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Revision 1.258 by root, Wed Jul 15 16:58:53 2009 UTC

…		…
2		2
3	libev - a high performance full-featured event loop written in C	3	libev - a high performance full-featured event loop written in C
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
8		8
9	=head1 DESCRIPTION	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	}
		66
		67	=head1 ABOUT THIS DOCUMENT
		68
		69	This document documents the libev software package.
		70
		71	The newest version of this document is also available as an html-formatted
		72	web page you might find easier to navigate when reading it for the first
		73	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		74
		75	While this document tries to be as complete as possible in documenting
		76	libev, its usage and the rationale behind its design, it is not a tutorial
		77	on event-based programming, nor will it introduce event-based programming
		78	with libev.
		79
		80	Familarity with event based programming techniques in general is assumed
		81	throughout this document.
		82
		83	=head1 ABOUT LIBEV
10		84
11	Libev is an event loop: you register interest in certain events (such as a	85	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	86	file descriptor being readable or a timeout occurring), and it will manage
13	these event sources and provide your program with events.	87	these event sources and provide your program with events.
14		88
15	To do this, it must take more or less complete control over your process	89	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	90	(or thread) by executing the I<event loop> handler, and will then
17	communicate events via a callback mechanism.	91	communicate events via a callback mechanism.
…		…
19	You register interest in certain events by registering so-called I<event	93	You register interest in certain events by registering so-called I<event
20	watchers>, which are relatively small C structures you initialise with the	94	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	95	details of the event, and then hand it over to libev by I<starting> the
22	watcher.	96	watcher.
23		97
24	=head1 FEATURES	98	=head2 FEATURES
25		99
26	Libev supports select, poll, the linux-specific epoll and the bsd-specific	100	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
27	kqueue mechanisms for file descriptor events, relative timers, absolute	101	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
28	timers with customised rescheduling, signal events, process status change	102	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
29	events (related to SIGCHLD), and event watchers dealing with the event	103	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
30	loop mechanism itself (idle, prepare and check watchers). It also is quite	104	with customised rescheduling (C<ev_periodic>), synchronous signals
		105	(C<ev_signal>), process status change events (C<ev_child>), and event
		106	watchers dealing with the event loop mechanism itself (C<ev_idle>,
		107	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as
		108	file watchers (C<ev_stat>) and even limited support for fork events
		109	(C<ev_fork>).
		110
		111	It also is quite fast (see this
31	fast (see this L<benchmark|http://libev.schmorp.de/bench.html> comparing	112	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
32	it to libevent for example).	113	for example).
33		114
34	=head1 CONVENTIONS	115	=head2 CONVENTIONS
35		116
36	Libev is very configurable. In this manual the default configuration	117	Libev is very configurable. In this manual the default (and most common)
37	will be described, which supports multiple event loops. For more info	118	configuration will be described, which supports multiple event loops. For
38	about various configuration options please have a look at the file	119	more info about various configuration options please have a look at
39	F<README.embed> in the libev distribution. If libev was configured without	120	B<EMBED> section in this manual. If libev was configured without support
40	support for multiple event loops, then all functions taking an initial	121	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 *>)	122	name C<loop> (which is always of type C<ev_loop *>) will not have
42	will not have this argument.	123	this argument.
43		124
44	=head1 TIME REPRESENTATION	125	=head2 TIME REPRESENTATION
45		126
46	Libev represents time as a single floating point number, representing the	127	Libev represents time as a single floating point number, representing
47	(fractional) number of seconds since the (POSIX) epoch (somewhere near	128	the (fractional) number of seconds since the (POSIX) epoch (somewhere
48	the beginning of 1970, details are complicated, don't ask). This type is	129	near the beginning of 1970, details are complicated, don't ask). This
49	called C<ev_tstamp>, which is what you should use too. It usually aliases	130	type is called C<ev_tstamp>, which is what you should use too. It usually
50	to the C<double> type in C, and when you need to do any calculations on	131	aliases to the C<double> type in C. When you need to do any calculations
51	it, you should treat it as such.	132	on it, you should treat it as some floating point value. Unlike the name
		133	component C<stamp> might indicate, it is also used for time differences
		134	throughout libev.
		135
		136	=head1 ERROR HANDLING
		137
		138	Libev knows three classes of errors: operating system errors, usage errors
		139	and internal errors (bugs).
		140
		141	When libev catches an operating system error it cannot handle (for example
		142	a system call indicating a condition libev cannot fix), it calls the callback
		143	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		144	abort. The default is to print a diagnostic message and to call C<abort
		145	()>.
		146
		147	When libev detects a usage error such as a negative timer interval, then
		148	it will print a diagnostic message and abort (via the C<assert> mechanism,
		149	so C<NDEBUG> will disable this checking): these are programming errors in
		150	the libev caller and need to be fixed there.
		151
		152	Libev also has a few internal error-checking C<assert>ions, and also has
		153	extensive consistency checking code. These do not trigger under normal
		154	circumstances, as they indicate either a bug in libev or worse.
52		155
53		156
54	=head1 GLOBAL FUNCTIONS	157	=head1 GLOBAL FUNCTIONS
55		158
56	These functions can be called anytime, even before initialising the	159	These functions can be called anytime, even before initialising the
…		…
62		165
63	Returns the current time as libev would use it. Please note that the	166	Returns the current time as libev would use it. Please note that the
64	C<ev_now> function is usually faster and also often returns the timestamp	167	C<ev_now> function is usually faster and also often returns the timestamp
65	you actually want to know.	168	you actually want to know.
66		169
		170	=item ev_sleep (ev_tstamp interval)
		171
		172	Sleep for the given interval: The current thread will be blocked until
		173	either it is interrupted or the given time interval has passed. Basically
		174	this is a sub-second-resolution C<sleep ()>.
		175
67	=item int ev_version_major ()	176	=item int ev_version_major ()
68		177
69	=item int ev_version_minor ()	178	=item int ev_version_minor ()
70		179
71	You can find out the major and minor version numbers of the library	180	You can find out the major and minor ABI version numbers of the library
72	you linked against by calling the functions C<ev_version_major> and	181	you linked against by calling the functions C<ev_version_major> and
73	C<ev_version_minor>. If you want, you can compare against the global	182	C<ev_version_minor>. If you want, you can compare against the global
74	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the	183	symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
75	version of the library your program was compiled against.	184	version of the library your program was compiled against.
76		185
		186	These version numbers refer to the ABI version of the library, not the
		187	release version.
		188
77	Usually, it's a good idea to terminate if the major versions mismatch,	189	Usually, it's a good idea to terminate if the major versions mismatch,
78	as this indicates an incompatible change. Minor versions are usually	190	as this indicates an incompatible change. Minor versions are usually
79	compatible to older versions, so a larger minor version alone is usually	191	compatible to older versions, so a larger minor version alone is usually
80	not a problem.	192	not a problem.
81		193
82	Example: make sure we haven't accidentally been linked against the wrong	194	Example: Make sure we haven't accidentally been linked against the wrong
83	version:	195	version.
84		196
85	assert (("libev version mismatch",	197	assert (("libev version mismatch",
86	ev_version_major () == EV_VERSION_MAJOR	198	ev_version_major () == EV_VERSION_MAJOR
87	&& ev_version_minor () >= EV_VERSION_MINOR));	199	&& ev_version_minor () >= EV_VERSION_MINOR));
88		200
89	=item unsigned int ev_supported_backends ()	201	=item unsigned int ev_supported_backends ()
90		202
91	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	203	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
92	value) compiled into this binary of libev (independent of their	204	value) compiled into this binary of libev (independent of their
…		…
94	a description of the set values.	206	a description of the set values.
95		207
96	Example: make sure we have the epoll method, because yeah this is cool and	208	Example: make sure we have the epoll method, because yeah this is cool and
97	a must have and can we have a torrent of it please!!!11	209	a must have and can we have a torrent of it please!!!11
98		210
99	assert (("sorry, no epoll, no sex",	211	assert (("sorry, no epoll, no sex",
100	ev_supported_backends () & EVBACKEND_EPOLL));	212	ev_supported_backends () & EVBACKEND_EPOLL));
101		213
102	=item unsigned int ev_recommended_backends ()	214	=item unsigned int ev_recommended_backends ()
103		215
104	Return the set of all backends compiled into this binary of libev and also	216	Return the set of all backends compiled into this binary of libev and also
105	recommended for this platform. This set is often smaller than the one	217	recommended for this platform. This set is often smaller than the one
106	returned by C<ev_supported_backends>, as for example kqueue is broken on	218	returned by C<ev_supported_backends>, as for example kqueue is broken on
107	most BSDs and will not be autodetected unless you explicitly request it	219	most BSDs and will not be auto-detected unless you explicitly request it
108	(assuming you know what you are doing). This is the set of backends that	220	(assuming you know what you are doing). This is the set of backends that
109	libev will probe for if you specify no backends explicitly.	221	libev will probe for if you specify no backends explicitly.
110		222
111	=item unsigned int ev_embeddable_backends ()	223	=item unsigned int ev_embeddable_backends ()
112		224
…		…
116	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	228	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
117	recommended ones.	229	recommended ones.
118		230
119	See the description of C<ev_embed> watchers for more info.	231	See the description of C<ev_embed> watchers for more info.
120		232
121	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	233	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
122		234
123	Sets the allocation function to use (the prototype is similar to the	235	Sets the allocation function to use (the prototype is similar - the
124	realloc C function, the semantics are identical). It is used to allocate	236	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
125	and free memory (no surprises here). If it returns zero when memory	237	used to allocate and free memory (no surprises here). If it returns zero
126	needs to be allocated, the library might abort or take some potentially	238	when memory needs to be allocated (C<size != 0>), the library might abort
127	destructive action. The default is your system realloc function.	239	or take some potentially destructive action.
		240
		241	Since some systems (at least OpenBSD and Darwin) fail to implement
		242	correct C<realloc> semantics, libev will use a wrapper around the system
		243	C<realloc> and C<free> functions by default.
128		244
129	You could override this function in high-availability programs to, say,	245	You could override this function in high-availability programs to, say,
130	free some memory if it cannot allocate memory, to use a special allocator,	246	free some memory if it cannot allocate memory, to use a special allocator,
131	or even to sleep a while and retry until some memory is available.	247	or even to sleep a while and retry until some memory is available.
132		248
133	Example: replace the libev allocator with one that waits a bit and then	249	Example: Replace the libev allocator with one that waits a bit and then
134	retries: better than mine).	250	retries (example requires a standards-compliant C<realloc>).
135		251
136	static void *	252	static void *
137	persistent_realloc (void *ptr, long size)	253	persistent_realloc (void *ptr, size_t size)
138	{	254	{
139	for (;;)	255	for (;;)
140	{	256	{
141	void *newptr = realloc (ptr, size);	257	void *newptr = realloc (ptr, size);
142		258
…		…
148	}	264	}
149		265
150	...	266	...
151	ev_set_allocator (persistent_realloc);	267	ev_set_allocator (persistent_realloc);
152		268
153	=item ev_set_syserr_cb (void (*cb)(const char *msg));	269	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
154		270
155	Set the callback function to call on a retryable syscall error (such	271	Set the callback function to call on a retryable system call error (such
156	as failed select, poll, epoll_wait). The message is a printable string	272	as failed select, poll, epoll_wait). The message is a printable string
157	indicating the system call or subsystem causing the problem. If this	273	indicating the system call or subsystem causing the problem. If this
158	callback is set, then libev will expect it to remedy the sitution, no	274	callback is set, then libev will expect it to remedy the situation, no
159	matter what, when it returns. That is, libev will generally retry the	275	matter what, when it returns. That is, libev will generally retry the
160	requested operation, or, if the condition doesn't go away, do bad stuff	276	requested operation, or, if the condition doesn't go away, do bad stuff
161	(such as abort).	277	(such as abort).
162		278
163	Example: do the same thing as libev does internally:	279	Example: This is basically the same thing that libev does internally, too.
164		280
165	static void	281	static void
166	fatal_error (const char *msg)	282	fatal_error (const char *msg)
167	{	283	{
168	perror (msg);	284	perror (msg);
…		…
174		290
175	=back	291	=back
176		292
177	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	293	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
178		294
179	An event loop is described by a C<struct ev_loop *>. The library knows two	295	An event loop is described by a C<struct ev_loop *> (the C<struct>
180	types of such loops, the I<default> loop, which supports signals and child	296	is I<not> optional in this case, as there is also an C<ev_loop>
181	events, and dynamically created loops which do not.	297	I<function>).
182		298
183	If you use threads, a common model is to run the default event loop	299	The library knows two types of such loops, the I<default> loop, which
184	in your main thread (or in a separate thread) and for each thread you	300	supports signals and child events, and dynamically created loops which do
185	create, you also create another event loop. Libev itself does no locking	301	not.
186	whatsoever, so if you mix calls to the same event loop in different
187	threads, make sure you lock (this is usually a bad idea, though, even if
188	done correctly, because it's hideous and inefficient).
189		302
190	=over 4	303	=over 4
191		304
192	=item struct ev_loop *ev_default_loop (unsigned int flags)	305	=item struct ev_loop *ev_default_loop (unsigned int flags)
193		306
…		…
197	flags. If that is troubling you, check C<ev_backend ()> afterwards).	310	flags. If that is troubling you, check C<ev_backend ()> afterwards).
198		311
199	If you don't know what event loop to use, use the one returned from this	312	If you don't know what event loop to use, use the one returned from this
200	function.	313	function.
201		314
		315	Note that this function is I<not> thread-safe, so if you want to use it
		316	from multiple threads, you have to lock (note also that this is unlikely,
		317	as loops cannot be shared easily between threads anyway).
		318
		319	The default loop is the only loop that can handle C<ev_signal> and
		320	C<ev_child> watchers, and to do this, it always registers a handler
		321	for C<SIGCHLD>. If this is a problem for your application you can either
		322	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
		323	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
		324	C<ev_default_init>.
		325
202	The flags argument can be used to specify special behaviour or specific	326	The flags argument can be used to specify special behaviour or specific
203	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	327	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
204		328
205	The following flags are supported:	329	The following flags are supported:
206		330
…		…
211	The default flags value. Use this if you have no clue (it's the right	335	The default flags value. Use this if you have no clue (it's the right
212	thing, believe me).	336	thing, believe me).
213		337
214	=item C<EVFLAG_NOENV>	338	=item C<EVFLAG_NOENV>
215		339
216	If this flag bit is ored into the flag value (or the program runs setuid	340	If this flag bit is or'ed into the flag value (or the program runs setuid
217	or setgid) then libev will I<not> look at the environment variable	341	or setgid) then libev will I<not> look at the environment variable
218	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	342	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
219	override the flags completely if it is found in the environment. This is	343	override the flags completely if it is found in the environment. This is
220	useful to try out specific backends to test their performance, or to work	344	useful to try out specific backends to test their performance, or to work
221	around bugs.	345	around bugs.
222		346
		347	=item C<EVFLAG_FORKCHECK>
		348
		349	Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after
		350	a fork, you can also make libev check for a fork in each iteration by
		351	enabling this flag.
		352
		353	This works by calling C<getpid ()> on every iteration of the loop,
		354	and thus this might slow down your event loop if you do a lot of loop
		355	iterations and little real work, but is usually not noticeable (on my
		356	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
		357	without a system call and thus I<very> fast, but my GNU/Linux system also has
		358	C<pthread_atfork> which is even faster).
		359
		360	The big advantage of this flag is that you can forget about fork (and
		361	forget about forgetting to tell libev about forking) when you use this
		362	flag.
		363
		364	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
		365	environment variable.
		366
223	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	367	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
224		368
225	This is your standard select(2) backend. Not I<completely> standard, as	369	This is your standard select(2) backend. Not I<completely> standard, as
226	libev tries to roll its own fd_set with no limits on the number of fds,	370	libev tries to roll its own fd_set with no limits on the number of fds,
227	but if that fails, expect a fairly low limit on the number of fds when	371	but if that fails, expect a fairly low limit on the number of fds when
228	using this backend. It doesn't scale too well (O(highest_fd)), but its usually	372	using this backend. It doesn't scale too well (O(highest_fd)), but its
229	the fastest backend for a low number of fds.	373	usually the fastest backend for a low number of (low-numbered :) fds.
		374
		375	To get good performance out of this backend you need a high amount of
		376	parallelism (most of the file descriptors should be busy). If you are
		377	writing a server, you should C<accept ()> in a loop to accept as many
		378	connections as possible during one iteration. You might also want to have
		379	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		380	readiness notifications you get per iteration.
		381
		382	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		383	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		384	C<exceptfds> set on that platform).
230		385
231	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	386	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
232		387
233	And this is your standard poll(2) backend. It's more complicated than	388	And this is your standard poll(2) backend. It's more complicated
234	select, but handles sparse fds better and has no artificial limit on the	389	than select, but handles sparse fds better and has no artificial
235	number of fds you can use (except it will slow down considerably with a	390	limit on the number of fds you can use (except it will slow down
236	lot of inactive fds). It scales similarly to select, i.e. O(total_fds).	391	considerably with a lot of inactive fds). It scales similarly to select,
		392	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		393	performance tips.
		394
		395	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		396	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
237		397
238	=item C<EVBACKEND_EPOLL> (value 4, Linux)	398	=item C<EVBACKEND_EPOLL> (value 4, Linux)
239		399
240	For few fds, this backend is a bit little slower than poll and select,	400	For few fds, this backend is a bit little slower than poll and select,
241	but it scales phenomenally better. While poll and select usually scale like	401	but it scales phenomenally better. While poll and select usually scale
242	O(total_fds) where n is the total number of fds (or the highest fd), epoll scales	402	like O(total_fds) where n is the total number of fds (or the highest fd),
243	either O(1) or O(active_fds).	403	epoll scales either O(1) or O(active_fds).
244		404
		405	The epoll mechanism deserves honorable mention as the most misdesigned
		406	of the more advanced event mechanisms: mere annoyances include silently
		407	dropping file descriptors, requiring a system call per change per file
		408	descriptor (and unnecessary guessing of parameters), problems with dup and
		409	so on. The biggest issue is fork races, however - if a program forks then
		410	I<both> parent and child process have to recreate the epoll set, which can
		411	take considerable time (one syscall per file descriptor) and is of course
		412	hard to detect.
		413
		414	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		415	of course I<doesn't>, and epoll just loves to report events for totally
		416	I<different> file descriptors (even already closed ones, so one cannot
		417	even remove them from the set) than registered in the set (especially
		418	on SMP systems). Libev tries to counter these spurious notifications by
		419	employing an additional generation counter and comparing that against the
		420	events to filter out spurious ones, recreating the set when required.
		421
245	While stopping and starting an I/O watcher in the same iteration will	422	While stopping, setting and starting an I/O watcher in the same iteration
246	result in some caching, there is still a syscall per such incident	423	will result in some caching, there is still a system call per such
247	(because the fd could point to a different file description now), so its	424	incident (because the same I<file descriptor> could point to a different
248	best to avoid that. Also, dup()ed file descriptors might not work very	425	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
249	well if you register events for both fds.	426	file descriptors might not work very well if you register events for both
		427	file descriptors.
250		428
251	Please note that epoll sometimes generates spurious notifications, so you	429	Best performance from this backend is achieved by not unregistering all
252	need to use non-blocking I/O or other means to avoid blocking when no data	430	watchers for a file descriptor until it has been closed, if possible,
253	(or space) is available.	431	i.e. keep at least one watcher active per fd at all times. Stopping and
		432	starting a watcher (without re-setting it) also usually doesn't cause
		433	extra overhead. A fork can both result in spurious notifications as well
		434	as in libev having to destroy and recreate the epoll object, which can
		435	take considerable time and thus should be avoided.
		436
		437	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		438	faster than epoll for maybe up to a hundred file descriptors, depending on
		439	the usage. So sad.
		440
		441	While nominally embeddable in other event loops, this feature is broken in
		442	all kernel versions tested so far.
		443
		444	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		445	C<EVBACKEND_POLL>.
254		446
255	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	447	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
256		448
257	Kqueue deserves special mention, as at the time of this writing, it	449	Kqueue deserves special mention, as at the time of this writing, it
258	was broken on all BSDs except NetBSD (usually it doesn't work with	450	was broken on all BSDs except NetBSD (usually it doesn't work reliably
259	anything but sockets and pipes, except on Darwin, where of course its	451	with anything but sockets and pipes, except on Darwin, where of course
260	completely useless). For this reason its not being "autodetected"	452	it's completely useless). Unlike epoll, however, whose brokenness
		453	is by design, these kqueue bugs can (and eventually will) be fixed
		454	without API changes to existing programs. For this reason it's not being
261	unless you explicitly specify it explicitly in the flags (i.e. using	455	"auto-detected" unless you explicitly specify it in the flags (i.e. using
262	C<EVBACKEND_KQUEUE>).	456	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		457	system like NetBSD.
		458
		459	You still can embed kqueue into a normal poll or select backend and use it
		460	only for sockets (after having made sure that sockets work with kqueue on
		461	the target platform). See C<ev_embed> watchers for more info.
263		462
264	It scales in the same way as the epoll backend, but the interface to the	463	It scales in the same way as the epoll backend, but the interface to the
265	kernel is more efficient (which says nothing about its actual speed, of	464	kernel is more efficient (which says nothing about its actual speed, of
266	course). While starting and stopping an I/O watcher does not cause an	465	course). While stopping, setting and starting an I/O watcher does never
267	extra syscall as with epoll, it still adds up to four event changes per	466	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
268	incident, so its best to avoid that.	467	two event changes per incident. Support for C<fork ()> is very bad (but
		468	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		469	cases
		470
		471	This backend usually performs well under most conditions.
		472
		473	While nominally embeddable in other event loops, this doesn't work
		474	everywhere, so you might need to test for this. And since it is broken
		475	almost everywhere, you should only use it when you have a lot of sockets
		476	(for which it usually works), by embedding it into another event loop
		477	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
		478	also broken on OS X)) and, did I mention it, using it only for sockets.
		479
		480	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		481	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		482	C<NOTE_EOF>.
269		483
270	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	484	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
271		485
272	This is not implemented yet (and might never be).	486	This is not implemented yet (and might never be, unless you send me an
		487	implementation). According to reports, C</dev/poll> only supports sockets
		488	and is not embeddable, which would limit the usefulness of this backend
		489	immensely.
273		490
274	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	491	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
275		492
276	This uses the Solaris 10 port mechanism. As with everything on Solaris,	493	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
277	it's really slow, but it still scales very well (O(active_fds)).	494	it's really slow, but it still scales very well (O(active_fds)).
278		495
279	Please note that solaris ports can result in a lot of spurious	496	Please note that Solaris event ports can deliver a lot of spurious
280	notifications, so you need to use non-blocking I/O or other means to avoid	497	notifications, so you need to use non-blocking I/O or other means to avoid
281	blocking when no data (or space) is available.	498	blocking when no data (or space) is available.
		499
		500	While this backend scales well, it requires one system call per active
		501	file descriptor per loop iteration. For small and medium numbers of file
		502	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		503	might perform better.
		504
		505	On the positive side, with the exception of the spurious readiness
		506	notifications, this backend actually performed fully to specification
		507	in all tests and is fully embeddable, which is a rare feat among the
		508	OS-specific backends (I vastly prefer correctness over speed hacks).
		509
		510	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		511	C<EVBACKEND_POLL>.
282		512
283	=item C<EVBACKEND_ALL>	513	=item C<EVBACKEND_ALL>
284		514
285	Try all backends (even potentially broken ones that wouldn't be tried	515	Try all backends (even potentially broken ones that wouldn't be tried
286	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	516	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
287	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	517	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
288		518
		519	It is definitely not recommended to use this flag.
		520
289	=back	521	=back
290		522
291	If one or more of these are ored into the flags value, then only these	523	If one or more of these are or'ed into the flags value, then only these
292	backends will be tried (in the reverse order as given here). If none are	524	backends will be tried (in the reverse order as listed here). If none are
293	specified, most compiled-in backend will be tried, usually in reverse	525	specified, all backends in C<ev_recommended_backends ()> will be tried.
