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Revision 1.388 by root, Tue Dec 20 04:08:35 2011 UTC

…		…
43		43
44	int	44	int
45	main (void)	45	main (void)
46	{	46	{
47	// use the default event loop unless you have special needs	47	// use the default event loop unless you have special needs
48	struct ev_loop *loop = ev_default_loop (0);	48	struct ev_loop *loop = EV_DEFAULT;
49		49
50	// initialise an io watcher, then start it	50	// initialise an io watcher, then start it
51	// this one will watch for stdin to become readable	51	// this one will watch for stdin to become readable
52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);	52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
53	ev_io_start (loop, &stdin_watcher);	53	ev_io_start (loop, &stdin_watcher);
…		…
58	ev_timer_start (loop, &timeout_watcher);	58	ev_timer_start (loop, &timeout_watcher);
59		59
60	// now wait for events to arrive	60	// now wait for events to arrive
61	ev_run (loop, 0);	61	ev_run (loop, 0);
62		62
63	// unloop was called, so exit	63	// break was called, so exit
64	return 0;	64	return 0;
65	}	65	}
66		66
67	=head1 ABOUT THIS DOCUMENT	67	=head1 ABOUT THIS DOCUMENT
68		68
…		…
77	on event-based programming, nor will it introduce event-based programming	77	on event-based programming, nor will it introduce event-based programming
78	with libev.	78	with libev.
79		79
80	Familiarity with event based programming techniques in general is assumed	80	Familiarity with event based programming techniques in general is assumed
81	throughout this document.	81	throughout this document.
		82
		83	=head1 WHAT TO READ WHEN IN A HURRY
		84
		85	This manual tries to be very detailed, but unfortunately, this also makes
		86	it very long. If you just want to know the basics of libev, I suggest
		87	reading L<ANATOMY OF A WATCHER>, then the L<EXAMPLE PROGRAM> above and
		88	look up the missing functions in L<GLOBAL FUNCTIONS> and the C<ev_io> and
		89	C<ev_timer> sections in L<WATCHER TYPES>.
82		90
83	=head1 ABOUT LIBEV	91	=head1 ABOUT LIBEV
84		92
85	Libev is an event loop: you register interest in certain events (such as a	93	Libev is an event loop: you register interest in certain events (such as a
86	file descriptor being readable or a timeout occurring), and it will manage	94	file descriptor being readable or a timeout occurring), and it will manage
…		…
124	this argument.	132	this argument.
125		133
126	=head2 TIME REPRESENTATION	134	=head2 TIME REPRESENTATION
127		135
128	Libev represents time as a single floating point number, representing	136	Libev represents time as a single floating point number, representing
129	the (fractional) number of seconds since the (POSIX) epoch (in practise	137	the (fractional) number of seconds since the (POSIX) epoch (in practice
130	somewhere near the beginning of 1970, details are complicated, don't	138	somewhere near the beginning of 1970, details are complicated, don't
131	ask). This type is called C<ev_tstamp>, which is what you should use	139	ask). This type is called C<ev_tstamp>, which is what you should use
132	too. It usually aliases to the C<double> type in C. When you need to do	140	too. It usually aliases to the C<double> type in C. When you need to do
133	any calculations on it, you should treat it as some floating point value.	141	any calculations on it, you should treat it as some floating point value.
134		142
…		…
165		173
166	=item ev_tstamp ev_time ()	174	=item ev_tstamp ev_time ()
167		175
168	Returns the current time as libev would use it. Please note that the	176	Returns the current time as libev would use it. Please note that the
169	C<ev_now> function is usually faster and also often returns the timestamp	177	C<ev_now> function is usually faster and also often returns the timestamp
170	you actually want to know.	178	you actually want to know. Also interesting is the combination of
		179	C<ev_now_update> and C<ev_now>.
171		180
172	=item ev_sleep (ev_tstamp interval)	181	=item ev_sleep (ev_tstamp interval)
173		182
174	Sleep for the given interval: The current thread will be blocked until	183	Sleep for the given interval: The current thread will be blocked
175	either it is interrupted or the given time interval has passed. Basically	184	until either it is interrupted or the given time interval has
		185	passed (approximately - it might return a bit earlier even if not
		186	interrupted). Returns immediately if C<< interval <= 0 >>.
		187
176	this is a sub-second-resolution C<sleep ()>.	188	Basically this is a sub-second-resolution C<sleep ()>.
		189
		190	The range of the C<interval> is limited - libev only guarantees to work
		191	with sleep times of up to one day (C<< interval <= 86400 >>).
177		192
178	=item int ev_version_major ()	193	=item int ev_version_major ()
179		194
180	=item int ev_version_minor ()	195	=item int ev_version_minor ()
181		196
…		…
192	as this indicates an incompatible change. Minor versions are usually	207	as this indicates an incompatible change. Minor versions are usually
193	compatible to older versions, so a larger minor version alone is usually	208	compatible to older versions, so a larger minor version alone is usually
194	not a problem.	209	not a problem.
195		210
196	Example: Make sure we haven't accidentally been linked against the wrong	211	Example: Make sure we haven't accidentally been linked against the wrong
197	version (note, however, that this will not detect ABI mismatches :).	212	version (note, however, that this will not detect other ABI mismatches,
		213	such as LFS or reentrancy).
198		214
199	assert (("libev version mismatch",	215	assert (("libev version mismatch",
200	ev_version_major () == EV_VERSION_MAJOR	216	ev_version_major () == EV_VERSION_MAJOR
201	&& ev_version_minor () >= EV_VERSION_MINOR));	217	&& ev_version_minor () >= EV_VERSION_MINOR));
202		218
…		…
213	assert (("sorry, no epoll, no sex",	229	assert (("sorry, no epoll, no sex",
214	ev_supported_backends () & EVBACKEND_EPOLL));	230	ev_supported_backends () & EVBACKEND_EPOLL));
215		231
216	=item unsigned int ev_recommended_backends ()	232	=item unsigned int ev_recommended_backends ()
217		233
218	Return the set of all backends compiled into this binary of libev and also	234	Return the set of all backends compiled into this binary of libev and
219	recommended for this platform. This set is often smaller than the one	235	also recommended for this platform, meaning it will work for most file
		236	descriptor types. This set is often smaller than the one returned by
220	returned by C<ev_supported_backends>, as for example kqueue is broken on	237	C<ev_supported_backends>, as for example kqueue is broken on most BSDs
221	most BSDs and will not be auto-detected unless you explicitly request it	238	and will not be auto-detected unless you explicitly request it (assuming
222	(assuming you know what you are doing). This is the set of backends that	239	you know what you are doing). This is the set of backends that libev will
223	libev will probe for if you specify no backends explicitly.	240	probe for if you specify no backends explicitly.
224		241
225	=item unsigned int ev_embeddable_backends ()	242	=item unsigned int ev_embeddable_backends ()
226		243
227	Returns the set of backends that are embeddable in other event loops. This	244	Returns the set of backends that are embeddable in other event loops. This
228	is the theoretical, all-platform, value. To find which backends	245	value is platform-specific but can include backends not available on the
229	might be supported on the current system, you would need to look at	246	current system. To find which embeddable backends might be supported on
230	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	247	the current system, you would need to look at C<ev_embeddable_backends ()
231	recommended ones.	248	& ev_supported_backends ()>, likewise for recommended ones.
232		249
233	See the description of C<ev_embed> watchers for more info.	250	See the description of C<ev_embed> watchers for more info.
234		251
235	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]	252	=item ev_set_allocator (void *(*cb)(void *ptr, long size))
236		253
237	Sets the allocation function to use (the prototype is similar - the	254	Sets the allocation function to use (the prototype is similar - the
238	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is	255	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
239	used to allocate and free memory (no surprises here). If it returns zero	256	used to allocate and free memory (no surprises here). If it returns zero
240	when memory needs to be allocated (C<size != 0>), the library might abort	257	when memory needs to be allocated (C<size != 0>), the library might abort
…		…
266	}	283	}
267		284
268	...	285	...
269	ev_set_allocator (persistent_realloc);	286	ev_set_allocator (persistent_realloc);
270		287
271	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]	288	=item ev_set_syserr_cb (void (*cb)(const char *msg))
272		289
273	Set the callback function to call on a retryable system call error (such	290	Set the callback function to call on a retryable system call error (such
274	as failed select, poll, epoll_wait). The message is a printable string	291	as failed select, poll, epoll_wait). The message is a printable string
275	indicating the system call or subsystem causing the problem. If this	292	indicating the system call or subsystem causing the problem. If this
276	callback is set, then libev will expect it to remedy the situation, no	293	callback is set, then libev will expect it to remedy the situation, no
…		…
288	}	305	}
289		306
290	...	307	...
291	ev_set_syserr_cb (fatal_error);	308	ev_set_syserr_cb (fatal_error);
292		309
		310	=item ev_feed_signal (int signum)
		311
		312	This function can be used to "simulate" a signal receive. It is completely
		313	safe to call this function at any time, from any context, including signal
		314	handlers or random threads.
		315
		316	Its main use is to customise signal handling in your process, especially
		317	in the presence of threads. For example, you could block signals
		318	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
		319	creating any loops), and in one thread, use C<sigwait> or any other
		320	mechanism to wait for signals, then "deliver" them to libev by calling
		321	C<ev_feed_signal>.
		322
293	=back	323	=back
294		324
295	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	325	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
296		326
297	An event loop is described by a C<struct ev_loop *> (the C<struct> is	327	An event loop is described by a C<struct ev_loop *> (the C<struct> is
298	I<not> optional in this case unless libev 3 compatibility is disabled, as	328	I<not> optional in this case unless libev 3 compatibility is disabled, as
299	libev 3 had an C<ev_loop> function colliding with the struct name).	329	libev 3 had an C<ev_loop> function colliding with the struct name).
300		330
301	The library knows two types of such loops, the I<default> loop, which	331	The library knows two types of such loops, the I<default> loop, which
302	supports signals and child events, and dynamically created event loops	332	supports child process events, and dynamically created event loops which
303	which do not.	333	do not.
304		334
305	=over 4	335	=over 4
306		336
307	=item struct ev_loop *ev_default_loop (unsigned int flags)	337	=item struct ev_loop *ev_default_loop (unsigned int flags)
308		338
309	This will initialise the default event loop if it hasn't been initialised	339	This returns the "default" event loop object, which is what you should
310	yet and return it. If the default loop could not be initialised, returns	340	normally use when you just need "the event loop". Event loop objects and
311	false. If it already was initialised it simply returns it (and ignores the	341	the C<flags> parameter are described in more detail in the entry for
312	flags. If that is troubling you, check C<ev_backend ()> afterwards).	342	C<ev_loop_new>.
		343
		344	If the default loop is already initialised then this function simply
		345	returns it (and ignores the flags. If that is troubling you, check
		346	C<ev_backend ()> afterwards). Otherwise it will create it with the given
		347	flags, which should almost always be C<0>, unless the caller is also the
		348	one calling C<ev_run> or otherwise qualifies as "the main program".
313		349
314	If you don't know what event loop to use, use the one returned from this	350	If you don't know what event loop to use, use the one returned from this
315	function.	351	function (or via the C<EV_DEFAULT> macro).
316		352
317	Note that this function is I<not> thread-safe, so if you want to use it	353	Note that this function is I<not> thread-safe, so if you want to use it
318	from multiple threads, you have to lock (note also that this is unlikely,	354	from multiple threads, you have to employ some kind of mutex (note also
319	as loops cannot be shared easily between threads anyway).	355	that this case is unlikely, as loops cannot be shared easily between
		356	threads anyway).
320		357
321	The default loop is the only loop that can handle C<ev_signal> and	358	The default loop is the only loop that can handle C<ev_child> watchers,
322	C<ev_child> watchers, and to do this, it always registers a handler	359	and to do this, it always registers a handler for C<SIGCHLD>. If this is
323	for C<SIGCHLD>. If this is a problem for your application you can either	360	a problem for your application you can either create a dynamic loop with
324	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you	361	C<ev_loop_new> which doesn't do that, or you can simply overwrite the
325	can simply overwrite the C<SIGCHLD> signal handler I<after> calling	362	C<SIGCHLD> signal handler I<after> calling C<ev_default_init>.
326	C<ev_default_init>.	363
		364	Example: This is the most typical usage.
		365
		366	if (!ev_default_loop (0))
		367	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		368
		369	Example: Restrict libev to the select and poll backends, and do not allow
		370	environment settings to be taken into account:
		371
		372	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		373
		374	=item struct ev_loop *ev_loop_new (unsigned int flags)
		375
		376	This will create and initialise a new event loop object. If the loop
		377	could not be initialised, returns false.
		378
		379	This function is thread-safe, and one common way to use libev with
		380	threads is indeed to create one loop per thread, and using the default
		381	loop in the "main" or "initial" thread.
327		382
328	The flags argument can be used to specify special behaviour or specific	383	The flags argument can be used to specify special behaviour or specific
329	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	384	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
330		385
331	The following flags are supported:	386	The following flags are supported:
…		…
366	environment variable.	421	environment variable.
367		422
368	=item C<EVFLAG_NOINOTIFY>	423	=item C<EVFLAG_NOINOTIFY>
369		424
370	When this flag is specified, then libev will not attempt to use the	425	When this flag is specified, then libev will not attempt to use the
371	I<inotify> API for it's C<ev_stat> watchers. Apart from debugging and	426	I<inotify> API for its C<ev_stat> watchers. Apart from debugging and
372	testing, this flag can be useful to conserve inotify file descriptors, as	427	testing, this flag can be useful to conserve inotify file descriptors, as
373	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.	428	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
374		429
375	=item C<EVFLAG_SIGNALFD>	430	=item C<EVFLAG_SIGNALFD>
376		431
377	When this flag is specified, then libev will attempt to use the	432	When this flag is specified, then libev will attempt to use the
378	I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This API	433	I<signalfd> API for its C<ev_signal> (and C<ev_child>) watchers. This API
379	delivers signals synchronously, which makes it both faster and might make	434	delivers signals synchronously, which makes it both faster and might make
380	it possible to get the queued signal data. It can also simplify signal	435	it possible to get the queued signal data. It can also simplify signal
381	handling with threads, as long as you properly block signals in your	436	handling with threads, as long as you properly block signals in your
382	threads that are not interested in handling them.	437	threads that are not interested in handling them.
383		438
384	Signalfd will not be used by default as this changes your signal mask, and	439	Signalfd will not be used by default as this changes your signal mask, and
385	there are a lot of shoddy libraries and programs (glib's threadpool for	440	there are a lot of shoddy libraries and programs (glib's threadpool for
386	example) that can't properly initialise their signal masks.	441	example) that can't properly initialise their signal masks.
		442
		443	=item C<EVFLAG_NOSIGMASK>
		444
		445	When this flag is specified, then libev will avoid to modify the signal
		446	mask. Specifically, this means you have to make sure signals are unblocked
		447	when you want to receive them.
		448
		449	This behaviour is useful when you want to do your own signal handling, or
		450	want to handle signals only in specific threads and want to avoid libev
		451	unblocking the signals.
