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Revision 1.35 by root, Fri Nov 23 19:35:09 2007 UTC vs.
Revision 1.211 by root, Mon Nov 3 14:34:16 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	While nominally embeddable in other event loops, this feature is broken in
		424	all kernel versions tested so far.
		425
		426	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		427	C<EVBACKEND_POLL>.
254		428
255	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	429	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
256		430
257	Kqueue deserves special mention, as at the time of this writing, it	431	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	432	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	433	with anything but sockets and pipes, except on Darwin, where of course
260	completely useless). For this reason its not being "autodetected"	434	it's completely useless). Unlike epoll, however, whose brokenness
		435	is by design, these kqueue bugs can (and eventually will) be fixed
		436	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	437	"auto-detected" unless you explicitly specify it in the flags (i.e. using
262	C<EVBACKEND_KQUEUE>).	438	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		439	system like NetBSD.
		440
		441	You still can embed kqueue into a normal poll or select backend and use it
		442	only for sockets (after having made sure that sockets work with kqueue on
		443	the target platform). See C<ev_embed> watchers for more info.
263		444
264	It scales in the same way as the epoll backend, but the interface to the	445	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	446	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	447	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	448	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
268	incident, so its best to avoid that.	449	two event changes per incident. Support for C<fork ()> is very bad (but
		450	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		451	cases
		452
		453	This backend usually performs well under most conditions.
		454
		455	While nominally embeddable in other event loops, this doesn't work
		456	everywhere, so you might need to test for this. And since it is broken
		457	almost everywhere, you should only use it when you have a lot of sockets
		458	(for which it usually works), by embedding it into another event loop
		459	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and, did I mention it,
		460	using it only for sockets.
		461
		462	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		463	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		464	C<NOTE_EOF>.
269		465
270	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	466	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
271		467
272	This is not implemented yet (and might never be).	468	This is not implemented yet (and might never be, unless you send me an
		469	implementation). According to reports, C</dev/poll> only supports sockets
		470	and is not embeddable, which would limit the usefulness of this backend
		471	immensely.
273		472
274	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	473	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
275		474
276	This uses the Solaris 10 port mechanism. As with everything on Solaris,	475	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)).	476	it's really slow, but it still scales very well (O(active_fds)).
278		477
279	Please note that solaris ports can result in a lot of spurious	478	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	479	notifications, so you need to use non-blocking I/O or other means to avoid
281	blocking when no data (or space) is available.	480	blocking when no data (or space) is available.
		481
		482	While this backend scales well, it requires one system call per active
		483	file descriptor per loop iteration. For small and medium numbers of file
		484	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		485	might perform better.
		486
		487	On the positive side, with the exception of the spurious readiness
		488	notifications, this backend actually performed fully to specification
		489	in all tests and is fully embeddable, which is a rare feat among the
		490	OS-specific backends (I vastly prefer correctness over speed hacks).
		491
		492	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		493	C<EVBACKEND_POLL>.
282		494
283	=item C<EVBACKEND_ALL>	495	=item C<EVBACKEND_ALL>
284		496
285	Try all backends (even potentially broken ones that wouldn't be tried	497	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	498	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
287	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	499	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
288		500
		501	It is definitely not recommended to use this flag.
		502
289	=back	503	=back
290		504
291	If one or more of these are ored into the flags value, then only these	505	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	506	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	507	specified, all backends in C<ev_recommended_backends ()> will be tried.
294	order of their flag values :)
295		508
296	The most typical usage is like this:	509	Example: This is the most typical usage.
297		510
298	if (!ev_default_loop (0))	511	if (!ev_default_loop (0))
299	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	512	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
300		513
301	Restrict libev to the select and poll backends, and do not allow	514	Example: Restrict libev to the select and poll backends, and do not allow
302	environment settings to be taken into account:	515	environment settings to be taken into account:
303		516
304	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	517	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
305		518
306	Use whatever libev has to offer, but make sure that kqueue is used if	519	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	520	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):	521	private event loop and only if you know the OS supports your types of
		522	fds):
309		523
310	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	524	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
311		525
312	=item struct ev_loop *ev_loop_new (unsigned int flags)	526	=item struct ev_loop *ev_loop_new (unsigned int flags)
313		527
314	Similar to C<ev_default_loop>, but always creates a new event loop that is	528	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	529	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	530	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).	531	undefined behaviour (or a failed assertion if assertions are enabled).
318		532
		533	Note that this function I<is> thread-safe, and the recommended way to use
		534	libev with threads is indeed to create one loop per thread, and using the
		535	default loop in the "main" or "initial" thread.
		536
319	Example: try to create a event loop that uses epoll and nothing else.	537	Example: Try to create a event loop that uses epoll and nothing else.
320		538
321	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	539	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
322	if (!epoller)	540	if (!epoller)
323	fatal ("no epoll found here, maybe it hides under your chair");	541	fatal ("no epoll found here, maybe it hides under your chair");
324		542
325	=item ev_default_destroy ()	543	=item ev_default_destroy ()
326		544
327	Destroys the default loop again (frees all memory and kernel state	545	Destroys the default loop again (frees all memory and kernel state
328	etc.). This stops all registered event watchers (by not touching them in	546	etc.). None of the active event watchers will be stopped in the normal
329	any way whatsoever, although you cannot rely on this :).	547	sense, so e.g. C<ev_is_active> might still return true. It is your
		548	responsibility to either stop all watchers cleanly yourself I<before>
		549	calling this function, or cope with the fact afterwards (which is usually
		550	the easiest thing, you can just ignore the watchers and/or C<free ()> them
		551	for example).
		552
		553	Note that certain global state, such as signal state (and installed signal
		554	handlers), will not be freed by this function, and related watchers (such
		555	as signal and child watchers) would need to be stopped manually.
		556
		557	In general it is not advisable to call this function except in the
		558	rare occasion where you really need to free e.g. the signal handling
		559	pipe fds. If you need dynamically allocated loops it is better to use
		560	C<ev_loop_new> and C<ev_loop_destroy>).
330		561
331	=item ev_loop_destroy (loop)	562	=item ev_loop_destroy (loop)
332		563
333	Like C<ev_default_destroy>, but destroys an event loop created by an	564	Like C<ev_default_destroy>, but destroys an event loop created by an
334	earlier call to C<ev_loop_new>.	565	earlier call to C<ev_loop_new>.
335		566
336	=item ev_default_fork ()	567	=item ev_default_fork ()
337		568
		569	This function sets a flag that causes subsequent C<ev_loop> iterations
338	This function reinitialises the kernel state for backends that have	570	to reinitialise the kernel state for backends that have one. Despite the
339	one. Despite the name, you can call it anytime, but it makes most sense	571	name, you can call it anytime, but it makes most sense after forking, in
340	after forking, in either the parent or child process (or both, but that	572	the child process (or both child and parent, but that again makes little
341	again makes little sense).	573	sense). You I<must> call it in the child before using any of the libev
		574	functions, and it will only take effect at the next C<ev_loop> iteration.
342		575
343	You I<must> call this function in the child process after forking if and	576	On the other hand, you only need to call this function in the child
344	only if you want to use the event library in both processes. If you just	577	process if and only if you want to use the event library in the child. If
345	fork+exec, you don't have to call it.	578	you just fork+exec, you don't have to call it at all.
346		579
347	The function itself is quite fast and it's usually not a problem to call	580	The function itself is quite fast and it's usually not a problem to call
348	it just in case after a fork. To make this easy, the function will fit in	581	it just in case after a fork. To make this easy, the function will fit in
349	quite nicely into a call to C<pthread_atfork>:	582	quite nicely into a call to C<pthread_atfork>:
350		583
351	pthread_atfork (0, 0, ev_default_fork);	584	pthread_atfork (0, 0, ev_default_fork);
352		585
353	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
354	without calling this function, so if you force one of those backends you
355	do not need to care.
356
357	=item ev_loop_fork (loop)	586	=item ev_loop_fork (loop)
358		587
359	Like C<ev_default_fork>, but acts on an event loop created by	588	Like C<ev_default_fork>, but acts on an event loop created by
360	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	589	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
361	after fork, and how you do this is entirely your own problem.	590	after fork that you want to re-use in the child, and how you do this is
		591	entirely your own problem.
		592
		593	=item int ev_is_default_loop (loop)
		594
		595	Returns true when the given loop is, in fact, the default loop, and false
		596	otherwise.
		597
		598	=item unsigned int ev_loop_count (loop)
		599
		600	Returns the count of loop iterations for the loop, which is identical to
		601	the number of times libev did poll for new events. It starts at C<0> and
		602	happily wraps around with enough iterations.
		603
		604	This value can sometimes be useful as a generation counter of sorts (it
		605	"ticks" the number of loop iterations), as it roughly corresponds with
		606	C<ev_prepare> and C<ev_check> calls.
362		607
363	=item unsigned int ev_backend (loop)	608	=item unsigned int ev_backend (loop)
364		609
365	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	610	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
366	use.	611	use.
…		…
369		614
370	Returns the current "event loop time", which is the time the event loop	615	Returns the current "event loop time", which is the time the event loop
371	received events and started processing them. This timestamp does not	616	received events and started processing them. This timestamp does not
372	change as long as callbacks are being processed, and this is also the base	617	change as long as callbacks are being processed, and this is also the base
373	time used for relative timers. You can treat it as the timestamp of the	618	time used for relative timers. You can treat it as the timestamp of the
374	event occuring (or more correctly, libev finding out about it).	619	event occurring (or more correctly, libev finding out about it).
		620
		621	=item ev_now_update (loop)
		622
		623	Establishes the current time by querying the kernel, updating the time
		624	returned by C<ev_now ()> in the progress. This is a costly operation and
		625	is usually done automatically within C<ev_loop ()>.
		626
		627	This function is rarely useful, but when some event callback runs for a
		628	very long time without entering the event loop, updating libev's idea of
		629	the current time is a good idea.
		630
		631	See also "The special problem of time updates" in the C<ev_timer> section.
375		632
376	=item ev_loop (loop, int flags)	633	=item ev_loop (loop, int flags)
377		634
378	Finally, this is it, the event handler. This function usually is called	635	Finally, this is it, the event handler. This function usually is called
379	after you initialised all your watchers and you want to start handling	636	after you initialised all your watchers and you want to start handling
…		…
382	If the flags argument is specified as C<0>, it will not return until	639	If the flags argument is specified as C<0>, it will not return until
383	either no event watchers are active anymore or C<ev_unloop> was called.	640	either no event watchers are active anymore or C<ev_unloop> was called.
384		641
385	Please note that an explicit C<ev_unloop> is usually better than	642	Please note that an explicit C<ev_unloop> is usually better than
386	relying on all watchers to be stopped when deciding when a program has	643	relying on all watchers to be stopped when deciding when a program has
387	finished (especially in interactive programs), but having a program that	644	finished (especially in interactive programs), but having a program
388	automatically loops as long as it has to and no longer by virtue of	645	that automatically loops as long as it has to and no longer by virtue
389	relying on its watchers stopping correctly is a thing of beauty.	646	of relying on its watchers stopping correctly, that is truly a thing of
		647	beauty.
390		648
391	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	649	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
392	those events and any outstanding ones, but will not block your process in	650	those events and any already outstanding ones, but will not block your
393	case there are no events and will return after one iteration of the loop.	651	process in case there are no events and will return after one iteration of
		652	the loop.
394		653
395	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	654	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
396	neccessary) and will handle those and any outstanding ones. It will block	655	necessary) and will handle those and any already outstanding ones. It
397	your process until at least one new event arrives, and will return after	656	will block your process until at least one new event arrives (which could
398	one iteration of the loop. This is useful if you are waiting for some	657	be an event internal to libev itself, so there is no guarantee that a
399	external event in conjunction with something not expressible using other	658	user-registered callback will be called), and will return after one
		659	iteration of the loop.
		660
		661	This is useful if you are waiting for some external event in conjunction
		662	with something not expressible using other libev watchers (i.e. "roll your
400	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	663	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
401	usually a better approach for this kind of thing.	664	usually a better approach for this kind of thing.
402		665
403	Here are the gory details of what C<ev_loop> does:	666	Here are the gory details of what C<ev_loop> does:
404		667
405	* If there are no active watchers (reference count is zero), return.	668	- Before the first iteration, call any pending watchers.
406	- Queue prepare watchers and then call all outstanding watchers.	669	* If EVFLAG_FORKCHECK was used, check for a fork.
		670	- If a fork was detected (by any means), queue and call all fork watchers.
		671	- Queue and call all prepare watchers.
407	- If we have been forked, recreate the kernel state.	672	- If we have been forked, detach and recreate the kernel state
		673	as to not disturb the other process.
408	- Update the kernel state with all outstanding changes.	674	- Update the kernel state with all outstanding changes.
409	- Update the "event loop time".	675	- Update the "event loop time" (ev_now ()).
410	- Calculate for how long to block.	676	- Calculate for how long to sleep or block, if at all
		677	(active idle watchers, EVLOOP_NONBLOCK or not having
		678	any active watchers at all will result in not sleeping).
		679	- Sleep if the I/O and timer collect interval say so.
411	- Block the process, waiting for any events.	680	- Block the process, waiting for any events.
412	- Queue all outstanding I/O (fd) events.	681	- Queue all outstanding I/O (fd) events.
413	- Update the "event loop time" and do time jump handling.	682	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
414	- Queue all outstanding timers.	683	- Queue all expired timers.
415	- Queue all outstanding periodics.	684	- Queue all expired periodics.
416	- If no events are pending now, queue all idle watchers.	685	- Unless any events are pending now, queue all idle watchers.
417	- Queue all check watchers.	686	- Queue all check watchers.
418	- Call all queued watchers in reverse order (i.e. check watchers first).	687	- Call all queued watchers in reverse order (i.e. check watchers first).
419	Signals and child watchers are implemented as I/O watchers, and will	688	Signals and child watchers are implemented as I/O watchers, and will
420	be handled here by queueing them when their watcher gets executed.	689	be handled here by queueing them when their watcher gets executed.
421	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	690	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
422	were used, return, otherwise continue with step *.	691	were used, or there are no active watchers, return, otherwise
		692	continue with step *.
423		693
424	Example: queue some jobs and then loop until no events are outsanding	694	Example: Queue some jobs and then loop until no events are outstanding
425	anymore.	695	anymore.
426		696
427	... queue jobs here, make sure they register event watchers as long	697	... queue jobs here, make sure they register event watchers as long
428	... as they still have work to do (even an idle watcher will do..)	698	... as they still have work to do (even an idle watcher will do..)
429	ev_loop (my_loop, 0);	699	ev_loop (my_loop, 0);
430	... jobs done. yeah!	700	... jobs done or somebody called unloop. yeah!
431		701
432	=item ev_unloop (loop, how)	702	=item ev_unloop (loop, how)
433		703
434	Can be used to make a call to C<ev_loop> return early (but only after it	704	Can be used to make a call to C<ev_loop> return early (but only after it
435	has processed all outstanding events). The C<how> argument must be either	705	has processed all outstanding events). The C<how> argument must be either
436	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	706	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
437	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	707	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
438		708
		709	This "unloop state" will be cleared when entering C<ev_loop> again.
		710
		711	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
		712
439	=item ev_ref (loop)	713	=item ev_ref (loop)
440		714
441	=item ev_unref (loop)	715	=item ev_unref (loop)
442		716
443	Ref/unref can be used to add or remove a reference count on the event	717	Ref/unref can be used to add or remove a reference count on the event
444	loop: Every watcher keeps one reference, and as long as the reference	718	loop: Every watcher keeps one reference, and as long as the reference
445	count is nonzero, C<ev_loop> will not return on its own. If you have	719	count is nonzero, C<ev_loop> will not return on its own.
		720
446	a watcher you never unregister that should not keep C<ev_loop> from	721	If you have a watcher you never unregister that should not keep C<ev_loop>
447	returning, ev_unref() after starting, and ev_ref() before stopping it. For	722	from returning, call ev_unref() after starting, and ev_ref() before
		723	stopping it.
		724
448	example, libev itself uses this for its internal signal pipe: It is not	725	As an example, libev itself uses this for its internal signal pipe: It is
449	visible to the libev user and should not keep C<ev_loop> from exiting if	726	not visible to the libev user and should not keep C<ev_loop> from exiting
450	no event watchers registered by it are active. It is also an excellent	727	if no event watchers registered by it are active. It is also an excellent
451	way to do this for generic recurring timers or from within third-party	728	way to do this for generic recurring timers or from within third-party
452	libraries. Just remember to I<unref after start> and I<ref before stop>.	729	libraries. Just remember to I<unref after start> and I<ref before stop>
		730	(but only if the watcher wasn't active before, or was active before,
		731	respectively).
453		732
454	Example: create a signal watcher, but keep it from keeping C<ev_loop>	733	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
455	running when nothing else is active.	734	running when nothing else is active.
456		735
457	struct dv_signal exitsig;	736	ev_signal exitsig;
458	ev_signal_init (&exitsig, sig_cb, SIGINT);	737	ev_signal_init (&exitsig, sig_cb, SIGINT);
459	ev_signal_start (myloop, &exitsig);	738	ev_signal_start (loop, &exitsig);
460	evf_unref (myloop);	739	evf_unref (loop);
461		740
462	Example: for some weird reason, unregister the above signal handler again.	741	Example: For some weird reason, unregister the above signal handler again.
463		742
464	ev_ref (myloop);	743	ev_ref (loop);
465	ev_signal_stop (myloop, &exitsig);	744	ev_signal_stop (loop, &exitsig);
		745
		746	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		747
		748	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		749
		750	These advanced functions influence the time that libev will spend waiting
		751	for events. Both time intervals are by default C<0>, meaning that libev
		752	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		753	latency.
		754
		755	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		756	allows libev to delay invocation of I/O and timer/periodic callbacks
		757	to increase efficiency of loop iterations (or to increase power-saving
		758	opportunities).
		759
		760	The idea is that sometimes your program runs just fast enough to handle
		761	one (or very few) event(s) per loop iteration. While this makes the
		762	program responsive, it also wastes a lot of CPU time to poll for new
		763	events, especially with backends like C<select ()> which have a high
		764	overhead for the actual polling but can deliver many events at once.
		765
		766	By setting a higher I<io collect interval> you allow libev to spend more
		767	time collecting I/O events, so you can handle more events per iteration,
		768	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		769	C<ev_timer>) will be not affected. Setting this to a non-null value will
		770	introduce an additional C<ev_sleep ()> call into most loop iterations.
		771
		772	Likewise, by setting a higher I<timeout collect interval> you allow libev
		773	to spend more time collecting timeouts, at the expense of increased
		774	latency/jitter/inexactness (the watcher callback will be called
		775	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		776	value will not introduce any overhead in libev.
