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Revision 1.50 by root, Tue Nov 27 10:59:11 2007 UTC vs.
Revision 1.231 by root, Wed Apr 15 19:35:53 2009 UTC

…		…
2		2
3	libev - a high performance full-featured event loop written in C	3	libev - a high performance full-featured event loop written in C
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
		8
		9	=head2 EXAMPLE PROGRAM
		10
		11	// a single header file is required
		12	#include <ev.h>
		13
		14	#include <stdio.h> // for puts
		15
		16	// every watcher type has its own typedef'd struct
		17	// with the name ev_TYPE
		18	ev_io stdin_watcher;
		19	ev_timer timeout_watcher;
		20
		21	// all watcher callbacks have a similar signature
		22	// this callback is called when data is readable on stdin
		23	static void
		24	stdin_cb (EV_P_ ev_io *w, int revents)
		25	{
		26	puts ("stdin ready");
		27	// for one-shot events, one must manually stop the watcher
		28	// with its corresponding stop function.
		29	ev_io_stop (EV_A_ w);
		30
		31	// this causes all nested ev_loop's to stop iterating
		32	ev_unloop (EV_A_ EVUNLOOP_ALL);
		33	}
		34
		35	// another callback, this time for a time-out
		36	static void
		37	timeout_cb (EV_P_ ev_timer *w, int revents)
		38	{
		39	puts ("timeout");
		40	// this causes the innermost ev_loop to stop iterating
		41	ev_unloop (EV_A_ EVUNLOOP_ONE);
		42	}
		43
		44	int
		45	main (void)
		46	{
		47	// use the default event loop unless you have special needs
		48	struct ev_loop *loop = ev_default_loop (0);
		49
		50	// initialise an io watcher, then start it
		51	// this one will watch for stdin to become readable
		52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
		53	ev_io_start (loop, &stdin_watcher);
		54
		55	// initialise a timer watcher, then start it
		56	// simple non-repeating 5.5 second timeout
		57	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		58	ev_timer_start (loop, &timeout_watcher);
		59
		60	// now wait for events to arrive
		61	ev_loop (loop, 0);
		62
		63	// unloop was called, so exit
		64	return 0;
		65	}
8		66
9	=head1 DESCRIPTION	67	=head1 DESCRIPTION
10		68
		69	The newest version of this document is also available as an html-formatted
		70	web page you might find easier to navigate when reading it for the first
		71	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		72
11	Libev is an event loop: you register interest in certain events (such as a	73	Libev is an event loop: you register interest in certain events (such as a
12	file descriptor being readable or a timeout occuring), and it will manage	74	file descriptor being readable or a timeout occurring), and it will manage
13	these event sources and provide your program with events.	75	these event sources and provide your program with events.
14		76
15	To do this, it must take more or less complete control over your process	77	To do this, it must take more or less complete control over your process
16	(or thread) by executing the I<event loop> handler, and will then	78	(or thread) by executing the I<event loop> handler, and will then
17	communicate events via a callback mechanism.	79	communicate events via a callback mechanism.
…		…
19	You register interest in certain events by registering so-called I<event	81	You register interest in certain events by registering so-called I<event
20	watchers>, which are relatively small C structures you initialise with the	82	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	83	details of the event, and then hand it over to libev by I<starting> the
22	watcher.	84	watcher.
23		85
24	=head1 FEATURES	86	=head2 FEATURES
25		87
26	Libev supports select, poll, the linux-specific epoll and the bsd-specific	88	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
27	kqueue mechanisms for file descriptor events, relative timers, absolute	89	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
28	timers with customised rescheduling, signal events, process status change	90	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
29	events (related to SIGCHLD), and event watchers dealing with the event	91	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
30	loop mechanism itself (idle, prepare and check watchers). It also is quite	92	with customised rescheduling (C<ev_periodic>), synchronous signals
		93	(C<ev_signal>), process status change events (C<ev_child>), and event
		94	watchers dealing with the event loop mechanism itself (C<ev_idle>,
		95	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as
		96	file watchers (C<ev_stat>) and even limited support for fork events
		97	(C<ev_fork>).
		98
		99	It also is quite fast (see this
31	fast (see this L<benchmark|http://libev.schmorp.de/bench.html> comparing	100	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
32	it to libevent for example).	101	for example).
33		102
34	=head1 CONVENTIONS	103	=head2 CONVENTIONS
35		104
36	Libev is very configurable. In this manual the default configuration	105	Libev is very configurable. In this manual the default (and most common)
37	will be described, which supports multiple event loops. For more info	106	configuration will be described, which supports multiple event loops. For
38	about various configuration options please have a look at the file	107	more info about various configuration options please have a look at
39	F<README.embed> in the libev distribution. If libev was configured without	108	B<EMBED> section in this manual. If libev was configured without support
40	support for multiple event loops, then all functions taking an initial	109	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 *>)	110	name C<loop> (which is always of type C<ev_loop *>) will not have
42	will not have this argument.	111	this argument.
43		112
44	=head1 TIME REPRESENTATION	113	=head2 TIME REPRESENTATION
45		114
46	Libev represents time as a single floating point number, representing the	115	Libev represents time as a single floating point number, representing the
47	(fractional) number of seconds since the (POSIX) epoch (somewhere near	116	(fractional) number of seconds since the (POSIX) epoch (somewhere near
48	the beginning of 1970, details are complicated, don't ask). This type is	117	the beginning of 1970, details are complicated, don't ask). This type is
49	called C<ev_tstamp>, which is what you should use too. It usually aliases	118	called C<ev_tstamp>, which is what you should use too. It usually aliases
50	to the C<double> type in C, and when you need to do any calculations on	119	to the C<double> type in C, and when you need to do any calculations on
51	it, you should treat it as such.	120	it, you should treat it as some floating point value. Unlike the name
		121	component C<stamp> might indicate, it is also used for time differences
		122	throughout libev.
		123
		124	=head1 ERROR HANDLING
		125
		126	Libev knows three classes of errors: operating system errors, usage errors
		127	and internal errors (bugs).
		128
		129	When libev catches an operating system error it cannot handle (for example
		130	a system call indicating a condition libev cannot fix), it calls the callback
		131	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		132	abort. The default is to print a diagnostic message and to call C<abort
		133	()>.
		134
		135	When libev detects a usage error such as a negative timer interval, then
		136	it will print a diagnostic message and abort (via the C<assert> mechanism,
		137	so C<NDEBUG> will disable this checking): these are programming errors in
		138	the libev caller and need to be fixed there.
		139
		140	Libev also has a few internal error-checking C<assert>ions, and also has
		141	extensive consistency checking code. These do not trigger under normal
		142	circumstances, as they indicate either a bug in libev or worse.
		143
52		144
53	=head1 GLOBAL FUNCTIONS	145	=head1 GLOBAL FUNCTIONS
54		146
55	These functions can be called anytime, even before initialising the	147	These functions can be called anytime, even before initialising the
56	library in any way.	148	library in any way.
…		…
61		153
62	Returns the current time as libev would use it. Please note that the	154	Returns the current time as libev would use it. Please note that the
63	C<ev_now> function is usually faster and also often returns the timestamp	155	C<ev_now> function is usually faster and also often returns the timestamp
64	you actually want to know.	156	you actually want to know.
65		157
		158	=item ev_sleep (ev_tstamp interval)
		159
		160	Sleep for the given interval: The current thread will be blocked until
		161	either it is interrupted or the given time interval has passed. Basically
		162	this is a sub-second-resolution C<sleep ()>.
		163
66	=item int ev_version_major ()	164	=item int ev_version_major ()
67		165
68	=item int ev_version_minor ()	166	=item int ev_version_minor ()
69		167
70	You can find out the major and minor version numbers of the library	168	You can find out the major and minor ABI version numbers of the library
71	you linked against by calling the functions C<ev_version_major> and	169	you linked against by calling the functions C<ev_version_major> and
72	C<ev_version_minor>. If you want, you can compare against the global	170	C<ev_version_minor>. If you want, you can compare against the global
73	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the	171	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
74	version of the library your program was compiled against.	172	version of the library your program was compiled against.
75		173
		174	These version numbers refer to the ABI version of the library, not the
		175	release version.
		176
76	Usually, it's a good idea to terminate if the major versions mismatch,	177	Usually, it's a good idea to terminate if the major versions mismatch,
77	as this indicates an incompatible change. Minor versions are usually	178	as this indicates an incompatible change. Minor versions are usually
78	compatible to older versions, so a larger minor version alone is usually	179	compatible to older versions, so a larger minor version alone is usually
79	not a problem.	180	not a problem.
80		181
81	Example: make sure we haven't accidentally been linked against the wrong	182	Example: Make sure we haven't accidentally been linked against the wrong
82	version:	183	version.
83		184
84	assert (("libev version mismatch",	185	assert (("libev version mismatch",
85	ev_version_major () == EV_VERSION_MAJOR	186	ev_version_major () == EV_VERSION_MAJOR
86	&& ev_version_minor () >= EV_VERSION_MINOR));	187	&& ev_version_minor () >= EV_VERSION_MINOR));
87		188
88	=item unsigned int ev_supported_backends ()	189	=item unsigned int ev_supported_backends ()
89		190
90	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	191	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
91	value) compiled into this binary of libev (independent of their	192	value) compiled into this binary of libev (independent of their
…		…
93	a description of the set values.	194	a description of the set values.
94		195
95	Example: make sure we have the epoll method, because yeah this is cool and	196	Example: make sure we have the epoll method, because yeah this is cool and
96	a must have and can we have a torrent of it please!!!11	197	a must have and can we have a torrent of it please!!!11
97		198
98	assert (("sorry, no epoll, no sex",	199	assert (("sorry, no epoll, no sex",
99	ev_supported_backends () & EVBACKEND_EPOLL));	200	ev_supported_backends () & EVBACKEND_EPOLL));
100		201
101	=item unsigned int ev_recommended_backends ()	202	=item unsigned int ev_recommended_backends ()
102		203
103	Return the set of all backends compiled into this binary of libev and also	204	Return the set of all backends compiled into this binary of libev and also
104	recommended for this platform. This set is often smaller than the one	205	recommended for this platform. This set is often smaller than the one
105	returned by C<ev_supported_backends>, as for example kqueue is broken on	206	returned by C<ev_supported_backends>, as for example kqueue is broken on
106	most BSDs and will not be autodetected unless you explicitly request it	207	most BSDs and will not be auto-detected unless you explicitly request it
107	(assuming you know what you are doing). This is the set of backends that	208	(assuming you know what you are doing). This is the set of backends that
108	libev will probe for if you specify no backends explicitly.	209	libev will probe for if you specify no backends explicitly.
109		210
110	=item unsigned int ev_embeddable_backends ()	211	=item unsigned int ev_embeddable_backends ()
111		212
…		…
115	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	216	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
116	recommended ones.	217	recommended ones.
117		218
118	See the description of C<ev_embed> watchers for more info.	219	See the description of C<ev_embed> watchers for more info.
119		220
120	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	221	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
121		222
122	Sets the allocation function to use (the prototype is similar to the	223	Sets the allocation function to use (the prototype is similar - the
123	realloc C function, the semantics are identical). It is used to allocate	224	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
124	and free memory (no surprises here). If it returns zero when memory	225	used to allocate and free memory (no surprises here). If it returns zero
125	needs to be allocated, the library might abort or take some potentially	226	when memory needs to be allocated (C<size != 0>), the library might abort
126	destructive action. The default is your system realloc function.	227	or take some potentially destructive action.
		228
		229	Since some systems (at least OpenBSD and Darwin) fail to implement
		230	correct C<realloc> semantics, libev will use a wrapper around the system
		231	C<realloc> and C<free> functions by default.
127		232
128	You could override this function in high-availability programs to, say,	233	You could override this function in high-availability programs to, say,
129	free some memory if it cannot allocate memory, to use a special allocator,	234	free some memory if it cannot allocate memory, to use a special allocator,
130	or even to sleep a while and retry until some memory is available.	235	or even to sleep a while and retry until some memory is available.
131		236
132	Example: replace the libev allocator with one that waits a bit and then	237	Example: Replace the libev allocator with one that waits a bit and then
133	retries: better than mine).	238	retries (example requires a standards-compliant C<realloc>).
134		239
135	static void *	240	static void *
136	persistent_realloc (void *ptr, long size)	241	persistent_realloc (void *ptr, size_t size)
137	{	242	{
138	for (;;)	243	for (;;)
139	{	244	{
140	void *newptr = realloc (ptr, size);	245	void *newptr = realloc (ptr, size);
141		246
…		…
147	}	252	}
148		253
149	...	254	...
150	ev_set_allocator (persistent_realloc);	255	ev_set_allocator (persistent_realloc);
151		256
152	=item ev_set_syserr_cb (void (*cb)(const char *msg));	257	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
153		258
154	Set the callback function to call on a retryable syscall error (such	259	Set the callback function to call on a retryable system call error (such
155	as failed select, poll, epoll_wait). The message is a printable string	260	as failed select, poll, epoll_wait). The message is a printable string
156	indicating the system call or subsystem causing the problem. If this	261	indicating the system call or subsystem causing the problem. If this
157	callback is set, then libev will expect it to remedy the sitution, no	262	callback is set, then libev will expect it to remedy the situation, no
158	matter what, when it returns. That is, libev will generally retry the	263	matter what, when it returns. That is, libev will generally retry the
159	requested operation, or, if the condition doesn't go away, do bad stuff	264	requested operation, or, if the condition doesn't go away, do bad stuff
160	(such as abort).	265	(such as abort).
161		266
162	Example: do the same thing as libev does internally:	267	Example: This is basically the same thing that libev does internally, too.
163		268
164	static void	269	static void
165	fatal_error (const char *msg)	270	fatal_error (const char *msg)
166	{	271	{
167	perror (msg);	272	perror (msg);
…		…
173		278
174	=back	279	=back
175		280
176	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	281	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
177		282
178	An event loop is described by a C<struct ev_loop *>. The library knows two	283	An event loop is described by a C<struct ev_loop *> (the C<struct>
179	types of such loops, the I<default> loop, which supports signals and child	284	is I<not> optional in this case, as there is also an C<ev_loop>
180	events, and dynamically created loops which do not.	285	I<function>).
181		286
182	If you use threads, a common model is to run the default event loop	287	The library knows two types of such loops, the I<default> loop, which
183	in your main thread (or in a separate thread) and for each thread you	288	supports signals and child events, and dynamically created loops which do
184	create, you also create another event loop. Libev itself does no locking	289	not.
185	whatsoever, so if you mix calls to the same event loop in different
186	threads, make sure you lock (this is usually a bad idea, though, even if
187	done correctly, because it's hideous and inefficient).
188		290
189	=over 4	291	=over 4
190		292
191	=item struct ev_loop *ev_default_loop (unsigned int flags)	293	=item struct ev_loop *ev_default_loop (unsigned int flags)
192		294
…		…
196	flags. If that is troubling you, check C<ev_backend ()> afterwards).	298	flags. If that is troubling you, check C<ev_backend ()> afterwards).
197		299
198	If you don't know what event loop to use, use the one returned from this	300	If you don't know what event loop to use, use the one returned from this
199	function.	301	function.
200		302
		303	Note that this function is I<not> thread-safe, so if you want to use it
		304	from multiple threads, you have to lock (note also that this is unlikely,
		305	as loops cannot be shared easily between threads anyway).
		306
		307	The default loop is the only loop that can handle C<ev_signal> and
		308	C<ev_child> watchers, and to do this, it always registers a handler
		309	for C<SIGCHLD>. If this is a problem for your application you can either
		310	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
		311	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
		312	C<ev_default_init>.
		313
201	The flags argument can be used to specify special behaviour or specific	314	The flags argument can be used to specify special behaviour or specific
202	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	315	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
203		316
204	The following flags are supported:	317	The following flags are supported:
205		318
…		…
210	The default flags value. Use this if you have no clue (it's the right	323	The default flags value. Use this if you have no clue (it's the right
211	thing, believe me).	324	thing, believe me).
212		325
213	=item C<EVFLAG_NOENV>	326	=item C<EVFLAG_NOENV>
214		327
215	If this flag bit is ored into the flag value (or the program runs setuid	328	If this flag bit is or'ed into the flag value (or the program runs setuid
216	or setgid) then libev will I<not> look at the environment variable	329	or setgid) then libev will I<not> look at the environment variable
217	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	330	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
218	override the flags completely if it is found in the environment. This is	331	override the flags completely if it is found in the environment. This is
219	useful to try out specific backends to test their performance, or to work	332	useful to try out specific backends to test their performance, or to work
220	around bugs.	333	around bugs.
221		334
		335	=item C<EVFLAG_FORKCHECK>
		336
		337	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after
		338	a fork, you can also make libev check for a fork in each iteration by
		339	enabling this flag.
		340
		341	This works by calling C<getpid ()> on every iteration of the loop,
		342	and thus this might slow down your event loop if you do a lot of loop
		343	iterations and little real work, but is usually not noticeable (on my
		344	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
		345	without a system call and thus I<very> fast, but my GNU/Linux system also has
		346	C<pthread_atfork> which is even faster).
		347
		348	The big advantage of this flag is that you can forget about fork (and
		349	forget about forgetting to tell libev about forking) when you use this
		350	flag.
		351
		352	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
		353	environment variable.
		354
222	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	355	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
223		356
224	This is your standard select(2) backend. Not I<completely> standard, as	357	This is your standard select(2) backend. Not I<completely> standard, as
225	libev tries to roll its own fd_set with no limits on the number of fds,	358	libev tries to roll its own fd_set with no limits on the number of fds,
226	but if that fails, expect a fairly low limit on the number of fds when	359	but if that fails, expect a fairly low limit on the number of fds when
227	using this backend. It doesn't scale too well (O(highest_fd)), but its usually	360	using this backend. It doesn't scale too well (O(highest_fd)), but its
228	the fastest backend for a low number of fds.	361	usually the fastest backend for a low number of (low-numbered :) fds.
		362
		363	To get good performance out of this backend you need a high amount of
		364	parallelism (most of the file descriptors should be busy). If you are
		365	writing a server, you should C<accept ()> in a loop to accept as many
		366	connections as possible during one iteration. You might also want to have
		367	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		368	readiness notifications you get per iteration.
		369
		370	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		371	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		372	C<exceptfds> set on that platform).
229		373
230	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	374	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
231		375
232	And this is your standard poll(2) backend. It's more complicated than	376	And this is your standard poll(2) backend. It's more complicated
233	select, but handles sparse fds better and has no artificial limit on the	377	than select, but handles sparse fds better and has no artificial
234	number of fds you can use (except it will slow down considerably with a	378	limit on the number of fds you can use (except it will slow down
235	lot of inactive fds). It scales similarly to select, i.e. O(total_fds).	379	considerably with a lot of inactive fds). It scales similarly to select,
		380	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		381	performance tips.
		382
		383	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		384	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
236		385
237	=item C<EVBACKEND_EPOLL> (value 4, Linux)	386	=item C<EVBACKEND_EPOLL> (value 4, Linux)
238		387
239	For few fds, this backend is a bit little slower than poll and select,	388	For few fds, this backend is a bit little slower than poll and select,
240	but it scales phenomenally better. While poll and select usually scale like	389	but it scales phenomenally better. While poll and select usually scale
241	O(total_fds) where n is the total number of fds (or the highest fd), epoll scales	390	like O(total_fds) where n is the total number of fds (or the highest fd),
242	either O(1) or O(active_fds).	391	epoll scales either O(1) or O(active_fds).
243		392
		393	The epoll mechanism deserves honorable mention as the most misdesigned
		394	of the more advanced event mechanisms: mere annoyances include silently
		395	dropping file descriptors, requiring a system call per change per file
		396	descriptor (and unnecessary guessing of parameters), problems with dup and
		397	so on. The biggest issue is fork races, however - if a program forks then
		398	I<both> parent and child process have to recreate the epoll set, which can
		399	take considerable time (one syscall per file descriptor) and is of course
		400	hard to detect.
		401
		402	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		403	of course I<doesn't>, and epoll just loves to report events for totally
		404	I<different> file descriptors (even already closed ones, so one cannot
		405	even remove them from the set) than registered in the set (especially
		406	on SMP systems). Libev tries to counter these spurious notifications by
		407	employing an additional generation counter and comparing that against the
		408	events to filter out spurious ones, recreating the set when required.
		409
244	While stopping and starting an I/O watcher in the same iteration will	410	While stopping, setting and starting an I/O watcher in the same iteration
245	result in some caching, there is still a syscall per such incident	411	will result in some caching, there is still a system call per such
246	(because the fd could point to a different file description now), so its	412	incident (because the same I<file descriptor> could point to a different
247	best to avoid that. Also, dup()ed file descriptors might not work very	413	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
248	well if you register events for both fds.	414	file descriptors might not work very well if you register events for both
		415	file descriptors.
249		416
250	Please note that epoll sometimes generates spurious notifications, so you	417	Best performance from this backend is achieved by not unregistering all
251	need to use non-blocking I/O or other means to avoid blocking when no data	418	watchers for a file descriptor until it has been closed, if possible,
252	(or space) is available.	419	i.e. keep at least one watcher active per fd at all times. Stopping and
		420	starting a watcher (without re-setting it) also usually doesn't cause
		421	extra overhead. A fork can both result in spurious notifications as well
		422	as in libev having to destroy and recreate the epoll object, which can
		423	take considerable time and thus should be avoided.
		424
		425	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		426	faster than epoll for maybe up to a hundred file descriptors, depending on
		427	the usage. So sad.
		428
		429	While nominally embeddable in other event loops, this feature is broken in
		430	all kernel versions tested so far.
		431
		432	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		433	C<EVBACKEND_POLL>.
253		434
254	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	435	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
255		436
256	Kqueue deserves special mention, as at the time of this writing, it	437	Kqueue deserves special mention, as at the time of this writing, it
257	was broken on all BSDs except NetBSD (usually it doesn't work with	438	was broken on all BSDs except NetBSD (usually it doesn't work reliably
258	anything but sockets and pipes, except on Darwin, where of course its	439	with anything but sockets and pipes, except on Darwin, where of course
259	completely useless). For this reason its not being "autodetected"	440	it's completely useless). Unlike epoll, however, whose brokenness
		441	is by design, these kqueue bugs can (and eventually will) be fixed
		442	without API changes to existing programs. For this reason it's not being
260	unless you explicitly specify it explicitly in the flags (i.e. using	443	"auto-detected" unless you explicitly specify it in the flags (i.e. using
261	C<EVBACKEND_KQUEUE>).	444	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		445	system like NetBSD.
		446
		447	You still can embed kqueue into a normal poll or select backend and use it
		448	only for sockets (after having made sure that sockets work with kqueue on
		449	the target platform). See C<ev_embed> watchers for more info.
262		450
263	It scales in the same way as the epoll backend, but the interface to the	451	It scales in the same way as the epoll backend, but the interface to the
264	kernel is more efficient (which says nothing about its actual speed, of	452	kernel is more efficient (which says nothing about its actual speed, of
265	course). While starting and stopping an I/O watcher does not cause an	453	course). While stopping, setting and starting an I/O watcher does never
266	extra syscall as with epoll, it still adds up to four event changes per	454	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
267	incident, so its best to avoid that.	455	two event changes per incident. Support for C<fork ()> is very bad (but
		456	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		457	cases
		458
		459	This backend usually performs well under most conditions.
		460
		461	While nominally embeddable in other event loops, this doesn't work
		462	everywhere, so you might need to test for this. And since it is broken
		463	almost everywhere, you should only use it when you have a lot of sockets
		464	(for which it usually works), by embedding it into another event loop
		465	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
		466	also broken on OS X)) and, did I mention it, using it only for sockets.
		467
		468	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		469	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		470	C<NOTE_EOF>.
268		471
269	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	472	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
270		473
271	This is not implemented yet (and might never be).	474	This is not implemented yet (and might never be, unless you send me an
		475	implementation). According to reports, C</dev/poll> only supports sockets
		476	and is not embeddable, which would limit the usefulness of this backend
		477	immensely.
272		478
273	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	479	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
274		480
275	This uses the Solaris 10 port mechanism. As with everything on Solaris,	481	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
276	it's really slow, but it still scales very well (O(active_fds)).	482	it's really slow, but it still scales very well (O(active_fds)).
