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		1	=encoding utf-8
		2
1	=head1 NAME	3	=head1 NAME
2		4
3	libev - a high performance full-featured event loop written in C	5	libev - a high performance full-featured event loop written in C
4		6
5	=head1 SYNOPSIS	7	=head1 SYNOPSIS
…		…
43		45
44	int	46	int
45	main (void)	47	main (void)
46	{	48	{
47	// use the default event loop unless you have special needs	49	// use the default event loop unless you have special needs
48	struct ev_loop *loop = ev_default_loop (0);	50	struct ev_loop *loop = EV_DEFAULT;
49		51
50	// initialise an io watcher, then start it	52	// initialise an io watcher, then start it
51	// this one will watch for stdin to become readable	53	// this one will watch for stdin to become readable
52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);	54	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
53	ev_io_start (loop, &stdin_watcher);	55	ev_io_start (loop, &stdin_watcher);
…		…
58	ev_timer_start (loop, &timeout_watcher);	60	ev_timer_start (loop, &timeout_watcher);
59		61
60	// now wait for events to arrive	62	// now wait for events to arrive
61	ev_run (loop, 0);	63	ev_run (loop, 0);
62		64
63	// unloop was called, so exit	65	// break was called, so exit
64	return 0;	66	return 0;
65	}	67	}
66		68
67	=head1 ABOUT THIS DOCUMENT	69	=head1 ABOUT THIS DOCUMENT
68		70
…		…
77	on event-based programming, nor will it introduce event-based programming	79	on event-based programming, nor will it introduce event-based programming
78	with libev.	80	with libev.
79		81
80	Familiarity with event based programming techniques in general is assumed	82	Familiarity with event based programming techniques in general is assumed
81	throughout this document.	83	throughout this document.
		84
		85	=head1 WHAT TO READ WHEN IN A HURRY
		86
		87	This manual tries to be very detailed, but unfortunately, this also makes
		88	it very long. If you just want to know the basics of libev, I suggest
		89	reading L</ANATOMY OF A WATCHER>, then the L</EXAMPLE PROGRAM> above and
		90	look up the missing functions in L</GLOBAL FUNCTIONS> and the C<ev_io> and
		91	C<ev_timer> sections in L</WATCHER TYPES>.
82		92
83	=head1 ABOUT LIBEV	93	=head1 ABOUT LIBEV
84		94
85	Libev is an event loop: you register interest in certain events (such as a	95	Libev is an event loop: you register interest in certain events (such as a
86	file descriptor being readable or a timeout occurring), and it will manage	96	file descriptor being readable or a timeout occurring), and it will manage
…		…
124	this argument.	134	this argument.
125		135
126	=head2 TIME REPRESENTATION	136	=head2 TIME REPRESENTATION
127		137
128	Libev represents time as a single floating point number, representing	138	Libev represents time as a single floating point number, representing
129	the (fractional) number of seconds since the (POSIX) epoch (in practise	139	the (fractional) number of seconds since the (POSIX) epoch (in practice
130	somewhere near the beginning of 1970, details are complicated, don't	140	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	141	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	142	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.	143	any calculations on it, you should treat it as some floating point value.
134		144
…		…
165		175
166	=item ev_tstamp ev_time ()	176	=item ev_tstamp ev_time ()
167		177
168	Returns the current time as libev would use it. Please note that the	178	Returns the current time as libev would use it. Please note that the
169	C<ev_now> function is usually faster and also often returns the timestamp	179	C<ev_now> function is usually faster and also often returns the timestamp
170	you actually want to know.	180	you actually want to know. Also interesting is the combination of
		181	C<ev_now_update> and C<ev_now>.
171		182
172	=item ev_sleep (ev_tstamp interval)	183	=item ev_sleep (ev_tstamp interval)
173		184
174	Sleep for the given interval: The current thread will be blocked until	185	Sleep for the given interval: The current thread will be blocked
175	either it is interrupted or the given time interval has passed. Basically	186	until either it is interrupted or the given time interval has
		187	passed (approximately - it might return a bit earlier even if not
		188	interrupted). Returns immediately if C<< interval <= 0 >>.
		189
176	this is a sub-second-resolution C<sleep ()>.	190	Basically this is a sub-second-resolution C<sleep ()>.
		191
		192	The range of the C<interval> is limited - libev only guarantees to work
		193	with sleep times of up to one day (C<< interval <= 86400 >>).
177		194
178	=item int ev_version_major ()	195	=item int ev_version_major ()
179		196
180	=item int ev_version_minor ()	197	=item int ev_version_minor ()
181		198
…		…
192	as this indicates an incompatible change. Minor versions are usually	209	as this indicates an incompatible change. Minor versions are usually
193	compatible to older versions, so a larger minor version alone is usually	210	compatible to older versions, so a larger minor version alone is usually
194	not a problem.	211	not a problem.
195		212
196	Example: Make sure we haven't accidentally been linked against the wrong	213	Example: Make sure we haven't accidentally been linked against the wrong
197	version (note, however, that this will not detect ABI mismatches :).	214	version (note, however, that this will not detect other ABI mismatches,
		215	such as LFS or reentrancy).
198		216
199	assert (("libev version mismatch",	217	assert (("libev version mismatch",
200	ev_version_major () == EV_VERSION_MAJOR	218	ev_version_major () == EV_VERSION_MAJOR
201	&& ev_version_minor () >= EV_VERSION_MINOR));	219	&& ev_version_minor () >= EV_VERSION_MINOR));
202		220
…		…
213	assert (("sorry, no epoll, no sex",	231	assert (("sorry, no epoll, no sex",
214	ev_supported_backends () & EVBACKEND_EPOLL));	232	ev_supported_backends () & EVBACKEND_EPOLL));
215		233
216	=item unsigned int ev_recommended_backends ()	234	=item unsigned int ev_recommended_backends ()
217		235
218	Return the set of all backends compiled into this binary of libev and also	236	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	237	also recommended for this platform, meaning it will work for most file
		238	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	239	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	240	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	241	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.	242	probe for if you specify no backends explicitly.
224		243
225	=item unsigned int ev_embeddable_backends ()	244	=item unsigned int ev_embeddable_backends ()
226		245
227	Returns the set of backends that are embeddable in other event loops. This	246	Returns the set of backends that are embeddable in other event loops. This
228	is the theoretical, all-platform, value. To find which backends	247	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	248	current system. To find which embeddable backends might be supported on
230	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	249	the current system, you would need to look at C<ev_embeddable_backends ()
231	recommended ones.	250	& ev_supported_backends ()>, likewise for recommended ones.
232		251
233	See the description of C<ev_embed> watchers for more info.	252	See the description of C<ev_embed> watchers for more info.
234		253
235	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]	254	=item ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())
236		255
237	Sets the allocation function to use (the prototype is similar - the	256	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	257	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	258	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	259	when memory needs to be allocated (C<size != 0>), the library might abort
…		…
266	}	285	}
267		286
268	...	287	...
269	ev_set_allocator (persistent_realloc);	288	ev_set_allocator (persistent_realloc);
270		289
271	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]	290	=item ev_set_syserr_cb (void (*cb)(const char *msg) throw ())
272		291
273	Set the callback function to call on a retryable system call error (such	292	Set the callback function to call on a retryable system call error (such
274	as failed select, poll, epoll_wait). The message is a printable string	293	as failed select, poll, epoll_wait). The message is a printable string
275	indicating the system call or subsystem causing the problem. If this	294	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	295	callback is set, then libev will expect it to remedy the situation, no
…		…
288	}	307	}
289		308
290	...	309	...
291	ev_set_syserr_cb (fatal_error);	310	ev_set_syserr_cb (fatal_error);
292		311
		312	=item ev_feed_signal (int signum)
		313
		314	This function can be used to "simulate" a signal receive. It is completely
		315	safe to call this function at any time, from any context, including signal
		316	handlers or random threads.
		317
		318	Its main use is to customise signal handling in your process, especially
		319	in the presence of threads. For example, you could block signals
		320	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
		321	creating any loops), and in one thread, use C<sigwait> or any other
		322	mechanism to wait for signals, then "deliver" them to libev by calling
		323	C<ev_feed_signal>.
		324
293	=back	325	=back
294		326
295	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	327	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
296		328
297	An event loop is described by a C<struct ev_loop *> (the C<struct> is	329	An event loop is described by a C<struct ev_loop *> (the C<struct> is
298	I<not> optional in case unless libev 3 compatibility is disabled, as libev	330	I<not> optional in this case unless libev 3 compatibility is disabled, as
299	3 had an C<ev_loop> function colliding with the struct name).	331	libev 3 had an C<ev_loop> function colliding with the struct name).
300		332
301	The library knows two types of such loops, the I<default> loop, which	333	The library knows two types of such loops, the I<default> loop, which
302	supports signals and child events, and dynamically created event loops	334	supports child process events, and dynamically created event loops which
303	which do not.	335	do not.
304		336
305	=over 4	337	=over 4
306		338
307	=item struct ev_loop *ev_default_loop (unsigned int flags)	339	=item struct ev_loop *ev_default_loop (unsigned int flags)
308		340
309	This will initialise the default event loop if it hasn't been initialised	341	This returns the "default" event loop object, which is what you should
310	yet and return it. If the default loop could not be initialised, returns	342	normally use when you just need "the event loop". Event loop objects and
311	false. If it already was initialised it simply returns it (and ignores the	343	the C<flags> parameter are described in more detail in the entry for
312	flags. If that is troubling you, check C<ev_backend ()> afterwards).	344	C<ev_loop_new>.
		345
		346	If the default loop is already initialised then this function simply
		347	returns it (and ignores the flags. If that is troubling you, check
		348	C<ev_backend ()> afterwards). Otherwise it will create it with the given
		349	flags, which should almost always be C<0>, unless the caller is also the
		350	one calling C<ev_run> or otherwise qualifies as "the main program".
313		351
314	If you don't know what event loop to use, use the one returned from this	352	If you don't know what event loop to use, use the one returned from this
315	function.	353	function (or via the C<EV_DEFAULT> macro).
316		354
317	Note that this function is I<not> thread-safe, so if you want to use it	355	Note that this function is I<not> thread-safe, so if you want to use it
318	from multiple threads, you have to lock (note also that this is unlikely,	356	from multiple threads, you have to employ some kind of mutex (note also
319	as loops cannot be shared easily between threads anyway).	357	that this case is unlikely, as loops cannot be shared easily between
		358	threads anyway).
320		359
321	The default loop is the only loop that can handle C<ev_signal> and	360	The default loop is the only loop that can handle C<ev_child> watchers,
322	C<ev_child> watchers, and to do this, it always registers a handler	361	and to do this, it always registers a handler for C<SIGCHLD>. If this is
323	for C<SIGCHLD>. If this is a problem for your application you can either	362	a problem for your application you can either create a dynamic loop with
324	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you	363	C<ev_loop_new> which doesn't do that, or you can simply overwrite the
325	can simply overwrite the C<SIGCHLD> signal handler I<after> calling	364	C<SIGCHLD> signal handler I<after> calling C<ev_default_init>.