		452
		453	It's also required by POSIX in a threaded program, as libev calls
		454	C<sigprocmask>, whose behaviour is officially unspecified.
		455
		456	This flag's behaviour will become the default in future versions of libev.
387		457
388	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	458	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
389		459
390	This is your standard select(2) backend. Not I<completely> standard, as	460	This is your standard select(2) backend. Not I<completely> standard, as
391	libev tries to roll its own fd_set with no limits on the number of fds,	461	libev tries to roll its own fd_set with no limits on the number of fds,
…		…
419	=item C<EVBACKEND_EPOLL> (value 4, Linux)	489	=item C<EVBACKEND_EPOLL> (value 4, Linux)
420		490
421	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9	491	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
422	kernels).	492	kernels).
423		493
424	For few fds, this backend is a bit little slower than poll and select,	494	For few fds, this backend is a bit little slower than poll and select, but
425	but it scales phenomenally better. While poll and select usually scale	495	it scales phenomenally better. While poll and select usually scale like
426	like O(total_fds) where n is the total number of fds (or the highest fd),	496	O(total_fds) where total_fds is the total number of fds (or the highest
427	epoll scales either O(1) or O(active_fds).	497	fd), epoll scales either O(1) or O(active_fds).
428		498
429	The epoll mechanism deserves honorable mention as the most misdesigned	499	The epoll mechanism deserves honorable mention as the most misdesigned
430	of the more advanced event mechanisms: mere annoyances include silently	500	of the more advanced event mechanisms: mere annoyances include silently
431	dropping file descriptors, requiring a system call per change per file	501	dropping file descriptors, requiring a system call per change per file
432	descriptor (and unnecessary guessing of parameters), problems with dup and	502	descriptor (and unnecessary guessing of parameters), problems with dup,
		503	returning before the timeout value, resulting in additional iterations
		504	(and only giving 5ms accuracy while select on the same platform gives
433	so on. The biggest issue is fork races, however - if a program forks then	505	0.1ms) and so on. The biggest issue is fork races, however - if a program
434	I<both> parent and child process have to recreate the epoll set, which can	506	forks then I<both> parent and child process have to recreate the epoll
435	take considerable time (one syscall per file descriptor) and is of course	507	set, which can take considerable time (one syscall per file descriptor)
436	hard to detect.	508	and is of course hard to detect.
437		509
438	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but	510	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
439	of course I<doesn't>, and epoll just loves to report events for totally	511	but of course I<doesn't>, and epoll just loves to report events for
440	I<different> file descriptors (even already closed ones, so one cannot	512	totally I<different> file descriptors (even already closed ones, so
441	even remove them from the set) than registered in the set (especially	513	one cannot even remove them from the set) than registered in the set
442	on SMP systems). Libev tries to counter these spurious notifications by	514	(especially on SMP systems). Libev tries to counter these spurious
443	employing an additional generation counter and comparing that against the	515	notifications by employing an additional generation counter and comparing
444	events to filter out spurious ones, recreating the set when required. Last	516	that against the events to filter out spurious ones, recreating the set
		517	when required. Epoll also erroneously rounds down timeouts, but gives you
		518	no way to know when and by how much, so sometimes you have to busy-wait
		519	because epoll returns immediately despite a nonzero timeout. And last
445	not least, it also refuses to work with some file descriptors which work	520	not least, it also refuses to work with some file descriptors which work
446	perfectly fine with C<select> (files, many character devices...).	521	perfectly fine with C<select> (files, many character devices...).
		522
		523	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		524	cobbled together in a hurry, no thought to design or interaction with
		525	others. Oh, the pain, will it ever stop...
447		526
448	While stopping, setting and starting an I/O watcher in the same iteration	527	While stopping, setting and starting an I/O watcher in the same iteration
449	will result in some caching, there is still a system call per such	528	will result in some caching, there is still a system call per such
450	incident (because the same I<file descriptor> could point to a different	529	incident (because the same I<file descriptor> could point to a different
451	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed	530	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
…		…
517	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	596	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
518		597
519	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	598	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
520	it's really slow, but it still scales very well (O(active_fds)).	599	it's really slow, but it still scales very well (O(active_fds)).
521		600
522	Please note that Solaris event ports can deliver a lot of spurious
523	notifications, so you need to use non-blocking I/O or other means to avoid
524	blocking when no data (or space) is available.
525
526	While this backend scales well, it requires one system call per active	601	While this backend scales well, it requires one system call per active
527	file descriptor per loop iteration. For small and medium numbers of file	602	file descriptor per loop iteration. For small and medium numbers of file
528	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	603	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
529	might perform better.	604	might perform better.
530		605
531	On the positive side, with the exception of the spurious readiness	606	On the positive side, this backend actually performed fully to
532	notifications, this backend actually performed fully to specification
533	in all tests and is fully embeddable, which is a rare feat among the	607	specification in all tests and is fully embeddable, which is a rare feat
534	OS-specific backends (I vastly prefer correctness over speed hacks).	608	among the OS-specific backends (I vastly prefer correctness over speed
		609	hacks).
		610
		611	On the negative side, the interface is I<bizarre> - so bizarre that
		612	even sun itself gets it wrong in their code examples: The event polling
		613	function sometimes returns events to the caller even though an error
		614	occurred, but with no indication whether it has done so or not (yes, it's
		615	even documented that way) - deadly for edge-triggered interfaces where you
		616	absolutely have to know whether an event occurred or not because you have
		617	to re-arm the watcher.
		618
		619	Fortunately libev seems to be able to work around these idiocies.
535		620
536	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	621	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
537	C<EVBACKEND_POLL>.	622	C<EVBACKEND_POLL>.
538		623
539	=item C<EVBACKEND_ALL>	624	=item C<EVBACKEND_ALL>
540		625
541	Try all backends (even potentially broken ones that wouldn't be tried	626	Try all backends (even potentially broken ones that wouldn't be tried
542	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	627	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
543	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	628	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
544		629
545	It is definitely not recommended to use this flag.	630	It is definitely not recommended to use this flag, use whatever
		631	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		632	at all.
		633
		634	=item C<EVBACKEND_MASK>
		635
		636	Not a backend at all, but a mask to select all backend bits from a
		637	C<flags> value, in case you want to mask out any backends from a flags
		638	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
546		639
547	=back	640	=back
548		641
549	If one or more of the backend flags are or'ed into the flags value,	642	If one or more of the backend flags are or'ed into the flags value,
550	then only these backends will be tried (in the reverse order as listed	643	then only these backends will be tried (in the reverse order as listed
551	here). If none are specified, all backends in C<ev_recommended_backends	644	here). If none are specified, all backends in C<ev_recommended_backends
552	()> will be tried.	645	()> will be tried.
553		646
554	Example: This is the most typical usage.
555
556	if (!ev_default_loop (0))
557	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
558
559	Example: Restrict libev to the select and poll backends, and do not allow
560	environment settings to be taken into account:
561
562	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
563
564	Example: Use whatever libev has to offer, but make sure that kqueue is
565	used if available (warning, breaks stuff, best use only with your own
566	private event loop and only if you know the OS supports your types of
567	fds):
568
569	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
570
571	=item struct ev_loop *ev_loop_new (unsigned int flags)
572
573	Similar to C<ev_default_loop>, but always creates a new event loop that is
574	always distinct from the default loop.
575
576	Note that this function I<is> thread-safe, and one common way to use
577	libev with threads is indeed to create one loop per thread, and using the
578	default loop in the "main" or "initial" thread.
579
580	Example: Try to create a event loop that uses epoll and nothing else.	647	Example: Try to create a event loop that uses epoll and nothing else.
581		648
582	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	649	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
583	if (!epoller)	650	if (!epoller)
584	fatal ("no epoll found here, maybe it hides under your chair");	651	fatal ("no epoll found here, maybe it hides under your chair");
585		652
		653	Example: Use whatever libev has to offer, but make sure that kqueue is
		654	used if available.
		655
		656	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		657
586	=item ev_default_destroy ()	658	=item ev_loop_destroy (loop)
587		659
588	Destroys the default loop (frees all memory and kernel state etc.). None	660	Destroys an event loop object (frees all memory and kernel state
589	of the active event watchers will be stopped in the normal sense, so	661	etc.). None of the active event watchers will be stopped in the normal
590	e.g. C<ev_is_active> might still return true. It is your responsibility to	662	sense, so e.g. C<ev_is_active> might still return true. It is your
591	either stop all watchers cleanly yourself I<before> calling this function,	663	responsibility to either stop all watchers cleanly yourself I<before>
592	or cope with the fact afterwards (which is usually the easiest thing, you	664	calling this function, or cope with the fact afterwards (which is usually
593	can just ignore the watchers and/or C<free ()> them for example).	665	the easiest thing, you can just ignore the watchers and/or C<free ()> them
		666	for example).
594		667
595	Note that certain global state, such as signal state (and installed signal	668	Note that certain global state, such as signal state (and installed signal
596	handlers), will not be freed by this function, and related watchers (such	669	handlers), will not be freed by this function, and related watchers (such
597	as signal and child watchers) would need to be stopped manually.	670	as signal and child watchers) would need to be stopped manually.
598		671
599	In general it is not advisable to call this function except in the	672	This function is normally used on loop objects allocated by
600	rare occasion where you really need to free e.g. the signal handling	673	C<ev_loop_new>, but it can also be used on the default loop returned by
		674	C<ev_default_loop>, in which case it is not thread-safe.
		675
		676	Note that it is not advisable to call this function on the default loop
		677	except in the rare occasion where you really need to free its resources.
601	pipe fds. If you need dynamically allocated loops it is better to use	678	If you need dynamically allocated loops it is better to use C<ev_loop_new>
602	C<ev_loop_new> and C<ev_loop_destroy>.	679	and C<ev_loop_destroy>.
603		680
604	=item ev_loop_destroy (loop)	681	=item ev_loop_fork (loop)
605		682
606	Like C<ev_default_destroy>, but destroys an event loop created by an
607	earlier call to C<ev_loop_new>.
608
609	=item ev_default_fork ()
610
611	This function sets a flag that causes subsequent C<ev_run> iterations	683	This function sets a flag that causes subsequent C<ev_run> iterations to
612	to reinitialise the kernel state for backends that have one. Despite the	684	reinitialise the kernel state for backends that have one. Despite the
613	name, you can call it anytime, but it makes most sense after forking, in	685	name, you can call it anytime, but it makes most sense after forking, in
614	the child process (or both child and parent, but that again makes little	686	the child process. You I<must> call it (or use C<EVFLAG_FORKCHECK>) in the
615	sense). You I<must> call it in the child before using any of the libev	687	child before resuming or calling C<ev_run>.
616	functions, and it will only take effect at the next C<ev_run> iteration.
617		688
618	Again, you I<have> to call it on I<any> loop that you want to re-use after	689	Again, you I<have> to call it on I<any> loop that you want to re-use after
619	a fork, I<even if you do not plan to use the loop in the parent>. This is	690	a fork, I<even if you do not plan to use the loop in the parent>. This is
620	because some kernel interfaces *cough* I<kqueue> *cough* do funny things	691	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
621	during fork.	692	during fork.
…		…
626	call it at all (in fact, C<epoll> is so badly broken that it makes a	697	call it at all (in fact, C<epoll> is so badly broken that it makes a
627	difference, but libev will usually detect this case on its own and do a	698	difference, but libev will usually detect this case on its own and do a
628	costly reset of the backend).	699	costly reset of the backend).
629		700
630	The function itself is quite fast and it's usually not a problem to call	701	The function itself is quite fast and it's usually not a problem to call
631	it just in case after a fork. To make this easy, the function will fit in	702	it just in case after a fork.
632	quite nicely into a call to C<pthread_atfork>:
633		703
		704	Example: Automate calling C<ev_loop_fork> on the default loop when
		705	using pthreads.
		706
		707	static void
		708	post_fork_child (void)
		709	{
		710	ev_loop_fork (EV_DEFAULT);
		711	}
		712
		713	...
634	pthread_atfork (0, 0, ev_default_fork);	714	pthread_atfork (0, 0, post_fork_child);
635
636	=item ev_loop_fork (loop)
637
638	Like C<ev_default_fork>, but acts on an event loop created by
639	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
640	after fork that you want to re-use in the child, and how you keep track of
641	them is entirely your own problem.
642		715
643	=item int ev_is_default_loop (loop)	716	=item int ev_is_default_loop (loop)
644		717
645	Returns true when the given loop is, in fact, the default loop, and false	718	Returns true when the given loop is, in fact, the default loop, and false
646	otherwise.	719	otherwise.
…		…
657	prepare and check phases.	730	prepare and check phases.
658		731
659	=item unsigned int ev_depth (loop)	732	=item unsigned int ev_depth (loop)
660		733
661	Returns the number of times C<ev_run> was entered minus the number of	734	Returns the number of times C<ev_run> was entered minus the number of
662	times C<ev_run> was exited, in other words, the recursion depth.	735	times C<ev_run> was exited normally, in other words, the recursion depth.
663		736
664	Outside C<ev_run>, this number is zero. In a callback, this number is	737	Outside C<ev_run>, this number is zero. In a callback, this number is
665	C<1>, unless C<ev_run> was invoked recursively (or from another thread),	738	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
666	in which case it is higher.	739	in which case it is higher.
667		740
668	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread	741	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
669	etc.), doesn't count as "exit" - consider this as a hint to avoid such	742	throwing an exception etc.), doesn't count as "exit" - consider this
670	ungentleman-like behaviour unless it's really convenient.	743	as a hint to avoid such ungentleman-like behaviour unless it's really
		744	convenient, in which case it is fully supported.
671		745
672	=item unsigned int ev_backend (loop)	746	=item unsigned int ev_backend (loop)
673		747
674	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	748	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
675	use.	749	use.
…		…
737	finished (especially in interactive programs), but having a program	811	finished (especially in interactive programs), but having a program
738	that automatically loops as long as it has to and no longer by virtue	812	that automatically loops as long as it has to and no longer by virtue
739	of relying on its watchers stopping correctly, that is truly a thing of	813	of relying on its watchers stopping correctly, that is truly a thing of
740	beauty.	814	beauty.
741		815
		816	This function is also I<mostly> exception-safe - you can break out of
		817	a C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		818	exception and so on. This does not decrement the C<ev_depth> value, nor
		819	will it clear any outstanding C<EVBREAK_ONE> breaks.
		820
742	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle	821	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
743	those events and any already outstanding ones, but will not wait and	822	those events and any already outstanding ones, but will not wait and
744	block your process in case there are no events and will return after one	823	block your process in case there are no events and will return after one
745	iteration of the loop. This is sometimes useful to poll and handle new	824	iteration of the loop. This is sometimes useful to poll and handle new
746	events while doing lengthy calculations, to keep the program responsive.	825	events while doing lengthy calculations, to keep the program responsive.
…		…
755	This is useful if you are waiting for some external event in conjunction	834	This is useful if you are waiting for some external event in conjunction
756	with something not expressible using other libev watchers (i.e. "roll your	835	with something not expressible using other libev watchers (i.e. "roll your
757	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is	836	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
758	usually a better approach for this kind of thing.	837	usually a better approach for this kind of thing.
759		838
760	Here are the gory details of what C<ev_run> does:	839	Here are the gory details of what C<ev_run> does (this is for your
		840	understanding, not a guarantee that things will work exactly like this in
		841	future versions):
761		842
762	- Increment loop depth.	843	- Increment loop depth.
763	- Reset the ev_break status.	844	- Reset the ev_break status.
764	- Before the first iteration, call any pending watchers.	845	- Before the first iteration, call any pending watchers.
