ViewVC Help

View File | Revision Log | Show Annotations | Download File

/cvs/libev/ev.pod

Comparing libev/ev.pod (file contents):
Revision 1.58 by root, Wed Nov 28 11:31:34 2007 UTC vs.
Revision 1.219 by root, Thu Nov 20 00:43:58 2008 UTC

…		…
2		2
3	libev - a high performance full-featured event loop written in C	3	libev - a high performance full-featured event loop written in C
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
8		8
9	=head1 EXAMPLE PROGRAM	9	=head2 EXAMPLE PROGRAM
10		10
		11	// a single header file is required
11	#include <ev.h>	12	#include <ev.h>
12		13
		14	#include <stdio.h> // for puts
		15
		16	// every watcher type has its own typedef'd struct
		17	// with the name ev_TYPE
13	ev_io stdin_watcher;	18	ev_io stdin_watcher;
14	ev_timer timeout_watcher;	19	ev_timer timeout_watcher;
15		20
16	/* called when data readable on stdin */	21	// all watcher callbacks have a similar signature
		22	// this callback is called when data is readable on stdin
17	static void	23	static void
18	stdin_cb (EV_P_ struct ev_io *w, int revents)	24	stdin_cb (EV_P_ ev_io *w, int revents)
19	{	25	{
20	/* puts ("stdin ready"); */	26	puts ("stdin ready");
21	ev_io_stop (EV_A_ w); /* just a syntax example */	27	// for one-shot events, one must manually stop the watcher
22	ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */	28	// with its corresponding stop function.
		29	ev_io_stop (EV_A_ w);
		30
		31	// this causes all nested ev_loop's to stop iterating
		32	ev_unloop (EV_A_ EVUNLOOP_ALL);
23	}	33	}
24		34
		35	// another callback, this time for a time-out
25	static void	36	static void
26	timeout_cb (EV_P_ struct ev_timer *w, int revents)	37	timeout_cb (EV_P_ ev_timer *w, int revents)
27	{	38	{
28	/* puts ("timeout"); */	39	puts ("timeout");
29	ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */	40	// this causes the innermost ev_loop to stop iterating
		41	ev_unloop (EV_A_ EVUNLOOP_ONE);
30	}	42	}
31		43
32	int	44	int
33	main (void)	45	main (void)
34	{	46	{
		47	// use the default event loop unless you have special needs
35	struct ev_loop *loop = ev_default_loop (0);	48	ev_loop *loop = ev_default_loop (0);
36		49
37	/* initialise an io watcher, then start it */	50	// initialise an io watcher, then start it
		51	// this one will watch for stdin to become readable
38	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);	52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
39	ev_io_start (loop, &stdin_watcher);	53	ev_io_start (loop, &stdin_watcher);
40		54
		55	// initialise a timer watcher, then start it
41	/* simple non-repeating 5.5 second timeout */	56	// simple non-repeating 5.5 second timeout
42	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);	57	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
43	ev_timer_start (loop, &timeout_watcher);	58	ev_timer_start (loop, &timeout_watcher);
44		59
45	/* loop till timeout or data ready */	60	// now wait for events to arrive
46	ev_loop (loop, 0);	61	ev_loop (loop, 0);
47		62
		63	// unloop was called, so exit
48	return 0;	64	return 0;
49	}	65	}
50		66
51	=head1 DESCRIPTION	67	=head1 DESCRIPTION
52		68
		69	The newest version of this document is also available as an html-formatted
		70	web page you might find easier to navigate when reading it for the first
		71	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		72
53	Libev is an event loop: you register interest in certain events (such as a	73	Libev is an event loop: you register interest in certain events (such as a
54	file descriptor being readable or a timeout occuring), and it will manage	74	file descriptor being readable or a timeout occurring), and it will manage
55	these event sources and provide your program with events.	75	these event sources and provide your program with events.
56		76
57	To do this, it must take more or less complete control over your process	77	To do this, it must take more or less complete control over your process
58	(or thread) by executing the I<event loop> handler, and will then	78	(or thread) by executing the I<event loop> handler, and will then
59	communicate events via a callback mechanism.	79	communicate events via a callback mechanism.
…		…
61	You register interest in certain events by registering so-called I<event	81	You register interest in certain events by registering so-called I<event
62	watchers>, which are relatively small C structures you initialise with the	82	watchers>, which are relatively small C structures you initialise with the
63	details of the event, and then hand it over to libev by I<starting> the	83	details of the event, and then hand it over to libev by I<starting> the
64	watcher.	84	watcher.
65		85
66	=head1 FEATURES	86	=head2 FEATURES
67		87
68	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	88	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
69	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	89	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
70	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	90	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
71	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	91	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
…		…
78		98
79	It also is quite fast (see this	99	It also is quite fast (see this
80	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent	100	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
81	for example).	101	for example).
82		102
83	=head1 CONVENTIONS	103	=head2 CONVENTIONS
84		104
85	Libev is very configurable. In this manual the default configuration will	105	Libev is very configurable. In this manual the default (and most common)
86	be described, which supports multiple event loops. For more info about	106	configuration will be described, which supports multiple event loops. For
87	various configuration options please have a look at B<EMBED> section in	107	more info about various configuration options please have a look at
88	this manual. If libev was configured without support for multiple event	108	B<EMBED> section in this manual. If libev was configured without support
89	loops, then all functions taking an initial argument of name C<loop>	109	for multiple event loops, then all functions taking an initial argument of
90	(which is always of type C<struct ev_loop *>) will not have this argument.	110	name C<loop> (which is always of type C<ev_loop *>) will not have
		111	this argument.
91		112
92	=head1 TIME REPRESENTATION	113	=head2 TIME REPRESENTATION
93		114
94	Libev represents time as a single floating point number, representing the	115	Libev represents time as a single floating point number, representing the
95	(fractional) number of seconds since the (POSIX) epoch (somewhere near	116	(fractional) number of seconds since the (POSIX) epoch (somewhere near
96	the beginning of 1970, details are complicated, don't ask). This type is	117	the beginning of 1970, details are complicated, don't ask). This type is
97	called C<ev_tstamp>, which is what you should use too. It usually aliases	118	called C<ev_tstamp>, which is what you should use too. It usually aliases
98	to the C<double> type in C, and when you need to do any calculations on	119	to the C<double> type in C, and when you need to do any calculations on
99	it, you should treat it as such.	120	it, you should treat it as some floating point value. Unlike the name
		121	component C<stamp> might indicate, it is also used for time differences
		122	throughout libev.
		123
		124	=head1 ERROR HANDLING
		125
		126	Libev knows three classes of errors: operating system errors, usage errors
		127	and internal errors (bugs).
		128
		129	When libev catches an operating system error it cannot handle (for example
		130	a system call indicating a condition libev cannot fix), it calls the callback
		131	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		132	abort. The default is to print a diagnostic message and to call C<abort
		133	()>.
		134
		135	When libev detects a usage error such as a negative timer interval, then
		136	it will print a diagnostic message and abort (via the C<assert> mechanism,
		137	so C<NDEBUG> will disable this checking): these are programming errors in
		138	the libev caller and need to be fixed there.
		139
		140	Libev also has a few internal error-checking C<assert>ions, and also has
		141	extensive consistency checking code. These do not trigger under normal
		142	circumstances, as they indicate either a bug in libev or worse.
		143
100		144
101	=head1 GLOBAL FUNCTIONS	145	=head1 GLOBAL FUNCTIONS
102		146
103	These functions can be called anytime, even before initialising the	147	These functions can be called anytime, even before initialising the
104	library in any way.	148	library in any way.
…		…
109		153
110	Returns the current time as libev would use it. Please note that the	154	Returns the current time as libev would use it. Please note that the
111	C<ev_now> function is usually faster and also often returns the timestamp	155	C<ev_now> function is usually faster and also often returns the timestamp
112	you actually want to know.	156	you actually want to know.
113		157
		158	=item ev_sleep (ev_tstamp interval)
		159
		160	Sleep for the given interval: The current thread will be blocked until
		161	either it is interrupted or the given time interval has passed. Basically
		162	this is a sub-second-resolution C<sleep ()>.
		163
114	=item int ev_version_major ()	164	=item int ev_version_major ()
115		165
116	=item int ev_version_minor ()	166	=item int ev_version_minor ()
117		167
118	You can find out the major and minor version numbers of the library	168	You can find out the major and minor ABI version numbers of the library
119	you linked against by calling the functions C<ev_version_major> and	169	you linked against by calling the functions C<ev_version_major> and
120	C<ev_version_minor>. If you want, you can compare against the global	170	C<ev_version_minor>. If you want, you can compare against the global
121	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the	171	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
122	version of the library your program was compiled against.	172	version of the library your program was compiled against.
123		173
		174	These version numbers refer to the ABI version of the library, not the
		175	release version.
		176
124	Usually, it's a good idea to terminate if the major versions mismatch,	177	Usually, it's a good idea to terminate if the major versions mismatch,
125	as this indicates an incompatible change. Minor versions are usually	178	as this indicates an incompatible change. Minor versions are usually
126	compatible to older versions, so a larger minor version alone is usually	179	compatible to older versions, so a larger minor version alone is usually
127	not a problem.	180	not a problem.
128		181
129	Example: Make sure we haven't accidentally been linked against the wrong	182	Example: Make sure we haven't accidentally been linked against the wrong
130	version.	183	version.
131		184
132	assert (("libev version mismatch",	185	assert (("libev version mismatch",
133	ev_version_major () == EV_VERSION_MAJOR	186	ev_version_major () == EV_VERSION_MAJOR
134	&& ev_version_minor () >= EV_VERSION_MINOR));	187	&& ev_version_minor () >= EV_VERSION_MINOR));
135		188
136	=item unsigned int ev_supported_backends ()	189	=item unsigned int ev_supported_backends ()
137		190
138	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	191	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
139	value) compiled into this binary of libev (independent of their	192	value) compiled into this binary of libev (independent of their
…		…
141	a description of the set values.	194	a description of the set values.
142		195
143	Example: make sure we have the epoll method, because yeah this is cool and	196	Example: make sure we have the epoll method, because yeah this is cool and
144	a must have and can we have a torrent of it please!!!11	197	a must have and can we have a torrent of it please!!!11
145		198
146	assert (("sorry, no epoll, no sex",	199	assert (("sorry, no epoll, no sex",
147	ev_supported_backends () & EVBACKEND_EPOLL));	200	ev_supported_backends () & EVBACKEND_EPOLL));
148		201
149	=item unsigned int ev_recommended_backends ()	202	=item unsigned int ev_recommended_backends ()
150		203
151	Return the set of all backends compiled into this binary of libev and also	204	Return the set of all backends compiled into this binary of libev and also
152	recommended for this platform. This set is often smaller than the one	205	recommended for this platform. This set is often smaller than the one
153	returned by C<ev_supported_backends>, as for example kqueue is broken on	206	returned by C<ev_supported_backends>, as for example kqueue is broken on
154	most BSDs and will not be autodetected unless you explicitly request it	207	most BSDs and will not be auto-detected unless you explicitly request it
155	(assuming you know what you are doing). This is the set of backends that	208	(assuming you know what you are doing). This is the set of backends that
156	libev will probe for if you specify no backends explicitly.	209	libev will probe for if you specify no backends explicitly.
157		210
158	=item unsigned int ev_embeddable_backends ()	211	=item unsigned int ev_embeddable_backends ()
159		212
…		…
163	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	216	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
164	recommended ones.	217	recommended ones.
165		218
166	See the description of C<ev_embed> watchers for more info.	219	See the description of C<ev_embed> watchers for more info.
167		220
168	=item ev_set_allocator (void *(*cb)(void *ptr, size_t size))	221	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
169		222
170	Sets the allocation function to use (the prototype and semantics are	223	Sets the allocation function to use (the prototype is similar - the
171	identical to the realloc C function). It is used to allocate and free	224	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
172	memory (no surprises here). If it returns zero when memory needs to be	225	used to allocate and free memory (no surprises here). If it returns zero
173	allocated, the library might abort or take some potentially destructive	226	when memory needs to be allocated (C<size != 0>), the library might abort
174	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.
175		232
176	You could override this function in high-availability programs to, say,	233	You could override this function in high-availability programs to, say,
177	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,
178	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.
179		236
180	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
181	retries).	238	retries (example requires a standards-compliant C<realloc>).
182		239
183	static void *	240	static void *
184	persistent_realloc (void *ptr, size_t size)	241	persistent_realloc (void *ptr, size_t size)
185	{	242	{
186	for (;;)	243	for (;;)
…		…
195	}	252	}
196		253
197	...	254	...
198	ev_set_allocator (persistent_realloc);	255	ev_set_allocator (persistent_realloc);
199		256
200	=item ev_set_syserr_cb (void (*cb)(const char *msg));	257	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
201		258
202	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
203	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
204	indicating the system call or subsystem causing the problem. If this	261	indicating the system call or subsystem causing the problem. If this
205	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
206	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
207	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
208	(such as abort).	265	(such as abort).
209		266
210	Example: This is basically the same thing that libev does internally, too.	267	Example: This is basically the same thing that libev does internally, too.
…		…
221		278
222	=back	279	=back
223		280
224	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	281	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
225		282
226	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>
227	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>
228	events, and dynamically created loops which do not.	285	I<function>).
229		286
230	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
231	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
232	create, you also create another event loop. Libev itself does no locking	289	not.
233	whatsoever, so if you mix calls to the same event loop in different
234	threads, make sure you lock (this is usually a bad idea, though, even if
235	done correctly, because it's hideous and inefficient).
236		290
237	=over 4	291	=over 4
238		292
239	=item struct ev_loop *ev_default_loop (unsigned int flags)	293	=item struct ev_loop *ev_default_loop (unsigned int flags)
240		294
…		…
244	flags. If that is troubling you, check C<ev_backend ()> afterwards).	298	flags. If that is troubling you, check C<ev_backend ()> afterwards).
245		299
246	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
247	function.	301	function.
248		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
249	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
250	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>).
251		316
252	The following flags are supported:	317	The following flags are supported:
253		318
…		…
258	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
259	thing, believe me).	324	thing, believe me).
260		325
261	=item C<EVFLAG_NOENV>	326	=item C<EVFLAG_NOENV>
262		327
263	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
264	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
265	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	330	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
266	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
267	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
268	around bugs.	333	around bugs.
269		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
270	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	355	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
271		356
272	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
273	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,
274	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
275	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
276	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).
277		373
278	=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)
279		375
280	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
281	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
282	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
283	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>.
284		385
285	=item C<EVBACKEND_EPOLL> (value 4, Linux)	386	=item C<EVBACKEND_EPOLL> (value 4, Linux)
286		387
287	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,
288	but it scales phenomenally better. While poll and select usually scale like	389	but it scales phenomenally better. While poll and select usually scale
289	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),
290	either O(1) or O(active_fds).	391	epoll scales either O(1) or O(active_fds).
291		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
292	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
293	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
294	(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
295	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
296	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.
297		416
298	Please note that epoll sometimes generates spurious notifications, so you	417	Best performance from this backend is achieved by not unregistering all
299	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,
300	(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>.
301		434
302	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	435	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
303		436
304	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
305	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
306	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
307	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
308	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
309	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.
310		450
311	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
312	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
313	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
314	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
315	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>) and, did I mention it,
		466	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>.
316		471
317	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	472	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
318		473
319	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.
320		478
321	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	479	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
322		480
323	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,
324	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)).
325		483
326	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
327	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
328	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>.
329		500
330	=item C<EVBACKEND_ALL>	501	=item C<EVBACKEND_ALL>
331		502
332	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
333	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
334	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	505	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
335		506
		507	It is definitely not recommended to use this flag.
		508
336	=back	509	=back
337		510
338	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
339	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
340	specified, most compiled-in backend will be tried, usually in reverse	513	specified, all backends in C<ev_recommended_backends ()> will be tried.
341	order of their flag values :)
342		514
343	The most typical usage is like this:	515	Example: This is the most typical usage.
344		516
345	if (!ev_default_loop (0))	517	if (!ev_default_loop (0))
346	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	518	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
347		519
348	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
349	environment settings to be taken into account:	521	environment settings to be taken into account:
350		522
351	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	523	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
352		524
353	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
354	available (warning, breaks stuff, best use only with your own private	526	used if available (warning, breaks stuff, best use only with your own
355	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):
356		529
357	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	530	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
358		531
359	=item struct ev_loop *ev_loop_new (unsigned int flags)	532	=item struct ev_loop *ev_loop_new (unsigned int flags)
360		533
361	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
362	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
363	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
364	undefined behaviour (or a failed assertion if assertions are enabled).	537	undefined behaviour (or a failed assertion if assertions are enabled).
365		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
366	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.
367		544
368	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	545	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
369	if (!epoller)	546	if (!epoller)
370	fatal ("no epoll found here, maybe it hides under your chair");	547	fatal ("no epoll found here, maybe it hides under your chair");
371		548
372	=item ev_default_destroy ()	549	=item ev_default_destroy ()
373		550
374	Destroys the default loop again (frees all memory and kernel state	551	Destroys the default loop again (frees all memory and kernel state
375	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
376	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
377	responsibility to either stop all watchers cleanly yoursef I<before>	554	responsibility to either stop all watchers cleanly yourself I<before>
378	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
379	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
380	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>).
381		567
382	=item ev_loop_destroy (loop)	568	=item ev_loop_destroy (loop)
383		569
384	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
385	earlier call to C<ev_loop_new>.	571	earlier call to C<ev_loop_new>.
386		572
387	=item ev_default_fork ()	573	=item ev_default_fork ()
388		574
		575	This function sets a flag that causes subsequent C<ev_loop> iterations
389	This function reinitialises the kernel state for backends that have	576	to reinitialise the kernel state for backends that have one. Despite the
390	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
391	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
392	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.
393		581
394	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
395	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
396	fork+exec, you don't have to call it.	584	you just fork+exec, you don't have to call it at all.
397		585
398	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
399	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
400	quite nicely into a call to C<pthread_atfork>:	588	quite nicely into a call to C<pthread_atfork>:
401		589
402	pthread_atfork (0, 0, ev_default_fork);	590	pthread_atfork (0, 0, ev_default_fork);
403		591
404	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
405	without calling this function, so if you force one of those backends you
406	do not need to care.
407
408	=item ev_loop_fork (loop)	592	=item ev_loop_fork (loop)
409		593
410	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
411	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
412	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.
413		613
414	=item unsigned int ev_backend (loop)	614	=item unsigned int ev_backend (loop)
415		615
416	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
417	use.	617	use.
…		…
420		620
421	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
422	received events and started processing them. This timestamp does not	622	received events and started processing them. This timestamp does not
423	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
424	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
425	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.
426		638
427	=item ev_loop (loop, int flags)	639	=item ev_loop (loop, int flags)
428		640
429	Finally, this is it, the event handler. This function usually is called	641	Finally, this is it, the event handler. This function usually is called
430	after you initialised all your watchers and you want to start handling	642	after you initialised all your watchers and you want to start handling
…		…
433	If the flags argument is specified as C<0>, it will not return until	645	If the flags argument is specified as C<0>, it will not return until
434	either no event watchers are active anymore or C<ev_unloop> was called.	646	either no event watchers are active anymore or C<ev_unloop> was called.
435		647
436	Please note that an explicit C<ev_unloop> is usually better than	648	Please note that an explicit C<ev_unloop> is usually better than
437	relying on all watchers to be stopped when deciding when a program has	649	relying on all watchers to be stopped when deciding when a program has
438	finished (especially in interactive programs), but having a program that	650	finished (especially in interactive programs), but having a program
439	automatically loops as long as it has to and no longer by virtue of	651	that automatically loops as long as it has to and no longer by virtue
440	relying on its watchers stopping correctly is a thing of beauty.	652	of relying on its watchers stopping correctly, that is truly a thing of
		653	beauty.
441		654
442	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	655	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
443	those events and any outstanding ones, but will not block your process in	656	those events and any already outstanding ones, but will not block your
444	case there are no events and will return after one iteration of the loop.	657	process in case there are no events and will return after one iteration of
		658	the loop.
445		659
446	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	660	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
447	neccessary) and will handle those and any outstanding ones. It will block	661	necessary) and will handle those and any already outstanding ones. It
448	your process until at least one new event arrives, and will return after	662	will block your process until at least one new event arrives (which could
449	one iteration of the loop. This is useful if you are waiting for some	663	be an event internal to libev itself, so there is no guarantee that a
450	external event in conjunction with something not expressible using other	664	user-registered callback will be called), and will return after one
		665	iteration of the loop.
		666
		667	This is useful if you are waiting for some external event in conjunction
		668	with something not expressible using other libev watchers (i.e. "roll your
451	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	669	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
452	usually a better approach for this kind of thing.	670	usually a better approach for this kind of thing.
453		671
454	Here are the gory details of what C<ev_loop> does:	672	Here are the gory details of what C<ev_loop> does:
455		673
456	* If there are no active watchers (reference count is zero), return.	674	- Before the first iteration, call any pending watchers.
457	- Queue prepare watchers and then call all outstanding watchers.	675	* If EVFLAG_FORKCHECK was used, check for a fork.
		676	- If a fork was detected (by any means), queue and call all fork watchers.
		677	- Queue and call all prepare watchers.
458	- If we have been forked, recreate the kernel state.	678	- If we have been forked, detach and recreate the kernel state
		679	as to not disturb the other process.
459	- Update the kernel state with all outstanding changes.	680	- Update the kernel state with all outstanding changes.
460	- Update the "event loop time".	681	- Update the "event loop time" (ev_now ()).
461	- Calculate for how long to block.	682	- Calculate for how long to sleep or block, if at all
		683	(active idle watchers, EVLOOP_NONBLOCK or not having
		684	any active watchers at all will result in not sleeping).
		685	- Sleep if the I/O and timer collect interval say so.
462	- Block the process, waiting for any events.	686	- Block the process, waiting for any events.
463	- Queue all outstanding I/O (fd) events.	687	- Queue all outstanding I/O (fd) events.
464	- Update the "event loop time" and do time jump handling.	688	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
465	- Queue all outstanding timers.	689	- Queue all expired timers.
466	- Queue all outstanding periodics.	690	- Queue all expired periodics.
467	- If no events are pending now, queue all idle watchers.	691	- Unless any events are pending now, queue all idle watchers.
468	- Queue all check watchers.	692	- Queue all check watchers.