294	order of their flag values :)
295		526
296	The most typical usage is like this:	527	Example: This is the most typical usage.
297		528
298	if (!ev_default_loop (0))	529	if (!ev_default_loop (0))
299	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	530	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
300		531
301	Restrict libev to the select and poll backends, and do not allow	532	Example: Restrict libev to the select and poll backends, and do not allow
302	environment settings to be taken into account:	533	environment settings to be taken into account:
303		534
304	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	535	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
305		536
306	Use whatever libev has to offer, but make sure that kqueue is used if	537	Example: Use whatever libev has to offer, but make sure that kqueue is
307	available (warning, breaks stuff, best use only with your own private	538	used if available (warning, breaks stuff, best use only with your own
308	event loop and only if you know the OS supports your types of fds):	539	private event loop and only if you know the OS supports your types of
		540	fds):
309		541
310	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	542	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
311		543
312	=item struct ev_loop *ev_loop_new (unsigned int flags)	544	=item struct ev_loop *ev_loop_new (unsigned int flags)
313		545
314	Similar to C<ev_default_loop>, but always creates a new event loop that is	546	Similar to C<ev_default_loop>, but always creates a new event loop that is
315	always distinct from the default loop. Unlike the default loop, it cannot	547	always distinct from the default loop. Unlike the default loop, it cannot
316	handle signal and child watchers, and attempts to do so will be greeted by	548	handle signal and child watchers, and attempts to do so will be greeted by
317	undefined behaviour (or a failed assertion if assertions are enabled).	549	undefined behaviour (or a failed assertion if assertions are enabled).
318		550
		551	Note that this function I<is> thread-safe, and the recommended way to use
		552	libev with threads is indeed to create one loop per thread, and using the
		553	default loop in the "main" or "initial" thread.
		554
319	Example: try to create a event loop that uses epoll and nothing else.	555	Example: Try to create a event loop that uses epoll and nothing else.
320		556
321	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	557	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
322	if (!epoller)	558	if (!epoller)
323	fatal ("no epoll found here, maybe it hides under your chair");	559	fatal ("no epoll found here, maybe it hides under your chair");
324		560
325	=item ev_default_destroy ()	561	=item ev_default_destroy ()
326		562
327	Destroys the default loop again (frees all memory and kernel state	563	Destroys the default loop again (frees all memory and kernel state
328	etc.). This stops all registered event watchers (by not touching them in	564	etc.). None of the active event watchers will be stopped in the normal
329	any way whatsoever, although you cannot rely on this :).	565	sense, so e.g. C<ev_is_active> might still return true. It is your
		566	responsibility to either stop all watchers cleanly yourself I<before>
		567	calling this function, or cope with the fact afterwards (which is usually
		568	the easiest thing, you can just ignore the watchers and/or C<free ()> them
		569	for example).
		570
		571	Note that certain global state, such as signal state (and installed signal
		572	handlers), will not be freed by this function, and related watchers (such
		573	as signal and child watchers) would need to be stopped manually.
		574
		575	In general it is not advisable to call this function except in the
		576	rare occasion where you really need to free e.g. the signal handling
		577	pipe fds. If you need dynamically allocated loops it is better to use
		578	C<ev_loop_new> and C<ev_loop_destroy>).
330		579
331	=item ev_loop_destroy (loop)	580	=item ev_loop_destroy (loop)
332		581
333	Like C<ev_default_destroy>, but destroys an event loop created by an	582	Like C<ev_default_destroy>, but destroys an event loop created by an
334	earlier call to C<ev_loop_new>.	583	earlier call to C<ev_loop_new>.
335		584
336	=item ev_default_fork ()	585	=item ev_default_fork ()
337		586
		587	This function sets a flag that causes subsequent C<ev_loop> iterations
338	This function reinitialises the kernel state for backends that have	588	to reinitialise the kernel state for backends that have one. Despite the
339	one. Despite the name, you can call it anytime, but it makes most sense	589	name, you can call it anytime, but it makes most sense after forking, in
340	after forking, in either the parent or child process (or both, but that	590	the child process (or both child and parent, but that again makes little
341	again makes little sense).	591	sense). You I<must> call it in the child before using any of the libev
		592	functions, and it will only take effect at the next C<ev_loop> iteration.
342		593
343	You I<must> call this function in the child process after forking if and	594	On the other hand, you only need to call this function in the child
344	only if you want to use the event library in both processes. If you just	595	process if and only if you want to use the event library in the child. If
345	fork+exec, you don't have to call it.	596	you just fork+exec, you don't have to call it at all.
346		597
347	The function itself is quite fast and it's usually not a problem to call	598	The function itself is quite fast and it's usually not a problem to call
348	it just in case after a fork. To make this easy, the function will fit in	599	it just in case after a fork. To make this easy, the function will fit in
349	quite nicely into a call to C<pthread_atfork>:	600	quite nicely into a call to C<pthread_atfork>:
350		601
351	pthread_atfork (0, 0, ev_default_fork);	602	pthread_atfork (0, 0, ev_default_fork);
352		603
353	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
354	without calling this function, so if you force one of those backends you
355	do not need to care.
356
357	=item ev_loop_fork (loop)	604	=item ev_loop_fork (loop)
358		605
359	Like C<ev_default_fork>, but acts on an event loop created by	606	Like C<ev_default_fork>, but acts on an event loop created by
360	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	607	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
361	after fork, and how you do this is entirely your own problem.	608	after fork that you want to re-use in the child, and how you do this is
		609	entirely your own problem.
		610
		611	=item int ev_is_default_loop (loop)
		612
		613	Returns true when the given loop is, in fact, the default loop, and false
		614	otherwise.
		615
		616	=item unsigned int ev_loop_count (loop)
		617
		618	Returns the count of loop iterations for the loop, which is identical to
		619	the number of times libev did poll for new events. It starts at C<0> and
		620	happily wraps around with enough iterations.
		621
		622	This value can sometimes be useful as a generation counter of sorts (it
		623	"ticks" the number of loop iterations), as it roughly corresponds with
		624	C<ev_prepare> and C<ev_check> calls.
		625
		626	=item unsigned int ev_loop_depth (loop)
		627
		628	Returns the number of times C<ev_loop> was entered minus the number of
		629	times C<ev_loop> was exited, in other words, the recursion depth.
		630
		631	Outside C<ev_loop>, this number is zero. In a callback, this number is
		632	C<1>, unless C<ev_loop> was invoked recursively (or from another thread),
		633	in which case it is higher.
		634
		635	Leaving C<ev_loop> abnormally (setjmp/longjmp, cancelling the thread
		636	etc.), doesn't count as exit.
362		637
363	=item unsigned int ev_backend (loop)	638	=item unsigned int ev_backend (loop)
364		639
365	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	640	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
366	use.	641	use.
…		…
369		644
370	Returns the current "event loop time", which is the time the event loop	645	Returns the current "event loop time", which is the time the event loop
371	received events and started processing them. This timestamp does not	646	received events and started processing them. This timestamp does not
372	change as long as callbacks are being processed, and this is also the base	647	change as long as callbacks are being processed, and this is also the base
373	time used for relative timers. You can treat it as the timestamp of the	648	time used for relative timers. You can treat it as the timestamp of the
374	event occuring (or more correctly, libev finding out about it).	649	event occurring (or more correctly, libev finding out about it).
		650
		651	=item ev_now_update (loop)
		652
		653	Establishes the current time by querying the kernel, updating the time
		654	returned by C<ev_now ()> in the progress. This is a costly operation and
		655	is usually done automatically within C<ev_loop ()>.
		656
		657	This function is rarely useful, but when some event callback runs for a
		658	very long time without entering the event loop, updating libev's idea of
		659	the current time is a good idea.
		660
		661	See also L<The special problem of time updates> in the C<ev_timer> section.
		662
		663	=item ev_suspend (loop)
		664
		665	=item ev_resume (loop)
		666
		667	These two functions suspend and resume a loop, for use when the loop is
		668	not used for a while and timeouts should not be processed.
		669
		670	A typical use case would be an interactive program such as a game: When
		671	the user presses C<^Z> to suspend the game and resumes it an hour later it
		672	would be best to handle timeouts as if no time had actually passed while
		673	the program was suspended. This can be achieved by calling C<ev_suspend>
		674	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		675	C<ev_resume> directly afterwards to resume timer processing.
		676
		677	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		678	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		679	will be rescheduled (that is, they will lose any events that would have
		680	occured while suspended).
		681
		682	After calling C<ev_suspend> you B<must not> call I<any> function on the
		683	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		684	without a previous call to C<ev_suspend>.
		685
		686	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		687	event loop time (see C<ev_now_update>).
375		688
376	=item ev_loop (loop, int flags)	689	=item ev_loop (loop, int flags)
377		690
378	Finally, this is it, the event handler. This function usually is called	691	Finally, this is it, the event handler. This function usually is called
379	after you initialised all your watchers and you want to start handling	692	after you initialised all your watchers and you want to start handling
…		…
382	If the flags argument is specified as C<0>, it will not return until	695	If the flags argument is specified as C<0>, it will not return until
383	either no event watchers are active anymore or C<ev_unloop> was called.	696	either no event watchers are active anymore or C<ev_unloop> was called.
384		697
385	Please note that an explicit C<ev_unloop> is usually better than	698	Please note that an explicit C<ev_unloop> is usually better than
386	relying on all watchers to be stopped when deciding when a program has	699	relying on all watchers to be stopped when deciding when a program has
387	finished (especially in interactive programs), but having a program that	700	finished (especially in interactive programs), but having a program
388	automatically loops as long as it has to and no longer by virtue of	701	that automatically loops as long as it has to and no longer by virtue
389	relying on its watchers stopping correctly is a thing of beauty.	702	of relying on its watchers stopping correctly, that is truly a thing of
		703	beauty.
390		704
391	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	705	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
392	those events and any outstanding ones, but will not block your process in	706	those events and any already outstanding ones, but will not block your
393	case there are no events and will return after one iteration of the loop.	707	process in case there are no events and will return after one iteration of
		708	the loop.
394		709
395	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	710	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
396	neccessary) and will handle those and any outstanding ones. It will block	711	necessary) and will handle those and any already outstanding ones. It
397	your process until at least one new event arrives, and will return after	712	will block your process until at least one new event arrives (which could
398	one iteration of the loop. This is useful if you are waiting for some	713	be an event internal to libev itself, so there is no guarantee that a
399	external event in conjunction with something not expressible using other	714	user-registered callback will be called), and will return after one
		715	iteration of the loop.
		716
		717	This is useful if you are waiting for some external event in conjunction
		718	with something not expressible using other libev watchers (i.e. "roll your
400	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	719	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
401	usually a better approach for this kind of thing.	720	usually a better approach for this kind of thing.
402		721
403	Here are the gory details of what C<ev_loop> does:	722	Here are the gory details of what C<ev_loop> does:
404		723
405	* If there are no active watchers (reference count is zero), return.	724	- Before the first iteration, call any pending watchers.
406	- Queue prepare watchers and then call all outstanding watchers.	725	* If EVFLAG_FORKCHECK was used, check for a fork.
		726	- If a fork was detected (by any means), queue and call all fork watchers.
		727	- Queue and call all prepare watchers.
407	- If we have been forked, recreate the kernel state.	728	- If we have been forked, detach and recreate the kernel state
		729	as to not disturb the other process.
408	- Update the kernel state with all outstanding changes.	730	- Update the kernel state with all outstanding changes.
409	- Update the "event loop time".	731	- Update the "event loop time" (ev_now ()).
410	- Calculate for how long to block.	732	- Calculate for how long to sleep or block, if at all
		733	(active idle watchers, EVLOOP_NONBLOCK or not having
		734	any active watchers at all will result in not sleeping).
		735	- Sleep if the I/O and timer collect interval say so.
411	- Block the process, waiting for any events.	736	- Block the process, waiting for any events.
412	- Queue all outstanding I/O (fd) events.	737	- Queue all outstanding I/O (fd) events.
413	- Update the "event loop time" and do time jump handling.	738	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
414	- Queue all outstanding timers.	739	- Queue all expired timers.
415	- Queue all outstanding periodics.	740	- Queue all expired periodics.
416	- If no events are pending now, queue all idle watchers.	741	- Unless any events are pending now, queue all idle watchers.
417	- Queue all check watchers.	742	- Queue all check watchers.
418	- Call all queued watchers in reverse order (i.e. check watchers first).	743	- Call all queued watchers in reverse order (i.e. check watchers first).
419	Signals and child watchers are implemented as I/O watchers, and will	744	Signals and child watchers are implemented as I/O watchers, and will
420	be handled here by queueing them when their watcher gets executed.	745	be handled here by queueing them when their watcher gets executed.
421	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	746	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
422	were used, return, otherwise continue with step *.	747	were used, or there are no active watchers, return, otherwise
		748	continue with step *.
423		749
424	Example: queue some jobs and then loop until no events are outsanding	750	Example: Queue some jobs and then loop until no events are outstanding
425	anymore.	751	anymore.
426		752
427	... queue jobs here, make sure they register event watchers as long	753	... queue jobs here, make sure they register event watchers as long
428	... as they still have work to do (even an idle watcher will do..)	754	... as they still have work to do (even an idle watcher will do..)
429	ev_loop (my_loop, 0);	755	ev_loop (my_loop, 0);
430	... jobs done. yeah!	756	... jobs done or somebody called unloop. yeah!
431		757
432	=item ev_unloop (loop, how)	758	=item ev_unloop (loop, how)
433		759
434	Can be used to make a call to C<ev_loop> return early (but only after it	760	Can be used to make a call to C<ev_loop> return early (but only after it
435	has processed all outstanding events). The C<how> argument must be either	761	has processed all outstanding events). The C<how> argument must be either
436	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	762	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
437	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	763	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
438		764
		765	This "unloop state" will be cleared when entering C<ev_loop> again.
		766
		767	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
		768
439	=item ev_ref (loop)	769	=item ev_ref (loop)
440		770
441	=item ev_unref (loop)	771	=item ev_unref (loop)
442		772
443	Ref/unref can be used to add or remove a reference count on the event	773	Ref/unref can be used to add or remove a reference count on the event
444	loop: Every watcher keeps one reference, and as long as the reference	774	loop: Every watcher keeps one reference, and as long as the reference
445	count is nonzero, C<ev_loop> will not return on its own. If you have	775	count is nonzero, C<ev_loop> will not return on its own.
		776
446	a watcher you never unregister that should not keep C<ev_loop> from	777	If you have a watcher you never unregister that should not keep C<ev_loop>
447	returning, ev_unref() after starting, and ev_ref() before stopping it. For	778	from returning, call ev_unref() after starting, and ev_ref() before
		779	stopping it.
		780
448	example, libev itself uses this for its internal signal pipe: It is not	781	As an example, libev itself uses this for its internal signal pipe: It
449	visible to the libev user and should not keep C<ev_loop> from exiting if	782	is not visible to the libev user and should not keep C<ev_loop> from
450	no event watchers registered by it are active. It is also an excellent	783	exiting if no event watchers registered by it are active. It is also an
451	way to do this for generic recurring timers or from within third-party	784	excellent way to do this for generic recurring timers or from within
452	libraries. Just remember to I<unref after start> and I<ref before stop>.	785	third-party libraries. Just remember to I<unref after start> and I<ref
		786	before stop> (but only if the watcher wasn't active before, or was active
		787	before, respectively. Note also that libev might stop watchers itself
		788	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		789	in the callback).
453		790
454	Example: create a signal watcher, but keep it from keeping C<ev_loop>	791	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
455	running when nothing else is active.	792	running when nothing else is active.
456		793
457	struct dv_signal exitsig;	794	ev_signal exitsig;
458	ev_signal_init (&exitsig, sig_cb, SIGINT);	795	ev_signal_init (&exitsig, sig_cb, SIGINT);
459	ev_signal_start (myloop, &exitsig);	796	ev_signal_start (loop, &exitsig);
460	evf_unref (myloop);	797	evf_unref (loop);
461		798
462	Example: for some weird reason, unregister the above signal handler again.	799	Example: For some weird reason, unregister the above signal handler again.
463		800
464	ev_ref (myloop);	801	ev_ref (loop);
465	ev_signal_stop (myloop, &exitsig);	802	ev_signal_stop (loop, &exitsig);
		803
		804	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		805
		806	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		807
		808	These advanced functions influence the time that libev will spend waiting
		809	for events. Both time intervals are by default C<0>, meaning that libev
		810	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		811	latency.
		812
		813	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		814	allows libev to delay invocation of I/O and timer/periodic callbacks
		815	to increase efficiency of loop iterations (or to increase power-saving
		816	opportunities).
		817
		818	The idea is that sometimes your program runs just fast enough to handle
		819	one (or very few) event(s) per loop iteration. While this makes the
		820	program responsive, it also wastes a lot of CPU time to poll for new
		821	events, especially with backends like C<select ()> which have a high
		822	overhead for the actual polling but can deliver many events at once.
		823
		824	By setting a higher I<io collect interval> you allow libev to spend more
		825	time collecting I/O events, so you can handle more events per iteration,
		826	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		827	C<ev_timer>) will be not affected. Setting this to a non-null value will
		828	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		829	sleep time ensures that libev will not poll for I/O events more often then
		830	once per this interval, on average.
		831
		832	Likewise, by setting a higher I<timeout collect interval> you allow libev
		833	to spend more time collecting timeouts, at the expense of increased
		834	latency/jitter/inexactness (the watcher callback will be called
		835	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		836	value will not introduce any overhead in libev.
		837
		838	Many (busy) programs can usually benefit by setting the I/O collect
		839	interval to a value near C<0.1> or so, which is often enough for
		840	interactive servers (of course not for games), likewise for timeouts. It
		841	usually doesn't make much sense to set it to a lower value than C<0.01>,
		842	as this approaches the timing granularity of most systems. Note that if
		843	you do transactions with the outside world and you can't increase the
		844	parallelity, then this setting will limit your transaction rate (if you
		845	need to poll once per transaction and the I/O collect interval is 0.01,
		846	then you can't do more than 100 transations per second).
		847
		848	Setting the I<timeout collect interval> can improve the opportunity for
		849	saving power, as the program will "bundle" timer callback invocations that
		850	are "near" in time together, by delaying some, thus reducing the number of
		851	times the process sleeps and wakes up again. Another useful technique to
		852	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		853	they fire on, say, one-second boundaries only.
		854
		855	Example: we only need 0.1s timeout granularity, and we wish not to poll
		856	more often than 100 times per second:
		857
		858	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		859	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		860
		861	=item ev_invoke_pending (loop)
		862
		863	This call will simply invoke all pending watchers while resetting their
		864	pending state. Normally, C<ev_loop> does this automatically when required,
		865	but when overriding the invoke callback this call comes handy.
		866
		867	=item int ev_pending_count (loop)
		868
		869	Returns the number of pending watchers - zero indicates that no watchers
		870	are pending.
		871
		872	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		873
		874	This overrides the invoke pending functionality of the loop: Instead of
		875	invoking all pending watchers when there are any, C<ev_loop> will call
		876	this callback instead. This is useful, for example, when you want to
		877	invoke the actual watchers inside another context (another thread etc.).
		878
		879	If you want to reset the callback, use C<ev_invoke_pending> as new
		880	callback.
		881
		882	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		883
		884	Sometimes you want to share the same loop between multiple threads. This
		885	can be done relatively simply by putting mutex_lock/unlock calls around
		886	each call to a libev function.
		887
		888	However, C<ev_loop> can run an indefinite time, so it is not feasible to
		889	wait for it to return. One way around this is to wake up the loop via
		890	C<ev_unloop> and C<av_async_send>, another way is to set these I<release>
		891	and I<acquire> callbacks on the loop.
		892
		893	When set, then C<release> will be called just before the thread is
		894	suspended waiting for new events, and C<acquire> is called just
		895	afterwards.
		896
		897	Ideally, C<release> will just call your mutex_unlock function, and
		898	C<acquire> will just call the mutex_lock function again.
		899
		900	While event loop modifications are allowed between invocations of
		901	C<release> and C<acquire> (that's their only purpose after all), no
		902	modifications done will affect the event loop, i.e. adding watchers will
		903	have no effect on the set of file descriptors being watched, or the time
		904	waited. USe an C<ev_async> watcher to wake up C<ev_loop> when you want it
		905	to take note of any changes you made.
		906
		907	In theory, threads executing C<ev_loop> will be async-cancel safe between
		908	invocations of C<release> and C<acquire>.
		909
		910	See also the locking example in the C<THREADS> section later in this
		911	document.
		912
		913	=item ev_set_userdata (loop, void *data)
		914
		915	=item ev_userdata (loop)
		916
		917	Set and retrieve a single C<void *> associated with a loop. When
		918	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		919	C<0.>
		920
		921	These two functions can be used to associate arbitrary data with a loop,
		922	and are intended solely for the C<invoke_pending_cb>, C<release> and
		923	C<acquire> callbacks described above, but of course can be (ab-)used for
		924	any other purpose as well.
		925
		926	=item ev_loop_verify (loop)
		927
		928	This function only does something when C<EV_VERIFY> support has been
		929	compiled in, which is the default for non-minimal builds. It tries to go
		930	through all internal structures and checks them for validity. If anything
		931	is found to be inconsistent, it will print an error message to standard
		932	error and call C<abort ()>.
		933
		934	This can be used to catch bugs inside libev itself: under normal
		935	circumstances, this function will never abort as of course libev keeps its
		936	data structures consistent.
466		937
467	=back	938	=back
468		939
		940
469	=head1 ANATOMY OF A WATCHER	941	=head1 ANATOMY OF A WATCHER
		942
		943	In the following description, uppercase C<TYPE> in names stands for the
		944	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		945	watchers and C<ev_io_start> for I/O watchers.
470		946
471	A watcher is a structure that you create and register to record your	947	A watcher is a structure that you create and register to record your
472	interest in some event. For instance, if you want to wait for STDIN to	948	interest in some event. For instance, if you want to wait for STDIN to
473	become readable, you would create an C<ev_io> watcher for that:	949	become readable, you would create an C<ev_io> watcher for that:
474		950
475	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	951	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
476	{	952	{
477	ev_io_stop (w);	953	ev_io_stop (w);
478	ev_unloop (loop, EVUNLOOP_ALL);	954	ev_unloop (loop, EVUNLOOP_ALL);
479	}	955	}
480		956
481	struct ev_loop *loop = ev_default_loop (0);	957	struct ev_loop *loop = ev_default_loop (0);
		958
482	struct ev_io stdin_watcher;	959	ev_io stdin_watcher;
		960
483	ev_init (&stdin_watcher, my_cb);	961	ev_init (&stdin_watcher, my_cb);
484	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	962	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
485	ev_io_start (loop, &stdin_watcher);	963	ev_io_start (loop, &stdin_watcher);
		964
486	ev_loop (loop, 0);	965	ev_loop (loop, 0);
487		966
488	As you can see, you are responsible for allocating the memory for your	967	As you can see, you are responsible for allocating the memory for your
489	watcher structures (and it is usually a bad idea to do this on the stack,	968	watcher structures (and it is I<usually> a bad idea to do this on the
490	although this can sometimes be quite valid).	969	stack).
		970
		971	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		972	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
491		973
492	Each watcher structure must be initialised by a call to C<ev_init	974	Each watcher structure must be initialised by a call to C<ev_init
493	(watcher *, callback)>, which expects a callback to be provided. This	975	(watcher *, callback)>, which expects a callback to be provided. This
494	callback gets invoked each time the event occurs (or, in the case of io	976	callback gets invoked each time the event occurs (or, in the case of I/O
495	watchers, each time the event loop detects that the file descriptor given	977	watchers, each time the event loop detects that the file descriptor given
496	is readable and/or writable).	978	is readable and/or writable).
497		979
498	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	980	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
499	with arguments specific to this watcher type. There is also a macro	981	macro to configure it, with arguments specific to the watcher type. There
500	to combine initialisation and setting in one call: C<< ev_<type>_init	982	is also a macro to combine initialisation and setting in one call: C<<
501	(watcher *, callback, ...) >>.	983	ev_TYPE_init (watcher *, callback, ...) >>.
502		984
503	To make the watcher actually watch out for events, you have to start it	985	To make the watcher actually watch out for events, you have to start it
504	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	986	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
505	*) >>), and you can stop watching for events at any time by calling the	987	*) >>), and you can stop watching for events at any time by calling the
506	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	988	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
507		989
508	As long as your watcher is active (has been started but not stopped) you	990	As long as your watcher is active (has been started but not stopped) you
509	must not touch the values stored in it. Most specifically you must never	991	must not touch the values stored in it. Most specifically you must never
510	reinitialise it or call its set macro.	992	reinitialise it or call its C<ev_TYPE_set> macro.
