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Revision 1.316 by root, Fri Oct 22 09:34:01 2010 UTC vs.
Revision 1.358 by sf-exg, Tue Jan 11 08:43:48 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);
…		…
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_update_now> 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 until
175	either it is interrupted or the given time interval has passed. Basically	184	either it is interrupted or the given time interval has passed. Basically
…		…
192	as this indicates an incompatible change. Minor versions are usually	201	as this indicates an incompatible change. Minor versions are usually
193	compatible to older versions, so a larger minor version alone is usually	202	compatible to older versions, so a larger minor version alone is usually
194	not a problem.	203	not a problem.
195		204
196	Example: Make sure we haven't accidentally been linked against the wrong	205	Example: Make sure we haven't accidentally been linked against the wrong
197	version (note, however, that this will not detect ABI mismatches :).	206	version (note, however, that this will not detect other ABI mismatches,
		207	such as LFS or reentrancy).
198		208
199	assert (("libev version mismatch",	209	assert (("libev version mismatch",
200	ev_version_major () == EV_VERSION_MAJOR	210	ev_version_major () == EV_VERSION_MAJOR
201	&& ev_version_minor () >= EV_VERSION_MINOR));	211	&& ev_version_minor () >= EV_VERSION_MINOR));
202		212
…		…
213	assert (("sorry, no epoll, no sex",	223	assert (("sorry, no epoll, no sex",
214	ev_supported_backends () & EVBACKEND_EPOLL));	224	ev_supported_backends () & EVBACKEND_EPOLL));
215		225
216	=item unsigned int ev_recommended_backends ()	226	=item unsigned int ev_recommended_backends ()
217		227
218	Return the set of all backends compiled into this binary of libev and also	228	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	229	also recommended for this platform, meaning it will work for most file
		230	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	231	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	232	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	233	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.	234	probe for if you specify no backends explicitly.
224		235
225	=item unsigned int ev_embeddable_backends ()	236	=item unsigned int ev_embeddable_backends ()
226		237
227	Returns the set of backends that are embeddable in other event loops. This	238	Returns the set of backends that are embeddable in other event loops. This
228	is the theoretical, all-platform, value. To find which backends	239	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	240	current system. To find which embeddable backends might be supported on
230	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	241	the current system, you would need to look at C<ev_embeddable_backends ()
231	recommended ones.	242	& ev_supported_backends ()>, likewise for recommended ones.
232		243
233	See the description of C<ev_embed> watchers for more info.	244	See the description of C<ev_embed> watchers for more info.
234		245
235	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]	246	=item ev_set_allocator (void *(*cb)(void *ptr, long size))
236		247
237	Sets the allocation function to use (the prototype is similar - the	248	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	249	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	250	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	251	when memory needs to be allocated (C<size != 0>), the library might abort
…		…
266	}	277	}
267		278
268	...	279	...
269	ev_set_allocator (persistent_realloc);	280	ev_set_allocator (persistent_realloc);
270		281
271	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]	282	=item ev_set_syserr_cb (void (*cb)(const char *msg))
272		283
273	Set the callback function to call on a retryable system call error (such	284	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	285	as failed select, poll, epoll_wait). The message is a printable string
275	indicating the system call or subsystem causing the problem. If this	286	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	287	callback is set, then libev will expect it to remedy the situation, no
…		…
288	}	299	}
289		300
290	...	301	...
291	ev_set_syserr_cb (fatal_error);	302	ev_set_syserr_cb (fatal_error);
292		303
		304	=item ev_feed_signal (int signum)
		305
		306	This function can be used to "simulate" a signal receive. It is completely
		307	safe to call this function at any time, from any context, including signal
		308	handlers or random threads.
		309
		310	Its main use is to customise signal handling in your process, especially
		311	in the presence of threads. For example, you could block signals
		312	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
		313	creating any loops), and in one thread, use C<sigwait> or any other
		314	mechanism to wait for signals, then "deliver" them to libev by calling
		315	C<ev_feed_signal>.
		316
293	=back	317	=back
294		318
295	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	319	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
296		320
297	An event loop is described by a C<struct ev_loop *> (the C<struct> is	321	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	322	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).	323	libev 3 had an C<ev_loop> function colliding with the struct name).
300		324
301	The library knows two types of such loops, the I<default> loop, which	325	The library knows two types of such loops, the I<default> loop, which
302	supports signals and child events, and dynamically created event loops	326	supports child process events, and dynamically created event loops which
303	which do not.	327	do not.
304		328
305	=over 4	329	=over 4
306		330
307	=item struct ev_loop *ev_default_loop (unsigned int flags)	331	=item struct ev_loop *ev_default_loop (unsigned int flags)
308		332
309	This will initialise the default event loop if it hasn't been initialised	333	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	334	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	335	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).	336	C<ev_loop_new>.
		337
		338	If the default loop is already initialised then this function simply
		339	returns it (and ignores the flags. If that is troubling you, check
		340	C<ev_backend ()> afterwards). Otherwise it will create it with the given
		341	flags, which should almost always be C<0>, unless the caller is also the
		342	one calling C<ev_run> or otherwise qualifies as "the main program".
313		343
314	If you don't know what event loop to use, use the one returned from this	344	If you don't know what event loop to use, use the one returned from this
315	function.	345	function (or via the C<EV_DEFAULT> macro).
316		346
317	Note that this function is I<not> thread-safe, so if you want to use it	347	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,	348	from multiple threads, you have to employ some kind of mutex (note also
319	as loops cannot be shared easily between threads anyway).	349	that this case is unlikely, as loops cannot be shared easily between
		350	threads anyway).
320		351
321	The default loop is the only loop that can handle C<ev_signal> and	352	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	353	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	354	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	355	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	356	C<SIGCHLD> signal handler I<after> calling C<ev_default_init>.
326	C<ev_default_init>.	357
		358	Example: This is the most typical usage.
		359
		360	if (!ev_default_loop (0))
		361	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		362
		363	Example: Restrict libev to the select and poll backends, and do not allow
		364	environment settings to be taken into account:
		365
		366	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		367
		368	=item struct ev_loop *ev_loop_new (unsigned int flags)
		369
		370	This will create and initialise a new event loop object. If the loop
		371	could not be initialised, returns false.
		372
		373	This function is thread-safe, and one common way to use libev with
		374	threads is indeed to create one loop per thread, and using the default
		375	loop in the "main" or "initial" thread.
327		376
328	The flags argument can be used to specify special behaviour or specific	377	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>).	378	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
330		379
331	The following flags are supported:	380	The following flags are supported:
…		…
366	environment variable.	415	environment variable.
367		416
368	=item C<EVFLAG_NOINOTIFY>	417	=item C<EVFLAG_NOINOTIFY>
369		418
370	When this flag is specified, then libev will not attempt to use the	419	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	420	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	421	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.	422	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
374		423
375	=item C<EVFLAG_SIGNALFD>	424	=item C<EVFLAG_SIGNALFD>
376		425
377	When this flag is specified, then libev will attempt to use the	426	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	427	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	428	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	429	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	430	handling with threads, as long as you properly block signals in your
382	threads that are not interested in handling them.	431	threads that are not interested in handling them.
383		432
384	Signalfd will not be used by default as this changes your signal mask, and	433	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	434	there are a lot of shoddy libraries and programs (glib's threadpool for
386	example) that can't properly initialise their signal masks.	435	example) that can't properly initialise their signal masks.
		436
		437	=item C<EVFLAG_NOSIGMASK>
		438
		439	When this flag is specified, then libev will avoid to modify the signal
		440	mask. Specifically, this means you ahve to make sure signals are unblocked
		441	when you want to receive them.
		442
		443	This behaviour is useful when you want to do your own signal handling, or
		444	want to handle signals only in specific threads and want to avoid libev
		445	unblocking the signals.
		446
		447	This flag's behaviour will become the default in future versions of libev.
387		448
388	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	449	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
389		450
390	This is your standard select(2) backend. Not I<completely> standard, as	451	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,	452	libev tries to roll its own fd_set with no limits on the number of fds,
…		…
427	epoll scales either O(1) or O(active_fds).	488	epoll scales either O(1) or O(active_fds).