277		483
278	Please note that solaris ports can result in a lot of spurious	484	Please note that Solaris event ports can deliver a lot of spurious
279	notifications, so you need to use non-blocking I/O or other means to avoid	485	notifications, so you need to use non-blocking I/O or other means to avoid
280	blocking when no data (or space) is available.	486	blocking when no data (or space) is available.
		487
		488	While this backend scales well, it requires one system call per active
		489	file descriptor per loop iteration. For small and medium numbers of file
		490	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		491	might perform better.
		492
		493	On the positive side, with the exception of the spurious readiness
		494	notifications, this backend actually performed fully to specification
		495	in all tests and is fully embeddable, which is a rare feat among the
		496	OS-specific backends (I vastly prefer correctness over speed hacks).
		497
		498	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		499	C<EVBACKEND_POLL>.
281		500
282	=item C<EVBACKEND_ALL>	501	=item C<EVBACKEND_ALL>
283		502
284	Try all backends (even potentially broken ones that wouldn't be tried	503	Try all backends (even potentially broken ones that wouldn't be tried
285	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	504	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
286	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	505	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
287		506
		507	It is definitely not recommended to use this flag.
		508
288	=back	509	=back
289		510
290	If one or more of these are ored into the flags value, then only these	511	If one or more of these are or'ed into the flags value, then only these
291	backends will be tried (in the reverse order as given here). If none are	512	backends will be tried (in the reverse order as listed here). If none are
292	specified, most compiled-in backend will be tried, usually in reverse	513	specified, all backends in C<ev_recommended_backends ()> will be tried.
293	order of their flag values :)
294		514
295	The most typical usage is like this:	515	Example: This is the most typical usage.
296		516
297	if (!ev_default_loop (0))	517	if (!ev_default_loop (0))
298	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	518	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
299		519
300	Restrict libev to the select and poll backends, and do not allow	520	Example: Restrict libev to the select and poll backends, and do not allow
301	environment settings to be taken into account:	521	environment settings to be taken into account:
302		522
303	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	523	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
304		524
305	Use whatever libev has to offer, but make sure that kqueue is used if	525	Example: Use whatever libev has to offer, but make sure that kqueue is
306	available (warning, breaks stuff, best use only with your own private	526	used if available (warning, breaks stuff, best use only with your own
307	event loop and only if you know the OS supports your types of fds):	527	private event loop and only if you know the OS supports your types of
		528	fds):
308		529
309	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	530	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
310		531
311	=item struct ev_loop *ev_loop_new (unsigned int flags)	532	=item struct ev_loop *ev_loop_new (unsigned int flags)
312		533
313	Similar to C<ev_default_loop>, but always creates a new event loop that is	534	Similar to C<ev_default_loop>, but always creates a new event loop that is
314	always distinct from the default loop. Unlike the default loop, it cannot	535	always distinct from the default loop. Unlike the default loop, it cannot
315	handle signal and child watchers, and attempts to do so will be greeted by	536	handle signal and child watchers, and attempts to do so will be greeted by
316	undefined behaviour (or a failed assertion if assertions are enabled).	537	undefined behaviour (or a failed assertion if assertions are enabled).
317		538
		539	Note that this function I<is> thread-safe, and the recommended way to use
		540	libev with threads is indeed to create one loop per thread, and using the
		541	default loop in the "main" or "initial" thread.
		542
318	Example: try to create a event loop that uses epoll and nothing else.	543	Example: Try to create a event loop that uses epoll and nothing else.
319		544
320	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	545	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
321	if (!epoller)	546	if (!epoller)
322	fatal ("no epoll found here, maybe it hides under your chair");	547	fatal ("no epoll found here, maybe it hides under your chair");
323		548
324	=item ev_default_destroy ()	549	=item ev_default_destroy ()
325		550
326	Destroys the default loop again (frees all memory and kernel state	551	Destroys the default loop again (frees all memory and kernel state
327	etc.). None of the active event watchers will be stopped in the normal	552	etc.). None of the active event watchers will be stopped in the normal
328	sense, so e.g. C<ev_is_active> might still return true. It is your	553	sense, so e.g. C<ev_is_active> might still return true. It is your
329	responsibility to either stop all watchers cleanly yoursef I<before>	554	responsibility to either stop all watchers cleanly yourself I<before>
330	calling this function, or cope with the fact afterwards (which is usually	555	calling this function, or cope with the fact afterwards (which is usually
331	the easiest thing, youc na just ignore the watchers and/or C<free ()> them	556	the easiest thing, you can just ignore the watchers and/or C<free ()> them
332	for example).	557	for example).
		558
		559	Note that certain global state, such as signal state (and installed signal
		560	handlers), will not be freed by this function, and related watchers (such
		561	as signal and child watchers) would need to be stopped manually.
		562
		563	In general it is not advisable to call this function except in the
		564	rare occasion where you really need to free e.g. the signal handling
		565	pipe fds. If you need dynamically allocated loops it is better to use
		566	C<ev_loop_new> and C<ev_loop_destroy>).
333		567
334	=item ev_loop_destroy (loop)	568	=item ev_loop_destroy (loop)
335		569
336	Like C<ev_default_destroy>, but destroys an event loop created by an	570	Like C<ev_default_destroy>, but destroys an event loop created by an
337	earlier call to C<ev_loop_new>.	571	earlier call to C<ev_loop_new>.
338		572
339	=item ev_default_fork ()	573	=item ev_default_fork ()
340		574
		575	This function sets a flag that causes subsequent C<ev_loop> iterations
341	This function reinitialises the kernel state for backends that have	576	to reinitialise the kernel state for backends that have one. Despite the
342	one. Despite the name, you can call it anytime, but it makes most sense	577	name, you can call it anytime, but it makes most sense after forking, in
343	after forking, in either the parent or child process (or both, but that	578	the child process (or both child and parent, but that again makes little
344	again makes little sense).	579	sense). You I<must> call it in the child before using any of the libev
		580	functions, and it will only take effect at the next C<ev_loop> iteration.
345		581
346	You I<must> call this function in the child process after forking if and	582	On the other hand, you only need to call this function in the child
347	only if you want to use the event library in both processes. If you just	583	process if and only if you want to use the event library in the child. If
348	fork+exec, you don't have to call it.	584	you just fork+exec, you don't have to call it at all.
349		585
350	The function itself is quite fast and it's usually not a problem to call	586	The function itself is quite fast and it's usually not a problem to call
351	it just in case after a fork. To make this easy, the function will fit in	587	it just in case after a fork. To make this easy, the function will fit in
352	quite nicely into a call to C<pthread_atfork>:	588	quite nicely into a call to C<pthread_atfork>:
353		589
354	pthread_atfork (0, 0, ev_default_fork);	590	pthread_atfork (0, 0, ev_default_fork);
355		591
356	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
357	without calling this function, so if you force one of those backends you
358	do not need to care.
359
360	=item ev_loop_fork (loop)	592	=item ev_loop_fork (loop)
361		593
362	Like C<ev_default_fork>, but acts on an event loop created by	594	Like C<ev_default_fork>, but acts on an event loop created by
363	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	595	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
364	after fork, and how you do this is entirely your own problem.	596	after fork that you want to re-use in the child, and how you do this is
		597	entirely your own problem.
		598
		599	=item int ev_is_default_loop (loop)
		600
		601	Returns true when the given loop is, in fact, the default loop, and false
		602	otherwise.
		603
		604	=item unsigned int ev_loop_count (loop)
		605
		606	Returns the count of loop iterations for the loop, which is identical to
		607	the number of times libev did poll for new events. It starts at C<0> and
		608	happily wraps around with enough iterations.
		609
		610	This value can sometimes be useful as a generation counter of sorts (it
		611	"ticks" the number of loop iterations), as it roughly corresponds with
		612	C<ev_prepare> and C<ev_check> calls.
365		613
366	=item unsigned int ev_backend (loop)	614	=item unsigned int ev_backend (loop)
367		615
368	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	616	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
369	use.	617	use.
…		…
372		620
373	Returns the current "event loop time", which is the time the event loop	621	Returns the current "event loop time", which is the time the event loop
374	received events and started processing them. This timestamp does not	622	received events and started processing them. This timestamp does not
375	change as long as callbacks are being processed, and this is also the base	623	change as long as callbacks are being processed, and this is also the base
376	time used for relative timers. You can treat it as the timestamp of the	624	time used for relative timers. You can treat it as the timestamp of the
377	event occuring (or more correctly, libev finding out about it).	625	event occurring (or more correctly, libev finding out about it).
		626
		627	=item ev_now_update (loop)
		628
		629	Establishes the current time by querying the kernel, updating the time
		630	returned by C<ev_now ()> in the progress. This is a costly operation and
		631	is usually done automatically within C<ev_loop ()>.
		632
		633	This function is rarely useful, but when some event callback runs for a
		634	very long time without entering the event loop, updating libev's idea of
		635	the current time is a good idea.
		636
		637	See also "The special problem of time updates" in the C<ev_timer> section.
		638
		639	=item ev_suspend (loop)
		640
		641	=item ev_resume (loop)
		642
		643	These two functions suspend and resume a loop, for use when the loop is
		644	not used for a while and timeouts should not be processed.
		645
		646	A typical use case would be an interactive program such as a game: When
		647	the user presses C<^Z> to suspend the game and resumes it an hour later it
		648	would be best to handle timeouts as if no time had actually passed while
		649	the program was suspended. This can be achieved by calling C<ev_suspend>
		650	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		651	C<ev_resume> directly afterwards to resume timer processing.
		652
		653	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		654	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		655	will be rescheduled (that is, they will lose any events that would have
		656	occured while suspended).
		657
		658	After calling C<ev_suspend> you B<must not> call I<any> function on the
		659	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		660	without a previous call to C<ev_suspend>.
		661
		662	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		663	event loop time (see C<ev_now_update>).
378		664
379	=item ev_loop (loop, int flags)	665	=item ev_loop (loop, int flags)
380		666
381	Finally, this is it, the event handler. This function usually is called	667	Finally, this is it, the event handler. This function usually is called
382	after you initialised all your watchers and you want to start handling	668	after you initialised all your watchers and you want to start handling
…		…
385	If the flags argument is specified as C<0>, it will not return until	671	If the flags argument is specified as C<0>, it will not return until
386	either no event watchers are active anymore or C<ev_unloop> was called.	672	either no event watchers are active anymore or C<ev_unloop> was called.
387		673
388	Please note that an explicit C<ev_unloop> is usually better than	674	Please note that an explicit C<ev_unloop> is usually better than
389	relying on all watchers to be stopped when deciding when a program has	675	relying on all watchers to be stopped when deciding when a program has
390	finished (especially in interactive programs), but having a program that	676	finished (especially in interactive programs), but having a program
391	automatically loops as long as it has to and no longer by virtue of	677	that automatically loops as long as it has to and no longer by virtue
392	relying on its watchers stopping correctly is a thing of beauty.	678	of relying on its watchers stopping correctly, that is truly a thing of
		679	beauty.
393		680
394	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	681	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
395	those events and any outstanding ones, but will not block your process in	682	those events and any already outstanding ones, but will not block your
396	case there are no events and will return after one iteration of the loop.	683	process in case there are no events and will return after one iteration of
		684	the loop.
397		685
398	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	686	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
399	neccessary) and will handle those and any outstanding ones. It will block	687	necessary) and will handle those and any already outstanding ones. It
400	your process until at least one new event arrives, and will return after	688	will block your process until at least one new event arrives (which could
401	one iteration of the loop. This is useful if you are waiting for some	689	be an event internal to libev itself, so there is no guarantee that a
402	external event in conjunction with something not expressible using other	690	user-registered callback will be called), and will return after one
		691	iteration of the loop.
		692
		693	This is useful if you are waiting for some external event in conjunction
		694	with something not expressible using other libev watchers (i.e. "roll your
403	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	695	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
404	usually a better approach for this kind of thing.	696	usually a better approach for this kind of thing.
405		697
406	Here are the gory details of what C<ev_loop> does:	698	Here are the gory details of what C<ev_loop> does:
407		699
408	* If there are no active watchers (reference count is zero), return.	700	- Before the first iteration, call any pending watchers.
409	- Queue prepare watchers and then call all outstanding watchers.	701	* If EVFLAG_FORKCHECK was used, check for a fork.
		702	- If a fork was detected (by any means), queue and call all fork watchers.
		703	- Queue and call all prepare watchers.
410	- If we have been forked, recreate the kernel state.	704	- If we have been forked, detach and recreate the kernel state
		705	as to not disturb the other process.
411	- Update the kernel state with all outstanding changes.	706	- Update the kernel state with all outstanding changes.
412	- Update the "event loop time".	707	- Update the "event loop time" (ev_now ()).
413	- Calculate for how long to block.	708	- Calculate for how long to sleep or block, if at all
		709	(active idle watchers, EVLOOP_NONBLOCK or not having
		710	any active watchers at all will result in not sleeping).
		711	- Sleep if the I/O and timer collect interval say so.
414	- Block the process, waiting for any events.	712	- Block the process, waiting for any events.
415	- Queue all outstanding I/O (fd) events.	713	- Queue all outstanding I/O (fd) events.
416	- Update the "event loop time" and do time jump handling.	714	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
417	- Queue all outstanding timers.	715	- Queue all expired timers.
418	- Queue all outstanding periodics.	716	- Queue all expired periodics.
419	- If no events are pending now, queue all idle watchers.	717	- Unless any events are pending now, queue all idle watchers.
420	- Queue all check watchers.	718	- Queue all check watchers.
421	- Call all queued watchers in reverse order (i.e. check watchers first).	719	- Call all queued watchers in reverse order (i.e. check watchers first).
422	Signals and child watchers are implemented as I/O watchers, and will	720	Signals and child watchers are implemented as I/O watchers, and will
423	be handled here by queueing them when their watcher gets executed.	721	be handled here by queueing them when their watcher gets executed.
424	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	722	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
425	were used, return, otherwise continue with step *.	723	were used, or there are no active watchers, return, otherwise
		724	continue with step *.
426		725
427	Example: queue some jobs and then loop until no events are outsanding	726	Example: Queue some jobs and then loop until no events are outstanding
428	anymore.	727	anymore.
429		728
430	... queue jobs here, make sure they register event watchers as long	729	... queue jobs here, make sure they register event watchers as long
431	... as they still have work to do (even an idle watcher will do..)	730	... as they still have work to do (even an idle watcher will do..)
432	ev_loop (my_loop, 0);	731	ev_loop (my_loop, 0);
433	... jobs done. yeah!	732	... jobs done or somebody called unloop. yeah!
434		733
435	=item ev_unloop (loop, how)	734	=item ev_unloop (loop, how)
436		735
437	Can be used to make a call to C<ev_loop> return early (but only after it	736	Can be used to make a call to C<ev_loop> return early (but only after it
438	has processed all outstanding events). The C<how> argument must be either	737	has processed all outstanding events). The C<how> argument must be either
439	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	738	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
440	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	739	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
441		740
		741	This "unloop state" will be cleared when entering C<ev_loop> again.
		742
		743	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
		744
442	=item ev_ref (loop)	745	=item ev_ref (loop)
443		746
444	=item ev_unref (loop)	747	=item ev_unref (loop)
445		748
446	Ref/unref can be used to add or remove a reference count on the event	749	Ref/unref can be used to add or remove a reference count on the event
447	loop: Every watcher keeps one reference, and as long as the reference	750	loop: Every watcher keeps one reference, and as long as the reference
448	count is nonzero, C<ev_loop> will not return on its own. If you have	751	count is nonzero, C<ev_loop> will not return on its own.
		752
449	a watcher you never unregister that should not keep C<ev_loop> from	753	If you have a watcher you never unregister that should not keep C<ev_loop>
450	returning, ev_unref() after starting, and ev_ref() before stopping it. For	754	from returning, call ev_unref() after starting, and ev_ref() before
		755	stopping it.
		756
451	example, libev itself uses this for its internal signal pipe: It is not	757	As an example, libev itself uses this for its internal signal pipe: It
452	visible to the libev user and should not keep C<ev_loop> from exiting if	758	is not visible to the libev user and should not keep C<ev_loop> from
453	no event watchers registered by it are active. It is also an excellent	759	exiting if no event watchers registered by it are active. It is also an
454	way to do this for generic recurring timers or from within third-party	760	excellent way to do this for generic recurring timers or from within
455	libraries. Just remember to I<unref after start> and I<ref before stop>.	761	third-party libraries. Just remember to I<unref after start> and I<ref
		762	before stop> (but only if the watcher wasn't active before, or was active
		763	before, respectively. Note also that libev might stop watchers itself
		764	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		765	in the callback).
456		766
457	Example: create a signal watcher, but keep it from keeping C<ev_loop>	767	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
458	running when nothing else is active.	768	running when nothing else is active.
459		769
460	struct dv_signal exitsig;	770	ev_signal exitsig;
461	ev_signal_init (&exitsig, sig_cb, SIGINT);	771	ev_signal_init (&exitsig, sig_cb, SIGINT);
462	ev_signal_start (myloop, &exitsig);	772	ev_signal_start (loop, &exitsig);
463	evf_unref (myloop);	773	evf_unref (loop);
464		774
465	Example: for some weird reason, unregister the above signal handler again.	775	Example: For some weird reason, unregister the above signal handler again.
466		776
467	ev_ref (myloop);	777	ev_ref (loop);
468	ev_signal_stop (myloop, &exitsig);	778	ev_signal_stop (loop, &exitsig);
		779
		780	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		781
		782	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		783
		784	These advanced functions influence the time that libev will spend waiting
		785	for events. Both time intervals are by default C<0>, meaning that libev
		786	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		787	latency.
		788
		789	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		790	allows libev to delay invocation of I/O and timer/periodic callbacks
		791	to increase efficiency of loop iterations (or to increase power-saving
		792	opportunities).
		793
		794	The idea is that sometimes your program runs just fast enough to handle
		795	one (or very few) event(s) per loop iteration. While this makes the
		796	program responsive, it also wastes a lot of CPU time to poll for new
		797	events, especially with backends like C<select ()> which have a high
		798	overhead for the actual polling but can deliver many events at once.
		799
		800	By setting a higher I<io collect interval> you allow libev to spend more
		801	time collecting I/O events, so you can handle more events per iteration,
		802	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		803	C<ev_timer>) will be not affected. Setting this to a non-null value will
		804	introduce an additional C<ev_sleep ()> call into most loop iterations.
		805
		806	Likewise, by setting a higher I<timeout collect interval> you allow libev
		807	to spend more time collecting timeouts, at the expense of increased
		808	latency/jitter/inexactness (the watcher callback will be called
		809	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		810	value will not introduce any overhead in libev.
		811
		812	Many (busy) programs can usually benefit by setting the I/O collect
		813	interval to a value near C<0.1> or so, which is often enough for
		814	interactive servers (of course not for games), likewise for timeouts. It
		815	usually doesn't make much sense to set it to a lower value than C<0.01>,
		816	as this approaches the timing granularity of most systems.
		817
		818	Setting the I<timeout collect interval> can improve the opportunity for
		819	saving power, as the program will "bundle" timer callback invocations that
		820	are "near" in time together, by delaying some, thus reducing the number of
		821	times the process sleeps and wakes up again. Another useful technique to
		822	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		823	they fire on, say, one-second boundaries only.
		824
		825	=item ev_loop_verify (loop)
		826
		827	This function only does something when C<EV_VERIFY> support has been
		828	compiled in, which is the default for non-minimal builds. It tries to go
		829	through all internal structures and checks them for validity. If anything
		830	is found to be inconsistent, it will print an error message to standard
		831	error and call C<abort ()>.
		832
		833	This can be used to catch bugs inside libev itself: under normal
		834	circumstances, this function will never abort as of course libev keeps its
		835	data structures consistent.
469		836
470	=back	837	=back
471		838
472		839
473	=head1 ANATOMY OF A WATCHER	840	=head1 ANATOMY OF A WATCHER
		841
		842	In the following description, uppercase C<TYPE> in names stands for the
		843	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		844	watchers and C<ev_io_start> for I/O watchers.
474		845
475	A watcher is a structure that you create and register to record your	846	A watcher is a structure that you create and register to record your
476	interest in some event. For instance, if you want to wait for STDIN to	847	interest in some event. For instance, if you want to wait for STDIN to
477	become readable, you would create an C<ev_io> watcher for that:	848	become readable, you would create an C<ev_io> watcher for that:
478		849
479	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	850	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
480	{	851	{
481	ev_io_stop (w);	852	ev_io_stop (w);
482	ev_unloop (loop, EVUNLOOP_ALL);	853	ev_unloop (loop, EVUNLOOP_ALL);
483	}	854	}
484		855
485	struct ev_loop *loop = ev_default_loop (0);	856	struct ev_loop *loop = ev_default_loop (0);
		857
486	struct ev_io stdin_watcher;	858	ev_io stdin_watcher;
		859
487	ev_init (&stdin_watcher, my_cb);	860	ev_init (&stdin_watcher, my_cb);
488	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	861	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
489	ev_io_start (loop, &stdin_watcher);	862	ev_io_start (loop, &stdin_watcher);
		863
490	ev_loop (loop, 0);	864	ev_loop (loop, 0);
491		865
492	As you can see, you are responsible for allocating the memory for your	866	As you can see, you are responsible for allocating the memory for your
493	watcher structures (and it is usually a bad idea to do this on the stack,	867	watcher structures (and it is I<usually> a bad idea to do this on the
494	although this can sometimes be quite valid).	868	stack).
		869
		870	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		871	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
495		872
496	Each watcher structure must be initialised by a call to C<ev_init	873	Each watcher structure must be initialised by a call to C<ev_init
497	(watcher *, callback)>, which expects a callback to be provided. This	874	(watcher *, callback)>, which expects a callback to be provided. This
498	callback gets invoked each time the event occurs (or, in the case of io	875	callback gets invoked each time the event occurs (or, in the case of I/O
499	watchers, each time the event loop detects that the file descriptor given	876	watchers, each time the event loop detects that the file descriptor given
500	is readable and/or writable).	877	is readable and/or writable).
501		878
502	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	879	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
503	with arguments specific to this watcher type. There is also a macro	880	macro to configure it, with arguments specific to the watcher type. There
504	to combine initialisation and setting in one call: C<< ev_<type>_init	881	is also a macro to combine initialisation and setting in one call: C<<
505	(watcher *, callback, ...) >>.	882	ev_TYPE_init (watcher *, callback, ...) >>.
506		883
507	To make the watcher actually watch out for events, you have to start it	884	To make the watcher actually watch out for events, you have to start it
508	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	885	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
509	*) >>), and you can stop watching for events at any time by calling the	886	*) >>), and you can stop watching for events at any time by calling the
510	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	887	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
511		888
512	As long as your watcher is active (has been started but not stopped) you	889	As long as your watcher is active (has been started but not stopped) you
513	must not touch the values stored in it. Most specifically you must never	890	must not touch the values stored in it. Most specifically you must never
514	reinitialise it or call its C<set> macro.	891	reinitialise it or call its C<ev_TYPE_set> macro.
515		892
516	Each and every callback receives the event loop pointer as first, the	893	Each and every callback receives the event loop pointer as first, the
517	registered watcher structure as second, and a bitset of received events as	894	registered watcher structure as second, and a bitset of received events as
518	third argument.	895	third argument.
519		896
…		…
573	=item C<EV_FORK>	950	=item C<EV_FORK>
574		951
575	The event loop has been resumed in the child process after fork (see	952	The event loop has been resumed in the child process after fork (see
576	C<ev_fork>).	953	C<ev_fork>).
577		954
		955	=item C<EV_ASYNC>
		956
		957	The given async watcher has been asynchronously notified (see C<ev_async>).
		958
		959	=item C<EV_CUSTOM>
		960
		961	Not ever sent (or otherwise used) by libev itself, but can be freely used
		962	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		963
578	=item C<EV_ERROR>	964	=item C<EV_ERROR>
579		965
580	An unspecified error has occured, the watcher has been stopped. This might	966	An unspecified error has occurred, the watcher has been stopped. This might
581	happen because the watcher could not be properly started because libev	967	happen because the watcher could not be properly started because libev
582	ran out of memory, a file descriptor was found to be closed or any other	968	ran out of memory, a file descriptor was found to be closed or any other
		969	problem. Libev considers these application bugs.
		970
583	problem. You best act on it by reporting the problem and somehow coping	971	You best act on it by reporting the problem and somehow coping with the
584	with the watcher being stopped.	972	watcher being stopped. Note that well-written programs should not receive
		973	an error ever, so when your watcher receives it, this usually indicates a
		974	bug in your program.
