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Revision 1.427 by root, Sun Apr 28 14:57:12 2013 UTC

…		…
43		43
44	int	44	int
45	main (void)	45	main (void)
46	{	46	{
47	// use the default event loop unless you have special needs	47	// use the default event loop unless you have special needs
48	struct ev_loop *loop = ev_default_loop (0);	48	struct ev_loop *loop = EV_DEFAULT;
49		49
50	// initialise an io watcher, then start it	50	// initialise an io watcher, then start it
51	// this one will watch for stdin to become readable	51	// this one will watch for stdin to become readable
52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);	52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
53	ev_io_start (loop, &stdin_watcher);	53	ev_io_start (loop, &stdin_watcher);
…		…
58	ev_timer_start (loop, &timeout_watcher);	58	ev_timer_start (loop, &timeout_watcher);
59		59
60	// now wait for events to arrive	60	// now wait for events to arrive
61	ev_run (loop, 0);	61	ev_run (loop, 0);
62		62
63	// unloop was called, so exit	63	// break was called, so exit
64	return 0;	64	return 0;
65	}	65	}
66		66
67	=head1 ABOUT THIS DOCUMENT	67	=head1 ABOUT THIS DOCUMENT
68		68
…		…
77	on event-based programming, nor will it introduce event-based programming	77	on event-based programming, nor will it introduce event-based programming
78	with libev.	78	with libev.
79		79
80	Familiarity with event based programming techniques in general is assumed	80	Familiarity with event based programming techniques in general is assumed
81	throughout this document.	81	throughout this document.
		82
		83	=head1 WHAT TO READ WHEN IN A HURRY
		84
		85	This manual tries to be very detailed, but unfortunately, this also makes
		86	it very long. If you just want to know the basics of libev, I suggest
		87	reading L</ANATOMY OF A WATCHER>, then the L</EXAMPLE PROGRAM> above and
		88	look up the missing functions in L</GLOBAL FUNCTIONS> and the C<ev_io> and
		89	C<ev_timer> sections in L</WATCHER TYPES>.
82		90
83	=head1 ABOUT LIBEV	91	=head1 ABOUT LIBEV
84		92
85	Libev is an event loop: you register interest in certain events (such as a	93	Libev is an event loop: you register interest in certain events (such as a
86	file descriptor being readable or a timeout occurring), and it will manage	94	file descriptor being readable or a timeout occurring), and it will manage
…		…
124	this argument.	132	this argument.
125		133
126	=head2 TIME REPRESENTATION	134	=head2 TIME REPRESENTATION
127		135
128	Libev represents time as a single floating point number, representing	136	Libev represents time as a single floating point number, representing
129	the (fractional) number of seconds since the (POSIX) epoch (in practise	137	the (fractional) number of seconds since the (POSIX) epoch (in practice
130	somewhere near the beginning of 1970, details are complicated, don't	138	somewhere near the beginning of 1970, details are complicated, don't
131	ask). This type is called C<ev_tstamp>, which is what you should use	139	ask). This type is called C<ev_tstamp>, which is what you should use
132	too. It usually aliases to the C<double> type in C. When you need to do	140	too. It usually aliases to the C<double> type in C. When you need to do
133	any calculations on it, you should treat it as some floating point value.	141	any calculations on it, you should treat it as some floating point value.
134		142
…		…
165		173
166	=item ev_tstamp ev_time ()	174	=item ev_tstamp ev_time ()
167		175
168	Returns the current time as libev would use it. Please note that the	176	Returns the current time as libev would use it. Please note that the
169	C<ev_now> function is usually faster and also often returns the timestamp	177	C<ev_now> function is usually faster and also often returns the timestamp
170	you actually want to know.	178	you actually want to know. Also interesting is the combination of
		179	C<ev_now_update> and C<ev_now>.
171		180
172	=item ev_sleep (ev_tstamp interval)	181	=item ev_sleep (ev_tstamp interval)
173		182
174	Sleep for the given interval: The current thread will be blocked until	183	Sleep for the given interval: The current thread will be blocked
175	either it is interrupted or the given time interval has passed. Basically	184	until either it is interrupted or the given time interval has
		185	passed (approximately - it might return a bit earlier even if not
		186	interrupted). Returns immediately if C<< interval <= 0 >>.
		187
176	this is a sub-second-resolution C<sleep ()>.	188	Basically this is a sub-second-resolution C<sleep ()>.
		189
		190	The range of the C<interval> is limited - libev only guarantees to work
		191	with sleep times of up to one day (C<< interval <= 86400 >>).
177		192
178	=item int ev_version_major ()	193	=item int ev_version_major ()
179		194
180	=item int ev_version_minor ()	195	=item int ev_version_minor ()
181		196
…		…
192	as this indicates an incompatible change. Minor versions are usually	207	as this indicates an incompatible change. Minor versions are usually
193	compatible to older versions, so a larger minor version alone is usually	208	compatible to older versions, so a larger minor version alone is usually
194	not a problem.	209	not a problem.
195		210
196	Example: Make sure we haven't accidentally been linked against the wrong	211	Example: Make sure we haven't accidentally been linked against the wrong
197	version (note, however, that this will not detect ABI mismatches :).	212	version (note, however, that this will not detect other ABI mismatches,
		213	such as LFS or reentrancy).
198		214
199	assert (("libev version mismatch",	215	assert (("libev version mismatch",
200	ev_version_major () == EV_VERSION_MAJOR	216	ev_version_major () == EV_VERSION_MAJOR
201	&& ev_version_minor () >= EV_VERSION_MINOR));	217	&& ev_version_minor () >= EV_VERSION_MINOR));
202		218
…		…
213	assert (("sorry, no epoll, no sex",	229	assert (("sorry, no epoll, no sex",
214	ev_supported_backends () & EVBACKEND_EPOLL));	230	ev_supported_backends () & EVBACKEND_EPOLL));
215		231
216	=item unsigned int ev_recommended_backends ()	232	=item unsigned int ev_recommended_backends ()
217		233
218	Return the set of all backends compiled into this binary of libev and also	234	Return the set of all backends compiled into this binary of libev and
219	recommended for this platform. This set is often smaller than the one	235	also recommended for this platform, meaning it will work for most file
		236	descriptor types. This set is often smaller than the one returned by
220	returned by C<ev_supported_backends>, as for example kqueue is broken on	237	C<ev_supported_backends>, as for example kqueue is broken on most BSDs
221	most BSDs and will not be auto-detected unless you explicitly request it	238	and will not be auto-detected unless you explicitly request it (assuming
222	(assuming you know what you are doing). This is the set of backends that	239	you know what you are doing). This is the set of backends that libev will
223	libev will probe for if you specify no backends explicitly.	240	probe for if you specify no backends explicitly.
224		241
225	=item unsigned int ev_embeddable_backends ()	242	=item unsigned int ev_embeddable_backends ()
226		243
227	Returns the set of backends that are embeddable in other event loops. This	244	Returns the set of backends that are embeddable in other event loops. This
228	is the theoretical, all-platform, value. To find which backends	245	value is platform-specific but can include backends not available on the
229	might be supported on the current system, you would need to look at	246	current system. To find which embeddable backends might be supported on
230	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	247	the current system, you would need to look at C<ev_embeddable_backends ()
231	recommended ones.	248	& ev_supported_backends ()>, likewise for recommended ones.
232		249
233	See the description of C<ev_embed> watchers for more info.	250	See the description of C<ev_embed> watchers for more info.
234		251
235	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]	252	=item ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())
236		253
237	Sets the allocation function to use (the prototype is similar - the	254	Sets the allocation function to use (the prototype is similar - the
238	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is	255	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
239	used to allocate and free memory (no surprises here). If it returns zero	256	used to allocate and free memory (no surprises here). If it returns zero
240	when memory needs to be allocated (C<size != 0>), the library might abort	257	when memory needs to be allocated (C<size != 0>), the library might abort
…		…
266	}	283	}
267		284
268	...	285	...
269	ev_set_allocator (persistent_realloc);	286	ev_set_allocator (persistent_realloc);
270		287
271	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]	288	=item ev_set_syserr_cb (void (*cb)(const char *msg) throw ())
272		289
273	Set the callback function to call on a retryable system call error (such	290	Set the callback function to call on a retryable system call error (such
274	as failed select, poll, epoll_wait). The message is a printable string	291	as failed select, poll, epoll_wait). The message is a printable string
275	indicating the system call or subsystem causing the problem. If this	292	indicating the system call or subsystem causing the problem. If this
276	callback is set, then libev will expect it to remedy the situation, no	293	callback is set, then libev will expect it to remedy the situation, no
…		…
288	}	305	}
289		306
290	...	307	...
291	ev_set_syserr_cb (fatal_error);	308	ev_set_syserr_cb (fatal_error);
292		309
		310	=item ev_feed_signal (int signum)
		311
		312	This function can be used to "simulate" a signal receive. It is completely
		313	safe to call this function at any time, from any context, including signal
		314	handlers or random threads.
		315
		316	Its main use is to customise signal handling in your process, especially
		317	in the presence of threads. For example, you could block signals
		318	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
		319	creating any loops), and in one thread, use C<sigwait> or any other
		320	mechanism to wait for signals, then "deliver" them to libev by calling
		321	C<ev_feed_signal>.
		322
293	=back	323	=back
294		324
295	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	325	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
296		326
297	An event loop is described by a C<struct ev_loop *> (the C<struct> is	327	An event loop is described by a C<struct ev_loop *> (the C<struct> is
298	I<not> optional in this case unless libev 3 compatibility is disabled, as	328	I<not> optional in this case unless libev 3 compatibility is disabled, as
299	libev 3 had an C<ev_loop> function colliding with the struct name).	329	libev 3 had an C<ev_loop> function colliding with the struct name).
300		330
301	The library knows two types of such loops, the I<default> loop, which	331	The library knows two types of such loops, the I<default> loop, which
302	supports signals and child events, and dynamically created event loops	332	supports child process events, and dynamically created event loops which
303	which do not.	333	do not.
304		334
305	=over 4	335	=over 4
306		336
307	=item struct ev_loop *ev_default_loop (unsigned int flags)	337	=item struct ev_loop *ev_default_loop (unsigned int flags)
308		338
309	This will initialise the default event loop if it hasn't been initialised	339	This returns the "default" event loop object, which is what you should
310	yet and return it. If the default loop could not be initialised, returns	340	normally use when you just need "the event loop". Event loop objects and
311	false. If it already was initialised it simply returns it (and ignores the	341	the C<flags> parameter are described in more detail in the entry for
312	flags. If that is troubling you, check C<ev_backend ()> afterwards).	342	C<ev_loop_new>.
		343
		344	If the default loop is already initialised then this function simply
		345	returns it (and ignores the flags. If that is troubling you, check
		346	C<ev_backend ()> afterwards). Otherwise it will create it with the given
		347	flags, which should almost always be C<0>, unless the caller is also the
		348	one calling C<ev_run> or otherwise qualifies as "the main program".
313		349
314	If you don't know what event loop to use, use the one returned from this	350	If you don't know what event loop to use, use the one returned from this
315	function.	351	function (or via the C<EV_DEFAULT> macro).
316		352
317	Note that this function is I<not> thread-safe, so if you want to use it	353	Note that this function is I<not> thread-safe, so if you want to use it
318	from multiple threads, you have to lock (note also that this is unlikely,	354	from multiple threads, you have to employ some kind of mutex (note also
319	as loops cannot be shared easily between threads anyway).	355	that this case is unlikely, as loops cannot be shared easily between
		356	threads anyway).
320		357
321	The default loop is the only loop that can handle C<ev_signal> and	358	The default loop is the only loop that can handle C<ev_child> watchers,
322	C<ev_child> watchers, and to do this, it always registers a handler	359	and to do this, it always registers a handler for C<SIGCHLD>. If this is
323	for C<SIGCHLD>. If this is a problem for your application you can either	360	a problem for your application you can either create a dynamic loop with
324	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you	361	C<ev_loop_new> which doesn't do that, or you can simply overwrite the
325	can simply overwrite the C<SIGCHLD> signal handler I<after> calling	362	C<SIGCHLD> signal handler I<after> calling C<ev_default_init>.
326	C<ev_default_init>.	363
		364	Example: This is the most typical usage.
		365
		366	if (!ev_default_loop (0))
		367	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		368
		369	Example: Restrict libev to the select and poll backends, and do not allow
		370	environment settings to be taken into account:
		371
		372	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		373
		374	=item struct ev_loop *ev_loop_new (unsigned int flags)
		375
		376	This will create and initialise a new event loop object. If the loop
		377	could not be initialised, returns false.
		378
		379	This function is thread-safe, and one common way to use libev with
		380	threads is indeed to create one loop per thread, and using the default
		381	loop in the "main" or "initial" thread.
327		382
328	The flags argument can be used to specify special behaviour or specific	383	The flags argument can be used to specify special behaviour or specific
329	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	384	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
330		385
331	The following flags are supported:	386	The following flags are supported:
…		…
341		396
342	If this flag bit is or'ed into the flag value (or the program runs setuid	397	If this flag bit is or'ed into the flag value (or the program runs setuid
343	or setgid) then libev will I<not> look at the environment variable	398	or setgid) then libev will I<not> look at the environment variable
344	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	399	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
345	override the flags completely if it is found in the environment. This is	400	override the flags completely if it is found in the environment. This is
346	useful to try out specific backends to test their performance, or to work	401	useful to try out specific backends to test their performance, to work
347	around bugs.	402	around bugs, or to make libev threadsafe (accessing environment variables
		403	cannot be done in a threadsafe way, but usually it works if no other
		404	thread modifies them).
348		405
349	=item C<EVFLAG_FORKCHECK>	406	=item C<EVFLAG_FORKCHECK>
350		407
351	Instead of calling C<ev_loop_fork> manually after a fork, you can also	408	Instead of calling C<ev_loop_fork> manually after a fork, you can also
352	make libev check for a fork in each iteration by enabling this flag.	409	make libev check for a fork in each iteration by enabling this flag.
…		…
366	environment variable.	423	environment variable.
367		424
368	=item C<EVFLAG_NOINOTIFY>	425	=item C<EVFLAG_NOINOTIFY>
369		426
370	When this flag is specified, then libev will not attempt to use the	427	When this flag is specified, then libev will not attempt to use the
371	I<inotify> API for it's C<ev_stat> watchers. Apart from debugging and	428	I<inotify> API for its C<ev_stat> watchers. Apart from debugging and
372	testing, this flag can be useful to conserve inotify file descriptors, as	429	testing, this flag can be useful to conserve inotify file descriptors, as
373	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.	430	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
374		431
375	=item C<EVFLAG_SIGNALFD>	432	=item C<EVFLAG_SIGNALFD>
376		433
377	When this flag is specified, then libev will attempt to use the	434	When this flag is specified, then libev will attempt to use the
378	I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This API	435	I<signalfd> API for its C<ev_signal> (and C<ev_child>) watchers. This API
379	delivers signals synchronously, which makes it both faster and might make	436	delivers signals synchronously, which makes it both faster and might make
380	it possible to get the queued signal data. It can also simplify signal	437	it possible to get the queued signal data. It can also simplify signal
381	handling with threads, as long as you properly block signals in your	438	handling with threads, as long as you properly block signals in your
382	threads that are not interested in handling them.	439	threads that are not interested in handling them.
383		440
384	Signalfd will not be used by default as this changes your signal mask, and	441	Signalfd will not be used by default as this changes your signal mask, and
385	there are a lot of shoddy libraries and programs (glib's threadpool for	442	there are a lot of shoddy libraries and programs (glib's threadpool for
386	example) that can't properly initialise their signal masks.	443	example) that can't properly initialise their signal masks.
		444
		445	=item C<EVFLAG_NOSIGMASK>
		446
		447	When this flag is specified, then libev will avoid to modify the signal
		448	mask. Specifically, this means you have to make sure signals are unblocked
		449	when you want to receive them.
		450
		451	This behaviour is useful when you want to do your own signal handling, or
		452	want to handle signals only in specific threads and want to avoid libev
		453	unblocking the signals.
		454
		455	It's also required by POSIX in a threaded program, as libev calls
		456	C<sigprocmask>, whose behaviour is officially unspecified.
		457
		458	This flag's behaviour will become the default in future versions of libev.
387		459
388	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	460	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
389		461
390	This is your standard select(2) backend. Not I<completely> standard, as	462	This is your standard select(2) backend. Not I<completely> standard, as
391	libev tries to roll its own fd_set with no limits on the number of fds,	463	libev tries to roll its own fd_set with no limits on the number of fds,
…		…
419	=item C<EVBACKEND_EPOLL> (value 4, Linux)	491	=item C<EVBACKEND_EPOLL> (value 4, Linux)
420		492
421	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9	493	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
422	kernels).	494	kernels).
423		495
424	For few fds, this backend is a bit little slower than poll and select,	496	For few fds, this backend is a bit little slower than poll and select, but
425	but it scales phenomenally better. While poll and select usually scale	497	it scales phenomenally better. While poll and select usually scale like
426	like O(total_fds) where n is the total number of fds (or the highest fd),	498	O(total_fds) where total_fds is the total number of fds (or the highest
427	epoll scales either O(1) or O(active_fds).	499	fd), epoll scales either O(1) or O(active_fds).
428		500
429	The epoll mechanism deserves honorable mention as the most misdesigned	501	The epoll mechanism deserves honorable mention as the most misdesigned
430	of the more advanced event mechanisms: mere annoyances include silently	502	of the more advanced event mechanisms: mere annoyances include silently
431	dropping file descriptors, requiring a system call per change per file	503	dropping file descriptors, requiring a system call per change per file
432	descriptor (and unnecessary guessing of parameters), problems with dup and	504	descriptor (and unnecessary guessing of parameters), problems with dup,
		505	returning before the timeout value, resulting in additional iterations
		506	(and only giving 5ms accuracy while select on the same platform gives
433	so on. The biggest issue is fork races, however - if a program forks then	507	0.1ms) and so on. The biggest issue is fork races, however - if a program
434	I<both> parent and child process have to recreate the epoll set, which can	508	forks then I<both> parent and child process have to recreate the epoll
435	take considerable time (one syscall per file descriptor) and is of course	509	set, which can take considerable time (one syscall per file descriptor)
436	hard to detect.	510	and is of course hard to detect.
