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		1	=encoding utf-8
		2
1	=head1 NAME	3	=head1 NAME
2		4
3	libev - a high performance full-featured event loop written in C	5	libev - a high performance full-featured event loop written in C
4		6
5	=head1 SYNOPSIS	7	=head1 SYNOPSIS
…		…
43		45
44	int	46	int
45	main (void)	47	main (void)
46	{	48	{
47	// use the default event loop unless you have special needs	49	// use the default event loop unless you have special needs
48	struct ev_loop *loop = ev_default_loop (0);	50	struct ev_loop *loop = EV_DEFAULT;
49		51
50	// initialise an io watcher, then start it	52	// initialise an io watcher, then start it
51	// this one will watch for stdin to become readable	53	// this one will watch for stdin to become readable
52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);	54	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
53	ev_io_start (loop, &stdin_watcher);	55	ev_io_start (loop, &stdin_watcher);
…		…
58	ev_timer_start (loop, &timeout_watcher);	60	ev_timer_start (loop, &timeout_watcher);
59		61
60	// now wait for events to arrive	62	// now wait for events to arrive
61	ev_run (loop, 0);	63	ev_run (loop, 0);
62		64
63	// unloop was called, so exit	65	// break was called, so exit
64	return 0;	66	return 0;
65	}	67	}
66		68
67	=head1 ABOUT THIS DOCUMENT	69	=head1 ABOUT THIS DOCUMENT
68		70
…		…
77	on event-based programming, nor will it introduce event-based programming	79	on event-based programming, nor will it introduce event-based programming
78	with libev.	80	with libev.
79		81
80	Familiarity with event based programming techniques in general is assumed	82	Familiarity with event based programming techniques in general is assumed
81	throughout this document.	83	throughout this document.
		84
		85	=head1 WHAT TO READ WHEN IN A HURRY
		86
		87	This manual tries to be very detailed, but unfortunately, this also makes
		88	it very long. If you just want to know the basics of libev, I suggest
		89	reading L</ANATOMY OF A WATCHER>, then the L</EXAMPLE PROGRAM> above and
		90	look up the missing functions in L</GLOBAL FUNCTIONS> and the C<ev_io> and
		91	C<ev_timer> sections in L</WATCHER TYPES>.
82		92
83	=head1 ABOUT LIBEV	93	=head1 ABOUT LIBEV
84		94
85	Libev is an event loop: you register interest in certain events (such as a	95	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	96	file descriptor being readable or a timeout occurring), and it will manage
…		…
165		175
166	=item ev_tstamp ev_time ()	176	=item ev_tstamp ev_time ()
167		177
168	Returns the current time as libev would use it. Please note that the	178	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	179	C<ev_now> function is usually faster and also often returns the timestamp
170	you actually want to know. Also interetsing is the combination of	180	you actually want to know. Also interesting is the combination of
171	C<ev_update_now> and C<ev_now>.	181	C<ev_now_update> and C<ev_now>.
172		182
173	=item ev_sleep (ev_tstamp interval)	183	=item ev_sleep (ev_tstamp interval)
174		184
175	Sleep for the given interval: The current thread will be blocked until	185	Sleep for the given interval: The current thread will be blocked
176	either it is interrupted or the given time interval has passed. Basically	186	until either it is interrupted or the given time interval has
		187	passed (approximately - it might return a bit earlier even if not
		188	interrupted). Returns immediately if C<< interval <= 0 >>.
		189
177	this is a sub-second-resolution C<sleep ()>.	190	Basically this is a sub-second-resolution C<sleep ()>.
		191
		192	The range of the C<interval> is limited - libev only guarantees to work
		193	with sleep times of up to one day (C<< interval <= 86400 >>).
178		194
179	=item int ev_version_major ()	195	=item int ev_version_major ()
180		196
181	=item int ev_version_minor ()	197	=item int ev_version_minor ()
182		198
…		…
233	the current system, you would need to look at C<ev_embeddable_backends ()	249	the current system, you would need to look at C<ev_embeddable_backends ()
234	& ev_supported_backends ()>, likewise for recommended ones.	250	& ev_supported_backends ()>, likewise for recommended ones.
235		251
236	See the description of C<ev_embed> watchers for more info.	252	See the description of C<ev_embed> watchers for more info.
237		253
238	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]	254	=item ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())
239		255
240	Sets the allocation function to use (the prototype is similar - the	256	Sets the allocation function to use (the prototype is similar - the
241	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is	257	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
242	used to allocate and free memory (no surprises here). If it returns zero	258	used to allocate and free memory (no surprises here). If it returns zero
243	when memory needs to be allocated (C<size != 0>), the library might abort	259	when memory needs to be allocated (C<size != 0>), the library might abort
…		…
269	}	285	}
270		286
271	...	287	...
272	ev_set_allocator (persistent_realloc);	288	ev_set_allocator (persistent_realloc);
273		289
274	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]	290	=item ev_set_syserr_cb (void (*cb)(const char *msg) throw ())
275		291
276	Set the callback function to call on a retryable system call error (such	292	Set the callback function to call on a retryable system call error (such
277	as failed select, poll, epoll_wait). The message is a printable string	293	as failed select, poll, epoll_wait). The message is a printable string
278	indicating the system call or subsystem causing the problem. If this	294	indicating the system call or subsystem causing the problem. If this
279	callback is set, then libev will expect it to remedy the situation, no	295	callback is set, then libev will expect it to remedy the situation, no
…		…
291	}	307	}
292		308
293	...	309	...
294	ev_set_syserr_cb (fatal_error);	310	ev_set_syserr_cb (fatal_error);
295		311
		312	=item ev_feed_signal (int signum)
		313
		314	This function can be used to "simulate" a signal receive. It is completely
		315	safe to call this function at any time, from any context, including signal
		316	handlers or random threads.
		317
		318	Its main use is to customise signal handling in your process, especially
		319	in the presence of threads. For example, you could block signals
		320	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
		321	creating any loops), and in one thread, use C<sigwait> or any other
		322	mechanism to wait for signals, then "deliver" them to libev by calling
		323	C<ev_feed_signal>.
		324
296	=back	325	=back
297		326
298	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	327	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
299		328
300	An event loop is described by a C<struct ev_loop *> (the C<struct> is	329	An event loop is described by a C<struct ev_loop *> (the C<struct> is
301	I<not> optional in this case unless libev 3 compatibility is disabled, as	330	I<not> optional in this case unless libev 3 compatibility is disabled, as
302	libev 3 had an C<ev_loop> function colliding with the struct name).	331	libev 3 had an C<ev_loop> function colliding with the struct name).
303		332
304	The library knows two types of such loops, the I<default> loop, which	333	The library knows two types of such loops, the I<default> loop, which
305	supports signals and child events, and dynamically created event loops	334	supports child process events, and dynamically created event loops which
306	which do not.	335	do not.
307		336
308	=over 4	337	=over 4
309		338
310	=item struct ev_loop *ev_default_loop (unsigned int flags)	339	=item struct ev_loop *ev_default_loop (unsigned int flags)
311		340
312	This will initialise the default event loop if it hasn't been initialised	341	This returns the "default" event loop object, which is what you should
313	yet and return it. If the default loop could not be initialised, returns	342	normally use when you just need "the event loop". Event loop objects and
314	false. If it already was initialised it simply returns it (and ignores the	343	the C<flags> parameter are described in more detail in the entry for
315	flags. If that is troubling you, check C<ev_backend ()> afterwards).	344	C<ev_loop_new>.
		345
		346	If the default loop is already initialised then this function simply
		347	returns it (and ignores the flags. If that is troubling you, check
		348	C<ev_backend ()> afterwards). Otherwise it will create it with the given
		349	flags, which should almost always be C<0>, unless the caller is also the
		350	one calling C<ev_run> or otherwise qualifies as "the main program".
316		351
317	If you don't know what event loop to use, use the one returned from this	352	If you don't know what event loop to use, use the one returned from this
318	function.	353	function (or via the C<EV_DEFAULT> macro).
319		354
320	Note that this function is I<not> thread-safe, so if you want to use it	355	Note that this function is I<not> thread-safe, so if you want to use it
321	from multiple threads, you have to lock (note also that this is unlikely,	356	from multiple threads, you have to employ some kind of mutex (note also
322	as loops cannot be shared easily between threads anyway).	357	that this case is unlikely, as loops cannot be shared easily between
		358	threads anyway).
323		359
324	The default loop is the only loop that can handle C<ev_signal> and	360	The default loop is the only loop that can handle C<ev_child> watchers,
325	C<ev_child> watchers, and to do this, it always registers a handler	361	and to do this, it always registers a handler for C<SIGCHLD>. If this is
326	for C<SIGCHLD>. If this is a problem for your application you can either	362	a problem for your application you can either create a dynamic loop with
327	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you	363	C<ev_loop_new> which doesn't do that, or you can simply overwrite the
328	can simply overwrite the C<SIGCHLD> signal handler I<after> calling	364	C<SIGCHLD> signal handler I<after> calling C<ev_default_init>.
329	C<ev_default_init>.	365
		366	Example: This is the most typical usage.
		367
		368	if (!ev_default_loop (0))
		369	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		370
		371	Example: Restrict libev to the select and poll backends, and do not allow
		372	environment settings to be taken into account:
		373
		374	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		375
		376	=item struct ev_loop *ev_loop_new (unsigned int flags)
		377
		378	This will create and initialise a new event loop object. If the loop
		379	could not be initialised, returns false.
		380
		381	This function is thread-safe, and one common way to use libev with
		382	threads is indeed to create one loop per thread, and using the default
		383	loop in the "main" or "initial" thread.
330		384
331	The flags argument can be used to specify special behaviour or specific	385	The flags argument can be used to specify special behaviour or specific
332	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	386	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
333		387
334	The following flags are supported:	388	The following flags are supported:
…		…
344		398
345	If this flag bit is or'ed into the flag value (or the program runs setuid	399	If this flag bit is or'ed into the flag value (or the program runs setuid
346	or setgid) then libev will I<not> look at the environment variable	400	or setgid) then libev will I<not> look at the environment variable
347	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	401	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
348	override the flags completely if it is found in the environment. This is	402	override the flags completely if it is found in the environment. This is
349	useful to try out specific backends to test their performance, or to work	403	useful to try out specific backends to test their performance, to work
350	around bugs.	404	around bugs, or to make libev threadsafe (accessing environment variables
		405	cannot be done in a threadsafe way, but usually it works if no other
		406	thread modifies them).
351		407
352	=item C<EVFLAG_FORKCHECK>	408	=item C<EVFLAG_FORKCHECK>
353		409
354	Instead of calling C<ev_loop_fork> manually after a fork, you can also	410	Instead of calling C<ev_loop_fork> manually after a fork, you can also
355	make libev check for a fork in each iteration by enabling this flag.	411	make libev check for a fork in each iteration by enabling this flag.
…		…
369	environment variable.	425	environment variable.
370		426
371	=item C<EVFLAG_NOINOTIFY>	427	=item C<EVFLAG_NOINOTIFY>
372		428
373	When this flag is specified, then libev will not attempt to use the	429	When this flag is specified, then libev will not attempt to use the
374	I<inotify> API for it's C<ev_stat> watchers. Apart from debugging and	430	I<inotify> API for its C<ev_stat> watchers. Apart from debugging and
375	testing, this flag can be useful to conserve inotify file descriptors, as	431	testing, this flag can be useful to conserve inotify file descriptors, as
376	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.	432	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
377		433
378	=item C<EVFLAG_SIGNALFD>	434	=item C<EVFLAG_SIGNALFD>
379		435
380	When this flag is specified, then libev will attempt to use the	436	When this flag is specified, then libev will attempt to use the
381	I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This API	437	I<signalfd> API for its C<ev_signal> (and C<ev_child>) watchers. This API
382	delivers signals synchronously, which makes it both faster and might make	438	delivers signals synchronously, which makes it both faster and might make
383	it possible to get the queued signal data. It can also simplify signal	439	it possible to get the queued signal data. It can also simplify signal
384	handling with threads, as long as you properly block signals in your	440	handling with threads, as long as you properly block signals in your
385	threads that are not interested in handling them.	441	threads that are not interested in handling them.
386		442
387	Signalfd will not be used by default as this changes your signal mask, and	443	Signalfd will not be used by default as this changes your signal mask, and
388	there are a lot of shoddy libraries and programs (glib's threadpool for	444	there are a lot of shoddy libraries and programs (glib's threadpool for
389	example) that can't properly initialise their signal masks.	445	example) that can't properly initialise their signal masks.
		446
		447	=item C<EVFLAG_NOSIGMASK>
		448
		449	When this flag is specified, then libev will avoid to modify the signal
		450	mask. Specifically, this means you have to make sure signals are unblocked
		451	when you want to receive them.
		452
		453	This behaviour is useful when you want to do your own signal handling, or
		454	want to handle signals only in specific threads and want to avoid libev
		455	unblocking the signals.
		456
		457	It's also required by POSIX in a threaded program, as libev calls
		458	C<sigprocmask>, whose behaviour is officially unspecified.
		459
		460	This flag's behaviour will become the default in future versions of libev.
390		461
391	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	462	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
392		463
393	This is your standard select(2) backend. Not I<completely> standard, as	464	This is your standard select(2) backend. Not I<completely> standard, as
394	libev tries to roll its own fd_set with no limits on the number of fds,	465	libev tries to roll its own fd_set with no limits on the number of fds,
…		…
422	=item C<EVBACKEND_EPOLL> (value 4, Linux)	493	=item C<EVBACKEND_EPOLL> (value 4, Linux)
423		494
424	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9	495	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
425	kernels).	496	kernels).
426		497
427	For few fds, this backend is a bit little slower than poll and select,	498	For few fds, this backend is a bit little slower than poll and select, but
428	but it scales phenomenally better. While poll and select usually scale	499	it scales phenomenally better. While poll and select usually scale like
429	like O(total_fds) where n is the total number of fds (or the highest fd),	500	O(total_fds) where total_fds is the total number of fds (or the highest
430	epoll scales either O(1) or O(active_fds).	501	fd), epoll scales either O(1) or O(active_fds).
431		502
432	The epoll mechanism deserves honorable mention as the most misdesigned	503	The epoll mechanism deserves honorable mention as the most misdesigned
433	of the more advanced event mechanisms: mere annoyances include silently	504	of the more advanced event mechanisms: mere annoyances include silently
434	dropping file descriptors, requiring a system call per change per file	505	dropping file descriptors, requiring a system call per change per file
435	descriptor (and unnecessary guessing of parameters), problems with dup and	506	descriptor (and unnecessary guessing of parameters), problems with dup,
		507	returning before the timeout value, resulting in additional iterations
		508	(and only giving 5ms accuracy while select on the same platform gives
436	so on. The biggest issue is fork races, however - if a program forks then	509	0.1ms) and so on. The biggest issue is fork races, however - if a program
437	I<both> parent and child process have to recreate the epoll set, which can	510	forks then I<both> parent and child process have to recreate the epoll
438	take considerable time (one syscall per file descriptor) and is of course	511	set, which can take considerable time (one syscall per file descriptor)
439	hard to detect.	512	and is of course hard to detect.
440		513
441	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but	514	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
442	of course I<doesn't>, and epoll just loves to report events for totally	515	but of course I<doesn't>, and epoll just loves to report events for
443	I<different> file descriptors (even already closed ones, so one cannot	516	totally I<different> file descriptors (even already closed ones, so
444	even remove them from the set) than registered in the set (especially	517	one cannot even remove them from the set) than registered in the set
445	on SMP systems). Libev tries to counter these spurious notifications by	518	(especially on SMP systems). Libev tries to counter these spurious
446	employing an additional generation counter and comparing that against the	519	notifications by employing an additional generation counter and comparing
447	events to filter out spurious ones, recreating the set when required. Last	520	that against the events to filter out spurious ones, recreating the set
		521	when required. Epoll also erroneously rounds down timeouts, but gives you
		522	no way to know when and by how much, so sometimes you have to busy-wait
		523	because epoll returns immediately despite a nonzero timeout. And last
448	not least, it also refuses to work with some file descriptors which work	524	not least, it also refuses to work with some file descriptors which work
449	perfectly fine with C<select> (files, many character devices...).	525	perfectly fine with C<select> (files, many character devices...).
		526
		527	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		528	cobbled together in a hurry, no thought to design or interaction with
		529	others. Oh, the pain, will it ever stop...
450		530
451	While stopping, setting and starting an I/O watcher in the same iteration	531	While stopping, setting and starting an I/O watcher in the same iteration
452	will result in some caching, there is still a system call per such	532	will result in some caching, there is still a system call per such
453	incident (because the same I<file descriptor> could point to a different	533	incident (because the same I<file descriptor> could point to a different
454	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed	534	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
…		…
491		571
492	It scales in the same way as the epoll backend, but the interface to the	572	It scales in the same way as the epoll backend, but the interface to the
493	kernel is more efficient (which says nothing about its actual speed, of	573	kernel is more efficient (which says nothing about its actual speed, of
494	course). While stopping, setting and starting an I/O watcher does never	574	course). While stopping, setting and starting an I/O watcher does never
495	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to	575	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
496	two event changes per incident. Support for C<fork ()> is very bad (but	576	two event changes per incident. Support for C<fork ()> is very bad (you
497	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect	577	might have to leak fd's on fork, but it's more sane than epoll) and it
498	cases	578	drops fds silently in similarly hard-to-detect cases.
499		579
500	This backend usually performs well under most conditions.	580	This backend usually performs well under most conditions.
501		581
502	While nominally embeddable in other event loops, this doesn't work	582	While nominally embeddable in other event loops, this doesn't work
503	everywhere, so you might need to test for this. And since it is broken	583	everywhere, so you might need to test for this. And since it is broken
…		…
520	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	600	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
521		601
522	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	602	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
523	it's really slow, but it still scales very well (O(active_fds)).	603	it's really slow, but it still scales very well (O(active_fds)).