765	LOOP:	846	LOOP:
…		…
798	anymore.	879	anymore.
799		880
800	... queue jobs here, make sure they register event watchers as long	881	... queue jobs here, make sure they register event watchers as long
801	... as they still have work to do (even an idle watcher will do..)	882	... as they still have work to do (even an idle watcher will do..)
802	ev_run (my_loop, 0);	883	ev_run (my_loop, 0);
803	... jobs done or somebody called unloop. yeah!	884	... jobs done or somebody called break. yeah!
804		885
805	=item ev_break (loop, how)	886	=item ev_break (loop, how)
806		887
807	Can be used to make a call to C<ev_run> return early (but only after it	888	Can be used to make a call to C<ev_run> return early (but only after it
808	has processed all outstanding events). The C<how> argument must be either	889	has processed all outstanding events). The C<how> argument must be either
809	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or	890	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
810	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.	891	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
811		892
812	This "unloop state" will be cleared when entering C<ev_run> again.	893	This "break state" will be cleared on the next call to C<ev_run>.
813		894
814	It is safe to call C<ev_break> from outside any C<ev_run> calls. ##TODO##	895	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		896	which case it will have no effect.
815		897
816	=item ev_ref (loop)	898	=item ev_ref (loop)
817		899
818	=item ev_unref (loop)	900	=item ev_unref (loop)
819		901
…		…
840	running when nothing else is active.	922	running when nothing else is active.
841		923
842	ev_signal exitsig;	924	ev_signal exitsig;
843	ev_signal_init (&exitsig, sig_cb, SIGINT);	925	ev_signal_init (&exitsig, sig_cb, SIGINT);
844	ev_signal_start (loop, &exitsig);	926	ev_signal_start (loop, &exitsig);
845	evf_unref (loop);	927	ev_unref (loop);
846		928
847	Example: For some weird reason, unregister the above signal handler again.	929	Example: For some weird reason, unregister the above signal handler again.
848		930
849	ev_ref (loop);	931	ev_ref (loop);
850	ev_signal_stop (loop, &exitsig);	932	ev_signal_stop (loop, &exitsig);
…		…
870	overhead for the actual polling but can deliver many events at once.	952	overhead for the actual polling but can deliver many events at once.
871		953
872	By setting a higher I<io collect interval> you allow libev to spend more	954	By setting a higher I<io collect interval> you allow libev to spend more
873	time collecting I/O events, so you can handle more events per iteration,	955	time collecting I/O events, so you can handle more events per iteration,
874	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	956	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
875	C<ev_timer>) will be not affected. Setting this to a non-null value will	957	C<ev_timer>) will not be affected. Setting this to a non-null value will
876	introduce an additional C<ev_sleep ()> call into most loop iterations. The	958	introduce an additional C<ev_sleep ()> call into most loop iterations. The
877	sleep time ensures that libev will not poll for I/O events more often then	959	sleep time ensures that libev will not poll for I/O events more often then
878	once per this interval, on average.	960	once per this interval, on average (as long as the host time resolution is
		961	good enough).
879		962
880	Likewise, by setting a higher I<timeout collect interval> you allow libev	963	Likewise, by setting a higher I<timeout collect interval> you allow libev
881	to spend more time collecting timeouts, at the expense of increased	964	to spend more time collecting timeouts, at the expense of increased
882	latency/jitter/inexactness (the watcher callback will be called	965	latency/jitter/inexactness (the watcher callback will be called
883	later). C<ev_io> watchers will not be affected. Setting this to a non-null	966	later). C<ev_io> watchers will not be affected. Setting this to a non-null
…		…
908		991
909	=item ev_invoke_pending (loop)	992	=item ev_invoke_pending (loop)
910		993
911	This call will simply invoke all pending watchers while resetting their	994	This call will simply invoke all pending watchers while resetting their
912	pending state. Normally, C<ev_run> does this automatically when required,	995	pending state. Normally, C<ev_run> does this automatically when required,
913	but when overriding the invoke callback this call comes handy.	996	but when overriding the invoke callback this call comes handy. This
		997	function can be invoked from a watcher - this can be useful for example
		998	when you want to do some lengthy calculation and want to pass further
		999	event handling to another thread (you still have to make sure only one
		1000	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
914		1001
915	=item int ev_pending_count (loop)	1002	=item int ev_pending_count (loop)
916		1003
917	Returns the number of pending watchers - zero indicates that no watchers	1004	Returns the number of pending watchers - zero indicates that no watchers
918	are pending.	1005	are pending.
…		…
933	can be done relatively simply by putting mutex_lock/unlock calls around	1020	can be done relatively simply by putting mutex_lock/unlock calls around
934	each call to a libev function.	1021	each call to a libev function.
935		1022
936	However, C<ev_run> can run an indefinite time, so it is not feasible	1023	However, C<ev_run> can run an indefinite time, so it is not feasible
937	to wait for it to return. One way around this is to wake up the event	1024	to wait for it to return. One way around this is to wake up the event
938	loop via C<ev_break> and C<av_async_send>, another way is to set these	1025	loop via C<ev_break> and C<ev_async_send>, another way is to set these
939	I<release> and I<acquire> callbacks on the loop.	1026	I<release> and I<acquire> callbacks on the loop.
940		1027
941	When set, then C<release> will be called just before the thread is	1028	When set, then C<release> will be called just before the thread is
942	suspended waiting for new events, and C<acquire> is called just	1029	suspended waiting for new events, and C<acquire> is called just
943	afterwards.	1030	afterwards.
…		…
958	See also the locking example in the C<THREADS> section later in this	1045	See also the locking example in the C<THREADS> section later in this
959	document.	1046	document.
960		1047
961	=item ev_set_userdata (loop, void *data)	1048	=item ev_set_userdata (loop, void *data)
962		1049
963	=item ev_userdata (loop)	1050	=item void *ev_userdata (loop)
964		1051
965	Set and retrieve a single C<void *> associated with a loop. When	1052	Set and retrieve a single C<void *> associated with a loop. When
966	C<ev_set_userdata> has never been called, then C<ev_userdata> returns	1053	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
967	C<0.>	1054	C<0>.
968		1055
969	These two functions can be used to associate arbitrary data with a loop,	1056	These two functions can be used to associate arbitrary data with a loop,
970	and are intended solely for the C<invoke_pending_cb>, C<release> and	1057	and are intended solely for the C<invoke_pending_cb>, C<release> and
971	C<acquire> callbacks described above, but of course can be (ab-)used for	1058	C<acquire> callbacks described above, but of course can be (ab-)used for
972	any other purpose as well.	1059	any other purpose as well.
…		…
1100	=item C<EV_FORK>	1187	=item C<EV_FORK>
1101		1188
1102	The event loop has been resumed in the child process after fork (see	1189	The event loop has been resumed in the child process after fork (see
1103	C<ev_fork>).	1190	C<ev_fork>).
1104		1191
		1192	=item C<EV_CLEANUP>
		1193
		1194	The event loop is about to be destroyed (see C<ev_cleanup>).
		1195
1105	=item C<EV_ASYNC>	1196	=item C<EV_ASYNC>
1106		1197
1107	The given async watcher has been asynchronously notified (see C<ev_async>).	1198	The given async watcher has been asynchronously notified (see C<ev_async>).
1108		1199
1109	=item C<EV_CUSTOM>	1200	=item C<EV_CUSTOM>
…		…
1130	programs, though, as the fd could already be closed and reused for another	1221	programs, though, as the fd could already be closed and reused for another
1131	thing, so beware.	1222	thing, so beware.
1132		1223
1133	=back	1224	=back
1134		1225
		1226	=head2 GENERIC WATCHER FUNCTIONS
		1227
		1228	=over 4
		1229
		1230	=item C<ev_init> (ev_TYPE *watcher, callback)
		1231
		1232	This macro initialises the generic portion of a watcher. The contents
		1233	of the watcher object can be arbitrary (so C<malloc> will do). Only
		1234	the generic parts of the watcher are initialised, you I<need> to call
		1235	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		1236	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		1237	which rolls both calls into one.
		1238
		1239	You can reinitialise a watcher at any time as long as it has been stopped
		1240	(or never started) and there are no pending events outstanding.
		1241
		1242	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
		1243	int revents)>.
		1244
		1245	Example: Initialise an C<ev_io> watcher in two steps.
		1246
		1247	ev_io w;
		1248	ev_init (&w, my_cb);
		1249	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1250
		1251	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
		1252
		1253	This macro initialises the type-specific parts of a watcher. You need to
		1254	call C<ev_init> at least once before you call this macro, but you can
		1255	call C<ev_TYPE_set> any number of times. You must not, however, call this
		1256	macro on a watcher that is active (it can be pending, however, which is a
		1257	difference to the C<ev_init> macro).
		1258
		1259	Although some watcher types do not have type-specific arguments
		1260	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		1261
		1262	See C<ev_init>, above, for an example.
		1263
		1264	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		1265
		1266	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		1267	calls into a single call. This is the most convenient method to initialise
		1268	a watcher. The same limitations apply, of course.
		1269
		1270	Example: Initialise and set an C<ev_io> watcher in one step.
		1271
		1272	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1273
		1274	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
		1275
		1276	Starts (activates) the given watcher. Only active watchers will receive
		1277	events. If the watcher is already active nothing will happen.
		1278
		1279	Example: Start the C<ev_io> watcher that is being abused as example in this
		1280	whole section.
		1281
		1282	ev_io_start (EV_DEFAULT_UC, &w);
		1283
		1284	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
		1285
		1286	Stops the given watcher if active, and clears the pending status (whether
		1287	the watcher was active or not).
		1288
		1289	It is possible that stopped watchers are pending - for example,
		1290	non-repeating timers are being stopped when they become pending - but
		1291	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
		1292	pending. If you want to free or reuse the memory used by the watcher it is
		1293	therefore a good idea to always call its C<ev_TYPE_stop> function.
		1294
		1295	=item bool ev_is_active (ev_TYPE *watcher)
		1296
		1297	Returns a true value iff the watcher is active (i.e. it has been started
		1298	and not yet been stopped). As long as a watcher is active you must not modify
		1299	it.
		1300
		1301	=item bool ev_is_pending (ev_TYPE *watcher)
		1302
		1303	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		1304	events but its callback has not yet been invoked). As long as a watcher
		1305	is pending (but not active) you must not call an init function on it (but
		1306	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		1307	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1308	it).
		1309
		1310	=item callback ev_cb (ev_TYPE *watcher)
		1311
		1312	Returns the callback currently set on the watcher.
		1313
		1314	=item ev_cb_set (ev_TYPE *watcher, callback)
		1315
		1316	Change the callback. You can change the callback at virtually any time
		1317	(modulo threads).
		1318
		1319	=item ev_set_priority (ev_TYPE *watcher, int priority)
		1320
		1321	=item int ev_priority (ev_TYPE *watcher)
		1322
		1323	Set and query the priority of the watcher. The priority is a small
		1324	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1325	(default: C<-2>). Pending watchers with higher priority will be invoked
		1326	before watchers with lower priority, but priority will not keep watchers
		1327	from being executed (except for C<ev_idle> watchers).
		1328
		1329	If you need to suppress invocation when higher priority events are pending
		1330	you need to look at C<ev_idle> watchers, which provide this functionality.
		1331
		1332	You I<must not> change the priority of a watcher as long as it is active or
		1333	pending.
		1334
		1335	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1336	fine, as long as you do not mind that the priority value you query might
		1337	or might not have been clamped to the valid range.
		1338
		1339	The default priority used by watchers when no priority has been set is
		1340	always C<0>, which is supposed to not be too high and not be too low :).
		1341
		1342	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1343	priorities.
		1344
		1345	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1346
		1347	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1348	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1349	can deal with that fact, as both are simply passed through to the
		1350	callback.
		1351
		1352	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1353
		1354	If the watcher is pending, this function clears its pending status and
		1355	returns its C<revents> bitset (as if its callback was invoked). If the
		1356	watcher isn't pending it does nothing and returns C<0>.
		1357
		1358	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1359	callback to be invoked, which can be accomplished with this function.
		1360
		1361	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1362
		1363	Feeds the given event set into the event loop, as if the specified event
		1364	had happened for the specified watcher (which must be a pointer to an
		1365	initialised but not necessarily started event watcher). Obviously you must
		1366	not free the watcher as long as it has pending events.
		1367
		1368	Stopping the watcher, letting libev invoke it, or calling
		1369	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1370	not started in the first place.
		1371
		1372	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1373	functions that do not need a watcher.
		1374
		1375	=back
		1376
		1377	See also the L<ASSOCIATING CUSTOM DATA WITH A WATCHER> and L<BUILDING YOUR
		1378	OWN COMPOSITE WATCHERS> idioms.
		1379
1135	=head2 WATCHER STATES	1380	=head2 WATCHER STATES
1136		1381
1137	There are various watcher states mentioned throughout this manual -	1382	There are various watcher states mentioned throughout this manual -
1138	active, pending and so on. In this section these states and the rules to	1383	active, pending and so on. In this section these states and the rules to
1139	transition between them will be described in more detail - and while these	1384	transition between them will be described in more detail - and while these
…		…
1141		1386
1142	=over 4	1387	=over 4
1143		1388
1144	=item initialiased	1389	=item initialiased
1145		1390
1146	Before a watcher can be registered with the event looop it has to be	1391	Before a watcher can be registered with the event loop it has to be
1147	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to	1392	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
1148	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.	1393	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1149		1394
1150	In this state it is simply some block of memory that is suitable for use	1395	In this state it is simply some block of memory that is suitable for
1151	in an event loop. It can be moved around, freed, reused etc. at will.	1396	use in an event loop. It can be moved around, freed, reused etc. at
		1397	will - as long as you either keep the memory contents intact, or call
		1398	C<ev_TYPE_init> again.
1152		1399
1153	=item started/running/active	1400	=item started/running/active
1154		1401
1155	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes	1402	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
1156	property of the event loop, and is actively waiting for events. While in	1403	property of the event loop, and is actively waiting for events. While in
…		…
1159	and call libev functions on it that are documented to work on active watchers.	1406	and call libev functions on it that are documented to work on active watchers.
1160		1407
1161	=item pending	1408	=item pending
1162		1409
1163	If a watcher is active and libev determines that an event it is interested	1410	If a watcher is active and libev determines that an event it is interested
1164	in has occured (such as a timer expiring), it will become pending. It will	1411	in has occurred (such as a timer expiring), it will become pending. It will
1165	stay in this pending state until either it is stopped or its callback is	1412	stay in this pending state until either it is stopped or its callback is
1166	about to be invoked, so it is not normally pending inside the watcher	1413	about to be invoked, so it is not normally pending inside the watcher
1167	callback.	1414	callback.
1168		1415
1169	The watcher might or might not be active while it is pending (for example,	1416	The watcher might or might not be active while it is pending (for example,
…		…
1184	latter will clear any pending state the watcher might be in, regardless	1431	latter will clear any pending state the watcher might be in, regardless
1185	of whether it was active or not, so stopping a watcher explicitly before	1432	of whether it was active or not, so stopping a watcher explicitly before
1186	freeing it is often a good idea.	1433	freeing it is often a good idea.
1187		1434
1188	While stopped (and not pending) the watcher is essentially in the	1435	While stopped (and not pending) the watcher is essentially in the
1189	initialised state, that is it can be reused, moved, modified in any way	1436	initialised state, that is, it can be reused, moved, modified in any way
1190	you wish.	1437	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1438	it again).