428		489
429	The epoll mechanism deserves honorable mention as the most misdesigned	490	The epoll mechanism deserves honorable mention as the most misdesigned
430	of the more advanced event mechanisms: mere annoyances include silently	491	of the more advanced event mechanisms: mere annoyances include silently
431	dropping file descriptors, requiring a system call per change per file	492	dropping file descriptors, requiring a system call per change per file
432	descriptor (and unnecessary guessing of parameters), problems with dup and	493	descriptor (and unnecessary guessing of parameters), problems with dup,
		494	returning before the timeout value, resulting in additional iterations
		495	(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	496	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	497	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	498	set, which can take considerable time (one syscall per file descriptor)
436	hard to detect.	499	and is of course hard to detect.
437		500
438	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but	501	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
439	of course I<doesn't>, and epoll just loves to report events for totally	502	of course I<doesn't>, and epoll just loves to report events for totally
440	I<different> file descriptors (even already closed ones, so one cannot	503	I<different> file descriptors (even already closed ones, so one cannot
441	even remove them from the set) than registered in the set (especially	504	even remove them from the set) than registered in the set (especially
…		…
443	employing an additional generation counter and comparing that against the	506	employing an additional generation counter and comparing that against the
444	events to filter out spurious ones, recreating the set when required. Last	507	events to filter out spurious ones, recreating the set when required. Last
445	not least, it also refuses to work with some file descriptors which work	508	not least, it also refuses to work with some file descriptors which work
446	perfectly fine with C<select> (files, many character devices...).	509	perfectly fine with C<select> (files, many character devices...).
447		510
		511	Epoll is truly the train wreck analog among event poll mechanisms,
		512	a frankenpoll, cobbled together in a hurry, no thought to design or
		513	interaction with others.
		514
448	While stopping, setting and starting an I/O watcher in the same iteration	515	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	516	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	517	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	518	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
452	file descriptors might not work very well if you register events for both	519	file descriptors might not work very well if you register events for both
…		…
517	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	584	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
518		585
519	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	586	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)).	587	it's really slow, but it still scales very well (O(active_fds)).
521		588
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	589	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	590	file descriptor per loop iteration. For small and medium numbers of file
528	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	591	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
529	might perform better.	592	might perform better.
530		593
531	On the positive side, with the exception of the spurious readiness	594	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	595	specification in all tests and is fully embeddable, which is a rare feat
534	OS-specific backends (I vastly prefer correctness over speed hacks).	596	among the OS-specific backends (I vastly prefer correctness over speed
		597	hacks).
		598
		599	On the negative side, the interface is I<bizarre> - so bizarre that
		600	even sun itself gets it wrong in their code examples: The event polling
		601	function sometimes returning events to the caller even though an error
		602	occurred, but with no indication whether it has done so or not (yes, it's
		603	even documented that way) - deadly for edge-triggered interfaces where
		604	you absolutely have to know whether an event occurred or not because you
		605	have to re-arm the watcher.
		606
		607	Fortunately libev seems to be able to work around these idiocies.
535		608
536	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	609	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
537	C<EVBACKEND_POLL>.	610	C<EVBACKEND_POLL>.
538		611
539	=item C<EVBACKEND_ALL>	612	=item C<EVBACKEND_ALL>
540		613
541	Try all backends (even potentially broken ones that wouldn't be tried	614	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	615	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
543	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	616	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
544		617
545	It is definitely not recommended to use this flag.	618	It is definitely not recommended to use this flag, use whatever
		619	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		620	at all.
		621
		622	=item C<EVBACKEND_MASK>
		623
		624	Not a backend at all, but a mask to select all backend bits from a
		625	C<flags> value, in case you want to mask out any backends from a flags
		626	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
546		627
547	=back	628	=back
548		629
549	If one or more of the backend flags are or'ed into the flags value,	630	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	631	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	632	here). If none are specified, all backends in C<ev_recommended_backends
552	()> will be tried.	633	()> will be tried.
553		634
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.	635	Example: Try to create a event loop that uses epoll and nothing else.
581		636
582	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	637	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
583	if (!epoller)	638	if (!epoller)
584	fatal ("no epoll found here, maybe it hides under your chair");	639	fatal ("no epoll found here, maybe it hides under your chair");
585		640
		641	Example: Use whatever libev has to offer, but make sure that kqueue is
		642	used if available.
		643
		644	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		645
586	=item ev_default_destroy ()	646	=item ev_loop_destroy (loop)
587		647
588	Destroys the default loop (frees all memory and kernel state etc.). None	648	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	649	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	650	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,	651	responsibility to either stop all watchers cleanly yourself I<before>
592	or cope with the fact afterwards (which is usually the easiest thing, you	652	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).	653	the easiest thing, you can just ignore the watchers and/or C<free ()> them
		654	for example).
594		655
595	Note that certain global state, such as signal state (and installed signal	656	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	657	handlers), will not be freed by this function, and related watchers (such
597	as signal and child watchers) would need to be stopped manually.	658	as signal and child watchers) would need to be stopped manually.
598		659
599	In general it is not advisable to call this function except in the	660	This function is normally used on loop objects allocated by
600	rare occasion where you really need to free e.g. the signal handling	661	C<ev_loop_new>, but it can also be used on the default loop returned by
		662	C<ev_default_loop>, in which case it is not thread-safe.
		663
		664	Note that it is not advisable to call this function on the default loop
		665	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	666	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>.	667	and C<ev_loop_destroy>.
603		668
604	=item ev_loop_destroy (loop)	669	=item ev_loop_fork (loop)
605		670
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	671	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	672	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	673	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	674	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	675	child before resuming or calling C<ev_run>.
616	functions, and it will only take effect at the next C<ev_run> iteration.
617		676
618	Again, you I<have> to call it on I<any> loop that you want to re-use after	677	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	678	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	679	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
621	during fork.	680	during fork.
…		…
626	call it at all (in fact, C<epoll> is so badly broken that it makes a	685	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	686	difference, but libev will usually detect this case on its own and do a
628	costly reset of the backend).	687	costly reset of the backend).
629		688
630	The function itself is quite fast and it's usually not a problem to call	689	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	690	it just in case after a fork.
632	quite nicely into a call to C<pthread_atfork>:
633		691
		692	Example: Automate calling C<ev_loop_fork> on the default loop when
		693	using pthreads.
		694
		695	static void
		696	post_fork_child (void)
		697	{
		698	ev_loop_fork (EV_DEFAULT);
		699	}
		700
		701	...
634	pthread_atfork (0, 0, ev_default_fork);	702	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		703
643	=item int ev_is_default_loop (loop)	704	=item int ev_is_default_loop (loop)
644		705
645	Returns true when the given loop is, in fact, the default loop, and false	706	Returns true when the given loop is, in fact, the default loop, and false
646	otherwise.	707	otherwise.
…		…
657	prepare and check phases.	718	prepare and check phases.
658		719
659	=item unsigned int ev_depth (loop)	720	=item unsigned int ev_depth (loop)
660		721
661	Returns the number of times C<ev_run> was entered minus the number of	722	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.	723	times C<ev_run> was exited normally, in other words, the recursion depth.
663		724
664	Outside C<ev_run>, this number is zero. In a callback, this number is	725	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),	726	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
666	in which case it is higher.	727	in which case it is higher.
667		728
668	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread	729	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	730	throwing an exception etc.), doesn't count as "exit" - consider this
670	ungentleman-like behaviour unless it's really convenient.	731	as a hint to avoid such ungentleman-like behaviour unless it's really
		732	convenient, in which case it is fully supported.
671		733
672	=item unsigned int ev_backend (loop)	734	=item unsigned int ev_backend (loop)
673		735
674	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	736	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
675	use.	737	use.
…		…
736	relying on all watchers to be stopped when deciding when a program has	798	relying on all watchers to be stopped when deciding when a program has
737	finished (especially in interactive programs), but having a program	799	finished (especially in interactive programs), but having a program
738	that automatically loops as long as it has to and no longer by virtue	800	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	801	of relying on its watchers stopping correctly, that is truly a thing of
740	beauty.	802	beauty.
		803
		804	This function is also I<mostly> exception-safe - you can break out of
		805	a C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		806	exception and so on. This does not decrement the C<ev_depth> value, nor
		807	will it clear any outstanding C<EVBREAK_ONE> breaks.
741		808
742	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle	809	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	810	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	811	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	812	iteration of the loop. This is sometimes useful to poll and handle new
…		…
807	Can be used to make a call to C<ev_run> return early (but only after it	874	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	875	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	876	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.	877	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
811		878
812	This "unloop state" will be cleared when entering C<ev_run> again.	879	This "break state" will be cleared on the next call to C<ev_run>.
813		880
814	It is safe to call C<ev_break> from outside any C<ev_run> calls. ##TODO##	881	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		882	which case it will have no effect.
