for calling
1575	yourself.	2446	C<ev_loop_fork> on the embedded loop.
1576		2447
1577	Unfortunately, not all backends are embeddable, only the ones returned by	2448	Unfortunately, not all backends are embeddable: only the ones returned by
1578	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2449	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1579	portable one.	2450	portable one.
1580		2451
1581	So when you want to use this feature you will always have to be prepared	2452	So when you want to use this feature you will always have to be prepared
1582	that you cannot get an embeddable loop. The recommended way to get around	2453	that you cannot get an embeddable loop. The recommended way to get around
1583	this is to have a separate variables for your embeddable loop, try to	2454	this is to have a separate variables for your embeddable loop, try to
1584	create it, and if that fails, use the normal loop for everything:	2455	create it, and if that fails, use the normal loop for everything.
1585		2456
1586	struct ev_loop *loop_hi = ev_default_init (0);	2457	=head3 C<ev_embed> and fork
1587	struct ev_loop *loop_lo = 0;
1588	struct ev_embed embed;
1589
1590	// see if there is a chance of getting one that works
1591	// (remember that a flags value of 0 means autodetection)
1592	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1593	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1594	: 0;
1595		2458
1596	// if we got one, then embed it, otherwise default to loop_hi	2459	While the C<ev_embed> watcher is running, forks in the embedding loop will
1597	if (loop_lo)	2460	automatically be applied to the embedded loop as well, so no special
1598	{	2461	fork handling is required in that case. When the watcher is not running,
1599	ev_embed_init (&embed, 0, loop_lo);	2462	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1600	ev_embed_start (loop_hi, &embed);	2463	as applicable.
1601	}	2464
1602	else	2465	=head3 Watcher-Specific Functions and Data Members
1603	loop_lo = loop_hi;
1604		2466
1605	=over 4	2467	=over 4
1606		2468
1607	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	2469	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
1608		2470
…		…
1610		2472
1611	Configures the watcher to embed the given loop, which must be	2473	Configures the watcher to embed the given loop, which must be
1612	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	2474	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1613	invoked automatically, otherwise it is the responsibility of the callback	2475	invoked automatically, otherwise it is the responsibility of the callback
1614	to invoke it (it will continue to be called until the sweep has been done,	2476	to invoke it (it will continue to be called until the sweep has been done,
1615	if you do not want thta, you need to temporarily stop the embed watcher).	2477	if you do not want that, you need to temporarily stop the embed watcher).
1616		2478
1617	=item ev_embed_sweep (loop, ev_embed *)	2479	=item ev_embed_sweep (loop, ev_embed *)
1618		2480
1619	Make a single, non-blocking sweep over the embedded loop. This works	2481	Make a single, non-blocking sweep over the embedded loop. This works
1620	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	2482	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
1621	apropriate way for embedded loops.	2483	appropriate way for embedded loops.
1622		2484
1623	=item struct ev_loop *loop [read-only]	2485	=item struct ev_loop *other [read-only]
1624		2486
1625	The embedded event loop.	2487	The embedded event loop.
1626		2488
1627	=back	2489	=back
		2490
		2491	=head3 Examples
		2492
		2493	Example: Try to get an embeddable event loop and embed it into the default
		2494	event loop. If that is not possible, use the default loop. The default
		2495	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2496	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2497	used).
		2498
		2499	struct ev_loop *loop_hi = ev_default_init (0);
		2500	struct ev_loop *loop_lo = 0;
		2501	ev_embed embed;
		2502
		2503	// see if there is a chance of getting one that works
		2504	// (remember that a flags value of 0 means autodetection)
		2505	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2506	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2507	: 0;
		2508
		2509	// if we got one, then embed it, otherwise default to loop_hi
		2510	if (loop_lo)
		2511	{
		2512	ev_embed_init (&embed, 0, loop_lo);
		2513	ev_embed_start (loop_hi, &embed);
		2514	}
		2515	else
		2516	loop_lo = loop_hi;
		2517
		2518	Example: Check if kqueue is available but not recommended and create
		2519	a kqueue backend for use with sockets (which usually work with any
		2520	kqueue implementation). Store the kqueue/socket-only event loop in
		2521	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2522
		2523	struct ev_loop *loop = ev_default_init (0);
		2524	struct ev_loop *loop_socket = 0;
		2525	ev_embed embed;
		2526
		2527	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2528	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2529	{
		2530	ev_embed_init (&embed, 0, loop_socket);
		2531	ev_embed_start (loop, &embed);
		2532	}
		2533
		2534	if (!loop_socket)
		2535	loop_socket = loop;
		2536
		2537	// now use loop_socket for all sockets, and loop for everything else
1628		2538
1629		2539
1630	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	2540	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
1631		2541
1632	Fork watchers are called when a C<fork ()> was detected (usually because	2542	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
1635	event loop blocks next and before C<ev_check> watchers are being called,	2545	event loop blocks next and before C<ev_check> watchers are being called,
1636	and only in the child after the fork. If whoever good citizen calling	2546	and only in the child after the fork. If whoever good citizen calling
1637	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2547	C<ev_default_fork> cheats and calls it in the wrong process, the fork
1638	handlers will be invoked, too, of course.	2548	handlers will be invoked, too, of course.
1639		2549
		2550	=head3 Watcher-Specific Functions and Data Members
		2551
1640	=over 4	2552	=over 4
1641		2553
1642	=item ev_fork_init (ev_signal *, callback)	2554	=item ev_fork_init (ev_signal *, callback)
1643		2555
1644	Initialises and configures the fork watcher - it has no parameters of any	2556	Initialises and configures the fork watcher - it has no parameters of any
…		…
1646	believe me.	2558	believe me.
1647		2559
1648	=back	2560	=back
1649		2561
1650		2562
		2563	=head2 C<ev_async> - how to wake up another event loop
		2564
		2565	In general, you cannot use an C<ev_loop> from multiple threads or other
		2566	asynchronous sources such as signal handlers (as opposed to multiple event
		2567	loops - those are of course safe to use in different threads).
		2568
		2569	Sometimes, however, you need to wake up another event loop you do not
		2570	control, for example because it belongs to another thread. This is what
		2571	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2572	can signal it by calling C<ev_async_send>, which is thread- and signal
		2573	safe.
		2574
		2575	This functionality is very similar to C<ev_signal> watchers, as signals,
		2576	too, are asynchronous in nature, and signals, too, will be compressed
		2577	(i.e. the number of callback invocations may be less than the number of
		2578	C<ev_async_sent> calls).
		2579
		2580	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2581	just the default loop.
		2582
		2583	=head3 Queueing
		2584
		2585	C<ev_async> does not support queueing of data in any way. The reason
		2586	is that the author does not know of a simple (or any) algorithm for a
		2587	multiple-writer-single-reader queue that works in all cases and doesn't
		2588	need elaborate support such as pthreads.
		2589
		2590	That means that if you want to queue data, you have to provide your own
		2591	queue. But at least I can tell you how to implement locking around your
		2592	queue:
		2593
		2594	=over 4
		2595
		2596	=item queueing from a signal handler context
		2597
		2598	To implement race-free queueing, you simply add to the queue in the signal
		2599	handler but you block the signal handler in the watcher callback. Here is
		2600	an example that does that for some fictitious SIGUSR1 handler:
		2601
		2602	static ev_async mysig;
		2603
		2604	static void
		2605	sigusr1_handler (void)
		2606	{
		2607	sometype data;
		2608
		2609	// no locking etc.
		2610	queue_put (data);
		2611	ev_async_send (EV_DEFAULT_ &mysig);
		2612	}
		2613
		2614	static void
		2615	mysig_cb (EV_P_ ev_async *w, int revents)
		2616	{
		2617	sometype data;
		2618	sigset_t block, prev;
		2619
		2620	sigemptyset (&block);
		2621	sigaddset (&block, SIGUSR1);
		2622	sigprocmask (SIG_BLOCK, &block, &prev);
		2623
		2624	while (queue_get (&data))
		2625	process (data);
		2626
		2627	if (sigismember (&prev, SIGUSR1)
		2628	sigprocmask (SIG_UNBLOCK, &block, 0);
		2629	}
		2630
		2631	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2632	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2633	either...).