437		511
438	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but	512	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
439	of course I<doesn't>, and epoll just loves to report events for totally	513	but of course I<doesn't>, and epoll just loves to report events for
440	I<different> file descriptors (even already closed ones, so one cannot	514	totally I<different> file descriptors (even already closed ones, so
441	even remove them from the set) than registered in the set (especially	515	one cannot even remove them from the set) than registered in the set
442	on SMP systems). Libev tries to counter these spurious notifications by	516	(especially on SMP systems). Libev tries to counter these spurious
443	employing an additional generation counter and comparing that against the	517	notifications by employing an additional generation counter and comparing
444	events to filter out spurious ones, recreating the set when required. Last	518	that against the events to filter out spurious ones, recreating the set
		519	when required. Epoll also erroneously rounds down timeouts, but gives you
		520	no way to know when and by how much, so sometimes you have to busy-wait
		521	because epoll returns immediately despite a nonzero timeout. And last
445	not least, it also refuses to work with some file descriptors which work	522	not least, it also refuses to work with some file descriptors which work
446	perfectly fine with C<select> (files, many character devices...).	523	perfectly fine with C<select> (files, many character devices...).
		524
		525	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		526	cobbled together in a hurry, no thought to design or interaction with
		527	others. Oh, the pain, will it ever stop...
447		528
448	While stopping, setting and starting an I/O watcher in the same iteration	529	While stopping, setting and starting an I/O watcher in the same iteration
449	will result in some caching, there is still a system call per such	530	will result in some caching, there is still a system call per such
450	incident (because the same I<file descriptor> could point to a different	531	incident (because the same I<file descriptor> could point to a different
451	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed	532	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
…		…
488		569
489	It scales in the same way as the epoll backend, but the interface to the	570	It scales in the same way as the epoll backend, but the interface to the
490	kernel is more efficient (which says nothing about its actual speed, of	571	kernel is more efficient (which says nothing about its actual speed, of
491	course). While stopping, setting and starting an I/O watcher does never	572	course). While stopping, setting and starting an I/O watcher does never
492	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to	573	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
493	two event changes per incident. Support for C<fork ()> is very bad (but	574	two event changes per incident. Support for C<fork ()> is very bad (you
494	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect	575	might have to leak fd's on fork, but it's more sane than epoll) and it
495	cases	576	drops fds silently in similarly hard-to-detect cases.
496		577
497	This backend usually performs well under most conditions.	578	This backend usually performs well under most conditions.
498		579
499	While nominally embeddable in other event loops, this doesn't work	580	While nominally embeddable in other event loops, this doesn't work
500	everywhere, so you might need to test for this. And since it is broken	581	everywhere, so you might need to test for this. And since it is broken
…		…
517	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	598	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
518		599
519	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	600	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
520	it's really slow, but it still scales very well (O(active_fds)).	601	it's really slow, but it still scales very well (O(active_fds)).
521		602
522	Please note that Solaris event ports can deliver a lot of spurious
523	notifications, so you need to use non-blocking I/O or other means to avoid
524	blocking when no data (or space) is available.
525
526	While this backend scales well, it requires one system call per active	603	While this backend scales well, it requires one system call per active
527	file descriptor per loop iteration. For small and medium numbers of file	604	file descriptor per loop iteration. For small and medium numbers of file
528	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	605	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
529	might perform better.	606	might perform better.
530		607
531	On the positive side, with the exception of the spurious readiness	608	On the positive side, this backend actually performed fully to
532	notifications, this backend actually performed fully to specification
533	in all tests and is fully embeddable, which is a rare feat among the	609	specification in all tests and is fully embeddable, which is a rare feat
534	OS-specific backends (I vastly prefer correctness over speed hacks).	610	among the OS-specific backends (I vastly prefer correctness over speed
		611	hacks).
		612
		613	On the negative side, the interface is I<bizarre> - so bizarre that
		614	even sun itself gets it wrong in their code examples: The event polling
		615	function sometimes returns events to the caller even though an error
		616	occurred, but with no indication whether it has done so or not (yes, it's
		617	even documented that way) - deadly for edge-triggered interfaces where you
		618	absolutely have to know whether an event occurred or not because you have
		619	to re-arm the watcher.
		620
		621	Fortunately libev seems to be able to work around these idiocies.
535		622
536	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	623	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
537	C<EVBACKEND_POLL>.	624	C<EVBACKEND_POLL>.
538		625
539	=item C<EVBACKEND_ALL>	626	=item C<EVBACKEND_ALL>
540		627
541	Try all backends (even potentially broken ones that wouldn't be tried	628	Try all backends (even potentially broken ones that wouldn't be tried
542	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	629	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
543	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	630	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
544		631
545	It is definitely not recommended to use this flag.	632	It is definitely not recommended to use this flag, use whatever
		633	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		634	at all.
		635
		636	=item C<EVBACKEND_MASK>
		637
		638	Not a backend at all, but a mask to select all backend bits from a
		639	C<flags> value, in case you want to mask out any backends from a flags
		640	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
546		641
547	=back	642	=back
548		643
549	If one or more of the backend flags are or'ed into the flags value,	644	If one or more of the backend flags are or'ed into the flags value,
550	then only these backends will be tried (in the reverse order as listed	645	then only these backends will be tried (in the reverse order as listed
551	here). If none are specified, all backends in C<ev_recommended_backends	646	here). If none are specified, all backends in C<ev_recommended_backends
552	()> will be tried.	647	()> will be tried.
553		648
554	Example: This is the most typical usage.
555
556	if (!ev_default_loop (0))
557	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
558
559	Example: Restrict libev to the select and poll backends, and do not allow
560	environment settings to be taken into account:
561
562	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
563
564	Example: Use whatever libev has to offer, but make sure that kqueue is
565	used if available (warning, breaks stuff, best use only with your own
566	private event loop and only if you know the OS supports your types of
567	fds):
568
569	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
570
571	=item struct ev_loop *ev_loop_new (unsigned int flags)
572
573	Similar to C<ev_default_loop>, but always creates a new event loop that is
574	always distinct from the default loop.
575
576	Note that this function I<is> thread-safe, and one common way to use
577	libev with threads is indeed to create one loop per thread, and using the
578	default loop in the "main" or "initial" thread.
579
580	Example: Try to create a event loop that uses epoll and nothing else.	649	Example: Try to create a event loop that uses epoll and nothing else.
581		650
582	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	651	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
583	if (!epoller)	652	if (!epoller)
584	fatal ("no epoll found here, maybe it hides under your chair");	653	fatal ("no epoll found here, maybe it hides under your chair");
585		654
		655	Example: Use whatever libev has to offer, but make sure that kqueue is
		656	used if available.
		657
		658	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		659
586	=item ev_default_destroy ()	660	=item ev_loop_destroy (loop)
587		661
588	Destroys the default loop (frees all memory and kernel state etc.). None	662	Destroys an event loop object (frees all memory and kernel state
589	of the active event watchers will be stopped in the normal sense, so	663	etc.). None of the active event watchers will be stopped in the normal
590	e.g. C<ev_is_active> might still return true. It is your responsibility to	664	sense, so e.g. C<ev_is_active> might still return true. It is your
591	either stop all watchers cleanly yourself I<before> calling this function,	665	responsibility to either stop all watchers cleanly yourself I<before>
592	or cope with the fact afterwards (which is usually the easiest thing, you	666	calling this function, or cope with the fact afterwards (which is usually
593	can just ignore the watchers and/or C<free ()> them for example).	667	the easiest thing, you can just ignore the watchers and/or C<free ()> them
		668	for example).
594		669
595	Note that certain global state, such as signal state (and installed signal	670	Note that certain global state, such as signal state (and installed signal
596	handlers), will not be freed by this function, and related watchers (such	671	handlers), will not be freed by this function, and related watchers (such
597	as signal and child watchers) would need to be stopped manually.	672	as signal and child watchers) would need to be stopped manually.
598		673
599	In general it is not advisable to call this function except in the	674	This function is normally used on loop objects allocated by
600	rare occasion where you really need to free e.g. the signal handling	675	C<ev_loop_new>, but it can also be used on the default loop returned by
		676	C<ev_default_loop>, in which case it is not thread-safe.
		677
		678	Note that it is not advisable to call this function on the default loop
		679	except in the rare occasion where you really need to free its resources.
601	pipe fds. If you need dynamically allocated loops it is better to use	680	If you need dynamically allocated loops it is better to use C<ev_loop_new>
602	C<ev_loop_new> and C<ev_loop_destroy>.	681	and C<ev_loop_destroy>.
603		682
604	=item ev_loop_destroy (loop)	683	=item ev_loop_fork (loop)
605		684
606	Like C<ev_default_destroy>, but destroys an event loop created by an
607	earlier call to C<ev_loop_new>.
608
609	=item ev_default_fork ()
610
611	This function sets a flag that causes subsequent C<ev_run> iterations	685	This function sets a flag that causes subsequent C<ev_run> iterations to
612	to reinitialise the kernel state for backends that have one. Despite the	686	reinitialise the kernel state for backends that have one. Despite the
613	name, you can call it anytime, but it makes most sense after forking, in	687	name, you can call it anytime, but it makes most sense after forking, in
614	the child process (or both child and parent, but that again makes little	688	the child process. You I<must> call it (or use C<EVFLAG_FORKCHECK>) in the
615	sense). You I<must> call it in the child before using any of the libev	689	child before resuming or calling C<ev_run>.
616	functions, and it will only take effect at the next C<ev_run> iteration.
617		690
618	Again, you I<have> to call it on I<any> loop that you want to re-use after	691	Again, you I<have> to call it on I<any> loop that you want to re-use after
619	a fork, I<even if you do not plan to use the loop in the parent>. This is	692	a fork, I<even if you do not plan to use the loop in the parent>. This is
620	because some kernel interfaces *cough* I<kqueue> *cough* do funny things	693	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
621	during fork.	694	during fork.
…		…
626	call it at all (in fact, C<epoll> is so badly broken that it makes a	699	call it at all (in fact, C<epoll> is so badly broken that it makes a
627	difference, but libev will usually detect this case on its own and do a	700	difference, but libev will usually detect this case on its own and do a
628	costly reset of the backend).	701	costly reset of the backend).
629		702
630	The function itself is quite fast and it's usually not a problem to call	703	The function itself is quite fast and it's usually not a problem to call
631	it just in case after a fork. To make this easy, the function will fit in	704	it just in case after a fork.
632	quite nicely into a call to C<pthread_atfork>:
633		705
		706	Example: Automate calling C<ev_loop_fork> on the default loop when
		707	using pthreads.
		708
		709	static void
		710	post_fork_child (void)
		711	{
		712	ev_loop_fork (EV_DEFAULT);
		713	}
		714
		715	...
634	pthread_atfork (0, 0, ev_default_fork);	716	pthread_atfork (0, 0, post_fork_child);
635
636	=item ev_loop_fork (loop)
637
638	Like C<ev_default_fork>, but acts on an event loop created by
639	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
640	after fork that you want to re-use in the child, and how you keep track of
641	them is entirely your own problem.
642		717
643	=item int ev_is_default_loop (loop)	718	=item int ev_is_default_loop (loop)
644		719
645	Returns true when the given loop is, in fact, the default loop, and false	720	Returns true when the given loop is, in fact, the default loop, and false
646	otherwise.	721	otherwise.
…		…
657	prepare and check phases.	732	prepare and check phases.
658		733
659	=item unsigned int ev_depth (loop)	734	=item unsigned int ev_depth (loop)
660		735
661	Returns the number of times C<ev_run> was entered minus the number of	736	Returns the number of times C<ev_run> was entered minus the number of
662	times C<ev_run> was exited, in other words, the recursion depth.	737	times C<ev_run> was exited normally, in other words, the recursion depth.
663		738
664	Outside C<ev_run>, this number is zero. In a callback, this number is	739	Outside C<ev_run>, this number is zero. In a callback, this number is
665	C<1>, unless C<ev_run> was invoked recursively (or from another thread),	740	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
666	in which case it is higher.	741	in which case it is higher.
667		742
668	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread	743	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread,
669	etc.), doesn't count as "exit" - consider this as a hint to avoid such	744	throwing an exception etc.), doesn't count as "exit" - consider this
670	ungentleman-like behaviour unless it's really convenient.	745	as a hint to avoid such ungentleman-like behaviour unless it's really
		746	convenient, in which case it is fully supported.
671		747
672	=item unsigned int ev_backend (loop)	748	=item unsigned int ev_backend (loop)
673		749
674	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	750	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
675	use.	751	use.
…		…
690		766
691	This function is rarely useful, but when some event callback runs for a	767	This function is rarely useful, but when some event callback runs for a
692	very long time without entering the event loop, updating libev's idea of	768	very long time without entering the event loop, updating libev's idea of
693	the current time is a good idea.	769	the current time is a good idea.
694		770
695	See also L<The special problem of time updates> in the C<ev_timer> section.	771	See also L</The special problem of time updates> in the C<ev_timer> section.
696		772
697	=item ev_suspend (loop)	773	=item ev_suspend (loop)
698		774
699	=item ev_resume (loop)	775	=item ev_resume (loop)
700		776
…		…
718	without a previous call to C<ev_suspend>.	794	without a previous call to C<ev_suspend>.
719		795
720	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the	796	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
721	event loop time (see C<ev_now_update>).	797	event loop time (see C<ev_now_update>).
722		798
723	=item ev_run (loop, int flags)	799	=item bool ev_run (loop, int flags)
724		800
725	Finally, this is it, the event handler. This function usually is called	801	Finally, this is it, the event handler. This function usually is called
726	after you have initialised all your watchers and you want to start	802	after you have initialised all your watchers and you want to start
727	handling events. It will ask the operating system for any new events, call	803	handling events. It will ask the operating system for any new events, call
728	the watcher callbacks, an then repeat the whole process indefinitely: This	804	the watcher callbacks, and then repeat the whole process indefinitely: This
729	is why event loops are called I<loops>.	805	is why event loops are called I<loops>.
730		806
731	If the flags argument is specified as C<0>, it will keep handling events	807	If the flags argument is specified as C<0>, it will keep handling events
732	until either no event watchers are active anymore or C<ev_break> was	808	until either no event watchers are active anymore or C<ev_break> was
733	called.	809	called.
		810
		811	The return value is false if there are no more active watchers (which
		812	usually means "all jobs done" or "deadlock"), and true in all other cases
		813	(which usually means " you should call C<ev_run> again").
734		814
735	Please note that an explicit C<ev_break> is usually better than	815	Please note that an explicit C<ev_break> is usually better than
736	relying on all watchers to be stopped when deciding when a program has	816	relying on all watchers to be stopped when deciding when a program has
737	finished (especially in interactive programs), but having a program	817	finished (especially in interactive programs), but having a program
738	that automatically loops as long as it has to and no longer by virtue	818	that automatically loops as long as it has to and no longer by virtue
739	of relying on its watchers stopping correctly, that is truly a thing of	819	of relying on its watchers stopping correctly, that is truly a thing of
740	beauty.	820	beauty.
741		821
		822	This function is I<mostly> exception-safe - you can break out of a
		823	C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		824	exception and so on. This does not decrement the C<ev_depth> value, nor
		825	will it clear any outstanding C<EVBREAK_ONE> breaks.
		826
742	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle	827	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
743	those events and any already outstanding ones, but will not wait and	828	those events and any already outstanding ones, but will not wait and
744	block your process in case there are no events and will return after one	829	block your process in case there are no events and will return after one
745	iteration of the loop. This is sometimes useful to poll and handle new	830	iteration of the loop. This is sometimes useful to poll and handle new
746	events while doing lengthy calculations, to keep the program responsive.	831	events while doing lengthy calculations, to keep the program responsive.
…		…
755	This is useful if you are waiting for some external event in conjunction	840	This is useful if you are waiting for some external event in conjunction
756	with something not expressible using other libev watchers (i.e. "roll your	841	with something not expressible using other libev watchers (i.e. "roll your
757	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is	842	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
758	usually a better approach for this kind of thing.	843	usually a better approach for this kind of thing.
759		844
760	Here are the gory details of what C<ev_run> does:	845	Here are the gory details of what C<ev_run> does (this is for your
		846	understanding, not a guarantee that things will work exactly like this in
		847	future versions):
761		848
762	- Increment loop depth.	849	- Increment loop depth.
763	- Reset the ev_break status.	850	- Reset the ev_break status.
764	- Before the first iteration, call any pending watchers.	851	- Before the first iteration, call any pending watchers.
765	LOOP:	852	LOOP:
…		…
798	anymore.	885	anymore.
799		886
800	... queue jobs here, make sure they register event watchers as long	887	... queue jobs here, make sure they register event watchers as long
801	... as they still have work to do (even an idle watcher will do..)	888	... as they still have work to do (even an idle watcher will do..)
802	ev_run (my_loop, 0);	889	ev_run (my_loop, 0);
803	... jobs done or somebody called unloop. yeah!	890	... jobs done or somebody called break. yeah!
804		891
805	=item ev_break (loop, how)	892	=item ev_break (loop, how)
806		893
807	Can be used to make a call to C<ev_run> return early (but only after it	894	Can be used to make a call to C<ev_run> return early (but only after it
808	has processed all outstanding events). The C<how> argument must be either	895	has processed all outstanding events). The C<how> argument must be either
809	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or	896	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
810	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.	897	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
811		898
812	This "unloop state" will be cleared when entering C<ev_run> again.	899	This "break state" will be cleared on the next call to C<ev_run>.
813		900
814	It is safe to call C<ev_break> from outside any C<ev_run> calls. ##TODO##	901	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		902	which case it will have no effect.
815		903
816	=item ev_ref (loop)	904	=item ev_ref (loop)
817		905
818	=item ev_unref (loop)	906	=item ev_unref (loop)
819		907
…		…
840	running when nothing else is active.	928	running when nothing else is active.
841		929
842	ev_signal exitsig;	930	ev_signal exitsig;
843	ev_signal_init (&exitsig, sig_cb, SIGINT);	931	ev_signal_init (&exitsig, sig_cb, SIGINT);
844	ev_signal_start (loop, &exitsig);	932	ev_signal_start (loop, &exitsig);
845	evf_unref (loop);	933	ev_unref (loop);
846		934
847	Example: For some weird reason, unregister the above signal handler again.	935	Example: For some weird reason, unregister the above signal handler again.
