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Revision 1.40 by root, Sat Nov 24 10:15:16 2007 UTC vs.
Revision 1.216 by root, Thu Nov 13 15:55:38 2008 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
		9	=head2 EXAMPLE PROGRAM
		10
		11	// a single header file is required
		12	#include <ev.h>
		13
		14	// every watcher type has its own typedef'd struct
		15	// with the name ev_TYPE
		16	ev_io stdin_watcher;
		17	ev_timer timeout_watcher;
		18
		19	// all watcher callbacks have a similar signature
		20	// this callback is called when data is readable on stdin
		21	static void
		22	stdin_cb (EV_P_ ev_io *w, int revents)
		23	{
		24	puts ("stdin ready");
		25	// for one-shot events, one must manually stop the watcher
		26	// with its corresponding stop function.
		27	ev_io_stop (EV_A_ w);
		28
		29	// this causes all nested ev_loop's to stop iterating
		30	ev_unloop (EV_A_ EVUNLOOP_ALL);
		31	}
		32
		33	// another callback, this time for a time-out
		34	static void
		35	timeout_cb (EV_P_ ev_timer *w, int revents)
		36	{
		37	puts ("timeout");
		38	// this causes the innermost ev_loop to stop iterating
		39	ev_unloop (EV_A_ EVUNLOOP_ONE);
		40	}
		41
		42	int
		43	main (void)
		44	{
		45	// use the default event loop unless you have special needs
		46	ev_loop *loop = ev_default_loop (0);
		47
		48	// initialise an io watcher, then start it
		49	// this one will watch for stdin to become readable
		50	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
		51	ev_io_start (loop, &stdin_watcher);
		52
		53	// initialise a timer watcher, then start it
		54	// simple non-repeating 5.5 second timeout
		55	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		56	ev_timer_start (loop, &timeout_watcher);
		57
		58	// now wait for events to arrive
		59	ev_loop (loop, 0);
		60
		61	// unloop was called, so exit
		62	return 0;
		63	}
8		64
9	=head1 DESCRIPTION	65	=head1 DESCRIPTION
10		66
		67	The newest version of this document is also available as an html-formatted
		68	web page you might find easier to navigate when reading it for the first
		69	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		70
11	Libev is an event loop: you register interest in certain events (such as a	71	Libev is an event loop: you register interest in certain events (such as a
12	file descriptor being readable or a timeout occuring), and it will manage	72	file descriptor being readable or a timeout occurring), and it will manage
13	these event sources and provide your program with events.	73	these event sources and provide your program with events.
14		74
15	To do this, it must take more or less complete control over your process	75	To do this, it must take more or less complete control over your process
16	(or thread) by executing the I<event loop> handler, and will then	76	(or thread) by executing the I<event loop> handler, and will then
17	communicate events via a callback mechanism.	77	communicate events via a callback mechanism.
…		…
19	You register interest in certain events by registering so-called I<event	79	You register interest in certain events by registering so-called I<event
20	watchers>, which are relatively small C structures you initialise with the	80	watchers>, which are relatively small C structures you initialise with the
21	details of the event, and then hand it over to libev by I<starting> the	81	details of the event, and then hand it over to libev by I<starting> the
22	watcher.	82	watcher.
23		83
24	=head1 FEATURES	84	=head2 FEATURES
25		85
26	Libev supports select, poll, the linux-specific epoll and the bsd-specific	86	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
27	kqueue mechanisms for file descriptor events, relative timers, absolute	87	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
28	timers with customised rescheduling, signal events, process status change	88	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
29	events (related to SIGCHLD), and event watchers dealing with the event	89	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
30	loop mechanism itself (idle, prepare and check watchers). It also is quite	90	with customised rescheduling (C<ev_periodic>), synchronous signals
		91	(C<ev_signal>), process status change events (C<ev_child>), and event
		92	watchers dealing with the event loop mechanism itself (C<ev_idle>,
		93	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as
		94	file watchers (C<ev_stat>) and even limited support for fork events
		95	(C<ev_fork>).
		96
		97	It also is quite fast (see this
31	fast (see this L<benchmark|http://libev.schmorp.de/bench.html> comparing	98	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
32	it to libevent for example).	99	for example).
33		100
34	=head1 CONVENTIONS	101	=head2 CONVENTIONS
35		102
36	Libev is very configurable. In this manual the default configuration	103	Libev is very configurable. In this manual the default (and most common)
37	will be described, which supports multiple event loops. For more info	104	configuration will be described, which supports multiple event loops. For
38	about various configuration options please have a look at the file	105	more info about various configuration options please have a look at
39	F<README.embed> in the libev distribution. If libev was configured without	106	B<EMBED> section in this manual. If libev was configured without support
40	support for multiple event loops, then all functions taking an initial	107	for multiple event loops, then all functions taking an initial argument of
41	argument of name C<loop> (which is always of type C<struct ev_loop *>)	108	name C<loop> (which is always of type C<ev_loop *>) will not have
42	will not have this argument.	109	this argument.
43		110
44	=head1 TIME REPRESENTATION	111	=head2 TIME REPRESENTATION
45		112
46	Libev represents time as a single floating point number, representing the	113	Libev represents time as a single floating point number, representing the
47	(fractional) number of seconds since the (POSIX) epoch (somewhere near	114	(fractional) number of seconds since the (POSIX) epoch (somewhere near
48	the beginning of 1970, details are complicated, don't ask). This type is	115	the beginning of 1970, details are complicated, don't ask). This type is
49	called C<ev_tstamp>, which is what you should use too. It usually aliases	116	called C<ev_tstamp>, which is what you should use too. It usually aliases
50	to the C<double> type in C, and when you need to do any calculations on	117	to the C<double> type in C, and when you need to do any calculations on
51	it, you should treat it as such.	118	it, you should treat it as some floating point value. Unlike the name
		119	component C<stamp> might indicate, it is also used for time differences
		120	throughout libev.
		121
		122	=head1 ERROR HANDLING
		123
		124	Libev knows three classes of errors: operating system errors, usage errors
		125	and internal errors (bugs).
		126
		127	When libev catches an operating system error it cannot handle (for example
		128	a system call indicating a condition libev cannot fix), it calls the callback
		129	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		130	abort. The default is to print a diagnostic message and to call C<abort
		131	()>.
		132
		133	When libev detects a usage error such as a negative timer interval, then
		134	it will print a diagnostic message and abort (via the C<assert> mechanism,
		135	so C<NDEBUG> will disable this checking): these are programming errors in
		136	the libev caller and need to be fixed there.
		137
		138	Libev also has a few internal error-checking C<assert>ions, and also has
		139	extensive consistency checking code. These do not trigger under normal
		140	circumstances, as they indicate either a bug in libev or worse.
52		141
53		142
54	=head1 GLOBAL FUNCTIONS	143	=head1 GLOBAL FUNCTIONS
55		144
56	These functions can be called anytime, even before initialising the	145	These functions can be called anytime, even before initialising the
…		…
62		151
63	Returns the current time as libev would use it. Please note that the	152	Returns the current time as libev would use it. Please note that the
64	C<ev_now> function is usually faster and also often returns the timestamp	153	C<ev_now> function is usually faster and also often returns the timestamp
65	you actually want to know.	154	you actually want to know.
66		155
		156	=item ev_sleep (ev_tstamp interval)
		157
		158	Sleep for the given interval: The current thread will be blocked until
		159	either it is interrupted or the given time interval has passed. Basically
		160	this is a sub-second-resolution C<sleep ()>.
		161
67	=item int ev_version_major ()	162	=item int ev_version_major ()
68		163
69	=item int ev_version_minor ()	164	=item int ev_version_minor ()
70		165
71	You can find out the major and minor version numbers of the library	166	You can find out the major and minor ABI version numbers of the library
72	you linked against by calling the functions C<ev_version_major> and	167	you linked against by calling the functions C<ev_version_major> and
73	C<ev_version_minor>. If you want, you can compare against the global	168	C<ev_version_minor>. If you want, you can compare against the global
74	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the	169	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
75	version of the library your program was compiled against.	170	version of the library your program was compiled against.
76		171
		172	These version numbers refer to the ABI version of the library, not the
		173	release version.
		174
77	Usually, it's a good idea to terminate if the major versions mismatch,	175	Usually, it's a good idea to terminate if the major versions mismatch,
78	as this indicates an incompatible change. Minor versions are usually	176	as this indicates an incompatible change. Minor versions are usually
79	compatible to older versions, so a larger minor version alone is usually	177	compatible to older versions, so a larger minor version alone is usually
80	not a problem.	178	not a problem.
81		179
82	Example: make sure we haven't accidentally been linked against the wrong	180	Example: Make sure we haven't accidentally been linked against the wrong
83	version:	181	version.
84		182
85	assert (("libev version mismatch",	183	assert (("libev version mismatch",
86	ev_version_major () == EV_VERSION_MAJOR	184	ev_version_major () == EV_VERSION_MAJOR
87	&& ev_version_minor () >= EV_VERSION_MINOR));	185	&& ev_version_minor () >= EV_VERSION_MINOR));
88		186
89	=item unsigned int ev_supported_backends ()	187	=item unsigned int ev_supported_backends ()
90		188
91	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	189	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
92	value) compiled into this binary of libev (independent of their	190	value) compiled into this binary of libev (independent of their
…		…
94	a description of the set values.	192	a description of the set values.
95		193
96	Example: make sure we have the epoll method, because yeah this is cool and	194	Example: make sure we have the epoll method, because yeah this is cool and
97	a must have and can we have a torrent of it please!!!11	195	a must have and can we have a torrent of it please!!!11
98		196
99	assert (("sorry, no epoll, no sex",	197	assert (("sorry, no epoll, no sex",
100	ev_supported_backends () & EVBACKEND_EPOLL));	198	ev_supported_backends () & EVBACKEND_EPOLL));
101		199
102	=item unsigned int ev_recommended_backends ()	200	=item unsigned int ev_recommended_backends ()
103		201
104	Return the set of all backends compiled into this binary of libev and also	202	Return the set of all backends compiled into this binary of libev and also
105	recommended for this platform. This set is often smaller than the one	203	recommended for this platform. This set is often smaller than the one
106	returned by C<ev_supported_backends>, as for example kqueue is broken on	204	returned by C<ev_supported_backends>, as for example kqueue is broken on
107	most BSDs and will not be autodetected unless you explicitly request it	205	most BSDs and will not be auto-detected unless you explicitly request it
108	(assuming you know what you are doing). This is the set of backends that	206	(assuming you know what you are doing). This is the set of backends that
109	libev will probe for if you specify no backends explicitly.	207	libev will probe for if you specify no backends explicitly.
110		208
111	=item unsigned int ev_embeddable_backends ()	209	=item unsigned int ev_embeddable_backends ()
112		210
…		…
116	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	214	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
117	recommended ones.	215	recommended ones.
118		216
119	See the description of C<ev_embed> watchers for more info.	217	See the description of C<ev_embed> watchers for more info.
120		218
121	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	219	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
122		220
123	Sets the allocation function to use (the prototype is similar to the	221	Sets the allocation function to use (the prototype is similar - the
124	realloc C function, the semantics are identical). It is used to allocate	222	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
125	and free memory (no surprises here). If it returns zero when memory	223	used to allocate and free memory (no surprises here). If it returns zero
126	needs to be allocated, the library might abort or take some potentially	224	when memory needs to be allocated (C<size != 0>), the library might abort
127	destructive action. The default is your system realloc function.	225	or take some potentially destructive action.
		226
		227	Since some systems (at least OpenBSD and Darwin) fail to implement
		228	correct C<realloc> semantics, libev will use a wrapper around the system
		229	C<realloc> and C<free> functions by default.
128		230
129	You could override this function in high-availability programs to, say,	231	You could override this function in high-availability programs to, say,
130	free some memory if it cannot allocate memory, to use a special allocator,	232	free some memory if it cannot allocate memory, to use a special allocator,
131	or even to sleep a while and retry until some memory is available.	233	or even to sleep a while and retry until some memory is available.
132		234
133	Example: replace the libev allocator with one that waits a bit and then	235	Example: Replace the libev allocator with one that waits a bit and then
134	retries: better than mine).	236	retries (example requires a standards-compliant C<realloc>).
135		237
136	static void *	238	static void *
137	persistent_realloc (void *ptr, long size)	239	persistent_realloc (void *ptr, size_t size)
138	{	240	{
139	for (;;)	241	for (;;)
140	{	242	{
141	void *newptr = realloc (ptr, size);	243	void *newptr = realloc (ptr, size);
142		244
…		…
148	}	250	}
149		251
150	...	252	...
151	ev_set_allocator (persistent_realloc);	253	ev_set_allocator (persistent_realloc);
152		254
153	=item ev_set_syserr_cb (void (*cb)(const char *msg));	255	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
154		256
155	Set the callback function to call on a retryable syscall error (such	257	Set the callback function to call on a retryable system call error (such
156	as failed select, poll, epoll_wait). The message is a printable string	258	as failed select, poll, epoll_wait). The message is a printable string
157	indicating the system call or subsystem causing the problem. If this	259	indicating the system call or subsystem causing the problem. If this
158	callback is set, then libev will expect it to remedy the sitution, no	260	callback is set, then libev will expect it to remedy the situation, no
159	matter what, when it returns. That is, libev will generally retry the	261	matter what, when it returns. That is, libev will generally retry the
160	requested operation, or, if the condition doesn't go away, do bad stuff	262	requested operation, or, if the condition doesn't go away, do bad stuff
161	(such as abort).	263	(such as abort).
162		264
163	Example: do the same thing as libev does internally:	265	Example: This is basically the same thing that libev does internally, too.
164		266
165	static void	267	static void
166	fatal_error (const char *msg)	268	fatal_error (const char *msg)
167	{	269	{
168	perror (msg);	270	perror (msg);
…		…
174		276
175	=back	277	=back
176		278
177	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	279	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
178		280
179	An event loop is described by a C<struct ev_loop *>. The library knows two	281	An event loop is described by a C<struct ev_loop *> (the C<struct>
180	types of such loops, the I<default> loop, which supports signals and child	282	is I<not> optional in this case, as there is also an C<ev_loop>
181	events, and dynamically created loops which do not.	283	I<function>).
182		284
183	If you use threads, a common model is to run the default event loop	285	The library knows two types of such loops, the I<default> loop, which
184	in your main thread (or in a separate thread) and for each thread you	286	supports signals and child events, and dynamically created loops which do
185	create, you also create another event loop. Libev itself does no locking	287	not.
186	whatsoever, so if you mix calls to the same event loop in different
187	threads, make sure you lock (this is usually a bad idea, though, even if
188	done correctly, because it's hideous and inefficient).
189		288
190	=over 4	289	=over 4
191		290
192	=item struct ev_loop *ev_default_loop (unsigned int flags)	291	=item struct ev_loop *ev_default_loop (unsigned int flags)
193		292
…		…
197	flags. If that is troubling you, check C<ev_backend ()> afterwards).	296	flags. If that is troubling you, check C<ev_backend ()> afterwards).
198		297
199	If you don't know what event loop to use, use the one returned from this	298	If you don't know what event loop to use, use the one returned from this
200	function.	299	function.
201		300
		301	Note that this function is I<not> thread-safe, so if you want to use it
		302	from multiple threads, you have to lock (note also that this is unlikely,
		303	as loops cannot be shared easily between threads anyway).
		304
		305	The default loop is the only loop that can handle C<ev_signal> and
		306	C<ev_child> watchers, and to do this, it always registers a handler
		307	for C<SIGCHLD>. If this is a problem for your application you can either
		308	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
		309	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
		310	C<ev_default_init>.
		311
202	The flags argument can be used to specify special behaviour or specific	312	The flags argument can be used to specify special behaviour or specific
203	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	313	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
204		314
205	The following flags are supported:	315	The following flags are supported:
206		316
…		…
211	The default flags value. Use this if you have no clue (it's the right	321	The default flags value. Use this if you have no clue (it's the right
212	thing, believe me).	322	thing, believe me).
213		323
214	=item C<EVFLAG_NOENV>	324	=item C<EVFLAG_NOENV>
215		325
216	If this flag bit is ored into the flag value (or the program runs setuid	326	If this flag bit is or'ed into the flag value (or the program runs setuid
217	or setgid) then libev will I<not> look at the environment variable	327	or setgid) then libev will I<not> look at the environment variable
218	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	328	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
219	override the flags completely if it is found in the environment. This is	329	override the flags completely if it is found in the environment. This is
220	useful to try out specific backends to test their performance, or to work	330	useful to try out specific backends to test their performance, or to work
221	around bugs.	331	around bugs.
222		332
		333	=item C<EVFLAG_FORKCHECK>
		334
		335	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after
		336	a fork, you can also make libev check for a fork in each iteration by
		337	enabling this flag.
		338
		339	This works by calling C<getpid ()> on every iteration of the loop,
		340	and thus this might slow down your event loop if you do a lot of loop
		341	iterations and little real work, but is usually not noticeable (on my
		342	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
		343	without a system call and thus I<very> fast, but my GNU/Linux system also has
		344	C<pthread_atfork> which is even faster).
		345
		346	The big advantage of this flag is that you can forget about fork (and
		347	forget about forgetting to tell libev about forking) when you use this
		348	flag.
		349
		350	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
		351	environment variable.
		352
223	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	353	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
224		354
225	This is your standard select(2) backend. Not I<completely> standard, as	355	This is your standard select(2) backend. Not I<completely> standard, as
226	libev tries to roll its own fd_set with no limits on the number of fds,	356	libev tries to roll its own fd_set with no limits on the number of fds,
227	but if that fails, expect a fairly low limit on the number of fds when	357	but if that fails, expect a fairly low limit on the number of fds when
228	using this backend. It doesn't scale too well (O(highest_fd)), but its usually	358	using this backend. It doesn't scale too well (O(highest_fd)), but its
229	the fastest backend for a low number of fds.	359	usually the fastest backend for a low number of (low-numbered :) fds.
		360
		361	To get good performance out of this backend you need a high amount of
		362	parallelism (most of the file descriptors should be busy). If you are
		363	writing a server, you should C<accept ()> in a loop to accept as many
		364	connections as possible during one iteration. You might also want to have
		365	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		366	readiness notifications you get per iteration.
		367
		368	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		369	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		370	C<exceptfds> set on that platform).
230		371
231	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	372	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
232		373
233	And this is your standard poll(2) backend. It's more complicated than	374	And this is your standard poll(2) backend. It's more complicated
234	select, but handles sparse fds better and has no artificial limit on the	375	than select, but handles sparse fds better and has no artificial
235	number of fds you can use (except it will slow down considerably with a	376	limit on the number of fds you can use (except it will slow down
236	lot of inactive fds). It scales similarly to select, i.e. O(total_fds).	377	considerably with a lot of inactive fds). It scales similarly to select,
		378	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		379	performance tips.
		380
		381	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		382	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
237		383
238	=item C<EVBACKEND_EPOLL> (value 4, Linux)	384	=item C<EVBACKEND_EPOLL> (value 4, Linux)
239		385
240	For few fds, this backend is a bit little slower than poll and select,	386	For few fds, this backend is a bit little slower than poll and select,
241	but it scales phenomenally better. While poll and select usually scale like	387	but it scales phenomenally better. While poll and select usually scale
242	O(total_fds) where n is the total number of fds (or the highest fd), epoll scales	388	like O(total_fds) where n is the total number of fds (or the highest fd),
243	either O(1) or O(active_fds).	389	epoll scales either O(1) or O(active_fds).
244		390
		391	The epoll mechanism deserves honorable mention as the most misdesigned
		392	of the more advanced event mechanisms: mere annoyances include silently
		393	dropping file descriptors, requiring a system call per change per file
		394	descriptor (and unnecessary guessing of parameters), problems with dup and
		395	so on. The biggest issue is fork races, however - if a program forks then
		396	I<both> parent and child process have to recreate the epoll set, which can
		397	take considerable time (one syscall per file descriptor) and is of course
		398	hard to detect.
		399
		400	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		401	of course I<doesn't>, and epoll just loves to report events for totally
		402	I<different> file descriptors (even already closed ones, so one cannot
		403	even remove them from the set) than registered in the set (especially
		404	on SMP systems). Libev tries to counter these spurious notifications by
		405	employing an additional generation counter and comparing that against the
		406	events to filter out spurious ones, recreating the set when required.
		407
245	While stopping and starting an I/O watcher in the same iteration will	408	While stopping, setting and starting an I/O watcher in the same iteration
246	result in some caching, there is still a syscall per such incident	409	will result in some caching, there is still a system call per such
247	(because the fd could point to a different file description now), so its	410	incident (because the same I<file descriptor> could point to a different
248	best to avoid that. Also, dup()ed file descriptors might not work very	411	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
249	well if you register events for both fds.	412	file descriptors might not work very well if you register events for both
		413	file descriptors.
250		414
251	Please note that epoll sometimes generates spurious notifications, so you	415	Best performance from this backend is achieved by not unregistering all
252	need to use non-blocking I/O or other means to avoid blocking when no data	416	watchers for a file descriptor until it has been closed, if possible,
253	(or space) is available.	417	i.e. keep at least one watcher active per fd at all times. Stopping and
		418	starting a watcher (without re-setting it) also usually doesn't cause
		419	extra overhead. A fork can both result in spurious notifications as well
		420	as in libev having to destroy and recreate the epoll object, which can
		421	take considerable time and thus should be avoided.
		422
		423	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		424	faster than epoll for maybe up to a hundred file descriptors, depending on
		425	the usage. So sad.
		426
		427	While nominally embeddable in other event loops, this feature is broken in
		428	all kernel versions tested so far.
		429
		430	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		431	C<EVBACKEND_POLL>.
254		432
255	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	433	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
256		434
257	Kqueue deserves special mention, as at the time of this writing, it	435	Kqueue deserves special mention, as at the time of this writing, it
258	was broken on all BSDs except NetBSD (usually it doesn't work with	436	was broken on all BSDs except NetBSD (usually it doesn't work reliably
259	anything but sockets and pipes, except on Darwin, where of course its	437	with anything but sockets and pipes, except on Darwin, where of course
260	completely useless). For this reason its not being "autodetected"	438	it's completely useless). Unlike epoll, however, whose brokenness
		439	is by design, these kqueue bugs can (and eventually will) be fixed
		440	without API changes to existing programs. For this reason it's not being
261	unless you explicitly specify it explicitly in the flags (i.e. using	441	"auto-detected" unless you explicitly specify it in the flags (i.e. using
262	C<EVBACKEND_KQUEUE>).	442	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		443	system like NetBSD.
		444
		445	You still can embed kqueue into a normal poll or select backend and use it
		446	only for sockets (after having made sure that sockets work with kqueue on
		447	the target platform). See C<ev_embed> watchers for more info.