		2634
		2635	=item queueing from a thread context
		2636
		2637	The strategy for threads is different, as you cannot (easily) block
		2638	threads but you can easily preempt them, so to queue safely you need to
		2639	employ a traditional mutex lock, such as in this pthread example:
		2640
		2641	static ev_async mysig;
		2642	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2643
		2644	static void
		2645	otherthread (void)
		2646	{
		2647	// only need to lock the actual queueing operation
		2648	pthread_mutex_lock (&mymutex);
		2649	queue_put (data);
		2650	pthread_mutex_unlock (&mymutex);
		2651
		2652	ev_async_send (EV_DEFAULT_ &mysig);
		2653	}
		2654
		2655	static void
		2656	mysig_cb (EV_P_ ev_async *w, int revents)
		2657	{
		2658	pthread_mutex_lock (&mymutex);
		2659
		2660	while (queue_get (&data))
		2661	process (data);
		2662
		2663	pthread_mutex_unlock (&mymutex);
		2664	}
		2665
		2666	=back
		2667
		2668
		2669	=head3 Watcher-Specific Functions and Data Members
		2670
		2671	=over 4
		2672
		2673	=item ev_async_init (ev_async *, callback)
		2674
		2675	Initialises and configures the async watcher - it has no parameters of any
		2676	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		2677	trust me.
		2678
		2679	=item ev_async_send (loop, ev_async *)
		2680
		2681	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2682	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2683	C<ev_feed_event>, this call is safe to do from other threads, signal or
		2684	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		2685	section below on what exactly this means).
		2686
		2687	This call incurs the overhead of a system call only once per loop iteration,
		2688	so while the overhead might be noticeable, it doesn't apply to repeated
		2689	calls to C<ev_async_send>.
		2690
		2691	=item bool = ev_async_pending (ev_async *)
		2692
		2693	Returns a non-zero value when C<ev_async_send> has been called on the
		2694	watcher but the event has not yet been processed (or even noted) by the
		2695	event loop.
		2696
		2697	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2698	the loop iterates next and checks for the watcher to have become active,
		2699	it will reset the flag again. C<ev_async_pending> can be used to very
		2700	quickly check whether invoking the loop might be a good idea.
		2701
		2702	Not that this does I<not> check whether the watcher itself is pending, only
		2703	whether it has been requested to make this watcher pending.
		2704
		2705	=back
		2706
		2707
1651	=head1 OTHER FUNCTIONS	2708	=head1 OTHER FUNCTIONS
1652		2709
1653	There are some other functions of possible interest. Described. Here. Now.	2710	There are some other functions of possible interest. Described. Here. Now.
1654		2711
1655	=over 4	2712	=over 4
1656		2713
1657	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	2714	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1658		2715
1659	This function combines a simple timer and an I/O watcher, calls your	2716	This function combines a simple timer and an I/O watcher, calls your
1660	callback on whichever event happens first and automatically stop both	2717	callback on whichever event happens first and automatically stops both
1661	watchers. This is useful if you want to wait for a single event on an fd	2718	watchers. This is useful if you want to wait for a single event on an fd
1662	or timeout without having to allocate/configure/start/stop/free one or	2719	or timeout without having to allocate/configure/start/stop/free one or
1663	more watchers yourself.	2720	more watchers yourself.
1664		2721
1665	If C<fd> is less than 0, then no I/O watcher will be started and events	2722	If C<fd> is less than 0, then no I/O watcher will be started and the
1666	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	2723	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1667	C<events> set will be craeted and started.	2724	the given C<fd> and C<events> set will be created and started.
1668		2725
1669	If C<timeout> is less than 0, then no timeout watcher will be	2726	If C<timeout> is less than 0, then no timeout watcher will be
1670	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	2727	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1671	repeat = 0) will be started. While C<0> is a valid timeout, it is of	2728	repeat = 0) will be started. C<0> is a valid timeout.
1672	dubious value.
1673		2729
1674	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	2730	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
1675	passed an C<revents> set like normal event callbacks (a combination of	2731	passed an C<revents> set like normal event callbacks (a combination of
1676	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	2732	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
1677	value passed to C<ev_once>:	2733	value passed to C<ev_once>. Note that it is possible to receive I<both>
		2734	a timeout and an io event at the same time - you probably should give io
		2735	events precedence.
1678		2736
		2737	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		2738
1679	static void stdin_ready (int revents, void *arg)	2739	static void stdin_ready (int revents, void *arg)
1680	{	2740	{
1681	if (revents & EV_TIMEOUT)
1682	/* doh, nothing entered */;
1683	else if (revents & EV_READ)	2741	if (revents & EV_READ)
1684	/* stdin might have data for us, joy! */;	2742	/* stdin might have data for us, joy! */;
		2743	else if (revents & EV_TIMEOUT)
		2744	/* doh, nothing entered */;
1685	}	2745	}
1686		2746
1687	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2747	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1688		2748
1689	=item ev_feed_event (ev_loop *, watcher *, int revents)	2749	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
1690		2750
1691	Feeds the given event set into the event loop, as if the specified event	2751	Feeds the given event set into the event loop, as if the specified event
1692	had happened for the specified watcher (which must be a pointer to an	2752	had happened for the specified watcher (which must be a pointer to an
1693	initialised but not necessarily started event watcher).	2753	initialised but not necessarily started event watcher).
1694		2754
1695	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	2755	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
1696		2756
1697	Feed an event on the given fd, as if a file descriptor backend detected	2757	Feed an event on the given fd, as if a file descriptor backend detected
1698	the given events it.	2758	the given events it.
1699		2759
1700	=item ev_feed_signal_event (ev_loop *loop, int signum)	2760	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
1701		2761
1702	Feed an event as if the given signal occured (C<loop> must be the default	2762	Feed an event as if the given signal occurred (C<loop> must be the default
1703	loop!).	2763	loop!).
1704		2764
1705	=back	2765	=back
1706		2766
1707		2767
…		…
1723		2783
1724	=item * Priorities are not currently supported. Initialising priorities	2784	=item * Priorities are not currently supported. Initialising priorities
1725	will fail and all watchers will have the same priority, even though there	2785	will fail and all watchers will have the same priority, even though there
1726	is an ev_pri field.	2786	is an ev_pri field.
1727		2787
		2788	=item * In libevent, the last base created gets the signals, in libev, the
		2789	first base created (== the default loop) gets the signals.
		2790
1728	=item * Other members are not supported.	2791	=item * Other members are not supported.
1729		2792
1730	=item * The libev emulation is I<not> ABI compatible to libevent, you need	2793	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1731	to use the libev header file and library.	2794	to use the libev header file and library.
1732		2795
1733	=back	2796	=back
1734		2797
1735	=head1 C++ SUPPORT	2798	=head1 C++ SUPPORT
1736		2799
1737	Libev comes with some simplistic wrapper classes for C++ that mainly allow	2800	Libev comes with some simplistic wrapper classes for C++ that mainly allow
1738	you to use some convinience methods to start/stop watchers and also change	2801	you to use some convenience methods to start/stop watchers and also change
1739	the callback model to a model using method callbacks on objects.	2802	the callback model to a model using method callbacks on objects.
1740		2803
1741	To use it,	2804	To use it,
1742		2805
1743	#include <ev++.h>	2806	#include <ev++.h>
1744		2807
1745	(it is not installed by default). This automatically includes F<ev.h>	2808	This automatically includes F<ev.h> and puts all of its definitions (many
1746	and puts all of its definitions (many of them macros) into the global	2809	of them macros) into the global namespace. All C++ specific things are
1747	namespace. All C++ specific things are put into the C<ev> namespace.	2810	put into the C<ev> namespace. It should support all the same embedding
		2811	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
1748		2812
1749	It should support all the same embedding options as F<ev.h>, most notably	2813	Care has been taken to keep the overhead low. The only data member the C++
1750	C<EV_MULTIPLICITY>.	2814	classes add (compared to plain C-style watchers) is the event loop pointer
		2815	that the watcher is associated with (or no additional members at all if
		2816	you disable C<EV_MULTIPLICITY> when embedding libev).
		2817
		2818	Currently, functions, and static and non-static member functions can be
		2819	used as callbacks. Other types should be easy to add as long as they only
		2820	need one additional pointer for context. If you need support for other
		2821	types of functors please contact the author (preferably after implementing
		2822	it).
1751		2823
1752	Here is a list of things available in the C<ev> namespace:	2824	Here is a list of things available in the C<ev> namespace:
1753		2825
1754	=over 4	2826	=over 4
1755		2827
…		…
1771		2843
1772	All of those classes have these methods:	2844	All of those classes have these methods:
1773		2845
1774	=over 4	2846	=over 4
1775		2847
1776	=item ev::TYPE::TYPE (object *, object::method *)	2848	=item ev::TYPE::TYPE ()
1777		2849
1778	=item ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)	2850	=item ev::TYPE::TYPE (struct ev_loop *)
1779		2851
1780	=item ev::TYPE::~TYPE	2852	=item ev::TYPE::~TYPE
1781		2853
1782	The constructor takes a pointer to an object and a method pointer to	2854	The constructor (optionally) takes an event loop to associate the watcher
1783	the event handler callback to call in this class. The constructor calls	2855	with. If it is omitted, it will use C<EV_DEFAULT>.