524		604
525	Please note that Solaris event ports can deliver a lot of spurious
526	notifications, so you need to use non-blocking I/O or other means to avoid
527	blocking when no data (or space) is available.
528
529	While this backend scales well, it requires one system call per active	605	While this backend scales well, it requires one system call per active
530	file descriptor per loop iteration. For small and medium numbers of file	606	file descriptor per loop iteration. For small and medium numbers of file
531	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	607	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
532	might perform better.	608	might perform better.
533		609
534	On the positive side, with the exception of the spurious readiness	610	On the positive side, this backend actually performed fully to
535	notifications, this backend actually performed fully to specification
536	in all tests and is fully embeddable, which is a rare feat among the	611	specification in all tests and is fully embeddable, which is a rare feat
537	OS-specific backends (I vastly prefer correctness over speed hacks).	612	among the OS-specific backends (I vastly prefer correctness over speed
		613	hacks).
		614
		615	On the negative side, the interface is I<bizarre> - so bizarre that
		616	even sun itself gets it wrong in their code examples: The event polling
		617	function sometimes returns events to the caller even though an error
		618	occurred, but with no indication whether it has done so or not (yes, it's
		619	even documented that way) - deadly for edge-triggered interfaces where you
		620	absolutely have to know whether an event occurred or not because you have
		621	to re-arm the watcher.
		622
		623	Fortunately libev seems to be able to work around these idiocies.
538		624
539	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	625	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
540	C<EVBACKEND_POLL>.	626	C<EVBACKEND_POLL>.
541		627
542	=item C<EVBACKEND_ALL>	628	=item C<EVBACKEND_ALL>
543		629
544	Try all backends (even potentially broken ones that wouldn't be tried	630	Try all backends (even potentially broken ones that wouldn't be tried
545	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	631	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
546	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	632	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
547		633
548	It is definitely not recommended to use this flag.	634	It is definitely not recommended to use this flag, use whatever
		635	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		636	at all.
		637
		638	=item C<EVBACKEND_MASK>
		639
		640	Not a backend at all, but a mask to select all backend bits from a
		641	C<flags> value, in case you want to mask out any backends from a flags
		642	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
549		643
550	=back	644	=back
551		645
552	If one or more of the backend flags are or'ed into the flags value,	646	If one or more of the backend flags are or'ed into the flags value,
553	then only these backends will be tried (in the reverse order as listed	647	then only these backends will be tried (in the reverse order as listed
554	here). If none are specified, all backends in C<ev_recommended_backends	648	here). If none are specified, all backends in C<ev_recommended_backends
555	()> will be tried.	649	()> will be tried.
556		650
557	Example: This is the most typical usage.
558
559	if (!ev_default_loop (0))
560	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
561
562	Example: Restrict libev to the select and poll backends, and do not allow
563	environment settings to be taken into account:
564
565	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
566
567	Example: Use whatever libev has to offer, but make sure that kqueue is
568	used if available (warning, breaks stuff, best use only with your own
569	private event loop and only if you know the OS supports your types of
570	fds):
571
572	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
573
574	=item struct ev_loop *ev_loop_new (unsigned int flags)
575
576	Similar to C<ev_default_loop>, but always creates a new event loop that is
577	always distinct from the default loop.
578
579	Note that this function I<is> thread-safe, and one common way to use
580	libev with threads is indeed to create one loop per thread, and using the
581	default loop in the "main" or "initial" thread.
582
583	Example: Try to create a event loop that uses epoll and nothing else.	651	Example: Try to create a event loop that uses epoll and nothing else.
584		652
585	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	653	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
586	if (!epoller)	654	if (!epoller)
587	fatal ("no epoll found here, maybe it hides under your chair");	655	fatal ("no epoll found here, maybe it hides under your chair");
588		656
		657	Example: Use whatever libev has to offer, but make sure that kqueue is
		658	used if available.
		659
		660	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		661
589	=item ev_default_destroy ()	662	=item ev_loop_destroy (loop)
590		663
591	Destroys the default loop (frees all memory and kernel state etc.). None	664	Destroys an event loop object (frees all memory and kernel state
592	of the active event watchers will be stopped in the normal sense, so	665	etc.). None of the active event watchers will be stopped in the normal
593	e.g. C<ev_is_active> might still return true. It is your responsibility to	666	sense, so e.g. C<ev_is_active> might still return true. It is your
594	either stop all watchers cleanly yourself I<before> calling this function,	667	responsibility to either stop all watchers cleanly yourself I<before>
595	or cope with the fact afterwards (which is usually the easiest thing, you	668	calling this function, or cope with the fact afterwards (which is usually
596	can just ignore the watchers and/or C<free ()> them for example).	669	the easiest thing, you can just ignore the watchers and/or C<free ()> them
		670	for example).
597		671
598	Note that certain global state, such as signal state (and installed signal	672	Note that certain global state, such as signal state (and installed signal
599	handlers), will not be freed by this function, and related watchers (such	673	handlers), will not be freed by this function, and related watchers (such
600	as signal and child watchers) would need to be stopped manually.	674	as signal and child watchers) would need to be stopped manually.
601		675
602	In general it is not advisable to call this function except in the	676	This function is normally used on loop objects allocated by
603	rare occasion where you really need to free e.g. the signal handling	677	C<ev_loop_new>, but it can also be used on the default loop returned by
		678	C<ev_default_loop>, in which case it is not thread-safe.
		679
		680	Note that it is not advisable to call this function on the default loop
		681	except in the rare occasion where you really need to free its resources.
604	pipe fds. If you need dynamically allocated loops it is better to use	682	If you need dynamically allocated loops it is better to use C<ev_loop_new>
605	C<ev_loop_new> and C<ev_loop_destroy>.	683	and C<ev_loop_destroy>.
606		684
607	=item ev_loop_destroy (loop)	685	=item ev_loop_fork (loop)
608
609	Like C<ev_default_destroy>, but destroys an event loop created by an
610	earlier call to C<ev_loop_new>.
611
612	=item ev_default_fork ()
613		686
614	This function sets a flag that causes subsequent C<ev_run> iterations	687	This function sets a flag that causes subsequent C<ev_run> iterations
615	to reinitialise the kernel state for backends that have one. Despite the	688	to reinitialise the kernel state for backends that have one. Despite
616	name, you can call it anytime, but it makes most sense after forking, in	689	the name, you can call it anytime you are allowed to start or stop
617	the child process (or both child and parent, but that again makes little	690	watchers (except inside an C<ev_prepare> callback), but it makes most
618	sense). You I<must> call it in the child before using any of the libev	691	sense after forking, in the child process. You I<must> call it (or use
619	functions, and it will only take effect at the next C<ev_run> iteration.	692	C<EVFLAG_FORKCHECK>) in the child before resuming or calling C<ev_run>.
620		693
621	Again, you I<have> to call it on I<any> loop that you want to re-use after	694	Again, you I<have> to call it on I<any> loop that you want to re-use after
622	a fork, I<even if you do not plan to use the loop in the parent>. This is	695	a fork, I<even if you do not plan to use the loop in the parent>. This is
623	because some kernel interfaces *cough* I<kqueue> *cough* do funny things	696	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
624	during fork.	697	during fork.
625		698
626	On the other hand, you only need to call this function in the child	699	On the other hand, you only need to call this function in the child
…		…
629	call it at all (in fact, C<epoll> is so badly broken that it makes a	702	call it at all (in fact, C<epoll> is so badly broken that it makes a
630	difference, but libev will usually detect this case on its own and do a	703	difference, but libev will usually detect this case on its own and do a
631	costly reset of the backend).	704	costly reset of the backend).
632		705
633	The function itself is quite fast and it's usually not a problem to call	706	The function itself is quite fast and it's usually not a problem to call
634	it just in case after a fork. To make this easy, the function will fit in	707	it just in case after a fork.
635	quite nicely into a call to C<pthread_atfork>:
636		708
		709	Example: Automate calling C<ev_loop_fork> on the default loop when
		710	using pthreads.
		711
		712	static void
		713	post_fork_child (void)
		714	{
		715	ev_loop_fork (EV_DEFAULT);
		716	}
		717
		718	...
637	pthread_atfork (0, 0, ev_default_fork);	719	pthread_atfork (0, 0, post_fork_child);
638
639	=item ev_loop_fork (loop)
640
641	Like C<ev_default_fork>, but acts on an event loop created by
642	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
643	after fork that you want to re-use in the child, and how you keep track of
644	them is entirely your own problem.
645		720
646	=item int ev_is_default_loop (loop)	721	=item int ev_is_default_loop (loop)
647		722
648	Returns true when the given loop is, in fact, the default loop, and false	723	Returns true when the given loop is, in fact, the default loop, and false
649	otherwise.	724	otherwise.
…		…
660	prepare and check phases.	735	prepare and check phases.
661		736
662	=item unsigned int ev_depth (loop)	737	=item unsigned int ev_depth (loop)
663		738
664	Returns the number of times C<ev_run> was entered minus the number of	739	Returns the number of times C<ev_run> was entered minus the number of
665	times C<ev_run> was exited, in other words, the recursion depth.	740	times C<ev_run> was exited normally, in other words, the recursion depth.
666		741
667	Outside C<ev_run>, this number is zero. In a callback, this number is	742	Outside C<ev_run>, this number is zero. In a callback, this number is
668	C<1>, unless C<ev_run> was invoked recursively (or from another thread),	743	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
669	in which case it is higher.	744	in which case it is higher.
670		745
671	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread	746	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
672	etc.), doesn't count as "exit" - consider this as a hint to avoid such	747	throwing an exception etc.), doesn't count as "exit" - consider this
673	ungentleman-like behaviour unless it's really convenient.	748	as a hint to avoid such ungentleman-like behaviour unless it's really
		749	convenient, in which case it is fully supported.
674		750
675	=item unsigned int ev_backend (loop)	751	=item unsigned int ev_backend (loop)
676		752
677	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	753	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
678	use.	754	use.
…		…
693		769
694	This function is rarely useful, but when some event callback runs for a	770	This function is rarely useful, but when some event callback runs for a
695	very long time without entering the event loop, updating libev's idea of	771	very long time without entering the event loop, updating libev's idea of
696	the current time is a good idea.	772	the current time is a good idea.
697		773
698	See also L<The special problem of time updates> in the C<ev_timer> section.	774	See also L</The special problem of time updates> in the C<ev_timer> section.
699		775
700	=item ev_suspend (loop)	776	=item ev_suspend (loop)
701		777
702	=item ev_resume (loop)	778	=item ev_resume (loop)
703		779
…		…
721	without a previous call to C<ev_suspend>.	797	without a previous call to C<ev_suspend>.
722		798
723	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the	799	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
724	event loop time (see C<ev_now_update>).	800	event loop time (see C<ev_now_update>).
725		801
726	=item ev_run (loop, int flags)	802	=item bool ev_run (loop, int flags)
727		803
728	Finally, this is it, the event handler. This function usually is called	804	Finally, this is it, the event handler. This function usually is called
729	after you have initialised all your watchers and you want to start	805	after you have initialised all your watchers and you want to start
730	handling events. It will ask the operating system for any new events, call	806	handling events. It will ask the operating system for any new events, call
731	the watcher callbacks, an then repeat the whole process indefinitely: This	807	the watcher callbacks, and then repeat the whole process indefinitely: This
732	is why event loops are called I<loops>.	808	is why event loops are called I<loops>.
733		809
734	If the flags argument is specified as C<0>, it will keep handling events	810	If the flags argument is specified as C<0>, it will keep handling events
735	until either no event watchers are active anymore or C<ev_break> was	811	until either no event watchers are active anymore or C<ev_break> was
736	called.	812	called.
		813
		814	The return value is false if there are no more active watchers (which
		815	usually means "all jobs done" or "deadlock"), and true in all other cases
		816	(which usually means " you should call C<ev_run> again").
737		817
738	Please note that an explicit C<ev_break> is usually better than	818	Please note that an explicit C<ev_break> is usually better than
739	relying on all watchers to be stopped when deciding when a program has	819	relying on all watchers to be stopped when deciding when a program has
740	finished (especially in interactive programs), but having a program	820	finished (especially in interactive programs), but having a program
741	that automatically loops as long as it has to and no longer by virtue	821	that automatically loops as long as it has to and no longer by virtue
742	of relying on its watchers stopping correctly, that is truly a thing of	822	of relying on its watchers stopping correctly, that is truly a thing of
743	beauty.	823	beauty.
744		824
		825	This function is I<mostly> exception-safe - you can break out of a
		826	C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		827	exception and so on. This does not decrement the C<ev_depth> value, nor
		828	will it clear any outstanding C<EVBREAK_ONE> breaks.
		829
745	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle	830	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
746	those events and any already outstanding ones, but will not wait and	831	those events and any already outstanding ones, but will not wait and
747	block your process in case there are no events and will return after one	832	block your process in case there are no events and will return after one
748	iteration of the loop. This is sometimes useful to poll and handle new	833	iteration of the loop. This is sometimes useful to poll and handle new
749	events while doing lengthy calculations, to keep the program responsive.	834	events while doing lengthy calculations, to keep the program responsive.
…		…
758	This is useful if you are waiting for some external event in conjunction	843	This is useful if you are waiting for some external event in conjunction
759	with something not expressible using other libev watchers (i.e. "roll your	844	with something not expressible using other libev watchers (i.e. "roll your
760	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is	845	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
761	usually a better approach for this kind of thing.	846	usually a better approach for this kind of thing.
762		847
763	Here are the gory details of what C<ev_run> does:	848	Here are the gory details of what C<ev_run> does (this is for your
		849	understanding, not a guarantee that things will work exactly like this in
		850	future versions):
764		851
765	- Increment loop depth.	852	- Increment loop depth.
766	- Reset the ev_break status.	853	- Reset the ev_break status.
767	- Before the first iteration, call any pending watchers.	854	- Before the first iteration, call any pending watchers.
768	LOOP:	855	LOOP:
…		…
801	anymore.	888	anymore.
802		889
803	... queue jobs here, make sure they register event watchers as long	890	... queue jobs here, make sure they register event watchers as long
804	... as they still have work to do (even an idle watcher will do..)	891	... as they still have work to do (even an idle watcher will do..)
805	ev_run (my_loop, 0);	892	ev_run (my_loop, 0);
806	... jobs done or somebody called unloop. yeah!	893	... jobs done or somebody called break. yeah!
807		894
808	=item ev_break (loop, how)	895	=item ev_break (loop, how)
809		896
810	Can be used to make a call to C<ev_run> return early (but only after it	897	Can be used to make a call to C<ev_run> return early (but only after it
811	has processed all outstanding events). The C<how> argument must be either	898	has processed all outstanding events). The C<how> argument must be either
812	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or	899	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
813	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.	900	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
814		901
815	This "unloop state" will be cleared when entering C<ev_run> again.	902	This "break state" will be cleared on the next call to C<ev_run>.
816		903
817	It is safe to call C<ev_break> from outside any C<ev_run> calls. ##TODO##	904	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		905	which case it will have no effect.
818		906
819	=item ev_ref (loop)	907	=item ev_ref (loop)
820		908
821	=item ev_unref (loop)	909	=item ev_unref (loop)
822		910
…		…
843	running when nothing else is active.	931	running when nothing else is active.
844		932
845	ev_signal exitsig;	933	ev_signal exitsig;
846	ev_signal_init (&exitsig, sig_cb, SIGINT);	934	ev_signal_init (&exitsig, sig_cb, SIGINT);
847	ev_signal_start (loop, &exitsig);	935	ev_signal_start (loop, &exitsig);
848	evf_unref (loop);	936	ev_unref (loop);
849		937
850	Example: For some weird reason, unregister the above signal handler again.	938	Example: For some weird reason, unregister the above signal handler again.
851		939
852	ev_ref (loop);	940	ev_ref (loop);
853	ev_signal_stop (loop, &exitsig);	941	ev_signal_stop (loop, &exitsig);
…		…
873	overhead for the actual polling but can deliver many events at once.	961	overhead for the actual polling but can deliver many events at once.
874		962
875	By setting a higher I<io collect interval> you allow libev to spend more	963	By setting a higher I<io collect interval> you allow libev to spend more
876	time collecting I/O events, so you can handle more events per iteration,	964	time collecting I/O events, so you can handle more events per iteration,
877	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	965	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
878	C<ev_timer>) will be not affected. Setting this to a non-null value will	966	C<ev_timer>) will not be affected. Setting this to a non-null value will
879	introduce an additional C<ev_sleep ()> call into most loop iterations. The	967	introduce an additional C<ev_sleep ()> call into most loop iterations. The
880	sleep time ensures that libev will not poll for I/O events more often then	968	sleep time ensures that libev will not poll for I/O events more often then
881	once per this interval, on average.	969	once per this interval, on average (as long as the host time resolution is
		970	good enough).
882		971
883	Likewise, by setting a higher I<timeout collect interval> you allow libev	972	Likewise, by setting a higher I<timeout collect interval> you allow libev
884	to spend more time collecting timeouts, at the expense of increased	973	to spend more time collecting timeouts, at the expense of increased
885	latency/jitter/inexactness (the watcher callback will be called	974	latency/jitter/inexactness (the watcher callback will be called
886	later). C<ev_io> watchers will not be affected. Setting this to a non-null	975	later). C<ev_io> watchers will not be affected. Setting this to a non-null
…		…
932	invoke the actual watchers inside another context (another thread etc.).	1021	invoke the actual watchers inside another context (another thread etc.).