815		883
816	=item ev_ref (loop)	884	=item ev_ref (loop)
817		885
818	=item ev_unref (loop)	886	=item ev_unref (loop)
819		887
…		…
840	running when nothing else is active.	908	running when nothing else is active.
841		909
842	ev_signal exitsig;	910	ev_signal exitsig;
843	ev_signal_init (&exitsig, sig_cb, SIGINT);	911	ev_signal_init (&exitsig, sig_cb, SIGINT);
844	ev_signal_start (loop, &exitsig);	912	ev_signal_start (loop, &exitsig);
845	evf_unref (loop);	913	ev_unref (loop);
846		914
847	Example: For some weird reason, unregister the above signal handler again.	915	Example: For some weird reason, unregister the above signal handler again.
848		916
849	ev_ref (loop);	917	ev_ref (loop);
850	ev_signal_stop (loop, &exitsig);	918	ev_signal_stop (loop, &exitsig);
…		…
962	See also the locking example in the C<THREADS> section later in this	1030	See also the locking example in the C<THREADS> section later in this
963	document.	1031	document.
964		1032
965	=item ev_set_userdata (loop, void *data)	1033	=item ev_set_userdata (loop, void *data)
966		1034
967	=item ev_userdata (loop)	1035	=item void *ev_userdata (loop)
968		1036
969	Set and retrieve a single C<void *> associated with a loop. When	1037	Set and retrieve a single C<void *> associated with a loop. When
970	C<ev_set_userdata> has never been called, then C<ev_userdata> returns	1038	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
971	C<0.>	1039	C<0>.
972		1040
973	These two functions can be used to associate arbitrary data with a loop,	1041	These two functions can be used to associate arbitrary data with a loop,
974	and are intended solely for the C<invoke_pending_cb>, C<release> and	1042	and are intended solely for the C<invoke_pending_cb>, C<release> and
975	C<acquire> callbacks described above, but of course can be (ab-)used for	1043	C<acquire> callbacks described above, but of course can be (ab-)used for
976	any other purpose as well.	1044	any other purpose as well.
…		…
1104	=item C<EV_FORK>	1172	=item C<EV_FORK>
1105		1173
1106	The event loop has been resumed in the child process after fork (see	1174	The event loop has been resumed in the child process after fork (see
1107	C<ev_fork>).	1175	C<ev_fork>).
1108		1176
		1177	=item C<EV_CLEANUP>
		1178
		1179	The event loop is about to be destroyed (see C<ev_cleanup>).
		1180
1109	=item C<EV_ASYNC>	1181	=item C<EV_ASYNC>
1110		1182
1111	The given async watcher has been asynchronously notified (see C<ev_async>).	1183	The given async watcher has been asynchronously notified (see C<ev_async>).
1112		1184
1113	=item C<EV_CUSTOM>	1185	=item C<EV_CUSTOM>
…		…
1134	programs, though, as the fd could already be closed and reused for another	1206	programs, though, as the fd could already be closed and reused for another
1135	thing, so beware.	1207	thing, so beware.
1136		1208
1137	=back	1209	=back
1138		1210
		1211	=head2 GENERIC WATCHER FUNCTIONS
		1212
		1213	=over 4
		1214
		1215	=item C<ev_init> (ev_TYPE *watcher, callback)
		1216
		1217	This macro initialises the generic portion of a watcher. The contents
		1218	of the watcher object can be arbitrary (so C<malloc> will do). Only
		1219	the generic parts of the watcher are initialised, you I<need> to call
		1220	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		1221	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		1222	which rolls both calls into one.
		1223
		1224	You can reinitialise a watcher at any time as long as it has been stopped
		1225	(or never started) and there are no pending events outstanding.
		1226
		1227	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
		1228	int revents)>.
		1229
		1230	Example: Initialise an C<ev_io> watcher in two steps.
		1231
		1232	ev_io w;
		1233	ev_init (&w, my_cb);
		1234	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1235
		1236	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
		1237
		1238	This macro initialises the type-specific parts of a watcher. You need to
		1239	call C<ev_init> at least once before you call this macro, but you can
		1240	call C<ev_TYPE_set> any number of times. You must not, however, call this
		1241	macro on a watcher that is active (it can be pending, however, which is a
		1242	difference to the C<ev_init> macro).
		1243
		1244	Although some watcher types do not have type-specific arguments
		1245	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		1246
		1247	See C<ev_init>, above, for an example.
		1248
		1249	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		1250
		1251	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		1252	calls into a single call. This is the most convenient method to initialise
		1253	a watcher. The same limitations apply, of course.
		1254
		1255	Example: Initialise and set an C<ev_io> watcher in one step.
		1256
		1257	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1258
		1259	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
		1260
		1261	Starts (activates) the given watcher. Only active watchers will receive
		1262	events. If the watcher is already active nothing will happen.
		1263
		1264	Example: Start the C<ev_io> watcher that is being abused as example in this
		1265	whole section.
		1266
		1267	ev_io_start (EV_DEFAULT_UC, &w);
		1268
		1269	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
		1270
		1271	Stops the given watcher if active, and clears the pending status (whether
		1272	the watcher was active or not).
		1273
		1274	It is possible that stopped watchers are pending - for example,
		1275	non-repeating timers are being stopped when they become pending - but
		1276	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
		1277	pending. If you want to free or reuse the memory used by the watcher it is
		1278	therefore a good idea to always call its C<ev_TYPE_stop> function.
		1279
		1280	=item bool ev_is_active (ev_TYPE *watcher)
		1281
		1282	Returns a true value iff the watcher is active (i.e. it has been started
		1283	and not yet been stopped). As long as a watcher is active you must not modify
		1284	it.
		1285
		1286	=item bool ev_is_pending (ev_TYPE *watcher)
		1287
		1288	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		1289	events but its callback has not yet been invoked). As long as a watcher
		1290	is pending (but not active) you must not call an init function on it (but
		1291	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		1292	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1293	it).
		1294
		1295	=item callback ev_cb (ev_TYPE *watcher)
		1296
		1297	Returns the callback currently set on the watcher.
		1298
		1299	=item ev_cb_set (ev_TYPE *watcher, callback)
		1300
		1301	Change the callback. You can change the callback at virtually any time
		1302	(modulo threads).
		1303
		1304	=item ev_set_priority (ev_TYPE *watcher, int priority)
		1305
		1306	=item int ev_priority (ev_TYPE *watcher)
		1307
		1308	Set and query the priority of the watcher. The priority is a small
		1309	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1310	(default: C<-2>). Pending watchers with higher priority will be invoked
		1311	before watchers with lower priority, but priority will not keep watchers
		1312	from being executed (except for C<ev_idle> watchers).
		1313
		1314	If you need to suppress invocation when higher priority events are pending
		1315	you need to look at C<ev_idle> watchers, which provide this functionality.
		1316
		1317	You I<must not> change the priority of a watcher as long as it is active or
		1318	pending.
		1319
		1320	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1321	fine, as long as you do not mind that the priority value you query might
		1322	or might not have been clamped to the valid range.
		1323
		1324	The default priority used by watchers when no priority has been set is
		1325	always C<0>, which is supposed to not be too high and not be too low :).
		1326
		1327	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1328	priorities.
		1329
		1330	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1331
		1332	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1333	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1334	can deal with that fact, as both are simply passed through to the
		1335	callback.
		1336
		1337	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1338
		1339	If the watcher is pending, this function clears its pending status and
		1340	returns its C<revents> bitset (as if its callback was invoked). If the
		1341	watcher isn't pending it does nothing and returns C<0>.
		1342
		1343	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1344	callback to be invoked, which can be accomplished with this function.
		1345
		1346	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1347
		1348	Feeds the given event set into the event loop, as if the specified event
		1349	had happened for the specified watcher (which must be a pointer to an
		1350	initialised but not necessarily started event watcher). Obviously you must
		1351	not free the watcher as long as it has pending events.
		1352
		1353	Stopping the watcher, letting libev invoke it, or calling
		1354	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1355	not started in the first place.
		1356
		1357	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1358	functions that do not need a watcher.
