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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
…		…
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
…		…
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 interesting 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
…		…
249		265
250	You could override this function in high-availability programs to, say,	266	You could override this function in high-availability programs to, say,
251	free some memory if it cannot allocate memory, to use a special allocator,	267	free some memory if it cannot allocate memory, to use a special allocator,
252	or even to sleep a while and retry until some memory is available.	268	or even to sleep a while and retry until some memory is available.
253		269
		270	Example: The following is the C<realloc> function that libev itself uses
		271	which should work with C<realloc> and C<free> functions of all kinds and
		272	is probably a good basis for your own implementation.
		273
		274	static void *
		275	ev_realloc_emul (void *ptr, long size) EV_NOEXCEPT
		276	{
		277	if (size)
		278	return realloc (ptr, size);
		279
		280	free (ptr);
		281	return 0;
		282	}
		283
254	Example: Replace the libev allocator with one that waits a bit and then	284	Example: Replace the libev allocator with one that waits a bit and then
255	retries (example requires a standards-compliant C<realloc>).	285	retries.
256		286
257	static void *	287	static void *
258	persistent_realloc (void *ptr, size_t size)	288	persistent_realloc (void *ptr, size_t size)
259	{	289	{
		290	if (!size)
		291	{
		292	free (ptr);
		293	return 0;
		294	}
		295
260	for (;;)	296	for (;;)
261	{	297	{
262	void *newptr = realloc (ptr, size);	298	void *newptr = realloc (ptr, size);
263		299
264	if (newptr)	300	if (newptr)
…		…
269	}	305	}
270		306
271	...	307	...
272	ev_set_allocator (persistent_realloc);	308	ev_set_allocator (persistent_realloc);
273		309
274	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]	310	=item ev_set_syserr_cb (void (*cb)(const char *msg) throw ())
275		311
276	Set the callback function to call on a retryable system call error (such	312	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	313	as failed select, poll, epoll_wait). The message is a printable string
278	indicating the system call or subsystem causing the problem. If this	314	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	315	callback is set, then libev will expect it to remedy the situation, no
…		…
291	}	327	}
292		328
293	...	329	...
294	ev_set_syserr_cb (fatal_error);	330	ev_set_syserr_cb (fatal_error);
295		331
		332	=item ev_feed_signal (int signum)
		333
		334	This function can be used to "simulate" a signal receive. It is completely
		335	safe to call this function at any time, from any context, including signal
		336	handlers or random threads.
		337
		338	Its main use is to customise signal handling in your process, especially
		339	in the presence of threads. For example, you could block signals
		340	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
		341	creating any loops), and in one thread, use C<sigwait> or any other
		342	mechanism to wait for signals, then "deliver" them to libev by calling
		343	C<ev_feed_signal>.
		344
296	=back	345	=back
297		346
298	=head1 FUNCTIONS CONTROLLING EVENT LOOPS	347	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
299		348
300	An event loop is described by a C<struct ev_loop *> (the C<struct> is	349	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	350	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).	351	libev 3 had an C<ev_loop> function colliding with the struct name).
303		352
304	The library knows two types of such loops, the I<default> loop, which	353	The library knows two types of such loops, the I<default> loop, which
305	supports signals and child events, and dynamically created event loops	354	supports child process events, and dynamically created event loops which
306	which do not.	355	do not.
307		356
308	=over 4	357	=over 4
309		358
310	=item struct ev_loop *ev_default_loop (unsigned int flags)	359	=item struct ev_loop *ev_default_loop (unsigned int flags)
311		360
…		…
342	Example: Restrict libev to the select and poll backends, and do not allow	391	Example: Restrict libev to the select and poll backends, and do not allow
343	environment settings to be taken into account:	392	environment settings to be taken into account:
344		393
345	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	394	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
346		395
347	Example: Use whatever libev has to offer, but make sure that kqueue is
348	used if available (warning, breaks stuff, best use only with your own
349	private event loop and only if you know the OS supports your types of
350	fds):
351
352	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
353
354	=item struct ev_loop *ev_loop_new (unsigned int flags)	396	=item struct ev_loop *ev_loop_new (unsigned int flags)
355		397
356	This will create and initialise a new event loop object. If the loop	398	This will create and initialise a new event loop object. If the loop
357	could not be initialised, returns false.	399	could not be initialised, returns false.
358		400
359	Note that this function I<is> thread-safe, and one common way to use	401	This function is thread-safe, and one common way to use libev with
360	libev with threads is indeed to create one loop per thread, and using the	402	threads is indeed to create one loop per thread, and using the default
361	default loop in the "main" or "initial" thread.	403	loop in the "main" or "initial" thread.
362		404
363	The flags argument can be used to specify special behaviour or specific	405	The flags argument can be used to specify special behaviour or specific
364	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	406	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
365		407
366	The following flags are supported:	408	The following flags are supported:
…		…
376		418
377	If this flag bit is or'ed into the flag value (or the program runs setuid	419	If this flag bit is or'ed into the flag value (or the program runs setuid
378	or setgid) then libev will I<not> look at the environment variable	420	or setgid) then libev will I<not> look at the environment variable
379	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	421	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
380	override the flags completely if it is found in the environment. This is	422	override the flags completely if it is found in the environment. This is
381	useful to try out specific backends to test their performance, or to work	423	useful to try out specific backends to test their performance, to work
382	around bugs.	424	around bugs, or to make libev threadsafe (accessing environment variables
		425	cannot be done in a threadsafe way, but usually it works if no other
		426	thread modifies them).
383		427
384	=item C<EVFLAG_FORKCHECK>	428	=item C<EVFLAG_FORKCHECK>
385		429
386	Instead of calling C<ev_loop_fork> manually after a fork, you can also	430	Instead of calling C<ev_loop_fork> manually after a fork, you can also
387	make libev check for a fork in each iteration by enabling this flag.	431	make libev check for a fork in each iteration by enabling this flag.
388		432
389	This works by calling C<getpid ()> on every iteration of the loop,	433	This works by calling C<getpid ()> on every iteration of the loop,
390	and thus this might slow down your event loop if you do a lot of loop	434	and thus this might slow down your event loop if you do a lot of loop
391	iterations and little real work, but is usually not noticeable (on my	435	iterations and little real work, but is usually not noticeable (on my
392	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence	436	GNU/Linux system for example, C<getpid> is actually a simple 5-insn
393	without a system call and thus I<very> fast, but my GNU/Linux system also has	437	sequence without a system call and thus I<very> fast, but my GNU/Linux
394	C<pthread_atfork> which is even faster).	438	system also has C<pthread_atfork> which is even faster). (Update: glibc
		439	versions 2.25 apparently removed the C<getpid> optimisation again).
395		440
396	The big advantage of this flag is that you can forget about fork (and	441	The big advantage of this flag is that you can forget about fork (and
397	forget about forgetting to tell libev about forking) when you use this	442	forget about forgetting to tell libev about forking, although you still
398	flag.	443	have to ignore C<SIGPIPE>) when you use this flag.
399		444
400	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>	445	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
401	environment variable.	446	environment variable.
402		447
403	=item C<EVFLAG_NOINOTIFY>	448	=item C<EVFLAG_NOINOTIFY>
404		449
405	When this flag is specified, then libev will not attempt to use the	450	When this flag is specified, then libev will not attempt to use the
406	I<inotify> API for it's C<ev_stat> watchers. Apart from debugging and	451	I<inotify> API for its C<ev_stat> watchers. Apart from debugging and
407	testing, this flag can be useful to conserve inotify file descriptors, as	452	testing, this flag can be useful to conserve inotify file descriptors, as
408	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.	453	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
409		454
410	=item C<EVFLAG_SIGNALFD>	455	=item C<EVFLAG_SIGNALFD>
411		456
412	When this flag is specified, then libev will attempt to use the	457	When this flag is specified, then libev will attempt to use the
413	I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This API	458	I<signalfd> API for its C<ev_signal> (and C<ev_child>) watchers. This API
414	delivers signals synchronously, which makes it both faster and might make	459	delivers signals synchronously, which makes it both faster and might make
415	it possible to get the queued signal data. It can also simplify signal	460	it possible to get the queued signal data. It can also simplify signal
416	handling with threads, as long as you properly block signals in your	461	handling with threads, as long as you properly block signals in your
417	threads that are not interested in handling them.	462	threads that are not interested in handling them.
418		463
419	Signalfd will not be used by default as this changes your signal mask, and	464	Signalfd will not be used by default as this changes your signal mask, and
420	there are a lot of shoddy libraries and programs (glib's threadpool for	465	there are a lot of shoddy libraries and programs (glib's threadpool for
421	example) that can't properly initialise their signal masks.	466	example) that can't properly initialise their signal masks.
		467
		468	=item C<EVFLAG_NOSIGMASK>
		469
		470	When this flag is specified, then libev will avoid to modify the signal
		471	mask. Specifically, this means you have to make sure signals are unblocked
		472	when you want to receive them.
		473
		474	This behaviour is useful when you want to do your own signal handling, or
		475	want to handle signals only in specific threads and want to avoid libev
		476	unblocking the signals.
		477
		478	It's also required by POSIX in a threaded program, as libev calls
		479	C<sigprocmask>, whose behaviour is officially unspecified.
		480
		481	This flag's behaviour will become the default in future versions of libev.
422		482
423	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	483	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
424		484
425	This is your standard select(2) backend. Not I<completely> standard, as	485	This is your standard select(2) backend. Not I<completely> standard, as
426	libev tries to roll its own fd_set with no limits on the number of fds,	486	libev tries to roll its own fd_set with no limits on the number of fds,
…		…
454	=item C<EVBACKEND_EPOLL> (value 4, Linux)	514	=item C<EVBACKEND_EPOLL> (value 4, Linux)
455		515
456	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9	516	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
457	kernels).	517	kernels).
458		518
459	For few fds, this backend is a bit little slower than poll and select,	519	For few fds, this backend is a bit little slower than poll and select, but
460	but it scales phenomenally better. While poll and select usually scale	520	it scales phenomenally better. While poll and select usually scale like
461	like O(total_fds) where n is the total number of fds (or the highest fd),	521	O(total_fds) where total_fds is the total number of fds (or the highest
462	epoll scales either O(1) or O(active_fds).	522	fd), epoll scales either O(1) or O(active_fds).
463		523
464	The epoll mechanism deserves honorable mention as the most misdesigned	524	The epoll mechanism deserves honorable mention as the most misdesigned
465	of the more advanced event mechanisms: mere annoyances include silently	525	of the more advanced event mechanisms: mere annoyances include silently
466	dropping file descriptors, requiring a system call per change per file	526	dropping file descriptors, requiring a system call per change per file
467	descriptor (and unnecessary guessing of parameters), problems with dup and	527	descriptor (and unnecessary guessing of parameters), problems with dup,
		528	returning before the timeout value, resulting in additional iterations
		529	(and only giving 5ms accuracy while select on the same platform gives
468	so on. The biggest issue is fork races, however - if a program forks then	530	0.1ms) and so on. The biggest issue is fork races, however - if a program
469	I<both> parent and child process have to recreate the epoll set, which can	531	forks then I<both> parent and child process have to recreate the epoll
470	take considerable time (one syscall per file descriptor) and is of course	532	set, which can take considerable time (one syscall per file descriptor)
471	hard to detect.	533	and is of course hard to detect.
472		534
473	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but	535	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
474	of course I<doesn't>, and epoll just loves to report events for totally	536	but of course I<doesn't>, and epoll just loves to report events for
475	I<different> file descriptors (even already closed ones, so one cannot	537	totally I<different> file descriptors (even already closed ones, so
476	even remove them from the set) than registered in the set (especially	538	one cannot even remove them from the set) than registered in the set
477	on SMP systems). Libev tries to counter these spurious notifications by	539	(especially on SMP systems). Libev tries to counter these spurious
478	employing an additional generation counter and comparing that against the	540	notifications by employing an additional generation counter and comparing
479	events to filter out spurious ones, recreating the set when required. Last	541	that against the events to filter out spurious ones, recreating the set
		542	when required. Epoll also erroneously rounds down timeouts, but gives you
		543	no way to know when and by how much, so sometimes you have to busy-wait
		544	because epoll returns immediately despite a nonzero timeout. And last
480	not least, it also refuses to work with some file descriptors which work	545	not least, it also refuses to work with some file descriptors which work
481	perfectly fine with C<select> (files, many character devices...).	546	perfectly fine with C<select> (files, many character devices...).
		547
		548	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		549	cobbled together in a hurry, no thought to design or interaction with
		550	others. Oh, the pain, will it ever stop...
482		551
483	While stopping, setting and starting an I/O watcher in the same iteration	552	While stopping, setting and starting an I/O watcher in the same iteration
484	will result in some caching, there is still a system call per such	553	will result in some caching, there is still a system call per such
485	incident (because the same I<file descriptor> could point to a different	554	incident (because the same I<file descriptor> could point to a different
486	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed	555	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
…		…
523		592
524	It scales in the same way as the epoll backend, but the interface to the	593	It scales in the same way as the epoll backend, but the interface to the
525	kernel is more efficient (which says nothing about its actual speed, of	594	kernel is more efficient (which says nothing about its actual speed, of
526	course). While stopping, setting and starting an I/O watcher does never	595	course). While stopping, setting and starting an I/O watcher does never
527	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to	596	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
528	two event changes per incident. Support for C<fork ()> is very bad (but	597	two event changes per incident. Support for C<fork ()> is very bad (you
529	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect	598	might have to leak fd's on fork, but it's more sane than epoll) and it
530	cases	599	drops fds silently in similarly hard-to-detect cases.
531		600
532	This backend usually performs well under most conditions.	601	This backend usually performs well under most conditions.
533		602
534	While nominally embeddable in other event loops, this doesn't work	603	While nominally embeddable in other event loops, this doesn't work
535	everywhere, so you might need to test for this. And since it is broken	604	everywhere, so you might need to test for this. And since it is broken
…		…
552	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	621	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
553		622
554	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	623	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
555	it's really slow, but it still scales very well (O(active_fds)).	624	it's really slow, but it still scales very well (O(active_fds)).
556		625
557	Please note that Solaris event ports can deliver a lot of spurious
558	notifications, so you need to use non-blocking I/O or other means to avoid
559	blocking when no data (or space) is available.
560
561	While this backend scales well, it requires one system call per active	626	While this backend scales well, it requires one system call per active
562	file descriptor per loop iteration. For small and medium numbers of file	627	file descriptor per loop iteration. For small and medium numbers of file
563	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	628	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
564	might perform better.	629	might perform better.
565		630
566	On the positive side, with the exception of the spurious readiness	631	On the positive side, this backend actually performed fully to
567	notifications, this backend actually performed fully to specification
568	in all tests and is fully embeddable, which is a rare feat among the	632	specification in all tests and is fully embeddable, which is a rare feat
569	OS-specific backends (I vastly prefer correctness over speed hacks).	633	among the OS-specific backends (I vastly prefer correctness over speed
		634	hacks).
		635
		636	On the negative side, the interface is I<bizarre> - so bizarre that
		637	even sun itself gets it wrong in their code examples: The event polling
		638	function sometimes returns events to the caller even though an error
		639	occurred, but with no indication whether it has done so or not (yes, it's
		640	even documented that way) - deadly for edge-triggered interfaces where you
		641	absolutely have to know whether an event occurred or not because you have
		642	to re-arm the watcher.
		643
		644	Fortunately libev seems to be able to work around these idiocies.
570		645
571	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	646	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
572	C<EVBACKEND_POLL>.	647	C<EVBACKEND_POLL>.
573		648
574	=item C<EVBACKEND_ALL>	649	=item C<EVBACKEND_ALL>
575		650
576	Try all backends (even potentially broken ones that wouldn't be tried	651	Try all backends (even potentially broken ones that wouldn't be tried
577	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	652	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
578	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	653	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
579		654
580	It is definitely not recommended to use this flag.	655	It is definitely not recommended to use this flag, use whatever
		656	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		657	at all.
		658
		659	=item C<EVBACKEND_MASK>
		660
		661	Not a backend at all, but a mask to select all backend bits from a
		662	C<flags> value, in case you want to mask out any backends from a flags
		663	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
581		664
582	=back	665	=back
583		666
584	If one or more of the backend flags are or'ed into the flags value,	667	If one or more of the backend flags are or'ed into the flags value,
585	then only these backends will be tried (in the reverse order as listed	668	then only these backends will be tried (in the reverse order as listed
…		…
589	Example: Try to create a event loop that uses epoll and nothing else.	672	Example: Try to create a event loop that uses epoll and nothing else.
590		673
591	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	674	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
592	if (!epoller)	675	if (!epoller)
593	fatal ("no epoll found here, maybe it hides under your chair");	676	fatal ("no epoll found here, maybe it hides under your chair");
		677
		678	Example: Use whatever libev has to offer, but make sure that kqueue is
		679	used if available.
		680
		681	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
594		682
595	=item ev_loop_destroy (loop)	683	=item ev_loop_destroy (loop)
596		684
597	Destroys an event loop object (frees all memory and kernel state	685	Destroys an event loop object (frees all memory and kernel state
598	etc.). None of the active event watchers will be stopped in the normal	686	etc.). None of the active event watchers will be stopped in the normal
…		…
609	This function is normally used on loop objects allocated by	697	This function is normally used on loop objects allocated by
610	C<ev_loop_new>, but it can also be used on the default loop returned by	698	C<ev_loop_new>, but it can also be used on the default loop returned by
611	C<ev_default_loop>, in which case it is not thread-safe.	699	C<ev_default_loop>, in which case it is not thread-safe.
612		700
613	Note that it is not advisable to call this function on the default loop	701	Note that it is not advisable to call this function on the default loop
614	except in the rare occasion where you really need to free it's resources.	702	except in the rare occasion where you really need to free its resources.