263		448
264	It scales in the same way as the epoll backend, but the interface to the	449	It scales in the same way as the epoll backend, but the interface to the
265	kernel is more efficient (which says nothing about its actual speed, of	450	kernel is more efficient (which says nothing about its actual speed, of
266	course). While starting and stopping an I/O watcher does not cause an	451	course). While stopping, setting and starting an I/O watcher does never
267	extra syscall as with epoll, it still adds up to four event changes per	452	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
268	incident, so its best to avoid that.	453	two event changes per incident. Support for C<fork ()> is very bad (but
		454	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		455	cases
		456
		457	This backend usually performs well under most conditions.
		458
		459	While nominally embeddable in other event loops, this doesn't work
		460	everywhere, so you might need to test for this. And since it is broken
		461	almost everywhere, you should only use it when you have a lot of sockets
		462	(for which it usually works), by embedding it into another event loop
		463	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and, did I mention it,
		464	using it only for sockets.
		465
		466	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		467	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		468	C<NOTE_EOF>.
269		469
270	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	470	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
271		471
272	This is not implemented yet (and might never be).	472	This is not implemented yet (and might never be, unless you send me an
		473	implementation). According to reports, C</dev/poll> only supports sockets
		474	and is not embeddable, which would limit the usefulness of this backend
		475	immensely.
273		476
274	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	477	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
275		478
276	This uses the Solaris 10 port mechanism. As with everything on Solaris,	479	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
277	it's really slow, but it still scales very well (O(active_fds)).	480	it's really slow, but it still scales very well (O(active_fds)).
278		481
279	Please note that solaris ports can result in a lot of spurious	482	Please note that Solaris event ports can deliver a lot of spurious
280	notifications, so you need to use non-blocking I/O or other means to avoid	483	notifications, so you need to use non-blocking I/O or other means to avoid
281	blocking when no data (or space) is available.	484	blocking when no data (or space) is available.
		485
		486	While this backend scales well, it requires one system call per active
		487	file descriptor per loop iteration. For small and medium numbers of file
		488	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		489	might perform better.
		490
		491	On the positive side, with the exception of the spurious readiness
		492	notifications, this backend actually performed fully to specification
		493	in all tests and is fully embeddable, which is a rare feat among the
		494	OS-specific backends (I vastly prefer correctness over speed hacks).
		495
		496	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		497	C<EVBACKEND_POLL>.
282		498
283	=item C<EVBACKEND_ALL>	499	=item C<EVBACKEND_ALL>
284		500
285	Try all backends (even potentially broken ones that wouldn't be tried	501	Try all backends (even potentially broken ones that wouldn't be tried
286	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	502	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
287	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	503	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
288		504
		505	It is definitely not recommended to use this flag.
		506
289	=back	507	=back
290		508
291	If one or more of these are ored into the flags value, then only these	509	If one or more of these are or'ed into the flags value, then only these
292	backends will be tried (in the reverse order as given here). If none are	510	backends will be tried (in the reverse order as listed here). If none are
293	specified, most compiled-in backend will be tried, usually in reverse	511	specified, all backends in C<ev_recommended_backends ()> will be tried.
294	order of their flag values :)
295		512
296	The most typical usage is like this:	513	Example: This is the most typical usage.
297		514
298	if (!ev_default_loop (0))	515	if (!ev_default_loop (0))
299	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	516	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
300		517
301	Restrict libev to the select and poll backends, and do not allow	518	Example: Restrict libev to the select and poll backends, and do not allow
302	environment settings to be taken into account:	519	environment settings to be taken into account:
303		520
304	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	521	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
305		522
306	Use whatever libev has to offer, but make sure that kqueue is used if	523	Example: Use whatever libev has to offer, but make sure that kqueue is
307	available (warning, breaks stuff, best use only with your own private	524	used if available (warning, breaks stuff, best use only with your own
308	event loop and only if you know the OS supports your types of fds):	525	private event loop and only if you know the OS supports your types of
		526	fds):
309		527
310	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	528	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
311		529
312	=item struct ev_loop *ev_loop_new (unsigned int flags)	530	=item struct ev_loop *ev_loop_new (unsigned int flags)
313		531
314	Similar to C<ev_default_loop>, but always creates a new event loop that is	532	Similar to C<ev_default_loop>, but always creates a new event loop that is
315	always distinct from the default loop. Unlike the default loop, it cannot	533	always distinct from the default loop. Unlike the default loop, it cannot
316	handle signal and child watchers, and attempts to do so will be greeted by	534	handle signal and child watchers, and attempts to do so will be greeted by
317	undefined behaviour (or a failed assertion if assertions are enabled).	535	undefined behaviour (or a failed assertion if assertions are enabled).
318		536
		537	Note that this function I<is> thread-safe, and the recommended way to use
		538	libev with threads is indeed to create one loop per thread, and using the
		539	default loop in the "main" or "initial" thread.
		540
319	Example: try to create a event loop that uses epoll and nothing else.	541	Example: Try to create a event loop that uses epoll and nothing else.
320		542
321	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	543	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
322	if (!epoller)	544	if (!epoller)
323	fatal ("no epoll found here, maybe it hides under your chair");	545	fatal ("no epoll found here, maybe it hides under your chair");
324		546
325	=item ev_default_destroy ()	547	=item ev_default_destroy ()
326		548
327	Destroys the default loop again (frees all memory and kernel state	549	Destroys the default loop again (frees all memory and kernel state
328	etc.). None of the active event watchers will be stopped in the normal	550	etc.). None of the active event watchers will be stopped in the normal
329	sense, so e.g. C<ev_is_active> might still return true. It is your	551	sense, so e.g. C<ev_is_active> might still return true. It is your
330	responsibility to either stop all watchers cleanly yoursef I<before>	552	responsibility to either stop all watchers cleanly yourself I<before>
331	calling this function, or cope with the fact afterwards (which is usually	553	calling this function, or cope with the fact afterwards (which is usually
332	the easiest thing, youc na just ignore the watchers and/or C<free ()> them	554	the easiest thing, you can just ignore the watchers and/or C<free ()> them
333	for example).	555	for example).
		556
		557	Note that certain global state, such as signal state (and installed signal
		558	handlers), will not be freed by this function, and related watchers (such
		559	as signal and child watchers) would need to be stopped manually.
		560
		561	In general it is not advisable to call this function except in the
		562	rare occasion where you really need to free e.g. the signal handling
		563	pipe fds. If you need dynamically allocated loops it is better to use
		564	C<ev_loop_new> and C<ev_loop_destroy>).
334		565
335	=item ev_loop_destroy (loop)	566	=item ev_loop_destroy (loop)
336		567
337	Like C<ev_default_destroy>, but destroys an event loop created by an	568	Like C<ev_default_destroy>, but destroys an event loop created by an
338	earlier call to C<ev_loop_new>.	569	earlier call to C<ev_loop_new>.
339		570
340	=item ev_default_fork ()	571	=item ev_default_fork ()
341		572
		573	This function sets a flag that causes subsequent C<ev_loop> iterations
342	This function reinitialises the kernel state for backends that have	574	to reinitialise the kernel state for backends that have one. Despite the
343	one. Despite the name, you can call it anytime, but it makes most sense	575	name, you can call it anytime, but it makes most sense after forking, in
344	after forking, in either the parent or child process (or both, but that	576	the child process (or both child and parent, but that again makes little
345	again makes little sense).	577	sense). You I<must> call it in the child before using any of the libev
		578	functions, and it will only take effect at the next C<ev_loop> iteration.
346		579
347	You I<must> call this function in the child process after forking if and	580	On the other hand, you only need to call this function in the child
348	only if you want to use the event library in both processes. If you just	581	process if and only if you want to use the event library in the child. If
349	fork+exec, you don't have to call it.	582	you just fork+exec, you don't have to call it at all.
350		583
351	The function itself is quite fast and it's usually not a problem to call	584	The function itself is quite fast and it's usually not a problem to call
352	it just in case after a fork. To make this easy, the function will fit in	585	it just in case after a fork. To make this easy, the function will fit in
353	quite nicely into a call to C<pthread_atfork>:	586	quite nicely into a call to C<pthread_atfork>:
354		587
355	pthread_atfork (0, 0, ev_default_fork);	588	pthread_atfork (0, 0, ev_default_fork);
356		589
357	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
358	without calling this function, so if you force one of those backends you
359	do not need to care.
360
361	=item ev_loop_fork (loop)	590	=item ev_loop_fork (loop)
362		591
363	Like C<ev_default_fork>, but acts on an event loop created by	592	Like C<ev_default_fork>, but acts on an event loop created by
364	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	593	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
365	after fork, and how you do this is entirely your own problem.	594	after fork that you want to re-use in the child, and how you do this is
		595	entirely your own problem.
		596
		597	=item int ev_is_default_loop (loop)
		598
		599	Returns true when the given loop is, in fact, the default loop, and false
		600	otherwise.
		601
		602	=item unsigned int ev_loop_count (loop)
		603
		604	Returns the count of loop iterations for the loop, which is identical to
		605	the number of times libev did poll for new events. It starts at C<0> and
		606	happily wraps around with enough iterations.
		607
		608	This value can sometimes be useful as a generation counter of sorts (it
		609	"ticks" the number of loop iterations), as it roughly corresponds with
		610	C<ev_prepare> and C<ev_check> calls.
366		611
367	=item unsigned int ev_backend (loop)	612	=item unsigned int ev_backend (loop)
368		613
369	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	614	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
370	use.	615	use.
…		…
373		618
374	Returns the current "event loop time", which is the time the event loop	619	Returns the current "event loop time", which is the time the event loop
375	received events and started processing them. This timestamp does not	620	received events and started processing them. This timestamp does not
376	change as long as callbacks are being processed, and this is also the base	621	change as long as callbacks are being processed, and this is also the base
377	time used for relative timers. You can treat it as the timestamp of the	622	time used for relative timers. You can treat it as the timestamp of the
378	event occuring (or more correctly, libev finding out about it).	623	event occurring (or more correctly, libev finding out about it).
		624
		625	=item ev_now_update (loop)
		626
		627	Establishes the current time by querying the kernel, updating the time
		628	returned by C<ev_now ()> in the progress. This is a costly operation and
		629	is usually done automatically within C<ev_loop ()>.
		630
		631	This function is rarely useful, but when some event callback runs for a
		632	very long time without entering the event loop, updating libev's idea of
		633	the current time is a good idea.
		634
		635	See also "The special problem of time updates" in the C<ev_timer> section.
379		636
380	=item ev_loop (loop, int flags)	637	=item ev_loop (loop, int flags)
381		638
382	Finally, this is it, the event handler. This function usually is called	639	Finally, this is it, the event handler. This function usually is called
383	after you initialised all your watchers and you want to start handling	640	after you initialised all your watchers and you want to start handling
…		…
386	If the flags argument is specified as C<0>, it will not return until	643	If the flags argument is specified as C<0>, it will not return until
387	either no event watchers are active anymore or C<ev_unloop> was called.	644	either no event watchers are active anymore or C<ev_unloop> was called.
388		645
389	Please note that an explicit C<ev_unloop> is usually better than	646	Please note that an explicit C<ev_unloop> is usually better than
390	relying on all watchers to be stopped when deciding when a program has	647	relying on all watchers to be stopped when deciding when a program has
391	finished (especially in interactive programs), but having a program that	648	finished (especially in interactive programs), but having a program
392	automatically loops as long as it has to and no longer by virtue of	649	that automatically loops as long as it has to and no longer by virtue
393	relying on its watchers stopping correctly is a thing of beauty.	650	of relying on its watchers stopping correctly, that is truly a thing of
		651	beauty.
394		652
395	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	653	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
396	those events and any outstanding ones, but will not block your process in	654	those events and any already outstanding ones, but will not block your
397	case there are no events and will return after one iteration of the loop.	655	process in case there are no events and will return after one iteration of
		656	the loop.
398		657
399	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	658	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
400	neccessary) and will handle those and any outstanding ones. It will block	659	necessary) and will handle those and any already outstanding ones. It
401	your process until at least one new event arrives, and will return after	660	will block your process until at least one new event arrives (which could
402	one iteration of the loop. This is useful if you are waiting for some	661	be an event internal to libev itself, so there is no guarantee that a
403	external event in conjunction with something not expressible using other	662	user-registered callback will be called), and will return after one
		663	iteration of the loop.
		664
		665	This is useful if you are waiting for some external event in conjunction
		666	with something not expressible using other libev watchers (i.e. "roll your
404	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	667	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
405	usually a better approach for this kind of thing.	668	usually a better approach for this kind of thing.
406		669
407	Here are the gory details of what C<ev_loop> does:	670	Here are the gory details of what C<ev_loop> does:
408		671
409	* If there are no active watchers (reference count is zero), return.	672	- Before the first iteration, call any pending watchers.
410	- Queue prepare watchers and then call all outstanding watchers.	673	* If EVFLAG_FORKCHECK was used, check for a fork.
		674	- If a fork was detected (by any means), queue and call all fork watchers.
		675	- Queue and call all prepare watchers.
411	- If we have been forked, recreate the kernel state.	676	- If we have been forked, detach and recreate the kernel state
		677	as to not disturb the other process.
412	- Update the kernel state with all outstanding changes.	678	- Update the kernel state with all outstanding changes.
413	- Update the "event loop time".	679	- Update the "event loop time" (ev_now ()).
414	- Calculate for how long to block.	680	- Calculate for how long to sleep or block, if at all
		681	(active idle watchers, EVLOOP_NONBLOCK or not having
		682	any active watchers at all will result in not sleeping).
		683	- Sleep if the I/O and timer collect interval say so.
415	- Block the process, waiting for any events.	684	- Block the process, waiting for any events.
416	- Queue all outstanding I/O (fd) events.	685	- Queue all outstanding I/O (fd) events.
417	- Update the "event loop time" and do time jump handling.	686	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
418	- Queue all outstanding timers.	687	- Queue all expired timers.
419	- Queue all outstanding periodics.	688	- Queue all expired periodics.
420	- If no events are pending now, queue all idle watchers.	689	- Unless any events are pending now, queue all idle watchers.
421	- Queue all check watchers.	690	- Queue all check watchers.
422	- Call all queued watchers in reverse order (i.e. check watchers first).	691	- Call all queued watchers in reverse order (i.e. check watchers first).
423	Signals and child watchers are implemented as I/O watchers, and will	692	Signals and child watchers are implemented as I/O watchers, and will
424	be handled here by queueing them when their watcher gets executed.	693	be handled here by queueing them when their watcher gets executed.
425	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	694	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
426	were used, return, otherwise continue with step *.	695	were used, or there are no active watchers, return, otherwise
		696	continue with step *.
427		697
428	Example: queue some jobs and then loop until no events are outsanding	698	Example: Queue some jobs and then loop until no events are outstanding
429	anymore.	699	anymore.
430		700
431	... queue jobs here, make sure they register event watchers as long	701	... queue jobs here, make sure they register event watchers as long
432	... as they still have work to do (even an idle watcher will do..)	702	... as they still have work to do (even an idle watcher will do..)
433	ev_loop (my_loop, 0);	703	ev_loop (my_loop, 0);
434	... jobs done. yeah!	704	... jobs done or somebody called unloop. yeah!
435		705
436	=item ev_unloop (loop, how)	706	=item ev_unloop (loop, how)
437		707
438	Can be used to make a call to C<ev_loop> return early (but only after it	708	Can be used to make a call to C<ev_loop> return early (but only after it
439	has processed all outstanding events). The C<how> argument must be either	709	has processed all outstanding events). The C<how> argument must be either
440	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	710	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
441	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	711	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
442		712
		713	This "unloop state" will be cleared when entering C<ev_loop> again.
		714
		715	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
		716
443	=item ev_ref (loop)	717	=item ev_ref (loop)
444		718
445	=item ev_unref (loop)	719	=item ev_unref (loop)
446		720
447	Ref/unref can be used to add or remove a reference count on the event	721	Ref/unref can be used to add or remove a reference count on the event
448	loop: Every watcher keeps one reference, and as long as the reference	722	loop: Every watcher keeps one reference, and as long as the reference
449	count is nonzero, C<ev_loop> will not return on its own. If you have	723	count is nonzero, C<ev_loop> will not return on its own.
		724
450	a watcher you never unregister that should not keep C<ev_loop> from	725	If you have a watcher you never unregister that should not keep C<ev_loop>
451	returning, ev_unref() after starting, and ev_ref() before stopping it. For	726	from returning, call ev_unref() after starting, and ev_ref() before
		727	stopping it.
		728
452	example, libev itself uses this for its internal signal pipe: It is not	729	As an example, libev itself uses this for its internal signal pipe: It is
453	visible to the libev user and should not keep C<ev_loop> from exiting if	730	not visible to the libev user and should not keep C<ev_loop> from exiting
454	no event watchers registered by it are active. It is also an excellent	731	if no event watchers registered by it are active. It is also an excellent
455	way to do this for generic recurring timers or from within third-party	732	way to do this for generic recurring timers or from within third-party
456	libraries. Just remember to I<unref after start> and I<ref before stop>.	733	libraries. Just remember to I<unref after start> and I<ref before stop>
		734	(but only if the watcher wasn't active before, or was active before,
		735	respectively).
457		736
458	Example: create a signal watcher, but keep it from keeping C<ev_loop>	737	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
459	running when nothing else is active.	738	running when nothing else is active.
460		739
461	struct dv_signal exitsig;	740	ev_signal exitsig;
462	ev_signal_init (&exitsig, sig_cb, SIGINT);	741	ev_signal_init (&exitsig, sig_cb, SIGINT);
463	ev_signal_start (myloop, &exitsig);	742	ev_signal_start (loop, &exitsig);
464	evf_unref (myloop);	743	evf_unref (loop);
465		744
466	Example: for some weird reason, unregister the above signal handler again.	745	Example: For some weird reason, unregister the above signal handler again.
467		746
468	ev_ref (myloop);	747	ev_ref (loop);
469	ev_signal_stop (myloop, &exitsig);	748	ev_signal_stop (loop, &exitsig);
		749
		750	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		751
		752	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		753
		754	These advanced functions influence the time that libev will spend waiting
		755	for events. Both time intervals are by default C<0>, meaning that libev
		756	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		757	latency.
		758
		759	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		760	allows libev to delay invocation of I/O and timer/periodic callbacks
		761	to increase efficiency of loop iterations (or to increase power-saving
		762	opportunities).
		763
		764	The idea is that sometimes your program runs just fast enough to handle
		765	one (or very few) event(s) per loop iteration. While this makes the
		766	program responsive, it also wastes a lot of CPU time to poll for new
		767	events, especially with backends like C<select ()> which have a high
		768	overhead for the actual polling but can deliver many events at once.
		769
		770	By setting a higher I<io collect interval> you allow libev to spend more
		771	time collecting I/O events, so you can handle more events per iteration,
		772	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		773	C<ev_timer>) will be not affected. Setting this to a non-null value will
		774	introduce an additional C<ev_sleep ()> call into most loop iterations.
		775
		776	Likewise, by setting a higher I<timeout collect interval> you allow libev
		777	to spend more time collecting timeouts, at the expense of increased
		778	latency/jitter/inexactness (the watcher callback will be called
		779	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		780	value will not introduce any overhead in libev.
		781
		782	Many (busy) programs can usually benefit by setting the I/O collect
		783	interval to a value near C<0.1> or so, which is often enough for
		784	interactive servers (of course not for games), likewise for timeouts. It
		785	usually doesn't make much sense to set it to a lower value than C<0.01>,
		786	as this approaches the timing granularity of most systems.
		787
		788	Setting the I<timeout collect interval> can improve the opportunity for
		789	saving power, as the program will "bundle" timer callback invocations that
		790	are "near" in time together, by delaying some, thus reducing the number of
		791	times the process sleeps and wakes up again. Another useful technique to
		792	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		793	they fire on, say, one-second boundaries only.
		794
		795	=item ev_loop_verify (loop)
		796
		797	This function only does something when C<EV_VERIFY> support has been
		798	compiled in, which is the default for non-minimal builds. It tries to go
		799	through all internal structures and checks them for validity. If anything
		800	is found to be inconsistent, it will print an error message to standard
		801	error and call C<abort ()>.
		802
		803	This can be used to catch bugs inside libev itself: under normal
		804	circumstances, this function will never abort as of course libev keeps its
		805	data structures consistent.
470		806
471	=back	807	=back
472		808
		809
473	=head1 ANATOMY OF A WATCHER	810	=head1 ANATOMY OF A WATCHER
		811
		812	In the following description, uppercase C<TYPE> in names stands for the
		813	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		814	watchers and C<ev_io_start> for I/O watchers.
474		815
475	A watcher is a structure that you create and register to record your	816	A watcher is a structure that you create and register to record your
476	interest in some event. For instance, if you want to wait for STDIN to	817	interest in some event. For instance, if you want to wait for STDIN to
477	become readable, you would create an C<ev_io> watcher for that:	818	become readable, you would create an C<ev_io> watcher for that:
478		819
479	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	820	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
480	{	821	{
481	ev_io_stop (w);	822	ev_io_stop (w);
482	ev_unloop (loop, EVUNLOOP_ALL);	823	ev_unloop (loop, EVUNLOOP_ALL);
483	}	824	}
484		825
485	struct ev_loop *loop = ev_default_loop (0);	826	struct ev_loop *loop = ev_default_loop (0);
		827
486	struct ev_io stdin_watcher;	828	ev_io stdin_watcher;
		829
487	ev_init (&stdin_watcher, my_cb);	830	ev_init (&stdin_watcher, my_cb);
488	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	831	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
489	ev_io_start (loop, &stdin_watcher);	832	ev_io_start (loop, &stdin_watcher);
		833
490	ev_loop (loop, 0);	834	ev_loop (loop, 0);
491		835
492	As you can see, you are responsible for allocating the memory for your	836	As you can see, you are responsible for allocating the memory for your
493	watcher structures (and it is usually a bad idea to do this on the stack,	837	watcher structures (and it is I<usually> a bad idea to do this on the
494	although this can sometimes be quite valid).	838	stack).
		839
		840	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		841	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
495		842
496	Each watcher structure must be initialised by a call to C<ev_init	843	Each watcher structure must be initialised by a call to C<ev_init
497	(watcher *, callback)>, which expects a callback to be provided. This	844	(watcher *, callback)>, which expects a callback to be provided. This
498	callback gets invoked each time the event occurs (or, in the case of io	845	callback gets invoked each time the event occurs (or, in the case of I/O
499	watchers, each time the event loop detects that the file descriptor given	846	watchers, each time the event loop detects that the file descriptor given
500	is readable and/or writable).	847	is readable and/or writable).
501		848
502	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	849	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
503	with arguments specific to this watcher type. There is also a macro	850	macro to configure it, with arguments specific to the watcher type. There
504	to combine initialisation and setting in one call: C<< ev_<type>_init	851	is also a macro to combine initialisation and setting in one call: C<<
505	(watcher *, callback, ...) >>.	852	ev_TYPE_init (watcher *, callback, ...) >>.
506		853
507	To make the watcher actually watch out for events, you have to start it	854	To make the watcher actually watch out for events, you have to start it
508	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	855	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
509	*) >>), and you can stop watching for events at any time by calling the	856	*) >>), and you can stop watching for events at any time by calling the
510	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	857	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
511		858
512	As long as your watcher is active (has been started but not stopped) you	859	As long as your watcher is active (has been started but not stopped) you
513	must not touch the values stored in it. Most specifically you must never	860	must not touch the values stored in it. Most specifically you must never
514	reinitialise it or call its C<set> macro.	861	reinitialise it or call its C<ev_TYPE_set> macro.