469	- Call all queued watchers in reverse order (i.e. check watchers first).	693	- Call all queued watchers in reverse order (i.e. check watchers first).
470	Signals and child watchers are implemented as I/O watchers, and will	694	Signals and child watchers are implemented as I/O watchers, and will
471	be handled here by queueing them when their watcher gets executed.	695	be handled here by queueing them when their watcher gets executed.
472	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	696	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
473	were used, return, otherwise continue with step *.	697	were used, or there are no active watchers, return, otherwise
		698	continue with step *.
474		699
475	Example: Queue some jobs and then loop until no events are outsanding	700	Example: Queue some jobs and then loop until no events are outstanding
476	anymore.	701	anymore.
477		702
478	... queue jobs here, make sure they register event watchers as long	703	... queue jobs here, make sure they register event watchers as long
479	... as they still have work to do (even an idle watcher will do..)	704	... as they still have work to do (even an idle watcher will do..)
480	ev_loop (my_loop, 0);	705	ev_loop (my_loop, 0);
481	... jobs done. yeah!	706	... jobs done or somebody called unloop. yeah!
482		707
483	=item ev_unloop (loop, how)	708	=item ev_unloop (loop, how)
484		709
485	Can be used to make a call to C<ev_loop> return early (but only after it	710	Can be used to make a call to C<ev_loop> return early (but only after it
486	has processed all outstanding events). The C<how> argument must be either	711	has processed all outstanding events). The C<how> argument must be either
487	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	712	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
488	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	713	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
489		714
		715	This "unloop state" will be cleared when entering C<ev_loop> again.
		716
		717	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
		718
490	=item ev_ref (loop)	719	=item ev_ref (loop)
491		720
492	=item ev_unref (loop)	721	=item ev_unref (loop)
493		722
494	Ref/unref can be used to add or remove a reference count on the event	723	Ref/unref can be used to add or remove a reference count on the event
495	loop: Every watcher keeps one reference, and as long as the reference	724	loop: Every watcher keeps one reference, and as long as the reference
496	count is nonzero, C<ev_loop> will not return on its own. If you have	725	count is nonzero, C<ev_loop> will not return on its own.
		726
497	a watcher you never unregister that should not keep C<ev_loop> from	727	If you have a watcher you never unregister that should not keep C<ev_loop>
498	returning, ev_unref() after starting, and ev_ref() before stopping it. For	728	from returning, call ev_unref() after starting, and ev_ref() before
		729	stopping it.
		730
499	example, libev itself uses this for its internal signal pipe: It is not	731	As an example, libev itself uses this for its internal signal pipe: It is
500	visible to the libev user and should not keep C<ev_loop> from exiting if	732	not visible to the libev user and should not keep C<ev_loop> from exiting
501	no event watchers registered by it are active. It is also an excellent	733	if no event watchers registered by it are active. It is also an excellent
502	way to do this for generic recurring timers or from within third-party	734	way to do this for generic recurring timers or from within third-party
503	libraries. Just remember to I<unref after start> and I<ref before stop>.	735	libraries. Just remember to I<unref after start> and I<ref before stop>
		736	(but only if the watcher wasn't active before, or was active before,
		737	respectively).
504		738
505	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	739	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
506	running when nothing else is active.	740	running when nothing else is active.
507		741
508	struct ev_signal exitsig;	742	ev_signal exitsig;
509	ev_signal_init (&exitsig, sig_cb, SIGINT);	743	ev_signal_init (&exitsig, sig_cb, SIGINT);
510	ev_signal_start (loop, &exitsig);	744	ev_signal_start (loop, &exitsig);
511	evf_unref (loop);	745	evf_unref (loop);
512		746
513	Example: For some weird reason, unregister the above signal handler again.	747	Example: For some weird reason, unregister the above signal handler again.
514		748
515	ev_ref (loop);	749	ev_ref (loop);
516	ev_signal_stop (loop, &exitsig);	750	ev_signal_stop (loop, &exitsig);
		751
		752	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		753
		754	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		755
		756	These advanced functions influence the time that libev will spend waiting
		757	for events. Both time intervals are by default C<0>, meaning that libev
		758	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		759	latency.
		760
		761	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		762	allows libev to delay invocation of I/O and timer/periodic callbacks
		763	to increase efficiency of loop iterations (or to increase power-saving
		764	opportunities).
		765
		766	The idea is that sometimes your program runs just fast enough to handle
		767	one (or very few) event(s) per loop iteration. While this makes the
		768	program responsive, it also wastes a lot of CPU time to poll for new
		769	events, especially with backends like C<select ()> which have a high
		770	overhead for the actual polling but can deliver many events at once.
		771
		772	By setting a higher I<io collect interval> you allow libev to spend more
		773	time collecting I/O events, so you can handle more events per iteration,
		774	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		775	C<ev_timer>) will be not affected. Setting this to a non-null value will
		776	introduce an additional C<ev_sleep ()> call into most loop iterations.
		777
		778	Likewise, by setting a higher I<timeout collect interval> you allow libev
		779	to spend more time collecting timeouts, at the expense of increased
		780	latency/jitter/inexactness (the watcher callback will be called
		781	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		782	value will not introduce any overhead in libev.
		783
		784	Many (busy) programs can usually benefit by setting the I/O collect
		785	interval to a value near C<0.1> or so, which is often enough for
		786	interactive servers (of course not for games), likewise for timeouts. It
		787	usually doesn't make much sense to set it to a lower value than C<0.01>,
		788	as this approaches the timing granularity of most systems.
		789
		790	Setting the I<timeout collect interval> can improve the opportunity for
		791	saving power, as the program will "bundle" timer callback invocations that
		792	are "near" in time together, by delaying some, thus reducing the number of
		793	times the process sleeps and wakes up again. Another useful technique to
		794	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		795	they fire on, say, one-second boundaries only.
		796
		797	=item ev_loop_verify (loop)
		798
		799	This function only does something when C<EV_VERIFY> support has been
		800	compiled in, which is the default for non-minimal builds. It tries to go
		801	through all internal structures and checks them for validity. If anything
		802	is found to be inconsistent, it will print an error message to standard
		803	error and call C<abort ()>.
		804
		805	This can be used to catch bugs inside libev itself: under normal
		806	circumstances, this function will never abort as of course libev keeps its
		807	data structures consistent.
517		808
518	=back	809	=back
519		810
520		811
521	=head1 ANATOMY OF A WATCHER	812	=head1 ANATOMY OF A WATCHER
		813
		814	In the following description, uppercase C<TYPE> in names stands for the
		815	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		816	watchers and C<ev_io_start> for I/O watchers.
522		817
523	A watcher is a structure that you create and register to record your	818	A watcher is a structure that you create and register to record your
524	interest in some event. For instance, if you want to wait for STDIN to	819	interest in some event. For instance, if you want to wait for STDIN to
525	become readable, you would create an C<ev_io> watcher for that:	820	become readable, you would create an C<ev_io> watcher for that:
526		821
527	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	822	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
528	{	823	{
529	ev_io_stop (w);	824	ev_io_stop (w);
530	ev_unloop (loop, EVUNLOOP_ALL);	825	ev_unloop (loop, EVUNLOOP_ALL);
531	}	826	}
532		827
533	struct ev_loop *loop = ev_default_loop (0);	828	struct ev_loop *loop = ev_default_loop (0);
		829
534	struct ev_io stdin_watcher;	830	ev_io stdin_watcher;
		831
535	ev_init (&stdin_watcher, my_cb);	832	ev_init (&stdin_watcher, my_cb);
536	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	833	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
537	ev_io_start (loop, &stdin_watcher);	834	ev_io_start (loop, &stdin_watcher);
		835
538	ev_loop (loop, 0);	836	ev_loop (loop, 0);
539		837
540	As you can see, you are responsible for allocating the memory for your	838	As you can see, you are responsible for allocating the memory for your
541	watcher structures (and it is usually a bad idea to do this on the stack,	839	watcher structures (and it is I<usually> a bad idea to do this on the
542	although this can sometimes be quite valid).	840	stack).
		841
		842	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		843	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
543		844
544	Each watcher structure must be initialised by a call to C<ev_init	845	Each watcher structure must be initialised by a call to C<ev_init
545	(watcher *, callback)>, which expects a callback to be provided. This	846	(watcher *, callback)>, which expects a callback to be provided. This
546	callback gets invoked each time the event occurs (or, in the case of io	847	callback gets invoked each time the event occurs (or, in the case of I/O
547	watchers, each time the event loop detects that the file descriptor given	848	watchers, each time the event loop detects that the file descriptor given
548	is readable and/or writable).	849	is readable and/or writable).
549		850
550	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	851	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
551	with arguments specific to this watcher type. There is also a macro	852	macro to configure it, with arguments specific to the watcher type. There
552	to combine initialisation and setting in one call: C<< ev_<type>_init	853	is also a macro to combine initialisation and setting in one call: C<<
553	(watcher *, callback, ...) >>.	854	ev_TYPE_init (watcher *, callback, ...) >>.
554		855
555	To make the watcher actually watch out for events, you have to start it	856	To make the watcher actually watch out for events, you have to start it
556	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	857	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
557	*) >>), and you can stop watching for events at any time by calling the	858	*) >>), and you can stop watching for events at any time by calling the
558	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	859	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
559		860
560	As long as your watcher is active (has been started but not stopped) you	861	As long as your watcher is active (has been started but not stopped) you
561	must not touch the values stored in it. Most specifically you must never	862	must not touch the values stored in it. Most specifically you must never
562	reinitialise it or call its C<set> macro.	863	reinitialise it or call its C<ev_TYPE_set> macro.
563		864
564	Each and every callback receives the event loop pointer as first, the	865	Each and every callback receives the event loop pointer as first, the
565	registered watcher structure as second, and a bitset of received events as	866	registered watcher structure as second, and a bitset of received events as
566	third argument.	867	third argument.
567		868
…		…
621	=item C<EV_FORK>	922	=item C<EV_FORK>
622		923
623	The event loop has been resumed in the child process after fork (see	924	The event loop has been resumed in the child process after fork (see
624	C<ev_fork>).	925	C<ev_fork>).
625		926
		927	=item C<EV_ASYNC>
		928
		929	The given async watcher has been asynchronously notified (see C<ev_async>).
		930
626	=item C<EV_ERROR>	931	=item C<EV_ERROR>
627		932
628	An unspecified error has occured, the watcher has been stopped. This might	933	An unspecified error has occurred, the watcher has been stopped. This might
629	happen because the watcher could not be properly started because libev	934	happen because the watcher could not be properly started because libev
630	ran out of memory, a file descriptor was found to be closed or any other	935	ran out of memory, a file descriptor was found to be closed or any other
		936	problem. Libev considers these application bugs.
		937
631	problem. You best act on it by reporting the problem and somehow coping	938	You best act on it by reporting the problem and somehow coping with the
632	with the watcher being stopped.	939	watcher being stopped. Note that well-written programs should not receive
		940	an error ever, so when your watcher receives it, this usually indicates a
		941	bug in your program.
633		942
634	Libev will usually signal a few "dummy" events together with an error,	943	Libev will usually signal a few "dummy" events together with an error, for
635	for example it might indicate that a fd is readable or writable, and if	944	example it might indicate that a fd is readable or writable, and if your
636	your callbacks is well-written it can just attempt the operation and cope	945	callbacks is well-written it can just attempt the operation and cope with
637	with the error from read() or write(). This will not work in multithreaded	946	the error from read() or write(). This will not work in multi-threaded
638	programs, though, so beware.	947	programs, though, as the fd could already be closed and reused for another
		948	thing, so beware.
639		949
640	=back	950	=back
641		951
642	=head2 GENERIC WATCHER FUNCTIONS	952	=head2 GENERIC WATCHER FUNCTIONS
643
644	In the following description, C<TYPE> stands for the watcher type,
645	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
646		953
647	=over 4	954	=over 4
648		955
649	=item C<ev_init> (ev_TYPE *watcher, callback)	956	=item C<ev_init> (ev_TYPE *watcher, callback)
650		957
…		…
656	which rolls both calls into one.	963	which rolls both calls into one.
657		964
658	You can reinitialise a watcher at any time as long as it has been stopped	965	You can reinitialise a watcher at any time as long as it has been stopped
659	(or never started) and there are no pending events outstanding.	966	(or never started) and there are no pending events outstanding.
660		967
661	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	968	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
662	int revents)>.	969	int revents)>.
		970
		971	Example: Initialise an C<ev_io> watcher in two steps.
		972
		973	ev_io w;
		974	ev_init (&w, my_cb);
		975	ev_io_set (&w, STDIN_FILENO, EV_READ);
663		976
664	=item C<ev_TYPE_set> (ev_TYPE *, [args])	977	=item C<ev_TYPE_set> (ev_TYPE *, [args])
665		978
666	This macro initialises the type-specific parts of a watcher. You need to	979	This macro initialises the type-specific parts of a watcher. You need to
667	call C<ev_init> at least once before you call this macro, but you can	980	call C<ev_init> at least once before you call this macro, but you can
…		…
670	difference to the C<ev_init> macro).	983	difference to the C<ev_init> macro).
671		984
672	Although some watcher types do not have type-specific arguments	985	Although some watcher types do not have type-specific arguments
673	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	986	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
674		987
		988	See C<ev_init>, above, for an example.
		989
675	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	990	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
676		991
677	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	992	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
678	calls into a single call. This is the most convinient method to initialise	993	calls into a single call. This is the most convenient method to initialise
679	a watcher. The same limitations apply, of course.	994	a watcher. The same limitations apply, of course.
		995
		996	Example: Initialise and set an C<ev_io> watcher in one step.
		997
		998	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
680		999
681	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1000	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
682		1001
683	Starts (activates) the given watcher. Only active watchers will receive	1002	Starts (activates) the given watcher. Only active watchers will receive
684	events. If the watcher is already active nothing will happen.	1003	events. If the watcher is already active nothing will happen.
685		1004
		1005	Example: Start the C<ev_io> watcher that is being abused as example in this
		1006	whole section.
		1007
		1008	ev_io_start (EV_DEFAULT_UC, &w);
		1009
686	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1010	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
687		1011
688	Stops the given watcher again (if active) and clears the pending	1012	Stops the given watcher if active, and clears the pending status (whether
		1013	the watcher was active or not).
		1014
689	status. It is possible that stopped watchers are pending (for example,	1015	It is possible that stopped watchers are pending - for example,
690	non-repeating timers are being stopped when they become pending), but	1016	non-repeating timers are being stopped when they become pending - but
691	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1017	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
692	you want to free or reuse the memory used by the watcher it is therefore a	1018	pending. If you want to free or reuse the memory used by the watcher it is
693	good idea to always call its C<ev_TYPE_stop> function.	1019	therefore a good idea to always call its C<ev_TYPE_stop> function.
694		1020
695	=item bool ev_is_active (ev_TYPE *watcher)	1021	=item bool ev_is_active (ev_TYPE *watcher)
696		1022
697	Returns a true value iff the watcher is active (i.e. it has been started	1023	Returns a true value iff the watcher is active (i.e. it has been started
698	and not yet been stopped). As long as a watcher is active you must not modify	1024	and not yet been stopped). As long as a watcher is active you must not modify
…		…
701	=item bool ev_is_pending (ev_TYPE *watcher)	1027	=item bool ev_is_pending (ev_TYPE *watcher)
702		1028
703	Returns a true value iff the watcher is pending, (i.e. it has outstanding	1029	Returns a true value iff the watcher is pending, (i.e. it has outstanding
704	events but its callback has not yet been invoked). As long as a watcher	1030	events but its callback has not yet been invoked). As long as a watcher
705	is pending (but not active) you must not call an init function on it (but	1031	is pending (but not active) you must not call an init function on it (but
706	C<ev_TYPE_set> is safe) and you must make sure the watcher is available to	1032	C<ev_TYPE_set> is safe), you must not change its priority, and you must
707	libev (e.g. you cnanot C<free ()> it).	1033	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1034	it).
708		1035
709	=item callback ev_cb (ev_TYPE *watcher)	1036	=item callback ev_cb (ev_TYPE *watcher)
710		1037
711	Returns the callback currently set on the watcher.	1038	Returns the callback currently set on the watcher.
712		1039
713	=item ev_cb_set (ev_TYPE *watcher, callback)	1040	=item ev_cb_set (ev_TYPE *watcher, callback)
714		1041
715	Change the callback. You can change the callback at virtually any time	1042	Change the callback. You can change the callback at virtually any time
716	(modulo threads).	1043	(modulo threads).
717		1044
		1045	=item ev_set_priority (ev_TYPE *watcher, priority)
		1046
		1047	=item int ev_priority (ev_TYPE *watcher)
		1048
		1049	Set and query the priority of the watcher. The priority is a small
		1050	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1051	(default: C<-2>). Pending watchers with higher priority will be invoked
		1052	before watchers with lower priority, but priority will not keep watchers
		1053	from being executed (except for C<ev_idle> watchers).
		1054
		1055	This means that priorities are I<only> used for ordering callback
		1056	invocation after new events have been received. This is useful, for
		1057	example, to reduce latency after idling, or more often, to bind two
		1058	watchers on the same event and make sure one is called first.
		1059
		1060	If you need to suppress invocation when higher priority events are pending
		1061	you need to look at C<ev_idle> watchers, which provide this functionality.
		1062
		1063	You I<must not> change the priority of a watcher as long as it is active or
		1064	pending.
		1065
		1066	The default priority used by watchers when no priority has been set is
		1067	always C<0>, which is supposed to not be too high and not be too low :).
		1068
		1069	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1070	fine, as long as you do not mind that the priority value you query might
		1071	or might not have been clamped to the valid range.
		1072
		1073	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1074
		1075	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1076	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1077	can deal with that fact, as both are simply passed through to the
		1078	callback.
		1079
		1080	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1081
		1082	If the watcher is pending, this function clears its pending status and
		1083	returns its C<revents> bitset (as if its callback was invoked). If the
		1084	watcher isn't pending it does nothing and returns C<0>.
		1085
		1086	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1087	callback to be invoked, which can be accomplished with this function.
		1088
718	=back	1089	=back
719		1090
720		1091
721	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1092	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
722		1093
723	Each watcher has, by default, a member C<void *data> that you can change	1094	Each watcher has, by default, a member C<void *data> that you can change
724	and read at any time, libev will completely ignore it. This can be used	1095	and read at any time: libev will completely ignore it. This can be used
725	to associate arbitrary data with your watcher. If you need more data and	1096	to associate arbitrary data with your watcher. If you need more data and
726	don't want to allocate memory and store a pointer to it in that data	1097	don't want to allocate memory and store a pointer to it in that data
727	member, you can also "subclass" the watcher type and provide your own	1098	member, you can also "subclass" the watcher type and provide your own
728	data:	1099	data:
729		1100
730	struct my_io	1101	struct my_io
731	{	1102	{
732	struct ev_io io;	1103	ev_io io;
733	int otherfd;	1104	int otherfd;
734	void *somedata;	1105	void *somedata;
735	struct whatever *mostinteresting;	1106	struct whatever *mostinteresting;
736	}	1107	};
		1108
		1109	...
		1110	struct my_io w;
		1111	ev_io_init (&w.io, my_cb, fd, EV_READ);
737		1112
738	And since your callback will be called with a pointer to the watcher, you	1113	And since your callback will be called with a pointer to the watcher, you
739	can cast it back to your own type:	1114	can cast it back to your own type:
740		1115
741	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1116	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
742	{	1117	{
743	struct my_io *w = (struct my_io *)w_;	1118	struct my_io *w = (struct my_io *)w_;
744	...	1119	...
745	}	1120	}
746		1121
747	More interesting and less C-conformant ways of casting your callback type	1122	More interesting and less C-conformant ways of casting your callback type
748	instead have been omitted.	1123	instead have been omitted.
749		1124
750	Another common scenario is having some data structure with multiple	1125	Another common scenario is to use some data structure with multiple
751	watchers:	1126	embedded watchers:
752		1127
753	struct my_biggy	1128	struct my_biggy
754	{	1129	{
755	int some_data;	1130	int some_data;
756	ev_timer t1;	1131	ev_timer t1;
757	ev_timer t2;	1132	ev_timer t2;
758	}	1133	}
759		1134
760	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1135	In this case getting the pointer to C<my_biggy> is a bit more
761	you need to use C<offsetof>:	1136	complicated: Either you store the address of your C<my_biggy> struct
		1137	in the C<data> member of the watcher (for woozies), or you need to use
		1138	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1139	programmers):
762		1140
763	#include <stddef.h>	1141	#include <stddef.h>
764		1142
765	static void	1143	static void
766	t1_cb (EV_P_ struct ev_timer *w, int revents)	1144	t1_cb (EV_P_ ev_timer *w, int revents)
767	{	1145	{
768	struct my_biggy big = (struct my_biggy *	1146	struct my_biggy big = (struct my_biggy *
769	(((char *)w) - offsetof (struct my_biggy, t1));	1147	(((char *)w) - offsetof (struct my_biggy, t1));
770	}	1148	}
771		1149
772	static void	1150	static void
773	t2_cb (EV_P_ struct ev_timer *w, int revents)	1151	t2_cb (EV_P_ ev_timer *w, int revents)
774	{	1152	{
775	struct my_biggy big = (struct my_biggy *	1153	struct my_biggy big = (struct my_biggy *
776	(((char *)w) - offsetof (struct my_biggy, t2));	1154	(((char *)w) - offsetof (struct my_biggy, t2));
777	}	1155	}
778		1156
779		1157
780	=head1 WATCHER TYPES	1158	=head1 WATCHER TYPES
781		1159
782	This section describes each watcher in detail, but will not repeat	1160	This section describes each watcher in detail, but will not repeat
…		…
806	In general you can register as many read and/or write event watchers per	1184	In general you can register as many read and/or write event watchers per
807	fd as you want (as long as you don't confuse yourself). Setting all file	1185	fd as you want (as long as you don't confuse yourself). Setting all file
808	descriptors to non-blocking mode is also usually a good idea (but not	1186	descriptors to non-blocking mode is also usually a good idea (but not
809	required if you know what you are doing).	1187	required if you know what you are doing).
810		1188
811	You have to be careful with dup'ed file descriptors, though. Some backends	1189	If you cannot use non-blocking mode, then force the use of a
812	(the linux epoll backend is a notable example) cannot handle dup'ed file	1190	known-to-be-good backend (at the time of this writing, this includes only
813	descriptors correctly if you register interest in two or more fds pointing	1191	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>).