933		1022
934	If you want to reset the callback, use C<ev_invoke_pending> as new	1023	If you want to reset the callback, use C<ev_invoke_pending> as new
935	callback.	1024	callback.
936		1025
937	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))	1026	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
938		1027
939	Sometimes you want to share the same loop between multiple threads. This	1028	Sometimes you want to share the same loop between multiple threads. This
940	can be done relatively simply by putting mutex_lock/unlock calls around	1029	can be done relatively simply by putting mutex_lock/unlock calls around
941	each call to a libev function.	1030	each call to a libev function.
942		1031
943	However, C<ev_run> can run an indefinite time, so it is not feasible	1032	However, C<ev_run> can run an indefinite time, so it is not feasible
944	to wait for it to return. One way around this is to wake up the event	1033	to wait for it to return. One way around this is to wake up the event
945	loop via C<ev_break> and C<av_async_send>, another way is to set these	1034	loop via C<ev_break> and C<ev_async_send>, another way is to set these
946	I<release> and I<acquire> callbacks on the loop.	1035	I<release> and I<acquire> callbacks on the loop.
947		1036
948	When set, then C<release> will be called just before the thread is	1037	When set, then C<release> will be called just before the thread is
949	suspended waiting for new events, and C<acquire> is called just	1038	suspended waiting for new events, and C<acquire> is called just
950	afterwards.	1039	afterwards.
…		…
965	See also the locking example in the C<THREADS> section later in this	1054	See also the locking example in the C<THREADS> section later in this
966	document.	1055	document.
967		1056
968	=item ev_set_userdata (loop, void *data)	1057	=item ev_set_userdata (loop, void *data)
969		1058
970	=item ev_userdata (loop)	1059	=item void *ev_userdata (loop)
971		1060
972	Set and retrieve a single C<void *> associated with a loop. When	1061	Set and retrieve a single C<void *> associated with a loop. When
973	C<ev_set_userdata> has never been called, then C<ev_userdata> returns	1062	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
974	C<0.>	1063	C<0>.
975		1064
976	These two functions can be used to associate arbitrary data with a loop,	1065	These two functions can be used to associate arbitrary data with a loop,
977	and are intended solely for the C<invoke_pending_cb>, C<release> and	1066	and are intended solely for the C<invoke_pending_cb>, C<release> and
978	C<acquire> callbacks described above, but of course can be (ab-)used for	1067	C<acquire> callbacks described above, but of course can be (ab-)used for
979	any other purpose as well.	1068	any other purpose as well.
…		…
1090		1179
1091	=item C<EV_PREPARE>	1180	=item C<EV_PREPARE>
1092		1181
1093	=item C<EV_CHECK>	1182	=item C<EV_CHECK>
1094		1183
1095	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts	1184	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts to
1096	to gather new events, and all C<ev_check> watchers are invoked just after	1185	gather new events, and all C<ev_check> watchers are queued (not invoked)
1097	C<ev_run> has gathered them, but before it invokes any callbacks for any	1186	just after C<ev_run> has gathered them, but before it queues any callbacks
		1187	for any received events. That means C<ev_prepare> watchers are the last
		1188	watchers invoked before the event loop sleeps or polls for new events, and
		1189	C<ev_check> watchers will be invoked before any other watchers of the same
		1190	or lower priority within an event loop iteration.
		1191
1098	received events. Callbacks of both watcher types can start and stop as	1192	Callbacks of both watcher types can start and stop as many watchers as
1099	many watchers as they want, and all of them will be taken into account	1193	they want, and all of them will be taken into account (for example, a
1100	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1194	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
1101	C<ev_run> from blocking).	1195	blocking).
1102		1196
1103	=item C<EV_EMBED>	1197	=item C<EV_EMBED>
1104		1198
1105	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1199	The embedded event loop specified in the C<ev_embed> watcher needs attention.
1106		1200
1107	=item C<EV_FORK>	1201	=item C<EV_FORK>
1108		1202
1109	The event loop has been resumed in the child process after fork (see	1203	The event loop has been resumed in the child process after fork (see
1110	C<ev_fork>).	1204	C<ev_fork>).
		1205
		1206	=item C<EV_CLEANUP>
		1207
		1208	The event loop is about to be destroyed (see C<ev_cleanup>).
1111		1209
1112	=item C<EV_ASYNC>	1210	=item C<EV_ASYNC>
1113		1211
1114	The given async watcher has been asynchronously notified (see C<ev_async>).	1212	The given async watcher has been asynchronously notified (see C<ev_async>).
1115		1213
…		…
1137	programs, though, as the fd could already be closed and reused for another	1235	programs, though, as the fd could already be closed and reused for another
1138	thing, so beware.	1236	thing, so beware.
1139		1237
1140	=back	1238	=back
1141		1239
		1240	=head2 GENERIC WATCHER FUNCTIONS
		1241
		1242	=over 4
		1243
		1244	=item C<ev_init> (ev_TYPE *watcher, callback)
		1245
		1246	This macro initialises the generic portion of a watcher. The contents
		1247	of the watcher object can be arbitrary (so C<malloc> will do). Only
		1248	the generic parts of the watcher are initialised, you I<need> to call
		1249	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		1250	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		1251	which rolls both calls into one.
		1252
		1253	You can reinitialise a watcher at any time as long as it has been stopped
		1254	(or never started) and there are no pending events outstanding.
		1255
		1256	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
		1257	int revents)>.
		1258
		1259	Example: Initialise an C<ev_io> watcher in two steps.
		1260
		1261	ev_io w;
		1262	ev_init (&w, my_cb);
		1263	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1264
		1265	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
		1266
		1267	This macro initialises the type-specific parts of a watcher. You need to
		1268	call C<ev_init> at least once before you call this macro, but you can
		1269	call C<ev_TYPE_set> any number of times. You must not, however, call this
		1270	macro on a watcher that is active (it can be pending, however, which is a
		1271	difference to the C<ev_init> macro).
		1272
		1273	Although some watcher types do not have type-specific arguments
		1274	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		1275
		1276	See C<ev_init>, above, for an example.
		1277
		1278	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		1279
		1280	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		1281	calls into a single call. This is the most convenient method to initialise
		1282	a watcher. The same limitations apply, of course.
		1283
		1284	Example: Initialise and set an C<ev_io> watcher in one step.
		1285
		1286	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1287
		1288	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
		1289
		1290	Starts (activates) the given watcher. Only active watchers will receive
		1291	events. If the watcher is already active nothing will happen.
		1292
		1293	Example: Start the C<ev_io> watcher that is being abused as example in this
		1294	whole section.
		1295
		1296	ev_io_start (EV_DEFAULT_UC, &w);
		1297
		1298	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
		1299
		1300	Stops the given watcher if active, and clears the pending status (whether
		1301	the watcher was active or not).
		1302
		1303	It is possible that stopped watchers are pending - for example,
		1304	non-repeating timers are being stopped when they become pending - but
		1305	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
		1306	pending. If you want to free or reuse the memory used by the watcher it is
		1307	therefore a good idea to always call its C<ev_TYPE_stop> function.
		1308
		1309	=item bool ev_is_active (ev_TYPE *watcher)
		1310
		1311	Returns a true value iff the watcher is active (i.e. it has been started
		1312	and not yet been stopped). As long as a watcher is active you must not modify
		1313	it.
		1314
		1315	=item bool ev_is_pending (ev_TYPE *watcher)
		1316
		1317	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		1318	events but its callback has not yet been invoked). As long as a watcher
		1319	is pending (but not active) you must not call an init function on it (but
		1320	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		1321	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1322	it).
		1323
		1324	=item callback ev_cb (ev_TYPE *watcher)
		1325
		1326	Returns the callback currently set on the watcher.
		1327
		1328	=item ev_set_cb (ev_TYPE *watcher, callback)
		1329
		1330	Change the callback. You can change the callback at virtually any time
		1331	(modulo threads).
		1332
		1333	=item ev_set_priority (ev_TYPE *watcher, int priority)
		1334
		1335	=item int ev_priority (ev_TYPE *watcher)
		1336
		1337	Set and query the priority of the watcher. The priority is a small
		1338	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1339	(default: C<-2>). Pending watchers with higher priority will be invoked
		1340	before watchers with lower priority, but priority will not keep watchers
		1341	from being executed (except for C<ev_idle> watchers).
		1342
		1343	If you need to suppress invocation when higher priority events are pending
		1344	you need to look at C<ev_idle> watchers, which provide this functionality.
		1345
		1346	You I<must not> change the priority of a watcher as long as it is active or
		1347	pending.
		1348
		1349	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1350	fine, as long as you do not mind that the priority value you query might
		1351	or might not have been clamped to the valid range.
		1352
		1353	The default priority used by watchers when no priority has been set is
		1354	always C<0>, which is supposed to not be too high and not be too low :).
		1355
		1356	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1357	priorities.
		1358
		1359	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1360
		1361	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1362	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1363	can deal with that fact, as both are simply passed through to the
		1364	callback.
		1365
		1366	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1367
		1368	If the watcher is pending, this function clears its pending status and
		1369	returns its C<revents> bitset (as if its callback was invoked). If the
		1370	watcher isn't pending it does nothing and returns C<0>.
		1371
		1372	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1373	callback to be invoked, which can be accomplished with this function.
		1374
		1375	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1376
		1377	Feeds the given event set into the event loop, as if the specified event
		1378	had happened for the specified watcher (which must be a pointer to an
		1379	initialised but not necessarily started event watcher). Obviously you must
		1380	not free the watcher as long as it has pending events.
		1381
		1382	Stopping the watcher, letting libev invoke it, or calling
		1383	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1384	not started in the first place.
		1385
		1386	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1387	functions that do not need a watcher.
		1388
		1389	=back
		1390
		1391	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
		1392	OWN COMPOSITE WATCHERS> idioms.
		1393
1142	=head2 WATCHER STATES	1394	=head2 WATCHER STATES
1143		1395
1144	There are various watcher states mentioned throughout this manual -	1396	There are various watcher states mentioned throughout this manual -
1145	active, pending and so on. In this section these states and the rules to	1397	active, pending and so on. In this section these states and the rules to
1146	transition between them will be described in more detail - and while these	1398	transition between them will be described in more detail - and while these
1147	rules might look complicated, they usually do "the right thing".	1399	rules might look complicated, they usually do "the right thing".
1148		1400
1149	=over 4	1401	=over 4
1150		1402
1151	=item initialiased	1403	=item initialised
1152		1404
1153	Before a watcher can be registered with the event looop it has to be	1405	Before a watcher can be registered with the event loop it has to be
1154	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to	1406	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
1155	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.	1407	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1156		1408
1157	In this state it is simply some block of memory that is suitable for use	1409	In this state it is simply some block of memory that is suitable for
1158	in an event loop. It can be moved around, freed, reused etc. at will.	1410	use in an event loop. It can be moved around, freed, reused etc. at
		1411	will - as long as you either keep the memory contents intact, or call
		1412	C<ev_TYPE_init> again.
1159		1413
1160	=item started/running/active	1414	=item started/running/active
1161		1415
1162	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes	1416	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
1163	property of the event loop, and is actively waiting for events. While in	1417	property of the event loop, and is actively waiting for events. While in
…		…
1191	latter will clear any pending state the watcher might be in, regardless	1445	latter will clear any pending state the watcher might be in, regardless
1192	of whether it was active or not, so stopping a watcher explicitly before	1446	of whether it was active or not, so stopping a watcher explicitly before
1193	freeing it is often a good idea.	1447	freeing it is often a good idea.
1194		1448
1195	While stopped (and not pending) the watcher is essentially in the	1449	While stopped (and not pending) the watcher is essentially in the
1196	initialised state, that is it can be reused, moved, modified in any way	1450	initialised state, that is, it can be reused, moved, modified in any way
1197	you wish.	1451	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1452	it again).
1198		1453
1199	=back	1454	=back
1200
1201	=head2 GENERIC WATCHER FUNCTIONS
1202
1203	=over 4
1204
1205	=item C<ev_init> (ev_TYPE *watcher, callback)
1206
1207	This macro initialises the generic portion of a watcher. The contents
1208	of the watcher object can be arbitrary (so C<malloc> will do). Only
1209	the generic parts of the watcher are initialised, you I<need> to call
1210	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
1211	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
1212	which rolls both calls into one.
1213
1214	You can reinitialise a watcher at any time as long as it has been stopped
1215	(or never started) and there are no pending events outstanding.
1216
1217	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
1218	int revents)>.
1219
1220	Example: Initialise an C<ev_io> watcher in two steps.
1221
1222	ev_io w;
1223	ev_init (&w, my_cb);
1224	ev_io_set (&w, STDIN_FILENO, EV_READ);
1225
1226	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
1227
1228	This macro initialises the type-specific parts of a watcher. You need to
1229	call C<ev_init> at least once before you call this macro, but you can
1230	call C<ev_TYPE_set> any number of times. You must not, however, call this
1231	macro on a watcher that is active (it can be pending, however, which is a
1232	difference to the C<ev_init> macro).
1233
1234	Although some watcher types do not have type-specific arguments
1235	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
1236
1237	See C<ev_init>, above, for an example.
1238
1239	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
1240
1241	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
1242	calls into a single call. This is the most convenient method to initialise
1243	a watcher. The same limitations apply, of course.
1244
1245	Example: Initialise and set an C<ev_io> watcher in one step.
1246
1247	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
1248
1249	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
1250
1251	Starts (activates) the given watcher. Only active watchers will receive
1252	events. If the watcher is already active nothing will happen.
1253
1254	Example: Start the C<ev_io> watcher that is being abused as example in this
1255	whole section.
1256
1257	ev_io_start (EV_DEFAULT_UC, &w);
1258
1259	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
1260
1261	Stops the given watcher if active, and clears the pending status (whether
1262	the watcher was active or not).
1263
1264	It is possible that stopped watchers are pending - for example,
1265	non-repeating timers are being stopped when they become pending - but
1266	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
1267	pending. If you want to free or reuse the memory used by the watcher it is
1268	therefore a good idea to always call its C<ev_TYPE_stop> function.
1269
1270	=item bool ev_is_active (ev_TYPE *watcher)
1271
1272	Returns a true value iff the watcher is active (i.e. it has been started
1273	and not yet been stopped). As long as a watcher is active you must not modify
1274	it.
1275
1276	=item bool ev_is_pending (ev_TYPE *watcher)
1277
1278	Returns a true value iff the watcher is pending, (i.e. it has outstanding
1279	events but its callback has not yet been invoked). As long as a watcher
1280	is pending (but not active) you must not call an init function on it (but
1281	C<ev_TYPE_set> is safe), you must not change its priority, and you must
1282	make sure the watcher is available to libev (e.g. you cannot C<free ()>
1283	it).
1284
1285	=item callback ev_cb (ev_TYPE *watcher)
1286
1287	Returns the callback currently set on the watcher.
1288
1289	=item ev_cb_set (ev_TYPE *watcher, callback)
1290
1291	Change the callback. You can change the callback at virtually any time
1292	(modulo threads).
1293
1294	=item ev_set_priority (ev_TYPE *watcher, int priority)
1295
1296	=item int ev_priority (ev_TYPE *watcher)
1297
1298	Set and query the priority of the watcher. The priority is a small
1299	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
1300	(default: C<-2>). Pending watchers with higher priority will be invoked
1301	before watchers with lower priority, but priority will not keep watchers
1302	from being executed (except for C<ev_idle> watchers).
1303
1304	If you need to suppress invocation when higher priority events are pending
1305	you need to look at C<ev_idle> watchers, which provide this functionality.
1306
1307	You I<must not> change the priority of a watcher as long as it is active or
1308	pending.
1309
1310	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
1311	fine, as long as you do not mind that the priority value you query might
1312	or might not have been clamped to the valid range.
1313
1314	The default priority used by watchers when no priority has been set is
1315	always C<0>, which is supposed to not be too high and not be too low :).
1316
1317	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
1318	priorities.
1319
1320	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1321
1322	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
1323	C<loop> nor C<revents> need to be valid as long as the watcher callback
1324	can deal with that fact, as both are simply passed through to the
1325	callback.
1326
1327	=item int ev_clear_pending (loop, ev_TYPE *watcher)
1328
1329	If the watcher is pending, this function clears its pending status and
1330	returns its C<revents> bitset (as if its callback was invoked). If the
1331	watcher isn't pending it does nothing and returns C<0>.
1332
1333	Sometimes it can be useful to "poll" a watcher instead of waiting for its
1334	callback to be invoked, which can be accomplished with this function.
1335
1336	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
1337
1338	Feeds the given event set into the event loop, as if the specified event
1339	had happened for the specified watcher (which must be a pointer to an
1340	initialised but not necessarily started event watcher). Obviously you must
1341	not free the watcher as long as it has pending events.
1342
1343	Stopping the watcher, letting libev invoke it, or calling
1344	C<ev_clear_pending> will clear the pending event, even if the watcher was
1345	not started in the first place.
1346
1347	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1348	functions that do not need a watcher.
1349
1350	=back
1351
1352
1353	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
1354
1355	Each watcher has, by default, a member C<void *data> that you can change
1356	and read at any time: libev will completely ignore it. This can be used
1357	to associate arbitrary data with your watcher. If you need more data and
1358	don't want to allocate memory and store a pointer to it in that data
1359	member, you can also "subclass" the watcher type and provide your own
1360	data:
1361
1362	struct my_io
1363	{
1364	ev_io io;
1365	int otherfd;
1366	void *somedata;
1367	struct whatever *mostinteresting;
1368	};
1369
1370	...
1371	struct my_io w;
1372	ev_io_init (&w.io, my_cb, fd, EV_READ);
1373
1374	And since your callback will be called with a pointer to the watcher, you
1375	can cast it back to your own type:
1376
1377	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1378	{
1379	struct my_io *w = (struct my_io *)w_;
1380	...