326	C<ev_default_init>.	365
		366	Example: This is the most typical usage.
		367
		368	if (!ev_default_loop (0))
		369	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		370
		371	Example: Restrict libev to the select and poll backends, and do not allow
		372	environment settings to be taken into account:
		373
		374	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
		375
		376	=item struct ev_loop *ev_loop_new (unsigned int flags)
		377
		378	This will create and initialise a new event loop object. If the loop
		379	could not be initialised, returns false.
		380
		381	This function is thread-safe, and one common way to use libev with
		382	threads is indeed to create one loop per thread, and using the default
		383	loop in the "main" or "initial" thread.
327		384
328	The flags argument can be used to specify special behaviour or specific	385	The flags argument can be used to specify special behaviour or specific
329	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	386	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
330		387
331	The following flags are supported:	388	The following flags are supported:
…		…
341		398
342	If this flag bit is or'ed into the flag value (or the program runs setuid	399	If this flag bit is or'ed into the flag value (or the program runs setuid
343	or setgid) then libev will I<not> look at the environment variable	400	or setgid) then libev will I<not> look at the environment variable
344	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	401	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
345	override the flags completely if it is found in the environment. This is	402	override the flags completely if it is found in the environment. This is
346	useful to try out specific backends to test their performance, or to work	403	useful to try out specific backends to test their performance, to work
347	around bugs.	404	around bugs, or to make libev threadsafe (accessing environment variables
		405	cannot be done in a threadsafe way, but usually it works if no other
		406	thread modifies them).
348		407
349	=item C<EVFLAG_FORKCHECK>	408	=item C<EVFLAG_FORKCHECK>
350		409
351	Instead of calling C<ev_loop_fork> manually after a fork, you can also	410	Instead of calling C<ev_loop_fork> manually after a fork, you can also
352	make libev check for a fork in each iteration by enabling this flag.	411	make libev check for a fork in each iteration by enabling this flag.
…		…
366	environment variable.	425	environment variable.
367		426
368	=item C<EVFLAG_NOINOTIFY>	427	=item C<EVFLAG_NOINOTIFY>
369		428
370	When this flag is specified, then libev will not attempt to use the	429	When this flag is specified, then libev will not attempt to use the
371	I<inotify> API for it's C<ev_stat> watchers. Apart from debugging and	430	I<inotify> API for its C<ev_stat> watchers. Apart from debugging and
372	testing, this flag can be useful to conserve inotify file descriptors, as	431	testing, this flag can be useful to conserve inotify file descriptors, as
373	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.	432	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
374		433
375	=item C<EVFLAG_SIGNALFD>	434	=item C<EVFLAG_SIGNALFD>
376		435
377	When this flag is specified, then libev will attempt to use the	436	When this flag is specified, then libev will attempt to use the
378	I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This API	437	I<signalfd> API for its C<ev_signal> (and C<ev_child>) watchers. This API
379	delivers signals synchronously, which makes it both faster and might make	438	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	439	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	440	handling with threads, as long as you properly block signals in your
382	threads that are not interested in handling them.	441	threads that are not interested in handling them.
383		442
384	Signalfd will not be used by default as this changes your signal mask, and	443	Signalfd will not be used by default as this changes your signal mask, and
385	there are a lot of shoddy libraries and programs (glib's threadpool for	444	there are a lot of shoddy libraries and programs (glib's threadpool for
386	example) that can't properly initialise their signal masks.	445	example) that can't properly initialise their signal masks.
		446
		447	=item C<EVFLAG_NOSIGMASK>
		448
		449	When this flag is specified, then libev will avoid to modify the signal
		450	mask. Specifically, this means you have to make sure signals are unblocked
		451	when you want to receive them.
		452
		453	This behaviour is useful when you want to do your own signal handling, or
		454	want to handle signals only in specific threads and want to avoid libev
		455	unblocking the signals.
		456
		457	It's also required by POSIX in a threaded program, as libev calls
		458	C<sigprocmask>, whose behaviour is officially unspecified.
		459
		460	This flag's behaviour will become the default in future versions of libev.
387		461
388	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	462	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
389		463
390	This is your standard select(2) backend. Not I<completely> standard, as	464	This is your standard select(2) backend. Not I<completely> standard, as
391	libev tries to roll its own fd_set with no limits on the number of fds,	465	libev tries to roll its own fd_set with no limits on the number of fds,
…		…
419	=item C<EVBACKEND_EPOLL> (value 4, Linux)	493	=item C<EVBACKEND_EPOLL> (value 4, Linux)
420		494
421	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9	495	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
422	kernels).	496	kernels).
423		497
424	For few fds, this backend is a bit little slower than poll and select,	498	For few fds, this backend is a bit little slower than poll and select, but
425	but it scales phenomenally better. While poll and select usually scale	499	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),	500	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).	501	fd), epoll scales either O(1) or O(active_fds).
428		502
429	The epoll mechanism deserves honorable mention as the most misdesigned	503	The epoll mechanism deserves honorable mention as the most misdesigned
430	of the more advanced event mechanisms: mere annoyances include silently	504	of the more advanced event mechanisms: mere annoyances include silently
431	dropping file descriptors, requiring a system call per change per file	505	dropping file descriptors, requiring a system call per change per file
432	descriptor (and unnecessary guessing of parameters), problems with dup and	506	descriptor (and unnecessary guessing of parameters), problems with dup,
		507	returning before the timeout value, resulting in additional iterations
		508	(and only giving 5ms accuracy while select on the same platform gives
433	so on. The biggest issue is fork races, however - if a program forks then	509	0.1ms) and so on. The biggest issue is fork races, however - if a program
434	I<both> parent and child process have to recreate the epoll set, which can	510	forks then I<both> parent and child process have to recreate the epoll
435	take considerable time (one syscall per file descriptor) and is of course	511	set, which can take considerable time (one syscall per file descriptor)
436	hard to detect.	512	and is of course hard to detect.
437		513
438	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but	514	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	515	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	516	totally I<different> file descriptors (even already closed ones, so
441	even remove them from the set) than registered in the set (especially	517	one cannot even remove them from the set) than registered in the set
442	on SMP systems). Libev tries to counter these spurious notifications by	518	(especially on SMP systems). Libev tries to counter these spurious
443	employing an additional generation counter and comparing that against the	519	notifications by employing an additional generation counter and comparing
444	events to filter out spurious ones, recreating the set when required. Last	520	that against the events to filter out spurious ones, recreating the set
		521	when required. Epoll also erroneously rounds down timeouts, but gives you
		522	no way to know when and by how much, so sometimes you have to busy-wait
		523	because epoll returns immediately despite a nonzero timeout. And last
445	not least, it also refuses to work with some file descriptors which work	524	not least, it also refuses to work with some file descriptors which work
446	perfectly fine with C<select> (files, many character devices...).	525	perfectly fine with C<select> (files, many character devices...).
		526
		527	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
		528	cobbled together in a hurry, no thought to design or interaction with
		529	others. Oh, the pain, will it ever stop...
447		530
448	While stopping, setting and starting an I/O watcher in the same iteration	531	While stopping, setting and starting an I/O watcher in the same iteration
449	will result in some caching, there is still a system call per such	532	will result in some caching, there is still a system call per such
450	incident (because the same I<file descriptor> could point to a different	533	incident (because the same I<file descriptor> could point to a different
451	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed	534	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
…		…
488		571
489	It scales in the same way as the epoll backend, but the interface to the	572	It scales in the same way as the epoll backend, but the interface to the
490	kernel is more efficient (which says nothing about its actual speed, of	573	kernel is more efficient (which says nothing about its actual speed, of
491	course). While stopping, setting and starting an I/O watcher does never	574	course). While stopping, setting and starting an I/O watcher does never
492	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to	575	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
493	two event changes per incident. Support for C<fork ()> is very bad (but	576	two event changes per incident. Support for C<fork ()> is very bad (you
494	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect	577	might have to leak fd's on fork, but it's more sane than epoll) and it
495	cases	578	drops fds silently in similarly hard-to-detect cases.
496		579
497	This backend usually performs well under most conditions.	580	This backend usually performs well under most conditions.
498		581
499	While nominally embeddable in other event loops, this doesn't work	582	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	583	everywhere, so you might need to test for this. And since it is broken
…		…
517	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	600	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
518		601
519	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	602	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
520	it's really slow, but it still scales very well (O(active_fds)).	603	it's really slow, but it still scales very well (O(active_fds)).
521		604
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	605	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	606	file descriptor per loop iteration. For small and medium numbers of file
528	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	607	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
529	might perform better.	608	might perform better.
530		609
531	On the positive side, with the exception of the spurious readiness	610	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	611	specification in all tests and is fully embeddable, which is a rare feat
534	OS-specific backends (I vastly prefer correctness over speed hacks).	612	among the OS-specific backends (I vastly prefer correctness over speed
		613	hacks).
		614
		615	On the negative side, the interface is I<bizarre> - so bizarre that
		616	even sun itself gets it wrong in their code examples: The event polling
		617	function sometimes returns events to the caller even though an error
		618	occurred, but with no indication whether it has done so or not (yes, it's
		619	even documented that way) - deadly for edge-triggered interfaces where you
		620	absolutely have to know whether an event occurred or not because you have
		621	to re-arm the watcher.
		622
		623	Fortunately libev seems to be able to work around these idiocies.
535		624
536	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	625	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
537	C<EVBACKEND_POLL>.	626	C<EVBACKEND_POLL>.
538		627
539	=item C<EVBACKEND_ALL>	628	=item C<EVBACKEND_ALL>
540		629
541	Try all backends (even potentially broken ones that wouldn't be tried	630	Try all backends (even potentially broken ones that wouldn't be tried
542	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	631	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
543	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	632	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
544		633
545	It is definitely not recommended to use this flag.	634	It is definitely not recommended to use this flag, use whatever
		635	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		636	at all.
		637
		638	=item C<EVBACKEND_MASK>
		639
		640	Not a backend at all, but a mask to select all backend bits from a
		641	C<flags> value, in case you want to mask out any backends from a flags
		642	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
546		643
547	=back	644	=back
548		645
549	If one or more of the backend flags are or'ed into the flags value,	646	If one or more of the backend flags are or'ed into the flags value,
550	then only these backends will be tried (in the reverse order as listed	647	then only these backends will be tried (in the reverse order as listed
551	here). If none are specified, all backends in C<ev_recommended_backends	648	here). If none are specified, all backends in C<ev_recommended_backends
552	()> will be tried.	649	()> will be tried.
553		650
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.	651	Example: Try to create a event loop that uses epoll and nothing else.
581		652
582	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	653	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
583	if (!epoller)	654	if (!epoller)
584	fatal ("no epoll found here, maybe it hides under your chair");	655	fatal ("no epoll found here, maybe it hides under your chair");
585		656
		657	Example: Use whatever libev has to offer, but make sure that kqueue is
		658	used if available.