515		862
516	Each and every callback receives the event loop pointer as first, the	863	Each and every callback receives the event loop pointer as first, the
517	registered watcher structure as second, and a bitset of received events as	864	registered watcher structure as second, and a bitset of received events as
518	third argument.	865	third argument.
519		866
…		…
543	The signal specified in the C<ev_signal> watcher has been received by a thread.	890	The signal specified in the C<ev_signal> watcher has been received by a thread.
544		891
545	=item C<EV_CHILD>	892	=item C<EV_CHILD>
546		893
547	The pid specified in the C<ev_child> watcher has received a status change.	894	The pid specified in the C<ev_child> watcher has received a status change.
		895
		896	=item C<EV_STAT>
		897
		898	The path specified in the C<ev_stat> watcher changed its attributes somehow.
548		899
549	=item C<EV_IDLE>	900	=item C<EV_IDLE>
550		901
551	The C<ev_idle> watcher has determined that you have nothing better to do.	902	The C<ev_idle> watcher has determined that you have nothing better to do.
552		903
…		…
560	received events. Callbacks of both watcher types can start and stop as	911	received events. Callbacks of both watcher types can start and stop as
561	many watchers as they want, and all of them will be taken into account	912	many watchers as they want, and all of them will be taken into account
562	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	913	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
563	C<ev_loop> from blocking).	914	C<ev_loop> from blocking).
564		915
		916	=item C<EV_EMBED>
		917
		918	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		919
		920	=item C<EV_FORK>
		921
		922	The event loop has been resumed in the child process after fork (see
		923	C<ev_fork>).
		924
		925	=item C<EV_ASYNC>
		926
		927	The given async watcher has been asynchronously notified (see C<ev_async>).
		928
565	=item C<EV_ERROR>	929	=item C<EV_ERROR>
566		930
567	An unspecified error has occured, the watcher has been stopped. This might	931	An unspecified error has occurred, the watcher has been stopped. This might
568	happen because the watcher could not be properly started because libev	932	happen because the watcher could not be properly started because libev
569	ran out of memory, a file descriptor was found to be closed or any other	933	ran out of memory, a file descriptor was found to be closed or any other
		934	problem. Libev considers these application bugs.
		935
570	problem. You best act on it by reporting the problem and somehow coping	936	You best act on it by reporting the problem and somehow coping with the
571	with the watcher being stopped.	937	watcher being stopped. Note that well-written programs should not receive
		938	an error ever, so when your watcher receives it, this usually indicates a
		939	bug in your program.
572		940
573	Libev will usually signal a few "dummy" events together with an error,	941	Libev will usually signal a few "dummy" events together with an error, for
574	for example it might indicate that a fd is readable or writable, and if	942	example it might indicate that a fd is readable or writable, and if your
575	your callbacks is well-written it can just attempt the operation and cope	943	callbacks is well-written it can just attempt the operation and cope with
576	with the error from read() or write(). This will not work in multithreaded	944	the error from read() or write(). This will not work in multi-threaded
577	programs, though, so beware.	945	programs, though, as the fd could already be closed and reused for another
		946	thing, so beware.
578		947
579	=back	948	=back
580		949
581	=head2 SUMMARY OF GENERIC WATCHER FUNCTIONS	950	=head2 GENERIC WATCHER FUNCTIONS
582
583	In the following description, C<TYPE> stands for the watcher type,
584	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
585		951
586	=over 4	952	=over 4
587		953
588	=item C<ev_init> (ev_TYPE *watcher, callback)	954	=item C<ev_init> (ev_TYPE *watcher, callback)
589		955
…		…
595	which rolls both calls into one.	961	which rolls both calls into one.
596		962
597	You can reinitialise a watcher at any time as long as it has been stopped	963	You can reinitialise a watcher at any time as long as it has been stopped
598	(or never started) and there are no pending events outstanding.	964	(or never started) and there are no pending events outstanding.
599		965
600	The callbakc is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	966	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
601	int revents)>.	967	int revents)>.
		968
		969	Example: Initialise an C<ev_io> watcher in two steps.
		970
		971	ev_io w;
		972	ev_init (&w, my_cb);
		973	ev_io_set (&w, STDIN_FILENO, EV_READ);
602		974
603	=item C<ev_TYPE_set> (ev_TYPE *, [args])	975	=item C<ev_TYPE_set> (ev_TYPE *, [args])
604		976
605	This macro initialises the type-specific parts of a watcher. You need to	977	This macro initialises the type-specific parts of a watcher. You need to
606	call C<ev_init> at least once before you call this macro, but you can	978	call C<ev_init> at least once before you call this macro, but you can
…		…
609	difference to the C<ev_init> macro).	981	difference to the C<ev_init> macro).
610		982
611	Although some watcher types do not have type-specific arguments	983	Although some watcher types do not have type-specific arguments
612	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	984	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
613		985
		986	See C<ev_init>, above, for an example.
		987
614	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	988	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
615		989
616	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	990	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
617	calls into a single call. This is the most convinient method to initialise	991	calls into a single call. This is the most convenient method to initialise
618	a watcher. The same limitations apply, of course.	992	a watcher. The same limitations apply, of course.
		993
		994	Example: Initialise and set an C<ev_io> watcher in one step.
		995
		996	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
619		997
620	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	998	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
621		999
622	Starts (activates) the given watcher. Only active watchers will receive	1000	Starts (activates) the given watcher. Only active watchers will receive
623	events. If the watcher is already active nothing will happen.	1001	events. If the watcher is already active nothing will happen.
624		1002
		1003	Example: Start the C<ev_io> watcher that is being abused as example in this
		1004	whole section.
		1005
		1006	ev_io_start (EV_DEFAULT_UC, &w);
		1007
625	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1008	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
626		1009
627	Stops the given watcher again (if active) and clears the pending	1010	Stops the given watcher if active, and clears the pending status (whether
		1011	the watcher was active or not).
		1012
628	status. It is possible that stopped watchers are pending (for example,	1013	It is possible that stopped watchers are pending - for example,
629	non-repeating timers are being stopped when they become pending), but	1014	non-repeating timers are being stopped when they become pending - but
630	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1015	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
631	you want to free or reuse the memory used by the watcher it is therefore a	1016	pending. If you want to free or reuse the memory used by the watcher it is
632	good idea to always call its C<ev_TYPE_stop> function.	1017	therefore a good idea to always call its C<ev_TYPE_stop> function.
633		1018
634	=item bool ev_is_active (ev_TYPE *watcher)	1019	=item bool ev_is_active (ev_TYPE *watcher)
635		1020
636	Returns a true value iff the watcher is active (i.e. it has been started	1021	Returns a true value iff the watcher is active (i.e. it has been started
637	and not yet been stopped). As long as a watcher is active you must not modify	1022	and not yet been stopped). As long as a watcher is active you must not modify
…		…
640	=item bool ev_is_pending (ev_TYPE *watcher)	1025	=item bool ev_is_pending (ev_TYPE *watcher)
641		1026
642	Returns a true value iff the watcher is pending, (i.e. it has outstanding	1027	Returns a true value iff the watcher is pending, (i.e. it has outstanding
643	events but its callback has not yet been invoked). As long as a watcher	1028	events but its callback has not yet been invoked). As long as a watcher
644	is pending (but not active) you must not call an init function on it (but	1029	is pending (but not active) you must not call an init function on it (but
645	C<ev_TYPE_set> is safe) and you must make sure the watcher is available to	1030	C<ev_TYPE_set> is safe), you must not change its priority, and you must
646	libev (e.g. you cnanot C<free ()> it).	1031	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1032	it).
647		1033
648	=item callback = ev_cb (ev_TYPE *watcher)	1034	=item callback ev_cb (ev_TYPE *watcher)
649		1035
650	Returns the callback currently set on the watcher.	1036	Returns the callback currently set on the watcher.
651		1037
652	=item ev_cb_set (ev_TYPE *watcher, callback)	1038	=item ev_cb_set (ev_TYPE *watcher, callback)
653		1039
654	Change the callback. You can change the callback at virtually any time	1040	Change the callback. You can change the callback at virtually any time
655	(modulo threads).	1041	(modulo threads).
656		1042
		1043	=item ev_set_priority (ev_TYPE *watcher, priority)
		1044
		1045	=item int ev_priority (ev_TYPE *watcher)
		1046
		1047	Set and query the priority of the watcher. The priority is a small
		1048	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1049	(default: C<-2>). Pending watchers with higher priority will be invoked
		1050	before watchers with lower priority, but priority will not keep watchers
		1051	from being executed (except for C<ev_idle> watchers).
		1052
		1053	This means that priorities are I<only> used for ordering callback
		1054	invocation after new events have been received. This is useful, for
		1055	example, to reduce latency after idling, or more often, to bind two
		1056	watchers on the same event and make sure one is called first.
		1057
		1058	If you need to suppress invocation when higher priority events are pending
		1059	you need to look at C<ev_idle> watchers, which provide this functionality.
		1060
		1061	You I<must not> change the priority of a watcher as long as it is active or
		1062	pending.
		1063
		1064	The default priority used by watchers when no priority has been set is
		1065	always C<0>, which is supposed to not be too high and not be too low :).
		1066
		1067	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1068	fine, as long as you do not mind that the priority value you query might
		1069	or might not have been clamped to the valid range.
		1070
		1071	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1072
		1073	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1074	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1075	can deal with that fact, as both are simply passed through to the
		1076	callback.
		1077
		1078	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1079
		1080	If the watcher is pending, this function clears its pending status and
		1081	returns its C<revents> bitset (as if its callback was invoked). If the
		1082	watcher isn't pending it does nothing and returns C<0>.
		1083
		1084	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1085	callback to be invoked, which can be accomplished with this function.
		1086
657	=back	1087	=back
658		1088
659		1089
660	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1090	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
661		1091
662	Each watcher has, by default, a member C<void *data> that you can change	1092	Each watcher has, by default, a member C<void *data> that you can change
663	and read at any time, libev will completely ignore it. This can be used	1093	and read at any time: libev will completely ignore it. This can be used
664	to associate arbitrary data with your watcher. If you need more data and	1094	to associate arbitrary data with your watcher. If you need more data and
665	don't want to allocate memory and store a pointer to it in that data	1095	don't want to allocate memory and store a pointer to it in that data
666	member, you can also "subclass" the watcher type and provide your own	1096	member, you can also "subclass" the watcher type and provide your own
667	data:	1097	data:
668		1098
669	struct my_io	1099	struct my_io
670	{	1100	{
671	struct ev_io io;	1101	ev_io io;
672	int otherfd;	1102	int otherfd;
673	void *somedata;	1103	void *somedata;
674	struct whatever *mostinteresting;	1104	struct whatever *mostinteresting;
675	}	1105	};
		1106
		1107	...
		1108	struct my_io w;
		1109	ev_io_init (&w.io, my_cb, fd, EV_READ);
676		1110
677	And since your callback will be called with a pointer to the watcher, you	1111	And since your callback will be called with a pointer to the watcher, you
678	can cast it back to your own type:	1112	can cast it back to your own type:
679		1113
680	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1114	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
681	{	1115	{
682	struct my_io *w = (struct my_io *)w_;	1116	struct my_io *w = (struct my_io *)w_;
683	...	1117	...
684	}	1118	}
685		1119
686	More interesting and less C-conformant ways of catsing your callback type	1120	More interesting and less C-conformant ways of casting your callback type
687	have been omitted....	1121	instead have been omitted.
		1122
		1123	Another common scenario is to use some data structure with multiple
		1124	embedded watchers:
		1125
		1126	struct my_biggy
		1127	{
		1128	int some_data;
		1129	ev_timer t1;
		1130	ev_timer t2;
		1131	}
		1132
		1133	In this case getting the pointer to C<my_biggy> is a bit more
		1134	complicated: Either you store the address of your C<my_biggy> struct
		1135	in the C<data> member of the watcher (for woozies), or you need to use
		1136	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1137	programmers):
		1138
		1139	#include <stddef.h>
		1140
		1141	static void
		1142	t1_cb (EV_P_ ev_timer *w, int revents)
		1143	{
		1144	struct my_biggy big = (struct my_biggy *
		1145	(((char *)w) - offsetof (struct my_biggy, t1));
		1146	}
		1147
		1148	static void
		1149	t2_cb (EV_P_ ev_timer *w, int revents)
		1150	{
		1151	struct my_biggy big = (struct my_biggy *
		1152	(((char *)w) - offsetof (struct my_biggy, t2));
		1153	}
688		1154
689		1155
690	=head1 WATCHER TYPES	1156	=head1 WATCHER TYPES
691		1157
692	This section describes each watcher in detail, but will not repeat	1158	This section describes each watcher in detail, but will not repeat
693	information given in the last section.	1159	information given in the last section. Any initialisation/set macros,
		1160	functions and members specific to the watcher type are explained.
694		1161
		1162	Members are additionally marked with either I<[read-only]>, meaning that,
		1163	while the watcher is active, you can look at the member and expect some
		1164	sensible content, but you must not modify it (you can modify it while the
		1165	watcher is stopped to your hearts content), or I<[read-write]>, which
		1166	means you can expect it to have some sensible content while the watcher
		1167	is active, but you can also modify it. Modifying it may not do something
		1168	sensible or take immediate effect (or do anything at all), but libev will
		1169	not crash or malfunction in any way.
695		1170
		1171
696	=head2 C<ev_io> - is this file descriptor readable or writable	1172	=head2 C<ev_io> - is this file descriptor readable or writable?
697		1173
698	I/O watchers check whether a file descriptor is readable or writable	1174	I/O watchers check whether a file descriptor is readable or writable
699	in each iteration of the event loop (This behaviour is called	1175	in each iteration of the event loop, or, more precisely, when reading
700	level-triggering because you keep receiving events as long as the	1176	would not block the process and writing would at least be able to write
701	condition persists. Remember you can stop the watcher if you don't want to	1177	some data. This behaviour is called level-triggering because you keep
702	act on the event and neither want to receive future events).	1178	receiving events as long as the condition persists. Remember you can stop
		1179	the watcher if you don't want to act on the event and neither want to
		1180	receive future events.
703		1181
704	In general you can register as many read and/or write event watchers per	1182	In general you can register as many read and/or write event watchers per
705	fd as you want (as long as you don't confuse yourself). Setting all file	1183	fd as you want (as long as you don't confuse yourself). Setting all file
706	descriptors to non-blocking mode is also usually a good idea (but not	1184	descriptors to non-blocking mode is also usually a good idea (but not
707	required if you know what you are doing).	1185	required if you know what you are doing).
708		1186
709	You have to be careful with dup'ed file descriptors, though. Some backends	1187	If you cannot use non-blocking mode, then force the use of a
710	(the linux epoll backend is a notable example) cannot handle dup'ed file	1188	known-to-be-good backend (at the time of this writing, this includes only
711	descriptors correctly if you register interest in two or more fds pointing	1189	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>).
712	to the same underlying file/socket etc. description (that is, they share
713	the same underlying "file open").
714		1190
715	If you must do this, then force the use of a known-to-be-good backend	1191	Another thing you have to watch out for is that it is quite easy to
716	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and	1192	receive "spurious" readiness notifications, that is your callback might
		1193	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
		1194	because there is no data. Not only are some backends known to create a
		1195	lot of those (for example Solaris ports), it is very easy to get into
		1196	this situation even with a relatively standard program structure. Thus
		1197	it is best to always use non-blocking I/O: An extra C<read>(2) returning
		1198	C<EAGAIN> is far preferable to a program hanging until some data arrives.
		1199
		1200	If you cannot run the fd in non-blocking mode (for example you should
		1201	not play around with an Xlib connection), then you have to separately
		1202	re-test whether a file descriptor is really ready with a known-to-be good
		1203	interface such as poll (fortunately in our Xlib example, Xlib already
		1204	does this on its own, so its quite safe to use). Some people additionally
		1205	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1206	indefinitely.
		1207
		1208	But really, best use non-blocking mode.
		1209
		1210	=head3 The special problem of disappearing file descriptors
		1211
		1212	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1213	descriptor (either due to calling C<close> explicitly or any other means,
		1214	such as C<dup2>). The reason is that you register interest in some file
		1215	descriptor, but when it goes away, the operating system will silently drop
		1216	this interest. If another file descriptor with the same number then is
		1217	registered with libev, there is no efficient way to see that this is, in
		1218	fact, a different file descriptor.
		1219
		1220	To avoid having to explicitly tell libev about such cases, libev follows
		1221	the following policy: Each time C<ev_io_set> is being called, libev
		1222	will assume that this is potentially a new file descriptor, otherwise
		1223	it is assumed that the file descriptor stays the same. That means that
		1224	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1225	descriptor even if the file descriptor number itself did not change.
		1226
		1227	This is how one would do it normally anyway, the important point is that
		1228	the libev application should not optimise around libev but should leave
		1229	optimisations to libev.
		1230
		1231	=head3 The special problem of dup'ed file descriptors
		1232
		1233	Some backends (e.g. epoll), cannot register events for file descriptors,
		1234	but only events for the underlying file descriptions. That means when you
		1235	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1236	events for them, only one file descriptor might actually receive events.
		1237
		1238	There is no workaround possible except not registering events
		1239	for potentially C<dup ()>'ed file descriptors, or to resort to
		1240	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1241
		1242	=head3 The special problem of fork
		1243
		1244	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1245	useless behaviour. Libev fully supports fork, but needs to be told about
		1246	it in the child.
		1247
		1248	To support fork in your programs, you either have to call
		1249	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1250	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
717	C<EVBACKEND_POLL>).	1251	C<EVBACKEND_POLL>.
		1252
		1253	=head3 The special problem of SIGPIPE
		1254
		1255	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1256	when writing to a pipe whose other end has been closed, your program gets
		1257	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1258	this is sensible behaviour, for daemons, this is usually undesirable.
		1259
		1260	So when you encounter spurious, unexplained daemon exits, make sure you
		1261	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1262	somewhere, as that would have given you a big clue).
		1263
		1264
		1265	=head3 Watcher-Specific Functions
718		1266
719	=over 4	1267	=over 4
720		1268
721	=item ev_io_init (ev_io *, callback, int fd, int events)	1269	=item ev_io_init (ev_io *, callback, int fd, int events)
722		1270
723	=item ev_io_set (ev_io *, int fd, int events)	1271	=item ev_io_set (ev_io *, int fd, int events)
724		1272
725	Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive	1273	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
726	events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ |	1274	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
727	EV_WRITE> to receive the given events.	1275	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
728		1276
729	Please note that most of the more scalable backend mechanisms (for example	1277	=item int fd [read-only]
730	epoll and solaris ports) can result in spurious readyness notifications	1278
731	for file descriptors, so you practically need to use non-blocking I/O (and	1279	The file descriptor being watched.
732	treat callback invocation as hint only), or retest separately with a safe	1280
733	interface before doing I/O (XLib can do this), or force the use of either	1281	=item int events [read-only]
734	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>, which don't suffer from this	1282
735	problem. Also note that it is quite easy to have your callback invoked	1283	The events being watched.
736	when the readyness condition is no longer valid even when employing
737	typical ways of handling events, so its a good idea to use non-blocking
738	I/O unconditionally.
739		1284
740	=back	1285	=back
741		1286
		1287	=head3 Examples
		1288
742	Example: call C<stdin_readable_cb> when STDIN_FILENO has become, well	1289	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
743	readable, but only once. Since it is likely line-buffered, you could	1290	readable, but only once. Since it is likely line-buffered, you could
744	attempt to read a whole line in the callback:	1291	attempt to read a whole line in the callback.
745		1292
746	static void	1293	static void
747	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1294	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
748	{	1295	{
749	ev_io_stop (loop, w);	1296	ev_io_stop (loop, w);
750	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1297	.. read from stdin here (or from w->fd) and handle any I/O errors
751	}	1298	}
752		1299
753	...	1300	...
754	struct ev_loop *loop = ev_default_init (0);	1301	struct ev_loop *loop = ev_default_init (0);
755	struct ev_io stdin_readable;	1302	ev_io stdin_readable;
756	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1303	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
757	ev_io_start (loop, &stdin_readable);	1304	ev_io_start (loop, &stdin_readable);
758	ev_loop (loop, 0);	1305	ev_loop (loop, 0);
759		1306
760		1307
761	=head2 C<ev_timer> - relative and optionally recurring timeouts	1308	=head2 C<ev_timer> - relative and optionally repeating timeouts
762		1309
763	Timer watchers are simple relative timers that generate an event after a	1310	Timer watchers are simple relative timers that generate an event after a
764	given time, and optionally repeating in regular intervals after that.	1311	given time, and optionally repeating in regular intervals after that.
765		1312
766	The timers are based on real time, that is, if you register an event that	1313	The timers are based on real time, that is, if you register an event that
767	times out after an hour and you reset your system clock to last years	1314	times out after an hour and you reset your system clock to January last
768	time, it will still time out after (roughly) and hour. "Roughly" because	1315	year, it will still time out after (roughly) one hour. "Roughly" because
769	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1316	detecting time jumps is hard, and some inaccuracies are unavoidable (the
770	monotonic clock option helps a lot here).	1317	monotonic clock option helps a lot here).
		1318
		1319	The callback is guaranteed to be invoked only I<after> its timeout has
		1320	passed, but if multiple timers become ready during the same loop iteration
		1321	then order of execution is undefined.
		1322
		1323	=head3 Be smart about timeouts
		1324
		1325	Many real-world problems involve some kind of timeout, usually for error
		1326	recovery. A typical example is an HTTP request - if the other side hangs,
		1327	you want to raise some error after a while.
		1328
		1329	What follows are some ways to handle this problem, from obvious and
		1330	inefficient to smart and efficient.
		1331
		1332	In the following, a 60 second activity timeout is assumed - a timeout that
		1333	gets reset to 60 seconds each time there is activity (e.g. each time some
		1334	data or other life sign was received).
		1335
		1336	=over 4
		1337
		1338	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1339
		1340	This is the most obvious, but not the most simple way: In the beginning,
		1341	start the watcher:
		1342
		1343	ev_timer_init (timer, callback, 60., 0.);
		1344	ev_timer_start (loop, timer);
		1345
		1346	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1347	and start it again:
		1348
		1349	ev_timer_stop (loop, timer);
		1350	ev_timer_set (timer, 60., 0.);
		1351	ev_timer_start (loop, timer);
		1352
		1353	This is relatively simple to implement, but means that each time there is
		1354	some activity, libev will first have to remove the timer from its internal
		1355	data structure and then add it again. Libev tries to be fast, but it's
		1356	still not a constant-time operation.
		1357
		1358	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1359
		1360	This is the easiest way, and involves using C<ev_timer_again> instead of
		1361	C<ev_timer_start>.
		1362
		1363	To implement this, configure an C<ev_timer> with a C<repeat> value
		1364	of C<60> and then call C<ev_timer_again> at start and each time you
		1365	successfully read or write some data. If you go into an idle state where
		1366	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1367	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1368
		1369	That means you can ignore both the C<ev_timer_start> function and the
		1370	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1371	member and C<ev_timer_again>.