1784	C<ev_init> for you, which means you have to call the C<set> method	2856
1785	before starting it. If you do not specify a loop then the constructor	2857	The constructor calls C<ev_init> for you, which means you have to call the
1786	automatically associates the default loop with this watcher.	2858	C<set> method before starting it.
		2859
		2860	It will not set a callback, however: You have to call the templated C<set>
		2861	method to set a callback before you can start the watcher.
		2862
		2863	(The reason why you have to use a method is a limitation in C++ which does
		2864	not allow explicit template arguments for constructors).
1787		2865
1788	The destructor automatically stops the watcher if it is active.	2866	The destructor automatically stops the watcher if it is active.
		2867
		2868	=item w->set<class, &class::method> (object *)
		2869
		2870	This method sets the callback method to call. The method has to have a
		2871	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		2872	first argument and the C<revents> as second. The object must be given as
		2873	parameter and is stored in the C<data> member of the watcher.
		2874
		2875	This method synthesizes efficient thunking code to call your method from
		2876	the C callback that libev requires. If your compiler can inline your
		2877	callback (i.e. it is visible to it at the place of the C<set> call and
		2878	your compiler is good :), then the method will be fully inlined into the
		2879	thunking function, making it as fast as a direct C callback.
		2880
		2881	Example: simple class declaration and watcher initialisation
		2882
		2883	struct myclass
		2884	{
		2885	void io_cb (ev::io &w, int revents) { }
		2886	}
		2887
		2888	myclass obj;
		2889	ev::io iow;
		2890	iow.set <myclass, &myclass::io_cb> (&obj);
		2891
		2892	=item w->set (object *)
		2893
		2894	This is an B<experimental> feature that might go away in a future version.
		2895
		2896	This is a variation of a method callback - leaving out the method to call
		2897	will default the method to C<operator ()>, which makes it possible to use
		2898	functor objects without having to manually specify the C<operator ()> all
		2899	the time. Incidentally, you can then also leave out the template argument
		2900	list.
		2901
		2902	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		2903	int revents)>.
		2904
		2905	See the method-C<set> above for more details.
		2906
		2907	Example: use a functor object as callback.
		2908
		2909	struct myfunctor
		2910	{
		2911	void operator() (ev::io &w, int revents)
		2912	{
		2913	...
		2914	}
		2915	}
		2916
		2917	myfunctor f;
		2918
		2919	ev::io w;
		2920	w.set (&f);
		2921
		2922	=item w->set<function> (void *data = 0)
		2923
		2924	Also sets a callback, but uses a static method or plain function as
		2925	callback. The optional C<data> argument will be stored in the watcher's
		2926	C<data> member and is free for you to use.
		2927
		2928	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		2929
		2930	See the method-C<set> above for more details.
		2931
		2932	Example: Use a plain function as callback.
		2933
		2934	static void io_cb (ev::io &w, int revents) { }
		2935	iow.set <io_cb> ();
1789		2936
1790	=item w->set (struct ev_loop *)	2937	=item w->set (struct ev_loop *)
1791		2938
1792	Associates a different C<struct ev_loop> with this watcher. You can only	2939	Associates a different C<struct ev_loop> with this watcher. You can only
1793	do this when the watcher is inactive (and not pending either).	2940	do this when the watcher is inactive (and not pending either).
1794		2941
1795	=item w->set ([args])	2942	=item w->set ([arguments])
1796		2943
1797	Basically the same as C<ev_TYPE_set>, with the same args. Must be	2944	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
1798	called at least once. Unlike the C counterpart, an active watcher gets	2945	called at least once. Unlike the C counterpart, an active watcher gets
1799	automatically stopped and restarted.	2946	automatically stopped and restarted when reconfiguring it with this
		2947	method.
1800		2948
1801	=item w->start ()	2949	=item w->start ()
1802		2950
1803	Starts the watcher. Note that there is no C<loop> argument as the	2951	Starts the watcher. Note that there is no C<loop> argument, as the
1804	constructor already takes the loop.	2952	constructor already stores the event loop.
1805		2953
1806	=item w->stop ()	2954	=item w->stop ()
1807		2955
1808	Stops the watcher if it is active. Again, no C<loop> argument.	2956	Stops the watcher if it is active. Again, no C<loop> argument.
1809		2957
1810	=item w->again () C<ev::timer>, C<ev::periodic> only	2958	=item w->again () (C<ev::timer>, C<ev::periodic> only)
1811		2959
1812	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding	2960	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
1813	C<ev_TYPE_again> function.	2961	C<ev_TYPE_again> function.
1814		2962
1815	=item w->sweep () C<ev::embed> only	2963	=item w->sweep () (C<ev::embed> only)
1816		2964
1817	Invokes C<ev_embed_sweep>.	2965	Invokes C<ev_embed_sweep>.
1818		2966
1819	=item w->update () C<ev::stat> only	2967	=item w->update () (C<ev::stat> only)
1820		2968
1821	Invokes C<ev_stat_stat>.	2969	Invokes C<ev_stat_stat>.
1822		2970
1823	=back	2971	=back
1824		2972
1825	=back	2973	=back
1826		2974
1827	Example: Define a class with an IO and idle watcher, start one of them in	2975	Example: Define a class with an IO and idle watcher, start one of them in
1828	the constructor.	2976	the constructor.
1829		2977
1830	class myclass	2978	class myclass
1831	{	2979	{
1832	ev_io io; void io_cb (ev::io &w, int revents);	2980	ev::io io ; void io_cb (ev::io &w, int revents);
1833	ev_idle idle void idle_cb (ev::idle &w, int revents);	2981	ev::idle idle; void idle_cb (ev::idle &w, int revents);
1834		2982
1835	myclass ();	2983	myclass (int fd)
1836	}	2984	{
		2985	io .set <myclass, &myclass::io_cb > (this);
		2986	idle.set <myclass, &myclass::idle_cb> (this);
1837		2987
1838	myclass::myclass (int fd)
1839	: io (this, &myclass::io_cb),
1840	idle (this, &myclass::idle_cb)
1841	{
1842	io.start (fd, ev::READ);	2988	io.start (fd, ev::READ);
		2989	}
1843	}	2990	};
		2991
		2992
		2993	=head1 OTHER LANGUAGE BINDINGS
		2994
		2995	Libev does not offer other language bindings itself, but bindings for a
		2996	number of languages exist in the form of third-party packages. If you know
		2997	any interesting language binding in addition to the ones listed here, drop
		2998	me a note.
		2999
		3000	=over 4
		3001
		3002	=item Perl
		3003
		3004	The EV module implements the full libev API and is actually used to test
		3005	libev. EV is developed together with libev. Apart from the EV core module,
		3006	there are additional modules that implement libev-compatible interfaces
		3007	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3008	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3009	and C<EV::Glib>).
		3010
		3011	It can be found and installed via CPAN, its homepage is at
		3012	L<http://software.schmorp.de/pkg/EV>.
		3013
		3014	=item Python
		3015
		3016	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3017	seems to be quite complete and well-documented. Note, however, that the
		3018	patch they require for libev is outright dangerous as it breaks the ABI
		3019	for everybody else, and therefore, should never be applied in an installed
		3020	libev (if python requires an incompatible ABI then it needs to embed
		3021	libev).
		3022
		3023	=item Ruby
		3024
		3025	Tony Arcieri has written a ruby extension that offers access to a subset
		3026	of the libev API and adds file handle abstractions, asynchronous DNS and
		3027	more on top of it. It can be found via gem servers. Its homepage is at
		3028	L<http://rev.rubyforge.org/>.
		3029
		3030	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3031	makes rev work even on mingw.
		3032
		3033	=item D
		3034
		3035	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3036	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3037
		3038	=item Ocaml
		3039
		3040	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3041	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3042
		3043	=back
1844		3044
1845		3045
1846	=head1 MACRO MAGIC	3046	=head1 MACRO MAGIC
1847		3047
1848	Libev can be compiled with a variety of options, the most fundemantal is	3048	Libev can be compiled with a variety of options, the most fundamental
1849	C<EV_MULTIPLICITY>. This option determines whether (most) functions and	3049	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
1850	callbacks have an initial C<struct ev_loop *> argument.	3050	functions and callbacks have an initial C<struct ev_loop *> argument.
1851		3051
1852	To make it easier to write programs that cope with either variant, the	3052	To make it easier to write programs that cope with either variant, the
1853	following macros are defined:	3053	following macros are defined:
1854		3054
1855	=over 4	3055	=over 4
…		…
1858		3058
1859	This provides the loop I<argument> for functions, if one is required ("ev	3059	This provides the loop I<argument> for functions, if one is required ("ev
1860	loop argument"). The C<EV_A> form is used when this is the sole argument,	3060	loop argument"). The C<EV_A> form is used when this is the sole argument,
1861	C<EV_A_> is used when other arguments are following. Example:	3061	C<EV_A_> is used when other arguments are following. Example:
1862		3062
1863	ev_unref (EV_A);	3063	ev_unref (EV_A);
1864	ev_timer_add (EV_A_ watcher);	3064	ev_timer_add (EV_A_ watcher);
1865	ev_loop (EV_A_ 0);	3065	ev_loop (EV_A_ 0);
1866		3066
1867	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	3067	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
1868	which is often provided by the following macro.	3068	which is often provided by the following macro.