585		975
586	Libev will usually signal a few "dummy" events together with an error,	976	Libev will usually signal a few "dummy" events together with an error, for
587	for example it might indicate that a fd is readable or writable, and if	977	example it might indicate that a fd is readable or writable, and if your
588	your callbacks is well-written it can just attempt the operation and cope	978	callbacks is well-written it can just attempt the operation and cope with
589	with the error from read() or write(). This will not work in multithreaded	979	the error from read() or write(). This will not work in multi-threaded
590	programs, though, so beware.	980	programs, though, as the fd could already be closed and reused for another
		981	thing, so beware.
591		982
592	=back	983	=back
593		984
594	=head2 GENERIC WATCHER FUNCTIONS	985	=head2 GENERIC WATCHER FUNCTIONS
595
596	In the following description, C<TYPE> stands for the watcher type,
597	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
598		986
599	=over 4	987	=over 4
600		988
601	=item C<ev_init> (ev_TYPE *watcher, callback)	989	=item C<ev_init> (ev_TYPE *watcher, callback)
602		990
…		…
608	which rolls both calls into one.	996	which rolls both calls into one.
609		997
610	You can reinitialise a watcher at any time as long as it has been stopped	998	You can reinitialise a watcher at any time as long as it has been stopped
611	(or never started) and there are no pending events outstanding.	999	(or never started) and there are no pending events outstanding.
612		1000
613	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1001	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
614	int revents)>.	1002	int revents)>.
		1003
		1004	Example: Initialise an C<ev_io> watcher in two steps.
		1005
		1006	ev_io w;
		1007	ev_init (&w, my_cb);
		1008	ev_io_set (&w, STDIN_FILENO, EV_READ);
615		1009
616	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1010	=item C<ev_TYPE_set> (ev_TYPE *, [args])
617		1011
618	This macro initialises the type-specific parts of a watcher. You need to	1012	This macro initialises the type-specific parts of a watcher. You need to
619	call C<ev_init> at least once before you call this macro, but you can	1013	call C<ev_init> at least once before you call this macro, but you can
…		…
622	difference to the C<ev_init> macro).	1016	difference to the C<ev_init> macro).
623		1017
624	Although some watcher types do not have type-specific arguments	1018	Although some watcher types do not have type-specific arguments
625	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1019	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
626		1020
		1021	See C<ev_init>, above, for an example.
		1022
627	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1023	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
628		1024
629	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1025	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
630	calls into a single call. This is the most convinient method to initialise	1026	calls into a single call. This is the most convenient method to initialise
631	a watcher. The same limitations apply, of course.	1027	a watcher. The same limitations apply, of course.
		1028
		1029	Example: Initialise and set an C<ev_io> watcher in one step.
		1030
		1031	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
632		1032
633	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1033	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
634		1034
635	Starts (activates) the given watcher. Only active watchers will receive	1035	Starts (activates) the given watcher. Only active watchers will receive
636	events. If the watcher is already active nothing will happen.	1036	events. If the watcher is already active nothing will happen.
637		1037
		1038	Example: Start the C<ev_io> watcher that is being abused as example in this
		1039	whole section.
		1040
		1041	ev_io_start (EV_DEFAULT_UC, &w);
		1042
638	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1043	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
639		1044
640	Stops the given watcher again (if active) and clears the pending	1045	Stops the given watcher if active, and clears the pending status (whether
		1046	the watcher was active or not).
		1047
641	status. It is possible that stopped watchers are pending (for example,	1048	It is possible that stopped watchers are pending - for example,
642	non-repeating timers are being stopped when they become pending), but	1049	non-repeating timers are being stopped when they become pending - but
643	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1050	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
644	you want to free or reuse the memory used by the watcher it is therefore a	1051	pending. If you want to free or reuse the memory used by the watcher it is
645	good idea to always call its C<ev_TYPE_stop> function.	1052	therefore a good idea to always call its C<ev_TYPE_stop> function.
646		1053
647	=item bool ev_is_active (ev_TYPE *watcher)	1054	=item bool ev_is_active (ev_TYPE *watcher)
648		1055
649	Returns a true value iff the watcher is active (i.e. it has been started	1056	Returns a true value iff the watcher is active (i.e. it has been started
650	and not yet been stopped). As long as a watcher is active you must not modify	1057	and not yet been stopped). As long as a watcher is active you must not modify
…		…
653	=item bool ev_is_pending (ev_TYPE *watcher)	1060	=item bool ev_is_pending (ev_TYPE *watcher)
654		1061
655	Returns a true value iff the watcher is pending, (i.e. it has outstanding	1062	Returns a true value iff the watcher is pending, (i.e. it has outstanding
656	events but its callback has not yet been invoked). As long as a watcher	1063	events but its callback has not yet been invoked). As long as a watcher
657	is pending (but not active) you must not call an init function on it (but	1064	is pending (but not active) you must not call an init function on it (but
658	C<ev_TYPE_set> is safe) and you must make sure the watcher is available to	1065	C<ev_TYPE_set> is safe), you must not change its priority, and you must
659	libev (e.g. you cnanot C<free ()> it).	1066	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1067	it).
660		1068
661	=item callback = ev_cb (ev_TYPE *watcher)	1069	=item callback ev_cb (ev_TYPE *watcher)
662		1070
663	Returns the callback currently set on the watcher.	1071	Returns the callback currently set on the watcher.
664		1072
665	=item ev_cb_set (ev_TYPE *watcher, callback)	1073	=item ev_cb_set (ev_TYPE *watcher, callback)
666		1074
667	Change the callback. You can change the callback at virtually any time	1075	Change the callback. You can change the callback at virtually any time
668	(modulo threads).	1076	(modulo threads).
669		1077
		1078	=item ev_set_priority (ev_TYPE *watcher, priority)
		1079
		1080	=item int ev_priority (ev_TYPE *watcher)
		1081
		1082	Set and query the priority of the watcher. The priority is a small
		1083	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1084	(default: C<-2>). Pending watchers with higher priority will be invoked
		1085	before watchers with lower priority, but priority will not keep watchers
		1086	from being executed (except for C<ev_idle> watchers).
		1087
		1088	This means that priorities are I<only> used for ordering callback
		1089	invocation after new events have been received. This is useful, for
		1090	example, to reduce latency after idling, or more often, to bind two
		1091	watchers on the same event and make sure one is called first.
		1092
		1093	If you need to suppress invocation when higher priority events are pending
		1094	you need to look at C<ev_idle> watchers, which provide this functionality.
		1095
		1096	You I<must not> change the priority of a watcher as long as it is active or
		1097	pending.
		1098
		1099	The default priority used by watchers when no priority has been set is
		1100	always C<0>, which is supposed to not be too high and not be too low :).
		1101
		1102	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1103	fine, as long as you do not mind that the priority value you query might
		1104	or might not have been clamped to the valid range.
		1105
		1106	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1107
		1108	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1109	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1110	can deal with that fact, as both are simply passed through to the
		1111	callback.
		1112
		1113	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1114
		1115	If the watcher is pending, this function clears its pending status and
		1116	returns its C<revents> bitset (as if its callback was invoked). If the
		1117	watcher isn't pending it does nothing and returns C<0>.
		1118
		1119	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1120	callback to be invoked, which can be accomplished with this function.
		1121
670	=back	1122	=back
671		1123
672		1124
673	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1125	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
674		1126
675	Each watcher has, by default, a member C<void *data> that you can change	1127	Each watcher has, by default, a member C<void *data> that you can change
676	and read at any time, libev will completely ignore it. This can be used	1128	and read at any time: libev will completely ignore it. This can be used
677	to associate arbitrary data with your watcher. If you need more data and	1129	to associate arbitrary data with your watcher. If you need more data and
678	don't want to allocate memory and store a pointer to it in that data	1130	don't want to allocate memory and store a pointer to it in that data
679	member, you can also "subclass" the watcher type and provide your own	1131	member, you can also "subclass" the watcher type and provide your own
680	data:	1132	data:
681		1133
682	struct my_io	1134	struct my_io
683	{	1135	{
684	struct ev_io io;	1136	ev_io io;
685	int otherfd;	1137	int otherfd;
686	void *somedata;	1138	void *somedata;
687	struct whatever *mostinteresting;	1139	struct whatever *mostinteresting;
688	}	1140	};
		1141
		1142	...
		1143	struct my_io w;
		1144	ev_io_init (&w.io, my_cb, fd, EV_READ);
689		1145
690	And since your callback will be called with a pointer to the watcher, you	1146	And since your callback will be called with a pointer to the watcher, you
691	can cast it back to your own type:	1147	can cast it back to your own type:
692		1148
693	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1149	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
694	{	1150	{
695	struct my_io *w = (struct my_io *)w_;	1151	struct my_io *w = (struct my_io *)w_;
696	...	1152	...
697	}	1153	}
698		1154
699	More interesting and less C-conformant ways of catsing your callback type	1155	More interesting and less C-conformant ways of casting your callback type
700	have been omitted....	1156	instead have been omitted.
		1157
		1158	Another common scenario is to use some data structure with multiple
		1159	embedded watchers:
		1160
		1161	struct my_biggy
		1162	{
		1163	int some_data;
		1164	ev_timer t1;
		1165	ev_timer t2;
		1166	}
		1167
		1168	In this case getting the pointer to C<my_biggy> is a bit more
		1169	complicated: Either you store the address of your C<my_biggy> struct
		1170	in the C<data> member of the watcher (for woozies), or you need to use
		1171	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1172	programmers):
		1173
		1174	#include <stddef.h>
		1175
		1176	static void
		1177	t1_cb (EV_P_ ev_timer *w, int revents)
		1178	{
		1179	struct my_biggy big = (struct my_biggy *
		1180	(((char *)w) - offsetof (struct my_biggy, t1));
		1181	}
		1182
		1183	static void
		1184	t2_cb (EV_P_ ev_timer *w, int revents)
		1185	{
		1186	struct my_biggy big = (struct my_biggy *
		1187	(((char *)w) - offsetof (struct my_biggy, t2));
		1188	}
701		1189
702		1190
703	=head1 WATCHER TYPES	1191	=head1 WATCHER TYPES
704		1192
705	This section describes each watcher in detail, but will not repeat	1193	This section describes each watcher in detail, but will not repeat
…		…
729	In general you can register as many read and/or write event watchers per	1217	In general you can register as many read and/or write event watchers per
730	fd as you want (as long as you don't confuse yourself). Setting all file	1218	fd as you want (as long as you don't confuse yourself). Setting all file
731	descriptors to non-blocking mode is also usually a good idea (but not	1219	descriptors to non-blocking mode is also usually a good idea (but not
732	required if you know what you are doing).	1220	required if you know what you are doing).
733		1221
734	You have to be careful with dup'ed file descriptors, though. Some backends	1222	If you cannot use non-blocking mode, then force the use of a
735	(the linux epoll backend is a notable example) cannot handle dup'ed file	1223	known-to-be-good backend (at the time of this writing, this includes only
736	descriptors correctly if you register interest in two or more fds pointing	1224	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>).
737	to the same underlying file/socket/etc. description (that is, they share
738	the same underlying "file open").
739
740	If you must do this, then force the use of a known-to-be-good backend
741	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
742	C<EVBACKEND_POLL>).
743		1225
744	Another thing you have to watch out for is that it is quite easy to	1226	Another thing you have to watch out for is that it is quite easy to
745	receive "spurious" readyness notifications, that is your callback might	1227	receive "spurious" readiness notifications, that is your callback might
746	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1228	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
747	because there is no data. Not only are some backends known to create a	1229	because there is no data. Not only are some backends known to create a
748	lot of those (for example solaris ports), it is very easy to get into	1230	lot of those (for example Solaris ports), it is very easy to get into
749	this situation even with a relatively standard program structure. Thus	1231	this situation even with a relatively standard program structure. Thus
750	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1232	it is best to always use non-blocking I/O: An extra C<read>(2) returning
751	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1233	C<EAGAIN> is far preferable to a program hanging until some data arrives.
752		1234
753	If you cannot run the fd in non-blocking mode (for example you should not	1235	If you cannot run the fd in non-blocking mode (for example you should
754	play around with an Xlib connection), then you have to seperately re-test	1236	not play around with an Xlib connection), then you have to separately
755	wether a file descriptor is really ready with a known-to-be good interface	1237	re-test whether a file descriptor is really ready with a known-to-be good
756	such as poll (fortunately in our Xlib example, Xlib already does this on	1238	interface such as poll (fortunately in our Xlib example, Xlib already
757	its own, so its quite safe to use).	1239	does this on its own, so its quite safe to use). Some people additionally
		1240	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1241	indefinitely.
		1242
		1243	But really, best use non-blocking mode.
		1244
		1245	=head3 The special problem of disappearing file descriptors
		1246
		1247	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1248	descriptor (either due to calling C<close> explicitly or any other means,
		1249	such as C<dup2>). The reason is that you register interest in some file
		1250	descriptor, but when it goes away, the operating system will silently drop
		1251	this interest. If another file descriptor with the same number then is
		1252	registered with libev, there is no efficient way to see that this is, in
		1253	fact, a different file descriptor.
		1254
		1255	To avoid having to explicitly tell libev about such cases, libev follows
		1256	the following policy: Each time C<ev_io_set> is being called, libev
		1257	will assume that this is potentially a new file descriptor, otherwise
		1258	it is assumed that the file descriptor stays the same. That means that
		1259	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1260	descriptor even if the file descriptor number itself did not change.
		1261
		1262	This is how one would do it normally anyway, the important point is that
		1263	the libev application should not optimise around libev but should leave
		1264	optimisations to libev.
		1265
		1266	=head3 The special problem of dup'ed file descriptors
		1267
		1268	Some backends (e.g. epoll), cannot register events for file descriptors,
		1269	but only events for the underlying file descriptions. That means when you
		1270	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1271	events for them, only one file descriptor might actually receive events.
		1272
		1273	There is no workaround possible except not registering events
		1274	for potentially C<dup ()>'ed file descriptors, or to resort to
		1275	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1276
		1277	=head3 The special problem of fork
		1278
		1279	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1280	useless behaviour. Libev fully supports fork, but needs to be told about
		1281	it in the child.
		1282
		1283	To support fork in your programs, you either have to call
		1284	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1285	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1286	C<EVBACKEND_POLL>.
		1287
		1288	=head3 The special problem of SIGPIPE
		1289
		1290	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1291	when writing to a pipe whose other end has been closed, your program gets
		1292	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1293	this is sensible behaviour, for daemons, this is usually undesirable.
		1294
		1295	So when you encounter spurious, unexplained daemon exits, make sure you
		1296	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1297	somewhere, as that would have given you a big clue).
		1298
		1299
		1300	=head3 Watcher-Specific Functions
758		1301
759	=over 4	1302	=over 4
760		1303
761	=item ev_io_init (ev_io *, callback, int fd, int events)	1304	=item ev_io_init (ev_io *, callback, int fd, int events)
762		1305
763	=item ev_io_set (ev_io *, int fd, int events)	1306	=item ev_io_set (ev_io *, int fd, int events)
764		1307
765	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1308	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
766	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1309	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
767	C<EV_READ | EV_WRITE> to receive the given events.	1310	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
768		1311
769	=item int fd [read-only]	1312	=item int fd [read-only]
770		1313
771	The file descriptor being watched.	1314	The file descriptor being watched.
772		1315
…		…
774		1317
775	The events being watched.	1318	The events being watched.
776		1319
777	=back	1320	=back
778		1321
		1322	=head3 Examples
		1323
779	Example: call C<stdin_readable_cb> when STDIN_FILENO has become, well	1324	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
780	readable, but only once. Since it is likely line-buffered, you could	1325	readable, but only once. Since it is likely line-buffered, you could
781	attempt to read a whole line in the callback:	1326	attempt to read a whole line in the callback.
782		1327
783	static void	1328	static void
784	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1329	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
785	{	1330	{
786	ev_io_stop (loop, w);	1331	ev_io_stop (loop, w);
787	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1332	.. read from stdin here (or from w->fd) and handle any I/O errors
788	}	1333	}
789		1334
790	...	1335	...
791	struct ev_loop *loop = ev_default_init (0);	1336	struct ev_loop *loop = ev_default_init (0);
792	struct ev_io stdin_readable;	1337	ev_io stdin_readable;
793	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1338	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
794	ev_io_start (loop, &stdin_readable);	1339	ev_io_start (loop, &stdin_readable);
795	ev_loop (loop, 0);	1340	ev_loop (loop, 0);
796		1341
797		1342
798	=head2 C<ev_timer> - relative and optionally repeating timeouts	1343	=head2 C<ev_timer> - relative and optionally repeating timeouts
799		1344
800	Timer watchers are simple relative timers that generate an event after a	1345	Timer watchers are simple relative timers that generate an event after a
801	given time, and optionally repeating in regular intervals after that.	1346	given time, and optionally repeating in regular intervals after that.
802		1347
803	The timers are based on real time, that is, if you register an event that	1348	The timers are based on real time, that is, if you register an event that
804	times out after an hour and you reset your system clock to last years	1349	times out after an hour and you reset your system clock to January last
805	time, it will still time out after (roughly) and hour. "Roughly" because	1350	year, it will still time out after (roughly) one hour. "Roughly" because
806	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1351	detecting time jumps is hard, and some inaccuracies are unavoidable (the
807	monotonic clock option helps a lot here).	1352	monotonic clock option helps a lot here).
		1353
		1354	The callback is guaranteed to be invoked only I<after> its timeout has
		1355	passed. If multiple timers become ready during the same loop iteration
		1356	then the ones with earlier time-out values are invoked before ones with
		1357	later time-out values (but this is no longer true when a callback calls
		1358	C<ev_loop> recursively).
		1359
		1360	=head3 Be smart about timeouts
		1361
		1362	Many real-world problems involve some kind of timeout, usually for error
		1363	recovery. A typical example is an HTTP request - if the other side hangs,
		1364	you want to raise some error after a while.
		1365
		1366	What follows are some ways to handle this problem, from obvious and
		1367	inefficient to smart and efficient.
		1368
		1369	In the following, a 60 second activity timeout is assumed - a timeout that
		1370	gets reset to 60 seconds each time there is activity (e.g. each time some
		1371	data or other life sign was received).
		1372
		1373	=over 4
		1374
		1375	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1376
		1377	This is the most obvious, but not the most simple way: In the beginning,
		1378	start the watcher:
		1379
		1380	ev_timer_init (timer, callback, 60., 0.);
		1381	ev_timer_start (loop, timer);
		1382
		1383	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1384	and start it again:
		1385
		1386	ev_timer_stop (loop, timer);
		1387	ev_timer_set (timer, 60., 0.);
		1388	ev_timer_start (loop, timer);
		1389
		1390	This is relatively simple to implement, but means that each time there is
		1391	some activity, libev will first have to remove the timer from its internal
		1392	data structure and then add it again. Libev tries to be fast, but it's
		1393	still not a constant-time operation.
		1394
		1395	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1396
		1397	This is the easiest way, and involves using C<ev_timer_again> instead of
		1398	C<ev_timer_start>.
		1399
		1400	To implement this, configure an C<ev_timer> with a C<repeat> value
		1401	of C<60> and then call C<ev_timer_again> at start and each time you
		1402	successfully read or write some data. If you go into an idle state where
		1403	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1404	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1405
		1406	That means you can ignore both the C<ev_timer_start> function and the
		1407	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1408	member and C<ev_timer_again>.
		1409
		1410	At start:
		1411
		1412	ev_timer_init (timer, callback);
		1413	timer->repeat = 60.;
		1414	ev_timer_again (loop, timer);
		1415
		1416	Each time there is some activity:
		1417
		1418	ev_timer_again (loop, timer);
		1419
		1420	It is even possible to change the time-out on the fly, regardless of
		1421	whether the watcher is active or not:
		1422
		1423	timer->repeat = 30.;
		1424	ev_timer_again (loop, timer);
		1425
		1426	This is slightly more efficient then stopping/starting the timer each time
		1427	you want to modify its timeout value, as libev does not have to completely
		1428	remove and re-insert the timer from/into its internal data structure.
		1429
		1430	It is, however, even simpler than the "obvious" way to do it.
		1431
		1432	=item 3. Let the timer time out, but then re-arm it as required.
		1433
		1434	This method is more tricky, but usually most efficient: Most timeouts are
		1435	relatively long compared to the intervals between other activity - in
		1436	our example, within 60 seconds, there are usually many I/O events with
		1437	associated activity resets.
		1438
		1439	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1440	but remember the time of last activity, and check for a real timeout only
		1441	within the callback:
		1442
		1443	ev_tstamp last_activity; // time of last activity
		1444
		1445	static void
		1446	callback (EV_P_ ev_timer *w, int revents)
		1447	{
		1448	ev_tstamp now = ev_now (EV_A);
		1449	ev_tstamp timeout = last_activity + 60.;
		1450
		1451	// if last_activity + 60. is older than now, we did time out
		1452	if (timeout < now)
		1453	{
		1454	// timeout occured, take action
		1455	}
		1456	else
		1457	{
		1458	// callback was invoked, but there was some activity, re-arm
		1459	// the watcher to fire in last_activity + 60, which is
		1460	// guaranteed to be in the future, so "again" is positive:
		1461	w->repeat = timeout - now;
		1462	ev_timer_again (EV_A_ w);
		1463	}
		1464	}
		1465
		1466	To summarise the callback: first calculate the real timeout (defined
		1467	as "60 seconds after the last activity"), then check if that time has
		1468	been reached, which means something I<did>, in fact, time out. Otherwise
		1469	the callback was invoked too early (C<timeout> is in the future), so
		1470	re-schedule the timer to fire at that future time, to see if maybe we have
		1471	a timeout then.
		1472
		1473	Note how C<ev_timer_again> is used, taking advantage of the
		1474	C<ev_timer_again> optimisation when the timer is already running.
		1475
		1476	This scheme causes more callback invocations (about one every 60 seconds
		1477	minus half the average time between activity), but virtually no calls to
		1478	libev to change the timeout.
		1479
		1480	To start the timer, simply initialise the watcher and set C<last_activity>
		1481	to the current time (meaning we just have some activity :), then call the
		1482	callback, which will "do the right thing" and start the timer:
		1483
		1484	ev_timer_init (timer, callback);
		1485	last_activity = ev_now (loop);
		1486	callback (loop, timer, EV_TIMEOUT);
		1487
		1488	And when there is some activity, simply store the current time in
		1489	C<last_activity>, no libev calls at all:
		1490
		1491	last_actiivty = ev_now (loop);
		1492
		1493	This technique is slightly more complex, but in most cases where the
		1494	time-out is unlikely to be triggered, much more efficient.
		1495
		1496	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1497	callback :) - just change the timeout and invoke the callback, which will
		1498	fix things for you.
		1499
		1500	=item 4. Wee, just use a double-linked list for your timeouts.
		1501
		1502	If there is not one request, but many thousands (millions...), all
		1503	employing some kind of timeout with the same timeout value, then one can
		1504	do even better:
		1505
		1506	When starting the timeout, calculate the timeout value and put the timeout
		1507	at the I<end> of the list.
		1508
		1509	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1510	the list is expected to fire (for example, using the technique #3).
		1511
		1512	When there is some activity, remove the timer from the list, recalculate
		1513	the timeout, append it to the end of the list again, and make sure to
		1514	update the C<ev_timer> if it was taken from the beginning of the list.
		1515
		1516	This way, one can manage an unlimited number of timeouts in O(1) time for
		1517	starting, stopping and updating the timers, at the expense of a major
		1518	complication, and having to use a constant timeout. The constant timeout
		1519	ensures that the list stays sorted.
		1520
		1521	=back
		1522
		1523	So which method the best?
		1524
		1525	Method #2 is a simple no-brain-required solution that is adequate in most
		1526	situations. Method #3 requires a bit more thinking, but handles many cases
		1527	better, and isn't very complicated either. In most case, choosing either
		1528	one is fine, with #3 being better in typical situations.
		1529
		1530	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1531	rather complicated, but extremely efficient, something that really pays
		1532	off after the first million or so of active timers, i.e. it's usually
		1533	overkill :)
		1534
		1535	=head3 The special problem of time updates
		1536
		1537	Establishing the current time is a costly operation (it usually takes at
		1538	least two system calls): EV therefore updates its idea of the current
		1539	time only before and after C<ev_loop> collects new events, which causes a
		1540	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1541	lots of events in one iteration.