814	to the same underlying file/socket/etc. description (that is, they share
815	the same underlying "file open").
816
817	If you must do this, then force the use of a known-to-be-good backend
818	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
819	C<EVBACKEND_POLL>).
820		1192
821	Another thing you have to watch out for is that it is quite easy to	1193	Another thing you have to watch out for is that it is quite easy to
822	receive "spurious" readyness notifications, that is your callback might	1194	receive "spurious" readiness notifications, that is your callback might
823	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1195	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
824	because there is no data. Not only are some backends known to create a	1196	because there is no data. Not only are some backends known to create a
825	lot of those (for example solaris ports), it is very easy to get into	1197	lot of those (for example Solaris ports), it is very easy to get into
826	this situation even with a relatively standard program structure. Thus	1198	this situation even with a relatively standard program structure. Thus
827	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1199	it is best to always use non-blocking I/O: An extra C<read>(2) returning
828	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1200	C<EAGAIN> is far preferable to a program hanging until some data arrives.
829		1201
830	If you cannot run the fd in non-blocking mode (for example you should not	1202	If you cannot run the fd in non-blocking mode (for example you should
831	play around with an Xlib connection), then you have to seperately re-test	1203	not play around with an Xlib connection), then you have to separately
832	wether a file descriptor is really ready with a known-to-be good interface	1204	re-test whether a file descriptor is really ready with a known-to-be good
833	such as poll (fortunately in our Xlib example, Xlib already does this on	1205	interface such as poll (fortunately in our Xlib example, Xlib already
834	its own, so its quite safe to use).	1206	does this on its own, so its quite safe to use). Some people additionally
		1207	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1208	indefinitely.
		1209
		1210	But really, best use non-blocking mode.
		1211
		1212	=head3 The special problem of disappearing file descriptors
		1213
		1214	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1215	descriptor (either due to calling C<close> explicitly or any other means,
		1216	such as C<dup2>). The reason is that you register interest in some file
		1217	descriptor, but when it goes away, the operating system will silently drop
		1218	this interest. If another file descriptor with the same number then is
		1219	registered with libev, there is no efficient way to see that this is, in
		1220	fact, a different file descriptor.
		1221
		1222	To avoid having to explicitly tell libev about such cases, libev follows
		1223	the following policy: Each time C<ev_io_set> is being called, libev
		1224	will assume that this is potentially a new file descriptor, otherwise
		1225	it is assumed that the file descriptor stays the same. That means that
		1226	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1227	descriptor even if the file descriptor number itself did not change.
		1228
		1229	This is how one would do it normally anyway, the important point is that
		1230	the libev application should not optimise around libev but should leave
		1231	optimisations to libev.
		1232
		1233	=head3 The special problem of dup'ed file descriptors
		1234
		1235	Some backends (e.g. epoll), cannot register events for file descriptors,
		1236	but only events for the underlying file descriptions. That means when you
		1237	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1238	events for them, only one file descriptor might actually receive events.
		1239
		1240	There is no workaround possible except not registering events
		1241	for potentially C<dup ()>'ed file descriptors, or to resort to
		1242	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1243
		1244	=head3 The special problem of fork
		1245
		1246	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1247	useless behaviour. Libev fully supports fork, but needs to be told about
		1248	it in the child.
		1249
		1250	To support fork in your programs, you either have to call
		1251	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1252	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1253	C<EVBACKEND_POLL>.
		1254
		1255	=head3 The special problem of SIGPIPE
		1256
		1257	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1258	when writing to a pipe whose other end has been closed, your program gets
		1259	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1260	this is sensible behaviour, for daemons, this is usually undesirable.
		1261
		1262	So when you encounter spurious, unexplained daemon exits, make sure you
		1263	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1264	somewhere, as that would have given you a big clue).
		1265
		1266
		1267	=head3 Watcher-Specific Functions
835		1268
836	=over 4	1269	=over 4
837		1270
838	=item ev_io_init (ev_io *, callback, int fd, int events)	1271	=item ev_io_init (ev_io *, callback, int fd, int events)
839		1272
840	=item ev_io_set (ev_io *, int fd, int events)	1273	=item ev_io_set (ev_io *, int fd, int events)
841		1274
842	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1275	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
843	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1276	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
844	C<EV_READ | EV_WRITE> to receive the given events.	1277	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
845		1278
846	=item int fd [read-only]	1279	=item int fd [read-only]
847		1280
848	The file descriptor being watched.	1281	The file descriptor being watched.
849		1282
850	=item int events [read-only]	1283	=item int events [read-only]
851		1284
852	The events being watched.	1285	The events being watched.
853		1286
854	=back	1287	=back
		1288
		1289	=head3 Examples
855		1290
856	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1291	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
857	readable, but only once. Since it is likely line-buffered, you could	1292	readable, but only once. Since it is likely line-buffered, you could
858	attempt to read a whole line in the callback.	1293	attempt to read a whole line in the callback.
859		1294
860	static void	1295	static void
861	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1296	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
862	{	1297	{
863	ev_io_stop (loop, w);	1298	ev_io_stop (loop, w);
864	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1299	.. read from stdin here (or from w->fd) and handle any I/O errors
865	}	1300	}
866		1301
867	...	1302	...
868	struct ev_loop *loop = ev_default_init (0);	1303	struct ev_loop *loop = ev_default_init (0);
869	struct ev_io stdin_readable;	1304	ev_io stdin_readable;
870	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1305	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
871	ev_io_start (loop, &stdin_readable);	1306	ev_io_start (loop, &stdin_readable);
872	ev_loop (loop, 0);	1307	ev_loop (loop, 0);
873		1308
874		1309
875	=head2 C<ev_timer> - relative and optionally repeating timeouts	1310	=head2 C<ev_timer> - relative and optionally repeating timeouts
876		1311
877	Timer watchers are simple relative timers that generate an event after a	1312	Timer watchers are simple relative timers that generate an event after a
878	given time, and optionally repeating in regular intervals after that.	1313	given time, and optionally repeating in regular intervals after that.
879		1314
880	The timers are based on real time, that is, if you register an event that	1315	The timers are based on real time, that is, if you register an event that
881	times out after an hour and you reset your system clock to last years	1316	times out after an hour and you reset your system clock to January last
882	time, it will still time out after (roughly) and hour. "Roughly" because	1317	year, it will still time out after (roughly) one hour. "Roughly" because
883	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1318	detecting time jumps is hard, and some inaccuracies are unavoidable (the
884	monotonic clock option helps a lot here).	1319	monotonic clock option helps a lot here).
		1320
		1321	The callback is guaranteed to be invoked only I<after> its timeout has
		1322	passed, but if multiple timers become ready during the same loop iteration
		1323	then order of execution is undefined.
		1324
		1325	=head3 Be smart about timeouts
		1326
		1327	Many real-world problems involve some kind of timeout, usually for error
		1328	recovery. A typical example is an HTTP request - if the other side hangs,
		1329	you want to raise some error after a while.
		1330
		1331	What follows are some ways to handle this problem, from obvious and
		1332	inefficient to smart and efficient.
		1333
		1334	In the following, a 60 second activity timeout is assumed - a timeout that
		1335	gets reset to 60 seconds each time there is activity (e.g. each time some
		1336	data or other life sign was received).
		1337
		1338	=over 4
		1339
		1340	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1341
		1342	This is the most obvious, but not the most simple way: In the beginning,
		1343	start the watcher:
		1344
		1345	ev_timer_init (timer, callback, 60., 0.);
		1346	ev_timer_start (loop, timer);
		1347
		1348	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1349	and start it again:
		1350
		1351	ev_timer_stop (loop, timer);
		1352	ev_timer_set (timer, 60., 0.);
		1353	ev_timer_start (loop, timer);
		1354
		1355	This is relatively simple to implement, but means that each time there is
		1356	some activity, libev will first have to remove the timer from its internal
		1357	data structure and then add it again. Libev tries to be fast, but it's
		1358	still not a constant-time operation.
		1359
		1360	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1361
		1362	This is the easiest way, and involves using C<ev_timer_again> instead of
		1363	C<ev_timer_start>.
		1364
		1365	To implement this, configure an C<ev_timer> with a C<repeat> value
		1366	of C<60> and then call C<ev_timer_again> at start and each time you
		1367	successfully read or write some data. If you go into an idle state where
		1368	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1369	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1370
		1371	That means you can ignore both the C<ev_timer_start> function and the
		1372	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1373	member and C<ev_timer_again>.
		1374
		1375	At start:
		1376
		1377	ev_timer_init (timer, callback);
		1378	timer->repeat = 60.;
		1379	ev_timer_again (loop, timer);
		1380
		1381	Each time there is some activity:
		1382
		1383	ev_timer_again (loop, timer);
		1384
		1385	It is even possible to change the time-out on the fly, regardless of
		1386	whether the watcher is active or not:
		1387
		1388	timer->repeat = 30.;
		1389	ev_timer_again (loop, timer);
		1390
		1391	This is slightly more efficient then stopping/starting the timer each time
		1392	you want to modify its timeout value, as libev does not have to completely
		1393	remove and re-insert the timer from/into its internal data structure.
		1394
		1395	It is, however, even simpler than the "obvious" way to do it.
		1396
		1397	=item 3. Let the timer time out, but then re-arm it as required.
		1398
		1399	This method is more tricky, but usually most efficient: Most timeouts are
		1400	relatively long compared to the intervals between other activity - in
		1401	our example, within 60 seconds, there are usually many I/O events with
		1402	associated activity resets.
		1403
		1404	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1405	but remember the time of last activity, and check for a real timeout only
		1406	within the callback:
		1407
		1408	ev_tstamp last_activity; // time of last activity
		1409
		1410	static void
		1411	callback (EV_P_ ev_timer *w, int revents)
		1412	{
		1413	ev_tstamp now = ev_now (EV_A);
		1414	ev_tstamp timeout = last_activity + 60.;
		1415
		1416	// if last_activity + 60. is older than now, we did time out
		1417	if (timeout < now)
		1418	{
		1419	// timeout occured, take action
		1420	}
		1421	else
		1422	{
		1423	// callback was invoked, but there was some activity, re-arm
		1424	// the watcher to fire in last_activity + 60, which is
		1425	// guaranteed to be in the future, so "again" is positive:
		1426	w->repeat = timeout - now;
		1427	ev_timer_again (EV_A_ w);
		1428	}
		1429	}
		1430
		1431	To summarise the callback: first calculate the real timeout (defined
		1432	as "60 seconds after the last activity"), then check if that time has
		1433	been reached, which means something I<did>, in fact, time out. Otherwise
		1434	the callback was invoked too early (C<timeout> is in the future), so
		1435	re-schedule the timer to fire at that future time, to see if maybe we have
		1436	a timeout then.
		1437
		1438	Note how C<ev_timer_again> is used, taking advantage of the
		1439	C<ev_timer_again> optimisation when the timer is already running.
		1440
		1441	This scheme causes more callback invocations (about one every 60 seconds
		1442	minus half the average time between activity), but virtually no calls to
		1443	libev to change the timeout.
		1444
		1445	To start the timer, simply initialise the watcher and set C<last_activity>
		1446	to the current time (meaning we just have some activity :), then call the
		1447	callback, which will "do the right thing" and start the timer:
		1448
		1449	ev_timer_init (timer, callback);
		1450	last_activity = ev_now (loop);
		1451	callback (loop, timer, EV_TIMEOUT);
		1452
		1453	And when there is some activity, simply store the current time in
		1454	C<last_activity>, no libev calls at all:
		1455
		1456	last_actiivty = ev_now (loop);
		1457
		1458	This technique is slightly more complex, but in most cases where the
		1459	time-out is unlikely to be triggered, much more efficient.
		1460
		1461	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1462	callback :) - just change the timeout and invoke the callback, which will
		1463	fix things for you.
		1464
		1465	=item 4. Wee, just use a double-linked list for your timeouts.
		1466
		1467	If there is not one request, but many thousands (millions...), all
		1468	employing some kind of timeout with the same timeout value, then one can
		1469	do even better:
		1470
		1471	When starting the timeout, calculate the timeout value and put the timeout
		1472	at the I<end> of the list.
		1473
		1474	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1475	the list is expected to fire (for example, using the technique #3).
		1476
		1477	When there is some activity, remove the timer from the list, recalculate
		1478	the timeout, append it to the end of the list again, and make sure to
		1479	update the C<ev_timer> if it was taken from the beginning of the list.
		1480
		1481	This way, one can manage an unlimited number of timeouts in O(1) time for
		1482	starting, stopping and updating the timers, at the expense of a major
		1483	complication, and having to use a constant timeout. The constant timeout
		1484	ensures that the list stays sorted.
		1485
		1486	=back
		1487
		1488	So which method the best?
		1489
		1490	Method #2 is a simple no-brain-required solution that is adequate in most
		1491	situations. Method #3 requires a bit more thinking, but handles many cases
		1492	better, and isn't very complicated either. In most case, choosing either
		1493	one is fine, with #3 being better in typical situations.
		1494
		1495	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1496	rather complicated, but extremely efficient, something that really pays
		1497	off after the first million or so of active timers, i.e. it's usually
		1498	overkill :)
		1499
		1500	=head3 The special problem of time updates
		1501
		1502	Establishing the current time is a costly operation (it usually takes at
		1503	least two system calls): EV therefore updates its idea of the current
		1504	time only before and after C<ev_loop> collects new events, which causes a
		1505	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1506	lots of events in one iteration.
885		1507
886	The relative timeouts are calculated relative to the C<ev_now ()>	1508	The relative timeouts are calculated relative to the C<ev_now ()>
887	time. This is usually the right thing as this timestamp refers to the time	1509	time. This is usually the right thing as this timestamp refers to the time
888	of the event triggering whatever timeout you are modifying/starting. If	1510	of the event triggering whatever timeout you are modifying/starting. If
889	you suspect event processing to be delayed and you I<need> to base the timeout	1511	you suspect event processing to be delayed and you I<need> to base the
890	on the current time, use something like this to adjust for this:	1512	timeout on the current time, use something like this to adjust for this:
891		1513
892	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1514	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
893		1515
894	The callback is guarenteed to be invoked only when its timeout has passed,	1516	If the event loop is suspended for a long time, you can also force an
895	but if multiple timers become ready during the same loop iteration then	1517	update of the time returned by C<ev_now ()> by calling C<ev_now_update
896	order of execution is undefined.	1518	()>.
		1519
		1520	=head3 Watcher-Specific Functions and Data Members
897		1521
898	=over 4	1522	=over 4
899		1523
900	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1524	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
901		1525
902	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1526	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
903		1527
904	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1528	Configure the timer to trigger after C<after> seconds. If C<repeat>
905	C<0.>, then it will automatically be stopped. If it is positive, then the	1529	is C<0.>, then it will automatically be stopped once the timeout is
906	timer will automatically be configured to trigger again C<repeat> seconds	1530	reached. If it is positive, then the timer will automatically be
907	later, again, and again, until stopped manually.	1531	configured to trigger again C<repeat> seconds later, again, and again,
		1532	until stopped manually.
908		1533
909	The timer itself will do a best-effort at avoiding drift, that is, if you	1534	The timer itself will do a best-effort at avoiding drift, that is, if
910	configure a timer to trigger every 10 seconds, then it will trigger at	1535	you configure a timer to trigger every 10 seconds, then it will normally
911	exactly 10 second intervals. If, however, your program cannot keep up with	1536	trigger at exactly 10 second intervals. If, however, your program cannot
912	the timer (because it takes longer than those 10 seconds to do stuff) the	1537	keep up with the timer (because it takes longer than those 10 seconds to
913	timer will not fire more than once per event loop iteration.	1538	do stuff) the timer will not fire more than once per event loop iteration.
914		1539
915	=item ev_timer_again (loop)	1540	=item ev_timer_again (loop, ev_timer *)
916		1541
917	This will act as if the timer timed out and restart it again if it is	1542	This will act as if the timer timed out and restart it again if it is
918	repeating. The exact semantics are:	1543	repeating. The exact semantics are:
919		1544
		1545	If the timer is pending, its pending status is cleared.
		1546
920	If the timer is started but nonrepeating, stop it.	1547	If the timer is started but non-repeating, stop it (as if it timed out).
921		1548
922	If the timer is repeating, either start it if necessary (with the repeat	1549	If the timer is repeating, either start it if necessary (with the
923	value), or reset the running timer to the repeat value.	1550	C<repeat> value), or reset the running timer to the C<repeat> value.
924		1551
925	This sounds a bit complicated, but here is a useful and typical	1552	This sounds a bit complicated, see "Be smart about timeouts", above, for a
926	example: Imagine you have a tcp connection and you want a so-called	1553	usage example.
927	idle timeout, that is, you want to be called when there have been,
928	say, 60 seconds of inactivity on the socket. The easiest way to do
929	this is to configure an C<ev_timer> with C<after>=C<repeat>=C<60> and calling
930	C<ev_timer_again> each time you successfully read or write some data. If
931	you go into an idle state where you do not expect data to travel on the
932	socket, you can stop the timer, and again will automatically restart it if
933	need be.
934
935	You can also ignore the C<after> value and C<ev_timer_start> altogether
936	and only ever use the C<repeat> value:
937
938	ev_timer_init (timer, callback, 0., 5.);
939	ev_timer_again (loop, timer);
940	...
941	timer->again = 17.;
942	ev_timer_again (loop, timer);
943	...
944	timer->again = 10.;
945	ev_timer_again (loop, timer);
946
947	This is more efficient then stopping/starting the timer eahc time you want
948	to modify its timeout value.
949		1554
950	=item ev_tstamp repeat [read-write]	1555	=item ev_tstamp repeat [read-write]
951		1556
952	The current C<repeat> value. Will be used each time the watcher times out	1557	The current C<repeat> value. Will be used each time the watcher times out
953	or C<ev_timer_again> is called and determines the next timeout (if any),	1558	or C<ev_timer_again> is called, and determines the next timeout (if any),
954	which is also when any modifications are taken into account.	1559	which is also when any modifications are taken into account.
955		1560
956	=back	1561	=back
957		1562
		1563	=head3 Examples
		1564
958	Example: Create a timer that fires after 60 seconds.	1565	Example: Create a timer that fires after 60 seconds.
959		1566
960	static void	1567	static void
961	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1568	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
962	{	1569	{
963	.. one minute over, w is actually stopped right here	1570	.. one minute over, w is actually stopped right here
964	}	1571	}
965		1572
966	struct ev_timer mytimer;	1573	ev_timer mytimer;
967	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1574	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
968	ev_timer_start (loop, &mytimer);	1575	ev_timer_start (loop, &mytimer);
969		1576
970	Example: Create a timeout timer that times out after 10 seconds of	1577	Example: Create a timeout timer that times out after 10 seconds of
971	inactivity.	1578	inactivity.
972		1579
973	static void	1580	static void
974	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1581	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
975	{	1582	{
976	.. ten seconds without any activity	1583	.. ten seconds without any activity
977	}	1584	}
978		1585
979	struct ev_timer mytimer;	1586	ev_timer mytimer;
980	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1587	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
981	ev_timer_again (&mytimer); /* start timer */	1588	ev_timer_again (&mytimer); /* start timer */
982	ev_loop (loop, 0);	1589	ev_loop (loop, 0);
983		1590
984	// and in some piece of code that gets executed on any "activity":	1591	// and in some piece of code that gets executed on any "activity":
985	// reset the timeout to start ticking again at 10 seconds	1592	// reset the timeout to start ticking again at 10 seconds
986	ev_timer_again (&mytimer);	1593	ev_timer_again (&mytimer);
987		1594
988		1595
989	=head2 C<ev_periodic> - to cron or not to cron?	1596	=head2 C<ev_periodic> - to cron or not to cron?
990		1597
991	Periodic watchers are also timers of a kind, but they are very versatile	1598	Periodic watchers are also timers of a kind, but they are very versatile
992	(and unfortunately a bit complex).	1599	(and unfortunately a bit complex).
993		1600
994	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1601	Unlike C<ev_timer>'s, they are not based on real time (or relative time)
995	but on wallclock time (absolute time). You can tell a periodic watcher	1602	but on wall clock time (absolute time). You can tell a periodic watcher
996	to trigger "at" some specific point in time. For example, if you tell a	1603	to trigger after some specific point in time. For example, if you tell a
997	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	1604	periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now ()
998	+ 10.>) and then reset your system clock to the last year, then it will	1605	+ 10.>, that is, an absolute time not a delay) and then reset your system
		1606	clock to January of the previous year, then it will take more than year
999	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1607	to trigger the event (unlike an C<ev_timer>, which would still trigger
1000	roughly 10 seconds later and of course not if you reset your system time	1608	roughly 10 seconds later as it uses a relative timeout).
1001	again).
1002		1609
1003	They can also be used to implement vastly more complex timers, such as	1610	C<ev_periodic>s can also be used to implement vastly more complex timers,
1004	triggering an event on eahc midnight, local time.	1611	such as triggering an event on each "midnight, local time", or other
		1612	complicated rules.
1005		1613
1006	As with timers, the callback is guarenteed to be invoked only when the	1614	As with timers, the callback is guaranteed to be invoked only when the
1007	time (C<at>) has been passed, but if multiple periodic timers become ready	1615	time (C<at>) has passed, but if multiple periodic timers become ready
1008	during the same loop iteration then order of execution is undefined.	1616	during the same loop iteration, then order of execution is undefined.
		1617
		1618	=head3 Watcher-Specific Functions and Data Members
1009		1619
1010	=over 4	1620	=over 4
1011		1621
1012	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1622	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
1013		1623
1014	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1624	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)
1015		1625
1016	Lots of arguments, lets sort it out... There are basically three modes of	1626	Lots of arguments, lets sort it out... There are basically three modes of
1017	operation, and we will explain them from simplest to complex:	1627	operation, and we will explain them from simplest to most complex:
1018		1628
1019	=over 4	1629	=over 4
1020		1630
1021	=item * absolute timer (interval = reschedule_cb = 0)	1631	=item * absolute timer (at = time, interval = reschedule_cb = 0)
1022		1632
1023	In this configuration the watcher triggers an event at the wallclock time	1633	In this configuration the watcher triggers an event after the wall clock
1024	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1634	time C<at> has passed. It will not repeat and will not adjust when a time
1025	that is, if it is to be run at January 1st 2011 then it will run when the	1635	jump occurs, that is, if it is to be run at January 1st 2011 then it will
1026	system time reaches or surpasses this time.	1636	only run when the system clock reaches or surpasses this time.