		659
		660	struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
		661
586	=item ev_default_destroy ()	662	=item ev_loop_destroy (loop)
587		663
588	Destroys the default loop (frees all memory and kernel state etc.). None	664	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	665	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	666	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,	667	responsibility to either stop all watchers cleanly yourself I<before>
592	or cope with the fact afterwards (which is usually the easiest thing, you	668	calling this function, or cope with the fact afterwards (which is usually
593	can just ignore the watchers and/or C<free ()> them for example).	669	the easiest thing, you can just ignore the watchers and/or C<free ()> them
		670	for example).
594		671
595	Note that certain global state, such as signal state (and installed signal	672	Note that certain global state, such as signal state (and installed signal
596	handlers), will not be freed by this function, and related watchers (such	673	handlers), will not be freed by this function, and related watchers (such
597	as signal and child watchers) would need to be stopped manually.	674	as signal and child watchers) would need to be stopped manually.
598		675
599	In general it is not advisable to call this function except in the	676	This function is normally used on loop objects allocated by
600	rare occasion where you really need to free e.g. the signal handling	677	C<ev_loop_new>, but it can also be used on the default loop returned by
		678	C<ev_default_loop>, in which case it is not thread-safe.
		679
		680	Note that it is not advisable to call this function on the default loop
		681	except in the rare occasion where you really need to free its resources.
601	pipe fds. If you need dynamically allocated loops it is better to use	682	If you need dynamically allocated loops it is better to use C<ev_loop_new>
602	C<ev_loop_new> and C<ev_loop_destroy>.	683	and C<ev_loop_destroy>.
603		684
604	=item ev_loop_destroy (loop)	685	=item ev_loop_fork (loop)
605
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		686
611	This function sets a flag that causes subsequent C<ev_run> iterations	687	This function sets a flag that causes subsequent C<ev_run> iterations
612	to reinitialise the kernel state for backends that have one. Despite the	688	to reinitialise the kernel state for backends that have one. Despite
613	name, you can call it anytime, but it makes most sense after forking, in	689	the name, you can call it anytime you are allowed to start or stop
614	the child process (or both child and parent, but that again makes little	690	watchers (except inside an C<ev_prepare> callback), but it makes most
615	sense). You I<must> call it in the child before using any of the libev	691	sense after forking, in the child process. You I<must> call it (or use
616	functions, and it will only take effect at the next C<ev_run> iteration.	692	C<EVFLAG_FORKCHECK>) in the child before resuming or calling C<ev_run>.
617		693
618	Again, you I<have> to call it on I<any> loop that you want to re-use after	694	Again, you I<have> to call it on I<any> loop that you want to re-use after
619	a fork, I<even if you do not plan to use the loop in the parent>. This is	695	a fork, I<even if you do not plan to use the loop in the parent>. This is
620	because some kernel interfaces *cough* I<kqueue> *cough* do funny things	696	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
621	during fork.	697	during fork.
622		698
623	On the other hand, you only need to call this function in the child	699	On the other hand, you only need to call this function in the child
…		…
626	call it at all (in fact, C<epoll> is so badly broken that it makes a	702	call it at all (in fact, C<epoll> is so badly broken that it makes a
627	difference, but libev will usually detect this case on its own and do a	703	difference, but libev will usually detect this case on its own and do a
628	costly reset of the backend).	704	costly reset of the backend).
629		705
630	The function itself is quite fast and it's usually not a problem to call	706	The function itself is quite fast and it's usually not a problem to call
631	it just in case after a fork. To make this easy, the function will fit in	707	it just in case after a fork.
632	quite nicely into a call to C<pthread_atfork>:
633		708
		709	Example: Automate calling C<ev_loop_fork> on the default loop when
		710	using pthreads.
		711
		712	static void
		713	post_fork_child (void)
		714	{
		715	ev_loop_fork (EV_DEFAULT);
		716	}
		717
		718	...
634	pthread_atfork (0, 0, ev_default_fork);	719	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		720
643	=item int ev_is_default_loop (loop)	721	=item int ev_is_default_loop (loop)
644		722
645	Returns true when the given loop is, in fact, the default loop, and false	723	Returns true when the given loop is, in fact, the default loop, and false
646	otherwise.	724	otherwise.
…		…
657	prepare and check phases.	735	prepare and check phases.
658		736
659	=item unsigned int ev_depth (loop)	737	=item unsigned int ev_depth (loop)
660		738
661	Returns the number of times C<ev_run> was entered minus the number of	739	Returns the number of times C<ev_run> was entered minus the number of
662	times C<ev_run> was exited, in other words, the recursion depth.	740	times C<ev_run> was exited normally, in other words, the recursion depth.
663		741
664	Outside C<ev_run>, this number is zero. In a callback, this number is	742	Outside C<ev_run>, this number is zero. In a callback, this number is
665	C<1>, unless C<ev_run> was invoked recursively (or from another thread),	743	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
666	in which case it is higher.	744	in which case it is higher.
667		745
668	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread	746	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	747	throwing an exception etc.), doesn't count as "exit" - consider this
670	ungentleman-like behaviour unless it's really convenient.	748	as a hint to avoid such ungentleman-like behaviour unless it's really
		749	convenient, in which case it is fully supported.
671		750
672	=item unsigned int ev_backend (loop)	751	=item unsigned int ev_backend (loop)
673		752
674	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	753	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
675	use.	754	use.
…		…
690		769
691	This function is rarely useful, but when some event callback runs for a	770	This function is rarely useful, but when some event callback runs for a
692	very long time without entering the event loop, updating libev's idea of	771	very long time without entering the event loop, updating libev's idea of
693	the current time is a good idea.	772	the current time is a good idea.
694		773
695	See also L<The special problem of time updates> in the C<ev_timer> section.	774	See also L</The special problem of time updates> in the C<ev_timer> section.
696		775
697	=item ev_suspend (loop)	776	=item ev_suspend (loop)
698		777
699	=item ev_resume (loop)	778	=item ev_resume (loop)
700		779
…		…
718	without a previous call to C<ev_suspend>.	797	without a previous call to C<ev_suspend>.
719		798
720	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the	799	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
721	event loop time (see C<ev_now_update>).	800	event loop time (see C<ev_now_update>).
722		801
723	=item ev_run (loop, int flags)	802	=item bool ev_run (loop, int flags)
724		803
725	Finally, this is it, the event handler. This function usually is called	804	Finally, this is it, the event handler. This function usually is called
726	after you have initialised all your watchers and you want to start	805	after you have initialised all your watchers and you want to start
727	handling events. It will ask the operating system for any new events, call	806	handling events. It will ask the operating system for any new events, call
728	the watcher callbacks, an then repeat the whole process indefinitely: This	807	the watcher callbacks, and then repeat the whole process indefinitely: This
729	is why event loops are called I<loops>.	808	is why event loops are called I<loops>.
730		809
731	If the flags argument is specified as C<0>, it will keep handling events	810	If the flags argument is specified as C<0>, it will keep handling events
732	until either no event watchers are active anymore or C<ev_break> was	811	until either no event watchers are active anymore or C<ev_break> was
733	called.	812	called.
		813
		814	The return value is false if there are no more active watchers (which
		815	usually means "all jobs done" or "deadlock"), and true in all other cases
		816	(which usually means " you should call C<ev_run> again").
734		817
735	Please note that an explicit C<ev_break> is usually better than	818	Please note that an explicit C<ev_break> is usually better than
736	relying on all watchers to be stopped when deciding when a program has	819	relying on all watchers to be stopped when deciding when a program has
737	finished (especially in interactive programs), but having a program	820	finished (especially in interactive programs), but having a program
738	that automatically loops as long as it has to and no longer by virtue	821	that automatically loops as long as it has to and no longer by virtue
739	of relying on its watchers stopping correctly, that is truly a thing of	822	of relying on its watchers stopping correctly, that is truly a thing of
740	beauty.	823	beauty.
741		824
		825	This function is I<mostly> exception-safe - you can break out of a
		826	C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		827	exception and so on. This does not decrement the C<ev_depth> value, nor
		828	will it clear any outstanding C<EVBREAK_ONE> breaks.
		829
742	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle	830	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle
743	those events and any already outstanding ones, but will not wait and	831	those events and any already outstanding ones, but will not wait and
744	block your process in case there are no events and will return after one	832	block your process in case there are no events and will return after one
745	iteration of the loop. This is sometimes useful to poll and handle new	833	iteration of the loop. This is sometimes useful to poll and handle new
746	events while doing lengthy calculations, to keep the program responsive.	834	events while doing lengthy calculations, to keep the program responsive.
…		…
755	This is useful if you are waiting for some external event in conjunction	843	This is useful if you are waiting for some external event in conjunction
756	with something not expressible using other libev watchers (i.e. "roll your	844	with something not expressible using other libev watchers (i.e. "roll your
757	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is	845	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
758	usually a better approach for this kind of thing.	846	usually a better approach for this kind of thing.
759		847
760	Here are the gory details of what C<ev_run> does:	848	Here are the gory details of what C<ev_run> does (this is for your
		849	understanding, not a guarantee that things will work exactly like this in
		850	future versions):
761		851
762	- Increment loop depth.	852	- Increment loop depth.
763	- Reset the ev_break status.	853	- Reset the ev_break status.
764	- Before the first iteration, call any pending watchers.	854	- Before the first iteration, call any pending watchers.
765	LOOP:	855	LOOP:
…		…
798	anymore.	888	anymore.
799		889
800	... queue jobs here, make sure they register event watchers as long	890	... 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..)	891	... as they still have work to do (even an idle watcher will do..)
802	ev_run (my_loop, 0);	892	ev_run (my_loop, 0);
803	... jobs done or somebody called unloop. yeah!	893	... jobs done or somebody called break. yeah!
804		894
805	=item ev_break (loop, how)	895	=item ev_break (loop, how)
806		896
807	Can be used to make a call to C<ev_run> return early (but only after it	897	Can be used to make a call to C<ev_run> return early (but only after it
808	has processed all outstanding events). The C<how> argument must be either	898	has processed all outstanding events). The C<how> argument must be either
809	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or	899	C<EVBREAK_ONE>, which will make the innermost C<ev_run> call return, or
810	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.	900	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
811		901
812	This "unloop state" will be cleared when entering C<ev_run> again.	902	This "break state" will be cleared on the next call to C<ev_run>.
813		903
814	It is safe to call C<ev_break> from outside any C<ev_run> calls. ##TODO##	904	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		905	which case it will have no effect.
815		906
816	=item ev_ref (loop)	907	=item ev_ref (loop)
817		908
818	=item ev_unref (loop)	909	=item ev_unref (loop)
819		910
…		…
840	running when nothing else is active.	931	running when nothing else is active.
841		932
842	ev_signal exitsig;	933	ev_signal exitsig;
843	ev_signal_init (&exitsig, sig_cb, SIGINT);	934	ev_signal_init (&exitsig, sig_cb, SIGINT);
844	ev_signal_start (loop, &exitsig);	935	ev_signal_start (loop, &exitsig);
845	evf_unref (loop);	936	ev_unref (loop);
846		937
847	Example: For some weird reason, unregister the above signal handler again.	938	Example: For some weird reason, unregister the above signal handler again.