511
512	You can check whether an event is active by calling the C<ev_is_active
513	(watcher *)> macro. To see whether an event is outstanding (but the
514	callback for it has not been called yet) you can use the C<ev_is_pending
515	(watcher *)> macro.
516		993
517	Each and every callback receives the event loop pointer as first, the	994	Each and every callback receives the event loop pointer as first, the
518	registered watcher structure as second, and a bitset of received events as	995	registered watcher structure as second, and a bitset of received events as
519	third argument.	996	third argument.
520		997
…		…
544	The signal specified in the C<ev_signal> watcher has been received by a thread.	1021	The signal specified in the C<ev_signal> watcher has been received by a thread.
545		1022
546	=item C<EV_CHILD>	1023	=item C<EV_CHILD>
547		1024
548	The pid specified in the C<ev_child> watcher has received a status change.	1025	The pid specified in the C<ev_child> watcher has received a status change.
		1026
		1027	=item C<EV_STAT>
		1028
		1029	The path specified in the C<ev_stat> watcher changed its attributes somehow.
549		1030
550	=item C<EV_IDLE>	1031	=item C<EV_IDLE>
551		1032
552	The C<ev_idle> watcher has determined that you have nothing better to do.	1033	The C<ev_idle> watcher has determined that you have nothing better to do.
553		1034
…		…
561	received events. Callbacks of both watcher types can start and stop as	1042	received events. Callbacks of both watcher types can start and stop as
562	many watchers as they want, and all of them will be taken into account	1043	many watchers as they want, and all of them will be taken into account
563	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1044	(for example, a C<ev_prepare> watcher might start an idle watcher to keep
564	C<ev_loop> from blocking).	1045	C<ev_loop> from blocking).
565		1046
		1047	=item C<EV_EMBED>
		1048
		1049	The embedded event loop specified in the C<ev_embed> watcher needs attention.
		1050
		1051	=item C<EV_FORK>
		1052
		1053	The event loop has been resumed in the child process after fork (see
		1054	C<ev_fork>).
		1055
		1056	=item C<EV_ASYNC>
		1057
		1058	The given async watcher has been asynchronously notified (see C<ev_async>).
		1059
		1060	=item C<EV_CUSTOM>
		1061
		1062	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1063	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1064
566	=item C<EV_ERROR>	1065	=item C<EV_ERROR>
567		1066
568	An unspecified error has occured, the watcher has been stopped. This might	1067	An unspecified error has occurred, the watcher has been stopped. This might
569	happen because the watcher could not be properly started because libev	1068	happen because the watcher could not be properly started because libev
570	ran out of memory, a file descriptor was found to be closed or any other	1069	ran out of memory, a file descriptor was found to be closed or any other
		1070	problem. Libev considers these application bugs.
		1071
571	problem. You best act on it by reporting the problem and somehow coping	1072	You best act on it by reporting the problem and somehow coping with the
572	with the watcher being stopped.	1073	watcher being stopped. Note that well-written programs should not receive
		1074	an error ever, so when your watcher receives it, this usually indicates a
		1075	bug in your program.
573		1076
574	Libev will usually signal a few "dummy" events together with an error,	1077	Libev will usually signal a few "dummy" events together with an error, for
575	for example it might indicate that a fd is readable or writable, and if	1078	example it might indicate that a fd is readable or writable, and if your
576	your callbacks is well-written it can just attempt the operation and cope	1079	callbacks is well-written it can just attempt the operation and cope with
577	with the error from read() or write(). This will not work in multithreaded	1080	the error from read() or write(). This will not work in multi-threaded
578	programs, though, so beware.	1081	programs, though, as the fd could already be closed and reused for another
		1082	thing, so beware.
579		1083
580	=back	1084	=back
581		1085
		1086	=head2 GENERIC WATCHER FUNCTIONS
		1087
		1088	=over 4
		1089
		1090	=item C<ev_init> (ev_TYPE *watcher, callback)
		1091
		1092	This macro initialises the generic portion of a watcher. The contents
		1093	of the watcher object can be arbitrary (so C<malloc> will do). Only
		1094	the generic parts of the watcher are initialised, you I<need> to call
		1095	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		1096	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		1097	which rolls both calls into one.
		1098
		1099	You can reinitialise a watcher at any time as long as it has been stopped
		1100	(or never started) and there are no pending events outstanding.
		1101
		1102	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
		1103	int revents)>.
		1104
		1105	Example: Initialise an C<ev_io> watcher in two steps.
		1106
		1107	ev_io w;
		1108	ev_init (&w, my_cb);
		1109	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1110
		1111	=item C<ev_TYPE_set> (ev_TYPE *, [args])
		1112
		1113	This macro initialises the type-specific parts of a watcher. You need to
		1114	call C<ev_init> at least once before you call this macro, but you can
		1115	call C<ev_TYPE_set> any number of times. You must not, however, call this
		1116	macro on a watcher that is active (it can be pending, however, which is a
		1117	difference to the C<ev_init> macro).
		1118
		1119	Although some watcher types do not have type-specific arguments
		1120	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		1121
		1122	See C<ev_init>, above, for an example.
		1123
		1124	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		1125
		1126	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		1127	calls into a single call. This is the most convenient method to initialise
		1128	a watcher. The same limitations apply, of course.
		1129
		1130	Example: Initialise and set an C<ev_io> watcher in one step.
		1131
		1132	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1133
		1134	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
		1135
		1136	Starts (activates) the given watcher. Only active watchers will receive
		1137	events. If the watcher is already active nothing will happen.
		1138
		1139	Example: Start the C<ev_io> watcher that is being abused as example in this
		1140	whole section.
		1141
		1142	ev_io_start (EV_DEFAULT_UC, &w);
		1143
		1144	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
		1145
		1146	Stops the given watcher if active, and clears the pending status (whether
		1147	the watcher was active or not).
		1148
		1149	It is possible that stopped watchers are pending - for example,
		1150	non-repeating timers are being stopped when they become pending - but
		1151	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
		1152	pending. If you want to free or reuse the memory used by the watcher it is
		1153	therefore a good idea to always call its C<ev_TYPE_stop> function.
		1154
		1155	=item bool ev_is_active (ev_TYPE *watcher)
		1156
		1157	Returns a true value iff the watcher is active (i.e. it has been started
		1158	and not yet been stopped). As long as a watcher is active you must not modify
		1159	it.
		1160
		1161	=item bool ev_is_pending (ev_TYPE *watcher)
		1162
		1163	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		1164	events but its callback has not yet been invoked). As long as a watcher
		1165	is pending (but not active) you must not call an init function on it (but
		1166	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		1167	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1168	it).
		1169
		1170	=item callback ev_cb (ev_TYPE *watcher)
		1171
		1172	Returns the callback currently set on the watcher.
		1173
		1174	=item ev_cb_set (ev_TYPE *watcher, callback)
		1175
		1176	Change the callback. You can change the callback at virtually any time
		1177	(modulo threads).
		1178
		1179	=item ev_set_priority (ev_TYPE *watcher, priority)
		1180
		1181	=item int ev_priority (ev_TYPE *watcher)
		1182
		1183	Set and query the priority of the watcher. The priority is a small
		1184	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1185	(default: C<-2>). Pending watchers with higher priority will be invoked
		1186	before watchers with lower priority, but priority will not keep watchers
		1187	from being executed (except for C<ev_idle> watchers).
		1188
		1189	If you need to suppress invocation when higher priority events are pending
		1190	you need to look at C<ev_idle> watchers, which provide this functionality.
		1191
		1192	You I<must not> change the priority of a watcher as long as it is active or
		1193	pending.
		1194
		1195	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1196	fine, as long as you do not mind that the priority value you query might
		1197	or might not have been clamped to the valid range.
		1198
		1199	The default priority used by watchers when no priority has been set is
		1200	always C<0>, which is supposed to not be too high and not be too low :).
		1201
		1202	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1203	priorities.
		1204
		1205	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1206
		1207	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1208	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1209	can deal with that fact, as both are simply passed through to the
		1210	callback.
		1211
		1212	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1213
		1214	If the watcher is pending, this function clears its pending status and
		1215	returns its C<revents> bitset (as if its callback was invoked). If the
		1216	watcher isn't pending it does nothing and returns C<0>.
		1217
		1218	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1219	callback to be invoked, which can be accomplished with this function.
		1220
		1221	=back
		1222
		1223
582	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1224	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
583		1225
584	Each watcher has, by default, a member C<void *data> that you can change	1226	Each watcher has, by default, a member C<void *data> that you can change
585	and read at any time, libev will completely ignore it. This can be used	1227	and read at any time: libev will completely ignore it. This can be used
586	to associate arbitrary data with your watcher. If you need more data and	1228	to associate arbitrary data with your watcher. If you need more data and
587	don't want to allocate memory and store a pointer to it in that data	1229	don't want to allocate memory and store a pointer to it in that data
588	member, you can also "subclass" the watcher type and provide your own	1230	member, you can also "subclass" the watcher type and provide your own
589	data:	1231	data:
590		1232
591	struct my_io	1233	struct my_io
592	{	1234	{
593	struct ev_io io;	1235	ev_io io;
594	int otherfd;	1236	int otherfd;
595	void *somedata;	1237	void *somedata;
596	struct whatever *mostinteresting;	1238	struct whatever *mostinteresting;
597	}	1239	};
		1240
		1241	...
		1242	struct my_io w;
		1243	ev_io_init (&w.io, my_cb, fd, EV_READ);
598		1244
599	And since your callback will be called with a pointer to the watcher, you	1245	And since your callback will be called with a pointer to the watcher, you
600	can cast it back to your own type:	1246	can cast it back to your own type:
601		1247
602	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1248	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
603	{	1249	{
604	struct my_io *w = (struct my_io *)w_;	1250	struct my_io *w = (struct my_io *)w_;
605	...	1251	...
606	}	1252	}
607		1253
608	More interesting and less C-conformant ways of catsing your callback type	1254	More interesting and less C-conformant ways of casting your callback type
609	have been omitted....	1255	instead have been omitted.
		1256
		1257	Another common scenario is to use some data structure with multiple
		1258	embedded watchers:
		1259
		1260	struct my_biggy
		1261	{
		1262	int some_data;
		1263	ev_timer t1;
		1264	ev_timer t2;
		1265	}
		1266
		1267	In this case getting the pointer to C<my_biggy> is a bit more
		1268	complicated: Either you store the address of your C<my_biggy> struct
		1269	in the C<data> member of the watcher (for woozies), or you need to use
		1270	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1271	programmers):
		1272
		1273	#include <stddef.h>
		1274
		1275	static void
		1276	t1_cb (EV_P_ ev_timer *w, int revents)
		1277	{
		1278	struct my_biggy big = (struct my_biggy *)
		1279	(((char *)w) - offsetof (struct my_biggy, t1));
		1280	}
		1281
		1282	static void
		1283	t2_cb (EV_P_ ev_timer *w, int revents)
		1284	{
		1285	struct my_biggy big = (struct my_biggy *)
		1286	(((char *)w) - offsetof (struct my_biggy, t2));
		1287	}
		1288
		1289	=head2 WATCHER PRIORITY MODELS
		1290
		1291	Many event loops support I<watcher priorities>, which are usually small
		1292	integers that influence the ordering of event callback invocation
		1293	between watchers in some way, all else being equal.
		1294
		1295	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1296	description for the more technical details such as the actual priority
		1297	range.
		1298
		1299	There are two common ways how these these priorities are being interpreted
		1300	by event loops:
		1301
		1302	In the more common lock-out model, higher priorities "lock out" invocation
		1303	of lower priority watchers, which means as long as higher priority
		1304	watchers receive events, lower priority watchers are not being invoked.
		1305
		1306	The less common only-for-ordering model uses priorities solely to order
		1307	callback invocation within a single event loop iteration: Higher priority
		1308	watchers are invoked before lower priority ones, but they all get invoked
		1309	before polling for new events.
		1310
		1311	Libev uses the second (only-for-ordering) model for all its watchers
		1312	except for idle watchers (which use the lock-out model).
		1313
		1314	The rationale behind this is that implementing the lock-out model for
		1315	watchers is not well supported by most kernel interfaces, and most event
		1316	libraries will just poll for the same events again and again as long as
		1317	their callbacks have not been executed, which is very inefficient in the
		1318	common case of one high-priority watcher locking out a mass of lower
		1319	priority ones.
		1320
		1321	Static (ordering) priorities are most useful when you have two or more
		1322	watchers handling the same resource: a typical usage example is having an
		1323	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1324	timeouts. Under load, data might be received while the program handles
		1325	other jobs, but since timers normally get invoked first, the timeout
		1326	handler will be executed before checking for data. In that case, giving
		1327	the timer a lower priority than the I/O watcher ensures that I/O will be
		1328	handled first even under adverse conditions (which is usually, but not
		1329	always, what you want).
		1330
		1331	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1332	will only be executed when no same or higher priority watchers have
		1333	received events, they can be used to implement the "lock-out" model when
		1334	required.
		1335
		1336	For example, to emulate how many other event libraries handle priorities,
		1337	you can associate an C<ev_idle> watcher to each such watcher, and in
		1338	the normal watcher callback, you just start the idle watcher. The real
		1339	processing is done in the idle watcher callback. This causes libev to
		1340	continously poll and process kernel event data for the watcher, but when
		1341	the lock-out case is known to be rare (which in turn is rare :), this is
		1342	workable.
		1343
		1344	Usually, however, the lock-out model implemented that way will perform
		1345	miserably under the type of load it was designed to handle. In that case,
		1346	it might be preferable to stop the real watcher before starting the
		1347	idle watcher, so the kernel will not have to process the event in case
		1348	the actual processing will be delayed for considerable time.
		1349
		1350	Here is an example of an I/O watcher that should run at a strictly lower
		1351	priority than the default, and which should only process data when no
		1352	other events are pending:
		1353
		1354	ev_idle idle; // actual processing watcher
		1355	ev_io io; // actual event watcher
		1356
		1357	static void
		1358	io_cb (EV_P_ ev_io *w, int revents)
		1359	{
		1360	// stop the I/O watcher, we received the event, but
		1361	// are not yet ready to handle it.
		1362	ev_io_stop (EV_A_ w);
		1363
		1364	// start the idle watcher to ahndle the actual event.
		1365	// it will not be executed as long as other watchers
		1366	// with the default priority are receiving events.
		1367	ev_idle_start (EV_A_ &idle);
		1368	}
		1369
		1370	static void
		1371	idle_cb (EV_P_ ev_idle *w, int revents)
		1372	{
		1373	// actual processing
		1374	read (STDIN_FILENO, ...);
		1375
		1376	// have to start the I/O watcher again, as
		1377	// we have handled the event
		1378	ev_io_start (EV_P_ &io);
		1379	}
		1380
		1381	// initialisation
		1382	ev_idle_init (&idle, idle_cb);
		1383	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1384	ev_io_start (EV_DEFAULT_ &io);
		1385
		1386	In the "real" world, it might also be beneficial to start a timer, so that
		1387	low-priority connections can not be locked out forever under load. This
		1388	enables your program to keep a lower latency for important connections
		1389	during short periods of high load, while not completely locking out less
		1390	important ones.
610		1391
611		1392
612	=head1 WATCHER TYPES	1393	=head1 WATCHER TYPES
613		1394
614	This section describes each watcher in detail, but will not repeat	1395	This section describes each watcher in detail, but will not repeat
615	information given in the last section.	1396	information given in the last section. Any initialisation/set macros,
		1397	functions and members specific to the watcher type are explained.
616		1398
		1399	Members are additionally marked with either I<[read-only]>, meaning that,
		1400	while the watcher is active, you can look at the member and expect some
		1401	sensible content, but you must not modify it (you can modify it while the
		1402	watcher is stopped to your hearts content), or I<[read-write]>, which
		1403	means you can expect it to have some sensible content while the watcher
		1404	is active, but you can also modify it. Modifying it may not do something
		1405	sensible or take immediate effect (or do anything at all), but libev will
		1406	not crash or malfunction in any way.
617		1407
		1408
618	=head2 C<ev_io> - is this file descriptor readable or writable	1409	=head2 C<ev_io> - is this file descriptor readable or writable?
619		1410
620	I/O watchers check whether a file descriptor is readable or writable	1411	I/O watchers check whether a file descriptor is readable or writable
621	in each iteration of the event loop (This behaviour is called	1412	in each iteration of the event loop, or, more precisely, when reading
622	level-triggering because you keep receiving events as long as the	1413	would not block the process and writing would at least be able to write
623	condition persists. Remember you can stop the watcher if you don't want to	1414	some data. This behaviour is called level-triggering because you keep
624	act on the event and neither want to receive future events).	1415	receiving events as long as the condition persists. Remember you can stop
		1416	the watcher if you don't want to act on the event and neither want to
		1417	receive future events.
625		1418
626	In general you can register as many read and/or write event watchers per	1419	In general you can register as many read and/or write event watchers per
627	fd as you want (as long as you don't confuse yourself). Setting all file	1420	fd as you want (as long as you don't confuse yourself). Setting all file
628	descriptors to non-blocking mode is also usually a good idea (but not	1421	descriptors to non-blocking mode is also usually a good idea (but not
629	required if you know what you are doing).	1422	required if you know what you are doing).
630		1423
631	You have to be careful with dup'ed file descriptors, though. Some backends	1424	If you cannot use non-blocking mode, then force the use of a
632	(the linux epoll backend is a notable example) cannot handle dup'ed file	1425	known-to-be-good backend (at the time of this writing, this includes only
633	descriptors correctly if you register interest in two or more fds pointing	1426	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
634	to the same underlying file/socket etc. description (that is, they share	1427	descriptors for which non-blocking operation makes no sense (such as
635	the same underlying "file open").	1428	files) - libev doesn't guarentee any specific behaviour in that case.
636		1429
637	If you must do this, then force the use of a known-to-be-good backend	1430	Another thing you have to watch out for is that it is quite easy to
638	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and	1431	receive "spurious" readiness notifications, that is your callback might
		1432	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
		1433	because there is no data. Not only are some backends known to create a
		1434	lot of those (for example Solaris ports), it is very easy to get into
		1435	this situation even with a relatively standard program structure. Thus
		1436	it is best to always use non-blocking I/O: An extra C<read>(2) returning
		1437	C<EAGAIN> is far preferable to a program hanging until some data arrives.
		1438
		1439	If you cannot run the fd in non-blocking mode (for example you should
		1440	not play around with an Xlib connection), then you have to separately
		1441	re-test whether a file descriptor is really ready with a known-to-be good
		1442	interface such as poll (fortunately in our Xlib example, Xlib already
		1443	does this on its own, so its quite safe to use). Some people additionally
		1444	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1445	indefinitely.
		1446
		1447	But really, best use non-blocking mode.
		1448
		1449	=head3 The special problem of disappearing file descriptors
		1450
		1451	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1452	descriptor (either due to calling C<close> explicitly or any other means,
		1453	such as C<dup2>). The reason is that you register interest in some file
		1454	descriptor, but when it goes away, the operating system will silently drop
		1455	this interest. If another file descriptor with the same number then is
		1456	registered with libev, there is no efficient way to see that this is, in
		1457	fact, a different file descriptor.
		1458
		1459	To avoid having to explicitly tell libev about such cases, libev follows
		1460	the following policy: Each time C<ev_io_set> is being called, libev
		1461	will assume that this is potentially a new file descriptor, otherwise
		1462	it is assumed that the file descriptor stays the same. That means that
		1463	you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the
		1464	descriptor even if the file descriptor number itself did not change.
		1465
		1466	This is how one would do it normally anyway, the important point is that
		1467	the libev application should not optimise around libev but should leave
		1468	optimisations to libev.
		1469
		1470	=head3 The special problem of dup'ed file descriptors
		1471
		1472	Some backends (e.g. epoll), cannot register events for file descriptors,
		1473	but only events for the underlying file descriptions. That means when you
		1474	have C<dup ()>'ed file descriptors or weirder constellations, and register
		1475	events for them, only one file descriptor might actually receive events.
		1476
		1477	There is no workaround possible except not registering events
		1478	for potentially C<dup ()>'ed file descriptors, or to resort to
		1479	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
		1480
		1481	=head3 The special problem of fork
		1482
		1483	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
		1484	useless behaviour. Libev fully supports fork, but needs to be told about
		1485	it in the child.
		1486
		1487	To support fork in your programs, you either have to call
		1488	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
		1489	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
639	C<EVBACKEND_POLL>).	1490	C<EVBACKEND_POLL>.
		1491
		1492	=head3 The special problem of SIGPIPE
		1493
		1494	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1495	when writing to a pipe whose other end has been closed, your program gets
		1496	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1497	this is sensible behaviour, for daemons, this is usually undesirable.
		1498
		1499	So when you encounter spurious, unexplained daemon exits, make sure you
		1500	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1501	somewhere, as that would have given you a big clue).
		1502
		1503
		1504	=head3 Watcher-Specific Functions
640		1505
641	=over 4	1506	=over 4
642		1507
643	=item ev_io_init (ev_io *, callback, int fd, int events)	1508	=item ev_io_init (ev_io *, callback, int fd, int events)
644		1509
645	=item ev_io_set (ev_io *, int fd, int events)	1510	=item ev_io_set (ev_io *, int fd, int events)
646		1511
647	Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive	1512	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
648	events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ |	1513	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
649	EV_WRITE> to receive the given events.	1514	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
650		1515
651	Please note that most of the more scalable backend mechanisms (for example	1516	=item int fd [read-only]
652	epoll and solaris ports) can result in spurious readyness notifications	1517
653	for file descriptors, so you practically need to use non-blocking I/O (and	1518	The file descriptor being watched.
654	treat callback invocation as hint only), or retest separately with a safe	1519
655	interface before doing I/O (XLib can do this), or force the use of either	1520	=item int events [read-only]
656	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>, which don't suffer from this	1521
657	problem. Also note that it is quite easy to have your callback invoked	1522	The events being watched.
658	when the readyness condition is no longer valid even when employing
659	typical ways of handling events, so its a good idea to use non-blocking
660	I/O unconditionally.
661		1523
662	=back	1524	=back
663		1525
		1526	=head3 Examples
		1527
664	Example: call C<stdin_readable_cb> when STDIN_FILENO has become, well	1528	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
665	readable, but only once. Since it is likely line-buffered, you could	1529	readable, but only once. Since it is likely line-buffered, you could
666	attempt to read a whole line in the callback:	1530	attempt to read a whole line in the callback.
667		1531
668	static void	1532	static void
669	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1533	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
670	{	1534	{
671	ev_io_stop (loop, w);	1535	ev_io_stop (loop, w);
672	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1536	.. read from stdin here (or from w->fd) and handle any I/O errors
673	}	1537	}
674		1538
675	...	1539	...
676	struct ev_loop *loop = ev_default_init (0);	1540	struct ev_loop *loop = ev_default_init (0);
677	struct ev_io stdin_readable;	1541	ev_io stdin_readable;
678	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1542	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
679	ev_io_start (loop, &stdin_readable);	1543	ev_io_start (loop, &stdin_readable);
680	ev_loop (loop, 0);	1544	ev_loop (loop, 0);
681		1545
682		1546
683	=head2 C<ev_timer> - relative and optionally recurring timeouts	1547	=head2 C<ev_timer> - relative and optionally repeating timeouts
684		1548
685	Timer watchers are simple relative timers that generate an event after a	1549	Timer watchers are simple relative timers that generate an event after a
686	given time, and optionally repeating in regular intervals after that.	1550	given time, and optionally repeating in regular intervals after that.
687		1551
688	The timers are based on real time, that is, if you register an event that	1552	The timers are based on real time, that is, if you register an event that
689	times out after an hour and you reset your system clock to last years	1553	times out after an hour and you reset your system clock to January last
690	time, it will still time out after (roughly) and hour. "Roughly" because	1554	year, it will still time out after (roughly) one hour. "Roughly" because
691	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1555	detecting time jumps is hard, and some inaccuracies are unavoidable (the
692	monotonic clock option helps a lot here).	1556	monotonic clock option helps a lot here).