		1359
		1360	=back
		1361
		1362	See also the L<ASSOCIATING CUSTOM DATA WITH A WATCHER> and L<BUILDING YOUR
		1363	OWN COMPOSITE WATCHERS> idioms.
		1364
1139	=head2 WATCHER STATES	1365	=head2 WATCHER STATES
1140		1366
1141	There are various watcher states mentioned throughout this manual -	1367	There are various watcher states mentioned throughout this manual -
1142	active, pending and so on. In this section these states and the rules to	1368	active, pending and so on. In this section these states and the rules to
1143	transition between them will be described in more detail - and while these	1369	transition between them will be described in more detail - and while these
…		…
1192	While stopped (and not pending) the watcher is essentially in the	1418	While stopped (and not pending) the watcher is essentially in the
1193	initialised state, that is it can be reused, moved, modified in any way	1419	initialised state, that is it can be reused, moved, modified in any way
1194	you wish.	1420	you wish.
1195		1421
1196	=back	1422	=back
1197
1198	=head2 GENERIC WATCHER FUNCTIONS
1199
1200	=over 4
1201
1202	=item C<ev_init> (ev_TYPE *watcher, callback)
1203
1204	This macro initialises the generic portion of a watcher. The contents
1205	of the watcher object can be arbitrary (so C<malloc> will do). Only
1206	the generic parts of the watcher are initialised, you I<need> to call
1207	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
1208	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
1209	which rolls both calls into one.
1210
1211	You can reinitialise a watcher at any time as long as it has been stopped
1212	(or never started) and there are no pending events outstanding.
1213
1214	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
1215	int revents)>.
1216
1217	Example: Initialise an C<ev_io> watcher in two steps.
1218
1219	ev_io w;
1220	ev_init (&w, my_cb);
1221	ev_io_set (&w, STDIN_FILENO, EV_READ);
1222
1223	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
1224
1225	This macro initialises the type-specific parts of a watcher. You need to
1226	call C<ev_init> at least once before you call this macro, but you can
1227	call C<ev_TYPE_set> any number of times. You must not, however, call this
1228	macro on a watcher that is active (it can be pending, however, which is a
1229	difference to the C<ev_init> macro).
1230
1231	Although some watcher types do not have type-specific arguments
1232	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
1233
1234	See C<ev_init>, above, for an example.
1235
1236	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
1237
1238	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
1239	calls into a single call. This is the most convenient method to initialise
1240	a watcher. The same limitations apply, of course.
1241
1242	Example: Initialise and set an C<ev_io> watcher in one step.
1243
1244	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
1245
1246	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
1247
1248	Starts (activates) the given watcher. Only active watchers will receive
1249	events. If the watcher is already active nothing will happen.
1250
1251	Example: Start the C<ev_io> watcher that is being abused as example in this
1252	whole section.
1253
1254	ev_io_start (EV_DEFAULT_UC, &w);
1255
1256	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
1257
1258	Stops the given watcher if active, and clears the pending status (whether
1259	the watcher was active or not).
1260
1261	It is possible that stopped watchers are pending - for example,
1262	non-repeating timers are being stopped when they become pending - but
1263	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
1264	pending. If you want to free or reuse the memory used by the watcher it is
1265	therefore a good idea to always call its C<ev_TYPE_stop> function.
1266
1267	=item bool ev_is_active (ev_TYPE *watcher)
1268
1269	Returns a true value iff the watcher is active (i.e. it has been started
1270	and not yet been stopped). As long as a watcher is active you must not modify
1271	it.
1272
1273	=item bool ev_is_pending (ev_TYPE *watcher)
1274
1275	Returns a true value iff the watcher is pending, (i.e. it has outstanding
1276	events but its callback has not yet been invoked). As long as a watcher
1277	is pending (but not active) you must not call an init function on it (but
1278	C<ev_TYPE_set> is safe), you must not change its priority, and you must
1279	make sure the watcher is available to libev (e.g. you cannot C<free ()>
1280	it).
1281
1282	=item callback ev_cb (ev_TYPE *watcher)
1283
1284	Returns the callback currently set on the watcher.
1285
1286	=item ev_cb_set (ev_TYPE *watcher, callback)
1287
1288	Change the callback. You can change the callback at virtually any time
1289	(modulo threads).
1290
1291	=item ev_set_priority (ev_TYPE *watcher, int priority)
1292
1293	=item int ev_priority (ev_TYPE *watcher)
1294
1295	Set and query the priority of the watcher. The priority is a small
1296	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
1297	(default: C<-2>). Pending watchers with higher priority will be invoked
1298	before watchers with lower priority, but priority will not keep watchers
1299	from being executed (except for C<ev_idle> watchers).
1300
1301	If you need to suppress invocation when higher priority events are pending
1302	you need to look at C<ev_idle> watchers, which provide this functionality.
1303
1304	You I<must not> change the priority of a watcher as long as it is active or
1305	pending.
1306
1307	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
1308	fine, as long as you do not mind that the priority value you query might
1309	or might not have been clamped to the valid range.
1310
1311	The default priority used by watchers when no priority has been set is
1312	always C<0>, which is supposed to not be too high and not be too low :).
1313
1314	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
1315	priorities.
1316
1317	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1318
1319	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
1320	C<loop> nor C<revents> need to be valid as long as the watcher callback
1321	can deal with that fact, as both are simply passed through to the
1322	callback.
1323
1324	=item int ev_clear_pending (loop, ev_TYPE *watcher)
1325
1326	If the watcher is pending, this function clears its pending status and
1327	returns its C<revents> bitset (as if its callback was invoked). If the
1328	watcher isn't pending it does nothing and returns C<0>.
1329
1330	Sometimes it can be useful to "poll" a watcher instead of waiting for its
1331	callback to be invoked, which can be accomplished with this function.
1332
1333	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
1334
1335	Feeds the given event set into the event loop, as if the specified event
1336	had happened for the specified watcher (which must be a pointer to an
1337	initialised but not necessarily started event watcher). Obviously you must
1338	not free the watcher as long as it has pending events.
1339
1340	Stopping the watcher, letting libev invoke it, or calling
1341	C<ev_clear_pending> will clear the pending event, even if the watcher was
1342	not started in the first place.
1343
1344	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1345	functions that do not need a watcher.
1346
1347	=back
1348
1349
1350	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
1351
1352	Each watcher has, by default, a member C<void *data> that you can change
1353	and read at any time: libev will completely ignore it. This can be used
1354	to associate arbitrary data with your watcher. If you need more data and
1355	don't want to allocate memory and store a pointer to it in that data
1356	member, you can also "subclass" the watcher type and provide your own
1357	data:
1358
1359	struct my_io
1360	{
1361	ev_io io;
1362	int otherfd;
1363	void *somedata;
1364	struct whatever *mostinteresting;
1365	};
1366
1367	...
1368	struct my_io w;
1369	ev_io_init (&w.io, my_cb, fd, EV_READ);
1370
1371	And since your callback will be called with a pointer to the watcher, you
1372	can cast it back to your own type:
1373
1374	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1375	{
1376	struct my_io *w = (struct my_io *)w_;
1377	...
1378	}
1379
1380	More interesting and less C-conformant ways of casting your callback type
1381	instead have been omitted.
1382
1383	Another common scenario is to use some data structure with multiple
1384	embedded watchers:
1385
1386	struct my_biggy
1387	{
1388	int some_data;
1389	ev_timer t1;
1390	ev_timer t2;
1391	}
1392
1393	In this case getting the pointer to C<my_biggy> is a bit more
1394	complicated: Either you store the address of your C<my_biggy> struct
1395	in the C<data> member of the watcher (for woozies), or you need to use
1396	some pointer arithmetic using C<offsetof> inside your watchers (for real
1397	programmers):
1398
1399	#include <stddef.h>
1400
1401	static void
1402	t1_cb (EV_P_ ev_timer *w, int revents)
1403	{
1404	struct my_biggy big = (struct my_biggy *)
1405	(((char *)w) - offsetof (struct my_biggy, t1));
1406	}
1407
1408	static void
1409	t2_cb (EV_P_ ev_timer *w, int revents)
1410	{
1411	struct my_biggy big = (struct my_biggy *)
1412	(((char *)w) - offsetof (struct my_biggy, t2));
1413	}
1414		1423
1415	=head2 WATCHER PRIORITY MODELS	1424	=head2 WATCHER PRIORITY MODELS
1416		1425
1417	Many event loops support I<watcher priorities>, which are usually small	1426	Many event loops support I<watcher priorities>, which are usually small
1418	integers that influence the ordering of event callback invocation	1427	integers that influence the ordering of event callback invocation
…		…
1545	In general you can register as many read and/or write event watchers per	1554	In general you can register as many read and/or write event watchers per
1546	fd as you want (as long as you don't confuse yourself). Setting all file	1555	fd as you want (as long as you don't confuse yourself). Setting all file
1547	descriptors to non-blocking mode is also usually a good idea (but not	1556	descriptors to non-blocking mode is also usually a good idea (but not
1548	required if you know what you are doing).	1557	required if you know what you are doing).