848		936
849	ev_ref (loop);	937	ev_ref (loop);
850	ev_signal_stop (loop, &exitsig);	938	ev_signal_stop (loop, &exitsig);
…		…
870	overhead for the actual polling but can deliver many events at once.	958	overhead for the actual polling but can deliver many events at once.
871		959
872	By setting a higher I<io collect interval> you allow libev to spend more	960	By setting a higher I<io collect interval> you allow libev to spend more
873	time collecting I/O events, so you can handle more events per iteration,	961	time collecting I/O events, so you can handle more events per iteration,
874	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	962	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
875	C<ev_timer>) will be not affected. Setting this to a non-null value will	963	C<ev_timer>) will not be affected. Setting this to a non-null value will
876	introduce an additional C<ev_sleep ()> call into most loop iterations. The	964	introduce an additional C<ev_sleep ()> call into most loop iterations. The
877	sleep time ensures that libev will not poll for I/O events more often then	965	sleep time ensures that libev will not poll for I/O events more often then
878	once per this interval, on average.	966	once per this interval, on average (as long as the host time resolution is
		967	good enough).
879		968
880	Likewise, by setting a higher I<timeout collect interval> you allow libev	969	Likewise, by setting a higher I<timeout collect interval> you allow libev
881	to spend more time collecting timeouts, at the expense of increased	970	to spend more time collecting timeouts, at the expense of increased
882	latency/jitter/inexactness (the watcher callback will be called	971	latency/jitter/inexactness (the watcher callback will be called
883	later). C<ev_io> watchers will not be affected. Setting this to a non-null	972	later). C<ev_io> watchers will not be affected. Setting this to a non-null
…		…
908		997
909	=item ev_invoke_pending (loop)	998	=item ev_invoke_pending (loop)
910		999
911	This call will simply invoke all pending watchers while resetting their	1000	This call will simply invoke all pending watchers while resetting their
912	pending state. Normally, C<ev_run> does this automatically when required,	1001	pending state. Normally, C<ev_run> does this automatically when required,
913	but when overriding the invoke callback this call comes handy.	1002	but when overriding the invoke callback this call comes handy. This
		1003	function can be invoked from a watcher - this can be useful for example
		1004	when you want to do some lengthy calculation and want to pass further
		1005	event handling to another thread (you still have to make sure only one
		1006	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
914		1007
915	=item int ev_pending_count (loop)	1008	=item int ev_pending_count (loop)
916		1009
917	Returns the number of pending watchers - zero indicates that no watchers	1010	Returns the number of pending watchers - zero indicates that no watchers
918	are pending.	1011	are pending.
…		…
925	invoke the actual watchers inside another context (another thread etc.).	1018	invoke the actual watchers inside another context (another thread etc.).
926		1019
927	If you want to reset the callback, use C<ev_invoke_pending> as new	1020	If you want to reset the callback, use C<ev_invoke_pending> as new
928	callback.	1021	callback.
929		1022
930	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))	1023	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
931		1024
932	Sometimes you want to share the same loop between multiple threads. This	1025	Sometimes you want to share the same loop between multiple threads. This
933	can be done relatively simply by putting mutex_lock/unlock calls around	1026	can be done relatively simply by putting mutex_lock/unlock calls around
934	each call to a libev function.	1027	each call to a libev function.
935		1028
936	However, C<ev_run> can run an indefinite time, so it is not feasible	1029	However, C<ev_run> can run an indefinite time, so it is not feasible
937	to wait for it to return. One way around this is to wake up the event	1030	to wait for it to return. One way around this is to wake up the event
938	loop via C<ev_break> and C<av_async_send>, another way is to set these	1031	loop via C<ev_break> and C<ev_async_send>, another way is to set these
939	I<release> and I<acquire> callbacks on the loop.	1032	I<release> and I<acquire> callbacks on the loop.
940		1033
941	When set, then C<release> will be called just before the thread is	1034	When set, then C<release> will be called just before the thread is
942	suspended waiting for new events, and C<acquire> is called just	1035	suspended waiting for new events, and C<acquire> is called just
943	afterwards.	1036	afterwards.
…		…
958	See also the locking example in the C<THREADS> section later in this	1051	See also the locking example in the C<THREADS> section later in this
959	document.	1052	document.
960		1053
961	=item ev_set_userdata (loop, void *data)	1054	=item ev_set_userdata (loop, void *data)
962		1055
963	=item ev_userdata (loop)	1056	=item void *ev_userdata (loop)
964		1057
965	Set and retrieve a single C<void *> associated with a loop. When	1058	Set and retrieve a single C<void *> associated with a loop. When
966	C<ev_set_userdata> has never been called, then C<ev_userdata> returns	1059	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
967	C<0.>	1060	C<0>.
968		1061
969	These two functions can be used to associate arbitrary data with a loop,	1062	These two functions can be used to associate arbitrary data with a loop,
970	and are intended solely for the C<invoke_pending_cb>, C<release> and	1063	and are intended solely for the C<invoke_pending_cb>, C<release> and
971	C<acquire> callbacks described above, but of course can be (ab-)used for	1064	C<acquire> callbacks described above, but of course can be (ab-)used for
972	any other purpose as well.	1065	any other purpose as well.
…		…
1083		1176
1084	=item C<EV_PREPARE>	1177	=item C<EV_PREPARE>
1085		1178
1086	=item C<EV_CHECK>	1179	=item C<EV_CHECK>
1087		1180
1088	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts	1181	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts to
1089	to gather new events, and all C<ev_check> watchers are invoked just after	1182	gather new events, and all C<ev_check> watchers are queued (not invoked)
1090	C<ev_run> has gathered them, but before it invokes any callbacks for any	1183	just after C<ev_run> has gathered them, but before it queues any callbacks
		1184	for any received events. That means C<ev_prepare> watchers are the last
		1185	watchers invoked before the event loop sleeps or polls for new events, and
		1186	C<ev_check> watchers will be invoked before any other watchers of the same
		1187	or lower priority within an event loop iteration.
		1188
1091	received events. Callbacks of both watcher types can start and stop as	1189	Callbacks of both watcher types can start and stop as many watchers as
1092	many watchers as they want, and all of them will be taken into account	1190	they want, and all of them will be taken into account (for example, a
1093	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1191	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
1094	C<ev_run> from blocking).	1192	blocking).
1095		1193
1096	=item C<EV_EMBED>	1194	=item C<EV_EMBED>
1097		1195
1098	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1196	The embedded event loop specified in the C<ev_embed> watcher needs attention.
1099		1197
1100	=item C<EV_FORK>	1198	=item C<EV_FORK>
1101		1199
1102	The event loop has been resumed in the child process after fork (see	1200	The event loop has been resumed in the child process after fork (see
1103	C<ev_fork>).	1201	C<ev_fork>).
		1202
		1203	=item C<EV_CLEANUP>
		1204
		1205	The event loop is about to be destroyed (see C<ev_cleanup>).
1104		1206
1105	=item C<EV_ASYNC>	1207	=item C<EV_ASYNC>
1106		1208
1107	The given async watcher has been asynchronously notified (see C<ev_async>).	1209	The given async watcher has been asynchronously notified (see C<ev_async>).
1108		1210
…		…
1130	programs, though, as the fd could already be closed and reused for another	1232	programs, though, as the fd could already be closed and reused for another
1131	thing, so beware.	1233	thing, so beware.
1132		1234
1133	=back	1235	=back
1134		1236
		1237	=head2 GENERIC WATCHER FUNCTIONS
		1238
		1239	=over 4
		1240
		1241	=item C<ev_init> (ev_TYPE *watcher, callback)
		1242
		1243	This macro initialises the generic portion of a watcher. The contents
		1244	of the watcher object can be arbitrary (so C<malloc> will do). Only
		1245	the generic parts of the watcher are initialised, you I<need> to call
		1246	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		1247	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		1248	which rolls both calls into one.
		1249
		1250	You can reinitialise a watcher at any time as long as it has been stopped
		1251	(or never started) and there are no pending events outstanding.
		1252
		1253	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
		1254	int revents)>.
		1255
		1256	Example: Initialise an C<ev_io> watcher in two steps.
		1257
		1258	ev_io w;
		1259	ev_init (&w, my_cb);
		1260	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1261
		1262	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
		1263
		1264	This macro initialises the type-specific parts of a watcher. You need to
		1265	call C<ev_init> at least once before you call this macro, but you can
		1266	call C<ev_TYPE_set> any number of times. You must not, however, call this
		1267	macro on a watcher that is active (it can be pending, however, which is a
		1268	difference to the C<ev_init> macro).
		1269
		1270	Although some watcher types do not have type-specific arguments
		1271	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		1272
		1273	See C<ev_init>, above, for an example.
		1274
		1275	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		1276
		1277	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		1278	calls into a single call. This is the most convenient method to initialise
		1279	a watcher. The same limitations apply, of course.
		1280
		1281	Example: Initialise and set an C<ev_io> watcher in one step.
		1282
		1283	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1284
		1285	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
		1286
		1287	Starts (activates) the given watcher. Only active watchers will receive
		1288	events. If the watcher is already active nothing will happen.
		1289
		1290	Example: Start the C<ev_io> watcher that is being abused as example in this
		1291	whole section.
		1292
		1293	ev_io_start (EV_DEFAULT_UC, &w);
		1294
		1295	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
		1296
		1297	Stops the given watcher if active, and clears the pending status (whether
		1298	the watcher was active or not).
		1299
		1300	It is possible that stopped watchers are pending - for example,
		1301	non-repeating timers are being stopped when they become pending - but
		1302	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
		1303	pending. If you want to free or reuse the memory used by the watcher it is
		1304	therefore a good idea to always call its C<ev_TYPE_stop> function.
		1305
		1306	=item bool ev_is_active (ev_TYPE *watcher)
		1307
		1308	Returns a true value iff the watcher is active (i.e. it has been started
		1309	and not yet been stopped). As long as a watcher is active you must not modify
		1310	it.
		1311
		1312	=item bool ev_is_pending (ev_TYPE *watcher)
		1313
		1314	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		1315	events but its callback has not yet been invoked). As long as a watcher
		1316	is pending (but not active) you must not call an init function on it (but
		1317	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		1318	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1319	it).
		1320
		1321	=item callback ev_cb (ev_TYPE *watcher)
		1322
		1323	Returns the callback currently set on the watcher.
		1324
		1325	=item ev_set_cb (ev_TYPE *watcher, callback)
		1326
		1327	Change the callback. You can change the callback at virtually any time
		1328	(modulo threads).
		1329
		1330	=item ev_set_priority (ev_TYPE *watcher, int priority)
		1331
		1332	=item int ev_priority (ev_TYPE *watcher)
		1333
		1334	Set and query the priority of the watcher. The priority is a small
		1335	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1336	(default: C<-2>). Pending watchers with higher priority will be invoked
		1337	before watchers with lower priority, but priority will not keep watchers
		1338	from being executed (except for C<ev_idle> watchers).
		1339
		1340	If you need to suppress invocation when higher priority events are pending
		1341	you need to look at C<ev_idle> watchers, which provide this functionality.
		1342
		1343	You I<must not> change the priority of a watcher as long as it is active or
		1344	pending.
		1345
		1346	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1347	fine, as long as you do not mind that the priority value you query might
		1348	or might not have been clamped to the valid range.
		1349
		1350	The default priority used by watchers when no priority has been set is
		1351	always C<0>, which is supposed to not be too high and not be too low :).
		1352
		1353	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1354	priorities.
		1355
		1356	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1357
		1358	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1359	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1360	can deal with that fact, as both are simply passed through to the
		1361	callback.
		1362
		1363	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1364
		1365	If the watcher is pending, this function clears its pending status and
		1366	returns its C<revents> bitset (as if its callback was invoked). If the
		1367	watcher isn't pending it does nothing and returns C<0>.
		1368
		1369	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1370	callback to be invoked, which can be accomplished with this function.
		1371
		1372	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1373
		1374	Feeds the given event set into the event loop, as if the specified event
		1375	had happened for the specified watcher (which must be a pointer to an
		1376	initialised but not necessarily started event watcher). Obviously you must
		1377	not free the watcher as long as it has pending events.
		1378
		1379	Stopping the watcher, letting libev invoke it, or calling
		1380	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1381	not started in the first place.
		1382
		1383	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1384	functions that do not need a watcher.
		1385
		1386	=back
		1387
		1388	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
		1389	OWN COMPOSITE WATCHERS> idioms.
		1390
1135	=head2 WATCHER STATES	1391	=head2 WATCHER STATES
1136		1392
1137	There are various watcher states mentioned throughout this manual -	1393	There are various watcher states mentioned throughout this manual -
1138	active, pending and so on. In this section these states and the rules to	1394	active, pending and so on. In this section these states and the rules to
1139	transition between them will be described in more detail - and while these	1395	transition between them will be described in more detail - and while these
1140	rules might look complicated, they usually do "the right thing".	1396	rules might look complicated, they usually do "the right thing".
1141		1397
1142	=over 4	1398	=over 4
1143		1399
1144	=item initialiased	1400	=item initialised
1145		1401
1146	Before a watcher can be registered with the event looop it has to be	1402	Before a watcher can be registered with the event loop it has to be
1147	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to	1403	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
1148	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.	1404	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1149		1405
1150	In this state it is simply some block of memory that is suitable for use	1406	In this state it is simply some block of memory that is suitable for
1151	in an event loop. It can be moved around, freed, reused etc. at will.	1407	use in an event loop. It can be moved around, freed, reused etc. at
		1408	will - as long as you either keep the memory contents intact, or call
		1409	C<ev_TYPE_init> again.
1152		1410
1153	=item started/running/active	1411	=item started/running/active
1154		1412
1155	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes	1413	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
1156	property of the event loop, and is actively waiting for events. While in	1414	property of the event loop, and is actively waiting for events. While in
…		…
1159	and call libev functions on it that are documented to work on active watchers.	1417	and call libev functions on it that are documented to work on active watchers.
1160		1418
1161	=item pending	1419	=item pending
1162		1420
1163	If a watcher is active and libev determines that an event it is interested	1421	If a watcher is active and libev determines that an event it is interested
1164	in has occured (such as a timer expiring), it will become pending. It will	1422	in has occurred (such as a timer expiring), it will become pending. It will
1165	stay in this pending state until either it is stopped or its callback is	1423	stay in this pending state until either it is stopped or its callback is
1166	about to be invoked, so it is not normally pending inside the watcher	1424	about to be invoked, so it is not normally pending inside the watcher
1167	callback.	1425	callback.
1168		1426
1169	The watcher might or might not be active while it is pending (for example,	1427	The watcher might or might not be active while it is pending (for example,
…		…
1184	latter will clear any pending state the watcher might be in, regardless	1442	latter will clear any pending state the watcher might be in, regardless
1185	of whether it was active or not, so stopping a watcher explicitly before	1443	of whether it was active or not, so stopping a watcher explicitly before
1186	freeing it is often a good idea.	1444	freeing it is often a good idea.
1187		1445
1188	While stopped (and not pending) the watcher is essentially in the	1446	While stopped (and not pending) the watcher is essentially in the
1189	initialised state, that is it can be reused, moved, modified in any way	1447	initialised state, that is, it can be reused, moved, modified in any way
1190	you wish.	1448	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1449	it again).
1191		1450
1192	=back	1451	=back
1193
1194	=head2 GENERIC WATCHER FUNCTIONS
1195
1196	=over 4
1197
1198	=item C<ev_init> (ev_TYPE *watcher, callback)
1199
1200	This macro initialises the generic portion of a watcher. The contents
1201	of the watcher object can be arbitrary (so C<malloc> will do). Only
1202	the generic parts of the watcher are initialised, you I<need> to call
1203	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
1204	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
1205	which rolls both calls into one.
1206
1207	You can reinitialise a watcher at any time as long as it has been stopped
1208	(or never started) and there are no pending events outstanding.
1209
1210	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
1211	int revents)>.
1212
1213	Example: Initialise an C<ev_io> watcher in two steps.
1214
1215	ev_io w;
1216	ev_init (&w, my_cb);
1217	ev_io_set (&w, STDIN_FILENO, EV_READ);
1218
1219	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
1220
1221	This macro initialises the type-specific parts of a watcher. You need to
1222	call C<ev_init> at least once before you call this macro, but you can
1223	call C<ev_TYPE_set> any number of times. You must not, however, call this
1224	macro on a watcher that is active (it can be pending, however, which is a
1225	difference to the C<ev_init> macro).
1226
1227	Although some watcher types do not have type-specific arguments
1228	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
1229
1230	See C<ev_init>, above, for an example.
1231
1232	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
1233
1234	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
1235	calls into a single call. This is the most convenient method to initialise
1236	a watcher. The same limitations apply, of course.
1237
1238	Example: Initialise and set an C<ev_io> watcher in one step.
1239
1240	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
1241
1242	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
1243
1244	Starts (activates) the given watcher. Only active watchers will receive
1245	events. If the watcher is already active nothing will happen.
1246
1247	Example: Start the C<ev_io> watcher that is being abused as example in this
1248	whole section.
1249
1250	ev_io_start (EV_DEFAULT_UC, &w);
1251
1252	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
1253
1254	Stops the given watcher if active, and clears the pending status (whether
1255	the watcher was active or not).
1256
1257	It is possible that stopped watchers are pending - for example,
1258	non-repeating timers are being stopped when they become pending - but
1259	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
1260	pending. If you want to free or reuse the memory used by the watcher it is
1261	therefore a good idea to always call its C<ev_TYPE_stop> function.
1262
1263	=item bool ev_is_active (ev_TYPE *watcher)
1264
1265	Returns a true value iff the watcher is active (i.e. it has been started
1266	and not yet been stopped). As long as a watcher is active you must not modify
1267	it.
1268
1269	=item bool ev_is_pending (ev_TYPE *watcher)
1270
1271	Returns a true value iff the watcher is pending, (i.e. it has outstanding
1272	events but its callback has not yet been invoked). As long as a watcher
1273	is pending (but not active) you must not call an init function on it (but
1274	C<ev_TYPE_set> is safe), you must not change its priority, and you must
1275	make sure the watcher is available to libev (e.g. you cannot C<free ()>
1276	it).