		1557
		1558	The callback is guaranteed to be invoked only I<after> its timeout has
		1559	passed (not I<at>, so on systems with very low-resolution clocks this
		1560	might introduce a small delay). If multiple timers become ready during the
		1561	same loop iteration then the ones with earlier time-out values are invoked
		1562	before ones of the same priority with later time-out values (but this is
		1563	no longer true when a callback calls C<ev_loop> recursively).
		1564
		1565	=head3 Be smart about timeouts
		1566
		1567	Many real-world problems involve some kind of timeout, usually for error
		1568	recovery. A typical example is an HTTP request - if the other side hangs,
		1569	you want to raise some error after a while.
		1570
		1571	What follows are some ways to handle this problem, from obvious and
		1572	inefficient to smart and efficient.
		1573
		1574	In the following, a 60 second activity timeout is assumed - a timeout that
		1575	gets reset to 60 seconds each time there is activity (e.g. each time some
		1576	data or other life sign was received).
		1577
		1578	=over 4
		1579
		1580	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1581
		1582	This is the most obvious, but not the most simple way: In the beginning,
		1583	start the watcher:
		1584
		1585	ev_timer_init (timer, callback, 60., 0.);
		1586	ev_timer_start (loop, timer);
		1587
		1588	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1589	and start it again:
		1590
		1591	ev_timer_stop (loop, timer);
		1592	ev_timer_set (timer, 60., 0.);
		1593	ev_timer_start (loop, timer);
		1594
		1595	This is relatively simple to implement, but means that each time there is
		1596	some activity, libev will first have to remove the timer from its internal
		1597	data structure and then add it again. Libev tries to be fast, but it's
		1598	still not a constant-time operation.
		1599
		1600	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1601
		1602	This is the easiest way, and involves using C<ev_timer_again> instead of
		1603	C<ev_timer_start>.
		1604
		1605	To implement this, configure an C<ev_timer> with a C<repeat> value
		1606	of C<60> and then call C<ev_timer_again> at start and each time you
		1607	successfully read or write some data. If you go into an idle state where
		1608	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1609	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1610
		1611	That means you can ignore both the C<ev_timer_start> function and the
		1612	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1613	member and C<ev_timer_again>.
		1614
		1615	At start:
		1616
		1617	ev_init (timer, callback);
		1618	timer->repeat = 60.;
		1619	ev_timer_again (loop, timer);
		1620
		1621	Each time there is some activity:
		1622
		1623	ev_timer_again (loop, timer);
		1624
		1625	It is even possible to change the time-out on the fly, regardless of
		1626	whether the watcher is active or not:
		1627
		1628	timer->repeat = 30.;
		1629	ev_timer_again (loop, timer);
		1630
		1631	This is slightly more efficient then stopping/starting the timer each time
		1632	you want to modify its timeout value, as libev does not have to completely
		1633	remove and re-insert the timer from/into its internal data structure.
		1634
		1635	It is, however, even simpler than the "obvious" way to do it.
		1636
		1637	=item 3. Let the timer time out, but then re-arm it as required.
		1638
		1639	This method is more tricky, but usually most efficient: Most timeouts are
		1640	relatively long compared to the intervals between other activity - in
		1641	our example, within 60 seconds, there are usually many I/O events with
		1642	associated activity resets.
		1643
		1644	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1645	but remember the time of last activity, and check for a real timeout only
		1646	within the callback:
		1647
		1648	ev_tstamp last_activity; // time of last activity
		1649
		1650	static void
		1651	callback (EV_P_ ev_timer *w, int revents)
		1652	{
		1653	ev_tstamp now = ev_now (EV_A);
		1654	ev_tstamp timeout = last_activity + 60.;
		1655
		1656	// if last_activity + 60. is older than now, we did time out
		1657	if (timeout < now)
		1658	{
		1659	// timeout occured, take action
		1660	}
		1661	else
		1662	{
		1663	// callback was invoked, but there was some activity, re-arm
		1664	// the watcher to fire in last_activity + 60, which is
		1665	// guaranteed to be in the future, so "again" is positive:
		1666	w->repeat = timeout - now;
		1667	ev_timer_again (EV_A_ w);
		1668	}
		1669	}
		1670
		1671	To summarise the callback: first calculate the real timeout (defined
		1672	as "60 seconds after the last activity"), then check if that time has
		1673	been reached, which means something I<did>, in fact, time out. Otherwise
		1674	the callback was invoked too early (C<timeout> is in the future), so
		1675	re-schedule the timer to fire at that future time, to see if maybe we have
		1676	a timeout then.
		1677
		1678	Note how C<ev_timer_again> is used, taking advantage of the
		1679	C<ev_timer_again> optimisation when the timer is already running.
		1680
		1681	This scheme causes more callback invocations (about one every 60 seconds
		1682	minus half the average time between activity), but virtually no calls to
		1683	libev to change the timeout.
		1684
		1685	To start the timer, simply initialise the watcher and set C<last_activity>
		1686	to the current time (meaning we just have some activity :), then call the
		1687	callback, which will "do the right thing" and start the timer:
		1688
		1689	ev_init (timer, callback);
		1690	last_activity = ev_now (loop);
		1691	callback (loop, timer, EV_TIMEOUT);
		1692
		1693	And when there is some activity, simply store the current time in
		1694	C<last_activity>, no libev calls at all:
		1695
		1696	last_actiivty = ev_now (loop);
		1697
		1698	This technique is slightly more complex, but in most cases where the
		1699	time-out is unlikely to be triggered, much more efficient.
		1700
		1701	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1702	callback :) - just change the timeout and invoke the callback, which will
		1703	fix things for you.
		1704
		1705	=item 4. Wee, just use a double-linked list for your timeouts.
		1706
		1707	If there is not one request, but many thousands (millions...), all
		1708	employing some kind of timeout with the same timeout value, then one can
		1709	do even better:
		1710
		1711	When starting the timeout, calculate the timeout value and put the timeout
		1712	at the I<end> of the list.
		1713
		1714	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1715	the list is expected to fire (for example, using the technique #3).
		1716
		1717	When there is some activity, remove the timer from the list, recalculate
		1718	the timeout, append it to the end of the list again, and make sure to
		1719	update the C<ev_timer> if it was taken from the beginning of the list.
		1720
		1721	This way, one can manage an unlimited number of timeouts in O(1) time for
		1722	starting, stopping and updating the timers, at the expense of a major
		1723	complication, and having to use a constant timeout. The constant timeout
		1724	ensures that the list stays sorted.
		1725
		1726	=back
		1727
		1728	So which method the best?
		1729
		1730	Method #2 is a simple no-brain-required solution that is adequate in most
		1731	situations. Method #3 requires a bit more thinking, but handles many cases
		1732	better, and isn't very complicated either. In most case, choosing either
		1733	one is fine, with #3 being better in typical situations.
		1734
		1735	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1736	rather complicated, but extremely efficient, something that really pays
		1737	off after the first million or so of active timers, i.e. it's usually
		1738	overkill :)
		1739
		1740	=head3 The special problem of time updates
		1741
		1742	Establishing the current time is a costly operation (it usually takes at
		1743	least two system calls): EV therefore updates its idea of the current
		1744	time only before and after C<ev_loop> collects new events, which causes a
		1745	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1746	lots of events in one iteration.
693		1747
694	The relative timeouts are calculated relative to the C<ev_now ()>	1748	The relative timeouts are calculated relative to the C<ev_now ()>
695	time. This is usually the right thing as this timestamp refers to the time	1749	time. This is usually the right thing as this timestamp refers to the time
696	of the event triggering whatever timeout you are modifying/starting. If	1750	of the event triggering whatever timeout you are modifying/starting. If
697	you suspect event processing to be delayed and you I<need> to base the timeout	1751	you suspect event processing to be delayed and you I<need> to base the
698	on the current time, use something like this to adjust for this:	1752	timeout on the current time, use something like this to adjust for this:
699		1753
700	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1754	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
701		1755
702	The callback is guarenteed to be invoked only when its timeout has passed,	1756	If the event loop is suspended for a long time, you can also force an
703	but if multiple timers become ready during the same loop iteration then	1757	update of the time returned by C<ev_now ()> by calling C<ev_now_update
704	order of execution is undefined.	1758	()>.
		1759
		1760	=head3 The special problems of suspended animation
		1761
		1762	When you leave the server world it is quite customary to hit machines that
		1763	can suspend/hibernate - what happens to the clocks during such a suspend?
		1764
		1765	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1766	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1767	to run until the system is suspended, but they will not advance while the
		1768	system is suspended. That means, on resume, it will be as if the program
		1769	was frozen for a few seconds, but the suspend time will not be counted
		1770	towards C<ev_timer> when a monotonic clock source is used. The real time
		1771	clock advanced as expected, but if it is used as sole clocksource, then a
		1772	long suspend would be detected as a time jump by libev, and timers would
		1773	be adjusted accordingly.
		1774
		1775	I would not be surprised to see different behaviour in different between
		1776	operating systems, OS versions or even different hardware.
		1777
		1778	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1779	time jump in the monotonic clocks and the realtime clock. If the program
		1780	is suspended for a very long time, and monotonic clock sources are in use,
		1781	then you can expect C<ev_timer>s to expire as the full suspension time
		1782	will be counted towards the timers. When no monotonic clock source is in
		1783	use, then libev will again assume a timejump and adjust accordingly.
		1784
		1785	It might be beneficial for this latter case to call C<ev_suspend>
		1786	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1787	deterministic behaviour in this case (you can do nothing against
		1788	C<SIGSTOP>).
		1789
		1790	=head3 Watcher-Specific Functions and Data Members
705		1791
706	=over 4	1792	=over 4
707		1793
708	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1794	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
709		1795
710	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1796	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
711		1797
712	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1798	Configure the timer to trigger after C<after> seconds. If C<repeat>
713	C<0.>, then it will automatically be stopped. If it is positive, then the	1799	is C<0.>, then it will automatically be stopped once the timeout is
714	timer will automatically be configured to trigger again C<repeat> seconds	1800	reached. If it is positive, then the timer will automatically be
715	later, again, and again, until stopped manually.	1801	configured to trigger again C<repeat> seconds later, again, and again,
		1802	until stopped manually.
716		1803
717	The timer itself will do a best-effort at avoiding drift, that is, if you	1804	The timer itself will do a best-effort at avoiding drift, that is, if
718	configure a timer to trigger every 10 seconds, then it will trigger at	1805	you configure a timer to trigger every 10 seconds, then it will normally
719	exactly 10 second intervals. If, however, your program cannot keep up with	1806	trigger at exactly 10 second intervals. If, however, your program cannot
720	the timer (because it takes longer than those 10 seconds to do stuff) the	1807	keep up with the timer (because it takes longer than those 10 seconds to
721	timer will not fire more than once per event loop iteration.	1808	do stuff) the timer will not fire more than once per event loop iteration.
722		1809
723	=item ev_timer_again (loop)	1810	=item ev_timer_again (loop, ev_timer *)
724		1811
725	This will act as if the timer timed out and restart it again if it is	1812	This will act as if the timer timed out and restart it again if it is
726	repeating. The exact semantics are:	1813	repeating. The exact semantics are:
727		1814
		1815	If the timer is pending, its pending status is cleared.
		1816
728	If the timer is started but nonrepeating, stop it.	1817	If the timer is started but non-repeating, stop it (as if it timed out).
729		1818
730	If the timer is repeating, either start it if necessary (with the repeat	1819	If the timer is repeating, either start it if necessary (with the
731	value), or reset the running timer to the repeat value.	1820	C<repeat> value), or reset the running timer to the C<repeat> value.
732		1821
733	This sounds a bit complicated, but here is a useful and typical	1822	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
734	example: Imagine you have a tcp connection and you want a so-called idle	1823	usage example.
735	timeout, that is, you want to be called when there have been, say, 60	1824
736	seconds of inactivity on the socket. The easiest way to do this is to	1825	=item ev_timer_remaining (loop, ev_timer *)
737	configure an C<ev_timer> with after=repeat=60 and calling ev_timer_again each	1826
738	time you successfully read or write some data. If you go into an idle	1827	Returns the remaining time until a timer fires. If the timer is active,
739	state where you do not expect data to travel on the socket, you can stop	1828	then this time is relative to the current event loop time, otherwise it's
740	the timer, and again will automatically restart it if need be.	1829	the timeout value currently configured.
		1830
		1831	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
		1832	C<5>. When the timer is started and one second passes, C<ev_timer_remain>
		1833	will return C<4>. When the timer expires and is restarted, it will return
		1834	roughly C<7> (likely slightly less as callback invocation takes some time,
		1835	too), and so on.
		1836
		1837	=item ev_tstamp repeat [read-write]
		1838
		1839	The current C<repeat> value. Will be used each time the watcher times out
		1840	or C<ev_timer_again> is called, and determines the next timeout (if any),
		1841	which is also when any modifications are taken into account.
741		1842
742	=back	1843	=back
743		1844
		1845	=head3 Examples
		1846
744	Example: create a timer that fires after 60 seconds.	1847	Example: Create a timer that fires after 60 seconds.
745		1848
746	static void	1849	static void
747	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1850	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
748	{	1851	{
749	.. one minute over, w is actually stopped right here	1852	.. one minute over, w is actually stopped right here
750	}	1853	}
751		1854
752	struct ev_timer mytimer;	1855	ev_timer mytimer;
753	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1856	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
754	ev_timer_start (loop, &mytimer);	1857	ev_timer_start (loop, &mytimer);
755		1858
756	Example: create a timeout timer that times out after 10 seconds of	1859	Example: Create a timeout timer that times out after 10 seconds of
757	inactivity.	1860	inactivity.
758		1861
759	static void	1862	static void
760	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1863	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
761	{	1864	{
762	.. ten seconds without any activity	1865	.. ten seconds without any activity
763	}	1866	}
764		1867
765	struct ev_timer mytimer;	1868	ev_timer mytimer;
766	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1869	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
767	ev_timer_again (&mytimer); /* start timer */	1870	ev_timer_again (&mytimer); /* start timer */
768	ev_loop (loop, 0);	1871	ev_loop (loop, 0);
769		1872
770	// and in some piece of code that gets executed on any "activity":	1873	// and in some piece of code that gets executed on any "activity":
771	// reset the timeout to start ticking again at 10 seconds	1874	// reset the timeout to start ticking again at 10 seconds
772	ev_timer_again (&mytimer);	1875	ev_timer_again (&mytimer);
773		1876
774		1877
775	=head2 C<ev_periodic> - to cron or not to cron	1878	=head2 C<ev_periodic> - to cron or not to cron?
776		1879
777	Periodic watchers are also timers of a kind, but they are very versatile	1880	Periodic watchers are also timers of a kind, but they are very versatile
778	(and unfortunately a bit complex).	1881	(and unfortunately a bit complex).
779		1882
780	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1883	Unlike C<ev_timer>, periodic watchers are not based on real time (or
781	but on wallclock time (absolute time). You can tell a periodic watcher	1884	relative time, the physical time that passes) but on wall clock time
782	to trigger "at" some specific point in time. For example, if you tell a	1885	(absolute time, the thing you can read on your calender or clock). The
783	periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()	1886	difference is that wall clock time can run faster or slower than real
784	+ 10.>) and then reset your system clock to the last year, then it will	1887	time, and time jumps are not uncommon (e.g. when you adjust your
785	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1888	wrist-watch).
786	roughly 10 seconds later and of course not if you reset your system time
787	again).
788		1889
789	They can also be used to implement vastly more complex timers, such as	1890	You can tell a periodic watcher to trigger after some specific point
		1891	in time: for example, if you tell a periodic watcher to trigger "in 10
		1892	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1893	not a delay) and then reset your system clock to January of the previous
		1894	year, then it will take a year or more to trigger the event (unlike an
		1895	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1896	it, as it uses a relative timeout).
		1897
		1898	C<ev_periodic> watchers can also be used to implement vastly more complex
790	triggering an event on eahc midnight, local time.	1899	timers, such as triggering an event on each "midnight, local time", or
		1900	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1901	those cannot react to time jumps.
791		1902
792	As with timers, the callback is guarenteed to be invoked only when the	1903	As with timers, the callback is guaranteed to be invoked only when the
793	time (C<at>) has been passed, but if multiple periodic timers become ready	1904	point in time where it is supposed to trigger has passed. If multiple
794	during the same loop iteration then order of execution is undefined.	1905	timers become ready during the same loop iteration then the ones with
		1906	earlier time-out values are invoked before ones with later time-out values
		1907	(but this is no longer true when a callback calls C<ev_loop> recursively).
		1908
		1909	=head3 Watcher-Specific Functions and Data Members
795		1910
796	=over 4	1911	=over 4
797		1912
798	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1913	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
799		1914
800	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1915	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
801		1916
802	Lots of arguments, lets sort it out... There are basically three modes of	1917	Lots of arguments, let's sort it out... There are basically three modes of
803	operation, and we will explain them from simplest to complex:	1918	operation, and we will explain them from simplest to most complex:
804		1919
805	=over 4	1920	=over 4
806		1921
807	=item * absolute timer (interval = reschedule_cb = 0)	1922	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
808		1923
809	In this configuration the watcher triggers an event at the wallclock time	1924	In this configuration the watcher triggers an event after the wall clock
810	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1925	time C<offset> has passed. It will not repeat and will not adjust when a
811	that is, if it is to be run at January 1st 2011 then it will run when the	1926	time jump occurs, that is, if it is to be run at January 1st 2011 then it
812	system time reaches or surpasses this time.	1927	will be stopped and invoked when the system clock reaches or surpasses
		1928	this point in time.
813		1929
814	=item * non-repeating interval timer (interval > 0, reschedule_cb = 0)	1930	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
815		1931
816	In this mode the watcher will always be scheduled to time out at the next	1932	In this mode the watcher will always be scheduled to time out at the next
817	C<at + N * interval> time (for some integer N) and then repeat, regardless	1933	C<offset + N * interval> time (for some integer N, which can also be
818	of any time jumps.	1934	negative) and then repeat, regardless of any time jumps. The C<offset>
		1935	argument is merely an offset into the C<interval> periods.
819		1936
820	This can be used to create timers that do not drift with respect to system	1937	This can be used to create timers that do not drift with respect to the
821	time:	1938	system clock, for example, here is an C<ev_periodic> that triggers each
		1939	hour, on the hour (with respect to UTC):
822		1940
823	ev_periodic_set (&periodic, 0., 3600., 0);	1941	ev_periodic_set (&periodic, 0., 3600., 0);
824		1942
825	This doesn't mean there will always be 3600 seconds in between triggers,	1943	This doesn't mean there will always be 3600 seconds in between triggers,
826	but only that the the callback will be called when the system time shows a	1944	but only that the callback will be called when the system time shows a
827	full hour (UTC), or more correctly, when the system time is evenly divisible	1945	full hour (UTC), or more correctly, when the system time is evenly divisible
828	by 3600.	1946	by 3600.
829		1947
830	Another way to think about it (for the mathematically inclined) is that	1948	Another way to think about it (for the mathematically inclined) is that
831	C<ev_periodic> will try to run the callback in this mode at the next possible	1949	C<ev_periodic> will try to run the callback in this mode at the next possible
832	time where C<time = at (mod interval)>, regardless of any time jumps.	1950	time where C<time = offset (mod interval)>, regardless of any time jumps.
833		1951
		1952	For numerical stability it is preferable that the C<offset> value is near
		1953	C<ev_now ()> (the current time), but there is no range requirement for
		1954	this value, and in fact is often specified as zero.
		1955
		1956	Note also that there is an upper limit to how often a timer can fire (CPU
		1957	speed for example), so if C<interval> is very small then timing stability
		1958	will of course deteriorate. Libev itself tries to be exact to be about one
		1959	millisecond (if the OS supports it and the machine is fast enough).
		1960
834	=item * manual reschedule mode (reschedule_cb = callback)	1961	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
835		1962
836	In this mode the values for C<interval> and C<at> are both being	1963	In this mode the values for C<interval> and C<offset> are both being
837	ignored. Instead, each time the periodic watcher gets scheduled, the	1964	ignored. Instead, each time the periodic watcher gets scheduled, the
838	reschedule callback will be called with the watcher as first, and the	1965	reschedule callback will be called with the watcher as first, and the
839	current time as second argument.	1966	current time as second argument.
840		1967
841	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1968	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
842	ever, or make any event loop modifications>. If you need to stop it,	1969	or make ANY other event loop modifications whatsoever, unless explicitly
843	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	1970	allowed by documentation here>.
844	starting a prepare watcher).
845		1971
		1972	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1973	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1974	only event loop modification you are allowed to do).
		1975
846	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1976	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
847	ev_tstamp now)>, e.g.:	1977	*w, ev_tstamp now)>, e.g.:
848		1978
		1979	static ev_tstamp
849	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1980	my_rescheduler (ev_periodic *w, ev_tstamp now)
850	{	1981	{
851	return now + 60.;	1982	return now + 60.;
852	}	1983	}
853		1984
854	It must return the next time to trigger, based on the passed time value	1985	It must return the next time to trigger, based on the passed time value
855	(that is, the lowest time value larger than to the second argument). It	1986	(that is, the lowest time value larger than to the second argument). It
856	will usually be called just before the callback will be triggered, but	1987	will usually be called just before the callback will be triggered, but
857	might be called at other times, too.	1988	might be called at other times, too.
858		1989
859	NOTE: I<< This callback must always return a time that is later than the	1990	NOTE: I<< This callback must always return a time that is higher than or
860	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	1991	equal to the passed C<now> value >>.
861		1992
862	This can be used to create very complex timers, such as a timer that	1993	This can be used to create very complex timers, such as a timer that
863	triggers on each midnight, local time. To do this, you would calculate the	1994	triggers on "next midnight, local time". To do this, you would calculate the
864	next midnight after C<now> and return the timestamp value for this. How	1995	next midnight after C<now> and return the timestamp value for this. How
865	you do this is, again, up to you (but it is not trivial, which is the main	1996	you do this is, again, up to you (but it is not trivial, which is the main
866	reason I omitted it as an example).	1997	reason I omitted it as an example).
867		1998
868	=back	1999	=back
…		…
872	Simply stops and restarts the periodic watcher again. This is only useful	2003	Simply stops and restarts the periodic watcher again. This is only useful
873	when you changed some parameters or the reschedule callback would return	2004	when you changed some parameters or the reschedule callback would return
874	a different time than the last time it was called (e.g. in a crond like	2005	a different time than the last time it was called (e.g. in a crond like
875	program when the crontabs have changed).	2006	program when the crontabs have changed).
876		2007
		2008	=item ev_tstamp ev_periodic_at (ev_periodic *)
		2009
		2010	When active, returns the absolute time that the watcher is supposed
		2011	to trigger next. This is not the same as the C<offset> argument to
		2012	C<ev_periodic_set>, but indeed works even in interval and manual
		2013	rescheduling modes.
		2014
		2015	=item ev_tstamp offset [read-write]
		2016
		2017	When repeating, this contains the offset value, otherwise this is the
		2018	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2019	although libev might modify this value for better numerical stability).
		2020
		2021	Can be modified any time, but changes only take effect when the periodic
		2022	timer fires or C<ev_periodic_again> is being called.
		2023
		2024	=item ev_tstamp interval [read-write]
		2025
		2026	The current interval value. Can be modified any time, but changes only
		2027	take effect when the periodic timer fires or C<ev_periodic_again> is being
		2028	called.
		2029
		2030	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
		2031
		2032	The current reschedule callback, or C<0>, if this functionality is
		2033	switched off. Can be changed any time, but changes only take effect when
		2034	the periodic timer fires or C<ev_periodic_again> is being called.
		2035
877	=back	2036	=back
878		2037
		2038	=head3 Examples
		2039
879	Example: call a callback every hour, or, more precisely, whenever the	2040	Example: Call a callback every hour, or, more precisely, whenever the
880	system clock is divisible by 3600. The callback invocation times have	2041	system time is divisible by 3600. The callback invocation times have
881	potentially a lot of jittering, but good long-term stability.	2042	potentially a lot of jitter, but good long-term stability.
