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Revision 1.30 by root, Fri Nov 23 04:36:03 2007 UTC vs.
Revision 1.235 by root, Thu Apr 16 07:50:39 2009 UTC

…		…
2		2
3	libev - a high performance full-featured event loop written in C	3	libev - a high performance full-featured event loop written in C
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
		8
		9	=head2 EXAMPLE PROGRAM
		10
		11	// a single header file is required
		12	#include <ev.h>
		13
		14	#include <stdio.h> // for puts
		15
		16	// every watcher type has its own typedef'd struct
		17	// with the name ev_TYPE
		18	ev_io stdin_watcher;
		19	ev_timer timeout_watcher;
		20
		21	// all watcher callbacks have a similar signature
		22	// this callback is called when data is readable on stdin
		23	static void
		24	stdin_cb (EV_P_ ev_io *w, int revents)
		25	{
		26	puts ("stdin ready");
		27	// for one-shot events, one must manually stop the watcher
		28	// with its corresponding stop function.
		29	ev_io_stop (EV_A_ w);
		30
		31	// this causes all nested ev_loop's to stop iterating
		32	ev_unloop (EV_A_ EVUNLOOP_ALL);
		33	}
		34
		35	// another callback, this time for a time-out
		36	static void
		37	timeout_cb (EV_P_ ev_timer *w, int revents)
		38	{
		39	puts ("timeout");
		40	// this causes the innermost ev_loop to stop iterating
		41	ev_unloop (EV_A_ EVUNLOOP_ONE);
		42	}
		43
		44	int
		45	main (void)
		46	{
		47	// use the default event loop unless you have special needs
		48	struct ev_loop *loop = ev_default_loop (0);
		49
		50	// initialise an io watcher, then start it
		51	// this one will watch for stdin to become readable
		52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
		53	ev_io_start (loop, &stdin_watcher);
		54
		55	// initialise a timer watcher, then start it
		56	// simple non-repeating 5.5 second timeout
		57	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		58	ev_timer_start (loop, &timeout_watcher);
		59
		60	// now wait for events to arrive
		61	ev_loop (loop, 0);
		62
		63	// unloop was called, so exit
		64	return 0;
		65	}
8		66
9	=head1 DESCRIPTION	67	=head1 DESCRIPTION
10		68
		69	The newest version of this document is also available as an html-formatted
		70	web page you might find easier to navigate when reading it for the first
		71	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		72
11	Libev is an event loop: you register interest in certain events (such as a	73	Libev is an event loop: you register interest in certain events (such as a
12	file descriptor being readable or a timeout occuring), and it will manage	74	file descriptor being readable or a timeout occurring), and it will manage
13	these event sources and provide your program with events.	75	these event sources and provide your program with events.
14		76
15	To do this, it must take more or less complete control over your process	77	To do this, it must take more or less complete control over your process
16	(or thread) by executing the I<event loop> handler, and will then	78	(or thread) by executing the I<event loop> handler, and will then
17	communicate events via a callback mechanism.	79	communicate events via a callback mechanism.
…		…
19	You register interest in certain events by registering so-called I<event	81	You register interest in certain events by registering so-called I<event
20	watchers>, which are relatively small C structures you initialise with the	82	watchers>, which are relatively small C structures you initialise with the
21	details of the event, and then hand it over to libev by I<starting> the	83	details of the event, and then hand it over to libev by I<starting> the
22	watcher.	84	watcher.
23		85
24	=head1 FEATURES	86	=head2 FEATURES
25		87
26	Libev supports select, poll, the linux-specific epoll and the bsd-specific	88	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
27	kqueue mechanisms for file descriptor events, relative timers, absolute	89	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
28	timers with customised rescheduling, signal events, process status change	90	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
29	events (related to SIGCHLD), and event watchers dealing with the event	91	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
30	loop mechanism itself (idle, prepare and check watchers). It also is quite	92	with customised rescheduling (C<ev_periodic>), synchronous signals
		93	(C<ev_signal>), process status change events (C<ev_child>), and event
		94	watchers dealing with the event loop mechanism itself (C<ev_idle>,
		95	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as
		96	file watchers (C<ev_stat>) and even limited support for fork events
		97	(C<ev_fork>).
		98
		99	It also is quite fast (see this
31	fast (see this L<benchmark|http://libev.schmorp.de/bench.html> comparing	100	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
32	it to libevent for example).	101	for example).
33		102
34	=head1 CONVENTIONS	103	=head2 CONVENTIONS
35		104
36	Libev is very configurable. In this manual the default configuration	105	Libev is very configurable. In this manual the default (and most common)
37	will be described, which supports multiple event loops. For more info	106	configuration will be described, which supports multiple event loops. For
38	about various configuration options please have a look at the file	107	more info about various configuration options please have a look at
39	F<README.embed> in the libev distribution. If libev was configured without	108	B<EMBED> section in this manual. If libev was configured without support
40	support for multiple event loops, then all functions taking an initial	109	for multiple event loops, then all functions taking an initial argument of
41	argument of name C<loop> (which is always of type C<struct ev_loop *>)	110	name C<loop> (which is always of type C<ev_loop *>) will not have
42	will not have this argument.	111	this argument.
43		112
44	=head1 TIME REPRESENTATION	113	=head2 TIME REPRESENTATION
45		114
46	Libev represents time as a single floating point number, representing the	115	Libev represents time as a single floating point number, representing the
47	(fractional) number of seconds since the (POSIX) epoch (somewhere near	116	(fractional) number of seconds since the (POSIX) epoch (somewhere near
48	the beginning of 1970, details are complicated, don't ask). This type is	117	the beginning of 1970, details are complicated, don't ask). This type is
49	called C<ev_tstamp>, which is what you should use too. It usually aliases	118	called C<ev_tstamp>, which is what you should use too. It usually aliases
50	to the double type in C.	119	to the C<double> type in C, and when you need to do any calculations on
		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
51		144
52	=head1 GLOBAL FUNCTIONS	145	=head1 GLOBAL FUNCTIONS
53		146
54	These functions can be called anytime, even before initialising the	147	These functions can be called anytime, even before initialising the
55	library in any way.	148	library in any way.
…		…
60		153
61	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
62	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
63	you actually want to know.	156	you actually want to know.
64		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
65	=item int ev_version_major ()	164	=item int ev_version_major ()
66		165
67	=item int ev_version_minor ()	166	=item int ev_version_minor ()
68		167
69	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
70	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
71	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
72	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
73	version of the library your program was compiled against.	172	version of the library your program was compiled against.
74		173
		174	These version numbers refer to the ABI version of the library, not the
		175	release version.
		176
75	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,
76	as this indicates an incompatible change. Minor versions are usually	178	as this indicates an incompatible change. Minor versions are usually
77	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
78	not a problem.	180	not a problem.
79		181
		182	Example: Make sure we haven't accidentally been linked against the wrong
		183	version.
		184
		185	assert (("libev version mismatch",
		186	ev_version_major () == EV_VERSION_MAJOR
		187	&& ev_version_minor () >= EV_VERSION_MINOR));
		188
		189	=item unsigned int ev_supported_backends ()
		190
		191	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
		192	value) compiled into this binary of libev (independent of their
		193	availability on the system you are running on). See C<ev_default_loop> for
		194	a description of the set values.
		195
		196	Example: make sure we have the epoll method, because yeah this is cool and
		197	a must have and can we have a torrent of it please!!!11
		198
		199	assert (("sorry, no epoll, no sex",
		200	ev_supported_backends () & EVBACKEND_EPOLL));
		201
		202	=item unsigned int ev_recommended_backends ()
		203
		204	Return the set of all backends compiled into this binary of libev and also
		205	recommended for this platform. This set is often smaller than the one
		206	returned by C<ev_supported_backends>, as for example kqueue is broken on
		207	most BSDs and will not be auto-detected unless you explicitly request it
		208	(assuming you know what you are doing). This is the set of backends that
		209	libev will probe for if you specify no backends explicitly.
		210
		211	=item unsigned int ev_embeddable_backends ()
		212
		213	Returns the set of backends that are embeddable in other event loops. This
		214	is the theoretical, all-platform, value. To find which backends
		215	might be supported on the current system, you would need to look at
		216	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
		217	recommended ones.
		218
		219	See the description of C<ev_embed> watchers for more info.
		220
80	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	221	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
81		222
82	Sets the allocation function to use (the prototype is similar to the	223	Sets the allocation function to use (the prototype is similar - the
83	realloc C function, the semantics are identical). It is used to allocate	224	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
84	and free memory (no surprises here). If it returns zero when memory	225	used to allocate and free memory (no surprises here). If it returns zero
85	needs to be allocated, the library might abort or take some potentially	226	when memory needs to be allocated (C<size != 0>), the library might abort
86	destructive action. The default is your system realloc function.	227	or take some potentially destructive action.
		228
		229	Since some systems (at least OpenBSD and Darwin) fail to implement
		230	correct C<realloc> semantics, libev will use a wrapper around the system
		231	C<realloc> and C<free> functions by default.
87		232
88	You could override this function in high-availability programs to, say,	233	You could override this function in high-availability programs to, say,
89	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,
90	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.
91		236
		237	Example: Replace the libev allocator with one that waits a bit and then
		238	retries (example requires a standards-compliant C<realloc>).
		239
		240	static void *
		241	persistent_realloc (void *ptr, size_t size)
		242	{
		243	for (;;)
		244	{
		245	void *newptr = realloc (ptr, size);
		246
		247	if (newptr)
		248	return newptr;
		249
		250	sleep (60);
		251	}
		252	}
		253
		254	...
		255	ev_set_allocator (persistent_realloc);
		256
92	=item ev_set_syserr_cb (void (*cb)(const char *msg));	257	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
93		258
94	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
95	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
96	indicating the system call or subsystem causing the problem. If this	261	indicating the system call or subsystem causing the problem. If this
97	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
98	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
99	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
100	(such as abort).	265	(such as abort).
101		266
		267	Example: This is basically the same thing that libev does internally, too.
		268
		269	static void
		270	fatal_error (const char *msg)
		271	{
		272	perror (msg);
		273	abort ();
		274	}
		275
		276	...
		277	ev_set_syserr_cb (fatal_error);
		278
102	=back	279	=back
103		280
104	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	281	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
105		282
106	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>
107	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>
108	events, and dynamically created loops which do not.	285	I<function>).
109		286
110	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
111	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
112	create, you also create another event loop. Libev itself does no locking	289	not.
113	whatsoever, so if you mix calls to the same event loop in different
114	threads, make sure you lock (this is usually a bad idea, though, even if
115	done correctly, because it's hideous and inefficient).
116		290
117	=over 4	291	=over 4
118		292
119	=item struct ev_loop *ev_default_loop (unsigned int flags)	293	=item struct ev_loop *ev_default_loop (unsigned int flags)
120		294
121	This will initialise the default event loop if it hasn't been initialised	295	This will initialise the default event loop if it hasn't been initialised
122	yet and return it. If the default loop could not be initialised, returns	296	yet and return it. If the default loop could not be initialised, returns
123	false. If it already was initialised it simply returns it (and ignores the	297	false. If it already was initialised it simply returns it (and ignores the
124	flags).	298	flags. If that is troubling you, check C<ev_backend ()> afterwards).
125		299
126	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
127	function.	301	function.
128		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
129	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
130	backends to use, and is usually specified as 0 (or EVFLAG_AUTO).	315	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
131		316
132	It supports the following flags:	317	The following flags are supported:
133		318
134	=over 4	319	=over 4
135		320
136	=item C<EVFLAG_AUTO>	321	=item C<EVFLAG_AUTO>
137		322
138	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
139	thing, believe me).	324	thing, believe me).
140		325
141	=item C<EVFLAG_NOENV>	326	=item C<EVFLAG_NOENV>
142		327
143	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
144	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
145	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	330	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
146	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
147	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
148	around bugs.	333	around bugs.
149		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
150	=item C<EVMETHOD_SELECT> (value 1, portable select backend)	355	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
151		356
152	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
153	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,
154	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
155	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
156	the fastest backend for a low number of fds.	361	usually the fastest backend for a low number of (low-numbered :) fds.
157		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).
		373
158	=item C<EVMETHOD_POLL> (value 2, poll backend, available everywhere except on windows)	374	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
159		375
160	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
161	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
162	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
163	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.
164		382
		383	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		384	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
		385
165	=item C<EVMETHOD_EPOLL> (value 4, Linux)	386	=item C<EVBACKEND_EPOLL> (value 4, Linux)
166		387
167	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,
168	but it scales phenomenally better. While poll and select usually scale like	389	but it scales phenomenally better. While poll and select usually scale
169	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),
170	either O(1) or O(active_fds).	391	epoll scales either O(1) or O(active_fds).
171		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
172	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
173	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
174	(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
175	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
176	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.
177		416
		417	Best performance from this backend is achieved by not unregistering all
		418	watchers for a file descriptor until it has been closed, if possible,
		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>.
		434
178	=item C<EVMETHOD_KQUEUE> (value 8, most BSD clones)	435	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
179		436
180	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
181	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
182	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
183	completely useless). For this reason its not being "autodetected" unless	440	it's completely useless). Unlike epoll, however, whose brokenness
184	you explicitly specify the flags (i.e. you don't use EVFLAG_AUTO).	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
		443	"auto-detected" unless you explicitly specify it in the flags (i.e. using
		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.
185		450
186	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
187	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
188	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
189	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
190	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
191		458
		459	This backend usually performs well under most conditions.
		460
		461	While nominally embeddable in other event loops, this doesn't work
		462	everywhere, so you might need to test for this. And since it is broken
		463	almost everywhere, you should only use it when you have a lot of sockets
		464	(for which it usually works), by embedding it into another event loop
		465	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
		466	also broken on OS X)) and, did I mention it, using it only for sockets.
		467
		468	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		469	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		470	C<NOTE_EOF>.
		471
192	=item C<EVMETHOD_DEVPOLL> (value 16, Solaris 8)	472	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
193		473
194	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.
195		478
196	=item C<EVMETHOD_PORT> (value 32, Solaris 10)	479	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
197		480
198	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,
199	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)).
200		483
		484	Please note that Solaris event ports can deliver a lot of spurious
		485	notifications, so you need to use non-blocking I/O or other means to avoid
		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>.
		500
201	=item C<EVMETHOD_ALL>	501	=item C<EVBACKEND_ALL>
202		502
203	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
204	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
205	C<EVMETHOD_ALL & ~EVMETHOD_KQUEUE>.	505	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
		506
		507	It is definitely not recommended to use this flag.
206		508
207	=back	509	=back
208		510
209	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
210	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
211	specified, most compiled-in backend will be tried, usually in reverse	513	specified, all backends in C<ev_recommended_backends ()> will be tried.
212	order of their flag values :)	514
		515	Example: This is the most typical usage.
		516
		517	if (!ev_default_loop (0))
		518	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		519
		520	Example: Restrict libev to the select and poll backends, and do not allow
		521	environment settings to be taken into account:
		522
		523	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		524
		525	Example: Use whatever libev has to offer, but make sure that kqueue is
		526	used if available (warning, breaks stuff, best use only with your own
		527	private event loop and only if you know the OS supports your types of
		528	fds):
		529
		530	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
213		531
214	=item struct ev_loop *ev_loop_new (unsigned int flags)	532	=item struct ev_loop *ev_loop_new (unsigned int flags)
215		533
216	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
217	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
218	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
219	undefined behaviour (or a failed assertion if assertions are enabled).	537	undefined behaviour (or a failed assertion if assertions are enabled).
220		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
		543	Example: Try to create a event loop that uses epoll and nothing else.
		544
		545	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
		546	if (!epoller)
		547	fatal ("no epoll found here, maybe it hides under your chair");
		548
221	=item ev_default_destroy ()	549	=item ev_default_destroy ()
222		550
223	Destroys the default loop again (frees all memory and kernel state	551	Destroys the default loop again (frees all memory and kernel state
224	etc.). This stops all registered event watchers (by not touching them in	552	etc.). None of the active event watchers will be stopped in the normal
225	any way whatsoever, although you cannot rely on this :).	553	sense, so e.g. C<ev_is_active> might still return true. It is your
		554	responsibility to either stop all watchers cleanly yourself I<before>
		555	calling this function, or cope with the fact afterwards (which is usually
		556	the easiest thing, you can just ignore the watchers and/or C<free ()> them
		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>).
226		567
227	=item ev_loop_destroy (loop)	568	=item ev_loop_destroy (loop)
228		569
229	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
230	earlier call to C<ev_loop_new>.	571	earlier call to C<ev_loop_new>.
231		572
232	=item ev_default_fork ()	573	=item ev_default_fork ()
233		574
		575	This function sets a flag that causes subsequent C<ev_loop> iterations
234	This function reinitialises the kernel state for backends that have	576	to reinitialise the kernel state for backends that have one. Despite the
235	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
236	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
237	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.
238		581
239	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
240	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
241	fork+exec, you don't have to call it.	584	you just fork+exec, you don't have to call it at all.
242		585
243	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
244	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
245	quite nicely into a call to C<pthread_atfork>:	588	quite nicely into a call to C<pthread_atfork>:
246		589
…		…
248		591
249	=item ev_loop_fork (loop)	592	=item ev_loop_fork (loop)
250		593
251	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
252	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
253	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.
254		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.
		613
255	=item unsigned int ev_method (loop)	614	=item unsigned int ev_backend (loop)
256		615
257	Returns one of the C<EVMETHOD_*> flags indicating the event backend in	616	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
258	use.	617	use.
259		618
260	=item ev_tstamp ev_now (loop)	619	=item ev_tstamp ev_now (loop)
261		620
262	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
263	got events and started processing them. This timestamp does not change	622	received events and started processing them. This timestamp does not
264	as long as callbacks are being processed, and this is also the base time	623	change as long as callbacks are being processed, and this is also the base
265	used for relative timers. You can treat it as the timestamp of the event	624	time used for relative timers. You can treat it as the timestamp of the
266	occuring (or more correctly, the mainloop finding out about it).	625	event occurring (or more correctly, libev finding out about it).
		626
		627	=item ev_now_update (loop)
		628
		629	Establishes the current time by querying the kernel, updating the time
		630	returned by C<ev_now ()> in the progress. This is a costly operation and
		631	is usually done automatically within C<ev_loop ()>.
		632
		633	This function is rarely useful, but when some event callback runs for a
		634	very long time without entering the event loop, updating libev's idea of
		635	the current time is a good idea.
		636
		637	See also "The special problem of time updates" in the C<ev_timer> section.
		638
		639	=item ev_suspend (loop)
		640
		641	=item ev_resume (loop)
		642
		643	These two functions suspend and resume a loop, for use when the loop is
		644	not used for a while and timeouts should not be processed.
		645
		646	A typical use case would be an interactive program such as a game: When
		647	the user presses C<^Z> to suspend the game and resumes it an hour later it
		648	would be best to handle timeouts as if no time had actually passed while
		649	the program was suspended. This can be achieved by calling C<ev_suspend>
		650	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		651	C<ev_resume> directly afterwards to resume timer processing.
		652
		653	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		654	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		655	will be rescheduled (that is, they will lose any events that would have
		656	occured while suspended).
		657
		658	After calling C<ev_suspend> you B<must not> call I<any> function on the
		659	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		660	without a previous call to C<ev_suspend>.
		661
		662	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		663	event loop time (see C<ev_now_update>).
267		664
268	=item ev_loop (loop, int flags)	665	=item ev_loop (loop, int flags)
269		666
270	Finally, this is it, the event handler. This function usually is called	667	Finally, this is it, the event handler. This function usually is called
271	after you initialised all your watchers and you want to start handling	668	after you initialised all your watchers and you want to start handling
272	events.	669	events.
273		670
274	If the flags argument is specified as 0, it will not return until either	671	If the flags argument is specified as C<0>, it will not return until
275	no event watchers are active anymore or C<ev_unloop> was called.	672	either no event watchers are active anymore or C<ev_unloop> was called.
		673
		674	Please note that an explicit C<ev_unloop> is usually better than
		675	relying on all watchers to be stopped when deciding when a program has
		676	finished (especially in interactive programs), but having a program
		677	that automatically loops as long as it has to and no longer by virtue
		678	of relying on its watchers stopping correctly, that is truly a thing of
		679	beauty.