1277
1278	=item callback ev_cb (ev_TYPE *watcher)
1279
1280	Returns the callback currently set on the watcher.
1281
1282	=item ev_cb_set (ev_TYPE *watcher, callback)
1283
1284	Change the callback. You can change the callback at virtually any time
1285	(modulo threads).
1286
1287	=item ev_set_priority (ev_TYPE *watcher, int priority)
1288
1289	=item int ev_priority (ev_TYPE *watcher)
1290
1291	Set and query the priority of the watcher. The priority is a small
1292	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
1293	(default: C<-2>). Pending watchers with higher priority will be invoked
1294	before watchers with lower priority, but priority will not keep watchers
1295	from being executed (except for C<ev_idle> watchers).
1296
1297	If you need to suppress invocation when higher priority events are pending
1298	you need to look at C<ev_idle> watchers, which provide this functionality.
1299
1300	You I<must not> change the priority of a watcher as long as it is active or
1301	pending.
1302
1303	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
1304	fine, as long as you do not mind that the priority value you query might
1305	or might not have been clamped to the valid range.
1306
1307	The default priority used by watchers when no priority has been set is
1308	always C<0>, which is supposed to not be too high and not be too low :).
1309
1310	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
1311	priorities.
1312
1313	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1314
1315	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
1316	C<loop> nor C<revents> need to be valid as long as the watcher callback
1317	can deal with that fact, as both are simply passed through to the
1318	callback.
1319
1320	=item int ev_clear_pending (loop, ev_TYPE *watcher)
1321
1322	If the watcher is pending, this function clears its pending status and
1323	returns its C<revents> bitset (as if its callback was invoked). If the
1324	watcher isn't pending it does nothing and returns C<0>.
1325
1326	Sometimes it can be useful to "poll" a watcher instead of waiting for its
1327	callback to be invoked, which can be accomplished with this function.
1328
1329	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
1330
1331	Feeds the given event set into the event loop, as if the specified event
1332	had happened for the specified watcher (which must be a pointer to an
1333	initialised but not necessarily started event watcher). Obviously you must
1334	not free the watcher as long as it has pending events.
1335
1336	Stopping the watcher, letting libev invoke it, or calling
1337	C<ev_clear_pending> will clear the pending event, even if the watcher was
1338	not started in the first place.
1339
1340	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1341	functions that do not need a watcher.
1342
1343	=back
1344
1345
1346	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
1347
1348	Each watcher has, by default, a member C<void *data> that you can change
1349	and read at any time: libev will completely ignore it. This can be used
1350	to associate arbitrary data with your watcher. If you need more data and
1351	don't want to allocate memory and store a pointer to it in that data
1352	member, you can also "subclass" the watcher type and provide your own
1353	data:
1354
1355	struct my_io
1356	{
1357	ev_io io;
1358	int otherfd;
1359	void *somedata;
1360	struct whatever *mostinteresting;
1361	};
1362
1363	...
1364	struct my_io w;
1365	ev_io_init (&w.io, my_cb, fd, EV_READ);
1366
1367	And since your callback will be called with a pointer to the watcher, you
1368	can cast it back to your own type:
1369
1370	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1371	{
1372	struct my_io *w = (struct my_io *)w_;
1373	...
1374	}
1375
1376	More interesting and less C-conformant ways of casting your callback type
1377	instead have been omitted.
1378
1379	Another common scenario is to use some data structure with multiple
1380	embedded watchers:
1381
1382	struct my_biggy
1383	{
1384	int some_data;
1385	ev_timer t1;
1386	ev_timer t2;
1387	}
1388
1389	In this case getting the pointer to C<my_biggy> is a bit more
1390	complicated: Either you store the address of your C<my_biggy> struct
1391	in the C<data> member of the watcher (for woozies), or you need to use
1392	some pointer arithmetic using C<offsetof> inside your watchers (for real
1393	programmers):
1394
1395	#include <stddef.h>
1396
1397	static void
1398	t1_cb (EV_P_ ev_timer *w, int revents)
1399	{
1400	struct my_biggy big = (struct my_biggy *)
1401	(((char *)w) - offsetof (struct my_biggy, t1));
1402	}
1403
1404	static void
1405	t2_cb (EV_P_ ev_timer *w, int revents)
1406	{
1407	struct my_biggy big = (struct my_biggy *)
1408	(((char *)w) - offsetof (struct my_biggy, t2));
1409	}
1410		1452
1411	=head2 WATCHER PRIORITY MODELS	1453	=head2 WATCHER PRIORITY MODELS
1412		1454
1413	Many event loops support I<watcher priorities>, which are usually small	1455	Many event loops support I<watcher priorities>, which are usually small
1414	integers that influence the ordering of event callback invocation	1456	integers that influence the ordering of event callback invocation
…		…
1541	In general you can register as many read and/or write event watchers per	1583	In general you can register as many read and/or write event watchers per
1542	fd as you want (as long as you don't confuse yourself). Setting all file	1584	fd as you want (as long as you don't confuse yourself). Setting all file
1543	descriptors to non-blocking mode is also usually a good idea (but not	1585	descriptors to non-blocking mode is also usually a good idea (but not
1544	required if you know what you are doing).	1586	required if you know what you are doing).
1545		1587
1546	If you cannot use non-blocking mode, then force the use of a
1547	known-to-be-good backend (at the time of this writing, this includes only
1548	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
1549	descriptors for which non-blocking operation makes no sense (such as
1550	files) - libev doesn't guarantee any specific behaviour in that case.
1551
1552	Another thing you have to watch out for is that it is quite easy to	1588	Another thing you have to watch out for is that it is quite easy to
1553	receive "spurious" readiness notifications, that is your callback might	1589	receive "spurious" readiness notifications, that is, your callback might
1554	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1590	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1555	because there is no data. Not only are some backends known to create a	1591	because there is no data. It is very easy to get into this situation even
1556	lot of those (for example Solaris ports), it is very easy to get into	1592	with a relatively standard program structure. Thus it is best to always
1557	this situation even with a relatively standard program structure. Thus	1593	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1558	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1559	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1594	preferable to a program hanging until some data arrives.
1560		1595
1561	If you cannot run the fd in non-blocking mode (for example you should	1596	If you cannot run the fd in non-blocking mode (for example you should
1562	not play around with an Xlib connection), then you have to separately	1597	not play around with an Xlib connection), then you have to separately
1563	re-test whether a file descriptor is really ready with a known-to-be good	1598	re-test whether a file descriptor is really ready with a known-to-be good
1564	interface such as poll (fortunately in our Xlib example, Xlib already	1599	interface such as poll (fortunately in the case of Xlib, it already does
1565	does this on its own, so its quite safe to use). Some people additionally	1600	this on its own, so its quite safe to use). Some people additionally
1566	use C<SIGALRM> and an interval timer, just to be sure you won't block	1601	use C<SIGALRM> and an interval timer, just to be sure you won't block
1567	indefinitely.	1602	indefinitely.
1568		1603
1569	But really, best use non-blocking mode.	1604	But really, best use non-blocking mode.
1570		1605
…		…
1598		1633
1599	There is no workaround possible except not registering events	1634	There is no workaround possible except not registering events
1600	for potentially C<dup ()>'ed file descriptors, or to resort to	1635	for potentially C<dup ()>'ed file descriptors, or to resort to
1601	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1636	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1602		1637
		1638	=head3 The special problem of files
		1639
		1640	Many people try to use C<select> (or libev) on file descriptors
		1641	representing files, and expect it to become ready when their program
		1642	doesn't block on disk accesses (which can take a long time on their own).
		1643
		1644	However, this cannot ever work in the "expected" way - you get a readiness
		1645	notification as soon as the kernel knows whether and how much data is
		1646	there, and in the case of open files, that's always the case, so you
		1647	always get a readiness notification instantly, and your read (or possibly
		1648	write) will still block on the disk I/O.
		1649
		1650	Another way to view it is that in the case of sockets, pipes, character
		1651	devices and so on, there is another party (the sender) that delivers data
		1652	on its own, but in the case of files, there is no such thing: the disk
		1653	will not send data on its own, simply because it doesn't know what you
		1654	wish to read - you would first have to request some data.
		1655
		1656	Since files are typically not-so-well supported by advanced notification
		1657	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1658	to files, even though you should not use it. The reason for this is
		1659	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1660	usually a tty, often a pipe, but also sometimes files or special devices
		1661	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1662	F</dev/urandom>), and even though the file might better be served with
		1663	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1664	it "just works" instead of freezing.
		1665
		1666	So avoid file descriptors pointing to files when you know it (e.g. use
		1667	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1668	when you rarely read from a file instead of from a socket, and want to
		1669	reuse the same code path.
		1670
1603	=head3 The special problem of fork	1671	=head3 The special problem of fork
1604		1672
1605	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1673	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
1606	useless behaviour. Libev fully supports fork, but needs to be told about	1674	useless behaviour. Libev fully supports fork, but needs to be told about
1607	it in the child.	1675	it in the child if you want to continue to use it in the child.
1608		1676
1609	To support fork in your programs, you either have to call	1677	To support fork in your child processes, you have to call C<ev_loop_fork
1610	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1678	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1611	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1679	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1612	C<EVBACKEND_POLL>.
1613		1680
1614	=head3 The special problem of SIGPIPE	1681	=head3 The special problem of SIGPIPE
1615		1682
1616	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1683	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1617	when writing to a pipe whose other end has been closed, your program gets	1684	when writing to a pipe whose other end has been closed, your program gets
…		…
1715	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1782	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1716	monotonic clock option helps a lot here).	1783	monotonic clock option helps a lot here).
1717		1784
1718	The callback is guaranteed to be invoked only I<after> its timeout has	1785	The callback is guaranteed to be invoked only I<after> its timeout has
1719	passed (not I<at>, so on systems with very low-resolution clocks this	1786	passed (not I<at>, so on systems with very low-resolution clocks this
1720	might introduce a small delay). If multiple timers become ready during the	1787	might introduce a small delay, see "the special problem of being too
		1788	early", below). If multiple timers become ready during the same loop
1721	same loop iteration then the ones with earlier time-out values are invoked	1789	iteration then the ones with earlier time-out values are invoked before
1722	before ones of the same priority with later time-out values (but this is	1790	ones of the same priority with later time-out values (but this is no
1723	no longer true when a callback calls C<ev_run> recursively).	1791	longer true when a callback calls C<ev_run> recursively).
1724		1792
1725	=head3 Be smart about timeouts	1793	=head3 Be smart about timeouts
1726		1794
1727	Many real-world problems involve some kind of timeout, usually for error	1795	Many real-world problems involve some kind of timeout, usually for error
1728	recovery. A typical example is an HTTP request - if the other side hangs,	1796	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1803		1871
1804	In this case, it would be more efficient to leave the C<ev_timer> alone,	1872	In this case, it would be more efficient to leave the C<ev_timer> alone,
1805	but remember the time of last activity, and check for a real timeout only	1873	but remember the time of last activity, and check for a real timeout only
1806	within the callback:	1874	within the callback:
1807		1875
		1876	ev_tstamp timeout = 60.;
1808	ev_tstamp last_activity; // time of last activity	1877	ev_tstamp last_activity; // time of last activity
		1878	ev_timer timer;
1809		1879
1810	static void	1880	static void
1811	callback (EV_P_ ev_timer *w, int revents)	1881	callback (EV_P_ ev_timer *w, int revents)
1812	{	1882	{
1813	ev_tstamp now = ev_now (EV_A);	1883	// calculate when the timeout would happen
1814	ev_tstamp timeout = last_activity + 60.;	1884	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
1815		1885
1816	// if last_activity + 60. is older than now, we did time out	1886	// if negative, it means we the timeout already occurred
1817	if (timeout < now)	1887	if (after < 0.)
1818	{	1888	{
1819	// timeout occurred, take action	1889	// timeout occurred, take action
1820	}	1890	}
1821	else	1891	else
1822	{	1892	{
1823	// callback was invoked, but there was some activity, re-arm	1893	// callback was invoked, but there was some recent
1824	// the watcher to fire in last_activity + 60, which is	1894	// activity. simply restart the timer to time out
1825	// guaranteed to be in the future, so "again" is positive:	1895	// after "after" seconds, which is the earliest time
1826	w->repeat = timeout - now;	1896	// the timeout can occur.
		1897	ev_timer_set (w, after, 0.);
1827	ev_timer_again (EV_A_ w);	1898	ev_timer_start (EV_A_ w);
1828	}	1899	}
1829	}	1900	}
1830		1901
1831	To summarise the callback: first calculate the real timeout (defined	1902	To summarise the callback: first calculate in how many seconds the
1832	as "60 seconds after the last activity"), then check if that time has	1903	timeout will occur (by calculating the absolute time when it would occur,
1833	been reached, which means something I<did>, in fact, time out. Otherwise	1904	C<last_activity + timeout>, and subtracting the current time, C<ev_now
1834	the callback was invoked too early (C<timeout> is in the future), so	1905	(EV_A)> from that).
1835	re-schedule the timer to fire at that future time, to see if maybe we have
1836	a timeout then.
1837		1906
1838	Note how C<ev_timer_again> is used, taking advantage of the	1907	If this value is negative, then we are already past the timeout, i.e. we
1839	C<ev_timer_again> optimisation when the timer is already running.	1908	timed out, and need to do whatever is needed in this case.
		1909
		1910	Otherwise, we now the earliest time at which the timeout would trigger,
		1911	and simply start the timer with this timeout value.
		1912
		1913	In other words, each time the callback is invoked it will check whether
		1914	the timeout occurred. If not, it will simply reschedule itself to check
		1915	again at the earliest time it could time out. Rinse. Repeat.
1840		1916
1841	This scheme causes more callback invocations (about one every 60 seconds	1917	This scheme causes more callback invocations (about one every 60 seconds
1842	minus half the average time between activity), but virtually no calls to	1918	minus half the average time between activity), but virtually no calls to
1843	libev to change the timeout.	1919	libev to change the timeout.
1844		1920
1845	To start the timer, simply initialise the watcher and set C<last_activity>	1921	To start the machinery, simply initialise the watcher and set
1846	to the current time (meaning we just have some activity :), then call the	1922	C<last_activity> to the current time (meaning there was some activity just
1847	callback, which will "do the right thing" and start the timer:	1923	now), then call the callback, which will "do the right thing" and start
		1924	the timer:
1848		1925
		1926	last_activity = ev_now (EV_A);
1849	ev_init (timer, callback);	1927	ev_init (&timer, callback);
1850	last_activity = ev_now (loop);	1928	callback (EV_A_ &timer, 0);
1851	callback (loop, timer, EV_TIMER);
1852		1929
1853	And when there is some activity, simply store the current time in	1930	When there is some activity, simply store the current time in
1854	C<last_activity>, no libev calls at all:	1931	C<last_activity>, no libev calls at all:
1855		1932
		1933	if (activity detected)
1856	last_activity = ev_now (loop);	1934	last_activity = ev_now (EV_A);
		1935
		1936	When your timeout value changes, then the timeout can be changed by simply
		1937	providing a new value, stopping the timer and calling the callback, which
		1938	will again do the right thing (for example, time out immediately :).
		1939
		1940	timeout = new_value;
		1941	ev_timer_stop (EV_A_ &timer);
		1942	callback (EV_A_ &timer, 0);
1857		1943
1858	This technique is slightly more complex, but in most cases where the	1944	This technique is slightly more complex, but in most cases where the
1859	time-out is unlikely to be triggered, much more efficient.	1945	time-out is unlikely to be triggered, much more efficient.
1860
1861	Changing the timeout is trivial as well (if it isn't hard-coded in the
1862	callback :) - just change the timeout and invoke the callback, which will
1863	fix things for you.
1864		1946
1865	=item 4. Wee, just use a double-linked list for your timeouts.	1947	=item 4. Wee, just use a double-linked list for your timeouts.
1866		1948
1867	If there is not one request, but many thousands (millions...), all	1949	If there is not one request, but many thousands (millions...), all
1868	employing some kind of timeout with the same timeout value, then one can	1950	employing some kind of timeout with the same timeout value, then one can
…		…
1895	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is	1977	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
1896	rather complicated, but extremely efficient, something that really pays	1978	rather complicated, but extremely efficient, something that really pays
1897	off after the first million or so of active timers, i.e. it's usually	1979	off after the first million or so of active timers, i.e. it's usually
1898	overkill :)	1980	overkill :)
1899		1981
		1982	=head3 The special problem of being too early
		1983
		1984	If you ask a timer to call your callback after three seconds, then
		1985	you expect it to be invoked after three seconds - but of course, this
		1986	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		1987	guaranteed to any precision by libev - imagine somebody suspending the
		1988	process with a STOP signal for a few hours for example.
		1989
		1990	So, libev tries to invoke your callback as soon as possible I<after> the
		1991	delay has occurred, but cannot guarantee this.
		1992
		1993	A less obvious failure mode is calling your callback too early: many event
		1994	loops compare timestamps with a "elapsed delay >= requested delay", but
		1995	this can cause your callback to be invoked much earlier than you would
		1996	expect.
		1997
		1998	To see why, imagine a system with a clock that only offers full second
		1999	resolution (think windows if you can't come up with a broken enough OS
		2000	yourself). If you schedule a one-second timer at the time 500.9, then the
		2001	event loop will schedule your timeout to elapse at a system time of 500
		2002	(500.9 truncated to the resolution) + 1, or 501.
		2003
		2004	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2005	501" and invoke the callback 0.1s after it was started, even though a
		2006	one-second delay was requested - this is being "too early", despite best
		2007	intentions.
		2008
		2009	This is the reason why libev will never invoke the callback if the elapsed
		2010	delay equals the requested delay, but only when the elapsed delay is
		2011	larger than the requested delay. In the example above, libev would only invoke
		2012	the callback at system time 502, or 1.1s after the timer was started.
		2013
		2014	So, while libev cannot guarantee that your callback will be invoked
		2015	exactly when requested, it I<can> and I<does> guarantee that the requested
		2016	delay has actually elapsed, or in other words, it always errs on the "too
		2017	late" side of things.