1191		1439
1192	=back	1440	=back
1193
1194	=head2 GENERIC WATCHER FUNCTIONS
1195
1196	=over 4
1197
1198	=item C<ev_init> (ev_TYPE *watcher, callback)
1199
1200	This macro initialises the generic portion of a watcher. The contents
1201	of the watcher object can be arbitrary (so C<malloc> will do). Only
1202	the generic parts of the watcher are initialised, you I<need> to call
1203	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
1204	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
1205	which rolls both calls into one.
1206
1207	You can reinitialise a watcher at any time as long as it has been stopped
1208	(or never started) and there are no pending events outstanding.
1209
1210	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
1211	int revents)>.
1212
1213	Example: Initialise an C<ev_io> watcher in two steps.
1214
1215	ev_io w;
1216	ev_init (&w, my_cb);
1217	ev_io_set (&w, STDIN_FILENO, EV_READ);
1218
1219	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
1220
1221	This macro initialises the type-specific parts of a watcher. You need to
1222	call C<ev_init> at least once before you call this macro, but you can
1223	call C<ev_TYPE_set> any number of times. You must not, however, call this
1224	macro on a watcher that is active (it can be pending, however, which is a
1225	difference to the C<ev_init> macro).
1226
1227	Although some watcher types do not have type-specific arguments
1228	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
1229
1230	See C<ev_init>, above, for an example.
1231
1232	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
1233
1234	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
1235	calls into a single call. This is the most convenient method to initialise
1236	a watcher. The same limitations apply, of course.
1237
1238	Example: Initialise and set an C<ev_io> watcher in one step.
1239
1240	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
1241
1242	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
1243
1244	Starts (activates) the given watcher. Only active watchers will receive
1245	events. If the watcher is already active nothing will happen.
1246
1247	Example: Start the C<ev_io> watcher that is being abused as example in this
1248	whole section.
1249
1250	ev_io_start (EV_DEFAULT_UC, &w);
1251
1252	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
1253
1254	Stops the given watcher if active, and clears the pending status (whether
1255	the watcher was active or not).
1256
1257	It is possible that stopped watchers are pending - for example,
1258	non-repeating timers are being stopped when they become pending - but
1259	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
1260	pending. If you want to free or reuse the memory used by the watcher it is
1261	therefore a good idea to always call its C<ev_TYPE_stop> function.
1262
1263	=item bool ev_is_active (ev_TYPE *watcher)
1264
1265	Returns a true value iff the watcher is active (i.e. it has been started
1266	and not yet been stopped). As long as a watcher is active you must not modify
1267	it.
1268
1269	=item bool ev_is_pending (ev_TYPE *watcher)
1270
1271	Returns a true value iff the watcher is pending, (i.e. it has outstanding
1272	events but its callback has not yet been invoked). As long as a watcher
1273	is pending (but not active) you must not call an init function on it (but
1274	C<ev_TYPE_set> is safe), you must not change its priority, and you must
1275	make sure the watcher is available to libev (e.g. you cannot C<free ()>
1276	it).
1277
1278	=item callback ev_cb (ev_TYPE *watcher)
1279
1280	Returns the callback currently set on the watcher.
1281
1282	=item ev_cb_set (ev_TYPE *watcher, callback)
1283
1284	Change the callback. You can change the callback at virtually any time
1285	(modulo threads).
1286
1287	=item ev_set_priority (ev_TYPE *watcher, int priority)
1288
1289	=item int ev_priority (ev_TYPE *watcher)
1290
1291	Set and query the priority of the watcher. The priority is a small
1292	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
1293	(default: C<-2>). Pending watchers with higher priority will be invoked
1294	before watchers with lower priority, but priority will not keep watchers
1295	from being executed (except for C<ev_idle> watchers).
1296
1297	If you need to suppress invocation when higher priority events are pending
1298	you need to look at C<ev_idle> watchers, which provide this functionality.
1299
1300	You I<must not> change the priority of a watcher as long as it is active or
1301	pending.
1302
1303	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
1304	fine, as long as you do not mind that the priority value you query might
1305	or might not have been clamped to the valid range.
1306
1307	The default priority used by watchers when no priority has been set is
1308	always C<0>, which is supposed to not be too high and not be too low :).
1309
1310	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
1311	priorities.
1312
1313	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1314
1315	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
1316	C<loop> nor C<revents> need to be valid as long as the watcher callback
1317	can deal with that fact, as both are simply passed through to the
1318	callback.
1319
1320	=item int ev_clear_pending (loop, ev_TYPE *watcher)
1321
1322	If the watcher is pending, this function clears its pending status and
1323	returns its C<revents> bitset (as if its callback was invoked). If the
1324	watcher isn't pending it does nothing and returns C<0>.
1325
1326	Sometimes it can be useful to "poll" a watcher instead of waiting for its
1327	callback to be invoked, which can be accomplished with this function.
1328
1329	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
1330
1331	Feeds the given event set into the event loop, as if the specified event
1332	had happened for the specified watcher (which must be a pointer to an
1333	initialised but not necessarily started event watcher). Obviously you must
1334	not free the watcher as long as it has pending events.
1335
1336	Stopping the watcher, letting libev invoke it, or calling
1337	C<ev_clear_pending> will clear the pending event, even if the watcher was
1338	not started in the first place.
1339
1340	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1341	functions that do not need a watcher.
1342
1343	=back
1344
1345
1346	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
1347
1348	Each watcher has, by default, a member C<void *data> that you can change
1349	and read at any time: libev will completely ignore it. This can be used
1350	to associate arbitrary data with your watcher. If you need more data and
1351	don't want to allocate memory and store a pointer to it in that data
1352	member, you can also "subclass" the watcher type and provide your own
1353	data:
1354
1355	struct my_io
1356	{
1357	ev_io io;
1358	int otherfd;
1359	void *somedata;
1360	struct whatever *mostinteresting;
1361	};
1362
1363	...
1364	struct my_io w;
1365	ev_io_init (&w.io, my_cb, fd, EV_READ);
1366
1367	And since your callback will be called with a pointer to the watcher, you
1368	can cast it back to your own type:
1369
1370	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1371	{
1372	struct my_io *w = (struct my_io *)w_;
1373	...
1374	}
1375
1376	More interesting and less C-conformant ways of casting your callback type
1377	instead have been omitted.
1378
1379	Another common scenario is to use some data structure with multiple
1380	embedded watchers:
1381
1382	struct my_biggy
1383	{
1384	int some_data;
1385	ev_timer t1;
1386	ev_timer t2;
1387	}
1388
1389	In this case getting the pointer to C<my_biggy> is a bit more
1390	complicated: Either you store the address of your C<my_biggy> struct
1391	in the C<data> member of the watcher (for woozies), or you need to use
1392	some pointer arithmetic using C<offsetof> inside your watchers (for real
1393	programmers):
1394
1395	#include <stddef.h>
1396
1397	static void
1398	t1_cb (EV_P_ ev_timer *w, int revents)
1399	{
1400	struct my_biggy big = (struct my_biggy *)
1401	(((char *)w) - offsetof (struct my_biggy, t1));
1402	}
1403
1404	static void
1405	t2_cb (EV_P_ ev_timer *w, int revents)
1406	{
1407	struct my_biggy big = (struct my_biggy *)
1408	(((char *)w) - offsetof (struct my_biggy, t2));
1409	}
1410		1441
1411	=head2 WATCHER PRIORITY MODELS	1442	=head2 WATCHER PRIORITY MODELS
1412		1443
1413	Many event loops support I<watcher priorities>, which are usually small	1444	Many event loops support I<watcher priorities>, which are usually small
1414	integers that influence the ordering of event callback invocation	1445	integers that influence the ordering of event callback invocation
…		…
1541	In general you can register as many read and/or write event watchers per	1572	In general you can register as many read and/or write event watchers per
1542	fd as you want (as long as you don't confuse yourself). Setting all file	1573	fd as you want (as long as you don't confuse yourself). Setting all file
1543	descriptors to non-blocking mode is also usually a good idea (but not	1574	descriptors to non-blocking mode is also usually a good idea (but not
1544	required if you know what you are doing).	1575	required if you know what you are doing).
1545		1576
1546	If you cannot use non-blocking mode, then force the use of a
1547	known-to-be-good backend (at the time of this writing, this includes only
1548	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
1549	descriptors for which non-blocking operation makes no sense (such as
1550	files) - libev doesn't guarantee any specific behaviour in that case.
1551
1552	Another thing you have to watch out for is that it is quite easy to	1577	Another thing you have to watch out for is that it is quite easy to
1553	receive "spurious" readiness notifications, that is your callback might	1578	receive "spurious" readiness notifications, that is, your callback might
1554	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1579	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1555	because there is no data. Not only are some backends known to create a	1580	because there is no data. It is very easy to get into this situation even
1556	lot of those (for example Solaris ports), it is very easy to get into	1581	with a relatively standard program structure. Thus it is best to always
1557	this situation even with a relatively standard program structure. Thus	1582	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1558	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1559	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1583	preferable to a program hanging until some data arrives.
1560		1584
1561	If you cannot run the fd in non-blocking mode (for example you should	1585	If you cannot run the fd in non-blocking mode (for example you should
1562	not play around with an Xlib connection), then you have to separately	1586	not play around with an Xlib connection), then you have to separately
1563	re-test whether a file descriptor is really ready with a known-to-be good	1587	re-test whether a file descriptor is really ready with a known-to-be good
1564	interface such as poll (fortunately in our Xlib example, Xlib already	1588	interface such as poll (fortunately in the case of Xlib, it already does
1565	does this on its own, so its quite safe to use). Some people additionally	1589	this on its own, so its quite safe to use). Some people additionally
1566	use C<SIGALRM> and an interval timer, just to be sure you won't block	1590	use C<SIGALRM> and an interval timer, just to be sure you won't block
1567	indefinitely.	1591	indefinitely.
1568		1592
1569	But really, best use non-blocking mode.	1593	But really, best use non-blocking mode.
1570		1594
…		…
1598		1622
1599	There is no workaround possible except not registering events	1623	There is no workaround possible except not registering events
1600	for potentially C<dup ()>'ed file descriptors, or to resort to	1624	for potentially C<dup ()>'ed file descriptors, or to resort to
1601	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1625	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1602		1626
		1627	=head3 The special problem of files
		1628
		1629	Many people try to use C<select> (or libev) on file descriptors
		1630	representing files, and expect it to become ready when their program
		1631	doesn't block on disk accesses (which can take a long time on their own).
		1632
		1633	However, this cannot ever work in the "expected" way - you get a readiness
		1634	notification as soon as the kernel knows whether and how much data is
		1635	there, and in the case of open files, that's always the case, so you
		1636	always get a readiness notification instantly, and your read (or possibly
		1637	write) will still block on the disk I/O.
		1638
		1639	Another way to view it is that in the case of sockets, pipes, character
		1640	devices and so on, there is another party (the sender) that delivers data
		1641	on its own, but in the case of files, there is no such thing: the disk
		1642	will not send data on its own, simply because it doesn't know what you
		1643	wish to read - you would first have to request some data.
		1644
		1645	Since files are typically not-so-well supported by advanced notification
		1646	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1647	to files, even though you should not use it. The reason for this is
		1648	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1649	usually a tty, often a pipe, but also sometimes files or special devices
		1650	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1651	F</dev/urandom>), and even though the file might better be served with
		1652	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1653	it "just works" instead of freezing.
		1654
		1655	So avoid file descriptors pointing to files when you know it (e.g. use
		1656	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1657	when you rarely read from a file instead of from a socket, and want to
		1658	reuse the same code path.
		1659
1603	=head3 The special problem of fork	1660	=head3 The special problem of fork
1604		1661
1605	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1662	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
1606	useless behaviour. Libev fully supports fork, but needs to be told about	1663	useless behaviour. Libev fully supports fork, but needs to be told about
1607	it in the child.	1664	it in the child if you want to continue to use it in the child.
1608		1665
1609	To support fork in your programs, you either have to call	1666	To support fork in your child processes, you have to call C<ev_loop_fork
1610	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1667	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1611	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1668	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1612	C<EVBACKEND_POLL>.
1613		1669
1614	=head3 The special problem of SIGPIPE	1670	=head3 The special problem of SIGPIPE
1615		1671
1616	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1672	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1617	when writing to a pipe whose other end has been closed, your program gets	1673	when writing to a pipe whose other end has been closed, your program gets
…		…
1715	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1771	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1716	monotonic clock option helps a lot here).	1772	monotonic clock option helps a lot here).
1717		1773
1718	The callback is guaranteed to be invoked only I<after> its timeout has	1774	The callback is guaranteed to be invoked only I<after> its timeout has
1719	passed (not I<at>, so on systems with very low-resolution clocks this	1775	passed (not I<at>, so on systems with very low-resolution clocks this
1720	might introduce a small delay). If multiple timers become ready during the	1776	might introduce a small delay, see "the special problem of being too
		1777	early", below). If multiple timers become ready during the same loop
1721	same loop iteration then the ones with earlier time-out values are invoked	1778	iteration then the ones with earlier time-out values are invoked before
1722	before ones of the same priority with later time-out values (but this is	1779	ones of the same priority with later time-out values (but this is no
1723	no longer true when a callback calls C<ev_run> recursively).	1780	longer true when a callback calls C<ev_run> recursively).
1724		1781
1725	=head3 Be smart about timeouts	1782	=head3 Be smart about timeouts
1726		1783
1727	Many real-world problems involve some kind of timeout, usually for error	1784	Many real-world problems involve some kind of timeout, usually for error
1728	recovery. A typical example is an HTTP request - if the other side hangs,	1785	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1803		1860
1804	In this case, it would be more efficient to leave the C<ev_timer> alone,	1861	In this case, it would be more efficient to leave the C<ev_timer> alone,
1805	but remember the time of last activity, and check for a real timeout only	1862	but remember the time of last activity, and check for a real timeout only
1806	within the callback:	1863	within the callback:
1807		1864
		1865	ev_tstamp timeout = 60.;
1808	ev_tstamp last_activity; // time of last activity	1866	ev_tstamp last_activity; // time of last activity
		1867	ev_timer timer;
1809		1868
1810	static void	1869	static void
1811	callback (EV_P_ ev_timer *w, int revents)	1870	callback (EV_P_ ev_timer *w, int revents)
1812	{	1871	{
1813	ev_tstamp now = ev_now (EV_A);	1872	// calculate when the timeout would happen
1814	ev_tstamp timeout = last_activity + 60.;	1873	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
1815		1874
1816	// if last_activity + 60. is older than now, we did time out	1875	// if negative, it means we the timeout already occured
1817	if (timeout < now)	1876	if (after < 0.)
1818	{	1877	{
1819	// timeout occurred, take action	1878	// timeout occurred, take action
1820	}	1879	}
1821	else	1880	else
1822	{	1881	{
1823	// callback was invoked, but there was some activity, re-arm	1882	// callback was invoked, but there was some recent
1824	// the watcher to fire in last_activity + 60, which is	1883	// activity. simply restart the timer to time out
1825	// guaranteed to be in the future, so "again" is positive:	1884	// after "after" seconds, which is the earliest time
1826	w->repeat = timeout - now;	1885	// the timeout can occur.