1381	}
1382
1383	More interesting and less C-conformant ways of casting your callback type
1384	instead have been omitted.
1385
1386	Another common scenario is to use some data structure with multiple
1387	embedded watchers:
1388
1389	struct my_biggy
1390	{
1391	int some_data;
1392	ev_timer t1;
1393	ev_timer t2;
1394	}
1395
1396	In this case getting the pointer to C<my_biggy> is a bit more
1397	complicated: Either you store the address of your C<my_biggy> struct
1398	in the C<data> member of the watcher (for woozies), or you need to use
1399	some pointer arithmetic using C<offsetof> inside your watchers (for real
1400	programmers):
1401
1402	#include <stddef.h>
1403
1404	static void
1405	t1_cb (EV_P_ ev_timer *w, int revents)
1406	{
1407	struct my_biggy big = (struct my_biggy *)
1408	(((char *)w) - offsetof (struct my_biggy, t1));
1409	}
1410
1411	static void
1412	t2_cb (EV_P_ ev_timer *w, int revents)
1413	{
1414	struct my_biggy big = (struct my_biggy *)
1415	(((char *)w) - offsetof (struct my_biggy, t2));
1416	}
1417		1455
1418	=head2 WATCHER PRIORITY MODELS	1456	=head2 WATCHER PRIORITY MODELS
1419		1457
1420	Many event loops support I<watcher priorities>, which are usually small	1458	Many event loops support I<watcher priorities>, which are usually small
1421	integers that influence the ordering of event callback invocation	1459	integers that influence the ordering of event callback invocation
…		…
1548	In general you can register as many read and/or write event watchers per	1586	In general you can register as many read and/or write event watchers per
1549	fd as you want (as long as you don't confuse yourself). Setting all file	1587	fd as you want (as long as you don't confuse yourself). Setting all file
1550	descriptors to non-blocking mode is also usually a good idea (but not	1588	descriptors to non-blocking mode is also usually a good idea (but not
1551	required if you know what you are doing).	1589	required if you know what you are doing).
1552		1590
1553	If you cannot use non-blocking mode, then force the use of a
1554	known-to-be-good backend (at the time of this writing, this includes only
1555	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
1556	descriptors for which non-blocking operation makes no sense (such as
1557	files) - libev doesn't guarantee any specific behaviour in that case.
1558
1559	Another thing you have to watch out for is that it is quite easy to	1591	Another thing you have to watch out for is that it is quite easy to
1560	receive "spurious" readiness notifications, that is your callback might	1592	receive "spurious" readiness notifications, that is, your callback might
1561	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1593	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1562	because there is no data. Not only are some backends known to create a	1594	because there is no data. It is very easy to get into this situation even
1563	lot of those (for example Solaris ports), it is very easy to get into	1595	with a relatively standard program structure. Thus it is best to always
1564	this situation even with a relatively standard program structure. Thus	1596	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1565	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1566	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1597	preferable to a program hanging until some data arrives.
1567		1598
1568	If you cannot run the fd in non-blocking mode (for example you should	1599	If you cannot run the fd in non-blocking mode (for example you should
1569	not play around with an Xlib connection), then you have to separately	1600	not play around with an Xlib connection), then you have to separately
1570	re-test whether a file descriptor is really ready with a known-to-be good	1601	re-test whether a file descriptor is really ready with a known-to-be good
1571	interface such as poll (fortunately in our Xlib example, Xlib already	1602	interface such as poll (fortunately in the case of Xlib, it already does
1572	does this on its own, so its quite safe to use). Some people additionally	1603	this on its own, so its quite safe to use). Some people additionally
1573	use C<SIGALRM> and an interval timer, just to be sure you won't block	1604	use C<SIGALRM> and an interval timer, just to be sure you won't block
1574	indefinitely.	1605	indefinitely.
1575		1606
1576	But really, best use non-blocking mode.	1607	But really, best use non-blocking mode.
1577		1608
…		…
1605		1636
1606	There is no workaround possible except not registering events	1637	There is no workaround possible except not registering events
1607	for potentially C<dup ()>'ed file descriptors, or to resort to	1638	for potentially C<dup ()>'ed file descriptors, or to resort to
1608	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1639	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1609		1640
		1641	=head3 The special problem of files
		1642
		1643	Many people try to use C<select> (or libev) on file descriptors
		1644	representing files, and expect it to become ready when their program
		1645	doesn't block on disk accesses (which can take a long time on their own).
		1646
		1647	However, this cannot ever work in the "expected" way - you get a readiness
		1648	notification as soon as the kernel knows whether and how much data is
		1649	there, and in the case of open files, that's always the case, so you
		1650	always get a readiness notification instantly, and your read (or possibly
		1651	write) will still block on the disk I/O.
		1652
		1653	Another way to view it is that in the case of sockets, pipes, character
		1654	devices and so on, there is another party (the sender) that delivers data
		1655	on its own, but in the case of files, there is no such thing: the disk
		1656	will not send data on its own, simply because it doesn't know what you
		1657	wish to read - you would first have to request some data.
		1658
		1659	Since files are typically not-so-well supported by advanced notification
		1660	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1661	to files, even though you should not use it. The reason for this is
		1662	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1663	usually a tty, often a pipe, but also sometimes files or special devices
		1664	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1665	F</dev/urandom>), and even though the file might better be served with
		1666	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1667	it "just works" instead of freezing.
		1668
		1669	So avoid file descriptors pointing to files when you know it (e.g. use
		1670	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1671	when you rarely read from a file instead of from a socket, and want to
		1672	reuse the same code path.
		1673
1610	=head3 The special problem of fork	1674	=head3 The special problem of fork
1611		1675
1612	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1676	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
1613	useless behaviour. Libev fully supports fork, but needs to be told about	1677	useless behaviour. Libev fully supports fork, but needs to be told about
1614	it in the child.	1678	it in the child if you want to continue to use it in the child.
1615		1679
1616	To support fork in your programs, you either have to call	1680	To support fork in your child processes, you have to call C<ev_loop_fork
1617	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1681	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1618	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1682	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1619	C<EVBACKEND_POLL>.
1620		1683
1621	=head3 The special problem of SIGPIPE	1684	=head3 The special problem of SIGPIPE
1622		1685
1623	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1686	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1624	when writing to a pipe whose other end has been closed, your program gets	1687	when writing to a pipe whose other end has been closed, your program gets
…		…
1722	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1785	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1723	monotonic clock option helps a lot here).	1786	monotonic clock option helps a lot here).
1724		1787
1725	The callback is guaranteed to be invoked only I<after> its timeout has	1788	The callback is guaranteed to be invoked only I<after> its timeout has
1726	passed (not I<at>, so on systems with very low-resolution clocks this	1789	passed (not I<at>, so on systems with very low-resolution clocks this
1727	might introduce a small delay). If multiple timers become ready during the	1790	might introduce a small delay, see "the special problem of being too
		1791	early", below). If multiple timers become ready during the same loop
1728	same loop iteration then the ones with earlier time-out values are invoked	1792	iteration then the ones with earlier time-out values are invoked before
1729	before ones of the same priority with later time-out values (but this is	1793	ones of the same priority with later time-out values (but this is no
1730	no longer true when a callback calls C<ev_run> recursively).	1794	longer true when a callback calls C<ev_run> recursively).
1731		1795
1732	=head3 Be smart about timeouts	1796	=head3 Be smart about timeouts
1733		1797
1734	Many real-world problems involve some kind of timeout, usually for error	1798	Many real-world problems involve some kind of timeout, usually for error
1735	recovery. A typical example is an HTTP request - if the other side hangs,	1799	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1810		1874
1811	In this case, it would be more efficient to leave the C<ev_timer> alone,	1875	In this case, it would be more efficient to leave the C<ev_timer> alone,
1812	but remember the time of last activity, and check for a real timeout only	1876	but remember the time of last activity, and check for a real timeout only
1813	within the callback:	1877	within the callback:
1814		1878
		1879	ev_tstamp timeout = 60.;
1815	ev_tstamp last_activity; // time of last activity	1880	ev_tstamp last_activity; // time of last activity
		1881	ev_timer timer;
1816		1882
1817	static void	1883	static void
1818	callback (EV_P_ ev_timer *w, int revents)	1884	callback (EV_P_ ev_timer *w, int revents)
1819	{	1885	{
1820	ev_tstamp now = ev_now (EV_A);	1886	// calculate when the timeout would happen
1821	ev_tstamp timeout = last_activity + 60.;	1887	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
1822		1888
1823	// if last_activity + 60. is older than now, we did time out	1889	// if negative, it means we the timeout already occurred
1824	if (timeout < now)	1890	if (after < 0.)
1825	{	1891	{
1826	// timeout occurred, take action	1892	// timeout occurred, take action
1827	}	1893	}
1828	else	1894	else
1829	{	1895	{
1830	// callback was invoked, but there was some activity, re-arm	1896	// callback was invoked, but there was some recent
1831	// the watcher to fire in last_activity + 60, which is	1897	// activity. simply restart the timer to time out
1832	// guaranteed to be in the future, so "again" is positive:	1898	// after "after" seconds, which is the earliest time
1833	w->repeat = timeout - now;	1899	// the timeout can occur.
		1900	ev_timer_set (w, after, 0.);
1834	ev_timer_again (EV_A_ w);	1901	ev_timer_start (EV_A_ w);
1835	}	1902	}
1836	}	1903	}
1837		1904
1838	To summarise the callback: first calculate the real timeout (defined	1905	To summarise the callback: first calculate in how many seconds the
1839	as "60 seconds after the last activity"), then check if that time has	1906	timeout will occur (by calculating the absolute time when it would occur,
1840	been reached, which means something I<did>, in fact, time out. Otherwise	1907	C<last_activity + timeout>, and subtracting the current time, C<ev_now
1841	the callback was invoked too early (C<timeout> is in the future), so	1908	(EV_A)> from that).
1842	re-schedule the timer to fire at that future time, to see if maybe we have
1843	a timeout then.
1844		1909
1845	Note how C<ev_timer_again> is used, taking advantage of the	1910	If this value is negative, then we are already past the timeout, i.e. we
1846	C<ev_timer_again> optimisation when the timer is already running.	1911	timed out, and need to do whatever is needed in this case.
		1912
		1913	Otherwise, we now the earliest time at which the timeout would trigger,
		1914	and simply start the timer with this timeout value.
		1915
		1916	In other words, each time the callback is invoked it will check whether
		1917	the timeout occurred. If not, it will simply reschedule itself to check
		1918	again at the earliest time it could time out. Rinse. Repeat.
1847		1919
1848	This scheme causes more callback invocations (about one every 60 seconds	1920	This scheme causes more callback invocations (about one every 60 seconds
1849	minus half the average time between activity), but virtually no calls to	1921	minus half the average time between activity), but virtually no calls to
1850	libev to change the timeout.	1922	libev to change the timeout.
1851		1923
1852	To start the timer, simply initialise the watcher and set C<last_activity>	1924	To start the machinery, simply initialise the watcher and set
1853	to the current time (meaning we just have some activity :), then call the	1925	C<last_activity> to the current time (meaning there was some activity just
1854	callback, which will "do the right thing" and start the timer:	1926	now), then call the callback, which will "do the right thing" and start
		1927	the timer:
1855		1928
		1929	last_activity = ev_now (EV_A);
1856	ev_init (timer, callback);	1930	ev_init (&timer, callback);
1857	last_activity = ev_now (loop);	1931	callback (EV_A_ &timer, 0);
1858	callback (loop, timer, EV_TIMER);
1859		1932
1860	And when there is some activity, simply store the current time in	1933	When there is some activity, simply store the current time in
1861	C<last_activity>, no libev calls at all:	1934	C<last_activity>, no libev calls at all:
1862		1935
		1936	if (activity detected)
1863	last_activity = ev_now (loop);	1937	last_activity = ev_now (EV_A);
		1938
		1939	When your timeout value changes, then the timeout can be changed by simply
		1940	providing a new value, stopping the timer and calling the callback, which
		1941	will again do the right thing (for example, time out immediately :).
		1942
		1943	timeout = new_value;
		1944	ev_timer_stop (EV_A_ &timer);
		1945	callback (EV_A_ &timer, 0);
1864		1946
1865	This technique is slightly more complex, but in most cases where the	1947	This technique is slightly more complex, but in most cases where the
1866	time-out is unlikely to be triggered, much more efficient.	1948	time-out is unlikely to be triggered, much more efficient.
1867
1868	Changing the timeout is trivial as well (if it isn't hard-coded in the
1869	callback :) - just change the timeout and invoke the callback, which will
1870	fix things for you.
1871		1949
1872	=item 4. Wee, just use a double-linked list for your timeouts.	1950	=item 4. Wee, just use a double-linked list for your timeouts.
1873		1951
1874	If there is not one request, but many thousands (millions...), all	1952	If there is not one request, but many thousands (millions...), all
1875	employing some kind of timeout with the same timeout value, then one can	1953	employing some kind of timeout with the same timeout value, then one can
…		…
1902	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is	1980	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
1903	rather complicated, but extremely efficient, something that really pays	1981	rather complicated, but extremely efficient, something that really pays
1904	off after the first million or so of active timers, i.e. it's usually	1982	off after the first million or so of active timers, i.e. it's usually
1905	overkill :)	1983	overkill :)
1906		1984
		1985	=head3 The special problem of being too early
		1986
		1987	If you ask a timer to call your callback after three seconds, then
		1988	you expect it to be invoked after three seconds - but of course, this
		1989	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		1990	guaranteed to any precision by libev - imagine somebody suspending the
		1991	process with a STOP signal for a few hours for example.
		1992
		1993	So, libev tries to invoke your callback as soon as possible I<after> the
		1994	delay has occurred, but cannot guarantee this.
		1995
		1996	A less obvious failure mode is calling your callback too early: many event
		1997	loops compare timestamps with a "elapsed delay >= requested delay", but
		1998	this can cause your callback to be invoked much earlier than you would
		1999	expect.
		2000
		2001	To see why, imagine a system with a clock that only offers full second
		2002	resolution (think windows if you can't come up with a broken enough OS
		2003	yourself). If you schedule a one-second timer at the time 500.9, then the
		2004	event loop will schedule your timeout to elapse at a system time of 500
		2005	(500.9 truncated to the resolution) + 1, or 501.
		2006
		2007	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2008	501" and invoke the callback 0.1s after it was started, even though a
		2009	one-second delay was requested - this is being "too early", despite best
		2010	intentions.
		2011
		2012	This is the reason why libev will never invoke the callback if the elapsed
		2013	delay equals the requested delay, but only when the elapsed delay is
		2014	larger than the requested delay. In the example above, libev would only invoke
		2015	the callback at system time 502, or 1.1s after the timer was started.
		2016
		2017	So, while libev cannot guarantee that your callback will be invoked
		2018	exactly when requested, it I<can> and I<does> guarantee that the requested
		2019	delay has actually elapsed, or in other words, it always errs on the "too
		2020	late" side of things.
		2021
1907	=head3 The special problem of time updates	2022	=head3 The special problem of time updates
1908		2023
1909	Establishing the current time is a costly operation (it usually takes at	2024	Establishing the current time is a costly operation (it usually takes
1910	least two system calls): EV therefore updates its idea of the current	2025	at least one system call): EV therefore updates its idea of the current
1911	time only before and after C<ev_run> collects new events, which causes a	2026	time only before and after C<ev_run> collects new events, which causes a
1912	growing difference between C<ev_now ()> and C<ev_time ()> when handling	2027	growing difference between C<ev_now ()> and C<ev_time ()> when handling
1913	lots of events in one iteration.	2028	lots of events in one iteration.
1914		2029
1915	The relative timeouts are calculated relative to the C<ev_now ()>	2030	The relative timeouts are calculated relative to the C<ev_now ()>
…		…
1921	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2036	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1922		2037
1923	If the event loop is suspended for a long time, you can also force an	2038	If the event loop is suspended for a long time, you can also force an
1924	update of the time returned by C<ev_now ()> by calling C<ev_now_update	2039	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1925	()>.	2040	()>.
		2041
		2042	=head3 The special problem of unsynchronised clocks
		2043
		2044	Modern systems have a variety of clocks - libev itself uses the normal
		2045	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2046	jumps).
		2047
		2048	Neither of these clocks is synchronised with each other or any other clock
		2049	on the system, so C<ev_time ()> might return a considerably different time
		2050	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2051	a call to C<gettimeofday> might return a second count that is one higher
		2052	than a directly following call to C<time>.
		2053
		2054	The moral of this is to only compare libev-related timestamps with
		2055	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2056	a second or so.
		2057
		2058	One more problem arises due to this lack of synchronisation: if libev uses
		2059	the system monotonic clock and you compare timestamps from C<ev_time>
		2060	or C<ev_now> from when you started your timer and when your callback is
		2061	invoked, you will find that sometimes the callback is a bit "early".
		2062
		2063	This is because C<ev_timer>s work in real time, not wall clock time, so
		2064	libev makes sure your callback is not invoked before the delay happened,
		2065	I<measured according to the real time>, not the system clock.
		2066
		2067	If your timeouts are based on a physical timescale (e.g. "time out this
		2068	connection after 100 seconds") then this shouldn't bother you as it is
		2069	exactly the right behaviour.
		2070
		2071	If you want to compare wall clock/system timestamps to your timers, then
		2072	you need to use C<ev_periodic>s, as these are based on the wall clock
		2073	time, where your comparisons will always generate correct results.
1926		2074
1927	=head3 The special problems of suspended animation	2075	=head3 The special problems of suspended animation
1928		2076
1929	When you leave the server world it is quite customary to hit machines that	2077	When you leave the server world it is quite customary to hit machines that
1930	can suspend/hibernate - what happens to the clocks during such a suspend?	2078	can suspend/hibernate - what happens to the clocks during such a suspend?