1027		1637
1028	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1638	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
1029		1639
1030	In this mode the watcher will always be scheduled to time out at the next	1640	In this mode the watcher will always be scheduled to time out at the next
1031	C<at + N * interval> time (for some integer N) and then repeat, regardless	1641	C<at + N * interval> time (for some integer N, which can also be negative)
1032	of any time jumps.	1642	and then repeat, regardless of any time jumps.
1033		1643
1034	This can be used to create timers that do not drift with respect to system	1644	This can be used to create timers that do not drift with respect to the
1035	time:	1645	system clock, for example, here is a C<ev_periodic> that triggers each
		1646	hour, on the hour:
1036		1647
1037	ev_periodic_set (&periodic, 0., 3600., 0);	1648	ev_periodic_set (&periodic, 0., 3600., 0);
1038		1649
1039	This doesn't mean there will always be 3600 seconds in between triggers,	1650	This doesn't mean there will always be 3600 seconds in between triggers,
1040	but only that the the callback will be called when the system time shows a	1651	but only that the callback will be called when the system time shows a
1041	full hour (UTC), or more correctly, when the system time is evenly divisible	1652	full hour (UTC), or more correctly, when the system time is evenly divisible
1042	by 3600.	1653	by 3600.
1043		1654
1044	Another way to think about it (for the mathematically inclined) is that	1655	Another way to think about it (for the mathematically inclined) is that
1045	C<ev_periodic> will try to run the callback in this mode at the next possible	1656	C<ev_periodic> will try to run the callback in this mode at the next possible
1046	time where C<time = at (mod interval)>, regardless of any time jumps.	1657	time where C<time = at (mod interval)>, regardless of any time jumps.
1047		1658
		1659	For numerical stability it is preferable that the C<at> value is near
		1660	C<ev_now ()> (the current time), but there is no range requirement for
		1661	this value, and in fact is often specified as zero.
		1662
		1663	Note also that there is an upper limit to how often a timer can fire (CPU
		1664	speed for example), so if C<interval> is very small then timing stability
		1665	will of course deteriorate. Libev itself tries to be exact to be about one
		1666	millisecond (if the OS supports it and the machine is fast enough).
		1667
1048	=item * manual reschedule mode (reschedule_cb = callback)	1668	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)
1049		1669
1050	In this mode the values for C<interval> and C<at> are both being	1670	In this mode the values for C<interval> and C<at> are both being
1051	ignored. Instead, each time the periodic watcher gets scheduled, the	1671	ignored. Instead, each time the periodic watcher gets scheduled, the
1052	reschedule callback will be called with the watcher as first, and the	1672	reschedule callback will be called with the watcher as first, and the
1053	current time as second argument.	1673	current time as second argument.
1054		1674
1055	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1675	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,
1056	ever, or make any event loop modifications>. If you need to stop it,	1676	ever, or make ANY event loop modifications whatsoever>.
1057	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by
1058	starting a prepare watcher).
1059		1677
		1678	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1679	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1680	only event loop modification you are allowed to do).
		1681
1060	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1682	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1061	ev_tstamp now)>, e.g.:	1683	*w, ev_tstamp now)>, e.g.:
1062		1684
		1685	static ev_tstamp
1063	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1686	my_rescheduler (ev_periodic *w, ev_tstamp now)
1064	{	1687	{
1065	return now + 60.;	1688	return now + 60.;
1066	}	1689	}
1067		1690
1068	It must return the next time to trigger, based on the passed time value	1691	It must return the next time to trigger, based on the passed time value
1069	(that is, the lowest time value larger than to the second argument). It	1692	(that is, the lowest time value larger than to the second argument). It
1070	will usually be called just before the callback will be triggered, but	1693	will usually be called just before the callback will be triggered, but
1071	might be called at other times, too.	1694	might be called at other times, too.
1072		1695
1073	NOTE: I<< This callback must always return a time that is later than the	1696	NOTE: I<< This callback must always return a time that is higher than or
1074	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	1697	equal to the passed C<now> value >>.
1075		1698
1076	This can be used to create very complex timers, such as a timer that	1699	This can be used to create very complex timers, such as a timer that
1077	triggers on each midnight, local time. To do this, you would calculate the	1700	triggers on "next midnight, local time". To do this, you would calculate the
1078	next midnight after C<now> and return the timestamp value for this. How	1701	next midnight after C<now> and return the timestamp value for this. How
1079	you do this is, again, up to you (but it is not trivial, which is the main	1702	you do this is, again, up to you (but it is not trivial, which is the main
1080	reason I omitted it as an example).	1703	reason I omitted it as an example).
1081		1704
1082	=back	1705	=back
…		…
1086	Simply stops and restarts the periodic watcher again. This is only useful	1709	Simply stops and restarts the periodic watcher again. This is only useful
1087	when you changed some parameters or the reschedule callback would return	1710	when you changed some parameters or the reschedule callback would return
1088	a different time than the last time it was called (e.g. in a crond like	1711	a different time than the last time it was called (e.g. in a crond like
1089	program when the crontabs have changed).	1712	program when the crontabs have changed).
1090		1713
		1714	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1715
		1716	When active, returns the absolute time that the watcher is supposed to
		1717	trigger next.
		1718
		1719	=item ev_tstamp offset [read-write]
		1720
		1721	When repeating, this contains the offset value, otherwise this is the
		1722	absolute point in time (the C<at> value passed to C<ev_periodic_set>).
		1723
		1724	Can be modified any time, but changes only take effect when the periodic
		1725	timer fires or C<ev_periodic_again> is being called.
		1726
1091	=item ev_tstamp interval [read-write]	1727	=item ev_tstamp interval [read-write]
1092		1728
1093	The current interval value. Can be modified any time, but changes only	1729	The current interval value. Can be modified any time, but changes only
1094	take effect when the periodic timer fires or C<ev_periodic_again> is being	1730	take effect when the periodic timer fires or C<ev_periodic_again> is being
1095	called.	1731	called.
1096		1732
1097	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	1733	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1098		1734
1099	The current reschedule callback, or C<0>, if this functionality is	1735	The current reschedule callback, or C<0>, if this functionality is
1100	switched off. Can be changed any time, but changes only take effect when	1736	switched off. Can be changed any time, but changes only take effect when
1101	the periodic timer fires or C<ev_periodic_again> is being called.	1737	the periodic timer fires or C<ev_periodic_again> is being called.
1102		1738
1103	=back	1739	=back
1104		1740
		1741	=head3 Examples
		1742
1105	Example: Call a callback every hour, or, more precisely, whenever the	1743	Example: Call a callback every hour, or, more precisely, whenever the
1106	system clock is divisible by 3600. The callback invocation times have	1744	system time is divisible by 3600. The callback invocation times have
1107	potentially a lot of jittering, but good long-term stability.	1745	potentially a lot of jitter, but good long-term stability.
1108		1746
1109	static void	1747	static void
1110	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1748	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1111	{	1749	{
1112	... its now a full hour (UTC, or TAI or whatever your clock follows)	1750	... its now a full hour (UTC, or TAI or whatever your clock follows)
1113	}	1751	}
1114		1752
1115	struct ev_periodic hourly_tick;	1753	ev_periodic hourly_tick;
1116	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	1754	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1117	ev_periodic_start (loop, &hourly_tick);	1755	ev_periodic_start (loop, &hourly_tick);
1118		1756
1119	Example: The same as above, but use a reschedule callback to do it:	1757	Example: The same as above, but use a reschedule callback to do it:
1120		1758
1121	#include <math.h>	1759	#include <math.h>
1122		1760
1123	static ev_tstamp	1761	static ev_tstamp
1124	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	1762	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1125	{	1763	{
1126	return fmod (now, 3600.) + 3600.;	1764	return now + (3600. - fmod (now, 3600.));
1127	}	1765	}
1128		1766
1129	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	1767	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1130		1768
1131	Example: Call a callback every hour, starting now:	1769	Example: Call a callback every hour, starting now:
1132		1770
1133	struct ev_periodic hourly_tick;	1771	ev_periodic hourly_tick;
1134	ev_periodic_init (&hourly_tick, clock_cb,	1772	ev_periodic_init (&hourly_tick, clock_cb,
1135	fmod (ev_now (loop), 3600.), 3600., 0);	1773	fmod (ev_now (loop), 3600.), 3600., 0);
1136	ev_periodic_start (loop, &hourly_tick);	1774	ev_periodic_start (loop, &hourly_tick);
1137		1775
1138		1776
1139	=head2 C<ev_signal> - signal me when a signal gets signalled!	1777	=head2 C<ev_signal> - signal me when a signal gets signalled!
1140		1778
1141	Signal watchers will trigger an event when the process receives a specific	1779	Signal watchers will trigger an event when the process receives a specific
1142	signal one or more times. Even though signals are very asynchronous, libev	1780	signal one or more times. Even though signals are very asynchronous, libev
1143	will try it's best to deliver signals synchronously, i.e. as part of the	1781	will try it's best to deliver signals synchronously, i.e. as part of the
1144	normal event processing, like any other event.	1782	normal event processing, like any other event.
1145		1783
		1784	If you want signals asynchronously, just use C<sigaction> as you would
		1785	do without libev and forget about sharing the signal. You can even use
		1786	C<ev_async> from a signal handler to synchronously wake up an event loop.
		1787
1146	You can configure as many watchers as you like per signal. Only when the	1788	You can configure as many watchers as you like per signal. Only when the
1147	first watcher gets started will libev actually register a signal watcher	1789	first watcher gets started will libev actually register a signal handler
1148	with the kernel (thus it coexists with your own signal handlers as long	1790	with the kernel (thus it coexists with your own signal handlers as long as
1149	as you don't register any with libev). Similarly, when the last signal	1791	you don't register any with libev for the same signal). Similarly, when
1150	watcher for a signal is stopped libev will reset the signal handler to	1792	the last signal watcher for a signal is stopped, libev will reset the
1151	SIG_DFL (regardless of what it was set to before).	1793	signal handler to SIG_DFL (regardless of what it was set to before).
		1794
		1795	If possible and supported, libev will install its handlers with
		1796	C<SA_RESTART> behaviour enabled, so system calls should not be unduly
		1797	interrupted. If you have a problem with system calls getting interrupted by
		1798	signals you can block all signals in an C<ev_check> watcher and unblock
		1799	them in an C<ev_prepare> watcher.
		1800
		1801	=head3 Watcher-Specific Functions and Data Members
1152		1802
1153	=over 4	1803	=over 4
1154		1804
1155	=item ev_signal_init (ev_signal *, callback, int signum)	1805	=item ev_signal_init (ev_signal *, callback, int signum)
1156		1806
…		…
1163		1813
1164	The signal the watcher watches out for.	1814	The signal the watcher watches out for.
1165		1815
1166	=back	1816	=back
1167		1817
		1818	=head3 Examples
		1819
		1820	Example: Try to exit cleanly on SIGINT.
		1821
		1822	static void
		1823	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		1824	{
		1825	ev_unloop (loop, EVUNLOOP_ALL);
		1826	}
		1827
		1828	ev_signal signal_watcher;
		1829	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1830	ev_signal_start (loop, &signal_watcher);
		1831
1168		1832
1169	=head2 C<ev_child> - watch out for process status changes	1833	=head2 C<ev_child> - watch out for process status changes
1170		1834
1171	Child watchers trigger when your process receives a SIGCHLD in response to	1835	Child watchers trigger when your process receives a SIGCHLD in response to
1172	some child status changes (most typically when a child of yours dies).	1836	some child status changes (most typically when a child of yours dies or
		1837	exits). It is permissible to install a child watcher I<after> the child
		1838	has been forked (which implies it might have already exited), as long
		1839	as the event loop isn't entered (or is continued from a watcher), i.e.,
		1840	forking and then immediately registering a watcher for the child is fine,
		1841	but forking and registering a watcher a few event loop iterations later is
		1842	not.
		1843
		1844	Only the default event loop is capable of handling signals, and therefore
		1845	you can only register child watchers in the default event loop.
		1846
		1847	=head3 Process Interaction
		1848
		1849	Libev grabs C<SIGCHLD> as soon as the default event loop is
		1850	initialised. This is necessary to guarantee proper behaviour even if
		1851	the first child watcher is started after the child exits. The occurrence
		1852	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		1853	synchronously as part of the event loop processing. Libev always reaps all
		1854	children, even ones not watched.
		1855
		1856	=head3 Overriding the Built-In Processing
		1857
		1858	Libev offers no special support for overriding the built-in child
		1859	processing, but if your application collides with libev's default child
		1860	handler, you can override it easily by installing your own handler for
		1861	C<SIGCHLD> after initialising the default loop, and making sure the
		1862	default loop never gets destroyed. You are encouraged, however, to use an
		1863	event-based approach to child reaping and thus use libev's support for
		1864	that, so other libev users can use C<ev_child> watchers freely.
		1865
		1866	=head3 Stopping the Child Watcher
		1867
		1868	Currently, the child watcher never gets stopped, even when the
		1869	child terminates, so normally one needs to stop the watcher in the
		1870	callback. Future versions of libev might stop the watcher automatically
		1871	when a child exit is detected.
		1872
		1873	=head3 Watcher-Specific Functions and Data Members
1173		1874
1174	=over 4	1875	=over 4
1175		1876
1176	=item ev_child_init (ev_child *, callback, int pid)	1877	=item ev_child_init (ev_child *, callback, int pid, int trace)
1177		1878
1178	=item ev_child_set (ev_child *, int pid)	1879	=item ev_child_set (ev_child *, int pid, int trace)
1179		1880
1180	Configures the watcher to wait for status changes of process C<pid> (or	1881	Configures the watcher to wait for status changes of process C<pid> (or
1181	I<any> process if C<pid> is specified as C<0>). The callback can look	1882	I<any> process if C<pid> is specified as C<0>). The callback can look
1182	at the C<rstatus> member of the C<ev_child> watcher structure to see	1883	at the C<rstatus> member of the C<ev_child> watcher structure to see
1183	the status word (use the macros from C<sys/wait.h> and see your systems	1884	the status word (use the macros from C<sys/wait.h> and see your systems
1184	C<waitpid> documentation). The C<rpid> member contains the pid of the	1885	C<waitpid> documentation). The C<rpid> member contains the pid of the
1185	process causing the status change.	1886	process causing the status change. C<trace> must be either C<0> (only
		1887	activate the watcher when the process terminates) or C<1> (additionally
		1888	activate the watcher when the process is stopped or continued).
1186		1889
1187	=item int pid [read-only]	1890	=item int pid [read-only]
1188		1891
1189	The process id this watcher watches out for, or C<0>, meaning any process id.	1892	The process id this watcher watches out for, or C<0>, meaning any process id.
1190		1893
…		…
1197	The process exit/trace status caused by C<rpid> (see your systems	1900	The process exit/trace status caused by C<rpid> (see your systems
1198	C<waitpid> and C<sys/wait.h> documentation for details).	1901	C<waitpid> and C<sys/wait.h> documentation for details).
1199		1902
1200	=back	1903	=back
1201		1904
1202	Example: Try to exit cleanly on SIGINT and SIGTERM.	1905	=head3 Examples
1203		1906
		1907	Example: C<fork()> a new process and install a child handler to wait for
		1908	its completion.
		1909
		1910	ev_child cw;
		1911
1204	static void	1912	static void
1205	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	1913	child_cb (EV_P_ ev_child *w, int revents)
1206	{	1914	{
1207	ev_unloop (loop, EVUNLOOP_ALL);	1915	ev_child_stop (EV_A_ w);
		1916	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1208	}	1917	}
1209		1918
1210	struct ev_signal signal_watcher;	1919	pid_t pid = fork ();
1211	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	1920
1212	ev_signal_start (loop, &sigint_cb);	1921	if (pid < 0)
		1922	// error
		1923	else if (pid == 0)
		1924	{
		1925	// the forked child executes here
		1926	exit (1);
		1927	}
		1928	else
		1929	{
		1930	ev_child_init (&cw, child_cb, pid, 0);
		1931	ev_child_start (EV_DEFAULT_ &cw);
		1932	}
1213		1933
1214		1934
1215	=head2 C<ev_stat> - did the file attributes just change?	1935	=head2 C<ev_stat> - did the file attributes just change?
1216		1936
1217	This watches a filesystem path for attribute changes. That is, it calls	1937	This watches a file system path for attribute changes. That is, it calls
1218	C<stat> regularly (or when the OS says it changed) and sees if it changed	1938	C<stat> on that path in regular intervals (or when the OS says it changed)
1219	compared to the last time, invoking the callback if it did.	1939	and sees if it changed compared to the last time, invoking the callback if
		1940	it did.
1220		1941
1221	The path does not need to exist: changing from "path exists" to "path does	1942	The path does not need to exist: changing from "path exists" to "path does
1222	not exist" is a status change like any other. The condition "path does	1943	not exist" is a status change like any other. The condition "path does not
1223	not exist" is signified by the C<st_nlink> field being zero (which is	1944	exist" (or more correctly "path cannot be stat'ed") is signified by the
1224	otherwise always forced to be at least one) and all the other fields of	1945	C<st_nlink> field being zero (which is otherwise always forced to be at
1225	the stat buffer having unspecified contents.	1946	least one) and all the other fields of the stat buffer having unspecified
		1947	contents.
1226		1948
1227	Since there is no standard to do this, the portable implementation simply	1949	The path I<must not> end in a slash or contain special components such as
1228	calls C<stat (2)> regularly on the path to see if it changed somehow. You	1950	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1229	can specify a recommended polling interval for this case. If you specify	1951	your working directory changes, then the behaviour is undefined.
1230	a polling interval of C<0> (highly recommended!) then a I<suitable,	1952
1231	unspecified default> value will be used (which you can expect to be around	1953	Since there is no portable change notification interface available, the
1232	five seconds, although this might change dynamically). Libev will also	1954	portable implementation simply calls C<stat(2)> regularly on the path
1233	impose a minimum interval which is currently around C<0.1>, but thats	1955	to see if it changed somehow. You can specify a recommended polling
1234	usually overkill.	1956	interval for this case. If you specify a polling interval of C<0> (highly
		1957	recommended!) then a I<suitable, unspecified default> value will be used
		1958	(which you can expect to be around five seconds, although this might
		1959	change dynamically). Libev will also impose a minimum interval which is
		1960	currently around C<0.1>, but that's usually overkill.
1235		1961
1236	This watcher type is not meant for massive numbers of stat watchers,	1962	This watcher type is not meant for massive numbers of stat watchers,
1237	as even with OS-supported change notifications, this can be	1963	as even with OS-supported change notifications, this can be
1238	resource-intensive.	1964	resource-intensive.
1239		1965
1240	At the time of this writing, only the Linux inotify interface is	1966	At the time of this writing, the only OS-specific interface implemented
1241	implemented (implementing kqueue support is left as an exercise for the	1967	is the Linux inotify interface (implementing kqueue support is left as an
1242	reader). Inotify will be used to give hints only and should not change the	1968	exercise for the reader. Note, however, that the author sees no way of
1243	semantics of C<ev_stat> watchers, which means that libev sometimes needs	1969	implementing C<ev_stat> semantics with kqueue, except as a hint).
1244	to fall back to regular polling again even with inotify, but changes are	1970
1245	usually detected immediately, and if the file exists there will be no	1971	=head3 ABI Issues (Largefile Support)
1246	polling.	1972
		1973	Libev by default (unless the user overrides this) uses the default
		1974	compilation environment, which means that on systems with large file
		1975	support disabled by default, you get the 32 bit version of the stat
		1976	structure. When using the library from programs that change the ABI to
		1977	use 64 bit file offsets the programs will fail. In that case you have to
		1978	compile libev with the same flags to get binary compatibility. This is
		1979	obviously the case with any flags that change the ABI, but the problem is
		1980	most noticeably displayed with ev_stat and large file support.
		1981
		1982	The solution for this is to lobby your distribution maker to make large
		1983	file interfaces available by default (as e.g. FreeBSD does) and not
		1984	optional. Libev cannot simply switch on large file support because it has
		1985	to exchange stat structures with application programs compiled using the
		1986	default compilation environment.
		1987
		1988	=head3 Inotify and Kqueue
		1989
		1990	When C<inotify (7)> support has been compiled into libev and present at
		1991	runtime, it will be used to speed up change detection where possible. The
		1992	inotify descriptor will be created lazily when the first C<ev_stat>
		1993	watcher is being started.
		1994
		1995	Inotify presence does not change the semantics of C<ev_stat> watchers
		1996	except that changes might be detected earlier, and in some cases, to avoid
		1997	making regular C<stat> calls. Even in the presence of inotify support
		1998	there are many cases where libev has to resort to regular C<stat> polling,
		1999	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2000	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2001	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2002	xfs are fully working) libev usually gets away without polling.
		2003
		2004	There is no support for kqueue, as apparently it cannot be used to
		2005	implement this functionality, due to the requirement of having a file
		2006	descriptor open on the object at all times, and detecting renames, unlinks
		2007	etc. is difficult.
		2008
		2009	=head3 C<stat ()> is a synchronous operation
		2010
		2011	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2012	the process. The exception are C<ev_stat> watchers - those call C<stat
		2013	()>, which is a synchronous operation.
		2014
		2015	For local paths, this usually doesn't matter: unless the system is very
		2016	busy or the intervals between stat's are large, a stat call will be fast,
		2017	as the path data is suually in memory already (except when starting the
		2018	watcher).
		2019
		2020	For networked file systems, calling C<stat ()> can block an indefinite
		2021	time due to network issues, and even under good conditions, a stat call
		2022	often takes multiple milliseconds.
		2023
		2024	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2025	paths, although this is fully supported by libev.
		2026
		2027	=head3 The special problem of stat time resolution
		2028
		2029	The C<stat ()> system call only supports full-second resolution portably,
		2030	and even on systems where the resolution is higher, most file systems
		2031	still only support whole seconds.
		2032
		2033	That means that, if the time is the only thing that changes, you can
		2034	easily miss updates: on the first update, C<ev_stat> detects a change and
		2035	calls your callback, which does something. When there is another update
		2036	within the same second, C<ev_stat> will be unable to detect unless the
		2037	stat data does change in other ways (e.g. file size).
		2038
		2039	The solution to this is to delay acting on a change for slightly more
		2040	than a second (or till slightly after the next full second boundary), using
		2041	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2042	ev_timer_again (loop, w)>).