1869		3069
1870	=item C<EV_P>, C<EV_P_>	3070	=item C<EV_P>, C<EV_P_>
1871		3071
1872	This provides the loop I<parameter> for functions, if one is required ("ev	3072	This provides the loop I<parameter> for functions, if one is required ("ev
1873	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	3073	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
1874	C<EV_P_> is used when other parameters are following. Example:	3074	C<EV_P_> is used when other parameters are following. Example:
1875		3075
1876	// this is how ev_unref is being declared	3076	// this is how ev_unref is being declared
1877	static void ev_unref (EV_P);	3077	static void ev_unref (EV_P);
1878		3078
1879	// this is how you can declare your typical callback	3079	// this is how you can declare your typical callback
1880	static void cb (EV_P_ ev_timer *w, int revents)	3080	static void cb (EV_P_ ev_timer *w, int revents)
1881		3081
1882	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	3082	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
1883	suitable for use with C<EV_A>.	3083	suitable for use with C<EV_A>.
1884		3084
1885	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3085	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
1886		3086
1887	Similar to the other two macros, this gives you the value of the default	3087	Similar to the other two macros, this gives you the value of the default
1888	loop, if multiple loops are supported ("ev loop default").	3088	loop, if multiple loops are supported ("ev loop default").
		3089
		3090	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3091
		3092	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3093	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3094	is undefined when the default loop has not been initialised by a previous
		3095	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3096
		3097	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3098	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
1889		3099
1890	=back	3100	=back
1891		3101
1892	Example: Declare and initialise a check watcher, utilising the above	3102	Example: Declare and initialise a check watcher, utilising the above
1893	macros so it will work regardless of whether multiple loops are supported	3103	macros so it will work regardless of whether multiple loops are supported
1894	or not.	3104	or not.
1895		3105
1896	static void	3106	static void
1897	check_cb (EV_P_ ev_timer *w, int revents)	3107	check_cb (EV_P_ ev_timer *w, int revents)
1898	{	3108	{
1899	ev_check_stop (EV_A_ w);	3109	ev_check_stop (EV_A_ w);
1900	}	3110	}
1901		3111
1902	ev_check check;	3112	ev_check check;
1903	ev_check_init (&check, check_cb);	3113	ev_check_init (&check, check_cb);
1904	ev_check_start (EV_DEFAULT_ &check);	3114	ev_check_start (EV_DEFAULT_ &check);
1905	ev_loop (EV_DEFAULT_ 0);	3115	ev_loop (EV_DEFAULT_ 0);
1906		3116
1907	=head1 EMBEDDING	3117	=head1 EMBEDDING
1908		3118
1909	Libev can (and often is) directly embedded into host	3119	Libev can (and often is) directly embedded into host
1910	applications. Examples of applications that embed it include the Deliantra	3120	applications. Examples of applications that embed it include the Deliantra
1911	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)	3121	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
1912	and rxvt-unicode.	3122	and rxvt-unicode.
1913		3123
1914	The goal is to enable you to just copy the neecssary files into your	3124	The goal is to enable you to just copy the necessary files into your
1915	source directory without having to change even a single line in them, so	3125	source directory without having to change even a single line in them, so
1916	you can easily upgrade by simply copying (or having a checked-out copy of	3126	you can easily upgrade by simply copying (or having a checked-out copy of
1917	libev somewhere in your source tree).	3127	libev somewhere in your source tree).
1918		3128
1919	=head2 FILESETS	3129	=head2 FILESETS
1920		3130
1921	Depending on what features you need you need to include one or more sets of files	3131	Depending on what features you need you need to include one or more sets of files
1922	in your app.	3132	in your application.
1923		3133
1924	=head3 CORE EVENT LOOP	3134	=head3 CORE EVENT LOOP
1925		3135
1926	To include only the libev core (all the C<ev_*> functions), with manual	3136	To include only the libev core (all the C<ev_*> functions), with manual
1927	configuration (no autoconf):	3137	configuration (no autoconf):
1928		3138
1929	#define EV_STANDALONE 1	3139	#define EV_STANDALONE 1
1930	#include "ev.c"	3140	#include "ev.c"
1931		3141
1932	This will automatically include F<ev.h>, too, and should be done in a	3142	This will automatically include F<ev.h>, too, and should be done in a
1933	single C source file only to provide the function implementations. To use	3143	single C source file only to provide the function implementations. To use
1934	it, do the same for F<ev.h> in all files wishing to use this API (best	3144	it, do the same for F<ev.h> in all files wishing to use this API (best
1935	done by writing a wrapper around F<ev.h> that you can include instead and	3145	done by writing a wrapper around F<ev.h> that you can include instead and
1936	where you can put other configuration options):	3146	where you can put other configuration options):
1937		3147
1938	#define EV_STANDALONE 1	3148	#define EV_STANDALONE 1
1939	#include "ev.h"	3149	#include "ev.h"
1940		3150
1941	Both header files and implementation files can be compiled with a C++	3151	Both header files and implementation files can be compiled with a C++
1942	compiler (at least, thats a stated goal, and breakage will be treated	3152	compiler (at least, that's a stated goal, and breakage will be treated
1943	as a bug).	3153	as a bug).
1944		3154
1945	You need the following files in your source tree, or in a directory	3155	You need the following files in your source tree, or in a directory
1946	in your include path (e.g. in libev/ when using -Ilibev):	3156	in your include path (e.g. in libev/ when using -Ilibev):
1947		3157
1948	ev.h	3158	ev.h
1949	ev.c	3159	ev.c
1950	ev_vars.h	3160	ev_vars.h
1951	ev_wrap.h	3161	ev_wrap.h
1952		3162
1953	ev_win32.c required on win32 platforms only	3163	ev_win32.c required on win32 platforms only
1954		3164
1955	ev_select.c only when select backend is enabled (which is enabled by default)	3165	ev_select.c only when select backend is enabled (which is enabled by default)
1956	ev_poll.c only when poll backend is enabled (disabled by default)	3166	ev_poll.c only when poll backend is enabled (disabled by default)
1957	ev_epoll.c only when the epoll backend is enabled (disabled by default)	3167	ev_epoll.c only when the epoll backend is enabled (disabled by default)
1958	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	3168	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
1959	ev_port.c only when the solaris port backend is enabled (disabled by default)	3169	ev_port.c only when the solaris port backend is enabled (disabled by default)
1960		3170
1961	F<ev.c> includes the backend files directly when enabled, so you only need	3171	F<ev.c> includes the backend files directly when enabled, so you only need
1962	to compile this single file.	3172	to compile this single file.
1963		3173
1964	=head3 LIBEVENT COMPATIBILITY API	3174	=head3 LIBEVENT COMPATIBILITY API
1965		3175
1966	To include the libevent compatibility API, also include:	3176	To include the libevent compatibility API, also include:
1967		3177
1968	#include "event.c"	3178	#include "event.c"
1969		3179
1970	in the file including F<ev.c>, and:	3180	in the file including F<ev.c>, and:
1971		3181
1972	#include "event.h"	3182	#include "event.h"
1973		3183
1974	in the files that want to use the libevent API. This also includes F<ev.h>.	3184	in the files that want to use the libevent API. This also includes F<ev.h>.
1975		3185
1976	You need the following additional files for this:	3186	You need the following additional files for this:
1977		3187
1978	event.h	3188	event.h
1979	event.c	3189	event.c
1980		3190
1981	=head3 AUTOCONF SUPPORT	3191	=head3 AUTOCONF SUPPORT
1982		3192
1983	Instead of using C<EV_STANDALONE=1> and providing your config in	3193	Instead of using C<EV_STANDALONE=1> and providing your configuration in
1984	whatever way you want, you can also C<m4_include([libev.m4])> in your	3194	whatever way you want, you can also C<m4_include([libev.m4])> in your
1985	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	3195	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
1986	include F<config.h> and configure itself accordingly.	3196	include F<config.h> and configure itself accordingly.
1987		3197
1988	For this of course you need the m4 file:	3198	For this of course you need the m4 file:
1989		3199
1990	libev.m4	3200	libev.m4
1991		3201
1992	=head2 PREPROCESSOR SYMBOLS/MACROS	3202	=head2 PREPROCESSOR SYMBOLS/MACROS
1993		3203
1994	Libev can be configured via a variety of preprocessor symbols you have to define	3204	Libev can be configured via a variety of preprocessor symbols you have to
1995	before including any of its files. The default is not to build for multiplicity	3205	define before including any of its files. The default in the absence of
1996	and only include the select backend.	3206	autoconf is documented for every option.