882		2043
883	static void	2044	static void
884	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2045	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
885	{	2046	{
886	... its now a full hour (UTC, or TAI or whatever your clock follows)	2047	... its now a full hour (UTC, or TAI or whatever your clock follows)
887	}	2048	}
888		2049
889	struct ev_periodic hourly_tick;	2050	ev_periodic hourly_tick;
890	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2051	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
891	ev_periodic_start (loop, &hourly_tick);	2052	ev_periodic_start (loop, &hourly_tick);
892		2053
893	Example: the same as above, but use a reschedule callback to do it:	2054	Example: The same as above, but use a reschedule callback to do it:
894		2055
895	#include <math.h>	2056	#include <math.h>
896		2057
897	static ev_tstamp	2058	static ev_tstamp
898	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2059	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
899	{	2060	{
900	return fmod (now, 3600.) + 3600.;	2061	return now + (3600. - fmod (now, 3600.));
901	}	2062	}
902		2063
903	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2064	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
904		2065
905	Example: call a callback every hour, starting now:	2066	Example: Call a callback every hour, starting now:
906		2067
907	struct ev_periodic hourly_tick;	2068	ev_periodic hourly_tick;
908	ev_periodic_init (&hourly_tick, clock_cb,	2069	ev_periodic_init (&hourly_tick, clock_cb,
909	fmod (ev_now (loop), 3600.), 3600., 0);	2070	fmod (ev_now (loop), 3600.), 3600., 0);
910	ev_periodic_start (loop, &hourly_tick);	2071	ev_periodic_start (loop, &hourly_tick);
911		2072
912		2073
913	=head2 C<ev_signal> - signal me when a signal gets signalled	2074	=head2 C<ev_signal> - signal me when a signal gets signalled!
914		2075
915	Signal watchers will trigger an event when the process receives a specific	2076	Signal watchers will trigger an event when the process receives a specific
916	signal one or more times. Even though signals are very asynchronous, libev	2077	signal one or more times. Even though signals are very asynchronous, libev
917	will try it's best to deliver signals synchronously, i.e. as part of the	2078	will try it's best to deliver signals synchronously, i.e. as part of the
918	normal event processing, like any other event.	2079	normal event processing, like any other event.
919		2080
		2081	If you want signals asynchronously, just use C<sigaction> as you would
		2082	do without libev and forget about sharing the signal. You can even use
		2083	C<ev_async> from a signal handler to synchronously wake up an event loop.
		2084
920	You can configure as many watchers as you like per signal. Only when the	2085	You can configure as many watchers as you like per signal. Only when the
921	first watcher gets started will libev actually register a signal watcher	2086	first watcher gets started will libev actually register a signal handler
922	with the kernel (thus it coexists with your own signal handlers as long	2087	with the kernel (thus it coexists with your own signal handlers as long as
923	as you don't register any with libev). Similarly, when the last signal	2088	you don't register any with libev for the same signal). Similarly, when
924	watcher for a signal is stopped libev will reset the signal handler to	2089	the last signal watcher for a signal is stopped, libev will reset the
925	SIG_DFL (regardless of what it was set to before).	2090	signal handler to SIG_DFL (regardless of what it was set to before).
		2091
		2092	If possible and supported, libev will install its handlers with
		2093	C<SA_RESTART> behaviour enabled, so system calls should not be unduly
		2094	interrupted. If you have a problem with system calls getting interrupted by
		2095	signals you can block all signals in an C<ev_check> watcher and unblock
		2096	them in an C<ev_prepare> watcher.
		2097
		2098	=head3 Watcher-Specific Functions and Data Members
926		2099
927	=over 4	2100	=over 4
928		2101
929	=item ev_signal_init (ev_signal *, callback, int signum)	2102	=item ev_signal_init (ev_signal *, callback, int signum)
930		2103
931	=item ev_signal_set (ev_signal *, int signum)	2104	=item ev_signal_set (ev_signal *, int signum)
932		2105
933	Configures the watcher to trigger on the given signal number (usually one	2106	Configures the watcher to trigger on the given signal number (usually one
934	of the C<SIGxxx> constants).	2107	of the C<SIGxxx> constants).
935		2108
		2109	=item int signum [read-only]
		2110
		2111	The signal the watcher watches out for.
		2112
936	=back	2113	=back
937		2114
		2115	=head3 Examples
938		2116
		2117	Example: Try to exit cleanly on SIGINT.
		2118
		2119	static void
		2120	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		2121	{
		2122	ev_unloop (loop, EVUNLOOP_ALL);
		2123	}
		2124
		2125	ev_signal signal_watcher;
		2126	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		2127	ev_signal_start (loop, &signal_watcher);
		2128
		2129
939	=head2 C<ev_child> - wait for pid status changes	2130	=head2 C<ev_child> - watch out for process status changes
940		2131
941	Child watchers trigger when your process receives a SIGCHLD in response to	2132	Child watchers trigger when your process receives a SIGCHLD in response to
942	some child status changes (most typically when a child of yours dies).	2133	some child status changes (most typically when a child of yours dies or
		2134	exits). It is permissible to install a child watcher I<after> the child
		2135	has been forked (which implies it might have already exited), as long
		2136	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2137	forking and then immediately registering a watcher for the child is fine,
		2138	but forking and registering a watcher a few event loop iterations later or
		2139	in the next callback invocation is not.
		2140
		2141	Only the default event loop is capable of handling signals, and therefore
		2142	you can only register child watchers in the default event loop.
		2143
		2144	Due to some design glitches inside libev, child watchers will always be
		2145	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2146	libev)
		2147
		2148	=head3 Process Interaction
		2149
		2150	Libev grabs C<SIGCHLD> as soon as the default event loop is
		2151	initialised. This is necessary to guarantee proper behaviour even if
		2152	the first child watcher is started after the child exits. The occurrence
		2153	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		2154	synchronously as part of the event loop processing. Libev always reaps all
		2155	children, even ones not watched.
		2156
		2157	=head3 Overriding the Built-In Processing
		2158
		2159	Libev offers no special support for overriding the built-in child
		2160	processing, but if your application collides with libev's default child
		2161	handler, you can override it easily by installing your own handler for
		2162	C<SIGCHLD> after initialising the default loop, and making sure the
		2163	default loop never gets destroyed. You are encouraged, however, to use an
		2164	event-based approach to child reaping and thus use libev's support for
		2165	that, so other libev users can use C<ev_child> watchers freely.
		2166
		2167	=head3 Stopping the Child Watcher
		2168
		2169	Currently, the child watcher never gets stopped, even when the
		2170	child terminates, so normally one needs to stop the watcher in the
		2171	callback. Future versions of libev might stop the watcher automatically
		2172	when a child exit is detected.
		2173
		2174	=head3 Watcher-Specific Functions and Data Members
943		2175
944	=over 4	2176	=over 4
945		2177
946	=item ev_child_init (ev_child *, callback, int pid)	2178	=item ev_child_init (ev_child *, callback, int pid, int trace)
947		2179
948	=item ev_child_set (ev_child *, int pid)	2180	=item ev_child_set (ev_child *, int pid, int trace)
949		2181
950	Configures the watcher to wait for status changes of process C<pid> (or	2182	Configures the watcher to wait for status changes of process C<pid> (or
951	I<any> process if C<pid> is specified as C<0>). The callback can look	2183	I<any> process if C<pid> is specified as C<0>). The callback can look
952	at the C<rstatus> member of the C<ev_child> watcher structure to see	2184	at the C<rstatus> member of the C<ev_child> watcher structure to see
953	the status word (use the macros from C<sys/wait.h> and see your systems	2185	the status word (use the macros from C<sys/wait.h> and see your systems
954	C<waitpid> documentation). The C<rpid> member contains the pid of the	2186	C<waitpid> documentation). The C<rpid> member contains the pid of the
955	process causing the status change.	2187	process causing the status change. C<trace> must be either C<0> (only
		2188	activate the watcher when the process terminates) or C<1> (additionally
		2189	activate the watcher when the process is stopped or continued).
		2190
		2191	=item int pid [read-only]
		2192
		2193	The process id this watcher watches out for, or C<0>, meaning any process id.
		2194
		2195	=item int rpid [read-write]
		2196
		2197	The process id that detected a status change.
		2198
		2199	=item int rstatus [read-write]
		2200
		2201	The process exit/trace status caused by C<rpid> (see your systems
		2202	C<waitpid> and C<sys/wait.h> documentation for details).
956		2203
957	=back	2204	=back
958		2205
959	Example: try to exit cleanly on SIGINT and SIGTERM.	2206	=head3 Examples
960		2207
		2208	Example: C<fork()> a new process and install a child handler to wait for
		2209	its completion.
		2210
		2211	ev_child cw;
		2212
961	static void	2213	static void
962	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2214	child_cb (EV_P_ ev_child *w, int revents)
963	{	2215	{
964	ev_unloop (loop, EVUNLOOP_ALL);	2216	ev_child_stop (EV_A_ w);
		2217	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
965	}	2218	}
966		2219
967	struct ev_signal signal_watcher;	2220	pid_t pid = fork ();
968	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
969	ev_signal_start (loop, &sigint_cb);
970		2221
		2222	if (pid < 0)
		2223	// error
		2224	else if (pid == 0)
		2225	{
		2226	// the forked child executes here
		2227	exit (1);
		2228	}
		2229	else
		2230	{
		2231	ev_child_init (&cw, child_cb, pid, 0);
		2232	ev_child_start (EV_DEFAULT_ &cw);
		2233	}
971		2234
		2235
		2236	=head2 C<ev_stat> - did the file attributes just change?
		2237
		2238	This watches a file system path for attribute changes. That is, it calls
		2239	C<stat> on that path in regular intervals (or when the OS says it changed)
		2240	and sees if it changed compared to the last time, invoking the callback if
		2241	it did.
		2242
		2243	The path does not need to exist: changing from "path exists" to "path does
		2244	not exist" is a status change like any other. The condition "path does not
		2245	exist" (or more correctly "path cannot be stat'ed") is signified by the
		2246	C<st_nlink> field being zero (which is otherwise always forced to be at
		2247	least one) and all the other fields of the stat buffer having unspecified
		2248	contents.
		2249
		2250	The path I<must not> end in a slash or contain special components such as
		2251	C<.> or C<..>. The path I<should> be absolute: If it is relative and
		2252	your working directory changes, then the behaviour is undefined.
		2253
		2254	Since there is no portable change notification interface available, the
		2255	portable implementation simply calls C<stat(2)> regularly on the path
		2256	to see if it changed somehow. You can specify a recommended polling
		2257	interval for this case. If you specify a polling interval of C<0> (highly
		2258	recommended!) then a I<suitable, unspecified default> value will be used
		2259	(which you can expect to be around five seconds, although this might
		2260	change dynamically). Libev will also impose a minimum interval which is
		2261	currently around C<0.1>, but that's usually overkill.
		2262
		2263	This watcher type is not meant for massive numbers of stat watchers,
		2264	as even with OS-supported change notifications, this can be
		2265	resource-intensive.
		2266
		2267	At the time of this writing, the only OS-specific interface implemented
		2268	is the Linux inotify interface (implementing kqueue support is left as an
		2269	exercise for the reader. Note, however, that the author sees no way of
		2270	implementing C<ev_stat> semantics with kqueue, except as a hint).
		2271
		2272	=head3 ABI Issues (Largefile Support)
		2273
		2274	Libev by default (unless the user overrides this) uses the default
		2275	compilation environment, which means that on systems with large file
		2276	support disabled by default, you get the 32 bit version of the stat
		2277	structure. When using the library from programs that change the ABI to
		2278	use 64 bit file offsets the programs will fail. In that case you have to
		2279	compile libev with the same flags to get binary compatibility. This is
		2280	obviously the case with any flags that change the ABI, but the problem is
		2281	most noticeably displayed with ev_stat and large file support.
		2282
		2283	The solution for this is to lobby your distribution maker to make large
		2284	file interfaces available by default (as e.g. FreeBSD does) and not
		2285	optional. Libev cannot simply switch on large file support because it has
		2286	to exchange stat structures with application programs compiled using the
		2287	default compilation environment.
		2288
		2289	=head3 Inotify and Kqueue
		2290
		2291	When C<inotify (7)> support has been compiled into libev and present at
		2292	runtime, it will be used to speed up change detection where possible. The
		2293	inotify descriptor will be created lazily when the first C<ev_stat>
		2294	watcher is being started.
		2295
		2296	Inotify presence does not change the semantics of C<ev_stat> watchers
		2297	except that changes might be detected earlier, and in some cases, to avoid
		2298	making regular C<stat> calls. Even in the presence of inotify support
		2299	there are many cases where libev has to resort to regular C<stat> polling,
		2300	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2301	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2302	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2303	xfs are fully working) libev usually gets away without polling.
		2304
		2305	There is no support for kqueue, as apparently it cannot be used to
		2306	implement this functionality, due to the requirement of having a file
		2307	descriptor open on the object at all times, and detecting renames, unlinks
		2308	etc. is difficult.
		2309
		2310	=head3 C<stat ()> is a synchronous operation
		2311
		2312	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2313	the process. The exception are C<ev_stat> watchers - those call C<stat
		2314	()>, which is a synchronous operation.
		2315
		2316	For local paths, this usually doesn't matter: unless the system is very
		2317	busy or the intervals between stat's are large, a stat call will be fast,
		2318	as the path data is usually in memory already (except when starting the
		2319	watcher).
		2320
		2321	For networked file systems, calling C<stat ()> can block an indefinite
		2322	time due to network issues, and even under good conditions, a stat call
		2323	often takes multiple milliseconds.
		2324
		2325	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2326	paths, although this is fully supported by libev.
		2327
		2328	=head3 The special problem of stat time resolution
		2329
		2330	The C<stat ()> system call only supports full-second resolution portably,
		2331	and even on systems where the resolution is higher, most file systems
		2332	still only support whole seconds.
		2333
		2334	That means that, if the time is the only thing that changes, you can
		2335	easily miss updates: on the first update, C<ev_stat> detects a change and
		2336	calls your callback, which does something. When there is another update
		2337	within the same second, C<ev_stat> will be unable to detect unless the
		2338	stat data does change in other ways (e.g. file size).
		2339
		2340	The solution to this is to delay acting on a change for slightly more
		2341	than a second (or till slightly after the next full second boundary), using
		2342	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2343	ev_timer_again (loop, w)>).
		2344
		2345	The C<.02> offset is added to work around small timing inconsistencies
		2346	of some operating systems (where the second counter of the current time
		2347	might be be delayed. One such system is the Linux kernel, where a call to
		2348	C<gettimeofday> might return a timestamp with a full second later than
		2349	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2350	update file times then there will be a small window where the kernel uses
		2351	the previous second to update file times but libev might already execute
		2352	the timer callback).
		2353
		2354	=head3 Watcher-Specific Functions and Data Members
		2355
		2356	=over 4
		2357
		2358	=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)
		2359
		2360	=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)
		2361
		2362	Configures the watcher to wait for status changes of the given
		2363	C<path>. The C<interval> is a hint on how quickly a change is expected to
		2364	be detected and should normally be specified as C<0> to let libev choose
		2365	a suitable value. The memory pointed to by C<path> must point to the same
		2366	path for as long as the watcher is active.
		2367
		2368	The callback will receive an C<EV_STAT> event when a change was detected,
		2369	relative to the attributes at the time the watcher was started (or the
		2370	last change was detected).
		2371
		2372	=item ev_stat_stat (loop, ev_stat *)
		2373
		2374	Updates the stat buffer immediately with new values. If you change the
		2375	watched path in your callback, you could call this function to avoid
		2376	detecting this change (while introducing a race condition if you are not
		2377	the only one changing the path). Can also be useful simply to find out the
		2378	new values.
		2379
		2380	=item ev_statdata attr [read-only]
		2381
		2382	The most-recently detected attributes of the file. Although the type is
		2383	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
		2384	suitable for your system, but you can only rely on the POSIX-standardised
		2385	members to be present. If the C<st_nlink> member is C<0>, then there was
		2386	some error while C<stat>ing the file.
		2387
		2388	=item ev_statdata prev [read-only]
		2389
		2390	The previous attributes of the file. The callback gets invoked whenever
		2391	C<prev> != C<attr>, or, more precisely, one or more of these members
		2392	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2393	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
		2394
		2395	=item ev_tstamp interval [read-only]
		2396
		2397	The specified interval.
		2398
		2399	=item const char *path [read-only]
		2400
		2401	The file system path that is being watched.
		2402
		2403	=back
		2404
		2405	=head3 Examples
		2406
		2407	Example: Watch C</etc/passwd> for attribute changes.
		2408
		2409	static void
		2410	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
		2411	{
		2412	/* /etc/passwd changed in some way */
		2413	if (w->attr.st_nlink)
		2414	{
		2415	printf ("passwd current size %ld\n", (long)w->attr.st_size);
		2416	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
		2417	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
		2418	}
		2419	else
		2420	/* you shalt not abuse printf for puts */
		2421	puts ("wow, /etc/passwd is not there, expect problems. "
		2422	"if this is windows, they already arrived\n");
		2423	}
		2424
		2425	...
		2426	ev_stat passwd;
		2427
		2428	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		2429	ev_stat_start (loop, &passwd);
		2430
		2431	Example: Like above, but additionally use a one-second delay so we do not
		2432	miss updates (however, frequent updates will delay processing, too, so
		2433	one might do the work both on C<ev_stat> callback invocation I<and> on
		2434	C<ev_timer> callback invocation).
		2435
		2436	static ev_stat passwd;
		2437	static ev_timer timer;
		2438
		2439	static void
		2440	timer_cb (EV_P_ ev_timer *w, int revents)
		2441	{
		2442	ev_timer_stop (EV_A_ w);
		2443
		2444	/* now it's one second after the most recent passwd change */
		2445	}
		2446
		2447	static void
		2448	stat_cb (EV_P_ ev_stat *w, int revents)
		2449	{
		2450	/* reset the one-second timer */
		2451	ev_timer_again (EV_A_ &timer);
		2452	}
		2453
		2454	...
		2455	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2456	ev_stat_start (loop, &passwd);
		2457	ev_timer_init (&timer, timer_cb, 0., 1.02);
		2458
		2459
972	=head2 C<ev_idle> - when you've got nothing better to do	2460	=head2 C<ev_idle> - when you've got nothing better to do...
973		2461
974	Idle watchers trigger events when there are no other events are pending	2462	Idle watchers trigger events when no other events of the same or higher
975	(prepare, check and other idle watchers do not count). That is, as long	2463	priority are pending (prepare, check and other idle watchers do not count
976	as your process is busy handling sockets or timeouts (or even signals,	2464	as receiving "events").
977	imagine) it will not be triggered. But when your process is idle all idle	2465
978	watchers are being called again and again, once per event loop iteration -	2466	That is, as long as your process is busy handling sockets or timeouts
		2467	(or even signals, imagine) of the same or higher priority it will not be
		2468	triggered. But when your process is idle (or only lower-priority watchers
		2469	are pending), the idle watchers are being called once per event loop
979	until stopped, that is, or your process receives more events and becomes	2470	iteration - until stopped, that is, or your process receives more events
980	busy.	2471	and becomes busy again with higher priority stuff.
981		2472
982	The most noteworthy effect is that as long as any idle watchers are	2473	The most noteworthy effect is that as long as any idle watchers are
983	active, the process will not block when waiting for new events.	2474	active, the process will not block when waiting for new events.
984		2475
985	Apart from keeping your process non-blocking (which is a useful	2476	Apart from keeping your process non-blocking (which is a useful
986	effect on its own sometimes), idle watchers are a good place to do	2477	effect on its own sometimes), idle watchers are a good place to do
987	"pseudo-background processing", or delay processing stuff to after the	2478	"pseudo-background processing", or delay processing stuff to after the
988	event loop has handled all outstanding events.	2479	event loop has handled all outstanding events.
989		2480
		2481	=head3 Watcher-Specific Functions and Data Members
		2482
990	=over 4	2483	=over 4
991		2484
992	=item ev_idle_init (ev_signal *, callback)	2485	=item ev_idle_init (ev_idle *, callback)
993		2486
994	Initialises and configures the idle watcher - it has no parameters of any	2487	Initialises and configures the idle watcher - it has no parameters of any
995	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2488	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
996	believe me.	2489	believe me.
997		2490
998	=back	2491	=back
999		2492
		2493	=head3 Examples
		2494
1000	Example: dynamically allocate an C<ev_idle>, start it, and in the	2495	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1001	callback, free it. Alos, use no error checking, as usual.	2496	callback, free it. Also, use no error checking, as usual.
1002		2497
1003	static void	2498	static void
1004	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2499	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1005	{	2500	{
1006	free (w);	2501	free (w);
1007	// now do something you wanted to do when the program has	2502	// now do something you wanted to do when the program has
1008	// no longer asnything immediate to do.	2503	// no longer anything immediate to do.
1009	}	2504	}
1010		2505
1011	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2506	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1012	ev_idle_init (idle_watcher, idle_cb);	2507	ev_idle_init (idle_watcher, idle_cb);
1013	ev_idle_start (loop, idle_cb);	2508	ev_idle_start (loop, idle_watcher);
1014		2509
1015		2510
1016	=head2 C<ev_prepare> and C<ev_check> - customise your event loop	2511	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1017		2512
1018	Prepare and check watchers are usually (but not always) used in tandem:	2513	Prepare and check watchers are usually (but not always) used in pairs:
1019	prepare watchers get invoked before the process blocks and check watchers	2514	prepare watchers get invoked before the process blocks and check watchers
1020	afterwards.	2515	afterwards.
1021		2516
		2517	You I<must not> call C<ev_loop> or similar functions that enter
		2518	the current event loop from either C<ev_prepare> or C<ev_check>
		2519	watchers. Other loops than the current one are fine, however. The
		2520	rationale behind this is that you do not need to check for recursion in
		2521	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
		2522	C<ev_check> so if you have one watcher of each kind they will always be
		2523	called in pairs bracketing the blocking call.
		2524
1022	Their main purpose is to integrate other event mechanisms into libev and	2525	Their main purpose is to integrate other event mechanisms into libev and
1023	their use is somewhat advanced. This could be used, for example, to track	2526	their use is somewhat advanced. They could be used, for example, to track
1024	variable changes, implement your own watchers, integrate net-snmp or a	2527	variable changes, implement your own watchers, integrate net-snmp or a
1025	coroutine library and lots more.	2528	coroutine library and lots more. They are also occasionally useful if
		2529	you cache some data and want to flush it before blocking (for example,
		2530	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
		2531	watcher).
1026		2532
1027	This is done by examining in each prepare call which file descriptors need	2533	This is done by examining in each prepare call which file descriptors
1028	to be watched by the other library, registering C<ev_io> watchers for	2534	need to be watched by the other library, registering C<ev_io> watchers
1029	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2535	for them and starting an C<ev_timer> watcher for any timeouts (many
1030	provide just this functionality). Then, in the check watcher you check for	2536	libraries provide exactly this functionality). Then, in the check watcher,
1031	any events that occured (by checking the pending status of all watchers	2537	you check for any events that occurred (by checking the pending status
1032	and stopping them) and call back into the library. The I/O and timer	2538	of all watchers and stopping them) and call back into the library. The
1033	callbacks will never actually be called (but must be valid nevertheless,	2539	I/O and timer callbacks will never actually be called (but must be valid
1034	because you never know, you know?).	2540	nevertheless, because you never know, you know?).
1035		2541
1036	As another example, the Perl Coro module uses these hooks to integrate	2542	As another example, the Perl Coro module uses these hooks to integrate
1037	coroutines into libev programs, by yielding to other active coroutines	2543	coroutines into libev programs, by yielding to other active coroutines
1038	during each prepare and only letting the process block if no coroutines	2544	during each prepare and only letting the process block if no coroutines
1039	are ready to run (it's actually more complicated: it only runs coroutines	2545	are ready to run (it's actually more complicated: it only runs coroutines
1040	with priority higher than or equal to the event loop and one coroutine	2546	with priority higher than or equal to the event loop and one coroutine
1041	of lower priority, but only once, using idle watchers to keep the event	2547	of lower priority, but only once, using idle watchers to keep the event
1042	loop from blocking if lower-priority coroutines are active, thus mapping	2548	loop from blocking if lower-priority coroutines are active, thus mapping
1043	low-priority coroutines to idle/background tasks).	2549	low-priority coroutines to idle/background tasks).
1044		2550
		2551	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
		2552	priority, to ensure that they are being run before any other watchers
		2553	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2554
		2555	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
		2556	activate ("feed") events into libev. While libev fully supports this, they
		2557	might get executed before other C<ev_check> watchers did their job. As
		2558	C<ev_check> watchers are often used to embed other (non-libev) event
		2559	loops those other event loops might be in an unusable state until their
		2560	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
		2561	others).