276		680
277	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	681	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
278	those events and any outstanding ones, but will not block your process in	682	those events and any already outstanding ones, but will not block your
279	case there are no events and will return after one iteration of the loop.	683	process in case there are no events and will return after one iteration of
		684	the loop.
280		685
281	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	686	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
282	neccessary) and will handle those and any outstanding ones. It will block	687	necessary) and will handle those and any already outstanding ones. It
283	your process until at least one new event arrives, and will return after	688	will block your process until at least one new event arrives (which could
		689	be an event internal to libev itself, so there is no guarantee that a
		690	user-registered callback will be called), and will return after one
284	one iteration of the loop.	691	iteration of the loop.
285		692
286	This flags value could be used to implement alternative looping	693	This is useful if you are waiting for some external event in conjunction
287	constructs, but the C<prepare> and C<check> watchers provide a better and	694	with something not expressible using other libev watchers (i.e. "roll your
288	more generic mechanism.	695	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
		696	usually a better approach for this kind of thing.
289		697
290	Here are the gory details of what ev_loop does:	698	Here are the gory details of what C<ev_loop> does:
291		699
292	1. If there are no active watchers (reference count is zero), return.	700	- Before the first iteration, call any pending watchers.
		701	* If EVFLAG_FORKCHECK was used, check for a fork.
		702	- If a fork was detected (by any means), queue and call all fork watchers.
293	2. Queue and immediately call all prepare watchers.	703	- Queue and call all prepare watchers.
294	3. If we have been forked, recreate the kernel state.	704	- If we have been forked, detach and recreate the kernel state
		705	as to not disturb the other process.
295	4. Update the kernel state with all outstanding changes.	706	- Update the kernel state with all outstanding changes.
296	5. Update the "event loop time".	707	- Update the "event loop time" (ev_now ()).
297	6. Calculate for how long to block.	708	- Calculate for how long to sleep or block, if at all
		709	(active idle watchers, EVLOOP_NONBLOCK or not having
		710	any active watchers at all will result in not sleeping).
		711	- Sleep if the I/O and timer collect interval say so.
298	7. Block the process, waiting for events.	712	- Block the process, waiting for any events.
		713	- Queue all outstanding I/O (fd) events.
299	8. Update the "event loop time" and do time jump handling.	714	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
300	9. Queue all outstanding timers.	715	- Queue all expired timers.
301	10. Queue all outstanding periodics.	716	- Queue all expired periodics.
302	11. If no events are pending now, queue all idle watchers.	717	- Unless any events are pending now, queue all idle watchers.
303	12. Queue all check watchers.	718	- Queue all check watchers.
304	13. Call all queued watchers in reverse order (i.e. check watchers first).	719	- Call all queued watchers in reverse order (i.e. check watchers first).
		720	Signals and child watchers are implemented as I/O watchers, and will
		721	be handled here by queueing them when their watcher gets executed.
305	14. If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	722	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
306	was used, return, otherwise continue with step #1.	723	were used, or there are no active watchers, return, otherwise
		724	continue with step *.
		725
		726	Example: Queue some jobs and then loop until no events are outstanding
		727	anymore.
		728
		729	... queue jobs here, make sure they register event watchers as long
		730	... as they still have work to do (even an idle watcher will do..)
		731	ev_loop (my_loop, 0);
		732	... jobs done or somebody called unloop. yeah!
307		733
308	=item ev_unloop (loop, how)	734	=item ev_unloop (loop, how)
309		735
310	Can be used to make a call to C<ev_loop> return early (but only after it	736	Can be used to make a call to C<ev_loop> return early (but only after it
311	has processed all outstanding events). The C<how> argument must be either	737	has processed all outstanding events). The C<how> argument must be either
312	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	738	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
313	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	739	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
314		740
		741	This "unloop state" will be cleared when entering C<ev_loop> again.
		742
		743	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
		744
315	=item ev_ref (loop)	745	=item ev_ref (loop)
316		746
317	=item ev_unref (loop)	747	=item ev_unref (loop)
318		748
319	Ref/unref can be used to add or remove a reference count on the event	749	Ref/unref can be used to add or remove a reference count on the event
320	loop: Every watcher keeps one reference, and as long as the reference	750	loop: Every watcher keeps one reference, and as long as the reference
321	count is nonzero, C<ev_loop> will not return on its own. If you have	751	count is nonzero, C<ev_loop> will not return on its own.
		752
322	a watcher you never unregister that should not keep C<ev_loop> from	753	If you have a watcher you never unregister that should not keep C<ev_loop>
323	returning, ev_unref() after starting, and ev_ref() before stopping it. For	754	from returning, call ev_unref() after starting, and ev_ref() before
		755	stopping it.
		756
324	example, libev itself uses this for its internal signal pipe: It is not	757	As an example, libev itself uses this for its internal signal pipe: It
325	visible to the libev user and should not keep C<ev_loop> from exiting if	758	is not visible to the libev user and should not keep C<ev_loop> from
326	no event watchers registered by it are active. It is also an excellent	759	exiting if no event watchers registered by it are active. It is also an
327	way to do this for generic recurring timers or from within third-party	760	excellent way to do this for generic recurring timers or from within
328	libraries. Just remember to I<unref after start> and I<ref before stop>.	761	third-party libraries. Just remember to I<unref after start> and I<ref
		762	before stop> (but only if the watcher wasn't active before, or was active
		763	before, respectively. Note also that libev might stop watchers itself
		764	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		765	in the callback).
		766
		767	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
		768	running when nothing else is active.
		769
		770	ev_signal exitsig;
		771	ev_signal_init (&exitsig, sig_cb, SIGINT);
		772	ev_signal_start (loop, &exitsig);
		773	evf_unref (loop);
		774
		775	Example: For some weird reason, unregister the above signal handler again.
		776
		777	ev_ref (loop);
		778	ev_signal_stop (loop, &exitsig);
		779
		780	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		781
		782	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		783
		784	These advanced functions influence the time that libev will spend waiting
		785	for events. Both time intervals are by default C<0>, meaning that libev
		786	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		787	latency.
		788
		789	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		790	allows libev to delay invocation of I/O and timer/periodic callbacks
		791	to increase efficiency of loop iterations (or to increase power-saving
		792	opportunities).
		793
		794	The idea is that sometimes your program runs just fast enough to handle
		795	one (or very few) event(s) per loop iteration. While this makes the
		796	program responsive, it also wastes a lot of CPU time to poll for new
		797	events, especially with backends like C<select ()> which have a high
		798	overhead for the actual polling but can deliver many events at once.
		799
		800	By setting a higher I<io collect interval> you allow libev to spend more
		801	time collecting I/O events, so you can handle more events per iteration,
		802	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		803	C<ev_timer>) will be not affected. Setting this to a non-null value will
		804	introduce an additional C<ev_sleep ()> call into most loop iterations.
		805
		806	Likewise, by setting a higher I<timeout collect interval> you allow libev
		807	to spend more time collecting timeouts, at the expense of increased
		808	latency/jitter/inexactness (the watcher callback will be called
		809	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		810	value will not introduce any overhead in libev.
		811
		812	Many (busy) programs can usually benefit by setting the I/O collect
		813	interval to a value near C<0.1> or so, which is often enough for
		814	interactive servers (of course not for games), likewise for timeouts. It
		815	usually doesn't make much sense to set it to a lower value than C<0.01>,
		816	as this approaches the timing granularity of most systems.
		817
		818	Setting the I<timeout collect interval> can improve the opportunity for
		819	saving power, as the program will "bundle" timer callback invocations that
		820	are "near" in time together, by delaying some, thus reducing the number of
		821	times the process sleeps and wakes up again. Another useful technique to
		822	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		823	they fire on, say, one-second boundaries only.
		824
		825	=item ev_loop_verify (loop)
		826
		827	This function only does something when C<EV_VERIFY> support has been
		828	compiled in, which is the default for non-minimal builds. It tries to go
		829	through all internal structures and checks them for validity. If anything
		830	is found to be inconsistent, it will print an error message to standard
		831	error and call C<abort ()>.
		832
		833	This can be used to catch bugs inside libev itself: under normal
		834	circumstances, this function will never abort as of course libev keeps its
		835	data structures consistent.
329		836
330	=back	837	=back
331		838
		839
332	=head1 ANATOMY OF A WATCHER	840	=head1 ANATOMY OF A WATCHER
		841
		842	In the following description, uppercase C<TYPE> in names stands for the
		843	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		844	watchers and C<ev_io_start> for I/O watchers.
333		845
334	A watcher is a structure that you create and register to record your	846	A watcher is a structure that you create and register to record your
335	interest in some event. For instance, if you want to wait for STDIN to	847	interest in some event. For instance, if you want to wait for STDIN to
336	become readable, you would create an C<ev_io> watcher for that:	848	become readable, you would create an C<ev_io> watcher for that:
337		849
338	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	850	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
339	{	851	{
340	ev_io_stop (w);	852	ev_io_stop (w);
341	ev_unloop (loop, EVUNLOOP_ALL);	853	ev_unloop (loop, EVUNLOOP_ALL);
342	}	854	}
343		855
344	struct ev_loop *loop = ev_default_loop (0);	856	struct ev_loop *loop = ev_default_loop (0);
		857
345	struct ev_io stdin_watcher;	858	ev_io stdin_watcher;
		859
346	ev_init (&stdin_watcher, my_cb);	860	ev_init (&stdin_watcher, my_cb);
347	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	861	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
348	ev_io_start (loop, &stdin_watcher);	862	ev_io_start (loop, &stdin_watcher);
		863
349	ev_loop (loop, 0);	864	ev_loop (loop, 0);
350		865
351	As you can see, you are responsible for allocating the memory for your	866	As you can see, you are responsible for allocating the memory for your
352	watcher structures (and it is usually a bad idea to do this on the stack,	867	watcher structures (and it is I<usually> a bad idea to do this on the
353	although this can sometimes be quite valid).	868	stack).
		869
		870	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		871	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
354		872
355	Each watcher structure must be initialised by a call to C<ev_init	873	Each watcher structure must be initialised by a call to C<ev_init
356	(watcher *, callback)>, which expects a callback to be provided. This	874	(watcher *, callback)>, which expects a callback to be provided. This
357	callback gets invoked each time the event occurs (or, in the case of io	875	callback gets invoked each time the event occurs (or, in the case of I/O
358	watchers, each time the event loop detects that the file descriptor given	876	watchers, each time the event loop detects that the file descriptor given
359	is readable and/or writable).	877	is readable and/or writable).
360		878
361	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	879	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
362	with arguments specific to this watcher type. There is also a macro	880	macro to configure it, with arguments specific to the watcher type. There
363	to combine initialisation and setting in one call: C<< ev_<type>_init	881	is also a macro to combine initialisation and setting in one call: C<<
364	(watcher *, callback, ...) >>.	882	ev_TYPE_init (watcher *, callback, ...) >>.
365		883
366	To make the watcher actually watch out for events, you have to start it	884	To make the watcher actually watch out for events, you have to start it
367	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	885	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
368	*) >>), and you can stop watching for events at any time by calling the	886	*) >>), and you can stop watching for events at any time by calling the
369	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	887	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
370		888
371	As long as your watcher is active (has been started but not stopped) you	889	As long as your watcher is active (has been started but not stopped) you
372	must not touch the values stored in it. Most specifically you must never	890	must not touch the values stored in it. Most specifically you must never
373	reinitialise it or call its set method.	891	reinitialise it or call its C<ev_TYPE_set> macro.
374
375	You can check whether an event is active by calling the C<ev_is_active
376	(watcher *)> macro. To see whether an event is outstanding (but the
377	callback for it has not been called yet) you can use the C<ev_is_pending
378	(watcher *)> macro.
379		892
380	Each and every callback receives the event loop pointer as first, the	893	Each and every callback receives the event loop pointer as first, the
381	registered watcher structure as second, and a bitset of received events as	894	registered watcher structure as second, and a bitset of received events as
382	third argument.	895	third argument.
383		896
…		…
407	The signal specified in the C<ev_signal> watcher has been received by a thread.	920	The signal specified in the C<ev_signal> watcher has been received by a thread.
408		921
409	=item C<EV_CHILD>	922	=item C<EV_CHILD>
410		923
411	The pid specified in the C<ev_child> watcher has received a status change.	924	The pid specified in the C<ev_child> watcher has received a status change.
		925
		926	=item C<EV_STAT>
		927
		928	The path specified in the C<ev_stat> watcher changed its attributes somehow.
412		929
413	=item C<EV_IDLE>	930	=item C<EV_IDLE>
414		931
415	The C<ev_idle> watcher has determined that you have nothing better to do.	932	The C<ev_idle> watcher has determined that you have nothing better to do.
416		933
…		…
424	received events. Callbacks of both watcher types can start and stop as	941	received events. Callbacks of both watcher types can start and stop as
425	many watchers as they want, and all of them will be taken into account	942	many watchers as they want, and all of them will be taken into account
426	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	943	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
427	C<ev_loop> from blocking).	944	C<ev_loop> from blocking).
428		945
		946	=item C<EV_EMBED>
		947
		948	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		949
		950	=item C<EV_FORK>
		951
		952	The event loop has been resumed in the child process after fork (see
		953	C<ev_fork>).
		954
		955	=item C<EV_ASYNC>
		956
		957	The given async watcher has been asynchronously notified (see C<ev_async>).
		958
		959	=item C<EV_CUSTOM>
		960
		961	Not ever sent (or otherwise used) by libev itself, but can be freely used
		962	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		963
429	=item C<EV_ERROR>	964	=item C<EV_ERROR>
430		965
431	An unspecified error has occured, the watcher has been stopped. This might	966	An unspecified error has occurred, the watcher has been stopped. This might
432	happen because the watcher could not be properly started because libev	967	happen because the watcher could not be properly started because libev
433	ran out of memory, a file descriptor was found to be closed or any other	968	ran out of memory, a file descriptor was found to be closed or any other
		969	problem. Libev considers these application bugs.
		970
434	problem. You best act on it by reporting the problem and somehow coping	971	You best act on it by reporting the problem and somehow coping with the
435	with the watcher being stopped.	972	watcher being stopped. Note that well-written programs should not receive
		973	an error ever, so when your watcher receives it, this usually indicates a
		974	bug in your program.
436		975
437	Libev will usually signal a few "dummy" events together with an error,	976	Libev will usually signal a few "dummy" events together with an error, for
438	for example it might indicate that a fd is readable or writable, and if	977	example it might indicate that a fd is readable or writable, and if your
439	your callbacks is well-written it can just attempt the operation and cope	978	callbacks is well-written it can just attempt the operation and cope with
440	with the error from read() or write(). This will not work in multithreaded	979	the error from read() or write(). This will not work in multi-threaded
441	programs, though, so beware.	980	programs, though, as the fd could already be closed and reused for another
		981	thing, so beware.
442		982
443	=back	983	=back
444		984
		985	=head2 GENERIC WATCHER FUNCTIONS
		986
		987	=over 4
		988
		989	=item C<ev_init> (ev_TYPE *watcher, callback)
		990
		991	This macro initialises the generic portion of a watcher. The contents
		992	of the watcher object can be arbitrary (so C<malloc> will do). Only
		993	the generic parts of the watcher are initialised, you I<need> to call
		994	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		995	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		996	which rolls both calls into one.
		997
		998	You can reinitialise a watcher at any time as long as it has been stopped
		999	(or never started) and there are no pending events outstanding.
		1000
		1001	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
		1002	int revents)>.
		1003
		1004	Example: Initialise an C<ev_io> watcher in two steps.
		1005
		1006	ev_io w;
		1007	ev_init (&w, my_cb);
		1008	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1009
		1010	=item C<ev_TYPE_set> (ev_TYPE *, [args])
		1011
		1012	This macro initialises the type-specific parts of a watcher. You need to
		1013	call C<ev_init> at least once before you call this macro, but you can
		1014	call C<ev_TYPE_set> any number of times. You must not, however, call this
		1015	macro on a watcher that is active (it can be pending, however, which is a
		1016	difference to the C<ev_init> macro).
		1017
		1018	Although some watcher types do not have type-specific arguments
		1019	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		1020
		1021	See C<ev_init>, above, for an example.
		1022
		1023	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		1024
		1025	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		1026	calls into a single call. This is the most convenient method to initialise
		1027	a watcher. The same limitations apply, of course.
		1028
		1029	Example: Initialise and set an C<ev_io> watcher in one step.
		1030
		1031	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1032
		1033	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
		1034
		1035	Starts (activates) the given watcher. Only active watchers will receive
		1036	events. If the watcher is already active nothing will happen.
		1037
		1038	Example: Start the C<ev_io> watcher that is being abused as example in this
		1039	whole section.
		1040
		1041	ev_io_start (EV_DEFAULT_UC, &w);
		1042
		1043	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
		1044
		1045	Stops the given watcher if active, and clears the pending status (whether
		1046	the watcher was active or not).
		1047
		1048	It is possible that stopped watchers are pending - for example,
		1049	non-repeating timers are being stopped when they become pending - but
		1050	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
		1051	pending. If you want to free or reuse the memory used by the watcher it is
		1052	therefore a good idea to always call its C<ev_TYPE_stop> function.
		1053
		1054	=item bool ev_is_active (ev_TYPE *watcher)
		1055
		1056	Returns a true value iff the watcher is active (i.e. it has been started
		1057	and not yet been stopped). As long as a watcher is active you must not modify
		1058	it.
		1059
		1060	=item bool ev_is_pending (ev_TYPE *watcher)
		1061
		1062	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		1063	events but its callback has not yet been invoked). As long as a watcher
		1064	is pending (but not active) you must not call an init function on it (but
		1065	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		1066	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1067	it).
		1068
		1069	=item callback ev_cb (ev_TYPE *watcher)
		1070
		1071	Returns the callback currently set on the watcher.
		1072
		1073	=item ev_cb_set (ev_TYPE *watcher, callback)
		1074
		1075	Change the callback. You can change the callback at virtually any time
		1076	(modulo threads).
		1077
		1078	=item ev_set_priority (ev_TYPE *watcher, priority)
		1079
		1080	=item int ev_priority (ev_TYPE *watcher)
		1081
		1082	Set and query the priority of the watcher. The priority is a small
		1083	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1084	(default: C<-2>). Pending watchers with higher priority will be invoked
		1085	before watchers with lower priority, but priority will not keep watchers
		1086	from being executed (except for C<ev_idle> watchers).
		1087
		1088	If you need to suppress invocation when higher priority events are pending
		1089	you need to look at C<ev_idle> watchers, which provide this functionality.
		1090
		1091	You I<must not> change the priority of a watcher as long as it is active or
		1092	pending.
		1093
		1094	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1095	fine, as long as you do not mind that the priority value you query might
		1096	or might not have been clamped to the valid range.
		1097
		1098	The default priority used by watchers when no priority has been set is
		1099	always C<0>, which is supposed to not be too high and not be too low :).
		1100
		1101	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1102	priorities.
		1103
		1104	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1105
		1106	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1107	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1108	can deal with that fact, as both are simply passed through to the
		1109	callback.
		1110
		1111	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1112
		1113	If the watcher is pending, this function clears its pending status and
		1114	returns its C<revents> bitset (as if its callback was invoked). If the
		1115	watcher isn't pending it does nothing and returns C<0>.
		1116
		1117	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1118	callback to be invoked, which can be accomplished with this function.
		1119
		1120	=back
		1121
		1122
445	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1123	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
446		1124
447	Each watcher has, by default, a member C<void *data> that you can change	1125	Each watcher has, by default, a member C<void *data> that you can change
448	and read at any time, libev will completely ignore it. This can be used	1126	and read at any time: libev will completely ignore it. This can be used
449	to associate arbitrary data with your watcher. If you need more data and	1127	to associate arbitrary data with your watcher. If you need more data and
450	don't want to allocate memory and store a pointer to it in that data	1128	don't want to allocate memory and store a pointer to it in that data
451	member, you can also "subclass" the watcher type and provide your own	1129	member, you can also "subclass" the watcher type and provide your own
452	data:	1130	data:
453		1131
454	struct my_io	1132	struct my_io
455	{	1133	{
456	struct ev_io io;	1134	ev_io io;
457	int otherfd;	1135	int otherfd;
458	void *somedata;	1136	void *somedata;
459	struct whatever *mostinteresting;	1137	struct whatever *mostinteresting;
460	}	1138	};
		1139
		1140	...