		1372
		1373	At start:
		1374
		1375	ev_timer_init (timer, callback);
		1376	timer->repeat = 60.;
		1377	ev_timer_again (loop, timer);
		1378
		1379	Each time there is some activity:
		1380
		1381	ev_timer_again (loop, timer);
		1382
		1383	It is even possible to change the time-out on the fly, regardless of
		1384	whether the watcher is active or not:
		1385
		1386	timer->repeat = 30.;
		1387	ev_timer_again (loop, timer);
		1388
		1389	This is slightly more efficient then stopping/starting the timer each time
		1390	you want to modify its timeout value, as libev does not have to completely
		1391	remove and re-insert the timer from/into its internal data structure.
		1392
		1393	It is, however, even simpler than the "obvious" way to do it.
		1394
		1395	=item 3. Let the timer time out, but then re-arm it as required.
		1396
		1397	This method is more tricky, but usually most efficient: Most timeouts are
		1398	relatively long compared to the intervals between other activity - in
		1399	our example, within 60 seconds, there are usually many I/O events with
		1400	associated activity resets.
		1401
		1402	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1403	but remember the time of last activity, and check for a real timeout only
		1404	within the callback:
		1405
		1406	ev_tstamp last_activity; // time of last activity
		1407
		1408	static void
		1409	callback (EV_P_ ev_timer *w, int revents)
		1410	{
		1411	ev_tstamp now = ev_now (EV_A);
		1412	ev_tstamp timeout = last_activity + 60.;
		1413
		1414	// if last_activity + 60. is older than now, we did time out
		1415	if (timeout < now)
		1416	{
		1417	// timeout occured, take action
		1418	}
		1419	else
		1420	{
		1421	// callback was invoked, but there was some activity, re-arm
		1422	// the watcher to fire in last_activity + 60, which is
		1423	// guaranteed to be in the future, so "again" is positive:
		1424	w->repeat = timeout - now;
		1425	ev_timer_again (EV_A_ w);
		1426	}
		1427	}
		1428
		1429	To summarise the callback: first calculate the real timeout (defined
		1430	as "60 seconds after the last activity"), then check if that time has
		1431	been reached, which means something I<did>, in fact, time out. Otherwise
		1432	the callback was invoked too early (C<timeout> is in the future), so
		1433	re-schedule the timer to fire at that future time, to see if maybe we have
		1434	a timeout then.
		1435
		1436	Note how C<ev_timer_again> is used, taking advantage of the
		1437	C<ev_timer_again> optimisation when the timer is already running.
		1438
		1439	This scheme causes more callback invocations (about one every 60 seconds
		1440	minus half the average time between activity), but virtually no calls to
		1441	libev to change the timeout.
		1442
		1443	To start the timer, simply initialise the watcher and set C<last_activity>
		1444	to the current time (meaning we just have some activity :), then call the
		1445	callback, which will "do the right thing" and start the timer:
		1446
		1447	ev_timer_init (timer, callback);
		1448	last_activity = ev_now (loop);
		1449	callback (loop, timer, EV_TIMEOUT);
		1450
		1451	And when there is some activity, simply store the current time in
		1452	C<last_activity>, no libev calls at all:
		1453
		1454	last_actiivty = ev_now (loop);
		1455
		1456	This technique is slightly more complex, but in most cases where the
		1457	time-out is unlikely to be triggered, much more efficient.
		1458
		1459	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1460	callback :) - just change the timeout and invoke the callback, which will
		1461	fix things for you.
		1462
		1463	=item 4. Wee, just use a double-linked list for your timeouts.
		1464
		1465	If there is not one request, but many thousands (millions...), all
		1466	employing some kind of timeout with the same timeout value, then one can
		1467	do even better:
		1468
		1469	When starting the timeout, calculate the timeout value and put the timeout
		1470	at the I<end> of the list.
		1471
		1472	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1473	the list is expected to fire (for example, using the technique #3).
		1474
		1475	When there is some activity, remove the timer from the list, recalculate
		1476	the timeout, append it to the end of the list again, and make sure to
		1477	update the C<ev_timer> if it was taken from the beginning of the list.
		1478
		1479	This way, one can manage an unlimited number of timeouts in O(1) time for
		1480	starting, stopping and updating the timers, at the expense of a major
		1481	complication, and having to use a constant timeout. The constant timeout
		1482	ensures that the list stays sorted.
		1483
		1484	=back
		1485
		1486	So which method the best?
		1487
		1488	Method #2 is a simple no-brain-required solution that is adequate in most
		1489	situations. Method #3 requires a bit more thinking, but handles many cases
		1490	better, and isn't very complicated either. In most case, choosing either
		1491	one is fine, with #3 being better in typical situations.
		1492
		1493	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1494	rather complicated, but extremely efficient, something that really pays
		1495	off after the first million or so of active timers, i.e. it's usually
		1496	overkill :)
		1497
		1498	=head3 The special problem of time updates
		1499
		1500	Establishing the current time is a costly operation (it usually takes at
		1501	least two system calls): EV therefore updates its idea of the current
		1502	time only before and after C<ev_loop> collects new events, which causes a
		1503	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1504	lots of events in one iteration.
771		1505
772	The relative timeouts are calculated relative to the C<ev_now ()>	1506	The relative timeouts are calculated relative to the C<ev_now ()>
773	time. This is usually the right thing as this timestamp refers to the time	1507	time. This is usually the right thing as this timestamp refers to the time
774	of the event triggering whatever timeout you are modifying/starting. If	1508	of the event triggering whatever timeout you are modifying/starting. If
775	you suspect event processing to be delayed and you I<need> to base the timeout	1509	you suspect event processing to be delayed and you I<need> to base the
776	on the current time, use something like this to adjust for this:	1510	timeout on the current time, use something like this to adjust for this:
777		1511
778	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1512	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
779		1513
780	The callback is guarenteed to be invoked only when its timeout has passed,	1514	If the event loop is suspended for a long time, you can also force an
781	but if multiple timers become ready during the same loop iteration then	1515	update of the time returned by C<ev_now ()> by calling C<ev_now_update
782	order of execution is undefined.	1516	()>.
		1517
		1518	=head3 Watcher-Specific Functions and Data Members
783		1519
784	=over 4	1520	=over 4
785		1521
786	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1522	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
787		1523
788	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1524	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
789		1525
790	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1526	Configure the timer to trigger after C<after> seconds. If C<repeat>
791	C<0.>, then it will automatically be stopped. If it is positive, then the	1527	is C<0.>, then it will automatically be stopped once the timeout is
792	timer will automatically be configured to trigger again C<repeat> seconds	1528	reached. If it is positive, then the timer will automatically be
793	later, again, and again, until stopped manually.	1529	configured to trigger again C<repeat> seconds later, again, and again,
		1530	until stopped manually.
794		1531
795	The timer itself will do a best-effort at avoiding drift, that is, if you	1532	The timer itself will do a best-effort at avoiding drift, that is, if
796	configure a timer to trigger every 10 seconds, then it will trigger at	1533	you configure a timer to trigger every 10 seconds, then it will normally
797	exactly 10 second intervals. If, however, your program cannot keep up with	1534	trigger at exactly 10 second intervals. If, however, your program cannot
798	the timer (because it takes longer than those 10 seconds to do stuff) the	1535	keep up with the timer (because it takes longer than those 10 seconds to
799	timer will not fire more than once per event loop iteration.	1536	do stuff) the timer will not fire more than once per event loop iteration.
800		1537
801	=item ev_timer_again (loop)	1538	=item ev_timer_again (loop, ev_timer *)
802		1539
803	This will act as if the timer timed out and restart it again if it is	1540	This will act as if the timer timed out and restart it again if it is
804	repeating. The exact semantics are:	1541	repeating. The exact semantics are:
805		1542
		1543	If the timer is pending, its pending status is cleared.
		1544
806	If the timer is started but nonrepeating, stop it.	1545	If the timer is started but non-repeating, stop it (as if it timed out).
807		1546
808	If the timer is repeating, either start it if necessary (with the repeat	1547	If the timer is repeating, either start it if necessary (with the
809	value), or reset the running timer to the repeat value.	1548	C<repeat> value), or reset the running timer to the C<repeat> value.
810		1549
811	This sounds a bit complicated, but here is a useful and typical	1550	This sounds a bit complicated, see "Be smart about timeouts", above, for a
812	example: Imagine you have a tcp connection and you want a so-called idle	1551	usage example.
813	timeout, that is, you want to be called when there have been, say, 60	1552
814	seconds of inactivity on the socket. The easiest way to do this is to	1553	=item ev_tstamp repeat [read-write]
815	configure an C<ev_timer> with after=repeat=60 and calling ev_timer_again each	1554
816	time you successfully read or write some data. If you go into an idle	1555	The current C<repeat> value. Will be used each time the watcher times out
817	state where you do not expect data to travel on the socket, you can stop	1556	or C<ev_timer_again> is called, and determines the next timeout (if any),
818	the timer, and again will automatically restart it if need be.	1557	which is also when any modifications are taken into account.
819		1558
820	=back	1559	=back
821		1560
		1561	=head3 Examples
		1562
822	Example: create a timer that fires after 60 seconds.	1563	Example: Create a timer that fires after 60 seconds.
823		1564
824	static void	1565	static void
825	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1566	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
826	{	1567	{
827	.. one minute over, w is actually stopped right here	1568	.. one minute over, w is actually stopped right here
828	}	1569	}
829		1570
830	struct ev_timer mytimer;	1571	ev_timer mytimer;
831	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1572	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
832	ev_timer_start (loop, &mytimer);	1573	ev_timer_start (loop, &mytimer);
833		1574
834	Example: create a timeout timer that times out after 10 seconds of	1575	Example: Create a timeout timer that times out after 10 seconds of
835	inactivity.	1576	inactivity.
836		1577
837	static void	1578	static void
838	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1579	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
839	{	1580	{
840	.. ten seconds without any activity	1581	.. ten seconds without any activity
841	}	1582	}
842		1583
843	struct ev_timer mytimer;	1584	ev_timer mytimer;
844	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1585	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
845	ev_timer_again (&mytimer); /* start timer */	1586	ev_timer_again (&mytimer); /* start timer */
846	ev_loop (loop, 0);	1587	ev_loop (loop, 0);
847		1588
848	// and in some piece of code that gets executed on any "activity":	1589	// and in some piece of code that gets executed on any "activity":
849	// reset the timeout to start ticking again at 10 seconds	1590	// reset the timeout to start ticking again at 10 seconds
850	ev_timer_again (&mytimer);	1591	ev_timer_again (&mytimer);
851		1592
852		1593
853	=head2 C<ev_periodic> - to cron or not to cron	1594	=head2 C<ev_periodic> - to cron or not to cron?
854		1595
855	Periodic watchers are also timers of a kind, but they are very versatile	1596	Periodic watchers are also timers of a kind, but they are very versatile
856	(and unfortunately a bit complex).	1597	(and unfortunately a bit complex).
857		1598
858	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1599	Unlike C<ev_timer>'s, they are not based on real time (or relative time)
859	but on wallclock time (absolute time). You can tell a periodic watcher	1600	but on wall clock time (absolute time). You can tell a periodic watcher
860	to trigger "at" some specific point in time. For example, if you tell a	1601	to trigger after some specific point in time. For example, if you tell a
861	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	1602	periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now ()
862	+ 10.>) and then reset your system clock to the last year, then it will	1603	+ 10.>, that is, an absolute time not a delay) and then reset your system
		1604	clock to January of the previous year, then it will take more than year
863	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1605	to trigger the event (unlike an C<ev_timer>, which would still trigger
864	roughly 10 seconds later and of course not if you reset your system time	1606	roughly 10 seconds later as it uses a relative timeout).
865	again).
866		1607
867	They can also be used to implement vastly more complex timers, such as	1608	C<ev_periodic>s can also be used to implement vastly more complex timers,
868	triggering an event on eahc midnight, local time.	1609	such as triggering an event on each "midnight, local time", or other
		1610	complicated rules.
869		1611
870	As with timers, the callback is guarenteed to be invoked only when the	1612	As with timers, the callback is guaranteed to be invoked only when the
871	time (C<at>) has been passed, but if multiple periodic timers become ready	1613	time (C<at>) has passed, but if multiple periodic timers become ready
872	during the same loop iteration then order of execution is undefined.	1614	during the same loop iteration, then order of execution is undefined.
		1615
		1616	=head3 Watcher-Specific Functions and Data Members
873		1617
874	=over 4	1618	=over 4
875		1619
876	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1620	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
877		1621
878	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1622	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)
879		1623
880	Lots of arguments, lets sort it out... There are basically three modes of	1624	Lots of arguments, lets sort it out... There are basically three modes of
881	operation, and we will explain them from simplest to complex:	1625	operation, and we will explain them from simplest to most complex:
882		1626
883	=over 4	1627	=over 4
884		1628
885	=item * absolute timer (interval = reschedule_cb = 0)	1629	=item * absolute timer (at = time, interval = reschedule_cb = 0)
886		1630
887	In this configuration the watcher triggers an event at the wallclock time	1631	In this configuration the watcher triggers an event after the wall clock
888	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1632	time C<at> has passed. It will not repeat and will not adjust when a time
889	that is, if it is to be run at January 1st 2011 then it will run when the	1633	jump occurs, that is, if it is to be run at January 1st 2011 then it will
890	system time reaches or surpasses this time.	1634	only run when the system clock reaches or surpasses this time.
891		1635
892	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1636	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
893		1637
894	In this mode the watcher will always be scheduled to time out at the next	1638	In this mode the watcher will always be scheduled to time out at the next
895	C<at + N * interval> time (for some integer N) and then repeat, regardless	1639	C<at + N * interval> time (for some integer N, which can also be negative)
896	of any time jumps.	1640	and then repeat, regardless of any time jumps.
897		1641
898	This can be used to create timers that do not drift with respect to system	1642	This can be used to create timers that do not drift with respect to the
899	time:	1643	system clock, for example, here is a C<ev_periodic> that triggers each
		1644	hour, on the hour:
900		1645
901	ev_periodic_set (&periodic, 0., 3600., 0);	1646	ev_periodic_set (&periodic, 0., 3600., 0);
902		1647
903	This doesn't mean there will always be 3600 seconds in between triggers,	1648	This doesn't mean there will always be 3600 seconds in between triggers,
904	but only that the the callback will be called when the system time shows a	1649	but only that the callback will be called when the system time shows a
905	full hour (UTC), or more correctly, when the system time is evenly divisible	1650	full hour (UTC), or more correctly, when the system time is evenly divisible
906	by 3600.	1651	by 3600.
907		1652
908	Another way to think about it (for the mathematically inclined) is that	1653	Another way to think about it (for the mathematically inclined) is that
909	C<ev_periodic> will try to run the callback in this mode at the next possible	1654	C<ev_periodic> will try to run the callback in this mode at the next possible
910	time where C<time = at (mod interval)>, regardless of any time jumps.	1655	time where C<time = at (mod interval)>, regardless of any time jumps.
911		1656
		1657	For numerical stability it is preferable that the C<at> value is near
		1658	C<ev_now ()> (the current time), but there is no range requirement for
		1659	this value, and in fact is often specified as zero.
		1660
		1661	Note also that there is an upper limit to how often a timer can fire (CPU
		1662	speed for example), so if C<interval> is very small then timing stability
		1663	will of course deteriorate. Libev itself tries to be exact to be about one
		1664	millisecond (if the OS supports it and the machine is fast enough).
		1665
912	=item * manual reschedule mode (reschedule_cb = callback)	1666	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
913		1667
914	In this mode the values for C<interval> and C<at> are both being	1668	In this mode the values for C<interval> and C<at> are both being
915	ignored. Instead, each time the periodic watcher gets scheduled, the	1669	ignored. Instead, each time the periodic watcher gets scheduled, the
916	reschedule callback will be called with the watcher as first, and the	1670	reschedule callback will be called with the watcher as first, and the
917	current time as second argument.	1671	current time as second argument.
918		1672
919	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1673	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,
920	ever, or make any event loop modifications>. If you need to stop it,	1674	ever, or make ANY event loop modifications whatsoever>.
921	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by
922	starting a prepare watcher).
923		1675
		1676	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1677	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1678	only event loop modification you are allowed to do).
		1679
924	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1680	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
925	ev_tstamp now)>, e.g.:	1681	*w, ev_tstamp now)>, e.g.:
926		1682
		1683	static ev_tstamp
927	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1684	my_rescheduler (ev_periodic *w, ev_tstamp now)
928	{	1685	{
929	return now + 60.;	1686	return now + 60.;
930	}	1687	}
931		1688
932	It must return the next time to trigger, based on the passed time value	1689	It must return the next time to trigger, based on the passed time value
933	(that is, the lowest time value larger than to the second argument). It	1690	(that is, the lowest time value larger than to the second argument). It
934	will usually be called just before the callback will be triggered, but	1691	will usually be called just before the callback will be triggered, but
935	might be called at other times, too.	1692	might be called at other times, too.
936		1693
937	NOTE: I<< This callback must always return a time that is later than the	1694	NOTE: I<< This callback must always return a time that is higher than or
938	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	1695	equal to the passed C<now> value >>.
939		1696
940	This can be used to create very complex timers, such as a timer that	1697	This can be used to create very complex timers, such as a timer that
941	triggers on each midnight, local time. To do this, you would calculate the	1698	triggers on "next midnight, local time". To do this, you would calculate the
942	next midnight after C<now> and return the timestamp value for this. How	1699	next midnight after C<now> and return the timestamp value for this. How
943	you do this is, again, up to you (but it is not trivial, which is the main	1700	you do this is, again, up to you (but it is not trivial, which is the main
944	reason I omitted it as an example).	1701	reason I omitted it as an example).
945		1702
946	=back	1703	=back
…		…
950	Simply stops and restarts the periodic watcher again. This is only useful	1707	Simply stops and restarts the periodic watcher again. This is only useful
951	when you changed some parameters or the reschedule callback would return	1708	when you changed some parameters or the reschedule callback would return
952	a different time than the last time it was called (e.g. in a crond like	1709	a different time than the last time it was called (e.g. in a crond like
953	program when the crontabs have changed).	1710	program when the crontabs have changed).
954		1711
		1712	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1713
		1714	When active, returns the absolute time that the watcher is supposed to
		1715	trigger next.
		1716
		1717	=item ev_tstamp offset [read-write]
		1718
		1719	When repeating, this contains the offset value, otherwise this is the
		1720	absolute point in time (the C<at> value passed to C<ev_periodic_set>).
		1721
		1722	Can be modified any time, but changes only take effect when the periodic
		1723	timer fires or C<ev_periodic_again> is being called.
		1724
		1725	=item ev_tstamp interval [read-write]
		1726
		1727	The current interval value. Can be modified any time, but changes only
		1728	take effect when the periodic timer fires or C<ev_periodic_again> is being
		1729	called.
		1730
		1731	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
		1732
		1733	The current reschedule callback, or C<0>, if this functionality is
		1734	switched off. Can be changed any time, but changes only take effect when
		1735	the periodic timer fires or C<ev_periodic_again> is being called.
		1736
955	=back	1737	=back
956		1738
		1739	=head3 Examples
		1740
957	Example: call a callback every hour, or, more precisely, whenever the	1741	Example: Call a callback every hour, or, more precisely, whenever the
958	system clock is divisible by 3600. The callback invocation times have	1742	system time is divisible by 3600. The callback invocation times have
959	potentially a lot of jittering, but good long-term stability.	1743	potentially a lot of jitter, but good long-term stability.
960		1744
961	static void	1745	static void
962	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1746	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
963	{	1747	{
964	... its now a full hour (UTC, or TAI or whatever your clock follows)	1748	... its now a full hour (UTC, or TAI or whatever your clock follows)
965	}	1749	}
966		1750
967	struct ev_periodic hourly_tick;	1751	ev_periodic hourly_tick;
968	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	1752	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
969	ev_periodic_start (loop, &hourly_tick);	1753	ev_periodic_start (loop, &hourly_tick);
970		1754
971	Example: the same as above, but use a reschedule callback to do it:	1755	Example: The same as above, but use a reschedule callback to do it:
972		1756
973	#include <math.h>	1757	#include <math.h>
974		1758
975	static ev_tstamp	1759	static ev_tstamp
976	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	1760	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
977	{	1761	{
978	return fmod (now, 3600.) + 3600.;	1762	return now + (3600. - fmod (now, 3600.));
979	}	1763	}
980		1764
981	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	1765	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
982		1766
983	Example: call a callback every hour, starting now:	1767	Example: Call a callback every hour, starting now:
984		1768
985	struct ev_periodic hourly_tick;	1769	ev_periodic hourly_tick;
986	ev_periodic_init (&hourly_tick, clock_cb,	1770	ev_periodic_init (&hourly_tick, clock_cb,
987	fmod (ev_now (loop), 3600.), 3600., 0);	1771	fmod (ev_now (loop), 3600.), 3600., 0);
988	ev_periodic_start (loop, &hourly_tick);	1772	ev_periodic_start (loop, &hourly_tick);
989		1773
990		1774
991	=head2 C<ev_signal> - signal me when a signal gets signalled	1775	=head2 C<ev_signal> - signal me when a signal gets signalled!
992		1776
993	Signal watchers will trigger an event when the process receives a specific	1777	Signal watchers will trigger an event when the process receives a specific
994	signal one or more times. Even though signals are very asynchronous, libev	1778	signal one or more times. Even though signals are very asynchronous, libev
995	will try it's best to deliver signals synchronously, i.e. as part of the	1779	will try it's best to deliver signals synchronously, i.e. as part of the
996	normal event processing, like any other event.	1780	normal event processing, like any other event.
997		1781
		1782	If you want signals asynchronously, just use C<sigaction> as you would
		1783	do without libev and forget about sharing the signal. You can even use
		1784	C<ev_async> from a signal handler to synchronously wake up an event loop.
		1785
998	You can configure as many watchers as you like per signal. Only when the	1786	You can configure as many watchers as you like per signal. Only when the
999	first watcher gets started will libev actually register a signal watcher	1787	first watcher gets started will libev actually register a signal handler
1000	with the kernel (thus it coexists with your own signal handlers as long	1788	with the kernel (thus it coexists with your own signal handlers as long as
1001	as you don't register any with libev). Similarly, when the last signal	1789	you don't register any with libev for the same signal). Similarly, when
1002	watcher for a signal is stopped libev will reset the signal handler to	1790	the last signal watcher for a signal is stopped, libev will reset the
1003	SIG_DFL (regardless of what it was set to before).	1791	signal handler to SIG_DFL (regardless of what it was set to before).
		1792
		1793	If possible and supported, libev will install its handlers with
		1794	C<SA_RESTART> behaviour enabled, so system calls should not be unduly
		1795	interrupted. If you have a problem with system calls getting interrupted by
		1796	signals you can block all signals in an C<ev_check> watcher and unblock
		1797	them in an C<ev_prepare> watcher.
		1798
		1799	=head3 Watcher-Specific Functions and Data Members
1004		1800
1005	=over 4	1801	=over 4
1006		1802
1007	=item ev_signal_init (ev_signal *, callback, int signum)	1803	=item ev_signal_init (ev_signal *, callback, int signum)
1008		1804
1009	=item ev_signal_set (ev_signal *, int signum)	1805	=item ev_signal_set (ev_signal *, int signum)
1010		1806
1011	Configures the watcher to trigger on the given signal number (usually one	1807	Configures the watcher to trigger on the given signal number (usually one
1012	of the C<SIGxxx> constants).	1808	of the C<SIGxxx> constants).