…		…
1974	keep up with the timer (because it takes longer than those 10 seconds to	2122	keep up with the timer (because it takes longer than those 10 seconds to
1975	do stuff) the timer will not fire more than once per event loop iteration.	2123	do stuff) the timer will not fire more than once per event loop iteration.
1976		2124
1977	=item ev_timer_again (loop, ev_timer *)	2125	=item ev_timer_again (loop, ev_timer *)
1978		2126
1979	This will act as if the timer timed out and restart it again if it is	2127	This will act as if the timer timed out, and restarts it again if it is
1980	repeating. The exact semantics are:	2128	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2129	timeout to the C<repeat> value and calling C<ev_timer_start>.
1981		2130
		2131	The exact semantics are as in the following rules, all of which will be
		2132	applied to the watcher:
		2133
		2134	=over 4
		2135
1982	If the timer is pending, its pending status is cleared.	2136	=item If the timer is pending, the pending status is always cleared.
1983		2137
1984	If the timer is started but non-repeating, stop it (as if it timed out).	2138	=item If the timer is started but non-repeating, stop it (as if it timed
		2139	out, without invoking it).
1985		2140
1986	If the timer is repeating, either start it if necessary (with the	2141	=item If the timer is repeating, make the C<repeat> value the new timeout
1987	C<repeat> value), or reset the running timer to the C<repeat> value.	2142	and start the timer, if necessary.
1988		2143
		2144	=back
		2145
1989	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a	2146	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
1990	usage example.	2147	usage example.
1991		2148
1992	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)	2149	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1993		2150
1994	Returns the remaining time until a timer fires. If the timer is active,	2151	Returns the remaining time until a timer fires. If the timer is active,
…		…
2114		2271
2115	Another way to think about it (for the mathematically inclined) is that	2272	Another way to think about it (for the mathematically inclined) is that
2116	C<ev_periodic> will try to run the callback in this mode at the next possible	2273	C<ev_periodic> will try to run the callback in this mode at the next possible
2117	time where C<time = offset (mod interval)>, regardless of any time jumps.	2274	time where C<time = offset (mod interval)>, regardless of any time jumps.
2118		2275
2119	For numerical stability it is preferable that the C<offset> value is near	2276	The C<interval> I<MUST> be positive, and for numerical stability, the
2120	C<ev_now ()> (the current time), but there is no range requirement for	2277	interval value should be higher than C<1/8192> (which is around 100
2121	this value, and in fact is often specified as zero.	2278	microseconds) and C<offset> should be higher than C<0> and should have
		2279	at most a similar magnitude as the current time (say, within a factor of
		2280	ten). Typical values for offset are, in fact, C<0> or something between
		2281	C<0> and C<interval>, which is also the recommended range.
2122		2282
2123	Note also that there is an upper limit to how often a timer can fire (CPU	2283	Note also that there is an upper limit to how often a timer can fire (CPU
2124	speed for example), so if C<interval> is very small then timing stability	2284	speed for example), so if C<interval> is very small then timing stability
2125	will of course deteriorate. Libev itself tries to be exact to be about one	2285	will of course deteriorate. Libev itself tries to be exact to be about one
2126	millisecond (if the OS supports it and the machine is fast enough).	2286	millisecond (if the OS supports it and the machine is fast enough).
…		…
2234		2394
2235	ev_periodic hourly_tick;	2395	ev_periodic hourly_tick;
2236	ev_periodic_init (&hourly_tick, clock_cb,	2396	ev_periodic_init (&hourly_tick, clock_cb,
2237	fmod (ev_now (loop), 3600.), 3600., 0);	2397	fmod (ev_now (loop), 3600.), 3600., 0);
2238	ev_periodic_start (loop, &hourly_tick);	2398	ev_periodic_start (loop, &hourly_tick);
2239		2399
2240		2400
2241	=head2 C<ev_signal> - signal me when a signal gets signalled!	2401	=head2 C<ev_signal> - signal me when a signal gets signalled!
2242		2402
2243	Signal watchers will trigger an event when the process receives a specific	2403	Signal watchers will trigger an event when the process receives a specific
2244	signal one or more times. Even though signals are very asynchronous, libev	2404	signal one or more times. Even though signals are very asynchronous, libev
2245	will try it's best to deliver signals synchronously, i.e. as part of the	2405	will try its best to deliver signals synchronously, i.e. as part of the
2246	normal event processing, like any other event.	2406	normal event processing, like any other event.
2247		2407
2248	If you want signals to be delivered truly asynchronously, just use	2408	If you want signals to be delivered truly asynchronously, just use
2249	C<sigaction> as you would do without libev and forget about sharing	2409	C<sigaction> as you would do without libev and forget about sharing
2250	the signal. You can even use C<ev_async> from a signal handler to	2410	the signal. You can even use C<ev_async> from a signal handler to
…		…
2254	only within the same loop, i.e. you can watch for C<SIGINT> in your	2414	only within the same loop, i.e. you can watch for C<SIGINT> in your
2255	default loop and for C<SIGIO> in another loop, but you cannot watch for	2415	default loop and for C<SIGIO> in another loop, but you cannot watch for
2256	C<SIGINT> in both the default loop and another loop at the same time. At	2416	C<SIGINT> in both the default loop and another loop at the same time. At
2257	the moment, C<SIGCHLD> is permanently tied to the default loop.	2417	the moment, C<SIGCHLD> is permanently tied to the default loop.
2258		2418
2259	When the first watcher gets started will libev actually register something	2419	Only after the first watcher for a signal is started will libev actually
2260	with the kernel (thus it coexists with your own signal handlers as long as	2420	register something with the kernel. It thus coexists with your own signal
2261	you don't register any with libev for the same signal).	2421	handlers as long as you don't register any with libev for the same signal.
2262		2422
2263	If possible and supported, libev will install its handlers with	2423	If possible and supported, libev will install its handlers with
2264	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should	2424	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
2265	not be unduly interrupted. If you have a problem with system calls getting	2425	not be unduly interrupted. If you have a problem with system calls getting
2266	interrupted by signals you can block all signals in an C<ev_check> watcher	2426	interrupted by signals you can block all signals in an C<ev_check> watcher
…		…
2269	=head3 The special problem of inheritance over fork/execve/pthread_create	2429	=head3 The special problem of inheritance over fork/execve/pthread_create
2270		2430
2271	Both the signal mask (C<sigprocmask>) and the signal disposition	2431	Both the signal mask (C<sigprocmask>) and the signal disposition
2272	(C<sigaction>) are unspecified after starting a signal watcher (and after	2432	(C<sigaction>) are unspecified after starting a signal watcher (and after
2273	stopping it again), that is, libev might or might not block the signal,	2433	stopping it again), that is, libev might or might not block the signal,
2274	and might or might not set or restore the installed signal handler.	2434	and might or might not set or restore the installed signal handler (but
		2435	see C<EVFLAG_NOSIGMASK>).
2275		2436
2276	While this does not matter for the signal disposition (libev never	2437	While this does not matter for the signal disposition (libev never
2277	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on	2438	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
2278	C<execve>), this matters for the signal mask: many programs do not expect	2439	C<execve>), this matters for the signal mask: many programs do not expect
2279	certain signals to be blocked.	2440	certain signals to be blocked.
…		…
2292	I<has> to modify the signal mask, at least temporarily.	2453	I<has> to modify the signal mask, at least temporarily.
2293		2454
2294	So I can't stress this enough: I<If you do not reset your signal mask when	2455	So I can't stress this enough: I<If you do not reset your signal mask when
2295	you expect it to be empty, you have a race condition in your code>. This	2456	you expect it to be empty, you have a race condition in your code>. This
2296	is not a libev-specific thing, this is true for most event libraries.	2457	is not a libev-specific thing, this is true for most event libraries.
		2458
		2459	=head3 The special problem of threads signal handling
		2460
		2461	POSIX threads has problematic signal handling semantics, specifically,
		2462	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2463	threads in a process block signals, which is hard to achieve.
		2464
		2465	When you want to use sigwait (or mix libev signal handling with your own
		2466	for the same signals), you can tackle this problem by globally blocking
		2467	all signals before creating any threads (or creating them with a fully set
		2468	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2469	loops. Then designate one thread as "signal receiver thread" which handles
		2470	these signals. You can pass on any signals that libev might be interested
		2471	in by calling C<ev_feed_signal>.
2297		2472
2298	=head3 Watcher-Specific Functions and Data Members	2473	=head3 Watcher-Specific Functions and Data Members
2299		2474
2300	=over 4	2475	=over 4
2301		2476
…		…
2436		2611
2437	=head2 C<ev_stat> - did the file attributes just change?	2612	=head2 C<ev_stat> - did the file attributes just change?
2438		2613
2439	This watches a file system path for attribute changes. That is, it calls	2614	This watches a file system path for attribute changes. That is, it calls
2440	C<stat> on that path in regular intervals (or when the OS says it changed)	2615	C<stat> on that path in regular intervals (or when the OS says it changed)
2441	and sees if it changed compared to the last time, invoking the callback if	2616	and sees if it changed compared to the last time, invoking the callback
2442	it did.	2617	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2618	happen after the watcher has been started will be reported.
2443		2619
2444	The path does not need to exist: changing from "path exists" to "path does	2620	The path does not need to exist: changing from "path exists" to "path does
2445	not exist" is a status change like any other. The condition "path does not	2621	not exist" is a status change like any other. The condition "path does not
2446	exist" (or more correctly "path cannot be stat'ed") is signified by the	2622	exist" (or more correctly "path cannot be stat'ed") is signified by the
2447	C<st_nlink> field being zero (which is otherwise always forced to be at	2623	C<st_nlink> field being zero (which is otherwise always forced to be at
…		…
2677	Apart from keeping your process non-blocking (which is a useful	2853	Apart from keeping your process non-blocking (which is a useful
2678	effect on its own sometimes), idle watchers are a good place to do	2854	effect on its own sometimes), idle watchers are a good place to do
2679	"pseudo-background processing", or delay processing stuff to after the	2855	"pseudo-background processing", or delay processing stuff to after the
2680	event loop has handled all outstanding events.	2856	event loop has handled all outstanding events.
2681		2857
		2858	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2859
		2860	As long as there is at least one active idle watcher, libev will never
		2861	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2862	For this to work, the idle watcher doesn't need to be invoked at all - the
		2863	lowest priority will do.
		2864
		2865	This mode of operation can be useful together with an C<ev_check> watcher,
		2866	to do something on each event loop iteration - for example to balance load
		2867	between different connections.
		2868
		2869	See L</Abusing an ev_check watcher for its side-effect> for a longer
		2870	example.
		2871
2682	=head3 Watcher-Specific Functions and Data Members	2872	=head3 Watcher-Specific Functions and Data Members
2683		2873
2684	=over 4	2874	=over 4
2685		2875
2686	=item ev_idle_init (ev_idle *, callback)	2876	=item ev_idle_init (ev_idle *, callback)
…		…
2697	callback, free it. Also, use no error checking, as usual.	2887	callback, free it. Also, use no error checking, as usual.
2698		2888
2699	static void	2889	static void
2700	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)	2890	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
2701	{	2891	{
		2892	// stop the watcher
		2893	ev_idle_stop (loop, w);
		2894
		2895	// now we can free it
2702	free (w);	2896	free (w);
		2897
2703	// now do something you wanted to do when the program has	2898	// now do something you wanted to do when the program has
2704	// no longer anything immediate to do.	2899	// no longer anything immediate to do.
2705	}	2900	}
2706		2901
2707	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	2902	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
…		…
2709	ev_idle_start (loop, idle_watcher);	2904	ev_idle_start (loop, idle_watcher);
2710		2905
2711		2906
2712	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2907	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2713		2908
2714	Prepare and check watchers are usually (but not always) used in pairs:	2909	Prepare and check watchers are often (but not always) used in pairs:
2715	prepare watchers get invoked before the process blocks and check watchers	2910	prepare watchers get invoked before the process blocks and check watchers
2716	afterwards.	2911	afterwards.
2717		2912
2718	You I<must not> call C<ev_run> or similar functions that enter	2913	You I<must not> call C<ev_run> (or similar functions that enter the
2719	the current event loop from either C<ev_prepare> or C<ev_check>	2914	current event loop) or C<ev_loop_fork> from either C<ev_prepare> or
2720	watchers. Other loops than the current one are fine, however. The	2915	C<ev_check> watchers. Other loops than the current one are fine,
2721	rationale behind this is that you do not need to check for recursion in	2916	however. The rationale behind this is that you do not need to check
2722	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2917	for recursion in those watchers, i.e. the sequence will always be
2723	C<ev_check> so if you have one watcher of each kind they will always be	2918	C<ev_prepare>, blocking, C<ev_check> so if you have one watcher of each
2724	called in pairs bracketing the blocking call.	2919	kind they will always be called in pairs bracketing the blocking call.
2725		2920
2726	Their main purpose is to integrate other event mechanisms into libev and	2921	Their main purpose is to integrate other event mechanisms into libev and
2727	their use is somewhat advanced. They could be used, for example, to track	2922	their use is somewhat advanced. They could be used, for example, to track
2728	variable changes, implement your own watchers, integrate net-snmp or a	2923	variable changes, implement your own watchers, integrate net-snmp or a
2729	coroutine library and lots more. They are also occasionally useful if	2924	coroutine library and lots more. They are also occasionally useful if
…		…
2747	with priority higher than or equal to the event loop and one coroutine	2942	with priority higher than or equal to the event loop and one coroutine
2748	of lower priority, but only once, using idle watchers to keep the event	2943	of lower priority, but only once, using idle watchers to keep the event
2749	loop from blocking if lower-priority coroutines are active, thus mapping	2944	loop from blocking if lower-priority coroutines are active, thus mapping
2750	low-priority coroutines to idle/background tasks).	2945	low-priority coroutines to idle/background tasks).
2751		2946
2752	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2947	When used for this purpose, it is recommended to give C<ev_check> watchers
2753	priority, to ensure that they are being run before any other watchers	2948	highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
2754	after the poll (this doesn't matter for C<ev_prepare> watchers).	2949	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		2950	watchers).
2755		2951
2756	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not	2952	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
2757	activate ("feed") events into libev. While libev fully supports this, they	2953	activate ("feed") events into libev. While libev fully supports this, they
2758	might get executed before other C<ev_check> watchers did their job. As	2954	might get executed before other C<ev_check> watchers did their job. As
2759	C<ev_check> watchers are often used to embed other (non-libev) event	2955	C<ev_check> watchers are often used to embed other (non-libev) event
2760	loops those other event loops might be in an unusable state until their	2956	loops those other event loops might be in an unusable state until their
2761	C<ev_check> watcher ran (always remind yourself to coexist peacefully with	2957	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
2762	others).	2958	others).
		2959
		2960	=head3 Abusing an C<ev_check> watcher for its side-effect
		2961
		2962	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		2963	useful because they are called once per event loop iteration. For
		2964	example, if you want to handle a large number of connections fairly, you
		2965	normally only do a bit of work for each active connection, and if there
		2966	is more work to do, you wait for the next event loop iteration, so other
		2967	connections have a chance of making progress.
		2968
		2969	Using an C<ev_check> watcher is almost enough: it will be called on the
		2970	next event loop iteration. However, that isn't as soon as possible -
		2971	without external events, your C<ev_check> watcher will not be invoked.
		2972
		2973	This is where C<ev_idle> watchers come in handy - all you need is a
		2974	single global idle watcher that is active as long as you have one active
		2975	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		2976	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		2977	invoked. Neither watcher alone can do that.
2763		2978
2764	=head3 Watcher-Specific Functions and Data Members	2979	=head3 Watcher-Specific Functions and Data Members
2765		2980
2766	=over 4	2981	=over 4
2767		2982
…		…
2968		3183
2969	=over 4	3184	=over 4
2970		3185
2971	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3186	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
2972		3187
2973	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)	3188	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
2974		3189
2975	Configures the watcher to embed the given loop, which must be	3190	Configures the watcher to embed the given loop, which must be
2976	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3191	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
2977	invoked automatically, otherwise it is the responsibility of the callback	3192	invoked automatically, otherwise it is the responsibility of the callback
2978	to invoke it (it will continue to be called until the sweep has been done,	3193	to invoke it (it will continue to be called until the sweep has been done,
…		…
2999	used).	3214	used).
3000		3215
3001	struct ev_loop *loop_hi = ev_default_init (0);	3216	struct ev_loop *loop_hi = ev_default_init (0);
3002	struct ev_loop *loop_lo = 0;	3217	struct ev_loop *loop_lo = 0;
3003	ev_embed embed;	3218	ev_embed embed;
3004		3219
3005	// see if there is a chance of getting one that works	3220	// see if there is a chance of getting one that works
3006	// (remember that a flags value of 0 means autodetection)	3221	// (remember that a flags value of 0 means autodetection)
3007	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3222	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3008	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3223	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3009	: 0;	3224	: 0;
…		…
3023	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3238	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
3024		3239
3025	struct ev_loop *loop = ev_default_init (0);	3240	struct ev_loop *loop = ev_default_init (0);
3026	struct ev_loop *loop_socket = 0;	3241	struct ev_loop *loop_socket = 0;
3027	ev_embed embed;	3242	ev_embed embed;
3028		3243
3029	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3244	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3030	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3245	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3031	{	3246	{
3032	ev_embed_init (&embed, 0, loop_socket);	3247	ev_embed_init (&embed, 0, loop_socket);
3033	ev_embed_start (loop, &embed);	3248	ev_embed_start (loop, &embed);
…		…
3041		3256
3042	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3257	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
3043		3258
3044	Fork watchers are called when a C<fork ()> was detected (usually because	3259	Fork watchers are called when a C<fork ()> was detected (usually because
3045	whoever is a good citizen cared to tell libev about it by calling	3260	whoever is a good citizen cared to tell libev about it by calling
3046	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the	3261	C<ev_loop_fork>). The invocation is done before the event loop blocks next
3047	event loop blocks next and before C<ev_check> watchers are being called,	3262	and before C<ev_check> watchers are being called, and only in the child
3048	and only in the child after the fork. If whoever good citizen calling	3263	after the fork. If whoever good citizen calling C<ev_default_fork> cheats
3049	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3264	and calls it in the wrong process, the fork handlers will be invoked, too,
3050	handlers will be invoked, too, of course.	3265	of course.