615	If you need dynamically allocated loops it is better to use C<ev_loop_new>	703	If you need dynamically allocated loops it is better to use C<ev_loop_new>
616	and C<ev_loop_destroy>.	704	and C<ev_loop_destroy>.
617		705
618	=item ev_loop_fork (loop)	706	=item ev_loop_fork (loop)
619		707
620	This function sets a flag that causes subsequent C<ev_run> iterations to	708	This function sets a flag that causes subsequent C<ev_run> iterations
621	reinitialise the kernel state for backends that have one. Despite the	709	to reinitialise the kernel state for backends that have one. Despite
622	name, you can call it anytime, but it makes most sense after forking, in	710	the name, you can call it anytime you are allowed to start or stop
623	the child process. You I<must> call it (or use C<EVFLAG_FORKCHECK>) in the	711	watchers (except inside an C<ev_prepare> callback), but it makes most
		712	sense after forking, in the child process. You I<must> call it (or use
624	child before resuming or calling C<ev_run>.	713	C<EVFLAG_FORKCHECK>) in the child before resuming or calling C<ev_run>.
625		714
		715	In addition, if you want to reuse a loop (via this function or
		716	C<EVFLAG_FORKCHECK>), you I<also> have to ignore C<SIGPIPE>.
		717
626	Again, you I<have> to call it on I<any> loop that you want to re-use after	718	Again, you I<have> to call it on I<any> loop that you want to re-use after
627	a fork, I<even if you do not plan to use the loop in the parent>. This is	719	a fork, I<even if you do not plan to use the loop in the parent>. This is
628	because some kernel interfaces *cough* I<kqueue> *cough* do funny things	720	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
629	during fork.	721	during fork.
630		722
631	On the other hand, you only need to call this function in the child	723	On the other hand, you only need to call this function in the child
…		…
667	prepare and check phases.	759	prepare and check phases.
668		760
669	=item unsigned int ev_depth (loop)	761	=item unsigned int ev_depth (loop)
670		762
671	Returns the number of times C<ev_run> was entered minus the number of	763	Returns the number of times C<ev_run> was entered minus the number of
672	times C<ev_run> was exited, in other words, the recursion depth.	764	times C<ev_run> was exited normally, in other words, the recursion depth.
673		765
674	Outside C<ev_run>, this number is zero. In a callback, this number is	766	Outside C<ev_run>, this number is zero. In a callback, this number is
675	C<1>, unless C<ev_run> was invoked recursively (or from another thread),	767	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
676	in which case it is higher.	768	in which case it is higher.
677		769
678	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread	770	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
679	etc.), doesn't count as "exit" - consider this as a hint to avoid such	771	throwing an exception etc.), doesn't count as "exit" - consider this
680	ungentleman-like behaviour unless it's really convenient.	772	as a hint to avoid such ungentleman-like behaviour unless it's really
		773	convenient, in which case it is fully supported.
681		774
682	=item unsigned int ev_backend (loop)	775	=item unsigned int ev_backend (loop)
683		776
684	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	777	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
685	use.	778	use.
…		…
700		793
701	This function is rarely useful, but when some event callback runs for a	794	This function is rarely useful, but when some event callback runs for a
702	very long time without entering the event loop, updating libev's idea of	795	very long time without entering the event loop, updating libev's idea of
703	the current time is a good idea.	796	the current time is a good idea.
704		797
705	See also L<The special problem of time updates> in the C<ev_timer> section.	798	See also L</The special problem of time updates> in the C<ev_timer> section.
706		799
707	=item ev_suspend (loop)	800	=item ev_suspend (loop)
708		801
709	=item ev_resume (loop)	802	=item ev_resume (loop)
710		803
…		…
728	without a previous call to C<ev_suspend>.	821	without a previous call to C<ev_suspend>.
729		822
730	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the	823	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
731	event loop time (see C<ev_now_update>).	824	event loop time (see C<ev_now_update>).
732		825
733	=item ev_run (loop, int flags)	826	=item bool ev_run (loop, int flags)
734		827
735	Finally, this is it, the event handler. This function usually is called	828	Finally, this is it, the event handler. This function usually is called
736	after you have initialised all your watchers and you want to start	829	after you have initialised all your watchers and you want to start
737	handling events. It will ask the operating system for any new events, call	830	handling events. It will ask the operating system for any new events, call
738	the watcher callbacks, an then repeat the whole process indefinitely: This	831	the watcher callbacks, and then repeat the whole process indefinitely: This
739	is why event loops are called I<loops>.	832	is why event loops are called I<loops>.
740		833
741	If the flags argument is specified as C<0>, it will keep handling events	834	If the flags argument is specified as C<0>, it will keep handling events
742	until either no event watchers are active anymore or C<ev_break> was	835	until either no event watchers are active anymore or C<ev_break> was
743	called.	836	called.
		837
		838	The return value is false if there are no more active watchers (which
		839	usually means "all jobs done" or "deadlock"), and true in all other cases
		840	(which usually means " you should call C<ev_run> again").
744		841
745	Please note that an explicit C<ev_break> is usually better than	842	Please note that an explicit C<ev_break> is usually better than
746	relying on all watchers to be stopped when deciding when a program has	843	relying on all watchers to be stopped when deciding when a program has
747	finished (especially in interactive programs), but having a program	844	finished (especially in interactive programs), but having a program
748	that automatically loops as long as it has to and no longer by virtue	845	that automatically loops as long as it has to and no longer by virtue
749	of relying on its watchers stopping correctly, that is truly a thing of	846	of relying on its watchers stopping correctly, that is truly a thing of
750	beauty.	847	beauty.
751		848
		849	This function is I<mostly> exception-safe - you can break out of a
		850	C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		851	exception and so on. This does not decrement the C<ev_depth> value, nor
		852	will it clear any outstanding C<EVBREAK_ONE> breaks.
		853
752	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle	854	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
753	those events and any already outstanding ones, but will not wait and	855	those events and any already outstanding ones, but will not wait and
754	block your process in case there are no events and will return after one	856	block your process in case there are no events and will return after one
755	iteration of the loop. This is sometimes useful to poll and handle new	857	iteration of the loop. This is sometimes useful to poll and handle new
756	events while doing lengthy calculations, to keep the program responsive.	858	events while doing lengthy calculations, to keep the program responsive.
…		…
765	This is useful if you are waiting for some external event in conjunction	867	This is useful if you are waiting for some external event in conjunction
766	with something not expressible using other libev watchers (i.e. "roll your	868	with something not expressible using other libev watchers (i.e. "roll your
767	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is	869	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
768	usually a better approach for this kind of thing.	870	usually a better approach for this kind of thing.
769		871
770	Here are the gory details of what C<ev_run> does:	872	Here are the gory details of what C<ev_run> does (this is for your
		873	understanding, not a guarantee that things will work exactly like this in
		874	future versions):
771		875
772	- Increment loop depth.	876	- Increment loop depth.
773	- Reset the ev_break status.	877	- Reset the ev_break status.
774	- Before the first iteration, call any pending watchers.	878	- Before the first iteration, call any pending watchers.
775	LOOP:	879	LOOP:
…		…
808	anymore.	912	anymore.
809		913
810	... queue jobs here, make sure they register event watchers as long	914	... queue jobs here, make sure they register event watchers as long
811	... as they still have work to do (even an idle watcher will do..)	915	... as they still have work to do (even an idle watcher will do..)
812	ev_run (my_loop, 0);	916	ev_run (my_loop, 0);
813	... jobs done or somebody called unloop. yeah!	917	... jobs done or somebody called break. yeah!
814		918
815	=item ev_break (loop, how)	919	=item ev_break (loop, how)
816		920
817	Can be used to make a call to C<ev_run> return early (but only after it	921	Can be used to make a call to C<ev_run> return early (but only after it
818	has processed all outstanding events). The C<how> argument must be either	922	has processed all outstanding events). The C<how> argument must be either
819	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or	923	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
820	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.	924	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
821		925
822	This "unloop state" will be cleared when entering C<ev_run> again.	926	This "break state" will be cleared on the next call to C<ev_run>.
823		927
824	It is safe to call C<ev_break> from outside any C<ev_run> calls. ##TODO##	928	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		929	which case it will have no effect.
825		930
826	=item ev_ref (loop)	931	=item ev_ref (loop)
827		932
828	=item ev_unref (loop)	933	=item ev_unref (loop)
829		934
…		…
850	running when nothing else is active.	955	running when nothing else is active.
851		956
852	ev_signal exitsig;	957	ev_signal exitsig;
853	ev_signal_init (&exitsig, sig_cb, SIGINT);	958	ev_signal_init (&exitsig, sig_cb, SIGINT);
854	ev_signal_start (loop, &exitsig);	959	ev_signal_start (loop, &exitsig);
855	evf_unref (loop);	960	ev_unref (loop);
856		961
857	Example: For some weird reason, unregister the above signal handler again.	962	Example: For some weird reason, unregister the above signal handler again.
858		963
859	ev_ref (loop);	964	ev_ref (loop);
860	ev_signal_stop (loop, &exitsig);	965	ev_signal_stop (loop, &exitsig);
…		…
880	overhead for the actual polling but can deliver many events at once.	985	overhead for the actual polling but can deliver many events at once.
881		986
882	By setting a higher I<io collect interval> you allow libev to spend more	987	By setting a higher I<io collect interval> you allow libev to spend more
883	time collecting I/O events, so you can handle more events per iteration,	988	time collecting I/O events, so you can handle more events per iteration,
884	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	989	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
885	C<ev_timer>) will be not affected. Setting this to a non-null value will	990	C<ev_timer>) will not be affected. Setting this to a non-null value will
886	introduce an additional C<ev_sleep ()> call into most loop iterations. The	991	introduce an additional C<ev_sleep ()> call into most loop iterations. The
887	sleep time ensures that libev will not poll for I/O events more often then	992	sleep time ensures that libev will not poll for I/O events more often then
888	once per this interval, on average.	993	once per this interval, on average (as long as the host time resolution is
		994	good enough).
889		995
890	Likewise, by setting a higher I<timeout collect interval> you allow libev	996	Likewise, by setting a higher I<timeout collect interval> you allow libev
891	to spend more time collecting timeouts, at the expense of increased	997	to spend more time collecting timeouts, at the expense of increased
892	latency/jitter/inexactness (the watcher callback will be called	998	latency/jitter/inexactness (the watcher callback will be called
893	later). C<ev_io> watchers will not be affected. Setting this to a non-null	999	later). C<ev_io> watchers will not be affected. Setting this to a non-null
…		…
939	invoke the actual watchers inside another context (another thread etc.).	1045	invoke the actual watchers inside another context (another thread etc.).
940		1046
941	If you want to reset the callback, use C<ev_invoke_pending> as new	1047	If you want to reset the callback, use C<ev_invoke_pending> as new
942	callback.	1048	callback.
943		1049
944	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))	1050	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
945		1051
946	Sometimes you want to share the same loop between multiple threads. This	1052	Sometimes you want to share the same loop between multiple threads. This
947	can be done relatively simply by putting mutex_lock/unlock calls around	1053	can be done relatively simply by putting mutex_lock/unlock calls around
948	each call to a libev function.	1054	each call to a libev function.
949		1055
950	However, C<ev_run> can run an indefinite time, so it is not feasible	1056	However, C<ev_run> can run an indefinite time, so it is not feasible
951	to wait for it to return. One way around this is to wake up the event	1057	to wait for it to return. One way around this is to wake up the event
952	loop via C<ev_break> and C<av_async_send>, another way is to set these	1058	loop via C<ev_break> and C<ev_async_send>, another way is to set these
953	I<release> and I<acquire> callbacks on the loop.	1059	I<release> and I<acquire> callbacks on the loop.
954		1060
955	When set, then C<release> will be called just before the thread is	1061	When set, then C<release> will be called just before the thread is
956	suspended waiting for new events, and C<acquire> is called just	1062	suspended waiting for new events, and C<acquire> is called just
957	afterwards.	1063	afterwards.
…		…
972	See also the locking example in the C<THREADS> section later in this	1078	See also the locking example in the C<THREADS> section later in this
973	document.	1079	document.
974		1080
975	=item ev_set_userdata (loop, void *data)	1081	=item ev_set_userdata (loop, void *data)
976		1082
977	=item ev_userdata (loop)	1083	=item void *ev_userdata (loop)
978		1084
979	Set and retrieve a single C<void *> associated with a loop. When	1085	Set and retrieve a single C<void *> associated with a loop. When
980	C<ev_set_userdata> has never been called, then C<ev_userdata> returns	1086	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
981	C<0.>	1087	C<0>.
982		1088
983	These two functions can be used to associate arbitrary data with a loop,	1089	These two functions can be used to associate arbitrary data with a loop,
984	and are intended solely for the C<invoke_pending_cb>, C<release> and	1090	and are intended solely for the C<invoke_pending_cb>, C<release> and
985	C<acquire> callbacks described above, but of course can be (ab-)used for	1091	C<acquire> callbacks described above, but of course can be (ab-)used for
986	any other purpose as well.	1092	any other purpose as well.
…		…
1097		1203
1098	=item C<EV_PREPARE>	1204	=item C<EV_PREPARE>
1099		1205
1100	=item C<EV_CHECK>	1206	=item C<EV_CHECK>
1101		1207
1102	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts	1208	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts to
1103	to gather new events, and all C<ev_check> watchers are invoked just after	1209	gather new events, and all C<ev_check> watchers are queued (not invoked)
1104	C<ev_run> has gathered them, but before it invokes any callbacks for any	1210	just after C<ev_run> has gathered them, but before it queues any callbacks
		1211	for any received events. That means C<ev_prepare> watchers are the last
		1212	watchers invoked before the event loop sleeps or polls for new events, and
		1213	C<ev_check> watchers will be invoked before any other watchers of the same
		1214	or lower priority within an event loop iteration.
		1215
1105	received events. Callbacks of both watcher types can start and stop as	1216	Callbacks of both watcher types can start and stop as many watchers as
1106	many watchers as they want, and all of them will be taken into account	1217	they want, and all of them will be taken into account (for example, a
1107	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1218	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
1108	C<ev_run> from blocking).	1219	blocking).
1109		1220
1110	=item C<EV_EMBED>	1221	=item C<EV_EMBED>
1111		1222
1112	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1223	The embedded event loop specified in the C<ev_embed> watcher needs attention.
1113		1224
1114	=item C<EV_FORK>	1225	=item C<EV_FORK>
1115		1226
1116	The event loop has been resumed in the child process after fork (see	1227	The event loop has been resumed in the child process after fork (see
1117	C<ev_fork>).	1228	C<ev_fork>).
		1229
		1230	=item C<EV_CLEANUP>
		1231
		1232	The event loop is about to be destroyed (see C<ev_cleanup>).
1118		1233
1119	=item C<EV_ASYNC>	1234	=item C<EV_ASYNC>
1120		1235
1121	The given async watcher has been asynchronously notified (see C<ev_async>).	1236	The given async watcher has been asynchronously notified (see C<ev_async>).
1122		1237
…		…
1144	programs, though, as the fd could already be closed and reused for another	1259	programs, though, as the fd could already be closed and reused for another
1145	thing, so beware.	1260	thing, so beware.
1146		1261
1147	=back	1262	=back
1148		1263
		1264	=head2 GENERIC WATCHER FUNCTIONS
		1265
		1266	=over 4
		1267
		1268	=item C<ev_init> (ev_TYPE *watcher, callback)
		1269
		1270	This macro initialises the generic portion of a watcher. The contents
		1271	of the watcher object can be arbitrary (so C<malloc> will do). Only
		1272	the generic parts of the watcher are initialised, you I<need> to call
		1273	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		1274	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		1275	which rolls both calls into one.
		1276
		1277	You can reinitialise a watcher at any time as long as it has been stopped
		1278	(or never started) and there are no pending events outstanding.
		1279
		1280	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
		1281	int revents)>.
		1282
		1283	Example: Initialise an C<ev_io> watcher in two steps.
		1284
		1285	ev_io w;
		1286	ev_init (&w, my_cb);
		1287	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1288
		1289	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
		1290
		1291	This macro initialises the type-specific parts of a watcher. You need to
		1292	call C<ev_init> at least once before you call this macro, but you can
		1293	call C<ev_TYPE_set> any number of times. You must not, however, call this
		1294	macro on a watcher that is active (it can be pending, however, which is a
		1295	difference to the C<ev_init> macro).
		1296
		1297	Although some watcher types do not have type-specific arguments
		1298	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		1299
		1300	See C<ev_init>, above, for an example.
		1301
		1302	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		1303
		1304	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		1305	calls into a single call. This is the most convenient method to initialise
		1306	a watcher. The same limitations apply, of course.
		1307
		1308	Example: Initialise and set an C<ev_io> watcher in one step.
		1309
		1310	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1311
		1312	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
		1313
		1314	Starts (activates) the given watcher. Only active watchers will receive
		1315	events. If the watcher is already active nothing will happen.
		1316
		1317	Example: Start the C<ev_io> watcher that is being abused as example in this
		1318	whole section.
		1319
		1320	ev_io_start (EV_DEFAULT_UC, &w);
		1321
		1322	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
		1323
		1324	Stops the given watcher if active, and clears the pending status (whether
		1325	the watcher was active or not).
		1326
		1327	It is possible that stopped watchers are pending - for example,
		1328	non-repeating timers are being stopped when they become pending - but
		1329	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
		1330	pending. If you want to free or reuse the memory used by the watcher it is
		1331	therefore a good idea to always call its C<ev_TYPE_stop> function.
		1332
		1333	=item bool ev_is_active (ev_TYPE *watcher)
		1334
		1335	Returns a true value iff the watcher is active (i.e. it has been started
		1336	and not yet been stopped). As long as a watcher is active you must not modify
		1337	it.