		2018
1900	=head3 The special problem of time updates	2019	=head3 The special problem of time updates
1901		2020
1902	Establishing the current time is a costly operation (it usually takes at	2021	Establishing the current time is a costly operation (it usually takes
1903	least two system calls): EV therefore updates its idea of the current	2022	at least one system call): EV therefore updates its idea of the current
1904	time only before and after C<ev_run> collects new events, which causes a	2023	time only before and after C<ev_run> collects new events, which causes a
1905	growing difference between C<ev_now ()> and C<ev_time ()> when handling	2024	growing difference between C<ev_now ()> and C<ev_time ()> when handling
1906	lots of events in one iteration.	2025	lots of events in one iteration.
1907		2026
1908	The relative timeouts are calculated relative to the C<ev_now ()>	2027	The relative timeouts are calculated relative to the C<ev_now ()>
…		…
1914	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2033	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1915		2034
1916	If the event loop is suspended for a long time, you can also force an	2035	If the event loop is suspended for a long time, you can also force an
1917	update of the time returned by C<ev_now ()> by calling C<ev_now_update	2036	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1918	()>.	2037	()>.
		2038
		2039	=head3 The special problem of unsynchronised clocks
		2040
		2041	Modern systems have a variety of clocks - libev itself uses the normal
		2042	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2043	jumps).
		2044
		2045	Neither of these clocks is synchronised with each other or any other clock
		2046	on the system, so C<ev_time ()> might return a considerably different time
		2047	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2048	a call to C<gettimeofday> might return a second count that is one higher
		2049	than a directly following call to C<time>.
		2050
		2051	The moral of this is to only compare libev-related timestamps with
		2052	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2053	a second or so.
		2054
		2055	One more problem arises due to this lack of synchronisation: if libev uses
		2056	the system monotonic clock and you compare timestamps from C<ev_time>
		2057	or C<ev_now> from when you started your timer and when your callback is
		2058	invoked, you will find that sometimes the callback is a bit "early".
		2059
		2060	This is because C<ev_timer>s work in real time, not wall clock time, so
		2061	libev makes sure your callback is not invoked before the delay happened,
		2062	I<measured according to the real time>, not the system clock.
		2063
		2064	If your timeouts are based on a physical timescale (e.g. "time out this
		2065	connection after 100 seconds") then this shouldn't bother you as it is
		2066	exactly the right behaviour.
		2067
		2068	If you want to compare wall clock/system timestamps to your timers, then
		2069	you need to use C<ev_periodic>s, as these are based on the wall clock
		2070	time, where your comparisons will always generate correct results.
1919		2071
1920	=head3 The special problems of suspended animation	2072	=head3 The special problems of suspended animation
1921		2073
1922	When you leave the server world it is quite customary to hit machines that	2074	When you leave the server world it is quite customary to hit machines that
1923	can suspend/hibernate - what happens to the clocks during such a suspend?	2075	can suspend/hibernate - what happens to the clocks during such a suspend?
…		…
1967	keep up with the timer (because it takes longer than those 10 seconds to	2119	keep up with the timer (because it takes longer than those 10 seconds to
1968	do stuff) the timer will not fire more than once per event loop iteration.	2120	do stuff) the timer will not fire more than once per event loop iteration.
1969		2121
1970	=item ev_timer_again (loop, ev_timer *)	2122	=item ev_timer_again (loop, ev_timer *)
1971		2123
1972	This will act as if the timer timed out and restart it again if it is	2124	This will act as if the timer timed out, and restarts it again if it is
1973	repeating. The exact semantics are:	2125	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2126	timeout to the C<repeat> value and calling C<ev_timer_start>.
1974		2127
		2128	The exact semantics are as in the following rules, all of which will be
		2129	applied to the watcher:
		2130
		2131	=over 4
		2132
1975	If the timer is pending, its pending status is cleared.	2133	=item If the timer is pending, the pending status is always cleared.
1976		2134
1977	If the timer is started but non-repeating, stop it (as if it timed out).	2135	=item If the timer is started but non-repeating, stop it (as if it timed
		2136	out, without invoking it).
1978		2137
1979	If the timer is repeating, either start it if necessary (with the	2138	=item If the timer is repeating, make the C<repeat> value the new timeout
1980	C<repeat> value), or reset the running timer to the C<repeat> value.	2139	and start the timer, if necessary.
1981		2140
		2141	=back
		2142
1982	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a	2143	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
1983	usage example.	2144	usage example.
1984		2145
1985	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)	2146	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1986		2147
1987	Returns the remaining time until a timer fires. If the timer is active,	2148	Returns the remaining time until a timer fires. If the timer is active,
…		…
2107		2268
2108	Another way to think about it (for the mathematically inclined) is that	2269	Another way to think about it (for the mathematically inclined) is that
2109	C<ev_periodic> will try to run the callback in this mode at the next possible	2270	C<ev_periodic> will try to run the callback in this mode at the next possible
2110	time where C<time = offset (mod interval)>, regardless of any time jumps.	2271	time where C<time = offset (mod interval)>, regardless of any time jumps.
2111		2272
2112	For numerical stability it is preferable that the C<offset> value is near	2273	The C<interval> I<MUST> be positive, and for numerical stability, the
2113	C<ev_now ()> (the current time), but there is no range requirement for	2274	interval value should be higher than C<1/8192> (which is around 100
2114	this value, and in fact is often specified as zero.	2275	microseconds) and C<offset> should be higher than C<0> and should have
		2276	at most a similar magnitude as the current time (say, within a factor of
		2277	ten). Typical values for offset are, in fact, C<0> or something between
		2278	C<0> and C<interval>, which is also the recommended range.
2115		2279
2116	Note also that there is an upper limit to how often a timer can fire (CPU	2280	Note also that there is an upper limit to how often a timer can fire (CPU
2117	speed for example), so if C<interval> is very small then timing stability	2281	speed for example), so if C<interval> is very small then timing stability
2118	will of course deteriorate. Libev itself tries to be exact to be about one	2282	will of course deteriorate. Libev itself tries to be exact to be about one
2119	millisecond (if the OS supports it and the machine is fast enough).	2283	millisecond (if the OS supports it and the machine is fast enough).
…		…
2233		2397
2234	=head2 C<ev_signal> - signal me when a signal gets signalled!	2398	=head2 C<ev_signal> - signal me when a signal gets signalled!
2235		2399
2236	Signal watchers will trigger an event when the process receives a specific	2400	Signal watchers will trigger an event when the process receives a specific
2237	signal one or more times. Even though signals are very asynchronous, libev	2401	signal one or more times. Even though signals are very asynchronous, libev
2238	will try it's best to deliver signals synchronously, i.e. as part of the	2402	will try its best to deliver signals synchronously, i.e. as part of the
2239	normal event processing, like any other event.	2403	normal event processing, like any other event.
2240		2404
2241	If you want signals to be delivered truly asynchronously, just use	2405	If you want signals to be delivered truly asynchronously, just use
2242	C<sigaction> as you would do without libev and forget about sharing	2406	C<sigaction> as you would do without libev and forget about sharing
2243	the signal. You can even use C<ev_async> from a signal handler to	2407	the signal. You can even use C<ev_async> from a signal handler to
…		…
2262	=head3 The special problem of inheritance over fork/execve/pthread_create	2426	=head3 The special problem of inheritance over fork/execve/pthread_create
2263		2427
2264	Both the signal mask (C<sigprocmask>) and the signal disposition	2428	Both the signal mask (C<sigprocmask>) and the signal disposition
2265	(C<sigaction>) are unspecified after starting a signal watcher (and after	2429	(C<sigaction>) are unspecified after starting a signal watcher (and after
2266	stopping it again), that is, libev might or might not block the signal,	2430	stopping it again), that is, libev might or might not block the signal,
2267	and might or might not set or restore the installed signal handler.	2431	and might or might not set or restore the installed signal handler (but
		2432	see C<EVFLAG_NOSIGMASK>).
2268		2433
2269	While this does not matter for the signal disposition (libev never	2434	While this does not matter for the signal disposition (libev never
2270	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on	2435	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
2271	C<execve>), this matters for the signal mask: many programs do not expect	2436	C<execve>), this matters for the signal mask: many programs do not expect
2272	certain signals to be blocked.	2437	certain signals to be blocked.
…		…
2285	I<has> to modify the signal mask, at least temporarily.	2450	I<has> to modify the signal mask, at least temporarily.
2286		2451
2287	So I can't stress this enough: I<If you do not reset your signal mask when	2452	So I can't stress this enough: I<If you do not reset your signal mask when
2288	you expect it to be empty, you have a race condition in your code>. This	2453	you expect it to be empty, you have a race condition in your code>. This
2289	is not a libev-specific thing, this is true for most event libraries.	2454	is not a libev-specific thing, this is true for most event libraries.
		2455
		2456	=head3 The special problem of threads signal handling
		2457
		2458	POSIX threads has problematic signal handling semantics, specifically,
		2459	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2460	threads in a process block signals, which is hard to achieve.
		2461
		2462	When you want to use sigwait (or mix libev signal handling with your own
		2463	for the same signals), you can tackle this problem by globally blocking
		2464	all signals before creating any threads (or creating them with a fully set
		2465	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2466	loops. Then designate one thread as "signal receiver thread" which handles
		2467	these signals. You can pass on any signals that libev might be interested
		2468	in by calling C<ev_feed_signal>.
2290		2469
2291	=head3 Watcher-Specific Functions and Data Members	2470	=head3 Watcher-Specific Functions and Data Members
2292		2471
2293	=over 4	2472	=over 4
2294		2473
…		…
2429		2608
2430	=head2 C<ev_stat> - did the file attributes just change?	2609	=head2 C<ev_stat> - did the file attributes just change?
2431		2610
2432	This watches a file system path for attribute changes. That is, it calls	2611	This watches a file system path for attribute changes. That is, it calls
2433	C<stat> on that path in regular intervals (or when the OS says it changed)	2612	C<stat> on that path in regular intervals (or when the OS says it changed)
2434	and sees if it changed compared to the last time, invoking the callback if	2613	and sees if it changed compared to the last time, invoking the callback
2435	it did.	2614	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2615	happen after the watcher has been started will be reported.
2436		2616
2437	The path does not need to exist: changing from "path exists" to "path does	2617	The path does not need to exist: changing from "path exists" to "path does
2438	not exist" is a status change like any other. The condition "path does not	2618	not exist" is a status change like any other. The condition "path does not
2439	exist" (or more correctly "path cannot be stat'ed") is signified by the	2619	exist" (or more correctly "path cannot be stat'ed") is signified by the
2440	C<st_nlink> field being zero (which is otherwise always forced to be at	2620	C<st_nlink> field being zero (which is otherwise always forced to be at
…		…
2670	Apart from keeping your process non-blocking (which is a useful	2850	Apart from keeping your process non-blocking (which is a useful
2671	effect on its own sometimes), idle watchers are a good place to do	2851	effect on its own sometimes), idle watchers are a good place to do
2672	"pseudo-background processing", or delay processing stuff to after the	2852	"pseudo-background processing", or delay processing stuff to after the
2673	event loop has handled all outstanding events.	2853	event loop has handled all outstanding events.
2674		2854
		2855	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2856
		2857	As long as there is at least one active idle watcher, libev will never
		2858	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2859	For this to work, the idle watcher doesn't need to be invoked at all - the
		2860	lowest priority will do.
		2861
		2862	This mode of operation can be useful together with an C<ev_check> watcher,
		2863	to do something on each event loop iteration - for example to balance load
		2864	between different connections.
		2865
		2866	See L</Abusing an ev_check watcher for its side-effect> for a longer
		2867	example.
		2868
2675	=head3 Watcher-Specific Functions and Data Members	2869	=head3 Watcher-Specific Functions and Data Members
2676		2870
2677	=over 4	2871	=over 4
2678		2872
2679	=item ev_idle_init (ev_idle *, callback)	2873	=item ev_idle_init (ev_idle *, callback)
…		…
2690	callback, free it. Also, use no error checking, as usual.	2884	callback, free it. Also, use no error checking, as usual.
2691		2885
2692	static void	2886	static void
2693	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)	2887	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
2694	{	2888	{
		2889	// stop the watcher
		2890	ev_idle_stop (loop, w);
		2891
		2892	// now we can free it
2695	free (w);	2893	free (w);
		2894
2696	// now do something you wanted to do when the program has	2895	// now do something you wanted to do when the program has
2697	// no longer anything immediate to do.	2896	// no longer anything immediate to do.
2698	}	2897	}
2699		2898
2700	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	2899	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
…		…
2702	ev_idle_start (loop, idle_watcher);	2901	ev_idle_start (loop, idle_watcher);
2703		2902
2704		2903
2705	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2904	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2706		2905
2707	Prepare and check watchers are usually (but not always) used in pairs:	2906	Prepare and check watchers are often (but not always) used in pairs:
2708	prepare watchers get invoked before the process blocks and check watchers	2907	prepare watchers get invoked before the process blocks and check watchers
2709	afterwards.	2908	afterwards.
2710		2909
2711	You I<must not> call C<ev_run> or similar functions that enter	2910	You I<must not> call C<ev_run> or similar functions that enter
2712	the current event loop from either C<ev_prepare> or C<ev_check>	2911	the current event loop from either C<ev_prepare> or C<ev_check>
…		…
2740	with priority higher than or equal to the event loop and one coroutine	2939	with priority higher than or equal to the event loop and one coroutine
2741	of lower priority, but only once, using idle watchers to keep the event	2940	of lower priority, but only once, using idle watchers to keep the event
2742	loop from blocking if lower-priority coroutines are active, thus mapping	2941	loop from blocking if lower-priority coroutines are active, thus mapping
2743	low-priority coroutines to idle/background tasks).	2942	low-priority coroutines to idle/background tasks).
2744		2943
2745	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2944	When used for this purpose, it is recommended to give C<ev_check> watchers
2746	priority, to ensure that they are being run before any other watchers	2945	highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
2747	after the poll (this doesn't matter for C<ev_prepare> watchers).	2946	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		2947	watchers).
2748		2948
2749	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not	2949	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
2750	activate ("feed") events into libev. While libev fully supports this, they	2950	activate ("feed") events into libev. While libev fully supports this, they
2751	might get executed before other C<ev_check> watchers did their job. As	2951	might get executed before other C<ev_check> watchers did their job. As
2752	C<ev_check> watchers are often used to embed other (non-libev) event	2952	C<ev_check> watchers are often used to embed other (non-libev) event
2753	loops those other event loops might be in an unusable state until their	2953	loops those other event loops might be in an unusable state until their
2754	C<ev_check> watcher ran (always remind yourself to coexist peacefully with	2954	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
2755	others).	2955	others).
		2956
		2957	=head3 Abusing an C<ev_check> watcher for its side-effect
		2958
		2959	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		2960	useful because they are called once per event loop iteration. For
		2961	example, if you want to handle a large number of connections fairly, you
		2962	normally only do a bit of work for each active connection, and if there
		2963	is more work to do, you wait for the next event loop iteration, so other
		2964	connections have a chance of making progress.
		2965
		2966	Using an C<ev_check> watcher is almost enough: it will be called on the
		2967	next event loop iteration. However, that isn't as soon as possible -
		2968	without external events, your C<ev_check> watcher will not be invoked.
		2969
		2970	This is where C<ev_idle> watchers come in handy - all you need is a
		2971	single global idle watcher that is active as long as you have one active
		2972	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		2973	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		2974	invoked. Neither watcher alone can do that.
2756		2975
2757	=head3 Watcher-Specific Functions and Data Members	2976	=head3 Watcher-Specific Functions and Data Members
2758		2977
2759	=over 4	2978	=over 4
2760		2979
…		…
2961		3180
2962	=over 4	3181	=over 4
2963		3182
2964	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3183	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
2965		3184
2966	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)	3185	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
2967		3186
2968	Configures the watcher to embed the given loop, which must be	3187	Configures the watcher to embed the given loop, which must be
2969	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3188	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
2970	invoked automatically, otherwise it is the responsibility of the callback	3189	invoked automatically, otherwise it is the responsibility of the callback
2971	to invoke it (it will continue to be called until the sweep has been done,	3190	to invoke it (it will continue to be called until the sweep has been done,
…		…
3034		3253
3035	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3254	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
3036		3255
3037	Fork watchers are called when a C<fork ()> was detected (usually because	3256	Fork watchers are called when a C<fork ()> was detected (usually because
3038	whoever is a good citizen cared to tell libev about it by calling	3257	whoever is a good citizen cared to tell libev about it by calling
3039	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the	3258	C<ev_loop_fork>). The invocation is done before the event loop blocks next
3040	event loop blocks next and before C<ev_check> watchers are being called,	3259	and before C<ev_check> watchers are being called, and only in the child
3041	and only in the child after the fork. If whoever good citizen calling	3260	after the fork. If whoever good citizen calling C<ev_default_fork> cheats
3042	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3261	and calls it in the wrong process, the fork handlers will be invoked, too,
3043	handlers will be invoked, too, of course.	3262	of course.
3044		3263
3045	=head3 The special problem of life after fork - how is it possible?	3264	=head3 The special problem of life after fork - how is it possible?
3046		3265
3047	Most uses of C<fork()> consist of forking, then some simple calls to set	3266	Most uses of C<fork()> consist of forking, then some simple calls to set
3048	up/change the process environment, followed by a call to C<exec()>. This	3267	up/change the process environment, followed by a call to C<exec()>. This
…		…
3068	disadvantage of having to use multiple event loops (which do not support	3287	disadvantage of having to use multiple event loops (which do not support
3069	signal watchers).	3288	signal watchers).
3070		3289
3071	When this is not possible, or you want to use the default loop for	3290	When this is not possible, or you want to use the default loop for
3072	other reasons, then in the process that wants to start "fresh", call	3291	other reasons, then in the process that wants to start "fresh", call
3073	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying	3292	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
3074	the default loop will "orphan" (not stop) all registered watchers, so you	3293	Destroying the default loop will "orphan" (not stop) all registered
3075	have to be careful not to execute code that modifies those watchers. Note	3294	watchers, so you have to be careful not to execute code that modifies
3076	also that in that case, you have to re-register any signal watchers.	3295	those watchers. Note also that in that case, you have to re-register any
		3296	signal watchers.