1549		1558
1550	If you cannot use non-blocking mode, then force the use of a
1551	known-to-be-good backend (at the time of this writing, this includes only
1552	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
1553	descriptors for which non-blocking operation makes no sense (such as
1554	files) - libev doesn't guarantee any specific behaviour in that case.
1555
1556	Another thing you have to watch out for is that it is quite easy to	1559	Another thing you have to watch out for is that it is quite easy to
1557	receive "spurious" readiness notifications, that is your callback might	1560	receive "spurious" readiness notifications, that is, your callback might
1558	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1561	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1559	because there is no data. Not only are some backends known to create a	1562	because there is no data. It is very easy to get into this situation even
1560	lot of those (for example Solaris ports), it is very easy to get into	1563	with a relatively standard program structure. Thus it is best to always
1561	this situation even with a relatively standard program structure. Thus	1564	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1562	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1563	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1565	preferable to a program hanging until some data arrives.
1564		1566
1565	If you cannot run the fd in non-blocking mode (for example you should	1567	If you cannot run the fd in non-blocking mode (for example you should
1566	not play around with an Xlib connection), then you have to separately	1568	not play around with an Xlib connection), then you have to separately
1567	re-test whether a file descriptor is really ready with a known-to-be good	1569	re-test whether a file descriptor is really ready with a known-to-be good
1568	interface such as poll (fortunately in our Xlib example, Xlib already	1570	interface such as poll (fortunately in the case of Xlib, it already does
1569	does this on its own, so its quite safe to use). Some people additionally	1571	this on its own, so its quite safe to use). Some people additionally
1570	use C<SIGALRM> and an interval timer, just to be sure you won't block	1572	use C<SIGALRM> and an interval timer, just to be sure you won't block
1571	indefinitely.	1573	indefinitely.
1572		1574
1573	But really, best use non-blocking mode.	1575	But really, best use non-blocking mode.
1574		1576
…		…
1602		1604
1603	There is no workaround possible except not registering events	1605	There is no workaround possible except not registering events
1604	for potentially C<dup ()>'ed file descriptors, or to resort to	1606	for potentially C<dup ()>'ed file descriptors, or to resort to
1605	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1607	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1606		1608
		1609	=head3 The special problem of files
		1610
		1611	Many people try to use C<select> (or libev) on file descriptors
		1612	representing files, and expect it to become ready when their program
		1613	doesn't block on disk accesses (which can take a long time on their own).
		1614
		1615	However, this cannot ever work in the "expected" way - you get a readiness
		1616	notification as soon as the kernel knows whether and how much data is
		1617	there, and in the case of open files, that's always the case, so you
		1618	always get a readiness notification instantly, and your read (or possibly
		1619	write) will still block on the disk I/O.
		1620
		1621	Another way to view it is that in the case of sockets, pipes, character
		1622	devices and so on, there is another party (the sender) that delivers data
		1623	on its own, but in the case of files, there is no such thing: the disk
		1624	will not send data on its own, simply because it doesn't know what you
		1625	wish to read - you would first have to request some data.
		1626
		1627	Since files are typically not-so-well supported by advanced notification
		1628	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1629	to files, even though you should not use it. The reason for this is
		1630	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1631	usually a tty, often a pipe, but also sometimes files or special devices
		1632	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1633	F</dev/urandom>), and even though the file might better be served with
		1634	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1635	it "just works" instead of freezing.
		1636
		1637	So avoid file descriptors pointing to files when you know it (e.g. use
		1638	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1639	when you rarely read from a file instead of from a socket, and want to
		1640	reuse the same code path.
		1641
1607	=head3 The special problem of fork	1642	=head3 The special problem of fork
1608		1643
1609	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1644	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
1610	useless behaviour. Libev fully supports fork, but needs to be told about	1645	useless behaviour. Libev fully supports fork, but needs to be told about
1611	it in the child.	1646	it in the child if you want to continue to use it in the child.
1612		1647
1613	To support fork in your programs, you either have to call	1648	To support fork in your child processes, you have to call C<ev_loop_fork
1614	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1649	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1615	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1650	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1616	C<EVBACKEND_POLL>.
1617		1651
1618	=head3 The special problem of SIGPIPE	1652	=head3 The special problem of SIGPIPE
1619		1653
1620	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1654	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1621	when writing to a pipe whose other end has been closed, your program gets	1655	when writing to a pipe whose other end has been closed, your program gets
…		…
2237		2271
2238	=head2 C<ev_signal> - signal me when a signal gets signalled!	2272	=head2 C<ev_signal> - signal me when a signal gets signalled!
2239		2273
2240	Signal watchers will trigger an event when the process receives a specific	2274	Signal watchers will trigger an event when the process receives a specific
2241	signal one or more times. Even though signals are very asynchronous, libev	2275	signal one or more times. Even though signals are very asynchronous, libev
2242	will try it's best to deliver signals synchronously, i.e. as part of the	2276	will try its best to deliver signals synchronously, i.e. as part of the
2243	normal event processing, like any other event.	2277	normal event processing, like any other event.
2244		2278
2245	If you want signals to be delivered truly asynchronously, just use	2279	If you want signals to be delivered truly asynchronously, just use
2246	C<sigaction> as you would do without libev and forget about sharing	2280	C<sigaction> as you would do without libev and forget about sharing
2247	the signal. You can even use C<ev_async> from a signal handler to	2281	the signal. You can even use C<ev_async> from a signal handler to
…		…
2289	I<has> to modify the signal mask, at least temporarily.	2323	I<has> to modify the signal mask, at least temporarily.
2290		2324
2291	So I can't stress this enough: I<If you do not reset your signal mask when	2325	So I can't stress this enough: I<If you do not reset your signal mask when
2292	you expect it to be empty, you have a race condition in your code>. This	2326	you expect it to be empty, you have a race condition in your code>. This
2293	is not a libev-specific thing, this is true for most event libraries.	2327	is not a libev-specific thing, this is true for most event libraries.
		2328
		2329	=head3 The special problem of threads signal handling
		2330
		2331	POSIX threads has problematic signal handling semantics, specifically,
		2332	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2333	threads in a process block signals, which is hard to achieve.
		2334
		2335	When you want to use sigwait (or mix libev signal handling with your own
		2336	for the same signals), you can tackle this problem by globally blocking
		2337	all signals before creating any threads (or creating them with a fully set
		2338	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2339	loops. Then designate one thread as "signal receiver thread" which handles
		2340	these signals. You can pass on any signals that libev might be interested
		2341	in by calling C<ev_feed_signal>.
2294		2342
2295	=head3 Watcher-Specific Functions and Data Members	2343	=head3 Watcher-Specific Functions and Data Members
2296		2344
2297	=over 4	2345	=over 4
2298		2346
…		…
3072	disadvantage of having to use multiple event loops (which do not support	3120	disadvantage of having to use multiple event loops (which do not support
3073	signal watchers).	3121	signal watchers).
3074		3122
3075	When this is not possible, or you want to use the default loop for	3123	When this is not possible, or you want to use the default loop for
3076	other reasons, then in the process that wants to start "fresh", call	3124	other reasons, then in the process that wants to start "fresh", call
3077	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying	3125	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
3078	the default loop will "orphan" (not stop) all registered watchers, so you	3126	Destroying the default loop will "orphan" (not stop) all registered
3079	have to be careful not to execute code that modifies those watchers. Note	3127	watchers, so you have to be careful not to execute code that modifies
3080	also that in that case, you have to re-register any signal watchers.	3128	those watchers. Note also that in that case, you have to re-register any
		3129	signal watchers.
3081		3130
3082	=head3 Watcher-Specific Functions and Data Members	3131	=head3 Watcher-Specific Functions and Data Members
3083		3132
3084	=over 4	3133	=over 4
3085		3134
3086	=item ev_fork_init (ev_signal *, callback)	3135	=item ev_fork_init (ev_fork *, callback)
3087		3136
3088	Initialises and configures the fork watcher - it has no parameters of any	3137	Initialises and configures the fork watcher - it has no parameters of any
3089	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,	3138	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
3090	believe me.	3139	really.
3091		3140
3092	=back	3141	=back
		3142
		3143
		3144	=head2 C<ev_cleanup> - even the best things end
		3145
		3146	Cleanup watchers are called just before the event loop is being destroyed
		3147	by a call to C<ev_loop_destroy>.