		777
		778	Many (busy) programs can usually benefit by setting the I/O collect
		779	interval to a value near C<0.1> or so, which is often enough for
		780	interactive servers (of course not for games), likewise for timeouts. It
		781	usually doesn't make much sense to set it to a lower value than C<0.01>,
		782	as this approaches the timing granularity of most systems.
		783
		784	Setting the I<timeout collect interval> can improve the opportunity for
		785	saving power, as the program will "bundle" timer callback invocations that
		786	are "near" in time together, by delaying some, thus reducing the number of
		787	times the process sleeps and wakes up again. Another useful technique to
		788	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		789	they fire on, say, one-second boundaries only.
		790
		791	=item ev_loop_verify (loop)
		792
		793	This function only does something when C<EV_VERIFY> support has been
		794	compiled in, which is the default for non-minimal builds. It tries to go
		795	through all internal structures and checks them for validity. If anything
		796	is found to be inconsistent, it will print an error message to standard
		797	error and call C<abort ()>.
		798
		799	This can be used to catch bugs inside libev itself: under normal
		800	circumstances, this function will never abort as of course libev keeps its
		801	data structures consistent.
466		802
467	=back	803	=back
468		804
		805
469	=head1 ANATOMY OF A WATCHER	806	=head1 ANATOMY OF A WATCHER
		807
		808	In the following description, uppercase C<TYPE> in names stands for the
		809	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		810	watchers and C<ev_io_start> for I/O watchers.
470		811
471	A watcher is a structure that you create and register to record your	812	A watcher is a structure that you create and register to record your
472	interest in some event. For instance, if you want to wait for STDIN to	813	interest in some event. For instance, if you want to wait for STDIN to
473	become readable, you would create an C<ev_io> watcher for that:	814	become readable, you would create an C<ev_io> watcher for that:
474		815
475	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	816	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
476	{	817	{
477	ev_io_stop (w);	818	ev_io_stop (w);
478	ev_unloop (loop, EVUNLOOP_ALL);	819	ev_unloop (loop, EVUNLOOP_ALL);
479	}	820	}
480		821
481	struct ev_loop *loop = ev_default_loop (0);	822	struct ev_loop *loop = ev_default_loop (0);
		823
482	struct ev_io stdin_watcher;	824	ev_io stdin_watcher;
		825
483	ev_init (&stdin_watcher, my_cb);	826	ev_init (&stdin_watcher, my_cb);
484	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	827	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
485	ev_io_start (loop, &stdin_watcher);	828	ev_io_start (loop, &stdin_watcher);
		829
486	ev_loop (loop, 0);	830	ev_loop (loop, 0);
487		831
488	As you can see, you are responsible for allocating the memory for your	832	As you can see, you are responsible for allocating the memory for your
489	watcher structures (and it is usually a bad idea to do this on the stack,	833	watcher structures (and it is I<usually> a bad idea to do this on the
490	although this can sometimes be quite valid).	834	stack).
		835
		836	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		837	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
491		838
492	Each watcher structure must be initialised by a call to C<ev_init	839	Each watcher structure must be initialised by a call to C<ev_init
493	(watcher *, callback)>, which expects a callback to be provided. This	840	(watcher *, callback)>, which expects a callback to be provided. This
494	callback gets invoked each time the event occurs (or, in the case of io	841	callback gets invoked each time the event occurs (or, in the case of I/O
495	watchers, each time the event loop detects that the file descriptor given	842	watchers, each time the event loop detects that the file descriptor given
496	is readable and/or writable).	843	is readable and/or writable).
497		844
498	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	845	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
499	with arguments specific to this watcher type. There is also a macro	846	macro to configure it, with arguments specific to the watcher type. There
500	to combine initialisation and setting in one call: C<< ev_<type>_init	847	is also a macro to combine initialisation and setting in one call: C<<
501	(watcher *, callback, ...) >>.	848	ev_TYPE_init (watcher *, callback, ...) >>.
502		849
503	To make the watcher actually watch out for events, you have to start it	850	To make the watcher actually watch out for events, you have to start it
504	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	851	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
505	*) >>), and you can stop watching for events at any time by calling the	852	*) >>), and you can stop watching for events at any time by calling the
506	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	853	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
507		854
508	As long as your watcher is active (has been started but not stopped) you	855	As long as your watcher is active (has been started but not stopped) you
509	must not touch the values stored in it. Most specifically you must never	856	must not touch the values stored in it. Most specifically you must never
510	reinitialise it or call its set macro.	857	reinitialise it or call its C<ev_TYPE_set> macro.
511
512	You can check whether an event is active by calling the C<ev_is_active
513	(watcher *)> macro. To see whether an event is outstanding (but the
514	callback for it has not been called yet) you can use the C<ev_is_pending
515	(watcher *)> macro.
516		858
517	Each and every callback receives the event loop pointer as first, the	859	Each and every callback receives the event loop pointer as first, the
518	registered watcher structure as second, and a bitset of received events as	860	registered watcher structure as second, and a bitset of received events as
519	third argument.	861	third argument.
520		862
…		…
544	The signal specified in the C<ev_signal> watcher has been received by a thread.	886	The signal specified in the C<ev_signal> watcher has been received by a thread.
545		887
546	=item C<EV_CHILD>	888	=item C<EV_CHILD>
547		889
548	The pid specified in the C<ev_child> watcher has received a status change.	890	The pid specified in the C<ev_child> watcher has received a status change.
		891
		892	=item C<EV_STAT>
		893
		894	The path specified in the C<ev_stat> watcher changed its attributes somehow.
549		895
550	=item C<EV_IDLE>	896	=item C<EV_IDLE>
551		897
552	The C<ev_idle> watcher has determined that you have nothing better to do.	898	The C<ev_idle> watcher has determined that you have nothing better to do.
553		899
…		…
561	received events. Callbacks of both watcher types can start and stop as	907	received events. Callbacks of both watcher types can start and stop as
562	many watchers as they want, and all of them will be taken into account	908	many watchers as they want, and all of them will be taken into account
563	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	909	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
564	C<ev_loop> from blocking).	910	C<ev_loop> from blocking).
565		911
		912	=item C<EV_EMBED>
		913
		914	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		915
		916	=item C<EV_FORK>
		917
		918	The event loop has been resumed in the child process after fork (see
		919	C<ev_fork>).
		920
		921	=item C<EV_ASYNC>
		922
		923	The given async watcher has been asynchronously notified (see C<ev_async>).
		924
566	=item C<EV_ERROR>	925	=item C<EV_ERROR>
567		926
568	An unspecified error has occured, the watcher has been stopped. This might	927	An unspecified error has occurred, the watcher has been stopped. This might
569	happen because the watcher could not be properly started because libev	928	happen because the watcher could not be properly started because libev
570	ran out of memory, a file descriptor was found to be closed or any other	929	ran out of memory, a file descriptor was found to be closed or any other
		930	problem. Libev considers these application bugs.
		931
571	problem. You best act on it by reporting the problem and somehow coping	932	You best act on it by reporting the problem and somehow coping with the
572	with the watcher being stopped.	933	watcher being stopped. Note that well-written programs should not receive
		934	an error ever, so when your watcher receives it, this usually indicates a
		935	bug in your program.
573		936
574	Libev will usually signal a few "dummy" events together with an error,	937	Libev will usually signal a few "dummy" events together with an error, for
575	for example it might indicate that a fd is readable or writable, and if	938	example it might indicate that a fd is readable or writable, and if your
576	your callbacks is well-written it can just attempt the operation and cope	939	callbacks is well-written it can just attempt the operation and cope with
577	with the error from read() or write(). This will not work in multithreaded	940	the error from read() or write(). This will not work in multi-threaded
578	programs, though, so beware.	941	programs, though, as the fd could already be closed and reused for another
		942	thing, so beware.
579		943
580	=back	944	=back
581		945
		946	=head2 GENERIC WATCHER FUNCTIONS
		947
		948	=over 4
		949
		950	=item C<ev_init> (ev_TYPE *watcher, callback)
		951
		952	This macro initialises the generic portion of a watcher. The contents
		953	of the watcher object can be arbitrary (so C<malloc> will do). Only
		954	the generic parts of the watcher are initialised, you I<need> to call
		955	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		956	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		957	which rolls both calls into one.
		958
		959	You can reinitialise a watcher at any time as long as it has been stopped
		960	(or never started) and there are no pending events outstanding.
		961
		962	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
		963	int revents)>.
		964
		965	Example: Initialise an C<ev_io> watcher in two steps.
		966
		967	ev_io w;
		968	ev_init (&w, my_cb);
		969	ev_io_set (&w, STDIN_FILENO, EV_READ);
		970
		971	=item C<ev_TYPE_set> (ev_TYPE *, [args])
		972
		973	This macro initialises the type-specific parts of a watcher. You need to
		974	call C<ev_init> at least once before you call this macro, but you can
		975	call C<ev_TYPE_set> any number of times. You must not, however, call this
		976	macro on a watcher that is active (it can be pending, however, which is a
		977	difference to the C<ev_init> macro).
		978
		979	Although some watcher types do not have type-specific arguments
		980	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		981
		982	See C<ev_init>, above, for an example.
		983
		984	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		985
		986	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		987	calls into a single call. This is the most convenient method to initialise
		988	a watcher. The same limitations apply, of course.
		989
		990	Example: Initialise and set an C<ev_io> watcher in one step.
		991
		992	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		993
		994	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
		995
		996	Starts (activates) the given watcher. Only active watchers will receive
		997	events. If the watcher is already active nothing will happen.
		998
		999	Example: Start the C<ev_io> watcher that is being abused as example in this
		1000	whole section.
		1001
		1002	ev_io_start (EV_DEFAULT_UC, &w);
		1003
		1004	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
		1005
		1006	Stops the given watcher if active, and clears the pending status (whether
		1007	the watcher was active or not).
		1008
		1009	It is possible that stopped watchers are pending - for example,
		1010	non-repeating timers are being stopped when they become pending - but
		1011	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
		1012	pending. If you want to free or reuse the memory used by the watcher it is
		1013	therefore a good idea to always call its C<ev_TYPE_stop> function.
		1014
		1015	=item bool ev_is_active (ev_TYPE *watcher)
		1016
		1017	Returns a true value iff the watcher is active (i.e. it has been started
		1018	and not yet been stopped). As long as a watcher is active you must not modify
		1019	it.
		1020
		1021	=item bool ev_is_pending (ev_TYPE *watcher)
		1022
		1023	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		1024	events but its callback has not yet been invoked). As long as a watcher
		1025	is pending (but not active) you must not call an init function on it (but
		1026	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		1027	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1028	it).
		1029
		1030	=item callback ev_cb (ev_TYPE *watcher)
		1031
		1032	Returns the callback currently set on the watcher.
		1033
		1034	=item ev_cb_set (ev_TYPE *watcher, callback)
		1035
		1036	Change the callback. You can change the callback at virtually any time
		1037	(modulo threads).
		1038
		1039	=item ev_set_priority (ev_TYPE *watcher, priority)
		1040
		1041	=item int ev_priority (ev_TYPE *watcher)
		1042
		1043	Set and query the priority of the watcher. The priority is a small
		1044	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1045	(default: C<-2>). Pending watchers with higher priority will be invoked
		1046	before watchers with lower priority, but priority will not keep watchers
		1047	from being executed (except for C<ev_idle> watchers).
		1048
		1049	This means that priorities are I<only> used for ordering callback
		1050	invocation after new events have been received. This is useful, for
		1051	example, to reduce latency after idling, or more often, to bind two
		1052	watchers on the same event and make sure one is called first.
		1053
		1054	If you need to suppress invocation when higher priority events are pending
		1055	you need to look at C<ev_idle> watchers, which provide this functionality.
		1056
		1057	You I<must not> change the priority of a watcher as long as it is active or
		1058	pending.
		1059
		1060	The default priority used by watchers when no priority has been set is
		1061	always C<0>, which is supposed to not be too high and not be too low :).
		1062
		1063	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1064	fine, as long as you do not mind that the priority value you query might
		1065	or might not have been clamped to the valid range.
		1066
		1067	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1068
		1069	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1070	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1071	can deal with that fact, as both are simply passed through to the
		1072	callback.
		1073
		1074	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1075
		1076	If the watcher is pending, this function clears its pending status and
		1077	returns its C<revents> bitset (as if its callback was invoked). If the
		1078	watcher isn't pending it does nothing and returns C<0>.
		1079
		1080	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1081	callback to be invoked, which can be accomplished with this function.
		1082
		1083	=back
		1084
		1085
582	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1086	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
583		1087
584	Each watcher has, by default, a member C<void *data> that you can change	1088	Each watcher has, by default, a member C<void *data> that you can change
585	and read at any time, libev will completely ignore it. This can be used	1089	and read at any time: libev will completely ignore it. This can be used
586	to associate arbitrary data with your watcher. If you need more data and	1090	to associate arbitrary data with your watcher. If you need more data and
587	don't want to allocate memory and store a pointer to it in that data	1091	don't want to allocate memory and store a pointer to it in that data
588	member, you can also "subclass" the watcher type and provide your own	1092	member, you can also "subclass" the watcher type and provide your own
589	data:	1093	data:
590		1094
591	struct my_io	1095	struct my_io
592	{	1096	{
593	struct ev_io io;	1097	ev_io io;
594	int otherfd;	1098	int otherfd;
595	void *somedata;	1099	void *somedata;
596	struct whatever *mostinteresting;	1100	struct whatever *mostinteresting;
597	}	1101	};
		1102
		1103	...
		1104	struct my_io w;
		1105	ev_io_init (&w.io, my_cb, fd, EV_READ);
598		1106
599	And since your callback will be called with a pointer to the watcher, you	1107	And since your callback will be called with a pointer to the watcher, you
600	can cast it back to your own type:	1108	can cast it back to your own type:
601		1109
602	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1110	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
603	{	1111	{
604	struct my_io *w = (struct my_io *)w_;	1112	struct my_io *w = (struct my_io *)w_;
605	...	1113	...
606	}	1114	}
607		1115
608	More interesting and less C-conformant ways of catsing your callback type	1116	More interesting and less C-conformant ways of casting your callback type
609	have been omitted....	1117	instead have been omitted.
		1118
		1119	Another common scenario is to use some data structure with multiple
		1120	embedded watchers:
		1121
		1122	struct my_biggy
		1123	{
		1124	int some_data;
		1125	ev_timer t1;
		1126	ev_timer t2;
		1127	}
		1128
		1129	In this case getting the pointer to C<my_biggy> is a bit more
		1130	complicated: Either you store the address of your C<my_biggy> struct
		1131	in the C<data> member of the watcher (for woozies), or you need to use
		1132	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1133	programmers):
		1134
		1135	#include <stddef.h>
		1136
		1137	static void
		1138	t1_cb (EV_P_ ev_timer *w, int revents)
		1139	{
		1140	struct my_biggy big = (struct my_biggy *
		1141	(((char *)w) - offsetof (struct my_biggy, t1));
		1142	}
		1143
		1144	static void
		1145	t2_cb (EV_P_ ev_timer *w, int revents)
		1146	{
		1147	struct my_biggy big = (struct my_biggy *
		1148	(((char *)w) - offsetof (struct my_biggy, t2));
		1149	}
610		1150
611		1151
612	=head1 WATCHER TYPES	1152	=head1 WATCHER TYPES
613		1153
614	This section describes each watcher in detail, but will not repeat	1154	This section describes each watcher in detail, but will not repeat
615	information given in the last section.	1155	information given in the last section. Any initialisation/set macros,
		1156	functions and members specific to the watcher type are explained.
616		1157
		1158	Members are additionally marked with either I<[read-only]>, meaning that,
		1159	while the watcher is active, you can look at the member and expect some
		1160	sensible content, but you must not modify it (you can modify it while the
		1161	watcher is stopped to your hearts content), or I<[read-write]>, which
		1162	means you can expect it to have some sensible content while the watcher
		1163	is active, but you can also modify it. Modifying it may not do something
		1164	sensible or take immediate effect (or do anything at all), but libev will
		1165	not crash or malfunction in any way.
617		1166
		1167
618	=head2 C<ev_io> - is this file descriptor readable or writable	1168	=head2 C<ev_io> - is this file descriptor readable or writable?
619		1169
620	I/O watchers check whether a file descriptor is readable or writable	1170	I/O watchers check whether a file descriptor is readable or writable
621	in each iteration of the event loop (This behaviour is called	1171	in each iteration of the event loop, or, more precisely, when reading
622	level-triggering because you keep receiving events as long as the	1172	would not block the process and writing would at least be able to write
623	condition persists. Remember you can stop the watcher if you don't want to	1173	some data. This behaviour is called level-triggering because you keep
624	act on the event and neither want to receive future events).	1174	receiving events as long as the condition persists. Remember you can stop
		1175	the watcher if you don't want to act on the event and neither want to
		1176	receive future events.
625		1177
626	In general you can register as many read and/or write event watchers per	1178	In general you can register as many read and/or write event watchers per
627	fd as you want (as long as you don't confuse yourself). Setting all file	1179	fd as you want (as long as you don't confuse yourself). Setting all file
628	descriptors to non-blocking mode is also usually a good idea (but not	1180	descriptors to non-blocking mode is also usually a good idea (but not
629	required if you know what you are doing).	1181	required if you know what you are doing).
630		1182
631	You have to be careful with dup'ed file descriptors, though. Some backends	1183	If you cannot use non-blocking mode, then force the use of a
632	(the linux epoll backend is a notable example) cannot handle dup'ed file	1184	known-to-be-good backend (at the time of this writing, this includes only
633	descriptors correctly if you register interest in two or more fds pointing	1185	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>).
634	to the same underlying file/socket etc. description (that is, they share
635	the same underlying "file open").
636		1186
637	If you must do this, then force the use of a known-to-be-good backend	1187	Another thing you have to watch out for is that it is quite easy to
638	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and	1188	receive "spurious" readiness notifications, that is your callback might
		1189	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
		1190	because there is no data. Not only are some backends known to create a
		1191	lot of those (for example Solaris ports), it is very easy to get into
		1192	this situation even with a relatively standard program structure. Thus
		1193	it is best to always use non-blocking I/O: An extra C<read>(2) returning
		1194	C<EAGAIN> is far preferable to a program hanging until some data arrives.
		1195
		1196	If you cannot run the fd in non-blocking mode (for example you should
		1197	not play around with an Xlib connection), then you have to separately
		1198	re-test whether a file descriptor is really ready with a known-to-be good
		1199	interface such as poll (fortunately in our Xlib example, Xlib already
		1200	does this on its own, so its quite safe to use). Some people additionally
		1201	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1202	indefinitely.
		1203
		1204	But really, best use non-blocking mode.
		1205
		1206	=head3 The special problem of disappearing file descriptors
		1207
		1208	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1209	descriptor (either due to calling C<close> explicitly or any other means,
		1210	such as C<dup2>). The reason is that you register interest in some file
		1211	descriptor, but when it goes away, the operating system will silently drop
		1212	this interest. If another file descriptor with the same number then is
		1213	registered with libev, there is no efficient way to see that this is, in
		1214	fact, a different file descriptor.