808		1542
809	The relative timeouts are calculated relative to the C<ev_now ()>	1543	The relative timeouts are calculated relative to the C<ev_now ()>
810	time. This is usually the right thing as this timestamp refers to the time	1544	time. This is usually the right thing as this timestamp refers to the time
811	of the event triggering whatever timeout you are modifying/starting. If	1545	of the event triggering whatever timeout you are modifying/starting. If
812	you suspect event processing to be delayed and you I<need> to base the timeout	1546	you suspect event processing to be delayed and you I<need> to base the
813	on the current time, use something like this to adjust for this:	1547	timeout on the current time, use something like this to adjust for this:
814		1548
815	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1549	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
816		1550
817	The callback is guarenteed to be invoked only when its timeout has passed,	1551	If the event loop is suspended for a long time, you can also force an
818	but if multiple timers become ready during the same loop iteration then	1552	update of the time returned by C<ev_now ()> by calling C<ev_now_update
819	order of execution is undefined.	1553	()>.
		1554
		1555	=head3 Watcher-Specific Functions and Data Members
820		1556
821	=over 4	1557	=over 4
822		1558
823	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1559	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
824		1560
825	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1561	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
826		1562
827	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1563	Configure the timer to trigger after C<after> seconds. If C<repeat>
828	C<0.>, then it will automatically be stopped. If it is positive, then the	1564	is C<0.>, then it will automatically be stopped once the timeout is
829	timer will automatically be configured to trigger again C<repeat> seconds	1565	reached. If it is positive, then the timer will automatically be
830	later, again, and again, until stopped manually.	1566	configured to trigger again C<repeat> seconds later, again, and again,
		1567	until stopped manually.
831		1568
832	The timer itself will do a best-effort at avoiding drift, that is, if you	1569	The timer itself will do a best-effort at avoiding drift, that is, if
833	configure a timer to trigger every 10 seconds, then it will trigger at	1570	you configure a timer to trigger every 10 seconds, then it will normally
834	exactly 10 second intervals. If, however, your program cannot keep up with	1571	trigger at exactly 10 second intervals. If, however, your program cannot
835	the timer (because it takes longer than those 10 seconds to do stuff) the	1572	keep up with the timer (because it takes longer than those 10 seconds to
836	timer will not fire more than once per event loop iteration.	1573	do stuff) the timer will not fire more than once per event loop iteration.
837		1574
838	=item ev_timer_again (loop)	1575	=item ev_timer_again (loop, ev_timer *)
839		1576
840	This will act as if the timer timed out and restart it again if it is	1577	This will act as if the timer timed out and restart it again if it is
841	repeating. The exact semantics are:	1578	repeating. The exact semantics are:
842		1579
		1580	If the timer is pending, its pending status is cleared.
		1581
843	If the timer is started but nonrepeating, stop it.	1582	If the timer is started but non-repeating, stop it (as if it timed out).
844		1583
845	If the timer is repeating, either start it if necessary (with the repeat	1584	If the timer is repeating, either start it if necessary (with the
846	value), or reset the running timer to the repeat value.	1585	C<repeat> value), or reset the running timer to the C<repeat> value.
847		1586
848	This sounds a bit complicated, but here is a useful and typical	1587	This sounds a bit complicated, see "Be smart about timeouts", above, for a
849	example: Imagine you have a tcp connection and you want a so-called	1588	usage example.
850	idle timeout, that is, you want to be called when there have been,
851	say, 60 seconds of inactivity on the socket. The easiest way to do
852	this is to configure an C<ev_timer> with C<after>=C<repeat>=C<60> and calling
853	C<ev_timer_again> each time you successfully read or write some data. If
854	you go into an idle state where you do not expect data to travel on the
855	socket, you can stop the timer, and again will automatically restart it if
856	need be.
857
858	You can also ignore the C<after> value and C<ev_timer_start> altogether
859	and only ever use the C<repeat> value:
860
861	ev_timer_init (timer, callback, 0., 5.);
862	ev_timer_again (loop, timer);
863	...
864	timer->again = 17.;
865	ev_timer_again (loop, timer);
866	...
867	timer->again = 10.;
868	ev_timer_again (loop, timer);
869
870	This is more efficient then stopping/starting the timer eahc time you want
871	to modify its timeout value.
872		1589
873	=item ev_tstamp repeat [read-write]	1590	=item ev_tstamp repeat [read-write]
874		1591
875	The current C<repeat> value. Will be used each time the watcher times out	1592	The current C<repeat> value. Will be used each time the watcher times out
876	or C<ev_timer_again> is called and determines the next timeout (if any),	1593	or C<ev_timer_again> is called, and determines the next timeout (if any),
877	which is also when any modifications are taken into account.	1594	which is also when any modifications are taken into account.
878		1595
879	=back	1596	=back
880		1597
		1598	=head3 Examples
		1599
881	Example: create a timer that fires after 60 seconds.	1600	Example: Create a timer that fires after 60 seconds.
882		1601
883	static void	1602	static void
884	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1603	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
885	{	1604	{
886	.. one minute over, w is actually stopped right here	1605	.. one minute over, w is actually stopped right here
887	}	1606	}
888		1607
889	struct ev_timer mytimer;	1608	ev_timer mytimer;
890	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1609	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
891	ev_timer_start (loop, &mytimer);	1610	ev_timer_start (loop, &mytimer);
892		1611
893	Example: create a timeout timer that times out after 10 seconds of	1612	Example: Create a timeout timer that times out after 10 seconds of
894	inactivity.	1613	inactivity.
895		1614
896	static void	1615	static void
897	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1616	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
898	{	1617	{
899	.. ten seconds without any activity	1618	.. ten seconds without any activity
900	}	1619	}
901		1620
902	struct ev_timer mytimer;	1621	ev_timer mytimer;
903	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1622	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
904	ev_timer_again (&mytimer); /* start timer */	1623	ev_timer_again (&mytimer); /* start timer */
905	ev_loop (loop, 0);	1624	ev_loop (loop, 0);
906		1625
907	// and in some piece of code that gets executed on any "activity":	1626	// and in some piece of code that gets executed on any "activity":
908	// reset the timeout to start ticking again at 10 seconds	1627	// reset the timeout to start ticking again at 10 seconds
909	ev_timer_again (&mytimer);	1628	ev_timer_again (&mytimer);
910		1629
911		1630
912	=head2 C<ev_periodic> - to cron or not to cron?	1631	=head2 C<ev_periodic> - to cron or not to cron?
913		1632
914	Periodic watchers are also timers of a kind, but they are very versatile	1633	Periodic watchers are also timers of a kind, but they are very versatile
915	(and unfortunately a bit complex).	1634	(and unfortunately a bit complex).
916		1635
917	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1636	Unlike C<ev_timer>, periodic watchers are not based on real time (or
918	but on wallclock time (absolute time). You can tell a periodic watcher	1637	relative time, the physical time that passes) but on wall clock time
919	to trigger "at" some specific point in time. For example, if you tell a	1638	(absolute time, the thing you can read on your calender or clock). The
920	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	1639	difference is that wall clock time can run faster or slower than real
921	+ 10.>) and then reset your system clock to the last year, then it will	1640	time, and time jumps are not uncommon (e.g. when you adjust your
922	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1641	wrist-watch).
923	roughly 10 seconds later and of course not if you reset your system time
924	again).
925		1642
926	They can also be used to implement vastly more complex timers, such as	1643	You can tell a periodic watcher to trigger after some specific point
		1644	in time: for example, if you tell a periodic watcher to trigger "in 10
		1645	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1646	not a delay) and then reset your system clock to January of the previous
		1647	year, then it will take a year or more to trigger the event (unlike an
		1648	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1649	it, as it uses a relative timeout).
		1650
		1651	C<ev_periodic> watchers can also be used to implement vastly more complex
927	triggering an event on eahc midnight, local time.	1652	timers, such as triggering an event on each "midnight, local time", or
		1653	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1654	those cannot react to time jumps.
928		1655
929	As with timers, the callback is guarenteed to be invoked only when the	1656	As with timers, the callback is guaranteed to be invoked only when the
930	time (C<at>) has been passed, but if multiple periodic timers become ready	1657	point in time where it is supposed to trigger has passed. If multiple
931	during the same loop iteration then order of execution is undefined.	1658	timers become ready during the same loop iteration then the ones with
		1659	earlier time-out values are invoked before ones with later time-out values
		1660	(but this is no longer true when a callback calls C<ev_loop> recursively).
		1661
		1662	=head3 Watcher-Specific Functions and Data Members
932		1663
933	=over 4	1664	=over 4
934		1665
935	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1666	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
936		1667
937	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1668	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
938		1669
939	Lots of arguments, lets sort it out... There are basically three modes of	1670	Lots of arguments, let's sort it out... There are basically three modes of
940	operation, and we will explain them from simplest to complex:	1671	operation, and we will explain them from simplest to most complex:
941		1672
942	=over 4	1673	=over 4
943		1674
944	=item * absolute timer (interval = reschedule_cb = 0)	1675	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
945		1676
946	In this configuration the watcher triggers an event at the wallclock time	1677	In this configuration the watcher triggers an event after the wall clock
947	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1678	time C<offset> has passed. It will not repeat and will not adjust when a
948	that is, if it is to be run at January 1st 2011 then it will run when the	1679	time jump occurs, that is, if it is to be run at January 1st 2011 then it
949	system time reaches or surpasses this time.	1680	will be stopped and invoked when the system clock reaches or surpasses
		1681	this point in time.
950		1682
951	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1683	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
952		1684
953	In this mode the watcher will always be scheduled to time out at the next	1685	In this mode the watcher will always be scheduled to time out at the next
954	C<at + N * interval> time (for some integer N) and then repeat, regardless	1686	C<offset + N * interval> time (for some integer N, which can also be
955	of any time jumps.	1687	negative) and then repeat, regardless of any time jumps. The C<offset>
		1688	argument is merely an offset into the C<interval> periods.
956		1689
957	This can be used to create timers that do not drift with respect to system	1690	This can be used to create timers that do not drift with respect to the
958	time:	1691	system clock, for example, here is an C<ev_periodic> that triggers each
		1692	hour, on the hour (with respect to UTC):
959		1693
960	ev_periodic_set (&periodic, 0., 3600., 0);	1694	ev_periodic_set (&periodic, 0., 3600., 0);
961		1695
962	This doesn't mean there will always be 3600 seconds in between triggers,	1696	This doesn't mean there will always be 3600 seconds in between triggers,
963	but only that the the callback will be called when the system time shows a	1697	but only that the callback will be called when the system time shows a
964	full hour (UTC), or more correctly, when the system time is evenly divisible	1698	full hour (UTC), or more correctly, when the system time is evenly divisible
965	by 3600.	1699	by 3600.
966		1700
967	Another way to think about it (for the mathematically inclined) is that	1701	Another way to think about it (for the mathematically inclined) is that
968	C<ev_periodic> will try to run the callback in this mode at the next possible	1702	C<ev_periodic> will try to run the callback in this mode at the next possible
969	time where C<time = at (mod interval)>, regardless of any time jumps.	1703	time where C<time = offset (mod interval)>, regardless of any time jumps.
970		1704
		1705	For numerical stability it is preferable that the C<offset> value is near
		1706	C<ev_now ()> (the current time), but there is no range requirement for
		1707	this value, and in fact is often specified as zero.
		1708
		1709	Note also that there is an upper limit to how often a timer can fire (CPU
		1710	speed for example), so if C<interval> is very small then timing stability
		1711	will of course deteriorate. Libev itself tries to be exact to be about one
		1712	millisecond (if the OS supports it and the machine is fast enough).
		1713
971	=item * manual reschedule mode (reschedule_cb = callback)	1714	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
972		1715
973	In this mode the values for C<interval> and C<at> are both being	1716	In this mode the values for C<interval> and C<offset> are both being
974	ignored. Instead, each time the periodic watcher gets scheduled, the	1717	ignored. Instead, each time the periodic watcher gets scheduled, the
975	reschedule callback will be called with the watcher as first, and the	1718	reschedule callback will be called with the watcher as first, and the
976	current time as second argument.	1719	current time as second argument.
977		1720
978	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1721	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
979	ever, or make any event loop modifications>. If you need to stop it,	1722	or make ANY other event loop modifications whatsoever, unless explicitly
980	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	1723	allowed by documentation here>.
981	starting a prepare watcher).
982		1724
		1725	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1726	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1727	only event loop modification you are allowed to do).
		1728
983	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1729	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
984	ev_tstamp now)>, e.g.:	1730	*w, ev_tstamp now)>, e.g.:
985		1731
		1732	static ev_tstamp
986	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1733	my_rescheduler (ev_periodic *w, ev_tstamp now)
987	{	1734	{
988	return now + 60.;	1735	return now + 60.;
989	}	1736	}
990		1737
991	It must return the next time to trigger, based on the passed time value	1738	It must return the next time to trigger, based on the passed time value
992	(that is, the lowest time value larger than to the second argument). It	1739	(that is, the lowest time value larger than to the second argument). It
993	will usually be called just before the callback will be triggered, but	1740	will usually be called just before the callback will be triggered, but
994	might be called at other times, too.	1741	might be called at other times, too.
995		1742
996	NOTE: I<< This callback must always return a time that is later than the	1743	NOTE: I<< This callback must always return a time that is higher than or
997	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	1744	equal to the passed C<now> value >>.
998		1745
999	This can be used to create very complex timers, such as a timer that	1746	This can be used to create very complex timers, such as a timer that
1000	triggers on each midnight, local time. To do this, you would calculate the	1747	triggers on "next midnight, local time". To do this, you would calculate the
1001	next midnight after C<now> and return the timestamp value for this. How	1748	next midnight after C<now> and return the timestamp value for this. How
1002	you do this is, again, up to you (but it is not trivial, which is the main	1749	you do this is, again, up to you (but it is not trivial, which is the main
1003	reason I omitted it as an example).	1750	reason I omitted it as an example).
1004		1751
1005	=back	1752	=back
…		…
1009	Simply stops and restarts the periodic watcher again. This is only useful	1756	Simply stops and restarts the periodic watcher again. This is only useful
1010	when you changed some parameters or the reschedule callback would return	1757	when you changed some parameters or the reschedule callback would return
1011	a different time than the last time it was called (e.g. in a crond like	1758	a different time than the last time it was called (e.g. in a crond like
1012	program when the crontabs have changed).	1759	program when the crontabs have changed).
1013		1760
		1761	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1762
		1763	When active, returns the absolute time that the watcher is supposed
		1764	to trigger next. This is not the same as the C<offset> argument to
		1765	C<ev_periodic_set>, but indeed works even in interval and manual
		1766	rescheduling modes.
		1767
		1768	=item ev_tstamp offset [read-write]
		1769
		1770	When repeating, this contains the offset value, otherwise this is the
		1771	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		1772	although libev might modify this value for better numerical stability).
		1773
		1774	Can be modified any time, but changes only take effect when the periodic
		1775	timer fires or C<ev_periodic_again> is being called.
		1776
1014	=item ev_tstamp interval [read-write]	1777	=item ev_tstamp interval [read-write]
1015		1778
1016	The current interval value. Can be modified any time, but changes only	1779	The current interval value. Can be modified any time, but changes only
1017	take effect when the periodic timer fires or C<ev_periodic_again> is being	1780	take effect when the periodic timer fires or C<ev_periodic_again> is being
1018	called.	1781	called.
1019		1782
1020	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	1783	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1021		1784
1022	The current reschedule callback, or C<0>, if this functionality is	1785	The current reschedule callback, or C<0>, if this functionality is
1023	switched off. Can be changed any time, but changes only take effect when	1786	switched off. Can be changed any time, but changes only take effect when
1024	the periodic timer fires or C<ev_periodic_again> is being called.	1787	the periodic timer fires or C<ev_periodic_again> is being called.
1025		1788
1026	=back	1789	=back
1027		1790
		1791	=head3 Examples
		1792
1028	Example: call a callback every hour, or, more precisely, whenever the	1793	Example: Call a callback every hour, or, more precisely, whenever the
1029	system clock is divisible by 3600. The callback invocation times have	1794	system time is divisible by 3600. The callback invocation times have
1030	potentially a lot of jittering, but good long-term stability.	1795	potentially a lot of jitter, but good long-term stability.
1031		1796
1032	static void	1797	static void
1033	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1798	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1034	{	1799	{
1035	... its now a full hour (UTC, or TAI or whatever your clock follows)	1800	... its now a full hour (UTC, or TAI or whatever your clock follows)
1036	}	1801	}
1037		1802
1038	struct ev_periodic hourly_tick;	1803	ev_periodic hourly_tick;
1039	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	1804	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1040	ev_periodic_start (loop, &hourly_tick);	1805	ev_periodic_start (loop, &hourly_tick);
1041		1806
1042	Example: the same as above, but use a reschedule callback to do it:	1807	Example: The same as above, but use a reschedule callback to do it:
1043		1808
1044	#include <math.h>	1809	#include <math.h>
1045		1810
1046	static ev_tstamp	1811	static ev_tstamp
1047	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	1812	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1048	{	1813	{
1049	return fmod (now, 3600.) + 3600.;	1814	return now + (3600. - fmod (now, 3600.));
1050	}	1815	}
1051		1816
1052	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	1817	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1053		1818
1054	Example: call a callback every hour, starting now:	1819	Example: Call a callback every hour, starting now:
1055		1820
1056	struct ev_periodic hourly_tick;	1821	ev_periodic hourly_tick;
1057	ev_periodic_init (&hourly_tick, clock_cb,	1822	ev_periodic_init (&hourly_tick, clock_cb,
1058	fmod (ev_now (loop), 3600.), 3600., 0);	1823	fmod (ev_now (loop), 3600.), 3600., 0);
1059	ev_periodic_start (loop, &hourly_tick);	1824	ev_periodic_start (loop, &hourly_tick);
1060		1825
1061		1826
1062	=head2 C<ev_signal> - signal me when a signal gets signalled!	1827	=head2 C<ev_signal> - signal me when a signal gets signalled!
1063		1828
1064	Signal watchers will trigger an event when the process receives a specific	1829	Signal watchers will trigger an event when the process receives a specific
1065	signal one or more times. Even though signals are very asynchronous, libev	1830	signal one or more times. Even though signals are very asynchronous, libev
1066	will try it's best to deliver signals synchronously, i.e. as part of the	1831	will try it's best to deliver signals synchronously, i.e. as part of the
1067	normal event processing, like any other event.	1832	normal event processing, like any other event.
1068		1833
		1834	If you want signals asynchronously, just use C<sigaction> as you would
		1835	do without libev and forget about sharing the signal. You can even use
		1836	C<ev_async> from a signal handler to synchronously wake up an event loop.
		1837
1069	You can configure as many watchers as you like per signal. Only when the	1838	You can configure as many watchers as you like per signal. Only when the
1070	first watcher gets started will libev actually register a signal watcher	1839	first watcher gets started will libev actually register a signal handler
1071	with the kernel (thus it coexists with your own signal handlers as long	1840	with the kernel (thus it coexists with your own signal handlers as long as
1072	as you don't register any with libev). Similarly, when the last signal	1841	you don't register any with libev for the same signal). Similarly, when
1073	watcher for a signal is stopped libev will reset the signal handler to	1842	the last signal watcher for a signal is stopped, libev will reset the
1074	SIG_DFL (regardless of what it was set to before).	1843	signal handler to SIG_DFL (regardless of what it was set to before).
		1844
		1845	If possible and supported, libev will install its handlers with
		1846	C<SA_RESTART> behaviour enabled, so system calls should not be unduly
		1847	interrupted. If you have a problem with system calls getting interrupted by
		1848	signals you can block all signals in an C<ev_check> watcher and unblock
		1849	them in an C<ev_prepare> watcher.
		1850
		1851	=head3 Watcher-Specific Functions and Data Members
1075		1852
1076	=over 4	1853	=over 4
1077		1854
1078	=item ev_signal_init (ev_signal *, callback, int signum)	1855	=item ev_signal_init (ev_signal *, callback, int signum)
1079		1856
…		…
1086		1863
1087	The signal the watcher watches out for.	1864	The signal the watcher watches out for.
1088		1865
1089	=back	1866	=back
1090		1867
		1868	=head3 Examples
		1869
		1870	Example: Try to exit cleanly on SIGINT.
		1871
		1872	static void
		1873	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		1874	{
		1875	ev_unloop (loop, EVUNLOOP_ALL);
		1876	}
		1877
		1878	ev_signal signal_watcher;
		1879	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1880	ev_signal_start (loop, &signal_watcher);
		1881
1091		1882
1092	=head2 C<ev_child> - watch out for process status changes	1883	=head2 C<ev_child> - watch out for process status changes
1093		1884
1094	Child watchers trigger when your process receives a SIGCHLD in response to	1885	Child watchers trigger when your process receives a SIGCHLD in response to
1095	some child status changes (most typically when a child of yours dies).	1886	some child status changes (most typically when a child of yours dies or
		1887	exits). It is permissible to install a child watcher I<after> the child
		1888	has been forked (which implies it might have already exited), as long
		1889	as the event loop isn't entered (or is continued from a watcher), i.e.,
		1890	forking and then immediately registering a watcher for the child is fine,
		1891	but forking and registering a watcher a few event loop iterations later is
		1892	not.
		1893
		1894	Only the default event loop is capable of handling signals, and therefore
		1895	you can only register child watchers in the default event loop.
		1896
		1897	=head3 Process Interaction
		1898
		1899	Libev grabs C<SIGCHLD> as soon as the default event loop is
		1900	initialised. This is necessary to guarantee proper behaviour even if
		1901	the first child watcher is started after the child exits. The occurrence
		1902	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		1903	synchronously as part of the event loop processing. Libev always reaps all
		1904	children, even ones not watched.
		1905
		1906	=head3 Overriding the Built-In Processing
		1907
		1908	Libev offers no special support for overriding the built-in child
		1909	processing, but if your application collides with libev's default child
		1910	handler, you can override it easily by installing your own handler for
		1911	C<SIGCHLD> after initialising the default loop, and making sure the
		1912	default loop never gets destroyed. You are encouraged, however, to use an
		1913	event-based approach to child reaping and thus use libev's support for
		1914	that, so other libev users can use C<ev_child> watchers freely.
		1915
		1916	=head3 Stopping the Child Watcher
		1917
		1918	Currently, the child watcher never gets stopped, even when the
		1919	child terminates, so normally one needs to stop the watcher in the
		1920	callback. Future versions of libev might stop the watcher automatically
		1921	when a child exit is detected.
		1922
		1923	=head3 Watcher-Specific Functions and Data Members
1096		1924
1097	=over 4	1925	=over 4
1098		1926
1099	=item ev_child_init (ev_child *, callback, int pid)	1927	=item ev_child_init (ev_child *, callback, int pid, int trace)
1100		1928
1101	=item ev_child_set (ev_child *, int pid)	1929	=item ev_child_set (ev_child *, int pid, int trace)
1102		1930
1103	Configures the watcher to wait for status changes of process C<pid> (or	1931	Configures the watcher to wait for status changes of process C<pid> (or
1104	I<any> process if C<pid> is specified as C<0>). The callback can look	1932	I<any> process if C<pid> is specified as C<0>). The callback can look
1105	at the C<rstatus> member of the C<ev_child> watcher structure to see	1933	at the C<rstatus> member of the C<ev_child> watcher structure to see
1106	the status word (use the macros from C<sys/wait.h> and see your systems	1934	the status word (use the macros from C<sys/wait.h> and see your systems
1107	C<waitpid> documentation). The C<rpid> member contains the pid of the	1935	C<waitpid> documentation). The C<rpid> member contains the pid of the
1108	process causing the status change.	1936	process causing the status change. C<trace> must be either C<0> (only
		1937	activate the watcher when the process terminates) or C<1> (additionally
		1938	activate the watcher when the process is stopped or continued).
1109		1939
1110	=item int pid [read-only]	1940	=item int pid [read-only]
1111		1941
1112	The process id this watcher watches out for, or C<0>, meaning any process id.	1942	The process id this watcher watches out for, or C<0>, meaning any process id.
1113		1943
…		…
1120	The process exit/trace status caused by C<rpid> (see your systems	1950	The process exit/trace status caused by C<rpid> (see your systems
1121	C<waitpid> and C<sys/wait.h> documentation for details).	1951	C<waitpid> and C<sys/wait.h> documentation for details).