1013		1809
		1810	=item int signum [read-only]
		1811
		1812	The signal the watcher watches out for.
		1813
1014	=back	1814	=back
1015		1815
		1816	=head3 Examples
1016		1817
		1818	Example: Try to exit cleanly on SIGINT.
		1819
		1820	static void
		1821	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		1822	{
		1823	ev_unloop (loop, EVUNLOOP_ALL);
		1824	}
		1825
		1826	ev_signal signal_watcher;
		1827	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1828	ev_signal_start (loop, &signal_watcher);
		1829
		1830
1017	=head2 C<ev_child> - wait for pid status changes	1831	=head2 C<ev_child> - watch out for process status changes
1018		1832
1019	Child watchers trigger when your process receives a SIGCHLD in response to	1833	Child watchers trigger when your process receives a SIGCHLD in response to
1020	some child status changes (most typically when a child of yours dies).	1834	some child status changes (most typically when a child of yours dies or
		1835	exits). It is permissible to install a child watcher I<after> the child
		1836	has been forked (which implies it might have already exited), as long
		1837	as the event loop isn't entered (or is continued from a watcher), i.e.,
		1838	forking and then immediately registering a watcher for the child is fine,
		1839	but forking and registering a watcher a few event loop iterations later is
		1840	not.
		1841
		1842	Only the default event loop is capable of handling signals, and therefore
		1843	you can only register child watchers in the default event loop.
		1844
		1845	=head3 Process Interaction
		1846
		1847	Libev grabs C<SIGCHLD> as soon as the default event loop is
		1848	initialised. This is necessary to guarantee proper behaviour even if
		1849	the first child watcher is started after the child exits. The occurrence
		1850	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		1851	synchronously as part of the event loop processing. Libev always reaps all
		1852	children, even ones not watched.
		1853
		1854	=head3 Overriding the Built-In Processing
		1855
		1856	Libev offers no special support for overriding the built-in child
		1857	processing, but if your application collides with libev's default child
		1858	handler, you can override it easily by installing your own handler for
		1859	C<SIGCHLD> after initialising the default loop, and making sure the
		1860	default loop never gets destroyed. You are encouraged, however, to use an
		1861	event-based approach to child reaping and thus use libev's support for
		1862	that, so other libev users can use C<ev_child> watchers freely.
		1863
		1864	=head3 Stopping the Child Watcher
		1865
		1866	Currently, the child watcher never gets stopped, even when the
		1867	child terminates, so normally one needs to stop the watcher in the
		1868	callback. Future versions of libev might stop the watcher automatically
		1869	when a child exit is detected.
		1870
		1871	=head3 Watcher-Specific Functions and Data Members
1021		1872
1022	=over 4	1873	=over 4
1023		1874
1024	=item ev_child_init (ev_child *, callback, int pid)	1875	=item ev_child_init (ev_child *, callback, int pid, int trace)
1025		1876
1026	=item ev_child_set (ev_child *, int pid)	1877	=item ev_child_set (ev_child *, int pid, int trace)
1027		1878
1028	Configures the watcher to wait for status changes of process C<pid> (or	1879	Configures the watcher to wait for status changes of process C<pid> (or
1029	I<any> process if C<pid> is specified as C<0>). The callback can look	1880	I<any> process if C<pid> is specified as C<0>). The callback can look
1030	at the C<rstatus> member of the C<ev_child> watcher structure to see	1881	at the C<rstatus> member of the C<ev_child> watcher structure to see
1031	the status word (use the macros from C<sys/wait.h> and see your systems	1882	the status word (use the macros from C<sys/wait.h> and see your systems
1032	C<waitpid> documentation). The C<rpid> member contains the pid of the	1883	C<waitpid> documentation). The C<rpid> member contains the pid of the
1033	process causing the status change.	1884	process causing the status change. C<trace> must be either C<0> (only
		1885	activate the watcher when the process terminates) or C<1> (additionally
		1886	activate the watcher when the process is stopped or continued).
		1887
		1888	=item int pid [read-only]
		1889
		1890	The process id this watcher watches out for, or C<0>, meaning any process id.
		1891
		1892	=item int rpid [read-write]
		1893
		1894	The process id that detected a status change.
		1895
		1896	=item int rstatus [read-write]
		1897
		1898	The process exit/trace status caused by C<rpid> (see your systems
		1899	C<waitpid> and C<sys/wait.h> documentation for details).
1034		1900
1035	=back	1901	=back
1036		1902
1037	Example: try to exit cleanly on SIGINT and SIGTERM.	1903	=head3 Examples
1038		1904
		1905	Example: C<fork()> a new process and install a child handler to wait for
		1906	its completion.
		1907
		1908	ev_child cw;
		1909
1039	static void	1910	static void
1040	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	1911	child_cb (EV_P_ ev_child *w, int revents)
1041	{	1912	{
1042	ev_unloop (loop, EVUNLOOP_ALL);	1913	ev_child_stop (EV_A_ w);
		1914	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1043	}	1915	}
1044		1916
1045	struct ev_signal signal_watcher;	1917	pid_t pid = fork ();
1046	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1047	ev_signal_start (loop, &sigint_cb);
1048		1918
		1919	if (pid < 0)
		1920	// error
		1921	else if (pid == 0)
		1922	{
		1923	// the forked child executes here
		1924	exit (1);
		1925	}
		1926	else
		1927	{
		1928	ev_child_init (&cw, child_cb, pid, 0);
		1929	ev_child_start (EV_DEFAULT_ &cw);
		1930	}
1049		1931
		1932
		1933	=head2 C<ev_stat> - did the file attributes just change?
		1934
		1935	This watches a file system path for attribute changes. That is, it calls
		1936	C<stat> on that path in regular intervals (or when the OS says it changed)
		1937	and sees if it changed compared to the last time, invoking the callback if
		1938	it did.
		1939
		1940	The path does not need to exist: changing from "path exists" to "path does
		1941	not exist" is a status change like any other. The condition "path does not
		1942	exist" (or more correctly "path cannot be stat'ed") is signified by the
		1943	C<st_nlink> field being zero (which is otherwise always forced to be at
		1944	least one) and all the other fields of the stat buffer having unspecified
		1945	contents.
		1946
		1947	The path I<must not> end in a slash or contain special components such as
		1948	C<.> or C<..>. The path I<should> be absolute: If it is relative and
		1949	your working directory changes, then the behaviour is undefined.
		1950
		1951	Since there is no portable change notification interface available, the
		1952	portable implementation simply calls C<stat(2)> regularly on the path
		1953	to see if it changed somehow. You can specify a recommended polling
		1954	interval for this case. If you specify a polling interval of C<0> (highly
		1955	recommended!) then a I<suitable, unspecified default> value will be used
		1956	(which you can expect to be around five seconds, although this might
		1957	change dynamically). Libev will also impose a minimum interval which is
		1958	currently around C<0.1>, but that's usually overkill.
		1959
		1960	This watcher type is not meant for massive numbers of stat watchers,
		1961	as even with OS-supported change notifications, this can be
		1962	resource-intensive.
		1963
		1964	At the time of this writing, the only OS-specific interface implemented
		1965	is the Linux inotify interface (implementing kqueue support is left as an
		1966	exercise for the reader. Note, however, that the author sees no way of
		1967	implementing C<ev_stat> semantics with kqueue, except as a hint).
		1968
		1969	=head3 ABI Issues (Largefile Support)
		1970
		1971	Libev by default (unless the user overrides this) uses the default
		1972	compilation environment, which means that on systems with large file
		1973	support disabled by default, you get the 32 bit version of the stat
		1974	structure. When using the library from programs that change the ABI to
		1975	use 64 bit file offsets the programs will fail. In that case you have to
		1976	compile libev with the same flags to get binary compatibility. This is
		1977	obviously the case with any flags that change the ABI, but the problem is
		1978	most noticeably displayed with ev_stat and large file support.
		1979
		1980	The solution for this is to lobby your distribution maker to make large
		1981	file interfaces available by default (as e.g. FreeBSD does) and not
		1982	optional. Libev cannot simply switch on large file support because it has
		1983	to exchange stat structures with application programs compiled using the
		1984	default compilation environment.
		1985
		1986	=head3 Inotify and Kqueue
		1987
		1988	When C<inotify (7)> support has been compiled into libev and present at
		1989	runtime, it will be used to speed up change detection where possible. The
		1990	inotify descriptor will be created lazily when the first C<ev_stat>
		1991	watcher is being started.
		1992
		1993	Inotify presence does not change the semantics of C<ev_stat> watchers
		1994	except that changes might be detected earlier, and in some cases, to avoid
		1995	making regular C<stat> calls. Even in the presence of inotify support
		1996	there are many cases where libev has to resort to regular C<stat> polling,
		1997	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		1998	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		1999	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2000	xfs are fully working) libev usually gets away without polling.
		2001
		2002	There is no support for kqueue, as apparently it cannot be used to
		2003	implement this functionality, due to the requirement of having a file
		2004	descriptor open on the object at all times, and detecting renames, unlinks
		2005	etc. is difficult.
		2006
		2007	=head3 C<stat ()> is a synchronous operation
		2008
		2009	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2010	the process. The exception are C<ev_stat> watchers - those call C<stat
		2011	()>, which is a synchronous operation.
		2012
		2013	For local paths, this usually doesn't matter: unless the system is very
		2014	busy or the intervals between stat's are large, a stat call will be fast,
		2015	as the path data is suually in memory already (except when starting the
		2016	watcher).
		2017
		2018	For networked file systems, calling C<stat ()> can block an indefinite
		2019	time due to network issues, and even under good conditions, a stat call
		2020	often takes multiple milliseconds.
		2021
		2022	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2023	paths, although this is fully supported by libev.
		2024
		2025	=head3 The special problem of stat time resolution
		2026
		2027	The C<stat ()> system call only supports full-second resolution portably,
		2028	and even on systems where the resolution is higher, most file systems
		2029	still only support whole seconds.
		2030
		2031	That means that, if the time is the only thing that changes, you can
		2032	easily miss updates: on the first update, C<ev_stat> detects a change and
		2033	calls your callback, which does something. When there is another update
		2034	within the same second, C<ev_stat> will be unable to detect unless the
		2035	stat data does change in other ways (e.g. file size).
		2036
		2037	The solution to this is to delay acting on a change for slightly more
		2038	than a second (or till slightly after the next full second boundary), using
		2039	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2040	ev_timer_again (loop, w)>).
		2041
		2042	The C<.02> offset is added to work around small timing inconsistencies
		2043	of some operating systems (where the second counter of the current time
		2044	might be be delayed. One such system is the Linux kernel, where a call to
		2045	C<gettimeofday> might return a timestamp with a full second later than
		2046	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2047	update file times then there will be a small window where the kernel uses
		2048	the previous second to update file times but libev might already execute
		2049	the timer callback).
		2050
		2051	=head3 Watcher-Specific Functions and Data Members
		2052
		2053	=over 4
		2054
		2055	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		2056
		2057	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		2058
		2059	Configures the watcher to wait for status changes of the given
		2060	C<path>. The C<interval> is a hint on how quickly a change is expected to
		2061	be detected and should normally be specified as C<0> to let libev choose
		2062	a suitable value. The memory pointed to by C<path> must point to the same
		2063	path for as long as the watcher is active.
		2064
		2065	The callback will receive an C<EV_STAT> event when a change was detected,
		2066	relative to the attributes at the time the watcher was started (or the
		2067	last change was detected).
		2068
		2069	=item ev_stat_stat (loop, ev_stat *)
		2070
		2071	Updates the stat buffer immediately with new values. If you change the
		2072	watched path in your callback, you could call this function to avoid
		2073	detecting this change (while introducing a race condition if you are not
		2074	the only one changing the path). Can also be useful simply to find out the
		2075	new values.
		2076
		2077	=item ev_statdata attr [read-only]
		2078
		2079	The most-recently detected attributes of the file. Although the type is
		2080	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		2081	suitable for your system, but you can only rely on the POSIX-standardised
		2082	members to be present. If the C<st_nlink> member is C<0>, then there was
		2083	some error while C<stat>ing the file.
		2084
		2085	=item ev_statdata prev [read-only]
		2086
		2087	The previous attributes of the file. The callback gets invoked whenever
		2088	C<prev> != C<attr>, or, more precisely, one or more of these members
		2089	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2090	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
		2091
		2092	=item ev_tstamp interval [read-only]
		2093
		2094	The specified interval.
		2095
		2096	=item const char *path [read-only]
		2097
		2098	The file system path that is being watched.
		2099
		2100	=back
		2101
		2102	=head3 Examples
		2103
		2104	Example: Watch C</etc/passwd> for attribute changes.
		2105
		2106	static void
		2107	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		2108	{
		2109	/* /etc/passwd changed in some way */
		2110	if (w->attr.st_nlink)
		2111	{
		2112	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		2113	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		2114	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		2115	}
		2116	else
		2117	/* you shalt not abuse printf for puts */
		2118	puts ("wow, /etc/passwd is not there, expect problems. "
		2119	"if this is windows, they already arrived\n");
		2120	}
		2121
		2122	...
		2123	ev_stat passwd;
		2124
		2125	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		2126	ev_stat_start (loop, &passwd);
		2127
		2128	Example: Like above, but additionally use a one-second delay so we do not
		2129	miss updates (however, frequent updates will delay processing, too, so
		2130	one might do the work both on C<ev_stat> callback invocation I<and> on
		2131	C<ev_timer> callback invocation).
		2132
		2133	static ev_stat passwd;
		2134	static ev_timer timer;
		2135
		2136	static void
		2137	timer_cb (EV_P_ ev_timer *w, int revents)
		2138	{
		2139	ev_timer_stop (EV_A_ w);
		2140
		2141	/* now it's one second after the most recent passwd change */
		2142	}
		2143
		2144	static void
		2145	stat_cb (EV_P_ ev_stat *w, int revents)
		2146	{
		2147	/* reset the one-second timer */
		2148	ev_timer_again (EV_A_ &timer);
		2149	}
		2150
		2151	...
		2152	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2153	ev_stat_start (loop, &passwd);
		2154	ev_timer_init (&timer, timer_cb, 0., 1.02);
		2155
		2156
1050	=head2 C<ev_idle> - when you've got nothing better to do	2157	=head2 C<ev_idle> - when you've got nothing better to do...
1051		2158
1052	Idle watchers trigger events when there are no other events are pending	2159	Idle watchers trigger events when no other events of the same or higher
1053	(prepare, check and other idle watchers do not count). That is, as long	2160	priority are pending (prepare, check and other idle watchers do not count
1054	as your process is busy handling sockets or timeouts (or even signals,	2161	as receiving "events").
1055	imagine) it will not be triggered. But when your process is idle all idle	2162
1056	watchers are being called again and again, once per event loop iteration -	2163	That is, as long as your process is busy handling sockets or timeouts
		2164	(or even signals, imagine) of the same or higher priority it will not be
		2165	triggered. But when your process is idle (or only lower-priority watchers
		2166	are pending), the idle watchers are being called once per event loop
1057	until stopped, that is, or your process receives more events and becomes	2167	iteration - until stopped, that is, or your process receives more events
1058	busy.	2168	and becomes busy again with higher priority stuff.
1059		2169
1060	The most noteworthy effect is that as long as any idle watchers are	2170	The most noteworthy effect is that as long as any idle watchers are
1061	active, the process will not block when waiting for new events.	2171	active, the process will not block when waiting for new events.
1062		2172
1063	Apart from keeping your process non-blocking (which is a useful	2173	Apart from keeping your process non-blocking (which is a useful
1064	effect on its own sometimes), idle watchers are a good place to do	2174	effect on its own sometimes), idle watchers are a good place to do
1065	"pseudo-background processing", or delay processing stuff to after the	2175	"pseudo-background processing", or delay processing stuff to after the
1066	event loop has handled all outstanding events.	2176	event loop has handled all outstanding events.
1067		2177
		2178	=head3 Watcher-Specific Functions and Data Members
		2179
1068	=over 4	2180	=over 4
1069		2181
1070	=item ev_idle_init (ev_signal *, callback)	2182	=item ev_idle_init (ev_signal *, callback)
1071		2183
1072	Initialises and configures the idle watcher - it has no parameters of any	2184	Initialises and configures the idle watcher - it has no parameters of any
1073	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2185	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1074	believe me.	2186	believe me.
1075		2187
1076	=back	2188	=back
1077		2189
		2190	=head3 Examples
		2191
1078	Example: dynamically allocate an C<ev_idle>, start it, and in the	2192	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1079	callback, free it. Alos, use no error checking, as usual.	2193	callback, free it. Also, use no error checking, as usual.
1080		2194
1081	static void	2195	static void
1082	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2196	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1083	{	2197	{
1084	free (w);	2198	free (w);
1085	// now do something you wanted to do when the program has	2199	// now do something you wanted to do when the program has
1086	// no longer asnything immediate to do.	2200	// no longer anything immediate to do.
1087	}	2201	}
1088		2202
1089	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2203	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1090	ev_idle_init (idle_watcher, idle_cb);	2204	ev_idle_init (idle_watcher, idle_cb);
1091	ev_idle_start (loop, idle_cb);	2205	ev_idle_start (loop, idle_cb);
1092		2206
1093		2207
1094	=head2 C<ev_prepare> and C<ev_check> - customise your event loop	2208	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1095		2209
1096	Prepare and check watchers are usually (but not always) used in tandem:	2210	Prepare and check watchers are usually (but not always) used in pairs:
1097	prepare watchers get invoked before the process blocks and check watchers	2211	prepare watchers get invoked before the process blocks and check watchers
1098	afterwards.	2212	afterwards.
1099		2213
		2214	You I<must not> call C<ev_loop> or similar functions that enter
		2215	the current event loop from either C<ev_prepare> or C<ev_check>
		2216	watchers. Other loops than the current one are fine, however. The
		2217	rationale behind this is that you do not need to check for recursion in
		2218	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
		2219	C<ev_check> so if you have one watcher of each kind they will always be
		2220	called in pairs bracketing the blocking call.
		2221
1100	Their main purpose is to integrate other event mechanisms into libev and	2222	Their main purpose is to integrate other event mechanisms into libev and
1101	their use is somewhat advanced. This could be used, for example, to track	2223	their use is somewhat advanced. They could be used, for example, to track
1102	variable changes, implement your own watchers, integrate net-snmp or a	2224	variable changes, implement your own watchers, integrate net-snmp or a
1103	coroutine library and lots more.	2225	coroutine library and lots more. They are also occasionally useful if
		2226	you cache some data and want to flush it before blocking (for example,
		2227	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		2228	watcher).
1104		2229
1105	This is done by examining in each prepare call which file descriptors need	2230	This is done by examining in each prepare call which file descriptors
1106	to be watched by the other library, registering C<ev_io> watchers for	2231	need to be watched by the other library, registering C<ev_io> watchers
1107	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2232	for them and starting an C<ev_timer> watcher for any timeouts (many
1108	provide just this functionality). Then, in the check watcher you check for	2233	libraries provide exactly this functionality). Then, in the check watcher,
1109	any events that occured (by checking the pending status of all watchers	2234	you check for any events that occurred (by checking the pending status
1110	and stopping them) and call back into the library. The I/O and timer	2235	of all watchers and stopping them) and call back into the library. The
1111	callbacks will never actually be called (but must be valid nevertheless,	2236	I/O and timer callbacks will never actually be called (but must be valid
1112	because you never know, you know?).	2237	nevertheless, because you never know, you know?).
1113		2238
1114	As another example, the Perl Coro module uses these hooks to integrate	2239	As another example, the Perl Coro module uses these hooks to integrate
1115	coroutines into libev programs, by yielding to other active coroutines	2240	coroutines into libev programs, by yielding to other active coroutines
1116	during each prepare and only letting the process block if no coroutines	2241	during each prepare and only letting the process block if no coroutines
1117	are ready to run (it's actually more complicated: it only runs coroutines	2242	are ready to run (it's actually more complicated: it only runs coroutines
1118	with priority higher than or equal to the event loop and one coroutine	2243	with priority higher than or equal to the event loop and one coroutine
1119	of lower priority, but only once, using idle watchers to keep the event	2244	of lower priority, but only once, using idle watchers to keep the event
1120	loop from blocking if lower-priority coroutines are active, thus mapping	2245	loop from blocking if lower-priority coroutines are active, thus mapping
1121	low-priority coroutines to idle/background tasks).	2246	low-priority coroutines to idle/background tasks).
1122		2247
		2248	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		2249	priority, to ensure that they are being run before any other watchers
		2250	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2251
		2252	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2253	activate ("feed") events into libev. While libev fully supports this, they
		2254	might get executed before other C<ev_check> watchers did their job. As
		2255	C<ev_check> watchers are often used to embed other (non-libev) event
		2256	loops those other event loops might be in an unusable state until their
		2257	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2258	others).
		2259
		2260	=head3 Watcher-Specific Functions and Data Members
		2261
1123	=over 4	2262	=over 4
1124		2263
1125	=item ev_prepare_init (ev_prepare *, callback)	2264	=item ev_prepare_init (ev_prepare *, callback)
1126		2265
1127	=item ev_check_init (ev_check *, callback)	2266	=item ev_check_init (ev_check *, callback)
1128		2267
1129	Initialises and configures the prepare or check watcher - they have no	2268	Initialises and configures the prepare or check watcher - they have no
1130	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2269	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1131	macros, but using them is utterly, utterly and completely pointless.	2270	macros, but using them is utterly, utterly, utterly and completely
		2271	pointless.
1132		2272
1133	=back	2273	=back
1134		2274
1135	Example: *TODO*.	2275	=head3 Examples
1136		2276
		2277	There are a number of principal ways to embed other event loops or modules
		2278	into libev. Here are some ideas on how to include libadns into libev
		2279	(there is a Perl module named C<EV::ADNS> that does this, which you could
		2280	use as a working example. Another Perl module named C<EV::Glib> embeds a
		2281	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		2282	Glib event loop).
1137		2283
		2284	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
		2285	and in a check watcher, destroy them and call into libadns. What follows
		2286	is pseudo-code only of course. This requires you to either use a low
		2287	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		2288	the callbacks for the IO/timeout watchers might not have been called yet.
		2289
		2290	static ev_io iow [nfd];
		2291	static ev_timer tw;
		2292
		2293	static void
		2294	io_cb (struct ev_loop *loop, ev_io *w, int revents)
		2295	{
		2296	}
		2297
		2298	// create io watchers for each fd and a timer before blocking
		2299	static void
		2300	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
		2301	{
		2302	int timeout = 3600000;
		2303	struct pollfd fds [nfd];
		2304	// actual code will need to loop here and realloc etc.