3051		3266
3052	=head3 The special problem of life after fork - how is it possible?	3267	=head3 The special problem of life after fork - how is it possible?
3053		3268
3054	Most uses of C<fork()> consist of forking, then some simple calls to set	3269	Most uses of C<fork ()> consist of forking, then some simple calls to set
3055	up/change the process environment, followed by a call to C<exec()>. This	3270	up/change the process environment, followed by a call to C<exec()>. This
3056	sequence should be handled by libev without any problems.	3271	sequence should be handled by libev without any problems.
3057		3272
3058	This changes when the application actually wants to do event handling	3273	This changes when the application actually wants to do event handling
3059	in the child, or both parent in child, in effect "continuing" after the	3274	in the child, or both parent in child, in effect "continuing" after the
…		…
3075	disadvantage of having to use multiple event loops (which do not support	3290	disadvantage of having to use multiple event loops (which do not support
3076	signal watchers).	3291	signal watchers).
3077		3292
3078	When this is not possible, or you want to use the default loop for	3293	When this is not possible, or you want to use the default loop for
3079	other reasons, then in the process that wants to start "fresh", call	3294	other reasons, then in the process that wants to start "fresh", call
3080	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying	3295	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
3081	the default loop will "orphan" (not stop) all registered watchers, so you	3296	Destroying the default loop will "orphan" (not stop) all registered
3082	have to be careful not to execute code that modifies those watchers. Note	3297	watchers, so you have to be careful not to execute code that modifies
3083	also that in that case, you have to re-register any signal watchers.	3298	those watchers. Note also that in that case, you have to re-register any
		3299	signal watchers.
3084		3300
3085	=head3 Watcher-Specific Functions and Data Members	3301	=head3 Watcher-Specific Functions and Data Members
3086		3302
3087	=over 4	3303	=over 4
3088		3304
3089	=item ev_fork_init (ev_signal *, callback)	3305	=item ev_fork_init (ev_fork *, callback)
3090		3306
3091	Initialises and configures the fork watcher - it has no parameters of any	3307	Initialises and configures the fork watcher - it has no parameters of any
3092	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,	3308	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
3093	believe me.	3309	really.
3094		3310
3095	=back	3311	=back
3096		3312
3097		3313
		3314	=head2 C<ev_cleanup> - even the best things end
		3315
		3316	Cleanup watchers are called just before the event loop is being destroyed
		3317	by a call to C<ev_loop_destroy>.
		3318
		3319	While there is no guarantee that the event loop gets destroyed, cleanup
		3320	watchers provide a convenient method to install cleanup hooks for your
		3321	program, worker threads and so on - you just to make sure to destroy the
		3322	loop when you want them to be invoked.
		3323
		3324	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3325	all other watchers, they do not keep a reference to the event loop (which
		3326	makes a lot of sense if you think about it). Like all other watchers, you
		3327	can call libev functions in the callback, except C<ev_cleanup_start>.
		3328
		3329	=head3 Watcher-Specific Functions and Data Members
		3330
		3331	=over 4
		3332
		3333	=item ev_cleanup_init (ev_cleanup *, callback)
		3334
		3335	Initialises and configures the cleanup watcher - it has no parameters of
		3336	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3337	pointless, I assure you.
		3338
		3339	=back
		3340
		3341	Example: Register an atexit handler to destroy the default loop, so any
		3342	cleanup functions are called.
		3343
		3344	static void
		3345	program_exits (void)
		3346	{
		3347	ev_loop_destroy (EV_DEFAULT_UC);
		3348	}
		3349
		3350	...
		3351	atexit (program_exits);
		3352
		3353
3098	=head2 C<ev_async> - how to wake up an event loop	3354	=head2 C<ev_async> - how to wake up an event loop
3099		3355
3100	In general, you cannot use an C<ev_run> from multiple threads or other	3356	In general, you cannot use an C<ev_loop> from multiple threads or other
3101	asynchronous sources such as signal handlers (as opposed to multiple event	3357	asynchronous sources such as signal handlers (as opposed to multiple event
3102	loops - those are of course safe to use in different threads).	3358	loops - those are of course safe to use in different threads).
3103		3359
3104	Sometimes, however, you need to wake up an event loop you do not control,	3360	Sometimes, however, you need to wake up an event loop you do not control,
3105	for example because it belongs to another thread. This is what C<ev_async>	3361	for example because it belongs to another thread. This is what C<ev_async>
…		…
3107	it by calling C<ev_async_send>, which is thread- and signal safe.	3363	it by calling C<ev_async_send>, which is thread- and signal safe.
3108		3364
3109	This functionality is very similar to C<ev_signal> watchers, as signals,	3365	This functionality is very similar to C<ev_signal> watchers, as signals,
3110	too, are asynchronous in nature, and signals, too, will be compressed	3366	too, are asynchronous in nature, and signals, too, will be compressed
3111	(i.e. the number of callback invocations may be less than the number of	3367	(i.e. the number of callback invocations may be less than the number of
3112	C<ev_async_sent> calls).	3368	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
3113		3369	of "global async watchers" by using a watcher on an otherwise unused
3114	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not	3370	signal, and C<ev_feed_signal> to signal this watcher from another thread,
3115	just the default loop.	3371	even without knowing which loop owns the signal.
3116		3372
3117	=head3 Queueing	3373	=head3 Queueing
3118		3374
3119	C<ev_async> does not support queueing of data in any way. The reason	3375	C<ev_async> does not support queueing of data in any way. The reason
3120	is that the author does not know of a simple (or any) algorithm for a	3376	is that the author does not know of a simple (or any) algorithm for a
…		…
3212	trust me.	3468	trust me.
3213		3469
3214	=item ev_async_send (loop, ev_async *)	3470	=item ev_async_send (loop, ev_async *)
3215		3471
3216	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3472	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
3217	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3473	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3474	returns.
		3475
3218	C<ev_feed_event>, this call is safe to do from other threads, signal or	3476	Unlike C<ev_feed_event>, this call is safe to do from other threads,
3219	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3477	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
3220	section below on what exactly this means).	3478	embedding section below on what exactly this means).
3221		3479
3222	Note that, as with other watchers in libev, multiple events might get	3480	Note that, as with other watchers in libev, multiple events might get
3223	compressed into a single callback invocation (another way to look at this	3481	compressed into a single callback invocation (another way to look at
3224	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,	3482	this is that C<ev_async> watchers are level-triggered: they are set on
3225	reset when the event loop detects that).	3483	C<ev_async_send>, reset when the event loop detects that).
3226		3484
3227	This call incurs the overhead of a system call only once per event loop	3485	This call incurs the overhead of at most one extra system call per event
3228	iteration, so while the overhead might be noticeable, it doesn't apply to	3486	loop iteration, if the event loop is blocked, and no syscall at all if
3229	repeated calls to C<ev_async_send> for the same event loop.	3487	the event loop (or your program) is processing events. That means that
		3488	repeated calls are basically free (there is no need to avoid calls for
		3489	performance reasons) and that the overhead becomes smaller (typically
		3490	zero) under load.
3230		3491
3231	=item bool = ev_async_pending (ev_async *)	3492	=item bool = ev_async_pending (ev_async *)
3232		3493
3233	Returns a non-zero value when C<ev_async_send> has been called on the	3494	Returns a non-zero value when C<ev_async_send> has been called on the
3234	watcher but the event has not yet been processed (or even noted) by the	3495	watcher but the event has not yet been processed (or even noted) by the
…		…
3289	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3550	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3290		3551
3291	=item ev_feed_fd_event (loop, int fd, int revents)	3552	=item ev_feed_fd_event (loop, int fd, int revents)
3292		3553
3293	Feed an event on the given fd, as if a file descriptor backend detected	3554	Feed an event on the given fd, as if a file descriptor backend detected
3294	the given events it.	3555	the given events.
3295		3556
3296	=item ev_feed_signal_event (loop, int signum)	3557	=item ev_feed_signal_event (loop, int signum)
3297		3558
3298	Feed an event as if the given signal occurred (C<loop> must be the default	3559	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3299	loop!).	3560	which is async-safe.
3300		3561
3301	=back	3562	=back
		3563
		3564
		3565	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3566
		3567	This section explains some common idioms that are not immediately
		3568	obvious. Note that examples are sprinkled over the whole manual, and this
		3569	section only contains stuff that wouldn't fit anywhere else.
		3570
		3571	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3572
		3573	Each watcher has, by default, a C<void *data> member that you can read
		3574	or modify at any time: libev will completely ignore it. This can be used
		3575	to associate arbitrary data with your watcher. If you need more data and
		3576	don't want to allocate memory separately and store a pointer to it in that
		3577	data member, you can also "subclass" the watcher type and provide your own
		3578	data:
		3579
		3580	struct my_io
		3581	{
		3582	ev_io io;
		3583	int otherfd;
		3584	void *somedata;
		3585	struct whatever *mostinteresting;
		3586	};
		3587
		3588	...
		3589	struct my_io w;
		3590	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3591
		3592	And since your callback will be called with a pointer to the watcher, you
		3593	can cast it back to your own type:
		3594
		3595	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3596	{
		3597	struct my_io *w = (struct my_io *)w_;
		3598	...
		3599	}
		3600
		3601	More interesting and less C-conformant ways of casting your callback
		3602	function type instead have been omitted.
		3603
		3604	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3605
		3606	Another common scenario is to use some data structure with multiple
		3607	embedded watchers, in effect creating your own watcher that combines
		3608	multiple libev event sources into one "super-watcher":
		3609
		3610	struct my_biggy
		3611	{
		3612	int some_data;
		3613	ev_timer t1;
		3614	ev_timer t2;
		3615	}
		3616
		3617	In this case getting the pointer to C<my_biggy> is a bit more
		3618	complicated: Either you store the address of your C<my_biggy> struct in
		3619	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3620	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3621	real programmers):
		3622
		3623	#include <stddef.h>
		3624
		3625	static void
		3626	t1_cb (EV_P_ ev_timer *w, int revents)
		3627	{
		3628	struct my_biggy big = (struct my_biggy *)
		3629	(((char *)w) - offsetof (struct my_biggy, t1));
		3630	}
		3631
		3632	static void
		3633	t2_cb (EV_P_ ev_timer *w, int revents)
		3634	{
		3635	struct my_biggy big = (struct my_biggy *)
		3636	(((char *)w) - offsetof (struct my_biggy, t2));
		3637	}
		3638
		3639	=head2 AVOIDING FINISHING BEFORE RETURNING
		3640
		3641	Often you have structures like this in event-based programs:
		3642
		3643	callback ()
		3644	{
		3645	free (request);
		3646	}
		3647
		3648	request = start_new_request (..., callback);
		3649
		3650	The intent is to start some "lengthy" operation. The C<request> could be
		3651	used to cancel the operation, or do other things with it.
		3652
		3653	It's not uncommon to have code paths in C<start_new_request> that
		3654	immediately invoke the callback, for example, to report errors. Or you add
		3655	some caching layer that finds that it can skip the lengthy aspects of the
		3656	operation and simply invoke the callback with the result.
		3657
		3658	The problem here is that this will happen I<before> C<start_new_request>
		3659	has returned, so C<request> is not set.
		3660
		3661	Even if you pass the request by some safer means to the callback, you
		3662	might want to do something to the request after starting it, such as
		3663	canceling it, which probably isn't working so well when the callback has
		3664	already been invoked.
		3665
		3666	A common way around all these issues is to make sure that
		3667	C<start_new_request> I<always> returns before the callback is invoked. If
		3668	C<start_new_request> immediately knows the result, it can artificially
		3669	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3670	example, or more sneakily, by reusing an existing (stopped) watcher and
		3671	pushing it into the pending queue:
		3672
		3673	ev_set_cb (watcher, callback);
		3674	ev_feed_event (EV_A_ watcher, 0);
		3675
		3676	This way, C<start_new_request> can safely return before the callback is
		3677	invoked, while not delaying callback invocation too much.
		3678
		3679	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3680
		3681	Often (especially in GUI toolkits) there are places where you have
		3682	I<modal> interaction, which is most easily implemented by recursively
		3683	invoking C<ev_run>.
		3684
		3685	This brings the problem of exiting - a callback might want to finish the
		3686	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3687	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3688	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3689	other combination: In these cases, a simple C<ev_break> will not work.
		3690
		3691	The solution is to maintain "break this loop" variable for each C<ev_run>
		3692	invocation, and use a loop around C<ev_run> until the condition is
		3693	triggered, using C<EVRUN_ONCE>:
		3694
		3695	// main loop
		3696	int exit_main_loop = 0;
		3697
		3698	while (!exit_main_loop)
		3699	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3700
		3701	// in a modal watcher
		3702	int exit_nested_loop = 0;
		3703
		3704	while (!exit_nested_loop)
		3705	ev_run (EV_A_ EVRUN_ONCE);
		3706
		3707	To exit from any of these loops, just set the corresponding exit variable:
		3708
		3709	// exit modal loop
		3710	exit_nested_loop = 1;
		3711
		3712	// exit main program, after modal loop is finished
		3713	exit_main_loop = 1;
		3714
		3715	// exit both
		3716	exit_main_loop = exit_nested_loop = 1;
		3717
		3718	=head2 THREAD LOCKING EXAMPLE
		3719
		3720	Here is a fictitious example of how to run an event loop in a different
		3721	thread from where callbacks are being invoked and watchers are
		3722	created/added/removed.
		3723
		3724	For a real-world example, see the C<EV::Loop::Async> perl module,
		3725	which uses exactly this technique (which is suited for many high-level
		3726	languages).
		3727
		3728	The example uses a pthread mutex to protect the loop data, a condition
		3729	variable to wait for callback invocations, an async watcher to notify the
		3730	event loop thread and an unspecified mechanism to wake up the main thread.
		3731
		3732	First, you need to associate some data with the event loop:
		3733
		3734	typedef struct {
		3735	mutex_t lock; /* global loop lock */
		3736	ev_async async_w;
		3737	thread_t tid;
		3738	cond_t invoke_cv;
		3739	} userdata;
		3740
		3741	void prepare_loop (EV_P)
		3742	{
		3743	// for simplicity, we use a static userdata struct.
		3744	static userdata u;
		3745
		3746	ev_async_init (&u->async_w, async_cb);
		3747	ev_async_start (EV_A_ &u->async_w);
		3748
		3749	pthread_mutex_init (&u->lock, 0);
		3750	pthread_cond_init (&u->invoke_cv, 0);
		3751
		3752	// now associate this with the loop
		3753	ev_set_userdata (EV_A_ u);
		3754	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3755	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3756
		3757	// then create the thread running ev_run
		3758	pthread_create (&u->tid, 0, l_run, EV_A);
		3759	}
		3760
		3761	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3762	solely to wake up the event loop so it takes notice of any new watchers
		3763	that might have been added:
		3764
		3765	static void
		3766	async_cb (EV_P_ ev_async *w, int revents)
		3767	{
		3768	// just used for the side effects
		3769	}
		3770
		3771	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3772	protecting the loop data, respectively.
		3773
		3774	static void
		3775	l_release (EV_P)
		3776	{
		3777	userdata *u = ev_userdata (EV_A);
		3778	pthread_mutex_unlock (&u->lock);
		3779	}
		3780
		3781	static void
		3782	l_acquire (EV_P)
		3783	{
		3784	userdata *u = ev_userdata (EV_A);
		3785	pthread_mutex_lock (&u->lock);
		3786	}
		3787
		3788	The event loop thread first acquires the mutex, and then jumps straight
		3789	into C<ev_run>:
		3790
		3791	void *
		3792	l_run (void *thr_arg)
		3793	{
		3794	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3795
		3796	l_acquire (EV_A);
		3797	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3798	ev_run (EV_A_ 0);
		3799	l_release (EV_A);
		3800
		3801	return 0;
		3802	}
		3803
		3804	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3805	signal the main thread via some unspecified mechanism (signals? pipe
		3806	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3807	have been called (in a while loop because a) spurious wakeups are possible
		3808	and b) skipping inter-thread-communication when there are no pending
		3809	watchers is very beneficial):
		3810
		3811	static void
		3812	l_invoke (EV_P)
		3813	{
		3814	userdata *u = ev_userdata (EV_A);
		3815
		3816	while (ev_pending_count (EV_A))
		3817	{
		3818	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3819	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3820	}
		3821	}
		3822
		3823	Now, whenever the main thread gets told to invoke pending watchers, it
		3824	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3825	thread to continue:
		3826
		3827	static void
		3828	real_invoke_pending (EV_P)
		3829	{
		3830	userdata *u = ev_userdata (EV_A);
		3831
		3832	pthread_mutex_lock (&u->lock);
		3833	ev_invoke_pending (EV_A);
		3834	pthread_cond_signal (&u->invoke_cv);
		3835	pthread_mutex_unlock (&u->lock);
		3836	}
		3837
		3838	Whenever you want to start/stop a watcher or do other modifications to an
		3839	event loop, you will now have to lock:
		3840
		3841	ev_timer timeout_watcher;
		3842	userdata *u = ev_userdata (EV_A);
		3843
		3844	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3845
		3846	pthread_mutex_lock (&u->lock);
		3847	ev_timer_start (EV_A_ &timeout_watcher);
		3848	ev_async_send (EV_A_ &u->async_w);
		3849	pthread_mutex_unlock (&u->lock);
		3850
		3851	Note that sending the C<ev_async> watcher is required because otherwise
		3852	an event loop currently blocking in the kernel will have no knowledge
		3853	about the newly added timer. By waking up the loop it will pick up any new
		3854	watchers in the next event loop iteration.