3077		3297
3078	=head3 Watcher-Specific Functions and Data Members	3298	=head3 Watcher-Specific Functions and Data Members
3079		3299
3080	=over 4	3300	=over 4
3081		3301
3082	=item ev_fork_init (ev_signal *, callback)	3302	=item ev_fork_init (ev_fork *, callback)
3083		3303
3084	Initialises and configures the fork watcher - it has no parameters of any	3304	Initialises and configures the fork watcher - it has no parameters of any
3085	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,	3305	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
3086	believe me.	3306	really.
3087		3307
3088	=back	3308	=back
3089		3309
3090		3310
		3311	=head2 C<ev_cleanup> - even the best things end
		3312
		3313	Cleanup watchers are called just before the event loop is being destroyed
		3314	by a call to C<ev_loop_destroy>.
		3315
		3316	While there is no guarantee that the event loop gets destroyed, cleanup
		3317	watchers provide a convenient method to install cleanup hooks for your
		3318	program, worker threads and so on - you just to make sure to destroy the
		3319	loop when you want them to be invoked.
		3320
		3321	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3322	all other watchers, they do not keep a reference to the event loop (which
		3323	makes a lot of sense if you think about it). Like all other watchers, you
		3324	can call libev functions in the callback, except C<ev_cleanup_start>.
		3325
		3326	=head3 Watcher-Specific Functions and Data Members
		3327
		3328	=over 4
		3329
		3330	=item ev_cleanup_init (ev_cleanup *, callback)
		3331
		3332	Initialises and configures the cleanup watcher - it has no parameters of
		3333	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3334	pointless, I assure you.
		3335
		3336	=back
		3337
		3338	Example: Register an atexit handler to destroy the default loop, so any
		3339	cleanup functions are called.
		3340
		3341	static void
		3342	program_exits (void)
		3343	{
		3344	ev_loop_destroy (EV_DEFAULT_UC);
		3345	}
		3346
		3347	...
		3348	atexit (program_exits);
		3349
		3350
3091	=head2 C<ev_async> - how to wake up an event loop	3351	=head2 C<ev_async> - how to wake up an event loop
3092		3352
3093	In general, you cannot use an C<ev_run> from multiple threads or other	3353	In general, you cannot use an C<ev_loop> from multiple threads or other
3094	asynchronous sources such as signal handlers (as opposed to multiple event	3354	asynchronous sources such as signal handlers (as opposed to multiple event
3095	loops - those are of course safe to use in different threads).	3355	loops - those are of course safe to use in different threads).
3096		3356
3097	Sometimes, however, you need to wake up an event loop you do not control,	3357	Sometimes, however, you need to wake up an event loop you do not control,
3098	for example because it belongs to another thread. This is what C<ev_async>	3358	for example because it belongs to another thread. This is what C<ev_async>
…		…
3100	it by calling C<ev_async_send>, which is thread- and signal safe.	3360	it by calling C<ev_async_send>, which is thread- and signal safe.
3101		3361
3102	This functionality is very similar to C<ev_signal> watchers, as signals,	3362	This functionality is very similar to C<ev_signal> watchers, as signals,
3103	too, are asynchronous in nature, and signals, too, will be compressed	3363	too, are asynchronous in nature, and signals, too, will be compressed
3104	(i.e. the number of callback invocations may be less than the number of	3364	(i.e. the number of callback invocations may be less than the number of
3105	C<ev_async_sent> calls).	3365	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
3106		3366	of "global async watchers" by using a watcher on an otherwise unused
3107	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not	3367	signal, and C<ev_feed_signal> to signal this watcher from another thread,
3108	just the default loop.	3368	even without knowing which loop owns the signal.
3109		3369
3110	=head3 Queueing	3370	=head3 Queueing
3111		3371
3112	C<ev_async> does not support queueing of data in any way. The reason	3372	C<ev_async> does not support queueing of data in any way. The reason
3113	is that the author does not know of a simple (or any) algorithm for a	3373	is that the author does not know of a simple (or any) algorithm for a
…		…
3205	trust me.	3465	trust me.
3206		3466
3207	=item ev_async_send (loop, ev_async *)	3467	=item ev_async_send (loop, ev_async *)
3208		3468
3209	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3469	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
3210	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3470	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3471	returns.
		3472
3211	C<ev_feed_event>, this call is safe to do from other threads, signal or	3473	Unlike C<ev_feed_event>, this call is safe to do from other threads,
3212	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3474	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
3213	section below on what exactly this means).	3475	embedding section below on what exactly this means).
3214		3476
3215	Note that, as with other watchers in libev, multiple events might get	3477	Note that, as with other watchers in libev, multiple events might get
3216	compressed into a single callback invocation (another way to look at this	3478	compressed into a single callback invocation (another way to look at
3217	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,	3479	this is that C<ev_async> watchers are level-triggered: they are set on
3218	reset when the event loop detects that).	3480	C<ev_async_send>, reset when the event loop detects that).
3219		3481
3220	This call incurs the overhead of a system call only once per event loop	3482	This call incurs the overhead of at most one extra system call per event
3221	iteration, so while the overhead might be noticeable, it doesn't apply to	3483	loop iteration, if the event loop is blocked, and no syscall at all if
3222	repeated calls to C<ev_async_send> for the same event loop.	3484	the event loop (or your program) is processing events. That means that
		3485	repeated calls are basically free (there is no need to avoid calls for
		3486	performance reasons) and that the overhead becomes smaller (typically
		3487	zero) under load.
3223		3488
3224	=item bool = ev_async_pending (ev_async *)	3489	=item bool = ev_async_pending (ev_async *)
3225		3490
3226	Returns a non-zero value when C<ev_async_send> has been called on the	3491	Returns a non-zero value when C<ev_async_send> has been called on the
3227	watcher but the event has not yet been processed (or even noted) by the	3492	watcher but the event has not yet been processed (or even noted) by the
…		…
3282	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3547	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3283		3548
3284	=item ev_feed_fd_event (loop, int fd, int revents)	3549	=item ev_feed_fd_event (loop, int fd, int revents)
3285		3550
3286	Feed an event on the given fd, as if a file descriptor backend detected	3551	Feed an event on the given fd, as if a file descriptor backend detected
3287	the given events it.	3552	the given events.
3288		3553
3289	=item ev_feed_signal_event (loop, int signum)	3554	=item ev_feed_signal_event (loop, int signum)
3290		3555
3291	Feed an event as if the given signal occurred (C<loop> must be the default	3556	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3292	loop!).	3557	which is async-safe.
3293		3558
3294	=back	3559	=back
		3560
		3561
		3562	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3563
		3564	This section explains some common idioms that are not immediately
		3565	obvious. Note that examples are sprinkled over the whole manual, and this
		3566	section only contains stuff that wouldn't fit anywhere else.
		3567
		3568	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3569
		3570	Each watcher has, by default, a C<void *data> member that you can read
		3571	or modify at any time: libev will completely ignore it. This can be used
		3572	to associate arbitrary data with your watcher. If you need more data and
		3573	don't want to allocate memory separately and store a pointer to it in that
		3574	data member, you can also "subclass" the watcher type and provide your own
		3575	data:
		3576
		3577	struct my_io
		3578	{
		3579	ev_io io;
		3580	int otherfd;
		3581	void *somedata;
		3582	struct whatever *mostinteresting;
		3583	};
		3584
		3585	...
		3586	struct my_io w;
		3587	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3588
		3589	And since your callback will be called with a pointer to the watcher, you
		3590	can cast it back to your own type:
		3591
		3592	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3593	{
		3594	struct my_io *w = (struct my_io *)w_;
		3595	...
		3596	}
		3597
		3598	More interesting and less C-conformant ways of casting your callback
		3599	function type instead have been omitted.
		3600
		3601	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3602
		3603	Another common scenario is to use some data structure with multiple
		3604	embedded watchers, in effect creating your own watcher that combines
		3605	multiple libev event sources into one "super-watcher":
		3606
		3607	struct my_biggy
		3608	{
		3609	int some_data;
		3610	ev_timer t1;
		3611	ev_timer t2;
		3612	}
		3613
		3614	In this case getting the pointer to C<my_biggy> is a bit more
		3615	complicated: Either you store the address of your C<my_biggy> struct in
		3616	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3617	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3618	real programmers):
		3619
		3620	#include <stddef.h>
		3621
		3622	static void
		3623	t1_cb (EV_P_ ev_timer *w, int revents)
		3624	{
		3625	struct my_biggy big = (struct my_biggy *)
		3626	(((char *)w) - offsetof (struct my_biggy, t1));
		3627	}
		3628
		3629	static void
		3630	t2_cb (EV_P_ ev_timer *w, int revents)
		3631	{
		3632	struct my_biggy big = (struct my_biggy *)
		3633	(((char *)w) - offsetof (struct my_biggy, t2));
		3634	}
		3635
		3636	=head2 AVOIDING FINISHING BEFORE RETURNING
		3637
		3638	Often you have structures like this in event-based programs:
		3639
		3640	callback ()
		3641	{
		3642	free (request);
		3643	}
		3644
		3645	request = start_new_request (..., callback);
		3646
		3647	The intent is to start some "lengthy" operation. The C<request> could be
		3648	used to cancel the operation, or do other things with it.
		3649
		3650	It's not uncommon to have code paths in C<start_new_request> that
		3651	immediately invoke the callback, for example, to report errors. Or you add
		3652	some caching layer that finds that it can skip the lengthy aspects of the
		3653	operation and simply invoke the callback with the result.
		3654
		3655	The problem here is that this will happen I<before> C<start_new_request>
		3656	has returned, so C<request> is not set.
		3657
		3658	Even if you pass the request by some safer means to the callback, you
		3659	might want to do something to the request after starting it, such as
		3660	canceling it, which probably isn't working so well when the callback has
		3661	already been invoked.
		3662
		3663	A common way around all these issues is to make sure that
		3664	C<start_new_request> I<always> returns before the callback is invoked. If
		3665	C<start_new_request> immediately knows the result, it can artificially
		3666	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3667	example, or more sneakily, by reusing an existing (stopped) watcher and
		3668	pushing it into the pending queue:
		3669
		3670	ev_set_cb (watcher, callback);
		3671	ev_feed_event (EV_A_ watcher, 0);
		3672
		3673	This way, C<start_new_request> can safely return before the callback is
		3674	invoked, while not delaying callback invocation too much.
		3675
		3676	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3677
		3678	Often (especially in GUI toolkits) there are places where you have
		3679	I<modal> interaction, which is most easily implemented by recursively
		3680	invoking C<ev_run>.
		3681
		3682	This brings the problem of exiting - a callback might want to finish the
		3683	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3684	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3685	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3686	other combination: In these cases, a simple C<ev_break> will not work.
		3687
		3688	The solution is to maintain "break this loop" variable for each C<ev_run>
		3689	invocation, and use a loop around C<ev_run> until the condition is
		3690	triggered, using C<EVRUN_ONCE>:
		3691
		3692	// main loop
		3693	int exit_main_loop = 0;
		3694
		3695	while (!exit_main_loop)
		3696	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3697
		3698	// in a modal watcher
		3699	int exit_nested_loop = 0;
		3700
		3701	while (!exit_nested_loop)
		3702	ev_run (EV_A_ EVRUN_ONCE);
		3703
		3704	To exit from any of these loops, just set the corresponding exit variable:
		3705
		3706	// exit modal loop
		3707	exit_nested_loop = 1;
		3708
		3709	// exit main program, after modal loop is finished
		3710	exit_main_loop = 1;
		3711
		3712	// exit both
		3713	exit_main_loop = exit_nested_loop = 1;
		3714
		3715	=head2 THREAD LOCKING EXAMPLE
		3716
		3717	Here is a fictitious example of how to run an event loop in a different
		3718	thread from where callbacks are being invoked and watchers are
		3719	created/added/removed.
		3720
		3721	For a real-world example, see the C<EV::Loop::Async> perl module,
		3722	which uses exactly this technique (which is suited for many high-level
		3723	languages).
		3724
		3725	The example uses a pthread mutex to protect the loop data, a condition
		3726	variable to wait for callback invocations, an async watcher to notify the
		3727	event loop thread and an unspecified mechanism to wake up the main thread.
		3728
		3729	First, you need to associate some data with the event loop:
		3730
		3731	typedef struct {
		3732	mutex_t lock; /* global loop lock */
		3733	ev_async async_w;
		3734	thread_t tid;
		3735	cond_t invoke_cv;
		3736	} userdata;
		3737
		3738	void prepare_loop (EV_P)
		3739	{
		3740	// for simplicity, we use a static userdata struct.
		3741	static userdata u;
		3742
		3743	ev_async_init (&u->async_w, async_cb);
		3744	ev_async_start (EV_A_ &u->async_w);
		3745
		3746	pthread_mutex_init (&u->lock, 0);
		3747	pthread_cond_init (&u->invoke_cv, 0);
		3748
		3749	// now associate this with the loop
		3750	ev_set_userdata (EV_A_ u);
		3751	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3752	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3753
		3754	// then create the thread running ev_run
		3755	pthread_create (&u->tid, 0, l_run, EV_A);
		3756	}
		3757
		3758	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3759	solely to wake up the event loop so it takes notice of any new watchers
		3760	that might have been added:
		3761
		3762	static void
		3763	async_cb (EV_P_ ev_async *w, int revents)
		3764	{
		3765	// just used for the side effects
		3766	}
		3767
		3768	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3769	protecting the loop data, respectively.
		3770
		3771	static void
		3772	l_release (EV_P)
		3773	{
		3774	userdata *u = ev_userdata (EV_A);
		3775	pthread_mutex_unlock (&u->lock);
		3776	}
		3777
		3778	static void
		3779	l_acquire (EV_P)
		3780	{
		3781	userdata *u = ev_userdata (EV_A);
		3782	pthread_mutex_lock (&u->lock);
		3783	}
		3784
		3785	The event loop thread first acquires the mutex, and then jumps straight
		3786	into C<ev_run>:
		3787
		3788	void *
		3789	l_run (void *thr_arg)
		3790	{
		3791	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3792
		3793	l_acquire (EV_A);
		3794	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3795	ev_run (EV_A_ 0);
		3796	l_release (EV_A);
		3797
		3798	return 0;
		3799	}
		3800
		3801	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3802	signal the main thread via some unspecified mechanism (signals? pipe
		3803	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3804	have been called (in a while loop because a) spurious wakeups are possible
		3805	and b) skipping inter-thread-communication when there are no pending
		3806	watchers is very beneficial):
		3807
		3808	static void
		3809	l_invoke (EV_P)
		3810	{
		3811	userdata *u = ev_userdata (EV_A);
		3812
		3813	while (ev_pending_count (EV_A))
		3814	{
		3815	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3816	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3817	}
		3818	}
		3819
		3820	Now, whenever the main thread gets told to invoke pending watchers, it
		3821	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3822	thread to continue:
		3823
		3824	static void
		3825	real_invoke_pending (EV_P)
		3826	{
		3827	userdata *u = ev_userdata (EV_A);
		3828
		3829	pthread_mutex_lock (&u->lock);
		3830	ev_invoke_pending (EV_A);
		3831	pthread_cond_signal (&u->invoke_cv);
		3832	pthread_mutex_unlock (&u->lock);
		3833	}
		3834
		3835	Whenever you want to start/stop a watcher or do other modifications to an
		3836	event loop, you will now have to lock:
		3837
		3838	ev_timer timeout_watcher;
		3839	userdata *u = ev_userdata (EV_A);
		3840
		3841	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3842
		3843	pthread_mutex_lock (&u->lock);
		3844	ev_timer_start (EV_A_ &timeout_watcher);
		3845	ev_async_send (EV_A_ &u->async_w);
		3846	pthread_mutex_unlock (&u->lock);
		3847
		3848	Note that sending the C<ev_async> watcher is required because otherwise
		3849	an event loop currently blocking in the kernel will have no knowledge
		3850	about the newly added timer. By waking up the loop it will pick up any new
		3851	watchers in the next event loop iteration.
		3852
		3853	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3854
		3855	While the overhead of a callback that e.g. schedules a thread is small, it
		3856	is still an overhead. If you embed libev, and your main usage is with some
		3857	kind of threads or coroutines, you might want to customise libev so that
		3858	doesn't need callbacks anymore.
		3859
		3860	Imagine you have coroutines that you can switch to using a function
		3861	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3862	and that due to some magic, the currently active coroutine is stored in a
		3863	global called C<current_coro>. Then you can build your own "wait for libev
		3864	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3865	the differing C<;> conventions):
		3866
		3867	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3868	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3869
		3870	That means instead of having a C callback function, you store the
		3871	coroutine to switch to in each watcher, and instead of having libev call
		3872	your callback, you instead have it switch to that coroutine.
		3873
		3874	A coroutine might now wait for an event with a function called
		3875	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3876	matter when, or whether the watcher is active or not when this function is
		3877	called):
		3878
		3879	void
		3880	wait_for_event (ev_watcher *w)
		3881	{
		3882	ev_set_cb (w, current_coro);
		3883	switch_to (libev_coro);
		3884	}
		3885
		3886	That basically suspends the coroutine inside C<wait_for_event> and
		3887	continues the libev coroutine, which, when appropriate, switches back to
		3888	this or any other coroutine.
		3889
		3890	You can do similar tricks if you have, say, threads with an event queue -
		3891	instead of storing a coroutine, you store the queue object and instead of
		3892	switching to a coroutine, you push the watcher onto the queue and notify
		3893	any waiters.
		3894
		3895	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		3896	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3897
		3898	// my_ev.h
		3899	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3900	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);
		3901	#include "../libev/ev.h"
		3902
		3903	// my_ev.c
		3904	#define EV_H "my_ev.h"
		3905	#include "../libev/ev.c"
		3906
		3907	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3908	F<my_ev.c> into your project. When properly specifying include paths, you
		3909	can even use F<ev.h> as header file name directly.
3295		3910
3296		3911
3297	=head1 LIBEVENT EMULATION	3912	=head1 LIBEVENT EMULATION
3298		3913
3299	Libev offers a compatibility emulation layer for libevent. It cannot	3914	Libev offers a compatibility emulation layer for libevent. It cannot
3300	emulate the internals of libevent, so here are some usage hints:	3915	emulate the internals of libevent, so here are some usage hints:
3301		3916
3302	=over 4	3917	=over 4
		3918
		3919	=item * Only the libevent-1.4.1-beta API is being emulated.