		2305	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		2306
		2307	/* the callback is illegal, but won't be called as we stop during check */
		2308	ev_timer_init (&tw, 0, timeout * 1e-3);
		2309	ev_timer_start (loop, &tw);
		2310
		2311	// create one ev_io per pollfd
		2312	for (int i = 0; i < nfd; ++i)
		2313	{
		2314	ev_io_init (iow + i, io_cb, fds [i].fd,
		2315	((fds [i].events & POLLIN ? EV_READ : 0)
		2316	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		2317
		2318	fds [i].revents = 0;
		2319	ev_io_start (loop, iow + i);
		2320	}
		2321	}
		2322
		2323	// stop all watchers after blocking
		2324	static void
		2325	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
		2326	{
		2327	ev_timer_stop (loop, &tw);
		2328
		2329	for (int i = 0; i < nfd; ++i)
		2330	{
		2331	// set the relevant poll flags
		2332	// could also call adns_processreadable etc. here
		2333	struct pollfd *fd = fds + i;
		2334	int revents = ev_clear_pending (iow + i);
		2335	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2336	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2337
		2338	// now stop the watcher
		2339	ev_io_stop (loop, iow + i);
		2340	}
		2341
		2342	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		2343	}
		2344
		2345	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2346	in the prepare watcher and would dispose of the check watcher.
		2347
		2348	Method 3: If the module to be embedded supports explicit event
		2349	notification (libadns does), you can also make use of the actual watcher
		2350	callbacks, and only destroy/create the watchers in the prepare watcher.
		2351
		2352	static void
		2353	timer_cb (EV_P_ ev_timer *w, int revents)
		2354	{
		2355	adns_state ads = (adns_state)w->data;
		2356	update_now (EV_A);
		2357
		2358	adns_processtimeouts (ads, &tv_now);
		2359	}
		2360
		2361	static void
		2362	io_cb (EV_P_ ev_io *w, int revents)
		2363	{
		2364	adns_state ads = (adns_state)w->data;
		2365	update_now (EV_A);
		2366
		2367	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2368	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2369	}
		2370
		2371	// do not ever call adns_afterpoll
		2372
		2373	Method 4: Do not use a prepare or check watcher because the module you
		2374	want to embed is not flexible enough to support it. Instead, you can
		2375	override their poll function. The drawback with this solution is that the
		2376	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		2377	this approach, effectively embedding EV as a client into the horrible
		2378	libglib event loop.
		2379
		2380	static gint
		2381	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2382	{
		2383	int got_events = 0;
		2384
		2385	for (n = 0; n < nfds; ++n)
		2386	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2387
		2388	if (timeout >= 0)
		2389	// create/start timer
		2390
		2391	// poll
		2392	ev_loop (EV_A_ 0);
		2393
		2394	// stop timer again
		2395	if (timeout >= 0)
		2396	ev_timer_stop (EV_A_ &to);
		2397
		2398	// stop io watchers again - their callbacks should have set
		2399	for (n = 0; n < nfds; ++n)
		2400	ev_io_stop (EV_A_ iow [n]);
		2401
		2402	return got_events;
		2403	}
		2404
		2405
1138	=head2 C<ev_embed> - when one backend isn't enough	2406	=head2 C<ev_embed> - when one backend isn't enough...
1139		2407
1140	This is a rather advanced watcher type that lets you embed one event loop	2408	This is a rather advanced watcher type that lets you embed one event loop
1141	into another (currently only C<ev_io> events are supported in the embedded	2409	into another (currently only C<ev_io> events are supported in the embedded
1142	loop, other types of watchers might be handled in a delayed or incorrect	2410	loop, other types of watchers might be handled in a delayed or incorrect
1143	fashion and must not be used).	2411	fashion and must not be used).
…		…
1146	prioritise I/O.	2414	prioritise I/O.
1147		2415
1148	As an example for a bug workaround, the kqueue backend might only support	2416	As an example for a bug workaround, the kqueue backend might only support
1149	sockets on some platform, so it is unusable as generic backend, but you	2417	sockets on some platform, so it is unusable as generic backend, but you
1150	still want to make use of it because you have many sockets and it scales	2418	still want to make use of it because you have many sockets and it scales
1151	so nicely. In this case, you would create a kqueue-based loop and embed it	2419	so nicely. In this case, you would create a kqueue-based loop and embed
1152	into your default loop (which might use e.g. poll). Overall operation will	2420	it into your default loop (which might use e.g. poll). Overall operation
1153	be a bit slower because first libev has to poll and then call kevent, but	2421	will be a bit slower because first libev has to call C<poll> and then
1154	at least you can use both at what they are best.	2422	C<kevent>, but at least you can use both mechanisms for what they are
		2423	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1155		2424
1156	As for prioritising I/O: rarely you have the case where some fds have	2425	As for prioritising I/O: under rare circumstances you have the case where
1157	to be watched and handled very quickly (with low latency), and even	2426	some fds have to be watched and handled very quickly (with low latency),
1158	priorities and idle watchers might have too much overhead. In this case	2427	and even priorities and idle watchers might have too much overhead. In
1159	you would put all the high priority stuff in one loop and all the rest in	2428	this case you would put all the high priority stuff in one loop and all
1160	a second one, and embed the second one in the first.	2429	the rest in a second one, and embed the second one in the first.
1161		2430
1162	As long as the watcher is active, the callback will be invoked every time	2431	As long as the watcher is active, the callback will be invoked every time
1163	there might be events pending in the embedded loop. The callback must then	2432	there might be events pending in the embedded loop. The callback must then
1164	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2433	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke
1165	their callbacks (you could also start an idle watcher to give the embedded	2434	their callbacks (you could also start an idle watcher to give the embedded
…		…
1173	interested in that.	2442	interested in that.
1174		2443
1175	Also, there have not currently been made special provisions for forking:	2444	Also, there have not currently been made special provisions for forking:
1176	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2445	when you fork, you not only have to call C<ev_loop_fork> on both loops,
1177	but you will also have to stop and restart any C<ev_embed> watchers	2446	but you will also have to stop and restart any C<ev_embed> watchers
1178	yourself.	2447	yourself - but you can use a fork watcher to handle this automatically,
		2448	and future versions of libev might do just that.
1179		2449
1180	Unfortunately, not all backends are embeddable, only the ones returned by	2450	Unfortunately, not all backends are embeddable: only the ones returned by
1181	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2451	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1182	portable one.	2452	portable one.
1183		2453
1184	So when you want to use this feature you will always have to be prepared	2454	So when you want to use this feature you will always have to be prepared
1185	that you cannot get an embeddable loop. The recommended way to get around	2455	that you cannot get an embeddable loop. The recommended way to get around
1186	this is to have a separate variables for your embeddable loop, try to	2456	this is to have a separate variables for your embeddable loop, try to
1187	create it, and if that fails, use the normal loop for everything:	2457	create it, and if that fails, use the normal loop for everything.
1188		2458
1189	struct ev_loop *loop_hi = ev_default_init (0);	2459	=head3 C<ev_embed> and fork
1190	struct ev_loop *loop_lo = 0;
1191	struct ev_embed embed;
1192
1193	// see if there is a chance of getting one that works
1194	// (remember that a flags value of 0 means autodetection)
1195	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1196	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1197	: 0;
1198		2460
1199	// if we got one, then embed it, otherwise default to loop_hi	2461	While the C<ev_embed> watcher is running, forks in the embedding loop will
1200	if (loop_lo)	2462	automatically be applied to the embedded loop as well, so no special
1201	{	2463	fork handling is required in that case. When the watcher is not running,
1202	ev_embed_init (&embed, 0, loop_lo);	2464	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1203	ev_embed_start (loop_hi, &embed);	2465	as applicable.
1204	}	2466
1205	else	2467	=head3 Watcher-Specific Functions and Data Members
1206	loop_lo = loop_hi;
1207		2468
1208	=over 4	2469	=over 4
1209		2470
1210	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	2471	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
1211		2472
…		…
1213		2474
1214	Configures the watcher to embed the given loop, which must be	2475	Configures the watcher to embed the given loop, which must be
1215	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	2476	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1216	invoked automatically, otherwise it is the responsibility of the callback	2477	invoked automatically, otherwise it is the responsibility of the callback
1217	to invoke it (it will continue to be called until the sweep has been done,	2478	to invoke it (it will continue to be called until the sweep has been done,
1218	if you do not want thta, you need to temporarily stop the embed watcher).	2479	if you do not want that, you need to temporarily stop the embed watcher).
1219		2480
1220	=item ev_embed_sweep (loop, ev_embed *)	2481	=item ev_embed_sweep (loop, ev_embed *)
1221		2482
1222	Make a single, non-blocking sweep over the embedded loop. This works	2483	Make a single, non-blocking sweep over the embedded loop. This works
1223	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	2484	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
1224	apropriate way for embedded loops.	2485	appropriate way for embedded loops.
		2486
		2487	=item struct ev_loop *other [read-only]
		2488
		2489	The embedded event loop.
1225		2490
1226	=back	2491	=back
1227		2492
		2493	=head3 Examples
		2494
		2495	Example: Try to get an embeddable event loop and embed it into the default
		2496	event loop. If that is not possible, use the default loop. The default
		2497	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2498	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2499	used).
		2500
		2501	struct ev_loop *loop_hi = ev_default_init (0);
		2502	struct ev_loop *loop_lo = 0;
		2503	ev_embed embed;
		2504
		2505	// see if there is a chance of getting one that works
		2506	// (remember that a flags value of 0 means autodetection)
		2507	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2508	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2509	: 0;
		2510
		2511	// if we got one, then embed it, otherwise default to loop_hi
		2512	if (loop_lo)
		2513	{
		2514	ev_embed_init (&embed, 0, loop_lo);
		2515	ev_embed_start (loop_hi, &embed);
		2516	}
		2517	else
		2518	loop_lo = loop_hi;
		2519
		2520	Example: Check if kqueue is available but not recommended and create
		2521	a kqueue backend for use with sockets (which usually work with any
		2522	kqueue implementation). Store the kqueue/socket-only event loop in
		2523	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2524
		2525	struct ev_loop *loop = ev_default_init (0);
		2526	struct ev_loop *loop_socket = 0;
		2527	ev_embed embed;
		2528
		2529	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2530	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2531	{
		2532	ev_embed_init (&embed, 0, loop_socket);
		2533	ev_embed_start (loop, &embed);
		2534	}
		2535
		2536	if (!loop_socket)
		2537	loop_socket = loop;
		2538
		2539	// now use loop_socket for all sockets, and loop for everything else
		2540
		2541
		2542	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		2543
		2544	Fork watchers are called when a C<fork ()> was detected (usually because
		2545	whoever is a good citizen cared to tell libev about it by calling
		2546	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		2547	event loop blocks next and before C<ev_check> watchers are being called,
		2548	and only in the child after the fork. If whoever good citizen calling
		2549	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		2550	handlers will be invoked, too, of course.
		2551
		2552	=head3 Watcher-Specific Functions and Data Members
		2553
		2554	=over 4
		2555
		2556	=item ev_fork_init (ev_signal *, callback)
		2557
		2558	Initialises and configures the fork watcher - it has no parameters of any
		2559	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		2560	believe me.
		2561
		2562	=back
		2563
		2564
		2565	=head2 C<ev_async> - how to wake up another event loop
		2566
		2567	In general, you cannot use an C<ev_loop> from multiple threads or other
		2568	asynchronous sources such as signal handlers (as opposed to multiple event
		2569	loops - those are of course safe to use in different threads).
		2570
		2571	Sometimes, however, you need to wake up another event loop you do not
		2572	control, for example because it belongs to another thread. This is what
		2573	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2574	can signal it by calling C<ev_async_send>, which is thread- and signal
		2575	safe.
		2576
		2577	This functionality is very similar to C<ev_signal> watchers, as signals,
		2578	too, are asynchronous in nature, and signals, too, will be compressed
		2579	(i.e. the number of callback invocations may be less than the number of
		2580	C<ev_async_sent> calls).
		2581
		2582	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2583	just the default loop.
		2584
		2585	=head3 Queueing
		2586
		2587	C<ev_async> does not support queueing of data in any way. The reason
		2588	is that the author does not know of a simple (or any) algorithm for a
		2589	multiple-writer-single-reader queue that works in all cases and doesn't
		2590	need elaborate support such as pthreads.
		2591
		2592	That means that if you want to queue data, you have to provide your own
		2593	queue. But at least I can tell you how to implement locking around your
		2594	queue:
		2595
		2596	=over 4
		2597
		2598	=item queueing from a signal handler context
		2599
		2600	To implement race-free queueing, you simply add to the queue in the signal
		2601	handler but you block the signal handler in the watcher callback. Here is
		2602	an example that does that for some fictitious SIGUSR1 handler:
		2603
		2604	static ev_async mysig;
		2605
		2606	static void
		2607	sigusr1_handler (void)
		2608	{
		2609	sometype data;
		2610
		2611	// no locking etc.
		2612	queue_put (data);
		2613	ev_async_send (EV_DEFAULT_ &mysig);
		2614	}
		2615
		2616	static void
		2617	mysig_cb (EV_P_ ev_async *w, int revents)
		2618	{
		2619	sometype data;
		2620	sigset_t block, prev;
		2621
		2622	sigemptyset (&block);
		2623	sigaddset (&block, SIGUSR1);
		2624	sigprocmask (SIG_BLOCK, &block, &prev);
		2625
		2626	while (queue_get (&data))
		2627	process (data);
		2628
		2629	if (sigismember (&prev, SIGUSR1)
		2630	sigprocmask (SIG_UNBLOCK, &block, 0);
		2631	}
		2632
		2633	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2634	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2635	either...).
		2636
		2637	=item queueing from a thread context
		2638
		2639	The strategy for threads is different, as you cannot (easily) block
		2640	threads but you can easily preempt them, so to queue safely you need to
		2641	employ a traditional mutex lock, such as in this pthread example:
		2642
		2643	static ev_async mysig;
		2644	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2645
		2646	static void
		2647	otherthread (void)
		2648	{
		2649	// only need to lock the actual queueing operation
		2650	pthread_mutex_lock (&mymutex);
		2651	queue_put (data);
		2652	pthread_mutex_unlock (&mymutex);
		2653
		2654	ev_async_send (EV_DEFAULT_ &mysig);
		2655	}
		2656
		2657	static void
		2658	mysig_cb (EV_P_ ev_async *w, int revents)
		2659	{
		2660	pthread_mutex_lock (&mymutex);
		2661
		2662	while (queue_get (&data))
		2663	process (data);
		2664
		2665	pthread_mutex_unlock (&mymutex);
		2666	}
		2667
		2668	=back
		2669
		2670
		2671	=head3 Watcher-Specific Functions and Data Members
		2672
		2673	=over 4
		2674
		2675	=item ev_async_init (ev_async *, callback)
		2676
		2677	Initialises and configures the async watcher - it has no parameters of any
		2678	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		2679	trust me.
		2680
		2681	=item ev_async_send (loop, ev_async *)
		2682
		2683	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2684	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2685	C<ev_feed_event>, this call is safe to do from other threads, signal or
		2686	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		2687	section below on what exactly this means).
		2688
		2689	This call incurs the overhead of a system call only once per loop iteration,
		2690	so while the overhead might be noticeable, it doesn't apply to repeated
		2691	calls to C<ev_async_send>.
		2692
		2693	=item bool = ev_async_pending (ev_async *)
		2694
		2695	Returns a non-zero value when C<ev_async_send> has been called on the
		2696	watcher but the event has not yet been processed (or even noted) by the
		2697	event loop.
		2698
		2699	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2700	the loop iterates next and checks for the watcher to have become active,
		2701	it will reset the flag again. C<ev_async_pending> can be used to very
		2702	quickly check whether invoking the loop might be a good idea.
		2703
		2704	Not that this does I<not> check whether the watcher itself is pending, only
		2705	whether it has been requested to make this watcher pending.
		2706
		2707	=back
		2708
1228		2709
1229	=head1 OTHER FUNCTIONS	2710	=head1 OTHER FUNCTIONS
1230		2711
1231	There are some other functions of possible interest. Described. Here. Now.	2712	There are some other functions of possible interest. Described. Here. Now.
1232		2713
1233	=over 4	2714	=over 4
1234		2715
1235	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	2716	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1236		2717
1237	This function combines a simple timer and an I/O watcher, calls your	2718	This function combines a simple timer and an I/O watcher, calls your
1238	callback on whichever event happens first and automatically stop both	2719	callback on whichever event happens first and automatically stops both
1239	watchers. This is useful if you want to wait for a single event on an fd	2720	watchers. This is useful if you want to wait for a single event on an fd
1240	or timeout without having to allocate/configure/start/stop/free one or	2721	or timeout without having to allocate/configure/start/stop/free one or
1241	more watchers yourself.	2722	more watchers yourself.
1242		2723
1243	If C<fd> is less than 0, then no I/O watcher will be started and events	2724	If C<fd> is less than 0, then no I/O watcher will be started and the
1244	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	2725	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1245	C<events> set will be craeted and started.	2726	the given C<fd> and C<events> set will be created and started.
1246		2727
1247	If C<timeout> is less than 0, then no timeout watcher will be	2728	If C<timeout> is less than 0, then no timeout watcher will be
1248	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	2729	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1249	repeat = 0) will be started. While C<0> is a valid timeout, it is of	2730	repeat = 0) will be started. C<0> is a valid timeout.
1250	dubious value.
1251		2731
1252	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	2732	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
1253	passed an C<revents> set like normal event callbacks (a combination of	2733	passed an C<revents> set like normal event callbacks (a combination of
1254	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	2734	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
1255	value passed to C<ev_once>:	2735	value passed to C<ev_once>. Note that it is possible to receive I<both>
		2736	a timeout and an io event at the same time - you probably should give io
		2737	events precedence.
1256		2738
		2739	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		2740
1257	static void stdin_ready (int revents, void *arg)	2741	static void stdin_ready (int revents, void *arg)
1258	{	2742	{
1259	if (revents & EV_TIMEOUT)
1260	/* doh, nothing entered */;
1261	else if (revents & EV_READ)	2743	if (revents & EV_READ)
1262	/* stdin might have data for us, joy! */;	2744	/* stdin might have data for us, joy! */;
		2745	else if (revents & EV_TIMEOUT)
		2746	/* doh, nothing entered */;
1263	}	2747	}
1264		2748
1265	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2749	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1266		2750
1267	=item ev_feed_event (ev_loop *, watcher *, int revents)	2751	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
1268		2752
1269	Feeds the given event set into the event loop, as if the specified event	2753	Feeds the given event set into the event loop, as if the specified event
1270	had happened for the specified watcher (which must be a pointer to an	2754	had happened for the specified watcher (which must be a pointer to an
1271	initialised but not necessarily started event watcher).	2755	initialised but not necessarily started event watcher).
1272		2756
1273	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	2757	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
1274		2758
1275	Feed an event on the given fd, as if a file descriptor backend detected	2759	Feed an event on the given fd, as if a file descriptor backend detected
1276	the given events it.	2760	the given events it.
1277		2761
1278	=item ev_feed_signal_event (ev_loop *loop, int signum)	2762	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
1279		2763
1280	Feed an event as if the given signal occured (C<loop> must be the default	2764	Feed an event as if the given signal occurred (C<loop> must be the default
1281	loop!).	2765	loop!).
1282		2766
1283	=back	2767	=back
1284		2768
1285		2769
…		…
1301		2785
1302	=item * Priorities are not currently supported. Initialising priorities	2786	=item * Priorities are not currently supported. Initialising priorities
1303	will fail and all watchers will have the same priority, even though there	2787	will fail and all watchers will have the same priority, even though there
1304	is an ev_pri field.	2788	is an ev_pri field.
1305		2789
		2790	=item * In libevent, the last base created gets the signals, in libev, the
		2791	first base created (== the default loop) gets the signals.
		2792
1306	=item * Other members are not supported.	2793	=item * Other members are not supported.
1307		2794
1308	=item * The libev emulation is I<not> ABI compatible to libevent, you need	2795	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1309	to use the libev header file and library.	2796	to use the libev header file and library.
1310		2797
1311	=back	2798	=back
1312		2799
1313	=head1 C++ SUPPORT	2800	=head1 C++ SUPPORT
1314		2801
1315	Libev comes with some simplistic wrapper classes for C++ that mainly allow	2802	Libev comes with some simplistic wrapper classes for C++ that mainly allow
1316	you to use some convinience methods to start/stop watchers and also change	2803	you to use some convenience methods to start/stop watchers and also change
1317	the callback model to a model using method callbacks on objects.	2804	the callback model to a model using method callbacks on objects.
1318		2805
1319	To use it,	2806	To use it,
1320		2807
1321	#include <ev++.h>	2808	#include <ev++.h>
1322		2809
1323	(it is not installed by default). This automatically includes F<ev.h>	2810	This automatically includes F<ev.h> and puts all of its definitions (many
1324	and puts all of its definitions (many of them macros) into the global	2811	of them macros) into the global namespace. All C++ specific things are
1325	namespace. All C++ specific things are put into the C<ev> namespace.	2812	put into the C<ev> namespace. It should support all the same embedding
		2813	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
1326		2814
1327	It should support all the same embedding options as F<ev.h>, most notably	2815	Care has been taken to keep the overhead low. The only data member the C++
1328	C<EV_MULTIPLICITY>.	2816	classes add (compared to plain C-style watchers) is the event loop pointer
		2817	that the watcher is associated with (or no additional members at all if
		2818	you disable C<EV_MULTIPLICITY> when embedding libev).
		2819
		2820	Currently, functions, and static and non-static member functions can be
		2821	used as callbacks. Other types should be easy to add as long as they only
		2822	need one additional pointer for context. If you need support for other
		2823	types of functors please contact the author (preferably after implementing
		2824	it).
1329		2825
1330	Here is a list of things available in the C<ev> namespace:	2826	Here is a list of things available in the C<ev> namespace:
1331		2827
1332	=over 4	2828	=over 4
1333		2829
…		…
1349		2845
1350	All of those classes have these methods:	2846	All of those classes have these methods:
1351		2847
1352	=over 4	2848	=over 4
1353		2849
1354	=item ev::TYPE::TYPE (object *, object::method *)	2850	=item ev::TYPE::TYPE ()
1355		2851
1356	=item ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)	2852	=item ev::TYPE::TYPE (struct ev_loop *)
1357		2853
1358	=item ev::TYPE::~TYPE	2854	=item ev::TYPE::~TYPE
1359		2855
1360	The constructor takes a pointer to an object and a method pointer to	2856	The constructor (optionally) takes an event loop to associate the watcher
1361	the event handler callback to call in this class. The constructor calls	2857	with. If it is omitted, it will use C<EV_DEFAULT>.
1362	C<ev_init> for you, which means you have to call the C<set> method	2858
1363	before starting it. If you do not specify a loop then the constructor	2859	The constructor calls C<ev_init> for you, which means you have to call the
1364	automatically associates the default loop with this watcher.	2860	C<set> method before starting it.
		2861
		2862	It will not set a callback, however: You have to call the templated C<set>
		2863	method to set a callback before you can start the watcher.
		2864
		2865	(The reason why you have to use a method is a limitation in C++ which does
		2866	not allow explicit template arguments for constructors).
1365		2867
1366	The destructor automatically stops the watcher if it is active.	2868	The destructor automatically stops the watcher if it is active.
		2869
		2870	=item w->set<class, &class::method> (object *)
		2871
		2872	This method sets the callback method to call. The method has to have a
		2873	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		2874	first argument and the C<revents> as second. The object must be given as
		2875	parameter and is stored in the C<data> member of the watcher.