848		939
849	ev_ref (loop);	940	ev_ref (loop);
850	ev_signal_stop (loop, &exitsig);	941	ev_signal_stop (loop, &exitsig);
…		…
870	overhead for the actual polling but can deliver many events at once.	961	overhead for the actual polling but can deliver many events at once.
871		962
872	By setting a higher I<io collect interval> you allow libev to spend more	963	By setting a higher I<io collect interval> you allow libev to spend more
873	time collecting I/O events, so you can handle more events per iteration,	964	time collecting I/O events, so you can handle more events per iteration,
874	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	965	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
875	C<ev_timer>) will be not affected. Setting this to a non-null value will	966	C<ev_timer>) will not be affected. Setting this to a non-null value will
876	introduce an additional C<ev_sleep ()> call into most loop iterations. The	967	introduce an additional C<ev_sleep ()> call into most loop iterations. The
877	sleep time ensures that libev will not poll for I/O events more often then	968	sleep time ensures that libev will not poll for I/O events more often then
878	once per this interval, on average.	969	once per this interval, on average (as long as the host time resolution is
		970	good enough).
879		971
880	Likewise, by setting a higher I<timeout collect interval> you allow libev	972	Likewise, by setting a higher I<timeout collect interval> you allow libev
881	to spend more time collecting timeouts, at the expense of increased	973	to spend more time collecting timeouts, at the expense of increased
882	latency/jitter/inexactness (the watcher callback will be called	974	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	975	later). C<ev_io> watchers will not be affected. Setting this to a non-null
…		…
908		1000
909	=item ev_invoke_pending (loop)	1001	=item ev_invoke_pending (loop)
910		1002
911	This call will simply invoke all pending watchers while resetting their	1003	This call will simply invoke all pending watchers while resetting their
912	pending state. Normally, C<ev_run> does this automatically when required,	1004	pending state. Normally, C<ev_run> does this automatically when required,
913	but when overriding the invoke callback this call comes handy.	1005	but when overriding the invoke callback this call comes handy. This
		1006	function can be invoked from a watcher - this can be useful for example
		1007	when you want to do some lengthy calculation and want to pass further
		1008	event handling to another thread (you still have to make sure only one
		1009	thread executes within C<ev_invoke_pending> or C<ev_run> of course).
914		1010
915	=item int ev_pending_count (loop)	1011	=item int ev_pending_count (loop)
916		1012
917	Returns the number of pending watchers - zero indicates that no watchers	1013	Returns the number of pending watchers - zero indicates that no watchers
918	are pending.	1014	are pending.
…		…
925	invoke the actual watchers inside another context (another thread etc.).	1021	invoke the actual watchers inside another context (another thread etc.).
926		1022
927	If you want to reset the callback, use C<ev_invoke_pending> as new	1023	If you want to reset the callback, use C<ev_invoke_pending> as new
928	callback.	1024	callback.
929		1025
930	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))	1026	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
931		1027
932	Sometimes you want to share the same loop between multiple threads. This	1028	Sometimes you want to share the same loop between multiple threads. This
933	can be done relatively simply by putting mutex_lock/unlock calls around	1029	can be done relatively simply by putting mutex_lock/unlock calls around
934	each call to a libev function.	1030	each call to a libev function.
935		1031
936	However, C<ev_run> can run an indefinite time, so it is not feasible	1032	However, C<ev_run> can run an indefinite time, so it is not feasible
937	to wait for it to return. One way around this is to wake up the event	1033	to wait for it to return. One way around this is to wake up the event
938	loop via C<ev_break> and C<av_async_send>, another way is to set these	1034	loop via C<ev_break> and C<ev_async_send>, another way is to set these
939	I<release> and I<acquire> callbacks on the loop.	1035	I<release> and I<acquire> callbacks on the loop.
940		1036
941	When set, then C<release> will be called just before the thread is	1037	When set, then C<release> will be called just before the thread is
942	suspended waiting for new events, and C<acquire> is called just	1038	suspended waiting for new events, and C<acquire> is called just
943	afterwards.	1039	afterwards.
…		…
958	See also the locking example in the C<THREADS> section later in this	1054	See also the locking example in the C<THREADS> section later in this
959	document.	1055	document.
960		1056
961	=item ev_set_userdata (loop, void *data)	1057	=item ev_set_userdata (loop, void *data)
962		1058
963	=item ev_userdata (loop)	1059	=item void *ev_userdata (loop)
964		1060
965	Set and retrieve a single C<void *> associated with a loop. When	1061	Set and retrieve a single C<void *> associated with a loop. When
966	C<ev_set_userdata> has never been called, then C<ev_userdata> returns	1062	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
967	C<0.>	1063	C<0>.
968		1064
969	These two functions can be used to associate arbitrary data with a loop,	1065	These two functions can be used to associate arbitrary data with a loop,
970	and are intended solely for the C<invoke_pending_cb>, C<release> and	1066	and are intended solely for the C<invoke_pending_cb>, C<release> and
971	C<acquire> callbacks described above, but of course can be (ab-)used for	1067	C<acquire> callbacks described above, but of course can be (ab-)used for
972	any other purpose as well.	1068	any other purpose as well.
…		…
990		1086
991	In the following description, uppercase C<TYPE> in names stands for the	1087	In the following description, uppercase C<TYPE> in names stands for the
992	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer	1088	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
993	watchers and C<ev_io_start> for I/O watchers.	1089	watchers and C<ev_io_start> for I/O watchers.
994		1090
995	A watcher is a structure that you create and register to record your	1091	A watcher is an opaque structure that you allocate and register to record
996	interest in some event. For instance, if you want to wait for STDIN to	1092	your interest in some event. To make a concrete example, imagine you want
997	become readable, you would create an C<ev_io> watcher for that:	1093	to wait for STDIN to become readable, you would create an C<ev_io> watcher
		1094	for that:
998		1095
999	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)	1096	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
1000	{	1097	{
1001	ev_io_stop (w);	1098	ev_io_stop (w);
1002	ev_break (loop, EVBREAK_ALL);	1099	ev_break (loop, EVBREAK_ALL);
…		…
1017	stack).	1114	stack).
1018		1115
1019	Each watcher has an associated watcher structure (called C<struct ev_TYPE>	1116	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
1020	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).	1117	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
1021		1118
1022	Each watcher structure must be initialised by a call to C<ev_init	1119	Each watcher structure must be initialised by a call to C<ev_init (watcher
1023	(watcher *, callback)>, which expects a callback to be provided. This	1120	*, callback)>, which expects a callback to be provided. This callback is
1024	callback gets invoked each time the event occurs (or, in the case of I/O	1121	invoked each time the event occurs (or, in the case of I/O watchers, each
1025	watchers, each time the event loop detects that the file descriptor given	1122	time the event loop detects that the file descriptor given is readable
1026	is readable and/or writable).	1123	and/or writable).
1027		1124
1028	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>	1125	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
1029	macro to configure it, with arguments specific to the watcher type. There	1126	macro to configure it, with arguments specific to the watcher type. There
1030	is also a macro to combine initialisation and setting in one call: C<<	1127	is also a macro to combine initialisation and setting in one call: C<<
1031	ev_TYPE_init (watcher *, callback, ...) >>.	1128	ev_TYPE_init (watcher *, callback, ...) >>.
…		…
1082		1179
1083	=item C<EV_PREPARE>	1180	=item C<EV_PREPARE>
1084		1181
1085	=item C<EV_CHECK>	1182	=item C<EV_CHECK>
1086		1183
1087	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts	1184	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts to
1088	to gather new events, and all C<ev_check> watchers are invoked just after	1185	gather new events, and all C<ev_check> watchers are queued (not invoked)
1089	C<ev_run> has gathered them, but before it invokes any callbacks for any	1186	just after C<ev_run> has gathered them, but before it queues any callbacks
		1187	for any received events. That means C<ev_prepare> watchers are the last
		1188	watchers invoked before the event loop sleeps or polls for new events, and
		1189	C<ev_check> watchers will be invoked before any other watchers of the same
		1190	or lower priority within an event loop iteration.
		1191
1090	received events. Callbacks of both watcher types can start and stop as	1192	Callbacks of both watcher types can start and stop as many watchers as
1091	many watchers as they want, and all of them will be taken into account	1193	they want, and all of them will be taken into account (for example, a
1092	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1194	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
1093	C<ev_run> from blocking).	1195	blocking).
1094		1196
1095	=item C<EV_EMBED>	1197	=item C<EV_EMBED>
1096		1198
1097	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1199	The embedded event loop specified in the C<ev_embed> watcher needs attention.
1098		1200
1099	=item C<EV_FORK>	1201	=item C<EV_FORK>
1100		1202
1101	The event loop has been resumed in the child process after fork (see	1203	The event loop has been resumed in the child process after fork (see
1102	C<ev_fork>).	1204	C<ev_fork>).
		1205
		1206	=item C<EV_CLEANUP>
		1207
		1208	The event loop is about to be destroyed (see C<ev_cleanup>).
1103		1209
1104	=item C<EV_ASYNC>	1210	=item C<EV_ASYNC>
1105		1211
1106	The given async watcher has been asynchronously notified (see C<ev_async>).	1212	The given async watcher has been asynchronously notified (see C<ev_async>).
1107		1213
…		…
1217		1323
1218	=item callback ev_cb (ev_TYPE *watcher)	1324	=item callback ev_cb (ev_TYPE *watcher)
1219		1325
1220	Returns the callback currently set on the watcher.	1326	Returns the callback currently set on the watcher.
1221		1327
1222	=item ev_cb_set (ev_TYPE *watcher, callback)	1328	=item ev_set_cb (ev_TYPE *watcher, callback)
1223		1329
1224	Change the callback. You can change the callback at virtually any time	1330	Change the callback. You can change the callback at virtually any time
1225	(modulo threads).	1331	(modulo threads).
1226		1332
1227	=item ev_set_priority (ev_TYPE *watcher, int priority)	1333	=item ev_set_priority (ev_TYPE *watcher, int priority)
…		…
1245	or might not have been clamped to the valid range.	1351	or might not have been clamped to the valid range.
1246		1352
1247	The default priority used by watchers when no priority has been set is	1353	The default priority used by watchers when no priority has been set is
1248	always C<0>, which is supposed to not be too high and not be too low :).	1354	always C<0>, which is supposed to not be too high and not be too low :).
1249		1355
1250	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of	1356	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
1251	priorities.	1357	priorities.
1252		1358
1253	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1359	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1254		1360
1255	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1361	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
…		…
1280	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related	1386	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1281	functions that do not need a watcher.	1387	functions that do not need a watcher.