		2043
		2044	The C<.02> offset is added to work around small timing inconsistencies
		2045	of some operating systems (where the second counter of the current time
		2046	might be be delayed. One such system is the Linux kernel, where a call to
		2047	C<gettimeofday> might return a timestamp with a full second later than
		2048	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2049	update file times then there will be a small window where the kernel uses
		2050	the previous second to update file times but libev might already execute
		2051	the timer callback).
		2052
		2053	=head3 Watcher-Specific Functions and Data Members
1247		2054
1248	=over 4	2055	=over 4
1249		2056
1250	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)	2057	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
1251		2058
…		…
1255	C<path>. The C<interval> is a hint on how quickly a change is expected to	2062	C<path>. The C<interval> is a hint on how quickly a change is expected to
1256	be detected and should normally be specified as C<0> to let libev choose	2063	be detected and should normally be specified as C<0> to let libev choose
1257	a suitable value. The memory pointed to by C<path> must point to the same	2064	a suitable value. The memory pointed to by C<path> must point to the same
1258	path for as long as the watcher is active.	2065	path for as long as the watcher is active.
1259		2066
1260	The callback will be receive C<EV_STAT> when a change was detected,	2067	The callback will receive an C<EV_STAT> event when a change was detected,
1261	relative to the attributes at the time the watcher was started (or the	2068	relative to the attributes at the time the watcher was started (or the
1262	last change was detected).	2069	last change was detected).
1263		2070
1264	=item ev_stat_stat (ev_stat *)	2071	=item ev_stat_stat (loop, ev_stat *)
1265		2072
1266	Updates the stat buffer immediately with new values. If you change the	2073	Updates the stat buffer immediately with new values. If you change the
1267	watched path in your callback, you could call this fucntion to avoid	2074	watched path in your callback, you could call this function to avoid
1268	detecting this change (while introducing a race condition). Can also be	2075	detecting this change (while introducing a race condition if you are not
1269	useful simply to find out the new values.	2076	the only one changing the path). Can also be useful simply to find out the
		2077	new values.
1270		2078
1271	=item ev_statdata attr [read-only]	2079	=item ev_statdata attr [read-only]
1272		2080
1273	The most-recently detected attributes of the file. Although the type is of	2081	The most-recently detected attributes of the file. Although the type is
1274	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2082	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1275	suitable for your system. If the C<st_nlink> member is C<0>, then there	2083	suitable for your system, but you can only rely on the POSIX-standardised
		2084	members to be present. If the C<st_nlink> member is C<0>, then there was
1276	was some error while C<stat>ing the file.	2085	some error while C<stat>ing the file.
1277		2086
1278	=item ev_statdata prev [read-only]	2087	=item ev_statdata prev [read-only]
1279		2088
1280	The previous attributes of the file. The callback gets invoked whenever	2089	The previous attributes of the file. The callback gets invoked whenever
1281	C<prev> != C<attr>.	2090	C<prev> != C<attr>, or, more precisely, one or more of these members
		2091	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2092	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1282		2093
1283	=item ev_tstamp interval [read-only]	2094	=item ev_tstamp interval [read-only]
1284		2095
1285	The specified interval.	2096	The specified interval.
1286		2097
1287	=item const char *path [read-only]	2098	=item const char *path [read-only]
1288		2099
1289	The filesystem path that is being watched.	2100	The file system path that is being watched.
1290		2101
1291	=back	2102	=back
1292		2103
		2104	=head3 Examples
		2105
1293	Example: Watch C</etc/passwd> for attribute changes.	2106	Example: Watch C</etc/passwd> for attribute changes.
1294		2107
1295	static void	2108	static void
1296	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2109	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1297	{	2110	{
1298	/* /etc/passwd changed in some way */	2111	/* /etc/passwd changed in some way */
1299	if (w->attr.st_nlink)	2112	if (w->attr.st_nlink)
1300	{	2113	{
1301	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2114	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1302	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2115	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1303	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2116	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1304	}	2117	}
1305	else	2118	else
1306	/* you shalt not abuse printf for puts */	2119	/* you shalt not abuse printf for puts */
1307	puts ("wow, /etc/passwd is not there, expect problems. "	2120	puts ("wow, /etc/passwd is not there, expect problems. "
1308	"if this is windows, they already arrived\n");	2121	"if this is windows, they already arrived\n");
1309	}	2122	}
1310		2123
1311	...	2124	...
1312	ev_stat passwd;	2125	ev_stat passwd;
1313		2126
1314	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	2127	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1315	ev_stat_start (loop, &passwd);	2128	ev_stat_start (loop, &passwd);
		2129
		2130	Example: Like above, but additionally use a one-second delay so we do not
		2131	miss updates (however, frequent updates will delay processing, too, so
		2132	one might do the work both on C<ev_stat> callback invocation I<and> on
		2133	C<ev_timer> callback invocation).
		2134
		2135	static ev_stat passwd;
		2136	static ev_timer timer;
		2137
		2138	static void
		2139	timer_cb (EV_P_ ev_timer *w, int revents)
		2140	{
		2141	ev_timer_stop (EV_A_ w);
		2142
		2143	/* now it's one second after the most recent passwd change */
		2144	}
		2145
		2146	static void
		2147	stat_cb (EV_P_ ev_stat *w, int revents)
		2148	{
		2149	/* reset the one-second timer */
		2150	ev_timer_again (EV_A_ &timer);
		2151	}
		2152
		2153	...
		2154	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2155	ev_stat_start (loop, &passwd);
		2156	ev_timer_init (&timer, timer_cb, 0., 1.02);
1316		2157
1317		2158
1318	=head2 C<ev_idle> - when you've got nothing better to do...	2159	=head2 C<ev_idle> - when you've got nothing better to do...
1319		2160
1320	Idle watchers trigger events when there are no other events are pending	2161	Idle watchers trigger events when no other events of the same or higher
1321	(prepare, check and other idle watchers do not count). That is, as long	2162	priority are pending (prepare, check and other idle watchers do not count
1322	as your process is busy handling sockets or timeouts (or even signals,	2163	as receiving "events").
1323	imagine) it will not be triggered. But when your process is idle all idle	2164
1324	watchers are being called again and again, once per event loop iteration -	2165	That is, as long as your process is busy handling sockets or timeouts
		2166	(or even signals, imagine) of the same or higher priority it will not be
		2167	triggered. But when your process is idle (or only lower-priority watchers
		2168	are pending), the idle watchers are being called once per event loop
1325	until stopped, that is, or your process receives more events and becomes	2169	iteration - until stopped, that is, or your process receives more events
1326	busy.	2170	and becomes busy again with higher priority stuff.
1327		2171
1328	The most noteworthy effect is that as long as any idle watchers are	2172	The most noteworthy effect is that as long as any idle watchers are
1329	active, the process will not block when waiting for new events.	2173	active, the process will not block when waiting for new events.
1330		2174
1331	Apart from keeping your process non-blocking (which is a useful	2175	Apart from keeping your process non-blocking (which is a useful
1332	effect on its own sometimes), idle watchers are a good place to do	2176	effect on its own sometimes), idle watchers are a good place to do
1333	"pseudo-background processing", or delay processing stuff to after the	2177	"pseudo-background processing", or delay processing stuff to after the
1334	event loop has handled all outstanding events.	2178	event loop has handled all outstanding events.
1335		2179
		2180	=head3 Watcher-Specific Functions and Data Members
		2181
1336	=over 4	2182	=over 4
1337		2183
1338	=item ev_idle_init (ev_signal *, callback)	2184	=item ev_idle_init (ev_signal *, callback)
1339		2185
1340	Initialises and configures the idle watcher - it has no parameters of any	2186	Initialises and configures the idle watcher - it has no parameters of any
1341	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2187	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1342	believe me.	2188	believe me.
1343		2189
1344	=back	2190	=back
1345		2191
		2192	=head3 Examples
		2193
1346	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2194	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1347	callback, free it. Also, use no error checking, as usual.	2195	callback, free it. Also, use no error checking, as usual.
1348		2196
1349	static void	2197	static void
1350	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2198	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1351	{	2199	{
1352	free (w);	2200	free (w);
1353	// now do something you wanted to do when the program has	2201	// now do something you wanted to do when the program has
1354	// no longer asnything immediate to do.	2202	// no longer anything immediate to do.
1355	}	2203	}
1356		2204
1357	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2205	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1358	ev_idle_init (idle_watcher, idle_cb);	2206	ev_idle_init (idle_watcher, idle_cb);
1359	ev_idle_start (loop, idle_cb);	2207	ev_idle_start (loop, idle_cb);
1360		2208
1361		2209
1362	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2210	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1363		2211
1364	Prepare and check watchers are usually (but not always) used in tandem:	2212	Prepare and check watchers are usually (but not always) used in pairs:
1365	prepare watchers get invoked before the process blocks and check watchers	2213	prepare watchers get invoked before the process blocks and check watchers
1366	afterwards.	2214	afterwards.
1367		2215
1368	You I<must not> call C<ev_loop> or similar functions that enter	2216	You I<must not> call C<ev_loop> or similar functions that enter
1369	the current event loop from either C<ev_prepare> or C<ev_check>	2217	the current event loop from either C<ev_prepare> or C<ev_check>
…		…
1372	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2220	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1373	C<ev_check> so if you have one watcher of each kind they will always be	2221	C<ev_check> so if you have one watcher of each kind they will always be
1374	called in pairs bracketing the blocking call.	2222	called in pairs bracketing the blocking call.
1375		2223
1376	Their main purpose is to integrate other event mechanisms into libev and	2224	Their main purpose is to integrate other event mechanisms into libev and
1377	their use is somewhat advanced. This could be used, for example, to track	2225	their use is somewhat advanced. They could be used, for example, to track
1378	variable changes, implement your own watchers, integrate net-snmp or a	2226	variable changes, implement your own watchers, integrate net-snmp or a
1379	coroutine library and lots more. They are also occasionally useful if	2227	coroutine library and lots more. They are also occasionally useful if
1380	you cache some data and want to flush it before blocking (for example,	2228	you cache some data and want to flush it before blocking (for example,
1381	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2229	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1382	watcher).	2230	watcher).
1383		2231
1384	This is done by examining in each prepare call which file descriptors need	2232	This is done by examining in each prepare call which file descriptors
1385	to be watched by the other library, registering C<ev_io> watchers for	2233	need to be watched by the other library, registering C<ev_io> watchers
1386	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2234	for them and starting an C<ev_timer> watcher for any timeouts (many
1387	provide just this functionality). Then, in the check watcher you check for	2235	libraries provide exactly this functionality). Then, in the check watcher,
1388	any events that occured (by checking the pending status of all watchers	2236	you check for any events that occurred (by checking the pending status
1389	and stopping them) and call back into the library. The I/O and timer	2237	of all watchers and stopping them) and call back into the library. The
1390	callbacks will never actually be called (but must be valid nevertheless,	2238	I/O and timer callbacks will never actually be called (but must be valid
1391	because you never know, you know?).	2239	nevertheless, because you never know, you know?).
1392		2240
1393	As another example, the Perl Coro module uses these hooks to integrate	2241	As another example, the Perl Coro module uses these hooks to integrate
1394	coroutines into libev programs, by yielding to other active coroutines	2242	coroutines into libev programs, by yielding to other active coroutines
1395	during each prepare and only letting the process block if no coroutines	2243	during each prepare and only letting the process block if no coroutines
1396	are ready to run (it's actually more complicated: it only runs coroutines	2244	are ready to run (it's actually more complicated: it only runs coroutines
1397	with priority higher than or equal to the event loop and one coroutine	2245	with priority higher than or equal to the event loop and one coroutine
1398	of lower priority, but only once, using idle watchers to keep the event	2246	of lower priority, but only once, using idle watchers to keep the event
1399	loop from blocking if lower-priority coroutines are active, thus mapping	2247	loop from blocking if lower-priority coroutines are active, thus mapping
1400	low-priority coroutines to idle/background tasks).	2248	low-priority coroutines to idle/background tasks).
1401		2249
		2250	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		2251	priority, to ensure that they are being run before any other watchers
		2252	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2253
		2254	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2255	activate ("feed") events into libev. While libev fully supports this, they
		2256	might get executed before other C<ev_check> watchers did their job. As
		2257	C<ev_check> watchers are often used to embed other (non-libev) event
		2258	loops those other event loops might be in an unusable state until their
		2259	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2260	others).
		2261
		2262	=head3 Watcher-Specific Functions and Data Members
		2263
1402	=over 4	2264	=over 4
1403		2265
1404	=item ev_prepare_init (ev_prepare *, callback)	2266	=item ev_prepare_init (ev_prepare *, callback)
1405		2267
1406	=item ev_check_init (ev_check *, callback)	2268	=item ev_check_init (ev_check *, callback)
1407		2269
1408	Initialises and configures the prepare or check watcher - they have no	2270	Initialises and configures the prepare or check watcher - they have no
1409	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2271	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1410	macros, but using them is utterly, utterly and completely pointless.	2272	macros, but using them is utterly, utterly, utterly and completely
		2273	pointless.
1411		2274
1412	=back	2275	=back
1413		2276
1414	Example: To include a library such as adns, you would add IO watchers	2277	=head3 Examples
1415	and a timeout watcher in a prepare handler, as required by libadns, and	2278
		2279	There are a number of principal ways to embed other event loops or modules
		2280	into libev. Here are some ideas on how to include libadns into libev
		2281	(there is a Perl module named C<EV::ADNS> that does this, which you could
		2282	use as a working example. Another Perl module named C<EV::Glib> embeds a
		2283	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		2284	Glib event loop).
		2285
		2286	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1416	in a check watcher, destroy them and call into libadns. What follows is	2287	and in a check watcher, destroy them and call into libadns. What follows
1417	pseudo-code only of course:	2288	is pseudo-code only of course. This requires you to either use a low
		2289	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		2290	the callbacks for the IO/timeout watchers might not have been called yet.
1418		2291
1419	static ev_io iow [nfd];	2292	static ev_io iow [nfd];
1420	static ev_timer tw;	2293	static ev_timer tw;
1421		2294
1422	static void	2295	static void
1423	io_cb (ev_loop *loop, ev_io *w, int revents)	2296	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1424	{	2297	{
1425	// set the relevant poll flags
1426	// could also call adns_processreadable etc. here
1427	struct pollfd *fd = (struct pollfd *)w->data;
1428	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1429	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1430	}	2298	}
1431		2299
1432	// create io watchers for each fd and a timer before blocking	2300	// create io watchers for each fd and a timer before blocking
1433	static void	2301	static void
1434	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2302	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1435	{	2303	{
1436	int timeout = 3600000;truct pollfd fds [nfd];	2304	int timeout = 3600000;
		2305	struct pollfd fds [nfd];
1437	// actual code will need to loop here and realloc etc.	2306	// actual code will need to loop here and realloc etc.
1438	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2307	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1439		2308
1440	/* the callback is illegal, but won't be called as we stop during check */	2309	/* the callback is illegal, but won't be called as we stop during check */
1441	ev_timer_init (&tw, 0, timeout * 1e-3);	2310	ev_timer_init (&tw, 0, timeout * 1e-3);
1442	ev_timer_start (loop, &tw);	2311	ev_timer_start (loop, &tw);
1443		2312
1444	// create on ev_io per pollfd	2313	// create one ev_io per pollfd
1445	for (int i = 0; i < nfd; ++i)	2314	for (int i = 0; i < nfd; ++i)
1446	{	2315	{
1447	ev_io_init (iow + i, io_cb, fds [i].fd,	2316	ev_io_init (iow + i, io_cb, fds [i].fd,
1448	((fds [i].events & POLLIN ? EV_READ : 0)	2317	((fds [i].events & POLLIN ? EV_READ : 0)
1449	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2318	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1450		2319
1451	fds [i].revents = 0;	2320	fds [i].revents = 0;
1452	iow [i].data = fds + i;
1453	ev_io_start (loop, iow + i);	2321	ev_io_start (loop, iow + i);
1454	}	2322	}
1455	}	2323	}
1456		2324
1457	// stop all watchers after blocking	2325	// stop all watchers after blocking
1458	static void	2326	static void
1459	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2327	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1460	{	2328	{
1461	ev_timer_stop (loop, &tw);	2329	ev_timer_stop (loop, &tw);
1462		2330
1463	for (int i = 0; i < nfd; ++i)	2331	for (int i = 0; i < nfd; ++i)
		2332	{
		2333	// set the relevant poll flags
		2334	// could also call adns_processreadable etc. here
		2335	struct pollfd *fd = fds + i;
		2336	int revents = ev_clear_pending (iow + i);
		2337	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2338	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2339
		2340	// now stop the watcher
1464	ev_io_stop (loop, iow + i);	2341	ev_io_stop (loop, iow + i);
		2342	}
1465		2343
1466	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2344	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1467	}	2345	}
		2346
		2347	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2348	in the prepare watcher and would dispose of the check watcher.
		2349
		2350	Method 3: If the module to be embedded supports explicit event
		2351	notification (libadns does), you can also make use of the actual watcher
		2352	callbacks, and only destroy/create the watchers in the prepare watcher.
		2353
		2354	static void
		2355	timer_cb (EV_P_ ev_timer *w, int revents)
		2356	{
		2357	adns_state ads = (adns_state)w->data;
		2358	update_now (EV_A);
		2359
		2360	adns_processtimeouts (ads, &tv_now);
		2361	}
		2362
		2363	static void
		2364	io_cb (EV_P_ ev_io *w, int revents)
		2365	{
		2366	adns_state ads = (adns_state)w->data;
		2367	update_now (EV_A);
		2368
		2369	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2370	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2371	}
		2372
		2373	// do not ever call adns_afterpoll
		2374
		2375	Method 4: Do not use a prepare or check watcher because the module you
		2376	want to embed is not flexible enough to support it. Instead, you can
		2377	override their poll function. The drawback with this solution is that the
		2378	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		2379	this approach, effectively embedding EV as a client into the horrible
		2380	libglib event loop.
		2381
		2382	static gint
		2383	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2384	{
		2385	int got_events = 0;
		2386
		2387	for (n = 0; n < nfds; ++n)
		2388	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2389
		2390	if (timeout >= 0)
		2391	// create/start timer
		2392
		2393	// poll
		2394	ev_loop (EV_A_ 0);
		2395
		2396	// stop timer again
		2397	if (timeout >= 0)
		2398	ev_timer_stop (EV_A_ &to);
		2399
		2400	// stop io watchers again - their callbacks should have set
		2401	for (n = 0; n < nfds; ++n)
		2402	ev_io_stop (EV_A_ iow [n]);
		2403
		2404	return got_events;
		2405	}
1468		2406
1469		2407
1470	=head2 C<ev_embed> - when one backend isn't enough...	2408	=head2 C<ev_embed> - when one backend isn't enough...
1471		2409
1472	This is a rather advanced watcher type that lets you embed one event loop	2410	This is a rather advanced watcher type that lets you embed one event loop
…		…
1478	prioritise I/O.	2416	prioritise I/O.
1479		2417
1480	As an example for a bug workaround, the kqueue backend might only support	2418	As an example for a bug workaround, the kqueue backend might only support
1481	sockets on some platform, so it is unusable as generic backend, but you	2419	sockets on some platform, so it is unusable as generic backend, but you
1482	still want to make use of it because you have many sockets and it scales	2420	still want to make use of it because you have many sockets and it scales
1483	so nicely. In this case, you would create a kqueue-based loop and embed it	2421	so nicely. In this case, you would create a kqueue-based loop and embed
1484	into your default loop (which might use e.g. poll). Overall operation will	2422	it into your default loop (which might use e.g. poll). Overall operation
1485	be a bit slower because first libev has to poll and then call kevent, but	2423	will be a bit slower because first libev has to call C<poll> and then
1486	at least you can use both at what they are best.	2424	C<kevent>, but at least you can use both mechanisms for what they are
		2425	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1487		2426
1488	As for prioritising I/O: rarely you have the case where some fds have	2427	As for prioritising I/O: under rare circumstances you have the case where
1489	to be watched and handled very quickly (with low latency), and even	2428	some fds have to be watched and handled very quickly (with low latency),
1490	priorities and idle watchers might have too much overhead. In this case	2429	and even priorities and idle watchers might have too much overhead. In
1491	you would put all the high priority stuff in one loop and all the rest in	2430	this case you would put all the high priority stuff in one loop and all
1492	a second one, and embed the second one in the first.	2431	the rest in a second one, and embed the second one in the first.
1493		2432
1494	As long as the watcher is active, the callback will be invoked every time	2433	As long as the watcher is active, the callback will be invoked every time
1495	there might be events pending in the embedded loop. The callback must then	2434	there might be events pending in the embedded loop. The callback must then
1496	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2435	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke
1497	their callbacks (you could also start an idle watcher to give the embedded	2436	their callbacks (you could also start an idle watcher to give the embedded
…		…
1505	interested in that.	2444	interested in that.
1506		2445
1507	Also, there have not currently been made special provisions for forking:	2446	Also, there have not currently been made special provisions for forking:
1508	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2447	when you fork, you not only have to call C<ev_loop_fork> on both loops,
1509	but you will also have to stop and restart any C<ev_embed> watchers	2448	but you will also have to stop and restart any C<ev_embed> watchers
1510	yourself.	2449	yourself - but you can use a fork watcher to handle this automatically,
		2450	and future versions of libev might do just that.
1511		2451
1512	Unfortunately, not all backends are embeddable, only the ones returned by	2452	Unfortunately, not all backends are embeddable: only the ones returned by
1513	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2453	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1514	portable one.	2454	portable one.
1515		2455
1516	So when you want to use this feature you will always have to be prepared	2456	So when you want to use this feature you will always have to be prepared
1517	that you cannot get an embeddable loop. The recommended way to get around	2457	that you cannot get an embeddable loop. The recommended way to get around
1518	this is to have a separate variables for your embeddable loop, try to	2458	this is to have a separate variables for your embeddable loop, try to
1519	create it, and if that fails, use the normal loop for everything:	2459	create it, and if that fails, use the normal loop for everything.
1520		2460
1521	struct ev_loop *loop_hi = ev_default_init (0);	2461	=head3 C<ev_embed> and fork
1522	struct ev_loop *loop_lo = 0;
1523	struct ev_embed embed;
1524
1525	// see if there is a chance of getting one that works
1526	// (remember that a flags value of 0 means autodetection)
1527	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1528	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1529	: 0;
1530		2462
1531	// if we got one, then embed it, otherwise default to loop_hi	2463	While the C<ev_embed> watcher is running, forks in the embedding loop will
1532	if (loop_lo)	2464	automatically be applied to the embedded loop as well, so no special
1533	{	2465	fork handling is required in that case. When the watcher is not running,
1534	ev_embed_init (&embed, 0, loop_lo);	2466	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1535	ev_embed_start (loop_hi, &embed);	2467	as applicable.