		1886	ev_timer_set (w, after, 0.);
1827	ev_timer_again (EV_A_ w);	1887	ev_timer_start (EV_A_ w);
1828	}	1888	}
1829	}	1889	}
1830		1890
1831	To summarise the callback: first calculate the real timeout (defined	1891	To summarise the callback: first calculate in how many seconds the
1832	as "60 seconds after the last activity"), then check if that time has	1892	timeout will occur (by calculating the absolute time when it would occur,
1833	been reached, which means something I<did>, in fact, time out. Otherwise	1893	C<last_activity + timeout>, and subtracting the current time, C<ev_now
1834	the callback was invoked too early (C<timeout> is in the future), so	1894	(EV_A)> from that).
1835	re-schedule the timer to fire at that future time, to see if maybe we have
1836	a timeout then.
1837		1895
1838	Note how C<ev_timer_again> is used, taking advantage of the	1896	If this value is negative, then we are already past the timeout, i.e. we
1839	C<ev_timer_again> optimisation when the timer is already running.	1897	timed out, and need to do whatever is needed in this case.
		1898
		1899	Otherwise, we now the earliest time at which the timeout would trigger,
		1900	and simply start the timer with this timeout value.
		1901
		1902	In other words, each time the callback is invoked it will check whether
		1903	the timeout cocured. If not, it will simply reschedule itself to check
		1904	again at the earliest time it could time out. Rinse. Repeat.
1840		1905
1841	This scheme causes more callback invocations (about one every 60 seconds	1906	This scheme causes more callback invocations (about one every 60 seconds
1842	minus half the average time between activity), but virtually no calls to	1907	minus half the average time between activity), but virtually no calls to
1843	libev to change the timeout.	1908	libev to change the timeout.
1844		1909
1845	To start the timer, simply initialise the watcher and set C<last_activity>	1910	To start the machinery, simply initialise the watcher and set
1846	to the current time (meaning we just have some activity :), then call the	1911	C<last_activity> to the current time (meaning there was some activity just
1847	callback, which will "do the right thing" and start the timer:	1912	now), then call the callback, which will "do the right thing" and start
		1913	the timer:
1848		1914
		1915	last_activity = ev_now (EV_A);
1849	ev_init (timer, callback);	1916	ev_init (&timer, callback);
1850	last_activity = ev_now (loop);	1917	callback (EV_A_ &timer, 0);
1851	callback (loop, timer, EV_TIMER);
1852		1918
1853	And when there is some activity, simply store the current time in	1919	When there is some activity, simply store the current time in
1854	C<last_activity>, no libev calls at all:	1920	C<last_activity>, no libev calls at all:
1855		1921
		1922	if (activity detected)
1856	last_activity = ev_now (loop);	1923	last_activity = ev_now (EV_A);
		1924
		1925	When your timeout value changes, then the timeout can be changed by simply
		1926	providing a new value, stopping the timer and calling the callback, which
		1927	will agaion do the right thing (for example, time out immediately :).
		1928
		1929	timeout = new_value;
		1930	ev_timer_stop (EV_A_ &timer);
		1931	callback (EV_A_ &timer, 0);
1857		1932
1858	This technique is slightly more complex, but in most cases where the	1933	This technique is slightly more complex, but in most cases where the
1859	time-out is unlikely to be triggered, much more efficient.	1934	time-out is unlikely to be triggered, much more efficient.
1860
1861	Changing the timeout is trivial as well (if it isn't hard-coded in the
1862	callback :) - just change the timeout and invoke the callback, which will
1863	fix things for you.
1864		1935
1865	=item 4. Wee, just use a double-linked list for your timeouts.	1936	=item 4. Wee, just use a double-linked list for your timeouts.
1866		1937
1867	If there is not one request, but many thousands (millions...), all	1938	If there is not one request, but many thousands (millions...), all
1868	employing some kind of timeout with the same timeout value, then one can	1939	employing some kind of timeout with the same timeout value, then one can
…		…
1895	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is	1966	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
1896	rather complicated, but extremely efficient, something that really pays	1967	rather complicated, but extremely efficient, something that really pays
1897	off after the first million or so of active timers, i.e. it's usually	1968	off after the first million or so of active timers, i.e. it's usually
1898	overkill :)	1969	overkill :)
1899		1970
		1971	=head3 The special problem of being too early
		1972
		1973	If you ask a timer to call your callback after three seconds, then
		1974	you expect it to be invoked after three seconds - but of course, this
		1975	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		1976	guaranteed to any precision by libev - imagine somebody suspending the
		1977	process with a STOP signal for a few hours for example.
		1978
		1979	So, libev tries to invoke your callback as soon as possible I<after> the
		1980	delay has occurred, but cannot guarantee this.
		1981
		1982	A less obvious failure mode is calling your callback too early: many event
		1983	loops compare timestamps with a "elapsed delay >= requested delay", but
		1984	this can cause your callback to be invoked much earlier than you would
		1985	expect.
		1986
		1987	To see why, imagine a system with a clock that only offers full second
		1988	resolution (think windows if you can't come up with a broken enough OS
		1989	yourself). If you schedule a one-second timer at the time 500.9, then the
		1990	event loop will schedule your timeout to elapse at a system time of 500
		1991	(500.9 truncated to the resolution) + 1, or 501.
		1992
		1993	If an event library looks at the timeout 0.1s later, it will see "501 >=
		1994	501" and invoke the callback 0.1s after it was started, even though a
		1995	one-second delay was requested - this is being "too early", despite best
		1996	intentions.
		1997
		1998	This is the reason why libev will never invoke the callback if the elapsed
		1999	delay equals the requested delay, but only when the elapsed delay is
		2000	larger than the requested delay. In the example above, libev would only invoke
		2001	the callback at system time 502, or 1.1s after the timer was started.
		2002
		2003	So, while libev cannot guarantee that your callback will be invoked
		2004	exactly when requested, it I<can> and I<does> guarantee that the requested
		2005	delay has actually elapsed, or in other words, it always errs on the "too
		2006	late" side of things.
		2007
1900	=head3 The special problem of time updates	2008	=head3 The special problem of time updates
1901		2009
1902	Establishing the current time is a costly operation (it usually takes at	2010	Establishing the current time is a costly operation (it usually takes
1903	least two system calls): EV therefore updates its idea of the current	2011	at least one system call): EV therefore updates its idea of the current
1904	time only before and after C<ev_run> collects new events, which causes a	2012	time only before and after C<ev_run> collects new events, which causes a
1905	growing difference between C<ev_now ()> and C<ev_time ()> when handling	2013	growing difference between C<ev_now ()> and C<ev_time ()> when handling
1906	lots of events in one iteration.	2014	lots of events in one iteration.
1907		2015
1908	The relative timeouts are calculated relative to the C<ev_now ()>	2016	The relative timeouts are calculated relative to the C<ev_now ()>
…		…
1914	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2022	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1915		2023
1916	If the event loop is suspended for a long time, you can also force an	2024	If the event loop is suspended for a long time, you can also force an
1917	update of the time returned by C<ev_now ()> by calling C<ev_now_update	2025	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1918	()>.	2026	()>.
		2027
		2028	=head3 The special problem of unsynchronised clocks
		2029
		2030	Modern systems have a variety of clocks - libev itself uses the normal
		2031	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2032	jumps).
		2033
		2034	Neither of these clocks is synchronised with each other or any other clock
		2035	on the system, so C<ev_time ()> might return a considerably different time
		2036	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2037	a call to C<gettimeofday> might return a second count that is one higher
		2038	than a directly following call to C<time>.
		2039
		2040	The moral of this is to only compare libev-related timestamps with
		2041	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2042	a second or so.
		2043
		2044	One more problem arises due to this lack of synchronisation: if libev uses
		2045	the system monotonic clock and you compare timestamps from C<ev_time>
		2046	or C<ev_now> from when you started your timer and when your callback is
		2047	invoked, you will find that sometimes the callback is a bit "early".
		2048
		2049	This is because C<ev_timer>s work in real time, not wall clock time, so
		2050	libev makes sure your callback is not invoked before the delay happened,
		2051	I<measured according to the real time>, not the system clock.
		2052
		2053	If your timeouts are based on a physical timescale (e.g. "time out this
		2054	connection after 100 seconds") then this shouldn't bother you as it is
		2055	exactly the right behaviour.
		2056
		2057	If you want to compare wall clock/system timestamps to your timers, then
		2058	you need to use C<ev_periodic>s, as these are based on the wall clock
		2059	time, where your comparisons will always generate correct results.
1919		2060
1920	=head3 The special problems of suspended animation	2061	=head3 The special problems of suspended animation
1921		2062
1922	When you leave the server world it is quite customary to hit machines that	2063	When you leave the server world it is quite customary to hit machines that
1923	can suspend/hibernate - what happens to the clocks during such a suspend?	2064	can suspend/hibernate - what happens to the clocks during such a suspend?
…		…
1967	keep up with the timer (because it takes longer than those 10 seconds to	2108	keep up with the timer (because it takes longer than those 10 seconds to
1968	do stuff) the timer will not fire more than once per event loop iteration.	2109	do stuff) the timer will not fire more than once per event loop iteration.
1969		2110
1970	=item ev_timer_again (loop, ev_timer *)	2111	=item ev_timer_again (loop, ev_timer *)
1971		2112
1972	This will act as if the timer timed out and restart it again if it is	2113	This will act as if the timer timed out and restarts it again if it is
1973	repeating. The exact semantics are:	2114	repeating. The exact semantics are:
1974		2115
1975	If the timer is pending, its pending status is cleared.	2116	If the timer is pending, its pending status is cleared.
1976		2117
1977	If the timer is started but non-repeating, stop it (as if it timed out).	2118	If the timer is started but non-repeating, stop it (as if it timed out).
…		…
2107		2248
2108	Another way to think about it (for the mathematically inclined) is that	2249	Another way to think about it (for the mathematically inclined) is that
2109	C<ev_periodic> will try to run the callback in this mode at the next possible	2250	C<ev_periodic> will try to run the callback in this mode at the next possible
2110	time where C<time = offset (mod interval)>, regardless of any time jumps.	2251	time where C<time = offset (mod interval)>, regardless of any time jumps.
2111		2252
2112	For numerical stability it is preferable that the C<offset> value is near	2253	The C<interval> I<MUST> be positive, and for numerical stability, the
2113	C<ev_now ()> (the current time), but there is no range requirement for	2254	interval value should be higher than C<1/8192> (which is around 100
2114	this value, and in fact is often specified as zero.	2255	microseconds) and C<offset> should be higher than C<0> and should have
		2256	at most a similar magnitude as the current time (say, within a factor of
		2257	ten). Typical values for offset are, in fact, C<0> or something between
		2258	C<0> and C<interval>, which is also the recommended range.
2115		2259
2116	Note also that there is an upper limit to how often a timer can fire (CPU	2260	Note also that there is an upper limit to how often a timer can fire (CPU
2117	speed for example), so if C<interval> is very small then timing stability	2261	speed for example), so if C<interval> is very small then timing stability
2118	will of course deteriorate. Libev itself tries to be exact to be about one	2262	will of course deteriorate. Libev itself tries to be exact to be about one
2119	millisecond (if the OS supports it and the machine is fast enough).	2263	millisecond (if the OS supports it and the machine is fast enough).
…		…
2233		2377
2234	=head2 C<ev_signal> - signal me when a signal gets signalled!	2378	=head2 C<ev_signal> - signal me when a signal gets signalled!
2235		2379
2236	Signal watchers will trigger an event when the process receives a specific	2380	Signal watchers will trigger an event when the process receives a specific
2237	signal one or more times. Even though signals are very asynchronous, libev	2381	signal one or more times. Even though signals are very asynchronous, libev
2238	will try it's best to deliver signals synchronously, i.e. as part of the	2382	will try its best to deliver signals synchronously, i.e. as part of the
2239	normal event processing, like any other event.	2383	normal event processing, like any other event.
2240		2384
2241	If you want signals to be delivered truly asynchronously, just use	2385	If you want signals to be delivered truly asynchronously, just use
2242	C<sigaction> as you would do without libev and forget about sharing	2386	C<sigaction> as you would do without libev and forget about sharing
2243	the signal. You can even use C<ev_async> from a signal handler to	2387	the signal. You can even use C<ev_async> from a signal handler to
…		…
2262	=head3 The special problem of inheritance over fork/execve/pthread_create	2406	=head3 The special problem of inheritance over fork/execve/pthread_create
2263		2407
2264	Both the signal mask (C<sigprocmask>) and the signal disposition	2408	Both the signal mask (C<sigprocmask>) and the signal disposition
2265	(C<sigaction>) are unspecified after starting a signal watcher (and after	2409	(C<sigaction>) are unspecified after starting a signal watcher (and after
2266	stopping it again), that is, libev might or might not block the signal,	2410	stopping it again), that is, libev might or might not block the signal,
2267	and might or might not set or restore the installed signal handler.	2411	and might or might not set or restore the installed signal handler (but
		2412	see C<EVFLAG_NOSIGMASK>).
2268		2413
2269	While this does not matter for the signal disposition (libev never	2414	While this does not matter for the signal disposition (libev never
2270	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on	2415	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
2271	C<execve>), this matters for the signal mask: many programs do not expect	2416	C<execve>), this matters for the signal mask: many programs do not expect
2272	certain signals to be blocked.	2417	certain signals to be blocked.
…		…
2285	I<has> to modify the signal mask, at least temporarily.	2430	I<has> to modify the signal mask, at least temporarily.
2286		2431
2287	So I can't stress this enough: I<If you do not reset your signal mask when	2432	So I can't stress this enough: I<If you do not reset your signal mask when
2288	you expect it to be empty, you have a race condition in your code>. This	2433	you expect it to be empty, you have a race condition in your code>. This
2289	is not a libev-specific thing, this is true for most event libraries.	2434	is not a libev-specific thing, this is true for most event libraries.
		2435
		2436	=head3 The special problem of threads signal handling
		2437
		2438	POSIX threads has problematic signal handling semantics, specifically,
		2439	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2440	threads in a process block signals, which is hard to achieve.
		2441
		2442	When you want to use sigwait (or mix libev signal handling with your own
		2443	for the same signals), you can tackle this problem by globally blocking
		2444	all signals before creating any threads (or creating them with a fully set
		2445	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2446	loops. Then designate one thread as "signal receiver thread" which handles
		2447	these signals. You can pass on any signals that libev might be interested
		2448	in by calling C<ev_feed_signal>.
2290		2449
2291	=head3 Watcher-Specific Functions and Data Members	2450	=head3 Watcher-Specific Functions and Data Members
2292		2451
2293	=over 4	2452	=over 4
2294		2453
…		…
3068	disadvantage of having to use multiple event loops (which do not support	3227	disadvantage of having to use multiple event loops (which do not support
3069	signal watchers).	3228	signal watchers).
3070		3229
3071	When this is not possible, or you want to use the default loop for	3230	When this is not possible, or you want to use the default loop for
3072	other reasons, then in the process that wants to start "fresh", call	3231	other reasons, then in the process that wants to start "fresh", call
3073	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying	3232	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
3074	the default loop will "orphan" (not stop) all registered watchers, so you	3233	Destroying the default loop will "orphan" (not stop) all registered
3075	have to be careful not to execute code that modifies those watchers. Note	3234	watchers, so you have to be careful not to execute code that modifies
3076	also that in that case, you have to re-register any signal watchers.	3235	those watchers. Note also that in that case, you have to re-register any
		3236	signal watchers.