1997		3207
1998	=over 4	3208	=over 4
1999		3209
2000	=item EV_STANDALONE	3210	=item EV_STANDALONE
2001		3211
…		…
2003	keeps libev from including F<config.h>, and it also defines dummy	3213	keeps libev from including F<config.h>, and it also defines dummy
2004	implementations for some libevent functions (such as logging, which is not	3214	implementations for some libevent functions (such as logging, which is not
2005	supported). It will also not define any of the structs usually found in	3215	supported). It will also not define any of the structs usually found in
2006	F<event.h> that are not directly supported by the libev core alone.	3216	F<event.h> that are not directly supported by the libev core alone.
2007		3217
		3218	In stanbdalone mode, libev will still try to automatically deduce the
		3219	configuration, but has to be more conservative.
		3220
2008	=item EV_USE_MONOTONIC	3221	=item EV_USE_MONOTONIC
2009		3222
2010	If defined to be C<1>, libev will try to detect the availability of the	3223	If defined to be C<1>, libev will try to detect the availability of the
2011	monotonic clock option at both compiletime and runtime. Otherwise no use	3224	monotonic clock option at both compile time and runtime. Otherwise no
2012	of the monotonic clock option will be attempted. If you enable this, you	3225	use of the monotonic clock option will be attempted. If you enable this,
2013	usually have to link against librt or something similar. Enabling it when	3226	you usually have to link against librt or something similar. Enabling it
2014	the functionality isn't available is safe, though, althoguh you have	3227	when the functionality isn't available is safe, though, although you have
2015	to make sure you link against any libraries where the C<clock_gettime>	3228	to make sure you link against any libraries where the C<clock_gettime>
2016	function is hiding in (often F<-lrt>).	3229	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2017		3230
2018	=item EV_USE_REALTIME	3231	=item EV_USE_REALTIME
2019		3232
2020	If defined to be C<1>, libev will try to detect the availability of the	3233	If defined to be C<1>, libev will try to detect the availability of the
2021	realtime clock option at compiletime (and assume its availability at	3234	real-time clock option at compile time (and assume its availability
2022	runtime if successful). Otherwise no use of the realtime clock option will	3235	at runtime if successful). Otherwise no use of the real-time clock
2023	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3236	option will be attempted. This effectively replaces C<gettimeofday>
2024	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See tzhe note about libraries	3237	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2025	in the description of C<EV_USE_MONOTONIC>, though.	3238	correctness. See the note about libraries in the description of
		3239	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3240	C<EV_USE_CLOCK_SYSCALL>.
		3241
		3242	=item EV_USE_CLOCK_SYSCALL
		3243
		3244	If defined to be C<1>, libev will try to use a direct syscall instead
		3245	of calling the system-provided C<clock_gettime> function. This option
		3246	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3247	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3248	programs needlessly. Using a direct syscall is slightly slower (in
		3249	theory), because no optimised vdso implementation can be used, but avoids
		3250	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3251	higher, as it simplifies linking (no need for C<-lrt>).
		3252
		3253	=item EV_USE_NANOSLEEP
		3254
		3255	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		3256	and will use it for delays. Otherwise it will use C<select ()>.
		3257
		3258	=item EV_USE_EVENTFD
		3259
		3260	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3261	available and will probe for kernel support at runtime. This will improve
		3262	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3263	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3264	2.7 or newer, otherwise disabled.
2026		3265
2027	=item EV_USE_SELECT	3266	=item EV_USE_SELECT
2028		3267
2029	If undefined or defined to be C<1>, libev will compile in support for the	3268	If undefined or defined to be C<1>, libev will compile in support for the
2030	C<select>(2) backend. No attempt at autodetection will be done: if no	3269	C<select>(2) backend. No attempt at auto-detection will be done: if no
2031	other method takes over, select will be it. Otherwise the select backend	3270	other method takes over, select will be it. Otherwise the select backend
2032	will not be compiled in.	3271	will not be compiled in.
2033		3272
2034	=item EV_SELECT_USE_FD_SET	3273	=item EV_SELECT_USE_FD_SET
2035		3274
2036	If defined to C<1>, then the select backend will use the system C<fd_set>	3275	If defined to C<1>, then the select backend will use the system C<fd_set>
2037	structure. This is useful if libev doesn't compile due to a missing	3276	structure. This is useful if libev doesn't compile due to a missing
2038	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	3277	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2039	exotic systems. This usually limits the range of file descriptors to some	3278	on exotic systems. This usually limits the range of file descriptors to
2040	low limit such as 1024 or might have other limitations (winsocket only	3279	some low limit such as 1024 or might have other limitations (winsocket
2041	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3280	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2042	influence the size of the C<fd_set> used.	3281	configures the maximum size of the C<fd_set>.
2043		3282
2044	=item EV_SELECT_IS_WINSOCKET	3283	=item EV_SELECT_IS_WINSOCKET
2045		3284
2046	When defined to C<1>, the select backend will assume that	3285	When defined to C<1>, the select backend will assume that
2047	select/socket/connect etc. don't understand file descriptors but	3286	select/socket/connect etc. don't understand file descriptors but
…		…
2049	be used is the winsock select). This means that it will call	3288	be used is the winsock select). This means that it will call
2050	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3289	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2051	it is assumed that all these functions actually work on fds, even	3290	it is assumed that all these functions actually work on fds, even
2052	on win32. Should not be defined on non-win32 platforms.	3291	on win32. Should not be defined on non-win32 platforms.
2053		3292
		3293	=item EV_FD_TO_WIN32_HANDLE
		3294
		3295	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3296	file descriptors to socket handles. When not defining this symbol (the
		3297	default), then libev will call C<_get_osfhandle>, which is usually
		3298	correct. In some cases, programs use their own file descriptor management,
		3299	in which case they can provide this function to map fds to socket handles.
		3300
2054	=item EV_USE_POLL	3301	=item EV_USE_POLL
2055		3302
2056	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3303	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2057	backend. Otherwise it will be enabled on non-win32 platforms. It	3304	backend. Otherwise it will be enabled on non-win32 platforms. It
2058	takes precedence over select.	3305	takes precedence over select.
2059		3306
2060	=item EV_USE_EPOLL	3307	=item EV_USE_EPOLL
2061		3308
2062	If defined to be C<1>, libev will compile in support for the Linux	3309	If defined to be C<1>, libev will compile in support for the Linux
2063	C<epoll>(7) backend. Its availability will be detected at runtime,	3310	C<epoll>(7) backend. Its availability will be detected at runtime,
2064	otherwise another method will be used as fallback. This is the	3311	otherwise another method will be used as fallback. This is the preferred
2065	preferred backend for GNU/Linux systems.	3312	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3313	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2066		3314
2067	=item EV_USE_KQUEUE	3315	=item EV_USE_KQUEUE
2068		3316
2069	If defined to be C<1>, libev will compile in support for the BSD style	3317	If defined to be C<1>, libev will compile in support for the BSD style
2070	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	3318	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2083	otherwise another method will be used as fallback. This is the preferred	3331	otherwise another method will be used as fallback. This is the preferred
2084	backend for Solaris 10 systems.	3332	backend for Solaris 10 systems.
2085		3333
2086	=item EV_USE_DEVPOLL	3334	=item EV_USE_DEVPOLL
2087		3335
2088	reserved for future expansion, works like the USE symbols above.	3336	Reserved for future expansion, works like the USE symbols above.
2089		3337
2090	=item EV_USE_INOTIFY	3338	=item EV_USE_INOTIFY
2091		3339
2092	If defined to be C<1>, libev will compile in support for the Linux inotify	3340	If defined to be C<1>, libev will compile in support for the Linux inotify
2093	interface to speed up C<ev_stat> watchers. Its actual availability will	3341	interface to speed up C<ev_stat> watchers. Its actual availability will
2094	be detected at runtime.	3342	be detected at runtime. If undefined, it will be enabled if the headers
		3343	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3344
		3345	=item EV_ATOMIC_T
		3346
		3347	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3348	access is atomic with respect to other threads or signal contexts. No such
		3349	type is easily found in the C language, so you can provide your own type
		3350	that you know is safe for your purposes. It is used both for signal handler "locking"
		3351	as well as for signal and thread safety in C<ev_async> watchers.
		3352
		3353	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3354	(from F<signal.h>), which is usually good enough on most platforms.
2095		3355
2096	=item EV_H	3356	=item EV_H
2097		3357
2098	The name of the F<ev.h> header file used to include it. The default if	3358	The name of the F<ev.h> header file used to include it. The default if
2099	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This	3359	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2100	can be used to virtually rename the F<ev.h> header file in case of conflicts.	3360	used to virtually rename the F<ev.h> header file in case of conflicts.