		3148
		3149	While there is no guarantee that the event loop gets destroyed, cleanup
		3150	watchers provide a convenient method to install cleanup hooks for your
		3151	program, worker threads and so on - you just to make sure to destroy the
		3152	loop when you want them to be invoked.
		3153
		3154	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3155	all other watchers, they do not keep a reference to the event loop (which
		3156	makes a lot of sense if you think about it). Like all other watchers, you
		3157	can call libev functions in the callback, except C<ev_cleanup_start>.
		3158
		3159	=head3 Watcher-Specific Functions and Data Members
		3160
		3161	=over 4
		3162
		3163	=item ev_cleanup_init (ev_cleanup *, callback)
		3164
		3165	Initialises and configures the cleanup watcher - it has no parameters of
		3166	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3167	pointless, I assure you.
		3168
		3169	=back
		3170
		3171	Example: Register an atexit handler to destroy the default loop, so any
		3172	cleanup functions are called.
		3173
		3174	static void
		3175	program_exits (void)
		3176	{
		3177	ev_loop_destroy (EV_DEFAULT_UC);
		3178	}
		3179
		3180	...
		3181	atexit (program_exits);
3093		3182
3094		3183
3095	=head2 C<ev_async> - how to wake up an event loop	3184	=head2 C<ev_async> - how to wake up an event loop
3096		3185
3097	In general, you cannot use an C<ev_run> from multiple threads or other	3186	In general, you cannot use an C<ev_run> from multiple threads or other
…		…
3104	it by calling C<ev_async_send>, which is thread- and signal safe.	3193	it by calling C<ev_async_send>, which is thread- and signal safe.
3105		3194
3106	This functionality is very similar to C<ev_signal> watchers, as signals,	3195	This functionality is very similar to C<ev_signal> watchers, as signals,
3107	too, are asynchronous in nature, and signals, too, will be compressed	3196	too, are asynchronous in nature, and signals, too, will be compressed
3108	(i.e. the number of callback invocations may be less than the number of	3197	(i.e. the number of callback invocations may be less than the number of
3109	C<ev_async_sent> calls).	3198	C<ev_async_sent> calls). In fact, you could use signal watchers as a kind
		3199	of "global async watchers" by using a watcher on an otherwise unused
		3200	signal, and C<ev_feed_signal> to signal this watcher from another thread,
		3201	even without knowing which loop owns the signal.
3110		3202
3111	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not	3203	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
3112	just the default loop.	3204	just the default loop.
3113		3205
3114	=head3 Queueing	3206	=head3 Queueing
…		…
3290	Feed an event on the given fd, as if a file descriptor backend detected	3382	Feed an event on the given fd, as if a file descriptor backend detected
3291	the given events it.	3383	the given events it.
3292		3384
3293	=item ev_feed_signal_event (loop, int signum)	3385	=item ev_feed_signal_event (loop, int signum)
3294		3386
3295	Feed an event as if the given signal occurred (C<loop> must be the default	3387	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3296	loop!).	3388	which is async-safe.
3297		3389
3298	=back	3390	=back
		3391
		3392
		3393	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3394
		3395	This section explains some common idioms that are not immediately
		3396	obvious. Note that examples are sprinkled over the whole manual, and this
		3397	section only contains stuff that wouldn't fit anywhere else.
		3398
		3399	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3400
		3401	Each watcher has, by default, a C<void *data> member that you can read
		3402	or modify at any time: libev will completely ignore it. This can be used
		3403	to associate arbitrary data with your watcher. If you need more data and
		3404	don't want to allocate memory separately and store a pointer to it in that
		3405	data member, you can also "subclass" the watcher type and provide your own
		3406	data:
		3407
		3408	struct my_io
		3409	{
		3410	ev_io io;
		3411	int otherfd;
		3412	void *somedata;
		3413	struct whatever *mostinteresting;
		3414	};
		3415
		3416	...
		3417	struct my_io w;
		3418	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3419
		3420	And since your callback will be called with a pointer to the watcher, you
		3421	can cast it back to your own type:
		3422
		3423	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3424	{
		3425	struct my_io *w = (struct my_io *)w_;
		3426	...
		3427	}
		3428
		3429	More interesting and less C-conformant ways of casting your callback
		3430	function type instead have been omitted.
		3431
		3432	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3433
		3434	Another common scenario is to use some data structure with multiple
		3435	embedded watchers, in effect creating your own watcher that combines
		3436	multiple libev event sources into one "super-watcher":
		3437
		3438	struct my_biggy
		3439	{
		3440	int some_data;
		3441	ev_timer t1;
		3442	ev_timer t2;
		3443	}
		3444
		3445	In this case getting the pointer to C<my_biggy> is a bit more
		3446	complicated: Either you store the address of your C<my_biggy> struct in
		3447	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3448	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3449	real programmers):
		3450
		3451	#include <stddef.h>
		3452
		3453	static void
		3454	t1_cb (EV_P_ ev_timer *w, int revents)
		3455	{
		3456	struct my_biggy big = (struct my_biggy *)
		3457	(((char *)w) - offsetof (struct my_biggy, t1));
		3458	}
		3459
		3460	static void
		3461	t2_cb (EV_P_ ev_timer *w, int revents)
		3462	{
		3463	struct my_biggy big = (struct my_biggy *)
		3464	(((char *)w) - offsetof (struct my_biggy, t2));
		3465	}
		3466
		3467	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3468
		3469	Often (especially in GUI toolkits) there are places where you have
		3470	I<modal> interaction, which is most easily implemented by recursively
		3471	invoking C<ev_run>.
		3472
		3473	This brings the problem of exiting - a callback might want to finish the
		3474	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3475	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3476	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3477	other combination: In these cases, C<ev_break> will not work alone.
		3478
		3479	The solution is to maintain "break this loop" variable for each C<ev_run>
		3480	invocation, and use a loop around C<ev_run> until the condition is
		3481	triggered, using C<EVRUN_ONCE>:
		3482
		3483	// main loop
		3484	int exit_main_loop = 0;
		3485
		3486	while (!exit_main_loop)
		3487	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3488
		3489	// in a model watcher
		3490	int exit_nested_loop = 0;
		3491
		3492	while (!exit_nested_loop)
		3493	ev_run (EV_A_ EVRUN_ONCE);
		3494
		3495	To exit from any of these loops, just set the corresponding exit variable:
		3496
		3497	// exit modal loop
		3498	exit_nested_loop = 1;
		3499
		3500	// exit main program, after modal loop is finished
		3501	exit_main_loop = 1;
		3502
		3503	// exit both
		3504	exit_main_loop = exit_nested_loop = 1;
		3505
		3506	=head2 THREAD LOCKING EXAMPLE
		3507
		3508	Here is a fictitious example of how to run an event loop in a different
		3509	thread than where callbacks are being invoked and watchers are
		3510	created/added/removed.
		3511
		3512	For a real-world example, see the C<EV::Loop::Async> perl module,
		3513	which uses exactly this technique (which is suited for many high-level
		3514	languages).
		3515
		3516	The example uses a pthread mutex to protect the loop data, a condition
		3517	variable to wait for callback invocations, an async watcher to notify the
		3518	event loop thread and an unspecified mechanism to wake up the main thread.
		3519
		3520	First, you need to associate some data with the event loop:
		3521
		3522	typedef struct {
		3523	mutex_t lock; /* global loop lock */
		3524	ev_async async_w;
		3525	thread_t tid;
		3526	cond_t invoke_cv;
		3527	} userdata;
		3528
		3529	void prepare_loop (EV_P)
		3530	{
		3531	// for simplicity, we use a static userdata struct.
		3532	static userdata u;
		3533
		3534	ev_async_init (&u->async_w, async_cb);
		3535	ev_async_start (EV_A_ &u->async_w);
		3536
		3537	pthread_mutex_init (&u->lock, 0);
		3538	pthread_cond_init (&u->invoke_cv, 0);
		3539
		3540	// now associate this with the loop
		3541	ev_set_userdata (EV_A_ u);
		3542	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3543	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3544
		3545	// then create the thread running ev_loop
		3546	pthread_create (&u->tid, 0, l_run, EV_A);
		3547	}
		3548
		3549	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3550	solely to wake up the event loop so it takes notice of any new watchers
		3551	that might have been added:
		3552
		3553	static void
		3554	async_cb (EV_P_ ev_async *w, int revents)
		3555	{
		3556	// just used for the side effects
		3557	}
		3558
		3559	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3560	protecting the loop data, respectively.