		3855
		3856	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3857
		3858	While the overhead of a callback that e.g. schedules a thread is small, it
		3859	is still an overhead. If you embed libev, and your main usage is with some
		3860	kind of threads or coroutines, you might want to customise libev so that
		3861	doesn't need callbacks anymore.
		3862
		3863	Imagine you have coroutines that you can switch to using a function
		3864	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3865	and that due to some magic, the currently active coroutine is stored in a
		3866	global called C<current_coro>. Then you can build your own "wait for libev
		3867	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3868	the differing C<;> conventions):
		3869
		3870	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3871	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3872
		3873	That means instead of having a C callback function, you store the
		3874	coroutine to switch to in each watcher, and instead of having libev call
		3875	your callback, you instead have it switch to that coroutine.
		3876
		3877	A coroutine might now wait for an event with a function called
		3878	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3879	matter when, or whether the watcher is active or not when this function is
		3880	called):
		3881
		3882	void
		3883	wait_for_event (ev_watcher *w)
		3884	{
		3885	ev_set_cb (w, current_coro);
		3886	switch_to (libev_coro);
		3887	}
		3888
		3889	That basically suspends the coroutine inside C<wait_for_event> and
		3890	continues the libev coroutine, which, when appropriate, switches back to
		3891	this or any other coroutine.
		3892
		3893	You can do similar tricks if you have, say, threads with an event queue -
		3894	instead of storing a coroutine, you store the queue object and instead of
		3895	switching to a coroutine, you push the watcher onto the queue and notify
		3896	any waiters.
		3897
		3898	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		3899	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3900
		3901	// my_ev.h
		3902	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3903	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);
		3904	#include "../libev/ev.h"
		3905
		3906	// my_ev.c
		3907	#define EV_H "my_ev.h"
		3908	#include "../libev/ev.c"
		3909
		3910	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3911	F<my_ev.c> into your project. When properly specifying include paths, you
		3912	can even use F<ev.h> as header file name directly.
3302		3913
3303		3914
3304	=head1 LIBEVENT EMULATION	3915	=head1 LIBEVENT EMULATION
3305		3916
3306	Libev offers a compatibility emulation layer for libevent. It cannot	3917	Libev offers a compatibility emulation layer for libevent. It cannot
3307	emulate the internals of libevent, so here are some usage hints:	3918	emulate the internals of libevent, so here are some usage hints:
3308		3919
3309	=over 4	3920	=over 4
		3921
		3922	=item * Only the libevent-1.4.1-beta API is being emulated.
		3923
		3924	This was the newest libevent version available when libev was implemented,
		3925	and is still mostly unchanged in 2010.
3310		3926
3311	=item * Use it by including <event.h>, as usual.	3927	=item * Use it by including <event.h>, as usual.
3312		3928
3313	=item * The following members are fully supported: ev_base, ev_callback,	3929	=item * The following members are fully supported: ev_base, ev_callback,
3314	ev_arg, ev_fd, ev_res, ev_events.	3930	ev_arg, ev_fd, ev_res, ev_events.
…		…
3320	=item * Priorities are not currently supported. Initialising priorities	3936	=item * Priorities are not currently supported. Initialising priorities
3321	will fail and all watchers will have the same priority, even though there	3937	will fail and all watchers will have the same priority, even though there
3322	is an ev_pri field.	3938	is an ev_pri field.
3323		3939
3324	=item * In libevent, the last base created gets the signals, in libev, the	3940	=item * In libevent, the last base created gets the signals, in libev, the
3325	first base created (== the default loop) gets the signals.	3941	base that registered the signal gets the signals.
3326		3942
3327	=item * Other members are not supported.	3943	=item * Other members are not supported.
3328		3944
3329	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3945	=item * The libev emulation is I<not> ABI compatible to libevent, you need
3330	to use the libev header file and library.	3946	to use the libev header file and library.
3331		3947
3332	=back	3948	=back
3333		3949
3334	=head1 C++ SUPPORT	3950	=head1 C++ SUPPORT
		3951
		3952	=head2 C API
		3953
		3954	The normal C API should work fine when used from C++: both ev.h and the
		3955	libev sources can be compiled as C++. Therefore, code that uses the C API
		3956	will work fine.
		3957
		3958	Proper exception specifications might have to be added to callbacks passed
		3959	to libev: exceptions may be thrown only from watcher callbacks, all
		3960	other callbacks (allocator, syserr, loop acquire/release and periodic
		3961	reschedule callbacks) must not throw exceptions, and might need a C<throw
		3962	()> specification. If you have code that needs to be compiled as both C
		3963	and C++ you can use the C<EV_THROW> macro for this:
		3964
		3965	static void
		3966	fatal_error (const char *msg) EV_THROW
		3967	{
		3968	perror (msg);
		3969	abort ();
		3970	}
		3971
		3972	...
		3973	ev_set_syserr_cb (fatal_error);
		3974
		3975	The only API functions that can currently throw exceptions are C<ev_run>,
		3976	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		3977	because it runs cleanup watchers).
		3978
		3979	Throwing exceptions in watcher callbacks is only supported if libev itself
		3980	is compiled with a C++ compiler or your C and C++ environments allow
		3981	throwing exceptions through C libraries (most do).
		3982
		3983	=head2 C++ API
3335		3984
3336	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3985	Libev comes with some simplistic wrapper classes for C++ that mainly allow
3337	you to use some convenience methods to start/stop watchers and also change	3986	you to use some convenience methods to start/stop watchers and also change
3338	the callback model to a model using method callbacks on objects.	3987	the callback model to a model using method callbacks on objects.
3339		3988
3340	To use it,	3989	To use it,
3341		3990
3342	#include <ev++.h>	3991	#include <ev++.h>
3343		3992
3344	This automatically includes F<ev.h> and puts all of its definitions (many	3993	This automatically includes F<ev.h> and puts all of its definitions (many
3345	of them macros) into the global namespace. All C++ specific things are	3994	of them macros) into the global namespace. All C++ specific things are
3346	put into the C<ev> namespace. It should support all the same embedding	3995	put into the C<ev> namespace. It should support all the same embedding
…		…
3349	Care has been taken to keep the overhead low. The only data member the C++	3998	Care has been taken to keep the overhead low. The only data member the C++
3350	classes add (compared to plain C-style watchers) is the event loop pointer	3999	classes add (compared to plain C-style watchers) is the event loop pointer
3351	that the watcher is associated with (or no additional members at all if	4000	that the watcher is associated with (or no additional members at all if
3352	you disable C<EV_MULTIPLICITY> when embedding libev).	4001	you disable C<EV_MULTIPLICITY> when embedding libev).
3353		4002
3354	Currently, functions, and static and non-static member functions can be	4003	Currently, functions, static and non-static member functions and classes
3355	used as callbacks. Other types should be easy to add as long as they only	4004	with C<operator ()> can be used as callbacks. Other types should be easy
3356	need one additional pointer for context. If you need support for other	4005	to add as long as they only need one additional pointer for context. If
3357	types of functors please contact the author (preferably after implementing	4006	you need support for other types of functors please contact the author
3358	it).	4007	(preferably after implementing it).
		4008
		4009	For all this to work, your C++ compiler either has to use the same calling
		4010	conventions as your C compiler (for static member functions), or you have
		4011	to embed libev and compile libev itself as C++.
3359		4012
3360	Here is a list of things available in the C<ev> namespace:	4013	Here is a list of things available in the C<ev> namespace:
3361		4014
3362	=over 4	4015	=over 4
3363		4016
…		…
3373	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	4026	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
3374		4027
3375	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4028	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
3376	the same name in the C<ev> namespace, with the exception of C<ev_signal>	4029	the same name in the C<ev> namespace, with the exception of C<ev_signal>
3377	which is called C<ev::sig> to avoid clashes with the C<signal> macro	4030	which is called C<ev::sig> to avoid clashes with the C<signal> macro
3378	defines by many implementations.	4031	defined by many implementations.
3379		4032
3380	All of those classes have these methods:	4033	All of those classes have these methods:
3381		4034
3382	=over 4	4035	=over 4
3383		4036
…		…
3445	void operator() (ev::io &w, int revents)	4098	void operator() (ev::io &w, int revents)
3446	{	4099	{
3447	...	4100	...
3448	}	4101	}
3449	}	4102	}
3450		4103
3451	myfunctor f;	4104	myfunctor f;
3452		4105
3453	ev::io w;	4106	ev::io w;
3454	w.set (&f);	4107	w.set (&f);
3455		4108
…		…
3473	Associates a different C<struct ev_loop> with this watcher. You can only	4126	Associates a different C<struct ev_loop> with this watcher. You can only
3474	do this when the watcher is inactive (and not pending either).	4127	do this when the watcher is inactive (and not pending either).
3475		4128
3476	=item w->set ([arguments])	4129	=item w->set ([arguments])
3477		4130
3478	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this	4131	Basically the same as C<ev_TYPE_set> (except for C<ev::embed> watchers>),
3479	method or a suitable start method must be called at least once. Unlike the	4132	with the same arguments. Either this method or a suitable start method
3480	C counterpart, an active watcher gets automatically stopped and restarted	4133	must be called at least once. Unlike the C counterpart, an active watcher
3481	when reconfiguring it with this method.	4134	gets automatically stopped and restarted when reconfiguring it with this
		4135	method.
		4136
		4137	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4138	clashing with the C<set (loop)> method.
3482		4139
3483	=item w->start ()	4140	=item w->start ()
3484		4141
3485	Starts the watcher. Note that there is no C<loop> argument, as the	4142	Starts the watcher. Note that there is no C<loop> argument, as the
3486	constructor already stores the event loop.	4143	constructor already stores the event loop.
…		…
3516	watchers in the constructor.	4173	watchers in the constructor.
3517		4174
3518	class myclass	4175	class myclass
3519	{	4176	{
3520	ev::io io ; void io_cb (ev::io &w, int revents);	4177	ev::io io ; void io_cb (ev::io &w, int revents);
3521	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);	4178	ev::io io2 ; void io2_cb (ev::io &w, int revents);
3522	ev::idle idle; void idle_cb (ev::idle &w, int revents);	4179	ev::idle idle; void idle_cb (ev::idle &w, int revents);
3523		4180
3524	myclass (int fd)	4181	myclass (int fd)
3525	{	4182	{
3526	io .set <myclass, &myclass::io_cb > (this);	4183	io .set <myclass, &myclass::io_cb > (this);
…		…
3577	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.	4234	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
3578		4235
3579	=item D	4236	=item D
3580		4237
3581	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4238	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
3582	be found at L<http://proj.llucax.com.ar/wiki/evd>.	4239	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
3583		4240
3584	=item Ocaml	4241	=item Ocaml
3585		4242
3586	Erkki Seppala has written Ocaml bindings for libev, to be found at	4243	Erkki Seppala has written Ocaml bindings for libev, to be found at
3587	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	4244	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
…		…
3590		4247
3591	Brian Maher has written a partial interface to libev for lua (at the	4248	Brian Maher has written a partial interface to libev for lua (at the
3592	time of this writing, only C<ev_io> and C<ev_timer>), to be found at	4249	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
3593	L<http://github.com/brimworks/lua-ev>.	4250	L<http://github.com/brimworks/lua-ev>.
3594		4251
		4252	=item Javascript
		4253
		4254	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4255
		4256	=item Others
		4257
		4258	There are others, and I stopped counting.
		4259
3595	=back	4260	=back
3596		4261
3597		4262
3598	=head1 MACRO MAGIC	4263	=head1 MACRO MAGIC
3599		4264
…		…
3635	suitable for use with C<EV_A>.	4300	suitable for use with C<EV_A>.
3636		4301
3637	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4302	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
3638		4303
3639	Similar to the other two macros, this gives you the value of the default	4304	Similar to the other two macros, this gives you the value of the default
3640	loop, if multiple loops are supported ("ev loop default").	4305	loop, if multiple loops are supported ("ev loop default"). The default loop
		4306	will be initialised if it isn't already initialised.
		4307
		4308	For non-multiplicity builds, these macros do nothing, so you always have
		4309	to initialise the loop somewhere.
3641		4310
3642	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4311	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
3643		4312
3644	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4313	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
3645	default loop has been initialised (C<UC> == unchecked). Their behaviour	4314	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
3790	supported). It will also not define any of the structs usually found in	4459	supported). It will also not define any of the structs usually found in
3791	F<event.h> that are not directly supported by the libev core alone.	4460	F<event.h> that are not directly supported by the libev core alone.
3792		4461
3793	In standalone mode, libev will still try to automatically deduce the	4462	In standalone mode, libev will still try to automatically deduce the
3794	configuration, but has to be more conservative.	4463	configuration, but has to be more conservative.
		4464
		4465	=item EV_USE_FLOOR
		4466
		4467	If defined to be C<1>, libev will use the C<floor ()> function for its
		4468	periodic reschedule calculations, otherwise libev will fall back on a
		4469	portable (slower) implementation. If you enable this, you usually have to
		4470	link against libm or something equivalent. Enabling this when the C<floor>
		4471	function is not available will fail, so the safe default is to not enable
		4472	this.
3795		4473
3796	=item EV_USE_MONOTONIC	4474	=item EV_USE_MONOTONIC
3797		4475
3798	If defined to be C<1>, libev will try to detect the availability of the	4476	If defined to be C<1>, libev will try to detect the availability of the
3799	monotonic clock option at both compile time and runtime. Otherwise no	4477	monotonic clock option at both compile time and runtime. Otherwise no
…		…
3884		4562
3885	If programs implement their own fd to handle mapping on win32, then this	4563	If programs implement their own fd to handle mapping on win32, then this
3886	macro can be used to override the C<close> function, useful to unregister	4564	macro can be used to override the C<close> function, useful to unregister
3887	file descriptors again. Note that the replacement function has to close	4565	file descriptors again. Note that the replacement function has to close
3888	the underlying OS handle.	4566	the underlying OS handle.
		4567
		4568	=item EV_USE_WSASOCKET
		4569
		4570	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4571	communication socket, which works better in some environments. Otherwise,
		4572	the normal C<socket> function will be used, which works better in other
		4573	environments.
3889		4574
3890	=item EV_USE_POLL	4575	=item EV_USE_POLL
3891		4576
3892	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4577	If defined to be C<1>, libev will compile in support for the C<poll>(2)
3893	backend. Otherwise it will be enabled on non-win32 platforms. It	4578	backend. Otherwise it will be enabled on non-win32 platforms. It
…		…
3929	If defined to be C<1>, libev will compile in support for the Linux inotify	4614	If defined to be C<1>, libev will compile in support for the Linux inotify
3930	interface to speed up C<ev_stat> watchers. Its actual availability will	4615	interface to speed up C<ev_stat> watchers. Its actual availability will
3931	be detected at runtime. If undefined, it will be enabled if the headers	4616	be detected at runtime. If undefined, it will be enabled if the headers
3932	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4617	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
3933		4618
		4619	=item EV_NO_SMP
		4620
		4621	If defined to be C<1>, libev will assume that memory is always coherent
		4622	between threads, that is, threads can be used, but threads never run on
		4623	different cpus (or different cpu cores). This reduces dependencies
		4624	and makes libev faster.
		4625
		4626	=item EV_NO_THREADS
		4627
		4628	If defined to be C<1>, libev will assume that it will never be called from
		4629	different threads (that includes signal handlers), which is a stronger
		4630	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4631	libev faster.
		4632
3934	=item EV_ATOMIC_T	4633	=item EV_ATOMIC_T
3935		4634
3936	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4635	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
3937	access is atomic with respect to other threads or signal contexts. No such	4636	access is atomic with respect to other threads or signal contexts. No
3938	type is easily found in the C language, so you can provide your own type	4637	such type is easily found in the C language, so you can provide your own
3939	that you know is safe for your purposes. It is used both for signal handler "locking"	4638	type that you know is safe for your purposes. It is used both for signal
3940	as well as for signal and thread safety in C<ev_async> watchers.	4639	handler "locking" as well as for signal and thread safety in C<ev_async>
		4640	watchers.
3941		4641
3942	In the absence of this define, libev will use C<sig_atomic_t volatile>	4642	In the absence of this define, libev will use C<sig_atomic_t volatile>
3943	(from F<signal.h>), which is usually good enough on most platforms.	4643	(from F<signal.h>), which is usually good enough on most platforms.
3944		4644
3945	=item EV_H (h)	4645	=item EV_H (h)
…		…
3972	will have the C<struct ev_loop *> as first argument, and you can create	4672	will have the C<struct ev_loop *> as first argument, and you can create
3973	additional independent event loops. Otherwise there will be no support	4673	additional independent event loops. Otherwise there will be no support
3974	for multiple event loops and there is no first event loop pointer	4674	for multiple event loops and there is no first event loop pointer
3975	argument. Instead, all functions act on the single default loop.	4675	argument. Instead, all functions act on the single default loop.
3976		4676
		4677	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4678	default loop when multiplicity is switched off - you always have to
		4679	initialise the loop manually in this case.