1282		1388
1283	=back	1389	=back
1284		1390
		1391	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
		1392	OWN COMPOSITE WATCHERS> idioms.
1285		1393
1286	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1394	=head2 WATCHER STATES
1287		1395
1288	Each watcher has, by default, a member C<void *data> that you can change	1396	There are various watcher states mentioned throughout this manual -
1289	and read at any time: libev will completely ignore it. This can be used	1397	active, pending and so on. In this section these states and the rules to
1290	to associate arbitrary data with your watcher. If you need more data and	1398	transition between them will be described in more detail - and while these
1291	don't want to allocate memory and store a pointer to it in that data	1399	rules might look complicated, they usually do "the right thing".
1292	member, you can also "subclass" the watcher type and provide your own
1293	data:
1294		1400
1295	struct my_io	1401	=over 4
1296	{
1297	ev_io io;
1298	int otherfd;
1299	void *somedata;
1300	struct whatever *mostinteresting;
1301	};
1302		1402
1303	...	1403	=item initialised
1304	struct my_io w;
1305	ev_io_init (&w.io, my_cb, fd, EV_READ);
1306		1404
1307	And since your callback will be called with a pointer to the watcher, you	1405	Before a watcher can be registered with the event loop it has to be
1308	can cast it back to your own type:	1406	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
		1407	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1309		1408
1310	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)	1409	In this state it is simply some block of memory that is suitable for
1311	{	1410	use in an event loop. It can be moved around, freed, reused etc. at
1312	struct my_io *w = (struct my_io *)w_;	1411	will - as long as you either keep the memory contents intact, or call
1313	...	1412	C<ev_TYPE_init> again.
1314	}
1315		1413
1316	More interesting and less C-conformant ways of casting your callback type	1414	=item started/running/active
1317	instead have been omitted.
1318		1415
1319	Another common scenario is to use some data structure with multiple	1416	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
1320	embedded watchers:	1417	property of the event loop, and is actively waiting for events. While in
		1418	this state it cannot be accessed (except in a few documented ways), moved,
		1419	freed or anything else - the only legal thing is to keep a pointer to it,
		1420	and call libev functions on it that are documented to work on active watchers.
1321		1421
1322	struct my_biggy	1422	=item pending
1323	{
1324	int some_data;
1325	ev_timer t1;
1326	ev_timer t2;
1327	}
1328		1423
1329	In this case getting the pointer to C<my_biggy> is a bit more	1424	If a watcher is active and libev determines that an event it is interested
1330	complicated: Either you store the address of your C<my_biggy> struct	1425	in has occurred (such as a timer expiring), it will become pending. It will
1331	in the C<data> member of the watcher (for woozies), or you need to use	1426	stay in this pending state until either it is stopped or its callback is
1332	some pointer arithmetic using C<offsetof> inside your watchers (for real	1427	about to be invoked, so it is not normally pending inside the watcher
1333	programmers):	1428	callback.
1334		1429
1335	#include <stddef.h>	1430	The watcher might or might not be active while it is pending (for example,
		1431	an expired non-repeating timer can be pending but no longer active). If it
		1432	is stopped, it can be freely accessed (e.g. by calling C<ev_TYPE_set>),
		1433	but it is still property of the event loop at this time, so cannot be
		1434	moved, freed or reused. And if it is active the rules described in the
		1435	previous item still apply.
1336		1436
1337	static void	1437	It is also possible to feed an event on a watcher that is not active (e.g.
1338	t1_cb (EV_P_ ev_timer *w, int revents)	1438	via C<ev_feed_event>), in which case it becomes pending without being
1339	{	1439	active.
1340	struct my_biggy big = (struct my_biggy *)
1341	(((char *)w) - offsetof (struct my_biggy, t1));
1342	}
1343		1440
1344	static void	1441	=item stopped
1345	t2_cb (EV_P_ ev_timer *w, int revents)	1442
1346	{	1443	A watcher can be stopped implicitly by libev (in which case it might still
1347	struct my_biggy big = (struct my_biggy *)	1444	be pending), or explicitly by calling its C<ev_TYPE_stop> function. The
1348	(((char *)w) - offsetof (struct my_biggy, t2));	1445	latter will clear any pending state the watcher might be in, regardless
1349	}	1446	of whether it was active or not, so stopping a watcher explicitly before
		1447	freeing it is often a good idea.
		1448
		1449	While stopped (and not pending) the watcher is essentially in the
		1450	initialised state, that is, it can be reused, moved, modified in any way
		1451	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1452	it again).
		1453
		1454	=back
1350		1455
1351	=head2 WATCHER PRIORITY MODELS	1456	=head2 WATCHER PRIORITY MODELS
1352		1457
1353	Many event loops support I<watcher priorities>, which are usually small	1458	Many event loops support I<watcher priorities>, which are usually small
1354	integers that influence the ordering of event callback invocation	1459	integers that influence the ordering of event callback invocation
…		…
1481	In general you can register as many read and/or write event watchers per	1586	In general you can register as many read and/or write event watchers per
1482	fd as you want (as long as you don't confuse yourself). Setting all file	1587	fd as you want (as long as you don't confuse yourself). Setting all file
1483	descriptors to non-blocking mode is also usually a good idea (but not	1588	descriptors to non-blocking mode is also usually a good idea (but not
1484	required if you know what you are doing).	1589	required if you know what you are doing).
1485		1590
1486	If you cannot use non-blocking mode, then force the use of a
1487	known-to-be-good backend (at the time of this writing, this includes only
1488	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
1489	descriptors for which non-blocking operation makes no sense (such as
1490	files) - libev doesn't guarantee any specific behaviour in that case.
1491
1492	Another thing you have to watch out for is that it is quite easy to	1591	Another thing you have to watch out for is that it is quite easy to
1493	receive "spurious" readiness notifications, that is your callback might	1592	receive "spurious" readiness notifications, that is, your callback might
1494	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1593	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1495	because there is no data. Not only are some backends known to create a	1594	because there is no data. It is very easy to get into this situation even
1496	lot of those (for example Solaris ports), it is very easy to get into	1595	with a relatively standard program structure. Thus it is best to always
1497	this situation even with a relatively standard program structure. Thus	1596	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1498	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1499	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1597	preferable to a program hanging until some data arrives.
1500		1598
1501	If you cannot run the fd in non-blocking mode (for example you should	1599	If you cannot run the fd in non-blocking mode (for example you should
1502	not play around with an Xlib connection), then you have to separately	1600	not play around with an Xlib connection), then you have to separately
1503	re-test whether a file descriptor is really ready with a known-to-be good	1601	re-test whether a file descriptor is really ready with a known-to-be good
1504	interface such as poll (fortunately in our Xlib example, Xlib already	1602	interface such as poll (fortunately in the case of Xlib, it already does
1505	does this on its own, so its quite safe to use). Some people additionally	1603	this on its own, so its quite safe to use). Some people additionally
1506	use C<SIGALRM> and an interval timer, just to be sure you won't block	1604	use C<SIGALRM> and an interval timer, just to be sure you won't block
1507	indefinitely.	1605	indefinitely.
1508		1606
1509	But really, best use non-blocking mode.	1607	But really, best use non-blocking mode.
1510		1608
…		…
1538		1636
1539	There is no workaround possible except not registering events	1637	There is no workaround possible except not registering events
1540	for potentially C<dup ()>'ed file descriptors, or to resort to	1638	for potentially C<dup ()>'ed file descriptors, or to resort to
1541	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1639	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1542		1640
		1641	=head3 The special problem of files
		1642
		1643	Many people try to use C<select> (or libev) on file descriptors
		1644	representing files, and expect it to become ready when their program
		1645	doesn't block on disk accesses (which can take a long time on their own).
		1646
		1647	However, this cannot ever work in the "expected" way - you get a readiness
		1648	notification as soon as the kernel knows whether and how much data is
		1649	there, and in the case of open files, that's always the case, so you
		1650	always get a readiness notification instantly, and your read (or possibly
		1651	write) will still block on the disk I/O.
		1652
		1653	Another way to view it is that in the case of sockets, pipes, character
		1654	devices and so on, there is another party (the sender) that delivers data
		1655	on its own, but in the case of files, there is no such thing: the disk
		1656	will not send data on its own, simply because it doesn't know what you
		1657	wish to read - you would first have to request some data.
		1658
		1659	Since files are typically not-so-well supported by advanced notification
		1660	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1661	to files, even though you should not use it. The reason for this is
		1662	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1663	usually a tty, often a pipe, but also sometimes files or special devices
		1664	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1665	F</dev/urandom>), and even though the file might better be served with
		1666	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1667	it "just works" instead of freezing.
		1668
		1669	So avoid file descriptors pointing to files when you know it (e.g. use
		1670	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1671	when you rarely read from a file instead of from a socket, and want to
		1672	reuse the same code path.
		1673
1543	=head3 The special problem of fork	1674	=head3 The special problem of fork
1544		1675
1545	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1676	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
1546	useless behaviour. Libev fully supports fork, but needs to be told about	1677	useless behaviour. Libev fully supports fork, but needs to be told about
1547	it in the child.	1678	it in the child if you want to continue to use it in the child.
1548		1679
1549	To support fork in your programs, you either have to call	1680	To support fork in your child processes, you have to call C<ev_loop_fork
1550	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1681	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1551	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1682	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1552	C<EVBACKEND_POLL>.
1553		1683
1554	=head3 The special problem of SIGPIPE	1684	=head3 The special problem of SIGPIPE
1555		1685
1556	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1686	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1557	when writing to a pipe whose other end has been closed, your program gets	1687	when writing to a pipe whose other end has been closed, your program gets
…		…
1655	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1785	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1656	monotonic clock option helps a lot here).	1786	monotonic clock option helps a lot here).
1657		1787
1658	The callback is guaranteed to be invoked only I<after> its timeout has	1788	The callback is guaranteed to be invoked only I<after> its timeout has
1659	passed (not I<at>, so on systems with very low-resolution clocks this	1789	passed (not I<at>, so on systems with very low-resolution clocks this
1660	might introduce a small delay). If multiple timers become ready during the	1790	might introduce a small delay, see "the special problem of being too
		1791	early", below). If multiple timers become ready during the same loop
1661	same loop iteration then the ones with earlier time-out values are invoked	1792	iteration then the ones with earlier time-out values are invoked before
1662	before ones of the same priority with later time-out values (but this is	1793	ones of the same priority with later time-out values (but this is no
1663	no longer true when a callback calls C<ev_run> recursively).	1794	longer true when a callback calls C<ev_run> recursively).