2101		3361
2102	=item EV_CONFIG_H	3362	=item EV_CONFIG_H
2103		3363
2104	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	3364	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2105	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	3365	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2106	C<EV_H>, above.	3366	C<EV_H>, above.
2107		3367
2108	=item EV_EVENT_H	3368	=item EV_EVENT_H
2109		3369
2110	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	3370	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2111	of how the F<event.h> header can be found.	3371	of how the F<event.h> header can be found, the default is C<"event.h">.
2112		3372
2113	=item EV_PROTOTYPES	3373	=item EV_PROTOTYPES
2114		3374
2115	If defined to be C<0>, then F<ev.h> will not define any function	3375	If defined to be C<0>, then F<ev.h> will not define any function
2116	prototypes, but still define all the structs and other symbols. This is	3376	prototypes, but still define all the structs and other symbols. This is
…		…
2123	will have the C<struct ev_loop *> as first argument, and you can create	3383	will have the C<struct ev_loop *> as first argument, and you can create
2124	additional independent event loops. Otherwise there will be no support	3384	additional independent event loops. Otherwise there will be no support
2125	for multiple event loops and there is no first event loop pointer	3385	for multiple event loops and there is no first event loop pointer
2126	argument. Instead, all functions act on the single default loop.	3386	argument. Instead, all functions act on the single default loop.
2127		3387
		3388	=item EV_MINPRI
		3389
		3390	=item EV_MAXPRI
		3391
		3392	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		3393	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		3394	provide for more priorities by overriding those symbols (usually defined
		3395	to be C<-2> and C<2>, respectively).
		3396
		3397	When doing priority-based operations, libev usually has to linearly search
		3398	all the priorities, so having many of them (hundreds) uses a lot of space
		3399	and time, so using the defaults of five priorities (-2 .. +2) is usually
		3400	fine.
		3401
		3402	If your embedding application does not need any priorities, defining these
		3403	both to C<0> will save some memory and CPU.
		3404
2128	=item EV_PERIODIC_ENABLE	3405	=item EV_PERIODIC_ENABLE
2129		3406
2130	If undefined or defined to be C<1>, then periodic timers are supported. If	3407	If undefined or defined to be C<1>, then periodic timers are supported. If
2131	defined to be C<0>, then they are not. Disabling them saves a few kB of	3408	defined to be C<0>, then they are not. Disabling them saves a few kB of
2132	code.	3409	code.
…		…
2138	code.	3415	code.
2139		3416
2140	=item EV_EMBED_ENABLE	3417	=item EV_EMBED_ENABLE
2141		3418
2142	If undefined or defined to be C<1>, then embed watchers are supported. If	3419	If undefined or defined to be C<1>, then embed watchers are supported. If
2143	defined to be C<0>, then they are not.	3420	defined to be C<0>, then they are not. Embed watchers rely on most other
		3421	watcher types, which therefore must not be disabled.
2144		3422
2145	=item EV_STAT_ENABLE	3423	=item EV_STAT_ENABLE
2146		3424
2147	If undefined or defined to be C<1>, then stat watchers are supported. If	3425	If undefined or defined to be C<1>, then stat watchers are supported. If
2148	defined to be C<0>, then they are not.	3426	defined to be C<0>, then they are not.
…		…
2150	=item EV_FORK_ENABLE	3428	=item EV_FORK_ENABLE
2151		3429
2152	If undefined or defined to be C<1>, then fork watchers are supported. If	3430	If undefined or defined to be C<1>, then fork watchers are supported. If
2153	defined to be C<0>, then they are not.	3431	defined to be C<0>, then they are not.
2154		3432
		3433	=item EV_ASYNC_ENABLE
		3434
		3435	If undefined or defined to be C<1>, then async watchers are supported. If
		3436	defined to be C<0>, then they are not.
		3437
2155	=item EV_MINIMAL	3438	=item EV_MINIMAL
2156		3439
2157	If you need to shave off some kilobytes of code at the expense of some	3440	If you need to shave off some kilobytes of code at the expense of some
2158	speed, define this symbol to C<1>. Currently only used for gcc to override	3441	speed, define this symbol to C<1>. Currently this is used to override some
2159	some inlining decisions, saves roughly 30% codesize of amd64.	3442	inlining decisions, saves roughly 30% code size on amd64. It also selects a
		3443	much smaller 2-heap for timer management over the default 4-heap.
2160		3444
2161	=item EV_PID_HASHSIZE	3445	=item EV_PID_HASHSIZE
2162		3446
2163	C<ev_child> watchers use a small hash table to distribute workload by	3447	C<ev_child> watchers use a small hash table to distribute workload by
2164	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3448	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
2165	than enough. If you need to manage thousands of children you might want to	3449	than enough. If you need to manage thousands of children you might want to
2166	increase this value (I<must> be a power of two).	3450	increase this value (I<must> be a power of two).
2167		3451
2168	=item EV_INOTIFY_HASHSIZE	3452	=item EV_INOTIFY_HASHSIZE
2169		3453
2170	C<ev_staz> watchers use a small hash table to distribute workload by	3454	C<ev_stat> watchers use a small hash table to distribute workload by
2171	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	3455	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
2172	usually more than enough. If you need to manage thousands of C<ev_stat>	3456	usually more than enough. If you need to manage thousands of C<ev_stat>
2173	watchers you might want to increase this value (I<must> be a power of	3457	watchers you might want to increase this value (I<must> be a power of
2174	two).	3458	two).
2175		3459
		3460	=item EV_USE_4HEAP
		3461
		3462	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3463	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		3464	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		3465	faster performance with many (thousands) of watchers.
		3466
		3467	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3468	(disabled).
		3469
		3470	=item EV_HEAP_CACHE_AT
		3471
		3472	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3473	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		3474	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3475	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3476	but avoids random read accesses on heap changes. This improves performance
		3477	noticeably with many (hundreds) of watchers.
		3478
		3479	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3480	(disabled).
		3481
		3482	=item EV_VERIFY
		3483
		3484	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3485	be done: If set to C<0>, no internal verification code will be compiled
		3486	in. If set to C<1>, then verification code will be compiled in, but not
		3487	called. If set to C<2>, then the internal verification code will be
		3488	called once per loop, which can slow down libev. If set to C<3>, then the
		3489	verification code will be called very frequently, which will slow down
		3490	libev considerably.
		3491
		3492	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3493	C<0>.
		3494
2176	=item EV_COMMON	3495	=item EV_COMMON
2177		3496
2178	By default, all watchers have a C<void *data> member. By redefining	3497	By default, all watchers have a C<void *data> member. By redefining
2179	this macro to a something else you can include more and other types of	3498	this macro to a something else you can include more and other types of
2180	members. You have to define it each time you include one of the files,	3499	members. You have to define it each time you include one of the files,
2181	though, and it must be identical each time.	3500	though, and it must be identical each time.
2182		3501
2183	For example, the perl EV module uses something like this:	3502	For example, the perl EV module uses something like this:
2184		3503
2185	#define EV_COMMON \	3504	#define EV_COMMON \
2186	SV *self; /* contains this struct */ \	3505	SV *self; /* contains this struct */ \
2187	SV *cb_sv, *fh /* note no trailing ";" */	3506	SV *cb_sv, *fh /* note no trailing ";" */
2188		3507
2189	=item EV_CB_DECLARE (type)	3508	=item EV_CB_DECLARE (type)
2190		3509
2191	=item EV_CB_INVOKE (watcher, revents)	3510	=item EV_CB_INVOKE (watcher, revents)
2192		3511
2193	=item ev_set_cb (ev, cb)	3512	=item ev_set_cb (ev, cb)
2194		3513
2195	Can be used to change the callback member declaration in each watcher,	3514	Can be used to change the callback member declaration in each watcher,
2196	and the way callbacks are invoked and set. Must expand to a struct member	3515	and the way callbacks are invoked and set. Must expand to a struct member
2197	definition and a statement, respectively. See the F<ev.v> header file for	3516	definition and a statement, respectively. See the F<ev.h> header file for
2198	their default definitions. One possible use for overriding these is to	3517	their default definitions. One possible use for overriding these is to
2199	avoid the C<struct ev_loop *> as first argument in all cases, or to use	3518	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2200	method calls instead of plain function calls in C++.	3519	method calls instead of plain function calls in C++.
		3520
		3521	=back
		3522
		3523	=head2 EXPORTED API SYMBOLS
		3524
		3525	If you need to re-export the API (e.g. via a DLL) and you need a list of
		3526	exported symbols, you can use the provided F<Symbol.*> files which list
		3527	all public symbols, one per line:
		3528
		3529	Symbols.ev for libev proper
		3530	Symbols.event for the libevent emulation
		3531
		3532	This can also be used to rename all public symbols to avoid clashes with
		3533	multiple versions of libev linked together (which is obviously bad in
		3534	itself, but sometimes it is inconvenient to avoid this).