1122		1952
1123	=back	1953	=back
1124		1954
1125	Example: try to exit cleanly on SIGINT and SIGTERM.	1955	=head3 Examples
1126		1956
		1957	Example: C<fork()> a new process and install a child handler to wait for
		1958	its completion.
		1959
		1960	ev_child cw;
		1961
1127	static void	1962	static void
1128	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	1963	child_cb (EV_P_ ev_child *w, int revents)
1129	{	1964	{
1130	ev_unloop (loop, EVUNLOOP_ALL);	1965	ev_child_stop (EV_A_ w);
		1966	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1131	}	1967	}
1132		1968
1133	struct ev_signal signal_watcher;	1969	pid_t pid = fork ();
1134	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	1970
1135	ev_signal_start (loop, &sigint_cb);	1971	if (pid < 0)
		1972	// error
		1973	else if (pid == 0)
		1974	{
		1975	// the forked child executes here
		1976	exit (1);
		1977	}
		1978	else
		1979	{
		1980	ev_child_init (&cw, child_cb, pid, 0);
		1981	ev_child_start (EV_DEFAULT_ &cw);
		1982	}
1136		1983
1137		1984
1138	=head2 C<ev_stat> - did the file attributes just change?	1985	=head2 C<ev_stat> - did the file attributes just change?
1139		1986
1140	This watches a filesystem path for attribute changes. That is, it calls	1987	This watches a file system path for attribute changes. That is, it calls
1141	C<stat> regularly (or when the OS says it changed) and sees if it changed	1988	C<stat> on that path in regular intervals (or when the OS says it changed)
1142	compared to the last time, invoking the callback if it did.	1989	and sees if it changed compared to the last time, invoking the callback if
		1990	it did.
1143		1991
1144	The path does not need to exist: changing from "path exists" to "path does	1992	The path does not need to exist: changing from "path exists" to "path does
1145	not exist" is a status change like any other. The condition "path does	1993	not exist" is a status change like any other. The condition "path does not
1146	not exist" is signified by the C<st_nlink> field being zero (which is	1994	exist" (or more correctly "path cannot be stat'ed") is signified by the
1147	otherwise always forced to be at least one) and all the other fields of	1995	C<st_nlink> field being zero (which is otherwise always forced to be at
1148	the stat buffer having unspecified contents.	1996	least one) and all the other fields of the stat buffer having unspecified
		1997	contents.
1149		1998
1150	Since there is no standard to do this, the portable implementation simply	1999	The path I<must not> end in a slash or contain special components such as
1151	calls C<stat (2)> regulalry on the path to see if it changed somehow. You	2000	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1152	can specify a recommended polling interval for this case. If you specify	2001	your working directory changes, then the behaviour is undefined.
1153	a polling interval of C<0> (highly recommended!) then a I<suitable,	2002
1154	unspecified default> value will be used (which you can expect to be around	2003	Since there is no portable change notification interface available, the
1155	five seconds, although this might change dynamically). Libev will also	2004	portable implementation simply calls C<stat(2)> regularly on the path
1156	impose a minimum interval which is currently around C<0.1>, but thats	2005	to see if it changed somehow. You can specify a recommended polling
1157	usually overkill.	2006	interval for this case. If you specify a polling interval of C<0> (highly
		2007	recommended!) then a I<suitable, unspecified default> value will be used
		2008	(which you can expect to be around five seconds, although this might
		2009	change dynamically). Libev will also impose a minimum interval which is
		2010	currently around C<0.1>, but that's usually overkill.
1158		2011
1159	This watcher type is not meant for massive numbers of stat watchers,	2012	This watcher type is not meant for massive numbers of stat watchers,
1160	as even with OS-supported change notifications, this can be	2013	as even with OS-supported change notifications, this can be
1161	resource-intensive.	2014	resource-intensive.
1162		2015
1163	At the time of this writing, no specific OS backends are implemented, but	2016	At the time of this writing, the only OS-specific interface implemented
1164	if demand increases, at least a kqueue and inotify backend will be added.	2017	is the Linux inotify interface (implementing kqueue support is left as an
		2018	exercise for the reader. Note, however, that the author sees no way of
		2019	implementing C<ev_stat> semantics with kqueue, except as a hint).
		2020
		2021	=head3 ABI Issues (Largefile Support)
		2022
		2023	Libev by default (unless the user overrides this) uses the default
		2024	compilation environment, which means that on systems with large file
		2025	support disabled by default, you get the 32 bit version of the stat
		2026	structure. When using the library from programs that change the ABI to
		2027	use 64 bit file offsets the programs will fail. In that case you have to
		2028	compile libev with the same flags to get binary compatibility. This is
		2029	obviously the case with any flags that change the ABI, but the problem is
		2030	most noticeably displayed with ev_stat and large file support.
		2031
		2032	The solution for this is to lobby your distribution maker to make large
		2033	file interfaces available by default (as e.g. FreeBSD does) and not
		2034	optional. Libev cannot simply switch on large file support because it has
		2035	to exchange stat structures with application programs compiled using the
		2036	default compilation environment.
		2037
		2038	=head3 Inotify and Kqueue
		2039
		2040	When C<inotify (7)> support has been compiled into libev and present at
		2041	runtime, it will be used to speed up change detection where possible. The
		2042	inotify descriptor will be created lazily when the first C<ev_stat>
		2043	watcher is being started.
		2044
		2045	Inotify presence does not change the semantics of C<ev_stat> watchers
		2046	except that changes might be detected earlier, and in some cases, to avoid
		2047	making regular C<stat> calls. Even in the presence of inotify support
		2048	there are many cases where libev has to resort to regular C<stat> polling,
		2049	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2050	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2051	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2052	xfs are fully working) libev usually gets away without polling.
		2053
		2054	There is no support for kqueue, as apparently it cannot be used to
		2055	implement this functionality, due to the requirement of having a file
		2056	descriptor open on the object at all times, and detecting renames, unlinks
		2057	etc. is difficult.
		2058
		2059	=head3 C<stat ()> is a synchronous operation
		2060
		2061	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2062	the process. The exception are C<ev_stat> watchers - those call C<stat
		2063	()>, which is a synchronous operation.
		2064
		2065	For local paths, this usually doesn't matter: unless the system is very
		2066	busy or the intervals between stat's are large, a stat call will be fast,
		2067	as the path data is usually in memory already (except when starting the
		2068	watcher).
		2069
		2070	For networked file systems, calling C<stat ()> can block an indefinite
		2071	time due to network issues, and even under good conditions, a stat call
		2072	often takes multiple milliseconds.
		2073
		2074	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2075	paths, although this is fully supported by libev.
		2076
		2077	=head3 The special problem of stat time resolution
		2078
		2079	The C<stat ()> system call only supports full-second resolution portably,
		2080	and even on systems where the resolution is higher, most file systems
		2081	still only support whole seconds.
		2082
		2083	That means that, if the time is the only thing that changes, you can
		2084	easily miss updates: on the first update, C<ev_stat> detects a change and
		2085	calls your callback, which does something. When there is another update
		2086	within the same second, C<ev_stat> will be unable to detect unless the
		2087	stat data does change in other ways (e.g. file size).
		2088
		2089	The solution to this is to delay acting on a change for slightly more
		2090	than a second (or till slightly after the next full second boundary), using
		2091	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2092	ev_timer_again (loop, w)>).
		2093
		2094	The C<.02> offset is added to work around small timing inconsistencies
		2095	of some operating systems (where the second counter of the current time
		2096	might be be delayed. One such system is the Linux kernel, where a call to
		2097	C<gettimeofday> might return a timestamp with a full second later than
		2098	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2099	update file times then there will be a small window where the kernel uses
		2100	the previous second to update file times but libev might already execute
		2101	the timer callback).
		2102
		2103	=head3 Watcher-Specific Functions and Data Members
1165		2104
1166	=over 4	2105	=over 4
1167		2106
1168	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)	2107	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
1169		2108
…		…
1173	C<path>. The C<interval> is a hint on how quickly a change is expected to	2112	C<path>. The C<interval> is a hint on how quickly a change is expected to
1174	be detected and should normally be specified as C<0> to let libev choose	2113	be detected and should normally be specified as C<0> to let libev choose
1175	a suitable value. The memory pointed to by C<path> must point to the same	2114	a suitable value. The memory pointed to by C<path> must point to the same
1176	path for as long as the watcher is active.	2115	path for as long as the watcher is active.
1177		2116
1178	The callback will be receive C<EV_STAT> when a change was detected,	2117	The callback will receive an C<EV_STAT> event when a change was detected,
1179	relative to the attributes at the time the watcher was started (or the	2118	relative to the attributes at the time the watcher was started (or the
1180	last change was detected).	2119	last change was detected).
1181		2120
1182	=item ev_stat_stat (ev_stat *)	2121	=item ev_stat_stat (loop, ev_stat *)
1183		2122
1184	Updates the stat buffer immediately with new values. If you change the	2123	Updates the stat buffer immediately with new values. If you change the
1185	watched path in your callback, you could call this fucntion to avoid	2124	watched path in your callback, you could call this function to avoid
1186	detecting this change (while introducing a race condition). Can also be	2125	detecting this change (while introducing a race condition if you are not
1187	useful simply to find out the new values.	2126	the only one changing the path). Can also be useful simply to find out the
		2127	new values.
1188		2128
1189	=item ev_statdata attr [read-only]	2129	=item ev_statdata attr [read-only]
1190		2130
1191	The most-recently detected attributes of the file. Although the type is of	2131	The most-recently detected attributes of the file. Although the type is
1192	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2132	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1193	suitable for your system. If the C<st_nlink> member is C<0>, then there	2133	suitable for your system, but you can only rely on the POSIX-standardised
		2134	members to be present. If the C<st_nlink> member is C<0>, then there was
1194	was some error while C<stat>ing the file.	2135	some error while C<stat>ing the file.
1195		2136
1196	=item ev_statdata prev [read-only]	2137	=item ev_statdata prev [read-only]
1197		2138
1198	The previous attributes of the file. The callback gets invoked whenever	2139	The previous attributes of the file. The callback gets invoked whenever
1199	C<prev> != C<attr>.	2140	C<prev> != C<attr>, or, more precisely, one or more of these members
		2141	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2142	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1200		2143
1201	=item ev_tstamp interval [read-only]	2144	=item ev_tstamp interval [read-only]
1202		2145
1203	The specified interval.	2146	The specified interval.
1204		2147
1205	=item const char *path [read-only]	2148	=item const char *path [read-only]
1206		2149
1207	The filesystem path that is being watched.	2150	The file system path that is being watched.
1208		2151
1209	=back	2152	=back
1210		2153
		2154	=head3 Examples
		2155
1211	Example: Watch C</etc/passwd> for attribute changes.	2156	Example: Watch C</etc/passwd> for attribute changes.
1212		2157
1213	static void	2158	static void
1214	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2159	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1215	{	2160	{
1216	/* /etc/passwd changed in some way */	2161	/* /etc/passwd changed in some way */
1217	if (w->attr.st_nlink)	2162	if (w->attr.st_nlink)
1218	{	2163	{
1219	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2164	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1220	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2165	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1221	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2166	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1222	}	2167	}
1223	else	2168	else
1224	/* you shalt not abuse printf for puts */	2169	/* you shalt not abuse printf for puts */
1225	puts ("wow, /etc/passwd is not there, expect problems. "	2170	puts ("wow, /etc/passwd is not there, expect problems. "
1226	"if this is windows, they already arrived\n");	2171	"if this is windows, they already arrived\n");
1227	}	2172	}
1228		2173
1229	...	2174	...
1230	ev_stat passwd;	2175	ev_stat passwd;
1231		2176
1232	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	2177	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1233	ev_stat_start (loop, &passwd);	2178	ev_stat_start (loop, &passwd);
		2179
		2180	Example: Like above, but additionally use a one-second delay so we do not
		2181	miss updates (however, frequent updates will delay processing, too, so
		2182	one might do the work both on C<ev_stat> callback invocation I<and> on
		2183	C<ev_timer> callback invocation).
		2184
		2185	static ev_stat passwd;
		2186	static ev_timer timer;
		2187
		2188	static void
		2189	timer_cb (EV_P_ ev_timer *w, int revents)
		2190	{
		2191	ev_timer_stop (EV_A_ w);
		2192
		2193	/* now it's one second after the most recent passwd change */
		2194	}
		2195
		2196	static void
		2197	stat_cb (EV_P_ ev_stat *w, int revents)
		2198	{
		2199	/* reset the one-second timer */
		2200	ev_timer_again (EV_A_ &timer);
		2201	}
		2202
		2203	...
		2204	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2205	ev_stat_start (loop, &passwd);
		2206	ev_timer_init (&timer, timer_cb, 0., 1.02);
1234		2207
1235		2208
1236	=head2 C<ev_idle> - when you've got nothing better to do...	2209	=head2 C<ev_idle> - when you've got nothing better to do...
1237		2210
1238	Idle watchers trigger events when there are no other events are pending	2211	Idle watchers trigger events when no other events of the same or higher
1239	(prepare, check and other idle watchers do not count). That is, as long	2212	priority are pending (prepare, check and other idle watchers do not count
1240	as your process is busy handling sockets or timeouts (or even signals,	2213	as receiving "events").
1241	imagine) it will not be triggered. But when your process is idle all idle	2214
1242	watchers are being called again and again, once per event loop iteration -	2215	That is, as long as your process is busy handling sockets or timeouts
		2216	(or even signals, imagine) of the same or higher priority it will not be
		2217	triggered. But when your process is idle (or only lower-priority watchers
		2218	are pending), the idle watchers are being called once per event loop
1243	until stopped, that is, or your process receives more events and becomes	2219	iteration - until stopped, that is, or your process receives more events
1244	busy.	2220	and becomes busy again with higher priority stuff.
1245		2221
1246	The most noteworthy effect is that as long as any idle watchers are	2222	The most noteworthy effect is that as long as any idle watchers are
1247	active, the process will not block when waiting for new events.	2223	active, the process will not block when waiting for new events.
1248		2224
1249	Apart from keeping your process non-blocking (which is a useful	2225	Apart from keeping your process non-blocking (which is a useful
1250	effect on its own sometimes), idle watchers are a good place to do	2226	effect on its own sometimes), idle watchers are a good place to do
1251	"pseudo-background processing", or delay processing stuff to after the	2227	"pseudo-background processing", or delay processing stuff to after the
1252	event loop has handled all outstanding events.	2228	event loop has handled all outstanding events.
1253		2229
		2230	=head3 Watcher-Specific Functions and Data Members
		2231
1254	=over 4	2232	=over 4
1255		2233
1256	=item ev_idle_init (ev_signal *, callback)	2234	=item ev_idle_init (ev_idle *, callback)
1257		2235
1258	Initialises and configures the idle watcher - it has no parameters of any	2236	Initialises and configures the idle watcher - it has no parameters of any
1259	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2237	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1260	believe me.	2238	believe me.
1261		2239
1262	=back	2240	=back
1263		2241
		2242	=head3 Examples
		2243
1264	Example: dynamically allocate an C<ev_idle>, start it, and in the	2244	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1265	callback, free it. Alos, use no error checking, as usual.	2245	callback, free it. Also, use no error checking, as usual.
1266		2246
1267	static void	2247	static void
1268	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2248	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1269	{	2249	{
1270	free (w);	2250	free (w);
1271	// now do something you wanted to do when the program has	2251	// now do something you wanted to do when the program has
1272	// no longer asnything immediate to do.	2252	// no longer anything immediate to do.
1273	}	2253	}
1274		2254
1275	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2255	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1276	ev_idle_init (idle_watcher, idle_cb);	2256	ev_idle_init (idle_watcher, idle_cb);
1277	ev_idle_start (loop, idle_cb);	2257	ev_idle_start (loop, idle_cb);
1278		2258
1279		2259
1280	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2260	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1281		2261
1282	Prepare and check watchers are usually (but not always) used in tandem:	2262	Prepare and check watchers are usually (but not always) used in pairs:
1283	prepare watchers get invoked before the process blocks and check watchers	2263	prepare watchers get invoked before the process blocks and check watchers
1284	afterwards.	2264	afterwards.
1285		2265
1286	You I<must not> call C<ev_loop> or similar functions that enter	2266	You I<must not> call C<ev_loop> or similar functions that enter
1287	the current event loop from either C<ev_prepare> or C<ev_check>	2267	the current event loop from either C<ev_prepare> or C<ev_check>
…		…
1290	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2270	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1291	C<ev_check> so if you have one watcher of each kind they will always be	2271	C<ev_check> so if you have one watcher of each kind they will always be
1292	called in pairs bracketing the blocking call.	2272	called in pairs bracketing the blocking call.
1293		2273
1294	Their main purpose is to integrate other event mechanisms into libev and	2274	Their main purpose is to integrate other event mechanisms into libev and
1295	their use is somewhat advanced. This could be used, for example, to track	2275	their use is somewhat advanced. They could be used, for example, to track
1296	variable changes, implement your own watchers, integrate net-snmp or a	2276	variable changes, implement your own watchers, integrate net-snmp or a
1297	coroutine library and lots more. They are also occasionally useful if	2277	coroutine library and lots more. They are also occasionally useful if
1298	you cache some data and want to flush it before blocking (for example,	2278	you cache some data and want to flush it before blocking (for example,
1299	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2279	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1300	watcher).	2280	watcher).
1301		2281
1302	This is done by examining in each prepare call which file descriptors need	2282	This is done by examining in each prepare call which file descriptors
1303	to be watched by the other library, registering C<ev_io> watchers for	2283	need to be watched by the other library, registering C<ev_io> watchers
1304	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2284	for them and starting an C<ev_timer> watcher for any timeouts (many
1305	provide just this functionality). Then, in the check watcher you check for	2285	libraries provide exactly this functionality). Then, in the check watcher,
1306	any events that occured (by checking the pending status of all watchers	2286	you check for any events that occurred (by checking the pending status
1307	and stopping them) and call back into the library. The I/O and timer	2287	of all watchers and stopping them) and call back into the library. The
1308	callbacks will never actually be called (but must be valid nevertheless,	2288	I/O and timer callbacks will never actually be called (but must be valid
1309	because you never know, you know?).	2289	nevertheless, because you never know, you know?).
1310		2290
1311	As another example, the Perl Coro module uses these hooks to integrate	2291	As another example, the Perl Coro module uses these hooks to integrate
1312	coroutines into libev programs, by yielding to other active coroutines	2292	coroutines into libev programs, by yielding to other active coroutines
1313	during each prepare and only letting the process block if no coroutines	2293	during each prepare and only letting the process block if no coroutines
1314	are ready to run (it's actually more complicated: it only runs coroutines	2294	are ready to run (it's actually more complicated: it only runs coroutines
1315	with priority higher than or equal to the event loop and one coroutine	2295	with priority higher than or equal to the event loop and one coroutine
1316	of lower priority, but only once, using idle watchers to keep the event	2296	of lower priority, but only once, using idle watchers to keep the event
1317	loop from blocking if lower-priority coroutines are active, thus mapping	2297	loop from blocking if lower-priority coroutines are active, thus mapping
1318	low-priority coroutines to idle/background tasks).	2298	low-priority coroutines to idle/background tasks).
1319		2299
		2300	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		2301	priority, to ensure that they are being run before any other watchers
		2302	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2303
		2304	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2305	activate ("feed") events into libev. While libev fully supports this, they
		2306	might get executed before other C<ev_check> watchers did their job. As
		2307	C<ev_check> watchers are often used to embed other (non-libev) event
		2308	loops those other event loops might be in an unusable state until their
		2309	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2310	others).
		2311
		2312	=head3 Watcher-Specific Functions and Data Members
		2313
1320	=over 4	2314	=over 4
1321		2315
1322	=item ev_prepare_init (ev_prepare *, callback)	2316	=item ev_prepare_init (ev_prepare *, callback)
1323		2317
1324	=item ev_check_init (ev_check *, callback)	2318	=item ev_check_init (ev_check *, callback)
1325		2319
1326	Initialises and configures the prepare or check watcher - they have no	2320	Initialises and configures the prepare or check watcher - they have no
1327	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2321	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1328	macros, but using them is utterly, utterly and completely pointless.	2322	macros, but using them is utterly, utterly, utterly and completely
		2323	pointless.
1329		2324
1330	=back	2325	=back
1331		2326
1332	Example: To include a library such as adns, you would add IO watchers	2327	=head3 Examples
1333	and a timeout watcher in a prepare handler, as required by libadns, and	2328
		2329	There are a number of principal ways to embed other event loops or modules
		2330	into libev. Here are some ideas on how to include libadns into libev
		2331	(there is a Perl module named C<EV::ADNS> that does this, which you could
		2332	use as a working example. Another Perl module named C<EV::Glib> embeds a
		2333	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		2334	Glib event loop).
		2335
		2336	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1334	in a check watcher, destroy them and call into libadns. What follows is	2337	and in a check watcher, destroy them and call into libadns. What follows
1335	pseudo-code only of course:	2338	is pseudo-code only of course. This requires you to either use a low
		2339	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		2340	the callbacks for the IO/timeout watchers might not have been called yet.
1336		2341
1337	static ev_io iow [nfd];	2342	static ev_io iow [nfd];
1338	static ev_timer tw;	2343	static ev_timer tw;
1339		2344
1340	static void	2345	static void
1341	io_cb (ev_loop *loop, ev_io *w, int revents)	2346	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1342	{	2347	{
1343	// set the relevant poll flags
1344	// could also call adns_processreadable etc. here
1345	struct pollfd *fd = (struct pollfd *)w->data;
1346	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1347	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1348	}	2348	}
1349		2349
1350	// create io watchers for each fd and a timer before blocking	2350	// create io watchers for each fd and a timer before blocking
1351	static void	2351	static void
1352	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2352	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1353	{	2353	{
1354	int timeout = 3600000;truct pollfd fds [nfd];	2354	int timeout = 3600000;
		2355	struct pollfd fds [nfd];
1355	// actual code will need to loop here and realloc etc.	2356	// actual code will need to loop here and realloc etc.
1356	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2357	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1357		2358
1358	/* the callback is illegal, but won't be called as we stop during check */	2359	/* the callback is illegal, but won't be called as we stop during check */
1359	ev_timer_init (&tw, 0, timeout * 1e-3);	2360	ev_timer_init (&tw, 0, timeout * 1e-3);
1360	ev_timer_start (loop, &tw);	2361	ev_timer_start (loop, &tw);
1361		2362
1362	// create on ev_io per pollfd	2363	// create one ev_io per pollfd
1363	for (int i = 0; i < nfd; ++i)	2364	for (int i = 0; i < nfd; ++i)
1364	{	2365	{
1365	ev_io_init (iow + i, io_cb, fds [i].fd,	2366	ev_io_init (iow + i, io_cb, fds [i].fd,
1366	((fds [i].events & POLLIN ? EV_READ : 0)	2367	((fds [i].events & POLLIN ? EV_READ : 0)
1367	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2368	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1368		2369
1369	fds [i].revents = 0;	2370	fds [i].revents = 0;
1370	iow [i].data = fds + i;
1371	ev_io_start (loop, iow + i);	2371	ev_io_start (loop, iow + i);
1372	}	2372	}
1373	}	2373	}
1374		2374
1375	// stop all watchers after blocking	2375	// stop all watchers after blocking
1376	static void	2376	static void
1377	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2377	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1378	{	2378	{
1379	ev_timer_stop (loop, &tw);	2379	ev_timer_stop (loop, &tw);
1380		2380
1381	for (int i = 0; i < nfd; ++i)	2381	for (int i = 0; i < nfd; ++i)
		2382	{
		2383	// set the relevant poll flags
		2384	// could also call adns_processreadable etc. here
		2385	struct pollfd *fd = fds + i;
		2386	int revents = ev_clear_pending (iow + i);
		2387	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2388	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2389
		2390	// now stop the watcher
1382	ev_io_stop (loop, iow + i);	2391	ev_io_stop (loop, iow + i);
		2392	}
1383		2393
1384	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2394	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1385	}	2395	}
		2396
		2397	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2398	in the prepare watcher and would dispose of the check watcher.
		2399
		2400	Method 3: If the module to be embedded supports explicit event
		2401	notification (libadns does), you can also make use of the actual watcher
		2402	callbacks, and only destroy/create the watchers in the prepare watcher.