		4680
3977	=item EV_MINPRI	4681	=item EV_MINPRI
3978		4682
3979	=item EV_MAXPRI	4683	=item EV_MAXPRI
3980		4684
3981	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4685	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
4017	#define EV_USE_POLL 1	4721	#define EV_USE_POLL 1
4018	#define EV_CHILD_ENABLE 1	4722	#define EV_CHILD_ENABLE 1
4019	#define EV_ASYNC_ENABLE 1	4723	#define EV_ASYNC_ENABLE 1
4020		4724
4021	The actual value is a bitset, it can be a combination of the following	4725	The actual value is a bitset, it can be a combination of the following
4022	values:	4726	values (by default, all of these are enabled):
4023		4727
4024	=over 4	4728	=over 4
4025		4729
4026	=item C<1> - faster/larger code	4730	=item C<1> - faster/larger code
4027		4731
…		…
4031	code size by roughly 30% on amd64).	4735	code size by roughly 30% on amd64).
4032		4736
4033	When optimising for size, use of compiler flags such as C<-Os> with	4737	When optimising for size, use of compiler flags such as C<-Os> with
4034	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of	4738	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
4035	assertions.	4739	assertions.
		4740
		4741	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4742	(e.g. gcc with C<-Os>).
4036		4743
4037	=item C<2> - faster/larger data structures	4744	=item C<2> - faster/larger data structures
4038		4745
4039	Replaces the small 2-heap for timer management by a faster 4-heap, larger	4746	Replaces the small 2-heap for timer management by a faster 4-heap, larger
4040	hash table sizes and so on. This will usually further increase code size	4747	hash table sizes and so on. This will usually further increase code size
4041	and can additionally have an effect on the size of data structures at	4748	and can additionally have an effect on the size of data structures at
4042	runtime.	4749	runtime.
4043		4750
		4751	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4752	(e.g. gcc with C<-Os>).
		4753
4044	=item C<4> - full API configuration	4754	=item C<4> - full API configuration
4045		4755
4046	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and	4756	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
4047	enables multiplicity (C<EV_MULTIPLICITY>=1).	4757	enables multiplicity (C<EV_MULTIPLICITY>=1).
4048		4758
…		…
4078		4788
4079	With an intelligent-enough linker (gcc+binutils are intelligent enough	4789	With an intelligent-enough linker (gcc+binutils are intelligent enough
4080	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by	4790	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
4081	your program might be left out as well - a binary starting a timer and an	4791	your program might be left out as well - a binary starting a timer and an
4082	I/O watcher then might come out at only 5Kb.	4792	I/O watcher then might come out at only 5Kb.
		4793
		4794	=item EV_API_STATIC
		4795
		4796	If this symbol is defined (by default it is not), then all identifiers
		4797	will have static linkage. This means that libev will not export any
		4798	identifiers, and you cannot link against libev anymore. This can be useful
		4799	when you embed libev, only want to use libev functions in a single file,
		4800	and do not want its identifiers to be visible.
		4801
		4802	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4803	wants to use libev.
		4804
		4805	This option only works when libev is compiled with a C compiler, as C++
		4806	doesn't support the required declaration syntax.
4083		4807
4084	=item EV_AVOID_STDIO	4808	=item EV_AVOID_STDIO
4085		4809
4086	If this is set to C<1> at compiletime, then libev will avoid using stdio	4810	If this is set to C<1> at compiletime, then libev will avoid using stdio
4087	functions (printf, scanf, perror etc.). This will increase the code size	4811	functions (printf, scanf, perror etc.). This will increase the code size
…		…
4231	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4955	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4232		4956
4233	#include "ev_cpp.h"	4957	#include "ev_cpp.h"
4234	#include "ev.c"	4958	#include "ev.c"
4235		4959
4236	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	4960	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4237		4961
4238	=head2 THREADS AND COROUTINES	4962	=head2 THREADS AND COROUTINES
4239		4963
4240	=head3 THREADS	4964	=head3 THREADS
4241		4965
…		…
4292	default loop and triggering an C<ev_async> watcher from the default loop	5016	default loop and triggering an C<ev_async> watcher from the default loop
4293	watcher callback into the event loop interested in the signal.	5017	watcher callback into the event loop interested in the signal.
4294		5018
4295	=back	5019	=back
4296		5020
4297	=head4 THREAD LOCKING EXAMPLE	5021	See also L</THREAD LOCKING EXAMPLE>.
4298
4299	Here is a fictitious example of how to run an event loop in a different
4300	thread than where callbacks are being invoked and watchers are
4301	created/added/removed.
4302
4303	For a real-world example, see the C<EV::Loop::Async> perl module,
4304	which uses exactly this technique (which is suited for many high-level
4305	languages).
4306
4307	The example uses a pthread mutex to protect the loop data, a condition
4308	variable to wait for callback invocations, an async watcher to notify the
4309	event loop thread and an unspecified mechanism to wake up the main thread.
4310
4311	First, you need to associate some data with the event loop:
4312
4313	typedef struct {
4314	mutex_t lock; /* global loop lock */
4315	ev_async async_w;
4316	thread_t tid;
4317	cond_t invoke_cv;
4318	} userdata;
4319
4320	void prepare_loop (EV_P)
4321	{
4322	// for simplicity, we use a static userdata struct.
4323	static userdata u;
4324
4325	ev_async_init (&u->async_w, async_cb);
4326	ev_async_start (EV_A_ &u->async_w);
4327
4328	pthread_mutex_init (&u->lock, 0);
4329	pthread_cond_init (&u->invoke_cv, 0);
4330
4331	// now associate this with the loop
4332	ev_set_userdata (EV_A_ u);
4333	ev_set_invoke_pending_cb (EV_A_ l_invoke);
4334	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4335
4336	// then create the thread running ev_loop
4337	pthread_create (&u->tid, 0, l_run, EV_A);
4338	}
4339
4340	The callback for the C<ev_async> watcher does nothing: the watcher is used
4341	solely to wake up the event loop so it takes notice of any new watchers
4342	that might have been added:
4343
4344	static void
4345	async_cb (EV_P_ ev_async *w, int revents)
4346	{
4347	// just used for the side effects
4348	}
4349
4350	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
4351	protecting the loop data, respectively.
4352
4353	static void
4354	l_release (EV_P)
4355	{
4356	userdata *u = ev_userdata (EV_A);
4357	pthread_mutex_unlock (&u->lock);
4358	}
4359
4360	static void
4361	l_acquire (EV_P)
4362	{
4363	userdata *u = ev_userdata (EV_A);
4364	pthread_mutex_lock (&u->lock);
4365	}
4366
4367	The event loop thread first acquires the mutex, and then jumps straight
4368	into C<ev_run>:
4369
4370	void *
4371	l_run (void *thr_arg)
4372	{
4373	struct ev_loop *loop = (struct ev_loop *)thr_arg;
4374
4375	l_acquire (EV_A);
4376	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4377	ev_run (EV_A_ 0);
4378	l_release (EV_A);
4379
4380	return 0;
4381	}
4382
4383	Instead of invoking all pending watchers, the C<l_invoke> callback will
4384	signal the main thread via some unspecified mechanism (signals? pipe
4385	writes? C<Async::Interrupt>?) and then waits until all pending watchers
4386	have been called (in a while loop because a) spurious wakeups are possible
4387	and b) skipping inter-thread-communication when there are no pending
4388	watchers is very beneficial):
4389
4390	static void
4391	l_invoke (EV_P)
4392	{
4393	userdata *u = ev_userdata (EV_A);
4394
4395	while (ev_pending_count (EV_A))
4396	{
4397	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4398	pthread_cond_wait (&u->invoke_cv, &u->lock);
4399	}
4400	}
4401
4402	Now, whenever the main thread gets told to invoke pending watchers, it
4403	will grab the lock, call C<ev_invoke_pending> and then signal the loop
4404	thread to continue:
4405
4406	static void
4407	real_invoke_pending (EV_P)
4408	{
4409	userdata *u = ev_userdata (EV_A);
4410
4411	pthread_mutex_lock (&u->lock);
4412	ev_invoke_pending (EV_A);
4413	pthread_cond_signal (&u->invoke_cv);
4414	pthread_mutex_unlock (&u->lock);
4415	}
4416
4417	Whenever you want to start/stop a watcher or do other modifications to an
4418	event loop, you will now have to lock:
4419
4420	ev_timer timeout_watcher;
4421	userdata *u = ev_userdata (EV_A);
4422
4423	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4424
4425	pthread_mutex_lock (&u->lock);
4426	ev_timer_start (EV_A_ &timeout_watcher);
4427	ev_async_send (EV_A_ &u->async_w);
4428	pthread_mutex_unlock (&u->lock);
4429
4430	Note that sending the C<ev_async> watcher is required because otherwise
4431	an event loop currently blocking in the kernel will have no knowledge
4432	about the newly added timer. By waking up the loop it will pick up any new
4433	watchers in the next event loop iteration.
4434		5022
4435	=head3 COROUTINES	5023	=head3 COROUTINES
4436		5024
4437	Libev is very accommodating to coroutines ("cooperative threads"):	5025	Libev is very accommodating to coroutines ("cooperative threads"):
4438	libev fully supports nesting calls to its functions from different	5026	libev fully supports nesting calls to its functions from different
…		…
4603	requires, and its I/O model is fundamentally incompatible with the POSIX	5191	requires, and its I/O model is fundamentally incompatible with the POSIX
4604	model. Libev still offers limited functionality on this platform in	5192	model. Libev still offers limited functionality on this platform in
4605	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5193	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
4606	descriptors. This only applies when using Win32 natively, not when using	5194	descriptors. This only applies when using Win32 natively, not when using
4607	e.g. cygwin. Actually, it only applies to the microsofts own compilers,	5195	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4608	as every compielr comes with a slightly differently broken/incompatible	5196	as every compiler comes with a slightly differently broken/incompatible
4609	environment.	5197	environment.
4610		5198
4611	Lifting these limitations would basically require the full	5199	Lifting these limitations would basically require the full
4612	re-implementation of the I/O system. If you are into this kind of thing,	5200	re-implementation of the I/O system. If you are into this kind of thing,
4613	then note that glib does exactly that for you in a very portable way (note	5201	then note that glib does exactly that for you in a very portable way (note
…		…
4707	structure (guaranteed by POSIX but not by ISO C for example), but it also	5295	structure (guaranteed by POSIX but not by ISO C for example), but it also
4708	assumes that the same (machine) code can be used to call any watcher	5296	assumes that the same (machine) code can be used to call any watcher
4709	callback: The watcher callbacks have different type signatures, but libev	5297	callback: The watcher callbacks have different type signatures, but libev
4710	calls them using an C<ev_watcher *> internally.	5298	calls them using an C<ev_watcher *> internally.
4711		5299
		5300	=item pointer accesses must be thread-atomic
		5301
		5302	Accessing a pointer value must be atomic, it must both be readable and
		5303	writable in one piece - this is the case on all current architectures.
		5304
4712	=item C<sig_atomic_t volatile> must be thread-atomic as well	5305	=item C<sig_atomic_t volatile> must be thread-atomic as well
4713		5306
4714	The type C<sig_atomic_t volatile> (or whatever is defined as	5307	The type C<sig_atomic_t volatile> (or whatever is defined as
4715	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different	5308	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
4716	threads. This is not part of the specification for C<sig_atomic_t>, but is	5309	threads. This is not part of the specification for C<sig_atomic_t>, but is
…		…
4724	thread" or will block signals process-wide, both behaviours would	5317	thread" or will block signals process-wide, both behaviours would
4725	be compatible with libev. Interaction between C<sigprocmask> and	5318	be compatible with libev. Interaction between C<sigprocmask> and
4726	C<pthread_sigmask> could complicate things, however.	5319	C<pthread_sigmask> could complicate things, however.
4727		5320
4728	The most portable way to handle signals is to block signals in all threads	5321	The most portable way to handle signals is to block signals in all threads
4729	except the initial one, and run the default loop in the initial thread as	5322	except the initial one, and run the signal handling loop in the initial
4730	well.	5323	thread as well.
4731		5324
4732	=item C<long> must be large enough for common memory allocation sizes	5325	=item C<long> must be large enough for common memory allocation sizes
4733		5326
4734	To improve portability and simplify its API, libev uses C<long> internally	5327	To improve portability and simplify its API, libev uses C<long> internally
4735	instead of C<size_t> when allocating its data structures. On non-POSIX	5328	instead of C<size_t> when allocating its data structures. On non-POSIX
…		…
4741		5334
4742	The type C<double> is used to represent timestamps. It is required to	5335	The type C<double> is used to represent timestamps. It is required to
4743	have at least 51 bits of mantissa (and 9 bits of exponent), which is	5336	have at least 51 bits of mantissa (and 9 bits of exponent), which is
4744	good enough for at least into the year 4000 with millisecond accuracy	5337	good enough for at least into the year 4000 with millisecond accuracy
4745	(the design goal for libev). This requirement is overfulfilled by	5338	(the design goal for libev). This requirement is overfulfilled by
4746	implementations using IEEE 754, which is basically all existing ones. With	5339	implementations using IEEE 754, which is basically all existing ones.
		5340
4747	IEEE 754 doubles, you get microsecond accuracy until at least 2200.	5341	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5342	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5343	is either obsolete or somebody patched it to use C<long double> or
		5344	something like that, just kidding).
4748		5345
4749	=back	5346	=back
4750		5347
4751	If you know of other additional requirements drop me a note.	5348	If you know of other additional requirements drop me a note.
4752		5349
…		…
4814	=item Processing ev_async_send: O(number_of_async_watchers)	5411	=item Processing ev_async_send: O(number_of_async_watchers)
4815		5412
4816	=item Processing signals: O(max_signal_number)	5413	=item Processing signals: O(max_signal_number)
4817		5414
4818	Sending involves a system call I<iff> there were no other C<ev_async_send>	5415	Sending involves a system call I<iff> there were no other C<ev_async_send>
4819	calls in the current loop iteration. Checking for async and signal events	5416	calls in the current loop iteration and the loop is currently
		5417	blocked. Checking for async and signal events involves iterating over all
4820	involves iterating over all running async watchers or all signal numbers.	5418	running async watchers or all signal numbers.
4821		5419
4822	=back	5420	=back
4823		5421
4824		5422
4825	=head1 PORTING FROM LIBEV 3.X TO 4.X	5423	=head1 PORTING FROM LIBEV 3.X TO 4.X
4826		5424
4827	The major version 4 introduced some minor incompatible changes to the API.	5425	The major version 4 introduced some incompatible changes to the API.
4828		5426
4829	At the moment, the C<ev.h> header file tries to implement superficial	5427	At the moment, the C<ev.h> header file provides compatibility definitions
4830	compatibility, so most programs should still compile. Those might be	5428	for all changes, so most programs should still compile. The compatibility
4831	removed in later versions of libev, so better update early than late.	5429	layer might be removed in later versions of libev, so better update to the
		5430	new API early than late.
4832		5431
4833	=over 4	5432	=over 4
		5433
		5434	=item C<EV_COMPAT3> backwards compatibility mechanism
		5435
		5436	The backward compatibility mechanism can be controlled by
		5437	C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
		5438	section.
		5439
		5440	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5441
		5442	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5443
		5444	ev_loop_destroy (EV_DEFAULT_UC);
		5445	ev_loop_fork (EV_DEFAULT);
4834		5446
4835	=item function/symbol renames	5447	=item function/symbol renames
4836		5448
4837	A number of functions and symbols have been renamed:	5449	A number of functions and symbols have been renamed:
4838		5450
…		…
4857	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme	5469	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
4858	as all other watcher types. Note that C<ev_loop_fork> is still called	5470	as all other watcher types. Note that C<ev_loop_fork> is still called
4859	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>	5471	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
4860	typedef.	5472	typedef.
4861		5473
4862	=item C<EV_COMPAT3> backwards compatibility mechanism
4863
4864	The backward compatibility mechanism can be controlled by
4865	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
4866	section.
4867
4868	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>	5474	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
4869		5475
4870	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different	5476	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
4871	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile	5477	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
4872	and work, but the library code will of course be larger.	5478	and work, but the library code will of course be larger.
…		…
4879	=over 4	5485	=over 4
4880		5486
4881	=item active	5487	=item active
4882		5488
4883	A watcher is active as long as it has been started and not yet stopped.	5489	A watcher is active as long as it has been started and not yet stopped.
4884	See L<WATCHER STATES> for details.	5490	See L</WATCHER STATES> for details.
4885		5491
4886	=item application	5492	=item application
4887		5493
4888	In this document, an application is whatever is using libev.	5494	In this document, an application is whatever is using libev.
4889		5495
…		…
4925	watchers and events.	5531	watchers and events.
4926		5532
4927	=item pending	5533	=item pending
4928		5534
4929	A watcher is pending as soon as the corresponding event has been	5535	A watcher is pending as soon as the corresponding event has been
4930	detected. See L<WATCHER STATES> for details.	5536	detected. See L</WATCHER STATES> for details.
4931		5537
4932	=item real time	5538	=item real time
4933		5539
4934	The physical time that is observed. It is apparently strictly monotonic :)	5540	The physical time that is observed. It is apparently strictly monotonic :)
4935		5541
4936	=item wall-clock time	5542	=item wall-clock time
4937		5543
4938	The time and date as shown on clocks. Unlike real time, it can actually	5544	The time and date as shown on clocks. Unlike real time, it can actually
4939	be wrong and jump forwards and backwards, e.g. when the you adjust your	5545	be wrong and jump forwards and backwards, e.g. when you adjust your
4940	clock.	5546	clock.
4941		5547
4942	=item watcher	5548	=item watcher
4943		5549
4944	A data structure that describes interest in certain events. Watchers need	5550	A data structure that describes interest in certain events. Watchers need
…		…
4946		5552
4947	=back	5553	=back
4948		5554
4949	=head1 AUTHOR	5555	=head1 AUTHOR
4950		5556
4951	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.	5557	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5558	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
4952		5559

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