		3561
		3562	static void
		3563	l_release (EV_P)
		3564	{
		3565	userdata *u = ev_userdata (EV_A);
		3566	pthread_mutex_unlock (&u->lock);
		3567	}
		3568
		3569	static void
		3570	l_acquire (EV_P)
		3571	{
		3572	userdata *u = ev_userdata (EV_A);
		3573	pthread_mutex_lock (&u->lock);
		3574	}
		3575
		3576	The event loop thread first acquires the mutex, and then jumps straight
		3577	into C<ev_run>:
		3578
		3579	void *
		3580	l_run (void *thr_arg)
		3581	{
		3582	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3583
		3584	l_acquire (EV_A);
		3585	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3586	ev_run (EV_A_ 0);
		3587	l_release (EV_A);
		3588
		3589	return 0;
		3590	}
		3591
		3592	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3593	signal the main thread via some unspecified mechanism (signals? pipe
		3594	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3595	have been called (in a while loop because a) spurious wakeups are possible
		3596	and b) skipping inter-thread-communication when there are no pending
		3597	watchers is very beneficial):
		3598
		3599	static void
		3600	l_invoke (EV_P)
		3601	{
		3602	userdata *u = ev_userdata (EV_A);
		3603
		3604	while (ev_pending_count (EV_A))
		3605	{
		3606	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3607	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3608	}
		3609	}
		3610
		3611	Now, whenever the main thread gets told to invoke pending watchers, it
		3612	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3613	thread to continue:
		3614
		3615	static void
		3616	real_invoke_pending (EV_P)
		3617	{
		3618	userdata *u = ev_userdata (EV_A);
		3619
		3620	pthread_mutex_lock (&u->lock);
		3621	ev_invoke_pending (EV_A);
		3622	pthread_cond_signal (&u->invoke_cv);
		3623	pthread_mutex_unlock (&u->lock);
		3624	}
		3625
		3626	Whenever you want to start/stop a watcher or do other modifications to an
		3627	event loop, you will now have to lock:
		3628
		3629	ev_timer timeout_watcher;
		3630	userdata *u = ev_userdata (EV_A);
		3631
		3632	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3633
		3634	pthread_mutex_lock (&u->lock);
		3635	ev_timer_start (EV_A_ &timeout_watcher);
		3636	ev_async_send (EV_A_ &u->async_w);
		3637	pthread_mutex_unlock (&u->lock);
		3638
		3639	Note that sending the C<ev_async> watcher is required because otherwise
		3640	an event loop currently blocking in the kernel will have no knowledge
		3641	about the newly added timer. By waking up the loop it will pick up any new
		3642	watchers in the next event loop iteration.
		3643
		3644	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3645
		3646	While the overhead of a callback that e.g. schedules a thread is small, it
		3647	is still an overhead. If you embed libev, and your main usage is with some
		3648	kind of threads or coroutines, you might want to customise libev so that
		3649	doesn't need callbacks anymore.
		3650
		3651	Imagine you have coroutines that you can switch to using a function
		3652	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3653	and that due to some magic, the currently active coroutine is stored in a
		3654	global called C<current_coro>. Then you can build your own "wait for libev
		3655	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3656	the differing C<;> conventions):
		3657
		3658	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3659	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3660
		3661	That means instead of having a C callback function, you store the
		3662	coroutine to switch to in each watcher, and instead of having libev call
		3663	your callback, you instead have it switch to that coroutine.
		3664
		3665	A coroutine might now wait for an event with a function called
		3666	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3667	matter when, or whether the watcher is active or not when this function is
		3668	called):
		3669
		3670	void
		3671	wait_for_event (ev_watcher *w)
		3672	{
		3673	ev_cb_set (w) = current_coro;
		3674	switch_to (libev_coro);
		3675	}
		3676
		3677	That basically suspends the coroutine inside C<wait_for_event> and
		3678	continues the libev coroutine, which, when appropriate, switches back to
		3679	this or any other coroutine. I am sure if you sue this your own :)
		3680
		3681	You can do similar tricks if you have, say, threads with an event queue -
		3682	instead of storing a coroutine, you store the queue object and instead of
		3683	switching to a coroutine, you push the watcher onto the queue and notify
		3684	any waiters.
		3685
		3686	To embed libev, see L<EMBEDDING>, but in short, it's easiest to create two
		3687	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3688
		3689	// my_ev.h
		3690	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3691	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);
		3692	#include "../libev/ev.h"
		3693
		3694	// my_ev.c
		3695	#define EV_H "my_ev.h"
		3696	#include "../libev/ev.c"
		3697
		3698	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3699	F<my_ev.c> into your project. When properly specifying include paths, you
		3700	can even use F<ev.h> as header file name directly.
3299		3701
3300		3702
3301	=head1 LIBEVENT EMULATION	3703	=head1 LIBEVENT EMULATION
3302		3704
3303	Libev offers a compatibility emulation layer for libevent. It cannot	3705	Libev offers a compatibility emulation layer for libevent. It cannot
3304	emulate the internals of libevent, so here are some usage hints:	3706	emulate the internals of libevent, so here are some usage hints:
3305		3707
3306	=over 4	3708	=over 4
		3709
		3710	=item * Only the libevent-1.4.1-beta API is being emulated.
		3711
		3712	This was the newest libevent version available when libev was implemented,
		3713	and is still mostly unchanged in 2010.
3307		3714
3308	=item * Use it by including <event.h>, as usual.	3715	=item * Use it by including <event.h>, as usual.
3309		3716
3310	=item * The following members are fully supported: ev_base, ev_callback,	3717	=item * The following members are fully supported: ev_base, ev_callback,
3311	ev_arg, ev_fd, ev_res, ev_events.	3718	ev_arg, ev_fd, ev_res, ev_events.
…		…
3317	=item * Priorities are not currently supported. Initialising priorities	3724	=item * Priorities are not currently supported. Initialising priorities
3318	will fail and all watchers will have the same priority, even though there	3725	will fail and all watchers will have the same priority, even though there
3319	is an ev_pri field.	3726	is an ev_pri field.
3320		3727
3321	=item * In libevent, the last base created gets the signals, in libev, the	3728	=item * In libevent, the last base created gets the signals, in libev, the
3322	first base created (== the default loop) gets the signals.	3729	base that registered the signal gets the signals.
3323		3730
3324	=item * Other members are not supported.	3731	=item * Other members are not supported.
3325		3732
3326	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3733	=item * The libev emulation is I<not> ABI compatible to libevent, you need
3327	to use the libev header file and library.	3734	to use the libev header file and library.
…		…
3346	Care has been taken to keep the overhead low. The only data member the C++	3753	Care has been taken to keep the overhead low. The only data member the C++
3347	classes add (compared to plain C-style watchers) is the event loop pointer	3754	classes add (compared to plain C-style watchers) is the event loop pointer
3348	that the watcher is associated with (or no additional members at all if	3755	that the watcher is associated with (or no additional members at all if
3349	you disable C<EV_MULTIPLICITY> when embedding libev).	3756	you disable C<EV_MULTIPLICITY> when embedding libev).
3350		3757
3351	Currently, functions, and static and non-static member functions can be	3758	Currently, functions, static and non-static member functions and classes
3352	used as callbacks. Other types should be easy to add as long as they only	3759	with C<operator ()> can be used as callbacks. Other types should be easy
3353	need one additional pointer for context. If you need support for other	3760	to add as long as they only need one additional pointer for context. If
3354	types of functors please contact the author (preferably after implementing	3761	you need support for other types of functors please contact the author
3355	it).	3762	(preferably after implementing it).
3356		3763
3357	Here is a list of things available in the C<ev> namespace:	3764	Here is a list of things available in the C<ev> namespace:
3358		3765
3359	=over 4	3766	=over 4
3360		3767
…		…
4228	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4635	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4229		4636
4230	#include "ev_cpp.h"	4637	#include "ev_cpp.h"
4231	#include "ev.c"	4638	#include "ev.c"
4232		4639
4233	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	4640	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4234		4641
4235	=head2 THREADS AND COROUTINES	4642	=head2 THREADS AND COROUTINES
4236		4643
4237	=head3 THREADS	4644	=head3 THREADS
4238		4645
…		…
4289	default loop and triggering an C<ev_async> watcher from the default loop	4696	default loop and triggering an C<ev_async> watcher from the default loop
4290	watcher callback into the event loop interested in the signal.	4697	watcher callback into the event loop interested in the signal.