1536	}	2468
1537	else	2469	=head3 Watcher-Specific Functions and Data Members
1538	loop_lo = loop_hi;
1539		2470
1540	=over 4	2471	=over 4
1541		2472
1542	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	2473	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
1543		2474
…		…
1545		2476
1546	Configures the watcher to embed the given loop, which must be	2477	Configures the watcher to embed the given loop, which must be
1547	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	2478	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1548	invoked automatically, otherwise it is the responsibility of the callback	2479	invoked automatically, otherwise it is the responsibility of the callback
1549	to invoke it (it will continue to be called until the sweep has been done,	2480	to invoke it (it will continue to be called until the sweep has been done,
1550	if you do not want thta, you need to temporarily stop the embed watcher).	2481	if you do not want that, you need to temporarily stop the embed watcher).
1551		2482
1552	=item ev_embed_sweep (loop, ev_embed *)	2483	=item ev_embed_sweep (loop, ev_embed *)
1553		2484
1554	Make a single, non-blocking sweep over the embedded loop. This works	2485	Make a single, non-blocking sweep over the embedded loop. This works
1555	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	2486	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
1556	apropriate way for embedded loops.	2487	appropriate way for embedded loops.
1557		2488
1558	=item struct ev_loop *loop [read-only]	2489	=item struct ev_loop *other [read-only]
1559		2490
1560	The embedded event loop.	2491	The embedded event loop.
1561		2492
1562	=back	2493	=back
		2494
		2495	=head3 Examples
		2496
		2497	Example: Try to get an embeddable event loop and embed it into the default
		2498	event loop. If that is not possible, use the default loop. The default
		2499	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2500	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2501	used).
		2502
		2503	struct ev_loop *loop_hi = ev_default_init (0);
		2504	struct ev_loop *loop_lo = 0;
		2505	ev_embed embed;
		2506
		2507	// see if there is a chance of getting one that works
		2508	// (remember that a flags value of 0 means autodetection)
		2509	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2510	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2511	: 0;
		2512
		2513	// if we got one, then embed it, otherwise default to loop_hi
		2514	if (loop_lo)
		2515	{
		2516	ev_embed_init (&embed, 0, loop_lo);
		2517	ev_embed_start (loop_hi, &embed);
		2518	}
		2519	else
		2520	loop_lo = loop_hi;
		2521
		2522	Example: Check if kqueue is available but not recommended and create
		2523	a kqueue backend for use with sockets (which usually work with any
		2524	kqueue implementation). Store the kqueue/socket-only event loop in
		2525	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2526
		2527	struct ev_loop *loop = ev_default_init (0);
		2528	struct ev_loop *loop_socket = 0;
		2529	ev_embed embed;
		2530
		2531	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2532	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2533	{
		2534	ev_embed_init (&embed, 0, loop_socket);
		2535	ev_embed_start (loop, &embed);
		2536	}
		2537
		2538	if (!loop_socket)
		2539	loop_socket = loop;
		2540
		2541	// now use loop_socket for all sockets, and loop for everything else
1563		2542
1564		2543
1565	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	2544	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
1566		2545
1567	Fork watchers are called when a C<fork ()> was detected (usually because	2546	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
1570	event loop blocks next and before C<ev_check> watchers are being called,	2549	event loop blocks next and before C<ev_check> watchers are being called,
1571	and only in the child after the fork. If whoever good citizen calling	2550	and only in the child after the fork. If whoever good citizen calling
1572	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2551	C<ev_default_fork> cheats and calls it in the wrong process, the fork
1573	handlers will be invoked, too, of course.	2552	handlers will be invoked, too, of course.
1574		2553
		2554	=head3 Watcher-Specific Functions and Data Members
		2555
1575	=over 4	2556	=over 4
1576		2557
1577	=item ev_fork_init (ev_signal *, callback)	2558	=item ev_fork_init (ev_signal *, callback)
1578		2559
1579	Initialises and configures the fork watcher - it has no parameters of any	2560	Initialises and configures the fork watcher - it has no parameters of any
…		…
1581	believe me.	2562	believe me.
1582		2563
1583	=back	2564	=back
1584		2565
1585		2566
		2567	=head2 C<ev_async> - how to wake up another event loop
		2568
		2569	In general, you cannot use an C<ev_loop> from multiple threads or other
		2570	asynchronous sources such as signal handlers (as opposed to multiple event
		2571	loops - those are of course safe to use in different threads).
		2572
		2573	Sometimes, however, you need to wake up another event loop you do not
		2574	control, for example because it belongs to another thread. This is what
		2575	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2576	can signal it by calling C<ev_async_send>, which is thread- and signal
		2577	safe.
		2578
		2579	This functionality is very similar to C<ev_signal> watchers, as signals,
		2580	too, are asynchronous in nature, and signals, too, will be compressed
		2581	(i.e. the number of callback invocations may be less than the number of
		2582	C<ev_async_sent> calls).
		2583
		2584	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2585	just the default loop.
		2586
		2587	=head3 Queueing
		2588
		2589	C<ev_async> does not support queueing of data in any way. The reason
		2590	is that the author does not know of a simple (or any) algorithm for a
		2591	multiple-writer-single-reader queue that works in all cases and doesn't
		2592	need elaborate support such as pthreads.
		2593
		2594	That means that if you want to queue data, you have to provide your own
		2595	queue. But at least I can tell you how to implement locking around your
		2596	queue:
		2597
		2598	=over 4
		2599
		2600	=item queueing from a signal handler context
		2601
		2602	To implement race-free queueing, you simply add to the queue in the signal
		2603	handler but you block the signal handler in the watcher callback. Here is
		2604	an example that does that for some fictitious SIGUSR1 handler:
		2605
		2606	static ev_async mysig;
		2607
		2608	static void
		2609	sigusr1_handler (void)
		2610	{
		2611	sometype data;
		2612
		2613	// no locking etc.
		2614	queue_put (data);
		2615	ev_async_send (EV_DEFAULT_ &mysig);
		2616	}
		2617
		2618	static void
		2619	mysig_cb (EV_P_ ev_async *w, int revents)
		2620	{
		2621	sometype data;
		2622	sigset_t block, prev;
		2623
		2624	sigemptyset (&block);
		2625	sigaddset (&block, SIGUSR1);
		2626	sigprocmask (SIG_BLOCK, &block, &prev);
		2627
		2628	while (queue_get (&data))
		2629	process (data);
		2630
		2631	if (sigismember (&prev, SIGUSR1)
		2632	sigprocmask (SIG_UNBLOCK, &block, 0);
		2633	}
		2634
		2635	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2636	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2637	either...).
		2638
		2639	=item queueing from a thread context
		2640
		2641	The strategy for threads is different, as you cannot (easily) block
		2642	threads but you can easily preempt them, so to queue safely you need to
		2643	employ a traditional mutex lock, such as in this pthread example:
		2644
		2645	static ev_async mysig;
		2646	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2647
		2648	static void
		2649	otherthread (void)
		2650	{
		2651	// only need to lock the actual queueing operation
		2652	pthread_mutex_lock (&mymutex);
		2653	queue_put (data);
		2654	pthread_mutex_unlock (&mymutex);
		2655
		2656	ev_async_send (EV_DEFAULT_ &mysig);
		2657	}
		2658
		2659	static void
		2660	mysig_cb (EV_P_ ev_async *w, int revents)
		2661	{
		2662	pthread_mutex_lock (&mymutex);
		2663
		2664	while (queue_get (&data))
		2665	process (data);
		2666
		2667	pthread_mutex_unlock (&mymutex);
		2668	}
		2669
		2670	=back
		2671
		2672
		2673	=head3 Watcher-Specific Functions and Data Members
		2674
		2675	=over 4
		2676
		2677	=item ev_async_init (ev_async *, callback)
		2678
		2679	Initialises and configures the async watcher - it has no parameters of any
		2680	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		2681	trust me.
		2682
		2683	=item ev_async_send (loop, ev_async *)
		2684
		2685	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2686	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2687	C<ev_feed_event>, this call is safe to do from other threads, signal or
		2688	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		2689	section below on what exactly this means).
		2690
		2691	This call incurs the overhead of a system call only once per loop iteration,
		2692	so while the overhead might be noticeable, it doesn't apply to repeated
		2693	calls to C<ev_async_send>.
		2694
		2695	=item bool = ev_async_pending (ev_async *)
		2696
		2697	Returns a non-zero value when C<ev_async_send> has been called on the
		2698	watcher but the event has not yet been processed (or even noted) by the
		2699	event loop.
		2700
		2701	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2702	the loop iterates next and checks for the watcher to have become active,
		2703	it will reset the flag again. C<ev_async_pending> can be used to very
		2704	quickly check whether invoking the loop might be a good idea.
		2705
		2706	Not that this does I<not> check whether the watcher itself is pending, only
		2707	whether it has been requested to make this watcher pending.
		2708
		2709	=back
		2710
		2711
1586	=head1 OTHER FUNCTIONS	2712	=head1 OTHER FUNCTIONS
1587		2713
1588	There are some other functions of possible interest. Described. Here. Now.	2714	There are some other functions of possible interest. Described. Here. Now.
1589		2715
1590	=over 4	2716	=over 4
1591		2717
1592	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	2718	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1593		2719
1594	This function combines a simple timer and an I/O watcher, calls your	2720	This function combines a simple timer and an I/O watcher, calls your
1595	callback on whichever event happens first and automatically stop both	2721	callback on whichever event happens first and automatically stops both
1596	watchers. This is useful if you want to wait for a single event on an fd	2722	watchers. This is useful if you want to wait for a single event on an fd
1597	or timeout without having to allocate/configure/start/stop/free one or	2723	or timeout without having to allocate/configure/start/stop/free one or
1598	more watchers yourself.	2724	more watchers yourself.
1599		2725
1600	If C<fd> is less than 0, then no I/O watcher will be started and events	2726	If C<fd> is less than 0, then no I/O watcher will be started and the
1601	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	2727	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1602	C<events> set will be craeted and started.	2728	the given C<fd> and C<events> set will be created and started.
1603		2729
1604	If C<timeout> is less than 0, then no timeout watcher will be	2730	If C<timeout> is less than 0, then no timeout watcher will be
1605	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	2731	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1606	repeat = 0) will be started. While C<0> is a valid timeout, it is of	2732	repeat = 0) will be started. C<0> is a valid timeout.
1607	dubious value.
1608		2733
1609	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	2734	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
1610	passed an C<revents> set like normal event callbacks (a combination of	2735	passed an C<revents> set like normal event callbacks (a combination of
1611	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	2736	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
1612	value passed to C<ev_once>:	2737	value passed to C<ev_once>. Note that it is possible to receive I<both>
		2738	a timeout and an io event at the same time - you probably should give io
		2739	events precedence.
1613		2740
		2741	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		2742
1614	static void stdin_ready (int revents, void *arg)	2743	static void stdin_ready (int revents, void *arg)
1615	{	2744	{
1616	if (revents & EV_TIMEOUT)
1617	/* doh, nothing entered */;
1618	else if (revents & EV_READ)	2745	if (revents & EV_READ)
1619	/* stdin might have data for us, joy! */;	2746	/* stdin might have data for us, joy! */;
		2747	else if (revents & EV_TIMEOUT)
		2748	/* doh, nothing entered */;
1620	}	2749	}
1621		2750
1622	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2751	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1623		2752
1624	=item ev_feed_event (ev_loop *, watcher *, int revents)	2753	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
1625		2754
1626	Feeds the given event set into the event loop, as if the specified event	2755	Feeds the given event set into the event loop, as if the specified event
1627	had happened for the specified watcher (which must be a pointer to an	2756	had happened for the specified watcher (which must be a pointer to an
1628	initialised but not necessarily started event watcher).	2757	initialised but not necessarily started event watcher).
1629		2758
1630	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	2759	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
1631		2760
1632	Feed an event on the given fd, as if a file descriptor backend detected	2761	Feed an event on the given fd, as if a file descriptor backend detected
1633	the given events it.	2762	the given events it.
1634		2763
1635	=item ev_feed_signal_event (ev_loop *loop, int signum)	2764	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
1636		2765
1637	Feed an event as if the given signal occured (C<loop> must be the default	2766	Feed an event as if the given signal occurred (C<loop> must be the default
1638	loop!).	2767	loop!).
1639		2768
1640	=back	2769	=back
1641		2770
1642		2771
…		…
1658		2787
1659	=item * Priorities are not currently supported. Initialising priorities	2788	=item * Priorities are not currently supported. Initialising priorities
1660	will fail and all watchers will have the same priority, even though there	2789	will fail and all watchers will have the same priority, even though there
1661	is an ev_pri field.	2790	is an ev_pri field.
1662		2791
		2792	=item * In libevent, the last base created gets the signals, in libev, the
		2793	first base created (== the default loop) gets the signals.
		2794
1663	=item * Other members are not supported.	2795	=item * Other members are not supported.
1664		2796
1665	=item * The libev emulation is I<not> ABI compatible to libevent, you need	2797	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1666	to use the libev header file and library.	2798	to use the libev header file and library.
1667		2799
1668	=back	2800	=back
1669		2801
1670	=head1 C++ SUPPORT	2802	=head1 C++ SUPPORT
1671		2803
1672	Libev comes with some simplistic wrapper classes for C++ that mainly allow	2804	Libev comes with some simplistic wrapper classes for C++ that mainly allow
1673	you to use some convinience methods to start/stop watchers and also change	2805	you to use some convenience methods to start/stop watchers and also change
1674	the callback model to a model using method callbacks on objects.	2806	the callback model to a model using method callbacks on objects.
1675		2807
1676	To use it,	2808	To use it,
1677		2809
1678	#include <ev++.h>	2810	#include <ev++.h>
1679		2811
1680	(it is not installed by default). This automatically includes F<ev.h>	2812	This automatically includes F<ev.h> and puts all of its definitions (many
1681	and puts all of its definitions (many of them macros) into the global	2813	of them macros) into the global namespace. All C++ specific things are
1682	namespace. All C++ specific things are put into the C<ev> namespace.	2814	put into the C<ev> namespace. It should support all the same embedding
		2815	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
1683		2816
1684	It should support all the same embedding options as F<ev.h>, most notably	2817	Care has been taken to keep the overhead low. The only data member the C++
1685	C<EV_MULTIPLICITY>.	2818	classes add (compared to plain C-style watchers) is the event loop pointer
		2819	that the watcher is associated with (or no additional members at all if
		2820	you disable C<EV_MULTIPLICITY> when embedding libev).
		2821
		2822	Currently, functions, and static and non-static member functions can be
		2823	used as callbacks. Other types should be easy to add as long as they only
		2824	need one additional pointer for context. If you need support for other
		2825	types of functors please contact the author (preferably after implementing
		2826	it).
1686		2827
1687	Here is a list of things available in the C<ev> namespace:	2828	Here is a list of things available in the C<ev> namespace:
1688		2829
1689	=over 4	2830	=over 4
1690		2831
…		…
1706		2847
1707	All of those classes have these methods:	2848	All of those classes have these methods:
1708		2849
1709	=over 4	2850	=over 4
1710		2851
1711	=item ev::TYPE::TYPE (object *, object::method *)	2852	=item ev::TYPE::TYPE ()
1712		2853
1713	=item ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)	2854	=item ev::TYPE::TYPE (struct ev_loop *)
1714		2855
1715	=item ev::TYPE::~TYPE	2856	=item ev::TYPE::~TYPE
1716		2857
1717	The constructor takes a pointer to an object and a method pointer to	2858	The constructor (optionally) takes an event loop to associate the watcher
1718	the event handler callback to call in this class. The constructor calls	2859	with. If it is omitted, it will use C<EV_DEFAULT>.
1719	C<ev_init> for you, which means you have to call the C<set> method	2860
1720	before starting it. If you do not specify a loop then the constructor	2861	The constructor calls C<ev_init> for you, which means you have to call the
1721	automatically associates the default loop with this watcher.	2862	C<set> method before starting it.
		2863
		2864	It will not set a callback, however: You have to call the templated C<set>
		2865	method to set a callback before you can start the watcher.
		2866
		2867	(The reason why you have to use a method is a limitation in C++ which does
		2868	not allow explicit template arguments for constructors).
1722		2869
1723	The destructor automatically stops the watcher if it is active.	2870	The destructor automatically stops the watcher if it is active.
		2871
		2872	=item w->set<class, &class::method> (object *)
		2873
		2874	This method sets the callback method to call. The method has to have a
		2875	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		2876	first argument and the C<revents> as second. The object must be given as
		2877	parameter and is stored in the C<data> member of the watcher.
		2878
		2879	This method synthesizes efficient thunking code to call your method from
		2880	the C callback that libev requires. If your compiler can inline your
		2881	callback (i.e. it is visible to it at the place of the C<set> call and
		2882	your compiler is good :), then the method will be fully inlined into the
		2883	thunking function, making it as fast as a direct C callback.
		2884
		2885	Example: simple class declaration and watcher initialisation
		2886
		2887	struct myclass
		2888	{
		2889	void io_cb (ev::io &w, int revents) { }
		2890	}
		2891
		2892	myclass obj;
		2893	ev::io iow;
		2894	iow.set <myclass, &myclass::io_cb> (&obj);
		2895
		2896	=item w->set<function> (void *data = 0)
		2897
		2898	Also sets a callback, but uses a static method or plain function as
		2899	callback. The optional C<data> argument will be stored in the watcher's
		2900	C<data> member and is free for you to use.
		2901
		2902	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		2903
		2904	See the method-C<set> above for more details.
		2905
		2906	Example: Use a plain function as callback.
		2907
		2908	static void io_cb (ev::io &w, int revents) { }
		2909	iow.set <io_cb> ();
1724		2910
1725	=item w->set (struct ev_loop *)	2911	=item w->set (struct ev_loop *)
1726		2912
1727	Associates a different C<struct ev_loop> with this watcher. You can only	2913	Associates a different C<struct ev_loop> with this watcher. You can only
1728	do this when the watcher is inactive (and not pending either).	2914	do this when the watcher is inactive (and not pending either).
1729		2915
1730	=item w->set ([args])	2916	=item w->set ([arguments])
1731		2917
1732	Basically the same as C<ev_TYPE_set>, with the same args. Must be	2918	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
1733	called at least once. Unlike the C counterpart, an active watcher gets	2919	called at least once. Unlike the C counterpart, an active watcher gets
1734	automatically stopped and restarted.	2920	automatically stopped and restarted when reconfiguring it with this
		2921	method.
1735		2922
1736	=item w->start ()	2923	=item w->start ()
1737		2924
1738	Starts the watcher. Note that there is no C<loop> argument as the	2925	Starts the watcher. Note that there is no C<loop> argument, as the
1739	constructor already takes the loop.	2926	constructor already stores the event loop.
1740		2927
1741	=item w->stop ()	2928	=item w->stop ()
1742		2929
1743	Stops the watcher if it is active. Again, no C<loop> argument.	2930	Stops the watcher if it is active. Again, no C<loop> argument.
1744		2931
1745	=item w->again () C<ev::timer>, C<ev::periodic> only	2932	=item w->again () (C<ev::timer>, C<ev::periodic> only)
1746		2933
1747	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding	2934	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
1748	C<ev_TYPE_again> function.	2935	C<ev_TYPE_again> function.
1749		2936
1750	=item w->sweep () C<ev::embed> only	2937	=item w->sweep () (C<ev::embed> only)
1751		2938
1752	Invokes C<ev_embed_sweep>.	2939	Invokes C<ev_embed_sweep>.
1753		2940
1754	=item w->update () C<ev::stat> only	2941	=item w->update () (C<ev::stat> only)
1755		2942
1756	Invokes C<ev_stat_stat>.	2943	Invokes C<ev_stat_stat>.
1757		2944
1758	=back	2945	=back
1759		2946
1760	=back	2947	=back
1761		2948
1762	Example: Define a class with an IO and idle watcher, start one of them in	2949	Example: Define a class with an IO and idle watcher, start one of them in
1763	the constructor.	2950	the constructor.
1764		2951
1765	class myclass	2952	class myclass
1766	{	2953	{
1767	ev_io io; void io_cb (ev::io &w, int revents);	2954	ev::io io ; void io_cb (ev::io &w, int revents);
1768	ev_idle idle void idle_cb (ev::idle &w, int revents);	2955	ev::idle idle; void idle_cb (ev::idle &w, int revents);
1769		2956
1770	myclass ();	2957	myclass (int fd)
1771	}	2958	{
		2959	io .set <myclass, &myclass::io_cb > (this);
		2960	idle.set <myclass, &myclass::idle_cb> (this);
1772		2961
1773	myclass::myclass (int fd)
1774	: io (this, &myclass::io_cb),
1775	idle (this, &myclass::idle_cb)
1776	{
1777	io.start (fd, ev::READ);	2962	io.start (fd, ev::READ);
		2963	}
1778	}	2964	};
		2965
		2966
		2967	=head1 OTHER LANGUAGE BINDINGS
		2968
		2969	Libev does not offer other language bindings itself, but bindings for a
		2970	number of languages exist in the form of third-party packages. If you know
		2971	any interesting language binding in addition to the ones listed here, drop
		2972	me a note.
		2973
		2974	=over 4
		2975
		2976	=item Perl
		2977
		2978	The EV module implements the full libev API and is actually used to test
		2979	libev. EV is developed together with libev. Apart from the EV core module,
		2980	there are additional modules that implement libev-compatible interfaces
		2981	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		2982	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		2983	and C<EV::Glib>).
		2984
		2985	It can be found and installed via CPAN, its homepage is at
		2986	L<http://software.schmorp.de/pkg/EV>.
		2987
		2988	=item Python
		2989
		2990	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		2991	seems to be quite complete and well-documented. Note, however, that the
		2992	patch they require for libev is outright dangerous as it breaks the ABI
		2993	for everybody else, and therefore, should never be applied in an installed
		2994	libev (if python requires an incompatible ABI then it needs to embed
		2995	libev).