		1141	struct my_io w;
		1142	ev_io_init (&w.io, my_cb, fd, EV_READ);
461		1143
462	And since your callback will be called with a pointer to the watcher, you	1144	And since your callback will be called with a pointer to the watcher, you
463	can cast it back to your own type:	1145	can cast it back to your own type:
464		1146
465	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1147	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
466	{	1148	{
467	struct my_io *w = (struct my_io *)w_;	1149	struct my_io *w = (struct my_io *)w_;
468	...	1150	...
469	}	1151	}
470		1152
471	More interesting and less C-conformant ways of catsing your callback type	1153	More interesting and less C-conformant ways of casting your callback type
472	have been omitted....	1154	instead have been omitted.
		1155
		1156	Another common scenario is to use some data structure with multiple
		1157	embedded watchers:
		1158
		1159	struct my_biggy
		1160	{
		1161	int some_data;
		1162	ev_timer t1;
		1163	ev_timer t2;
		1164	}
		1165
		1166	In this case getting the pointer to C<my_biggy> is a bit more
		1167	complicated: Either you store the address of your C<my_biggy> struct
		1168	in the C<data> member of the watcher (for woozies), or you need to use
		1169	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1170	programmers):
		1171
		1172	#include <stddef.h>
		1173
		1174	static void
		1175	t1_cb (EV_P_ ev_timer *w, int revents)
		1176	{
		1177	struct my_biggy big = (struct my_biggy *
		1178	(((char *)w) - offsetof (struct my_biggy, t1));
		1179	}
		1180
		1181	static void
		1182	t2_cb (EV_P_ ev_timer *w, int revents)
		1183	{
		1184	struct my_biggy big = (struct my_biggy *
		1185	(((char *)w) - offsetof (struct my_biggy, t2));
		1186	}
		1187
		1188	=head2 WATCHER PRIORITY MODELS
		1189
		1190	Many event loops support I<watcher priorities>, which are usually small
		1191	integers that influence the ordering of event callback invocation
		1192	between watchers in some way, all else being equal.
		1193
		1194	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1195	description for the more technical details such as the actual priority
		1196	range.
		1197
		1198	There are two common ways how these these priorities are being interpreted
		1199	by event loops:
		1200
		1201	In the more common lock-out model, higher priorities "lock out" invocation
		1202	of lower priority watchers, which means as long as higher priority
		1203	watchers receive events, lower priority watchers are not being invoked.
		1204
		1205	The less common only-for-ordering model uses priorities solely to order
		1206	callback invocation within a single event loop iteration: Higher priority
		1207	watchers are invoked before lower priority ones, but they all get invoked
		1208	before polling for new events.
		1209
		1210	Libev uses the second (only-for-ordering) model for all its watchers
		1211	except for idle watchers (which use the lock-out model).
		1212
		1213	The rationale behind this is that implementing the lock-out model for
		1214	watchers is not well supported by most kernel interfaces, and most event
		1215	libraries will just poll for the same events again and again as long as
		1216	their callbacks have not been executed, which is very inefficient in the
		1217	common case of one high-priority watcher locking out a mass of lower
		1218	priority ones.
		1219
		1220	Static (ordering) priorities are most useful when you have two or more
		1221	watchers handling the same resource: a typical usage example is having an
		1222	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1223	timeouts. Under load, data might be received while the program handles
		1224	other jobs, but since timers normally get invoked first, the timeout
		1225	handler will be executed before checking for data. In that case, giving
		1226	the timer a lower priority than the I/O watcher ensures that I/O will be
		1227	handled first even under adverse conditions (which is usually, but not
		1228	always, what you want).
		1229
		1230	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1231	will only be executed when no same or higher priority watchers have
		1232	received events, they can be used to implement the "lock-out" model when
		1233	required.
		1234
		1235	For example, to emulate how many other event libraries handle priorities,
		1236	you can associate an C<ev_idle> watcher to each such watcher, and in
		1237	the normal watcher callback, you just start the idle watcher. The real
		1238	processing is done in the idle watcher callback. This causes libev to
		1239	continously poll and process kernel event data for the watcher, but when
		1240	the lock-out case is known to be rare (which in turn is rare :), this is
		1241	workable.
		1242
		1243	Usually, however, the lock-out model implemented that way will perform
		1244	miserably under the type of load it was designed to handle. In that case,
		1245	it might be preferable to stop the real watcher before starting the
		1246	idle watcher, so the kernel will not have to process the event in case
		1247	the actual processing will be delayed for considerable time.
		1248
		1249	Here is an example of an I/O watcher that should run at a strictly lower
		1250	priority than the default, and which should only process data when no
		1251	other events are pending:
		1252
		1253	ev_idle idle; // actual processing watcher
		1254	ev_io io; // actual event watcher
		1255
		1256	static void
		1257	io_cb (EV_P_ ev_io *w, int revents)
		1258	{
		1259	// stop the I/O watcher, we received the event, but
		1260	// are not yet ready to handle it.
		1261	ev_io_stop (EV_A_ w);
		1262
		1263	// start the idle watcher to ahndle the actual event.
		1264	// it will not be executed as long as other watchers
		1265	// with the default priority are receiving events.
		1266	ev_idle_start (EV_A_ &idle);
		1267	}
		1268
		1269	static void
		1270	idle-cb (EV_P_ ev_idle *w, int revents)
		1271	{
		1272	// actual processing
		1273	read (STDIN_FILENO, ...);
		1274
		1275	// have to start the I/O watcher again, as
		1276	// we have handled the event
		1277	ev_io_start (EV_P_ &io);
		1278	}
		1279
		1280	// initialisation
		1281	ev_idle_init (&idle, idle_cb);
		1282	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1283	ev_io_start (EV_DEFAULT_ &io);
		1284
		1285	In the "real" world, it might also be beneficial to start a timer, so that
		1286	low-priority connections can not be locked out forever under load. This
		1287	enables your program to keep a lower latency for important connections
		1288	during short periods of high load, while not completely locking out less
		1289	important ones.
473		1290
474		1291
475	=head1 WATCHER TYPES	1292	=head1 WATCHER TYPES
476		1293
477	This section describes each watcher in detail, but will not repeat	1294	This section describes each watcher in detail, but will not repeat
478	information given in the last section.	1295	information given in the last section. Any initialisation/set macros,
		1296	functions and members specific to the watcher type are explained.
479		1297
		1298	Members are additionally marked with either I<[read-only]>, meaning that,
		1299	while the watcher is active, you can look at the member and expect some
		1300	sensible content, but you must not modify it (you can modify it while the
		1301	watcher is stopped to your hearts content), or I<[read-write]>, which
		1302	means you can expect it to have some sensible content while the watcher
		1303	is active, but you can also modify it. Modifying it may not do something
		1304	sensible or take immediate effect (or do anything at all), but libev will
		1305	not crash or malfunction in any way.
		1306
		1307
480	=head2 C<ev_io> - is this file descriptor readable or writable	1308	=head2 C<ev_io> - is this file descriptor readable or writable?
481		1309
482	I/O watchers check whether a file descriptor is readable or writable	1310	I/O watchers check whether a file descriptor is readable or writable
483	in each iteration of the event loop (This behaviour is called	1311	in each iteration of the event loop, or, more precisely, when reading
484	level-triggering because you keep receiving events as long as the	1312	would not block the process and writing would at least be able to write
485	condition persists. Remember you can stop the watcher if you don't want to	1313	some data. This behaviour is called level-triggering because you keep
486	act on the event and neither want to receive future events).	1314	receiving events as long as the condition persists. Remember you can stop
		1315	the watcher if you don't want to act on the event and neither want to
		1316	receive future events.
487		1317
488	In general you can register as many read and/or write event watchers per	1318	In general you can register as many read and/or write event watchers per
489	fd as you want (as long as you don't confuse yourself). Setting all file	1319	fd as you want (as long as you don't confuse yourself). Setting all file
490	descriptors to non-blocking mode is also usually a good idea (but not	1320	descriptors to non-blocking mode is also usually a good idea (but not
491	required if you know what you are doing).	1321	required if you know what you are doing).
492		1322
493	You have to be careful with dup'ed file descriptors, though. Some backends	1323	If you cannot use non-blocking mode, then force the use of a
494	(the linux epoll backend is a notable example) cannot handle dup'ed file	1324	known-to-be-good backend (at the time of this writing, this includes only
495	descriptors correctly if you register interest in two or more fds pointing	1325	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>).
496	to the same underlying file/socket etc. description (that is, they share
497	the same underlying "file open").
498		1326
499	If you must do this, then force the use of a known-to-be-good backend	1327	Another thing you have to watch out for is that it is quite easy to
500	(at the time of this writing, this includes only EVMETHOD_SELECT and	1328	receive "spurious" readiness notifications, that is your callback might
501	EVMETHOD_POLL).	1329	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
		1330	because there is no data. Not only are some backends known to create a
		1331	lot of those (for example Solaris ports), it is very easy to get into
		1332	this situation even with a relatively standard program structure. Thus
		1333	it is best to always use non-blocking I/O: An extra C<read>(2) returning
		1334	C<EAGAIN> is far preferable to a program hanging until some data arrives.
		1335
		1336	If you cannot run the fd in non-blocking mode (for example you should
		1337	not play around with an Xlib connection), then you have to separately
		1338	re-test whether a file descriptor is really ready with a known-to-be good
		1339	interface such as poll (fortunately in our Xlib example, Xlib already
		1340	does this on its own, so its quite safe to use). Some people additionally
		1341	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1342	indefinitely.
		1343
		1344	But really, best use non-blocking mode.
		1345
		1346	=head3 The special problem of disappearing file descriptors
		1347
		1348	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1349	descriptor (either due to calling C<close> explicitly or any other means,
		1350	such as C<dup2>). The reason is that you register interest in some file
		1351	descriptor, but when it goes away, the operating system will silently drop
		1352	this interest. If another file descriptor with the same number then is
		1353	registered with libev, there is no efficient way to see that this is, in
		1354	fact, a different file descriptor.
		1355
		1356	To avoid having to explicitly tell libev about such cases, libev follows
		1357	the following policy: Each time C<ev_io_set> is being called, libev
		1358	will assume that this is potentially a new file descriptor, otherwise
		1359	it is assumed that the file descriptor stays the same. That means that
		1360	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1361	descriptor even if the file descriptor number itself did not change.
		1362
		1363	This is how one would do it normally anyway, the important point is that
		1364	the libev application should not optimise around libev but should leave
		1365	optimisations to libev.
		1366
		1367	=head3 The special problem of dup'ed file descriptors
		1368
		1369	Some backends (e.g. epoll), cannot register events for file descriptors,
		1370	but only events for the underlying file descriptions. That means when you
		1371	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1372	events for them, only one file descriptor might actually receive events.
		1373
		1374	There is no workaround possible except not registering events
		1375	for potentially C<dup ()>'ed file descriptors, or to resort to
		1376	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1377
		1378	=head3 The special problem of fork
		1379
		1380	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1381	useless behaviour. Libev fully supports fork, but needs to be told about
		1382	it in the child.
		1383
		1384	To support fork in your programs, you either have to call
		1385	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1386	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
		1387	C<EVBACKEND_POLL>.
		1388
		1389	=head3 The special problem of SIGPIPE
		1390
		1391	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1392	when writing to a pipe whose other end has been closed, your program gets
		1393	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1394	this is sensible behaviour, for daemons, this is usually undesirable.
		1395
		1396	So when you encounter spurious, unexplained daemon exits, make sure you
		1397	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1398	somewhere, as that would have given you a big clue).
		1399
		1400
		1401	=head3 Watcher-Specific Functions
502		1402
503	=over 4	1403	=over 4
504		1404
505	=item ev_io_init (ev_io *, callback, int fd, int events)	1405	=item ev_io_init (ev_io *, callback, int fd, int events)
506		1406
507	=item ev_io_set (ev_io *, int fd, int events)	1407	=item ev_io_set (ev_io *, int fd, int events)
508		1408
509	Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive	1409	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
510	events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ |	1410	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
511	EV_WRITE> to receive the given events.	1411	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
		1412
		1413	=item int fd [read-only]
		1414
		1415	The file descriptor being watched.
		1416
		1417	=item int events [read-only]
		1418
		1419	The events being watched.
512		1420
513	=back	1421	=back
514		1422
		1423	=head3 Examples
		1424
		1425	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
		1426	readable, but only once. Since it is likely line-buffered, you could
		1427	attempt to read a whole line in the callback.
		1428
		1429	static void
		1430	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
		1431	{
		1432	ev_io_stop (loop, w);
		1433	.. read from stdin here (or from w->fd) and handle any I/O errors
		1434	}
		1435
		1436	...
		1437	struct ev_loop *loop = ev_default_init (0);
		1438	ev_io stdin_readable;
		1439	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
		1440	ev_io_start (loop, &stdin_readable);
		1441	ev_loop (loop, 0);
		1442
		1443
515	=head2 C<ev_timer> - relative and optionally recurring timeouts	1444	=head2 C<ev_timer> - relative and optionally repeating timeouts
516		1445
517	Timer watchers are simple relative timers that generate an event after a	1446	Timer watchers are simple relative timers that generate an event after a
518	given time, and optionally repeating in regular intervals after that.	1447	given time, and optionally repeating in regular intervals after that.
519		1448
520	The timers are based on real time, that is, if you register an event that	1449	The timers are based on real time, that is, if you register an event that
521	times out after an hour and you reset your system clock to last years	1450	times out after an hour and you reset your system clock to January last
522	time, it will still time out after (roughly) and hour. "Roughly" because	1451	year, it will still time out after (roughly) one hour. "Roughly" because
523	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1452	detecting time jumps is hard, and some inaccuracies are unavoidable (the
524	monotonic clock option helps a lot here).	1453	monotonic clock option helps a lot here).
		1454
		1455	The callback is guaranteed to be invoked only I<after> its timeout has
		1456	passed. If multiple timers become ready during the same loop iteration
		1457	then the ones with earlier time-out values are invoked before ones with
		1458	later time-out values (but this is no longer true when a callback calls
		1459	C<ev_loop> recursively).
		1460
		1461	=head3 Be smart about timeouts
		1462
		1463	Many real-world problems involve some kind of timeout, usually for error
		1464	recovery. A typical example is an HTTP request - if the other side hangs,
		1465	you want to raise some error after a while.
		1466
		1467	What follows are some ways to handle this problem, from obvious and
		1468	inefficient to smart and efficient.
		1469
		1470	In the following, a 60 second activity timeout is assumed - a timeout that
		1471	gets reset to 60 seconds each time there is activity (e.g. each time some
		1472	data or other life sign was received).
		1473
		1474	=over 4
		1475
		1476	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1477
		1478	This is the most obvious, but not the most simple way: In the beginning,
		1479	start the watcher:
		1480
		1481	ev_timer_init (timer, callback, 60., 0.);
		1482	ev_timer_start (loop, timer);
		1483
		1484	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1485	and start it again:
		1486
		1487	ev_timer_stop (loop, timer);
		1488	ev_timer_set (timer, 60., 0.);
		1489	ev_timer_start (loop, timer);
		1490
		1491	This is relatively simple to implement, but means that each time there is
		1492	some activity, libev will first have to remove the timer from its internal
		1493	data structure and then add it again. Libev tries to be fast, but it's
		1494	still not a constant-time operation.
		1495
		1496	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1497
		1498	This is the easiest way, and involves using C<ev_timer_again> instead of
		1499	C<ev_timer_start>.
		1500
		1501	To implement this, configure an C<ev_timer> with a C<repeat> value
		1502	of C<60> and then call C<ev_timer_again> at start and each time you
		1503	successfully read or write some data. If you go into an idle state where
		1504	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1505	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1506
		1507	That means you can ignore both the C<ev_timer_start> function and the
		1508	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1509	member and C<ev_timer_again>.
		1510
		1511	At start:
		1512
		1513	ev_timer_init (timer, callback);
		1514	timer->repeat = 60.;
		1515	ev_timer_again (loop, timer);
		1516
		1517	Each time there is some activity:
		1518
		1519	ev_timer_again (loop, timer);
		1520
		1521	It is even possible to change the time-out on the fly, regardless of
		1522	whether the watcher is active or not:
		1523
		1524	timer->repeat = 30.;
		1525	ev_timer_again (loop, timer);
		1526
		1527	This is slightly more efficient then stopping/starting the timer each time
		1528	you want to modify its timeout value, as libev does not have to completely
		1529	remove and re-insert the timer from/into its internal data structure.
		1530
		1531	It is, however, even simpler than the "obvious" way to do it.
		1532
		1533	=item 3. Let the timer time out, but then re-arm it as required.
		1534
		1535	This method is more tricky, but usually most efficient: Most timeouts are
		1536	relatively long compared to the intervals between other activity - in
		1537	our example, within 60 seconds, there are usually many I/O events with
		1538	associated activity resets.
		1539
		1540	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1541	but remember the time of last activity, and check for a real timeout only
		1542	within the callback:
		1543
		1544	ev_tstamp last_activity; // time of last activity
		1545
		1546	static void
		1547	callback (EV_P_ ev_timer *w, int revents)
		1548	{
		1549	ev_tstamp now = ev_now (EV_A);
		1550	ev_tstamp timeout = last_activity + 60.;
		1551
		1552	// if last_activity + 60. is older than now, we did time out
		1553	if (timeout < now)
		1554	{
		1555	// timeout occured, take action
		1556	}
		1557	else
		1558	{
		1559	// callback was invoked, but there was some activity, re-arm
		1560	// the watcher to fire in last_activity + 60, which is
		1561	// guaranteed to be in the future, so "again" is positive:
		1562	w->repeat = timeout - now;
		1563	ev_timer_again (EV_A_ w);
		1564	}
		1565	}
		1566
		1567	To summarise the callback: first calculate the real timeout (defined
		1568	as "60 seconds after the last activity"), then check if that time has
		1569	been reached, which means something I<did>, in fact, time out. Otherwise
		1570	the callback was invoked too early (C<timeout> is in the future), so
		1571	re-schedule the timer to fire at that future time, to see if maybe we have
		1572	a timeout then.
		1573
		1574	Note how C<ev_timer_again> is used, taking advantage of the
		1575	C<ev_timer_again> optimisation when the timer is already running.
		1576
		1577	This scheme causes more callback invocations (about one every 60 seconds
		1578	minus half the average time between activity), but virtually no calls to
		1579	libev to change the timeout.
		1580
		1581	To start the timer, simply initialise the watcher and set C<last_activity>
		1582	to the current time (meaning we just have some activity :), then call the
		1583	callback, which will "do the right thing" and start the timer:
		1584
		1585	ev_timer_init (timer, callback);
		1586	last_activity = ev_now (loop);
		1587	callback (loop, timer, EV_TIMEOUT);
		1588
		1589	And when there is some activity, simply store the current time in
		1590	C<last_activity>, no libev calls at all:
		1591
		1592	last_actiivty = ev_now (loop);
		1593
		1594	This technique is slightly more complex, but in most cases where the
		1595	time-out is unlikely to be triggered, much more efficient.
		1596
		1597	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1598	callback :) - just change the timeout and invoke the callback, which will
		1599	fix things for you.
		1600
		1601	=item 4. Wee, just use a double-linked list for your timeouts.
		1602
		1603	If there is not one request, but many thousands (millions...), all
		1604	employing some kind of timeout with the same timeout value, then one can
		1605	do even better:
		1606
		1607	When starting the timeout, calculate the timeout value and put the timeout
		1608	at the I<end> of the list.
		1609
		1610	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1611	the list is expected to fire (for example, using the technique #3).
		1612
		1613	When there is some activity, remove the timer from the list, recalculate
		1614	the timeout, append it to the end of the list again, and make sure to
		1615	update the C<ev_timer> if it was taken from the beginning of the list.
		1616
		1617	This way, one can manage an unlimited number of timeouts in O(1) time for
		1618	starting, stopping and updating the timers, at the expense of a major
		1619	complication, and having to use a constant timeout. The constant timeout
		1620	ensures that the list stays sorted.
		1621
		1622	=back
		1623
		1624	So which method the best?
		1625
		1626	Method #2 is a simple no-brain-required solution that is adequate in most
		1627	situations. Method #3 requires a bit more thinking, but handles many cases
		1628	better, and isn't very complicated either. In most case, choosing either
		1629	one is fine, with #3 being better in typical situations.