		1215
		1216	To avoid having to explicitly tell libev about such cases, libev follows
		1217	the following policy: Each time C<ev_io_set> is being called, libev
		1218	will assume that this is potentially a new file descriptor, otherwise
		1219	it is assumed that the file descriptor stays the same. That means that
		1220	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1221	descriptor even if the file descriptor number itself did not change.
		1222
		1223	This is how one would do it normally anyway, the important point is that
		1224	the libev application should not optimise around libev but should leave
		1225	optimisations to libev.
		1226
		1227	=head3 The special problem of dup'ed file descriptors
		1228
		1229	Some backends (e.g. epoll), cannot register events for file descriptors,
		1230	but only events for the underlying file descriptions. That means when you
		1231	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1232	events for them, only one file descriptor might actually receive events.
		1233
		1234	There is no workaround possible except not registering events
		1235	for potentially C<dup ()>'ed file descriptors, or to resort to
		1236	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1237
		1238	=head3 The special problem of fork
		1239
		1240	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1241	useless behaviour. Libev fully supports fork, but needs to be told about
		1242	it in the child.
		1243
		1244	To support fork in your programs, you either have to call
		1245	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1246	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
639	C<EVBACKEND_POLL>).	1247	C<EVBACKEND_POLL>.
		1248
		1249	=head3 The special problem of SIGPIPE
		1250
		1251	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1252	when writing to a pipe whose other end has been closed, your program gets
		1253	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1254	this is sensible behaviour, for daemons, this is usually undesirable.
		1255
		1256	So when you encounter spurious, unexplained daemon exits, make sure you
		1257	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1258	somewhere, as that would have given you a big clue).
		1259
		1260
		1261	=head3 Watcher-Specific Functions
640		1262
641	=over 4	1263	=over 4
642		1264
643	=item ev_io_init (ev_io *, callback, int fd, int events)	1265	=item ev_io_init (ev_io *, callback, int fd, int events)
644		1266
645	=item ev_io_set (ev_io *, int fd, int events)	1267	=item ev_io_set (ev_io *, int fd, int events)
646		1268
647	Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive	1269	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
648	events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ |	1270	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
649	EV_WRITE> to receive the given events.	1271	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
650		1272
651	Please note that most of the more scalable backend mechanisms (for example	1273	=item int fd [read-only]
652	epoll and solaris ports) can result in spurious readyness notifications	1274
653	for file descriptors, so you practically need to use non-blocking I/O (and	1275	The file descriptor being watched.
654	treat callback invocation as hint only), or retest separately with a safe	1276
655	interface before doing I/O (XLib can do this), or force the use of either	1277	=item int events [read-only]
656	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>, which don't suffer from this	1278
657	problem. Also note that it is quite easy to have your callback invoked	1279	The events being watched.
658	when the readyness condition is no longer valid even when employing
659	typical ways of handling events, so its a good idea to use non-blocking
660	I/O unconditionally.
661		1280
662	=back	1281	=back
663		1282
		1283	=head3 Examples
		1284
664	Example: call C<stdin_readable_cb> when STDIN_FILENO has become, well	1285	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
665	readable, but only once. Since it is likely line-buffered, you could	1286	readable, but only once. Since it is likely line-buffered, you could
666	attempt to read a whole line in the callback:	1287	attempt to read a whole line in the callback.
667		1288
668	static void	1289	static void
669	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1290	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
670	{	1291	{
671	ev_io_stop (loop, w);	1292	ev_io_stop (loop, w);
672	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1293	.. read from stdin here (or from w->fd) and handle any I/O errors
673	}	1294	}
674		1295
675	...	1296	...
676	struct ev_loop *loop = ev_default_init (0);	1297	struct ev_loop *loop = ev_default_init (0);
677	struct ev_io stdin_readable;	1298	ev_io stdin_readable;
678	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1299	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
679	ev_io_start (loop, &stdin_readable);	1300	ev_io_start (loop, &stdin_readable);
680	ev_loop (loop, 0);	1301	ev_loop (loop, 0);
681		1302
682		1303
683	=head2 C<ev_timer> - relative and optionally recurring timeouts	1304	=head2 C<ev_timer> - relative and optionally repeating timeouts
684		1305
685	Timer watchers are simple relative timers that generate an event after a	1306	Timer watchers are simple relative timers that generate an event after a
686	given time, and optionally repeating in regular intervals after that.	1307	given time, and optionally repeating in regular intervals after that.
687		1308
688	The timers are based on real time, that is, if you register an event that	1309	The timers are based on real time, that is, if you register an event that
689	times out after an hour and you reset your system clock to last years	1310	times out after an hour and you reset your system clock to January last
690	time, it will still time out after (roughly) and hour. "Roughly" because	1311	year, it will still time out after (roughly) one hour. "Roughly" because
691	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1312	detecting time jumps is hard, and some inaccuracies are unavoidable (the
692	monotonic clock option helps a lot here).	1313	monotonic clock option helps a lot here).
		1314
		1315	The callback is guaranteed to be invoked only I<after> its timeout has
		1316	passed, but if multiple timers become ready during the same loop iteration
		1317	then order of execution is undefined.
		1318
		1319	=head3 Be smart about timeouts
		1320
		1321	Many real-world problems involve some kind of timeout, usually for error
		1322	recovery. A typical example is an HTTP request - if the other side hangs,
		1323	you want to raise some error after a while.
		1324
		1325	What follows are some ways to handle this problem, from obvious and
		1326	inefficient to smart and efficient.
		1327
		1328	In the following, a 60 second activity timeout is assumed - a timeout that
		1329	gets reset to 60 seconds each time there is activity (e.g. each time some
		1330	data or other life sign was received).
		1331
		1332	=over 4
		1333
		1334	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1335
		1336	This is the most obvious, but not the most simple way: In the beginning,
		1337	start the watcher:
		1338
		1339	ev_timer_init (timer, callback, 60., 0.);
		1340	ev_timer_start (loop, timer);
		1341
		1342	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1343	and start it again:
		1344
		1345	ev_timer_stop (loop, timer);
		1346	ev_timer_set (timer, 60., 0.);
		1347	ev_timer_start (loop, timer);
		1348
		1349	This is relatively simple to implement, but means that each time there is
		1350	some activity, libev will first have to remove the timer from its internal
		1351	data structure and then add it again. Libev tries to be fast, but it's
		1352	still not a constant-time operation.
		1353
		1354	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1355
		1356	This is the easiest way, and involves using C<ev_timer_again> instead of
		1357	C<ev_timer_start>.
		1358
		1359	To implement this, configure an C<ev_timer> with a C<repeat> value
		1360	of C<60> and then call C<ev_timer_again> at start and each time you
		1361	successfully read or write some data. If you go into an idle state where
		1362	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1363	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1364
		1365	That means you can ignore both the C<ev_timer_start> function and the
		1366	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1367	member and C<ev_timer_again>.
		1368
		1369	At start:
		1370
		1371	ev_timer_init (timer, callback);
		1372	timer->repeat = 60.;
		1373	ev_timer_again (loop, timer);
		1374
		1375	Each time there is some activity:
		1376
		1377	ev_timer_again (loop, timer);
		1378
		1379	It is even possible to change the time-out on the fly, regardless of
		1380	whether the watcher is active or not:
		1381
		1382	timer->repeat = 30.;
		1383	ev_timer_again (loop, timer);
		1384
		1385	This is slightly more efficient then stopping/starting the timer each time
		1386	you want to modify its timeout value, as libev does not have to completely
		1387	remove and re-insert the timer from/into its internal data structure.
		1388
		1389	It is, however, even simpler than the "obvious" way to do it.
		1390
		1391	=item 3. Let the timer time out, but then re-arm it as required.
		1392
		1393	This method is more tricky, but usually most efficient: Most timeouts are
		1394	relatively long compared to the intervals between other activity - in
		1395	our example, within 60 seconds, there are usually many I/O events with
		1396	associated activity resets.
		1397
		1398	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1399	but remember the time of last activity, and check for a real timeout only
		1400	within the callback:
		1401
		1402	ev_tstamp last_activity; // time of last activity
		1403
		1404	static void
		1405	callback (EV_P_ ev_timer *w, int revents)
		1406	{
		1407	ev_tstamp now = ev_now (EV_A);
		1408	ev_tstamp timeout = last_activity + 60.;
		1409
		1410	// if last_activity + 60. is older than now, we did time out
		1411	if (timeout < now)
		1412	{
		1413	// timeout occured, take action
		1414	}
		1415	else
		1416	{
		1417	// callback was invoked, but there was some activity, re-arm
		1418	// the watcher to fire in last_activity + 60, which is
		1419	// guaranteed to be in the future, so "again" is positive:
		1420	w->again = timeout - now;
		1421	ev_timer_again (EV_A_ w);
		1422	}
		1423	}
		1424
		1425	To summarise the callback: first calculate the real timeout (defined
		1426	as "60 seconds after the last activity"), then check if that time has
		1427	been reached, which means something I<did>, in fact, time out. Otherwise
		1428	the callback was invoked too early (C<timeout> is in the future), so
		1429	re-schedule the timer to fire at that future time, to see if maybe we have
		1430	a timeout then.
		1431
		1432	Note how C<ev_timer_again> is used, taking advantage of the
		1433	C<ev_timer_again> optimisation when the timer is already running.
		1434
		1435	This scheme causes more callback invocations (about one every 60 seconds
		1436	minus half the average time between activity), but virtually no calls to
		1437	libev to change the timeout.
		1438
		1439	To start the timer, simply initialise the watcher and set C<last_activity>
		1440	to the current time (meaning we just have some activity :), then call the
		1441	callback, which will "do the right thing" and start the timer:
		1442
		1443	ev_timer_init (timer, callback);
		1444	last_activity = ev_now (loop);
		1445	callback (loop, timer, EV_TIMEOUT);
		1446
		1447	And when there is some activity, simply store the current time in
		1448	C<last_activity>, no libev calls at all:
		1449
		1450	last_actiivty = ev_now (loop);
		1451
		1452	This technique is slightly more complex, but in most cases where the
		1453	time-out is unlikely to be triggered, much more efficient.
		1454
		1455	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1456	callback :) - just change the timeout and invoke the callback, which will
		1457	fix things for you.
		1458
		1459	=item 4. Wee, just use a double-linked list for your timeouts.
		1460
		1461	If there is not one request, but many thousands (millions...), all
		1462	employing some kind of timeout with the same timeout value, then one can
		1463	do even better:
		1464
		1465	When starting the timeout, calculate the timeout value and put the timeout
		1466	at the I<end> of the list.
		1467
		1468	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1469	the list is expected to fire (for example, using the technique #3).
		1470
		1471	When there is some activity, remove the timer from the list, recalculate
		1472	the timeout, append it to the end of the list again, and make sure to
		1473	update the C<ev_timer> if it was taken from the beginning of the list.
		1474
		1475	This way, one can manage an unlimited number of timeouts in O(1) time for
		1476	starting, stopping and updating the timers, at the expense of a major
		1477	complication, and having to use a constant timeout. The constant timeout
		1478	ensures that the list stays sorted.
		1479
		1480	=back
		1481
		1482	So which method the best?
		1483
		1484	Method #2 is a simple no-brain-required solution that is adequate in most
		1485	situations. Method #3 requires a bit more thinking, but handles many cases
		1486	better, and isn't very complicated either. In most case, choosing either
		1487	one is fine, with #3 being better in typical situations.
		1488
		1489	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1490	rather complicated, but extremely efficient, something that really pays
		1491	off after the first million or so of active timers, i.e. it's usually
		1492	overkill :)
		1493
		1494	=head3 The special problem of time updates
		1495
		1496	Establishing the current time is a costly operation (it usually takes at
		1497	least two system calls): EV therefore updates its idea of the current
		1498	time only before and after C<ev_loop> collects new events, which causes a
		1499	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1500	lots of events in one iteration.
693		1501
694	The relative timeouts are calculated relative to the C<ev_now ()>	1502	The relative timeouts are calculated relative to the C<ev_now ()>
695	time. This is usually the right thing as this timestamp refers to the time	1503	time. This is usually the right thing as this timestamp refers to the time
696	of the event triggering whatever timeout you are modifying/starting. If	1504	of the event triggering whatever timeout you are modifying/starting. If
697	you suspect event processing to be delayed and you I<need> to base the timeout	1505	you suspect event processing to be delayed and you I<need> to base the
698	on the current time, use something like this to adjust for this:	1506	timeout on the current time, use something like this to adjust for this:
699		1507
700	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1508	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
701		1509
702	The callback is guarenteed to be invoked only when its timeout has passed,	1510	If the event loop is suspended for a long time, you can also force an
703	but if multiple timers become ready during the same loop iteration then	1511	update of the time returned by C<ev_now ()> by calling C<ev_now_update
704	order of execution is undefined.	1512	()>.
		1513
		1514	=head3 Watcher-Specific Functions and Data Members
705		1515
706	=over 4	1516	=over 4
707		1517
708	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1518	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
709		1519
710	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1520	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
711		1521
712	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1522	Configure the timer to trigger after C<after> seconds. If C<repeat>
713	C<0.>, then it will automatically be stopped. If it is positive, then the	1523	is C<0.>, then it will automatically be stopped once the timeout is
714	timer will automatically be configured to trigger again C<repeat> seconds	1524	reached. If it is positive, then the timer will automatically be
715	later, again, and again, until stopped manually.	1525	configured to trigger again C<repeat> seconds later, again, and again,
		1526	until stopped manually.
716		1527
717	The timer itself will do a best-effort at avoiding drift, that is, if you	1528	The timer itself will do a best-effort at avoiding drift, that is, if
718	configure a timer to trigger every 10 seconds, then it will trigger at	1529	you configure a timer to trigger every 10 seconds, then it will normally
719	exactly 10 second intervals. If, however, your program cannot keep up with	1530	trigger at exactly 10 second intervals. If, however, your program cannot
720	the timer (because it takes longer than those 10 seconds to do stuff) the	1531	keep up with the timer (because it takes longer than those 10 seconds to
721	timer will not fire more than once per event loop iteration.	1532	do stuff) the timer will not fire more than once per event loop iteration.
722		1533
723	=item ev_timer_again (loop)	1534	=item ev_timer_again (loop, ev_timer *)
724		1535
725	This will act as if the timer timed out and restart it again if it is	1536	This will act as if the timer timed out and restart it again if it is
726	repeating. The exact semantics are:	1537	repeating. The exact semantics are:
727		1538
		1539	If the timer is pending, its pending status is cleared.
		1540
728	If the timer is started but nonrepeating, stop it.	1541	If the timer is started but non-repeating, stop it (as if it timed out).
729		1542
730	If the timer is repeating, either start it if necessary (with the repeat	1543	If the timer is repeating, either start it if necessary (with the
731	value), or reset the running timer to the repeat value.	1544	C<repeat> value), or reset the running timer to the C<repeat> value.
732		1545
733	This sounds a bit complicated, but here is a useful and typical	1546	This sounds a bit complicated, see "Be smart about timeouts", above, for a
734	example: Imagine you have a tcp connection and you want a so-called idle	1547	usage example.
735	timeout, that is, you want to be called when there have been, say, 60	1548
736	seconds of inactivity on the socket. The easiest way to do this is to	1549	=item ev_tstamp repeat [read-write]
737	configure an C<ev_timer> with after=repeat=60 and calling ev_timer_again each	1550
738	time you successfully read or write some data. If you go into an idle	1551	The current C<repeat> value. Will be used each time the watcher times out
739	state where you do not expect data to travel on the socket, you can stop	1552	or C<ev_timer_again> is called, and determines the next timeout (if any),
740	the timer, and again will automatically restart it if need be.	1553	which is also when any modifications are taken into account.
741		1554
742	=back	1555	=back
743		1556
		1557	=head3 Examples
		1558
744	Example: create a timer that fires after 60 seconds.	1559	Example: Create a timer that fires after 60 seconds.
745		1560
746	static void	1561	static void
747	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1562	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
748	{	1563	{
749	.. one minute over, w is actually stopped right here	1564	.. one minute over, w is actually stopped right here
750	}	1565	}
751		1566
752	struct ev_timer mytimer;	1567	ev_timer mytimer;
753	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1568	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
754	ev_timer_start (loop, &mytimer);	1569	ev_timer_start (loop, &mytimer);
755		1570
756	Example: create a timeout timer that times out after 10 seconds of	1571	Example: Create a timeout timer that times out after 10 seconds of
757	inactivity.	1572	inactivity.
758		1573
759	static void	1574	static void
760	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1575	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
761	{	1576	{
762	.. ten seconds without any activity	1577	.. ten seconds without any activity
763	}	1578	}
764		1579
765	struct ev_timer mytimer;	1580	ev_timer mytimer;
766	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1581	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
767	ev_timer_again (&mytimer); /* start timer */	1582	ev_timer_again (&mytimer); /* start timer */
768	ev_loop (loop, 0);	1583	ev_loop (loop, 0);
769		1584
770	// and in some piece of code that gets executed on any "activity":	1585	// and in some piece of code that gets executed on any "activity":
771	// reset the timeout to start ticking again at 10 seconds	1586	// reset the timeout to start ticking again at 10 seconds
772	ev_timer_again (&mytimer);	1587	ev_timer_again (&mytimer);
773		1588
774		1589
775	=head2 C<ev_periodic> - to cron or not to cron	1590	=head2 C<ev_periodic> - to cron or not to cron?
776		1591
777	Periodic watchers are also timers of a kind, but they are very versatile	1592	Periodic watchers are also timers of a kind, but they are very versatile
778	(and unfortunately a bit complex).	1593	(and unfortunately a bit complex).
779		1594
780	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1595	Unlike C<ev_timer>'s, they are not based on real time (or relative time)
781	but on wallclock time (absolute time). You can tell a periodic watcher	1596	but on wall clock time (absolute time). You can tell a periodic watcher
782	to trigger "at" some specific point in time. For example, if you tell a	1597	to trigger after some specific point in time. For example, if you tell a
783	periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()	1598	periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now ()
784	+ 10.>) and then reset your system clock to the last year, then it will	1599	+ 10.>, that is, an absolute time not a delay) and then reset your system
		1600	clock to January of the previous year, then it will take more than year
785	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1601	to trigger the event (unlike an C<ev_timer>, which would still trigger
786	roughly 10 seconds later and of course not if you reset your system time	1602	roughly 10 seconds later as it uses a relative timeout).
787	again).
788		1603
789	They can also be used to implement vastly more complex timers, such as	1604	C<ev_periodic>s can also be used to implement vastly more complex timers,
790	triggering an event on eahc midnight, local time.	1605	such as triggering an event on each "midnight, local time", or other
		1606	complicated rules.