3077		3237
3078	=head3 Watcher-Specific Functions and Data Members	3238	=head3 Watcher-Specific Functions and Data Members
3079		3239
3080	=over 4	3240	=over 4
3081		3241
3082	=item ev_fork_init (ev_signal *, callback)	3242	=item ev_fork_init (ev_fork *, callback)
3083		3243
3084	Initialises and configures the fork watcher - it has no parameters of any	3244	Initialises and configures the fork watcher - it has no parameters of any
3085	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,	3245	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
3086	believe me.	3246	really.
3087		3247
3088	=back	3248	=back
3089		3249
3090		3250
		3251	=head2 C<ev_cleanup> - even the best things end
		3252
		3253	Cleanup watchers are called just before the event loop is being destroyed
		3254	by a call to C<ev_loop_destroy>.
		3255
		3256	While there is no guarantee that the event loop gets destroyed, cleanup
		3257	watchers provide a convenient method to install cleanup hooks for your
		3258	program, worker threads and so on - you just to make sure to destroy the
		3259	loop when you want them to be invoked.
		3260
		3261	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3262	all other watchers, they do not keep a reference to the event loop (which
		3263	makes a lot of sense if you think about it). Like all other watchers, you
		3264	can call libev functions in the callback, except C<ev_cleanup_start>.
		3265
		3266	=head3 Watcher-Specific Functions and Data Members
		3267
		3268	=over 4
		3269
		3270	=item ev_cleanup_init (ev_cleanup *, callback)
		3271
		3272	Initialises and configures the cleanup watcher - it has no parameters of
		3273	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3274	pointless, I assure you.
		3275
		3276	=back
		3277
		3278	Example: Register an atexit handler to destroy the default loop, so any
		3279	cleanup functions are called.
		3280
		3281	static void
		3282	program_exits (void)
		3283	{
		3284	ev_loop_destroy (EV_DEFAULT_UC);
		3285	}
		3286
		3287	...
		3288	atexit (program_exits);
		3289
		3290
3091	=head2 C<ev_async> - how to wake up an event loop	3291	=head2 C<ev_async> - how to wake up an event loop
3092		3292
3093	In general, you cannot use an C<ev_run> from multiple threads or other	3293	In general, you cannot use an C<ev_loop> from multiple threads or other
3094	asynchronous sources such as signal handlers (as opposed to multiple event	3294	asynchronous sources such as signal handlers (as opposed to multiple event
3095	loops - those are of course safe to use in different threads).	3295	loops - those are of course safe to use in different threads).
3096		3296
3097	Sometimes, however, you need to wake up an event loop you do not control,	3297	Sometimes, however, you need to wake up an event loop you do not control,
3098	for example because it belongs to another thread. This is what C<ev_async>	3298	for example because it belongs to another thread. This is what C<ev_async>
…		…
3100	it by calling C<ev_async_send>, which is thread- and signal safe.	3300	it by calling C<ev_async_send>, which is thread- and signal safe.
3101		3301
3102	This functionality is very similar to C<ev_signal> watchers, as signals,	3302	This functionality is very similar to C<ev_signal> watchers, as signals,
3103	too, are asynchronous in nature, and signals, too, will be compressed	3303	too, are asynchronous in nature, and signals, too, will be compressed
3104	(i.e. the number of callback invocations may be less than the number of	3304	(i.e. the number of callback invocations may be less than the number of
3105	C<ev_async_sent> calls).	3305	C<ev_async_sent> calls). In fact, you could use signal watchers as a kind
3106		3306	of "global async watchers" by using a watcher on an otherwise unused
3107	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not	3307	signal, and C<ev_feed_signal> to signal this watcher from another thread,
3108	just the default loop.	3308	even without knowing which loop owns the signal.
3109		3309
3110	=head3 Queueing	3310	=head3 Queueing
3111		3311
3112	C<ev_async> does not support queueing of data in any way. The reason	3312	C<ev_async> does not support queueing of data in any way. The reason
3113	is that the author does not know of a simple (or any) algorithm for a	3313	is that the author does not know of a simple (or any) algorithm for a
…		…
3205	trust me.	3405	trust me.
3206		3406
3207	=item ev_async_send (loop, ev_async *)	3407	=item ev_async_send (loop, ev_async *)
3208		3408
3209	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3409	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
3210	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3410	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3411	returns.
		3412
3211	C<ev_feed_event>, this call is safe to do from other threads, signal or	3413	Unlike C<ev_feed_event>, this call is safe to do from other threads,
3212	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3414	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
3213	section below on what exactly this means).	3415	embedding section below on what exactly this means).
3214		3416
3215	Note that, as with other watchers in libev, multiple events might get	3417	Note that, as with other watchers in libev, multiple events might get
3216	compressed into a single callback invocation (another way to look at this	3418	compressed into a single callback invocation (another way to look at
3217	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,	3419	this is that C<ev_async> watchers are level-triggered: they are set on
3218	reset when the event loop detects that).	3420	C<ev_async_send>, reset when the event loop detects that).
3219		3421
3220	This call incurs the overhead of a system call only once per event loop	3422	This call incurs the overhead of at most one extra system call per event
3221	iteration, so while the overhead might be noticeable, it doesn't apply to	3423	loop iteration, if the event loop is blocked, and no syscall at all if
3222	repeated calls to C<ev_async_send> for the same event loop.	3424	the event loop (or your program) is processing events. That means that
		3425	repeated calls are basically free (there is no need to avoid calls for
		3426	performance reasons) and that the overhead becomes smaller (typically
		3427	zero) under load.
3223		3428
3224	=item bool = ev_async_pending (ev_async *)	3429	=item bool = ev_async_pending (ev_async *)
3225		3430
3226	Returns a non-zero value when C<ev_async_send> has been called on the	3431	Returns a non-zero value when C<ev_async_send> has been called on the
3227	watcher but the event has not yet been processed (or even noted) by the	3432	watcher but the event has not yet been processed (or even noted) by the
…		…
3282	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3487	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3283		3488
3284	=item ev_feed_fd_event (loop, int fd, int revents)	3489	=item ev_feed_fd_event (loop, int fd, int revents)
3285		3490
3286	Feed an event on the given fd, as if a file descriptor backend detected	3491	Feed an event on the given fd, as if a file descriptor backend detected
3287	the given events it.	3492	the given events.
3288		3493
3289	=item ev_feed_signal_event (loop, int signum)	3494	=item ev_feed_signal_event (loop, int signum)
3290		3495
3291	Feed an event as if the given signal occurred (C<loop> must be the default	3496	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3292	loop!).	3497	which is async-safe.
3293		3498
3294	=back	3499	=back
		3500
		3501
		3502	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3503
		3504	This section explains some common idioms that are not immediately
		3505	obvious. Note that examples are sprinkled over the whole manual, and this
		3506	section only contains stuff that wouldn't fit anywhere else.
		3507
		3508	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3509
		3510	Each watcher has, by default, a C<void *data> member that you can read
		3511	or modify at any time: libev will completely ignore it. This can be used
		3512	to associate arbitrary data with your watcher. If you need more data and
		3513	don't want to allocate memory separately and store a pointer to it in that
		3514	data member, you can also "subclass" the watcher type and provide your own
		3515	data:
		3516
		3517	struct my_io
		3518	{
		3519	ev_io io;
		3520	int otherfd;
		3521	void *somedata;
		3522	struct whatever *mostinteresting;
		3523	};
		3524
		3525	...
		3526	struct my_io w;
		3527	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3528
		3529	And since your callback will be called with a pointer to the watcher, you
		3530	can cast it back to your own type:
		3531
		3532	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3533	{
		3534	struct my_io *w = (struct my_io *)w_;
		3535	...
		3536	}
		3537
		3538	More interesting and less C-conformant ways of casting your callback
		3539	function type instead have been omitted.
		3540
		3541	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3542
		3543	Another common scenario is to use some data structure with multiple
		3544	embedded watchers, in effect creating your own watcher that combines
		3545	multiple libev event sources into one "super-watcher":
		3546
		3547	struct my_biggy
		3548	{
		3549	int some_data;
		3550	ev_timer t1;
		3551	ev_timer t2;
		3552	}
		3553
		3554	In this case getting the pointer to C<my_biggy> is a bit more
		3555	complicated: Either you store the address of your C<my_biggy> struct in
		3556	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3557	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3558	real programmers):
		3559
		3560	#include <stddef.h>
		3561
		3562	static void
		3563	t1_cb (EV_P_ ev_timer *w, int revents)
		3564	{
		3565	struct my_biggy big = (struct my_biggy *)
		3566	(((char *)w) - offsetof (struct my_biggy, t1));
		3567	}
		3568
		3569	static void
		3570	t2_cb (EV_P_ ev_timer *w, int revents)
		3571	{
		3572	struct my_biggy big = (struct my_biggy *)
		3573	(((char *)w) - offsetof (struct my_biggy, t2));
		3574	}
		3575
		3576	=head2 AVOIDING FINISHING BEFORE RETURNING
		3577
		3578	Often you have structures like this in event-based programs:
		3579
		3580	callback ()
		3581	{
		3582	free (request);
		3583	}
		3584
		3585	request = start_new_request (..., callback);
		3586
		3587	The intent is to start some "lengthy" operation. The C<request> could be
		3588	used to cancel the operation, or do other things with it.
		3589
		3590	It's not uncommon to have code paths in C<start_new_request> that
		3591	immediately invoke the callback, for example, to report errors. Or you add
		3592	some caching layer that finds that it can skip the lengthy aspects of the
		3593	operation and simply invoke the callback with the result.
		3594
		3595	The problem here is that this will happen I<before> C<start_new_request>
		3596	has returned, so C<request> is not set.
		3597
		3598	Even if you pass the request by some safer means to the callback, you
		3599	might want to do something to the request after starting it, such as
		3600	canceling it, which probably isn't working so well when the callback has
		3601	already been invoked.
		3602
		3603	A common way around all these issues is to make sure that
		3604	C<start_new_request> I<always> returns before the callback is invoked. If
		3605	C<start_new_request> immediately knows the result, it can artificially
		3606	delay invoking the callback by e.g. using a C<prepare> or C<idle> watcher
		3607	for example, or more sneakily, by reusing an existing (stopped) watcher
		3608	and pushing it into the pending queue:
		3609
		3610	ev_set_cb (watcher, callback);
		3611	ev_feed_event (EV_A_ watcher, 0);
		3612
		3613	This way, C<start_new_request> can safely return before the callback is
		3614	invoked, while not delaying callback invocation too much.
		3615
		3616	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3617
		3618	Often (especially in GUI toolkits) there are places where you have
		3619	I<modal> interaction, which is most easily implemented by recursively
		3620	invoking C<ev_run>.
		3621
		3622	This brings the problem of exiting - a callback might want to finish the
		3623	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3624	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3625	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3626	other combination: In these cases, C<ev_break> will not work alone.
		3627
		3628	The solution is to maintain "break this loop" variable for each C<ev_run>
		3629	invocation, and use a loop around C<ev_run> until the condition is
		3630	triggered, using C<EVRUN_ONCE>:
		3631
		3632	// main loop
		3633	int exit_main_loop = 0;
		3634
		3635	while (!exit_main_loop)
		3636	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3637
		3638	// in a model watcher
		3639	int exit_nested_loop = 0;
		3640
		3641	while (!exit_nested_loop)
		3642	ev_run (EV_A_ EVRUN_ONCE);
		3643
		3644	To exit from any of these loops, just set the corresponding exit variable:
		3645
		3646	// exit modal loop
		3647	exit_nested_loop = 1;
		3648
		3649	// exit main program, after modal loop is finished
		3650	exit_main_loop = 1;
		3651
		3652	// exit both
		3653	exit_main_loop = exit_nested_loop = 1;
		3654
		3655	=head2 THREAD LOCKING EXAMPLE
		3656
		3657	Here is a fictitious example of how to run an event loop in a different
		3658	thread from where callbacks are being invoked and watchers are
		3659	created/added/removed.
		3660
		3661	For a real-world example, see the C<EV::Loop::Async> perl module,
		3662	which uses exactly this technique (which is suited for many high-level
		3663	languages).
		3664
		3665	The example uses a pthread mutex to protect the loop data, a condition
		3666	variable to wait for callback invocations, an async watcher to notify the
		3667	event loop thread and an unspecified mechanism to wake up the main thread.
		3668
		3669	First, you need to associate some data with the event loop:
		3670
		3671	typedef struct {
		3672	mutex_t lock; /* global loop lock */
		3673	ev_async async_w;
		3674	thread_t tid;
		3675	cond_t invoke_cv;
		3676	} userdata;
		3677
		3678	void prepare_loop (EV_P)
		3679	{
		3680	// for simplicity, we use a static userdata struct.
		3681	static userdata u;
		3682
		3683	ev_async_init (&u->async_w, async_cb);
		3684	ev_async_start (EV_A_ &u->async_w);
		3685
		3686	pthread_mutex_init (&u->lock, 0);
		3687	pthread_cond_init (&u->invoke_cv, 0);
		3688
		3689	// now associate this with the loop
		3690	ev_set_userdata (EV_A_ u);
		3691	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3692	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3693
		3694	// then create the thread running ev_run
		3695	pthread_create (&u->tid, 0, l_run, EV_A);
		3696	}
		3697
		3698	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3699	solely to wake up the event loop so it takes notice of any new watchers
		3700	that might have been added:
		3701
		3702	static void
		3703	async_cb (EV_P_ ev_async *w, int revents)
		3704	{
		3705	// just used for the side effects
		3706	}
		3707
		3708	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3709	protecting the loop data, respectively.
		3710
		3711	static void
		3712	l_release (EV_P)
		3713	{
		3714	userdata *u = ev_userdata (EV_A);
		3715	pthread_mutex_unlock (&u->lock);
		3716	}
		3717
		3718	static void
		3719	l_acquire (EV_P)
		3720	{
		3721	userdata *u = ev_userdata (EV_A);
		3722	pthread_mutex_lock (&u->lock);
		3723	}
		3724
		3725	The event loop thread first acquires the mutex, and then jumps straight
		3726	into C<ev_run>:
		3727
		3728	void *
		3729	l_run (void *thr_arg)
		3730	{
		3731	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3732
		3733	l_acquire (EV_A);
		3734	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3735	ev_run (EV_A_ 0);
		3736	l_release (EV_A);
		3737
		3738	return 0;
		3739	}
		3740
		3741	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3742	signal the main thread via some unspecified mechanism (signals? pipe
		3743	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3744	have been called (in a while loop because a) spurious wakeups are possible
		3745	and b) skipping inter-thread-communication when there are no pending
		3746	watchers is very beneficial):
		3747
		3748	static void
		3749	l_invoke (EV_P)
		3750	{
		3751	userdata *u = ev_userdata (EV_A);
		3752
		3753	while (ev_pending_count (EV_A))
		3754	{
		3755	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3756	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3757	}
		3758	}
		3759
		3760	Now, whenever the main thread gets told to invoke pending watchers, it
		3761	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3762	thread to continue:
		3763
		3764	static void
		3765	real_invoke_pending (EV_P)
		3766	{
		3767	userdata *u = ev_userdata (EV_A);
		3768
		3769	pthread_mutex_lock (&u->lock);
		3770	ev_invoke_pending (EV_A);
		3771	pthread_cond_signal (&u->invoke_cv);
		3772	pthread_mutex_unlock (&u->lock);
		3773	}
		3774
		3775	Whenever you want to start/stop a watcher or do other modifications to an
		3776	event loop, you will now have to lock:
		3777
		3778	ev_timer timeout_watcher;
		3779	userdata *u = ev_userdata (EV_A);
		3780
		3781	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3782
		3783	pthread_mutex_lock (&u->lock);
		3784	ev_timer_start (EV_A_ &timeout_watcher);
		3785	ev_async_send (EV_A_ &u->async_w);
		3786	pthread_mutex_unlock (&u->lock);
		3787
		3788	Note that sending the C<ev_async> watcher is required because otherwise
		3789	an event loop currently blocking in the kernel will have no knowledge
		3790	about the newly added timer. By waking up the loop it will pick up any new
		3791	watchers in the next event loop iteration.