		1338
		1339	=item bool ev_is_pending (ev_TYPE *watcher)
		1340
		1341	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		1342	events but its callback has not yet been invoked). As long as a watcher
		1343	is pending (but not active) you must not call an init function on it (but
		1344	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		1345	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1346	it).
		1347
		1348	=item callback ev_cb (ev_TYPE *watcher)
		1349
		1350	Returns the callback currently set on the watcher.
		1351
		1352	=item ev_set_cb (ev_TYPE *watcher, callback)
		1353
		1354	Change the callback. You can change the callback at virtually any time
		1355	(modulo threads).
		1356
		1357	=item ev_set_priority (ev_TYPE *watcher, int priority)
		1358
		1359	=item int ev_priority (ev_TYPE *watcher)
		1360
		1361	Set and query the priority of the watcher. The priority is a small
		1362	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1363	(default: C<-2>). Pending watchers with higher priority will be invoked
		1364	before watchers with lower priority, but priority will not keep watchers
		1365	from being executed (except for C<ev_idle> watchers).
		1366
		1367	If you need to suppress invocation when higher priority events are pending
		1368	you need to look at C<ev_idle> watchers, which provide this functionality.
		1369
		1370	You I<must not> change the priority of a watcher as long as it is active or
		1371	pending.
		1372
		1373	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1374	fine, as long as you do not mind that the priority value you query might
		1375	or might not have been clamped to the valid range.
		1376
		1377	The default priority used by watchers when no priority has been set is
		1378	always C<0>, which is supposed to not be too high and not be too low :).
		1379
		1380	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1381	priorities.
		1382
		1383	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1384
		1385	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1386	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1387	can deal with that fact, as both are simply passed through to the
		1388	callback.
		1389
		1390	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1391
		1392	If the watcher is pending, this function clears its pending status and
		1393	returns its C<revents> bitset (as if its callback was invoked). If the
		1394	watcher isn't pending it does nothing and returns C<0>.
		1395
		1396	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1397	callback to be invoked, which can be accomplished with this function.
		1398
		1399	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1400
		1401	Feeds the given event set into the event loop, as if the specified event
		1402	had happened for the specified watcher (which must be a pointer to an
		1403	initialised but not necessarily started event watcher). Obviously you must
		1404	not free the watcher as long as it has pending events.
		1405
		1406	Stopping the watcher, letting libev invoke it, or calling
		1407	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1408	not started in the first place.
		1409
		1410	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1411	functions that do not need a watcher.
		1412
		1413	=back
		1414
		1415	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
		1416	OWN COMPOSITE WATCHERS> idioms.
		1417
1149	=head2 WATCHER STATES	1418	=head2 WATCHER STATES
1150		1419
1151	There are various watcher states mentioned throughout this manual -	1420	There are various watcher states mentioned throughout this manual -
1152	active, pending and so on. In this section these states and the rules to	1421	active, pending and so on. In this section these states and the rules to
1153	transition between them will be described in more detail - and while these	1422	transition between them will be described in more detail - and while these
1154	rules might look complicated, they usually do "the right thing".	1423	rules might look complicated, they usually do "the right thing".
1155		1424
1156	=over 4	1425	=over 4
1157		1426
1158	=item initialiased	1427	=item initialised
1159		1428
1160	Before a watcher can be registered with the event looop it has to be	1429	Before a watcher can be registered with the event loop it has to be
1161	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to	1430	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
1162	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.	1431	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1163		1432
1164	In this state it is simply some block of memory that is suitable for use	1433	In this state it is simply some block of memory that is suitable for
1165	in an event loop. It can be moved around, freed, reused etc. at will.	1434	use in an event loop. It can be moved around, freed, reused etc. at
		1435	will - as long as you either keep the memory contents intact, or call
		1436	C<ev_TYPE_init> again.
1166		1437
1167	=item started/running/active	1438	=item started/running/active
1168		1439
1169	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes	1440	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
1170	property of the event loop, and is actively waiting for events. While in	1441	property of the event loop, and is actively waiting for events. While in
…		…
1198	latter will clear any pending state the watcher might be in, regardless	1469	latter will clear any pending state the watcher might be in, regardless
1199	of whether it was active or not, so stopping a watcher explicitly before	1470	of whether it was active or not, so stopping a watcher explicitly before
1200	freeing it is often a good idea.	1471	freeing it is often a good idea.
1201		1472
1202	While stopped (and not pending) the watcher is essentially in the	1473	While stopped (and not pending) the watcher is essentially in the
1203	initialised state, that is it can be reused, moved, modified in any way	1474	initialised state, that is, it can be reused, moved, modified in any way
1204	you wish.	1475	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1476	it again).
1205		1477
1206	=back	1478	=back
1207
1208	=head2 GENERIC WATCHER FUNCTIONS
1209
1210	=over 4
1211
1212	=item C<ev_init> (ev_TYPE *watcher, callback)
1213
1214	This macro initialises the generic portion of a watcher. The contents
1215	of the watcher object can be arbitrary (so C<malloc> will do). Only
1216	the generic parts of the watcher are initialised, you I<need> to call
1217	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
1218	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
1219	which rolls both calls into one.
1220
1221	You can reinitialise a watcher at any time as long as it has been stopped
1222	(or never started) and there are no pending events outstanding.
1223
1224	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
1225	int revents)>.
1226
1227	Example: Initialise an C<ev_io> watcher in two steps.
1228
1229	ev_io w;
1230	ev_init (&w, my_cb);
1231	ev_io_set (&w, STDIN_FILENO, EV_READ);
1232
1233	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
1234
1235	This macro initialises the type-specific parts of a watcher. You need to
1236	call C<ev_init> at least once before you call this macro, but you can
1237	call C<ev_TYPE_set> any number of times. You must not, however, call this
1238	macro on a watcher that is active (it can be pending, however, which is a
1239	difference to the C<ev_init> macro).
1240
1241	Although some watcher types do not have type-specific arguments
1242	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
1243
1244	See C<ev_init>, above, for an example.
1245
1246	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
1247
1248	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
1249	calls into a single call. This is the most convenient method to initialise
1250	a watcher. The same limitations apply, of course.
1251
1252	Example: Initialise and set an C<ev_io> watcher in one step.
1253
1254	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
1255
1256	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
1257
1258	Starts (activates) the given watcher. Only active watchers will receive
1259	events. If the watcher is already active nothing will happen.
1260
1261	Example: Start the C<ev_io> watcher that is being abused as example in this
1262	whole section.
1263
1264	ev_io_start (EV_DEFAULT_UC, &w);
1265
1266	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
1267
1268	Stops the given watcher if active, and clears the pending status (whether
1269	the watcher was active or not).
1270
1271	It is possible that stopped watchers are pending - for example,
1272	non-repeating timers are being stopped when they become pending - but
1273	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
1274	pending. If you want to free or reuse the memory used by the watcher it is
1275	therefore a good idea to always call its C<ev_TYPE_stop> function.
1276
1277	=item bool ev_is_active (ev_TYPE *watcher)
1278
1279	Returns a true value iff the watcher is active (i.e. it has been started
1280	and not yet been stopped). As long as a watcher is active you must not modify
1281	it.
1282
1283	=item bool ev_is_pending (ev_TYPE *watcher)
1284
1285	Returns a true value iff the watcher is pending, (i.e. it has outstanding
1286	events but its callback has not yet been invoked). As long as a watcher
1287	is pending (but not active) you must not call an init function on it (but
1288	C<ev_TYPE_set> is safe), you must not change its priority, and you must
1289	make sure the watcher is available to libev (e.g. you cannot C<free ()>
1290	it).
1291
1292	=item callback ev_cb (ev_TYPE *watcher)
1293
1294	Returns the callback currently set on the watcher.
1295
1296	=item ev_cb_set (ev_TYPE *watcher, callback)
1297
1298	Change the callback. You can change the callback at virtually any time
1299	(modulo threads).
1300
1301	=item ev_set_priority (ev_TYPE *watcher, int priority)
1302
1303	=item int ev_priority (ev_TYPE *watcher)
1304
1305	Set and query the priority of the watcher. The priority is a small
1306	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
1307	(default: C<-2>). Pending watchers with higher priority will be invoked
1308	before watchers with lower priority, but priority will not keep watchers
1309	from being executed (except for C<ev_idle> watchers).
1310
1311	If you need to suppress invocation when higher priority events are pending
1312	you need to look at C<ev_idle> watchers, which provide this functionality.
1313
1314	You I<must not> change the priority of a watcher as long as it is active or
1315	pending.
1316
1317	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
1318	fine, as long as you do not mind that the priority value you query might
1319	or might not have been clamped to the valid range.
1320
1321	The default priority used by watchers when no priority has been set is
1322	always C<0>, which is supposed to not be too high and not be too low :).
1323
1324	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
1325	priorities.
1326
1327	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1328
1329	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
1330	C<loop> nor C<revents> need to be valid as long as the watcher callback
1331	can deal with that fact, as both are simply passed through to the
1332	callback.
1333
1334	=item int ev_clear_pending (loop, ev_TYPE *watcher)
1335
1336	If the watcher is pending, this function clears its pending status and
1337	returns its C<revents> bitset (as if its callback was invoked). If the
1338	watcher isn't pending it does nothing and returns C<0>.
1339
1340	Sometimes it can be useful to "poll" a watcher instead of waiting for its
1341	callback to be invoked, which can be accomplished with this function.
1342
1343	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
1344
1345	Feeds the given event set into the event loop, as if the specified event
1346	had happened for the specified watcher (which must be a pointer to an
1347	initialised but not necessarily started event watcher). Obviously you must
1348	not free the watcher as long as it has pending events.
1349
1350	Stopping the watcher, letting libev invoke it, or calling
1351	C<ev_clear_pending> will clear the pending event, even if the watcher was
1352	not started in the first place.
1353
1354	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1355	functions that do not need a watcher.
1356
1357	=back
1358
1359
1360	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
1361
1362	Each watcher has, by default, a member C<void *data> that you can change
1363	and read at any time: libev will completely ignore it. This can be used
1364	to associate arbitrary data with your watcher. If you need more data and
1365	don't want to allocate memory and store a pointer to it in that data
1366	member, you can also "subclass" the watcher type and provide your own
1367	data:
1368
1369	struct my_io
1370	{
1371	ev_io io;
1372	int otherfd;
1373	void *somedata;
1374	struct whatever *mostinteresting;
1375	};
1376
1377	...
1378	struct my_io w;
1379	ev_io_init (&w.io, my_cb, fd, EV_READ);
1380
1381	And since your callback will be called with a pointer to the watcher, you
1382	can cast it back to your own type:
1383
1384	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1385	{
1386	struct my_io *w = (struct my_io *)w_;
1387	...
1388	}
1389
1390	More interesting and less C-conformant ways of casting your callback type
1391	instead have been omitted.
1392
1393	Another common scenario is to use some data structure with multiple
1394	embedded watchers:
1395
1396	struct my_biggy
1397	{
1398	int some_data;
1399	ev_timer t1;
1400	ev_timer t2;
1401	}
1402
1403	In this case getting the pointer to C<my_biggy> is a bit more
1404	complicated: Either you store the address of your C<my_biggy> struct
1405	in the C<data> member of the watcher (for woozies), or you need to use
1406	some pointer arithmetic using C<offsetof> inside your watchers (for real
1407	programmers):
1408
1409	#include <stddef.h>
1410
1411	static void
1412	t1_cb (EV_P_ ev_timer *w, int revents)
1413	{
1414	struct my_biggy big = (struct my_biggy *)
1415	(((char *)w) - offsetof (struct my_biggy, t1));
1416	}
1417
1418	static void
1419	t2_cb (EV_P_ ev_timer *w, int revents)
1420	{
1421	struct my_biggy big = (struct my_biggy *)
1422	(((char *)w) - offsetof (struct my_biggy, t2));
1423	}
1424		1479
1425	=head2 WATCHER PRIORITY MODELS	1480	=head2 WATCHER PRIORITY MODELS
1426		1481
1427	Many event loops support I<watcher priorities>, which are usually small	1482	Many event loops support I<watcher priorities>, which are usually small
1428	integers that influence the ordering of event callback invocation	1483	integers that influence the ordering of event callback invocation
…		…
1555	In general you can register as many read and/or write event watchers per	1610	In general you can register as many read and/or write event watchers per
1556	fd as you want (as long as you don't confuse yourself). Setting all file	1611	fd as you want (as long as you don't confuse yourself). Setting all file
1557	descriptors to non-blocking mode is also usually a good idea (but not	1612	descriptors to non-blocking mode is also usually a good idea (but not
1558	required if you know what you are doing).	1613	required if you know what you are doing).
1559		1614
1560	If you cannot use non-blocking mode, then force the use of a
1561	known-to-be-good backend (at the time of this writing, this includes only
1562	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
1563	descriptors for which non-blocking operation makes no sense (such as
1564	files) - libev doesn't guarantee any specific behaviour in that case.
1565
1566	Another thing you have to watch out for is that it is quite easy to	1615	Another thing you have to watch out for is that it is quite easy to
1567	receive "spurious" readiness notifications, that is your callback might	1616	receive "spurious" readiness notifications, that is, your callback might
1568	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1617	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1569	because there is no data. Not only are some backends known to create a	1618	because there is no data. It is very easy to get into this situation even
1570	lot of those (for example Solaris ports), it is very easy to get into	1619	with a relatively standard program structure. Thus it is best to always
1571	this situation even with a relatively standard program structure. Thus	1620	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1572	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1573	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1621	preferable to a program hanging until some data arrives.
1574		1622
1575	If you cannot run the fd in non-blocking mode (for example you should	1623	If you cannot run the fd in non-blocking mode (for example you should
1576	not play around with an Xlib connection), then you have to separately	1624	not play around with an Xlib connection), then you have to separately
1577	re-test whether a file descriptor is really ready with a known-to-be good	1625	re-test whether a file descriptor is really ready with a known-to-be good
1578	interface such as poll (fortunately in our Xlib example, Xlib already	1626	interface such as poll (fortunately in the case of Xlib, it already does
1579	does this on its own, so its quite safe to use). Some people additionally	1627	this on its own, so its quite safe to use). Some people additionally
1580	use C<SIGALRM> and an interval timer, just to be sure you won't block	1628	use C<SIGALRM> and an interval timer, just to be sure you won't block
1581	indefinitely.	1629	indefinitely.
1582		1630
1583	But really, best use non-blocking mode.	1631	But really, best use non-blocking mode.
1584		1632
…		…
1612		1660
1613	There is no workaround possible except not registering events	1661	There is no workaround possible except not registering events
1614	for potentially C<dup ()>'ed file descriptors, or to resort to	1662	for potentially C<dup ()>'ed file descriptors, or to resort to
1615	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1663	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1616		1664
		1665	=head3 The special problem of files
		1666
		1667	Many people try to use C<select> (or libev) on file descriptors
		1668	representing files, and expect it to become ready when their program
		1669	doesn't block on disk accesses (which can take a long time on their own).
		1670
		1671	However, this cannot ever work in the "expected" way - you get a readiness
		1672	notification as soon as the kernel knows whether and how much data is
		1673	there, and in the case of open files, that's always the case, so you
		1674	always get a readiness notification instantly, and your read (or possibly
		1675	write) will still block on the disk I/O.
		1676
		1677	Another way to view it is that in the case of sockets, pipes, character
		1678	devices and so on, there is another party (the sender) that delivers data
		1679	on its own, but in the case of files, there is no such thing: the disk
		1680	will not send data on its own, simply because it doesn't know what you
		1681	wish to read - you would first have to request some data.
		1682
		1683	Since files are typically not-so-well supported by advanced notification
		1684	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1685	to files, even though you should not use it. The reason for this is
		1686	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1687	usually a tty, often a pipe, but also sometimes files or special devices
		1688	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1689	F</dev/urandom>), and even though the file might better be served with
		1690	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1691	it "just works" instead of freezing.
		1692
		1693	So avoid file descriptors pointing to files when you know it (e.g. use
		1694	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1695	when you rarely read from a file instead of from a socket, and want to
		1696	reuse the same code path.
		1697
1617	=head3 The special problem of fork	1698	=head3 The special problem of fork
1618		1699
1619	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1700	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
1620	useless behaviour. Libev fully supports fork, but needs to be told about	1701	useless behaviour. Libev fully supports fork, but needs to be told about
1621	it in the child.	1702	it in the child if you want to continue to use it in the child.
1622		1703
1623	To support fork in your programs, you either have to call	1704	To support fork in your child processes, you have to call C<ev_loop_fork
1624	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1705	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1625	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1706	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1626	C<EVBACKEND_POLL>.
1627		1707
1628	=head3 The special problem of SIGPIPE	1708	=head3 The special problem of SIGPIPE
1629		1709
1630	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1710	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1631	when writing to a pipe whose other end has been closed, your program gets	1711	when writing to a pipe whose other end has been closed, your program gets
…		…
1729	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1809	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1730	monotonic clock option helps a lot here).	1810	monotonic clock option helps a lot here).
1731		1811
1732	The callback is guaranteed to be invoked only I<after> its timeout has	1812	The callback is guaranteed to be invoked only I<after> its timeout has
1733	passed (not I<at>, so on systems with very low-resolution clocks this	1813	passed (not I<at>, so on systems with very low-resolution clocks this
1734	might introduce a small delay). If multiple timers become ready during the	1814	might introduce a small delay, see "the special problem of being too
		1815	early", below). If multiple timers become ready during the same loop
1735	same loop iteration then the ones with earlier time-out values are invoked	1816	iteration then the ones with earlier time-out values are invoked before
1736	before ones of the same priority with later time-out values (but this is	1817	ones of the same priority with later time-out values (but this is no
1737	no longer true when a callback calls C<ev_run> recursively).	1818	longer true when a callback calls C<ev_run> recursively).