		1630
		1631	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1632	rather complicated, but extremely efficient, something that really pays
		1633	off after the first million or so of active timers, i.e. it's usually
		1634	overkill :)
		1635
		1636	=head3 The special problem of time updates
		1637
		1638	Establishing the current time is a costly operation (it usually takes at
		1639	least two system calls): EV therefore updates its idea of the current
		1640	time only before and after C<ev_loop> collects new events, which causes a
		1641	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1642	lots of events in one iteration.
525		1643
526	The relative timeouts are calculated relative to the C<ev_now ()>	1644	The relative timeouts are calculated relative to the C<ev_now ()>
527	time. This is usually the right thing as this timestamp refers to the time	1645	time. This is usually the right thing as this timestamp refers to the time
528	of the event triggering whatever timeout you are modifying/starting. If	1646	of the event triggering whatever timeout you are modifying/starting. If
529	you suspect event processing to be delayed and you I<need> to base the timeout	1647	you suspect event processing to be delayed and you I<need> to base the
530	on the current time, use something like this to adjust for this:	1648	timeout on the current time, use something like this to adjust for this:
531		1649
532	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1650	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
533		1651
534	The callback is guarenteed to be invoked only when its timeout has passed,	1652	If the event loop is suspended for a long time, you can also force an
535	but if multiple timers become ready during the same loop iteration then	1653	update of the time returned by C<ev_now ()> by calling C<ev_now_update
536	order of execution is undefined.	1654	()>.
		1655
		1656	=head3 Watcher-Specific Functions and Data Members
537		1657
538	=over 4	1658	=over 4
539		1659
540	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1660	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
541		1661
542	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1662	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
543		1663
544	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1664	Configure the timer to trigger after C<after> seconds. If C<repeat>
545	C<0.>, then it will automatically be stopped. If it is positive, then the	1665	is C<0.>, then it will automatically be stopped once the timeout is
546	timer will automatically be configured to trigger again C<repeat> seconds	1666	reached. If it is positive, then the timer will automatically be
547	later, again, and again, until stopped manually.	1667	configured to trigger again C<repeat> seconds later, again, and again,
		1668	until stopped manually.
548		1669
549	The timer itself will do a best-effort at avoiding drift, that is, if you	1670	The timer itself will do a best-effort at avoiding drift, that is, if
550	configure a timer to trigger every 10 seconds, then it will trigger at	1671	you configure a timer to trigger every 10 seconds, then it will normally
551	exactly 10 second intervals. If, however, your program cannot keep up with	1672	trigger at exactly 10 second intervals. If, however, your program cannot
552	the timer (because it takes longer than those 10 seconds to do stuff) the	1673	keep up with the timer (because it takes longer than those 10 seconds to
553	timer will not fire more than once per event loop iteration.	1674	do stuff) the timer will not fire more than once per event loop iteration.
554		1675
555	=item ev_timer_again (loop)	1676	=item ev_timer_again (loop, ev_timer *)
556		1677
557	This will act as if the timer timed out and restart it again if it is	1678	This will act as if the timer timed out and restart it again if it is
558	repeating. The exact semantics are:	1679	repeating. The exact semantics are:
559		1680
		1681	If the timer is pending, its pending status is cleared.
		1682
560	If the timer is started but nonrepeating, stop it.	1683	If the timer is started but non-repeating, stop it (as if it timed out).
561		1684
562	If the timer is repeating, either start it if necessary (with the repeat	1685	If the timer is repeating, either start it if necessary (with the
563	value), or reset the running timer to the repeat value.	1686	C<repeat> value), or reset the running timer to the C<repeat> value.
564		1687
565	This sounds a bit complicated, but here is a useful and typical	1688	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
566	example: Imagine you have a tcp connection and you want a so-called idle	1689	usage example.
567	timeout, that is, you want to be called when there have been, say, 60	1690
568	seconds of inactivity on the socket. The easiest way to do this is to	1691	=item ev_tstamp repeat [read-write]
569	configure an C<ev_timer> with after=repeat=60 and calling ev_timer_again each	1692
570	time you successfully read or write some data. If you go into an idle	1693	The current C<repeat> value. Will be used each time the watcher times out
571	state where you do not expect data to travel on the socket, you can stop	1694	or C<ev_timer_again> is called, and determines the next timeout (if any),
572	the timer, and again will automatically restart it if need be.	1695	which is also when any modifications are taken into account.
573		1696
574	=back	1697	=back
575		1698
		1699	=head3 Examples
		1700
		1701	Example: Create a timer that fires after 60 seconds.
		1702
		1703	static void
		1704	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
		1705	{
		1706	.. one minute over, w is actually stopped right here
		1707	}
		1708
		1709	ev_timer mytimer;
		1710	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
		1711	ev_timer_start (loop, &mytimer);
		1712
		1713	Example: Create a timeout timer that times out after 10 seconds of
		1714	inactivity.
		1715
		1716	static void
		1717	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
		1718	{
		1719	.. ten seconds without any activity
		1720	}
		1721
		1722	ev_timer mytimer;
		1723	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
		1724	ev_timer_again (&mytimer); /* start timer */
		1725	ev_loop (loop, 0);
		1726
		1727	// and in some piece of code that gets executed on any "activity":
		1728	// reset the timeout to start ticking again at 10 seconds
		1729	ev_timer_again (&mytimer);
		1730
		1731
576	=head2 C<ev_periodic> - to cron or not to cron	1732	=head2 C<ev_periodic> - to cron or not to cron?
577		1733
578	Periodic watchers are also timers of a kind, but they are very versatile	1734	Periodic watchers are also timers of a kind, but they are very versatile
579	(and unfortunately a bit complex).	1735	(and unfortunately a bit complex).
580		1736
581	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1737	Unlike C<ev_timer>, periodic watchers are not based on real time (or
582	but on wallclock time (absolute time). You can tell a periodic watcher	1738	relative time, the physical time that passes) but on wall clock time
583	to trigger "at" some specific point in time. For example, if you tell a	1739	(absolute time, the thing you can read on your calender or clock). The
584	periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()	1740	difference is that wall clock time can run faster or slower than real
585	+ 10.>) and then reset your system clock to the last year, then it will	1741	time, and time jumps are not uncommon (e.g. when you adjust your
586	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1742	wrist-watch).
587	roughly 10 seconds later and of course not if you reset your system time
588	again).
589		1743
590	They can also be used to implement vastly more complex timers, such as	1744	You can tell a periodic watcher to trigger after some specific point
		1745	in time: for example, if you tell a periodic watcher to trigger "in 10
		1746	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1747	not a delay) and then reset your system clock to January of the previous
		1748	year, then it will take a year or more to trigger the event (unlike an
		1749	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1750	it, as it uses a relative timeout).
		1751
		1752	C<ev_periodic> watchers can also be used to implement vastly more complex
591	triggering an event on eahc midnight, local time.	1753	timers, such as triggering an event on each "midnight, local time", or
		1754	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1755	those cannot react to time jumps.
592		1756
593	As with timers, the callback is guarenteed to be invoked only when the	1757	As with timers, the callback is guaranteed to be invoked only when the
594	time (C<at>) has been passed, but if multiple periodic timers become ready	1758	point in time where it is supposed to trigger has passed. If multiple
595	during the same loop iteration then order of execution is undefined.	1759	timers become ready during the same loop iteration then the ones with
		1760	earlier time-out values are invoked before ones with later time-out values
		1761	(but this is no longer true when a callback calls C<ev_loop> recursively).
		1762
		1763	=head3 Watcher-Specific Functions and Data Members
596		1764
597	=over 4	1765	=over 4
598		1766
599	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1767	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
600		1768
601	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1769	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
602		1770
603	Lots of arguments, lets sort it out... There are basically three modes of	1771	Lots of arguments, let's sort it out... There are basically three modes of
604	operation, and we will explain them from simplest to complex:	1772	operation, and we will explain them from simplest to most complex:
605		1773
606	=over 4	1774	=over 4
607		1775
608	=item * absolute timer (interval = reschedule_cb = 0)	1776	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
609		1777
610	In this configuration the watcher triggers an event at the wallclock time	1778	In this configuration the watcher triggers an event after the wall clock
611	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1779	time C<offset> has passed. It will not repeat and will not adjust when a
612	that is, if it is to be run at January 1st 2011 then it will run when the	1780	time jump occurs, that is, if it is to be run at January 1st 2011 then it
613	system time reaches or surpasses this time.	1781	will be stopped and invoked when the system clock reaches or surpasses
		1782	this point in time.
614		1783
615	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1784	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
616		1785
617	In this mode the watcher will always be scheduled to time out at the next	1786	In this mode the watcher will always be scheduled to time out at the next
618	C<at + N * interval> time (for some integer N) and then repeat, regardless	1787	C<offset + N * interval> time (for some integer N, which can also be
619	of any time jumps.	1788	negative) and then repeat, regardless of any time jumps. The C<offset>
		1789	argument is merely an offset into the C<interval> periods.
620		1790
621	This can be used to create timers that do not drift with respect to system	1791	This can be used to create timers that do not drift with respect to the
622	time:	1792	system clock, for example, here is an C<ev_periodic> that triggers each
		1793	hour, on the hour (with respect to UTC):
623		1794
624	ev_periodic_set (&periodic, 0., 3600., 0);	1795	ev_periodic_set (&periodic, 0., 3600., 0);
625		1796
626	This doesn't mean there will always be 3600 seconds in between triggers,	1797	This doesn't mean there will always be 3600 seconds in between triggers,
627	but only that the the callback will be called when the system time shows a	1798	but only that the callback will be called when the system time shows a
628	full hour (UTC), or more correctly, when the system time is evenly divisible	1799	full hour (UTC), or more correctly, when the system time is evenly divisible
629	by 3600.	1800	by 3600.
630		1801
631	Another way to think about it (for the mathematically inclined) is that	1802	Another way to think about it (for the mathematically inclined) is that
632	C<ev_periodic> will try to run the callback in this mode at the next possible	1803	C<ev_periodic> will try to run the callback in this mode at the next possible
633	time where C<time = at (mod interval)>, regardless of any time jumps.	1804	time where C<time = offset (mod interval)>, regardless of any time jumps.
634		1805
		1806	For numerical stability it is preferable that the C<offset> value is near
		1807	C<ev_now ()> (the current time), but there is no range requirement for
		1808	this value, and in fact is often specified as zero.
		1809
		1810	Note also that there is an upper limit to how often a timer can fire (CPU
		1811	speed for example), so if C<interval> is very small then timing stability
		1812	will of course deteriorate. Libev itself tries to be exact to be about one
		1813	millisecond (if the OS supports it and the machine is fast enough).
		1814
635	=item * manual reschedule mode (reschedule_cb = callback)	1815	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
636		1816
637	In this mode the values for C<interval> and C<at> are both being	1817	In this mode the values for C<interval> and C<offset> are both being
638	ignored. Instead, each time the periodic watcher gets scheduled, the	1818	ignored. Instead, each time the periodic watcher gets scheduled, the
639	reschedule callback will be called with the watcher as first, and the	1819	reschedule callback will be called with the watcher as first, and the
640	current time as second argument.	1820	current time as second argument.
641		1821
642	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1822	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
643	ever, or make any event loop modifications>. If you need to stop it,	1823	or make ANY other event loop modifications whatsoever, unless explicitly
644	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	1824	allowed by documentation here>.
645	starting a prepare watcher).
646		1825
		1826	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1827	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1828	only event loop modification you are allowed to do).
		1829
647	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1830	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
648	ev_tstamp now)>, e.g.:	1831	*w, ev_tstamp now)>, e.g.:
649		1832
		1833	static ev_tstamp
650	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1834	my_rescheduler (ev_periodic *w, ev_tstamp now)
651	{	1835	{
652	return now + 60.;	1836	return now + 60.;
653	}	1837	}
654		1838
655	It must return the next time to trigger, based on the passed time value	1839	It must return the next time to trigger, based on the passed time value
656	(that is, the lowest time value larger than to the second argument). It	1840	(that is, the lowest time value larger than to the second argument). It
657	will usually be called just before the callback will be triggered, but	1841	will usually be called just before the callback will be triggered, but
658	might be called at other times, too.	1842	might be called at other times, too.
659		1843
660	NOTE: I<< This callback must always return a time that is later than the	1844	NOTE: I<< This callback must always return a time that is higher than or
661	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	1845	equal to the passed C<now> value >>.
662		1846
663	This can be used to create very complex timers, such as a timer that	1847	This can be used to create very complex timers, such as a timer that
664	triggers on each midnight, local time. To do this, you would calculate the	1848	triggers on "next midnight, local time". To do this, you would calculate the
665	next midnight after C<now> and return the timestamp value for this. How	1849	next midnight after C<now> and return the timestamp value for this. How
666	you do this is, again, up to you (but it is not trivial, which is the main	1850	you do this is, again, up to you (but it is not trivial, which is the main
667	reason I omitted it as an example).	1851	reason I omitted it as an example).
668		1852
669	=back	1853	=back
…		…
673	Simply stops and restarts the periodic watcher again. This is only useful	1857	Simply stops and restarts the periodic watcher again. This is only useful
674	when you changed some parameters or the reschedule callback would return	1858	when you changed some parameters or the reschedule callback would return
675	a different time than the last time it was called (e.g. in a crond like	1859	a different time than the last time it was called (e.g. in a crond like
676	program when the crontabs have changed).	1860	program when the crontabs have changed).
677		1861
		1862	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1863
		1864	When active, returns the absolute time that the watcher is supposed
		1865	to trigger next. This is not the same as the C<offset> argument to
		1866	C<ev_periodic_set>, but indeed works even in interval and manual
		1867	rescheduling modes.
		1868
		1869	=item ev_tstamp offset [read-write]
		1870
		1871	When repeating, this contains the offset value, otherwise this is the
		1872	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		1873	although libev might modify this value for better numerical stability).
		1874
		1875	Can be modified any time, but changes only take effect when the periodic
		1876	timer fires or C<ev_periodic_again> is being called.
		1877
		1878	=item ev_tstamp interval [read-write]
		1879
		1880	The current interval value. Can be modified any time, but changes only
		1881	take effect when the periodic timer fires or C<ev_periodic_again> is being
		1882	called.
		1883
		1884	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
		1885
		1886	The current reschedule callback, or C<0>, if this functionality is
		1887	switched off. Can be changed any time, but changes only take effect when
		1888	the periodic timer fires or C<ev_periodic_again> is being called.
		1889
678	=back	1890	=back
679		1891
		1892	=head3 Examples
		1893
		1894	Example: Call a callback every hour, or, more precisely, whenever the
		1895	system time is divisible by 3600. The callback invocation times have
		1896	potentially a lot of jitter, but good long-term stability.
		1897
		1898	static void
		1899	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
		1900	{
		1901	... its now a full hour (UTC, or TAI or whatever your clock follows)
		1902	}
		1903
		1904	ev_periodic hourly_tick;
		1905	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
		1906	ev_periodic_start (loop, &hourly_tick);
		1907
		1908	Example: The same as above, but use a reschedule callback to do it:
		1909
		1910	#include <math.h>
		1911
		1912	static ev_tstamp
		1913	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
		1914	{
		1915	return now + (3600. - fmod (now, 3600.));
		1916	}
		1917
		1918	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
		1919
		1920	Example: Call a callback every hour, starting now:
		1921
		1922	ev_periodic hourly_tick;
		1923	ev_periodic_init (&hourly_tick, clock_cb,
		1924	fmod (ev_now (loop), 3600.), 3600., 0);
		1925	ev_periodic_start (loop, &hourly_tick);
		1926
		1927
680	=head2 C<ev_signal> - signal me when a signal gets signalled	1928	=head2 C<ev_signal> - signal me when a signal gets signalled!
681		1929
682	Signal watchers will trigger an event when the process receives a specific	1930	Signal watchers will trigger an event when the process receives a specific
683	signal one or more times. Even though signals are very asynchronous, libev	1931	signal one or more times. Even though signals are very asynchronous, libev
684	will try it's best to deliver signals synchronously, i.e. as part of the	1932	will try it's best to deliver signals synchronously, i.e. as part of the
685	normal event processing, like any other event.	1933	normal event processing, like any other event.
686		1934
		1935	If you want signals asynchronously, just use C<sigaction> as you would
		1936	do without libev and forget about sharing the signal. You can even use
		1937	C<ev_async> from a signal handler to synchronously wake up an event loop.
		1938
687	You can configure as many watchers as you like per signal. Only when the	1939	You can configure as many watchers as you like per signal. Only when the
688	first watcher gets started will libev actually register a signal watcher	1940	first watcher gets started will libev actually register a signal handler
689	with the kernel (thus it coexists with your own signal handlers as long	1941	with the kernel (thus it coexists with your own signal handlers as long as
690	as you don't register any with libev). Similarly, when the last signal	1942	you don't register any with libev for the same signal). Similarly, when
691	watcher for a signal is stopped libev will reset the signal handler to	1943	the last signal watcher for a signal is stopped, libev will reset the
692	SIG_DFL (regardless of what it was set to before).	1944	signal handler to SIG_DFL (regardless of what it was set to before).
		1945
		1946	If possible and supported, libev will install its handlers with
		1947	C<SA_RESTART> behaviour enabled, so system calls should not be unduly
		1948	interrupted. If you have a problem with system calls getting interrupted by
		1949	signals you can block all signals in an C<ev_check> watcher and unblock
		1950	them in an C<ev_prepare> watcher.
		1951
		1952	=head3 Watcher-Specific Functions and Data Members
693		1953
694	=over 4	1954	=over 4
695		1955
696	=item ev_signal_init (ev_signal *, callback, int signum)	1956	=item ev_signal_init (ev_signal *, callback, int signum)
697		1957
698	=item ev_signal_set (ev_signal *, int signum)	1958	=item ev_signal_set (ev_signal *, int signum)
699		1959
700	Configures the watcher to trigger on the given signal number (usually one	1960	Configures the watcher to trigger on the given signal number (usually one
701	of the C<SIGxxx> constants).	1961	of the C<SIGxxx> constants).
702		1962
		1963	=item int signum [read-only]
		1964
		1965	The signal the watcher watches out for.
		1966
703	=back	1967	=back
704		1968
		1969	=head3 Examples
		1970
		1971	Example: Try to exit cleanly on SIGINT.
		1972
		1973	static void
		1974	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		1975	{
		1976	ev_unloop (loop, EVUNLOOP_ALL);
		1977	}
		1978
		1979	ev_signal signal_watcher;
		1980	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1981	ev_signal_start (loop, &signal_watcher);
		1982
		1983
705	=head2 C<ev_child> - wait for pid status changes	1984	=head2 C<ev_child> - watch out for process status changes
706		1985
707	Child watchers trigger when your process receives a SIGCHLD in response to	1986	Child watchers trigger when your process receives a SIGCHLD in response to
708	some child status changes (most typically when a child of yours dies).	1987	some child status changes (most typically when a child of yours dies or
		1988	exits). It is permissible to install a child watcher I<after> the child
		1989	has been forked (which implies it might have already exited), as long
		1990	as the event loop isn't entered (or is continued from a watcher), i.e.,
		1991	forking and then immediately registering a watcher for the child is fine,
		1992	but forking and registering a watcher a few event loop iterations later is
		1993	not.
		1994
		1995	Only the default event loop is capable of handling signals, and therefore
		1996	you can only register child watchers in the default event loop.
		1997
		1998	=head3 Process Interaction
		1999
		2000	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2001	initialised. This is necessary to guarantee proper behaviour even if
		2002	the first child watcher is started after the child exits. The occurrence
		2003	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2004	synchronously as part of the event loop processing. Libev always reaps all
		2005	children, even ones not watched.
		2006
		2007	=head3 Overriding the Built-In Processing
		2008
		2009	Libev offers no special support for overriding the built-in child
		2010	processing, but if your application collides with libev's default child
		2011	handler, you can override it easily by installing your own handler for
		2012	C<SIGCHLD> after initialising the default loop, and making sure the
		2013	default loop never gets destroyed. You are encouraged, however, to use an
		2014	event-based approach to child reaping and thus use libev's support for
		2015	that, so other libev users can use C<ev_child> watchers freely.