		2562
		2563	=head3 Watcher-Specific Functions and Data Members
		2564
1045	=over 4	2565	=over 4
1046		2566
1047	=item ev_prepare_init (ev_prepare *, callback)	2567	=item ev_prepare_init (ev_prepare *, callback)
1048		2568
1049	=item ev_check_init (ev_check *, callback)	2569	=item ev_check_init (ev_check *, callback)
1050		2570
1051	Initialises and configures the prepare or check watcher - they have no	2571	Initialises and configures the prepare or check watcher - they have no
1052	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2572	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1053	macros, but using them is utterly, utterly and completely pointless.	2573	macros, but using them is utterly, utterly, utterly and completely
		2574	pointless.
1054		2575
1055	=back	2576	=back
1056		2577
1057	Example: *TODO*.	2578	=head3 Examples
1058		2579
		2580	There are a number of principal ways to embed other event loops or modules
		2581	into libev. Here are some ideas on how to include libadns into libev
		2582	(there is a Perl module named C<EV::ADNS> that does this, which you could
		2583	use as a working example. Another Perl module named C<EV::Glib> embeds a
		2584	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
		2585	Glib event loop).
1059		2586
		2587	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
		2588	and in a check watcher, destroy them and call into libadns. What follows
		2589	is pseudo-code only of course. This requires you to either use a low
		2590	priority for the check watcher or use C<ev_clear_pending> explicitly, as
		2591	the callbacks for the IO/timeout watchers might not have been called yet.
		2592
		2593	static ev_io iow [nfd];
		2594	static ev_timer tw;
		2595
		2596	static void
		2597	io_cb (struct ev_loop *loop, ev_io *w, int revents)
		2598	{
		2599	}
		2600
		2601	// create io watchers for each fd and a timer before blocking
		2602	static void
		2603	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
		2604	{
		2605	int timeout = 3600000;
		2606	struct pollfd fds [nfd];
		2607	// actual code will need to loop here and realloc etc.
		2608	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		2609
		2610	/* the callback is illegal, but won't be called as we stop during check */
		2611	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
		2612	ev_timer_start (loop, &tw);
		2613
		2614	// create one ev_io per pollfd
		2615	for (int i = 0; i < nfd; ++i)
		2616	{
		2617	ev_io_init (iow + i, io_cb, fds [i].fd,
		2618	((fds [i].events & POLLIN ? EV_READ : 0)
		2619	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		2620
		2621	fds [i].revents = 0;
		2622	ev_io_start (loop, iow + i);
		2623	}
		2624	}
		2625
		2626	// stop all watchers after blocking
		2627	static void
		2628	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
		2629	{
		2630	ev_timer_stop (loop, &tw);
		2631
		2632	for (int i = 0; i < nfd; ++i)
		2633	{
		2634	// set the relevant poll flags
		2635	// could also call adns_processreadable etc. here
		2636	struct pollfd *fd = fds + i;
		2637	int revents = ev_clear_pending (iow + i);
		2638	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
		2639	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
		2640
		2641	// now stop the watcher
		2642	ev_io_stop (loop, iow + i);
		2643	}
		2644
		2645	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		2646	}
		2647
		2648	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
		2649	in the prepare watcher and would dispose of the check watcher.
		2650
		2651	Method 3: If the module to be embedded supports explicit event
		2652	notification (libadns does), you can also make use of the actual watcher
		2653	callbacks, and only destroy/create the watchers in the prepare watcher.
		2654
		2655	static void
		2656	timer_cb (EV_P_ ev_timer *w, int revents)
		2657	{
		2658	adns_state ads = (adns_state)w->data;
		2659	update_now (EV_A);
		2660
		2661	adns_processtimeouts (ads, &tv_now);
		2662	}
		2663
		2664	static void
		2665	io_cb (EV_P_ ev_io *w, int revents)
		2666	{
		2667	adns_state ads = (adns_state)w->data;
		2668	update_now (EV_A);
		2669
		2670	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
		2671	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
		2672	}
		2673
		2674	// do not ever call adns_afterpoll
		2675
		2676	Method 4: Do not use a prepare or check watcher because the module you
		2677	want to embed is not flexible enough to support it. Instead, you can
		2678	override their poll function. The drawback with this solution is that the
		2679	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
		2680	this approach, effectively embedding EV as a client into the horrible
		2681	libglib event loop.
		2682
		2683	static gint
		2684	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2685	{
		2686	int got_events = 0;
		2687
		2688	for (n = 0; n < nfds; ++n)
		2689	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2690
		2691	if (timeout >= 0)
		2692	// create/start timer
		2693
		2694	// poll
		2695	ev_loop (EV_A_ 0);
		2696
		2697	// stop timer again
		2698	if (timeout >= 0)
		2699	ev_timer_stop (EV_A_ &to);
		2700
		2701	// stop io watchers again - their callbacks should have set
		2702	for (n = 0; n < nfds; ++n)
		2703	ev_io_stop (EV_A_ iow [n]);
		2704
		2705	return got_events;
		2706	}
		2707
		2708
1060	=head2 C<ev_embed> - when one backend isn't enough	2709	=head2 C<ev_embed> - when one backend isn't enough...
1061		2710
1062	This is a rather advanced watcher type that lets you embed one event loop	2711	This is a rather advanced watcher type that lets you embed one event loop
1063	into another.	2712	into another (currently only C<ev_io> events are supported in the embedded
		2713	loop, other types of watchers might be handled in a delayed or incorrect
		2714	fashion and must not be used).
1064		2715
1065	There are primarily two reasons you would want that: work around bugs and	2716	There are primarily two reasons you would want that: work around bugs and
1066	prioritise I/O.	2717	prioritise I/O.
1067		2718
1068	As an example for a bug workaround, the kqueue backend might only support	2719	As an example for a bug workaround, the kqueue backend might only support
1069	sockets on some platform, so it is unusable as generic backend, but you	2720	sockets on some platform, so it is unusable as generic backend, but you
1070	still want to make use of it because you have many sockets and it scales	2721	still want to make use of it because you have many sockets and it scales
1071	so nicely. In this case, you would create a kqueue-based loop and embed it	2722	so nicely. In this case, you would create a kqueue-based loop and embed
1072	into your default loop (which might use e.g. poll). Overall operation will	2723	it into your default loop (which might use e.g. poll). Overall operation
1073	be a bit slower because first libev has to poll and then call kevent, but	2724	will be a bit slower because first libev has to call C<poll> and then
1074	at least you can use both at what they are best.	2725	C<kevent>, but at least you can use both mechanisms for what they are
		2726	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1075		2727
1076	As for prioritising I/O: rarely you have the case where some fds have	2728	As for prioritising I/O: under rare circumstances you have the case where
1077	to be watched and handled very quickly (with low latency), and even	2729	some fds have to be watched and handled very quickly (with low latency),
1078	priorities and idle watchers might have too much overhead. In this case	2730	and even priorities and idle watchers might have too much overhead. In
1079	you would put all the high priority stuff in one loop and all the rest in	2731	this case you would put all the high priority stuff in one loop and all
1080	a second one, and embed the second one in the first.	2732	the rest in a second one, and embed the second one in the first.
1081		2733
1082	As long as the watcher is started it will automatically handle events. The	2734	As long as the watcher is active, the callback will be invoked every
1083	callback will be invoked whenever some events have been handled. You can	2735	time there might be events pending in the embedded loop. The callback
1084	set the callback to C<0> to avoid having to specify one if you are not	2736	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1085	interested in that.	2737	sweep and invoke their callbacks (the callback doesn't need to invoke the
		2738	C<ev_embed_sweep> function directly, it could also start an idle watcher
		2739	to give the embedded loop strictly lower priority for example).
1086		2740
1087	Also, there have not currently been made special provisions for forking:	2741	You can also set the callback to C<0>, in which case the embed watcher
1088	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2742	will automatically execute the embedded loop sweep whenever necessary.
1089	but you will also have to stop and restart any C<ev_embed> watchers
1090	yourself.
1091		2743
		2744	Fork detection will be handled transparently while the C<ev_embed> watcher
		2745	is active, i.e., the embedded loop will automatically be forked when the
		2746	embedding loop forks. In other cases, the user is responsible for calling
		2747	C<ev_loop_fork> on the embedded loop.
		2748
1092	Unfortunately, not all backends are embeddable, only the ones returned by	2749	Unfortunately, not all backends are embeddable: only the ones returned by
1093	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2750	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1094	portable one.	2751	portable one.
1095		2752
1096	So when you want to use this feature you will always have to be prepared	2753	So when you want to use this feature you will always have to be prepared
1097	that you cannot get an embeddable loop. The recommended way to get around	2754	that you cannot get an embeddable loop. The recommended way to get around
1098	this is to have a separate variables for your embeddable loop, try to	2755	this is to have a separate variables for your embeddable loop, try to
1099	create it, and if that fails, use the normal loop for everything:	2756	create it, and if that fails, use the normal loop for everything.
1100		2757
1101	struct ev_loop *loop_hi = ev_default_init (0);	2758	=head3 C<ev_embed> and fork
1102	struct ev_loop *loop_lo = 0;
1103	struct ev_embed embed;
1104
1105	// see if there is a chance of getting one that works
1106	// (remember that a flags value of 0 means autodetection)
1107	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1108	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1109	: 0;
1110		2759
1111	// if we got one, then embed it, otherwise default to loop_hi	2760	While the C<ev_embed> watcher is running, forks in the embedding loop will
1112	if (loop_lo)	2761	automatically be applied to the embedded loop as well, so no special
1113	{	2762	fork handling is required in that case. When the watcher is not running,
1114	ev_embed_init (&embed, 0, loop_lo);	2763	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1115	ev_embed_start (loop_hi, &embed);	2764	as applicable.
1116	}	2765
1117	else	2766	=head3 Watcher-Specific Functions and Data Members
1118	loop_lo = loop_hi;
1119		2767
1120	=over 4	2768	=over 4
1121		2769
1122	=item ev_embed_init (ev_embed *, callback, struct ev_loop *loop)	2770	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
1123		2771
1124	=item ev_embed_set (ev_embed *, callback, struct ev_loop *loop)	2772	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)
1125		2773
1126	Configures the watcher to embed the given loop, which must be embeddable.	2774	Configures the watcher to embed the given loop, which must be
		2775	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
		2776	invoked automatically, otherwise it is the responsibility of the callback
		2777	to invoke it (it will continue to be called until the sweep has been done,
		2778	if you do not want that, you need to temporarily stop the embed watcher).
		2779
		2780	=item ev_embed_sweep (loop, ev_embed *)
		2781
		2782	Make a single, non-blocking sweep over the embedded loop. This works
		2783	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
		2784	appropriate way for embedded loops.
		2785
		2786	=item struct ev_loop *other [read-only]
		2787
		2788	The embedded event loop.
1127		2789
1128	=back	2790	=back
1129		2791
		2792	=head3 Examples
		2793
		2794	Example: Try to get an embeddable event loop and embed it into the default
		2795	event loop. If that is not possible, use the default loop. The default
		2796	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2797	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2798	used).
		2799
		2800	struct ev_loop *loop_hi = ev_default_init (0);
		2801	struct ev_loop *loop_lo = 0;
		2802	ev_embed embed;
		2803
		2804	// see if there is a chance of getting one that works
		2805	// (remember that a flags value of 0 means autodetection)
		2806	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2807	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2808	: 0;
		2809
		2810	// if we got one, then embed it, otherwise default to loop_hi
		2811	if (loop_lo)
		2812	{
		2813	ev_embed_init (&embed, 0, loop_lo);
		2814	ev_embed_start (loop_hi, &embed);
		2815	}
		2816	else
		2817	loop_lo = loop_hi;
		2818
		2819	Example: Check if kqueue is available but not recommended and create
		2820	a kqueue backend for use with sockets (which usually work with any
		2821	kqueue implementation). Store the kqueue/socket-only event loop in
		2822	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2823
		2824	struct ev_loop *loop = ev_default_init (0);
		2825	struct ev_loop *loop_socket = 0;
		2826	ev_embed embed;
		2827
		2828	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2829	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2830	{
		2831	ev_embed_init (&embed, 0, loop_socket);
		2832	ev_embed_start (loop, &embed);
		2833	}
		2834
		2835	if (!loop_socket)
		2836	loop_socket = loop;
		2837
		2838	// now use loop_socket for all sockets, and loop for everything else
		2839
		2840
		2841	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
		2842
		2843	Fork watchers are called when a C<fork ()> was detected (usually because
		2844	whoever is a good citizen cared to tell libev about it by calling
		2845	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the
		2846	event loop blocks next and before C<ev_check> watchers are being called,
		2847	and only in the child after the fork. If whoever good citizen calling
		2848	C<ev_default_fork> cheats and calls it in the wrong process, the fork
		2849	handlers will be invoked, too, of course.
		2850
		2851	=head3 The special problem of life after fork - how is it possible?
		2852
		2853	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2854	up/change the process environment, followed by a call to C<exec()>. This
		2855	sequence should be handled by libev without any problems.
		2856
		2857	This changes when the application actually wants to do event handling
		2858	in the child, or both parent in child, in effect "continuing" after the
		2859	fork.
		2860
		2861	The default mode of operation (for libev, with application help to detect
		2862	forks) is to duplicate all the state in the child, as would be expected
		2863	when I<either> the parent I<or> the child process continues.
		2864
		2865	When both processes want to continue using libev, then this is usually the
		2866	wrong result. In that case, usually one process (typically the parent) is
		2867	supposed to continue with all watchers in place as before, while the other
		2868	process typically wants to start fresh, i.e. without any active watchers.
		2869
		2870	The cleanest and most efficient way to achieve that with libev is to
		2871	simply create a new event loop, which of course will be "empty", and
		2872	use that for new watchers. This has the advantage of not touching more
		2873	memory than necessary, and thus avoiding the copy-on-write, and the
		2874	disadvantage of having to use multiple event loops (which do not support
		2875	signal watchers).
		2876
		2877	When this is not possible, or you want to use the default loop for
		2878	other reasons, then in the process that wants to start "fresh", call
		2879	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2880	the default loop will "orphan" (not stop) all registered watchers, so you
		2881	have to be careful not to execute code that modifies those watchers. Note
		2882	also that in that case, you have to re-register any signal watchers.
		2883
		2884	=head3 Watcher-Specific Functions and Data Members
		2885
		2886	=over 4
		2887
		2888	=item ev_fork_init (ev_signal *, callback)
		2889
		2890	Initialises and configures the fork watcher - it has no parameters of any
		2891	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
		2892	believe me.
		2893
		2894	=back
		2895
		2896
		2897	=head2 C<ev_async> - how to wake up another event loop
		2898
		2899	In general, you cannot use an C<ev_loop> from multiple threads or other
		2900	asynchronous sources such as signal handlers (as opposed to multiple event
		2901	loops - those are of course safe to use in different threads).
		2902
		2903	Sometimes, however, you need to wake up another event loop you do not
		2904	control, for example because it belongs to another thread. This is what
		2905	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2906	can signal it by calling C<ev_async_send>, which is thread- and signal
		2907	safe.
		2908
		2909	This functionality is very similar to C<ev_signal> watchers, as signals,
		2910	too, are asynchronous in nature, and signals, too, will be compressed
		2911	(i.e. the number of callback invocations may be less than the number of
		2912	C<ev_async_sent> calls).
		2913
		2914	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2915	just the default loop.
		2916
		2917	=head3 Queueing
		2918
		2919	C<ev_async> does not support queueing of data in any way. The reason
		2920	is that the author does not know of a simple (or any) algorithm for a
		2921	multiple-writer-single-reader queue that works in all cases and doesn't
		2922	need elaborate support such as pthreads.
		2923
		2924	That means that if you want to queue data, you have to provide your own
		2925	queue. But at least I can tell you how to implement locking around your
		2926	queue:
		2927
		2928	=over 4
		2929
		2930	=item queueing from a signal handler context
		2931
		2932	To implement race-free queueing, you simply add to the queue in the signal
		2933	handler but you block the signal handler in the watcher callback. Here is
		2934	an example that does that for some fictitious SIGUSR1 handler:
		2935
		2936	static ev_async mysig;
		2937
		2938	static void
		2939	sigusr1_handler (void)
		2940	{
		2941	sometype data;
		2942
		2943	// no locking etc.
		2944	queue_put (data);
		2945	ev_async_send (EV_DEFAULT_ &mysig);
		2946	}
		2947
		2948	static void
		2949	mysig_cb (EV_P_ ev_async *w, int revents)
		2950	{
		2951	sometype data;
		2952	sigset_t block, prev;
		2953
		2954	sigemptyset (&block);
		2955	sigaddset (&block, SIGUSR1);
		2956	sigprocmask (SIG_BLOCK, &block, &prev);
		2957
		2958	while (queue_get (&data))
		2959	process (data);
		2960
		2961	if (sigismember (&prev, SIGUSR1)
		2962	sigprocmask (SIG_UNBLOCK, &block, 0);
		2963	}
		2964
		2965	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2966	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2967	either...).
		2968
		2969	=item queueing from a thread context
		2970
		2971	The strategy for threads is different, as you cannot (easily) block
		2972	threads but you can easily preempt them, so to queue safely you need to
		2973	employ a traditional mutex lock, such as in this pthread example:
		2974
		2975	static ev_async mysig;
		2976	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2977
		2978	static void
		2979	otherthread (void)
		2980	{
		2981	// only need to lock the actual queueing operation
		2982	pthread_mutex_lock (&mymutex);
		2983	queue_put (data);
		2984	pthread_mutex_unlock (&mymutex);
		2985
		2986	ev_async_send (EV_DEFAULT_ &mysig);
		2987	}
		2988
		2989	static void
		2990	mysig_cb (EV_P_ ev_async *w, int revents)
		2991	{
		2992	pthread_mutex_lock (&mymutex);
		2993
		2994	while (queue_get (&data))
		2995	process (data);
		2996
		2997	pthread_mutex_unlock (&mymutex);
		2998	}
		2999
		3000	=back
		3001
		3002
		3003	=head3 Watcher-Specific Functions and Data Members
		3004
		3005	=over 4
		3006
		3007	=item ev_async_init (ev_async *, callback)
		3008
		3009	Initialises and configures the async watcher - it has no parameters of any
		3010	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		3011	trust me.
		3012
		3013	=item ev_async_send (loop, ev_async *)
		3014
		3015	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		3016	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		3017	C<ev_feed_event>, this call is safe to do from other threads, signal or
		3018	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		3019	section below on what exactly this means).
		3020
		3021	Note that, as with other watchers in libev, multiple events might get
		3022	compressed into a single callback invocation (another way to look at this
		3023	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3024	reset when the event loop detects that).
		3025
		3026	This call incurs the overhead of a system call only once per event loop
		3027	iteration, so while the overhead might be noticeable, it doesn't apply to
		3028	repeated calls to C<ev_async_send> for the same event loop.
		3029
		3030	=item bool = ev_async_pending (ev_async *)
		3031
		3032	Returns a non-zero value when C<ev_async_send> has been called on the
		3033	watcher but the event has not yet been processed (or even noted) by the
		3034	event loop.
		3035
		3036	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		3037	the loop iterates next and checks for the watcher to have become active,
		3038	it will reset the flag again. C<ev_async_pending> can be used to very
		3039	quickly check whether invoking the loop might be a good idea.
		3040
		3041	Not that this does I<not> check whether the watcher itself is pending,
		3042	only whether it has been requested to make this watcher pending: there
		3043	is a time window between the event loop checking and resetting the async
		3044	notification, and the callback being invoked.
		3045
		3046	=back
		3047
1130		3048
1131	=head1 OTHER FUNCTIONS	3049	=head1 OTHER FUNCTIONS
1132		3050
1133	There are some other functions of possible interest. Described. Here. Now.	3051	There are some other functions of possible interest. Described. Here. Now.
1134		3052
1135	=over 4	3053	=over 4
1136		3054
1137	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3055	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1138		3056
1139	This function combines a simple timer and an I/O watcher, calls your	3057	This function combines a simple timer and an I/O watcher, calls your
1140	callback on whichever event happens first and automatically stop both	3058	callback on whichever event happens first and automatically stops both
1141	watchers. This is useful if you want to wait for a single event on an fd	3059	watchers. This is useful if you want to wait for a single event on an fd
1142	or timeout without having to allocate/configure/start/stop/free one or	3060	or timeout without having to allocate/configure/start/stop/free one or
1143	more watchers yourself.	3061	more watchers yourself.
1144		3062
1145	If C<fd> is less than 0, then no I/O watcher will be started and events	3063	If C<fd> is less than 0, then no I/O watcher will be started and the
1146	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3064	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1147	C<events> set will be craeted and started.	3065	the given C<fd> and C<events> set will be created and started.
1148		3066
1149	If C<timeout> is less than 0, then no timeout watcher will be	3067	If C<timeout> is less than 0, then no timeout watcher will be
1150	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3068	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1151	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3069	repeat = 0) will be started. C<0> is a valid timeout.
1152	dubious value.
1153		3070
1154	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3071	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
1155	passed an C<revents> set like normal event callbacks (a combination of	3072	passed an C<revents> set like normal event callbacks (a combination of
1156	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3073	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
1157	value passed to C<ev_once>:	3074	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3075	a timeout and an io event at the same time - you probably should give io
		3076	events precedence.
1158		3077
		3078	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		3079
1159	static void stdin_ready (int revents, void *arg)	3080	static void stdin_ready (int revents, void *arg)
1160	{	3081	{
1161	if (revents & EV_TIMEOUT)
1162	/* doh, nothing entered */;
1163	else if (revents & EV_READ)	3082	if (revents & EV_READ)
1164	/* stdin might have data for us, joy! */;	3083	/* stdin might have data for us, joy! */;
		3084	else if (revents & EV_TIMEOUT)
		3085	/* doh, nothing entered */;
1165	}	3086	}
1166		3087
1167	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3088	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1168		3089
1169	=item ev_feed_event (loop, watcher, int events)	3090	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
1170		3091
1171	Feeds the given event set into the event loop, as if the specified event	3092	Feeds the given event set into the event loop, as if the specified event
1172	had happened for the specified watcher (which must be a pointer to an	3093	had happened for the specified watcher (which must be a pointer to an
1173	initialised but not necessarily started event watcher).	3094	initialised but not necessarily started event watcher).
1174		3095
1175	=item ev_feed_fd_event (loop, int fd, int revents)	3096	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
1176		3097
1177	Feed an event on the given fd, as if a file descriptor backend detected	3098	Feed an event on the given fd, as if a file descriptor backend detected
1178	the given events it.	3099	the given events it.
1179		3100
1180	=item ev_feed_signal_event (loop, int signum)	3101	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
1181		3102
1182	Feed an event as if the given signal occured (loop must be the default loop!).	3103	Feed an event as if the given signal occurred (C<loop> must be the default
		3104	loop!).
1183		3105
1184	=back	3106	=back
1185		3107
1186		3108
1187	=head1 LIBEVENT EMULATION	3109	=head1 LIBEVENT EMULATION
…		…
1202		3124
1203	=item * Priorities are not currently supported. Initialising priorities	3125	=item * Priorities are not currently supported. Initialising priorities
1204	will fail and all watchers will have the same priority, even though there	3126	will fail and all watchers will have the same priority, even though there
1205	is an ev_pri field.	3127	is an ev_pri field.
1206		3128
		3129	=item * In libevent, the last base created gets the signals, in libev, the
		3130	first base created (== the default loop) gets the signals.
		3131
1207	=item * Other members are not supported.	3132	=item * Other members are not supported.
1208		3133
1209	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3134	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1210	to use the libev header file and library.	3135	to use the libev header file and library.
1211		3136
1212	=back	3137	=back
1213		3138
1214	=head1 C++ SUPPORT	3139	=head1 C++ SUPPORT
1215		3140
1216	TBD.	3141	Libev comes with some simplistic wrapper classes for C++ that mainly allow
		3142	you to use some convenience methods to start/stop watchers and also change
		3143	the callback model to a model using method callbacks on objects.