		2403
		2404	static void
		2405	timer_cb (EV_P_ ev_timer *w, int revents)
		2406	{
		2407	adns_state ads = (adns_state)w->data;
		2408	update_now (EV_A);
		2409
		2410	adns_processtimeouts (ads, &tv_now);
		2411	}
		2412
		2413	static void
		2414	io_cb (EV_P_ ev_io *w, int revents)
		2415	{
		2416	adns_state ads = (adns_state)w->data;
		2417	update_now (EV_A);
		2418
		2419	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2420	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2421	}
		2422
		2423	// do not ever call adns_afterpoll
		2424
		2425	Method 4: Do not use a prepare or check watcher because the module you
		2426	want to embed is not flexible enough to support it. Instead, you can
		2427	override their poll function. The drawback with this solution is that the
		2428	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		2429	this approach, effectively embedding EV as a client into the horrible
		2430	libglib event loop.
		2431
		2432	static gint
		2433	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2434	{
		2435	int got_events = 0;
		2436
		2437	for (n = 0; n < nfds; ++n)
		2438	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2439
		2440	if (timeout >= 0)
		2441	// create/start timer
		2442
		2443	// poll
		2444	ev_loop (EV_A_ 0);
		2445
		2446	// stop timer again
		2447	if (timeout >= 0)
		2448	ev_timer_stop (EV_A_ &to);
		2449
		2450	// stop io watchers again - their callbacks should have set
		2451	for (n = 0; n < nfds; ++n)
		2452	ev_io_stop (EV_A_ iow [n]);
		2453
		2454	return got_events;
		2455	}
1386		2456
1387		2457
1388	=head2 C<ev_embed> - when one backend isn't enough...	2458	=head2 C<ev_embed> - when one backend isn't enough...
1389		2459
1390	This is a rather advanced watcher type that lets you embed one event loop	2460	This is a rather advanced watcher type that lets you embed one event loop
…		…
1396	prioritise I/O.	2466	prioritise I/O.
1397		2467
1398	As an example for a bug workaround, the kqueue backend might only support	2468	As an example for a bug workaround, the kqueue backend might only support
1399	sockets on some platform, so it is unusable as generic backend, but you	2469	sockets on some platform, so it is unusable as generic backend, but you
1400	still want to make use of it because you have many sockets and it scales	2470	still want to make use of it because you have many sockets and it scales
1401	so nicely. In this case, you would create a kqueue-based loop and embed it	2471	so nicely. In this case, you would create a kqueue-based loop and embed
1402	into your default loop (which might use e.g. poll). Overall operation will	2472	it into your default loop (which might use e.g. poll). Overall operation
1403	be a bit slower because first libev has to poll and then call kevent, but	2473	will be a bit slower because first libev has to call C<poll> and then
1404	at least you can use both at what they are best.	2474	C<kevent>, but at least you can use both mechanisms for what they are
		2475	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1405		2476
1406	As for prioritising I/O: rarely you have the case where some fds have	2477	As for prioritising I/O: under rare circumstances you have the case where
1407	to be watched and handled very quickly (with low latency), and even	2478	some fds have to be watched and handled very quickly (with low latency),
1408	priorities and idle watchers might have too much overhead. In this case	2479	and even priorities and idle watchers might have too much overhead. In
1409	you would put all the high priority stuff in one loop and all the rest in	2480	this case you would put all the high priority stuff in one loop and all
1410	a second one, and embed the second one in the first.	2481	the rest in a second one, and embed the second one in the first.
1411		2482
1412	As long as the watcher is active, the callback will be invoked every time	2483	As long as the watcher is active, the callback will be invoked every
1413	there might be events pending in the embedded loop. The callback must then	2484	time there might be events pending in the embedded loop. The callback
1414	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2485	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1415	their callbacks (you could also start an idle watcher to give the embedded	2486	sweep and invoke their callbacks (the callback doesn't need to invoke the
1416	loop strictly lower priority for example). You can also set the callback	2487	C<ev_embed_sweep> function directly, it could also start an idle watcher
1417	to C<0>, in which case the embed watcher will automatically execute the	2488	to give the embedded loop strictly lower priority for example).
1418	embedded loop sweep.
1419		2489
1420	As long as the watcher is started it will automatically handle events. The	2490	You can also set the callback to C<0>, in which case the embed watcher
1421	callback will be invoked whenever some events have been handled. You can	2491	will automatically execute the embedded loop sweep whenever necessary.
1422	set the callback to C<0> to avoid having to specify one if you are not
1423	interested in that.
1424		2492
1425	Also, there have not currently been made special provisions for forking:	2493	Fork detection will be handled transparently while the C<ev_embed> watcher
1426	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2494	is active, i.e., the embedded loop will automatically be forked when the
1427	but you will also have to stop and restart any C<ev_embed> watchers	2495	embedding loop forks. In other cases, the user is responsible for calling
1428	yourself.	2496	C<ev_loop_fork> on the embedded loop.
1429		2497
1430	Unfortunately, not all backends are embeddable, only the ones returned by	2498	Unfortunately, not all backends are embeddable: only the ones returned by
1431	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2499	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1432	portable one.	2500	portable one.
1433		2501
1434	So when you want to use this feature you will always have to be prepared	2502	So when you want to use this feature you will always have to be prepared
1435	that you cannot get an embeddable loop. The recommended way to get around	2503	that you cannot get an embeddable loop. The recommended way to get around
1436	this is to have a separate variables for your embeddable loop, try to	2504	this is to have a separate variables for your embeddable loop, try to
1437	create it, and if that fails, use the normal loop for everything:	2505	create it, and if that fails, use the normal loop for everything.
1438		2506
1439	struct ev_loop *loop_hi = ev_default_init (0);	2507	=head3 C<ev_embed> and fork
1440	struct ev_loop *loop_lo = 0;
1441	struct ev_embed embed;
1442
1443	// see if there is a chance of getting one that works
1444	// (remember that a flags value of 0 means autodetection)
1445	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1446	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1447	: 0;
1448		2508
1449	// if we got one, then embed it, otherwise default to loop_hi	2509	While the C<ev_embed> watcher is running, forks in the embedding loop will
1450	if (loop_lo)	2510	automatically be applied to the embedded loop as well, so no special
1451	{	2511	fork handling is required in that case. When the watcher is not running,
1452	ev_embed_init (&embed, 0, loop_lo);	2512	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1453	ev_embed_start (loop_hi, &embed);	2513	as applicable.
1454	}	2514
1455	else	2515	=head3 Watcher-Specific Functions and Data Members
1456	loop_lo = loop_hi;
1457		2516
1458	=over 4	2517	=over 4
1459		2518
1460	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	2519	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
1461		2520
…		…
1463		2522
1464	Configures the watcher to embed the given loop, which must be	2523	Configures the watcher to embed the given loop, which must be
1465	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	2524	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1466	invoked automatically, otherwise it is the responsibility of the callback	2525	invoked automatically, otherwise it is the responsibility of the callback
1467	to invoke it (it will continue to be called until the sweep has been done,	2526	to invoke it (it will continue to be called until the sweep has been done,
1468	if you do not want thta, you need to temporarily stop the embed watcher).	2527	if you do not want that, you need to temporarily stop the embed watcher).
1469		2528
1470	=item ev_embed_sweep (loop, ev_embed *)	2529	=item ev_embed_sweep (loop, ev_embed *)
1471		2530
1472	Make a single, non-blocking sweep over the embedded loop. This works	2531	Make a single, non-blocking sweep over the embedded loop. This works
1473	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	2532	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
1474	apropriate way for embedded loops.	2533	appropriate way for embedded loops.
1475		2534
1476	=item struct ev_loop *loop [read-only]	2535	=item struct ev_loop *other [read-only]
1477		2536
1478	The embedded event loop.	2537	The embedded event loop.
1479		2538
1480	=back	2539	=back
		2540
		2541	=head3 Examples
		2542
		2543	Example: Try to get an embeddable event loop and embed it into the default
		2544	event loop. If that is not possible, use the default loop. The default
		2545	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2546	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2547	used).
		2548
		2549	struct ev_loop *loop_hi = ev_default_init (0);
		2550	struct ev_loop *loop_lo = 0;
		2551	ev_embed embed;
		2552
		2553	// see if there is a chance of getting one that works
		2554	// (remember that a flags value of 0 means autodetection)
		2555	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2556	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2557	: 0;
		2558
		2559	// if we got one, then embed it, otherwise default to loop_hi
		2560	if (loop_lo)
		2561	{
		2562	ev_embed_init (&embed, 0, loop_lo);
		2563	ev_embed_start (loop_hi, &embed);
		2564	}
		2565	else
		2566	loop_lo = loop_hi;
		2567
		2568	Example: Check if kqueue is available but not recommended and create
		2569	a kqueue backend for use with sockets (which usually work with any
		2570	kqueue implementation). Store the kqueue/socket-only event loop in
		2571	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2572
		2573	struct ev_loop *loop = ev_default_init (0);
		2574	struct ev_loop *loop_socket = 0;
		2575	ev_embed embed;
		2576
		2577	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2578	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2579	{
		2580	ev_embed_init (&embed, 0, loop_socket);
		2581	ev_embed_start (loop, &embed);
		2582	}
		2583
		2584	if (!loop_socket)
		2585	loop_socket = loop;
		2586
		2587	// now use loop_socket for all sockets, and loop for everything else
1481		2588
1482		2589
1483	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	2590	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
1484		2591
1485	Fork watchers are called when a C<fork ()> was detected (usually because	2592	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
1488	event loop blocks next and before C<ev_check> watchers are being called,	2595	event loop blocks next and before C<ev_check> watchers are being called,
1489	and only in the child after the fork. If whoever good citizen calling	2596	and only in the child after the fork. If whoever good citizen calling
1490	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2597	C<ev_default_fork> cheats and calls it in the wrong process, the fork
1491	handlers will be invoked, too, of course.	2598	handlers will be invoked, too, of course.
1492		2599
		2600	=head3 Watcher-Specific Functions and Data Members
		2601
1493	=over 4	2602	=over 4
1494		2603
1495	=item ev_fork_init (ev_signal *, callback)	2604	=item ev_fork_init (ev_signal *, callback)
1496		2605
1497	Initialises and configures the fork watcher - it has no parameters of any	2606	Initialises and configures the fork watcher - it has no parameters of any
…		…
1499	believe me.	2608	believe me.
1500		2609
1501	=back	2610	=back
1502		2611
1503		2612
		2613	=head2 C<ev_async> - how to wake up another event loop
		2614
		2615	In general, you cannot use an C<ev_loop> from multiple threads or other
		2616	asynchronous sources such as signal handlers (as opposed to multiple event
		2617	loops - those are of course safe to use in different threads).
		2618
		2619	Sometimes, however, you need to wake up another event loop you do not
		2620	control, for example because it belongs to another thread. This is what
		2621	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2622	can signal it by calling C<ev_async_send>, which is thread- and signal
		2623	safe.
		2624
		2625	This functionality is very similar to C<ev_signal> watchers, as signals,
		2626	too, are asynchronous in nature, and signals, too, will be compressed
		2627	(i.e. the number of callback invocations may be less than the number of
		2628	C<ev_async_sent> calls).
		2629
		2630	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2631	just the default loop.
		2632
		2633	=head3 Queueing
		2634
		2635	C<ev_async> does not support queueing of data in any way. The reason
		2636	is that the author does not know of a simple (or any) algorithm for a
		2637	multiple-writer-single-reader queue that works in all cases and doesn't
		2638	need elaborate support such as pthreads.
		2639
		2640	That means that if you want to queue data, you have to provide your own
		2641	queue. But at least I can tell you how to implement locking around your
		2642	queue:
		2643
		2644	=over 4
		2645
		2646	=item queueing from a signal handler context
		2647
		2648	To implement race-free queueing, you simply add to the queue in the signal
		2649	handler but you block the signal handler in the watcher callback. Here is
		2650	an example that does that for some fictitious SIGUSR1 handler:
		2651
		2652	static ev_async mysig;
		2653
		2654	static void
		2655	sigusr1_handler (void)
		2656	{
		2657	sometype data;
		2658
		2659	// no locking etc.
		2660	queue_put (data);
		2661	ev_async_send (EV_DEFAULT_ &mysig);
		2662	}
		2663
		2664	static void
		2665	mysig_cb (EV_P_ ev_async *w, int revents)
		2666	{
		2667	sometype data;
		2668	sigset_t block, prev;
		2669
		2670	sigemptyset (&block);
		2671	sigaddset (&block, SIGUSR1);
		2672	sigprocmask (SIG_BLOCK, &block, &prev);
		2673
		2674	while (queue_get (&data))
		2675	process (data);
		2676
		2677	if (sigismember (&prev, SIGUSR1)
		2678	sigprocmask (SIG_UNBLOCK, &block, 0);
		2679	}
		2680
		2681	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2682	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2683	either...).
		2684
		2685	=item queueing from a thread context
		2686
		2687	The strategy for threads is different, as you cannot (easily) block
		2688	threads but you can easily preempt them, so to queue safely you need to
		2689	employ a traditional mutex lock, such as in this pthread example:
		2690
		2691	static ev_async mysig;
		2692	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2693
		2694	static void
		2695	otherthread (void)
		2696	{
		2697	// only need to lock the actual queueing operation
		2698	pthread_mutex_lock (&mymutex);
		2699	queue_put (data);
		2700	pthread_mutex_unlock (&mymutex);
		2701
		2702	ev_async_send (EV_DEFAULT_ &mysig);
		2703	}
		2704
		2705	static void
		2706	mysig_cb (EV_P_ ev_async *w, int revents)
		2707	{
		2708	pthread_mutex_lock (&mymutex);
		2709
		2710	while (queue_get (&data))
		2711	process (data);
		2712
		2713	pthread_mutex_unlock (&mymutex);
		2714	}
		2715
		2716	=back
		2717
		2718
		2719	=head3 Watcher-Specific Functions and Data Members
		2720
		2721	=over 4
		2722
		2723	=item ev_async_init (ev_async *, callback)
		2724
		2725	Initialises and configures the async watcher - it has no parameters of any
		2726	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		2727	trust me.
		2728
		2729	=item ev_async_send (loop, ev_async *)
		2730
		2731	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2732	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2733	C<ev_feed_event>, this call is safe to do from other threads, signal or
		2734	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		2735	section below on what exactly this means).
		2736
		2737	Note that, as with other watchers in libev, multiple events might get
		2738	compressed into a single callback invocation (another way to look at this
		2739	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		2740	reset when the event loop detects that).
		2741
		2742	This call incurs the overhead of a system call only once per event loop
		2743	iteration, so while the overhead might be noticeable, it doesn't apply to
		2744	repeated calls to C<ev_async_send> for the same event loop.
		2745
		2746	=item bool = ev_async_pending (ev_async *)
		2747
		2748	Returns a non-zero value when C<ev_async_send> has been called on the
		2749	watcher but the event has not yet been processed (or even noted) by the
		2750	event loop.
		2751
		2752	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2753	the loop iterates next and checks for the watcher to have become active,
		2754	it will reset the flag again. C<ev_async_pending> can be used to very
		2755	quickly check whether invoking the loop might be a good idea.
		2756
		2757	Not that this does I<not> check whether the watcher itself is pending,
		2758	only whether it has been requested to make this watcher pending: there
		2759	is a time window between the event loop checking and resetting the async
		2760	notification, and the callback being invoked.
		2761
		2762	=back
		2763
		2764
1504	=head1 OTHER FUNCTIONS	2765	=head1 OTHER FUNCTIONS
1505		2766
1506	There are some other functions of possible interest. Described. Here. Now.	2767	There are some other functions of possible interest. Described. Here. Now.
1507		2768
1508	=over 4	2769	=over 4
1509		2770
1510	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	2771	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1511		2772
1512	This function combines a simple timer and an I/O watcher, calls your	2773	This function combines a simple timer and an I/O watcher, calls your
1513	callback on whichever event happens first and automatically stop both	2774	callback on whichever event happens first and automatically stops both
1514	watchers. This is useful if you want to wait for a single event on an fd	2775	watchers. This is useful if you want to wait for a single event on an fd
1515	or timeout without having to allocate/configure/start/stop/free one or	2776	or timeout without having to allocate/configure/start/stop/free one or
1516	more watchers yourself.	2777	more watchers yourself.
1517		2778
1518	If C<fd> is less than 0, then no I/O watcher will be started and events	2779	If C<fd> is less than 0, then no I/O watcher will be started and the
1519	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	2780	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1520	C<events> set will be craeted and started.	2781	the given C<fd> and C<events> set will be created and started.
1521		2782
1522	If C<timeout> is less than 0, then no timeout watcher will be	2783	If C<timeout> is less than 0, then no timeout watcher will be
1523	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	2784	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1524	repeat = 0) will be started. While C<0> is a valid timeout, it is of	2785	repeat = 0) will be started. C<0> is a valid timeout.
1525	dubious value.
1526		2786
1527	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	2787	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
1528	passed an C<revents> set like normal event callbacks (a combination of	2788	passed an C<revents> set like normal event callbacks (a combination of
1529	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	2789	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
1530	value passed to C<ev_once>:	2790	value passed to C<ev_once>. Note that it is possible to receive I<both>
		2791	a timeout and an io event at the same time - you probably should give io
		2792	events precedence.
1531		2793
		2794	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		2795
1532	static void stdin_ready (int revents, void *arg)	2796	static void stdin_ready (int revents, void *arg)
1533	{	2797	{
1534	if (revents & EV_TIMEOUT)
1535	/* doh, nothing entered */;
1536	else if (revents & EV_READ)	2798	if (revents & EV_READ)
1537	/* stdin might have data for us, joy! */;	2799	/* stdin might have data for us, joy! */;
		2800	else if (revents & EV_TIMEOUT)
		2801	/* doh, nothing entered */;
1538	}	2802	}
1539		2803
1540	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2804	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1541		2805
1542	=item ev_feed_event (ev_loop *, watcher *, int revents)	2806	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
1543		2807
1544	Feeds the given event set into the event loop, as if the specified event	2808	Feeds the given event set into the event loop, as if the specified event
1545	had happened for the specified watcher (which must be a pointer to an	2809	had happened for the specified watcher (which must be a pointer to an
1546	initialised but not necessarily started event watcher).	2810	initialised but not necessarily started event watcher).
1547		2811
1548	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	2812	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
1549		2813
1550	Feed an event on the given fd, as if a file descriptor backend detected	2814	Feed an event on the given fd, as if a file descriptor backend detected
1551	the given events it.	2815	the given events it.
1552		2816
1553	=item ev_feed_signal_event (ev_loop *loop, int signum)	2817	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
1554		2818
1555	Feed an event as if the given signal occured (C<loop> must be the default	2819	Feed an event as if the given signal occurred (C<loop> must be the default
1556	loop!).	2820	loop!).
1557		2821
1558	=back	2822	=back
1559		2823
1560		2824
…		…
1576		2840
1577	=item * Priorities are not currently supported. Initialising priorities	2841	=item * Priorities are not currently supported. Initialising priorities
1578	will fail and all watchers will have the same priority, even though there	2842	will fail and all watchers will have the same priority, even though there
1579	is an ev_pri field.	2843	is an ev_pri field.
1580		2844
		2845	=item * In libevent, the last base created gets the signals, in libev, the
		2846	first base created (== the default loop) gets the signals.
		2847
1581	=item * Other members are not supported.	2848	=item * Other members are not supported.
1582		2849
1583	=item * The libev emulation is I<not> ABI compatible to libevent, you need	2850	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1584	to use the libev header file and library.	2851	to use the libev header file and library.
1585		2852
1586	=back	2853	=back
1587		2854
1588	=head1 C++ SUPPORT	2855	=head1 C++ SUPPORT
1589		2856
1590	Libev comes with some simplistic wrapper classes for C++ that mainly allow	2857	Libev comes with some simplistic wrapper classes for C++ that mainly allow
1591	you to use some convinience methods to start/stop watchers and also change	2858	you to use some convenience methods to start/stop watchers and also change
1592	the callback model to a model using method callbacks on objects.	2859	the callback model to a model using method callbacks on objects.
1593		2860
1594	To use it,	2861	To use it,
1595		2862
1596	#include <ev++.h>	2863	#include <ev++.h>
1597		2864
1598	(it is not installed by default). This automatically includes F<ev.h>	2865	This automatically includes F<ev.h> and puts all of its definitions (many
1599	and puts all of its definitions (many of them macros) into the global	2866	of them macros) into the global namespace. All C++ specific things are
1600	namespace. All C++ specific things are put into the C<ev> namespace.	2867	put into the C<ev> namespace. It should support all the same embedding
		2868	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
1601		2869
1602	It should support all the same embedding options as F<ev.h>, most notably	2870	Care has been taken to keep the overhead low. The only data member the C++
1603	C<EV_MULTIPLICITY>.	2871	classes add (compared to plain C-style watchers) is the event loop pointer
		2872	that the watcher is associated with (or no additional members at all if
		2873	you disable C<EV_MULTIPLICITY> when embedding libev).
		2874
		2875	Currently, functions, and static and non-static member functions can be
		2876	used as callbacks. Other types should be easy to add as long as they only
		2877	need one additional pointer for context. If you need support for other
		2878	types of functors please contact the author (preferably after implementing
		2879	it).
1604		2880
1605	Here is a list of things available in the C<ev> namespace:	2881	Here is a list of things available in the C<ev> namespace:
1606		2882
1607	=over 4	2883	=over 4
1608		2884
…		…
1624		2900
1625	All of those classes have these methods:	2901	All of those classes have these methods:
1626		2902
1627	=over 4	2903	=over 4
1628		2904
1629	=item ev::TYPE::TYPE (object *, object::method *)	2905	=item ev::TYPE::TYPE ()
1630		2906
1631	=item ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)	2907	=item ev::TYPE::TYPE (struct ev_loop *)
1632		2908
1633	=item ev::TYPE::~TYPE	2909	=item ev::TYPE::~TYPE
1634		2910
1635	The constructor takes a pointer to an object and a method pointer to	2911	The constructor (optionally) takes an event loop to associate the watcher
1636	the event handler callback to call in this class. The constructor calls	2912	with. If it is omitted, it will use C<EV_DEFAULT>.
1637	C<ev_init> for you, which means you have to call the C<set> method	2913
1638	before starting it. If you do not specify a loop then the constructor	2914	The constructor calls C<ev_init> for you, which means you have to call the
1639	automatically associates the default loop with this watcher.	2915	C<set> method before starting it.
		2916
		2917	It will not set a callback, however: You have to call the templated C<set>
		2918	method to set a callback before you can start the watcher.
		2919
		2920	(The reason why you have to use a method is a limitation in C++ which does
		2921	not allow explicit template arguments for constructors).
1640		2922
1641	The destructor automatically stops the watcher if it is active.	2923	The destructor automatically stops the watcher if it is active.
		2924
		2925	=item w->set<class, &class::method> (object *)
		2926
		2927	This method sets the callback method to call. The method has to have a
		2928	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		2929	first argument and the C<revents> as second. The object must be given as
		2930	parameter and is stored in the C<data> member of the watcher.
		2931
		2932	This method synthesizes efficient thunking code to call your method from
		2933	the C callback that libev requires. If your compiler can inline your
		2934	callback (i.e. it is visible to it at the place of the C<set> call and
		2935	your compiler is good :), then the method will be fully inlined into the
		2936	thunking function, making it as fast as a direct C callback.
		2937
		2938	Example: simple class declaration and watcher initialisation
		2939
		2940	struct myclass
		2941	{
		2942	void io_cb (ev::io &w, int revents) { }
		2943	}
		2944
		2945	myclass obj;
		2946	ev::io iow;
		2947	iow.set <myclass, &myclass::io_cb> (&obj);
		2948
		2949	=item w->set (object *)
		2950
		2951	This is an B<experimental> feature that might go away in a future version.
		2952
		2953	This is a variation of a method callback - leaving out the method to call
		2954	will default the method to C<operator ()>, which makes it possible to use
		2955	functor objects without having to manually specify the C<operator ()> all
		2956	the time. Incidentally, you can then also leave out the template argument
		2957	list.
		2958
		2959	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		2960	int revents)>.
		2961
		2962	See the method-C<set> above for more details.
		2963
		2964	Example: use a functor object as callback.
		2965
		2966	struct myfunctor
		2967	{
		2968	void operator() (ev::io &w, int revents)
		2969	{
		2970	...