1664		1795
1665	=head3 Be smart about timeouts	1796	=head3 Be smart about timeouts
1666		1797
1667	Many real-world problems involve some kind of timeout, usually for error	1798	Many real-world problems involve some kind of timeout, usually for error
1668	recovery. A typical example is an HTTP request - if the other side hangs,	1799	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1743		1874
1744	In this case, it would be more efficient to leave the C<ev_timer> alone,	1875	In this case, it would be more efficient to leave the C<ev_timer> alone,
1745	but remember the time of last activity, and check for a real timeout only	1876	but remember the time of last activity, and check for a real timeout only
1746	within the callback:	1877	within the callback:
1747		1878
		1879	ev_tstamp timeout = 60.;
1748	ev_tstamp last_activity; // time of last activity	1880	ev_tstamp last_activity; // time of last activity
		1881	ev_timer timer;
1749		1882
1750	static void	1883	static void
1751	callback (EV_P_ ev_timer *w, int revents)	1884	callback (EV_P_ ev_timer *w, int revents)
1752	{	1885	{
1753	ev_tstamp now = ev_now (EV_A);	1886	// calculate when the timeout would happen
1754	ev_tstamp timeout = last_activity + 60.;	1887	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
1755		1888
1756	// if last_activity + 60. is older than now, we did time out	1889	// if negative, it means we the timeout already occurred
1757	if (timeout < now)	1890	if (after < 0.)
1758	{	1891	{
1759	// timeout occurred, take action	1892	// timeout occurred, take action
1760	}	1893	}
1761	else	1894	else
1762	{	1895	{
1763	// callback was invoked, but there was some activity, re-arm	1896	// callback was invoked, but there was some recent
1764	// the watcher to fire in last_activity + 60, which is	1897	// activity. simply restart the timer to time out
1765	// guaranteed to be in the future, so "again" is positive:	1898	// after "after" seconds, which is the earliest time
1766	w->repeat = timeout - now;	1899	// the timeout can occur.
		1900	ev_timer_set (w, after, 0.);
1767	ev_timer_again (EV_A_ w);	1901	ev_timer_start (EV_A_ w);
1768	}	1902	}
1769	}	1903	}
1770		1904
1771	To summarise the callback: first calculate the real timeout (defined	1905	To summarise the callback: first calculate in how many seconds the
1772	as "60 seconds after the last activity"), then check if that time has	1906	timeout will occur (by calculating the absolute time when it would occur,
1773	been reached, which means something I<did>, in fact, time out. Otherwise	1907	C<last_activity + timeout>, and subtracting the current time, C<ev_now
1774	the callback was invoked too early (C<timeout> is in the future), so	1908	(EV_A)> from that).
1775	re-schedule the timer to fire at that future time, to see if maybe we have
1776	a timeout then.
1777		1909
1778	Note how C<ev_timer_again> is used, taking advantage of the	1910	If this value is negative, then we are already past the timeout, i.e. we
1779	C<ev_timer_again> optimisation when the timer is already running.	1911	timed out, and need to do whatever is needed in this case.
		1912
		1913	Otherwise, we now the earliest time at which the timeout would trigger,
		1914	and simply start the timer with this timeout value.
		1915
		1916	In other words, each time the callback is invoked it will check whether
		1917	the timeout occurred. If not, it will simply reschedule itself to check
		1918	again at the earliest time it could time out. Rinse. Repeat.
1780		1919
1781	This scheme causes more callback invocations (about one every 60 seconds	1920	This scheme causes more callback invocations (about one every 60 seconds
1782	minus half the average time between activity), but virtually no calls to	1921	minus half the average time between activity), but virtually no calls to
1783	libev to change the timeout.	1922	libev to change the timeout.
1784		1923
1785	To start the timer, simply initialise the watcher and set C<last_activity>	1924	To start the machinery, simply initialise the watcher and set
1786	to the current time (meaning we just have some activity :), then call the	1925	C<last_activity> to the current time (meaning there was some activity just
1787	callback, which will "do the right thing" and start the timer:	1926	now), then call the callback, which will "do the right thing" and start
		1927	the timer:
1788		1928
		1929	last_activity = ev_now (EV_A);
1789	ev_init (timer, callback);	1930	ev_init (&timer, callback);
1790	last_activity = ev_now (loop);	1931	callback (EV_A_ &timer, 0);
1791	callback (loop, timer, EV_TIMER);
1792		1932
1793	And when there is some activity, simply store the current time in	1933	When there is some activity, simply store the current time in
1794	C<last_activity>, no libev calls at all:	1934	C<last_activity>, no libev calls at all:
1795		1935
		1936	if (activity detected)
1796	last_activity = ev_now (loop);	1937	last_activity = ev_now (EV_A);
		1938
		1939	When your timeout value changes, then the timeout can be changed by simply
		1940	providing a new value, stopping the timer and calling the callback, which
		1941	will again do the right thing (for example, time out immediately :).
		1942
		1943	timeout = new_value;
		1944	ev_timer_stop (EV_A_ &timer);
		1945	callback (EV_A_ &timer, 0);
1797		1946
1798	This technique is slightly more complex, but in most cases where the	1947	This technique is slightly more complex, but in most cases where the
1799	time-out is unlikely to be triggered, much more efficient.	1948	time-out is unlikely to be triggered, much more efficient.
1800
1801	Changing the timeout is trivial as well (if it isn't hard-coded in the
1802	callback :) - just change the timeout and invoke the callback, which will
1803	fix things for you.
1804		1949
1805	=item 4. Wee, just use a double-linked list for your timeouts.	1950	=item 4. Wee, just use a double-linked list for your timeouts.
1806		1951
1807	If there is not one request, but many thousands (millions...), all	1952	If there is not one request, but many thousands (millions...), all
1808	employing some kind of timeout with the same timeout value, then one can	1953	employing some kind of timeout with the same timeout value, then one can
…		…
1835	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is	1980	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
1836	rather complicated, but extremely efficient, something that really pays	1981	rather complicated, but extremely efficient, something that really pays
1837	off after the first million or so of active timers, i.e. it's usually	1982	off after the first million or so of active timers, i.e. it's usually
1838	overkill :)	1983	overkill :)
1839		1984
		1985	=head3 The special problem of being too early
		1986
		1987	If you ask a timer to call your callback after three seconds, then
		1988	you expect it to be invoked after three seconds - but of course, this
		1989	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		1990	guaranteed to any precision by libev - imagine somebody suspending the
		1991	process with a STOP signal for a few hours for example.
		1992
		1993	So, libev tries to invoke your callback as soon as possible I<after> the
		1994	delay has occurred, but cannot guarantee this.
		1995
		1996	A less obvious failure mode is calling your callback too early: many event
		1997	loops compare timestamps with a "elapsed delay >= requested delay", but
		1998	this can cause your callback to be invoked much earlier than you would
		1999	expect.
		2000
		2001	To see why, imagine a system with a clock that only offers full second
		2002	resolution (think windows if you can't come up with a broken enough OS
		2003	yourself). If you schedule a one-second timer at the time 500.9, then the
		2004	event loop will schedule your timeout to elapse at a system time of 500
		2005	(500.9 truncated to the resolution) + 1, or 501.
		2006
		2007	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2008	501" and invoke the callback 0.1s after it was started, even though a
		2009	one-second delay was requested - this is being "too early", despite best
		2010	intentions.
		2011
		2012	This is the reason why libev will never invoke the callback if the elapsed
		2013	delay equals the requested delay, but only when the elapsed delay is
		2014	larger than the requested delay. In the example above, libev would only invoke
		2015	the callback at system time 502, or 1.1s after the timer was started.
		2016
		2017	So, while libev cannot guarantee that your callback will be invoked
		2018	exactly when requested, it I<can> and I<does> guarantee that the requested
		2019	delay has actually elapsed, or in other words, it always errs on the "too
		2020	late" side of things.
		2021
1840	=head3 The special problem of time updates	2022	=head3 The special problem of time updates
1841		2023
1842	Establishing the current time is a costly operation (it usually takes at	2024	Establishing the current time is a costly operation (it usually takes
1843	least two system calls): EV therefore updates its idea of the current	2025	at least one system call): EV therefore updates its idea of the current
1844	time only before and after C<ev_run> collects new events, which causes a	2026	time only before and after C<ev_run> collects new events, which causes a
1845	growing difference between C<ev_now ()> and C<ev_time ()> when handling	2027	growing difference between C<ev_now ()> and C<ev_time ()> when handling
1846	lots of events in one iteration.	2028	lots of events in one iteration.
1847		2029
1848	The relative timeouts are calculated relative to the C<ev_now ()>	2030	The relative timeouts are calculated relative to the C<ev_now ()>
1849	time. This is usually the right thing as this timestamp refers to the time	2031	time. This is usually the right thing as this timestamp refers to the time
1850	of the event triggering whatever timeout you are modifying/starting. If	2032	of the event triggering whatever timeout you are modifying/starting. If
1851	you suspect event processing to be delayed and you I<need> to base the	2033	you suspect event processing to be delayed and you I<need> to base the
1852	timeout on the current time, use something like this to adjust for this:	2034	timeout on the current time, use something like the following to adjust
		2035	for it:
1853		2036
1854	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2037	ev_timer_set (&timer, after + (ev_time () - ev_now ()), 0.);
1855		2038
1856	If the event loop is suspended for a long time, you can also force an	2039	If the event loop is suspended for a long time, you can also force an
1857	update of the time returned by C<ev_now ()> by calling C<ev_now_update	2040	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1858	()>.	2041	()>, although that will push the event time of all outstanding events
		2042	further into the future.
		2043
		2044	=head3 The special problem of unsynchronised clocks
		2045
		2046	Modern systems have a variety of clocks - libev itself uses the normal
		2047	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2048	jumps).
		2049
		2050	Neither of these clocks is synchronised with each other or any other clock
		2051	on the system, so C<ev_time ()> might return a considerably different time
		2052	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2053	a call to C<gettimeofday> might return a second count that is one higher
		2054	than a directly following call to C<time>.
		2055
		2056	The moral of this is to only compare libev-related timestamps with
		2057	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2058	a second or so.
		2059
		2060	One more problem arises due to this lack of synchronisation: if libev uses
		2061	the system monotonic clock and you compare timestamps from C<ev_time>
		2062	or C<ev_now> from when you started your timer and when your callback is
		2063	invoked, you will find that sometimes the callback is a bit "early".
		2064
		2065	This is because C<ev_timer>s work in real time, not wall clock time, so
		2066	libev makes sure your callback is not invoked before the delay happened,
		2067	I<measured according to the real time>, not the system clock.
		2068
		2069	If your timeouts are based on a physical timescale (e.g. "time out this
		2070	connection after 100 seconds") then this shouldn't bother you as it is
		2071	exactly the right behaviour.
		2072
		2073	If you want to compare wall clock/system timestamps to your timers, then
		2074	you need to use C<ev_periodic>s, as these are based on the wall clock
		2075	time, where your comparisons will always generate correct results.
1859		2076
1860	=head3 The special problems of suspended animation	2077	=head3 The special problems of suspended animation
1861		2078
1862	When you leave the server world it is quite customary to hit machines that	2079	When you leave the server world it is quite customary to hit machines that
1863	can suspend/hibernate - what happens to the clocks during such a suspend?	2080	can suspend/hibernate - what happens to the clocks during such a suspend?
…		…
1907	keep up with the timer (because it takes longer than those 10 seconds to	2124	keep up with the timer (because it takes longer than those 10 seconds to
1908	do stuff) the timer will not fire more than once per event loop iteration.	2125	do stuff) the timer will not fire more than once per event loop iteration.