		3792
		3793	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3794
		3795	While the overhead of a callback that e.g. schedules a thread is small, it
		3796	is still an overhead. If you embed libev, and your main usage is with some
		3797	kind of threads or coroutines, you might want to customise libev so that
		3798	doesn't need callbacks anymore.
		3799
		3800	Imagine you have coroutines that you can switch to using a function
		3801	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3802	and that due to some magic, the currently active coroutine is stored in a
		3803	global called C<current_coro>. Then you can build your own "wait for libev
		3804	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3805	the differing C<;> conventions):
		3806
		3807	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3808	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3809
		3810	That means instead of having a C callback function, you store the
		3811	coroutine to switch to in each watcher, and instead of having libev call
		3812	your callback, you instead have it switch to that coroutine.
		3813
		3814	A coroutine might now wait for an event with a function called
		3815	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3816	matter when, or whether the watcher is active or not when this function is
		3817	called):
		3818
		3819	void
		3820	wait_for_event (ev_watcher *w)
		3821	{
		3822	ev_cb_set (w) = current_coro;
		3823	switch_to (libev_coro);
		3824	}
		3825
		3826	That basically suspends the coroutine inside C<wait_for_event> and
		3827	continues the libev coroutine, which, when appropriate, switches back to
		3828	this or any other coroutine. I am sure if you sue this your own :)
		3829
		3830	You can do similar tricks if you have, say, threads with an event queue -
		3831	instead of storing a coroutine, you store the queue object and instead of
		3832	switching to a coroutine, you push the watcher onto the queue and notify
		3833	any waiters.
		3834
		3835	To embed libev, see L<EMBEDDING>, but in short, it's easiest to create two
		3836	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3837
		3838	// my_ev.h
		3839	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3840	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);
		3841	#include "../libev/ev.h"
		3842
		3843	// my_ev.c
		3844	#define EV_H "my_ev.h"
		3845	#include "../libev/ev.c"
		3846
		3847	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3848	F<my_ev.c> into your project. When properly specifying include paths, you
		3849	can even use F<ev.h> as header file name directly.
3295		3850
3296		3851
3297	=head1 LIBEVENT EMULATION	3852	=head1 LIBEVENT EMULATION
3298		3853
3299	Libev offers a compatibility emulation layer for libevent. It cannot	3854	Libev offers a compatibility emulation layer for libevent. It cannot
3300	emulate the internals of libevent, so here are some usage hints:	3855	emulate the internals of libevent, so here are some usage hints:
3301		3856
3302	=over 4	3857	=over 4
		3858
		3859	=item * Only the libevent-1.4.1-beta API is being emulated.
		3860
		3861	This was the newest libevent version available when libev was implemented,
		3862	and is still mostly unchanged in 2010.
3303		3863
3304	=item * Use it by including <event.h>, as usual.	3864	=item * Use it by including <event.h>, as usual.
3305		3865
3306	=item * The following members are fully supported: ev_base, ev_callback,	3866	=item * The following members are fully supported: ev_base, ev_callback,
3307	ev_arg, ev_fd, ev_res, ev_events.	3867	ev_arg, ev_fd, ev_res, ev_events.
…		…
3313	=item * Priorities are not currently supported. Initialising priorities	3873	=item * Priorities are not currently supported. Initialising priorities
3314	will fail and all watchers will have the same priority, even though there	3874	will fail and all watchers will have the same priority, even though there
3315	is an ev_pri field.	3875	is an ev_pri field.
3316		3876
3317	=item * In libevent, the last base created gets the signals, in libev, the	3877	=item * In libevent, the last base created gets the signals, in libev, the
3318	first base created (== the default loop) gets the signals.	3878	base that registered the signal gets the signals.
3319		3879
3320	=item * Other members are not supported.	3880	=item * Other members are not supported.
3321		3881
3322	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3882	=item * The libev emulation is I<not> ABI compatible to libevent, you need
3323	to use the libev header file and library.	3883	to use the libev header file and library.
…		…
3342	Care has been taken to keep the overhead low. The only data member the C++	3902	Care has been taken to keep the overhead low. The only data member the C++
3343	classes add (compared to plain C-style watchers) is the event loop pointer	3903	classes add (compared to plain C-style watchers) is the event loop pointer
3344	that the watcher is associated with (or no additional members at all if	3904	that the watcher is associated with (or no additional members at all if
3345	you disable C<EV_MULTIPLICITY> when embedding libev).	3905	you disable C<EV_MULTIPLICITY> when embedding libev).
3346		3906
3347	Currently, functions, and static and non-static member functions can be	3907	Currently, functions, static and non-static member functions and classes
3348	used as callbacks. Other types should be easy to add as long as they only	3908	with C<operator ()> can be used as callbacks. Other types should be easy
3349	need one additional pointer for context. If you need support for other	3909	to add as long as they only need one additional pointer for context. If
3350	types of functors please contact the author (preferably after implementing	3910	you need support for other types of functors please contact the author
3351	it).	3911	(preferably after implementing it).
3352		3912
3353	Here is a list of things available in the C<ev> namespace:	3913	Here is a list of things available in the C<ev> namespace:
3354		3914
3355	=over 4	3915	=over 4
3356		3916
…		…
3509	watchers in the constructor.	4069	watchers in the constructor.
3510		4070
3511	class myclass	4071	class myclass
3512	{	4072	{
3513	ev::io io ; void io_cb (ev::io &w, int revents);	4073	ev::io io ; void io_cb (ev::io &w, int revents);
3514	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);	4074	ev::io io2 ; void io2_cb (ev::io &w, int revents);
3515	ev::idle idle; void idle_cb (ev::idle &w, int revents);	4075	ev::idle idle; void idle_cb (ev::idle &w, int revents);
3516		4076
3517	myclass (int fd)	4077	myclass (int fd)
3518	{	4078	{
3519	io .set <myclass, &myclass::io_cb > (this);	4079	io .set <myclass, &myclass::io_cb > (this);
…		…
3570	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.	4130	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
3571		4131
3572	=item D	4132	=item D
3573		4133
3574	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4134	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
3575	be found at L<http://proj.llucax.com.ar/wiki/evd>.	4135	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
3576		4136
3577	=item Ocaml	4137	=item Ocaml
3578		4138
3579	Erkki Seppala has written Ocaml bindings for libev, to be found at	4139	Erkki Seppala has written Ocaml bindings for libev, to be found at
3580	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	4140	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
…		…
3628	suitable for use with C<EV_A>.	4188	suitable for use with C<EV_A>.
3629		4189
3630	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4190	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
3631		4191
3632	Similar to the other two macros, this gives you the value of the default	4192	Similar to the other two macros, this gives you the value of the default
3633	loop, if multiple loops are supported ("ev loop default").	4193	loop, if multiple loops are supported ("ev loop default"). The default loop
		4194	will be initialised if it isn't already initialised.
		4195
		4196	For non-multiplicity builds, these macros do nothing, so you always have
		4197	to initialise the loop somewhere.
3634		4198
3635	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4199	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
3636		4200
3637	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4201	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
3638	default loop has been initialised (C<UC> == unchecked). Their behaviour	4202	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
3783	supported). It will also not define any of the structs usually found in	4347	supported). It will also not define any of the structs usually found in
3784	F<event.h> that are not directly supported by the libev core alone.	4348	F<event.h> that are not directly supported by the libev core alone.
3785		4349
3786	In standalone mode, libev will still try to automatically deduce the	4350	In standalone mode, libev will still try to automatically deduce the
3787	configuration, but has to be more conservative.	4351	configuration, but has to be more conservative.
		4352
		4353	=item EV_USE_FLOOR
		4354
		4355	If defined to be C<1>, libev will use the C<floor ()> function for its
		4356	periodic reschedule calculations, otherwise libev will fall back on a
		4357	portable (slower) implementation. If you enable this, you usually have to
		4358	link against libm or something equivalent. Enabling this when the C<floor>
		4359	function is not available will fail, so the safe default is to not enable
		4360	this.
3788		4361
3789	=item EV_USE_MONOTONIC	4362	=item EV_USE_MONOTONIC
3790		4363
3791	If defined to be C<1>, libev will try to detect the availability of the	4364	If defined to be C<1>, libev will try to detect the availability of the
3792	monotonic clock option at both compile time and runtime. Otherwise no	4365	monotonic clock option at both compile time and runtime. Otherwise no
…		…
3925	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4498	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
3926		4499
3927	=item EV_ATOMIC_T	4500	=item EV_ATOMIC_T
3928		4501
3929	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4502	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
3930	access is atomic with respect to other threads or signal contexts. No such	4503	access is atomic and serialised with respect to other threads or signal
3931	type is easily found in the C language, so you can provide your own type	4504	contexts. No such type is easily found in the C language, so you can
3932	that you know is safe for your purposes. It is used both for signal handler "locking"	4505	provide your own type that you know is safe for your purposes. It is used
3933	as well as for signal and thread safety in C<ev_async> watchers.	4506	both for signal handler "locking" as well as for signal and thread safety
		4507	in C<ev_async> watchers.
3934		4508
3935	In the absence of this define, libev will use C<sig_atomic_t volatile>	4509	In the absence of this define, libev will use C<sig_atomic_t volatile>
3936	(from F<signal.h>), which is usually good enough on most platforms.	4510	(from F<signal.h>), which is usually good enough on most platforms,
		4511	although strictly speaking using a type that also implies a memory fence
		4512	is required.
3937		4513
3938	=item EV_H (h)	4514	=item EV_H (h)
3939		4515
3940	The name of the F<ev.h> header file used to include it. The default if	4516	The name of the F<ev.h> header file used to include it. The default if
3941	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be	4517	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
…		…
3965	will have the C<struct ev_loop *> as first argument, and you can create	4541	will have the C<struct ev_loop *> as first argument, and you can create
3966	additional independent event loops. Otherwise there will be no support	4542	additional independent event loops. Otherwise there will be no support
3967	for multiple event loops and there is no first event loop pointer	4543	for multiple event loops and there is no first event loop pointer
3968	argument. Instead, all functions act on the single default loop.	4544	argument. Instead, all functions act on the single default loop.
3969		4545
		4546	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4547	default loop when multiplicity is switched off - you always have to
		4548	initialise the loop manually in this case.
		4549
3970	=item EV_MINPRI	4550	=item EV_MINPRI
3971		4551
3972	=item EV_MAXPRI	4552	=item EV_MAXPRI
3973		4553
3974	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4554	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
4071		4651
4072	With an intelligent-enough linker (gcc+binutils are intelligent enough	4652	With an intelligent-enough linker (gcc+binutils are intelligent enough
4073	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by	4653	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
4074	your program might be left out as well - a binary starting a timer and an	4654	your program might be left out as well - a binary starting a timer and an
4075	I/O watcher then might come out at only 5Kb.	4655	I/O watcher then might come out at only 5Kb.
		4656
		4657	=item EV_API_STATIC
		4658
		4659	If this symbol is defined (by default it is not), then all identifiers
		4660	will have static linkage. This means that libev will not export any
		4661	identifiers, and you cannot link against libev anymore. This can be useful
		4662	when you embed libev, only want to use libev functions in a single file,
		4663	and do not want its identifiers to be visible.
		4664
		4665	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4666	wants to use libev.
4076		4667
4077	=item EV_AVOID_STDIO	4668	=item EV_AVOID_STDIO
4078		4669
4079	If this is set to C<1> at compiletime, then libev will avoid using stdio	4670	If this is set to C<1> at compiletime, then libev will avoid using stdio
4080	functions (printf, scanf, perror etc.). This will increase the code size	4671	functions (printf, scanf, perror etc.). This will increase the code size
…		…
4224	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4815	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4225		4816
4226	#include "ev_cpp.h"	4817	#include "ev_cpp.h"
4227	#include "ev.c"	4818	#include "ev.c"
4228		4819
4229	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	4820	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4230		4821
4231	=head2 THREADS AND COROUTINES	4822	=head2 THREADS AND COROUTINES
4232		4823
4233	=head3 THREADS	4824	=head3 THREADS
4234		4825
…		…
4285	default loop and triggering an C<ev_async> watcher from the default loop	4876	default loop and triggering an C<ev_async> watcher from the default loop
4286	watcher callback into the event loop interested in the signal.	4877	watcher callback into the event loop interested in the signal.
4287		4878
4288	=back	4879	=back
4289		4880
4290	=head4 THREAD LOCKING EXAMPLE	4881	See also L<THREAD LOCKING EXAMPLE>.
4291
4292	Here is a fictitious example of how to run an event loop in a different
4293	thread than where callbacks are being invoked and watchers are
4294	created/added/removed.
4295
4296	For a real-world example, see the C<EV::Loop::Async> perl module,
4297	which uses exactly this technique (which is suited for many high-level
4298	languages).
4299
4300	The example uses a pthread mutex to protect the loop data, a condition
4301	variable to wait for callback invocations, an async watcher to notify the
4302	event loop thread and an unspecified mechanism to wake up the main thread.
4303
4304	First, you need to associate some data with the event loop:
4305
4306	typedef struct {
4307	mutex_t lock; /* global loop lock */
4308	ev_async async_w;
4309	thread_t tid;
4310	cond_t invoke_cv;
4311	} userdata;
4312
4313	void prepare_loop (EV_P)
4314	{
4315	// for simplicity, we use a static userdata struct.
4316	static userdata u;
4317
4318	ev_async_init (&u->async_w, async_cb);
4319	ev_async_start (EV_A_ &u->async_w);
4320
4321	pthread_mutex_init (&u->lock, 0);
4322	pthread_cond_init (&u->invoke_cv, 0);
4323
4324	// now associate this with the loop
4325	ev_set_userdata (EV_A_ u);
4326	ev_set_invoke_pending_cb (EV_A_ l_invoke);
4327	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4328
4329	// then create the thread running ev_loop
4330	pthread_create (&u->tid, 0, l_run, EV_A);
4331	}
4332
4333	The callback for the C<ev_async> watcher does nothing: the watcher is used
4334	solely to wake up the event loop so it takes notice of any new watchers
4335	that might have been added:
4336
4337	static void
4338	async_cb (EV_P_ ev_async *w, int revents)
4339	{
4340	// just used for the side effects
4341	}
4342
4343	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
4344	protecting the loop data, respectively.