		2876
		2877	This method synthesizes efficient thunking code to call your method from
		2878	the C callback that libev requires. If your compiler can inline your
		2879	callback (i.e. it is visible to it at the place of the C<set> call and
		2880	your compiler is good :), then the method will be fully inlined into the
		2881	thunking function, making it as fast as a direct C callback.
		2882
		2883	Example: simple class declaration and watcher initialisation
		2884
		2885	struct myclass
		2886	{
		2887	void io_cb (ev::io &w, int revents) { }
		2888	}
		2889
		2890	myclass obj;
		2891	ev::io iow;
		2892	iow.set <myclass, &myclass::io_cb> (&obj);
		2893
		2894	=item w->set<function> (void *data = 0)
		2895
		2896	Also sets a callback, but uses a static method or plain function as
		2897	callback. The optional C<data> argument will be stored in the watcher's
		2898	C<data> member and is free for you to use.
		2899
		2900	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		2901
		2902	See the method-C<set> above for more details.
		2903
		2904	Example: Use a plain function as callback.
		2905
		2906	static void io_cb (ev::io &w, int revents) { }
		2907	iow.set <io_cb> ();
1367		2908
1368	=item w->set (struct ev_loop *)	2909	=item w->set (struct ev_loop *)
1369		2910
1370	Associates a different C<struct ev_loop> with this watcher. You can only	2911	Associates a different C<struct ev_loop> with this watcher. You can only
1371	do this when the watcher is inactive (and not pending either).	2912	do this when the watcher is inactive (and not pending either).
1372		2913
1373	=item w->set ([args])	2914	=item w->set ([arguments])
1374		2915
1375	Basically the same as C<ev_TYPE_set>, with the same args. Must be	2916	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
1376	called at least once. Unlike the C counterpart, an active watcher gets	2917	called at least once. Unlike the C counterpart, an active watcher gets
1377	automatically stopped and restarted.	2918	automatically stopped and restarted when reconfiguring it with this
		2919	method.
1378		2920
1379	=item w->start ()	2921	=item w->start ()
1380		2922
1381	Starts the watcher. Note that there is no C<loop> argument as the	2923	Starts the watcher. Note that there is no C<loop> argument, as the
1382	constructor already takes the loop.	2924	constructor already stores the event loop.
1383		2925
1384	=item w->stop ()	2926	=item w->stop ()
1385		2927
1386	Stops the watcher if it is active. Again, no C<loop> argument.	2928	Stops the watcher if it is active. Again, no C<loop> argument.
1387		2929
1388	=item w->again () C<ev::timer>, C<ev::periodic> only	2930	=item w->again () (C<ev::timer>, C<ev::periodic> only)
1389		2931
1390	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding	2932	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
1391	C<ev_TYPE_again> function.	2933	C<ev_TYPE_again> function.
1392		2934
1393	=item w->sweep () C<ev::embed> only	2935	=item w->sweep () (C<ev::embed> only)
1394		2936
1395	Invokes C<ev_embed_sweep>.	2937	Invokes C<ev_embed_sweep>.
		2938
		2939	=item w->update () (C<ev::stat> only)
		2940
		2941	Invokes C<ev_stat_stat>.
1396		2942
1397	=back	2943	=back
1398		2944
1399	=back	2945	=back
1400		2946
1401	Example: Define a class with an IO and idle watcher, start one of them in	2947	Example: Define a class with an IO and idle watcher, start one of them in
1402	the constructor.	2948	the constructor.
1403		2949
1404	class myclass	2950	class myclass
1405	{	2951	{
1406	ev_io io; void io_cb (ev::io &w, int revents);	2952	ev::io io ; void io_cb (ev::io &w, int revents);
1407	ev_idle idle void idle_cb (ev::idle &w, int revents);	2953	ev::idle idle; void idle_cb (ev::idle &w, int revents);
1408		2954
1409	myclass ();	2955	myclass (int fd)
1410	}	2956	{
		2957	io .set <myclass, &myclass::io_cb > (this);
		2958	idle.set <myclass, &myclass::idle_cb> (this);
1411		2959
1412	myclass::myclass (int fd)
1413	: io (this, &myclass::io_cb),
1414	idle (this, &myclass::idle_cb)
1415	{
1416	io.start (fd, ev::READ);	2960	io.start (fd, ev::READ);
		2961	}
		2962	};
		2963
		2964
		2965	=head1 OTHER LANGUAGE BINDINGS
		2966
		2967	Libev does not offer other language bindings itself, but bindings for a
		2968	number of languages exist in the form of third-party packages. If you know
		2969	any interesting language binding in addition to the ones listed here, drop
		2970	me a note.
		2971
		2972	=over 4
		2973
		2974	=item Perl
		2975
		2976	The EV module implements the full libev API and is actually used to test
		2977	libev. EV is developed together with libev. Apart from the EV core module,
		2978	there are additional modules that implement libev-compatible interfaces
		2979	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		2980	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		2981	and C<EV::Glib>).
		2982
		2983	It can be found and installed via CPAN, its homepage is at
		2984	L<http://software.schmorp.de/pkg/EV>.
		2985
		2986	=item Python
		2987
		2988	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		2989	seems to be quite complete and well-documented. Note, however, that the
		2990	patch they require for libev is outright dangerous as it breaks the ABI
		2991	for everybody else, and therefore, should never be applied in an installed
		2992	libev (if python requires an incompatible ABI then it needs to embed
		2993	libev).
		2994
		2995	=item Ruby
		2996
		2997	Tony Arcieri has written a ruby extension that offers access to a subset
		2998	of the libev API and adds file handle abstractions, asynchronous DNS and
		2999	more on top of it. It can be found via gem servers. Its homepage is at
		3000	L<http://rev.rubyforge.org/>.
		3001
		3002	=item D
		3003
		3004	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3005	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3006
		3007	=item Ocaml
		3008
		3009	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3010	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3011
		3012	=back
		3013
		3014
		3015	=head1 MACRO MAGIC
		3016
		3017	Libev can be compiled with a variety of options, the most fundamental
		3018	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		3019	functions and callbacks have an initial C<struct ev_loop *> argument.
		3020
		3021	To make it easier to write programs that cope with either variant, the
		3022	following macros are defined:
		3023
		3024	=over 4
		3025
		3026	=item C<EV_A>, C<EV_A_>
		3027
		3028	This provides the loop I<argument> for functions, if one is required ("ev
		3029	loop argument"). The C<EV_A> form is used when this is the sole argument,
		3030	C<EV_A_> is used when other arguments are following. Example:
		3031
		3032	ev_unref (EV_A);
		3033	ev_timer_add (EV_A_ watcher);
		3034	ev_loop (EV_A_ 0);
		3035
		3036	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		3037	which is often provided by the following macro.
		3038
		3039	=item C<EV_P>, C<EV_P_>
		3040
		3041	This provides the loop I<parameter> for functions, if one is required ("ev
		3042	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		3043	C<EV_P_> is used when other parameters are following. Example:
		3044
		3045	// this is how ev_unref is being declared
		3046	static void ev_unref (EV_P);
		3047
		3048	// this is how you can declare your typical callback
		3049	static void cb (EV_P_ ev_timer *w, int revents)
		3050
		3051	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		3052	suitable for use with C<EV_A>.
		3053
		3054	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		3055
		3056	Similar to the other two macros, this gives you the value of the default
		3057	loop, if multiple loops are supported ("ev loop default").
		3058
		3059	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3060
		3061	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3062	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3063	is undefined when the default loop has not been initialised by a previous
		3064	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3065
		3066	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3067	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		3068
		3069	=back
		3070
		3071	Example: Declare and initialise a check watcher, utilising the above
		3072	macros so it will work regardless of whether multiple loops are supported
		3073	or not.
		3074
		3075	static void
		3076	check_cb (EV_P_ ev_timer *w, int revents)
		3077	{
		3078	ev_check_stop (EV_A_ w);
1417	}	3079	}
		3080
		3081	ev_check check;
		3082	ev_check_init (&check, check_cb);
		3083	ev_check_start (EV_DEFAULT_ &check);
		3084	ev_loop (EV_DEFAULT_ 0);
1418		3085
1419	=head1 EMBEDDING	3086	=head1 EMBEDDING
1420		3087
1421	Libev can (and often is) directly embedded into host	3088	Libev can (and often is) directly embedded into host
1422	applications. Examples of applications that embed it include the Deliantra	3089	applications. Examples of applications that embed it include the Deliantra
1423	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)	3090	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
1424	and rxvt-unicode.	3091	and rxvt-unicode.
1425		3092
1426	The goal is to enable you to just copy the neecssary files into your	3093	The goal is to enable you to just copy the necessary files into your
1427	source directory without having to change even a single line in them, so	3094	source directory without having to change even a single line in them, so
1428	you can easily upgrade by simply copying (or having a checked-out copy of	3095	you can easily upgrade by simply copying (or having a checked-out copy of
1429	libev somewhere in your source tree).	3096	libev somewhere in your source tree).
1430		3097
1431	=head2 FILESETS	3098	=head2 FILESETS
1432		3099
1433	Depending on what features you need you need to include one or more sets of files	3100	Depending on what features you need you need to include one or more sets of files
1434	in your app.	3101	in your application.
1435		3102
1436	=head3 CORE EVENT LOOP	3103	=head3 CORE EVENT LOOP
1437		3104
1438	To include only the libev core (all the C<ev_*> functions), with manual	3105	To include only the libev core (all the C<ev_*> functions), with manual
1439	configuration (no autoconf):	3106	configuration (no autoconf):
1440		3107
1441	#define EV_STANDALONE 1	3108	#define EV_STANDALONE 1
1442	#include "ev.c"	3109	#include "ev.c"
1443		3110
1444	This will automatically include F<ev.h>, too, and should be done in a	3111	This will automatically include F<ev.h>, too, and should be done in a
1445	single C source file only to provide the function implementations. To use	3112	single C source file only to provide the function implementations. To use
1446	it, do the same for F<ev.h> in all files wishing to use this API (best	3113	it, do the same for F<ev.h> in all files wishing to use this API (best
1447	done by writing a wrapper around F<ev.h> that you can include instead and	3114	done by writing a wrapper around F<ev.h> that you can include instead and
1448	where you can put other configuration options):	3115	where you can put other configuration options):
1449		3116
1450	#define EV_STANDALONE 1	3117	#define EV_STANDALONE 1
1451	#include "ev.h"	3118	#include "ev.h"
1452		3119
1453	Both header files and implementation files can be compiled with a C++	3120	Both header files and implementation files can be compiled with a C++
1454	compiler (at least, thats a stated goal, and breakage will be treated	3121	compiler (at least, that's a stated goal, and breakage will be treated
1455	as a bug).	3122	as a bug).
1456		3123
1457	You need the following files in your source tree, or in a directory	3124	You need the following files in your source tree, or in a directory
1458	in your include path (e.g. in libev/ when using -Ilibev):	3125	in your include path (e.g. in libev/ when using -Ilibev):
1459		3126
1460	ev.h	3127	ev.h
1461	ev.c	3128	ev.c
1462	ev_vars.h	3129	ev_vars.h
1463	ev_wrap.h	3130	ev_wrap.h
1464		3131
1465	ev_win32.c required on win32 platforms only	3132	ev_win32.c required on win32 platforms only
1466		3133
1467	ev_select.c only when select backend is enabled (which is is by default)	3134	ev_select.c only when select backend is enabled (which is enabled by default)
1468	ev_poll.c only when poll backend is enabled (disabled by default)	3135	ev_poll.c only when poll backend is enabled (disabled by default)
1469	ev_epoll.c only when the epoll backend is enabled (disabled by default)	3136	ev_epoll.c only when the epoll backend is enabled (disabled by default)
1470	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	3137	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
1471	ev_port.c only when the solaris port backend is enabled (disabled by default)	3138	ev_port.c only when the solaris port backend is enabled (disabled by default)
1472		3139
1473	F<ev.c> includes the backend files directly when enabled, so you only need	3140	F<ev.c> includes the backend files directly when enabled, so you only need
1474	to compile a single file.	3141	to compile this single file.
1475		3142
1476	=head3 LIBEVENT COMPATIBILITY API	3143	=head3 LIBEVENT COMPATIBILITY API
1477		3144
1478	To include the libevent compatibility API, also include:	3145	To include the libevent compatibility API, also include:
1479		3146
1480	#include "event.c"	3147	#include "event.c"
1481		3148
1482	in the file including F<ev.c>, and:	3149	in the file including F<ev.c>, and:
1483		3150
1484	#include "event.h"	3151	#include "event.h"
1485		3152
1486	in the files that want to use the libevent API. This also includes F<ev.h>.	3153	in the files that want to use the libevent API. This also includes F<ev.h>.
1487		3154
1488	You need the following additional files for this:	3155	You need the following additional files for this:
1489		3156
1490	event.h	3157	event.h
1491	event.c	3158	event.c
1492		3159
1493	=head3 AUTOCONF SUPPORT	3160	=head3 AUTOCONF SUPPORT
1494		3161
1495	Instead of using C<EV_STANDALONE=1> and providing your config in	3162	Instead of using C<EV_STANDALONE=1> and providing your configuration in
1496	whatever way you want, you can also C<m4_include([libev.m4])> in your	3163	whatever way you want, you can also C<m4_include([libev.m4])> in your
1497	F<configure.ac> and leave C<EV_STANDALONE> off. F<ev.c> will then include	3164	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
1498	F<config.h> and configure itself accordingly.	3165	include F<config.h> and configure itself accordingly.
1499		3166
1500	For this of course you need the m4 file:	3167	For this of course you need the m4 file:
1501		3168
1502	libev.m4	3169	libev.m4
1503		3170
1504	=head2 PREPROCESSOR SYMBOLS/MACROS	3171	=head2 PREPROCESSOR SYMBOLS/MACROS
1505		3172
1506	Libev can be configured via a variety of preprocessor symbols you have to define	3173	Libev can be configured via a variety of preprocessor symbols you have to
1507	before including any of its files. The default is not to build for multiplicity	3174	define before including any of its files. The default in the absence of
1508	and only include the select backend.	3175	autoconf is documented for every option.
1509		3176
1510	=over 4	3177	=over 4
1511		3178
1512	=item EV_STANDALONE	3179	=item EV_STANDALONE
1513		3180
…		…
1518	F<event.h> that are not directly supported by the libev core alone.	3185	F<event.h> that are not directly supported by the libev core alone.
1519		3186
1520	=item EV_USE_MONOTONIC	3187	=item EV_USE_MONOTONIC
1521		3188
1522	If defined to be C<1>, libev will try to detect the availability of the	3189	If defined to be C<1>, libev will try to detect the availability of the
1523	monotonic clock option at both compiletime and runtime. Otherwise no use	3190	monotonic clock option at both compile time and runtime. Otherwise no use
1524	of the monotonic clock option will be attempted. If you enable this, you	3191	of the monotonic clock option will be attempted. If you enable this, you
1525	usually have to link against librt or something similar. Enabling it when	3192	usually have to link against librt or something similar. Enabling it when
1526	the functionality isn't available is safe, though, althoguh you have	3193	the functionality isn't available is safe, though, although you have
1527	to make sure you link against any libraries where the C<clock_gettime>	3194	to make sure you link against any libraries where the C<clock_gettime>
1528	function is hiding in (often F<-lrt>).	3195	function is hiding in (often F<-lrt>).
1529		3196
1530	=item EV_USE_REALTIME	3197	=item EV_USE_REALTIME
1531		3198
1532	If defined to be C<1>, libev will try to detect the availability of the	3199	If defined to be C<1>, libev will try to detect the availability of the
1533	realtime clock option at compiletime (and assume its availability at	3200	real-time clock option at compile time (and assume its availability at
1534	runtime if successful). Otherwise no use of the realtime clock option will	3201	runtime if successful). Otherwise no use of the real-time clock option will
1535	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3202	be attempted. This effectively replaces C<gettimeofday> by C<clock_get
1536	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See tzhe note about libraries	3203	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the
1537	in the description of C<EV_USE_MONOTONIC>, though.	3204	note about libraries in the description of C<EV_USE_MONOTONIC>, though.
		3205
		3206	=item EV_USE_NANOSLEEP
		3207
		3208	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		3209	and will use it for delays. Otherwise it will use C<select ()>.
		3210
		3211	=item EV_USE_EVENTFD
		3212
		3213	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3214	available and will probe for kernel support at runtime. This will improve
		3215	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3216	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3217	2.7 or newer, otherwise disabled.
1538		3218
1539	=item EV_USE_SELECT	3219	=item EV_USE_SELECT
1540		3220
1541	If undefined or defined to be C<1>, libev will compile in support for the	3221	If undefined or defined to be C<1>, libev will compile in support for the
1542	C<select>(2) backend. No attempt at autodetection will be done: if no	3222	C<select>(2) backend. No attempt at auto-detection will be done: if no
1543	other method takes over, select will be it. Otherwise the select backend	3223	other method takes over, select will be it. Otherwise the select backend
1544	will not be compiled in.	3224	will not be compiled in.
1545		3225
1546	=item EV_SELECT_USE_FD_SET	3226	=item EV_SELECT_USE_FD_SET
1547		3227
1548	If defined to C<1>, then the select backend will use the system C<fd_set>	3228	If defined to C<1>, then the select backend will use the system C<fd_set>
1549	structure. This is useful if libev doesn't compile due to a missing	3229	structure. This is useful if libev doesn't compile due to a missing
1550	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	3230	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout on
1551	exotic systems. This usually limits the range of file descriptors to some	3231	exotic systems. This usually limits the range of file descriptors to some
1552	low limit such as 1024 or might have other limitations (winsocket only	3232	low limit such as 1024 or might have other limitations (winsocket only
1553	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3233	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might
1554	influence the size of the C<fd_set> used.	3234	influence the size of the C<fd_set> used.
1555		3235
…		…
1561	be used is the winsock select). This means that it will call	3241	be used is the winsock select). This means that it will call
1562	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3242	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
1563	it is assumed that all these functions actually work on fds, even	3243	it is assumed that all these functions actually work on fds, even
1564	on win32. Should not be defined on non-win32 platforms.	3244	on win32. Should not be defined on non-win32 platforms.
1565		3245
		3246	=item EV_FD_TO_WIN32_HANDLE
		3247
		3248	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3249	file descriptors to socket handles. When not defining this symbol (the
		3250	default), then libev will call C<_get_osfhandle>, which is usually
		3251	correct. In some cases, programs use their own file descriptor management,
		3252	in which case they can provide this function to map fds to socket handles.
		3253
1566	=item EV_USE_POLL	3254	=item EV_USE_POLL
1567		3255
1568	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3256	If defined to be C<1>, libev will compile in support for the C<poll>(2)
1569	backend. Otherwise it will be enabled on non-win32 platforms. It	3257	backend. Otherwise it will be enabled on non-win32 platforms. It
1570	takes precedence over select.	3258	takes precedence over select.
1571		3259
1572	=item EV_USE_EPOLL	3260	=item EV_USE_EPOLL
1573		3261
1574	If defined to be C<1>, libev will compile in support for the Linux	3262	If defined to be C<1>, libev will compile in support for the Linux
1575	C<epoll>(7) backend. Its availability will be detected at runtime,	3263	C<epoll>(7) backend. Its availability will be detected at runtime,
1576	otherwise another method will be used as fallback. This is the	3264	otherwise another method will be used as fallback. This is the preferred
1577	preferred backend for GNU/Linux systems.	3265	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3266	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
1578		3267
1579	=item EV_USE_KQUEUE	3268	=item EV_USE_KQUEUE
1580		3269
1581	If defined to be C<1>, libev will compile in support for the BSD style	3270	If defined to be C<1>, libev will compile in support for the BSD style
1582	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	3271	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
1583	otherwise another method will be used as fallback. This is the preferred	3272	otherwise another method will be used as fallback. This is the preferred
1584	backend for BSD and BSD-like systems, although on most BSDs kqueue only	3273	backend for BSD and BSD-like systems, although on most BSDs kqueue only
1585	supports some types of fds correctly (the only platform we found that	3274	supports some types of fds correctly (the only platform we found that
1586	supports ptys for example was NetBSD), so kqueue might be compiled in, but	3275	supports ptys for example was NetBSD), so kqueue might be compiled in, but
1587	not be used unless explicitly requested. The best way to use it is to find	3276	not be used unless explicitly requested. The best way to use it is to find
1588	out wether kqueue supports your type of fd properly and use an embedded	3277	out whether kqueue supports your type of fd properly and use an embedded
1589	kqueue loop.	3278	kqueue loop.
1590		3279
1591	=item EV_USE_PORT	3280	=item EV_USE_PORT
1592		3281
1593	If defined to be C<1>, libev will compile in support for the Solaris	3282	If defined to be C<1>, libev will compile in support for the Solaris
…		…
1595	otherwise another method will be used as fallback. This is the preferred	3284	otherwise another method will be used as fallback. This is the preferred
1596	backend for Solaris 10 systems.	3285	backend for Solaris 10 systems.
1597		3286
1598	=item EV_USE_DEVPOLL	3287	=item EV_USE_DEVPOLL
1599		3288
1600	reserved for future expansion, works like the USE symbols above.	3289	Reserved for future expansion, works like the USE symbols above.
		3290
		3291	=item EV_USE_INOTIFY
		3292
		3293	If defined to be C<1>, libev will compile in support for the Linux inotify
		3294	interface to speed up C<ev_stat> watchers. Its actual availability will
		3295	be detected at runtime. If undefined, it will be enabled if the headers
		3296	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3297
		3298	=item EV_ATOMIC_T
		3299
		3300	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3301	access is atomic with respect to other threads or signal contexts. No such
		3302	type is easily found in the C language, so you can provide your own type
		3303	that you know is safe for your purposes. It is used both for signal handler "locking"
		3304	as well as for signal and thread safety in C<ev_async> watchers.
		3305
		3306	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3307	(from F<signal.h>), which is usually good enough on most platforms.
1601		3308
1602	=item EV_H	3309	=item EV_H
1603		3310
1604	The name of the F<ev.h> header file used to include it. The default if	3311	The name of the F<ev.h> header file used to include it. The default if
1605	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This	3312	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
1606	can be used to virtually rename the F<ev.h> header file in case of conflicts.	3313	used to virtually rename the F<ev.h> header file in case of conflicts.
1607		3314
1608	=item EV_CONFIG_H	3315	=item EV_CONFIG_H
1609		3316
1610	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	3317	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
1611	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	3318	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
1612	C<EV_H>, above.	3319	C<EV_H>, above.
1613		3320
1614	=item EV_EVENT_H	3321	=item EV_EVENT_H
1615		3322
1616	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	3323	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
1617	of how the F<event.h> header can be found.	3324	of how the F<event.h> header can be found, the default is C<"event.h">.
1618		3325
1619	=item EV_PROTOTYPES	3326	=item EV_PROTOTYPES
1620		3327
1621	If defined to be C<0>, then F<ev.h> will not define any function	3328	If defined to be C<0>, then F<ev.h> will not define any function
1622	prototypes, but still define all the structs and other symbols. This is	3329	prototypes, but still define all the structs and other symbols. This is
…		…
1629	will have the C<struct ev_loop *> as first argument, and you can create	3336	will have the C<struct ev_loop *> as first argument, and you can create
1630	additional independent event loops. Otherwise there will be no support	3337	additional independent event loops. Otherwise there will be no support
1631	for multiple event loops and there is no first event loop pointer	3338	for multiple event loops and there is no first event loop pointer
1632	argument. Instead, all functions act on the single default loop.	3339	argument. Instead, all functions act on the single default loop.