		3535
		3536	A sed command like this will create wrapper C<#define>'s that you need to
		3537	include before including F<ev.h>:
		3538
		3539	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		3540
		3541	This would create a file F<wrap.h> which essentially looks like this:
		3542
		3543	#define ev_backend myprefix_ev_backend
		3544	#define ev_check_start myprefix_ev_check_start
		3545	#define ev_check_stop myprefix_ev_check_stop
		3546	...
2201		3547
2202	=head2 EXAMPLES	3548	=head2 EXAMPLES
2203		3549
2204	For a real-world example of a program the includes libev	3550	For a real-world example of a program the includes libev
2205	verbatim, you can have a look at the EV perl module	3551	verbatim, you can have a look at the EV perl module
…		…
2210	file.	3556	file.
2211		3557
2212	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	3558	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2213	that everybody includes and which overrides some configure choices:	3559	that everybody includes and which overrides some configure choices:
2214		3560
2215	#define EV_MINIMAL 1	3561	#define EV_MINIMAL 1
2216	#define EV_USE_POLL 0	3562	#define EV_USE_POLL 0
2217	#define EV_MULTIPLICITY 0	3563	#define EV_MULTIPLICITY 0
2218	#define EV_PERIODIC_ENABLE 0	3564	#define EV_PERIODIC_ENABLE 0
2219	#define EV_STAT_ENABLE 0	3565	#define EV_STAT_ENABLE 0
2220	#define EV_FORK_ENABLE 0	3566	#define EV_FORK_ENABLE 0
2221	#define EV_CONFIG_H <config.h>	3567	#define EV_CONFIG_H <config.h>
2222	#define EV_MINPRI 0	3568	#define EV_MINPRI 0
2223	#define EV_MAXPRI 0	3569	#define EV_MAXPRI 0
2224		3570
2225	#include "ev++.h"	3571	#include "ev++.h"
2226		3572
2227	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	3573	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2228		3574
2229	#include "ev_cpp.h"	3575	#include "ev_cpp.h"
2230	#include "ev.c"	3576	#include "ev.c"
2231		3577
		3578	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
2232		3579
		3580	=head2 THREADS AND COROUTINES
		3581
		3582	=head3 THREADS
		3583
		3584	All libev functions are reentrant and thread-safe unless explicitly
		3585	documented otherwise, but libev implements no locking itself. This means
		3586	that you can use as many loops as you want in parallel, as long as there
		3587	are no concurrent calls into any libev function with the same loop
		3588	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		3589	of course): libev guarantees that different event loops share no data
		3590	structures that need any locking.
		3591
		3592	Or to put it differently: calls with different loop parameters can be done
		3593	concurrently from multiple threads, calls with the same loop parameter
		3594	must be done serially (but can be done from different threads, as long as
		3595	only one thread ever is inside a call at any point in time, e.g. by using
		3596	a mutex per loop).
		3597
		3598	Specifically to support threads (and signal handlers), libev implements
		3599	so-called C<ev_async> watchers, which allow some limited form of
		3600	concurrency on the same event loop, namely waking it up "from the
		3601	outside".
		3602
		3603	If you want to know which design (one loop, locking, or multiple loops
		3604	without or something else still) is best for your problem, then I cannot
		3605	help you, but here is some generic advice:
		3606
		3607	=over 4
		3608
		3609	=item * most applications have a main thread: use the default libev loop
		3610	in that thread, or create a separate thread running only the default loop.
		3611
		3612	This helps integrating other libraries or software modules that use libev
		3613	themselves and don't care/know about threading.
		3614
		3615	=item * one loop per thread is usually a good model.
		3616
		3617	Doing this is almost never wrong, sometimes a better-performance model
		3618	exists, but it is always a good start.
		3619
		3620	=item * other models exist, such as the leader/follower pattern, where one
		3621	loop is handed through multiple threads in a kind of round-robin fashion.
		3622
		3623	Choosing a model is hard - look around, learn, know that usually you can do
		3624	better than you currently do :-)
		3625
		3626	=item * often you need to talk to some other thread which blocks in the
		3627	event loop.
		3628
		3629	C<ev_async> watchers can be used to wake them up from other threads safely
		3630	(or from signal contexts...).
		3631
		3632	An example use would be to communicate signals or other events that only
		3633	work in the default loop by registering the signal watcher with the
		3634	default loop and triggering an C<ev_async> watcher from the default loop
		3635	watcher callback into the event loop interested in the signal.
		3636
		3637	=back
		3638
		3639	=head3 COROUTINES
		3640
		3641	Libev is very accommodating to coroutines ("cooperative threads"):
		3642	libev fully supports nesting calls to its functions from different
		3643	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3644	different coroutines, and switch freely between both coroutines running the
		3645	loop, as long as you don't confuse yourself). The only exception is that
		3646	you must not do this from C<ev_periodic> reschedule callbacks.
		3647
		3648	Care has been taken to ensure that libev does not keep local state inside
		3649	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		3650	they do not call any callbacks.
		3651
		3652	=head2 COMPILER WARNINGS
		3653
		3654	Depending on your compiler and compiler settings, you might get no or a
		3655	lot of warnings when compiling libev code. Some people are apparently
		3656	scared by this.
		3657
		3658	However, these are unavoidable for many reasons. For one, each compiler
		3659	has different warnings, and each user has different tastes regarding
		3660	warning options. "Warn-free" code therefore cannot be a goal except when
		3661	targeting a specific compiler and compiler-version.
		3662
		3663	Another reason is that some compiler warnings require elaborate
		3664	workarounds, or other changes to the code that make it less clear and less
		3665	maintainable.
		3666
		3667	And of course, some compiler warnings are just plain stupid, or simply
		3668	wrong (because they don't actually warn about the condition their message
		3669	seems to warn about). For example, certain older gcc versions had some
		3670	warnings that resulted an extreme number of false positives. These have
		3671	been fixed, but some people still insist on making code warn-free with
		3672	such buggy versions.
		3673
		3674	While libev is written to generate as few warnings as possible,
		3675	"warn-free" code is not a goal, and it is recommended not to build libev
		3676	with any compiler warnings enabled unless you are prepared to cope with
		3677	them (e.g. by ignoring them). Remember that warnings are just that:
		3678	warnings, not errors, or proof of bugs.
		3679
		3680
		3681	=head2 VALGRIND
		3682
		3683	Valgrind has a special section here because it is a popular tool that is
		3684	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		3685
		3686	If you think you found a bug (memory leak, uninitialised data access etc.)
		3687	in libev, then check twice: If valgrind reports something like:
		3688
		3689	==2274== definitely lost: 0 bytes in 0 blocks.
		3690	==2274== possibly lost: 0 bytes in 0 blocks.
		3691	==2274== still reachable: 256 bytes in 1 blocks.
		3692
		3693	Then there is no memory leak, just as memory accounted to global variables
		3694	is not a memleak - the memory is still being referenced, and didn't leak.
		3695
		3696	Similarly, under some circumstances, valgrind might report kernel bugs
		3697	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		3698	although an acceptable workaround has been found here), or it might be
		3699	confused.
		3700
		3701	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		3702	make it into some kind of religion.
		3703
		3704	If you are unsure about something, feel free to contact the mailing list
		3705	with the full valgrind report and an explanation on why you think this
		3706	is a bug in libev (best check the archives, too :). However, don't be
		3707	annoyed when you get a brisk "this is no bug" answer and take the chance
		3708	of learning how to interpret valgrind properly.
		3709
		3710	If you need, for some reason, empty reports from valgrind for your project
		3711	I suggest using suppression lists.
		3712
		3713
		3714	=head1 PORTABILITY NOTES
		3715
		3716	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		3717
		3718	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		3719	requires, and its I/O model is fundamentally incompatible with the POSIX
		3720	model. Libev still offers limited functionality on this platform in
		3721	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		3722	descriptors. This only applies when using Win32 natively, not when using
		3723	e.g. cygwin.
		3724
		3725	Lifting these limitations would basically require the full
		3726	re-implementation of the I/O system. If you are into these kinds of
		3727	things, then note that glib does exactly that for you in a very portable
		3728	way (note also that glib is the slowest event library known to man).
		3729
		3730	There is no supported compilation method available on windows except
		3731	embedding it into other applications.
		3732
		3733	Not a libev limitation but worth mentioning: windows apparently doesn't
		3734	accept large writes: instead of resulting in a partial write, windows will
		3735	either accept everything or return C<ENOBUFS> if the buffer is too large,
		3736	so make sure you only write small amounts into your sockets (less than a
		3737	megabyte seems safe, but this apparently depends on the amount of memory
		3738	available).