4345
4346	static void
4347	l_release (EV_P)
4348	{
4349	userdata *u = ev_userdata (EV_A);
4350	pthread_mutex_unlock (&u->lock);
4351	}
4352
4353	static void
4354	l_acquire (EV_P)
4355	{
4356	userdata *u = ev_userdata (EV_A);
4357	pthread_mutex_lock (&u->lock);
4358	}
4359
4360	The event loop thread first acquires the mutex, and then jumps straight
4361	into C<ev_run>:
4362
4363	void *
4364	l_run (void *thr_arg)
4365	{
4366	struct ev_loop *loop = (struct ev_loop *)thr_arg;
4367
4368	l_acquire (EV_A);
4369	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4370	ev_run (EV_A_ 0);
4371	l_release (EV_A);
4372
4373	return 0;
4374	}
4375
4376	Instead of invoking all pending watchers, the C<l_invoke> callback will
4377	signal the main thread via some unspecified mechanism (signals? pipe
4378	writes? C<Async::Interrupt>?) and then waits until all pending watchers
4379	have been called (in a while loop because a) spurious wakeups are possible
4380	and b) skipping inter-thread-communication when there are no pending
4381	watchers is very beneficial):
4382
4383	static void
4384	l_invoke (EV_P)
4385	{
4386	userdata *u = ev_userdata (EV_A);
4387
4388	while (ev_pending_count (EV_A))
4389	{
4390	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4391	pthread_cond_wait (&u->invoke_cv, &u->lock);
4392	}
4393	}
4394
4395	Now, whenever the main thread gets told to invoke pending watchers, it
4396	will grab the lock, call C<ev_invoke_pending> and then signal the loop
4397	thread to continue:
4398
4399	static void
4400	real_invoke_pending (EV_P)
4401	{
4402	userdata *u = ev_userdata (EV_A);
4403
4404	pthread_mutex_lock (&u->lock);
4405	ev_invoke_pending (EV_A);
4406	pthread_cond_signal (&u->invoke_cv);
4407	pthread_mutex_unlock (&u->lock);
4408	}
4409
4410	Whenever you want to start/stop a watcher or do other modifications to an
4411	event loop, you will now have to lock:
4412
4413	ev_timer timeout_watcher;
4414	userdata *u = ev_userdata (EV_A);
4415
4416	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4417
4418	pthread_mutex_lock (&u->lock);
4419	ev_timer_start (EV_A_ &timeout_watcher);
4420	ev_async_send (EV_A_ &u->async_w);
4421	pthread_mutex_unlock (&u->lock);
4422
4423	Note that sending the C<ev_async> watcher is required because otherwise
4424	an event loop currently blocking in the kernel will have no knowledge
4425	about the newly added timer. By waking up the loop it will pick up any new
4426	watchers in the next event loop iteration.
4427		4882
4428	=head3 COROUTINES	4883	=head3 COROUTINES
4429		4884
4430	Libev is very accommodating to coroutines ("cooperative threads"):	4885	Libev is very accommodating to coroutines ("cooperative threads"):
4431	libev fully supports nesting calls to its functions from different	4886	libev fully supports nesting calls to its functions from different
…		…
4527	=head3 C<kqueue> is buggy	4982	=head3 C<kqueue> is buggy
4528		4983
4529	The kqueue syscall is broken in all known versions - most versions support	4984	The kqueue syscall is broken in all known versions - most versions support
4530	only sockets, many support pipes.	4985	only sockets, many support pipes.
4531		4986
4532	Libev tries to work around this by not using C<kqueue> by default on	4987	Libev tries to work around this by not using C<kqueue> by default on this
4533	this rotten platform, but of course you can still ask for it when creating	4988	rotten platform, but of course you can still ask for it when creating a
4534	a loop.	4989	loop - embedding a socket-only kqueue loop into a select-based one is
		4990	probably going to work well.
4535		4991
4536	=head3 C<poll> is buggy	4992	=head3 C<poll> is buggy
4537		4993
4538	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>	4994	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
4539	implementation by something calling C<kqueue> internally around the 10.5.6	4995	implementation by something calling C<kqueue> internally around the 10.5.6
…		…
4558		5014
4559	=head3 C<errno> reentrancy	5015	=head3 C<errno> reentrancy
4560		5016
4561	The default compile environment on Solaris is unfortunately so	5017	The default compile environment on Solaris is unfortunately so
4562	thread-unsafe that you can't even use components/libraries compiled	5018	thread-unsafe that you can't even use components/libraries compiled
4563	without C<-D_REENTRANT> (as long as they use C<errno>), which, of course,	5019	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
4564	isn't defined by default.	5020	defined by default. A valid, if stupid, implementation choice.
4565		5021
4566	If you want to use libev in threaded environments you have to make sure	5022	If you want to use libev in threaded environments you have to make sure
4567	it's compiled with C<_REENTRANT> defined.	5023	it's compiled with C<_REENTRANT> defined.
4568		5024
4569	=head3 Event port backend	5025	=head3 Event port backend
4570		5026
4571	The scalable event interface for Solaris is called "event ports". Unfortunately,	5027	The scalable event interface for Solaris is called "event
4572	this mechanism is very buggy. If you run into high CPU usage, your program	5028	ports". Unfortunately, this mechanism is very buggy in all major
		5029	releases. If you run into high CPU usage, your program freezes or you get
4573	freezes or you get a large number of spurious wakeups, make sure you have	5030	a large number of spurious wakeups, make sure you have all the relevant
4574	all the relevant and latest kernel patches applied. No, I don't know which	5031	and latest kernel patches applied. No, I don't know which ones, but there
4575	ones, but there are multiple ones.	5032	are multiple ones to apply, and afterwards, event ports actually work
		5033	great.
4576		5034
4577	If you can't get it to work, you can try running the program by setting	5035	If you can't get it to work, you can try running the program by setting
4578	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and	5036	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
4579	C<select> backends.	5037	C<select> backends.
4580		5038
4581	=head2 AIX POLL BUG	5039	=head2 AIX POLL BUG
4582		5040
4583	AIX unfortunately has a broken C<poll.h> header. Libev works around	5041	AIX unfortunately has a broken C<poll.h> header. Libev works around
4584	this by trying to avoid the poll backend altogether (i.e. it's not even	5042	this by trying to avoid the poll backend altogether (i.e. it's not even
4585	compiled in), which normally isn't a big problem as C<select> works fine	5043	compiled in), which normally isn't a big problem as C<select> works fine
4586	with large bitsets, and AIX is dead anyway.	5044	with large bitsets on AIX, and AIX is dead anyway.
4587		5045
4588	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS	5046	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
4589		5047
4590	=head3 General issues	5048	=head3 General issues
4591		5049
…		…
4593	requires, and its I/O model is fundamentally incompatible with the POSIX	5051	requires, and its I/O model is fundamentally incompatible with the POSIX
4594	model. Libev still offers limited functionality on this platform in	5052	model. Libev still offers limited functionality on this platform in
4595	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5053	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
4596	descriptors. This only applies when using Win32 natively, not when using	5054	descriptors. This only applies when using Win32 natively, not when using
4597	e.g. cygwin. Actually, it only applies to the microsofts own compilers,	5055	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4598	as every compielr comes with a slightly differently broken/incompatible	5056	as every compiler comes with a slightly differently broken/incompatible
4599	environment.	5057	environment.
4600		5058
4601	Lifting these limitations would basically require the full	5059	Lifting these limitations would basically require the full
4602	re-implementation of the I/O system. If you are into this kind of thing,	5060	re-implementation of the I/O system. If you are into this kind of thing,
4603	then note that glib does exactly that for you in a very portable way (note	5061	then note that glib does exactly that for you in a very portable way (note
…		…
4697	structure (guaranteed by POSIX but not by ISO C for example), but it also	5155	structure (guaranteed by POSIX but not by ISO C for example), but it also
4698	assumes that the same (machine) code can be used to call any watcher	5156	assumes that the same (machine) code can be used to call any watcher
4699	callback: The watcher callbacks have different type signatures, but libev	5157	callback: The watcher callbacks have different type signatures, but libev
4700	calls them using an C<ev_watcher *> internally.	5158	calls them using an C<ev_watcher *> internally.
4701		5159
		5160	=item pointer accesses must be thread-atomic
		5161
		5162	Accessing a pointer value must be atomic, it must both be readable and
		5163	writable in one piece - this is the case on all current architectures.
		5164
4702	=item C<sig_atomic_t volatile> must be thread-atomic as well	5165	=item C<sig_atomic_t volatile> must be thread-atomic as well
4703		5166
4704	The type C<sig_atomic_t volatile> (or whatever is defined as	5167	The type C<sig_atomic_t volatile> (or whatever is defined as
4705	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different	5168	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
4706	threads. This is not part of the specification for C<sig_atomic_t>, but is	5169	threads. This is not part of the specification for C<sig_atomic_t>, but is
…		…
4731		5194
4732	The type C<double> is used to represent timestamps. It is required to	5195	The type C<double> is used to represent timestamps. It is required to
4733	have at least 51 bits of mantissa (and 9 bits of exponent), which is	5196	have at least 51 bits of mantissa (and 9 bits of exponent), which is
4734	good enough for at least into the year 4000 with millisecond accuracy	5197	good enough for at least into the year 4000 with millisecond accuracy
4735	(the design goal for libev). This requirement is overfulfilled by	5198	(the design goal for libev). This requirement is overfulfilled by
4736	implementations using IEEE 754, which is basically all existing ones. With	5199	implementations using IEEE 754, which is basically all existing ones.
		5200
4737	IEEE 754 doubles, you get microsecond accuracy until at least 2200.	5201	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5202	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5203	is either obsolete or somebody patched it to use C<long double> or
		5204	something like that, just kidding).
4738		5205
4739	=back	5206	=back
4740		5207
4741	If you know of other additional requirements drop me a note.	5208	If you know of other additional requirements drop me a note.
4742		5209
…		…
4804	=item Processing ev_async_send: O(number_of_async_watchers)	5271	=item Processing ev_async_send: O(number_of_async_watchers)
4805		5272
4806	=item Processing signals: O(max_signal_number)	5273	=item Processing signals: O(max_signal_number)
4807		5274
4808	Sending involves a system call I<iff> there were no other C<ev_async_send>	5275	Sending involves a system call I<iff> there were no other C<ev_async_send>
4809	calls in the current loop iteration. Checking for async and signal events	5276	calls in the current loop iteration and the loop is currently
		5277	blocked. Checking for async and signal events involves iterating over all
4810	involves iterating over all running async watchers or all signal numbers.	5278	running async watchers or all signal numbers.
4811		5279
4812	=back	5280	=back
4813		5281
4814		5282
4815	=head1 PORTING FROM LIBEV 3.X TO 4.X	5283	=head1 PORTING FROM LIBEV 3.X TO 4.X
4816		5284
4817	The major version 4 introduced some minor incompatible changes to the API.	5285	The major version 4 introduced some incompatible changes to the API.
4818		5286
4819	At the moment, the C<ev.h> header file tries to implement superficial	5287	At the moment, the C<ev.h> header file provides compatibility definitions
4820	compatibility, so most programs should still compile. Those might be	5288	for all changes, so most programs should still compile. The compatibility
4821	removed in later versions of libev, so better update early than late.	5289	layer might be removed in later versions of libev, so better update to the
		5290	new API early than late.
4822		5291
4823	=over 4	5292	=over 4
		5293
		5294	=item C<EV_COMPAT3> backwards compatibility mechanism
		5295
		5296	The backward compatibility mechanism can be controlled by
		5297	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
		5298	section.
		5299
		5300	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5301
		5302	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5303
		5304	ev_loop_destroy (EV_DEFAULT_UC);
		5305	ev_loop_fork (EV_DEFAULT);
4824		5306
4825	=item function/symbol renames	5307	=item function/symbol renames
4826		5308
4827	A number of functions and symbols have been renamed:	5309	A number of functions and symbols have been renamed:
4828		5310
…		…
4847	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme	5329	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
4848	as all other watcher types. Note that C<ev_loop_fork> is still called	5330	as all other watcher types. Note that C<ev_loop_fork> is still called
4849	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>	5331	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
4850	typedef.	5332	typedef.
4851		5333
4852	=item C<EV_COMPAT3> backwards compatibility mechanism
4853
4854	The backward compatibility mechanism can be controlled by
4855	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
4856	section.
4857
4858	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>	5334	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
4859		5335
4860	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different	5336	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
4861	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile	5337	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
4862	and work, but the library code will of course be larger.	5338	and work, but the library code will of course be larger.
…		…
4868		5344
4869	=over 4	5345	=over 4
4870		5346
4871	=item active	5347	=item active
4872		5348
4873	A watcher is active as long as it has been started (has been attached to	5349	A watcher is active as long as it has been started and not yet stopped.
4874	an event loop) but not yet stopped (disassociated from the event loop).	5350	See L<WATCHER STATES> for details.
4875		5351
4876	=item application	5352	=item application
4877		5353
4878	In this document, an application is whatever is using libev.	5354	In this document, an application is whatever is using libev.
		5355
		5356	=item backend
		5357
		5358	The part of the code dealing with the operating system interfaces.
4879		5359
4880	=item callback	5360	=item callback
4881		5361
4882	The address of a function that is called when some event has been	5362	The address of a function that is called when some event has been
4883	detected. Callbacks are being passed the event loop, the watcher that	5363	detected. Callbacks are being passed the event loop, the watcher that
4884	received the event, and the actual event bitset.	5364	received the event, and the actual event bitset.
4885		5365
4886	=item callback invocation	5366	=item callback/watcher invocation
4887		5367
4888	The act of calling the callback associated with a watcher.	5368	The act of calling the callback associated with a watcher.
4889		5369
4890	=item event	5370	=item event
4891		5371
…		…
4910	The model used to describe how an event loop handles and processes	5390	The model used to describe how an event loop handles and processes
4911	watchers and events.	5391	watchers and events.
4912		5392
4913	=item pending	5393	=item pending
4914		5394
4915	A watcher is pending as soon as the corresponding event has been detected,	5395	A watcher is pending as soon as the corresponding event has been
4916	and stops being pending as soon as the watcher will be invoked or its	5396	detected. See L<WATCHER STATES> for details.
4917	pending status is explicitly cleared by the application.
4918
4919	A watcher can be pending, but not active. Stopping a watcher also clears
4920	its pending status.
4921		5397
4922	=item real time	5398	=item real time
4923		5399
4924	The physical time that is observed. It is apparently strictly monotonic :)	5400	The physical time that is observed. It is apparently strictly monotonic :)
4925		5401
4926	=item wall-clock time	5402	=item wall-clock time
4927		5403
4928	The time and date as shown on clocks. Unlike real time, it can actually	5404	The time and date as shown on clocks. Unlike real time, it can actually
4929	be wrong and jump forwards and backwards, e.g. when the you adjust your	5405	be wrong and jump forwards and backwards, e.g. when you adjust your
4930	clock.	5406	clock.
4931		5407
4932	=item watcher	5408	=item watcher
4933		5409
4934	A data structure that describes interest in certain events. Watchers need	5410	A data structure that describes interest in certain events. Watchers need
4935	to be started (attached to an event loop) before they can receive events.	5411	to be started (attached to an event loop) before they can receive events.
4936		5412
4937	=item watcher invocation
4938
4939	The act of calling the callback associated with a watcher.
4940
4941	=back	5413	=back
4942		5414
4943	=head1 AUTHOR	5415	=head1 AUTHOR
4944		5416
4945	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.	5417	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5418	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
4946		5419

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