		3144
		3145	To use it,
		3146
		3147	#include <ev++.h>
		3148
		3149	This automatically includes F<ev.h> and puts all of its definitions (many
		3150	of them macros) into the global namespace. All C++ specific things are
		3151	put into the C<ev> namespace. It should support all the same embedding
		3152	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
		3153
		3154	Care has been taken to keep the overhead low. The only data member the C++
		3155	classes add (compared to plain C-style watchers) is the event loop pointer
		3156	that the watcher is associated with (or no additional members at all if
		3157	you disable C<EV_MULTIPLICITY> when embedding libev).
		3158
		3159	Currently, functions, and static and non-static member functions can be
		3160	used as callbacks. Other types should be easy to add as long as they only
		3161	need one additional pointer for context. If you need support for other
		3162	types of functors please contact the author (preferably after implementing
		3163	it).
		3164
		3165	Here is a list of things available in the C<ev> namespace:
		3166
		3167	=over 4
		3168
		3169	=item C<ev::READ>, C<ev::WRITE> etc.
		3170
		3171	These are just enum values with the same values as the C<EV_READ> etc.
		3172	macros from F<ev.h>.
		3173
		3174	=item C<ev::tstamp>, C<ev::now>
		3175
		3176	Aliases to the same types/functions as with the C<ev_> prefix.
		3177
		3178	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
		3179
		3180	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
		3181	the same name in the C<ev> namespace, with the exception of C<ev_signal>
		3182	which is called C<ev::sig> to avoid clashes with the C<signal> macro
		3183	defines by many implementations.
		3184
		3185	All of those classes have these methods:
		3186
		3187	=over 4
		3188
		3189	=item ev::TYPE::TYPE ()
		3190
		3191	=item ev::TYPE::TYPE (struct ev_loop *)
		3192
		3193	=item ev::TYPE::~TYPE
		3194
		3195	The constructor (optionally) takes an event loop to associate the watcher
		3196	with. If it is omitted, it will use C<EV_DEFAULT>.
		3197
		3198	The constructor calls C<ev_init> for you, which means you have to call the
		3199	C<set> method before starting it.
		3200
		3201	It will not set a callback, however: You have to call the templated C<set>
		3202	method to set a callback before you can start the watcher.
		3203
		3204	(The reason why you have to use a method is a limitation in C++ which does
		3205	not allow explicit template arguments for constructors).
		3206
		3207	The destructor automatically stops the watcher if it is active.
		3208
		3209	=item w->set<class, &class::method> (object *)
		3210
		3211	This method sets the callback method to call. The method has to have a
		3212	signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
		3213	first argument and the C<revents> as second. The object must be given as
		3214	parameter and is stored in the C<data> member of the watcher.
		3215
		3216	This method synthesizes efficient thunking code to call your method from
		3217	the C callback that libev requires. If your compiler can inline your
		3218	callback (i.e. it is visible to it at the place of the C<set> call and
		3219	your compiler is good :), then the method will be fully inlined into the
		3220	thunking function, making it as fast as a direct C callback.
		3221
		3222	Example: simple class declaration and watcher initialisation
		3223
		3224	struct myclass
		3225	{
		3226	void io_cb (ev::io &w, int revents) { }
		3227	}
		3228
		3229	myclass obj;
		3230	ev::io iow;
		3231	iow.set <myclass, &myclass::io_cb> (&obj);
		3232
		3233	=item w->set (object *)
		3234
		3235	This is an B<experimental> feature that might go away in a future version.
		3236
		3237	This is a variation of a method callback - leaving out the method to call
		3238	will default the method to C<operator ()>, which makes it possible to use
		3239	functor objects without having to manually specify the C<operator ()> all
		3240	the time. Incidentally, you can then also leave out the template argument
		3241	list.
		3242
		3243	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3244	int revents)>.
		3245
		3246	See the method-C<set> above for more details.
		3247
		3248	Example: use a functor object as callback.
		3249
		3250	struct myfunctor
		3251	{
		3252	void operator() (ev::io &w, int revents)
		3253	{
		3254	...
		3255	}
		3256	}
		3257
		3258	myfunctor f;
		3259
		3260	ev::io w;
		3261	w.set (&f);
		3262
		3263	=item w->set<function> (void *data = 0)
		3264
		3265	Also sets a callback, but uses a static method or plain function as
		3266	callback. The optional C<data> argument will be stored in the watcher's
		3267	C<data> member and is free for you to use.
		3268
		3269	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
		3270
		3271	See the method-C<set> above for more details.
		3272
		3273	Example: Use a plain function as callback.
		3274
		3275	static void io_cb (ev::io &w, int revents) { }
		3276	iow.set <io_cb> ();
		3277
		3278	=item w->set (struct ev_loop *)
		3279
		3280	Associates a different C<struct ev_loop> with this watcher. You can only
		3281	do this when the watcher is inactive (and not pending either).
		3282
		3283	=item w->set ([arguments])
		3284
		3285	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
		3286	called at least once. Unlike the C counterpart, an active watcher gets
		3287	automatically stopped and restarted when reconfiguring it with this
		3288	method.
		3289
		3290	=item w->start ()
		3291
		3292	Starts the watcher. Note that there is no C<loop> argument, as the
		3293	constructor already stores the event loop.
		3294
		3295	=item w->stop ()
		3296
		3297	Stops the watcher if it is active. Again, no C<loop> argument.
		3298
		3299	=item w->again () (C<ev::timer>, C<ev::periodic> only)
		3300
		3301	For C<ev::timer> and C<ev::periodic>, this invokes the corresponding
		3302	C<ev_TYPE_again> function.
		3303
		3304	=item w->sweep () (C<ev::embed> only)
		3305
		3306	Invokes C<ev_embed_sweep>.
		3307
		3308	=item w->update () (C<ev::stat> only)
		3309
		3310	Invokes C<ev_stat_stat>.
		3311
		3312	=back
		3313
		3314	=back
		3315
		3316	Example: Define a class with an IO and idle watcher, start one of them in
		3317	the constructor.
		3318
		3319	class myclass
		3320	{
		3321	ev::io io ; void io_cb (ev::io &w, int revents);
		3322	ev::idle idle; void idle_cb (ev::idle &w, int revents);
		3323
		3324	myclass (int fd)
		3325	{
		3326	io .set <myclass, &myclass::io_cb > (this);
		3327	idle.set <myclass, &myclass::idle_cb> (this);
		3328
		3329	io.start (fd, ev::READ);
		3330	}
		3331	};
		3332
		3333
		3334	=head1 OTHER LANGUAGE BINDINGS
		3335
		3336	Libev does not offer other language bindings itself, but bindings for a
		3337	number of languages exist in the form of third-party packages. If you know
		3338	any interesting language binding in addition to the ones listed here, drop
		3339	me a note.
		3340
		3341	=over 4
		3342
		3343	=item Perl
		3344
		3345	The EV module implements the full libev API and is actually used to test
		3346	libev. EV is developed together with libev. Apart from the EV core module,
		3347	there are additional modules that implement libev-compatible interfaces
		3348	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3349	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3350	and C<EV::Glib>).
		3351
		3352	It can be found and installed via CPAN, its homepage is at
		3353	L<http://software.schmorp.de/pkg/EV>.
		3354
		3355	=item Python
		3356
		3357	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3358	seems to be quite complete and well-documented.
		3359
		3360	=item Ruby
		3361
		3362	Tony Arcieri has written a ruby extension that offers access to a subset
		3363	of the libev API and adds file handle abstractions, asynchronous DNS and
		3364	more on top of it. It can be found via gem servers. Its homepage is at
		3365	L<http://rev.rubyforge.org/>.
		3366
		3367	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3368	makes rev work even on mingw.
		3369
		3370	=item Haskell
		3371
		3372	A haskell binding to libev is available at
		3373	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3374
		3375	=item D
		3376
		3377	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3378	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3379
		3380	=item Ocaml
		3381
		3382	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3383	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3384
		3385	=back
		3386
		3387
		3388	=head1 MACRO MAGIC
		3389
		3390	Libev can be compiled with a variety of options, the most fundamental
		3391	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
		3392	functions and callbacks have an initial C<struct ev_loop *> argument.
		3393
		3394	To make it easier to write programs that cope with either variant, the
		3395	following macros are defined:
		3396
		3397	=over 4
		3398
		3399	=item C<EV_A>, C<EV_A_>
		3400
		3401	This provides the loop I<argument> for functions, if one is required ("ev
		3402	loop argument"). The C<EV_A> form is used when this is the sole argument,
		3403	C<EV_A_> is used when other arguments are following. Example:
		3404
		3405	ev_unref (EV_A);
		3406	ev_timer_add (EV_A_ watcher);
		3407	ev_loop (EV_A_ 0);
		3408
		3409	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
		3410	which is often provided by the following macro.
		3411
		3412	=item C<EV_P>, C<EV_P_>
		3413
		3414	This provides the loop I<parameter> for functions, if one is required ("ev
		3415	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
		3416	C<EV_P_> is used when other parameters are following. Example:
		3417
		3418	// this is how ev_unref is being declared
		3419	static void ev_unref (EV_P);
		3420
		3421	// this is how you can declare your typical callback
		3422	static void cb (EV_P_ ev_timer *w, int revents)
		3423
		3424	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
		3425	suitable for use with C<EV_A>.
		3426
		3427	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
		3428
		3429	Similar to the other two macros, this gives you the value of the default
		3430	loop, if multiple loops are supported ("ev loop default").
		3431
		3432	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3433
		3434	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3435	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3436	is undefined when the default loop has not been initialised by a previous
		3437	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3438
		3439	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3440	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		3441
		3442	=back
		3443
		3444	Example: Declare and initialise a check watcher, utilising the above
		3445	macros so it will work regardless of whether multiple loops are supported
		3446	or not.
		3447
		3448	static void
		3449	check_cb (EV_P_ ev_timer *w, int revents)
		3450	{
		3451	ev_check_stop (EV_A_ w);
		3452	}
		3453
		3454	ev_check check;
		3455	ev_check_init (&check, check_cb);
		3456	ev_check_start (EV_DEFAULT_ &check);
		3457	ev_loop (EV_DEFAULT_ 0);
		3458
		3459	=head1 EMBEDDING
		3460
		3461	Libev can (and often is) directly embedded into host
		3462	applications. Examples of applications that embed it include the Deliantra
		3463	Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe)
		3464	and rxvt-unicode.
		3465
		3466	The goal is to enable you to just copy the necessary files into your
		3467	source directory without having to change even a single line in them, so
		3468	you can easily upgrade by simply copying (or having a checked-out copy of
		3469	libev somewhere in your source tree).
		3470
		3471	=head2 FILESETS
		3472
		3473	Depending on what features you need you need to include one or more sets of files
		3474	in your application.
		3475
		3476	=head3 CORE EVENT LOOP
		3477
		3478	To include only the libev core (all the C<ev_*> functions), with manual
		3479	configuration (no autoconf):
		3480
		3481	#define EV_STANDALONE 1
		3482	#include "ev.c"
		3483
		3484	This will automatically include F<ev.h>, too, and should be done in a
		3485	single C source file only to provide the function implementations. To use
		3486	it, do the same for F<ev.h> in all files wishing to use this API (best
		3487	done by writing a wrapper around F<ev.h> that you can include instead and
		3488	where you can put other configuration options):
		3489
		3490	#define EV_STANDALONE 1
		3491	#include "ev.h"
		3492
		3493	Both header files and implementation files can be compiled with a C++
		3494	compiler (at least, that's a stated goal, and breakage will be treated
		3495	as a bug).
		3496
		3497	You need the following files in your source tree, or in a directory
		3498	in your include path (e.g. in libev/ when using -Ilibev):
		3499
		3500	ev.h
		3501	ev.c
		3502	ev_vars.h
		3503	ev_wrap.h
		3504
		3505	ev_win32.c required on win32 platforms only
		3506
		3507	ev_select.c only when select backend is enabled (which is enabled by default)
		3508	ev_poll.c only when poll backend is enabled (disabled by default)
		3509	ev_epoll.c only when the epoll backend is enabled (disabled by default)
		3510	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		3511	ev_port.c only when the solaris port backend is enabled (disabled by default)
		3512
		3513	F<ev.c> includes the backend files directly when enabled, so you only need
		3514	to compile this single file.
		3515
		3516	=head3 LIBEVENT COMPATIBILITY API
		3517
		3518	To include the libevent compatibility API, also include:
		3519
		3520	#include "event.c"
		3521
		3522	in the file including F<ev.c>, and:
		3523
		3524	#include "event.h"
		3525
		3526	in the files that want to use the libevent API. This also includes F<ev.h>.
		3527
		3528	You need the following additional files for this:
		3529
		3530	event.h
		3531	event.c
		3532
		3533	=head3 AUTOCONF SUPPORT
		3534
		3535	Instead of using C<EV_STANDALONE=1> and providing your configuration in
		3536	whatever way you want, you can also C<m4_include([libev.m4])> in your
		3537	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
		3538	include F<config.h> and configure itself accordingly.
		3539
		3540	For this of course you need the m4 file:
		3541
		3542	libev.m4
		3543
		3544	=head2 PREPROCESSOR SYMBOLS/MACROS
		3545
		3546	Libev can be configured via a variety of preprocessor symbols you have to
		3547	define before including any of its files. The default in the absence of
		3548	autoconf is documented for every option.
		3549
		3550	=over 4
		3551
		3552	=item EV_STANDALONE
		3553
		3554	Must always be C<1> if you do not use autoconf configuration, which
		3555	keeps libev from including F<config.h>, and it also defines dummy
		3556	implementations for some libevent functions (such as logging, which is not
		3557	supported). It will also not define any of the structs usually found in
		3558	F<event.h> that are not directly supported by the libev core alone.
		3559
		3560	In stanbdalone mode, libev will still try to automatically deduce the
		3561	configuration, but has to be more conservative.
		3562
		3563	=item EV_USE_MONOTONIC
		3564
		3565	If defined to be C<1>, libev will try to detect the availability of the
		3566	monotonic clock option at both compile time and runtime. Otherwise no
		3567	use of the monotonic clock option will be attempted. If you enable this,
		3568	you usually have to link against librt or something similar. Enabling it
		3569	when the functionality isn't available is safe, though, although you have
		3570	to make sure you link against any libraries where the C<clock_gettime>
		3571	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
		3572
		3573	=item EV_USE_REALTIME
		3574
		3575	If defined to be C<1>, libev will try to detect the availability of the
		3576	real-time clock option at compile time (and assume its availability
		3577	at runtime if successful). Otherwise no use of the real-time clock
		3578	option will be attempted. This effectively replaces C<gettimeofday>
		3579	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
		3580	correctness. See the note about libraries in the description of
		3581	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3582	C<EV_USE_CLOCK_SYSCALL>.
		3583
		3584	=item EV_USE_CLOCK_SYSCALL
		3585
		3586	If defined to be C<1>, libev will try to use a direct syscall instead
		3587	of calling the system-provided C<clock_gettime> function. This option
		3588	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3589	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3590	programs needlessly. Using a direct syscall is slightly slower (in
		3591	theory), because no optimised vdso implementation can be used, but avoids
		3592	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3593	higher, as it simplifies linking (no need for C<-lrt>).
		3594
		3595	=item EV_USE_NANOSLEEP
		3596
		3597	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		3598	and will use it for delays. Otherwise it will use C<select ()>.
		3599
		3600	=item EV_USE_EVENTFD
		3601
		3602	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3603	available and will probe for kernel support at runtime. This will improve
		3604	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3605	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3606	2.7 or newer, otherwise disabled.
		3607
		3608	=item EV_USE_SELECT
		3609
		3610	If undefined or defined to be C<1>, libev will compile in support for the
		3611	C<select>(2) backend. No attempt at auto-detection will be done: if no
		3612	other method takes over, select will be it. Otherwise the select backend
		3613	will not be compiled in.
		3614
		3615	=item EV_SELECT_USE_FD_SET
		3616
		3617	If defined to C<1>, then the select backend will use the system C<fd_set>
		3618	structure. This is useful if libev doesn't compile due to a missing
		3619	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
		3620	on exotic systems. This usually limits the range of file descriptors to
		3621	some low limit such as 1024 or might have other limitations (winsocket
		3622	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
		3623	configures the maximum size of the C<fd_set>.
		3624
		3625	=item EV_SELECT_IS_WINSOCKET
		3626
		3627	When defined to C<1>, the select backend will assume that
		3628	select/socket/connect etc. don't understand file descriptors but
		3629	wants osf handles on win32 (this is the case when the select to
		3630	be used is the winsock select). This means that it will call
		3631	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
		3632	it is assumed that all these functions actually work on fds, even
		3633	on win32. Should not be defined on non-win32 platforms.
		3634
		3635	=item EV_FD_TO_WIN32_HANDLE
		3636
		3637	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3638	file descriptors to socket handles. When not defining this symbol (the
		3639	default), then libev will call C<_get_osfhandle>, which is usually
		3640	correct. In some cases, programs use their own file descriptor management,
		3641	in which case they can provide this function to map fds to socket handles.
		3642
		3643	=item EV_USE_POLL
		3644
		3645	If defined to be C<1>, libev will compile in support for the C<poll>(2)
		3646	backend. Otherwise it will be enabled on non-win32 platforms. It
		3647	takes precedence over select.
		3648
		3649	=item EV_USE_EPOLL
		3650
		3651	If defined to be C<1>, libev will compile in support for the Linux
		3652	C<epoll>(7) backend. Its availability will be detected at runtime,
		3653	otherwise another method will be used as fallback. This is the preferred
		3654	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3655	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3656
		3657	=item EV_USE_KQUEUE
		3658
		3659	If defined to be C<1>, libev will compile in support for the BSD style
		3660	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
		3661	otherwise another method will be used as fallback. This is the preferred
		3662	backend for BSD and BSD-like systems, although on most BSDs kqueue only
		3663	supports some types of fds correctly (the only platform we found that
		3664	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		3665	not be used unless explicitly requested. The best way to use it is to find
		3666	out whether kqueue supports your type of fd properly and use an embedded
		3667	kqueue loop.
		3668
		3669	=item EV_USE_PORT
		3670
		3671	If defined to be C<1>, libev will compile in support for the Solaris
		3672	10 port style backend. Its availability will be detected at runtime,
		3673	otherwise another method will be used as fallback. This is the preferred
		3674	backend for Solaris 10 systems.
		3675
		3676	=item EV_USE_DEVPOLL
		3677
		3678	Reserved for future expansion, works like the USE symbols above.
		3679
		3680	=item EV_USE_INOTIFY
		3681
		3682	If defined to be C<1>, libev will compile in support for the Linux inotify
		3683	interface to speed up C<ev_stat> watchers. Its actual availability will
		3684	be detected at runtime. If undefined, it will be enabled if the headers
		3685	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3686
		3687	=item EV_ATOMIC_T
		3688
		3689	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3690	access is atomic with respect to other threads or signal contexts. No such
		3691	type is easily found in the C language, so you can provide your own type
		3692	that you know is safe for your purposes. It is used both for signal handler "locking"
		3693	as well as for signal and thread safety in C<ev_async> watchers.
		3694
		3695	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3696	(from F<signal.h>), which is usually good enough on most platforms.
		3697
		3698	=item EV_H
		3699
		3700	The name of the F<ev.h> header file used to include it. The default if
		3701	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
		3702	used to virtually rename the F<ev.h> header file in case of conflicts.
		3703
		3704	=item EV_CONFIG_H
		3705
		3706	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
		3707	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
		3708	C<EV_H>, above.
		3709
		3710	=item EV_EVENT_H
		3711
		3712	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
		3713	of how the F<event.h> header can be found, the default is C<"event.h">.
		3714
		3715	=item EV_PROTOTYPES
		3716
		3717	If defined to be C<0>, then F<ev.h> will not define any function
		3718	prototypes, but still define all the structs and other symbols. This is
		3719	occasionally useful if you want to provide your own wrapper functions
		3720	around libev functions.
		3721
		3722	=item EV_MULTIPLICITY
		3723
		3724	If undefined or defined to C<1>, then all event-loop-specific functions
		3725	will have the C<struct ev_loop *> as first argument, and you can create
		3726	additional independent event loops. Otherwise there will be no support
		3727	for multiple event loops and there is no first event loop pointer
		3728	argument. Instead, all functions act on the single default loop.
		3729
		3730	=item EV_MINPRI
		3731
		3732	=item EV_MAXPRI
		3733
		3734	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
		3735	C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
		3736	provide for more priorities by overriding those symbols (usually defined
		3737	to be C<-2> and C<2>, respectively).
		3738
		3739	When doing priority-based operations, libev usually has to linearly search
		3740	all the priorities, so having many of them (hundreds) uses a lot of space
		3741	and time, so using the defaults of five priorities (-2 .. +2) is usually
		3742	fine.
		3743
		3744	If your embedding application does not need any priorities, defining these
		3745	both to C<0> will save some memory and CPU.
		3746
		3747	=item EV_PERIODIC_ENABLE
		3748
		3749	If undefined or defined to be C<1>, then periodic timers are supported. If
		3750	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3751	code.
		3752
		3753	=item EV_IDLE_ENABLE
		3754
		3755	If undefined or defined to be C<1>, then idle watchers are supported. If
		3756	defined to be C<0>, then they are not. Disabling them saves a few kB of
		3757	code.
		3758
		3759	=item EV_EMBED_ENABLE
		3760
		3761	If undefined or defined to be C<1>, then embed watchers are supported. If
		3762	defined to be C<0>, then they are not. Embed watchers rely on most other
		3763	watcher types, which therefore must not be disabled.
		3764
		3765	=item EV_STAT_ENABLE
		3766
		3767	If undefined or defined to be C<1>, then stat watchers are supported. If
		3768	defined to be C<0>, then they are not.
		3769
		3770	=item EV_FORK_ENABLE
		3771
		3772	If undefined or defined to be C<1>, then fork watchers are supported. If
		3773	defined to be C<0>, then they are not.
		3774
		3775	=item EV_ASYNC_ENABLE
		3776
		3777	If undefined or defined to be C<1>, then async watchers are supported. If
		3778	defined to be C<0>, then they are not.
		3779
		3780	=item EV_MINIMAL
		3781
		3782	If you need to shave off some kilobytes of code at the expense of some
		3783	speed (but with the full API), define this symbol to C<1>. Currently this
		3784	is used to override some inlining decisions, saves roughly 30% code size
		3785	on amd64. It also selects a much smaller 2-heap for timer management over
		3786	the default 4-heap.
		3787
		3788	You can save even more by disabling watcher types you do not need
		3789	and setting C<EV_MAXPRI> == C<EV_MINPRI>. Also, disabling C<assert>
		3790	(C<-DNDEBUG>) will usually reduce code size a lot.
		3791
		3792	Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to
		3793	provide a bare-bones event library. See C<ev.h> for details on what parts
		3794	of the API are still available, and do not complain if this subset changes
		3795	over time.
		3796
		3797	=item EV_PID_HASHSIZE
		3798
		3799	C<ev_child> watchers use a small hash table to distribute workload by
		3800	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
		3801	than enough. If you need to manage thousands of children you might want to
		3802	increase this value (I<must> be a power of two).
		3803
		3804	=item EV_INOTIFY_HASHSIZE
		3805
		3806	C<ev_stat> watchers use a small hash table to distribute workload by
		3807	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
		3808	usually more than enough. If you need to manage thousands of C<ev_stat>
		3809	watchers you might want to increase this value (I<must> be a power of
		3810	two).
		3811
		3812	=item EV_USE_4HEAP
		3813
		3814	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3815	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		3816	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		3817	faster performance with many (thousands) of watchers.
		3818
		3819	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3820	(disabled).
		3821
		3822	=item EV_HEAP_CACHE_AT
		3823
		3824	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3825	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		3826	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3827	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3828	but avoids random read accesses on heap changes. This improves performance
		3829	noticeably with many (hundreds) of watchers.
		3830
		3831	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3832	(disabled).
		3833
		3834	=item EV_VERIFY
		3835
		3836	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3837	be done: If set to C<0>, no internal verification code will be compiled
		3838	in. If set to C<1>, then verification code will be compiled in, but not
		3839	called. If set to C<2>, then the internal verification code will be
		3840	called once per loop, which can slow down libev. If set to C<3>, then the
		3841	verification code will be called very frequently, which will slow down
		3842	libev considerably.
		3843
		3844	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3845	C<0>.