4291		4698
4292	=back	4699	=back
4293		4700
4294	=head4 THREAD LOCKING EXAMPLE	4701	See also L<THREAD LOCKING EXAMPLE>.
4295
4296	Here is a fictitious example of how to run an event loop in a different
4297	thread than where callbacks are being invoked and watchers are
4298	created/added/removed.
4299
4300	For a real-world example, see the C<EV::Loop::Async> perl module,
4301	which uses exactly this technique (which is suited for many high-level
4302	languages).
4303
4304	The example uses a pthread mutex to protect the loop data, a condition
4305	variable to wait for callback invocations, an async watcher to notify the
4306	event loop thread and an unspecified mechanism to wake up the main thread.
4307
4308	First, you need to associate some data with the event loop:
4309
4310	typedef struct {
4311	mutex_t lock; /* global loop lock */
4312	ev_async async_w;
4313	thread_t tid;
4314	cond_t invoke_cv;
4315	} userdata;
4316
4317	void prepare_loop (EV_P)
4318	{
4319	// for simplicity, we use a static userdata struct.
4320	static userdata u;
4321
4322	ev_async_init (&u->async_w, async_cb);
4323	ev_async_start (EV_A_ &u->async_w);
4324
4325	pthread_mutex_init (&u->lock, 0);
4326	pthread_cond_init (&u->invoke_cv, 0);
4327
4328	// now associate this with the loop
4329	ev_set_userdata (EV_A_ u);
4330	ev_set_invoke_pending_cb (EV_A_ l_invoke);
4331	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4332
4333	// then create the thread running ev_loop
4334	pthread_create (&u->tid, 0, l_run, EV_A);
4335	}
4336
4337	The callback for the C<ev_async> watcher does nothing: the watcher is used
4338	solely to wake up the event loop so it takes notice of any new watchers
4339	that might have been added:
4340
4341	static void
4342	async_cb (EV_P_ ev_async *w, int revents)
4343	{
4344	// just used for the side effects
4345	}
4346
4347	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
4348	protecting the loop data, respectively.
4349
4350	static void
4351	l_release (EV_P)
4352	{
4353	userdata *u = ev_userdata (EV_A);
4354	pthread_mutex_unlock (&u->lock);
4355	}
4356
4357	static void
4358	l_acquire (EV_P)
4359	{
4360	userdata *u = ev_userdata (EV_A);
4361	pthread_mutex_lock (&u->lock);
4362	}
4363
4364	The event loop thread first acquires the mutex, and then jumps straight
4365	into C<ev_run>:
4366
4367	void *
4368	l_run (void *thr_arg)
4369	{
4370	struct ev_loop *loop = (struct ev_loop *)thr_arg;
4371
4372	l_acquire (EV_A);
4373	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4374	ev_run (EV_A_ 0);
4375	l_release (EV_A);
4376
4377	return 0;
4378	}
4379
4380	Instead of invoking all pending watchers, the C<l_invoke> callback will
4381	signal the main thread via some unspecified mechanism (signals? pipe
4382	writes? C<Async::Interrupt>?) and then waits until all pending watchers
4383	have been called (in a while loop because a) spurious wakeups are possible
4384	and b) skipping inter-thread-communication when there are no pending
4385	watchers is very beneficial):
4386
4387	static void
4388	l_invoke (EV_P)
4389	{
4390	userdata *u = ev_userdata (EV_A);
4391
4392	while (ev_pending_count (EV_A))
4393	{
4394	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4395	pthread_cond_wait (&u->invoke_cv, &u->lock);
4396	}
4397	}
4398
4399	Now, whenever the main thread gets told to invoke pending watchers, it
4400	will grab the lock, call C<ev_invoke_pending> and then signal the loop
4401	thread to continue:
4402
4403	static void
4404	real_invoke_pending (EV_P)
4405	{
4406	userdata *u = ev_userdata (EV_A);
4407
4408	pthread_mutex_lock (&u->lock);
4409	ev_invoke_pending (EV_A);
4410	pthread_cond_signal (&u->invoke_cv);
4411	pthread_mutex_unlock (&u->lock);
4412	}
4413
4414	Whenever you want to start/stop a watcher or do other modifications to an
4415	event loop, you will now have to lock:
4416
4417	ev_timer timeout_watcher;
4418	userdata *u = ev_userdata (EV_A);
4419
4420	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4421
4422	pthread_mutex_lock (&u->lock);
4423	ev_timer_start (EV_A_ &timeout_watcher);
4424	ev_async_send (EV_A_ &u->async_w);
4425	pthread_mutex_unlock (&u->lock);
4426
4427	Note that sending the C<ev_async> watcher is required because otherwise
4428	an event loop currently blocking in the kernel will have no knowledge
4429	about the newly added timer. By waking up the loop it will pick up any new
4430	watchers in the next event loop iteration.
4431		4702
4432	=head3 COROUTINES	4703	=head3 COROUTINES
4433		4704
4434	Libev is very accommodating to coroutines ("cooperative threads"):	4705	Libev is very accommodating to coroutines ("cooperative threads"):
4435	libev fully supports nesting calls to its functions from different	4706	libev fully supports nesting calls to its functions from different
…		…
4704	structure (guaranteed by POSIX but not by ISO C for example), but it also	4975	structure (guaranteed by POSIX but not by ISO C for example), but it also
4705	assumes that the same (machine) code can be used to call any watcher	4976	assumes that the same (machine) code can be used to call any watcher
4706	callback: The watcher callbacks have different type signatures, but libev	4977	callback: The watcher callbacks have different type signatures, but libev
4707	calls them using an C<ev_watcher *> internally.	4978	calls them using an C<ev_watcher *> internally.
4708		4979
		4980	=item pointer accesses must be thread-atomic
		4981
		4982	Accessing a pointer value must be atomic, it must both be readable and
		4983	writable in one piece - this is the case on all current architectures.
		4984
4709	=item C<sig_atomic_t volatile> must be thread-atomic as well	4985	=item C<sig_atomic_t volatile> must be thread-atomic as well
4710		4986
4711	The type C<sig_atomic_t volatile> (or whatever is defined as	4987	The type C<sig_atomic_t volatile> (or whatever is defined as
4712	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different	4988	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
4713	threads. This is not part of the specification for C<sig_atomic_t>, but is	4989	threads. This is not part of the specification for C<sig_atomic_t>, but is
…		…
4819	=back	5095	=back
4820		5096
4821		5097
4822	=head1 PORTING FROM LIBEV 3.X TO 4.X	5098	=head1 PORTING FROM LIBEV 3.X TO 4.X
4823		5099
4824	The major version 4 introduced some minor incompatible changes to the API.	5100	The major version 4 introduced some incompatible changes to the API.
4825		5101
4826	At the moment, the C<ev.h> header file tries to implement superficial	5102	At the moment, the C<ev.h> header file provides compatibility definitions
4827	compatibility, so most programs should still compile. Those might be	5103	for all changes, so most programs should still compile. The compatibility
4828	removed in later versions of libev, so better update early than late.	5104	layer might be removed in later versions of libev, so better update to the
		5105	new API early than late.
4829		5106
4830	=over 4	5107	=over 4
		5108
		5109	=item C<EV_COMPAT3> backwards compatibility mechanism
		5110
		5111	The backward compatibility mechanism can be controlled by
		5112	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
		5113	section.
		5114
		5115	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5116
		5117	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5118
		5119	ev_loop_destroy (EV_DEFAULT_UC);
		5120	ev_loop_fork (EV_DEFAULT);
4831		5121
4832	=item function/symbol renames	5122	=item function/symbol renames
4833		5123
4834	A number of functions and symbols have been renamed:	5124	A number of functions and symbols have been renamed:
4835		5125
…		…
4854	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme	5144	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
4855	as all other watcher types. Note that C<ev_loop_fork> is still called	5145	as all other watcher types. Note that C<ev_loop_fork> is still called
4856	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>	5146	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
4857	typedef.	5147	typedef.
4858		5148
4859	=item C<EV_COMPAT3> backwards compatibility mechanism
4860
4861	The backward compatibility mechanism can be controlled by
4862	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
4863	section.
4864
4865	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>	5149	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
4866		5150
4867	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different	5151	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
4868	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile	5152	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
4869	and work, but the library code will of course be larger.	5153	and work, but the library code will of course be larger.
…		…
4943		5227
4944	=back	5228	=back
4945		5229
4946	=head1 AUTHOR	5230	=head1 AUTHOR
4947		5231
4948	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.	5232	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5233	Magnusson and Emanuele Giaquinta.
4949		5234

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