1738		1819
1739	=head3 Be smart about timeouts	1820	=head3 Be smart about timeouts
1740		1821
1741	Many real-world problems involve some kind of timeout, usually for error	1822	Many real-world problems involve some kind of timeout, usually for error
1742	recovery. A typical example is an HTTP request - if the other side hangs,	1823	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1817		1898
1818	In this case, it would be more efficient to leave the C<ev_timer> alone,	1899	In this case, it would be more efficient to leave the C<ev_timer> alone,
1819	but remember the time of last activity, and check for a real timeout only	1900	but remember the time of last activity, and check for a real timeout only
1820	within the callback:	1901	within the callback:
1821		1902
		1903	ev_tstamp timeout = 60.;
1822	ev_tstamp last_activity; // time of last activity	1904	ev_tstamp last_activity; // time of last activity
		1905	ev_timer timer;
1823		1906
1824	static void	1907	static void
1825	callback (EV_P_ ev_timer *w, int revents)	1908	callback (EV_P_ ev_timer *w, int revents)
1826	{	1909	{
1827	ev_tstamp now = ev_now (EV_A);	1910	// calculate when the timeout would happen
1828	ev_tstamp timeout = last_activity + 60.;	1911	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
1829		1912
1830	// if last_activity + 60. is older than now, we did time out	1913	// if negative, it means we the timeout already occurred
1831	if (timeout < now)	1914	if (after < 0.)
1832	{	1915	{
1833	// timeout occurred, take action	1916	// timeout occurred, take action
1834	}	1917	}
1835	else	1918	else
1836	{	1919	{
1837	// callback was invoked, but there was some activity, re-arm	1920	// callback was invoked, but there was some recent
1838	// the watcher to fire in last_activity + 60, which is	1921	// activity. simply restart the timer to time out
1839	// guaranteed to be in the future, so "again" is positive:	1922	// after "after" seconds, which is the earliest time
1840	w->repeat = timeout - now;	1923	// the timeout can occur.
		1924	ev_timer_set (w, after, 0.);
1841	ev_timer_again (EV_A_ w);	1925	ev_timer_start (EV_A_ w);
1842	}	1926	}
1843	}	1927	}
1844		1928
1845	To summarise the callback: first calculate the real timeout (defined	1929	To summarise the callback: first calculate in how many seconds the
1846	as "60 seconds after the last activity"), then check if that time has	1930	timeout will occur (by calculating the absolute time when it would occur,
1847	been reached, which means something I<did>, in fact, time out. Otherwise	1931	C<last_activity + timeout>, and subtracting the current time, C<ev_now
1848	the callback was invoked too early (C<timeout> is in the future), so	1932	(EV_A)> from that).
1849	re-schedule the timer to fire at that future time, to see if maybe we have
1850	a timeout then.
1851		1933
1852	Note how C<ev_timer_again> is used, taking advantage of the	1934	If this value is negative, then we are already past the timeout, i.e. we
1853	C<ev_timer_again> optimisation when the timer is already running.	1935	timed out, and need to do whatever is needed in this case.
		1936
		1937	Otherwise, we now the earliest time at which the timeout would trigger,
		1938	and simply start the timer with this timeout value.
		1939
		1940	In other words, each time the callback is invoked it will check whether
		1941	the timeout occurred. If not, it will simply reschedule itself to check
		1942	again at the earliest time it could time out. Rinse. Repeat.
1854		1943
1855	This scheme causes more callback invocations (about one every 60 seconds	1944	This scheme causes more callback invocations (about one every 60 seconds
1856	minus half the average time between activity), but virtually no calls to	1945	minus half the average time between activity), but virtually no calls to
1857	libev to change the timeout.	1946	libev to change the timeout.
1858		1947
1859	To start the timer, simply initialise the watcher and set C<last_activity>	1948	To start the machinery, simply initialise the watcher and set
1860	to the current time (meaning we just have some activity :), then call the	1949	C<last_activity> to the current time (meaning there was some activity just
1861	callback, which will "do the right thing" and start the timer:	1950	now), then call the callback, which will "do the right thing" and start
		1951	the timer:
1862		1952
		1953	last_activity = ev_now (EV_A);
1863	ev_init (timer, callback);	1954	ev_init (&timer, callback);
1864	last_activity = ev_now (loop);	1955	callback (EV_A_ &timer, 0);
1865	callback (loop, timer, EV_TIMER);
1866		1956
1867	And when there is some activity, simply store the current time in	1957	When there is some activity, simply store the current time in
1868	C<last_activity>, no libev calls at all:	1958	C<last_activity>, no libev calls at all:
1869		1959
		1960	if (activity detected)
1870	last_activity = ev_now (loop);	1961	last_activity = ev_now (EV_A);
		1962
		1963	When your timeout value changes, then the timeout can be changed by simply
		1964	providing a new value, stopping the timer and calling the callback, which
		1965	will again do the right thing (for example, time out immediately :).
		1966
		1967	timeout = new_value;
		1968	ev_timer_stop (EV_A_ &timer);
		1969	callback (EV_A_ &timer, 0);
1871		1970
1872	This technique is slightly more complex, but in most cases where the	1971	This technique is slightly more complex, but in most cases where the
1873	time-out is unlikely to be triggered, much more efficient.	1972	time-out is unlikely to be triggered, much more efficient.
1874
1875	Changing the timeout is trivial as well (if it isn't hard-coded in the
1876	callback :) - just change the timeout and invoke the callback, which will
1877	fix things for you.
1878		1973
1879	=item 4. Wee, just use a double-linked list for your timeouts.	1974	=item 4. Wee, just use a double-linked list for your timeouts.
1880		1975
1881	If there is not one request, but many thousands (millions...), all	1976	If there is not one request, but many thousands (millions...), all
1882	employing some kind of timeout with the same timeout value, then one can	1977	employing some kind of timeout with the same timeout value, then one can
…		…
1909	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is	2004	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
1910	rather complicated, but extremely efficient, something that really pays	2005	rather complicated, but extremely efficient, something that really pays
1911	off after the first million or so of active timers, i.e. it's usually	2006	off after the first million or so of active timers, i.e. it's usually
1912	overkill :)	2007	overkill :)
1913		2008
		2009	=head3 The special problem of being too early
		2010
		2011	If you ask a timer to call your callback after three seconds, then
		2012	you expect it to be invoked after three seconds - but of course, this
		2013	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		2014	guaranteed to any precision by libev - imagine somebody suspending the
		2015	process with a STOP signal for a few hours for example.
		2016
		2017	So, libev tries to invoke your callback as soon as possible I<after> the
		2018	delay has occurred, but cannot guarantee this.
		2019
		2020	A less obvious failure mode is calling your callback too early: many event
		2021	loops compare timestamps with a "elapsed delay >= requested delay", but
		2022	this can cause your callback to be invoked much earlier than you would
		2023	expect.
		2024
		2025	To see why, imagine a system with a clock that only offers full second
		2026	resolution (think windows if you can't come up with a broken enough OS
		2027	yourself). If you schedule a one-second timer at the time 500.9, then the
		2028	event loop will schedule your timeout to elapse at a system time of 500
		2029	(500.9 truncated to the resolution) + 1, or 501.
		2030
		2031	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2032	501" and invoke the callback 0.1s after it was started, even though a
		2033	one-second delay was requested - this is being "too early", despite best
		2034	intentions.
		2035
		2036	This is the reason why libev will never invoke the callback if the elapsed
		2037	delay equals the requested delay, but only when the elapsed delay is
		2038	larger than the requested delay. In the example above, libev would only invoke
		2039	the callback at system time 502, or 1.1s after the timer was started.
		2040
		2041	So, while libev cannot guarantee that your callback will be invoked
		2042	exactly when requested, it I<can> and I<does> guarantee that the requested
		2043	delay has actually elapsed, or in other words, it always errs on the "too
		2044	late" side of things.
		2045
1914	=head3 The special problem of time updates	2046	=head3 The special problem of time updates
1915		2047
1916	Establishing the current time is a costly operation (it usually takes at	2048	Establishing the current time is a costly operation (it usually takes
1917	least two system calls): EV therefore updates its idea of the current	2049	at least one system call): EV therefore updates its idea of the current
1918	time only before and after C<ev_run> collects new events, which causes a	2050	time only before and after C<ev_run> collects new events, which causes a
1919	growing difference between C<ev_now ()> and C<ev_time ()> when handling	2051	growing difference between C<ev_now ()> and C<ev_time ()> when handling
1920	lots of events in one iteration.	2052	lots of events in one iteration.
1921		2053
1922	The relative timeouts are calculated relative to the C<ev_now ()>	2054	The relative timeouts are calculated relative to the C<ev_now ()>
1923	time. This is usually the right thing as this timestamp refers to the time	2055	time. This is usually the right thing as this timestamp refers to the time
1924	of the event triggering whatever timeout you are modifying/starting. If	2056	of the event triggering whatever timeout you are modifying/starting. If
1925	you suspect event processing to be delayed and you I<need> to base the	2057	you suspect event processing to be delayed and you I<need> to base the
1926	timeout on the current time, use something like this to adjust for this:	2058	timeout on the current time, use something like the following to adjust
		2059	for it:
1927		2060
1928	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2061	ev_timer_set (&timer, after + (ev_time () - ev_now ()), 0.);
1929		2062
1930	If the event loop is suspended for a long time, you can also force an	2063	If the event loop is suspended for a long time, you can also force an
1931	update of the time returned by C<ev_now ()> by calling C<ev_now_update	2064	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1932	()>.	2065	()>, although that will push the event time of all outstanding events
		2066	further into the future.
		2067
		2068	=head3 The special problem of unsynchronised clocks
		2069
		2070	Modern systems have a variety of clocks - libev itself uses the normal
		2071	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2072	jumps).
		2073
		2074	Neither of these clocks is synchronised with each other or any other clock
		2075	on the system, so C<ev_time ()> might return a considerably different time
		2076	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2077	a call to C<gettimeofday> might return a second count that is one higher
		2078	than a directly following call to C<time>.
		2079
		2080	The moral of this is to only compare libev-related timestamps with
		2081	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2082	a second or so.
		2083
		2084	One more problem arises due to this lack of synchronisation: if libev uses
		2085	the system monotonic clock and you compare timestamps from C<ev_time>
		2086	or C<ev_now> from when you started your timer and when your callback is
		2087	invoked, you will find that sometimes the callback is a bit "early".
		2088
		2089	This is because C<ev_timer>s work in real time, not wall clock time, so
		2090	libev makes sure your callback is not invoked before the delay happened,
		2091	I<measured according to the real time>, not the system clock.
		2092
		2093	If your timeouts are based on a physical timescale (e.g. "time out this
		2094	connection after 100 seconds") then this shouldn't bother you as it is
		2095	exactly the right behaviour.
		2096
		2097	If you want to compare wall clock/system timestamps to your timers, then
		2098	you need to use C<ev_periodic>s, as these are based on the wall clock
		2099	time, where your comparisons will always generate correct results.
1933		2100
1934	=head3 The special problems of suspended animation	2101	=head3 The special problems of suspended animation
1935		2102
1936	When you leave the server world it is quite customary to hit machines that	2103	When you leave the server world it is quite customary to hit machines that
1937	can suspend/hibernate - what happens to the clocks during such a suspend?	2104	can suspend/hibernate - what happens to the clocks during such a suspend?
…		…
1967		2134
1968	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	2135	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1969		2136
1970	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	2137	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1971		2138
1972	Configure the timer to trigger after C<after> seconds. If C<repeat>	2139	Configure the timer to trigger after C<after> seconds (fractional and
1973	is C<0.>, then it will automatically be stopped once the timeout is	2140	negative values are supported). If C<repeat> is C<0.>, then it will
1974	reached. If it is positive, then the timer will automatically be	2141	automatically be stopped once the timeout is reached. If it is positive,
1975	configured to trigger again C<repeat> seconds later, again, and again,	2142	then the timer will automatically be configured to trigger again C<repeat>
1976	until stopped manually.	2143	seconds later, again, and again, until stopped manually.
1977		2144
1978	The timer itself will do a best-effort at avoiding drift, that is, if	2145	The timer itself will do a best-effort at avoiding drift, that is, if
1979	you configure a timer to trigger every 10 seconds, then it will normally	2146	you configure a timer to trigger every 10 seconds, then it will normally
1980	trigger at exactly 10 second intervals. If, however, your program cannot	2147	trigger at exactly 10 second intervals. If, however, your program cannot
1981	keep up with the timer (because it takes longer than those 10 seconds to	2148	keep up with the timer (because it takes longer than those 10 seconds to
1982	do stuff) the timer will not fire more than once per event loop iteration.	2149	do stuff) the timer will not fire more than once per event loop iteration.
1983		2150
1984	=item ev_timer_again (loop, ev_timer *)	2151	=item ev_timer_again (loop, ev_timer *)
1985		2152
1986	This will act as if the timer timed out and restart it again if it is	2153	This will act as if the timer timed out, and restarts it again if it is
1987	repeating. The exact semantics are:	2154	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2155	timeout to the C<repeat> value and calling C<ev_timer_start>.
1988		2156
		2157	The exact semantics are as in the following rules, all of which will be
		2158	applied to the watcher:
		2159
		2160	=over 4
		2161
1989	If the timer is pending, its pending status is cleared.	2162	=item If the timer is pending, the pending status is always cleared.
1990		2163
1991	If the timer is started but non-repeating, stop it (as if it timed out).	2164	=item If the timer is started but non-repeating, stop it (as if it timed
		2165	out, without invoking it).
1992		2166
1993	If the timer is repeating, either start it if necessary (with the	2167	=item If the timer is repeating, make the C<repeat> value the new timeout
1994	C<repeat> value), or reset the running timer to the C<repeat> value.	2168	and start the timer, if necessary.
1995		2169
		2170	=back
		2171
1996	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a	2172	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
1997	usage example.	2173	usage example.
1998		2174
1999	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)	2175	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
2000		2176
2001	Returns the remaining time until a timer fires. If the timer is active,	2177	Returns the remaining time until a timer fires. If the timer is active,
…		…
2054	Periodic watchers are also timers of a kind, but they are very versatile	2230	Periodic watchers are also timers of a kind, but they are very versatile
2055	(and unfortunately a bit complex).	2231	(and unfortunately a bit complex).
2056		2232
2057	Unlike C<ev_timer>, periodic watchers are not based on real time (or	2233	Unlike C<ev_timer>, periodic watchers are not based on real time (or
2058	relative time, the physical time that passes) but on wall clock time	2234	relative time, the physical time that passes) but on wall clock time
2059	(absolute time, the thing you can read on your calender or clock). The	2235	(absolute time, the thing you can read on your calendar or clock). The
2060	difference is that wall clock time can run faster or slower than real	2236	difference is that wall clock time can run faster or slower than real
2061	time, and time jumps are not uncommon (e.g. when you adjust your	2237	time, and time jumps are not uncommon (e.g. when you adjust your
2062	wrist-watch).	2238	wrist-watch).
2063		2239
2064	You can tell a periodic watcher to trigger after some specific point	2240	You can tell a periodic watcher to trigger after some specific point
…		…
2069	C<ev_timer>, which would still trigger roughly 10 seconds after starting	2245	C<ev_timer>, which would still trigger roughly 10 seconds after starting
2070	it, as it uses a relative timeout).	2246	it, as it uses a relative timeout).
2071		2247
2072	C<ev_periodic> watchers can also be used to implement vastly more complex	2248	C<ev_periodic> watchers can also be used to implement vastly more complex
2073	timers, such as triggering an event on each "midnight, local time", or	2249	timers, such as triggering an event on each "midnight, local time", or
2074	other complicated rules. This cannot be done with C<ev_timer> watchers, as	2250	other complicated rules. This cannot easily be done with C<ev_timer>
2075	those cannot react to time jumps.	2251	watchers, as those cannot react to time jumps.
2076		2252
2077	As with timers, the callback is guaranteed to be invoked only when the	2253	As with timers, the callback is guaranteed to be invoked only when the
2078	point in time where it is supposed to trigger has passed. If multiple	2254	point in time where it is supposed to trigger has passed. If multiple
2079	timers become ready during the same loop iteration then the ones with	2255	timers become ready during the same loop iteration then the ones with
2080	earlier time-out values are invoked before ones with later time-out values	2256	earlier time-out values are invoked before ones with later time-out values
…		…
2121		2297
2122	Another way to think about it (for the mathematically inclined) is that	2298	Another way to think about it (for the mathematically inclined) is that
2123	C<ev_periodic> will try to run the callback in this mode at the next possible	2299	C<ev_periodic> will try to run the callback in this mode at the next possible
2124	time where C<time = offset (mod interval)>, regardless of any time jumps.	2300	time where C<time = offset (mod interval)>, regardless of any time jumps.
2125		2301
2126	For numerical stability it is preferable that the C<offset> value is near	2302	The C<interval> I<MUST> be positive, and for numerical stability, the
2127	C<ev_now ()> (the current time), but there is no range requirement for	2303	interval value should be higher than C<1/8192> (which is around 100
2128	this value, and in fact is often specified as zero.	2304	microseconds) and C<offset> should be higher than C<0> and should have
		2305	at most a similar magnitude as the current time (say, within a factor of
		2306	ten). Typical values for offset are, in fact, C<0> or something between
		2307	C<0> and C<interval>, which is also the recommended range.
2129		2308
2130	Note also that there is an upper limit to how often a timer can fire (CPU	2309	Note also that there is an upper limit to how often a timer can fire (CPU
2131	speed for example), so if C<interval> is very small then timing stability	2310	speed for example), so if C<interval> is very small then timing stability
2132	will of course deteriorate. Libev itself tries to be exact to be about one	2311	will of course deteriorate. Libev itself tries to be exact to be about one
2133	millisecond (if the OS supports it and the machine is fast enough).	2312	millisecond (if the OS supports it and the machine is fast enough).