		3846
		3847	=item EV_COMMON
		3848
		3849	By default, all watchers have a C<void *data> member. By redefining
		3850	this macro to a something else you can include more and other types of
		3851	members. You have to define it each time you include one of the files,
		3852	though, and it must be identical each time.
		3853
		3854	For example, the perl EV module uses something like this:
		3855
		3856	#define EV_COMMON \
		3857	SV *self; /* contains this struct */ \
		3858	SV *cb_sv, *fh /* note no trailing ";" */
		3859
		3860	=item EV_CB_DECLARE (type)
		3861
		3862	=item EV_CB_INVOKE (watcher, revents)
		3863
		3864	=item ev_set_cb (ev, cb)
		3865
		3866	Can be used to change the callback member declaration in each watcher,
		3867	and the way callbacks are invoked and set. Must expand to a struct member
		3868	definition and a statement, respectively. See the F<ev.h> header file for
		3869	their default definitions. One possible use for overriding these is to
		3870	avoid the C<struct ev_loop *> as first argument in all cases, or to use
		3871	method calls instead of plain function calls in C++.
		3872
		3873	=back
		3874
		3875	=head2 EXPORTED API SYMBOLS
		3876
		3877	If you need to re-export the API (e.g. via a DLL) and you need a list of
		3878	exported symbols, you can use the provided F<Symbol.*> files which list
		3879	all public symbols, one per line:
		3880
		3881	Symbols.ev for libev proper
		3882	Symbols.event for the libevent emulation
		3883
		3884	This can also be used to rename all public symbols to avoid clashes with
		3885	multiple versions of libev linked together (which is obviously bad in
		3886	itself, but sometimes it is inconvenient to avoid this).
		3887
		3888	A sed command like this will create wrapper C<#define>'s that you need to
		3889	include before including F<ev.h>:
		3890
		3891	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
		3892
		3893	This would create a file F<wrap.h> which essentially looks like this:
		3894
		3895	#define ev_backend myprefix_ev_backend
		3896	#define ev_check_start myprefix_ev_check_start
		3897	#define ev_check_stop myprefix_ev_check_stop
		3898	...
		3899
		3900	=head2 EXAMPLES
		3901
		3902	For a real-world example of a program the includes libev
		3903	verbatim, you can have a look at the EV perl module
		3904	(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		3905	the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public
		3906	interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file
		3907	will be compiled. It is pretty complex because it provides its own header
		3908	file.
		3909
		3910	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
		3911	that everybody includes and which overrides some configure choices:
		3912
		3913	#define EV_MINIMAL 1
		3914	#define EV_USE_POLL 0
		3915	#define EV_MULTIPLICITY 0
		3916	#define EV_PERIODIC_ENABLE 0
		3917	#define EV_STAT_ENABLE 0
		3918	#define EV_FORK_ENABLE 0
		3919	#define EV_CONFIG_H <config.h>
		3920	#define EV_MINPRI 0
		3921	#define EV_MAXPRI 0
		3922
		3923	#include "ev++.h"
		3924
		3925	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
		3926
		3927	#include "ev_cpp.h"
		3928	#include "ev.c"
		3929
		3930	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
		3931
		3932	=head2 THREADS AND COROUTINES
		3933
		3934	=head3 THREADS
		3935
		3936	All libev functions are reentrant and thread-safe unless explicitly
		3937	documented otherwise, but libev implements no locking itself. This means
		3938	that you can use as many loops as you want in parallel, as long as there
		3939	are no concurrent calls into any libev function with the same loop
		3940	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		3941	of course): libev guarantees that different event loops share no data
		3942	structures that need any locking.
		3943
		3944	Or to put it differently: calls with different loop parameters can be done
		3945	concurrently from multiple threads, calls with the same loop parameter
		3946	must be done serially (but can be done from different threads, as long as
		3947	only one thread ever is inside a call at any point in time, e.g. by using
		3948	a mutex per loop).
		3949
		3950	Specifically to support threads (and signal handlers), libev implements
		3951	so-called C<ev_async> watchers, which allow some limited form of
		3952	concurrency on the same event loop, namely waking it up "from the
		3953	outside".
		3954
		3955	If you want to know which design (one loop, locking, or multiple loops
		3956	without or something else still) is best for your problem, then I cannot
		3957	help you, but here is some generic advice:
		3958
		3959	=over 4
		3960
		3961	=item * most applications have a main thread: use the default libev loop
		3962	in that thread, or create a separate thread running only the default loop.
		3963
		3964	This helps integrating other libraries or software modules that use libev
		3965	themselves and don't care/know about threading.
		3966
		3967	=item * one loop per thread is usually a good model.
		3968
		3969	Doing this is almost never wrong, sometimes a better-performance model
		3970	exists, but it is always a good start.
		3971
		3972	=item * other models exist, such as the leader/follower pattern, where one
		3973	loop is handed through multiple threads in a kind of round-robin fashion.
		3974
		3975	Choosing a model is hard - look around, learn, know that usually you can do
		3976	better than you currently do :-)
		3977
		3978	=item * often you need to talk to some other thread which blocks in the
		3979	event loop.
		3980
		3981	C<ev_async> watchers can be used to wake them up from other threads safely
		3982	(or from signal contexts...).
		3983
		3984	An example use would be to communicate signals or other events that only
		3985	work in the default loop by registering the signal watcher with the
		3986	default loop and triggering an C<ev_async> watcher from the default loop
		3987	watcher callback into the event loop interested in the signal.
		3988
		3989	=back
		3990
		3991	=head4 THREAD LOCKING EXAMPLE
		3992
		3993	Here is a fictitious example of how to run an event loop in a different
		3994	thread than where callbacks are being invoked and watchers are
		3995	created/added/removed.
		3996
		3997	For a real-world example, see the C<EV::Loop::Async> perl module,
		3998	which uses exactly this technique (which is suited for many high-level
		3999	languages).
		4000
		4001	The example uses a pthread mutex to protect the loop data, a condition
		4002	variable to wait for callback invocations, an async watcher to notify the
		4003	event loop thread and an unspecified mechanism to wake up the main thread.
		4004
		4005	First, you need to associate some data with the event loop:
		4006
		4007	typedef struct {
		4008	mutex_t lock; /* global loop lock */
		4009	ev_async async_w;
		4010	thread_t tid;
		4011	cond_t invoke_cv;
		4012	} userdata;
		4013
		4014	void prepare_loop (EV_P)
		4015	{
		4016	// for simplicity, we use a static userdata struct.
		4017	static userdata u;
		4018
		4019	ev_async_init (&u->async_w, async_cb);
		4020	ev_async_start (EV_A_ &u->async_w);
		4021
		4022	pthread_mutex_init (&u->lock, 0);
		4023	pthread_cond_init (&u->invoke_cv, 0);
		4024
		4025	// now associate this with the loop
		4026	ev_set_userdata (EV_A_ u);
		4027	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4028	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4029
		4030	// then create the thread running ev_loop
		4031	pthread_create (&u->tid, 0, l_run, EV_A);
		4032	}
		4033
		4034	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4035	solely to wake up the event loop so it takes notice of any new watchers
		4036	that might have been added:
		4037
		4038	static void
		4039	async_cb (EV_P_ ev_async *w, int revents)
		4040	{
		4041	// just used for the side effects
		4042	}
		4043
		4044	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4045	protecting the loop data, respectively.
		4046
		4047	static void
		4048	l_release (EV_P)
		4049	{
		4050	userdata *u = ev_userdata (EV_A);
		4051	pthread_mutex_unlock (&u->lock);
		4052	}
		4053
		4054	static void
		4055	l_acquire (EV_P)
		4056	{
		4057	userdata *u = ev_userdata (EV_A);
		4058	pthread_mutex_lock (&u->lock);
		4059	}
		4060
		4061	The event loop thread first acquires the mutex, and then jumps straight
		4062	into C<ev_loop>:
		4063
		4064	void *
		4065	l_run (void *thr_arg)
		4066	{
		4067	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		4068
		4069	l_acquire (EV_A);
		4070	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4071	ev_loop (EV_A_ 0);
		4072	l_release (EV_A);
		4073
		4074	return 0;
		4075	}
		4076
		4077	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4078	signal the main thread via some unspecified mechanism (signals? pipe
		4079	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4080	have been called (in a while loop because a) spurious wakeups are possible
		4081	and b) skipping inter-thread-communication when there are no pending
		4082	watchers is very beneficial):
		4083
		4084	static void
		4085	l_invoke (EV_P)
		4086	{
		4087	userdata *u = ev_userdata (EV_A);
		4088
		4089	while (ev_pending_count (EV_A))
		4090	{
		4091	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4092	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4093	}
		4094	}
		4095
		4096	Now, whenever the main thread gets told to invoke pending watchers, it
		4097	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4098	thread to continue:
		4099
		4100	static void
		4101	real_invoke_pending (EV_P)
		4102	{
		4103	userdata *u = ev_userdata (EV_A);
		4104
		4105	pthread_mutex_lock (&u->lock);
		4106	ev_invoke_pending (EV_A);
		4107	pthread_cond_signal (&u->invoke_cv);
		4108	pthread_mutex_unlock (&u->lock);
		4109	}
		4110
		4111	Whenever you want to start/stop a watcher or do other modifications to an
		4112	event loop, you will now have to lock:
		4113
		4114	ev_timer timeout_watcher;
		4115	userdata *u = ev_userdata (EV_A);
		4116
		4117	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4118
		4119	pthread_mutex_lock (&u->lock);
		4120	ev_timer_start (EV_A_ &timeout_watcher);
		4121	ev_async_send (EV_A_ &u->async_w);
		4122	pthread_mutex_unlock (&u->lock);
		4123
		4124	Note that sending the C<ev_async> watcher is required because otherwise
		4125	an event loop currently blocking in the kernel will have no knowledge
		4126	about the newly added timer. By waking up the loop it will pick up any new
		4127	watchers in the next event loop iteration.
		4128
		4129	=head3 COROUTINES
		4130
		4131	Libev is very accommodating to coroutines ("cooperative threads"):
		4132	libev fully supports nesting calls to its functions from different
		4133	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		4134	different coroutines, and switch freely between both coroutines running
		4135	the loop, as long as you don't confuse yourself). The only exception is
		4136	that you must not do this from C<ev_periodic> reschedule callbacks.
		4137
		4138	Care has been taken to ensure that libev does not keep local state inside
		4139	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		4140	they do not call any callbacks.
		4141
		4142	=head2 COMPILER WARNINGS
		4143
		4144	Depending on your compiler and compiler settings, you might get no or a
		4145	lot of warnings when compiling libev code. Some people are apparently
		4146	scared by this.
		4147
		4148	However, these are unavoidable for many reasons. For one, each compiler
		4149	has different warnings, and each user has different tastes regarding
		4150	warning options. "Warn-free" code therefore cannot be a goal except when
		4151	targeting a specific compiler and compiler-version.
		4152
		4153	Another reason is that some compiler warnings require elaborate
		4154	workarounds, or other changes to the code that make it less clear and less
		4155	maintainable.
		4156
		4157	And of course, some compiler warnings are just plain stupid, or simply
		4158	wrong (because they don't actually warn about the condition their message
		4159	seems to warn about). For example, certain older gcc versions had some
		4160	warnings that resulted an extreme number of false positives. These have
		4161	been fixed, but some people still insist on making code warn-free with
		4162	such buggy versions.
		4163
		4164	While libev is written to generate as few warnings as possible,
		4165	"warn-free" code is not a goal, and it is recommended not to build libev
		4166	with any compiler warnings enabled unless you are prepared to cope with
		4167	them (e.g. by ignoring them). Remember that warnings are just that:
		4168	warnings, not errors, or proof of bugs.
		4169
		4170
		4171	=head2 VALGRIND
		4172
		4173	Valgrind has a special section here because it is a popular tool that is
		4174	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		4175
		4176	If you think you found a bug (memory leak, uninitialised data access etc.)
		4177	in libev, then check twice: If valgrind reports something like:
		4178
		4179	==2274== definitely lost: 0 bytes in 0 blocks.
		4180	==2274== possibly lost: 0 bytes in 0 blocks.
		4181	==2274== still reachable: 256 bytes in 1 blocks.
		4182
		4183	Then there is no memory leak, just as memory accounted to global variables
		4184	is not a memleak - the memory is still being referenced, and didn't leak.
		4185
		4186	Similarly, under some circumstances, valgrind might report kernel bugs
		4187	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4188	although an acceptable workaround has been found here), or it might be
		4189	confused.
		4190
		4191	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		4192	make it into some kind of religion.
		4193
		4194	If you are unsure about something, feel free to contact the mailing list
		4195	with the full valgrind report and an explanation on why you think this
		4196	is a bug in libev (best check the archives, too :). However, don't be
		4197	annoyed when you get a brisk "this is no bug" answer and take the chance
		4198	of learning how to interpret valgrind properly.
		4199
		4200	If you need, for some reason, empty reports from valgrind for your project
		4201	I suggest using suppression lists.
		4202
		4203
		4204	=head1 PORTABILITY NOTES
		4205
		4206	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		4207
		4208	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		4209	requires, and its I/O model is fundamentally incompatible with the POSIX
		4210	model. Libev still offers limited functionality on this platform in
		4211	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		4212	descriptors. This only applies when using Win32 natively, not when using
		4213	e.g. cygwin.
		4214
		4215	Lifting these limitations would basically require the full
		4216	re-implementation of the I/O system. If you are into these kinds of
		4217	things, then note that glib does exactly that for you in a very portable
		4218	way (note also that glib is the slowest event library known to man).
		4219
		4220	There is no supported compilation method available on windows except
		4221	embedding it into other applications.
		4222
		4223	Sensible signal handling is officially unsupported by Microsoft - libev
		4224	tries its best, but under most conditions, signals will simply not work.
		4225
		4226	Not a libev limitation but worth mentioning: windows apparently doesn't
		4227	accept large writes: instead of resulting in a partial write, windows will
		4228	either accept everything or return C<ENOBUFS> if the buffer is too large,
		4229	so make sure you only write small amounts into your sockets (less than a
		4230	megabyte seems safe, but this apparently depends on the amount of memory
		4231	available).
		4232
		4233	Due to the many, low, and arbitrary limits on the win32 platform and
		4234	the abysmal performance of winsockets, using a large number of sockets
		4235	is not recommended (and not reasonable). If your program needs to use
		4236	more than a hundred or so sockets, then likely it needs to use a totally
		4237	different implementation for windows, as libev offers the POSIX readiness
		4238	notification model, which cannot be implemented efficiently on windows
		4239	(due to Microsoft monopoly games).
		4240
		4241	A typical way to use libev under windows is to embed it (see the embedding
		4242	section for details) and use the following F<evwrap.h> header file instead
		4243	of F<ev.h>:
		4244
		4245	#define EV_STANDALONE /* keeps ev from requiring config.h */
		4246	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		4247
		4248	#include "ev.h"
		4249
		4250	And compile the following F<evwrap.c> file into your project (make sure
		4251	you do I<not> compile the F<ev.c> or any other embedded source files!):
		4252
		4253	#include "evwrap.h"
		4254	#include "ev.c"
		4255
		4256	=over 4
		4257
		4258	=item The winsocket select function
		4259
		4260	The winsocket C<select> function doesn't follow POSIX in that it
		4261	requires socket I<handles> and not socket I<file descriptors> (it is
		4262	also extremely buggy). This makes select very inefficient, and also
		4263	requires a mapping from file descriptors to socket handles (the Microsoft
		4264	C runtime provides the function C<_open_osfhandle> for this). See the
		4265	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		4266	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		4267
		4268	The configuration for a "naked" win32 using the Microsoft runtime
		4269	libraries and raw winsocket select is:
		4270
		4271	#define EV_USE_SELECT 1
		4272	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		4273
		4274	Note that winsockets handling of fd sets is O(n), so you can easily get a
		4275	complexity in the O(n²) range when using win32.
		4276
		4277	=item Limited number of file descriptors
		4278
		4279	Windows has numerous arbitrary (and low) limits on things.
		4280
		4281	Early versions of winsocket's select only supported waiting for a maximum
		4282	of C<64> handles (probably owning to the fact that all windows kernels
		4283	can only wait for C<64> things at the same time internally; Microsoft
		4284	recommends spawning a chain of threads and wait for 63 handles and the
		4285	previous thread in each. Sounds great!).
		4286
		4287	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		4288	to some high number (e.g. C<2048>) before compiling the winsocket select
		4289	call (which might be in libev or elsewhere, for example, perl and many
		4290	other interpreters do their own select emulation on windows).
		4291
		4292	Another limit is the number of file descriptors in the Microsoft runtime
		4293	libraries, which by default is C<64> (there must be a hidden I<64>
		4294	fetish or something like this inside Microsoft). You can increase this
		4295	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
		4296	(another arbitrary limit), but is broken in many versions of the Microsoft
		4297	runtime libraries. This might get you to about C<512> or C<2048> sockets
		4298	(depending on windows version and/or the phase of the moon). To get more,
		4299	you need to wrap all I/O functions and provide your own fd management, but
		4300	the cost of calling select (O(n²)) will likely make this unworkable.
		4301
		4302	=back
		4303
		4304	=head2 PORTABILITY REQUIREMENTS
		4305
		4306	In addition to a working ISO-C implementation and of course the
		4307	backend-specific APIs, libev relies on a few additional extensions:
		4308
		4309	=over 4
		4310
		4311	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		4312	calling conventions regardless of C<ev_watcher_type *>.
		4313
		4314	Libev assumes not only that all watcher pointers have the same internal
		4315	structure (guaranteed by POSIX but not by ISO C for example), but it also
		4316	assumes that the same (machine) code can be used to call any watcher
		4317	callback: The watcher callbacks have different type signatures, but libev
		4318	calls them using an C<ev_watcher *> internally.
		4319
		4320	=item C<sig_atomic_t volatile> must be thread-atomic as well
		4321
		4322	The type C<sig_atomic_t volatile> (or whatever is defined as
		4323	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		4324	threads. This is not part of the specification for C<sig_atomic_t>, but is
		4325	believed to be sufficiently portable.
		4326
		4327	=item C<sigprocmask> must work in a threaded environment
		4328
		4329	Libev uses C<sigprocmask> to temporarily block signals. This is not
		4330	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		4331	pthread implementations will either allow C<sigprocmask> in the "main
		4332	thread" or will block signals process-wide, both behaviours would
		4333	be compatible with libev. Interaction between C<sigprocmask> and
		4334	C<pthread_sigmask> could complicate things, however.
		4335
		4336	The most portable way to handle signals is to block signals in all threads
		4337	except the initial one, and run the default loop in the initial thread as
		4338	well.
		4339
		4340	=item C<long> must be large enough for common memory allocation sizes
		4341
		4342	To improve portability and simplify its API, libev uses C<long> internally
		4343	instead of C<size_t> when allocating its data structures. On non-POSIX
		4344	systems (Microsoft...) this might be unexpectedly low, but is still at
		4345	least 31 bits everywhere, which is enough for hundreds of millions of
		4346	watchers.
		4347
		4348	=item C<double> must hold a time value in seconds with enough accuracy
		4349
		4350	The type C<double> is used to represent timestamps. It is required to
		4351	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		4352	enough for at least into the year 4000. This requirement is fulfilled by
		4353	implementations implementing IEEE 754, which is basically all existing
		4354	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4355	2200.
		4356
		4357	=back
		4358
		4359	If you know of other additional requirements drop me a note.
		4360
		4361
		4362	=head1 ALGORITHMIC COMPLEXITIES
		4363
		4364	In this section the complexities of (many of) the algorithms used inside
		4365	libev will be documented. For complexity discussions about backends see
		4366	the documentation for C<ev_default_init>.
		4367
		4368	All of the following are about amortised time: If an array needs to be
		4369	extended, libev needs to realloc and move the whole array, but this
		4370	happens asymptotically rarer with higher number of elements, so O(1) might
		4371	mean that libev does a lengthy realloc operation in rare cases, but on
		4372	average it is much faster and asymptotically approaches constant time.
		4373
		4374	=over 4
		4375
		4376	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
		4377
		4378	This means that, when you have a watcher that triggers in one hour and
		4379	there are 100 watchers that would trigger before that, then inserting will
		4380	have to skip roughly seven (C<ld 100>) of these watchers.
		4381
		4382	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
		4383
		4384	That means that changing a timer costs less than removing/adding them,
		4385	as only the relative motion in the event queue has to be paid for.
		4386
		4387	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
		4388
		4389	These just add the watcher into an array or at the head of a list.
		4390
		4391	=item Stopping check/prepare/idle/fork/async watchers: O(1)
		4392
		4393	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
		4394
		4395	These watchers are stored in lists, so they need to be walked to find the
		4396	correct watcher to remove. The lists are usually short (you don't usually
		4397	have many watchers waiting for the same fd or signal: one is typical, two
		4398	is rare).
		4399
		4400	=item Finding the next timer in each loop iteration: O(1)
		4401
		4402	By virtue of using a binary or 4-heap, the next timer is always found at a
		4403	fixed position in the storage array.
		4404
		4405	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		4406
		4407	A change means an I/O watcher gets started or stopped, which requires
		4408	libev to recalculate its status (and possibly tell the kernel, depending
		4409	on backend and whether C<ev_io_set> was used).
		4410
		4411	=item Activating one watcher (putting it into the pending state): O(1)
		4412
		4413	=item Priority handling: O(number_of_priorities)
		4414
		4415	Priorities are implemented by allocating some space for each
		4416	priority. When doing priority-based operations, libev usually has to
		4417	linearly search all the priorities, but starting/stopping and activating
		4418	watchers becomes O(1) with respect to priority handling.
		4419
		4420	=item Sending an ev_async: O(1)
		4421
		4422	=item Processing ev_async_send: O(number_of_async_watchers)
		4423
		4424	=item Processing signals: O(max_signal_number)
		4425
		4426	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4427	calls in the current loop iteration. Checking for async and signal events
		4428	involves iterating over all running async watchers or all signal numbers.
		4429
		4430	=back
		4431
		4432
		4433	=head1 GLOSSARY
		4434
		4435	=over 4
		4436
		4437	=item active
		4438
		4439	A watcher is active as long as it has been started (has been attached to
		4440	an event loop) but not yet stopped (disassociated from the event loop).
		4441
		4442	=item application
		4443
		4444	In this document, an application is whatever is using libev.
		4445
		4446	=item callback
		4447
		4448	The address of a function that is called when some event has been
		4449	detected. Callbacks are being passed the event loop, the watcher that
		4450	received the event, and the actual event bitset.
		4451
		4452	=item callback invocation
		4453
		4454	The act of calling the callback associated with a watcher.
		4455
		4456	=item event
		4457
		4458	A change of state of some external event, such as data now being available
		4459	for reading on a file descriptor, time having passed or simply not having
		4460	any other events happening anymore.
		4461
		4462	In libev, events are represented as single bits (such as C<EV_READ> or
		4463	C<EV_TIMEOUT>).
		4464
		4465	=item event library
		4466
		4467	A software package implementing an event model and loop.
		4468
		4469	=item event loop
		4470
		4471	An entity that handles and processes external events and converts them
		4472	into callback invocations.
		4473
		4474	=item event model
		4475
		4476	The model used to describe how an event loop handles and processes
		4477	watchers and events.
		4478
		4479	=item pending
		4480
		4481	A watcher is pending as soon as the corresponding event has been detected,
		4482	and stops being pending as soon as the watcher will be invoked or its
		4483	pending status is explicitly cleared by the application.
		4484
		4485	A watcher can be pending, but not active. Stopping a watcher also clears
		4486	its pending status.
		4487
		4488	=item real time
		4489
		4490	The physical time that is observed. It is apparently strictly monotonic :)
		4491
		4492	=item wall-clock time
		4493
		4494	The time and date as shown on clocks. Unlike real time, it can actually
		4495	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4496	clock.
		4497
		4498	=item watcher
		4499
		4500	A data structure that describes interest in certain events. Watchers need
		4501	to be started (attached to an event loop) before they can receive events.
		4502
		4503	=item watcher invocation
		4504
		4505	The act of calling the callback associated with a watcher.
		4506
		4507	=back
1217		4508
1218	=head1 AUTHOR	4509	=head1 AUTHOR
1219		4510
1220	Marc Lehmann <libev@schmorp.de>.	4511	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
1221		4512

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