		2996
		2997	=item Ruby
		2998
		2999	Tony Arcieri has written a ruby extension that offers access to a subset
		3000	of the libev API and adds file handle abstractions, asynchronous DNS and
		3001	more on top of it. It can be found via gem servers. Its homepage is at
		3002	L<http://rev.rubyforge.org/>.
		3003
		3004	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3005	makes rev work even on mingw.
		3006
		3007	=item D
		3008
		3009	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3010	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3011
		3012	=item Ocaml
		3013
		3014	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3015	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3016
		3017	=back
1779		3018
1780		3019
1781	=head1 MACRO MAGIC	3020	=head1 MACRO MAGIC
1782		3021
1783	Libev can be compiled with a variety of options, the most fundemantal is	3022	Libev can be compiled with a variety of options, the most fundamental
1784	C<EV_MULTIPLICITY>. This option determines wether (most) functions and	3023	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
1785	callbacks have an initial C<struct ev_loop *> argument.	3024	functions and callbacks have an initial C<struct ev_loop *> argument.
1786		3025
1787	To make it easier to write programs that cope with either variant, the	3026	To make it easier to write programs that cope with either variant, the
1788	following macros are defined:	3027	following macros are defined:
1789		3028
1790	=over 4	3029	=over 4
…		…
1793		3032
1794	This provides the loop I<argument> for functions, if one is required ("ev	3033	This provides the loop I<argument> for functions, if one is required ("ev
1795	loop argument"). The C<EV_A> form is used when this is the sole argument,	3034	loop argument"). The C<EV_A> form is used when this is the sole argument,
1796	C<EV_A_> is used when other arguments are following. Example:	3035	C<EV_A_> is used when other arguments are following. Example:
1797		3036
1798	ev_unref (EV_A);	3037	ev_unref (EV_A);
1799	ev_timer_add (EV_A_ watcher);	3038	ev_timer_add (EV_A_ watcher);
1800	ev_loop (EV_A_ 0);	3039	ev_loop (EV_A_ 0);
1801		3040
1802	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	3041	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
1803	which is often provided by the following macro.	3042	which is often provided by the following macro.
1804		3043
1805	=item C<EV_P>, C<EV_P_>	3044	=item C<EV_P>, C<EV_P_>
1806		3045
1807	This provides the loop I<parameter> for functions, if one is required ("ev	3046	This provides the loop I<parameter> for functions, if one is required ("ev
1808	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	3047	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
1809	C<EV_P_> is used when other parameters are following. Example:	3048	C<EV_P_> is used when other parameters are following. Example:
1810		3049
1811	// this is how ev_unref is being declared	3050	// this is how ev_unref is being declared
1812	static void ev_unref (EV_P);	3051	static void ev_unref (EV_P);
1813		3052
1814	// this is how you can declare your typical callback	3053	// this is how you can declare your typical callback
1815	static void cb (EV_P_ ev_timer *w, int revents)	3054	static void cb (EV_P_ ev_timer *w, int revents)
1816		3055
1817	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	3056	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
1818	suitable for use with C<EV_A>.	3057	suitable for use with C<EV_A>.
1819		3058
1820	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3059	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
1821		3060
1822	Similar to the other two macros, this gives you the value of the default	3061	Similar to the other two macros, this gives you the value of the default
1823	loop, if multiple loops are supported ("ev loop default").	3062	loop, if multiple loops are supported ("ev loop default").
1824		3063
		3064	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3065
		3066	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3067	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3068	is undefined when the default loop has not been initialised by a previous
		3069	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3070
		3071	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3072	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		3073
1825	=back	3074	=back
1826		3075
1827	Example: Declare and initialise a check watcher, working regardless of	3076	Example: Declare and initialise a check watcher, utilising the above
1828	wether multiple loops are supported or not.	3077	macros so it will work regardless of whether multiple loops are supported
		3078	or not.
1829		3079
1830	static void	3080	static void
1831	check_cb (EV_P_ ev_timer *w, int revents)	3081	check_cb (EV_P_ ev_timer *w, int revents)
1832	{	3082	{
1833	ev_check_stop (EV_A_ w);	3083	ev_check_stop (EV_A_ w);
1834	}	3084	}
1835		3085
1836	ev_check check;	3086	ev_check check;
1837	ev_check_init (&check, check_cb);	3087	ev_check_init (&check, check_cb);
1838	ev_check_start (EV_DEFAULT_ &check);	3088	ev_check_start (EV_DEFAULT_ &check);
1839	ev_loop (EV_DEFAULT_ 0);	3089	ev_loop (EV_DEFAULT_ 0);
1840
1841		3090
1842	=head1 EMBEDDING	3091	=head1 EMBEDDING
1843		3092
1844	Libev can (and often is) directly embedded into host	3093	Libev can (and often is) directly embedded into host
1845	applications. Examples of applications that embed it include the Deliantra	3094	applications. Examples of applications that embed it include the Deliantra
1846	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)	3095	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
1847	and rxvt-unicode.	3096	and rxvt-unicode.
1848		3097
1849	The goal is to enable you to just copy the neecssary files into your	3098	The goal is to enable you to just copy the necessary files into your
1850	source directory without having to change even a single line in them, so	3099	source directory without having to change even a single line in them, so
1851	you can easily upgrade by simply copying (or having a checked-out copy of	3100	you can easily upgrade by simply copying (or having a checked-out copy of
1852	libev somewhere in your source tree).	3101	libev somewhere in your source tree).
1853		3102
1854	=head2 FILESETS	3103	=head2 FILESETS
1855		3104
1856	Depending on what features you need you need to include one or more sets of files	3105	Depending on what features you need you need to include one or more sets of files
1857	in your app.	3106	in your application.
1858		3107
1859	=head3 CORE EVENT LOOP	3108	=head3 CORE EVENT LOOP
1860		3109
1861	To include only the libev core (all the C<ev_*> functions), with manual	3110	To include only the libev core (all the C<ev_*> functions), with manual
1862	configuration (no autoconf):	3111	configuration (no autoconf):
1863		3112
1864	#define EV_STANDALONE 1	3113	#define EV_STANDALONE 1
1865	#include "ev.c"	3114	#include "ev.c"
1866		3115
1867	This will automatically include F<ev.h>, too, and should be done in a	3116	This will automatically include F<ev.h>, too, and should be done in a
1868	single C source file only to provide the function implementations. To use	3117	single C source file only to provide the function implementations. To use
1869	it, do the same for F<ev.h> in all files wishing to use this API (best	3118	it, do the same for F<ev.h> in all files wishing to use this API (best
1870	done by writing a wrapper around F<ev.h> that you can include instead and	3119	done by writing a wrapper around F<ev.h> that you can include instead and
1871	where you can put other configuration options):	3120	where you can put other configuration options):
1872		3121
1873	#define EV_STANDALONE 1	3122	#define EV_STANDALONE 1
1874	#include "ev.h"	3123	#include "ev.h"
1875		3124
1876	Both header files and implementation files can be compiled with a C++	3125	Both header files and implementation files can be compiled with a C++
1877	compiler (at least, thats a stated goal, and breakage will be treated	3126	compiler (at least, that's a stated goal, and breakage will be treated
1878	as a bug).	3127	as a bug).
1879		3128
1880	You need the following files in your source tree, or in a directory	3129	You need the following files in your source tree, or in a directory
1881	in your include path (e.g. in libev/ when using -Ilibev):	3130	in your include path (e.g. in libev/ when using -Ilibev):
1882		3131
1883	ev.h	3132	ev.h
1884	ev.c	3133	ev.c
1885	ev_vars.h	3134	ev_vars.h
1886	ev_wrap.h	3135	ev_wrap.h
1887		3136
1888	ev_win32.c required on win32 platforms only	3137	ev_win32.c required on win32 platforms only
1889		3138
1890	ev_select.c only when select backend is enabled (which is by default)	3139	ev_select.c only when select backend is enabled (which is enabled by default)
1891	ev_poll.c only when poll backend is enabled (disabled by default)	3140	ev_poll.c only when poll backend is enabled (disabled by default)
1892	ev_epoll.c only when the epoll backend is enabled (disabled by default)	3141	ev_epoll.c only when the epoll backend is enabled (disabled by default)
1893	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	3142	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
1894	ev_port.c only when the solaris port backend is enabled (disabled by default)	3143	ev_port.c only when the solaris port backend is enabled (disabled by default)
1895		3144
1896	F<ev.c> includes the backend files directly when enabled, so you only need	3145	F<ev.c> includes the backend files directly when enabled, so you only need
1897	to compile this single file.	3146	to compile this single file.
1898		3147
1899	=head3 LIBEVENT COMPATIBILITY API	3148	=head3 LIBEVENT COMPATIBILITY API
1900		3149
1901	To include the libevent compatibility API, also include:	3150	To include the libevent compatibility API, also include:
1902		3151
1903	#include "event.c"	3152	#include "event.c"
1904		3153
1905	in the file including F<ev.c>, and:	3154	in the file including F<ev.c>, and:
1906		3155
1907	#include "event.h"	3156	#include "event.h"
1908		3157
1909	in the files that want to use the libevent API. This also includes F<ev.h>.	3158	in the files that want to use the libevent API. This also includes F<ev.h>.
1910		3159
1911	You need the following additional files for this:	3160	You need the following additional files for this:
1912		3161
1913	event.h	3162	event.h
1914	event.c	3163	event.c
1915		3164
1916	=head3 AUTOCONF SUPPORT	3165	=head3 AUTOCONF SUPPORT
1917		3166
1918	Instead of using C<EV_STANDALONE=1> and providing your config in	3167	Instead of using C<EV_STANDALONE=1> and providing your configuration in
1919	whatever way you want, you can also C<m4_include([libev.m4])> in your	3168	whatever way you want, you can also C<m4_include([libev.m4])> in your
1920	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	3169	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
1921	include F<config.h> and configure itself accordingly.	3170	include F<config.h> and configure itself accordingly.
1922		3171
1923	For this of course you need the m4 file:	3172	For this of course you need the m4 file:
1924		3173
1925	libev.m4	3174	libev.m4
1926		3175
1927	=head2 PREPROCESSOR SYMBOLS/MACROS	3176	=head2 PREPROCESSOR SYMBOLS/MACROS
1928		3177
1929	Libev can be configured via a variety of preprocessor symbols you have to define	3178	Libev can be configured via a variety of preprocessor symbols you have to
1930	before including any of its files. The default is not to build for multiplicity	3179	define before including any of its files. The default in the absence of
1931	and only include the select backend.	3180	autoconf is documented for every option.
1932		3181
1933	=over 4	3182	=over 4
1934		3183
1935	=item EV_STANDALONE	3184	=item EV_STANDALONE
1936		3185
…		…
1938	keeps libev from including F<config.h>, and it also defines dummy	3187	keeps libev from including F<config.h>, and it also defines dummy
1939	implementations for some libevent functions (such as logging, which is not	3188	implementations for some libevent functions (such as logging, which is not
1940	supported). It will also not define any of the structs usually found in	3189	supported). It will also not define any of the structs usually found in
1941	F<event.h> that are not directly supported by the libev core alone.	3190	F<event.h> that are not directly supported by the libev core alone.
1942		3191
		3192	In stanbdalone mode, libev will still try to automatically deduce the
		3193	configuration, but has to be more conservative.
		3194
1943	=item EV_USE_MONOTONIC	3195	=item EV_USE_MONOTONIC
1944		3196
1945	If defined to be C<1>, libev will try to detect the availability of the	3197	If defined to be C<1>, libev will try to detect the availability of the
1946	monotonic clock option at both compiletime and runtime. Otherwise no use	3198	monotonic clock option at both compile time and runtime. Otherwise no
1947	of the monotonic clock option will be attempted. If you enable this, you	3199	use of the monotonic clock option will be attempted. If you enable this,
1948	usually have to link against librt or something similar. Enabling it when	3200	you usually have to link against librt or something similar. Enabling it
1949	the functionality isn't available is safe, though, althoguh you have	3201	when the functionality isn't available is safe, though, although you have
1950	to make sure you link against any libraries where the C<clock_gettime>	3202	to make sure you link against any libraries where the C<clock_gettime>
1951	function is hiding in (often F<-lrt>).	3203	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
1952		3204
1953	=item EV_USE_REALTIME	3205	=item EV_USE_REALTIME
1954		3206
1955	If defined to be C<1>, libev will try to detect the availability of the	3207	If defined to be C<1>, libev will try to detect the availability of the
1956	realtime clock option at compiletime (and assume its availability at	3208	real-time clock option at compile time (and assume its availability at
1957	runtime if successful). Otherwise no use of the realtime clock option will	3209	runtime if successful). Otherwise no use of the real-time clock option will
1958	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3210	be attempted. This effectively replaces C<gettimeofday> by C<clock_get
1959	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See tzhe note about libraries	3211	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the
1960	in the description of C<EV_USE_MONOTONIC>, though.	3212	note about libraries in the description of C<EV_USE_MONOTONIC>, though.
		3213
		3214	=item EV_USE_CLOCK_SYSCALL
		3215
		3216	If defined to be C<1>, libev will try to use a direct syscall instead
		3217	of calling the system-provided C<clock_gettime> function. This option
		3218	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3219	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3220	programs needlessly. Using a direct syscall is slightly slower (in
		3221	theory), because no optimised vdso implementation can be used, but avoids
		3222	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3223	higher, as it simplifies linking (no need for C<-lrt>).
		3224
		3225	=item EV_USE_NANOSLEEP
		3226
		3227	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		3228	and will use it for delays. Otherwise it will use C<select ()>.
		3229
		3230	=item EV_USE_EVENTFD
		3231
		3232	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3233	available and will probe for kernel support at runtime. This will improve
		3234	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3235	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3236	2.7 or newer, otherwise disabled.
1961		3237
1962	=item EV_USE_SELECT	3238	=item EV_USE_SELECT
1963		3239
1964	If undefined or defined to be C<1>, libev will compile in support for the	3240	If undefined or defined to be C<1>, libev will compile in support for the
1965	C<select>(2) backend. No attempt at autodetection will be done: if no	3241	C<select>(2) backend. No attempt at auto-detection will be done: if no
1966	other method takes over, select will be it. Otherwise the select backend	3242	other method takes over, select will be it. Otherwise the select backend
1967	will not be compiled in.	3243	will not be compiled in.
1968		3244
1969	=item EV_SELECT_USE_FD_SET	3245	=item EV_SELECT_USE_FD_SET
1970		3246
1971	If defined to C<1>, then the select backend will use the system C<fd_set>	3247	If defined to C<1>, then the select backend will use the system C<fd_set>
1972	structure. This is useful if libev doesn't compile due to a missing	3248	structure. This is useful if libev doesn't compile due to a missing
1973	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	3249	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
1974	exotic systems. This usually limits the range of file descriptors to some	3250	on exotic systems. This usually limits the range of file descriptors to
1975	low limit such as 1024 or might have other limitations (winsocket only	3251	some low limit such as 1024 or might have other limitations (winsocket
1976	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3252	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
1977	influence the size of the C<fd_set> used.	3253	configures the maximum size of the C<fd_set>.
1978		3254
1979	=item EV_SELECT_IS_WINSOCKET	3255	=item EV_SELECT_IS_WINSOCKET
1980		3256
1981	When defined to C<1>, the select backend will assume that	3257	When defined to C<1>, the select backend will assume that
1982	select/socket/connect etc. don't understand file descriptors but	3258	select/socket/connect etc. don't understand file descriptors but
…		…
1984	be used is the winsock select). This means that it will call	3260	be used is the winsock select). This means that it will call
1985	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3261	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
1986	it is assumed that all these functions actually work on fds, even	3262	it is assumed that all these functions actually work on fds, even
1987	on win32. Should not be defined on non-win32 platforms.	3263	on win32. Should not be defined on non-win32 platforms.
1988		3264
		3265	=item EV_FD_TO_WIN32_HANDLE
		3266
		3267	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3268	file descriptors to socket handles. When not defining this symbol (the
		3269	default), then libev will call C<_get_osfhandle>, which is usually
		3270	correct. In some cases, programs use their own file descriptor management,
		3271	in which case they can provide this function to map fds to socket handles.
		3272
1989	=item EV_USE_POLL	3273	=item EV_USE_POLL
1990		3274
1991	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3275	If defined to be C<1>, libev will compile in support for the C<poll>(2)
1992	backend. Otherwise it will be enabled on non-win32 platforms. It	3276	backend. Otherwise it will be enabled on non-win32 platforms. It
1993	takes precedence over select.	3277	takes precedence over select.
1994		3278
1995	=item EV_USE_EPOLL	3279	=item EV_USE_EPOLL
1996		3280
1997	If defined to be C<1>, libev will compile in support for the Linux	3281	If defined to be C<1>, libev will compile in support for the Linux
1998	C<epoll>(7) backend. Its availability will be detected at runtime,	3282	C<epoll>(7) backend. Its availability will be detected at runtime,
1999	otherwise another method will be used as fallback. This is the	3283	otherwise another method will be used as fallback. This is the preferred
2000	preferred backend for GNU/Linux systems.	3284	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3285	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2001		3286
2002	=item EV_USE_KQUEUE	3287	=item EV_USE_KQUEUE
2003		3288
2004	If defined to be C<1>, libev will compile in support for the BSD style	3289	If defined to be C<1>, libev will compile in support for the BSD style
2005	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	3290	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2018	otherwise another method will be used as fallback. This is the preferred	3303	otherwise another method will be used as fallback. This is the preferred
2019	backend for Solaris 10 systems.	3304	backend for Solaris 10 systems.
2020		3305
2021	=item EV_USE_DEVPOLL	3306	=item EV_USE_DEVPOLL
2022		3307
2023	reserved for future expansion, works like the USE symbols above.	3308	Reserved for future expansion, works like the USE symbols above.
2024		3309
2025	=item EV_USE_INOTIFY	3310	=item EV_USE_INOTIFY
2026		3311
2027	If defined to be C<1>, libev will compile in support for the Linux inotify	3312	If defined to be C<1>, libev will compile in support for the Linux inotify
2028	interface to speed up C<ev_stat> watchers. Its actual availability will	3313	interface to speed up C<ev_stat> watchers. Its actual availability will
2029	be detected at runtime.	3314	be detected at runtime. If undefined, it will be enabled if the headers
		3315	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3316
		3317	=item EV_ATOMIC_T
		3318
		3319	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3320	access is atomic with respect to other threads or signal contexts. No such
		3321	type is easily found in the C language, so you can provide your own type
		3322	that you know is safe for your purposes. It is used both for signal handler "locking"
		3323	as well as for signal and thread safety in C<ev_async> watchers.
		3324
		3325	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3326	(from F<signal.h>), which is usually good enough on most platforms.
2030		3327
2031	=item EV_H	3328	=item EV_H
2032		3329
2033	The name of the F<ev.h> header file used to include it. The default if	3330	The name of the F<ev.h> header file used to include it. The default if
2034	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This	3331	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2035	can be used to virtually rename the F<ev.h> header file in case of conflicts.	3332	used to virtually rename the F<ev.h> header file in case of conflicts.
2036		3333
2037	=item EV_CONFIG_H	3334	=item EV_CONFIG_H
2038		3335
2039	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	3336	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2040	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	3337	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2041	C<EV_H>, above.	3338	C<EV_H>, above.
2042		3339
2043	=item EV_EVENT_H	3340	=item EV_EVENT_H
2044		3341
2045	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	3342	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2046	of how the F<event.h> header can be found.	3343	of how the F<event.h> header can be found, the default is C<"event.h">.
2047		3344
2048	=item EV_PROTOTYPES	3345	=item EV_PROTOTYPES
2049		3346
2050	If defined to be C<0>, then F<ev.h> will not define any function	3347	If defined to be C<0>, then F<ev.h> will not define any function
2051	prototypes, but still define all the structs and other symbols. This is	3348	prototypes, but still define all the structs and other symbols. This is
…		…
2058	will have the C<struct ev_loop *> as first argument, and you can create	3355	will have the C<struct ev_loop *> as first argument, and you can create
2059	additional independent event loops. Otherwise there will be no support	3356	additional independent event loops. Otherwise there will be no support
2060	for multiple event loops and there is no first event loop pointer	3357	for multiple event loops and there is no first event loop pointer
2061	argument. Instead, all functions act on the single default loop.	3358	argument. Instead, all functions act on the single default loop.
2062		3359
		3360	=item EV_MINPRI
		3361
		3362	=item EV_MAXPRI
		3363
		3364	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		3365	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		3366	provide for more priorities by overriding those symbols (usually defined
		3367	to be C<-2> and C<2>, respectively).
		3368
		3369	When doing priority-based operations, libev usually has to linearly search
		3370	all the priorities, so having many of them (hundreds) uses a lot of space
		3371	and time, so using the defaults of five priorities (-2 .. +2) is usually
		3372	fine.
		3373
		3374	If your embedding application does not need any priorities, defining these
		3375	both to C<0> will save some memory and CPU.
		3376
2063	=item EV_PERIODIC_ENABLE	3377	=item EV_PERIODIC_ENABLE
2064		3378
2065	If undefined or defined to be C<1>, then periodic timers are supported. If	3379	If undefined or defined to be C<1>, then periodic timers are supported. If
2066	defined to be C<0>, then they are not. Disabling them saves a few kB of	3380	defined to be C<0>, then they are not. Disabling them saves a few kB of
2067	code.	3381	code.
2068		3382
		3383	=item EV_IDLE_ENABLE
		3384
		3385	If undefined or defined to be C<1>, then idle watchers are supported. If
		3386	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3387	code.
		3388
2069	=item EV_EMBED_ENABLE	3389	=item EV_EMBED_ENABLE
2070		3390
2071	If undefined or defined to be C<1>, then embed watchers are supported. If	3391	If undefined or defined to be C<1>, then embed watchers are supported. If
2072	defined to be C<0>, then they are not.	3392	defined to be C<0>, then they are not. Embed watchers rely on most other
		3393	watcher types, which therefore must not be disabled.
2073		3394
2074	=item EV_STAT_ENABLE	3395	=item EV_STAT_ENABLE
2075		3396
2076	If undefined or defined to be C<1>, then stat watchers are supported. If	3397	If undefined or defined to be C<1>, then stat watchers are supported. If
2077	defined to be C<0>, then they are not.	3398	defined to be C<0>, then they are not.
…		…
2079	=item EV_FORK_ENABLE	3400	=item EV_FORK_ENABLE
2080		3401
2081	If undefined or defined to be C<1>, then fork watchers are supported. If	3402	If undefined or defined to be C<1>, then fork watchers are supported. If
2082	defined to be C<0>, then they are not.	3403	defined to be C<0>, then they are not.