		2016
		2017	=head3 Stopping the Child Watcher
		2018
		2019	Currently, the child watcher never gets stopped, even when the
		2020	child terminates, so normally one needs to stop the watcher in the
		2021	callback. Future versions of libev might stop the watcher automatically
		2022	when a child exit is detected.
		2023
		2024	=head3 Watcher-Specific Functions and Data Members
709		2025
710	=over 4	2026	=over 4
711		2027
712	=item ev_child_init (ev_child *, callback, int pid)	2028	=item ev_child_init (ev_child *, callback, int pid, int trace)
713		2029
714	=item ev_child_set (ev_child *, int pid)	2030	=item ev_child_set (ev_child *, int pid, int trace)
715		2031
716	Configures the watcher to wait for status changes of process C<pid> (or	2032	Configures the watcher to wait for status changes of process C<pid> (or
717	I<any> process if C<pid> is specified as C<0>). The callback can look	2033	I<any> process if C<pid> is specified as C<0>). The callback can look
718	at the C<rstatus> member of the C<ev_child> watcher structure to see	2034	at the C<rstatus> member of the C<ev_child> watcher structure to see
719	the status word (use the macros from C<sys/wait.h> and see your systems	2035	the status word (use the macros from C<sys/wait.h> and see your systems
720	C<waitpid> documentation). The C<rpid> member contains the pid of the	2036	C<waitpid> documentation). The C<rpid> member contains the pid of the
721	process causing the status change.	2037	process causing the status change. C<trace> must be either C<0> (only
		2038	activate the watcher when the process terminates) or C<1> (additionally
		2039	activate the watcher when the process is stopped or continued).
		2040
		2041	=item int pid [read-only]
		2042
		2043	The process id this watcher watches out for, or C<0>, meaning any process id.
		2044
		2045	=item int rpid [read-write]
		2046
		2047	The process id that detected a status change.
		2048
		2049	=item int rstatus [read-write]
		2050
		2051	The process exit/trace status caused by C<rpid> (see your systems
		2052	C<waitpid> and C<sys/wait.h> documentation for details).
722		2053
723	=back	2054	=back
724		2055
		2056	=head3 Examples
		2057
		2058	Example: C<fork()> a new process and install a child handler to wait for
		2059	its completion.
		2060
		2061	ev_child cw;
		2062
		2063	static void
		2064	child_cb (EV_P_ ev_child *w, int revents)
		2065	{
		2066	ev_child_stop (EV_A_ w);
		2067	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
		2068	}
		2069
		2070	pid_t pid = fork ();
		2071
		2072	if (pid < 0)
		2073	// error
		2074	else if (pid == 0)
		2075	{
		2076	// the forked child executes here
		2077	exit (1);
		2078	}
		2079	else
		2080	{
		2081	ev_child_init (&cw, child_cb, pid, 0);
		2082	ev_child_start (EV_DEFAULT_ &cw);
		2083	}
		2084
		2085
		2086	=head2 C<ev_stat> - did the file attributes just change?
		2087
		2088	This watches a file system path for attribute changes. That is, it calls
		2089	C<stat> on that path in regular intervals (or when the OS says it changed)
		2090	and sees if it changed compared to the last time, invoking the callback if
		2091	it did.
		2092
		2093	The path does not need to exist: changing from "path exists" to "path does
		2094	not exist" is a status change like any other. The condition "path does not
		2095	exist" (or more correctly "path cannot be stat'ed") is signified by the
		2096	C<st_nlink> field being zero (which is otherwise always forced to be at
		2097	least one) and all the other fields of the stat buffer having unspecified
		2098	contents.
		2099
		2100	The path I<must not> end in a slash or contain special components such as
		2101	C<.> or C<..>. The path I<should> be absolute: If it is relative and
		2102	your working directory changes, then the behaviour is undefined.
		2103
		2104	Since there is no portable change notification interface available, the
		2105	portable implementation simply calls C<stat(2)> regularly on the path
		2106	to see if it changed somehow. You can specify a recommended polling
		2107	interval for this case. If you specify a polling interval of C<0> (highly
		2108	recommended!) then a I<suitable, unspecified default> value will be used
		2109	(which you can expect to be around five seconds, although this might
		2110	change dynamically). Libev will also impose a minimum interval which is
		2111	currently around C<0.1>, but that's usually overkill.
		2112
		2113	This watcher type is not meant for massive numbers of stat watchers,
		2114	as even with OS-supported change notifications, this can be
		2115	resource-intensive.
		2116
		2117	At the time of this writing, the only OS-specific interface implemented
		2118	is the Linux inotify interface (implementing kqueue support is left as an
		2119	exercise for the reader. Note, however, that the author sees no way of
		2120	implementing C<ev_stat> semantics with kqueue, except as a hint).
		2121
		2122	=head3 ABI Issues (Largefile Support)
		2123
		2124	Libev by default (unless the user overrides this) uses the default
		2125	compilation environment, which means that on systems with large file
		2126	support disabled by default, you get the 32 bit version of the stat
		2127	structure. When using the library from programs that change the ABI to
		2128	use 64 bit file offsets the programs will fail. In that case you have to
		2129	compile libev with the same flags to get binary compatibility. This is
		2130	obviously the case with any flags that change the ABI, but the problem is
		2131	most noticeably displayed with ev_stat and large file support.
		2132
		2133	The solution for this is to lobby your distribution maker to make large
		2134	file interfaces available by default (as e.g. FreeBSD does) and not
		2135	optional. Libev cannot simply switch on large file support because it has
		2136	to exchange stat structures with application programs compiled using the
		2137	default compilation environment.
		2138
		2139	=head3 Inotify and Kqueue
		2140
		2141	When C<inotify (7)> support has been compiled into libev and present at
		2142	runtime, it will be used to speed up change detection where possible. The
		2143	inotify descriptor will be created lazily when the first C<ev_stat>
		2144	watcher is being started.
		2145
		2146	Inotify presence does not change the semantics of C<ev_stat> watchers
		2147	except that changes might be detected earlier, and in some cases, to avoid
		2148	making regular C<stat> calls. Even in the presence of inotify support
		2149	there are many cases where libev has to resort to regular C<stat> polling,
		2150	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2151	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2152	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2153	xfs are fully working) libev usually gets away without polling.
		2154
		2155	There is no support for kqueue, as apparently it cannot be used to
		2156	implement this functionality, due to the requirement of having a file
		2157	descriptor open on the object at all times, and detecting renames, unlinks
		2158	etc. is difficult.
		2159
		2160	=head3 C<stat ()> is a synchronous operation
		2161
		2162	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2163	the process. The exception are C<ev_stat> watchers - those call C<stat
		2164	()>, which is a synchronous operation.
		2165
		2166	For local paths, this usually doesn't matter: unless the system is very
		2167	busy or the intervals between stat's are large, a stat call will be fast,
		2168	as the path data is usually in memory already (except when starting the
		2169	watcher).
		2170
		2171	For networked file systems, calling C<stat ()> can block an indefinite
		2172	time due to network issues, and even under good conditions, a stat call
		2173	often takes multiple milliseconds.
		2174
		2175	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2176	paths, although this is fully supported by libev.
		2177
		2178	=head3 The special problem of stat time resolution
		2179
		2180	The C<stat ()> system call only supports full-second resolution portably,
		2181	and even on systems where the resolution is higher, most file systems
		2182	still only support whole seconds.
		2183
		2184	That means that, if the time is the only thing that changes, you can
		2185	easily miss updates: on the first update, C<ev_stat> detects a change and
		2186	calls your callback, which does something. When there is another update
		2187	within the same second, C<ev_stat> will be unable to detect unless the
		2188	stat data does change in other ways (e.g. file size).
		2189
		2190	The solution to this is to delay acting on a change for slightly more
		2191	than a second (or till slightly after the next full second boundary), using
		2192	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2193	ev_timer_again (loop, w)>).
		2194
		2195	The C<.02> offset is added to work around small timing inconsistencies
		2196	of some operating systems (where the second counter of the current time
		2197	might be be delayed. One such system is the Linux kernel, where a call to
		2198	C<gettimeofday> might return a timestamp with a full second later than
		2199	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2200	update file times then there will be a small window where the kernel uses
		2201	the previous second to update file times but libev might already execute
		2202	the timer callback).
		2203
		2204	=head3 Watcher-Specific Functions and Data Members
		2205
		2206	=over 4
		2207
		2208	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		2209
		2210	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		2211
		2212	Configures the watcher to wait for status changes of the given
		2213	C<path>. The C<interval> is a hint on how quickly a change is expected to
		2214	be detected and should normally be specified as C<0> to let libev choose
		2215	a suitable value. The memory pointed to by C<path> must point to the same
		2216	path for as long as the watcher is active.
		2217
		2218	The callback will receive an C<EV_STAT> event when a change was detected,
		2219	relative to the attributes at the time the watcher was started (or the
		2220	last change was detected).
		2221
		2222	=item ev_stat_stat (loop, ev_stat *)
		2223
		2224	Updates the stat buffer immediately with new values. If you change the
		2225	watched path in your callback, you could call this function to avoid
		2226	detecting this change (while introducing a race condition if you are not
		2227	the only one changing the path). Can also be useful simply to find out the
		2228	new values.
		2229
		2230	=item ev_statdata attr [read-only]
		2231
		2232	The most-recently detected attributes of the file. Although the type is
		2233	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		2234	suitable for your system, but you can only rely on the POSIX-standardised
		2235	members to be present. If the C<st_nlink> member is C<0>, then there was
		2236	some error while C<stat>ing the file.
		2237
		2238	=item ev_statdata prev [read-only]
		2239
		2240	The previous attributes of the file. The callback gets invoked whenever
		2241	C<prev> != C<attr>, or, more precisely, one or more of these members
		2242	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2243	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
		2244
		2245	=item ev_tstamp interval [read-only]
		2246
		2247	The specified interval.
		2248
		2249	=item const char *path [read-only]
		2250
		2251	The file system path that is being watched.
		2252
		2253	=back
		2254
		2255	=head3 Examples
		2256
		2257	Example: Watch C</etc/passwd> for attribute changes.
		2258
		2259	static void
		2260	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		2261	{
		2262	/* /etc/passwd changed in some way */
		2263	if (w->attr.st_nlink)
		2264	{
		2265	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		2266	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		2267	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		2268	}
		2269	else
		2270	/* you shalt not abuse printf for puts */
		2271	puts ("wow, /etc/passwd is not there, expect problems. "
		2272	"if this is windows, they already arrived\n");
		2273	}
		2274
		2275	...
		2276	ev_stat passwd;
		2277
		2278	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		2279	ev_stat_start (loop, &passwd);
		2280
		2281	Example: Like above, but additionally use a one-second delay so we do not
		2282	miss updates (however, frequent updates will delay processing, too, so
		2283	one might do the work both on C<ev_stat> callback invocation I<and> on
		2284	C<ev_timer> callback invocation).
		2285
		2286	static ev_stat passwd;
		2287	static ev_timer timer;
		2288
		2289	static void
		2290	timer_cb (EV_P_ ev_timer *w, int revents)
		2291	{
		2292	ev_timer_stop (EV_A_ w);
		2293
		2294	/* now it's one second after the most recent passwd change */
		2295	}
		2296
		2297	static void
		2298	stat_cb (EV_P_ ev_stat *w, int revents)
		2299	{
		2300	/* reset the one-second timer */
		2301	ev_timer_again (EV_A_ &timer);
		2302	}
		2303
		2304	...
		2305	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2306	ev_stat_start (loop, &passwd);
		2307	ev_timer_init (&timer, timer_cb, 0., 1.02);
		2308
		2309
725	=head2 C<ev_idle> - when you've got nothing better to do	2310	=head2 C<ev_idle> - when you've got nothing better to do...
726		2311
727	Idle watchers trigger events when there are no other events are pending	2312	Idle watchers trigger events when no other events of the same or higher
728	(prepare, check and other idle watchers do not count). That is, as long	2313	priority are pending (prepare, check and other idle watchers do not count
729	as your process is busy handling sockets or timeouts (or even signals,	2314	as receiving "events").
730	imagine) it will not be triggered. But when your process is idle all idle	2315
731	watchers are being called again and again, once per event loop iteration -	2316	That is, as long as your process is busy handling sockets or timeouts
		2317	(or even signals, imagine) of the same or higher priority it will not be
		2318	triggered. But when your process is idle (or only lower-priority watchers
		2319	are pending), the idle watchers are being called once per event loop
732	until stopped, that is, or your process receives more events and becomes	2320	iteration - until stopped, that is, or your process receives more events
733	busy.	2321	and becomes busy again with higher priority stuff.
734		2322
735	The most noteworthy effect is that as long as any idle watchers are	2323	The most noteworthy effect is that as long as any idle watchers are
736	active, the process will not block when waiting for new events.	2324	active, the process will not block when waiting for new events.
737		2325
738	Apart from keeping your process non-blocking (which is a useful	2326	Apart from keeping your process non-blocking (which is a useful
739	effect on its own sometimes), idle watchers are a good place to do	2327	effect on its own sometimes), idle watchers are a good place to do
740	"pseudo-background processing", or delay processing stuff to after the	2328	"pseudo-background processing", or delay processing stuff to after the
741	event loop has handled all outstanding events.	2329	event loop has handled all outstanding events.
742		2330
		2331	=head3 Watcher-Specific Functions and Data Members
		2332
743	=over 4	2333	=over 4
744		2334
745	=item ev_idle_init (ev_signal *, callback)	2335	=item ev_idle_init (ev_idle *, callback)
746		2336
747	Initialises and configures the idle watcher - it has no parameters of any	2337	Initialises and configures the idle watcher - it has no parameters of any
748	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2338	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
749	believe me.	2339	believe me.
750		2340
751	=back	2341	=back
752		2342
		2343	=head3 Examples
		2344
		2345	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
		2346	callback, free it. Also, use no error checking, as usual.
		2347
		2348	static void
		2349	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
		2350	{
		2351	free (w);
		2352	// now do something you wanted to do when the program has
		2353	// no longer anything immediate to do.
		2354	}
		2355
		2356	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
		2357	ev_idle_init (idle_watcher, idle_cb);
		2358	ev_idle_start (loop, idle_cb);
		2359
		2360
753	=head2 C<ev_prepare> and C<ev_check> - customise your event loop	2361	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
754		2362
755	Prepare and check watchers are usually (but not always) used in tandem:	2363	Prepare and check watchers are usually (but not always) used in pairs:
756	prepare watchers get invoked before the process blocks and check watchers	2364	prepare watchers get invoked before the process blocks and check watchers
757	afterwards.	2365	afterwards.
758		2366
		2367	You I<must not> call C<ev_loop> or similar functions that enter
		2368	the current event loop from either C<ev_prepare> or C<ev_check>
		2369	watchers. Other loops than the current one are fine, however. The
		2370	rationale behind this is that you do not need to check for recursion in
		2371	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
		2372	C<ev_check> so if you have one watcher of each kind they will always be
		2373	called in pairs bracketing the blocking call.
		2374
759	Their main purpose is to integrate other event mechanisms into libev. This	2375	Their main purpose is to integrate other event mechanisms into libev and
760	could be used, for example, to track variable changes, implement your own	2376	their use is somewhat advanced. They could be used, for example, to track
761	watchers, integrate net-snmp or a coroutine library and lots more.	2377	variable changes, implement your own watchers, integrate net-snmp or a
		2378	coroutine library and lots more. They are also occasionally useful if
		2379	you cache some data and want to flush it before blocking (for example,
		2380	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		2381	watcher).
762		2382
763	This is done by examining in each prepare call which file descriptors need	2383	This is done by examining in each prepare call which file descriptors
764	to be watched by the other library, registering C<ev_io> watchers for	2384	need to be watched by the other library, registering C<ev_io> watchers
765	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2385	for them and starting an C<ev_timer> watcher for any timeouts (many
766	provide just this functionality). Then, in the check watcher you check for	2386	libraries provide exactly this functionality). Then, in the check watcher,
767	any events that occured (by checking the pending status of all watchers	2387	you check for any events that occurred (by checking the pending status
768	and stopping them) and call back into the library. The I/O and timer	2388	of all watchers and stopping them) and call back into the library. The
769	callbacks will never actually be called (but must be valid nevertheless,	2389	I/O and timer callbacks will never actually be called (but must be valid
770	because you never know, you know?).	2390	nevertheless, because you never know, you know?).
771		2391
772	As another example, the Perl Coro module uses these hooks to integrate	2392	As another example, the Perl Coro module uses these hooks to integrate
773	coroutines into libev programs, by yielding to other active coroutines	2393	coroutines into libev programs, by yielding to other active coroutines
774	during each prepare and only letting the process block if no coroutines	2394	during each prepare and only letting the process block if no coroutines
775	are ready to run (it's actually more complicated: it only runs coroutines	2395	are ready to run (it's actually more complicated: it only runs coroutines
776	with priority higher than or equal to the event loop and one coroutine	2396	with priority higher than or equal to the event loop and one coroutine
777	of lower priority, but only once, using idle watchers to keep the event	2397	of lower priority, but only once, using idle watchers to keep the event
778	loop from blocking if lower-priority coroutines are active, thus mapping	2398	loop from blocking if lower-priority coroutines are active, thus mapping
779	low-priority coroutines to idle/background tasks).	2399	low-priority coroutines to idle/background tasks).
780		2400
		2401	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		2402	priority, to ensure that they are being run before any other watchers
		2403	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2404
		2405	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2406	activate ("feed") events into libev. While libev fully supports this, they
		2407	might get executed before other C<ev_check> watchers did their job. As
		2408	C<ev_check> watchers are often used to embed other (non-libev) event
		2409	loops those other event loops might be in an unusable state until their
		2410	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2411	others).
		2412
		2413	=head3 Watcher-Specific Functions and Data Members
		2414
781	=over 4	2415	=over 4
782		2416
783	=item ev_prepare_init (ev_prepare *, callback)	2417	=item ev_prepare_init (ev_prepare *, callback)
784		2418
785	=item ev_check_init (ev_check *, callback)	2419	=item ev_check_init (ev_check *, callback)
786		2420
787	Initialises and configures the prepare or check watcher - they have no	2421	Initialises and configures the prepare or check watcher - they have no
788	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2422	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
789	macros, but using them is utterly, utterly and completely pointless.	2423	macros, but using them is utterly, utterly, utterly and completely
		2424	pointless.
790		2425
791	=back	2426	=back
792		2427
		2428	=head3 Examples
		2429
		2430	There are a number of principal ways to embed other event loops or modules
		2431	into libev. Here are some ideas on how to include libadns into libev
		2432	(there is a Perl module named C<EV::ADNS> that does this, which you could
		2433	use as a working example. Another Perl module named C<EV::Glib> embeds a
		2434	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		2435	Glib event loop).
		2436
		2437	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
		2438	and in a check watcher, destroy them and call into libadns. What follows
		2439	is pseudo-code only of course. This requires you to either use a low
		2440	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		2441	the callbacks for the IO/timeout watchers might not have been called yet.
		2442
		2443	static ev_io iow [nfd];
		2444	static ev_timer tw;
		2445
		2446	static void
		2447	io_cb (struct ev_loop *loop, ev_io *w, int revents)
		2448	{
		2449	}
		2450
		2451	// create io watchers for each fd and a timer before blocking
		2452	static void
		2453	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
		2454	{
		2455	int timeout = 3600000;
		2456	struct pollfd fds [nfd];
		2457	// actual code will need to loop here and realloc etc.
		2458	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		2459
		2460	/* the callback is illegal, but won't be called as we stop during check */
		2461	ev_timer_init (&tw, 0, timeout * 1e-3);
		2462	ev_timer_start (loop, &tw);
		2463
		2464	// create one ev_io per pollfd
		2465	for (int i = 0; i < nfd; ++i)
		2466	{
		2467	ev_io_init (iow + i, io_cb, fds [i].fd,
		2468	((fds [i].events & POLLIN ? EV_READ : 0)
		2469	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		2470
		2471	fds [i].revents = 0;
		2472	ev_io_start (loop, iow + i);
		2473	}
		2474	}
		2475
		2476	// stop all watchers after blocking
		2477	static void
		2478	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
		2479	{
		2480	ev_timer_stop (loop, &tw);
		2481
		2482	for (int i = 0; i < nfd; ++i)
		2483	{
		2484	// set the relevant poll flags
		2485	// could also call adns_processreadable etc. here
		2486	struct pollfd *fd = fds + i;
		2487	int revents = ev_clear_pending (iow + i);
		2488	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2489	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2490
		2491	// now stop the watcher
		2492	ev_io_stop (loop, iow + i);
		2493	}
		2494
		2495	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		2496	}
		2497
		2498	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2499	in the prepare watcher and would dispose of the check watcher.