…		…
2163		2342
2164	NOTE: I<< This callback must always return a time that is higher than or	2343	NOTE: I<< This callback must always return a time that is higher than or
2165	equal to the passed C<now> value >>.	2344	equal to the passed C<now> value >>.
2166		2345
2167	This can be used to create very complex timers, such as a timer that	2346	This can be used to create very complex timers, such as a timer that
2168	triggers on "next midnight, local time". To do this, you would calculate the	2347	triggers on "next midnight, local time". To do this, you would calculate
2169	next midnight after C<now> and return the timestamp value for this. How	2348	the next midnight after C<now> and return the timestamp value for
2170	you do this is, again, up to you (but it is not trivial, which is the main	2349	this. Here is a (completely untested, no error checking) example on how to
2171	reason I omitted it as an example).	2350	do this:
		2351
		2352	#include <time.h>
		2353
		2354	static ev_tstamp
		2355	my_rescheduler (ev_periodic *w, ev_tstamp now)
		2356	{
		2357	time_t tnow = (time_t)now;
		2358	struct tm tm;
		2359	localtime_r (&tnow, &tm);
		2360
		2361	tm.tm_sec = tm.tm_min = tm.tm_hour = 0; // midnight current day
		2362	++tm.tm_mday; // midnight next day
		2363
		2364	return mktime (&tm);
		2365	}
		2366
		2367	Note: this code might run into trouble on days that have more then two
		2368	midnights (beginning and end).
2172		2369
2173	=back	2370	=back
2174		2371
2175	=item ev_periodic_again (loop, ev_periodic *)	2372	=item ev_periodic_again (loop, ev_periodic *)
2176		2373
…		…
2241		2438
2242	ev_periodic hourly_tick;	2439	ev_periodic hourly_tick;
2243	ev_periodic_init (&hourly_tick, clock_cb,	2440	ev_periodic_init (&hourly_tick, clock_cb,
2244	fmod (ev_now (loop), 3600.), 3600., 0);	2441	fmod (ev_now (loop), 3600.), 3600., 0);
2245	ev_periodic_start (loop, &hourly_tick);	2442	ev_periodic_start (loop, &hourly_tick);
2246		2443
2247		2444
2248	=head2 C<ev_signal> - signal me when a signal gets signalled!	2445	=head2 C<ev_signal> - signal me when a signal gets signalled!
2249		2446
2250	Signal watchers will trigger an event when the process receives a specific	2447	Signal watchers will trigger an event when the process receives a specific
2251	signal one or more times. Even though signals are very asynchronous, libev	2448	signal one or more times. Even though signals are very asynchronous, libev
2252	will try it's best to deliver signals synchronously, i.e. as part of the	2449	will try its best to deliver signals synchronously, i.e. as part of the
2253	normal event processing, like any other event.	2450	normal event processing, like any other event.
2254		2451
2255	If you want signals to be delivered truly asynchronously, just use	2452	If you want signals to be delivered truly asynchronously, just use
2256	C<sigaction> as you would do without libev and forget about sharing	2453	C<sigaction> as you would do without libev and forget about sharing
2257	the signal. You can even use C<ev_async> from a signal handler to	2454	the signal. You can even use C<ev_async> from a signal handler to
…		…
2261	only within the same loop, i.e. you can watch for C<SIGINT> in your	2458	only within the same loop, i.e. you can watch for C<SIGINT> in your
2262	default loop and for C<SIGIO> in another loop, but you cannot watch for	2459	default loop and for C<SIGIO> in another loop, but you cannot watch for
2263	C<SIGINT> in both the default loop and another loop at the same time. At	2460	C<SIGINT> in both the default loop and another loop at the same time. At
2264	the moment, C<SIGCHLD> is permanently tied to the default loop.	2461	the moment, C<SIGCHLD> is permanently tied to the default loop.
2265		2462
2266	When the first watcher gets started will libev actually register something	2463	Only after the first watcher for a signal is started will libev actually
2267	with the kernel (thus it coexists with your own signal handlers as long as	2464	register something with the kernel. It thus coexists with your own signal
2268	you don't register any with libev for the same signal).	2465	handlers as long as you don't register any with libev for the same signal.
2269		2466
2270	If possible and supported, libev will install its handlers with	2467	If possible and supported, libev will install its handlers with
2271	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should	2468	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
2272	not be unduly interrupted. If you have a problem with system calls getting	2469	not be unduly interrupted. If you have a problem with system calls getting
2273	interrupted by signals you can block all signals in an C<ev_check> watcher	2470	interrupted by signals you can block all signals in an C<ev_check> watcher
…		…
2276	=head3 The special problem of inheritance over fork/execve/pthread_create	2473	=head3 The special problem of inheritance over fork/execve/pthread_create
2277		2474
2278	Both the signal mask (C<sigprocmask>) and the signal disposition	2475	Both the signal mask (C<sigprocmask>) and the signal disposition
2279	(C<sigaction>) are unspecified after starting a signal watcher (and after	2476	(C<sigaction>) are unspecified after starting a signal watcher (and after
2280	stopping it again), that is, libev might or might not block the signal,	2477	stopping it again), that is, libev might or might not block the signal,
2281	and might or might not set or restore the installed signal handler.	2478	and might or might not set or restore the installed signal handler (but
		2479	see C<EVFLAG_NOSIGMASK>).
2282		2480
2283	While this does not matter for the signal disposition (libev never	2481	While this does not matter for the signal disposition (libev never
2284	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on	2482	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
2285	C<execve>), this matters for the signal mask: many programs do not expect	2483	C<execve>), this matters for the signal mask: many programs do not expect
2286	certain signals to be blocked.	2484	certain signals to be blocked.
…		…
2299	I<has> to modify the signal mask, at least temporarily.	2497	I<has> to modify the signal mask, at least temporarily.
2300		2498
2301	So I can't stress this enough: I<If you do not reset your signal mask when	2499	So I can't stress this enough: I<If you do not reset your signal mask when
2302	you expect it to be empty, you have a race condition in your code>. This	2500	you expect it to be empty, you have a race condition in your code>. This
2303	is not a libev-specific thing, this is true for most event libraries.	2501	is not a libev-specific thing, this is true for most event libraries.
		2502
		2503	=head3 The special problem of threads signal handling
		2504
		2505	POSIX threads has problematic signal handling semantics, specifically,
		2506	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2507	threads in a process block signals, which is hard to achieve.
		2508
		2509	When you want to use sigwait (or mix libev signal handling with your own
		2510	for the same signals), you can tackle this problem by globally blocking
		2511	all signals before creating any threads (or creating them with a fully set
		2512	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2513	loops. Then designate one thread as "signal receiver thread" which handles
		2514	these signals. You can pass on any signals that libev might be interested
		2515	in by calling C<ev_feed_signal>.
2304		2516
2305	=head3 Watcher-Specific Functions and Data Members	2517	=head3 Watcher-Specific Functions and Data Members
2306		2518
2307	=over 4	2519	=over 4
2308		2520
…		…
2443		2655
2444	=head2 C<ev_stat> - did the file attributes just change?	2656	=head2 C<ev_stat> - did the file attributes just change?
2445		2657
2446	This watches a file system path for attribute changes. That is, it calls	2658	This watches a file system path for attribute changes. That is, it calls
2447	C<stat> on that path in regular intervals (or when the OS says it changed)	2659	C<stat> on that path in regular intervals (or when the OS says it changed)
2448	and sees if it changed compared to the last time, invoking the callback if	2660	and sees if it changed compared to the last time, invoking the callback
2449	it did.	2661	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2662	happen after the watcher has been started will be reported.
2450		2663
2451	The path does not need to exist: changing from "path exists" to "path does	2664	The path does not need to exist: changing from "path exists" to "path does
2452	not exist" is a status change like any other. The condition "path does not	2665	not exist" is a status change like any other. The condition "path does not
2453	exist" (or more correctly "path cannot be stat'ed") is signified by the	2666	exist" (or more correctly "path cannot be stat'ed") is signified by the
2454	C<st_nlink> field being zero (which is otherwise always forced to be at	2667	C<st_nlink> field being zero (which is otherwise always forced to be at
…		…
2684	Apart from keeping your process non-blocking (which is a useful	2897	Apart from keeping your process non-blocking (which is a useful
2685	effect on its own sometimes), idle watchers are a good place to do	2898	effect on its own sometimes), idle watchers are a good place to do
2686	"pseudo-background processing", or delay processing stuff to after the	2899	"pseudo-background processing", or delay processing stuff to after the
2687	event loop has handled all outstanding events.	2900	event loop has handled all outstanding events.
2688		2901
		2902	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2903
		2904	As long as there is at least one active idle watcher, libev will never
		2905	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2906	For this to work, the idle watcher doesn't need to be invoked at all - the
		2907	lowest priority will do.
		2908
		2909	This mode of operation can be useful together with an C<ev_check> watcher,
		2910	to do something on each event loop iteration - for example to balance load
		2911	between different connections.
		2912
		2913	See L</Abusing an ev_check watcher for its side-effect> for a longer
		2914	example.
		2915
2689	=head3 Watcher-Specific Functions and Data Members	2916	=head3 Watcher-Specific Functions and Data Members
2690		2917
2691	=over 4	2918	=over 4
2692		2919
2693	=item ev_idle_init (ev_idle *, callback)	2920	=item ev_idle_init (ev_idle *, callback)
…		…
2704	callback, free it. Also, use no error checking, as usual.	2931	callback, free it. Also, use no error checking, as usual.
2705		2932
2706	static void	2933	static void
2707	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)	2934	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
2708	{	2935	{
		2936	// stop the watcher
		2937	ev_idle_stop (loop, w);
		2938
		2939	// now we can free it
2709	free (w);	2940	free (w);
		2941
2710	// now do something you wanted to do when the program has	2942	// now do something you wanted to do when the program has
2711	// no longer anything immediate to do.	2943	// no longer anything immediate to do.
2712	}	2944	}
2713		2945
2714	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	2946	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
…		…
2716	ev_idle_start (loop, idle_watcher);	2948	ev_idle_start (loop, idle_watcher);
2717		2949
2718		2950
2719	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2951	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2720		2952
2721	Prepare and check watchers are usually (but not always) used in pairs:	2953	Prepare and check watchers are often (but not always) used in pairs:
2722	prepare watchers get invoked before the process blocks and check watchers	2954	prepare watchers get invoked before the process blocks and check watchers
2723	afterwards.	2955	afterwards.
2724		2956
2725	You I<must not> call C<ev_run> or similar functions that enter	2957	You I<must not> call C<ev_run> (or similar functions that enter the
2726	the current event loop from either C<ev_prepare> or C<ev_check>	2958	current event loop) or C<ev_loop_fork> from either C<ev_prepare> or
2727	watchers. Other loops than the current one are fine, however. The	2959	C<ev_check> watchers. Other loops than the current one are fine,
2728	rationale behind this is that you do not need to check for recursion in	2960	however. The rationale behind this is that you do not need to check
2729	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2961	for recursion in those watchers, i.e. the sequence will always be
2730	C<ev_check> so if you have one watcher of each kind they will always be	2962	C<ev_prepare>, blocking, C<ev_check> so if you have one watcher of each
2731	called in pairs bracketing the blocking call.	2963	kind they will always be called in pairs bracketing the blocking call.
2732		2964
2733	Their main purpose is to integrate other event mechanisms into libev and	2965	Their main purpose is to integrate other event mechanisms into libev and
2734	their use is somewhat advanced. They could be used, for example, to track	2966	their use is somewhat advanced. They could be used, for example, to track
2735	variable changes, implement your own watchers, integrate net-snmp or a	2967	variable changes, implement your own watchers, integrate net-snmp or a
2736	coroutine library and lots more. They are also occasionally useful if	2968	coroutine library and lots more. They are also occasionally useful if
…		…
2754	with priority higher than or equal to the event loop and one coroutine	2986	with priority higher than or equal to the event loop and one coroutine
2755	of lower priority, but only once, using idle watchers to keep the event	2987	of lower priority, but only once, using idle watchers to keep the event
2756	loop from blocking if lower-priority coroutines are active, thus mapping	2988	loop from blocking if lower-priority coroutines are active, thus mapping
2757	low-priority coroutines to idle/background tasks).	2989	low-priority coroutines to idle/background tasks).
2758		2990
2759	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2991	When used for this purpose, it is recommended to give C<ev_check> watchers
2760	priority, to ensure that they are being run before any other watchers	2992	highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
2761	after the poll (this doesn't matter for C<ev_prepare> watchers).	2993	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		2994	watchers).
2762		2995
2763	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not	2996	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
2764	activate ("feed") events into libev. While libev fully supports this, they	2997	activate ("feed") events into libev. While libev fully supports this, they
2765	might get executed before other C<ev_check> watchers did their job. As	2998	might get executed before other C<ev_check> watchers did their job. As
2766	C<ev_check> watchers are often used to embed other (non-libev) event	2999	C<ev_check> watchers are often used to embed other (non-libev) event
2767	loops those other event loops might be in an unusable state until their	3000	loops those other event loops might be in an unusable state until their
2768	C<ev_check> watcher ran (always remind yourself to coexist peacefully with	3001	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
2769	others).	3002	others).
		3003
		3004	=head3 Abusing an C<ev_check> watcher for its side-effect
		3005
		3006	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		3007	useful because they are called once per event loop iteration. For
		3008	example, if you want to handle a large number of connections fairly, you
		3009	normally only do a bit of work for each active connection, and if there
		3010	is more work to do, you wait for the next event loop iteration, so other
		3011	connections have a chance of making progress.
		3012
		3013	Using an C<ev_check> watcher is almost enough: it will be called on the
		3014	next event loop iteration. However, that isn't as soon as possible -
		3015	without external events, your C<ev_check> watcher will not be invoked.
		3016
		3017	This is where C<ev_idle> watchers come in handy - all you need is a
		3018	single global idle watcher that is active as long as you have one active
		3019	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		3020	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		3021	invoked. Neither watcher alone can do that.
2770		3022
2771	=head3 Watcher-Specific Functions and Data Members	3023	=head3 Watcher-Specific Functions and Data Members
2772		3024
2773	=over 4	3025	=over 4
2774		3026
…		…
2975		3227
2976	=over 4	3228	=over 4
2977		3229
2978	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3230	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
2979		3231
2980	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)	3232	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
2981		3233
2982	Configures the watcher to embed the given loop, which must be	3234	Configures the watcher to embed the given loop, which must be
2983	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3235	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
2984	invoked automatically, otherwise it is the responsibility of the callback	3236	invoked automatically, otherwise it is the responsibility of the callback
2985	to invoke it (it will continue to be called until the sweep has been done,	3237	to invoke it (it will continue to be called until the sweep has been done,
…		…
3006	used).	3258	used).
3007		3259
3008	struct ev_loop *loop_hi = ev_default_init (0);	3260	struct ev_loop *loop_hi = ev_default_init (0);
3009	struct ev_loop *loop_lo = 0;	3261	struct ev_loop *loop_lo = 0;
3010	ev_embed embed;	3262	ev_embed embed;
3011		3263
3012	// see if there is a chance of getting one that works	3264	// see if there is a chance of getting one that works
3013	// (remember that a flags value of 0 means autodetection)	3265	// (remember that a flags value of 0 means autodetection)
3014	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3266	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3015	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3267	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3016	: 0;	3268	: 0;
…		…
3030	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3282	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
3031		3283
3032	struct ev_loop *loop = ev_default_init (0);	3284	struct ev_loop *loop = ev_default_init (0);
3033	struct ev_loop *loop_socket = 0;	3285	struct ev_loop *loop_socket = 0;
3034	ev_embed embed;	3286	ev_embed embed;
3035		3287
3036	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3288	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3037	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3289	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3038	{	3290	{
3039	ev_embed_init (&embed, 0, loop_socket);	3291	ev_embed_init (&embed, 0, loop_socket);
3040	ev_embed_start (loop, &embed);	3292	ev_embed_start (loop, &embed);
…		…
3048		3300
3049	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3301	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
3050		3302
3051	Fork watchers are called when a C<fork ()> was detected (usually because	3303	Fork watchers are called when a C<fork ()> was detected (usually because
3052	whoever is a good citizen cared to tell libev about it by calling	3304	whoever is a good citizen cared to tell libev about it by calling
3053	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the	3305	C<ev_loop_fork>). The invocation is done before the event loop blocks next
3054	event loop blocks next and before C<ev_check> watchers are being called,	3306	and before C<ev_check> watchers are being called, and only in the child
3055	and only in the child after the fork. If whoever good citizen calling	3307	after the fork. If whoever good citizen calling C<ev_default_fork> cheats
3056	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3308	and calls it in the wrong process, the fork handlers will be invoked, too,
3057	handlers will be invoked, too, of course.	3309	of course.
3058		3310
3059	=head3 The special problem of life after fork - how is it possible?	3311	=head3 The special problem of life after fork - how is it possible?
3060		3312
3061	Most uses of C<fork()> consist of forking, then some simple calls to set	3313	Most uses of C<fork ()> consist of forking, then some simple calls to set
3062	up/change the process environment, followed by a call to C<exec()>. This	3314	up/change the process environment, followed by a call to C<exec()>. This
3063	sequence should be handled by libev without any problems.	3315	sequence should be handled by libev without any problems.