2083		3404
		3405	=item EV_ASYNC_ENABLE
		3406
		3407	If undefined or defined to be C<1>, then async watchers are supported. If
		3408	defined to be C<0>, then they are not.
		3409
2084	=item EV_MINIMAL	3410	=item EV_MINIMAL
2085		3411
2086	If you need to shave off some kilobytes of code at the expense of some	3412	If you need to shave off some kilobytes of code at the expense of some
2087	speed, define this symbol to C<1>. Currently only used for gcc to override	3413	speed, define this symbol to C<1>. Currently this is used to override some
2088	some inlining decisions, saves roughly 30% codesize of amd64.	3414	inlining decisions, saves roughly 30% code size on amd64. It also selects a
		3415	much smaller 2-heap for timer management over the default 4-heap.
2089		3416
2090	=item EV_PID_HASHSIZE	3417	=item EV_PID_HASHSIZE
2091		3418
2092	C<ev_child> watchers use a small hash table to distribute workload by	3419	C<ev_child> watchers use a small hash table to distribute workload by
2093	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3420	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
2094	than enough. If you need to manage thousands of children you might want to	3421	than enough. If you need to manage thousands of children you might want to
2095	increase this value (I<must> be a power of two).	3422	increase this value (I<must> be a power of two).
2096		3423
2097	=item EV_INOTIFY_HASHSIZE	3424	=item EV_INOTIFY_HASHSIZE
2098		3425
2099	C<ev_staz> watchers use a small hash table to distribute workload by	3426	C<ev_stat> watchers use a small hash table to distribute workload by
2100	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	3427	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
2101	usually more than enough. If you need to manage thousands of C<ev_stat>	3428	usually more than enough. If you need to manage thousands of C<ev_stat>
2102	watchers you might want to increase this value (I<must> be a power of	3429	watchers you might want to increase this value (I<must> be a power of
2103	two).	3430	two).
2104		3431
		3432	=item EV_USE_4HEAP
		3433
		3434	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3435	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		3436	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		3437	faster performance with many (thousands) of watchers.
		3438
		3439	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3440	(disabled).
		3441
		3442	=item EV_HEAP_CACHE_AT
		3443
		3444	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3445	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		3446	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3447	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3448	but avoids random read accesses on heap changes. This improves performance
		3449	noticeably with many (hundreds) of watchers.
		3450
		3451	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3452	(disabled).
		3453
		3454	=item EV_VERIFY
		3455
		3456	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3457	be done: If set to C<0>, no internal verification code will be compiled
		3458	in. If set to C<1>, then verification code will be compiled in, but not
		3459	called. If set to C<2>, then the internal verification code will be
		3460	called once per loop, which can slow down libev. If set to C<3>, then the
		3461	verification code will be called very frequently, which will slow down
		3462	libev considerably.
		3463
		3464	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3465	C<0>.
		3466
2105	=item EV_COMMON	3467	=item EV_COMMON
2106		3468
2107	By default, all watchers have a C<void *data> member. By redefining	3469	By default, all watchers have a C<void *data> member. By redefining
2108	this macro to a something else you can include more and other types of	3470	this macro to a something else you can include more and other types of
2109	members. You have to define it each time you include one of the files,	3471	members. You have to define it each time you include one of the files,
2110	though, and it must be identical each time.	3472	though, and it must be identical each time.
2111		3473
2112	For example, the perl EV module uses something like this:	3474	For example, the perl EV module uses something like this:
2113		3475
2114	#define EV_COMMON \	3476	#define EV_COMMON \
2115	SV *self; /* contains this struct */ \	3477	SV *self; /* contains this struct */ \
2116	SV *cb_sv, *fh /* note no trailing ";" */	3478	SV *cb_sv, *fh /* note no trailing ";" */
2117		3479
2118	=item EV_CB_DECLARE (type)	3480	=item EV_CB_DECLARE (type)
2119		3481
2120	=item EV_CB_INVOKE (watcher, revents)	3482	=item EV_CB_INVOKE (watcher, revents)
2121		3483
2122	=item ev_set_cb (ev, cb)	3484	=item ev_set_cb (ev, cb)
2123		3485
2124	Can be used to change the callback member declaration in each watcher,	3486	Can be used to change the callback member declaration in each watcher,
2125	and the way callbacks are invoked and set. Must expand to a struct member	3487	and the way callbacks are invoked and set. Must expand to a struct member
2126	definition and a statement, respectively. See the F<ev.v> header file for	3488	definition and a statement, respectively. See the F<ev.h> header file for
2127	their default definitions. One possible use for overriding these is to	3489	their default definitions. One possible use for overriding these is to
2128	avoid the C<struct ev_loop *> as first argument in all cases, or to use	3490	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2129	method calls instead of plain function calls in C++.	3491	method calls instead of plain function calls in C++.
		3492
		3493	=back
		3494
		3495	=head2 EXPORTED API SYMBOLS
		3496
		3497	If you need to re-export the API (e.g. via a DLL) and you need a list of
		3498	exported symbols, you can use the provided F<Symbol.*> files which list
		3499	all public symbols, one per line:
		3500
		3501	Symbols.ev for libev proper
		3502	Symbols.event for the libevent emulation
		3503
		3504	This can also be used to rename all public symbols to avoid clashes with
		3505	multiple versions of libev linked together (which is obviously bad in
		3506	itself, but sometimes it is inconvenient to avoid this).
		3507
		3508	A sed command like this will create wrapper C<#define>'s that you need to
		3509	include before including F<ev.h>:
		3510
		3511	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		3512
		3513	This would create a file F<wrap.h> which essentially looks like this:
		3514
		3515	#define ev_backend myprefix_ev_backend
		3516	#define ev_check_start myprefix_ev_check_start
		3517	#define ev_check_stop myprefix_ev_check_stop
		3518	...
2130		3519
2131	=head2 EXAMPLES	3520	=head2 EXAMPLES
2132		3521
2133	For a real-world example of a program the includes libev	3522	For a real-world example of a program the includes libev
2134	verbatim, you can have a look at the EV perl module	3523	verbatim, you can have a look at the EV perl module
…		…
2137	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file	3526	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
2138	will be compiled. It is pretty complex because it provides its own header	3527	will be compiled. It is pretty complex because it provides its own header
2139	file.	3528	file.
2140		3529
2141	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	3530	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2142	that everybody includes and which overrides some autoconf choices:	3531	that everybody includes and which overrides some configure choices:
2143		3532
		3533	#define EV_MINIMAL 1
2144	#define EV_USE_POLL 0	3534	#define EV_USE_POLL 0
2145	#define EV_MULTIPLICITY 0	3535	#define EV_MULTIPLICITY 0
2146	#define EV_PERIODICS 0	3536	#define EV_PERIODIC_ENABLE 0
		3537	#define EV_STAT_ENABLE 0
		3538	#define EV_FORK_ENABLE 0
2147	#define EV_CONFIG_H <config.h>	3539	#define EV_CONFIG_H <config.h>
		3540	#define EV_MINPRI 0
		3541	#define EV_MAXPRI 0
2148		3542
2149	#include "ev++.h"	3543	#include "ev++.h"
2150		3544
2151	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	3545	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2152		3546
2153	#include "ev_cpp.h"	3547	#include "ev_cpp.h"
2154	#include "ev.c"	3548	#include "ev.c"
2155		3549
		3550	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
2156		3551
		3552	=head2 THREADS AND COROUTINES
		3553
		3554	=head3 THREADS
		3555
		3556	All libev functions are reentrant and thread-safe unless explicitly
		3557	documented otherwise, but libev implements no locking itself. This means
		3558	that you can use as many loops as you want in parallel, as long as there
		3559	are no concurrent calls into any libev function with the same loop
		3560	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		3561	of course): libev guarantees that different event loops share no data
		3562	structures that need any locking.
		3563
		3564	Or to put it differently: calls with different loop parameters can be done
		3565	concurrently from multiple threads, calls with the same loop parameter
		3566	must be done serially (but can be done from different threads, as long as
		3567	only one thread ever is inside a call at any point in time, e.g. by using
		3568	a mutex per loop).
		3569
		3570	Specifically to support threads (and signal handlers), libev implements
		3571	so-called C<ev_async> watchers, which allow some limited form of
		3572	concurrency on the same event loop, namely waking it up "from the
		3573	outside".
		3574
		3575	If you want to know which design (one loop, locking, or multiple loops
		3576	without or something else still) is best for your problem, then I cannot
		3577	help you, but here is some generic advice:
		3578
		3579	=over 4
		3580
		3581	=item * most applications have a main thread: use the default libev loop
		3582	in that thread, or create a separate thread running only the default loop.
		3583
		3584	This helps integrating other libraries or software modules that use libev
		3585	themselves and don't care/know about threading.
		3586
		3587	=item * one loop per thread is usually a good model.
		3588
		3589	Doing this is almost never wrong, sometimes a better-performance model
		3590	exists, but it is always a good start.
		3591
		3592	=item * other models exist, such as the leader/follower pattern, where one
		3593	loop is handed through multiple threads in a kind of round-robin fashion.
		3594
		3595	Choosing a model is hard - look around, learn, know that usually you can do
		3596	better than you currently do :-)
		3597
		3598	=item * often you need to talk to some other thread which blocks in the
		3599	event loop.
		3600
		3601	C<ev_async> watchers can be used to wake them up from other threads safely
		3602	(or from signal contexts...).
		3603
		3604	An example use would be to communicate signals or other events that only
		3605	work in the default loop by registering the signal watcher with the
		3606	default loop and triggering an C<ev_async> watcher from the default loop
		3607	watcher callback into the event loop interested in the signal.
		3608
		3609	=back
		3610
		3611	=head3 COROUTINES
		3612
		3613	Libev is very accommodating to coroutines ("cooperative threads"):
		3614	libev fully supports nesting calls to its functions from different
		3615	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3616	different coroutines, and switch freely between both coroutines running the
		3617	loop, as long as you don't confuse yourself). The only exception is that
		3618	you must not do this from C<ev_periodic> reschedule callbacks.
		3619
		3620	Care has been taken to ensure that libev does not keep local state inside
		3621	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		3622	they do not call any callbacks.
		3623
		3624	=head2 COMPILER WARNINGS
		3625
		3626	Depending on your compiler and compiler settings, you might get no or a
		3627	lot of warnings when compiling libev code. Some people are apparently
		3628	scared by this.
		3629
		3630	However, these are unavoidable for many reasons. For one, each compiler
		3631	has different warnings, and each user has different tastes regarding
		3632	warning options. "Warn-free" code therefore cannot be a goal except when
		3633	targeting a specific compiler and compiler-version.
		3634
		3635	Another reason is that some compiler warnings require elaborate
		3636	workarounds, or other changes to the code that make it less clear and less
		3637	maintainable.
		3638
		3639	And of course, some compiler warnings are just plain stupid, or simply
		3640	wrong (because they don't actually warn about the condition their message
		3641	seems to warn about). For example, certain older gcc versions had some
		3642	warnings that resulted an extreme number of false positives. These have
		3643	been fixed, but some people still insist on making code warn-free with
		3644	such buggy versions.
		3645
		3646	While libev is written to generate as few warnings as possible,
		3647	"warn-free" code is not a goal, and it is recommended not to build libev
		3648	with any compiler warnings enabled unless you are prepared to cope with
		3649	them (e.g. by ignoring them). Remember that warnings are just that:
		3650	warnings, not errors, or proof of bugs.
		3651
		3652
		3653	=head2 VALGRIND
		3654
		3655	Valgrind has a special section here because it is a popular tool that is
		3656	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		3657
		3658	If you think you found a bug (memory leak, uninitialised data access etc.)
		3659	in libev, then check twice: If valgrind reports something like:
		3660
		3661	==2274== definitely lost: 0 bytes in 0 blocks.
		3662	==2274== possibly lost: 0 bytes in 0 blocks.
		3663	==2274== still reachable: 256 bytes in 1 blocks.
		3664
		3665	Then there is no memory leak, just as memory accounted to global variables
		3666	is not a memleak - the memory is still being referenced, and didn't leak.
		3667
		3668	Similarly, under some circumstances, valgrind might report kernel bugs
		3669	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		3670	although an acceptable workaround has been found here), or it might be
		3671	confused.
		3672
		3673	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		3674	make it into some kind of religion.
		3675
		3676	If you are unsure about something, feel free to contact the mailing list
		3677	with the full valgrind report and an explanation on why you think this
		3678	is a bug in libev (best check the archives, too :). However, don't be
		3679	annoyed when you get a brisk "this is no bug" answer and take the chance
		3680	of learning how to interpret valgrind properly.
		3681
		3682	If you need, for some reason, empty reports from valgrind for your project
		3683	I suggest using suppression lists.
		3684
		3685
		3686	=head1 PORTABILITY NOTES
		3687
		3688	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		3689
		3690	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		3691	requires, and its I/O model is fundamentally incompatible with the POSIX
		3692	model. Libev still offers limited functionality on this platform in
		3693	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		3694	descriptors. This only applies when using Win32 natively, not when using
		3695	e.g. cygwin.
		3696
		3697	Lifting these limitations would basically require the full
		3698	re-implementation of the I/O system. If you are into these kinds of
		3699	things, then note that glib does exactly that for you in a very portable
		3700	way (note also that glib is the slowest event library known to man).
		3701
		3702	There is no supported compilation method available on windows except
		3703	embedding it into other applications.
		3704
		3705	Not a libev limitation but worth mentioning: windows apparently doesn't
		3706	accept large writes: instead of resulting in a partial write, windows will
		3707	either accept everything or return C<ENOBUFS> if the buffer is too large,
		3708	so make sure you only write small amounts into your sockets (less than a
		3709	megabyte seems safe, but this apparently depends on the amount of memory
		3710	available).
		3711
		3712	Due to the many, low, and arbitrary limits on the win32 platform and
		3713	the abysmal performance of winsockets, using a large number of sockets
		3714	is not recommended (and not reasonable). If your program needs to use
		3715	more than a hundred or so sockets, then likely it needs to use a totally
		3716	different implementation for windows, as libev offers the POSIX readiness
		3717	notification model, which cannot be implemented efficiently on windows
		3718	(Microsoft monopoly games).
		3719
		3720	A typical way to use libev under windows is to embed it (see the embedding
		3721	section for details) and use the following F<evwrap.h> header file instead
		3722	of F<ev.h>:
		3723
		3724	#define EV_STANDALONE /* keeps ev from requiring config.h */
		3725	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		3726
		3727	#include "ev.h"
		3728
		3729	And compile the following F<evwrap.c> file into your project (make sure
		3730	you do I<not> compile the F<ev.c> or any other embedded source files!):
		3731
		3732	#include "evwrap.h"
		3733	#include "ev.c"
		3734
		3735	=over 4
		3736
		3737	=item The winsocket select function
		3738
		3739	The winsocket C<select> function doesn't follow POSIX in that it
		3740	requires socket I<handles> and not socket I<file descriptors> (it is
		3741	also extremely buggy). This makes select very inefficient, and also
		3742	requires a mapping from file descriptors to socket handles (the Microsoft
		3743	C runtime provides the function C<_open_osfhandle> for this). See the
		3744	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		3745	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		3746
		3747	The configuration for a "naked" win32 using the Microsoft runtime
		3748	libraries and raw winsocket select is:
		3749
		3750	#define EV_USE_SELECT 1
		3751	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		3752
		3753	Note that winsockets handling of fd sets is O(n), so you can easily get a
		3754	complexity in the O(n²) range when using win32.
		3755
		3756	=item Limited number of file descriptors
		3757
		3758	Windows has numerous arbitrary (and low) limits on things.
		3759
		3760	Early versions of winsocket's select only supported waiting for a maximum
		3761	of C<64> handles (probably owning to the fact that all windows kernels
		3762	can only wait for C<64> things at the same time internally; Microsoft
		3763	recommends spawning a chain of threads and wait for 63 handles and the
		3764	previous thread in each. Great).
		3765
		3766	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		3767	to some high number (e.g. C<2048>) before compiling the winsocket select
		3768	call (which might be in libev or elsewhere, for example, perl does its own
		3769	select emulation on windows).
		3770
		3771	Another limit is the number of file descriptors in the Microsoft runtime
		3772	libraries, which by default is C<64> (there must be a hidden I<64> fetish
		3773	or something like this inside Microsoft). You can increase this by calling
		3774	C<_setmaxstdio>, which can increase this limit to C<2048> (another
		3775	arbitrary limit), but is broken in many versions of the Microsoft runtime
		3776	libraries.
		3777
		3778	This might get you to about C<512> or C<2048> sockets (depending on
		3779	windows version and/or the phase of the moon). To get more, you need to
		3780	wrap all I/O functions and provide your own fd management, but the cost of
		3781	calling select (O(n²)) will likely make this unworkable.
		3782
		3783	=back
		3784
		3785	=head2 PORTABILITY REQUIREMENTS
		3786
		3787	In addition to a working ISO-C implementation and of course the
		3788	backend-specific APIs, libev relies on a few additional extensions:
		3789
		3790	=over 4
		3791
		3792	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		3793	calling conventions regardless of C<ev_watcher_type *>.
		3794
		3795	Libev assumes not only that all watcher pointers have the same internal
		3796	structure (guaranteed by POSIX but not by ISO C for example), but it also
		3797	assumes that the same (machine) code can be used to call any watcher
		3798	callback: The watcher callbacks have different type signatures, but libev
		3799	calls them using an C<ev_watcher *> internally.
		3800
		3801	=item C<sig_atomic_t volatile> must be thread-atomic as well
		3802
		3803	The type C<sig_atomic_t volatile> (or whatever is defined as
		3804	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		3805	threads. This is not part of the specification for C<sig_atomic_t>, but is
		3806	believed to be sufficiently portable.
		3807
		3808	=item C<sigprocmask> must work in a threaded environment
		3809
		3810	Libev uses C<sigprocmask> to temporarily block signals. This is not
		3811	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		3812	pthread implementations will either allow C<sigprocmask> in the "main
		3813	thread" or will block signals process-wide, both behaviours would
		3814	be compatible with libev. Interaction between C<sigprocmask> and
		3815	C<pthread_sigmask> could complicate things, however.
		3816
		3817	The most portable way to handle signals is to block signals in all threads
		3818	except the initial one, and run the default loop in the initial thread as
		3819	well.
		3820
		3821	=item C<long> must be large enough for common memory allocation sizes
		3822
		3823	To improve portability and simplify its API, libev uses C<long> internally
		3824	instead of C<size_t> when allocating its data structures. On non-POSIX
		3825	systems (Microsoft...) this might be unexpectedly low, but is still at
		3826	least 31 bits everywhere, which is enough for hundreds of millions of
		3827	watchers.
		3828
		3829	=item C<double> must hold a time value in seconds with enough accuracy
		3830
		3831	The type C<double> is used to represent timestamps. It is required to
		3832	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		3833	enough for at least into the year 4000. This requirement is fulfilled by
		3834	implementations implementing IEEE 754 (basically all existing ones).
		3835
		3836	=back
		3837
		3838	If you know of other additional requirements drop me a note.
		3839
		3840
2157	=head1 COMPLEXITIES	3841	=head1 ALGORITHMIC COMPLEXITIES
2158		3842
2159	In this section the complexities of (many of) the algorithms used inside	3843	In this section the complexities of (many of) the algorithms used inside
2160	libev will be explained. For complexity discussions about backends see the	3844	libev will be documented. For complexity discussions about backends see
2161	documentation for C<ev_default_init>.	3845	the documentation for C<ev_default_init>.
		3846
		3847	All of the following are about amortised time: If an array needs to be
		3848	extended, libev needs to realloc and move the whole array, but this
		3849	happens asymptotically rarer with higher number of elements, so O(1) might
		3850	mean that libev does a lengthy realloc operation in rare cases, but on
		3851	average it is much faster and asymptotically approaches constant time.
2162		3852
2163	=over 4	3853	=over 4
2164		3854
2165	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	3855	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2166		3856
		3857	This means that, when you have a watcher that triggers in one hour and
		3858	there are 100 watchers that would trigger before that, then inserting will
		3859	have to skip roughly seven (C<ld 100>) of these watchers.
		3860
2167	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	3861	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2168		3862
		3863	That means that changing a timer costs less than removing/adding them,
		3864	as only the relative motion in the event queue has to be paid for.
		3865
2169	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	3866	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
2170		3867
		3868	These just add the watcher into an array or at the head of a list.
		3869
2171	=item Stopping check/prepare/idle watchers: O(1)	3870	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2172		3871
2173	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	3872	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2174		3873
		3874	These watchers are stored in lists, so they need to be walked to find the
		3875	correct watcher to remove. The lists are usually short (you don't usually
		3876	have many watchers waiting for the same fd or signal: one is typical, two
		3877	is rare).
		3878
2175	=item Finding the next timer per loop iteration: O(1)	3879	=item Finding the next timer in each loop iteration: O(1)
		3880
		3881	By virtue of using a binary or 4-heap, the next timer is always found at a
		3882	fixed position in the storage array.
2176		3883
2177	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	3884	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2178		3885
2179	=item Activating one watcher: O(1)	3886	A change means an I/O watcher gets started or stopped, which requires
		3887	libev to recalculate its status (and possibly tell the kernel, depending
		3888	on backend and whether C<ev_io_set> was used).
		3889
		3890	=item Activating one watcher (putting it into the pending state): O(1)
		3891
		3892	=item Priority handling: O(number_of_priorities)
		3893
		3894	Priorities are implemented by allocating some space for each
		3895	priority. When doing priority-based operations, libev usually has to
		3896	linearly search all the priorities, but starting/stopping and activating
		3897	watchers becomes O(1) with respect to priority handling.
		3898
		3899	=item Sending an ev_async: O(1)
		3900
		3901	=item Processing ev_async_send: O(number_of_async_watchers)
		3902
		3903	=item Processing signals: O(max_signal_number)
		3904
		3905	Sending involves a system call I<iff> there were no other C<ev_async_send>
		3906	calls in the current loop iteration. Checking for async and signal events
		3907	involves iterating over all running async watchers or all signal numbers.
2180		3908
2181	=back	3909	=back
2182		3910
2183		3911
2184	=head1 AUTHOR	3912	=head1 AUTHOR
2185		3913
2186	Marc Lehmann <libev@schmorp.de>.	3914	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
2187		3915

Diff Legend

–	Removed lines
+	Added lines
<	Changed lines
>	Changed lines