		3920
		3921	This was the newest libevent version available when libev was implemented,
		3922	and is still mostly unchanged in 2010.
3303		3923
3304	=item * Use it by including <event.h>, as usual.	3924	=item * Use it by including <event.h>, as usual.
3305		3925
3306	=item * The following members are fully supported: ev_base, ev_callback,	3926	=item * The following members are fully supported: ev_base, ev_callback,
3307	ev_arg, ev_fd, ev_res, ev_events.	3927	ev_arg, ev_fd, ev_res, ev_events.
…		…
3313	=item * Priorities are not currently supported. Initialising priorities	3933	=item * Priorities are not currently supported. Initialising priorities
3314	will fail and all watchers will have the same priority, even though there	3934	will fail and all watchers will have the same priority, even though there
3315	is an ev_pri field.	3935	is an ev_pri field.
3316		3936
3317	=item * In libevent, the last base created gets the signals, in libev, the	3937	=item * In libevent, the last base created gets the signals, in libev, the
3318	first base created (== the default loop) gets the signals.	3938	base that registered the signal gets the signals.
3319		3939
3320	=item * Other members are not supported.	3940	=item * Other members are not supported.
3321		3941
3322	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3942	=item * The libev emulation is I<not> ABI compatible to libevent, you need
3323	to use the libev header file and library.	3943	to use the libev header file and library.
3324		3944
3325	=back	3945	=back
3326		3946
3327	=head1 C++ SUPPORT	3947	=head1 C++ SUPPORT
		3948
		3949	=head2 C API
		3950
		3951	The normal C API should work fine when used from C++: both ev.h and the
		3952	libev sources can be compiled as C++. Therefore, code that uses the C API
		3953	will work fine.
		3954
		3955	Proper exception specifications might have to be added to callbacks passed
		3956	to libev: exceptions may be thrown only from watcher callbacks, all
		3957	other callbacks (allocator, syserr, loop acquire/release and periodic
		3958	reschedule callbacks) must not throw exceptions, and might need a C<throw
		3959	()> specification. If you have code that needs to be compiled as both C
		3960	and C++ you can use the C<EV_THROW> macro for this:
		3961
		3962	static void
		3963	fatal_error (const char *msg) EV_THROW
		3964	{
		3965	perror (msg);
		3966	abort ();
		3967	}
		3968
		3969	...
		3970	ev_set_syserr_cb (fatal_error);
		3971
		3972	The only API functions that can currently throw exceptions are C<ev_run>,
		3973	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		3974	because it runs cleanup watchers).
		3975
		3976	Throwing exceptions in watcher callbacks is only supported if libev itself
		3977	is compiled with a C++ compiler or your C and C++ environments allow
		3978	throwing exceptions through C libraries (most do).
		3979
		3980	=head2 C++ API
3328		3981
3329	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3982	Libev comes with some simplistic wrapper classes for C++ that mainly allow
3330	you to use some convenience methods to start/stop watchers and also change	3983	you to use some convenience methods to start/stop watchers and also change
3331	the callback model to a model using method callbacks on objects.	3984	the callback model to a model using method callbacks on objects.
3332		3985
…		…
3342	Care has been taken to keep the overhead low. The only data member the C++	3995	Care has been taken to keep the overhead low. The only data member the C++
3343	classes add (compared to plain C-style watchers) is the event loop pointer	3996	classes add (compared to plain C-style watchers) is the event loop pointer
3344	that the watcher is associated with (or no additional members at all if	3997	that the watcher is associated with (or no additional members at all if
3345	you disable C<EV_MULTIPLICITY> when embedding libev).	3998	you disable C<EV_MULTIPLICITY> when embedding libev).
3346		3999
3347	Currently, functions, and static and non-static member functions can be	4000	Currently, functions, static and non-static member functions and classes
3348	used as callbacks. Other types should be easy to add as long as they only	4001	with C<operator ()> can be used as callbacks. Other types should be easy
3349	need one additional pointer for context. If you need support for other	4002	to add as long as they only need one additional pointer for context. If
3350	types of functors please contact the author (preferably after implementing	4003	you need support for other types of functors please contact the author
3351	it).	4004	(preferably after implementing it).
		4005
		4006	For all this to work, your C++ compiler either has to use the same calling
		4007	conventions as your C compiler (for static member functions), or you have
		4008	to embed libev and compile libev itself as C++.
3352		4009
3353	Here is a list of things available in the C<ev> namespace:	4010	Here is a list of things available in the C<ev> namespace:
3354		4011
3355	=over 4	4012	=over 4
3356		4013
…		…
3366	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	4023	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
3367		4024
3368	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4025	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
3369	the same name in the C<ev> namespace, with the exception of C<ev_signal>	4026	the same name in the C<ev> namespace, with the exception of C<ev_signal>
3370	which is called C<ev::sig> to avoid clashes with the C<signal> macro	4027	which is called C<ev::sig> to avoid clashes with the C<signal> macro
3371	defines by many implementations.	4028	defined by many implementations.
3372		4029
3373	All of those classes have these methods:	4030	All of those classes have these methods:
3374		4031
3375	=over 4	4032	=over 4
3376		4033
…		…
3466	Associates a different C<struct ev_loop> with this watcher. You can only	4123	Associates a different C<struct ev_loop> with this watcher. You can only
3467	do this when the watcher is inactive (and not pending either).	4124	do this when the watcher is inactive (and not pending either).
3468		4125
3469	=item w->set ([arguments])	4126	=item w->set ([arguments])
3470		4127
3471	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this	4128	Basically the same as C<ev_TYPE_set> (except for C<ev::embed> watchers>),
3472	method or a suitable start method must be called at least once. Unlike the	4129	with the same arguments. Either this method or a suitable start method
3473	C counterpart, an active watcher gets automatically stopped and restarted	4130	must be called at least once. Unlike the C counterpart, an active watcher
3474	when reconfiguring it with this method.	4131	gets automatically stopped and restarted when reconfiguring it with this
		4132	method.
		4133
		4134	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4135	clashing with the C<set (loop)> method.
3475		4136
3476	=item w->start ()	4137	=item w->start ()
3477		4138
3478	Starts the watcher. Note that there is no C<loop> argument, as the	4139	Starts the watcher. Note that there is no C<loop> argument, as the
3479	constructor already stores the event loop.	4140	constructor already stores the event loop.
…		…
3509	watchers in the constructor.	4170	watchers in the constructor.
3510		4171
3511	class myclass	4172	class myclass
3512	{	4173	{
3513	ev::io io ; void io_cb (ev::io &w, int revents);	4174	ev::io io ; void io_cb (ev::io &w, int revents);
3514	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);	4175	ev::io io2 ; void io2_cb (ev::io &w, int revents);
3515	ev::idle idle; void idle_cb (ev::idle &w, int revents);	4176	ev::idle idle; void idle_cb (ev::idle &w, int revents);
3516		4177
3517	myclass (int fd)	4178	myclass (int fd)
3518	{	4179	{
3519	io .set <myclass, &myclass::io_cb > (this);	4180	io .set <myclass, &myclass::io_cb > (this);
…		…
3570	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.	4231	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
3571		4232
3572	=item D	4233	=item D
3573		4234
3574	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4235	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
3575	be found at L<http://proj.llucax.com.ar/wiki/evd>.	4236	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
3576		4237
3577	=item Ocaml	4238	=item Ocaml
3578		4239
3579	Erkki Seppala has written Ocaml bindings for libev, to be found at	4240	Erkki Seppala has written Ocaml bindings for libev, to be found at
3580	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	4241	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
…		…
3583		4244
3584	Brian Maher has written a partial interface to libev for lua (at the	4245	Brian Maher has written a partial interface to libev for lua (at the
3585	time of this writing, only C<ev_io> and C<ev_timer>), to be found at	4246	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
3586	L<http://github.com/brimworks/lua-ev>.	4247	L<http://github.com/brimworks/lua-ev>.
3587		4248
		4249	=item Javascript
		4250
		4251	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4252
		4253	=item Others
		4254
		4255	There are others, and I stopped counting.
		4256
3588	=back	4257	=back
3589		4258
3590		4259
3591	=head1 MACRO MAGIC	4260	=head1 MACRO MAGIC
3592		4261
…		…
3628	suitable for use with C<EV_A>.	4297	suitable for use with C<EV_A>.
3629		4298
3630	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4299	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
3631		4300
3632	Similar to the other two macros, this gives you the value of the default	4301	Similar to the other two macros, this gives you the value of the default
3633	loop, if multiple loops are supported ("ev loop default").	4302	loop, if multiple loops are supported ("ev loop default"). The default loop
		4303	will be initialised if it isn't already initialised.
		4304
		4305	For non-multiplicity builds, these macros do nothing, so you always have
		4306	to initialise the loop somewhere.
3634		4307
3635	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4308	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
3636		4309
3637	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4310	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
3638	default loop has been initialised (C<UC> == unchecked). Their behaviour	4311	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
3783	supported). It will also not define any of the structs usually found in	4456	supported). It will also not define any of the structs usually found in
3784	F<event.h> that are not directly supported by the libev core alone.	4457	F<event.h> that are not directly supported by the libev core alone.
3785		4458
3786	In standalone mode, libev will still try to automatically deduce the	4459	In standalone mode, libev will still try to automatically deduce the
3787	configuration, but has to be more conservative.	4460	configuration, but has to be more conservative.
		4461
		4462	=item EV_USE_FLOOR
		4463
		4464	If defined to be C<1>, libev will use the C<floor ()> function for its
		4465	periodic reschedule calculations, otherwise libev will fall back on a
		4466	portable (slower) implementation. If you enable this, you usually have to
		4467	link against libm or something equivalent. Enabling this when the C<floor>
		4468	function is not available will fail, so the safe default is to not enable
		4469	this.
3788		4470
3789	=item EV_USE_MONOTONIC	4471	=item EV_USE_MONOTONIC
3790		4472
3791	If defined to be C<1>, libev will try to detect the availability of the	4473	If defined to be C<1>, libev will try to detect the availability of the
3792	monotonic clock option at both compile time and runtime. Otherwise no	4474	monotonic clock option at both compile time and runtime. Otherwise no
…		…
3877		4559
3878	If programs implement their own fd to handle mapping on win32, then this	4560	If programs implement their own fd to handle mapping on win32, then this
3879	macro can be used to override the C<close> function, useful to unregister	4561	macro can be used to override the C<close> function, useful to unregister
3880	file descriptors again. Note that the replacement function has to close	4562	file descriptors again. Note that the replacement function has to close
3881	the underlying OS handle.	4563	the underlying OS handle.
		4564
		4565	=item EV_USE_WSASOCKET
		4566
		4567	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4568	communication socket, which works better in some environments. Otherwise,
		4569	the normal C<socket> function will be used, which works better in other
		4570	environments.
3882		4571
3883	=item EV_USE_POLL	4572	=item EV_USE_POLL
3884		4573
3885	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4574	If defined to be C<1>, libev will compile in support for the C<poll>(2)
3886	backend. Otherwise it will be enabled on non-win32 platforms. It	4575	backend. Otherwise it will be enabled on non-win32 platforms. It
…		…
3922	If defined to be C<1>, libev will compile in support for the Linux inotify	4611	If defined to be C<1>, libev will compile in support for the Linux inotify
3923	interface to speed up C<ev_stat> watchers. Its actual availability will	4612	interface to speed up C<ev_stat> watchers. Its actual availability will
3924	be detected at runtime. If undefined, it will be enabled if the headers	4613	be detected at runtime. If undefined, it will be enabled if the headers
3925	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4614	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
3926		4615
		4616	=item EV_NO_SMP
		4617
		4618	If defined to be C<1>, libev will assume that memory is always coherent
		4619	between threads, that is, threads can be used, but threads never run on
		4620	different cpus (or different cpu cores). This reduces dependencies
		4621	and makes libev faster.
		4622
		4623	=item EV_NO_THREADS
		4624
		4625	If defined to be C<1>, libev will assume that it will never be called from
		4626	different threads (that includes signal handlers), which is a stronger
		4627	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4628	libev faster.
		4629
3927	=item EV_ATOMIC_T	4630	=item EV_ATOMIC_T
3928		4631
3929	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4632	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
3930	access is atomic with respect to other threads or signal contexts. No such	4633	access is atomic with respect to other threads or signal contexts. No
3931	type is easily found in the C language, so you can provide your own type	4634	such type is easily found in the C language, so you can provide your own
3932	that you know is safe for your purposes. It is used both for signal handler "locking"	4635	type that you know is safe for your purposes. It is used both for signal
3933	as well as for signal and thread safety in C<ev_async> watchers.	4636	handler "locking" as well as for signal and thread safety in C<ev_async>
		4637	watchers.
3934		4638
3935	In the absence of this define, libev will use C<sig_atomic_t volatile>	4639	In the absence of this define, libev will use C<sig_atomic_t volatile>
3936	(from F<signal.h>), which is usually good enough on most platforms.	4640	(from F<signal.h>), which is usually good enough on most platforms.
3937		4641
3938	=item EV_H (h)	4642	=item EV_H (h)
…		…
3965	will have the C<struct ev_loop *> as first argument, and you can create	4669	will have the C<struct ev_loop *> as first argument, and you can create
3966	additional independent event loops. Otherwise there will be no support	4670	additional independent event loops. Otherwise there will be no support
3967	for multiple event loops and there is no first event loop pointer	4671	for multiple event loops and there is no first event loop pointer
3968	argument. Instead, all functions act on the single default loop.	4672	argument. Instead, all functions act on the single default loop.
3969		4673
		4674	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4675	default loop when multiplicity is switched off - you always have to
		4676	initialise the loop manually in this case.
		4677
3970	=item EV_MINPRI	4678	=item EV_MINPRI
3971		4679
3972	=item EV_MAXPRI	4680	=item EV_MAXPRI
3973		4681
3974	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4682	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
4010	#define EV_USE_POLL 1	4718	#define EV_USE_POLL 1
4011	#define EV_CHILD_ENABLE 1	4719	#define EV_CHILD_ENABLE 1
4012	#define EV_ASYNC_ENABLE 1	4720	#define EV_ASYNC_ENABLE 1
4013		4721
4014	The actual value is a bitset, it can be a combination of the following	4722	The actual value is a bitset, it can be a combination of the following
4015	values:	4723	values (by default, all of these are enabled):
4016		4724
4017	=over 4	4725	=over 4
4018		4726
4019	=item C<1> - faster/larger code	4727	=item C<1> - faster/larger code
4020		4728
…		…
4024	code size by roughly 30% on amd64).	4732	code size by roughly 30% on amd64).
4025		4733
4026	When optimising for size, use of compiler flags such as C<-Os> with	4734	When optimising for size, use of compiler flags such as C<-Os> with
4027	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of	4735	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
4028	assertions.	4736	assertions.
		4737
		4738	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4739	(e.g. gcc with C<-Os>).
4029		4740
4030	=item C<2> - faster/larger data structures	4741	=item C<2> - faster/larger data structures
4031		4742
4032	Replaces the small 2-heap for timer management by a faster 4-heap, larger	4743	Replaces the small 2-heap for timer management by a faster 4-heap, larger
4033	hash table sizes and so on. This will usually further increase code size	4744	hash table sizes and so on. This will usually further increase code size
4034	and can additionally have an effect on the size of data structures at	4745	and can additionally have an effect on the size of data structures at
4035	runtime.	4746	runtime.
4036		4747
		4748	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4749	(e.g. gcc with C<-Os>).
		4750
4037	=item C<4> - full API configuration	4751	=item C<4> - full API configuration
4038		4752
4039	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and	4753	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
4040	enables multiplicity (C<EV_MULTIPLICITY>=1).	4754	enables multiplicity (C<EV_MULTIPLICITY>=1).
4041		4755
…		…
4071		4785
4072	With an intelligent-enough linker (gcc+binutils are intelligent enough	4786	With an intelligent-enough linker (gcc+binutils are intelligent enough
4073	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by	4787	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
4074	your program might be left out as well - a binary starting a timer and an	4788	your program might be left out as well - a binary starting a timer and an
4075	I/O watcher then might come out at only 5Kb.	4789	I/O watcher then might come out at only 5Kb.
		4790
		4791	=item EV_API_STATIC
		4792
		4793	If this symbol is defined (by default it is not), then all identifiers
		4794	will have static linkage. This means that libev will not export any
		4795	identifiers, and you cannot link against libev anymore. This can be useful
		4796	when you embed libev, only want to use libev functions in a single file,
		4797	and do not want its identifiers to be visible.
		4798
		4799	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4800	wants to use libev.
		4801
		4802	This option only works when libev is compiled with a C compiler, as C++
		4803	doesn't support the required declaration syntax.
4076		4804
4077	=item EV_AVOID_STDIO	4805	=item EV_AVOID_STDIO
4078		4806
4079	If this is set to C<1> at compiletime, then libev will avoid using stdio	4807	If this is set to C<1> at compiletime, then libev will avoid using stdio
4080	functions (printf, scanf, perror etc.). This will increase the code size	4808	functions (printf, scanf, perror etc.). This will increase the code size
…		…
4224	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4952	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4225		4953
4226	#include "ev_cpp.h"	4954	#include "ev_cpp.h"
4227	#include "ev.c"	4955	#include "ev.c"
4228		4956
4229	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	4957	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4230		4958
4231	=head2 THREADS AND COROUTINES	4959	=head2 THREADS AND COROUTINES
4232		4960
4233	=head3 THREADS	4961	=head3 THREADS
4234		4962
…		…
4285	default loop and triggering an C<ev_async> watcher from the default loop	5013	default loop and triggering an C<ev_async> watcher from the default loop
4286	watcher callback into the event loop interested in the signal.	5014	watcher callback into the event loop interested in the signal.
4287		5015
4288	=back	5016	=back
4289		5017
4290	=head4 THREAD LOCKING EXAMPLE	5018	See also L</THREAD LOCKING EXAMPLE>.
4291
4292	Here is a fictitious example of how to run an event loop in a different
4293	thread than where callbacks are being invoked and watchers are
4294	created/added/removed.
4295
4296	For a real-world example, see the C<EV::Loop::Async> perl module,
4297	which uses exactly this technique (which is suited for many high-level
4298	languages).