791		1607
792	As with timers, the callback is guarenteed to be invoked only when the	1608	As with timers, the callback is guaranteed to be invoked only when the
793	time (C<at>) has been passed, but if multiple periodic timers become ready	1609	time (C<at>) has passed, but if multiple periodic timers become ready
794	during the same loop iteration then order of execution is undefined.	1610	during the same loop iteration, then order of execution is undefined.
		1611
		1612	=head3 Watcher-Specific Functions and Data Members
795		1613
796	=over 4	1614	=over 4
797		1615
798	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1616	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
799		1617
800	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1618	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)
801		1619
802	Lots of arguments, lets sort it out... There are basically three modes of	1620	Lots of arguments, lets sort it out... There are basically three modes of
803	operation, and we will explain them from simplest to complex:	1621	operation, and we will explain them from simplest to most complex:
804		1622
805	=over 4	1623	=over 4
806		1624
807	=item * absolute timer (interval = reschedule_cb = 0)	1625	=item * absolute timer (at = time, interval = reschedule_cb = 0)
808		1626
809	In this configuration the watcher triggers an event at the wallclock time	1627	In this configuration the watcher triggers an event after the wall clock
810	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1628	time C<at> has passed. It will not repeat and will not adjust when a time
811	that is, if it is to be run at January 1st 2011 then it will run when the	1629	jump occurs, that is, if it is to be run at January 1st 2011 then it will
812	system time reaches or surpasses this time.	1630	only run when the system clock reaches or surpasses this time.
813		1631
814	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1632	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
815		1633
816	In this mode the watcher will always be scheduled to time out at the next	1634	In this mode the watcher will always be scheduled to time out at the next
817	C<at + N * interval> time (for some integer N) and then repeat, regardless	1635	C<at + N * interval> time (for some integer N, which can also be negative)
818	of any time jumps.	1636	and then repeat, regardless of any time jumps.
819		1637
820	This can be used to create timers that do not drift with respect to system	1638	This can be used to create timers that do not drift with respect to the
821	time:	1639	system clock, for example, here is a C<ev_periodic> that triggers each
		1640	hour, on the hour:
822		1641
823	ev_periodic_set (&periodic, 0., 3600., 0);	1642	ev_periodic_set (&periodic, 0., 3600., 0);
824		1643
825	This doesn't mean there will always be 3600 seconds in between triggers,	1644	This doesn't mean there will always be 3600 seconds in between triggers,
826	but only that the the callback will be called when the system time shows a	1645	but only that the callback will be called when the system time shows a
827	full hour (UTC), or more correctly, when the system time is evenly divisible	1646	full hour (UTC), or more correctly, when the system time is evenly divisible
828	by 3600.	1647	by 3600.
829		1648
830	Another way to think about it (for the mathematically inclined) is that	1649	Another way to think about it (for the mathematically inclined) is that
831	C<ev_periodic> will try to run the callback in this mode at the next possible	1650	C<ev_periodic> will try to run the callback in this mode at the next possible
832	time where C<time = at (mod interval)>, regardless of any time jumps.	1651	time where C<time = at (mod interval)>, regardless of any time jumps.
833		1652
		1653	For numerical stability it is preferable that the C<at> value is near
		1654	C<ev_now ()> (the current time), but there is no range requirement for
		1655	this value, and in fact is often specified as zero.
		1656
		1657	Note also that there is an upper limit to how often a timer can fire (CPU
		1658	speed for example), so if C<interval> is very small then timing stability
		1659	will of course deteriorate. Libev itself tries to be exact to be about one
		1660	millisecond (if the OS supports it and the machine is fast enough).
		1661
834	=item * manual reschedule mode (reschedule_cb = callback)	1662	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
835		1663
836	In this mode the values for C<interval> and C<at> are both being	1664	In this mode the values for C<interval> and C<at> are both being
837	ignored. Instead, each time the periodic watcher gets scheduled, the	1665	ignored. Instead, each time the periodic watcher gets scheduled, the
838	reschedule callback will be called with the watcher as first, and the	1666	reschedule callback will be called with the watcher as first, and the
839	current time as second argument.	1667	current time as second argument.
840		1668
841	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1669	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,
842	ever, or make any event loop modifications>. If you need to stop it,	1670	ever, or make ANY event loop modifications whatsoever>.
843	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by
844	starting a prepare watcher).
845		1671
		1672	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1673	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1674	only event loop modification you are allowed to do).
		1675
846	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1676	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
847	ev_tstamp now)>, e.g.:	1677	*w, ev_tstamp now)>, e.g.:
848		1678
		1679	static ev_tstamp
849	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1680	my_rescheduler (ev_periodic *w, ev_tstamp now)
850	{	1681	{
851	return now + 60.;	1682	return now + 60.;
852	}	1683	}
853		1684
854	It must return the next time to trigger, based on the passed time value	1685	It must return the next time to trigger, based on the passed time value
855	(that is, the lowest time value larger than to the second argument). It	1686	(that is, the lowest time value larger than to the second argument). It
856	will usually be called just before the callback will be triggered, but	1687	will usually be called just before the callback will be triggered, but
857	might be called at other times, too.	1688	might be called at other times, too.
858		1689
859	NOTE: I<< This callback must always return a time that is later than the	1690	NOTE: I<< This callback must always return a time that is higher than or
860	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	1691	equal to the passed C<now> value >>.
861		1692
862	This can be used to create very complex timers, such as a timer that	1693	This can be used to create very complex timers, such as a timer that
863	triggers on each midnight, local time. To do this, you would calculate the	1694	triggers on "next midnight, local time". To do this, you would calculate the
864	next midnight after C<now> and return the timestamp value for this. How	1695	next midnight after C<now> and return the timestamp value for this. How
865	you do this is, again, up to you (but it is not trivial, which is the main	1696	you do this is, again, up to you (but it is not trivial, which is the main
866	reason I omitted it as an example).	1697	reason I omitted it as an example).
867		1698
868	=back	1699	=back
…		…
872	Simply stops and restarts the periodic watcher again. This is only useful	1703	Simply stops and restarts the periodic watcher again. This is only useful
873	when you changed some parameters or the reschedule callback would return	1704	when you changed some parameters or the reschedule callback would return
874	a different time than the last time it was called (e.g. in a crond like	1705	a different time than the last time it was called (e.g. in a crond like
875	program when the crontabs have changed).	1706	program when the crontabs have changed).
876		1707
		1708	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1709
		1710	When active, returns the absolute time that the watcher is supposed to
		1711	trigger next.
		1712
		1713	=item ev_tstamp offset [read-write]
		1714
		1715	When repeating, this contains the offset value, otherwise this is the
		1716	absolute point in time (the C<at> value passed to C<ev_periodic_set>).
		1717
		1718	Can be modified any time, but changes only take effect when the periodic
		1719	timer fires or C<ev_periodic_again> is being called.
		1720
		1721	=item ev_tstamp interval [read-write]
		1722
		1723	The current interval value. Can be modified any time, but changes only
		1724	take effect when the periodic timer fires or C<ev_periodic_again> is being
		1725	called.
		1726
		1727	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
		1728
		1729	The current reschedule callback, or C<0>, if this functionality is
		1730	switched off. Can be changed any time, but changes only take effect when
		1731	the periodic timer fires or C<ev_periodic_again> is being called.
		1732
877	=back	1733	=back
878		1734
		1735	=head3 Examples
		1736
879	Example: call a callback every hour, or, more precisely, whenever the	1737	Example: Call a callback every hour, or, more precisely, whenever the
880	system clock is divisible by 3600. The callback invocation times have	1738	system time is divisible by 3600. The callback invocation times have
881	potentially a lot of jittering, but good long-term stability.	1739	potentially a lot of jitter, but good long-term stability.
882		1740
883	static void	1741	static void
884	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1742	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
885	{	1743	{
886	... its now a full hour (UTC, or TAI or whatever your clock follows)	1744	... its now a full hour (UTC, or TAI or whatever your clock follows)
887	}	1745	}
888		1746
889	struct ev_periodic hourly_tick;	1747	ev_periodic hourly_tick;
890	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	1748	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
891	ev_periodic_start (loop, &hourly_tick);	1749	ev_periodic_start (loop, &hourly_tick);
892		1750
893	Example: the same as above, but use a reschedule callback to do it:	1751	Example: The same as above, but use a reschedule callback to do it:
894		1752
895	#include <math.h>	1753	#include <math.h>
896		1754
897	static ev_tstamp	1755	static ev_tstamp
898	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	1756	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
899	{	1757	{
900	return fmod (now, 3600.) + 3600.;	1758	return now + (3600. - fmod (now, 3600.));
901	}	1759	}
902		1760
903	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	1761	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
904		1762
905	Example: call a callback every hour, starting now:	1763	Example: Call a callback every hour, starting now:
906		1764
907	struct ev_periodic hourly_tick;	1765	ev_periodic hourly_tick;
908	ev_periodic_init (&hourly_tick, clock_cb,	1766	ev_periodic_init (&hourly_tick, clock_cb,
909	fmod (ev_now (loop), 3600.), 3600., 0);	1767	fmod (ev_now (loop), 3600.), 3600., 0);
910	ev_periodic_start (loop, &hourly_tick);	1768	ev_periodic_start (loop, &hourly_tick);
911		1769
912		1770
913	=head2 C<ev_signal> - signal me when a signal gets signalled	1771	=head2 C<ev_signal> - signal me when a signal gets signalled!
914		1772
915	Signal watchers will trigger an event when the process receives a specific	1773	Signal watchers will trigger an event when the process receives a specific
916	signal one or more times. Even though signals are very asynchronous, libev	1774	signal one or more times. Even though signals are very asynchronous, libev
917	will try it's best to deliver signals synchronously, i.e. as part of the	1775	will try it's best to deliver signals synchronously, i.e. as part of the
918	normal event processing, like any other event.	1776	normal event processing, like any other event.
919		1777
		1778	If you want signals asynchronously, just use C<sigaction> as you would
		1779	do without libev and forget about sharing the signal. You can even use
		1780	C<ev_async> from a signal handler to synchronously wake up an event loop.
		1781
920	You can configure as many watchers as you like per signal. Only when the	1782	You can configure as many watchers as you like per signal. Only when the
921	first watcher gets started will libev actually register a signal watcher	1783	first watcher gets started will libev actually register a signal handler
922	with the kernel (thus it coexists with your own signal handlers as long	1784	with the kernel (thus it coexists with your own signal handlers as long as
923	as you don't register any with libev). Similarly, when the last signal	1785	you don't register any with libev for the same signal). Similarly, when
924	watcher for a signal is stopped libev will reset the signal handler to	1786	the last signal watcher for a signal is stopped, libev will reset the
925	SIG_DFL (regardless of what it was set to before).	1787	signal handler to SIG_DFL (regardless of what it was set to before).
		1788
		1789	If possible and supported, libev will install its handlers with
		1790	C<SA_RESTART> behaviour enabled, so system calls should not be unduly
		1791	interrupted. If you have a problem with system calls getting interrupted by
		1792	signals you can block all signals in an C<ev_check> watcher and unblock
		1793	them in an C<ev_prepare> watcher.
		1794
		1795	=head3 Watcher-Specific Functions and Data Members
926		1796
927	=over 4	1797	=over 4
928		1798
929	=item ev_signal_init (ev_signal *, callback, int signum)	1799	=item ev_signal_init (ev_signal *, callback, int signum)
930		1800
931	=item ev_signal_set (ev_signal *, int signum)	1801	=item ev_signal_set (ev_signal *, int signum)
932		1802
933	Configures the watcher to trigger on the given signal number (usually one	1803	Configures the watcher to trigger on the given signal number (usually one
934	of the C<SIGxxx> constants).	1804	of the C<SIGxxx> constants).
935		1805
		1806	=item int signum [read-only]
		1807
		1808	The signal the watcher watches out for.
		1809
936	=back	1810	=back
937		1811
		1812	=head3 Examples
938		1813
		1814	Example: Try to exit cleanly on SIGINT.
		1815
		1816	static void
		1817	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		1818	{
		1819	ev_unloop (loop, EVUNLOOP_ALL);
		1820	}
		1821
		1822	ev_signal signal_watcher;
		1823	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1824	ev_signal_start (loop, &signal_watcher);
		1825
		1826
939	=head2 C<ev_child> - wait for pid status changes	1827	=head2 C<ev_child> - watch out for process status changes
940		1828
941	Child watchers trigger when your process receives a SIGCHLD in response to	1829	Child watchers trigger when your process receives a SIGCHLD in response to
942	some child status changes (most typically when a child of yours dies).	1830	some child status changes (most typically when a child of yours dies or
		1831	exits). It is permissible to install a child watcher I<after> the child
		1832	has been forked (which implies it might have already exited), as long
		1833	as the event loop isn't entered (or is continued from a watcher), i.e.,
		1834	forking and then immediately registering a watcher for the child is fine,
		1835	but forking and registering a watcher a few event loop iterations later is
		1836	not.
		1837
		1838	Only the default event loop is capable of handling signals, and therefore
		1839	you can only register child watchers in the default event loop.
		1840
		1841	=head3 Process Interaction
		1842
		1843	Libev grabs C<SIGCHLD> as soon as the default event loop is
		1844	initialised. This is necessary to guarantee proper behaviour even if
		1845	the first child watcher is started after the child exits. The occurrence
		1846	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		1847	synchronously as part of the event loop processing. Libev always reaps all
		1848	children, even ones not watched.
		1849
		1850	=head3 Overriding the Built-In Processing
		1851
		1852	Libev offers no special support for overriding the built-in child
		1853	processing, but if your application collides with libev's default child
		1854	handler, you can override it easily by installing your own handler for
		1855	C<SIGCHLD> after initialising the default loop, and making sure the
		1856	default loop never gets destroyed. You are encouraged, however, to use an
		1857	event-based approach to child reaping and thus use libev's support for
		1858	that, so other libev users can use C<ev_child> watchers freely.
		1859
		1860	=head3 Stopping the Child Watcher
		1861
		1862	Currently, the child watcher never gets stopped, even when the
		1863	child terminates, so normally one needs to stop the watcher in the
		1864	callback. Future versions of libev might stop the watcher automatically
		1865	when a child exit is detected.
		1866
		1867	=head3 Watcher-Specific Functions and Data Members
943		1868
944	=over 4	1869	=over 4
945		1870
946	=item ev_child_init (ev_child *, callback, int pid)	1871	=item ev_child_init (ev_child *, callback, int pid, int trace)
947		1872
948	=item ev_child_set (ev_child *, int pid)	1873	=item ev_child_set (ev_child *, int pid, int trace)
949		1874
950	Configures the watcher to wait for status changes of process C<pid> (or	1875	Configures the watcher to wait for status changes of process C<pid> (or
951	I<any> process if C<pid> is specified as C<0>). The callback can look	1876	I<any> process if C<pid> is specified as C<0>). The callback can look
952	at the C<rstatus> member of the C<ev_child> watcher structure to see	1877	at the C<rstatus> member of the C<ev_child> watcher structure to see
953	the status word (use the macros from C<sys/wait.h> and see your systems	1878	the status word (use the macros from C<sys/wait.h> and see your systems
954	C<waitpid> documentation). The C<rpid> member contains the pid of the	1879	C<waitpid> documentation). The C<rpid> member contains the pid of the
955	process causing the status change.	1880	process causing the status change. C<trace> must be either C<0> (only
		1881	activate the watcher when the process terminates) or C<1> (additionally
		1882	activate the watcher when the process is stopped or continued).
		1883
		1884	=item int pid [read-only]
		1885
		1886	The process id this watcher watches out for, or C<0>, meaning any process id.
		1887
		1888	=item int rpid [read-write]
		1889
		1890	The process id that detected a status change.
		1891
		1892	=item int rstatus [read-write]
		1893
		1894	The process exit/trace status caused by C<rpid> (see your systems
		1895	C<waitpid> and C<sys/wait.h> documentation for details).
956		1896
957	=back	1897	=back
958		1898
959	Example: try to exit cleanly on SIGINT and SIGTERM.	1899	=head3 Examples
960		1900
		1901	Example: C<fork()> a new process and install a child handler to wait for
		1902	its completion.
		1903
		1904	ev_child cw;
		1905
961	static void	1906	static void
962	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	1907	child_cb (EV_P_ ev_child *w, int revents)
963	{	1908	{
964	ev_unloop (loop, EVUNLOOP_ALL);	1909	ev_child_stop (EV_A_ w);
		1910	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
965	}	1911	}
966		1912
967	struct ev_signal signal_watcher;	1913	pid_t pid = fork ();
968	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
969	ev_signal_start (loop, &sigint_cb);
970		1914
		1915	if (pid < 0)
		1916	// error
		1917	else if (pid == 0)
		1918	{
		1919	// the forked child executes here
		1920	exit (1);
		1921	}
		1922	else
		1923	{
		1924	ev_child_init (&cw, child_cb, pid, 0);
		1925	ev_child_start (EV_DEFAULT_ &cw);
		1926	}
971		1927
		1928
		1929	=head2 C<ev_stat> - did the file attributes just change?
		1930
		1931	This watches a file system path for attribute changes. That is, it calls
		1932	C<stat> on that path in regular intervals (or when the OS says it changed)
		1933	and sees if it changed compared to the last time, invoking the callback if
		1934	it did.
		1935
		1936	The path does not need to exist: changing from "path exists" to "path does
		1937	not exist" is a status change like any other. The condition "path does not
		1938	exist" (or more correctly "path cannot be stat'ed") is signified by the
		1939	C<st_nlink> field being zero (which is otherwise always forced to be at
		1940	least one) and all the other fields of the stat buffer having unspecified
		1941	contents.
		1942
		1943	The path I<must not> end in a slash or contain special components such as
		1944	C<.> or C<..>. The path I<should> be absolute: If it is relative and
		1945	your working directory changes, then the behaviour is undefined.
		1946
		1947	Since there is no portable change notification interface available, the
		1948	portable implementation simply calls C<stat(2)> regularly on the path
		1949	to see if it changed somehow. You can specify a recommended polling
		1950	interval for this case. If you specify a polling interval of C<0> (highly
		1951	recommended!) then a I<suitable, unspecified default> value will be used
		1952	(which you can expect to be around five seconds, although this might
		1953	change dynamically). Libev will also impose a minimum interval which is
		1954	currently around C<0.1>, but that's usually overkill.
		1955
		1956	This watcher type is not meant for massive numbers of stat watchers,
		1957	as even with OS-supported change notifications, this can be
		1958	resource-intensive.
		1959
		1960	At the time of this writing, the only OS-specific interface implemented
		1961	is the Linux inotify interface (implementing kqueue support is left as an
		1962	exercise for the reader. Note, however, that the author sees no way of
		1963	implementing C<ev_stat> semantics with kqueue, except as a hint).