		2500
		2501	Method 3: If the module to be embedded supports explicit event
		2502	notification (libadns does), you can also make use of the actual watcher
		2503	callbacks, and only destroy/create the watchers in the prepare watcher.
		2504
		2505	static void
		2506	timer_cb (EV_P_ ev_timer *w, int revents)
		2507	{
		2508	adns_state ads = (adns_state)w->data;
		2509	update_now (EV_A);
		2510
		2511	adns_processtimeouts (ads, &tv_now);
		2512	}
		2513
		2514	static void
		2515	io_cb (EV_P_ ev_io *w, int revents)
		2516	{
		2517	adns_state ads = (adns_state)w->data;
		2518	update_now (EV_A);
		2519
		2520	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2521	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2522	}
		2523
		2524	// do not ever call adns_afterpoll
		2525
		2526	Method 4: Do not use a prepare or check watcher because the module you
		2527	want to embed is not flexible enough to support it. Instead, you can
		2528	override their poll function. The drawback with this solution is that the
		2529	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		2530	this approach, effectively embedding EV as a client into the horrible
		2531	libglib event loop.
		2532
		2533	static gint
		2534	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2535	{
		2536	int got_events = 0;
		2537
		2538	for (n = 0; n < nfds; ++n)
		2539	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2540
		2541	if (timeout >= 0)
		2542	// create/start timer
		2543
		2544	// poll
		2545	ev_loop (EV_A_ 0);
		2546
		2547	// stop timer again
		2548	if (timeout >= 0)
		2549	ev_timer_stop (EV_A_ &to);
		2550
		2551	// stop io watchers again - their callbacks should have set
		2552	for (n = 0; n < nfds; ++n)
		2553	ev_io_stop (EV_A_ iow [n]);
		2554
		2555	return got_events;
		2556	}
		2557
		2558
		2559	=head2 C<ev_embed> - when one backend isn't enough...
		2560
		2561	This is a rather advanced watcher type that lets you embed one event loop
		2562	into another (currently only C<ev_io> events are supported in the embedded
		2563	loop, other types of watchers might be handled in a delayed or incorrect
		2564	fashion and must not be used).
		2565
		2566	There are primarily two reasons you would want that: work around bugs and
		2567	prioritise I/O.
		2568
		2569	As an example for a bug workaround, the kqueue backend might only support
		2570	sockets on some platform, so it is unusable as generic backend, but you
		2571	still want to make use of it because you have many sockets and it scales
		2572	so nicely. In this case, you would create a kqueue-based loop and embed
		2573	it into your default loop (which might use e.g. poll). Overall operation
		2574	will be a bit slower because first libev has to call C<poll> and then
		2575	C<kevent>, but at least you can use both mechanisms for what they are
		2576	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
		2577
		2578	As for prioritising I/O: under rare circumstances you have the case where
		2579	some fds have to be watched and handled very quickly (with low latency),
		2580	and even priorities and idle watchers might have too much overhead. In
		2581	this case you would put all the high priority stuff in one loop and all
		2582	the rest in a second one, and embed the second one in the first.
		2583
		2584	As long as the watcher is active, the callback will be invoked every
		2585	time there might be events pending in the embedded loop. The callback
		2586	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
		2587	sweep and invoke their callbacks (the callback doesn't need to invoke the
		2588	C<ev_embed_sweep> function directly, it could also start an idle watcher
		2589	to give the embedded loop strictly lower priority for example).
		2590
		2591	You can also set the callback to C<0>, in which case the embed watcher
		2592	will automatically execute the embedded loop sweep whenever necessary.
		2593
		2594	Fork detection will be handled transparently while the C<ev_embed> watcher
		2595	is active, i.e., the embedded loop will automatically be forked when the
		2596	embedding loop forks. In other cases, the user is responsible for calling
		2597	C<ev_loop_fork> on the embedded loop.
		2598
		2599	Unfortunately, not all backends are embeddable: only the ones returned by
		2600	C<ev_embeddable_backends> are, which, unfortunately, does not include any
		2601	portable one.
		2602
		2603	So when you want to use this feature you will always have to be prepared
		2604	that you cannot get an embeddable loop. The recommended way to get around
		2605	this is to have a separate variables for your embeddable loop, try to
		2606	create it, and if that fails, use the normal loop for everything.
		2607
		2608	=head3 C<ev_embed> and fork
		2609
		2610	While the C<ev_embed> watcher is running, forks in the embedding loop will
		2611	automatically be applied to the embedded loop as well, so no special
		2612	fork handling is required in that case. When the watcher is not running,
		2613	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		2614	as applicable.
		2615
		2616	=head3 Watcher-Specific Functions and Data Members
		2617
		2618	=over 4
		2619
		2620	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
		2621
		2622	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
		2623
		2624	Configures the watcher to embed the given loop, which must be
		2625	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		2626	invoked automatically, otherwise it is the responsibility of the callback
		2627	to invoke it (it will continue to be called until the sweep has been done,
		2628	if you do not want that, you need to temporarily stop the embed watcher).
		2629
		2630	=item ev_embed_sweep (loop, ev_embed *)
		2631
		2632	Make a single, non-blocking sweep over the embedded loop. This works
		2633	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
		2634	appropriate way for embedded loops.
		2635
		2636	=item struct ev_loop *other [read-only]
		2637
		2638	The embedded event loop.
		2639
		2640	=back
		2641
		2642	=head3 Examples
		2643
		2644	Example: Try to get an embeddable event loop and embed it into the default
		2645	event loop. If that is not possible, use the default loop. The default
		2646	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2647	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2648	used).
		2649
		2650	struct ev_loop *loop_hi = ev_default_init (0);
		2651	struct ev_loop *loop_lo = 0;
		2652	ev_embed embed;
		2653
		2654	// see if there is a chance of getting one that works
		2655	// (remember that a flags value of 0 means autodetection)
		2656	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2657	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2658	: 0;
		2659
		2660	// if we got one, then embed it, otherwise default to loop_hi
		2661	if (loop_lo)
		2662	{
		2663	ev_embed_init (&embed, 0, loop_lo);
		2664	ev_embed_start (loop_hi, &embed);
		2665	}
		2666	else
		2667	loop_lo = loop_hi;
		2668
		2669	Example: Check if kqueue is available but not recommended and create
		2670	a kqueue backend for use with sockets (which usually work with any
		2671	kqueue implementation). Store the kqueue/socket-only event loop in
		2672	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2673
		2674	struct ev_loop *loop = ev_default_init (0);
		2675	struct ev_loop *loop_socket = 0;
		2676	ev_embed embed;
		2677
		2678	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2679	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2680	{
		2681	ev_embed_init (&embed, 0, loop_socket);
		2682	ev_embed_start (loop, &embed);
		2683	}
		2684
		2685	if (!loop_socket)
		2686	loop_socket = loop;
		2687
		2688	// now use loop_socket for all sockets, and loop for everything else
		2689
		2690
		2691	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		2692
		2693	Fork watchers are called when a C<fork ()> was detected (usually because
		2694	whoever is a good citizen cared to tell libev about it by calling
		2695	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		2696	event loop blocks next and before C<ev_check> watchers are being called,
		2697	and only in the child after the fork. If whoever good citizen calling
		2698	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		2699	handlers will be invoked, too, of course.
		2700
		2701	=head3 Watcher-Specific Functions and Data Members
		2702
		2703	=over 4
		2704
		2705	=item ev_fork_init (ev_signal *, callback)
		2706
		2707	Initialises and configures the fork watcher - it has no parameters of any
		2708	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		2709	believe me.
		2710
		2711	=back
		2712
		2713
		2714	=head2 C<ev_async> - how to wake up another event loop
		2715
		2716	In general, you cannot use an C<ev_loop> from multiple threads or other
		2717	asynchronous sources such as signal handlers (as opposed to multiple event
		2718	loops - those are of course safe to use in different threads).
		2719
		2720	Sometimes, however, you need to wake up another event loop you do not
		2721	control, for example because it belongs to another thread. This is what
		2722	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2723	can signal it by calling C<ev_async_send>, which is thread- and signal
		2724	safe.
		2725
		2726	This functionality is very similar to C<ev_signal> watchers, as signals,
		2727	too, are asynchronous in nature, and signals, too, will be compressed
		2728	(i.e. the number of callback invocations may be less than the number of
		2729	C<ev_async_sent> calls).
		2730
		2731	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2732	just the default loop.
		2733
		2734	=head3 Queueing
		2735
		2736	C<ev_async> does not support queueing of data in any way. The reason
		2737	is that the author does not know of a simple (or any) algorithm for a
		2738	multiple-writer-single-reader queue that works in all cases and doesn't
		2739	need elaborate support such as pthreads.
		2740
		2741	That means that if you want to queue data, you have to provide your own
		2742	queue. But at least I can tell you how to implement locking around your
		2743	queue:
		2744
		2745	=over 4
		2746
		2747	=item queueing from a signal handler context
		2748
		2749	To implement race-free queueing, you simply add to the queue in the signal
		2750	handler but you block the signal handler in the watcher callback. Here is
		2751	an example that does that for some fictitious SIGUSR1 handler:
		2752
		2753	static ev_async mysig;
		2754
		2755	static void
		2756	sigusr1_handler (void)
		2757	{
		2758	sometype data;
		2759
		2760	// no locking etc.
		2761	queue_put (data);
		2762	ev_async_send (EV_DEFAULT_ &mysig);
		2763	}
		2764
		2765	static void
		2766	mysig_cb (EV_P_ ev_async *w, int revents)
		2767	{
		2768	sometype data;
		2769	sigset_t block, prev;
		2770
		2771	sigemptyset (&block);
		2772	sigaddset (&block, SIGUSR1);
		2773	sigprocmask (SIG_BLOCK, &block, &prev);
		2774
		2775	while (queue_get (&data))
		2776	process (data);
		2777
		2778	if (sigismember (&prev, SIGUSR1)
		2779	sigprocmask (SIG_UNBLOCK, &block, 0);
		2780	}
		2781
		2782	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2783	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2784	either...).
		2785
		2786	=item queueing from a thread context
		2787
		2788	The strategy for threads is different, as you cannot (easily) block
		2789	threads but you can easily preempt them, so to queue safely you need to
		2790	employ a traditional mutex lock, such as in this pthread example:
		2791
		2792	static ev_async mysig;
		2793	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2794
		2795	static void
		2796	otherthread (void)
		2797	{
		2798	// only need to lock the actual queueing operation
		2799	pthread_mutex_lock (&mymutex);
		2800	queue_put (data);
		2801	pthread_mutex_unlock (&mymutex);
		2802
		2803	ev_async_send (EV_DEFAULT_ &mysig);
		2804	}
		2805
		2806	static void
		2807	mysig_cb (EV_P_ ev_async *w, int revents)
		2808	{
		2809	pthread_mutex_lock (&mymutex);
		2810
		2811	while (queue_get (&data))
		2812	process (data);
		2813
		2814	pthread_mutex_unlock (&mymutex);
		2815	}
		2816
		2817	=back
		2818
		2819
		2820	=head3 Watcher-Specific Functions and Data Members
		2821
		2822	=over 4
		2823
		2824	=item ev_async_init (ev_async *, callback)
		2825
		2826	Initialises and configures the async watcher - it has no parameters of any
		2827	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		2828	trust me.
		2829
		2830	=item ev_async_send (loop, ev_async *)
		2831
		2832	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2833	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2834	C<ev_feed_event>, this call is safe to do from other threads, signal or
		2835	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		2836	section below on what exactly this means).
		2837
		2838	Note that, as with other watchers in libev, multiple events might get
		2839	compressed into a single callback invocation (another way to look at this
		2840	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		2841	reset when the event loop detects that).
		2842
		2843	This call incurs the overhead of a system call only once per event loop
		2844	iteration, so while the overhead might be noticeable, it doesn't apply to
		2845	repeated calls to C<ev_async_send> for the same event loop.
		2846
		2847	=item bool = ev_async_pending (ev_async *)
		2848
		2849	Returns a non-zero value when C<ev_async_send> has been called on the
		2850	watcher but the event has not yet been processed (or even noted) by the
		2851	event loop.
		2852
		2853	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2854	the loop iterates next and checks for the watcher to have become active,
		2855	it will reset the flag again. C<ev_async_pending> can be used to very
		2856	quickly check whether invoking the loop might be a good idea.
		2857
		2858	Not that this does I<not> check whether the watcher itself is pending,
		2859	only whether it has been requested to make this watcher pending: there
		2860	is a time window between the event loop checking and resetting the async
		2861	notification, and the callback being invoked.
		2862
		2863	=back
		2864
		2865
793	=head1 OTHER FUNCTIONS	2866	=head1 OTHER FUNCTIONS
794		2867
795	There are some other functions of possible interest. Described. Here. Now.	2868	There are some other functions of possible interest. Described. Here. Now.
796		2869
797	=over 4	2870	=over 4
798		2871
799	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	2872	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
800		2873
801	This function combines a simple timer and an I/O watcher, calls your	2874	This function combines a simple timer and an I/O watcher, calls your
802	callback on whichever event happens first and automatically stop both	2875	callback on whichever event happens first and automatically stops both
803	watchers. This is useful if you want to wait for a single event on an fd	2876	watchers. This is useful if you want to wait for a single event on an fd
804	or timeout without having to allocate/configure/start/stop/free one or	2877	or timeout without having to allocate/configure/start/stop/free one or
805	more watchers yourself.	2878	more watchers yourself.
806		2879
807	If C<fd> is less than 0, then no I/O watcher will be started and events	2880	If C<fd> is less than 0, then no I/O watcher will be started and the
808	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	2881	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
809	C<events> set will be craeted and started.	2882	the given C<fd> and C<events> set will be created and started.
810		2883
811	If C<timeout> is less than 0, then no timeout watcher will be	2884	If C<timeout> is less than 0, then no timeout watcher will be
812	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	2885	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
813	repeat = 0) will be started. While C<0> is a valid timeout, it is of	2886	repeat = 0) will be started. C<0> is a valid timeout.
814	dubious value.
815		2887
816	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	2888	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
817	passed an C<revents> set like normal event callbacks (a combination of	2889	passed an C<revents> set like normal event callbacks (a combination of
818	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	2890	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
819	value passed to C<ev_once>:	2891	value passed to C<ev_once>. Note that it is possible to receive I<both>
		2892	a timeout and an io event at the same time - you probably should give io
		2893	events precedence.
820		2894
		2895	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		2896
821	static void stdin_ready (int revents, void *arg)	2897	static void stdin_ready (int revents, void *arg)
822	{	2898	{
823	if (revents & EV_TIMEOUT)
824	/* doh, nothing entered */;
825	else if (revents & EV_READ)	2899	if (revents & EV_READ)
826	/* stdin might have data for us, joy! */;	2900	/* stdin might have data for us, joy! */;
		2901	else if (revents & EV_TIMEOUT)
		2902	/* doh, nothing entered */;
827	}	2903	}
828		2904
829	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2905	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
830		2906
831	=item ev_feed_event (loop, watcher, int events)	2907	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
832		2908
833	Feeds the given event set into the event loop, as if the specified event	2909	Feeds the given event set into the event loop, as if the specified event
834	had happened for the specified watcher (which must be a pointer to an	2910	had happened for the specified watcher (which must be a pointer to an
835	initialised but not necessarily started event watcher).	2911	initialised but not necessarily started event watcher).
836		2912
837	=item ev_feed_fd_event (loop, int fd, int revents)	2913	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
838		2914
839	Feed an event on the given fd, as if a file descriptor backend detected	2915	Feed an event on the given fd, as if a file descriptor backend detected
840	the given events it.	2916	the given events it.
841		2917
842	=item ev_feed_signal_event (loop, int signum)	2918	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
843		2919
844	Feed an event as if the given signal occured (loop must be the default loop!).	2920	Feed an event as if the given signal occurred (C<loop> must be the default
		2921	loop!).
845		2922
846	=back	2923	=back
		2924
847		2925
848	=head1 LIBEVENT EMULATION	2926	=head1 LIBEVENT EMULATION
849		2927
850	Libev offers a compatibility emulation layer for libevent. It cannot	2928	Libev offers a compatibility emulation layer for libevent. It cannot
851	emulate the internals of libevent, so here are some usage hints:	2929	emulate the internals of libevent, so here are some usage hints:
…		…
863		2941
864	=item * Priorities are not currently supported. Initialising priorities	2942	=item * Priorities are not currently supported. Initialising priorities
865	will fail and all watchers will have the same priority, even though there	2943	will fail and all watchers will have the same priority, even though there
866	is an ev_pri field.	2944	is an ev_pri field.
867		2945
		2946	=item * In libevent, the last base created gets the signals, in libev, the
		2947	first base created (== the default loop) gets the signals.
		2948
868	=item * Other members are not supported.	2949	=item * Other members are not supported.
869		2950
870	=item * The libev emulation is I<not> ABI compatible to libevent, you need	2951	=item * The libev emulation is I<not> ABI compatible to libevent, you need
871	to use the libev header file and library.	2952	to use the libev header file and library.
872		2953
873	=back	2954	=back
874		2955
875	=head1 C++ SUPPORT	2956	=head1 C++ SUPPORT
876		2957
877	TBD.	2958	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		2959	you to use some convenience methods to start/stop watchers and also change
		2960	the callback model to a model using method callbacks on objects.
		2961
		2962	To use it,
		2963
		2964	#include <ev++.h>
		2965
		2966	This automatically includes F<ev.h> and puts all of its definitions (many
		2967	of them macros) into the global namespace. All C++ specific things are
		2968	put into the C<ev> namespace. It should support all the same embedding
		2969	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
		2970
		2971	Care has been taken to keep the overhead low. The only data member the C++
		2972	classes add (compared to plain C-style watchers) is the event loop pointer
		2973	that the watcher is associated with (or no additional members at all if
		2974	you disable C<EV_MULTIPLICITY> when embedding libev).
		2975
		2976	Currently, functions, and static and non-static member functions can be
		2977	used as callbacks. Other types should be easy to add as long as they only
		2978	need one additional pointer for context. If you need support for other
		2979	types of functors please contact the author (preferably after implementing
		2980	it).
		2981
		2982	Here is a list of things available in the C<ev> namespace:
		2983
		2984	=over 4
		2985
		2986	=item C<ev::READ>, C<ev::WRITE> etc.
		2987
		2988	These are just enum values with the same values as the C<EV_READ> etc.
		2989	macros from F<ev.h>.
		2990
		2991	=item C<ev::tstamp>, C<ev::now>
		2992
		2993	Aliases to the same types/functions as with the C<ev_> prefix.
		2994
		2995	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		2996
		2997	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		2998	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		2999	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		3000	defines by many implementations.
		3001
		3002	All of those classes have these methods:
		3003
		3004	=over 4
		3005
		3006	=item ev::TYPE::TYPE ()
		3007
		3008	=item ev::TYPE::TYPE (struct ev_loop *)
		3009
		3010	=item ev::TYPE::~TYPE
		3011
		3012	The constructor (optionally) takes an event loop to associate the watcher
		3013	with. If it is omitted, it will use C<EV_DEFAULT>.
		3014
		3015	The constructor calls C<ev_init> for you, which means you have to call the
		3016	C<set> method before starting it.
		3017
		3018	It will not set a callback, however: You have to call the templated C<set>
		3019	method to set a callback before you can start the watcher.
		3020
		3021	(The reason why you have to use a method is a limitation in C++ which does
		3022	not allow explicit template arguments for constructors).
		3023
		3024	The destructor automatically stops the watcher if it is active.
		3025
		3026	=item w->set<class, &class::method> (object *)
		3027
		3028	This method sets the callback method to call. The method has to have a
		3029	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		3030	first argument and the C<revents> as second. The object must be given as
		3031	parameter and is stored in the C<data> member of the watcher.