4299
4300	The example uses a pthread mutex to protect the loop data, a condition
4301	variable to wait for callback invocations, an async watcher to notify the
4302	event loop thread and an unspecified mechanism to wake up the main thread.
4303
4304	First, you need to associate some data with the event loop:
4305
4306	typedef struct {
4307	mutex_t lock; /* global loop lock */
4308	ev_async async_w;
4309	thread_t tid;
4310	cond_t invoke_cv;
4311	} userdata;
4312
4313	void prepare_loop (EV_P)
4314	{
4315	// for simplicity, we use a static userdata struct.
4316	static userdata u;
4317
4318	ev_async_init (&u->async_w, async_cb);
4319	ev_async_start (EV_A_ &u->async_w);
4320
4321	pthread_mutex_init (&u->lock, 0);
4322	pthread_cond_init (&u->invoke_cv, 0);
4323
4324	// now associate this with the loop
4325	ev_set_userdata (EV_A_ u);
4326	ev_set_invoke_pending_cb (EV_A_ l_invoke);
4327	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4328
4329	// then create the thread running ev_loop
4330	pthread_create (&u->tid, 0, l_run, EV_A);
4331	}
4332
4333	The callback for the C<ev_async> watcher does nothing: the watcher is used
4334	solely to wake up the event loop so it takes notice of any new watchers
4335	that might have been added:
4336
4337	static void
4338	async_cb (EV_P_ ev_async *w, int revents)
4339	{
4340	// just used for the side effects
4341	}
4342
4343	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
4344	protecting the loop data, respectively.
4345
4346	static void
4347	l_release (EV_P)
4348	{
4349	userdata *u = ev_userdata (EV_A);
4350	pthread_mutex_unlock (&u->lock);
4351	}
4352
4353	static void
4354	l_acquire (EV_P)
4355	{
4356	userdata *u = ev_userdata (EV_A);
4357	pthread_mutex_lock (&u->lock);
4358	}
4359
4360	The event loop thread first acquires the mutex, and then jumps straight
4361	into C<ev_run>:
4362
4363	void *
4364	l_run (void *thr_arg)
4365	{
4366	struct ev_loop *loop = (struct ev_loop *)thr_arg;
4367
4368	l_acquire (EV_A);
4369	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4370	ev_run (EV_A_ 0);
4371	l_release (EV_A);
4372
4373	return 0;
4374	}
4375
4376	Instead of invoking all pending watchers, the C<l_invoke> callback will
4377	signal the main thread via some unspecified mechanism (signals? pipe
4378	writes? C<Async::Interrupt>?) and then waits until all pending watchers
4379	have been called (in a while loop because a) spurious wakeups are possible
4380	and b) skipping inter-thread-communication when there are no pending
4381	watchers is very beneficial):
4382
4383	static void
4384	l_invoke (EV_P)
4385	{
4386	userdata *u = ev_userdata (EV_A);
4387
4388	while (ev_pending_count (EV_A))
4389	{
4390	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4391	pthread_cond_wait (&u->invoke_cv, &u->lock);
4392	}
4393	}
4394
4395	Now, whenever the main thread gets told to invoke pending watchers, it
4396	will grab the lock, call C<ev_invoke_pending> and then signal the loop
4397	thread to continue:
4398
4399	static void
4400	real_invoke_pending (EV_P)
4401	{
4402	userdata *u = ev_userdata (EV_A);
4403
4404	pthread_mutex_lock (&u->lock);
4405	ev_invoke_pending (EV_A);
4406	pthread_cond_signal (&u->invoke_cv);
4407	pthread_mutex_unlock (&u->lock);
4408	}
4409
4410	Whenever you want to start/stop a watcher or do other modifications to an
4411	event loop, you will now have to lock:
4412
4413	ev_timer timeout_watcher;
4414	userdata *u = ev_userdata (EV_A);
4415
4416	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4417
4418	pthread_mutex_lock (&u->lock);
4419	ev_timer_start (EV_A_ &timeout_watcher);
4420	ev_async_send (EV_A_ &u->async_w);
4421	pthread_mutex_unlock (&u->lock);
4422
4423	Note that sending the C<ev_async> watcher is required because otherwise
4424	an event loop currently blocking in the kernel will have no knowledge
4425	about the newly added timer. By waking up the loop it will pick up any new
4426	watchers in the next event loop iteration.
4427		5019
4428	=head3 COROUTINES	5020	=head3 COROUTINES
4429		5021
4430	Libev is very accommodating to coroutines ("cooperative threads"):	5022	Libev is very accommodating to coroutines ("cooperative threads"):
4431	libev fully supports nesting calls to its functions from different	5023	libev fully supports nesting calls to its functions from different
…		…
4527	=head3 C<kqueue> is buggy	5119	=head3 C<kqueue> is buggy
4528		5120
4529	The kqueue syscall is broken in all known versions - most versions support	5121	The kqueue syscall is broken in all known versions - most versions support
4530	only sockets, many support pipes.	5122	only sockets, many support pipes.
4531		5123
4532	Libev tries to work around this by not using C<kqueue> by default on	5124	Libev tries to work around this by not using C<kqueue> by default on this
4533	this rotten platform, but of course you can still ask for it when creating	5125	rotten platform, but of course you can still ask for it when creating a
4534	a loop.	5126	loop - embedding a socket-only kqueue loop into a select-based one is
		5127	probably going to work well.
4535		5128
4536	=head3 C<poll> is buggy	5129	=head3 C<poll> is buggy
4537		5130
4538	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>	5131	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
4539	implementation by something calling C<kqueue> internally around the 10.5.6	5132	implementation by something calling C<kqueue> internally around the 10.5.6
…		…
4558		5151
4559	=head3 C<errno> reentrancy	5152	=head3 C<errno> reentrancy
4560		5153
4561	The default compile environment on Solaris is unfortunately so	5154	The default compile environment on Solaris is unfortunately so
4562	thread-unsafe that you can't even use components/libraries compiled	5155	thread-unsafe that you can't even use components/libraries compiled
4563	without C<-D_REENTRANT> (as long as they use C<errno>), which, of course,	5156	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
4564	isn't defined by default.	5157	defined by default. A valid, if stupid, implementation choice.
4565		5158
4566	If you want to use libev in threaded environments you have to make sure	5159	If you want to use libev in threaded environments you have to make sure
4567	it's compiled with C<_REENTRANT> defined.	5160	it's compiled with C<_REENTRANT> defined.
4568		5161
4569	=head3 Event port backend	5162	=head3 Event port backend
4570		5163
4571	The scalable event interface for Solaris is called "event ports". Unfortunately,	5164	The scalable event interface for Solaris is called "event
4572	this mechanism is very buggy. If you run into high CPU usage, your program	5165	ports". Unfortunately, this mechanism is very buggy in all major
		5166	releases. If you run into high CPU usage, your program freezes or you get
4573	freezes or you get a large number of spurious wakeups, make sure you have	5167	a large number of spurious wakeups, make sure you have all the relevant
4574	all the relevant and latest kernel patches applied. No, I don't know which	5168	and latest kernel patches applied. No, I don't know which ones, but there
4575	ones, but there are multiple ones.	5169	are multiple ones to apply, and afterwards, event ports actually work
		5170	great.
4576		5171
4577	If you can't get it to work, you can try running the program by setting	5172	If you can't get it to work, you can try running the program by setting
4578	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and	5173	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
4579	C<select> backends.	5174	C<select> backends.
4580		5175
4581	=head2 AIX POLL BUG	5176	=head2 AIX POLL BUG
4582		5177
4583	AIX unfortunately has a broken C<poll.h> header. Libev works around	5178	AIX unfortunately has a broken C<poll.h> header. Libev works around
4584	this by trying to avoid the poll backend altogether (i.e. it's not even	5179	this by trying to avoid the poll backend altogether (i.e. it's not even
4585	compiled in), which normally isn't a big problem as C<select> works fine	5180	compiled in), which normally isn't a big problem as C<select> works fine
4586	with large bitsets, and AIX is dead anyway.	5181	with large bitsets on AIX, and AIX is dead anyway.
4587		5182
4588	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS	5183	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
4589		5184
4590	=head3 General issues	5185	=head3 General issues
4591		5186
…		…
4593	requires, and its I/O model is fundamentally incompatible with the POSIX	5188	requires, and its I/O model is fundamentally incompatible with the POSIX
4594	model. Libev still offers limited functionality on this platform in	5189	model. Libev still offers limited functionality on this platform in
4595	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5190	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
4596	descriptors. This only applies when using Win32 natively, not when using	5191	descriptors. This only applies when using Win32 natively, not when using
4597	e.g. cygwin. Actually, it only applies to the microsofts own compilers,	5192	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4598	as every compielr comes with a slightly differently broken/incompatible	5193	as every compiler comes with a slightly differently broken/incompatible
4599	environment.	5194	environment.
4600		5195
4601	Lifting these limitations would basically require the full	5196	Lifting these limitations would basically require the full
4602	re-implementation of the I/O system. If you are into this kind of thing,	5197	re-implementation of the I/O system. If you are into this kind of thing,
4603	then note that glib does exactly that for you in a very portable way (note	5198	then note that glib does exactly that for you in a very portable way (note
…		…
4697	structure (guaranteed by POSIX but not by ISO C for example), but it also	5292	structure (guaranteed by POSIX but not by ISO C for example), but it also
4698	assumes that the same (machine) code can be used to call any watcher	5293	assumes that the same (machine) code can be used to call any watcher
4699	callback: The watcher callbacks have different type signatures, but libev	5294	callback: The watcher callbacks have different type signatures, but libev
4700	calls them using an C<ev_watcher *> internally.	5295	calls them using an C<ev_watcher *> internally.
4701		5296
		5297	=item pointer accesses must be thread-atomic
		5298
		5299	Accessing a pointer value must be atomic, it must both be readable and
		5300	writable in one piece - this is the case on all current architectures.
		5301
4702	=item C<sig_atomic_t volatile> must be thread-atomic as well	5302	=item C<sig_atomic_t volatile> must be thread-atomic as well
4703		5303
4704	The type C<sig_atomic_t volatile> (or whatever is defined as	5304	The type C<sig_atomic_t volatile> (or whatever is defined as
4705	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different	5305	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
4706	threads. This is not part of the specification for C<sig_atomic_t>, but is	5306	threads. This is not part of the specification for C<sig_atomic_t>, but is
…		…
4714	thread" or will block signals process-wide, both behaviours would	5314	thread" or will block signals process-wide, both behaviours would
4715	be compatible with libev. Interaction between C<sigprocmask> and	5315	be compatible with libev. Interaction between C<sigprocmask> and
4716	C<pthread_sigmask> could complicate things, however.	5316	C<pthread_sigmask> could complicate things, however.
4717		5317
4718	The most portable way to handle signals is to block signals in all threads	5318	The most portable way to handle signals is to block signals in all threads
4719	except the initial one, and run the default loop in the initial thread as	5319	except the initial one, and run the signal handling loop in the initial
4720	well.	5320	thread as well.
4721		5321
4722	=item C<long> must be large enough for common memory allocation sizes	5322	=item C<long> must be large enough for common memory allocation sizes
4723		5323
4724	To improve portability and simplify its API, libev uses C<long> internally	5324	To improve portability and simplify its API, libev uses C<long> internally
4725	instead of C<size_t> when allocating its data structures. On non-POSIX	5325	instead of C<size_t> when allocating its data structures. On non-POSIX
…		…
4731		5331
4732	The type C<double> is used to represent timestamps. It is required to	5332	The type C<double> is used to represent timestamps. It is required to
4733	have at least 51 bits of mantissa (and 9 bits of exponent), which is	5333	have at least 51 bits of mantissa (and 9 bits of exponent), which is
4734	good enough for at least into the year 4000 with millisecond accuracy	5334	good enough for at least into the year 4000 with millisecond accuracy
4735	(the design goal for libev). This requirement is overfulfilled by	5335	(the design goal for libev). This requirement is overfulfilled by
4736	implementations using IEEE 754, which is basically all existing ones. With	5336	implementations using IEEE 754, which is basically all existing ones.
		5337
4737	IEEE 754 doubles, you get microsecond accuracy until at least 2200.	5338	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5339	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5340	is either obsolete or somebody patched it to use C<long double> or
		5341	something like that, just kidding).
4738		5342
4739	=back	5343	=back
4740		5344
4741	If you know of other additional requirements drop me a note.	5345	If you know of other additional requirements drop me a note.
4742		5346
…		…
4804	=item Processing ev_async_send: O(number_of_async_watchers)	5408	=item Processing ev_async_send: O(number_of_async_watchers)
4805		5409
4806	=item Processing signals: O(max_signal_number)	5410	=item Processing signals: O(max_signal_number)
4807		5411
4808	Sending involves a system call I<iff> there were no other C<ev_async_send>	5412	Sending involves a system call I<iff> there were no other C<ev_async_send>
4809	calls in the current loop iteration. Checking for async and signal events	5413	calls in the current loop iteration and the loop is currently
		5414	blocked. Checking for async and signal events involves iterating over all
4810	involves iterating over all running async watchers or all signal numbers.	5415	running async watchers or all signal numbers.
4811		5416
4812	=back	5417	=back
4813		5418
4814		5419
4815	=head1 PORTING FROM LIBEV 3.X TO 4.X	5420	=head1 PORTING FROM LIBEV 3.X TO 4.X
4816		5421
4817	The major version 4 introduced some minor incompatible changes to the API.	5422	The major version 4 introduced some incompatible changes to the API.
4818		5423
4819	At the moment, the C<ev.h> header file tries to implement superficial	5424	At the moment, the C<ev.h> header file provides compatibility definitions
4820	compatibility, so most programs should still compile. Those might be	5425	for all changes, so most programs should still compile. The compatibility
4821	removed in later versions of libev, so better update early than late.	5426	layer might be removed in later versions of libev, so better update to the
		5427	new API early than late.
4822		5428
4823	=over 4	5429	=over 4
		5430
		5431	=item C<EV_COMPAT3> backwards compatibility mechanism
		5432
		5433	The backward compatibility mechanism can be controlled by
		5434	C<EV_COMPAT3>. See L</PREPROCESSOR SYMBOLS/MACROS> in the L</EMBEDDING>
		5435	section.
		5436
		5437	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5438
		5439	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5440
		5441	ev_loop_destroy (EV_DEFAULT_UC);
		5442	ev_loop_fork (EV_DEFAULT);
4824		5443
4825	=item function/symbol renames	5444	=item function/symbol renames
4826		5445
4827	A number of functions and symbols have been renamed:	5446	A number of functions and symbols have been renamed:
4828		5447
…		…
4847	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme	5466	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
4848	as all other watcher types. Note that C<ev_loop_fork> is still called	5467	as all other watcher types. Note that C<ev_loop_fork> is still called
4849	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>	5468	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
4850	typedef.	5469	typedef.
4851		5470
4852	=item C<EV_COMPAT3> backwards compatibility mechanism
4853
4854	The backward compatibility mechanism can be controlled by
4855	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
4856	section.
4857
4858	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>	5471	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
4859		5472
4860	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different	5473	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
4861	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile	5474	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
4862	and work, but the library code will of course be larger.	5475	and work, but the library code will of course be larger.
…		…
4868		5481
4869	=over 4	5482	=over 4
4870		5483
4871	=item active	5484	=item active
4872		5485
4873	A watcher is active as long as it has been started (has been attached to	5486	A watcher is active as long as it has been started and not yet stopped.
4874	an event loop) but not yet stopped (disassociated from the event loop).	5487	See L</WATCHER STATES> for details.
4875		5488
4876	=item application	5489	=item application
4877		5490
4878	In this document, an application is whatever is using libev.	5491	In this document, an application is whatever is using libev.
		5492
		5493	=item backend
		5494
		5495	The part of the code dealing with the operating system interfaces.
4879		5496
4880	=item callback	5497	=item callback
4881		5498
4882	The address of a function that is called when some event has been	5499	The address of a function that is called when some event has been
4883	detected. Callbacks are being passed the event loop, the watcher that	5500	detected. Callbacks are being passed the event loop, the watcher that
4884	received the event, and the actual event bitset.	5501	received the event, and the actual event bitset.
4885		5502
4886	=item callback invocation	5503	=item callback/watcher invocation
4887		5504
4888	The act of calling the callback associated with a watcher.	5505	The act of calling the callback associated with a watcher.
4889		5506
4890	=item event	5507	=item event
4891		5508
…		…
4910	The model used to describe how an event loop handles and processes	5527	The model used to describe how an event loop handles and processes
4911	watchers and events.	5528	watchers and events.
4912		5529
4913	=item pending	5530	=item pending
4914		5531
4915	A watcher is pending as soon as the corresponding event has been detected,	5532	A watcher is pending as soon as the corresponding event has been
4916	and stops being pending as soon as the watcher will be invoked or its	5533	detected. See L</WATCHER STATES> for details.
4917	pending status is explicitly cleared by the application.
4918
4919	A watcher can be pending, but not active. Stopping a watcher also clears
4920	its pending status.
4921		5534
4922	=item real time	5535	=item real time
4923		5536
4924	The physical time that is observed. It is apparently strictly monotonic :)	5537	The physical time that is observed. It is apparently strictly monotonic :)
4925		5538
4926	=item wall-clock time	5539	=item wall-clock time
4927		5540
4928	The time and date as shown on clocks. Unlike real time, it can actually	5541	The time and date as shown on clocks. Unlike real time, it can actually
4929	be wrong and jump forwards and backwards, e.g. when the you adjust your	5542	be wrong and jump forwards and backwards, e.g. when you adjust your
4930	clock.	5543	clock.
4931		5544
4932	=item watcher	5545	=item watcher
4933		5546
4934	A data structure that describes interest in certain events. Watchers need	5547	A data structure that describes interest in certain events. Watchers need
4935	to be started (attached to an event loop) before they can receive events.	5548	to be started (attached to an event loop) before they can receive events.
4936		5549
4937	=item watcher invocation
4938
4939	The act of calling the callback associated with a watcher.
4940
4941	=back	5550	=back
4942		5551
4943	=head1 AUTHOR	5552	=head1 AUTHOR
4944		5553
4945	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.	5554	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5555	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
4946		5556

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