		2971	}
		2972	}
		2973
		2974	myfunctor f;
		2975
		2976	ev::io w;
		2977	w.set (&f);
		2978
		2979	=item w->set<function> (void *data = 0)
		2980
		2981	Also sets a callback, but uses a static method or plain function as
		2982	callback. The optional C<data> argument will be stored in the watcher's
		2983	C<data> member and is free for you to use.
		2984
		2985	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		2986
		2987	See the method-C<set> above for more details.
		2988
		2989	Example: Use a plain function as callback.
		2990
		2991	static void io_cb (ev::io &w, int revents) { }
		2992	iow.set <io_cb> ();
1642		2993
1643	=item w->set (struct ev_loop *)	2994	=item w->set (struct ev_loop *)
1644		2995
1645	Associates a different C<struct ev_loop> with this watcher. You can only	2996	Associates a different C<struct ev_loop> with this watcher. You can only
1646	do this when the watcher is inactive (and not pending either).	2997	do this when the watcher is inactive (and not pending either).
1647		2998
1648	=item w->set ([args])	2999	=item w->set ([arguments])
1649		3000
1650	Basically the same as C<ev_TYPE_set>, with the same args. Must be	3001	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
1651	called at least once. Unlike the C counterpart, an active watcher gets	3002	called at least once. Unlike the C counterpart, an active watcher gets
1652	automatically stopped and restarted.	3003	automatically stopped and restarted when reconfiguring it with this
		3004	method.
1653		3005
1654	=item w->start ()	3006	=item w->start ()
1655		3007
1656	Starts the watcher. Note that there is no C<loop> argument as the	3008	Starts the watcher. Note that there is no C<loop> argument, as the
1657	constructor already takes the loop.	3009	constructor already stores the event loop.
1658		3010
1659	=item w->stop ()	3011	=item w->stop ()
1660		3012
1661	Stops the watcher if it is active. Again, no C<loop> argument.	3013	Stops the watcher if it is active. Again, no C<loop> argument.
1662		3014
1663	=item w->again () C<ev::timer>, C<ev::periodic> only	3015	=item w->again () (C<ev::timer>, C<ev::periodic> only)
1664		3016
1665	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding	3017	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
1666	C<ev_TYPE_again> function.	3018	C<ev_TYPE_again> function.
1667		3019
1668	=item w->sweep () C<ev::embed> only	3020	=item w->sweep () (C<ev::embed> only)
1669		3021
1670	Invokes C<ev_embed_sweep>.	3022	Invokes C<ev_embed_sweep>.
1671		3023
1672	=item w->update () C<ev::stat> only	3024	=item w->update () (C<ev::stat> only)
1673		3025
1674	Invokes C<ev_stat_stat>.	3026	Invokes C<ev_stat_stat>.
1675		3027
1676	=back	3028	=back
1677		3029
1678	=back	3030	=back
1679		3031
1680	Example: Define a class with an IO and idle watcher, start one of them in	3032	Example: Define a class with an IO and idle watcher, start one of them in
1681	the constructor.	3033	the constructor.
1682		3034
1683	class myclass	3035	class myclass
1684	{	3036	{
1685	ev_io io; void io_cb (ev::io &w, int revents);	3037	ev::io io ; void io_cb (ev::io &w, int revents);
1686	ev_idle idle void idle_cb (ev::idle &w, int revents);	3038	ev::idle idle; void idle_cb (ev::idle &w, int revents);
1687		3039
1688	myclass ();	3040	myclass (int fd)
1689	}	3041	{
		3042	io .set <myclass, &myclass::io_cb > (this);
		3043	idle.set <myclass, &myclass::idle_cb> (this);
1690		3044
1691	myclass::myclass (int fd)
1692	: io (this, &myclass::io_cb),
1693	idle (this, &myclass::idle_cb)
1694	{
1695	io.start (fd, ev::READ);	3045	io.start (fd, ev::READ);
		3046	}
1696	}	3047	};
		3048
		3049
		3050	=head1 OTHER LANGUAGE BINDINGS
		3051
		3052	Libev does not offer other language bindings itself, but bindings for a
		3053	number of languages exist in the form of third-party packages. If you know
		3054	any interesting language binding in addition to the ones listed here, drop
		3055	me a note.
		3056
		3057	=over 4
		3058
		3059	=item Perl
		3060
		3061	The EV module implements the full libev API and is actually used to test
		3062	libev. EV is developed together with libev. Apart from the EV core module,
		3063	there are additional modules that implement libev-compatible interfaces
		3064	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3065	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3066	and C<EV::Glib>).
		3067
		3068	It can be found and installed via CPAN, its homepage is at
		3069	L<http://software.schmorp.de/pkg/EV>.
		3070
		3071	=item Python
		3072
		3073	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3074	seems to be quite complete and well-documented.
		3075
		3076	=item Ruby
		3077
		3078	Tony Arcieri has written a ruby extension that offers access to a subset
		3079	of the libev API and adds file handle abstractions, asynchronous DNS and
		3080	more on top of it. It can be found via gem servers. Its homepage is at
		3081	L<http://rev.rubyforge.org/>.
		3082
		3083	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3084	makes rev work even on mingw.
		3085
		3086	=item Haskell
		3087
		3088	A haskell binding to libev is available at
		3089	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3090
		3091	=item D
		3092
		3093	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3094	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3095
		3096	=item Ocaml
		3097
		3098	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3099	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3100
		3101	=back
1697		3102
1698		3103
1699	=head1 MACRO MAGIC	3104	=head1 MACRO MAGIC
1700		3105
1701	Libev can be compiled with a variety of options, the most fundemantal is	3106	Libev can be compiled with a variety of options, the most fundamental
1702	C<EV_MULTIPLICITY>. This option determines wether (most) functions and	3107	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
1703	callbacks have an initial C<struct ev_loop *> argument.	3108	functions and callbacks have an initial C<struct ev_loop *> argument.
1704		3109
1705	To make it easier to write programs that cope with either variant, the	3110	To make it easier to write programs that cope with either variant, the
1706	following macros are defined:	3111	following macros are defined:
1707		3112
1708	=over 4	3113	=over 4
…		…
1711		3116
1712	This provides the loop I<argument> for functions, if one is required ("ev	3117	This provides the loop I<argument> for functions, if one is required ("ev
1713	loop argument"). The C<EV_A> form is used when this is the sole argument,	3118	loop argument"). The C<EV_A> form is used when this is the sole argument,
1714	C<EV_A_> is used when other arguments are following. Example:	3119	C<EV_A_> is used when other arguments are following. Example:
1715		3120
1716	ev_unref (EV_A);	3121	ev_unref (EV_A);
1717	ev_timer_add (EV_A_ watcher);	3122	ev_timer_add (EV_A_ watcher);
1718	ev_loop (EV_A_ 0);	3123	ev_loop (EV_A_ 0);
1719		3124
1720	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	3125	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
1721	which is often provided by the following macro.	3126	which is often provided by the following macro.
1722		3127
1723	=item C<EV_P>, C<EV_P_>	3128	=item C<EV_P>, C<EV_P_>
1724		3129
1725	This provides the loop I<parameter> for functions, if one is required ("ev	3130	This provides the loop I<parameter> for functions, if one is required ("ev
1726	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	3131	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
1727	C<EV_P_> is used when other parameters are following. Example:	3132	C<EV_P_> is used when other parameters are following. Example:
1728		3133
1729	// this is how ev_unref is being declared	3134	// this is how ev_unref is being declared
1730	static void ev_unref (EV_P);	3135	static void ev_unref (EV_P);
1731		3136
1732	// this is how you can declare your typical callback	3137	// this is how you can declare your typical callback
1733	static void cb (EV_P_ ev_timer *w, int revents)	3138	static void cb (EV_P_ ev_timer *w, int revents)
1734		3139
1735	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	3140	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
1736	suitable for use with C<EV_A>.	3141	suitable for use with C<EV_A>.
1737		3142
1738	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3143	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
1739		3144
1740	Similar to the other two macros, this gives you the value of the default	3145	Similar to the other two macros, this gives you the value of the default
1741	loop, if multiple loops are supported ("ev loop default").	3146	loop, if multiple loops are supported ("ev loop default").
1742		3147
		3148	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3149
		3150	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3151	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3152	is undefined when the default loop has not been initialised by a previous
		3153	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3154
		3155	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3156	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		3157
1743	=back	3158	=back
1744		3159
1745	Example: Declare and initialise a check watcher, working regardless of	3160	Example: Declare and initialise a check watcher, utilising the above
1746	wether multiple loops are supported or not.	3161	macros so it will work regardless of whether multiple loops are supported
		3162	or not.
1747		3163
1748	static void	3164	static void
1749	check_cb (EV_P_ ev_timer *w, int revents)	3165	check_cb (EV_P_ ev_timer *w, int revents)
1750	{	3166	{
1751	ev_check_stop (EV_A_ w);	3167	ev_check_stop (EV_A_ w);
1752	}	3168	}
1753		3169
1754	ev_check check;	3170	ev_check check;
1755	ev_check_init (&check, check_cb);	3171	ev_check_init (&check, check_cb);
1756	ev_check_start (EV_DEFAULT_ &check);	3172	ev_check_start (EV_DEFAULT_ &check);
1757	ev_loop (EV_DEFAULT_ 0);	3173	ev_loop (EV_DEFAULT_ 0);
1758
1759		3174
1760	=head1 EMBEDDING	3175	=head1 EMBEDDING
1761		3176
1762	Libev can (and often is) directly embedded into host	3177	Libev can (and often is) directly embedded into host
1763	applications. Examples of applications that embed it include the Deliantra	3178	applications. Examples of applications that embed it include the Deliantra
1764	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)	3179	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
1765	and rxvt-unicode.	3180	and rxvt-unicode.
1766		3181
1767	The goal is to enable you to just copy the neecssary files into your	3182	The goal is to enable you to just copy the necessary files into your
1768	source directory without having to change even a single line in them, so	3183	source directory without having to change even a single line in them, so
1769	you can easily upgrade by simply copying (or having a checked-out copy of	3184	you can easily upgrade by simply copying (or having a checked-out copy of
1770	libev somewhere in your source tree).	3185	libev somewhere in your source tree).
1771		3186
1772	=head2 FILESETS	3187	=head2 FILESETS
1773		3188
1774	Depending on what features you need you need to include one or more sets of files	3189	Depending on what features you need you need to include one or more sets of files
1775	in your app.	3190	in your application.
1776		3191
1777	=head3 CORE EVENT LOOP	3192	=head3 CORE EVENT LOOP
1778		3193
1779	To include only the libev core (all the C<ev_*> functions), with manual	3194	To include only the libev core (all the C<ev_*> functions), with manual
1780	configuration (no autoconf):	3195	configuration (no autoconf):
1781		3196
1782	#define EV_STANDALONE 1	3197	#define EV_STANDALONE 1
1783	#include "ev.c"	3198	#include "ev.c"
1784		3199
1785	This will automatically include F<ev.h>, too, and should be done in a	3200	This will automatically include F<ev.h>, too, and should be done in a
1786	single C source file only to provide the function implementations. To use	3201	single C source file only to provide the function implementations. To use
1787	it, do the same for F<ev.h> in all files wishing to use this API (best	3202	it, do the same for F<ev.h> in all files wishing to use this API (best
1788	done by writing a wrapper around F<ev.h> that you can include instead and	3203	done by writing a wrapper around F<ev.h> that you can include instead and
1789	where you can put other configuration options):	3204	where you can put other configuration options):
1790		3205
1791	#define EV_STANDALONE 1	3206	#define EV_STANDALONE 1
1792	#include "ev.h"	3207	#include "ev.h"
1793		3208
1794	Both header files and implementation files can be compiled with a C++	3209	Both header files and implementation files can be compiled with a C++
1795	compiler (at least, thats a stated goal, and breakage will be treated	3210	compiler (at least, that's a stated goal, and breakage will be treated
1796	as a bug).	3211	as a bug).
1797		3212
1798	You need the following files in your source tree, or in a directory	3213	You need the following files in your source tree, or in a directory
1799	in your include path (e.g. in libev/ when using -Ilibev):	3214	in your include path (e.g. in libev/ when using -Ilibev):
1800		3215
1801	ev.h	3216	ev.h
1802	ev.c	3217	ev.c
1803	ev_vars.h	3218	ev_vars.h
1804	ev_wrap.h	3219	ev_wrap.h
1805		3220
1806	ev_win32.c required on win32 platforms only	3221	ev_win32.c required on win32 platforms only
1807		3222
1808	ev_select.c only when select backend is enabled (which is by default)	3223	ev_select.c only when select backend is enabled (which is enabled by default)
1809	ev_poll.c only when poll backend is enabled (disabled by default)	3224	ev_poll.c only when poll backend is enabled (disabled by default)
1810	ev_epoll.c only when the epoll backend is enabled (disabled by default)	3225	ev_epoll.c only when the epoll backend is enabled (disabled by default)
1811	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	3226	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
1812	ev_port.c only when the solaris port backend is enabled (disabled by default)	3227	ev_port.c only when the solaris port backend is enabled (disabled by default)
1813		3228
1814	F<ev.c> includes the backend files directly when enabled, so you only need	3229	F<ev.c> includes the backend files directly when enabled, so you only need
1815	to compile this single file.	3230	to compile this single file.
1816		3231
1817	=head3 LIBEVENT COMPATIBILITY API	3232	=head3 LIBEVENT COMPATIBILITY API
1818		3233
1819	To include the libevent compatibility API, also include:	3234	To include the libevent compatibility API, also include:
1820		3235
1821	#include "event.c"	3236	#include "event.c"
1822		3237
1823	in the file including F<ev.c>, and:	3238	in the file including F<ev.c>, and:
1824		3239
1825	#include "event.h"	3240	#include "event.h"
1826		3241
1827	in the files that want to use the libevent API. This also includes F<ev.h>.	3242	in the files that want to use the libevent API. This also includes F<ev.h>.
1828		3243
1829	You need the following additional files for this:	3244	You need the following additional files for this:
1830		3245
1831	event.h	3246	event.h
1832	event.c	3247	event.c
1833		3248
1834	=head3 AUTOCONF SUPPORT	3249	=head3 AUTOCONF SUPPORT
1835		3250
1836	Instead of using C<EV_STANDALONE=1> and providing your config in	3251	Instead of using C<EV_STANDALONE=1> and providing your configuration in
1837	whatever way you want, you can also C<m4_include([libev.m4])> in your	3252	whatever way you want, you can also C<m4_include([libev.m4])> in your
1838	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	3253	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
1839	include F<config.h> and configure itself accordingly.	3254	include F<config.h> and configure itself accordingly.
1840		3255
1841	For this of course you need the m4 file:	3256	For this of course you need the m4 file:
1842		3257
1843	libev.m4	3258	libev.m4
1844		3259
1845	=head2 PREPROCESSOR SYMBOLS/MACROS	3260	=head2 PREPROCESSOR SYMBOLS/MACROS
1846		3261
1847	Libev can be configured via a variety of preprocessor symbols you have to define	3262	Libev can be configured via a variety of preprocessor symbols you have to
1848	before including any of its files. The default is not to build for multiplicity	3263	define before including any of its files. The default in the absence of
1849	and only include the select backend.	3264	autoconf is documented for every option.
1850		3265
1851	=over 4	3266	=over 4
1852		3267
1853	=item EV_STANDALONE	3268	=item EV_STANDALONE
1854		3269
…		…
1856	keeps libev from including F<config.h>, and it also defines dummy	3271	keeps libev from including F<config.h>, and it also defines dummy
1857	implementations for some libevent functions (such as logging, which is not	3272	implementations for some libevent functions (such as logging, which is not
1858	supported). It will also not define any of the structs usually found in	3273	supported). It will also not define any of the structs usually found in
1859	F<event.h> that are not directly supported by the libev core alone.	3274	F<event.h> that are not directly supported by the libev core alone.
1860		3275
		3276	In stanbdalone mode, libev will still try to automatically deduce the
		3277	configuration, but has to be more conservative.
		3278
1861	=item EV_USE_MONOTONIC	3279	=item EV_USE_MONOTONIC
1862		3280
1863	If defined to be C<1>, libev will try to detect the availability of the	3281	If defined to be C<1>, libev will try to detect the availability of the
1864	monotonic clock option at both compiletime and runtime. Otherwise no use	3282	monotonic clock option at both compile time and runtime. Otherwise no
1865	of the monotonic clock option will be attempted. If you enable this, you	3283	use of the monotonic clock option will be attempted. If you enable this,
1866	usually have to link against librt or something similar. Enabling it when	3284	you usually have to link against librt or something similar. Enabling it
1867	the functionality isn't available is safe, though, althoguh you have	3285	when the functionality isn't available is safe, though, although you have
1868	to make sure you link against any libraries where the C<clock_gettime>	3286	to make sure you link against any libraries where the C<clock_gettime>
1869	function is hiding in (often F<-lrt>).	3287	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
1870		3288
1871	=item EV_USE_REALTIME	3289	=item EV_USE_REALTIME
1872		3290
1873	If defined to be C<1>, libev will try to detect the availability of the	3291	If defined to be C<1>, libev will try to detect the availability of the
1874	realtime clock option at compiletime (and assume its availability at	3292	real-time clock option at compile time (and assume its availability
1875	runtime if successful). Otherwise no use of the realtime clock option will	3293	at runtime if successful). Otherwise no use of the real-time clock
1876	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3294	option will be attempted. This effectively replaces C<gettimeofday>
1877	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See tzhe note about libraries	3295	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
1878	in the description of C<EV_USE_MONOTONIC>, though.	3296	correctness. See the note about libraries in the description of
		3297	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3298	C<EV_USE_CLOCK_SYSCALL>.
		3299
		3300	=item EV_USE_CLOCK_SYSCALL
		3301
		3302	If defined to be C<1>, libev will try to use a direct syscall instead
		3303	of calling the system-provided C<clock_gettime> function. This option
		3304	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3305	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3306	programs needlessly. Using a direct syscall is slightly slower (in
		3307	theory), because no optimised vdso implementation can be used, but avoids
		3308	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3309	higher, as it simplifies linking (no need for C<-lrt>).
		3310
		3311	=item EV_USE_NANOSLEEP
		3312
		3313	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		3314	and will use it for delays. Otherwise it will use C<select ()>.
		3315
		3316	=item EV_USE_EVENTFD
		3317
		3318	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3319	available and will probe for kernel support at runtime. This will improve
		3320	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3321	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3322	2.7 or newer, otherwise disabled.
1879		3323
1880	=item EV_USE_SELECT	3324	=item EV_USE_SELECT
1881		3325
1882	If undefined or defined to be C<1>, libev will compile in support for the	3326	If undefined or defined to be C<1>, libev will compile in support for the
1883	C<select>(2) backend. No attempt at autodetection will be done: if no	3327	C<select>(2) backend. No attempt at auto-detection will be done: if no
1884	other method takes over, select will be it. Otherwise the select backend	3328	other method takes over, select will be it. Otherwise the select backend
1885	will not be compiled in.	3329	will not be compiled in.
1886		3330
1887	=item EV_SELECT_USE_FD_SET	3331	=item EV_SELECT_USE_FD_SET
1888		3332
1889	If defined to C<1>, then the select backend will use the system C<fd_set>	3333	If defined to C<1>, then the select backend will use the system C<fd_set>
1890	structure. This is useful if libev doesn't compile due to a missing	3334	structure. This is useful if libev doesn't compile due to a missing
1891	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	3335	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
1892	exotic systems. This usually limits the range of file descriptors to some	3336	on exotic systems. This usually limits the range of file descriptors to
1893	low limit such as 1024 or might have other limitations (winsocket only	3337	some low limit such as 1024 or might have other limitations (winsocket
1894	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3338	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
1895	influence the size of the C<fd_set> used.	3339	configures the maximum size of the C<fd_set>.
1896		3340
1897	=item EV_SELECT_IS_WINSOCKET	3341	=item EV_SELECT_IS_WINSOCKET
1898		3342
1899	When defined to C<1>, the select backend will assume that	3343	When defined to C<1>, the select backend will assume that
1900	select/socket/connect etc. don't understand file descriptors but	3344	select/socket/connect etc. don't understand file descriptors but
…		…
1902	be used is the winsock select). This means that it will call	3346	be used is the winsock select). This means that it will call
1903	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3347	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
1904	it is assumed that all these functions actually work on fds, even	3348	it is assumed that all these functions actually work on fds, even
1905	on win32. Should not be defined on non-win32 platforms.	3349	on win32. Should not be defined on non-win32 platforms.
1906		3350
		3351	=item EV_FD_TO_WIN32_HANDLE
		3352
		3353	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3354	file descriptors to socket handles. When not defining this symbol (the
		3355	default), then libev will call C<_get_osfhandle>, which is usually
		3356	correct. In some cases, programs use their own file descriptor management,
		3357	in which case they can provide this function to map fds to socket handles.
		3358
1907	=item EV_USE_POLL	3359	=item EV_USE_POLL
1908		3360
1909	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3361	If defined to be C<1>, libev will compile in support for the C<poll>(2)
1910	backend. Otherwise it will be enabled on non-win32 platforms. It	3362	backend. Otherwise it will be enabled on non-win32 platforms. It
1911	takes precedence over select.	3363	takes precedence over select.
1912		3364
1913	=item EV_USE_EPOLL	3365	=item EV_USE_EPOLL
1914		3366
1915	If defined to be C<1>, libev will compile in support for the Linux	3367	If defined to be C<1>, libev will compile in support for the Linux
1916	C<epoll>(7) backend. Its availability will be detected at runtime,	3368	C<epoll>(7) backend. Its availability will be detected at runtime,
1917	otherwise another method will be used as fallback. This is the	3369	otherwise another method will be used as fallback. This is the preferred
1918	preferred backend for GNU/Linux systems.	3370	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3371	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
1919		3372
1920	=item EV_USE_KQUEUE	3373	=item EV_USE_KQUEUE
1921		3374
1922	If defined to be C<1>, libev will compile in support for the BSD style	3375	If defined to be C<1>, libev will compile in support for the BSD style
1923	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	3376	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
1936	otherwise another method will be used as fallback. This is the preferred	3389	otherwise another method will be used as fallback. This is the preferred
1937	backend for Solaris 10 systems.	3390	backend for Solaris 10 systems.
1938		3391
1939	=item EV_USE_DEVPOLL	3392	=item EV_USE_DEVPOLL
1940		3393
1941	reserved for future expansion, works like the USE symbols above.	3394	Reserved for future expansion, works like the USE symbols above.
		3395
		3396	=item EV_USE_INOTIFY
		3397
		3398	If defined to be C<1>, libev will compile in support for the Linux inotify
		3399	interface to speed up C<ev_stat> watchers. Its actual availability will
		3400	be detected at runtime. If undefined, it will be enabled if the headers
		3401	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3402
		3403	=item EV_ATOMIC_T
		3404
		3405	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3406	access is atomic with respect to other threads or signal contexts. No such
		3407	type is easily found in the C language, so you can provide your own type
		3408	that you know is safe for your purposes. It is used both for signal handler "locking"
		3409	as well as for signal and thread safety in C<ev_async> watchers.
		3410
		3411	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3412	(from F<signal.h>), which is usually good enough on most platforms.
1942		3413
1943	=item EV_H	3414	=item EV_H
1944		3415
1945	The name of the F<ev.h> header file used to include it. The default if	3416	The name of the F<ev.h> header file used to include it. The default if
1946	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This	3417	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
1947	can be used to virtually rename the F<ev.h> header file in case of conflicts.	3418	used to virtually rename the F<ev.h> header file in case of conflicts.
1948		3419
1949	=item EV_CONFIG_H	3420	=item EV_CONFIG_H
1950		3421
1951	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	3422	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
1952	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	3423	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
1953	C<EV_H>, above.	3424	C<EV_H>, above.
1954		3425
1955	=item EV_EVENT_H	3426	=item EV_EVENT_H
1956		3427
1957	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	3428	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
1958	of how the F<event.h> header can be found.	3429	of how the F<event.h> header can be found, the default is C<"event.h">.
1959		3430
1960	=item EV_PROTOTYPES	3431	=item EV_PROTOTYPES
1961		3432
1962	If defined to be C<0>, then F<ev.h> will not define any function	3433	If defined to be C<0>, then F<ev.h> will not define any function
1963	prototypes, but still define all the structs and other symbols. This is	3434	prototypes, but still define all the structs and other symbols. This is
…		…
1970	will have the C<struct ev_loop *> as first argument, and you can create	3441	will have the C<struct ev_loop *> as first argument, and you can create
1971	additional independent event loops. Otherwise there will be no support	3442	additional independent event loops. Otherwise there will be no support
1972	for multiple event loops and there is no first event loop pointer	3443	for multiple event loops and there is no first event loop pointer
1973	argument. Instead, all functions act on the single default loop.	3444	argument. Instead, all functions act on the single default loop.