		1964
		1965	=head3 ABI Issues (Largefile Support)
		1966
		1967	Libev by default (unless the user overrides this) uses the default
		1968	compilation environment, which means that on systems with large file
		1969	support disabled by default, you get the 32 bit version of the stat
		1970	structure. When using the library from programs that change the ABI to
		1971	use 64 bit file offsets the programs will fail. In that case you have to
		1972	compile libev with the same flags to get binary compatibility. This is
		1973	obviously the case with any flags that change the ABI, but the problem is
		1974	most noticeably displayed with ev_stat and large file support.
		1975
		1976	The solution for this is to lobby your distribution maker to make large
		1977	file interfaces available by default (as e.g. FreeBSD does) and not
		1978	optional. Libev cannot simply switch on large file support because it has
		1979	to exchange stat structures with application programs compiled using the
		1980	default compilation environment.
		1981
		1982	=head3 Inotify and Kqueue
		1983
		1984	When C<inotify (7)> support has been compiled into libev and present at
		1985	runtime, it will be used to speed up change detection where possible. The
		1986	inotify descriptor will be created lazily when the first C<ev_stat>
		1987	watcher is being started.
		1988
		1989	Inotify presence does not change the semantics of C<ev_stat> watchers
		1990	except that changes might be detected earlier, and in some cases, to avoid
		1991	making regular C<stat> calls. Even in the presence of inotify support
		1992	there are many cases where libev has to resort to regular C<stat> polling,
		1993	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		1994	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		1995	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		1996	xfs are fully working) libev usually gets away without polling.
		1997
		1998	There is no support for kqueue, as apparently it cannot be used to
		1999	implement this functionality, due to the requirement of having a file
		2000	descriptor open on the object at all times, and detecting renames, unlinks
		2001	etc. is difficult.
		2002
		2003	=head3 The special problem of stat time resolution
		2004
		2005	The C<stat ()> system call only supports full-second resolution portably,
		2006	and even on systems where the resolution is higher, most file systems
		2007	still only support whole seconds.
		2008
		2009	That means that, if the time is the only thing that changes, you can
		2010	easily miss updates: on the first update, C<ev_stat> detects a change and
		2011	calls your callback, which does something. When there is another update
		2012	within the same second, C<ev_stat> will be unable to detect unless the
		2013	stat data does change in other ways (e.g. file size).
		2014
		2015	The solution to this is to delay acting on a change for slightly more
		2016	than a second (or till slightly after the next full second boundary), using
		2017	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2018	ev_timer_again (loop, w)>).
		2019
		2020	The C<.02> offset is added to work around small timing inconsistencies
		2021	of some operating systems (where the second counter of the current time
		2022	might be be delayed. One such system is the Linux kernel, where a call to
		2023	C<gettimeofday> might return a timestamp with a full second later than
		2024	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2025	update file times then there will be a small window where the kernel uses
		2026	the previous second to update file times but libev might already execute
		2027	the timer callback).
		2028
		2029	=head3 Watcher-Specific Functions and Data Members
		2030
		2031	=over 4
		2032
		2033	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		2034
		2035	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		2036
		2037	Configures the watcher to wait for status changes of the given
		2038	C<path>. The C<interval> is a hint on how quickly a change is expected to
		2039	be detected and should normally be specified as C<0> to let libev choose
		2040	a suitable value. The memory pointed to by C<path> must point to the same
		2041	path for as long as the watcher is active.
		2042
		2043	The callback will receive an C<EV_STAT> event when a change was detected,
		2044	relative to the attributes at the time the watcher was started (or the
		2045	last change was detected).
		2046
		2047	=item ev_stat_stat (loop, ev_stat *)
		2048
		2049	Updates the stat buffer immediately with new values. If you change the
		2050	watched path in your callback, you could call this function to avoid
		2051	detecting this change (while introducing a race condition if you are not
		2052	the only one changing the path). Can also be useful simply to find out the
		2053	new values.
		2054
		2055	=item ev_statdata attr [read-only]
		2056
		2057	The most-recently detected attributes of the file. Although the type is
		2058	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		2059	suitable for your system, but you can only rely on the POSIX-standardised
		2060	members to be present. If the C<st_nlink> member is C<0>, then there was
		2061	some error while C<stat>ing the file.
		2062
		2063	=item ev_statdata prev [read-only]
		2064
		2065	The previous attributes of the file. The callback gets invoked whenever
		2066	C<prev> != C<attr>, or, more precisely, one or more of these members
		2067	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2068	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
		2069
		2070	=item ev_tstamp interval [read-only]
		2071
		2072	The specified interval.
		2073
		2074	=item const char *path [read-only]
		2075
		2076	The file system path that is being watched.
		2077
		2078	=back
		2079
		2080	=head3 Examples
		2081
		2082	Example: Watch C</etc/passwd> for attribute changes.
		2083
		2084	static void
		2085	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		2086	{
		2087	/* /etc/passwd changed in some way */
		2088	if (w->attr.st_nlink)
		2089	{
		2090	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		2091	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		2092	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		2093	}
		2094	else
		2095	/* you shalt not abuse printf for puts */
		2096	puts ("wow, /etc/passwd is not there, expect problems. "
		2097	"if this is windows, they already arrived\n");
		2098	}
		2099
		2100	...
		2101	ev_stat passwd;
		2102
		2103	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		2104	ev_stat_start (loop, &passwd);
		2105
		2106	Example: Like above, but additionally use a one-second delay so we do not
		2107	miss updates (however, frequent updates will delay processing, too, so
		2108	one might do the work both on C<ev_stat> callback invocation I<and> on
		2109	C<ev_timer> callback invocation).
		2110
		2111	static ev_stat passwd;
		2112	static ev_timer timer;
		2113
		2114	static void
		2115	timer_cb (EV_P_ ev_timer *w, int revents)
		2116	{
		2117	ev_timer_stop (EV_A_ w);
		2118
		2119	/* now it's one second after the most recent passwd change */
		2120	}
		2121
		2122	static void
		2123	stat_cb (EV_P_ ev_stat *w, int revents)
		2124	{
		2125	/* reset the one-second timer */
		2126	ev_timer_again (EV_A_ &timer);
		2127	}
		2128
		2129	...
		2130	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2131	ev_stat_start (loop, &passwd);
		2132	ev_timer_init (&timer, timer_cb, 0., 1.02);
		2133
		2134
972	=head2 C<ev_idle> - when you've got nothing better to do	2135	=head2 C<ev_idle> - when you've got nothing better to do...
973		2136
974	Idle watchers trigger events when there are no other events are pending	2137	Idle watchers trigger events when no other events of the same or higher
975	(prepare, check and other idle watchers do not count). That is, as long	2138	priority are pending (prepare, check and other idle watchers do not count
976	as your process is busy handling sockets or timeouts (or even signals,	2139	as receiving "events").
977	imagine) it will not be triggered. But when your process is idle all idle	2140
978	watchers are being called again and again, once per event loop iteration -	2141	That is, as long as your process is busy handling sockets or timeouts
		2142	(or even signals, imagine) of the same or higher priority it will not be
		2143	triggered. But when your process is idle (or only lower-priority watchers
		2144	are pending), the idle watchers are being called once per event loop
979	until stopped, that is, or your process receives more events and becomes	2145	iteration - until stopped, that is, or your process receives more events
980	busy.	2146	and becomes busy again with higher priority stuff.
981		2147
982	The most noteworthy effect is that as long as any idle watchers are	2148	The most noteworthy effect is that as long as any idle watchers are
983	active, the process will not block when waiting for new events.	2149	active, the process will not block when waiting for new events.
984		2150
985	Apart from keeping your process non-blocking (which is a useful	2151	Apart from keeping your process non-blocking (which is a useful
986	effect on its own sometimes), idle watchers are a good place to do	2152	effect on its own sometimes), idle watchers are a good place to do
987	"pseudo-background processing", or delay processing stuff to after the	2153	"pseudo-background processing", or delay processing stuff to after the
988	event loop has handled all outstanding events.	2154	event loop has handled all outstanding events.
989		2155
		2156	=head3 Watcher-Specific Functions and Data Members
		2157
990	=over 4	2158	=over 4
991		2159
992	=item ev_idle_init (ev_signal *, callback)	2160	=item ev_idle_init (ev_signal *, callback)
993		2161
994	Initialises and configures the idle watcher - it has no parameters of any	2162	Initialises and configures the idle watcher - it has no parameters of any
995	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2163	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
996	believe me.	2164	believe me.
997		2165
998	=back	2166	=back
999		2167
		2168	=head3 Examples
		2169
1000	Example: dynamically allocate an C<ev_idle>, start it, and in the	2170	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1001	callback, free it. Alos, use no error checking, as usual.	2171	callback, free it. Also, use no error checking, as usual.
1002		2172
1003	static void	2173	static void
1004	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2174	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1005	{	2175	{
1006	free (w);	2176	free (w);
1007	// now do something you wanted to do when the program has	2177	// now do something you wanted to do when the program has
1008	// no longer asnything immediate to do.	2178	// no longer anything immediate to do.
1009	}	2179	}
1010		2180
1011	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2181	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1012	ev_idle_init (idle_watcher, idle_cb);	2182	ev_idle_init (idle_watcher, idle_cb);
1013	ev_idle_start (loop, idle_cb);	2183	ev_idle_start (loop, idle_cb);
1014		2184
1015		2185
1016	=head2 C<ev_prepare> and C<ev_check> - customise your event loop	2186	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1017		2187
1018	Prepare and check watchers are usually (but not always) used in tandem:	2188	Prepare and check watchers are usually (but not always) used in pairs:
1019	prepare watchers get invoked before the process blocks and check watchers	2189	prepare watchers get invoked before the process blocks and check watchers
1020	afterwards.	2190	afterwards.
1021		2191
		2192	You I<must not> call C<ev_loop> or similar functions that enter
		2193	the current event loop from either C<ev_prepare> or C<ev_check>
		2194	watchers. Other loops than the current one are fine, however. The
		2195	rationale behind this is that you do not need to check for recursion in
		2196	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
		2197	C<ev_check> so if you have one watcher of each kind they will always be
		2198	called in pairs bracketing the blocking call.
		2199
1022	Their main purpose is to integrate other event mechanisms into libev and	2200	Their main purpose is to integrate other event mechanisms into libev and
1023	their use is somewhat advanced. This could be used, for example, to track	2201	their use is somewhat advanced. They could be used, for example, to track
1024	variable changes, implement your own watchers, integrate net-snmp or a	2202	variable changes, implement your own watchers, integrate net-snmp or a
1025	coroutine library and lots more.	2203	coroutine library and lots more. They are also occasionally useful if
		2204	you cache some data and want to flush it before blocking (for example,
		2205	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		2206	watcher).
1026		2207
1027	This is done by examining in each prepare call which file descriptors need	2208	This is done by examining in each prepare call which file descriptors
1028	to be watched by the other library, registering C<ev_io> watchers for	2209	need to be watched by the other library, registering C<ev_io> watchers
1029	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2210	for them and starting an C<ev_timer> watcher for any timeouts (many
1030	provide just this functionality). Then, in the check watcher you check for	2211	libraries provide exactly this functionality). Then, in the check watcher,
1031	any events that occured (by checking the pending status of all watchers	2212	you check for any events that occurred (by checking the pending status
1032	and stopping them) and call back into the library. The I/O and timer	2213	of all watchers and stopping them) and call back into the library. The
1033	callbacks will never actually be called (but must be valid nevertheless,	2214	I/O and timer callbacks will never actually be called (but must be valid
1034	because you never know, you know?).	2215	nevertheless, because you never know, you know?).
1035		2216
1036	As another example, the Perl Coro module uses these hooks to integrate	2217	As another example, the Perl Coro module uses these hooks to integrate
1037	coroutines into libev programs, by yielding to other active coroutines	2218	coroutines into libev programs, by yielding to other active coroutines
1038	during each prepare and only letting the process block if no coroutines	2219	during each prepare and only letting the process block if no coroutines
1039	are ready to run (it's actually more complicated: it only runs coroutines	2220	are ready to run (it's actually more complicated: it only runs coroutines
1040	with priority higher than or equal to the event loop and one coroutine	2221	with priority higher than or equal to the event loop and one coroutine
1041	of lower priority, but only once, using idle watchers to keep the event	2222	of lower priority, but only once, using idle watchers to keep the event
1042	loop from blocking if lower-priority coroutines are active, thus mapping	2223	loop from blocking if lower-priority coroutines are active, thus mapping
1043	low-priority coroutines to idle/background tasks).	2224	low-priority coroutines to idle/background tasks).
1044		2225
		2226	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		2227	priority, to ensure that they are being run before any other watchers
		2228	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2229
		2230	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2231	activate ("feed") events into libev. While libev fully supports this, they
		2232	might get executed before other C<ev_check> watchers did their job. As
		2233	C<ev_check> watchers are often used to embed other (non-libev) event
		2234	loops those other event loops might be in an unusable state until their
		2235	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2236	others).
		2237
		2238	=head3 Watcher-Specific Functions and Data Members
		2239
1045	=over 4	2240	=over 4
1046		2241
1047	=item ev_prepare_init (ev_prepare *, callback)	2242	=item ev_prepare_init (ev_prepare *, callback)
1048		2243
1049	=item ev_check_init (ev_check *, callback)	2244	=item ev_check_init (ev_check *, callback)
1050		2245
1051	Initialises and configures the prepare or check watcher - they have no	2246	Initialises and configures the prepare or check watcher - they have no
1052	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2247	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1053	macros, but using them is utterly, utterly and completely pointless.	2248	macros, but using them is utterly, utterly, utterly and completely
		2249	pointless.
1054		2250
1055	=back	2251	=back
1056		2252
1057	Example: *TODO*.	2253	=head3 Examples
1058		2254
		2255	There are a number of principal ways to embed other event loops or modules
		2256	into libev. Here are some ideas on how to include libadns into libev
		2257	(there is a Perl module named C<EV::ADNS> that does this, which you could
		2258	use as a working example. Another Perl module named C<EV::Glib> embeds a
		2259	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		2260	Glib event loop).
1059		2261
		2262	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
		2263	and in a check watcher, destroy them and call into libadns. What follows
		2264	is pseudo-code only of course. This requires you to either use a low
		2265	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		2266	the callbacks for the IO/timeout watchers might not have been called yet.
		2267
		2268	static ev_io iow [nfd];
		2269	static ev_timer tw;
		2270
		2271	static void
		2272	io_cb (struct ev_loop *loop, ev_io *w, int revents)
		2273	{
		2274	}
		2275
		2276	// create io watchers for each fd and a timer before blocking
		2277	static void
		2278	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
		2279	{
		2280	int timeout = 3600000;
		2281	struct pollfd fds [nfd];
		2282	// actual code will need to loop here and realloc etc.
		2283	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		2284
		2285	/* the callback is illegal, but won't be called as we stop during check */
		2286	ev_timer_init (&tw, 0, timeout * 1e-3);
		2287	ev_timer_start (loop, &tw);
		2288
		2289	// create one ev_io per pollfd
		2290	for (int i = 0; i < nfd; ++i)
		2291	{
		2292	ev_io_init (iow + i, io_cb, fds [i].fd,
		2293	((fds [i].events & POLLIN ? EV_READ : 0)
		2294	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		2295
		2296	fds [i].revents = 0;
		2297	ev_io_start (loop, iow + i);
		2298	}
		2299	}
		2300
		2301	// stop all watchers after blocking
		2302	static void
		2303	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
		2304	{
		2305	ev_timer_stop (loop, &tw);
		2306
		2307	for (int i = 0; i < nfd; ++i)
		2308	{
		2309	// set the relevant poll flags
		2310	// could also call adns_processreadable etc. here
		2311	struct pollfd *fd = fds + i;
		2312	int revents = ev_clear_pending (iow + i);
		2313	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2314	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2315
		2316	// now stop the watcher
		2317	ev_io_stop (loop, iow + i);
		2318	}
		2319
		2320	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		2321	}
		2322
		2323	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2324	in the prepare watcher and would dispose of the check watcher.
		2325
		2326	Method 3: If the module to be embedded supports explicit event
		2327	notification (libadns does), you can also make use of the actual watcher
		2328	callbacks, and only destroy/create the watchers in the prepare watcher.
		2329
		2330	static void
		2331	timer_cb (EV_P_ ev_timer *w, int revents)
		2332	{
		2333	adns_state ads = (adns_state)w->data;
		2334	update_now (EV_A);
		2335
		2336	adns_processtimeouts (ads, &tv_now);
		2337	}
		2338
		2339	static void
		2340	io_cb (EV_P_ ev_io *w, int revents)
		2341	{
		2342	adns_state ads = (adns_state)w->data;
		2343	update_now (EV_A);
		2344
		2345	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2346	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2347	}
		2348
		2349	// do not ever call adns_afterpoll
		2350
		2351	Method 4: Do not use a prepare or check watcher because the module you
		2352	want to embed is not flexible enough to support it. Instead, you can
		2353	override their poll function. The drawback with this solution is that the
		2354	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		2355	this approach, effectively embedding EV as a client into the horrible
		2356	libglib event loop.
		2357
		2358	static gint
		2359	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2360	{
		2361	int got_events = 0;
		2362
		2363	for (n = 0; n < nfds; ++n)
		2364	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2365
		2366	if (timeout >= 0)
		2367	// create/start timer
		2368
		2369	// poll
		2370	ev_loop (EV_A_ 0);
		2371
		2372	// stop timer again
		2373	if (timeout >= 0)
		2374	ev_timer_stop (EV_A_ &to);
		2375
		2376	// stop io watchers again - their callbacks should have set
		2377	for (n = 0; n < nfds; ++n)
		2378	ev_io_stop (EV_A_ iow [n]);
		2379
		2380	return got_events;
		2381	}
		2382
		2383
1060	=head2 C<ev_embed> - when one backend isn't enough	2384	=head2 C<ev_embed> - when one backend isn't enough...
1061		2385
1062	This is a rather advanced watcher type that lets you embed one event loop	2386	This is a rather advanced watcher type that lets you embed one event loop
1063	into another.	2387	into another (currently only C<ev_io> events are supported in the embedded
		2388	loop, other types of watchers might be handled in a delayed or incorrect
		2389	fashion and must not be used).
1064		2390
1065	There are primarily two reasons you would want that: work around bugs and	2391	There are primarily two reasons you would want that: work around bugs and
1066	prioritise I/O.	2392	prioritise I/O.