		3032
		3033	This method synthesizes efficient thunking code to call your method from
		3034	the C callback that libev requires. If your compiler can inline your
		3035	callback (i.e. it is visible to it at the place of the C<set> call and
		3036	your compiler is good :), then the method will be fully inlined into the
		3037	thunking function, making it as fast as a direct C callback.
		3038
		3039	Example: simple class declaration and watcher initialisation
		3040
		3041	struct myclass
		3042	{
		3043	void io_cb (ev::io &w, int revents) { }
		3044	}
		3045
		3046	myclass obj;
		3047	ev::io iow;
		3048	iow.set <myclass, &myclass::io_cb> (&obj);
		3049
		3050	=item w->set (object *)
		3051
		3052	This is an B<experimental> feature that might go away in a future version.
		3053
		3054	This is a variation of a method callback - leaving out the method to call
		3055	will default the method to C<operator ()>, which makes it possible to use
		3056	functor objects without having to manually specify the C<operator ()> all
		3057	the time. Incidentally, you can then also leave out the template argument
		3058	list.
		3059
		3060	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3061	int revents)>.
		3062
		3063	See the method-C<set> above for more details.
		3064
		3065	Example: use a functor object as callback.
		3066
		3067	struct myfunctor
		3068	{
		3069	void operator() (ev::io &w, int revents)
		3070	{
		3071	...
		3072	}
		3073	}
		3074
		3075	myfunctor f;
		3076
		3077	ev::io w;
		3078	w.set (&f);
		3079
		3080	=item w->set<function> (void *data = 0)
		3081
		3082	Also sets a callback, but uses a static method or plain function as
		3083	callback. The optional C<data> argument will be stored in the watcher's
		3084	C<data> member and is free for you to use.
		3085
		3086	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		3087
		3088	See the method-C<set> above for more details.
		3089
		3090	Example: Use a plain function as callback.
		3091
		3092	static void io_cb (ev::io &w, int revents) { }
		3093	iow.set <io_cb> ();
		3094
		3095	=item w->set (struct ev_loop *)
		3096
		3097	Associates a different C<struct ev_loop> with this watcher. You can only
		3098	do this when the watcher is inactive (and not pending either).
		3099
		3100	=item w->set ([arguments])
		3101
		3102	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
		3103	called at least once. Unlike the C counterpart, an active watcher gets
		3104	automatically stopped and restarted when reconfiguring it with this
		3105	method.
		3106
		3107	=item w->start ()
		3108
		3109	Starts the watcher. Note that there is no C<loop> argument, as the
		3110	constructor already stores the event loop.
		3111
		3112	=item w->stop ()
		3113
		3114	Stops the watcher if it is active. Again, no C<loop> argument.
		3115
		3116	=item w->again () (C<ev::timer>, C<ev::periodic> only)
		3117
		3118	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		3119	C<ev_TYPE_again> function.
		3120
		3121	=item w->sweep () (C<ev::embed> only)
		3122
		3123	Invokes C<ev_embed_sweep>.
		3124
		3125	=item w->update () (C<ev::stat> only)
		3126
		3127	Invokes C<ev_stat_stat>.
		3128
		3129	=back
		3130
		3131	=back
		3132
		3133	Example: Define a class with an IO and idle watcher, start one of them in
		3134	the constructor.
		3135
		3136	class myclass
		3137	{
		3138	ev::io io ; void io_cb (ev::io &w, int revents);
		3139	ev::idle idle; void idle_cb (ev::idle &w, int revents);
		3140
		3141	myclass (int fd)
		3142	{
		3143	io .set <myclass, &myclass::io_cb > (this);
		3144	idle.set <myclass, &myclass::idle_cb> (this);
		3145
		3146	io.start (fd, ev::READ);
		3147	}
		3148	};
		3149
		3150
		3151	=head1 OTHER LANGUAGE BINDINGS
		3152
		3153	Libev does not offer other language bindings itself, but bindings for a
		3154	number of languages exist in the form of third-party packages. If you know
		3155	any interesting language binding in addition to the ones listed here, drop
		3156	me a note.
		3157
		3158	=over 4
		3159
		3160	=item Perl
		3161
		3162	The EV module implements the full libev API and is actually used to test
		3163	libev. EV is developed together with libev. Apart from the EV core module,
		3164	there are additional modules that implement libev-compatible interfaces
		3165	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3166	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3167	and C<EV::Glib>).
		3168
		3169	It can be found and installed via CPAN, its homepage is at
		3170	L<http://software.schmorp.de/pkg/EV>.
		3171
		3172	=item Python
		3173
		3174	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3175	seems to be quite complete and well-documented.
		3176
		3177	=item Ruby
		3178
		3179	Tony Arcieri has written a ruby extension that offers access to a subset
		3180	of the libev API and adds file handle abstractions, asynchronous DNS and
		3181	more on top of it. It can be found via gem servers. Its homepage is at
		3182	L<http://rev.rubyforge.org/>.
		3183
		3184	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3185	makes rev work even on mingw.
		3186
		3187	=item Haskell
		3188
		3189	A haskell binding to libev is available at
		3190	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3191
		3192	=item D
		3193
		3194	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3195	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3196
		3197	=item Ocaml
		3198
		3199	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3200	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3201
		3202	=back
		3203
		3204
		3205	=head1 MACRO MAGIC
		3206
		3207	Libev can be compiled with a variety of options, the most fundamental
		3208	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		3209	functions and callbacks have an initial C<struct ev_loop *> argument.
		3210
		3211	To make it easier to write programs that cope with either variant, the
		3212	following macros are defined:
		3213
		3214	=over 4
		3215
		3216	=item C<EV_A>, C<EV_A_>
		3217
		3218	This provides the loop I<argument> for functions, if one is required ("ev
		3219	loop argument"). The C<EV_A> form is used when this is the sole argument,
		3220	C<EV_A_> is used when other arguments are following. Example:
		3221
		3222	ev_unref (EV_A);
		3223	ev_timer_add (EV_A_ watcher);
		3224	ev_loop (EV_A_ 0);
		3225
		3226	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		3227	which is often provided by the following macro.
		3228
		3229	=item C<EV_P>, C<EV_P_>
		3230
		3231	This provides the loop I<parameter> for functions, if one is required ("ev
		3232	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		3233	C<EV_P_> is used when other parameters are following. Example:
		3234
		3235	// this is how ev_unref is being declared
		3236	static void ev_unref (EV_P);
		3237
		3238	// this is how you can declare your typical callback
		3239	static void cb (EV_P_ ev_timer *w, int revents)
		3240
		3241	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		3242	suitable for use with C<EV_A>.
		3243
		3244	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		3245
		3246	Similar to the other two macros, this gives you the value of the default
		3247	loop, if multiple loops are supported ("ev loop default").
		3248
		3249	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3250
		3251	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3252	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3253	is undefined when the default loop has not been initialised by a previous
		3254	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3255
		3256	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3257	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		3258
		3259	=back
		3260
		3261	Example: Declare and initialise a check watcher, utilising the above
		3262	macros so it will work regardless of whether multiple loops are supported
		3263	or not.
		3264
		3265	static void
		3266	check_cb (EV_P_ ev_timer *w, int revents)
		3267	{
		3268	ev_check_stop (EV_A_ w);
		3269	}
		3270
		3271	ev_check check;
		3272	ev_check_init (&check, check_cb);
		3273	ev_check_start (EV_DEFAULT_ &check);
		3274	ev_loop (EV_DEFAULT_ 0);
		3275
		3276	=head1 EMBEDDING
		3277
		3278	Libev can (and often is) directly embedded into host
		3279	applications. Examples of applications that embed it include the Deliantra
		3280	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		3281	and rxvt-unicode.
		3282
		3283	The goal is to enable you to just copy the necessary files into your
		3284	source directory without having to change even a single line in them, so
		3285	you can easily upgrade by simply copying (or having a checked-out copy of
		3286	libev somewhere in your source tree).
		3287
		3288	=head2 FILESETS
		3289
		3290	Depending on what features you need you need to include one or more sets of files
		3291	in your application.
		3292
		3293	=head3 CORE EVENT LOOP
		3294
		3295	To include only the libev core (all the C<ev_*> functions), with manual
		3296	configuration (no autoconf):
		3297
		3298	#define EV_STANDALONE 1
		3299	#include "ev.c"
		3300
		3301	This will automatically include F<ev.h>, too, and should be done in a
		3302	single C source file only to provide the function implementations. To use
		3303	it, do the same for F<ev.h> in all files wishing to use this API (best
		3304	done by writing a wrapper around F<ev.h> that you can include instead and
		3305	where you can put other configuration options):
		3306
		3307	#define EV_STANDALONE 1
		3308	#include "ev.h"
		3309
		3310	Both header files and implementation files can be compiled with a C++
		3311	compiler (at least, that's a stated goal, and breakage will be treated
		3312	as a bug).
		3313
		3314	You need the following files in your source tree, or in a directory
		3315	in your include path (e.g. in libev/ when using -Ilibev):
		3316
		3317	ev.h
		3318	ev.c
		3319	ev_vars.h
		3320	ev_wrap.h
		3321
		3322	ev_win32.c required on win32 platforms only
		3323
		3324	ev_select.c only when select backend is enabled (which is enabled by default)
		3325	ev_poll.c only when poll backend is enabled (disabled by default)
		3326	ev_epoll.c only when the epoll backend is enabled (disabled by default)
		3327	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		3328	ev_port.c only when the solaris port backend is enabled (disabled by default)
		3329
		3330	F<ev.c> includes the backend files directly when enabled, so you only need
		3331	to compile this single file.
		3332
		3333	=head3 LIBEVENT COMPATIBILITY API
		3334
		3335	To include the libevent compatibility API, also include:
		3336
		3337	#include "event.c"
		3338
		3339	in the file including F<ev.c>, and:
		3340
		3341	#include "event.h"
		3342
		3343	in the files that want to use the libevent API. This also includes F<ev.h>.
		3344
		3345	You need the following additional files for this:
		3346
		3347	event.h
		3348	event.c
		3349
		3350	=head3 AUTOCONF SUPPORT
		3351
		3352	Instead of using C<EV_STANDALONE=1> and providing your configuration in
		3353	whatever way you want, you can also C<m4_include([libev.m4])> in your
		3354	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		3355	include F<config.h> and configure itself accordingly.
		3356
		3357	For this of course you need the m4 file:
		3358
		3359	libev.m4
		3360
		3361	=head2 PREPROCESSOR SYMBOLS/MACROS
		3362
		3363	Libev can be configured via a variety of preprocessor symbols you have to
		3364	define before including any of its files. The default in the absence of
		3365	autoconf is documented for every option.
		3366
		3367	=over 4
		3368
		3369	=item EV_STANDALONE
		3370
		3371	Must always be C<1> if you do not use autoconf configuration, which
		3372	keeps libev from including F<config.h>, and it also defines dummy
		3373	implementations for some libevent functions (such as logging, which is not
		3374	supported). It will also not define any of the structs usually found in
		3375	F<event.h> that are not directly supported by the libev core alone.
		3376
		3377	In stanbdalone mode, libev will still try to automatically deduce the
		3378	configuration, but has to be more conservative.
		3379
		3380	=item EV_USE_MONOTONIC
		3381
		3382	If defined to be C<1>, libev will try to detect the availability of the
		3383	monotonic clock option at both compile time and runtime. Otherwise no
		3384	use of the monotonic clock option will be attempted. If you enable this,
		3385	you usually have to link against librt or something similar. Enabling it
		3386	when the functionality isn't available is safe, though, although you have
		3387	to make sure you link against any libraries where the C<clock_gettime>
		3388	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
		3389
		3390	=item EV_USE_REALTIME
		3391
		3392	If defined to be C<1>, libev will try to detect the availability of the
		3393	real-time clock option at compile time (and assume its availability
		3394	at runtime if successful). Otherwise no use of the real-time clock
		3395	option will be attempted. This effectively replaces C<gettimeofday>
		3396	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
		3397	correctness. See the note about libraries in the description of
		3398	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3399	C<EV_USE_CLOCK_SYSCALL>.
		3400
		3401	=item EV_USE_CLOCK_SYSCALL
		3402
		3403	If defined to be C<1>, libev will try to use a direct syscall instead
		3404	of calling the system-provided C<clock_gettime> function. This option
		3405	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3406	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3407	programs needlessly. Using a direct syscall is slightly slower (in
		3408	theory), because no optimised vdso implementation can be used, but avoids
		3409	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3410	higher, as it simplifies linking (no need for C<-lrt>).
		3411
		3412	=item EV_USE_NANOSLEEP
		3413
		3414	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		3415	and will use it for delays. Otherwise it will use C<select ()>.
		3416
		3417	=item EV_USE_EVENTFD
		3418
		3419	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3420	available and will probe for kernel support at runtime. This will improve
		3421	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3422	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3423	2.7 or newer, otherwise disabled.
		3424
		3425	=item EV_USE_SELECT
		3426
		3427	If undefined or defined to be C<1>, libev will compile in support for the
		3428	C<select>(2) backend. No attempt at auto-detection will be done: if no
		3429	other method takes over, select will be it. Otherwise the select backend
		3430	will not be compiled in.
		3431
		3432	=item EV_SELECT_USE_FD_SET
		3433
		3434	If defined to C<1>, then the select backend will use the system C<fd_set>
		3435	structure. This is useful if libev doesn't compile due to a missing
		3436	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
		3437	on exotic systems. This usually limits the range of file descriptors to
		3438	some low limit such as 1024 or might have other limitations (winsocket
		3439	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
		3440	configures the maximum size of the C<fd_set>.
		3441
		3442	=item EV_SELECT_IS_WINSOCKET
		3443
		3444	When defined to C<1>, the select backend will assume that
		3445	select/socket/connect etc. don't understand file descriptors but
		3446	wants osf handles on win32 (this is the case when the select to
		3447	be used is the winsock select). This means that it will call
		3448	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		3449	it is assumed that all these functions actually work on fds, even
		3450	on win32. Should not be defined on non-win32 platforms.
		3451
		3452	=item EV_FD_TO_WIN32_HANDLE
		3453
		3454	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3455	file descriptors to socket handles. When not defining this symbol (the
		3456	default), then libev will call C<_get_osfhandle>, which is usually
		3457	correct. In some cases, programs use their own file descriptor management,
		3458	in which case they can provide this function to map fds to socket handles.
		3459
		3460	=item EV_USE_POLL
		3461
		3462	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		3463	backend. Otherwise it will be enabled on non-win32 platforms. It
		3464	takes precedence over select.
		3465
		3466	=item EV_USE_EPOLL
		3467
		3468	If defined to be C<1>, libev will compile in support for the Linux
		3469	C<epoll>(7) backend. Its availability will be detected at runtime,
		3470	otherwise another method will be used as fallback. This is the preferred
		3471	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3472	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3473
		3474	=item EV_USE_KQUEUE
		3475
		3476	If defined to be C<1>, libev will compile in support for the BSD style
		3477	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		3478	otherwise another method will be used as fallback. This is the preferred
		3479	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		3480	supports some types of fds correctly (the only platform we found that
		3481	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		3482	not be used unless explicitly requested. The best way to use it is to find
		3483	out whether kqueue supports your type of fd properly and use an embedded
		3484	kqueue loop.
		3485
		3486	=item EV_USE_PORT
		3487
		3488	If defined to be C<1>, libev will compile in support for the Solaris
		3489	10 port style backend. Its availability will be detected at runtime,
		3490	otherwise another method will be used as fallback. This is the preferred
		3491	backend for Solaris 10 systems.
		3492
		3493	=item EV_USE_DEVPOLL
		3494
		3495	Reserved for future expansion, works like the USE symbols above.
		3496
		3497	=item EV_USE_INOTIFY
		3498
		3499	If defined to be C<1>, libev will compile in support for the Linux inotify
		3500	interface to speed up C<ev_stat> watchers. Its actual availability will
		3501	be detected at runtime. If undefined, it will be enabled if the headers
		3502	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3503
		3504	=item EV_ATOMIC_T
		3505
		3506	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3507	access is atomic with respect to other threads or signal contexts. No such
		3508	type is easily found in the C language, so you can provide your own type
		3509	that you know is safe for your purposes. It is used both for signal handler "locking"
		3510	as well as for signal and thread safety in C<ev_async> watchers.
		3511
		3512	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3513	(from F<signal.h>), which is usually good enough on most platforms.
		3514
		3515	=item EV_H
		3516
		3517	The name of the F<ev.h> header file used to include it. The default if
		3518	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
		3519	used to virtually rename the F<ev.h> header file in case of conflicts.
		3520
		3521	=item EV_CONFIG_H
		3522
		3523	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		3524	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		3525	C<EV_H>, above.
		3526
		3527	=item EV_EVENT_H
		3528
		3529	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		3530	of how the F<event.h> header can be found, the default is C<"event.h">.
		3531
		3532	=item EV_PROTOTYPES
		3533
		3534	If defined to be C<0>, then F<ev.h> will not define any function
		3535	prototypes, but still define all the structs and other symbols. This is
		3536	occasionally useful if you want to provide your own wrapper functions
		3537	around libev functions.
		3538
		3539	=item EV_MULTIPLICITY
		3540
		3541	If undefined or defined to C<1>, then all event-loop-specific functions
		3542	will have the C<struct ev_loop *> as first argument, and you can create
		3543	additional independent event loops. Otherwise there will be no support
		3544	for multiple event loops and there is no first event loop pointer
		3545	argument. Instead, all functions act on the single default loop.
		3546
		3547	=item EV_MINPRI
		3548
		3549	=item EV_MAXPRI
		3550
		3551	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		3552	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		3553	provide for more priorities by overriding those symbols (usually defined
		3554	to be C<-2> and C<2>, respectively).
		3555
		3556	When doing priority-based operations, libev usually has to linearly search
		3557	all the priorities, so having many of them (hundreds) uses a lot of space
		3558	and time, so using the defaults of five priorities (-2 .. +2) is usually
		3559	fine.
		3560
		3561	If your embedding application does not need any priorities, defining these
		3562	both to C<0> will save some memory and CPU.
		3563
		3564	=item EV_PERIODIC_ENABLE
		3565
		3566	If undefined or defined to be C<1>, then periodic timers are supported. If
		3567	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3568	code.
		3569
		3570	=item EV_IDLE_ENABLE
		3571
		3572	If undefined or defined to be C<1>, then idle watchers are supported. If
		3573	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3574	code.
		3575
		3576	=item EV_EMBED_ENABLE
		3577
		3578	If undefined or defined to be C<1>, then embed watchers are supported. If
		3579	defined to be C<0>, then they are not. Embed watchers rely on most other
		3580	watcher types, which therefore must not be disabled.
		3581
		3582	=item EV_STAT_ENABLE
		3583
		3584	If undefined or defined to be C<1>, then stat watchers are supported. If
		3585	defined to be C<0>, then they are not.
		3586
		3587	=item EV_FORK_ENABLE
		3588
		3589	If undefined or defined to be C<1>, then fork watchers are supported. If
		3590	defined to be C<0>, then they are not.
		3591
		3592	=item EV_ASYNC_ENABLE
		3593
		3594	If undefined or defined to be C<1>, then async watchers are supported. If
		3595	defined to be C<0>, then they are not.
		3596
		3597	=item EV_MINIMAL
		3598
		3599	If you need to shave off some kilobytes of code at the expense of some
		3600	speed, define this symbol to C<1>. Currently this is used to override some
		3601	inlining decisions, saves roughly 30% code size on amd64. It also selects a
		3602	much smaller 2-heap for timer management over the default 4-heap.
		3603
		3604	=item EV_PID_HASHSIZE
		3605
		3606	C<ev_child> watchers use a small hash table to distribute workload by
		3607	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
		3608	than enough. If you need to manage thousands of children you might want to
		3609	increase this value (I<must> be a power of two).
		3610
		3611	=item EV_INOTIFY_HASHSIZE
		3612
		3613	C<ev_stat> watchers use a small hash table to distribute workload by
		3614	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
		3615	usually more than enough. If you need to manage thousands of C<ev_stat>
		3616	watchers you might want to increase this value (I<must> be a power of
		3617	two).
		3618
		3619	=item EV_USE_4HEAP
		3620
		3621	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3622	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		3623	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		3624	faster performance with many (thousands) of watchers.
		3625
		3626	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3627	(disabled).