1909		2126
1910	=item ev_timer_again (loop, ev_timer *)	2127	=item ev_timer_again (loop, ev_timer *)
1911		2128
1912	This will act as if the timer timed out and restart it again if it is	2129	This will act as if the timer timed out, and restarts it again if it is
1913	repeating. The exact semantics are:	2130	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2131	timeout to the C<repeat> value and calling C<ev_timer_start>.
1914		2132
		2133	The exact semantics are as in the following rules, all of which will be
		2134	applied to the watcher:
		2135
		2136	=over 4
		2137
1915	If the timer is pending, its pending status is cleared.	2138	=item If the timer is pending, the pending status is always cleared.
1916		2139
1917	If the timer is started but non-repeating, stop it (as if it timed out).	2140	=item If the timer is started but non-repeating, stop it (as if it timed
		2141	out, without invoking it).
1918		2142
1919	If the timer is repeating, either start it if necessary (with the	2143	=item If the timer is repeating, make the C<repeat> value the new timeout
1920	C<repeat> value), or reset the running timer to the C<repeat> value.	2144	and start the timer, if necessary.
1921		2145
		2146	=back
		2147
1922	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a	2148	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
1923	usage example.	2149	usage example.
1924		2150
1925	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)	2151	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1926		2152
1927	Returns the remaining time until a timer fires. If the timer is active,	2153	Returns the remaining time until a timer fires. If the timer is active,
…		…
2047		2273
2048	Another way to think about it (for the mathematically inclined) is that	2274	Another way to think about it (for the mathematically inclined) is that
2049	C<ev_periodic> will try to run the callback in this mode at the next possible	2275	C<ev_periodic> will try to run the callback in this mode at the next possible
2050	time where C<time = offset (mod interval)>, regardless of any time jumps.	2276	time where C<time = offset (mod interval)>, regardless of any time jumps.
2051		2277
2052	For numerical stability it is preferable that the C<offset> value is near	2278	The C<interval> I<MUST> be positive, and for numerical stability, the
2053	C<ev_now ()> (the current time), but there is no range requirement for	2279	interval value should be higher than C<1/8192> (which is around 100
2054	this value, and in fact is often specified as zero.	2280	microseconds) and C<offset> should be higher than C<0> and should have
		2281	at most a similar magnitude as the current time (say, within a factor of
		2282	ten). Typical values for offset are, in fact, C<0> or something between
		2283	C<0> and C<interval>, which is also the recommended range.
2055		2284
2056	Note also that there is an upper limit to how often a timer can fire (CPU	2285	Note also that there is an upper limit to how often a timer can fire (CPU
2057	speed for example), so if C<interval> is very small then timing stability	2286	speed for example), so if C<interval> is very small then timing stability
2058	will of course deteriorate. Libev itself tries to be exact to be about one	2287	will of course deteriorate. Libev itself tries to be exact to be about one
2059	millisecond (if the OS supports it and the machine is fast enough).	2288	millisecond (if the OS supports it and the machine is fast enough).
…		…
2167		2396
2168	ev_periodic hourly_tick;	2397	ev_periodic hourly_tick;
2169	ev_periodic_init (&hourly_tick, clock_cb,	2398	ev_periodic_init (&hourly_tick, clock_cb,
2170	fmod (ev_now (loop), 3600.), 3600., 0);	2399	fmod (ev_now (loop), 3600.), 3600., 0);
2171	ev_periodic_start (loop, &hourly_tick);	2400	ev_periodic_start (loop, &hourly_tick);
2172		2401
2173		2402
2174	=head2 C<ev_signal> - signal me when a signal gets signalled!	2403	=head2 C<ev_signal> - signal me when a signal gets signalled!
2175		2404
2176	Signal watchers will trigger an event when the process receives a specific	2405	Signal watchers will trigger an event when the process receives a specific
2177	signal one or more times. Even though signals are very asynchronous, libev	2406	signal one or more times. Even though signals are very asynchronous, libev
2178	will try it's best to deliver signals synchronously, i.e. as part of the	2407	will try its best to deliver signals synchronously, i.e. as part of the
2179	normal event processing, like any other event.	2408	normal event processing, like any other event.
2180		2409
2181	If you want signals to be delivered truly asynchronously, just use	2410	If you want signals to be delivered truly asynchronously, just use
2182	C<sigaction> as you would do without libev and forget about sharing	2411	C<sigaction> as you would do without libev and forget about sharing
2183	the signal. You can even use C<ev_async> from a signal handler to	2412	the signal. You can even use C<ev_async> from a signal handler to
…		…
2187	only within the same loop, i.e. you can watch for C<SIGINT> in your	2416	only within the same loop, i.e. you can watch for C<SIGINT> in your
2188	default loop and for C<SIGIO> in another loop, but you cannot watch for	2417	default loop and for C<SIGIO> in another loop, but you cannot watch for
2189	C<SIGINT> in both the default loop and another loop at the same time. At	2418	C<SIGINT> in both the default loop and another loop at the same time. At
2190	the moment, C<SIGCHLD> is permanently tied to the default loop.	2419	the moment, C<SIGCHLD> is permanently tied to the default loop.
2191		2420
2192	When the first watcher gets started will libev actually register something	2421	Only after the first watcher for a signal is started will libev actually
2193	with the kernel (thus it coexists with your own signal handlers as long as	2422	register something with the kernel. It thus coexists with your own signal
2194	you don't register any with libev for the same signal).	2423	handlers as long as you don't register any with libev for the same signal.
2195		2424
2196	If possible and supported, libev will install its handlers with	2425	If possible and supported, libev will install its handlers with
2197	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should	2426	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
2198	not be unduly interrupted. If you have a problem with system calls getting	2427	not be unduly interrupted. If you have a problem with system calls getting
2199	interrupted by signals you can block all signals in an C<ev_check> watcher	2428	interrupted by signals you can block all signals in an C<ev_check> watcher
…		…
2202	=head3 The special problem of inheritance over fork/execve/pthread_create	2431	=head3 The special problem of inheritance over fork/execve/pthread_create
2203		2432
2204	Both the signal mask (C<sigprocmask>) and the signal disposition	2433	Both the signal mask (C<sigprocmask>) and the signal disposition
2205	(C<sigaction>) are unspecified after starting a signal watcher (and after	2434	(C<sigaction>) are unspecified after starting a signal watcher (and after
2206	stopping it again), that is, libev might or might not block the signal,	2435	stopping it again), that is, libev might or might not block the signal,
2207	and might or might not set or restore the installed signal handler.	2436	and might or might not set or restore the installed signal handler (but
		2437	see C<EVFLAG_NOSIGMASK>).
2208		2438
2209	While this does not matter for the signal disposition (libev never	2439	While this does not matter for the signal disposition (libev never
2210	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on	2440	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
2211	C<execve>), this matters for the signal mask: many programs do not expect	2441	C<execve>), this matters for the signal mask: many programs do not expect
2212	certain signals to be blocked.	2442	certain signals to be blocked.
…		…
2225	I<has> to modify the signal mask, at least temporarily.	2455	I<has> to modify the signal mask, at least temporarily.
2226		2456
2227	So I can't stress this enough: I<If you do not reset your signal mask when	2457	So I can't stress this enough: I<If you do not reset your signal mask when
2228	you expect it to be empty, you have a race condition in your code>. This	2458	you expect it to be empty, you have a race condition in your code>. This
2229	is not a libev-specific thing, this is true for most event libraries.	2459	is not a libev-specific thing, this is true for most event libraries.
		2460
		2461	=head3 The special problem of threads signal handling
		2462
		2463	POSIX threads has problematic signal handling semantics, specifically,
		2464	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2465	threads in a process block signals, which is hard to achieve.
		2466
		2467	When you want to use sigwait (or mix libev signal handling with your own
		2468	for the same signals), you can tackle this problem by globally blocking
		2469	all signals before creating any threads (or creating them with a fully set
		2470	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2471	loops. Then designate one thread as "signal receiver thread" which handles
		2472	these signals. You can pass on any signals that libev might be interested
		2473	in by calling C<ev_feed_signal>.
2230		2474
2231	=head3 Watcher-Specific Functions and Data Members	2475	=head3 Watcher-Specific Functions and Data Members
2232		2476
2233	=over 4	2477	=over 4
2234		2478
…		…
2369		2613
2370	=head2 C<ev_stat> - did the file attributes just change?	2614	=head2 C<ev_stat> - did the file attributes just change?
2371		2615
2372	This watches a file system path for attribute changes. That is, it calls	2616	This watches a file system path for attribute changes. That is, it calls
2373	C<stat> on that path in regular intervals (or when the OS says it changed)	2617	C<stat> on that path in regular intervals (or when the OS says it changed)
2374	and sees if it changed compared to the last time, invoking the callback if	2618	and sees if it changed compared to the last time, invoking the callback
2375	it did.	2619	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2620	happen after the watcher has been started will be reported.
2376		2621
2377	The path does not need to exist: changing from "path exists" to "path does	2622	The path does not need to exist: changing from "path exists" to "path does
2378	not exist" is a status change like any other. The condition "path does not	2623	not exist" is a status change like any other. The condition "path does not
2379	exist" (or more correctly "path cannot be stat'ed") is signified by the	2624	exist" (or more correctly "path cannot be stat'ed") is signified by the
2380	C<st_nlink> field being zero (which is otherwise always forced to be at	2625	C<st_nlink> field being zero (which is otherwise always forced to be at
…		…
2610	Apart from keeping your process non-blocking (which is a useful	2855	Apart from keeping your process non-blocking (which is a useful
2611	effect on its own sometimes), idle watchers are a good place to do	2856	effect on its own sometimes), idle watchers are a good place to do
2612	"pseudo-background processing", or delay processing stuff to after the	2857	"pseudo-background processing", or delay processing stuff to after the
2613	event loop has handled all outstanding events.	2858	event loop has handled all outstanding events.
2614		2859
		2860	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2861
		2862	As long as there is at least one active idle watcher, libev will never
		2863	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2864	For this to work, the idle watcher doesn't need to be invoked at all - the
		2865	lowest priority will do.
		2866
		2867	This mode of operation can be useful together with an C<ev_check> watcher,
		2868	to do something on each event loop iteration - for example to balance load
		2869	between different connections.
		2870
		2871	See L</Abusing an ev_check watcher for its side-effect> for a longer
		2872	example.
		2873
2615	=head3 Watcher-Specific Functions and Data Members	2874	=head3 Watcher-Specific Functions and Data Members
2616		2875
2617	=over 4	2876	=over 4
2618		2877
2619	=item ev_idle_init (ev_idle *, callback)	2878	=item ev_idle_init (ev_idle *, callback)
…		…
2630	callback, free it. Also, use no error checking, as usual.	2889	callback, free it. Also, use no error checking, as usual.