1067		2393
1068	As an example for a bug workaround, the kqueue backend might only support	2394	As an example for a bug workaround, the kqueue backend might only support
1069	sockets on some platform, so it is unusable as generic backend, but you	2395	sockets on some platform, so it is unusable as generic backend, but you
1070	still want to make use of it because you have many sockets and it scales	2396	still want to make use of it because you have many sockets and it scales
1071	so nicely. In this case, you would create a kqueue-based loop and embed it	2397	so nicely. In this case, you would create a kqueue-based loop and embed
1072	into your default loop (which might use e.g. poll). Overall operation will	2398	it into your default loop (which might use e.g. poll). Overall operation
1073	be a bit slower because first libev has to poll and then call kevent, but	2399	will be a bit slower because first libev has to call C<poll> and then
1074	at least you can use both at what they are best.	2400	C<kevent>, but at least you can use both mechanisms for what they are
		2401	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1075		2402
1076	As for prioritising I/O: rarely you have the case where some fds have	2403	As for prioritising I/O: under rare circumstances you have the case where
1077	to be watched and handled very quickly (with low latency), and even	2404	some fds have to be watched and handled very quickly (with low latency),
1078	priorities and idle watchers might have too much overhead. In this case	2405	and even priorities and idle watchers might have too much overhead. In
1079	you would put all the high priority stuff in one loop and all the rest in	2406	this case you would put all the high priority stuff in one loop and all
1080	a second one, and embed the second one in the first.	2407	the rest in a second one, and embed the second one in the first.
		2408
		2409	As long as the watcher is active, the callback will be invoked every time
		2410	there might be events pending in the embedded loop. The callback must then
		2411	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke
		2412	their callbacks (you could also start an idle watcher to give the embedded
		2413	loop strictly lower priority for example). You can also set the callback
		2414	to C<0>, in which case the embed watcher will automatically execute the
		2415	embedded loop sweep.
1081		2416
1082	As long as the watcher is started it will automatically handle events. The	2417	As long as the watcher is started it will automatically handle events. The
1083	callback will be invoked whenever some events have been handled. You can	2418	callback will be invoked whenever some events have been handled. You can
1084	set the callback to C<0> to avoid having to specify one if you are not	2419	set the callback to C<0> to avoid having to specify one if you are not
1085	interested in that.	2420	interested in that.
1086		2421
1087	Also, there have not currently been made special provisions for forking:	2422	Also, there have not currently been made special provisions for forking:
1088	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2423	when you fork, you not only have to call C<ev_loop_fork> on both loops,
1089	but you will also have to stop and restart any C<ev_embed> watchers	2424	but you will also have to stop and restart any C<ev_embed> watchers
1090	yourself.	2425	yourself - but you can use a fork watcher to handle this automatically,
		2426	and future versions of libev might do just that.
1091		2427
1092	Unfortunately, not all backends are embeddable, only the ones returned by	2428	Unfortunately, not all backends are embeddable: only the ones returned by
1093	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2429	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1094	portable one.	2430	portable one.
1095		2431
1096	So when you want to use this feature you will always have to be prepared	2432	So when you want to use this feature you will always have to be prepared
1097	that you cannot get an embeddable loop. The recommended way to get around	2433	that you cannot get an embeddable loop. The recommended way to get around
1098	this is to have a separate variables for your embeddable loop, try to	2434	this is to have a separate variables for your embeddable loop, try to
1099	create it, and if that fails, use the normal loop for everything:	2435	create it, and if that fails, use the normal loop for everything.
1100		2436
1101	struct ev_loop *loop_hi = ev_default_init (0);	2437	=head3 C<ev_embed> and fork
1102	struct ev_loop *loop_lo = 0;
1103	struct ev_embed embed;
1104
1105	// see if there is a chance of getting one that works
1106	// (remember that a flags value of 0 means autodetection)
1107	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1108	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1109	: 0;
1110		2438
1111	// if we got one, then embed it, otherwise default to loop_hi	2439	While the C<ev_embed> watcher is running, forks in the embedding loop will
1112	if (loop_lo)	2440	automatically be applied to the embedded loop as well, so no special
1113	{	2441	fork handling is required in that case. When the watcher is not running,
1114	ev_embed_init (&embed, 0, loop_lo);	2442	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1115	ev_embed_start (loop_hi, &embed);	2443	as applicable.
1116	}	2444
1117	else	2445	=head3 Watcher-Specific Functions and Data Members
1118	loop_lo = loop_hi;
1119		2446
1120	=over 4	2447	=over 4
1121		2448
1122	=item ev_embed_init (ev_embed *, callback, struct ev_loop *loop)	2449	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
1123		2450
1124	=item ev_embed_set (ev_embed *, callback, struct ev_loop *loop)	2451	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
1125		2452
1126	Configures the watcher to embed the given loop, which must be embeddable.	2453	Configures the watcher to embed the given loop, which must be
		2454	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		2455	invoked automatically, otherwise it is the responsibility of the callback
		2456	to invoke it (it will continue to be called until the sweep has been done,
		2457	if you do not want that, you need to temporarily stop the embed watcher).
		2458
		2459	=item ev_embed_sweep (loop, ev_embed *)
		2460
		2461	Make a single, non-blocking sweep over the embedded loop. This works
		2462	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
		2463	appropriate way for embedded loops.
		2464
		2465	=item struct ev_loop *other [read-only]
		2466
		2467	The embedded event loop.
1127		2468
1128	=back	2469	=back
1129		2470
		2471	=head3 Examples
		2472
		2473	Example: Try to get an embeddable event loop and embed it into the default
		2474	event loop. If that is not possible, use the default loop. The default
		2475	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2476	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2477	used).
		2478
		2479	struct ev_loop *loop_hi = ev_default_init (0);
		2480	struct ev_loop *loop_lo = 0;
		2481	ev_embed embed;
		2482
		2483	// see if there is a chance of getting one that works
		2484	// (remember that a flags value of 0 means autodetection)
		2485	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2486	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2487	: 0;
		2488
		2489	// if we got one, then embed it, otherwise default to loop_hi
		2490	if (loop_lo)
		2491	{
		2492	ev_embed_init (&embed, 0, loop_lo);
		2493	ev_embed_start (loop_hi, &embed);
		2494	}
		2495	else
		2496	loop_lo = loop_hi;
		2497
		2498	Example: Check if kqueue is available but not recommended and create
		2499	a kqueue backend for use with sockets (which usually work with any
		2500	kqueue implementation). Store the kqueue/socket-only event loop in
		2501	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2502
		2503	struct ev_loop *loop = ev_default_init (0);
		2504	struct ev_loop *loop_socket = 0;
		2505	ev_embed embed;
		2506
		2507	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2508	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2509	{
		2510	ev_embed_init (&embed, 0, loop_socket);
		2511	ev_embed_start (loop, &embed);
		2512	}
		2513
		2514	if (!loop_socket)
		2515	loop_socket = loop;
		2516
		2517	// now use loop_socket for all sockets, and loop for everything else
		2518
		2519
		2520	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		2521
		2522	Fork watchers are called when a C<fork ()> was detected (usually because
		2523	whoever is a good citizen cared to tell libev about it by calling
		2524	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		2525	event loop blocks next and before C<ev_check> watchers are being called,
		2526	and only in the child after the fork. If whoever good citizen calling
		2527	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		2528	handlers will be invoked, too, of course.
		2529
		2530	=head3 Watcher-Specific Functions and Data Members
		2531
		2532	=over 4
		2533
		2534	=item ev_fork_init (ev_signal *, callback)
		2535
		2536	Initialises and configures the fork watcher - it has no parameters of any
		2537	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		2538	believe me.
		2539
		2540	=back
		2541
		2542
		2543	=head2 C<ev_async> - how to wake up another event loop
		2544
		2545	In general, you cannot use an C<ev_loop> from multiple threads or other
		2546	asynchronous sources such as signal handlers (as opposed to multiple event
		2547	loops - those are of course safe to use in different threads).
		2548
		2549	Sometimes, however, you need to wake up another event loop you do not
		2550	control, for example because it belongs to another thread. This is what
		2551	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2552	can signal it by calling C<ev_async_send>, which is thread- and signal
		2553	safe.
		2554
		2555	This functionality is very similar to C<ev_signal> watchers, as signals,
		2556	too, are asynchronous in nature, and signals, too, will be compressed
		2557	(i.e. the number of callback invocations may be less than the number of
		2558	C<ev_async_sent> calls).
		2559
		2560	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2561	just the default loop.
		2562
		2563	=head3 Queueing
		2564
		2565	C<ev_async> does not support queueing of data in any way. The reason
		2566	is that the author does not know of a simple (or any) algorithm for a
		2567	multiple-writer-single-reader queue that works in all cases and doesn't
		2568	need elaborate support such as pthreads.
		2569
		2570	That means that if you want to queue data, you have to provide your own
		2571	queue. But at least I can tell you how to implement locking around your
		2572	queue:
		2573
		2574	=over 4
		2575
		2576	=item queueing from a signal handler context
		2577
		2578	To implement race-free queueing, you simply add to the queue in the signal
		2579	handler but you block the signal handler in the watcher callback. Here is
		2580	an example that does that for some fictitious SIGUSR1 handler:
		2581
		2582	static ev_async mysig;
		2583
		2584	static void
		2585	sigusr1_handler (void)
		2586	{
		2587	sometype data;
		2588
		2589	// no locking etc.
		2590	queue_put (data);
		2591	ev_async_send (EV_DEFAULT_ &mysig);
		2592	}
		2593
		2594	static void
		2595	mysig_cb (EV_P_ ev_async *w, int revents)
		2596	{
		2597	sometype data;
		2598	sigset_t block, prev;
		2599
		2600	sigemptyset (&block);
		2601	sigaddset (&block, SIGUSR1);
		2602	sigprocmask (SIG_BLOCK, &block, &prev);
		2603
		2604	while (queue_get (&data))
		2605	process (data);
		2606
		2607	if (sigismember (&prev, SIGUSR1)
		2608	sigprocmask (SIG_UNBLOCK, &block, 0);
		2609	}
		2610
		2611	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2612	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2613	either...).
		2614
		2615	=item queueing from a thread context
		2616
		2617	The strategy for threads is different, as you cannot (easily) block
		2618	threads but you can easily preempt them, so to queue safely you need to
		2619	employ a traditional mutex lock, such as in this pthread example:
		2620
		2621	static ev_async mysig;
		2622	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2623
		2624	static void
		2625	otherthread (void)
		2626	{
		2627	// only need to lock the actual queueing operation
		2628	pthread_mutex_lock (&mymutex);
		2629	queue_put (data);
		2630	pthread_mutex_unlock (&mymutex);
		2631
		2632	ev_async_send (EV_DEFAULT_ &mysig);
		2633	}
		2634
		2635	static void
		2636	mysig_cb (EV_P_ ev_async *w, int revents)
		2637	{
		2638	pthread_mutex_lock (&mymutex);
		2639
		2640	while (queue_get (&data))
		2641	process (data);
		2642
		2643	pthread_mutex_unlock (&mymutex);
		2644	}
		2645
		2646	=back
		2647
		2648
		2649	=head3 Watcher-Specific Functions and Data Members
		2650
		2651	=over 4
		2652
		2653	=item ev_async_init (ev_async *, callback)
		2654
		2655	Initialises and configures the async watcher - it has no parameters of any
		2656	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		2657	trust me.
		2658
		2659	=item ev_async_send (loop, ev_async *)
		2660
		2661	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2662	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2663	C<ev_feed_event>, this call is safe to do from other threads, signal or
		2664	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		2665	section below on what exactly this means).
		2666
		2667	This call incurs the overhead of a system call only once per loop iteration,
		2668	so while the overhead might be noticeable, it doesn't apply to repeated
		2669	calls to C<ev_async_send>.
		2670
		2671	=item bool = ev_async_pending (ev_async *)
		2672
		2673	Returns a non-zero value when C<ev_async_send> has been called on the
		2674	watcher but the event has not yet been processed (or even noted) by the
		2675	event loop.
		2676
		2677	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2678	the loop iterates next and checks for the watcher to have become active,
		2679	it will reset the flag again. C<ev_async_pending> can be used to very
		2680	quickly check whether invoking the loop might be a good idea.
		2681
		2682	Not that this does I<not> check whether the watcher itself is pending, only
		2683	whether it has been requested to make this watcher pending.
		2684
		2685	=back
		2686
1130		2687
1131	=head1 OTHER FUNCTIONS	2688	=head1 OTHER FUNCTIONS
1132		2689
1133	There are some other functions of possible interest. Described. Here. Now.	2690	There are some other functions of possible interest. Described. Here. Now.
1134		2691
1135	=over 4	2692	=over 4
1136		2693
1137	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	2694	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1138		2695
1139	This function combines a simple timer and an I/O watcher, calls your	2696	This function combines a simple timer and an I/O watcher, calls your
1140	callback on whichever event happens first and automatically stop both	2697	callback on whichever event happens first and automatically stops both
1141	watchers. This is useful if you want to wait for a single event on an fd	2698	watchers. This is useful if you want to wait for a single event on an fd
1142	or timeout without having to allocate/configure/start/stop/free one or	2699	or timeout without having to allocate/configure/start/stop/free one or
1143	more watchers yourself.	2700	more watchers yourself.
1144		2701
1145	If C<fd> is less than 0, then no I/O watcher will be started and events	2702	If C<fd> is less than 0, then no I/O watcher will be started and the
1146	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	2703	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1147	C<events> set will be craeted and started.	2704	the given C<fd> and C<events> set will be created and started.
1148		2705
1149	If C<timeout> is less than 0, then no timeout watcher will be	2706	If C<timeout> is less than 0, then no timeout watcher will be
1150	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	2707	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1151	repeat = 0) will be started. While C<0> is a valid timeout, it is of	2708	repeat = 0) will be started. C<0> is a valid timeout.
1152	dubious value.
1153		2709
1154	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	2710	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
1155	passed an C<revents> set like normal event callbacks (a combination of	2711	passed an C<revents> set like normal event callbacks (a combination of
1156	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	2712	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
1157	value passed to C<ev_once>:	2713	value passed to C<ev_once>. Note that it is possible to receive I<both>
		2714	a timeout and an io event at the same time - you probably should give io
		2715	events precedence.
1158		2716
		2717	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		2718
1159	static void stdin_ready (int revents, void *arg)	2719	static void stdin_ready (int revents, void *arg)
1160	{	2720	{
1161	if (revents & EV_TIMEOUT)
1162	/* doh, nothing entered */;
1163	else if (revents & EV_READ)	2721	if (revents & EV_READ)
1164	/* stdin might have data for us, joy! */;	2722	/* stdin might have data for us, joy! */;
		2723	else if (revents & EV_TIMEOUT)
		2724	/* doh, nothing entered */;
1165	}	2725	}
1166		2726
1167	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2727	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1168		2728
1169	=item ev_feed_event (loop, watcher, int events)	2729	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
1170		2730
1171	Feeds the given event set into the event loop, as if the specified event	2731	Feeds the given event set into the event loop, as if the specified event
1172	had happened for the specified watcher (which must be a pointer to an	2732	had happened for the specified watcher (which must be a pointer to an
1173	initialised but not necessarily started event watcher).	2733	initialised but not necessarily started event watcher).
1174		2734
1175	=item ev_feed_fd_event (loop, int fd, int revents)	2735	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
1176		2736
1177	Feed an event on the given fd, as if a file descriptor backend detected	2737	Feed an event on the given fd, as if a file descriptor backend detected
1178	the given events it.	2738	the given events it.
1179		2739
1180	=item ev_feed_signal_event (loop, int signum)	2740	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
1181		2741
1182	Feed an event as if the given signal occured (loop must be the default loop!).	2742	Feed an event as if the given signal occurred (C<loop> must be the default
		2743	loop!).
1183		2744
1184	=back	2745	=back
1185		2746
1186		2747
1187	=head1 LIBEVENT EMULATION	2748	=head1 LIBEVENT EMULATION
…		…
1202		2763
1203	=item * Priorities are not currently supported. Initialising priorities	2764	=item * Priorities are not currently supported. Initialising priorities
1204	will fail and all watchers will have the same priority, even though there	2765	will fail and all watchers will have the same priority, even though there
1205	is an ev_pri field.	2766	is an ev_pri field.
1206		2767
		2768	=item * In libevent, the last base created gets the signals, in libev, the
		2769	first base created (== the default loop) gets the signals.
		2770
1207	=item * Other members are not supported.	2771	=item * Other members are not supported.
1208		2772
1209	=item * The libev emulation is I<not> ABI compatible to libevent, you need	2773	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1210	to use the libev header file and library.	2774	to use the libev header file and library.
1211		2775
1212	=back	2776	=back
1213		2777
1214	=head1 C++ SUPPORT	2778	=head1 C++ SUPPORT
1215		2779
1216	TBD.	2780	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		2781	you to use some convenience methods to start/stop watchers and also change
		2782	the callback model to a model using method callbacks on objects.
		2783
		2784	To use it,
		2785
		2786	#include <ev++.h>
		2787
		2788	This automatically includes F<ev.h> and puts all of its definitions (many
		2789	of them macros) into the global namespace. All C++ specific things are
		2790	put into the C<ev> namespace. It should support all the same embedding
		2791	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
		2792
		2793	Care has been taken to keep the overhead low. The only data member the C++
		2794	classes add (compared to plain C-style watchers) is the event loop pointer
		2795	that the watcher is associated with (or no additional members at all if
		2796	you disable C<EV_MULTIPLICITY> when embedding libev).
		2797
		2798	Currently, functions, and static and non-static member functions can be
		2799	used as callbacks. Other types should be easy to add as long as they only
		2800	need one additional pointer for context. If you need support for other
		2801	types of functors please contact the author (preferably after implementing
		2802	it).
		2803
		2804	Here is a list of things available in the C<ev> namespace:
		2805
		2806	=over 4
		2807
		2808	=item C<ev::READ>, C<ev::WRITE> etc.
		2809
		2810	These are just enum values with the same values as the C<EV_READ> etc.
		2811	macros from F<ev.h>.
		2812
		2813	=item C<ev::tstamp>, C<ev::now>
		2814
		2815	Aliases to the same types/functions as with the C<ev_> prefix.
		2816
		2817	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		2818
		2819	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		2820	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		2821	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		2822	defines by many implementations.
		2823
		2824	All of those classes have these methods:
		2825
		2826	=over 4
		2827
		2828	=item ev::TYPE::TYPE ()
		2829
		2830	=item ev::TYPE::TYPE (struct ev_loop *)
		2831
		2832	=item ev::TYPE::~TYPE
		2833
		2834	The constructor (optionally) takes an event loop to associate the watcher
		2835	with. If it is omitted, it will use C<EV_DEFAULT>.
		2836
		2837	The constructor calls C<ev_init> for you, which means you have to call the
		2838	C<set> method before starting it.
		2839
		2840	It will not set a callback, however: You have to call the templated C<set>
		2841	method to set a callback before you can start the watcher.
		2842
		2843	(The reason why you have to use a method is a limitation in C++ which does
		2844	not allow explicit template arguments for constructors).