3064		3316
3065	This changes when the application actually wants to do event handling	3317	This changes when the application actually wants to do event handling
3066	in the child, or both parent in child, in effect "continuing" after the	3318	in the child, or both parent in child, in effect "continuing" after the
…		…
3092		3344
3093	=head3 Watcher-Specific Functions and Data Members	3345	=head3 Watcher-Specific Functions and Data Members
3094		3346
3095	=over 4	3347	=over 4
3096		3348
3097	=item ev_fork_init (ev_signal *, callback)	3349	=item ev_fork_init (ev_fork *, callback)
3098		3350
3099	Initialises and configures the fork watcher - it has no parameters of any	3351	Initialises and configures the fork watcher - it has no parameters of any
3100	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,	3352	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
3101	believe me.	3353	really.
3102		3354
3103	=back	3355	=back
3104		3356
3105		3357
		3358	=head2 C<ev_cleanup> - even the best things end
		3359
		3360	Cleanup watchers are called just before the event loop is being destroyed
		3361	by a call to C<ev_loop_destroy>.
		3362
		3363	While there is no guarantee that the event loop gets destroyed, cleanup
		3364	watchers provide a convenient method to install cleanup hooks for your
		3365	program, worker threads and so on - you just to make sure to destroy the
		3366	loop when you want them to be invoked.
		3367
		3368	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3369	all other watchers, they do not keep a reference to the event loop (which
		3370	makes a lot of sense if you think about it). Like all other watchers, you
		3371	can call libev functions in the callback, except C<ev_cleanup_start>.
		3372
		3373	=head3 Watcher-Specific Functions and Data Members
		3374
		3375	=over 4
		3376
		3377	=item ev_cleanup_init (ev_cleanup *, callback)
		3378
		3379	Initialises and configures the cleanup watcher - it has no parameters of
		3380	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3381	pointless, I assure you.
		3382
		3383	=back
		3384
		3385	Example: Register an atexit handler to destroy the default loop, so any
		3386	cleanup functions are called.
		3387
		3388	static void
		3389	program_exits (void)
		3390	{
		3391	ev_loop_destroy (EV_DEFAULT_UC);
		3392	}
		3393
		3394	...
		3395	atexit (program_exits);
		3396
		3397
3106	=head2 C<ev_async> - how to wake up an event loop	3398	=head2 C<ev_async> - how to wake up an event loop
3107		3399
3108	In general, you cannot use an C<ev_run> from multiple threads or other	3400	In general, you cannot use an C<ev_loop> from multiple threads or other
3109	asynchronous sources such as signal handlers (as opposed to multiple event	3401	asynchronous sources such as signal handlers (as opposed to multiple event
3110	loops - those are of course safe to use in different threads).	3402	loops - those are of course safe to use in different threads).
3111		3403
3112	Sometimes, however, you need to wake up an event loop you do not control,	3404	Sometimes, however, you need to wake up an event loop you do not control,
3113	for example because it belongs to another thread. This is what C<ev_async>	3405	for example because it belongs to another thread. This is what C<ev_async>
…		…
3115	it by calling C<ev_async_send>, which is thread- and signal safe.	3407	it by calling C<ev_async_send>, which is thread- and signal safe.
3116		3408
3117	This functionality is very similar to C<ev_signal> watchers, as signals,	3409	This functionality is very similar to C<ev_signal> watchers, as signals,
3118	too, are asynchronous in nature, and signals, too, will be compressed	3410	too, are asynchronous in nature, and signals, too, will be compressed
3119	(i.e. the number of callback invocations may be less than the number of	3411	(i.e. the number of callback invocations may be less than the number of
3120	C<ev_async_sent> calls).	3412	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
3121		3413	of "global async watchers" by using a watcher on an otherwise unused
3122	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not	3414	signal, and C<ev_feed_signal> to signal this watcher from another thread,
3123	just the default loop.	3415	even without knowing which loop owns the signal.
3124		3416
3125	=head3 Queueing	3417	=head3 Queueing
3126		3418
3127	C<ev_async> does not support queueing of data in any way. The reason	3419	C<ev_async> does not support queueing of data in any way. The reason
3128	is that the author does not know of a simple (or any) algorithm for a	3420	is that the author does not know of a simple (or any) algorithm for a
…		…
3220	trust me.	3512	trust me.
3221		3513
3222	=item ev_async_send (loop, ev_async *)	3514	=item ev_async_send (loop, ev_async *)
3223		3515
3224	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3516	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
3225	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3517	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3518	returns.
		3519
3226	C<ev_feed_event>, this call is safe to do from other threads, signal or	3520	Unlike C<ev_feed_event>, this call is safe to do from other threads,
3227	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3521	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
3228	section below on what exactly this means).	3522	embedding section below on what exactly this means).
3229		3523
3230	Note that, as with other watchers in libev, multiple events might get	3524	Note that, as with other watchers in libev, multiple events might get
3231	compressed into a single callback invocation (another way to look at this	3525	compressed into a single callback invocation (another way to look at
3232	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,	3526	this is that C<ev_async> watchers are level-triggered: they are set on
3233	reset when the event loop detects that).	3527	C<ev_async_send>, reset when the event loop detects that).
3234		3528
3235	This call incurs the overhead of a system call only once per event loop	3529	This call incurs the overhead of at most one extra system call per event
3236	iteration, so while the overhead might be noticeable, it doesn't apply to	3530	loop iteration, if the event loop is blocked, and no syscall at all if
3237	repeated calls to C<ev_async_send> for the same event loop.	3531	the event loop (or your program) is processing events. That means that
		3532	repeated calls are basically free (there is no need to avoid calls for
		3533	performance reasons) and that the overhead becomes smaller (typically
		3534	zero) under load.
3238		3535
3239	=item bool = ev_async_pending (ev_async *)	3536	=item bool = ev_async_pending (ev_async *)
3240		3537
3241	Returns a non-zero value when C<ev_async_send> has been called on the	3538	Returns a non-zero value when C<ev_async_send> has been called on the
3242	watcher but the event has not yet been processed (or even noted) by the	3539	watcher but the event has not yet been processed (or even noted) by the
…		…
3259		3556
3260	There are some other functions of possible interest. Described. Here. Now.	3557	There are some other functions of possible interest. Described. Here. Now.
3261		3558
3262	=over 4	3559	=over 4
3263		3560
3264	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3561	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)
3265		3562
3266	This function combines a simple timer and an I/O watcher, calls your	3563	This function combines a simple timer and an I/O watcher, calls your
3267	callback on whichever event happens first and automatically stops both	3564	callback on whichever event happens first and automatically stops both
3268	watchers. This is useful if you want to wait for a single event on an fd	3565	watchers. This is useful if you want to wait for a single event on an fd
3269	or timeout without having to allocate/configure/start/stop/free one or	3566	or timeout without having to allocate/configure/start/stop/free one or
…		…
3297	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3594	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3298		3595
3299	=item ev_feed_fd_event (loop, int fd, int revents)	3596	=item ev_feed_fd_event (loop, int fd, int revents)
3300		3597
3301	Feed an event on the given fd, as if a file descriptor backend detected	3598	Feed an event on the given fd, as if a file descriptor backend detected
3302	the given events it.	3599	the given events.
3303		3600
3304	=item ev_feed_signal_event (loop, int signum)	3601	=item ev_feed_signal_event (loop, int signum)
3305		3602
3306	Feed an event as if the given signal occurred (C<loop> must be the default	3603	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3307	loop!).	3604	which is async-safe.
3308		3605
3309	=back	3606	=back
		3607
		3608
		3609	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3610
		3611	This section explains some common idioms that are not immediately
		3612	obvious. Note that examples are sprinkled over the whole manual, and this
		3613	section only contains stuff that wouldn't fit anywhere else.
		3614
		3615	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3616
		3617	Each watcher has, by default, a C<void *data> member that you can read
		3618	or modify at any time: libev will completely ignore it. This can be used
		3619	to associate arbitrary data with your watcher. If you need more data and
		3620	don't want to allocate memory separately and store a pointer to it in that
		3621	data member, you can also "subclass" the watcher type and provide your own
		3622	data:
		3623
		3624	struct my_io
		3625	{
		3626	ev_io io;
		3627	int otherfd;
		3628	void *somedata;
		3629	struct whatever *mostinteresting;
		3630	};
		3631
		3632	...
		3633	struct my_io w;
		3634	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3635
		3636	And since your callback will be called with a pointer to the watcher, you
		3637	can cast it back to your own type:
		3638
		3639	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3640	{
		3641	struct my_io *w = (struct my_io *)w_;
		3642	...
		3643	}
		3644
		3645	More interesting and less C-conformant ways of casting your callback
		3646	function type instead have been omitted.
		3647
		3648	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3649
		3650	Another common scenario is to use some data structure with multiple
		3651	embedded watchers, in effect creating your own watcher that combines
		3652	multiple libev event sources into one "super-watcher":
		3653
		3654	struct my_biggy
		3655	{
		3656	int some_data;
		3657	ev_timer t1;
		3658	ev_timer t2;
		3659	}
		3660
		3661	In this case getting the pointer to C<my_biggy> is a bit more
		3662	complicated: Either you store the address of your C<my_biggy> struct in
		3663	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3664	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3665	real programmers):
		3666
		3667	#include <stddef.h>
		3668
		3669	static void
		3670	t1_cb (EV_P_ ev_timer *w, int revents)
		3671	{
		3672	struct my_biggy big = (struct my_biggy *)
		3673	(((char *)w) - offsetof (struct my_biggy, t1));
		3674	}
		3675
		3676	static void
		3677	t2_cb (EV_P_ ev_timer *w, int revents)
		3678	{
		3679	struct my_biggy big = (struct my_biggy *)
		3680	(((char *)w) - offsetof (struct my_biggy, t2));
		3681	}
		3682
		3683	=head2 AVOIDING FINISHING BEFORE RETURNING
		3684
		3685	Often you have structures like this in event-based programs:
		3686
		3687	callback ()
		3688	{
		3689	free (request);
		3690	}
		3691
		3692	request = start_new_request (..., callback);
		3693
		3694	The intent is to start some "lengthy" operation. The C<request> could be
		3695	used to cancel the operation, or do other things with it.
		3696
		3697	It's not uncommon to have code paths in C<start_new_request> that
		3698	immediately invoke the callback, for example, to report errors. Or you add
		3699	some caching layer that finds that it can skip the lengthy aspects of the
		3700	operation and simply invoke the callback with the result.
		3701
		3702	The problem here is that this will happen I<before> C<start_new_request>
		3703	has returned, so C<request> is not set.
		3704
		3705	Even if you pass the request by some safer means to the callback, you
		3706	might want to do something to the request after starting it, such as
		3707	canceling it, which probably isn't working so well when the callback has
		3708	already been invoked.
		3709
		3710	A common way around all these issues is to make sure that
		3711	C<start_new_request> I<always> returns before the callback is invoked. If
		3712	C<start_new_request> immediately knows the result, it can artificially
		3713	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3714	example, or more sneakily, by reusing an existing (stopped) watcher and
		3715	pushing it into the pending queue:
		3716
		3717	ev_set_cb (watcher, callback);
		3718	ev_feed_event (EV_A_ watcher, 0);
		3719
		3720	This way, C<start_new_request> can safely return before the callback is
		3721	invoked, while not delaying callback invocation too much.
		3722
		3723	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3724
		3725	Often (especially in GUI toolkits) there are places where you have
		3726	I<modal> interaction, which is most easily implemented by recursively
		3727	invoking C<ev_run>.
		3728
		3729	This brings the problem of exiting - a callback might want to finish the
		3730	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3731	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3732	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3733	other combination: In these cases, a simple C<ev_break> will not work.
		3734
		3735	The solution is to maintain "break this loop" variable for each C<ev_run>
		3736	invocation, and use a loop around C<ev_run> until the condition is
		3737	triggered, using C<EVRUN_ONCE>:
		3738
		3739	// main loop
		3740	int exit_main_loop = 0;
		3741
		3742	while (!exit_main_loop)
		3743	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3744
		3745	// in a modal watcher
		3746	int exit_nested_loop = 0;
		3747
		3748	while (!exit_nested_loop)
		3749	ev_run (EV_A_ EVRUN_ONCE);
		3750
		3751	To exit from any of these loops, just set the corresponding exit variable:
		3752
		3753	// exit modal loop
		3754	exit_nested_loop = 1;
		3755
		3756	// exit main program, after modal loop is finished
		3757	exit_main_loop = 1;
		3758
		3759	// exit both
		3760	exit_main_loop = exit_nested_loop = 1;
		3761
		3762	=head2 THREAD LOCKING EXAMPLE
		3763
		3764	Here is a fictitious example of how to run an event loop in a different
		3765	thread from where callbacks are being invoked and watchers are
		3766	created/added/removed.
		3767
		3768	For a real-world example, see the C<EV::Loop::Async> perl module,
		3769	which uses exactly this technique (which is suited for many high-level
		3770	languages).
		3771
		3772	The example uses a pthread mutex to protect the loop data, a condition
		3773	variable to wait for callback invocations, an async watcher to notify the
		3774	event loop thread and an unspecified mechanism to wake up the main thread.
		3775
		3776	First, you need to associate some data with the event loop:
		3777
		3778	typedef struct {
		3779	mutex_t lock; /* global loop lock */
		3780	ev_async async_w;
		3781	thread_t tid;
		3782	cond_t invoke_cv;
		3783	} userdata;
		3784
		3785	void prepare_loop (EV_P)
		3786	{
		3787	// for simplicity, we use a static userdata struct.
		3788	static userdata u;
		3789
		3790	ev_async_init (&u->async_w, async_cb);
		3791	ev_async_start (EV_A_ &u->async_w);
		3792
		3793	pthread_mutex_init (&u->lock, 0);
		3794	pthread_cond_init (&u->invoke_cv, 0);
		3795
		3796	// now associate this with the loop
		3797	ev_set_userdata (EV_A_ u);
		3798	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3799	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3800
		3801	// then create the thread running ev_run
		3802	pthread_create (&u->tid, 0, l_run, EV_A);
		3803	}
		3804
		3805	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3806	solely to wake up the event loop so it takes notice of any new watchers
		3807	that might have been added:
		3808
		3809	static void
		3810	async_cb (EV_P_ ev_async *w, int revents)
		3811	{
		3812	// just used for the side effects
		3813	}
		3814
		3815	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3816	protecting the loop data, respectively.
		3817
		3818	static void
		3819	l_release (EV_P)
		3820	{
		3821	userdata *u = ev_userdata (EV_A);
		3822	pthread_mutex_unlock (&u->lock);
		3823	}
		3824
		3825	static void
		3826	l_acquire (EV_P)
		3827	{
		3828	userdata *u = ev_userdata (EV_A);
		3829	pthread_mutex_lock (&u->lock);
		3830	}
		3831
		3832	The event loop thread first acquires the mutex, and then jumps straight
		3833	into C<ev_run>:
		3834
		3835	void *
		3836	l_run (void *thr_arg)
		3837	{
		3838	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3839
		3840	l_acquire (EV_A);
		3841	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3842	ev_run (EV_A_ 0);
		3843	l_release (EV_A);
		3844
		3845	return 0;
		3846	}
		3847
		3848	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3849	signal the main thread via some unspecified mechanism (signals? pipe
		3850	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3851	have been called (in a while loop because a) spurious wakeups are possible
		3852	and b) skipping inter-thread-communication when there are no pending
		3853	watchers is very beneficial):
		3854
		3855	static void
		3856	l_invoke (EV_P)
		3857	{
		3858	userdata *u = ev_userdata (EV_A);
		3859
		3860	while (ev_pending_count (EV_A))
		3861	{
		3862	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3863	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3864	}
		3865	}
		3866
		3867	Now, whenever the main thread gets told to invoke pending watchers, it
		3868	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3869	thread to continue:
		3870
		3871	static void
		3872	real_invoke_pending (EV_P)
		3873	{
		3874	userdata *u = ev_userdata (EV_A);
		3875
		3876	pthread_mutex_lock (&u->lock);
		3877	ev_invoke_pending (EV_A);
		3878	pthread_cond_signal (&u->invoke_cv);
		3879	pthread_mutex_unlock (&u->lock);
		3880	}
		3881
		3882	Whenever you want to start/stop a watcher or do other modifications to an
		3883	event loop, you will now have to lock:
		3884
		3885	ev_timer timeout_watcher;
		3886	userdata *u = ev_userdata (EV_A);
		3887
		3888	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3889
		3890	pthread_mutex_lock (&u->lock);
		3891	ev_timer_start (EV_A_ &timeout_watcher);
		3892	ev_async_send (EV_A_ &u->async_w);
		3893	pthread_mutex_unlock (&u->lock);
		3894
		3895	Note that sending the C<ev_async> watcher is required because otherwise
		3896	an event loop currently blocking in the kernel will have no knowledge
		3897	about the newly added timer. By waking up the loop it will pick up any new
		3898	watchers in the next event loop iteration.
		3899
		3900	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3901
		3902	While the overhead of a callback that e.g. schedules a thread is small, it
		3903	is still an overhead. If you embed libev, and your main usage is with some
		3904	kind of threads or coroutines, you might want to customise libev so that
		3905	doesn't need callbacks anymore.
		3906
		3907	Imagine you have coroutines that you can switch to using a function
		3908	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3909	and that due to some magic, the currently active coroutine is stored in a
		3910	global called C<current_coro>. Then you can build your own "wait for libev
		3911	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3912	the differing C<;> conventions):
		3913
		3914	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3915	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3916
		3917	That means instead of having a C callback function, you store the
		3918	coroutine to switch to in each watcher, and instead of having libev call
		3919	your callback, you instead have it switch to that coroutine.
		3920
		3921	A coroutine might now wait for an event with a function called
		3922	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3923	matter when, or whether the watcher is active or not when this function is
		3924	called):
		3925
		3926	void
		3927	wait_for_event (ev_watcher *w)
		3928	{
		3929	ev_set_cb (w, current_coro);
		3930	switch_to (libev_coro);
		3931	}
		3932
		3933	That basically suspends the coroutine inside C<wait_for_event> and
		3934	continues the libev coroutine, which, when appropriate, switches back to
		3935	this or any other coroutine.