		3628
		3629	=item EV_HEAP_CACHE_AT
		3630
		3631	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3632	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		3633	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3634	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3635	but avoids random read accesses on heap changes. This improves performance
		3636	noticeably with many (hundreds) of watchers.
		3637
		3638	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3639	(disabled).
		3640
		3641	=item EV_VERIFY
		3642
		3643	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3644	be done: If set to C<0>, no internal verification code will be compiled
		3645	in. If set to C<1>, then verification code will be compiled in, but not
		3646	called. If set to C<2>, then the internal verification code will be
		3647	called once per loop, which can slow down libev. If set to C<3>, then the
		3648	verification code will be called very frequently, which will slow down
		3649	libev considerably.
		3650
		3651	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3652	C<0>.
		3653
		3654	=item EV_COMMON
		3655
		3656	By default, all watchers have a C<void *data> member. By redefining
		3657	this macro to a something else you can include more and other types of
		3658	members. You have to define it each time you include one of the files,
		3659	though, and it must be identical each time.
		3660
		3661	For example, the perl EV module uses something like this:
		3662
		3663	#define EV_COMMON \
		3664	SV *self; /* contains this struct */ \
		3665	SV *cb_sv, *fh /* note no trailing ";" */
		3666
		3667	=item EV_CB_DECLARE (type)
		3668
		3669	=item EV_CB_INVOKE (watcher, revents)
		3670
		3671	=item ev_set_cb (ev, cb)
		3672
		3673	Can be used to change the callback member declaration in each watcher,
		3674	and the way callbacks are invoked and set. Must expand to a struct member
		3675	definition and a statement, respectively. See the F<ev.h> header file for
		3676	their default definitions. One possible use for overriding these is to
		3677	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		3678	method calls instead of plain function calls in C++.
		3679
		3680	=back
		3681
		3682	=head2 EXPORTED API SYMBOLS
		3683
		3684	If you need to re-export the API (e.g. via a DLL) and you need a list of
		3685	exported symbols, you can use the provided F<Symbol.*> files which list
		3686	all public symbols, one per line:
		3687
		3688	Symbols.ev for libev proper
		3689	Symbols.event for the libevent emulation
		3690
		3691	This can also be used to rename all public symbols to avoid clashes with
		3692	multiple versions of libev linked together (which is obviously bad in
		3693	itself, but sometimes it is inconvenient to avoid this).
		3694
		3695	A sed command like this will create wrapper C<#define>'s that you need to
		3696	include before including F<ev.h>:
		3697
		3698	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		3699
		3700	This would create a file F<wrap.h> which essentially looks like this:
		3701
		3702	#define ev_backend myprefix_ev_backend
		3703	#define ev_check_start myprefix_ev_check_start
		3704	#define ev_check_stop myprefix_ev_check_stop
		3705	...
		3706
		3707	=head2 EXAMPLES
		3708
		3709	For a real-world example of a program the includes libev
		3710	verbatim, you can have a look at the EV perl module
		3711	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		3712	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		3713	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		3714	will be compiled. It is pretty complex because it provides its own header
		3715	file.
		3716
		3717	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		3718	that everybody includes and which overrides some configure choices:
		3719
		3720	#define EV_MINIMAL 1
		3721	#define EV_USE_POLL 0
		3722	#define EV_MULTIPLICITY 0
		3723	#define EV_PERIODIC_ENABLE 0
		3724	#define EV_STAT_ENABLE 0
		3725	#define EV_FORK_ENABLE 0
		3726	#define EV_CONFIG_H <config.h>
		3727	#define EV_MINPRI 0
		3728	#define EV_MAXPRI 0
		3729
		3730	#include "ev++.h"
		3731
		3732	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		3733
		3734	#include "ev_cpp.h"
		3735	#include "ev.c"
		3736
		3737	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
		3738
		3739	=head2 THREADS AND COROUTINES
		3740
		3741	=head3 THREADS
		3742
		3743	All libev functions are reentrant and thread-safe unless explicitly
		3744	documented otherwise, but libev implements no locking itself. This means
		3745	that you can use as many loops as you want in parallel, as long as there
		3746	are no concurrent calls into any libev function with the same loop
		3747	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		3748	of course): libev guarantees that different event loops share no data
		3749	structures that need any locking.
		3750
		3751	Or to put it differently: calls with different loop parameters can be done
		3752	concurrently from multiple threads, calls with the same loop parameter
		3753	must be done serially (but can be done from different threads, as long as
		3754	only one thread ever is inside a call at any point in time, e.g. by using
		3755	a mutex per loop).
		3756
		3757	Specifically to support threads (and signal handlers), libev implements
		3758	so-called C<ev_async> watchers, which allow some limited form of
		3759	concurrency on the same event loop, namely waking it up "from the
		3760	outside".
		3761
		3762	If you want to know which design (one loop, locking, or multiple loops
		3763	without or something else still) is best for your problem, then I cannot
		3764	help you, but here is some generic advice:
		3765
		3766	=over 4
		3767
		3768	=item * most applications have a main thread: use the default libev loop
		3769	in that thread, or create a separate thread running only the default loop.
		3770
		3771	This helps integrating other libraries or software modules that use libev
		3772	themselves and don't care/know about threading.
		3773
		3774	=item * one loop per thread is usually a good model.
		3775
		3776	Doing this is almost never wrong, sometimes a better-performance model
		3777	exists, but it is always a good start.
		3778
		3779	=item * other models exist, such as the leader/follower pattern, where one
		3780	loop is handed through multiple threads in a kind of round-robin fashion.
		3781
		3782	Choosing a model is hard - look around, learn, know that usually you can do
		3783	better than you currently do :-)
		3784
		3785	=item * often you need to talk to some other thread which blocks in the
		3786	event loop.
		3787
		3788	C<ev_async> watchers can be used to wake them up from other threads safely
		3789	(or from signal contexts...).
		3790
		3791	An example use would be to communicate signals or other events that only
		3792	work in the default loop by registering the signal watcher with the
		3793	default loop and triggering an C<ev_async> watcher from the default loop
		3794	watcher callback into the event loop interested in the signal.
		3795
		3796	=back
		3797
		3798	=head3 COROUTINES
		3799
		3800	Libev is very accommodating to coroutines ("cooperative threads"):
		3801	libev fully supports nesting calls to its functions from different
		3802	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3803	different coroutines, and switch freely between both coroutines running the
		3804	loop, as long as you don't confuse yourself). The only exception is that
		3805	you must not do this from C<ev_periodic> reschedule callbacks.
		3806
		3807	Care has been taken to ensure that libev does not keep local state inside
		3808	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		3809	they do not call any callbacks.
		3810
		3811	=head2 COMPILER WARNINGS
		3812
		3813	Depending on your compiler and compiler settings, you might get no or a
		3814	lot of warnings when compiling libev code. Some people are apparently
		3815	scared by this.
		3816
		3817	However, these are unavoidable for many reasons. For one, each compiler
		3818	has different warnings, and each user has different tastes regarding
		3819	warning options. "Warn-free" code therefore cannot be a goal except when
		3820	targeting a specific compiler and compiler-version.
		3821
		3822	Another reason is that some compiler warnings require elaborate
		3823	workarounds, or other changes to the code that make it less clear and less
		3824	maintainable.
		3825
		3826	And of course, some compiler warnings are just plain stupid, or simply
		3827	wrong (because they don't actually warn about the condition their message
		3828	seems to warn about). For example, certain older gcc versions had some
		3829	warnings that resulted an extreme number of false positives. These have
		3830	been fixed, but some people still insist on making code warn-free with
		3831	such buggy versions.
		3832
		3833	While libev is written to generate as few warnings as possible,
		3834	"warn-free" code is not a goal, and it is recommended not to build libev
		3835	with any compiler warnings enabled unless you are prepared to cope with
		3836	them (e.g. by ignoring them). Remember that warnings are just that:
		3837	warnings, not errors, or proof of bugs.
		3838
		3839
		3840	=head2 VALGRIND
		3841
		3842	Valgrind has a special section here because it is a popular tool that is
		3843	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		3844
		3845	If you think you found a bug (memory leak, uninitialised data access etc.)
		3846	in libev, then check twice: If valgrind reports something like:
		3847
		3848	==2274== definitely lost: 0 bytes in 0 blocks.
		3849	==2274== possibly lost: 0 bytes in 0 blocks.
		3850	==2274== still reachable: 256 bytes in 1 blocks.
		3851
		3852	Then there is no memory leak, just as memory accounted to global variables
		3853	is not a memleak - the memory is still being referenced, and didn't leak.
		3854
		3855	Similarly, under some circumstances, valgrind might report kernel bugs
		3856	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		3857	although an acceptable workaround has been found here), or it might be
		3858	confused.
		3859
		3860	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		3861	make it into some kind of religion.
		3862
		3863	If you are unsure about something, feel free to contact the mailing list
		3864	with the full valgrind report and an explanation on why you think this
		3865	is a bug in libev (best check the archives, too :). However, don't be
		3866	annoyed when you get a brisk "this is no bug" answer and take the chance
		3867	of learning how to interpret valgrind properly.
		3868
		3869	If you need, for some reason, empty reports from valgrind for your project
		3870	I suggest using suppression lists.
		3871
		3872
		3873	=head1 PORTABILITY NOTES
		3874
		3875	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		3876
		3877	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		3878	requires, and its I/O model is fundamentally incompatible with the POSIX
		3879	model. Libev still offers limited functionality on this platform in
		3880	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		3881	descriptors. This only applies when using Win32 natively, not when using
		3882	e.g. cygwin.
		3883
		3884	Lifting these limitations would basically require the full
		3885	re-implementation of the I/O system. If you are into these kinds of
		3886	things, then note that glib does exactly that for you in a very portable
		3887	way (note also that glib is the slowest event library known to man).
		3888
		3889	There is no supported compilation method available on windows except
		3890	embedding it into other applications.
		3891
		3892	Not a libev limitation but worth mentioning: windows apparently doesn't
		3893	accept large writes: instead of resulting in a partial write, windows will
		3894	either accept everything or return C<ENOBUFS> if the buffer is too large,
		3895	so make sure you only write small amounts into your sockets (less than a
		3896	megabyte seems safe, but this apparently depends on the amount of memory
		3897	available).
		3898
		3899	Due to the many, low, and arbitrary limits on the win32 platform and
		3900	the abysmal performance of winsockets, using a large number of sockets
		3901	is not recommended (and not reasonable). If your program needs to use
		3902	more than a hundred or so sockets, then likely it needs to use a totally
		3903	different implementation for windows, as libev offers the POSIX readiness
		3904	notification model, which cannot be implemented efficiently on windows
		3905	(Microsoft monopoly games).
		3906
		3907	A typical way to use libev under windows is to embed it (see the embedding
		3908	section for details) and use the following F<evwrap.h> header file instead
		3909	of F<ev.h>:
		3910
		3911	#define EV_STANDALONE /* keeps ev from requiring config.h */
		3912	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		3913
		3914	#include "ev.h"
		3915
		3916	And compile the following F<evwrap.c> file into your project (make sure
		3917	you do I<not> compile the F<ev.c> or any other embedded source files!):
		3918
		3919	#include "evwrap.h"
		3920	#include "ev.c"
		3921
		3922	=over 4
		3923
		3924	=item The winsocket select function
		3925
		3926	The winsocket C<select> function doesn't follow POSIX in that it
		3927	requires socket I<handles> and not socket I<file descriptors> (it is
		3928	also extremely buggy). This makes select very inefficient, and also
		3929	requires a mapping from file descriptors to socket handles (the Microsoft
		3930	C runtime provides the function C<_open_osfhandle> for this). See the
		3931	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		3932	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		3933
		3934	The configuration for a "naked" win32 using the Microsoft runtime
		3935	libraries and raw winsocket select is:
		3936
		3937	#define EV_USE_SELECT 1
		3938	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		3939
		3940	Note that winsockets handling of fd sets is O(n), so you can easily get a
		3941	complexity in the O(n²) range when using win32.
		3942
		3943	=item Limited number of file descriptors
		3944
		3945	Windows has numerous arbitrary (and low) limits on things.
		3946
		3947	Early versions of winsocket's select only supported waiting for a maximum
		3948	of C<64> handles (probably owning to the fact that all windows kernels
		3949	can only wait for C<64> things at the same time internally; Microsoft
		3950	recommends spawning a chain of threads and wait for 63 handles and the
		3951	previous thread in each. Great).
		3952
		3953	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		3954	to some high number (e.g. C<2048>) before compiling the winsocket select
		3955	call (which might be in libev or elsewhere, for example, perl does its own
		3956	select emulation on windows).
		3957
		3958	Another limit is the number of file descriptors in the Microsoft runtime
		3959	libraries, which by default is C<64> (there must be a hidden I<64> fetish
		3960	or something like this inside Microsoft). You can increase this by calling
		3961	C<_setmaxstdio>, which can increase this limit to C<2048> (another
		3962	arbitrary limit), but is broken in many versions of the Microsoft runtime
		3963	libraries.
		3964
		3965	This might get you to about C<512> or C<2048> sockets (depending on
		3966	windows version and/or the phase of the moon). To get more, you need to
		3967	wrap all I/O functions and provide your own fd management, but the cost of
		3968	calling select (O(n²)) will likely make this unworkable.
		3969
		3970	=back
		3971
		3972	=head2 PORTABILITY REQUIREMENTS
		3973
		3974	In addition to a working ISO-C implementation and of course the
		3975	backend-specific APIs, libev relies on a few additional extensions:
		3976
		3977	=over 4
		3978
		3979	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		3980	calling conventions regardless of C<ev_watcher_type *>.
		3981
		3982	Libev assumes not only that all watcher pointers have the same internal
		3983	structure (guaranteed by POSIX but not by ISO C for example), but it also
		3984	assumes that the same (machine) code can be used to call any watcher
		3985	callback: The watcher callbacks have different type signatures, but libev
		3986	calls them using an C<ev_watcher *> internally.
		3987
		3988	=item C<sig_atomic_t volatile> must be thread-atomic as well
		3989
		3990	The type C<sig_atomic_t volatile> (or whatever is defined as
		3991	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		3992	threads. This is not part of the specification for C<sig_atomic_t>, but is
		3993	believed to be sufficiently portable.
		3994
		3995	=item C<sigprocmask> must work in a threaded environment
		3996
		3997	Libev uses C<sigprocmask> to temporarily block signals. This is not
		3998	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		3999	pthread implementations will either allow C<sigprocmask> in the "main
		4000	thread" or will block signals process-wide, both behaviours would
		4001	be compatible with libev. Interaction between C<sigprocmask> and
		4002	C<pthread_sigmask> could complicate things, however.
		4003
		4004	The most portable way to handle signals is to block signals in all threads
		4005	except the initial one, and run the default loop in the initial thread as
		4006	well.
		4007
		4008	=item C<long> must be large enough for common memory allocation sizes
		4009
		4010	To improve portability and simplify its API, libev uses C<long> internally
		4011	instead of C<size_t> when allocating its data structures. On non-POSIX
		4012	systems (Microsoft...) this might be unexpectedly low, but is still at
		4013	least 31 bits everywhere, which is enough for hundreds of millions of
		4014	watchers.
		4015
		4016	=item C<double> must hold a time value in seconds with enough accuracy
		4017
		4018	The type C<double> is used to represent timestamps. It is required to
		4019	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		4020	enough for at least into the year 4000. This requirement is fulfilled by
		4021	implementations implementing IEEE 754 (basically all existing ones).
		4022
		4023	=back
		4024
		4025	If you know of other additional requirements drop me a note.
		4026
		4027
		4028	=head1 ALGORITHMIC COMPLEXITIES
		4029
		4030	In this section the complexities of (many of) the algorithms used inside
		4031	libev will be documented. For complexity discussions about backends see
		4032	the documentation for C<ev_default_init>.
		4033
		4034	All of the following are about amortised time: If an array needs to be
		4035	extended, libev needs to realloc and move the whole array, but this
		4036	happens asymptotically rarer with higher number of elements, so O(1) might
		4037	mean that libev does a lengthy realloc operation in rare cases, but on
		4038	average it is much faster and asymptotically approaches constant time.
		4039
		4040	=over 4
		4041
		4042	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		4043
		4044	This means that, when you have a watcher that triggers in one hour and
		4045	there are 100 watchers that would trigger before that, then inserting will
		4046	have to skip roughly seven (C<ld 100>) of these watchers.
		4047
		4048	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		4049
		4050	That means that changing a timer costs less than removing/adding them,
		4051	as only the relative motion in the event queue has to be paid for.
		4052
		4053	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		4054
		4055	These just add the watcher into an array or at the head of a list.
		4056
		4057	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		4058
		4059	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		4060
		4061	These watchers are stored in lists, so they need to be walked to find the
		4062	correct watcher to remove. The lists are usually short (you don't usually
		4063	have many watchers waiting for the same fd or signal: one is typical, two
		4064	is rare).
		4065
		4066	=item Finding the next timer in each loop iteration: O(1)
		4067
		4068	By virtue of using a binary or 4-heap, the next timer is always found at a
		4069	fixed position in the storage array.
		4070
		4071	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		4072
		4073	A change means an I/O watcher gets started or stopped, which requires
		4074	libev to recalculate its status (and possibly tell the kernel, depending
		4075	on backend and whether C<ev_io_set> was used).
		4076
		4077	=item Activating one watcher (putting it into the pending state): O(1)
		4078
		4079	=item Priority handling: O(number_of_priorities)
		4080
		4081	Priorities are implemented by allocating some space for each
		4082	priority. When doing priority-based operations, libev usually has to
		4083	linearly search all the priorities, but starting/stopping and activating
		4084	watchers becomes O(1) with respect to priority handling.
		4085
		4086	=item Sending an ev_async: O(1)
		4087
		4088	=item Processing ev_async_send: O(number_of_async_watchers)
		4089
		4090	=item Processing signals: O(max_signal_number)
		4091
		4092	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4093	calls in the current loop iteration. Checking for async and signal events
		4094	involves iterating over all running async watchers or all signal numbers.
		4095
		4096	=back
		4097
		4098
		4099	=head1 GLOSSARY
		4100
		4101	=over 4
		4102
		4103	=item active
		4104
		4105	A watcher is active as long as it has been started (has been attached to
		4106	an event loop) but not yet stopped (disassociated from the event loop).
		4107
		4108	=item application
		4109
		4110	In this document, an application is whatever is using libev.
		4111
		4112	=item callback
		4113
		4114	The address of a function that is called when some event has been
		4115	detected. Callbacks are being passed the event loop, the watcher that
		4116	received the event, and the actual event bitset.
		4117
		4118	=item callback invocation
		4119
		4120	The act of calling the callback associated with a watcher.
		4121
		4122	=item event
		4123
		4124	A change of state of some external event, such as data now being available
		4125	for reading on a file descriptor, time having passed or simply not having
		4126	any other events happening anymore.
		4127
		4128	In libev, events are represented as single bits (such as C<EV_READ> or
		4129	C<EV_TIMEOUT>).
		4130
		4131	=item event library
		4132
		4133	A software package implementing an event model and loop.
		4134
		4135	=item event loop
		4136
		4137	An entity that handles and processes external events and converts them
		4138	into callback invocations.
		4139
		4140	=item event model
		4141
		4142	The model used to describe how an event loop handles and processes
		4143	watchers and events.
		4144
		4145	=item pending
		4146
		4147	A watcher is pending as soon as the corresponding event has been detected,
		4148	and stops being pending as soon as the watcher will be invoked or its
		4149	pending status is explicitly cleared by the application.
		4150
		4151	A watcher can be pending, but not active. Stopping a watcher also clears
		4152	its pending status.
		4153
		4154	=item real time
		4155
		4156	The physical time that is observed. It is apparently strictly monotonic :)
		4157
		4158	=item wall-clock time
		4159
		4160	The time and date as shown on clocks. Unlike real time, it can actually
		4161	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4162	clock.
		4163
		4164	=item watcher
		4165
		4166	A data structure that describes interest in certain events. Watchers need
		4167	to be started (attached to an event loop) before they can receive events.
		4168
		4169	=item watcher invocation
		4170
		4171	The act of calling the callback associated with a watcher.
		4172
		4173	=back
878		4174
879	=head1 AUTHOR	4175	=head1 AUTHOR
880		4176
881	Marc Lehmann <libev@schmorp.de>.	4177	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
882		4178

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