		2845
		2846	The destructor automatically stops the watcher if it is active.
		2847
		2848	=item w->set<class, &class::method> (object *)
		2849
		2850	This method sets the callback method to call. The method has to have a
		2851	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		2852	first argument and the C<revents> as second. The object must be given as
		2853	parameter and is stored in the C<data> member of the watcher.
		2854
		2855	This method synthesizes efficient thunking code to call your method from
		2856	the C callback that libev requires. If your compiler can inline your
		2857	callback (i.e. it is visible to it at the place of the C<set> call and
		2858	your compiler is good :), then the method will be fully inlined into the
		2859	thunking function, making it as fast as a direct C callback.
		2860
		2861	Example: simple class declaration and watcher initialisation
		2862
		2863	struct myclass
		2864	{
		2865	void io_cb (ev::io &w, int revents) { }
		2866	}
		2867
		2868	myclass obj;
		2869	ev::io iow;
		2870	iow.set <myclass, &myclass::io_cb> (&obj);
		2871
		2872	=item w->set<function> (void *data = 0)
		2873
		2874	Also sets a callback, but uses a static method or plain function as
		2875	callback. The optional C<data> argument will be stored in the watcher's
		2876	C<data> member and is free for you to use.
		2877
		2878	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		2879
		2880	See the method-C<set> above for more details.
		2881
		2882	Example: Use a plain function as callback.
		2883
		2884	static void io_cb (ev::io &w, int revents) { }
		2885	iow.set <io_cb> ();
		2886
		2887	=item w->set (struct ev_loop *)
		2888
		2889	Associates a different C<struct ev_loop> with this watcher. You can only
		2890	do this when the watcher is inactive (and not pending either).
		2891
		2892	=item w->set ([arguments])
		2893
		2894	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
		2895	called at least once. Unlike the C counterpart, an active watcher gets
		2896	automatically stopped and restarted when reconfiguring it with this
		2897	method.
		2898
		2899	=item w->start ()
		2900
		2901	Starts the watcher. Note that there is no C<loop> argument, as the
		2902	constructor already stores the event loop.
		2903
		2904	=item w->stop ()
		2905
		2906	Stops the watcher if it is active. Again, no C<loop> argument.
		2907
		2908	=item w->again () (C<ev::timer>, C<ev::periodic> only)
		2909
		2910	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		2911	C<ev_TYPE_again> function.
		2912
		2913	=item w->sweep () (C<ev::embed> only)
		2914
		2915	Invokes C<ev_embed_sweep>.
		2916
		2917	=item w->update () (C<ev::stat> only)
		2918
		2919	Invokes C<ev_stat_stat>.
		2920
		2921	=back
		2922
		2923	=back
		2924
		2925	Example: Define a class with an IO and idle watcher, start one of them in
		2926	the constructor.
		2927
		2928	class myclass
		2929	{
		2930	ev::io io ; void io_cb (ev::io &w, int revents);
		2931	ev::idle idle; void idle_cb (ev::idle &w, int revents);
		2932
		2933	myclass (int fd)
		2934	{
		2935	io .set <myclass, &myclass::io_cb > (this);
		2936	idle.set <myclass, &myclass::idle_cb> (this);
		2937
		2938	io.start (fd, ev::READ);
		2939	}
		2940	};
		2941
		2942
		2943	=head1 OTHER LANGUAGE BINDINGS
		2944
		2945	Libev does not offer other language bindings itself, but bindings for a
		2946	number of languages exist in the form of third-party packages. If you know
		2947	any interesting language binding in addition to the ones listed here, drop
		2948	me a note.
		2949
		2950	=over 4
		2951
		2952	=item Perl
		2953
		2954	The EV module implements the full libev API and is actually used to test
		2955	libev. EV is developed together with libev. Apart from the EV core module,
		2956	there are additional modules that implement libev-compatible interfaces
		2957	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		2958	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		2959	and C<EV::Glib>).
		2960
		2961	It can be found and installed via CPAN, its homepage is at
		2962	L<http://software.schmorp.de/pkg/EV>.
		2963
		2964	=item Python
		2965
		2966	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		2967	seems to be quite complete and well-documented. Note, however, that the
		2968	patch they require for libev is outright dangerous as it breaks the ABI
		2969	for everybody else, and therefore, should never be applied in an installed
		2970	libev (if python requires an incompatible ABI then it needs to embed
		2971	libev).
		2972
		2973	=item Ruby
		2974
		2975	Tony Arcieri has written a ruby extension that offers access to a subset
		2976	of the libev API and adds file handle abstractions, asynchronous DNS and
		2977	more on top of it. It can be found via gem servers. Its homepage is at
		2978	L<http://rev.rubyforge.org/>.
		2979
		2980	=item D
		2981
		2982	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		2983	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		2984
		2985	=item Ocaml
		2986
		2987	Erkki Seppala has written Ocaml bindings for libev, to be found at
		2988	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		2989
		2990	=back
		2991
		2992
		2993	=head1 MACRO MAGIC
		2994
		2995	Libev can be compiled with a variety of options, the most fundamental
		2996	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		2997	functions and callbacks have an initial C<struct ev_loop *> argument.
		2998
		2999	To make it easier to write programs that cope with either variant, the
		3000	following macros are defined:
		3001
		3002	=over 4
		3003
		3004	=item C<EV_A>, C<EV_A_>
		3005
		3006	This provides the loop I<argument> for functions, if one is required ("ev
		3007	loop argument"). The C<EV_A> form is used when this is the sole argument,
		3008	C<EV_A_> is used when other arguments are following. Example:
		3009
		3010	ev_unref (EV_A);
		3011	ev_timer_add (EV_A_ watcher);
		3012	ev_loop (EV_A_ 0);
		3013
		3014	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		3015	which is often provided by the following macro.
		3016
		3017	=item C<EV_P>, C<EV_P_>
		3018
		3019	This provides the loop I<parameter> for functions, if one is required ("ev
		3020	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		3021	C<EV_P_> is used when other parameters are following. Example:
		3022
		3023	// this is how ev_unref is being declared
		3024	static void ev_unref (EV_P);
		3025
		3026	// this is how you can declare your typical callback
		3027	static void cb (EV_P_ ev_timer *w, int revents)
		3028
		3029	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		3030	suitable for use with C<EV_A>.
		3031
		3032	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		3033
		3034	Similar to the other two macros, this gives you the value of the default
		3035	loop, if multiple loops are supported ("ev loop default").
		3036
		3037	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3038
		3039	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3040	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3041	is undefined when the default loop has not been initialised by a previous
		3042	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3043
		3044	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3045	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		3046
		3047	=back
		3048
		3049	Example: Declare and initialise a check watcher, utilising the above
		3050	macros so it will work regardless of whether multiple loops are supported
		3051	or not.
		3052
		3053	static void
		3054	check_cb (EV_P_ ev_timer *w, int revents)
		3055	{
		3056	ev_check_stop (EV_A_ w);
		3057	}
		3058
		3059	ev_check check;
		3060	ev_check_init (&check, check_cb);
		3061	ev_check_start (EV_DEFAULT_ &check);
		3062	ev_loop (EV_DEFAULT_ 0);
		3063
		3064	=head1 EMBEDDING
		3065
		3066	Libev can (and often is) directly embedded into host
		3067	applications. Examples of applications that embed it include the Deliantra
		3068	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		3069	and rxvt-unicode.
		3070
		3071	The goal is to enable you to just copy the necessary files into your
		3072	source directory without having to change even a single line in them, so
		3073	you can easily upgrade by simply copying (or having a checked-out copy of
		3074	libev somewhere in your source tree).
		3075
		3076	=head2 FILESETS
		3077
		3078	Depending on what features you need you need to include one or more sets of files
		3079	in your application.
		3080
		3081	=head3 CORE EVENT LOOP
		3082
		3083	To include only the libev core (all the C<ev_*> functions), with manual
		3084	configuration (no autoconf):
		3085
		3086	#define EV_STANDALONE 1
		3087	#include "ev.c"
		3088
		3089	This will automatically include F<ev.h>, too, and should be done in a
		3090	single C source file only to provide the function implementations. To use
		3091	it, do the same for F<ev.h> in all files wishing to use this API (best
		3092	done by writing a wrapper around F<ev.h> that you can include instead and
		3093	where you can put other configuration options):
		3094
		3095	#define EV_STANDALONE 1
		3096	#include "ev.h"
		3097
		3098	Both header files and implementation files can be compiled with a C++
		3099	compiler (at least, that's a stated goal, and breakage will be treated
		3100	as a bug).
		3101
		3102	You need the following files in your source tree, or in a directory
		3103	in your include path (e.g. in libev/ when using -Ilibev):
		3104
		3105	ev.h
		3106	ev.c
		3107	ev_vars.h
		3108	ev_wrap.h
		3109
		3110	ev_win32.c required on win32 platforms only
		3111
		3112	ev_select.c only when select backend is enabled (which is enabled by default)
		3113	ev_poll.c only when poll backend is enabled (disabled by default)
		3114	ev_epoll.c only when the epoll backend is enabled (disabled by default)
		3115	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		3116	ev_port.c only when the solaris port backend is enabled (disabled by default)
		3117
		3118	F<ev.c> includes the backend files directly when enabled, so you only need
		3119	to compile this single file.
		3120
		3121	=head3 LIBEVENT COMPATIBILITY API
		3122
		3123	To include the libevent compatibility API, also include:
		3124
		3125	#include "event.c"
		3126
		3127	in the file including F<ev.c>, and:
		3128
		3129	#include "event.h"
		3130
		3131	in the files that want to use the libevent API. This also includes F<ev.h>.
		3132
		3133	You need the following additional files for this:
		3134
		3135	event.h
		3136	event.c
		3137
		3138	=head3 AUTOCONF SUPPORT
		3139
		3140	Instead of using C<EV_STANDALONE=1> and providing your configuration in
		3141	whatever way you want, you can also C<m4_include([libev.m4])> in your
		3142	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		3143	include F<config.h> and configure itself accordingly.
		3144
		3145	For this of course you need the m4 file:
		3146
		3147	libev.m4
		3148
		3149	=head2 PREPROCESSOR SYMBOLS/MACROS
		3150
		3151	Libev can be configured via a variety of preprocessor symbols you have to
		3152	define before including any of its files. The default in the absence of
		3153	autoconf is documented for every option.
		3154
		3155	=over 4
		3156
		3157	=item EV_STANDALONE
		3158
		3159	Must always be C<1> if you do not use autoconf configuration, which
		3160	keeps libev from including F<config.h>, and it also defines dummy
		3161	implementations for some libevent functions (such as logging, which is not
		3162	supported). It will also not define any of the structs usually found in
		3163	F<event.h> that are not directly supported by the libev core alone.
		3164
		3165	=item EV_USE_MONOTONIC
		3166
		3167	If defined to be C<1>, libev will try to detect the availability of the
		3168	monotonic clock option at both compile time and runtime. Otherwise no use
		3169	of the monotonic clock option will be attempted. If you enable this, you
		3170	usually have to link against librt or something similar. Enabling it when
		3171	the functionality isn't available is safe, though, although you have
		3172	to make sure you link against any libraries where the C<clock_gettime>
		3173	function is hiding in (often F<-lrt>).
		3174
		3175	=item EV_USE_REALTIME
		3176
		3177	If defined to be C<1>, libev will try to detect the availability of the
		3178	real-time clock option at compile time (and assume its availability at
		3179	runtime if successful). Otherwise no use of the real-time clock option will
		3180	be attempted. This effectively replaces C<gettimeofday> by C<clock_get
		3181	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the
		3182	note about libraries in the description of C<EV_USE_MONOTONIC>, though.
		3183
		3184	=item EV_USE_NANOSLEEP
		3185
		3186	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		3187	and will use it for delays. Otherwise it will use C<select ()>.
		3188
		3189	=item EV_USE_EVENTFD
		3190
		3191	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3192	available and will probe for kernel support at runtime. This will improve
		3193	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3194	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3195	2.7 or newer, otherwise disabled.
		3196
		3197	=item EV_USE_SELECT
		3198
		3199	If undefined or defined to be C<1>, libev will compile in support for the
		3200	C<select>(2) backend. No attempt at auto-detection will be done: if no
		3201	other method takes over, select will be it. Otherwise the select backend
		3202	will not be compiled in.
		3203
		3204	=item EV_SELECT_USE_FD_SET
		3205
		3206	If defined to C<1>, then the select backend will use the system C<fd_set>
		3207	structure. This is useful if libev doesn't compile due to a missing
		3208	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout on
		3209	exotic systems. This usually limits the range of file descriptors to some
		3210	low limit such as 1024 or might have other limitations (winsocket only
		3211	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might
		3212	influence the size of the C<fd_set> used.
		3213
		3214	=item EV_SELECT_IS_WINSOCKET
		3215
		3216	When defined to C<1>, the select backend will assume that
		3217	select/socket/connect etc. don't understand file descriptors but
		3218	wants osf handles on win32 (this is the case when the select to
		3219	be used is the winsock select). This means that it will call
		3220	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		3221	it is assumed that all these functions actually work on fds, even
		3222	on win32. Should not be defined on non-win32 platforms.
		3223
		3224	=item EV_FD_TO_WIN32_HANDLE
		3225
		3226	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3227	file descriptors to socket handles. When not defining this symbol (the
		3228	default), then libev will call C<_get_osfhandle>, which is usually
		3229	correct. In some cases, programs use their own file descriptor management,
		3230	in which case they can provide this function to map fds to socket handles.
		3231
		3232	=item EV_USE_POLL
		3233
		3234	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		3235	backend. Otherwise it will be enabled on non-win32 platforms. It
		3236	takes precedence over select.
		3237
		3238	=item EV_USE_EPOLL
		3239
		3240	If defined to be C<1>, libev will compile in support for the Linux
		3241	C<epoll>(7) backend. Its availability will be detected at runtime,
		3242	otherwise another method will be used as fallback. This is the preferred
		3243	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3244	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3245
		3246	=item EV_USE_KQUEUE
		3247
		3248	If defined to be C<1>, libev will compile in support for the BSD style
		3249	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		3250	otherwise another method will be used as fallback. This is the preferred
		3251	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		3252	supports some types of fds correctly (the only platform we found that
		3253	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		3254	not be used unless explicitly requested. The best way to use it is to find
		3255	out whether kqueue supports your type of fd properly and use an embedded
		3256	kqueue loop.
		3257
		3258	=item EV_USE_PORT
		3259
		3260	If defined to be C<1>, libev will compile in support for the Solaris
		3261	10 port style backend. Its availability will be detected at runtime,
		3262	otherwise another method will be used as fallback. This is the preferred
		3263	backend for Solaris 10 systems.
		3264
		3265	=item EV_USE_DEVPOLL
		3266
		3267	Reserved for future expansion, works like the USE symbols above.
		3268
		3269	=item EV_USE_INOTIFY
		3270
		3271	If defined to be C<1>, libev will compile in support for the Linux inotify
		3272	interface to speed up C<ev_stat> watchers. Its actual availability will
		3273	be detected at runtime. If undefined, it will be enabled if the headers
		3274	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3275
		3276	=item EV_ATOMIC_T
		3277
		3278	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3279	access is atomic with respect to other threads or signal contexts. No such
		3280	type is easily found in the C language, so you can provide your own type
		3281	that you know is safe for your purposes. It is used both for signal handler "locking"
		3282	as well as for signal and thread safety in C<ev_async> watchers.
		3283
		3284	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3285	(from F<signal.h>), which is usually good enough on most platforms.
		3286
		3287	=item EV_H
		3288
		3289	The name of the F<ev.h> header file used to include it. The default if
		3290	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
		3291	used to virtually rename the F<ev.h> header file in case of conflicts.
		3292
		3293	=item EV_CONFIG_H
		3294
		3295	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		3296	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		3297	C<EV_H>, above.
		3298
		3299	=item EV_EVENT_H
		3300
		3301	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		3302	of how the F<event.h> header can be found, the default is C<"event.h">.
		3303
		3304	=item EV_PROTOTYPES
		3305
		3306	If defined to be C<0>, then F<ev.h> will not define any function
		3307	prototypes, but still define all the structs and other symbols. This is
		3308	occasionally useful if you want to provide your own wrapper functions
		3309	around libev functions.
		3310
		3311	=item EV_MULTIPLICITY
		3312
		3313	If undefined or defined to C<1>, then all event-loop-specific functions
		3314	will have the C<struct ev_loop *> as first argument, and you can create
		3315	additional independent event loops. Otherwise there will be no support
		3316	for multiple event loops and there is no first event loop pointer
		3317	argument. Instead, all functions act on the single default loop.
		3318
		3319	=item EV_MINPRI
		3320
		3321	=item EV_MAXPRI
		3322
		3323	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		3324	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		3325	provide for more priorities by overriding those symbols (usually defined
		3326	to be C<-2> and C<2>, respectively).
		3327
		3328	When doing priority-based operations, libev usually has to linearly search
		3329	all the priorities, so having many of them (hundreds) uses a lot of space
		3330	and time, so using the defaults of five priorities (-2 .. +2) is usually
		3331	fine.
		3332
		3333	If your embedding application does not need any priorities, defining these
		3334	both to C<0> will save some memory and CPU.
		3335
		3336	=item EV_PERIODIC_ENABLE
		3337
		3338	If undefined or defined to be C<1>, then periodic timers are supported. If
		3339	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3340	code.
		3341
		3342	=item EV_IDLE_ENABLE
		3343
		3344	If undefined or defined to be C<1>, then idle watchers are supported. If
		3345	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3346	code.
		3347
		3348	=item EV_EMBED_ENABLE
		3349
		3350	If undefined or defined to be C<1>, then embed watchers are supported. If
		3351	defined to be C<0>, then they are not. Embed watchers rely on most other
		3352	watcher types, which therefore must not be disabled.
		3353
		3354	=item EV_STAT_ENABLE
		3355
		3356	If undefined or defined to be C<1>, then stat watchers are supported. If
		3357	defined to be C<0>, then they are not.
		3358
		3359	=item EV_FORK_ENABLE
		3360
		3361	If undefined or defined to be C<1>, then fork watchers are supported. If
		3362	defined to be C<0>, then they are not.
		3363
		3364	=item EV_ASYNC_ENABLE
		3365
		3366	If undefined or defined to be C<1>, then async watchers are supported. If
		3367	defined to be C<0>, then they are not.
		3368
		3369	=item EV_MINIMAL
		3370
		3371	If you need to shave off some kilobytes of code at the expense of some
		3372	speed, define this symbol to C<1>. Currently this is used to override some
		3373	inlining decisions, saves roughly 30% code size on amd64. It also selects a
		3374	much smaller 2-heap for timer management over the default 4-heap.
		3375
		3376	=item EV_PID_HASHSIZE
		3377
		3378	C<ev_child> watchers use a small hash table to distribute workload by
		3379	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
		3380	than enough. If you need to manage thousands of children you might want to
		3381	increase this value (I<must> be a power of two).