		3936
		3937	You can do similar tricks if you have, say, threads with an event queue -
		3938	instead of storing a coroutine, you store the queue object and instead of
		3939	switching to a coroutine, you push the watcher onto the queue and notify
		3940	any waiters.
		3941
		3942	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		3943	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3944
		3945	// my_ev.h
		3946	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3947	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3948	#include "../libev/ev.h"
		3949
		3950	// my_ev.c
		3951	#define EV_H "my_ev.h"
		3952	#include "../libev/ev.c"
		3953
		3954	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3955	F<my_ev.c> into your project. When properly specifying include paths, you
		3956	can even use F<ev.h> as header file name directly.
3310		3957
3311		3958
3312	=head1 LIBEVENT EMULATION	3959	=head1 LIBEVENT EMULATION
3313		3960
3314	Libev offers a compatibility emulation layer for libevent. It cannot	3961	Libev offers a compatibility emulation layer for libevent. It cannot
3315	emulate the internals of libevent, so here are some usage hints:	3962	emulate the internals of libevent, so here are some usage hints:
3316		3963
3317	=over 4	3964	=over 4
		3965
		3966	=item * Only the libevent-1.4.1-beta API is being emulated.
		3967
		3968	This was the newest libevent version available when libev was implemented,
		3969	and is still mostly unchanged in 2010.
3318		3970
3319	=item * Use it by including <event.h>, as usual.	3971	=item * Use it by including <event.h>, as usual.
3320		3972
3321	=item * The following members are fully supported: ev_base, ev_callback,	3973	=item * The following members are fully supported: ev_base, ev_callback,
3322	ev_arg, ev_fd, ev_res, ev_events.	3974	ev_arg, ev_fd, ev_res, ev_events.
…		…
3328	=item * Priorities are not currently supported. Initialising priorities	3980	=item * Priorities are not currently supported. Initialising priorities
3329	will fail and all watchers will have the same priority, even though there	3981	will fail and all watchers will have the same priority, even though there
3330	is an ev_pri field.	3982	is an ev_pri field.
3331		3983
3332	=item * In libevent, the last base created gets the signals, in libev, the	3984	=item * In libevent, the last base created gets the signals, in libev, the
3333	first base created (== the default loop) gets the signals.	3985	base that registered the signal gets the signals.
3334		3986
3335	=item * Other members are not supported.	3987	=item * Other members are not supported.
3336		3988
3337	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3989	=item * The libev emulation is I<not> ABI compatible to libevent, you need
3338	to use the libev header file and library.	3990	to use the libev header file and library.
3339		3991
3340	=back	3992	=back
3341		3993
3342	=head1 C++ SUPPORT	3994	=head1 C++ SUPPORT
		3995
		3996	=head2 C API
		3997
		3998	The normal C API should work fine when used from C++: both ev.h and the
		3999	libev sources can be compiled as C++. Therefore, code that uses the C API
		4000	will work fine.
		4001
		4002	Proper exception specifications might have to be added to callbacks passed
		4003	to libev: exceptions may be thrown only from watcher callbacks, all other
		4004	callbacks (allocator, syserr, loop acquire/release and periodic reschedule
		4005	callbacks) must not throw exceptions, and might need a C<noexcept>
		4006	specification. If you have code that needs to be compiled as both C and
		4007	C++ you can use the C<EV_NOEXCEPT> macro for this:
		4008
		4009	static void
		4010	fatal_error (const char *msg) EV_NOEXCEPT
		4011	{
		4012	perror (msg);
		4013	abort ();
		4014	}
		4015
		4016	...
		4017	ev_set_syserr_cb (fatal_error);
		4018
		4019	The only API functions that can currently throw exceptions are C<ev_run>,
		4020	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		4021	because it runs cleanup watchers).
		4022
		4023	Throwing exceptions in watcher callbacks is only supported if libev itself
		4024	is compiled with a C++ compiler or your C and C++ environments allow
		4025	throwing exceptions through C libraries (most do).
		4026
		4027	=head2 C++ API
3343		4028
3344	Libev comes with some simplistic wrapper classes for C++ that mainly allow	4029	Libev comes with some simplistic wrapper classes for C++ that mainly allow
3345	you to use some convenience methods to start/stop watchers and also change	4030	you to use some convenience methods to start/stop watchers and also change
3346	the callback model to a model using method callbacks on objects.	4031	the callback model to a model using method callbacks on objects.
3347		4032
3348	To use it,	4033	To use it,
3349		4034
3350	#include <ev++.h>	4035	#include <ev++.h>
3351		4036
3352	This automatically includes F<ev.h> and puts all of its definitions (many	4037	This automatically includes F<ev.h> and puts all of its definitions (many
3353	of them macros) into the global namespace. All C++ specific things are	4038	of them macros) into the global namespace. All C++ specific things are
3354	put into the C<ev> namespace. It should support all the same embedding	4039	put into the C<ev> namespace. It should support all the same embedding
…		…
3357	Care has been taken to keep the overhead low. The only data member the C++	4042	Care has been taken to keep the overhead low. The only data member the C++
3358	classes add (compared to plain C-style watchers) is the event loop pointer	4043	classes add (compared to plain C-style watchers) is the event loop pointer
3359	that the watcher is associated with (or no additional members at all if	4044	that the watcher is associated with (or no additional members at all if
3360	you disable C<EV_MULTIPLICITY> when embedding libev).	4045	you disable C<EV_MULTIPLICITY> when embedding libev).
3361		4046
3362	Currently, functions, and static and non-static member functions can be	4047	Currently, functions, static and non-static member functions and classes
3363	used as callbacks. Other types should be easy to add as long as they only	4048	with C<operator ()> can be used as callbacks. Other types should be easy
3364	need one additional pointer for context. If you need support for other	4049	to add as long as they only need one additional pointer for context. If
3365	types of functors please contact the author (preferably after implementing	4050	you need support for other types of functors please contact the author
3366	it).	4051	(preferably after implementing it).
		4052
		4053	For all this to work, your C++ compiler either has to use the same calling
		4054	conventions as your C compiler (for static member functions), or you have
		4055	to embed libev and compile libev itself as C++.
3367		4056
3368	Here is a list of things available in the C<ev> namespace:	4057	Here is a list of things available in the C<ev> namespace:
3369		4058
3370	=over 4	4059	=over 4
3371		4060
…		…
3381	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	4070	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
3382		4071
3383	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4072	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
3384	the same name in the C<ev> namespace, with the exception of C<ev_signal>	4073	the same name in the C<ev> namespace, with the exception of C<ev_signal>
3385	which is called C<ev::sig> to avoid clashes with the C<signal> macro	4074	which is called C<ev::sig> to avoid clashes with the C<signal> macro
3386	defines by many implementations.	4075	defined by many implementations.
3387		4076
3388	All of those classes have these methods:	4077	All of those classes have these methods:
3389		4078
3390	=over 4	4079	=over 4
3391		4080
…		…
3453	void operator() (ev::io &w, int revents)	4142	void operator() (ev::io &w, int revents)
3454	{	4143	{
3455	...	4144	...
3456	}	4145	}
3457	}	4146	}
3458		4147
3459	myfunctor f;	4148	myfunctor f;
3460		4149
3461	ev::io w;	4150	ev::io w;
3462	w.set (&f);	4151	w.set (&f);
3463		4152
…		…
3481	Associates a different C<struct ev_loop> with this watcher. You can only	4170	Associates a different C<struct ev_loop> with this watcher. You can only
3482	do this when the watcher is inactive (and not pending either).	4171	do this when the watcher is inactive (and not pending either).
3483		4172
3484	=item w->set ([arguments])	4173	=item w->set ([arguments])
3485		4174
3486	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this	4175	Basically the same as C<ev_TYPE_set> (except for C<ev::embed> watchers>),
3487	method or a suitable start method must be called at least once. Unlike the	4176	with the same arguments. Either this method or a suitable start method
3488	C counterpart, an active watcher gets automatically stopped and restarted	4177	must be called at least once. Unlike the C counterpart, an active watcher
3489	when reconfiguring it with this method.	4178	gets automatically stopped and restarted when reconfiguring it with this
		4179	method.
		4180
		4181	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4182	clashing with the C<set (loop)> method.
3490		4183
3491	=item w->start ()	4184	=item w->start ()
3492		4185
3493	Starts the watcher. Note that there is no C<loop> argument, as the	4186	Starts the watcher. Note that there is no C<loop> argument, as the
3494	constructor already stores the event loop.	4187	constructor already stores the event loop.
…		…
3524	watchers in the constructor.	4217	watchers in the constructor.
3525		4218
3526	class myclass	4219	class myclass
3527	{	4220	{
3528	ev::io io ; void io_cb (ev::io &w, int revents);	4221	ev::io io ; void io_cb (ev::io &w, int revents);
3529	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);	4222	ev::io io2 ; void io2_cb (ev::io &w, int revents);
3530	ev::idle idle; void idle_cb (ev::idle &w, int revents);	4223	ev::idle idle; void idle_cb (ev::idle &w, int revents);
3531		4224
3532	myclass (int fd)	4225	myclass (int fd)
3533	{	4226	{
3534	io .set <myclass, &myclass::io_cb > (this);	4227	io .set <myclass, &myclass::io_cb > (this);
…		…
3585	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.	4278	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
3586		4279
3587	=item D	4280	=item D
3588		4281
3589	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4282	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
3590	be found at L<http://proj.llucax.com.ar/wiki/evd>.	4283	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
3591		4284
3592	=item Ocaml	4285	=item Ocaml
3593		4286
3594	Erkki Seppala has written Ocaml bindings for libev, to be found at	4287	Erkki Seppala has written Ocaml bindings for libev, to be found at
3595	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	4288	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
…		…
3598		4291
3599	Brian Maher has written a partial interface to libev for lua (at the	4292	Brian Maher has written a partial interface to libev for lua (at the
3600	time of this writing, only C<ev_io> and C<ev_timer>), to be found at	4293	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
3601	L<http://github.com/brimworks/lua-ev>.	4294	L<http://github.com/brimworks/lua-ev>.
3602		4295
		4296	=item Javascript
		4297
		4298	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4299
		4300	=item Others
		4301
		4302	There are others, and I stopped counting.
		4303
3603	=back	4304	=back
3604		4305
3605		4306
3606	=head1 MACRO MAGIC	4307	=head1 MACRO MAGIC
3607		4308
…		…
3643	suitable for use with C<EV_A>.	4344	suitable for use with C<EV_A>.
3644		4345
3645	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4346	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
3646		4347
3647	Similar to the other two macros, this gives you the value of the default	4348	Similar to the other two macros, this gives you the value of the default
3648	loop, if multiple loops are supported ("ev loop default").	4349	loop, if multiple loops are supported ("ev loop default"). The default loop
		4350	will be initialised if it isn't already initialised.
		4351
		4352	For non-multiplicity builds, these macros do nothing, so you always have
		4353	to initialise the loop somewhere.
3649		4354
3650	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4355	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
3651		4356
3652	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4357	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
3653	default loop has been initialised (C<UC> == unchecked). Their behaviour	4358	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
3720	ev_vars.h	4425	ev_vars.h
3721	ev_wrap.h	4426	ev_wrap.h
3722		4427
3723	ev_win32.c required on win32 platforms only	4428	ev_win32.c required on win32 platforms only
3724		4429
3725	ev_select.c only when select backend is enabled (which is enabled by default)	4430	ev_select.c only when select backend is enabled
3726	ev_poll.c only when poll backend is enabled (disabled by default)	4431	ev_poll.c only when poll backend is enabled
3727	ev_epoll.c only when the epoll backend is enabled (disabled by default)	4432	ev_epoll.c only when the epoll backend is enabled
3728	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	4433	ev_kqueue.c only when the kqueue backend is enabled
3729	ev_port.c only when the solaris port backend is enabled (disabled by default)	4434	ev_port.c only when the solaris port backend is enabled
3730		4435
3731	F<ev.c> includes the backend files directly when enabled, so you only need	4436	F<ev.c> includes the backend files directly when enabled, so you only need
3732	to compile this single file.	4437	to compile this single file.
3733		4438
3734	=head3 LIBEVENT COMPATIBILITY API	4439	=head3 LIBEVENT COMPATIBILITY API
…		…
3798	supported). It will also not define any of the structs usually found in	4503	supported). It will also not define any of the structs usually found in
3799	F<event.h> that are not directly supported by the libev core alone.	4504	F<event.h> that are not directly supported by the libev core alone.
3800		4505
3801	In standalone mode, libev will still try to automatically deduce the	4506	In standalone mode, libev will still try to automatically deduce the
3802	configuration, but has to be more conservative.	4507	configuration, but has to be more conservative.
		4508
		4509	=item EV_USE_FLOOR
		4510
		4511	If defined to be C<1>, libev will use the C<floor ()> function for its
		4512	periodic reschedule calculations, otherwise libev will fall back on a
		4513	portable (slower) implementation. If you enable this, you usually have to
		4514	link against libm or something equivalent. Enabling this when the C<floor>
		4515	function is not available will fail, so the safe default is to not enable
		4516	this.
3803		4517
3804	=item EV_USE_MONOTONIC	4518	=item EV_USE_MONOTONIC
3805		4519
3806	If defined to be C<1>, libev will try to detect the availability of the	4520	If defined to be C<1>, libev will try to detect the availability of the
3807	monotonic clock option at both compile time and runtime. Otherwise no	4521	monotonic clock option at both compile time and runtime. Otherwise no
…		…
3892		4606
3893	If programs implement their own fd to handle mapping on win32, then this	4607	If programs implement their own fd to handle mapping on win32, then this
3894	macro can be used to override the C<close> function, useful to unregister	4608	macro can be used to override the C<close> function, useful to unregister
3895	file descriptors again. Note that the replacement function has to close	4609	file descriptors again. Note that the replacement function has to close
3896	the underlying OS handle.	4610	the underlying OS handle.
		4611
		4612	=item EV_USE_WSASOCKET
		4613
		4614	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4615	communication socket, which works better in some environments. Otherwise,
		4616	the normal C<socket> function will be used, which works better in other
		4617	environments.
3897		4618
3898	=item EV_USE_POLL	4619	=item EV_USE_POLL
3899		4620
3900	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4621	If defined to be C<1>, libev will compile in support for the C<poll>(2)
3901	backend. Otherwise it will be enabled on non-win32 platforms. It	4622	backend. Otherwise it will be enabled on non-win32 platforms. It
…		…
3937	If defined to be C<1>, libev will compile in support for the Linux inotify	4658	If defined to be C<1>, libev will compile in support for the Linux inotify
3938	interface to speed up C<ev_stat> watchers. Its actual availability will	4659	interface to speed up C<ev_stat> watchers. Its actual availability will
3939	be detected at runtime. If undefined, it will be enabled if the headers	4660	be detected at runtime. If undefined, it will be enabled if the headers
3940	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4661	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
3941		4662
		4663	=item EV_NO_SMP
		4664
		4665	If defined to be C<1>, libev will assume that memory is always coherent
		4666	between threads, that is, threads can be used, but threads never run on
		4667	different cpus (or different cpu cores). This reduces dependencies
		4668	and makes libev faster.
		4669
		4670	=item EV_NO_THREADS
		4671
		4672	If defined to be C<1>, libev will assume that it will never be called from
		4673	different threads (that includes signal handlers), which is a stronger
		4674	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4675	libev faster.
		4676
3942	=item EV_ATOMIC_T	4677	=item EV_ATOMIC_T
3943		4678
3944	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4679	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
3945	access is atomic with respect to other threads or signal contexts. No such	4680	access is atomic with respect to other threads or signal contexts. No
3946	type is easily found in the C language, so you can provide your own type	4681	such type is easily found in the C language, so you can provide your own
3947	that you know is safe for your purposes. It is used both for signal handler "locking"	4682	type that you know is safe for your purposes. It is used both for signal
3948	as well as for signal and thread safety in C<ev_async> watchers.	4683	handler "locking" as well as for signal and thread safety in C<ev_async>
		4684	watchers.
3949		4685
3950	In the absence of this define, libev will use C<sig_atomic_t volatile>	4686	In the absence of this define, libev will use C<sig_atomic_t volatile>
3951	(from F<signal.h>), which is usually good enough on most platforms.	4687	(from F<signal.h>), which is usually good enough on most platforms.
3952		4688
3953	=item EV_H (h)	4689	=item EV_H (h)
…		…
3980	will have the C<struct ev_loop *> as first argument, and you can create	4716	will have the C<struct ev_loop *> as first argument, and you can create
3981	additional independent event loops. Otherwise there will be no support	4717	additional independent event loops. Otherwise there will be no support
3982	for multiple event loops and there is no first event loop pointer	4718	for multiple event loops and there is no first event loop pointer
3983	argument. Instead, all functions act on the single default loop.	4719	argument. Instead, all functions act on the single default loop.
3984		4720
		4721	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4722	default loop when multiplicity is switched off - you always have to
		4723	initialise the loop manually in this case.
		4724
3985	=item EV_MINPRI	4725	=item EV_MINPRI
3986		4726
3987	=item EV_MAXPRI	4727	=item EV_MAXPRI
3988		4728
3989	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4729	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
4025	#define EV_USE_POLL 1	4765	#define EV_USE_POLL 1
4026	#define EV_CHILD_ENABLE 1	4766	#define EV_CHILD_ENABLE 1
4027	#define EV_ASYNC_ENABLE 1	4767	#define EV_ASYNC_ENABLE 1
4028		4768
4029	The actual value is a bitset, it can be a combination of the following	4769	The actual value is a bitset, it can be a combination of the following
4030	values:	4770	values (by default, all of these are enabled):
4031		4771
4032	=over 4	4772	=over 4
4033		4773
4034	=item C<1> - faster/larger code	4774	=item C<1> - faster/larger code
4035		4775
…		…
4039	code size by roughly 30% on amd64).	4779	code size by roughly 30% on amd64).