1633		3340
		3341	=item EV_MINPRI
		3342
		3343	=item EV_MAXPRI
		3344
		3345	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		3346	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		3347	provide for more priorities by overriding those symbols (usually defined
		3348	to be C<-2> and C<2>, respectively).
		3349
		3350	When doing priority-based operations, libev usually has to linearly search
		3351	all the priorities, so having many of them (hundreds) uses a lot of space
		3352	and time, so using the defaults of five priorities (-2 .. +2) is usually
		3353	fine.
		3354
		3355	If your embedding application does not need any priorities, defining these
		3356	both to C<0> will save some memory and CPU.
		3357
1634	=item EV_PERIODICS	3358	=item EV_PERIODIC_ENABLE
1635		3359
1636	If undefined or defined to be C<1>, then periodic timers are supported,	3360	If undefined or defined to be C<1>, then periodic timers are supported. If
1637	otherwise not. This saves a few kb of code.	3361	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3362	code.
		3363
		3364	=item EV_IDLE_ENABLE
		3365
		3366	If undefined or defined to be C<1>, then idle watchers are supported. If
		3367	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3368	code.
		3369
		3370	=item EV_EMBED_ENABLE
		3371
		3372	If undefined or defined to be C<1>, then embed watchers are supported. If
		3373	defined to be C<0>, then they are not. Embed watchers rely on most other
		3374	watcher types, which therefore must not be disabled.
		3375
		3376	=item EV_STAT_ENABLE
		3377
		3378	If undefined or defined to be C<1>, then stat watchers are supported. If
		3379	defined to be C<0>, then they are not.
		3380
		3381	=item EV_FORK_ENABLE
		3382
		3383	If undefined or defined to be C<1>, then fork watchers are supported. If
		3384	defined to be C<0>, then they are not.
		3385
		3386	=item EV_ASYNC_ENABLE
		3387
		3388	If undefined or defined to be C<1>, then async watchers are supported. If
		3389	defined to be C<0>, then they are not.
		3390
		3391	=item EV_MINIMAL
		3392
		3393	If you need to shave off some kilobytes of code at the expense of some
		3394	speed, define this symbol to C<1>. Currently this is used to override some
		3395	inlining decisions, saves roughly 30% code size on amd64. It also selects a
		3396	much smaller 2-heap for timer management over the default 4-heap.
		3397
		3398	=item EV_PID_HASHSIZE
		3399
		3400	C<ev_child> watchers use a small hash table to distribute workload by
		3401	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
		3402	than enough. If you need to manage thousands of children you might want to
		3403	increase this value (I<must> be a power of two).
		3404
		3405	=item EV_INOTIFY_HASHSIZE
		3406
		3407	C<ev_stat> watchers use a small hash table to distribute workload by
		3408	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
		3409	usually more than enough. If you need to manage thousands of C<ev_stat>
		3410	watchers you might want to increase this value (I<must> be a power of
		3411	two).
		3412
		3413	=item EV_USE_4HEAP
		3414
		3415	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3416	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		3417	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		3418	faster performance with many (thousands) of watchers.
		3419
		3420	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3421	(disabled).
		3422
		3423	=item EV_HEAP_CACHE_AT
		3424
		3425	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3426	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		3427	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3428	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3429	but avoids random read accesses on heap changes. This improves performance
		3430	noticeably with many (hundreds) of watchers.
		3431
		3432	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3433	(disabled).
		3434
		3435	=item EV_VERIFY
		3436
		3437	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3438	be done: If set to C<0>, no internal verification code will be compiled
		3439	in. If set to C<1>, then verification code will be compiled in, but not
		3440	called. If set to C<2>, then the internal verification code will be
		3441	called once per loop, which can slow down libev. If set to C<3>, then the
		3442	verification code will be called very frequently, which will slow down
		3443	libev considerably.
		3444
		3445	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3446	C<0>.
1638		3447
1639	=item EV_COMMON	3448	=item EV_COMMON
1640		3449
1641	By default, all watchers have a C<void *data> member. By redefining	3450	By default, all watchers have a C<void *data> member. By redefining
1642	this macro to a something else you can include more and other types of	3451	this macro to a something else you can include more and other types of
1643	members. You have to define it each time you include one of the files,	3452	members. You have to define it each time you include one of the files,
1644	though, and it must be identical each time.	3453	though, and it must be identical each time.
1645		3454
1646	For example, the perl EV module uses something like this:	3455	For example, the perl EV module uses something like this:
1647		3456
1648	#define EV_COMMON \	3457	#define EV_COMMON \
1649	SV *self; /* contains this struct */ \	3458	SV *self; /* contains this struct */ \
1650	SV *cb_sv, *fh /* note no trailing ";" */	3459	SV *cb_sv, *fh /* note no trailing ";" */
1651		3460
1652	=item EV_CB_DECLARE(type)	3461	=item EV_CB_DECLARE (type)
1653		3462
1654	=item EV_CB_INVOKE(watcher,revents)	3463	=item EV_CB_INVOKE (watcher, revents)
1655		3464
1656	=item ev_set_cb(ev,cb)	3465	=item ev_set_cb (ev, cb)
1657		3466
1658	Can be used to change the callback member declaration in each watcher,	3467	Can be used to change the callback member declaration in each watcher,
1659	and the way callbacks are invoked and set. Must expand to a struct member	3468	and the way callbacks are invoked and set. Must expand to a struct member
1660	definition and a statement, respectively. See the F<ev.v> header file for	3469	definition and a statement, respectively. See the F<ev.h> header file for
1661	their default definitions. One possible use for overriding these is to	3470	their default definitions. One possible use for overriding these is to
1662	avoid the ev_loop pointer as first argument in all cases, or to use method	3471	avoid the C<struct ev_loop *> as first argument in all cases, or to use
1663	calls instead of plain function calls in C++.	3472	method calls instead of plain function calls in C++.
		3473
		3474	=back
		3475
		3476	=head2 EXPORTED API SYMBOLS
		3477
		3478	If you need to re-export the API (e.g. via a DLL) and you need a list of
		3479	exported symbols, you can use the provided F<Symbol.*> files which list
		3480	all public symbols, one per line:
		3481
		3482	Symbols.ev for libev proper
		3483	Symbols.event for the libevent emulation
		3484
		3485	This can also be used to rename all public symbols to avoid clashes with
		3486	multiple versions of libev linked together (which is obviously bad in
		3487	itself, but sometimes it is inconvenient to avoid this).
		3488
		3489	A sed command like this will create wrapper C<#define>'s that you need to
		3490	include before including F<ev.h>:
		3491
		3492	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		3493
		3494	This would create a file F<wrap.h> which essentially looks like this:
		3495
		3496	#define ev_backend myprefix_ev_backend
		3497	#define ev_check_start myprefix_ev_check_start
		3498	#define ev_check_stop myprefix_ev_check_stop
		3499	...
1664		3500
1665	=head2 EXAMPLES	3501	=head2 EXAMPLES
1666		3502
1667	For a real-world example of a program the includes libev	3503	For a real-world example of a program the includes libev
1668	verbatim, you can have a look at the EV perl module	3504	verbatim, you can have a look at the EV perl module
…		…
1671	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file	3507	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
1672	will be compiled. It is pretty complex because it provides its own header	3508	will be compiled. It is pretty complex because it provides its own header
1673	file.	3509	file.
1674		3510
1675	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	3511	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
1676	that everybody includes and which overrides some autoconf choices:	3512	that everybody includes and which overrides some configure choices:
1677		3513
		3514	#define EV_MINIMAL 1
1678	#define EV_USE_POLL 0	3515	#define EV_USE_POLL 0
1679	#define EV_MULTIPLICITY 0	3516	#define EV_MULTIPLICITY 0
1680	#define EV_PERIODICS 0	3517	#define EV_PERIODIC_ENABLE 0
		3518	#define EV_STAT_ENABLE 0
		3519	#define EV_FORK_ENABLE 0
1681	#define EV_CONFIG_H <config.h>	3520	#define EV_CONFIG_H <config.h>
		3521	#define EV_MINPRI 0
		3522	#define EV_MAXPRI 0
1682		3523
1683	#include "ev++.h"	3524	#include "ev++.h"
1684		3525
1685	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	3526	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
1686		3527
1687	#include "ev_cpp.h"	3528	#include "ev_cpp.h"
1688	#include "ev.c"	3529	#include "ev.c"
		3530
		3531	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
		3532
		3533	=head2 THREADS AND COROUTINES
		3534
		3535	=head3 THREADS
		3536
		3537	All libev functions are reentrant and thread-safe unless explicitly
		3538	documented otherwise, but libev implements no locking itself. This means
		3539	that you can use as many loops as you want in parallel, as long as there
		3540	are no concurrent calls into any libev function with the same loop
		3541	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		3542	of course): libev guarantees that different event loops share no data
		3543	structures that need any locking.
		3544
		3545	Or to put it differently: calls with different loop parameters can be done
		3546	concurrently from multiple threads, calls with the same loop parameter
		3547	must be done serially (but can be done from different threads, as long as
		3548	only one thread ever is inside a call at any point in time, e.g. by using
		3549	a mutex per loop).
		3550
		3551	Specifically to support threads (and signal handlers), libev implements
		3552	so-called C<ev_async> watchers, which allow some limited form of
		3553	concurrency on the same event loop, namely waking it up "from the
		3554	outside".
		3555
		3556	If you want to know which design (one loop, locking, or multiple loops
		3557	without or something else still) is best for your problem, then I cannot
		3558	help you, but here is some generic advice:
		3559
		3560	=over 4
		3561
		3562	=item * most applications have a main thread: use the default libev loop
		3563	in that thread, or create a separate thread running only the default loop.
		3564
		3565	This helps integrating other libraries or software modules that use libev
		3566	themselves and don't care/know about threading.
		3567
		3568	=item * one loop per thread is usually a good model.
		3569
		3570	Doing this is almost never wrong, sometimes a better-performance model
		3571	exists, but it is always a good start.
		3572
		3573	=item * other models exist, such as the leader/follower pattern, where one
		3574	loop is handed through multiple threads in a kind of round-robin fashion.
		3575
		3576	Choosing a model is hard - look around, learn, know that usually you can do
		3577	better than you currently do :-)
		3578
		3579	=item * often you need to talk to some other thread which blocks in the
		3580	event loop.
		3581
		3582	C<ev_async> watchers can be used to wake them up from other threads safely
		3583	(or from signal contexts...).
		3584
		3585	An example use would be to communicate signals or other events that only
		3586	work in the default loop by registering the signal watcher with the
		3587	default loop and triggering an C<ev_async> watcher from the default loop
		3588	watcher callback into the event loop interested in the signal.
		3589
		3590	=back
		3591
		3592	=head3 COROUTINES
		3593
		3594	Libev is very accommodating to coroutines ("cooperative threads"):
		3595	libev fully supports nesting calls to its functions from different
		3596	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3597	different coroutines, and switch freely between both coroutines running the
		3598	loop, as long as you don't confuse yourself). The only exception is that
		3599	you must not do this from C<ev_periodic> reschedule callbacks.
		3600
		3601	Care has been taken to ensure that libev does not keep local state inside
		3602	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		3603	they do not call any callbacks.
		3604
		3605	=head2 COMPILER WARNINGS
		3606
		3607	Depending on your compiler and compiler settings, you might get no or a
		3608	lot of warnings when compiling libev code. Some people are apparently
		3609	scared by this.
		3610
		3611	However, these are unavoidable for many reasons. For one, each compiler
		3612	has different warnings, and each user has different tastes regarding
		3613	warning options. "Warn-free" code therefore cannot be a goal except when
		3614	targeting a specific compiler and compiler-version.
		3615
		3616	Another reason is that some compiler warnings require elaborate
		3617	workarounds, or other changes to the code that make it less clear and less
		3618	maintainable.
		3619
		3620	And of course, some compiler warnings are just plain stupid, or simply
		3621	wrong (because they don't actually warn about the condition their message
		3622	seems to warn about). For example, certain older gcc versions had some
		3623	warnings that resulted an extreme number of false positives. These have
		3624	been fixed, but some people still insist on making code warn-free with
		3625	such buggy versions.
		3626
		3627	While libev is written to generate as few warnings as possible,
		3628	"warn-free" code is not a goal, and it is recommended not to build libev
		3629	with any compiler warnings enabled unless you are prepared to cope with
		3630	them (e.g. by ignoring them). Remember that warnings are just that:
		3631	warnings, not errors, or proof of bugs.
		3632
		3633
		3634	=head2 VALGRIND
		3635
		3636	Valgrind has a special section here because it is a popular tool that is
		3637	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		3638
		3639	If you think you found a bug (memory leak, uninitialised data access etc.)
		3640	in libev, then check twice: If valgrind reports something like:
		3641
		3642	==2274== definitely lost: 0 bytes in 0 blocks.
		3643	==2274== possibly lost: 0 bytes in 0 blocks.
		3644	==2274== still reachable: 256 bytes in 1 blocks.
		3645
		3646	Then there is no memory leak, just as memory accounted to global variables
		3647	is not a memleak - the memory is still being referenced, and didn't leak.
		3648
		3649	Similarly, under some circumstances, valgrind might report kernel bugs
		3650	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		3651	although an acceptable workaround has been found here), or it might be
		3652	confused.
		3653
		3654	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		3655	make it into some kind of religion.
		3656
		3657	If you are unsure about something, feel free to contact the mailing list
		3658	with the full valgrind report and an explanation on why you think this
		3659	is a bug in libev (best check the archives, too :). However, don't be
		3660	annoyed when you get a brisk "this is no bug" answer and take the chance
		3661	of learning how to interpret valgrind properly.
		3662
		3663	If you need, for some reason, empty reports from valgrind for your project
		3664	I suggest using suppression lists.
		3665
		3666
		3667	=head1 PORTABILITY NOTES
		3668
		3669	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		3670
		3671	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		3672	requires, and its I/O model is fundamentally incompatible with the POSIX
		3673	model. Libev still offers limited functionality on this platform in
		3674	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		3675	descriptors. This only applies when using Win32 natively, not when using
		3676	e.g. cygwin.
		3677
		3678	Lifting these limitations would basically require the full
		3679	re-implementation of the I/O system. If you are into these kinds of
		3680	things, then note that glib does exactly that for you in a very portable
		3681	way (note also that glib is the slowest event library known to man).
		3682
		3683	There is no supported compilation method available on windows except
		3684	embedding it into other applications.
		3685
		3686	Not a libev limitation but worth mentioning: windows apparently doesn't
		3687	accept large writes: instead of resulting in a partial write, windows will
		3688	either accept everything or return C<ENOBUFS> if the buffer is too large,
		3689	so make sure you only write small amounts into your sockets (less than a
		3690	megabyte seems safe, but this apparently depends on the amount of memory
		3691	available).
		3692
		3693	Due to the many, low, and arbitrary limits on the win32 platform and
		3694	the abysmal performance of winsockets, using a large number of sockets
		3695	is not recommended (and not reasonable). If your program needs to use
		3696	more than a hundred or so sockets, then likely it needs to use a totally
		3697	different implementation for windows, as libev offers the POSIX readiness
		3698	notification model, which cannot be implemented efficiently on windows
		3699	(Microsoft monopoly games).
		3700
		3701	A typical way to use libev under windows is to embed it (see the embedding
		3702	section for details) and use the following F<evwrap.h> header file instead
		3703	of F<ev.h>:
		3704
		3705	#define EV_STANDALONE /* keeps ev from requiring config.h */
		3706	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		3707
		3708	#include "ev.h"
		3709
		3710	And compile the following F<evwrap.c> file into your project (make sure
		3711	you do I<not> compile the F<ev.c> or any other embedded source files!):
		3712
		3713	#include "evwrap.h"
		3714	#include "ev.c"
		3715
		3716	=over 4
		3717
		3718	=item The winsocket select function
		3719
		3720	The winsocket C<select> function doesn't follow POSIX in that it
		3721	requires socket I<handles> and not socket I<file descriptors> (it is
		3722	also extremely buggy). This makes select very inefficient, and also
		3723	requires a mapping from file descriptors to socket handles (the Microsoft
		3724	C runtime provides the function C<_open_osfhandle> for this). See the
		3725	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		3726	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		3727
		3728	The configuration for a "naked" win32 using the Microsoft runtime
		3729	libraries and raw winsocket select is:
		3730
		3731	#define EV_USE_SELECT 1
		3732	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		3733
		3734	Note that winsockets handling of fd sets is O(n), so you can easily get a
		3735	complexity in the O(n²) range when using win32.
		3736
		3737	=item Limited number of file descriptors
		3738
		3739	Windows has numerous arbitrary (and low) limits on things.
		3740
		3741	Early versions of winsocket's select only supported waiting for a maximum
		3742	of C<64> handles (probably owning to the fact that all windows kernels
		3743	can only wait for C<64> things at the same time internally; Microsoft
		3744	recommends spawning a chain of threads and wait for 63 handles and the
		3745	previous thread in each. Great).
		3746
		3747	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		3748	to some high number (e.g. C<2048>) before compiling the winsocket select
		3749	call (which might be in libev or elsewhere, for example, perl does its own
		3750	select emulation on windows).
		3751
		3752	Another limit is the number of file descriptors in the Microsoft runtime
		3753	libraries, which by default is C<64> (there must be a hidden I<64> fetish
		3754	or something like this inside Microsoft). You can increase this by calling
		3755	C<_setmaxstdio>, which can increase this limit to C<2048> (another
		3756	arbitrary limit), but is broken in many versions of the Microsoft runtime
		3757	libraries.
		3758
		3759	This might get you to about C<512> or C<2048> sockets (depending on
		3760	windows version and/or the phase of the moon). To get more, you need to
		3761	wrap all I/O functions and provide your own fd management, but the cost of
		3762	calling select (O(n²)) will likely make this unworkable.
		3763
		3764	=back
		3765
		3766	=head2 PORTABILITY REQUIREMENTS
		3767
		3768	In addition to a working ISO-C implementation and of course the
		3769	backend-specific APIs, libev relies on a few additional extensions:
		3770
		3771	=over 4
		3772
		3773	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		3774	calling conventions regardless of C<ev_watcher_type *>.
		3775
		3776	Libev assumes not only that all watcher pointers have the same internal
		3777	structure (guaranteed by POSIX but not by ISO C for example), but it also
		3778	assumes that the same (machine) code can be used to call any watcher
		3779	callback: The watcher callbacks have different type signatures, but libev
		3780	calls them using an C<ev_watcher *> internally.
		3781
		3782	=item C<sig_atomic_t volatile> must be thread-atomic as well
		3783
		3784	The type C<sig_atomic_t volatile> (or whatever is defined as
		3785	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		3786	threads. This is not part of the specification for C<sig_atomic_t>, but is
		3787	believed to be sufficiently portable.
		3788
		3789	=item C<sigprocmask> must work in a threaded environment
		3790
		3791	Libev uses C<sigprocmask> to temporarily block signals. This is not
		3792	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		3793	pthread implementations will either allow C<sigprocmask> in the "main
		3794	thread" or will block signals process-wide, both behaviours would
		3795	be compatible with libev. Interaction between C<sigprocmask> and
		3796	C<pthread_sigmask> could complicate things, however.
		3797
		3798	The most portable way to handle signals is to block signals in all threads
		3799	except the initial one, and run the default loop in the initial thread as
		3800	well.
		3801
		3802	=item C<long> must be large enough for common memory allocation sizes
		3803
		3804	To improve portability and simplify its API, libev uses C<long> internally
		3805	instead of C<size_t> when allocating its data structures. On non-POSIX
		3806	systems (Microsoft...) this might be unexpectedly low, but is still at
		3807	least 31 bits everywhere, which is enough for hundreds of millions of
		3808	watchers.
		3809
		3810	=item C<double> must hold a time value in seconds with enough accuracy
		3811
		3812	The type C<double> is used to represent timestamps. It is required to
		3813	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		3814	enough for at least into the year 4000. This requirement is fulfilled by
		3815	implementations implementing IEEE 754 (basically all existing ones).
		3816
		3817	=back
		3818
		3819	If you know of other additional requirements drop me a note.
		3820
		3821
		3822	=head1 ALGORITHMIC COMPLEXITIES
		3823
		3824	In this section the complexities of (many of) the algorithms used inside
		3825	libev will be documented. For complexity discussions about backends see
		3826	the documentation for C<ev_default_init>.
		3827
		3828	All of the following are about amortised time: If an array needs to be
		3829	extended, libev needs to realloc and move the whole array, but this
		3830	happens asymptotically rarer with higher number of elements, so O(1) might
		3831	mean that libev does a lengthy realloc operation in rare cases, but on
		3832	average it is much faster and asymptotically approaches constant time.
		3833
		3834	=over 4
		3835
		3836	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		3837
		3838	This means that, when you have a watcher that triggers in one hour and
		3839	there are 100 watchers that would trigger before that, then inserting will
		3840	have to skip roughly seven (C<ld 100>) of these watchers.
		3841
		3842	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		3843
		3844	That means that changing a timer costs less than removing/adding them,
		3845	as only the relative motion in the event queue has to be paid for.
		3846
		3847	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		3848
		3849	These just add the watcher into an array or at the head of a list.
		3850
		3851	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		3852
		3853	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		3854
		3855	These watchers are stored in lists, so they need to be walked to find the
		3856	correct watcher to remove. The lists are usually short (you don't usually
		3857	have many watchers waiting for the same fd or signal: one is typical, two
		3858	is rare).
		3859
		3860	=item Finding the next timer in each loop iteration: O(1)
		3861
		3862	By virtue of using a binary or 4-heap, the next timer is always found at a
		3863	fixed position in the storage array.
		3864
		3865	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		3866
		3867	A change means an I/O watcher gets started or stopped, which requires
		3868	libev to recalculate its status (and possibly tell the kernel, depending
		3869	on backend and whether C<ev_io_set> was used).
		3870
		3871	=item Activating one watcher (putting it into the pending state): O(1)
		3872
		3873	=item Priority handling: O(number_of_priorities)
		3874
		3875	Priorities are implemented by allocating some space for each
		3876	priority. When doing priority-based operations, libev usually has to
		3877	linearly search all the priorities, but starting/stopping and activating
		3878	watchers becomes O(1) with respect to priority handling.
		3879
		3880	=item Sending an ev_async: O(1)
		3881
		3882	=item Processing ev_async_send: O(number_of_async_watchers)
		3883
		3884	=item Processing signals: O(max_signal_number)
		3885
		3886	Sending involves a system call I<iff> there were no other C<ev_async_send>
		3887	calls in the current loop iteration. Checking for async and signal events
		3888	involves iterating over all running async watchers or all signal numbers.
		3889
		3890	=back
		3891
1689		3892
1690	=head1 AUTHOR	3893	=head1 AUTHOR
1691		3894
1692	Marc Lehmann <libev@schmorp.de>.	3895	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
1693		3896

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