		3382
		3383	=item EV_INOTIFY_HASHSIZE
		3384
		3385	C<ev_stat> watchers use a small hash table to distribute workload by
		3386	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
		3387	usually more than enough. If you need to manage thousands of C<ev_stat>
		3388	watchers you might want to increase this value (I<must> be a power of
		3389	two).
		3390
		3391	=item EV_USE_4HEAP
		3392
		3393	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3394	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		3395	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		3396	faster performance with many (thousands) of watchers.
		3397
		3398	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3399	(disabled).
		3400
		3401	=item EV_HEAP_CACHE_AT
		3402
		3403	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3404	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		3405	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3406	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3407	but avoids random read accesses on heap changes. This improves performance
		3408	noticeably with many (hundreds) of watchers.
		3409
		3410	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3411	(disabled).
		3412
		3413	=item EV_VERIFY
		3414
		3415	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3416	be done: If set to C<0>, no internal verification code will be compiled
		3417	in. If set to C<1>, then verification code will be compiled in, but not
		3418	called. If set to C<2>, then the internal verification code will be
		3419	called once per loop, which can slow down libev. If set to C<3>, then the
		3420	verification code will be called very frequently, which will slow down
		3421	libev considerably.
		3422
		3423	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3424	C<0>.
		3425
		3426	=item EV_COMMON
		3427
		3428	By default, all watchers have a C<void *data> member. By redefining
		3429	this macro to a something else you can include more and other types of
		3430	members. You have to define it each time you include one of the files,
		3431	though, and it must be identical each time.
		3432
		3433	For example, the perl EV module uses something like this:
		3434
		3435	#define EV_COMMON \
		3436	SV *self; /* contains this struct */ \
		3437	SV *cb_sv, *fh /* note no trailing ";" */
		3438
		3439	=item EV_CB_DECLARE (type)
		3440
		3441	=item EV_CB_INVOKE (watcher, revents)
		3442
		3443	=item ev_set_cb (ev, cb)
		3444
		3445	Can be used to change the callback member declaration in each watcher,
		3446	and the way callbacks are invoked and set. Must expand to a struct member
		3447	definition and a statement, respectively. See the F<ev.h> header file for
		3448	their default definitions. One possible use for overriding these is to
		3449	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		3450	method calls instead of plain function calls in C++.
		3451
		3452	=back
		3453
		3454	=head2 EXPORTED API SYMBOLS
		3455
		3456	If you need to re-export the API (e.g. via a DLL) and you need a list of
		3457	exported symbols, you can use the provided F<Symbol.*> files which list
		3458	all public symbols, one per line:
		3459
		3460	Symbols.ev for libev proper
		3461	Symbols.event for the libevent emulation
		3462
		3463	This can also be used to rename all public symbols to avoid clashes with
		3464	multiple versions of libev linked together (which is obviously bad in
		3465	itself, but sometimes it is inconvenient to avoid this).
		3466
		3467	A sed command like this will create wrapper C<#define>'s that you need to
		3468	include before including F<ev.h>:
		3469
		3470	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		3471
		3472	This would create a file F<wrap.h> which essentially looks like this:
		3473
		3474	#define ev_backend myprefix_ev_backend
		3475	#define ev_check_start myprefix_ev_check_start
		3476	#define ev_check_stop myprefix_ev_check_stop
		3477	...
		3478
		3479	=head2 EXAMPLES
		3480
		3481	For a real-world example of a program the includes libev
		3482	verbatim, you can have a look at the EV perl module
		3483	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		3484	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		3485	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		3486	will be compiled. It is pretty complex because it provides its own header
		3487	file.
		3488
		3489	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		3490	that everybody includes and which overrides some configure choices:
		3491
		3492	#define EV_MINIMAL 1
		3493	#define EV_USE_POLL 0
		3494	#define EV_MULTIPLICITY 0
		3495	#define EV_PERIODIC_ENABLE 0
		3496	#define EV_STAT_ENABLE 0
		3497	#define EV_FORK_ENABLE 0
		3498	#define EV_CONFIG_H <config.h>
		3499	#define EV_MINPRI 0
		3500	#define EV_MAXPRI 0
		3501
		3502	#include "ev++.h"
		3503
		3504	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		3505
		3506	#include "ev_cpp.h"
		3507	#include "ev.c"
		3508
		3509	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
		3510
		3511	=head2 THREADS AND COROUTINES
		3512
		3513	=head3 THREADS
		3514
		3515	All libev functions are reentrant and thread-safe unless explicitly
		3516	documented otherwise, but libev implements no locking itself. This means
		3517	that you can use as many loops as you want in parallel, as long as there
		3518	are no concurrent calls into any libev function with the same loop
		3519	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		3520	of course): libev guarantees that different event loops share no data
		3521	structures that need any locking.
		3522
		3523	Or to put it differently: calls with different loop parameters can be done
		3524	concurrently from multiple threads, calls with the same loop parameter
		3525	must be done serially (but can be done from different threads, as long as
		3526	only one thread ever is inside a call at any point in time, e.g. by using
		3527	a mutex per loop).
		3528
		3529	Specifically to support threads (and signal handlers), libev implements
		3530	so-called C<ev_async> watchers, which allow some limited form of
		3531	concurrency on the same event loop, namely waking it up "from the
		3532	outside".
		3533
		3534	If you want to know which design (one loop, locking, or multiple loops
		3535	without or something else still) is best for your problem, then I cannot
		3536	help you, but here is some generic advice:
		3537
		3538	=over 4
		3539
		3540	=item * most applications have a main thread: use the default libev loop
		3541	in that thread, or create a separate thread running only the default loop.
		3542
		3543	This helps integrating other libraries or software modules that use libev
		3544	themselves and don't care/know about threading.
		3545
		3546	=item * one loop per thread is usually a good model.
		3547
		3548	Doing this is almost never wrong, sometimes a better-performance model
		3549	exists, but it is always a good start.
		3550
		3551	=item * other models exist, such as the leader/follower pattern, where one
		3552	loop is handed through multiple threads in a kind of round-robin fashion.
		3553
		3554	Choosing a model is hard - look around, learn, know that usually you can do
		3555	better than you currently do :-)
		3556
		3557	=item * often you need to talk to some other thread which blocks in the
		3558	event loop.
		3559
		3560	C<ev_async> watchers can be used to wake them up from other threads safely
		3561	(or from signal contexts...).
		3562
		3563	An example use would be to communicate signals or other events that only
		3564	work in the default loop by registering the signal watcher with the
		3565	default loop and triggering an C<ev_async> watcher from the default loop
		3566	watcher callback into the event loop interested in the signal.
		3567
		3568	=back
		3569
		3570	=head3 COROUTINES
		3571
		3572	Libev is very accommodating to coroutines ("cooperative threads"):
		3573	libev fully supports nesting calls to its functions from different
		3574	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3575	different coroutines, and switch freely between both coroutines running the
		3576	loop, as long as you don't confuse yourself). The only exception is that
		3577	you must not do this from C<ev_periodic> reschedule callbacks.
		3578
		3579	Care has been taken to ensure that libev does not keep local state inside
		3580	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		3581	they do not call any callbacks.
		3582
		3583	=head2 COMPILER WARNINGS
		3584
		3585	Depending on your compiler and compiler settings, you might get no or a
		3586	lot of warnings when compiling libev code. Some people are apparently
		3587	scared by this.
		3588
		3589	However, these are unavoidable for many reasons. For one, each compiler
		3590	has different warnings, and each user has different tastes regarding
		3591	warning options. "Warn-free" code therefore cannot be a goal except when
		3592	targeting a specific compiler and compiler-version.
		3593
		3594	Another reason is that some compiler warnings require elaborate
		3595	workarounds, or other changes to the code that make it less clear and less
		3596	maintainable.
		3597
		3598	And of course, some compiler warnings are just plain stupid, or simply
		3599	wrong (because they don't actually warn about the condition their message
		3600	seems to warn about). For example, certain older gcc versions had some
		3601	warnings that resulted an extreme number of false positives. These have
		3602	been fixed, but some people still insist on making code warn-free with
		3603	such buggy versions.
		3604
		3605	While libev is written to generate as few warnings as possible,
		3606	"warn-free" code is not a goal, and it is recommended not to build libev
		3607	with any compiler warnings enabled unless you are prepared to cope with
		3608	them (e.g. by ignoring them). Remember that warnings are just that:
		3609	warnings, not errors, or proof of bugs.
		3610
		3611
		3612	=head2 VALGRIND
		3613
		3614	Valgrind has a special section here because it is a popular tool that is
		3615	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		3616
		3617	If you think you found a bug (memory leak, uninitialised data access etc.)
		3618	in libev, then check twice: If valgrind reports something like:
		3619
		3620	==2274== definitely lost: 0 bytes in 0 blocks.
		3621	==2274== possibly lost: 0 bytes in 0 blocks.
		3622	==2274== still reachable: 256 bytes in 1 blocks.
		3623
		3624	Then there is no memory leak, just as memory accounted to global variables
		3625	is not a memleak - the memory is still being referenced, and didn't leak.
		3626
		3627	Similarly, under some circumstances, valgrind might report kernel bugs
		3628	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		3629	although an acceptable workaround has been found here), or it might be
		3630	confused.
		3631
		3632	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		3633	make it into some kind of religion.
		3634
		3635	If you are unsure about something, feel free to contact the mailing list
		3636	with the full valgrind report and an explanation on why you think this
		3637	is a bug in libev (best check the archives, too :). However, don't be
		3638	annoyed when you get a brisk "this is no bug" answer and take the chance
		3639	of learning how to interpret valgrind properly.
		3640
		3641	If you need, for some reason, empty reports from valgrind for your project
		3642	I suggest using suppression lists.
		3643
		3644
		3645	=head1 PORTABILITY NOTES
		3646
		3647	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		3648
		3649	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		3650	requires, and its I/O model is fundamentally incompatible with the POSIX
		3651	model. Libev still offers limited functionality on this platform in
		3652	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		3653	descriptors. This only applies when using Win32 natively, not when using
		3654	e.g. cygwin.
		3655
		3656	Lifting these limitations would basically require the full
		3657	re-implementation of the I/O system. If you are into these kinds of
		3658	things, then note that glib does exactly that for you in a very portable
		3659	way (note also that glib is the slowest event library known to man).
		3660
		3661	There is no supported compilation method available on windows except
		3662	embedding it into other applications.
		3663
		3664	Not a libev limitation but worth mentioning: windows apparently doesn't
		3665	accept large writes: instead of resulting in a partial write, windows will
		3666	either accept everything or return C<ENOBUFS> if the buffer is too large,
		3667	so make sure you only write small amounts into your sockets (less than a
		3668	megabyte seems safe, but this apparently depends on the amount of memory
		3669	available).
		3670
		3671	Due to the many, low, and arbitrary limits on the win32 platform and
		3672	the abysmal performance of winsockets, using a large number of sockets
		3673	is not recommended (and not reasonable). If your program needs to use
		3674	more than a hundred or so sockets, then likely it needs to use a totally
		3675	different implementation for windows, as libev offers the POSIX readiness
		3676	notification model, which cannot be implemented efficiently on windows
		3677	(Microsoft monopoly games).
		3678
		3679	A typical way to use libev under windows is to embed it (see the embedding
		3680	section for details) and use the following F<evwrap.h> header file instead
		3681	of F<ev.h>:
		3682
		3683	#define EV_STANDALONE /* keeps ev from requiring config.h */
		3684	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		3685
		3686	#include "ev.h"
		3687
		3688	And compile the following F<evwrap.c> file into your project (make sure
		3689	you do I<not> compile the F<ev.c> or any other embedded source files!):
		3690
		3691	#include "evwrap.h"
		3692	#include "ev.c"
		3693
		3694	=over 4
		3695
		3696	=item The winsocket select function
		3697
		3698	The winsocket C<select> function doesn't follow POSIX in that it
		3699	requires socket I<handles> and not socket I<file descriptors> (it is
		3700	also extremely buggy). This makes select very inefficient, and also
		3701	requires a mapping from file descriptors to socket handles (the Microsoft
		3702	C runtime provides the function C<_open_osfhandle> for this). See the
		3703	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		3704	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		3705
		3706	The configuration for a "naked" win32 using the Microsoft runtime
		3707	libraries and raw winsocket select is:
		3708
		3709	#define EV_USE_SELECT 1
		3710	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		3711
		3712	Note that winsockets handling of fd sets is O(n), so you can easily get a
		3713	complexity in the O(n²) range when using win32.
		3714
		3715	=item Limited number of file descriptors
		3716
		3717	Windows has numerous arbitrary (and low) limits on things.
		3718
		3719	Early versions of winsocket's select only supported waiting for a maximum
		3720	of C<64> handles (probably owning to the fact that all windows kernels
		3721	can only wait for C<64> things at the same time internally; Microsoft
		3722	recommends spawning a chain of threads and wait for 63 handles and the
		3723	previous thread in each. Great).
		3724
		3725	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		3726	to some high number (e.g. C<2048>) before compiling the winsocket select
		3727	call (which might be in libev or elsewhere, for example, perl does its own
		3728	select emulation on windows).
		3729
		3730	Another limit is the number of file descriptors in the Microsoft runtime
		3731	libraries, which by default is C<64> (there must be a hidden I<64> fetish
		3732	or something like this inside Microsoft). You can increase this by calling
		3733	C<_setmaxstdio>, which can increase this limit to C<2048> (another
		3734	arbitrary limit), but is broken in many versions of the Microsoft runtime
		3735	libraries.
		3736
		3737	This might get you to about C<512> or C<2048> sockets (depending on
		3738	windows version and/or the phase of the moon). To get more, you need to
		3739	wrap all I/O functions and provide your own fd management, but the cost of
		3740	calling select (O(n²)) will likely make this unworkable.
		3741
		3742	=back
		3743
		3744	=head2 PORTABILITY REQUIREMENTS
		3745
		3746	In addition to a working ISO-C implementation and of course the
		3747	backend-specific APIs, libev relies on a few additional extensions:
		3748
		3749	=over 4
		3750
		3751	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		3752	calling conventions regardless of C<ev_watcher_type *>.
		3753
		3754	Libev assumes not only that all watcher pointers have the same internal
		3755	structure (guaranteed by POSIX but not by ISO C for example), but it also
		3756	assumes that the same (machine) code can be used to call any watcher
		3757	callback: The watcher callbacks have different type signatures, but libev
		3758	calls them using an C<ev_watcher *> internally.
		3759
		3760	=item C<sig_atomic_t volatile> must be thread-atomic as well
		3761
		3762	The type C<sig_atomic_t volatile> (or whatever is defined as
		3763	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		3764	threads. This is not part of the specification for C<sig_atomic_t>, but is
		3765	believed to be sufficiently portable.
		3766
		3767	=item C<sigprocmask> must work in a threaded environment
		3768
		3769	Libev uses C<sigprocmask> to temporarily block signals. This is not
		3770	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		3771	pthread implementations will either allow C<sigprocmask> in the "main
		3772	thread" or will block signals process-wide, both behaviours would
		3773	be compatible with libev. Interaction between C<sigprocmask> and
		3774	C<pthread_sigmask> could complicate things, however.
		3775
		3776	The most portable way to handle signals is to block signals in all threads
		3777	except the initial one, and run the default loop in the initial thread as
		3778	well.
		3779
		3780	=item C<long> must be large enough for common memory allocation sizes
		3781
		3782	To improve portability and simplify its API, libev uses C<long> internally
		3783	instead of C<size_t> when allocating its data structures. On non-POSIX
		3784	systems (Microsoft...) this might be unexpectedly low, but is still at
		3785	least 31 bits everywhere, which is enough for hundreds of millions of
		3786	watchers.
		3787
		3788	=item C<double> must hold a time value in seconds with enough accuracy
		3789
		3790	The type C<double> is used to represent timestamps. It is required to
		3791	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		3792	enough for at least into the year 4000. This requirement is fulfilled by
		3793	implementations implementing IEEE 754 (basically all existing ones).
		3794
		3795	=back
		3796
		3797	If you know of other additional requirements drop me a note.
		3798
		3799
		3800	=head1 ALGORITHMIC COMPLEXITIES
		3801
		3802	In this section the complexities of (many of) the algorithms used inside
		3803	libev will be documented. For complexity discussions about backends see
		3804	the documentation for C<ev_default_init>.
		3805
		3806	All of the following are about amortised time: If an array needs to be
		3807	extended, libev needs to realloc and move the whole array, but this
		3808	happens asymptotically rarer with higher number of elements, so O(1) might
		3809	mean that libev does a lengthy realloc operation in rare cases, but on
		3810	average it is much faster and asymptotically approaches constant time.
		3811
		3812	=over 4
		3813
		3814	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		3815
		3816	This means that, when you have a watcher that triggers in one hour and
		3817	there are 100 watchers that would trigger before that, then inserting will
		3818	have to skip roughly seven (C<ld 100>) of these watchers.
		3819
		3820	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		3821
		3822	That means that changing a timer costs less than removing/adding them,
		3823	as only the relative motion in the event queue has to be paid for.
		3824
		3825	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		3826
		3827	These just add the watcher into an array or at the head of a list.
		3828
		3829	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		3830
		3831	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		3832
		3833	These watchers are stored in lists, so they need to be walked to find the
		3834	correct watcher to remove. The lists are usually short (you don't usually
		3835	have many watchers waiting for the same fd or signal: one is typical, two
		3836	is rare).
		3837
		3838	=item Finding the next timer in each loop iteration: O(1)
		3839
		3840	By virtue of using a binary or 4-heap, the next timer is always found at a
		3841	fixed position in the storage array.
		3842
		3843	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		3844
		3845	A change means an I/O watcher gets started or stopped, which requires
		3846	libev to recalculate its status (and possibly tell the kernel, depending
		3847	on backend and whether C<ev_io_set> was used).
		3848
		3849	=item Activating one watcher (putting it into the pending state): O(1)
		3850
		3851	=item Priority handling: O(number_of_priorities)
		3852
		3853	Priorities are implemented by allocating some space for each
		3854	priority. When doing priority-based operations, libev usually has to
		3855	linearly search all the priorities, but starting/stopping and activating
		3856	watchers becomes O(1) with respect to priority handling.
		3857
		3858	=item Sending an ev_async: O(1)
		3859
		3860	=item Processing ev_async_send: O(number_of_async_watchers)
		3861
		3862	=item Processing signals: O(max_signal_number)
		3863
		3864	Sending involves a system call I<iff> there were no other C<ev_async_send>
		3865	calls in the current loop iteration. Checking for async and signal events
		3866	involves iterating over all running async watchers or all signal numbers.
		3867
		3868	=back
		3869
1217		3870
1218	=head1 AUTHOR	3871	=head1 AUTHOR
1219		3872
1220	Marc Lehmann <libev@schmorp.de>.	3873	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
1221		3874

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