1974		3445
		3446	=item EV_MINPRI
		3447
		3448	=item EV_MAXPRI
		3449
		3450	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		3451	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		3452	provide for more priorities by overriding those symbols (usually defined
		3453	to be C<-2> and C<2>, respectively).
		3454
		3455	When doing priority-based operations, libev usually has to linearly search
		3456	all the priorities, so having many of them (hundreds) uses a lot of space
		3457	and time, so using the defaults of five priorities (-2 .. +2) is usually
		3458	fine.
		3459
		3460	If your embedding application does not need any priorities, defining these
		3461	both to C<0> will save some memory and CPU.
		3462
1975	=item EV_PERIODIC_ENABLE	3463	=item EV_PERIODIC_ENABLE
1976		3464
1977	If undefined or defined to be C<1>, then periodic timers are supported. If	3465	If undefined or defined to be C<1>, then periodic timers are supported. If
1978	defined to be C<0>, then they are not. Disabling them saves a few kB of	3466	defined to be C<0>, then they are not. Disabling them saves a few kB of
1979	code.	3467	code.
1980		3468
		3469	=item EV_IDLE_ENABLE
		3470
		3471	If undefined or defined to be C<1>, then idle watchers are supported. If
		3472	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3473	code.
		3474
1981	=item EV_EMBED_ENABLE	3475	=item EV_EMBED_ENABLE
1982		3476
1983	If undefined or defined to be C<1>, then embed watchers are supported. If	3477	If undefined or defined to be C<1>, then embed watchers are supported. If
1984	defined to be C<0>, then they are not.	3478	defined to be C<0>, then they are not. Embed watchers rely on most other
		3479	watcher types, which therefore must not be disabled.
1985		3480
1986	=item EV_STAT_ENABLE	3481	=item EV_STAT_ENABLE
1987		3482
1988	If undefined or defined to be C<1>, then stat watchers are supported. If	3483	If undefined or defined to be C<1>, then stat watchers are supported. If
1989	defined to be C<0>, then they are not.	3484	defined to be C<0>, then they are not.
…		…
1991	=item EV_FORK_ENABLE	3486	=item EV_FORK_ENABLE
1992		3487
1993	If undefined or defined to be C<1>, then fork watchers are supported. If	3488	If undefined or defined to be C<1>, then fork watchers are supported. If
1994	defined to be C<0>, then they are not.	3489	defined to be C<0>, then they are not.
1995		3490
		3491	=item EV_ASYNC_ENABLE
		3492
		3493	If undefined or defined to be C<1>, then async watchers are supported. If
		3494	defined to be C<0>, then they are not.
		3495
1996	=item EV_MINIMAL	3496	=item EV_MINIMAL
1997		3497
1998	If you need to shave off some kilobytes of code at the expense of some	3498	If you need to shave off some kilobytes of code at the expense of some
1999	speed, define this symbol to C<1>. Currently only used for gcc to override	3499	speed, define this symbol to C<1>. Currently this is used to override some
2000	some inlining decisions, saves roughly 30% codesize of amd64.	3500	inlining decisions, saves roughly 30% code size on amd64. It also selects a
		3501	much smaller 2-heap for timer management over the default 4-heap.
		3502
		3503	=item EV_PID_HASHSIZE
		3504
		3505	C<ev_child> watchers use a small hash table to distribute workload by
		3506	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
		3507	than enough. If you need to manage thousands of children you might want to
		3508	increase this value (I<must> be a power of two).
		3509
		3510	=item EV_INOTIFY_HASHSIZE
		3511
		3512	C<ev_stat> watchers use a small hash table to distribute workload by
		3513	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
		3514	usually more than enough. If you need to manage thousands of C<ev_stat>
		3515	watchers you might want to increase this value (I<must> be a power of
		3516	two).
		3517
		3518	=item EV_USE_4HEAP
		3519
		3520	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3521	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		3522	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		3523	faster performance with many (thousands) of watchers.
		3524
		3525	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3526	(disabled).
		3527
		3528	=item EV_HEAP_CACHE_AT
		3529
		3530	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3531	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		3532	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3533	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3534	but avoids random read accesses on heap changes. This improves performance
		3535	noticeably with many (hundreds) of watchers.
		3536
		3537	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3538	(disabled).
		3539
		3540	=item EV_VERIFY
		3541
		3542	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3543	be done: If set to C<0>, no internal verification code will be compiled
		3544	in. If set to C<1>, then verification code will be compiled in, but not
		3545	called. If set to C<2>, then the internal verification code will be
		3546	called once per loop, which can slow down libev. If set to C<3>, then the
		3547	verification code will be called very frequently, which will slow down
		3548	libev considerably.
		3549
		3550	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3551	C<0>.
2001		3552
2002	=item EV_COMMON	3553	=item EV_COMMON
2003		3554
2004	By default, all watchers have a C<void *data> member. By redefining	3555	By default, all watchers have a C<void *data> member. By redefining
2005	this macro to a something else you can include more and other types of	3556	this macro to a something else you can include more and other types of
2006	members. You have to define it each time you include one of the files,	3557	members. You have to define it each time you include one of the files,
2007	though, and it must be identical each time.	3558	though, and it must be identical each time.
2008		3559
2009	For example, the perl EV module uses something like this:	3560	For example, the perl EV module uses something like this:
2010		3561
2011	#define EV_COMMON \	3562	#define EV_COMMON \
2012	SV *self; /* contains this struct */ \	3563	SV *self; /* contains this struct */ \
2013	SV *cb_sv, *fh /* note no trailing ";" */	3564	SV *cb_sv, *fh /* note no trailing ";" */
2014		3565
2015	=item EV_CB_DECLARE (type)	3566	=item EV_CB_DECLARE (type)
2016		3567
2017	=item EV_CB_INVOKE (watcher, revents)	3568	=item EV_CB_INVOKE (watcher, revents)
2018		3569
2019	=item ev_set_cb (ev, cb)	3570	=item ev_set_cb (ev, cb)
2020		3571
2021	Can be used to change the callback member declaration in each watcher,	3572	Can be used to change the callback member declaration in each watcher,
2022	and the way callbacks are invoked and set. Must expand to a struct member	3573	and the way callbacks are invoked and set. Must expand to a struct member
2023	definition and a statement, respectively. See the F<ev.v> header file for	3574	definition and a statement, respectively. See the F<ev.h> header file for
2024	their default definitions. One possible use for overriding these is to	3575	their default definitions. One possible use for overriding these is to
2025	avoid the C<struct ev_loop *> as first argument in all cases, or to use	3576	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2026	method calls instead of plain function calls in C++.	3577	method calls instead of plain function calls in C++.
		3578
		3579	=back
		3580
		3581	=head2 EXPORTED API SYMBOLS
		3582
		3583	If you need to re-export the API (e.g. via a DLL) and you need a list of
		3584	exported symbols, you can use the provided F<Symbol.*> files which list
		3585	all public symbols, one per line:
		3586
		3587	Symbols.ev for libev proper
		3588	Symbols.event for the libevent emulation
		3589
		3590	This can also be used to rename all public symbols to avoid clashes with
		3591	multiple versions of libev linked together (which is obviously bad in
		3592	itself, but sometimes it is inconvenient to avoid this).
		3593
		3594	A sed command like this will create wrapper C<#define>'s that you need to
		3595	include before including F<ev.h>:
		3596
		3597	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		3598
		3599	This would create a file F<wrap.h> which essentially looks like this:
		3600
		3601	#define ev_backend myprefix_ev_backend
		3602	#define ev_check_start myprefix_ev_check_start
		3603	#define ev_check_stop myprefix_ev_check_stop
		3604	...
2027		3605
2028	=head2 EXAMPLES	3606	=head2 EXAMPLES
2029		3607
2030	For a real-world example of a program the includes libev	3608	For a real-world example of a program the includes libev
2031	verbatim, you can have a look at the EV perl module	3609	verbatim, you can have a look at the EV perl module
…		…
2034	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file	3612	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
2035	will be compiled. It is pretty complex because it provides its own header	3613	will be compiled. It is pretty complex because it provides its own header
2036	file.	3614	file.
2037		3615
2038	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	3616	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2039	that everybody includes and which overrides some autoconf choices:	3617	that everybody includes and which overrides some configure choices:
2040		3618
		3619	#define EV_MINIMAL 1
2041	#define EV_USE_POLL 0	3620	#define EV_USE_POLL 0
2042	#define EV_MULTIPLICITY 0	3621	#define EV_MULTIPLICITY 0
2043	#define EV_PERIODICS 0	3622	#define EV_PERIODIC_ENABLE 0
		3623	#define EV_STAT_ENABLE 0
		3624	#define EV_FORK_ENABLE 0
2044	#define EV_CONFIG_H <config.h>	3625	#define EV_CONFIG_H <config.h>
		3626	#define EV_MINPRI 0
		3627	#define EV_MAXPRI 0
2045		3628
2046	#include "ev++.h"	3629	#include "ev++.h"
2047		3630
2048	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	3631	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2049		3632
2050	#include "ev_cpp.h"	3633	#include "ev_cpp.h"
2051	#include "ev.c"	3634	#include "ev.c"
2052		3635
		3636	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
2053		3637
		3638	=head2 THREADS AND COROUTINES
		3639
		3640	=head3 THREADS
		3641
		3642	All libev functions are reentrant and thread-safe unless explicitly
		3643	documented otherwise, but libev implements no locking itself. This means
		3644	that you can use as many loops as you want in parallel, as long as there
		3645	are no concurrent calls into any libev function with the same loop
		3646	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		3647	of course): libev guarantees that different event loops share no data
		3648	structures that need any locking.
		3649
		3650	Or to put it differently: calls with different loop parameters can be done
		3651	concurrently from multiple threads, calls with the same loop parameter
		3652	must be done serially (but can be done from different threads, as long as
		3653	only one thread ever is inside a call at any point in time, e.g. by using
		3654	a mutex per loop).
		3655
		3656	Specifically to support threads (and signal handlers), libev implements
		3657	so-called C<ev_async> watchers, which allow some limited form of
		3658	concurrency on the same event loop, namely waking it up "from the
		3659	outside".
		3660
		3661	If you want to know which design (one loop, locking, or multiple loops
		3662	without or something else still) is best for your problem, then I cannot
		3663	help you, but here is some generic advice:
		3664
		3665	=over 4
		3666
		3667	=item * most applications have a main thread: use the default libev loop
		3668	in that thread, or create a separate thread running only the default loop.
		3669
		3670	This helps integrating other libraries or software modules that use libev
		3671	themselves and don't care/know about threading.
		3672
		3673	=item * one loop per thread is usually a good model.
		3674
		3675	Doing this is almost never wrong, sometimes a better-performance model
		3676	exists, but it is always a good start.
		3677
		3678	=item * other models exist, such as the leader/follower pattern, where one
		3679	loop is handed through multiple threads in a kind of round-robin fashion.
		3680
		3681	Choosing a model is hard - look around, learn, know that usually you can do
		3682	better than you currently do :-)
		3683
		3684	=item * often you need to talk to some other thread which blocks in the
		3685	event loop.
		3686
		3687	C<ev_async> watchers can be used to wake them up from other threads safely
		3688	(or from signal contexts...).
		3689
		3690	An example use would be to communicate signals or other events that only
		3691	work in the default loop by registering the signal watcher with the
		3692	default loop and triggering an C<ev_async> watcher from the default loop
		3693	watcher callback into the event loop interested in the signal.
		3694
		3695	=back
		3696
		3697	=head3 COROUTINES
		3698
		3699	Libev is very accommodating to coroutines ("cooperative threads"):
		3700	libev fully supports nesting calls to its functions from different
		3701	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3702	different coroutines, and switch freely between both coroutines running the
		3703	loop, as long as you don't confuse yourself). The only exception is that
		3704	you must not do this from C<ev_periodic> reschedule callbacks.
		3705
		3706	Care has been taken to ensure that libev does not keep local state inside
		3707	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		3708	they do not call any callbacks.
		3709
		3710	=head2 COMPILER WARNINGS
		3711
		3712	Depending on your compiler and compiler settings, you might get no or a
		3713	lot of warnings when compiling libev code. Some people are apparently
		3714	scared by this.
		3715
		3716	However, these are unavoidable for many reasons. For one, each compiler
		3717	has different warnings, and each user has different tastes regarding
		3718	warning options. "Warn-free" code therefore cannot be a goal except when
		3719	targeting a specific compiler and compiler-version.
		3720
		3721	Another reason is that some compiler warnings require elaborate
		3722	workarounds, or other changes to the code that make it less clear and less
		3723	maintainable.
		3724
		3725	And of course, some compiler warnings are just plain stupid, or simply
		3726	wrong (because they don't actually warn about the condition their message
		3727	seems to warn about). For example, certain older gcc versions had some
		3728	warnings that resulted an extreme number of false positives. These have
		3729	been fixed, but some people still insist on making code warn-free with
		3730	such buggy versions.
		3731
		3732	While libev is written to generate as few warnings as possible,
		3733	"warn-free" code is not a goal, and it is recommended not to build libev
		3734	with any compiler warnings enabled unless you are prepared to cope with
		3735	them (e.g. by ignoring them). Remember that warnings are just that:
		3736	warnings, not errors, or proof of bugs.
		3737
		3738
		3739	=head2 VALGRIND
		3740
		3741	Valgrind has a special section here because it is a popular tool that is
		3742	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		3743
		3744	If you think you found a bug (memory leak, uninitialised data access etc.)
		3745	in libev, then check twice: If valgrind reports something like:
		3746
		3747	==2274== definitely lost: 0 bytes in 0 blocks.
		3748	==2274== possibly lost: 0 bytes in 0 blocks.
		3749	==2274== still reachable: 256 bytes in 1 blocks.
		3750
		3751	Then there is no memory leak, just as memory accounted to global variables
		3752	is not a memleak - the memory is still being referenced, and didn't leak.
		3753
		3754	Similarly, under some circumstances, valgrind might report kernel bugs
		3755	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		3756	although an acceptable workaround has been found here), or it might be
		3757	confused.
		3758
		3759	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		3760	make it into some kind of religion.
		3761
		3762	If you are unsure about something, feel free to contact the mailing list
		3763	with the full valgrind report and an explanation on why you think this
		3764	is a bug in libev (best check the archives, too :). However, don't be
		3765	annoyed when you get a brisk "this is no bug" answer and take the chance
		3766	of learning how to interpret valgrind properly.
		3767
		3768	If you need, for some reason, empty reports from valgrind for your project
		3769	I suggest using suppression lists.
		3770
		3771
		3772	=head1 PORTABILITY NOTES
		3773
		3774	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		3775
		3776	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		3777	requires, and its I/O model is fundamentally incompatible with the POSIX
		3778	model. Libev still offers limited functionality on this platform in
		3779	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		3780	descriptors. This only applies when using Win32 natively, not when using
		3781	e.g. cygwin.
		3782
		3783	Lifting these limitations would basically require the full
		3784	re-implementation of the I/O system. If you are into these kinds of
		3785	things, then note that glib does exactly that for you in a very portable
		3786	way (note also that glib is the slowest event library known to man).
		3787
		3788	There is no supported compilation method available on windows except
		3789	embedding it into other applications.
		3790
		3791	Not a libev limitation but worth mentioning: windows apparently doesn't
		3792	accept large writes: instead of resulting in a partial write, windows will
		3793	either accept everything or return C<ENOBUFS> if the buffer is too large,
		3794	so make sure you only write small amounts into your sockets (less than a
		3795	megabyte seems safe, but this apparently depends on the amount of memory
		3796	available).
		3797
		3798	Due to the many, low, and arbitrary limits on the win32 platform and
		3799	the abysmal performance of winsockets, using a large number of sockets
		3800	is not recommended (and not reasonable). If your program needs to use
		3801	more than a hundred or so sockets, then likely it needs to use a totally
		3802	different implementation for windows, as libev offers the POSIX readiness
		3803	notification model, which cannot be implemented efficiently on windows
		3804	(Microsoft monopoly games).
		3805
		3806	A typical way to use libev under windows is to embed it (see the embedding
		3807	section for details) and use the following F<evwrap.h> header file instead
		3808	of F<ev.h>:
		3809
		3810	#define EV_STANDALONE /* keeps ev from requiring config.h */
		3811	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		3812
		3813	#include "ev.h"
		3814
		3815	And compile the following F<evwrap.c> file into your project (make sure
		3816	you do I<not> compile the F<ev.c> or any other embedded source files!):
		3817
		3818	#include "evwrap.h"
		3819	#include "ev.c"
		3820
		3821	=over 4
		3822
		3823	=item The winsocket select function
		3824
		3825	The winsocket C<select> function doesn't follow POSIX in that it
		3826	requires socket I<handles> and not socket I<file descriptors> (it is
		3827	also extremely buggy). This makes select very inefficient, and also
		3828	requires a mapping from file descriptors to socket handles (the Microsoft
		3829	C runtime provides the function C<_open_osfhandle> for this). See the
		3830	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		3831	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		3832
		3833	The configuration for a "naked" win32 using the Microsoft runtime
		3834	libraries and raw winsocket select is:
		3835
		3836	#define EV_USE_SELECT 1
		3837	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		3838
		3839	Note that winsockets handling of fd sets is O(n), so you can easily get a
		3840	complexity in the O(n²) range when using win32.
		3841
		3842	=item Limited number of file descriptors
		3843
		3844	Windows has numerous arbitrary (and low) limits on things.
		3845
		3846	Early versions of winsocket's select only supported waiting for a maximum
		3847	of C<64> handles (probably owning to the fact that all windows kernels
		3848	can only wait for C<64> things at the same time internally; Microsoft
		3849	recommends spawning a chain of threads and wait for 63 handles and the
		3850	previous thread in each. Great).
		3851
		3852	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		3853	to some high number (e.g. C<2048>) before compiling the winsocket select
		3854	call (which might be in libev or elsewhere, for example, perl does its own
		3855	select emulation on windows).
		3856
		3857	Another limit is the number of file descriptors in the Microsoft runtime
		3858	libraries, which by default is C<64> (there must be a hidden I<64> fetish
		3859	or something like this inside Microsoft). You can increase this by calling
		3860	C<_setmaxstdio>, which can increase this limit to C<2048> (another
		3861	arbitrary limit), but is broken in many versions of the Microsoft runtime
		3862	libraries.
		3863
		3864	This might get you to about C<512> or C<2048> sockets (depending on
		3865	windows version and/or the phase of the moon). To get more, you need to
		3866	wrap all I/O functions and provide your own fd management, but the cost of
		3867	calling select (O(n²)) will likely make this unworkable.
		3868
		3869	=back
		3870
		3871	=head2 PORTABILITY REQUIREMENTS
		3872
		3873	In addition to a working ISO-C implementation and of course the
		3874	backend-specific APIs, libev relies on a few additional extensions:
		3875
		3876	=over 4
		3877
		3878	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		3879	calling conventions regardless of C<ev_watcher_type *>.
		3880
		3881	Libev assumes not only that all watcher pointers have the same internal
		3882	structure (guaranteed by POSIX but not by ISO C for example), but it also
		3883	assumes that the same (machine) code can be used to call any watcher
		3884	callback: The watcher callbacks have different type signatures, but libev
		3885	calls them using an C<ev_watcher *> internally.
		3886
		3887	=item C<sig_atomic_t volatile> must be thread-atomic as well
		3888
		3889	The type C<sig_atomic_t volatile> (or whatever is defined as
		3890	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		3891	threads. This is not part of the specification for C<sig_atomic_t>, but is
		3892	believed to be sufficiently portable.
		3893
		3894	=item C<sigprocmask> must work in a threaded environment
		3895
		3896	Libev uses C<sigprocmask> to temporarily block signals. This is not
		3897	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		3898	pthread implementations will either allow C<sigprocmask> in the "main
		3899	thread" or will block signals process-wide, both behaviours would
		3900	be compatible with libev. Interaction between C<sigprocmask> and
		3901	C<pthread_sigmask> could complicate things, however.
		3902
		3903	The most portable way to handle signals is to block signals in all threads
		3904	except the initial one, and run the default loop in the initial thread as
		3905	well.
		3906
		3907	=item C<long> must be large enough for common memory allocation sizes
		3908
		3909	To improve portability and simplify its API, libev uses C<long> internally
		3910	instead of C<size_t> when allocating its data structures. On non-POSIX
		3911	systems (Microsoft...) this might be unexpectedly low, but is still at
		3912	least 31 bits everywhere, which is enough for hundreds of millions of
		3913	watchers.
		3914
		3915	=item C<double> must hold a time value in seconds with enough accuracy
		3916
		3917	The type C<double> is used to represent timestamps. It is required to
		3918	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		3919	enough for at least into the year 4000. This requirement is fulfilled by
		3920	implementations implementing IEEE 754 (basically all existing ones).
		3921
		3922	=back
		3923
		3924	If you know of other additional requirements drop me a note.
		3925
		3926
2054	=head1 COMPLEXITIES	3927	=head1 ALGORITHMIC COMPLEXITIES
2055		3928
2056	In this section the complexities of (many of) the algorithms used inside	3929	In this section the complexities of (many of) the algorithms used inside
2057	libev will be explained. For complexity discussions about backends see the	3930	libev will be documented. For complexity discussions about backends see
2058	documentation for C<ev_default_init>.	3931	the documentation for C<ev_default_init>.
		3932
		3933	All of the following are about amortised time: If an array needs to be
		3934	extended, libev needs to realloc and move the whole array, but this
		3935	happens asymptotically rarer with higher number of elements, so O(1) might
		3936	mean that libev does a lengthy realloc operation in rare cases, but on
		3937	average it is much faster and asymptotically approaches constant time.
2059		3938
2060	=over 4	3939	=over 4
2061		3940
2062	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	3941	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2063		3942
		3943	This means that, when you have a watcher that triggers in one hour and
		3944	there are 100 watchers that would trigger before that, then inserting will
		3945	have to skip roughly seven (C<ld 100>) of these watchers.
		3946
2064	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	3947	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2065		3948
		3949	That means that changing a timer costs less than removing/adding them,
		3950	as only the relative motion in the event queue has to be paid for.
		3951
2066	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	3952	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
2067		3953
		3954	These just add the watcher into an array or at the head of a list.
		3955
2068	=item Stopping check/prepare/idle watchers: O(1)	3956	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2069		3957
2070	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % 16))	3958	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2071		3959
		3960	These watchers are stored in lists, so they need to be walked to find the
		3961	correct watcher to remove. The lists are usually short (you don't usually
		3962	have many watchers waiting for the same fd or signal: one is typical, two
		3963	is rare).
		3964
2072	=item Finding the next timer per loop iteration: O(1)	3965	=item Finding the next timer in each loop iteration: O(1)
		3966
		3967	By virtue of using a binary or 4-heap, the next timer is always found at a
		3968	fixed position in the storage array.
2073		3969
2074	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	3970	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2075		3971
2076	=item Activating one watcher: O(1)	3972	A change means an I/O watcher gets started or stopped, which requires
		3973	libev to recalculate its status (and possibly tell the kernel, depending
		3974	on backend and whether C<ev_io_set> was used).
		3975
		3976	=item Activating one watcher (putting it into the pending state): O(1)
		3977
		3978	=item Priority handling: O(number_of_priorities)
		3979
		3980	Priorities are implemented by allocating some space for each
		3981	priority. When doing priority-based operations, libev usually has to
		3982	linearly search all the priorities, but starting/stopping and activating
		3983	watchers becomes O(1) with respect to priority handling.
		3984
		3985	=item Sending an ev_async: O(1)
		3986
		3987	=item Processing ev_async_send: O(number_of_async_watchers)
		3988
		3989	=item Processing signals: O(max_signal_number)
		3990
		3991	Sending involves a system call I<iff> there were no other C<ev_async_send>
		3992	calls in the current loop iteration. Checking for async and signal events
		3993	involves iterating over all running async watchers or all signal numbers.
2077		3994
2078	=back	3995	=back
2079		3996
2080		3997
2081	=head1 AUTHOR	3998	=head1 AUTHOR
2082		3999
2083	Marc Lehmann <libev@schmorp.de>.	4000	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
2084		4001

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