		3739
		3740	Due to the many, low, and arbitrary limits on the win32 platform and
		3741	the abysmal performance of winsockets, using a large number of sockets
		3742	is not recommended (and not reasonable). If your program needs to use
		3743	more than a hundred or so sockets, then likely it needs to use a totally
		3744	different implementation for windows, as libev offers the POSIX readiness
		3745	notification model, which cannot be implemented efficiently on windows
		3746	(Microsoft monopoly games).
		3747
		3748	A typical way to use libev under windows is to embed it (see the embedding
		3749	section for details) and use the following F<evwrap.h> header file instead
		3750	of F<ev.h>:
		3751
		3752	#define EV_STANDALONE /* keeps ev from requiring config.h */
		3753	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		3754
		3755	#include "ev.h"
		3756
		3757	And compile the following F<evwrap.c> file into your project (make sure
		3758	you do I<not> compile the F<ev.c> or any other embedded source files!):
		3759
		3760	#include "evwrap.h"
		3761	#include "ev.c"
		3762
		3763	=over 4
		3764
		3765	=item The winsocket select function
		3766
		3767	The winsocket C<select> function doesn't follow POSIX in that it
		3768	requires socket I<handles> and not socket I<file descriptors> (it is
		3769	also extremely buggy). This makes select very inefficient, and also
		3770	requires a mapping from file descriptors to socket handles (the Microsoft
		3771	C runtime provides the function C<_open_osfhandle> for this). See the
		3772	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		3773	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		3774
		3775	The configuration for a "naked" win32 using the Microsoft runtime
		3776	libraries and raw winsocket select is:
		3777
		3778	#define EV_USE_SELECT 1
		3779	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		3780
		3781	Note that winsockets handling of fd sets is O(n), so you can easily get a
		3782	complexity in the O(n²) range when using win32.
		3783
		3784	=item Limited number of file descriptors
		3785
		3786	Windows has numerous arbitrary (and low) limits on things.
		3787
		3788	Early versions of winsocket's select only supported waiting for a maximum
		3789	of C<64> handles (probably owning to the fact that all windows kernels
		3790	can only wait for C<64> things at the same time internally; Microsoft
		3791	recommends spawning a chain of threads and wait for 63 handles and the
		3792	previous thread in each. Great).
		3793
		3794	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		3795	to some high number (e.g. C<2048>) before compiling the winsocket select
		3796	call (which might be in libev or elsewhere, for example, perl does its own
		3797	select emulation on windows).
		3798
		3799	Another limit is the number of file descriptors in the Microsoft runtime
		3800	libraries, which by default is C<64> (there must be a hidden I<64> fetish
		3801	or something like this inside Microsoft). You can increase this by calling
		3802	C<_setmaxstdio>, which can increase this limit to C<2048> (another
		3803	arbitrary limit), but is broken in many versions of the Microsoft runtime
		3804	libraries.
		3805
		3806	This might get you to about C<512> or C<2048> sockets (depending on
		3807	windows version and/or the phase of the moon). To get more, you need to
		3808	wrap all I/O functions and provide your own fd management, but the cost of
		3809	calling select (O(n²)) will likely make this unworkable.
		3810
		3811	=back
		3812
		3813	=head2 PORTABILITY REQUIREMENTS
		3814
		3815	In addition to a working ISO-C implementation and of course the
		3816	backend-specific APIs, libev relies on a few additional extensions:
		3817
		3818	=over 4
		3819
		3820	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		3821	calling conventions regardless of C<ev_watcher_type *>.
		3822
		3823	Libev assumes not only that all watcher pointers have the same internal
		3824	structure (guaranteed by POSIX but not by ISO C for example), but it also
		3825	assumes that the same (machine) code can be used to call any watcher
		3826	callback: The watcher callbacks have different type signatures, but libev
		3827	calls them using an C<ev_watcher *> internally.
		3828
		3829	=item C<sig_atomic_t volatile> must be thread-atomic as well
		3830
		3831	The type C<sig_atomic_t volatile> (or whatever is defined as
		3832	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		3833	threads. This is not part of the specification for C<sig_atomic_t>, but is
		3834	believed to be sufficiently portable.
		3835
		3836	=item C<sigprocmask> must work in a threaded environment
		3837
		3838	Libev uses C<sigprocmask> to temporarily block signals. This is not
		3839	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		3840	pthread implementations will either allow C<sigprocmask> in the "main
		3841	thread" or will block signals process-wide, both behaviours would
		3842	be compatible with libev. Interaction between C<sigprocmask> and
		3843	C<pthread_sigmask> could complicate things, however.
		3844
		3845	The most portable way to handle signals is to block signals in all threads
		3846	except the initial one, and run the default loop in the initial thread as
		3847	well.
		3848
		3849	=item C<long> must be large enough for common memory allocation sizes
		3850
		3851	To improve portability and simplify its API, libev uses C<long> internally
		3852	instead of C<size_t> when allocating its data structures. On non-POSIX
		3853	systems (Microsoft...) this might be unexpectedly low, but is still at
		3854	least 31 bits everywhere, which is enough for hundreds of millions of
		3855	watchers.
		3856
		3857	=item C<double> must hold a time value in seconds with enough accuracy
		3858
		3859	The type C<double> is used to represent timestamps. It is required to
		3860	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		3861	enough for at least into the year 4000. This requirement is fulfilled by
		3862	implementations implementing IEEE 754 (basically all existing ones).
		3863
		3864	=back
		3865
		3866	If you know of other additional requirements drop me a note.
		3867
		3868
2233	=head1 COMPLEXITIES	3869	=head1 ALGORITHMIC COMPLEXITIES
2234		3870
2235	In this section the complexities of (many of) the algorithms used inside	3871	In this section the complexities of (many of) the algorithms used inside
2236	libev will be explained. For complexity discussions about backends see the	3872	libev will be documented. For complexity discussions about backends see
2237	documentation for C<ev_default_init>.	3873	the documentation for C<ev_default_init>.
		3874
		3875	All of the following are about amortised time: If an array needs to be
		3876	extended, libev needs to realloc and move the whole array, but this
		3877	happens asymptotically rarer with higher number of elements, so O(1) might
		3878	mean that libev does a lengthy realloc operation in rare cases, but on
		3879	average it is much faster and asymptotically approaches constant time.
2238		3880
2239	=over 4	3881	=over 4
2240		3882
2241	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	3883	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2242		3884
		3885	This means that, when you have a watcher that triggers in one hour and
		3886	there are 100 watchers that would trigger before that, then inserting will
		3887	have to skip roughly seven (C<ld 100>) of these watchers.
		3888
2243	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	3889	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2244		3890
		3891	That means that changing a timer costs less than removing/adding them,
		3892	as only the relative motion in the event queue has to be paid for.
		3893
2245	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	3894	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
2246		3895
		3896	These just add the watcher into an array or at the head of a list.
		3897
2247	=item Stopping check/prepare/idle watchers: O(1)	3898	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2248		3899
2249	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	3900	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2250		3901
		3902	These watchers are stored in lists, so they need to be walked to find the
		3903	correct watcher to remove. The lists are usually short (you don't usually
		3904	have many watchers waiting for the same fd or signal: one is typical, two
		3905	is rare).
		3906
2251	=item Finding the next timer per loop iteration: O(1)	3907	=item Finding the next timer in each loop iteration: O(1)
		3908
		3909	By virtue of using a binary or 4-heap, the next timer is always found at a
		3910	fixed position in the storage array.
2252		3911
2253	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	3912	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2254		3913
2255	=item Activating one watcher: O(1)	3914	A change means an I/O watcher gets started or stopped, which requires
		3915	libev to recalculate its status (and possibly tell the kernel, depending
		3916	on backend and whether C<ev_io_set> was used).
		3917
		3918	=item Activating one watcher (putting it into the pending state): O(1)
		3919
		3920	=item Priority handling: O(number_of_priorities)
		3921
		3922	Priorities are implemented by allocating some space for each
		3923	priority. When doing priority-based operations, libev usually has to
		3924	linearly search all the priorities, but starting/stopping and activating
		3925	watchers becomes O(1) with respect to priority handling.
		3926
		3927	=item Sending an ev_async: O(1)
		3928
		3929	=item Processing ev_async_send: O(number_of_async_watchers)
		3930
		3931	=item Processing signals: O(max_signal_number)
		3932
		3933	Sending involves a system call I<iff> there were no other C<ev_async_send>
		3934	calls in the current loop iteration. Checking for async and signal events
		3935	involves iterating over all running async watchers or all signal numbers.
2256		3936
2257	=back	3937	=back
2258		3938
2259		3939
2260	=head1 AUTHOR	3940	=head1 AUTHOR
2261		3941
2262	Marc Lehmann <libev@schmorp.de>.	3942	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
2263		3943

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