4040		4780
4041	When optimising for size, use of compiler flags such as C<-Os> with	4781	When optimising for size, use of compiler flags such as C<-Os> with
4042	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of	4782	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
4043	assertions.	4783	assertions.
		4784
		4785	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4786	(e.g. gcc with C<-Os>).
4044		4787
4045	=item C<2> - faster/larger data structures	4788	=item C<2> - faster/larger data structures
4046		4789
4047	Replaces the small 2-heap for timer management by a faster 4-heap, larger	4790	Replaces the small 2-heap for timer management by a faster 4-heap, larger
4048	hash table sizes and so on. This will usually further increase code size	4791	hash table sizes and so on. This will usually further increase code size
4049	and can additionally have an effect on the size of data structures at	4792	and can additionally have an effect on the size of data structures at
4050	runtime.	4793	runtime.
4051		4794
		4795	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4796	(e.g. gcc with C<-Os>).
		4797
4052	=item C<4> - full API configuration	4798	=item C<4> - full API configuration
4053		4799
4054	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and	4800	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
4055	enables multiplicity (C<EV_MULTIPLICITY>=1).	4801	enables multiplicity (C<EV_MULTIPLICITY>=1).
4056		4802
…		…
4086		4832
4087	With an intelligent-enough linker (gcc+binutils are intelligent enough	4833	With an intelligent-enough linker (gcc+binutils are intelligent enough
4088	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by	4834	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
4089	your program might be left out as well - a binary starting a timer and an	4835	your program might be left out as well - a binary starting a timer and an
4090	I/O watcher then might come out at only 5Kb.	4836	I/O watcher then might come out at only 5Kb.
		4837
		4838	=item EV_API_STATIC
		4839
		4840	If this symbol is defined (by default it is not), then all identifiers
		4841	will have static linkage. This means that libev will not export any
		4842	identifiers, and you cannot link against libev anymore. This can be useful
		4843	when you embed libev, only want to use libev functions in a single file,
		4844	and do not want its identifiers to be visible.
		4845
		4846	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4847	wants to use libev.
		4848
		4849	This option only works when libev is compiled with a C compiler, as C++
		4850	doesn't support the required declaration syntax.
4091		4851
4092	=item EV_AVOID_STDIO	4852	=item EV_AVOID_STDIO
4093		4853
4094	If this is set to C<1> at compiletime, then libev will avoid using stdio	4854	If this is set to C<1> at compiletime, then libev will avoid using stdio
4095	functions (printf, scanf, perror etc.). This will increase the code size	4855	functions (printf, scanf, perror etc.). This will increase the code size
…		…
4239	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4999	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4240		5000
4241	#include "ev_cpp.h"	5001	#include "ev_cpp.h"
4242	#include "ev.c"	5002	#include "ev.c"
4243		5003
4244	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	5004	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4245		5005
4246	=head2 THREADS AND COROUTINES	5006	=head2 THREADS AND COROUTINES
4247		5007
4248	=head3 THREADS	5008	=head3 THREADS
4249		5009
…		…
4300	default loop and triggering an C<ev_async> watcher from the default loop	5060	default loop and triggering an C<ev_async> watcher from the default loop
4301	watcher callback into the event loop interested in the signal.	5061	watcher callback into the event loop interested in the signal.
4302		5062
4303	=back	5063	=back
4304		5064
4305	=head4 THREAD LOCKING EXAMPLE	5065	See also L</THREAD LOCKING EXAMPLE>.
4306
4307	Here is a fictitious example of how to run an event loop in a different
4308	thread than where callbacks are being invoked and watchers are
4309	created/added/removed.
4310
4311	For a real-world example, see the C<EV::Loop::Async> perl module,
4312	which uses exactly this technique (which is suited for many high-level
4313	languages).
4314
4315	The example uses a pthread mutex to protect the loop data, a condition
4316	variable to wait for callback invocations, an async watcher to notify the
4317	event loop thread and an unspecified mechanism to wake up the main thread.
4318
4319	First, you need to associate some data with the event loop:
4320
4321	typedef struct {
4322	mutex_t lock; /* global loop lock */
4323	ev_async async_w;
4324	thread_t tid;
4325	cond_t invoke_cv;
4326	} userdata;
4327
4328	void prepare_loop (EV_P)
4329	{
4330	// for simplicity, we use a static userdata struct.
4331	static userdata u;
4332
4333	ev_async_init (&u->async_w, async_cb);
4334	ev_async_start (EV_A_ &u->async_w);
4335
4336	pthread_mutex_init (&u->lock, 0);
4337	pthread_cond_init (&u->invoke_cv, 0);
4338
4339	// now associate this with the loop
4340	ev_set_userdata (EV_A_ u);
4341	ev_set_invoke_pending_cb (EV_A_ l_invoke);
4342	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4343
4344	// then create the thread running ev_loop
4345	pthread_create (&u->tid, 0, l_run, EV_A);
4346	}
4347
4348	The callback for the C<ev_async> watcher does nothing: the watcher is used
4349	solely to wake up the event loop so it takes notice of any new watchers
4350	that might have been added:
4351
4352	static void
4353	async_cb (EV_P_ ev_async *w, int revents)
4354	{
4355	// just used for the side effects
4356	}
4357
4358	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
4359	protecting the loop data, respectively.
4360
4361	static void
4362	l_release (EV_P)
4363	{
4364	userdata *u = ev_userdata (EV_A);
4365	pthread_mutex_unlock (&u->lock);
4366	}
4367
4368	static void
4369	l_acquire (EV_P)
4370	{
4371	userdata *u = ev_userdata (EV_A);
4372	pthread_mutex_lock (&u->lock);
4373	}
4374
4375	The event loop thread first acquires the mutex, and then jumps straight
4376	into C<ev_run>:
4377
4378	void *
4379	l_run (void *thr_arg)
4380	{
4381	struct ev_loop *loop = (struct ev_loop *)thr_arg;
4382
4383	l_acquire (EV_A);
4384	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4385	ev_run (EV_A_ 0);
4386	l_release (EV_A);
4387
4388	return 0;
4389	}
4390
4391	Instead of invoking all pending watchers, the C<l_invoke> callback will
4392	signal the main thread via some unspecified mechanism (signals? pipe
4393	writes? C<Async::Interrupt>?) and then waits until all pending watchers
4394	have been called (in a while loop because a) spurious wakeups are possible
4395	and b) skipping inter-thread-communication when there are no pending
4396	watchers is very beneficial):
4397
4398	static void
4399	l_invoke (EV_P)
4400	{
4401	userdata *u = ev_userdata (EV_A);
4402
4403	while (ev_pending_count (EV_A))
4404	{
4405	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4406	pthread_cond_wait (&u->invoke_cv, &u->lock);
4407	}
4408	}
4409
4410	Now, whenever the main thread gets told to invoke pending watchers, it
4411	will grab the lock, call C<ev_invoke_pending> and then signal the loop
4412	thread to continue:
4413
4414	static void
4415	real_invoke_pending (EV_P)
4416	{
4417	userdata *u = ev_userdata (EV_A);
4418
4419	pthread_mutex_lock (&u->lock);
4420	ev_invoke_pending (EV_A);
4421	pthread_cond_signal (&u->invoke_cv);
4422	pthread_mutex_unlock (&u->lock);
4423	}
4424
4425	Whenever you want to start/stop a watcher or do other modifications to an
4426	event loop, you will now have to lock:
4427
4428	ev_timer timeout_watcher;
4429	userdata *u = ev_userdata (EV_A);
4430
4431	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4432
4433	pthread_mutex_lock (&u->lock);
4434	ev_timer_start (EV_A_ &timeout_watcher);
4435	ev_async_send (EV_A_ &u->async_w);
4436	pthread_mutex_unlock (&u->lock);
4437
4438	Note that sending the C<ev_async> watcher is required because otherwise
4439	an event loop currently blocking in the kernel will have no knowledge
4440	about the newly added timer. By waking up the loop it will pick up any new
4441	watchers in the next event loop iteration.
4442		5066
4443	=head3 COROUTINES	5067	=head3 COROUTINES
4444		5068
4445	Libev is very accommodating to coroutines ("cooperative threads"):	5069	Libev is very accommodating to coroutines ("cooperative threads"):
4446	libev fully supports nesting calls to its functions from different	5070	libev fully supports nesting calls to its functions from different
…		…
4611	requires, and its I/O model is fundamentally incompatible with the POSIX	5235	requires, and its I/O model is fundamentally incompatible with the POSIX
4612	model. Libev still offers limited functionality on this platform in	5236	model. Libev still offers limited functionality on this platform in
4613	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5237	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
4614	descriptors. This only applies when using Win32 natively, not when using	5238	descriptors. This only applies when using Win32 natively, not when using
4615	e.g. cygwin. Actually, it only applies to the microsofts own compilers,	5239	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4616	as every compielr comes with a slightly differently broken/incompatible	5240	as every compiler comes with a slightly differently broken/incompatible
4617	environment.	5241	environment.
4618		5242
4619	Lifting these limitations would basically require the full	5243	Lifting these limitations would basically require the full
4620	re-implementation of the I/O system. If you are into this kind of thing,	5244	re-implementation of the I/O system. If you are into this kind of thing,
4621	then note that glib does exactly that for you in a very portable way (note	5245	then note that glib does exactly that for you in a very portable way (note
…		…
4715	structure (guaranteed by POSIX but not by ISO C for example), but it also	5339	structure (guaranteed by POSIX but not by ISO C for example), but it also
4716	assumes that the same (machine) code can be used to call any watcher	5340	assumes that the same (machine) code can be used to call any watcher
4717	callback: The watcher callbacks have different type signatures, but libev	5341	callback: The watcher callbacks have different type signatures, but libev
4718	calls them using an C<ev_watcher *> internally.	5342	calls them using an C<ev_watcher *> internally.
4719		5343
		5344	=item null pointers and integer zero are represented by 0 bytes
		5345
		5346	Libev uses C<memset> to initialise structs and arrays to C<0> bytes, and
		5347	relies on this setting pointers and integers to null.
		5348
		5349	=item pointer accesses must be thread-atomic
		5350
		5351	Accessing a pointer value must be atomic, it must both be readable and
		5352	writable in one piece - this is the case on all current architectures.
		5353
4720	=item C<sig_atomic_t volatile> must be thread-atomic as well	5354	=item C<sig_atomic_t volatile> must be thread-atomic as well
4721		5355
4722	The type C<sig_atomic_t volatile> (or whatever is defined as	5356	The type C<sig_atomic_t volatile> (or whatever is defined as
4723	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different	5357	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
4724	threads. This is not part of the specification for C<sig_atomic_t>, but is	5358	threads. This is not part of the specification for C<sig_atomic_t>, but is
…		…
4732	thread" or will block signals process-wide, both behaviours would	5366	thread" or will block signals process-wide, both behaviours would
4733	be compatible with libev. Interaction between C<sigprocmask> and	5367	be compatible with libev. Interaction between C<sigprocmask> and
4734	C<pthread_sigmask> could complicate things, however.	5368	C<pthread_sigmask> could complicate things, however.
4735		5369
4736	The most portable way to handle signals is to block signals in all threads	5370	The most portable way to handle signals is to block signals in all threads
4737	except the initial one, and run the default loop in the initial thread as	5371	except the initial one, and run the signal handling loop in the initial
4738	well.	5372	thread as well.
4739		5373
4740	=item C<long> must be large enough for common memory allocation sizes	5374	=item C<long> must be large enough for common memory allocation sizes
4741		5375
4742	To improve portability and simplify its API, libev uses C<long> internally	5376	To improve portability and simplify its API, libev uses C<long> internally
4743	instead of C<size_t> when allocating its data structures. On non-POSIX	5377	instead of C<size_t> when allocating its data structures. On non-POSIX
…		…
4749		5383
4750	The type C<double> is used to represent timestamps. It is required to	5384	The type C<double> is used to represent timestamps. It is required to
4751	have at least 51 bits of mantissa (and 9 bits of exponent), which is	5385	have at least 51 bits of mantissa (and 9 bits of exponent), which is
4752	good enough for at least into the year 4000 with millisecond accuracy	5386	good enough for at least into the year 4000 with millisecond accuracy
4753	(the design goal for libev). This requirement is overfulfilled by	5387	(the design goal for libev). This requirement is overfulfilled by
4754	implementations using IEEE 754, which is basically all existing ones. With	5388	implementations using IEEE 754, which is basically all existing ones.
		5389
4755	IEEE 754 doubles, you get microsecond accuracy until at least 2200.	5390	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5391	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5392	is either obsolete or somebody patched it to use C<long double> or
		5393	something like that, just kidding).
4756		5394
4757	=back	5395	=back
4758		5396
4759	If you know of other additional requirements drop me a note.	5397	If you know of other additional requirements drop me a note.
4760		5398
…		…
4822	=item Processing ev_async_send: O(number_of_async_watchers)	5460	=item Processing ev_async_send: O(number_of_async_watchers)
4823		5461
4824	=item Processing signals: O(max_signal_number)	5462	=item Processing signals: O(max_signal_number)
4825		5463
4826	Sending involves a system call I<iff> there were no other C<ev_async_send>	5464	Sending involves a system call I<iff> there were no other C<ev_async_send>
4827	calls in the current loop iteration. Checking for async and signal events	5465	calls in the current loop iteration and the loop is currently
		5466	blocked. Checking for async and signal events involves iterating over all
4828	involves iterating over all running async watchers or all signal numbers.	5467	running async watchers or all signal numbers.
4829		5468
4830	=back	5469	=back
4831		5470
4832		5471
4833	=head1 PORTING FROM LIBEV 3.X TO 4.X	5472	=head1 PORTING FROM LIBEV 3.X TO 4.X
4834		5473
4835	The major version 4 introduced some minor incompatible changes to the API.	5474	The major version 4 introduced some incompatible changes to the API.
4836		5475
4837	At the moment, the C<ev.h> header file tries to implement superficial	5476	At the moment, the C<ev.h> header file provides compatibility definitions
4838	compatibility, so most programs should still compile. Those might be	5477	for all changes, so most programs should still compile. The compatibility
4839	removed in later versions of libev, so better update early than late.	5478	layer might be removed in later versions of libev, so better update to the
		5479	new API early than late.
4840		5480
4841	=over 4	5481	=over 4
4842		5482
		5483	=item C<EV_COMPAT3> backwards compatibility mechanism
		5484
		5485	The backward compatibility mechanism can be controlled by
		5486	C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
		5487	section.
		5488
4843	=item C<ev_default_destroy> and C<ev_default_fork> have been removed	5489	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
4844		5490
4845	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:	5491	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
4846		5492
4847	ev_loop_destroy (EV_DEFAULT);	5493	ev_loop_destroy (EV_DEFAULT_UC);
4848	ev_loop_fork (EV_DEFAULT);	5494	ev_loop_fork (EV_DEFAULT);
4849		5495
4850	=item function/symbol renames	5496	=item function/symbol renames
4851		5497
4852	A number of functions and symbols have been renamed:	5498	A number of functions and symbols have been renamed:
…		…
4872	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme	5518	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
4873	as all other watcher types. Note that C<ev_loop_fork> is still called	5519	as all other watcher types. Note that C<ev_loop_fork> is still called
4874	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>	5520	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
4875	typedef.	5521	typedef.
4876		5522
4877	=item C<EV_COMPAT3> backwards compatibility mechanism
4878
4879	The backward compatibility mechanism can be controlled by
4880	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
4881	section.
4882
4883	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>	5523	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
4884		5524
4885	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different	5525	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
4886	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile	5526	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
4887	and work, but the library code will of course be larger.	5527	and work, but the library code will of course be larger.
…		…
4894	=over 4	5534	=over 4
4895		5535
4896	=item active	5536	=item active
4897		5537
4898	A watcher is active as long as it has been started and not yet stopped.	5538	A watcher is active as long as it has been started and not yet stopped.
4899	See L<WATCHER STATES> for details.	5539	See L</WATCHER STATES> for details.
4900		5540
4901	=item application	5541	=item application
4902		5542
4903	In this document, an application is whatever is using libev.	5543	In this document, an application is whatever is using libev.
4904		5544
…		…
4940	watchers and events.	5580	watchers and events.
4941		5581
4942	=item pending	5582	=item pending
4943		5583
4944	A watcher is pending as soon as the corresponding event has been	5584	A watcher is pending as soon as the corresponding event has been
4945	detected. See L<WATCHER STATES> for details.	5585	detected. See L</WATCHER STATES> for details.
4946		5586
4947	=item real time	5587	=item real time
4948		5588
4949	The physical time that is observed. It is apparently strictly monotonic :)	5589	The physical time that is observed. It is apparently strictly monotonic :)
4950		5590
4951	=item wall-clock time	5591	=item wall-clock time
4952		5592
4953	The time and date as shown on clocks. Unlike real time, it can actually	5593	The time and date as shown on clocks. Unlike real time, it can actually
4954	be wrong and jump forwards and backwards, e.g. when the you adjust your	5594	be wrong and jump forwards and backwards, e.g. when you adjust your
4955	clock.	5595	clock.
4956		5596
4957	=item watcher	5597	=item watcher
4958		5598
4959	A data structure that describes interest in certain events. Watchers need	5599	A data structure that describes interest in certain events. Watchers need
…		…
4961		5601
4962	=back	5602	=back
4963		5603
4964	=head1 AUTHOR	5604	=head1 AUTHOR
4965		5605
4966	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.	5606	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5607	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
4967		5608

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