2631		2890
2632	static void	2891	static void
2633	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)	2892	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
2634	{	2893	{
		2894	// stop the watcher
		2895	ev_idle_stop (loop, w);
		2896
		2897	// now we can free it
2635	free (w);	2898	free (w);
		2899
2636	// now do something you wanted to do when the program has	2900	// now do something you wanted to do when the program has
2637	// no longer anything immediate to do.	2901	// no longer anything immediate to do.
2638	}	2902	}
2639		2903
2640	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	2904	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
…		…
2642	ev_idle_start (loop, idle_watcher);	2906	ev_idle_start (loop, idle_watcher);
2643		2907
2644		2908
2645	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2909	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2646		2910
2647	Prepare and check watchers are usually (but not always) used in pairs:	2911	Prepare and check watchers are often (but not always) used in pairs:
2648	prepare watchers get invoked before the process blocks and check watchers	2912	prepare watchers get invoked before the process blocks and check watchers
2649	afterwards.	2913	afterwards.
2650		2914
2651	You I<must not> call C<ev_run> or similar functions that enter	2915	You I<must not> call C<ev_run> (or similar functions that enter the
2652	the current event loop from either C<ev_prepare> or C<ev_check>	2916	current event loop) or C<ev_loop_fork> from either C<ev_prepare> or
2653	watchers. Other loops than the current one are fine, however. The	2917	C<ev_check> watchers. Other loops than the current one are fine,
2654	rationale behind this is that you do not need to check for recursion in	2918	however. The rationale behind this is that you do not need to check
2655	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2919	for recursion in those watchers, i.e. the sequence will always be
2656	C<ev_check> so if you have one watcher of each kind they will always be	2920	C<ev_prepare>, blocking, C<ev_check> so if you have one watcher of each
2657	called in pairs bracketing the blocking call.	2921	kind they will always be called in pairs bracketing the blocking call.
2658		2922
2659	Their main purpose is to integrate other event mechanisms into libev and	2923	Their main purpose is to integrate other event mechanisms into libev and
2660	their use is somewhat advanced. They could be used, for example, to track	2924	their use is somewhat advanced. They could be used, for example, to track
2661	variable changes, implement your own watchers, integrate net-snmp or a	2925	variable changes, implement your own watchers, integrate net-snmp or a
2662	coroutine library and lots more. They are also occasionally useful if	2926	coroutine library and lots more. They are also occasionally useful if
…		…
2680	with priority higher than or equal to the event loop and one coroutine	2944	with priority higher than or equal to the event loop and one coroutine
2681	of lower priority, but only once, using idle watchers to keep the event	2945	of lower priority, but only once, using idle watchers to keep the event
2682	loop from blocking if lower-priority coroutines are active, thus mapping	2946	loop from blocking if lower-priority coroutines are active, thus mapping
2683	low-priority coroutines to idle/background tasks).	2947	low-priority coroutines to idle/background tasks).
2684		2948
2685	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2949	When used for this purpose, it is recommended to give C<ev_check> watchers
2686	priority, to ensure that they are being run before any other watchers	2950	highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
2687	after the poll (this doesn't matter for C<ev_prepare> watchers).	2951	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		2952	watchers).
2688		2953
2689	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not	2954	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
2690	activate ("feed") events into libev. While libev fully supports this, they	2955	activate ("feed") events into libev. While libev fully supports this, they
2691	might get executed before other C<ev_check> watchers did their job. As	2956	might get executed before other C<ev_check> watchers did their job. As
2692	C<ev_check> watchers are often used to embed other (non-libev) event	2957	C<ev_check> watchers are often used to embed other (non-libev) event
2693	loops those other event loops might be in an unusable state until their	2958	loops those other event loops might be in an unusable state until their
2694	C<ev_check> watcher ran (always remind yourself to coexist peacefully with	2959	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
2695	others).	2960	others).
		2961
		2962	=head3 Abusing an C<ev_check> watcher for its side-effect
		2963
		2964	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		2965	useful because they are called once per event loop iteration. For
		2966	example, if you want to handle a large number of connections fairly, you
		2967	normally only do a bit of work for each active connection, and if there
		2968	is more work to do, you wait for the next event loop iteration, so other
		2969	connections have a chance of making progress.
		2970
		2971	Using an C<ev_check> watcher is almost enough: it will be called on the
		2972	next event loop iteration. However, that isn't as soon as possible -
		2973	without external events, your C<ev_check> watcher will not be invoked.
		2974
		2975	This is where C<ev_idle> watchers come in handy - all you need is a
		2976	single global idle watcher that is active as long as you have one active
		2977	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		2978	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		2979	invoked. Neither watcher alone can do that.
2696		2980
2697	=head3 Watcher-Specific Functions and Data Members	2981	=head3 Watcher-Specific Functions and Data Members
2698		2982
2699	=over 4	2983	=over 4
2700		2984
…		…
2901		3185
2902	=over 4	3186	=over 4
2903		3187
2904	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3188	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
2905		3189
2906	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)	3190	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
2907		3191
2908	Configures the watcher to embed the given loop, which must be	3192	Configures the watcher to embed the given loop, which must be
2909	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3193	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
2910	invoked automatically, otherwise it is the responsibility of the callback	3194	invoked automatically, otherwise it is the responsibility of the callback
2911	to invoke it (it will continue to be called until the sweep has been done,	3195	to invoke it (it will continue to be called until the sweep has been done,
…		…
2932	used).	3216	used).
2933		3217
2934	struct ev_loop *loop_hi = ev_default_init (0);	3218	struct ev_loop *loop_hi = ev_default_init (0);
2935	struct ev_loop *loop_lo = 0;	3219	struct ev_loop *loop_lo = 0;
2936	ev_embed embed;	3220	ev_embed embed;
2937		3221
2938	// see if there is a chance of getting one that works	3222	// see if there is a chance of getting one that works
2939	// (remember that a flags value of 0 means autodetection)	3223	// (remember that a flags value of 0 means autodetection)
2940	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3224	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2941	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3225	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
2942	: 0;	3226	: 0;
…		…
2956	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3240	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2957		3241
2958	struct ev_loop *loop = ev_default_init (0);	3242	struct ev_loop *loop = ev_default_init (0);
2959	struct ev_loop *loop_socket = 0;	3243	struct ev_loop *loop_socket = 0;
2960	ev_embed embed;	3244	ev_embed embed;
2961		3245
2962	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3246	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2963	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3247	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2964	{	3248	{
2965	ev_embed_init (&embed, 0, loop_socket);	3249	ev_embed_init (&embed, 0, loop_socket);
2966	ev_embed_start (loop, &embed);	3250	ev_embed_start (loop, &embed);
…		…
2974		3258
2975	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3259	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
2976		3260
2977	Fork watchers are called when a C<fork ()> was detected (usually because	3261	Fork watchers are called when a C<fork ()> was detected (usually because
2978	whoever is a good citizen cared to tell libev about it by calling	3262	whoever is a good citizen cared to tell libev about it by calling
2979	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the	3263	C<ev_loop_fork>). The invocation is done before the event loop blocks next
2980	event loop blocks next and before C<ev_check> watchers are being called,	3264	and before C<ev_check> watchers are being called, and only in the child
2981	and only in the child after the fork. If whoever good citizen calling	3265	after the fork. If whoever good citizen calling C<ev_default_fork> cheats
2982	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3266	and calls it in the wrong process, the fork handlers will be invoked, too,
2983	handlers will be invoked, too, of course.	3267	of course.
2984		3268
2985	=head3 The special problem of life after fork - how is it possible?	3269	=head3 The special problem of life after fork - how is it possible?
2986		3270
2987	Most uses of C<fork()> consist of forking, then some simple calls to set	3271	Most uses of C<fork ()> consist of forking, then some simple calls to set
2988	up/change the process environment, followed by a call to C<exec()>. This	3272	up/change the process environment, followed by a call to C<exec()>. This
2989	sequence should be handled by libev without any problems.	3273	sequence should be handled by libev without any problems.
2990		3274
2991	This changes when the application actually wants to do event handling	3275	This changes when the application actually wants to do event handling
2992	in the child, or both parent in child, in effect "continuing" after the	3276	in the child, or both parent in child, in effect "continuing" after the
…		…
3008	disadvantage of having to use multiple event loops (which do not support	3292	disadvantage of having to use multiple event loops (which do not support
3009	signal watchers).	3293	signal watchers).
3010		3294
3011	When this is not possible, or you want to use the default loop for	3295	When this is not possible, or you want to use the default loop for
3012	other reasons, then in the process that wants to start "fresh", call	3296	other reasons, then in the process that wants to start "fresh", call
3013	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying	3297	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
3014	the default loop will "orphan" (not stop) all registered watchers, so you	3298	Destroying the default loop will "orphan" (not stop) all registered
3015	have to be careful not to execute code that modifies those watchers. Note	3299	watchers, so you have to be careful not to execute code that modifies
3016	also that in that case, you have to re-register any signal watchers.	3300	those watchers. Note also that in that case, you have to re-register any
		3301	signal watchers.
3017		3302
3018	=head3 Watcher-Specific Functions and Data Members	3303	=head3 Watcher-Specific Functions and Data Members
3019		3304
3020	=over 4	3305	=over 4
3021		3306
3022	=item ev_fork_init (ev_signal *, callback)	3307	=item ev_fork_init (ev_fork *, callback)
3023		3308
3024	Initialises and configures the fork watcher - it has no parameters of any	3309	Initialises and configures the fork watcher - it has no parameters of any
3025	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,	3310	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
3026	believe me.	3311	really.
3027		3312
3028	=back	3313	=back
3029		3314
3030		3315
		3316	=head2 C<ev_cleanup> - even the best things end
		3317
		3318	Cleanup watchers are called just before the event loop is being destroyed
		3319	by a call to C<ev_loop_destroy>.
		3320
		3321	While there is no guarantee that the event loop gets destroyed, cleanup
		3322	watchers provide a convenient method to install cleanup hooks for your
		3323	program, worker threads and so on - you just to make sure to destroy the
		3324	loop when you want them to be invoked.
		3325
		3326	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3327	all other watchers, they do not keep a reference to the event loop (which
		3328	makes a lot of sense if you think about it). Like all other watchers, you
		3329	can call libev functions in the callback, except C<ev_cleanup_start>.
		3330
		3331	=head3 Watcher-Specific Functions and Data Members
		3332
		3333	=over 4
		3334
		3335	=item ev_cleanup_init (ev_cleanup *, callback)
		3336
		3337	Initialises and configures the cleanup watcher - it has no parameters of
		3338	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3339	pointless, I assure you.
		3340
		3341	=back
		3342
		3343	Example: Register an atexit handler to destroy the default loop, so any
		3344	cleanup functions are called.
		3345
		3346	static void
		3347	program_exits (void)
		3348	{
		3349	ev_loop_destroy (EV_DEFAULT_UC);
		3350	}
		3351
		3352	...
		3353	atexit (program_exits);
		3354
		3355
3031	=head2 C<ev_async> - how to wake up an event loop	3356	=head2 C<ev_async> - how to wake up an event loop
3032		3357
3033	In general, you cannot use an C<ev_run> from multiple threads or other	3358	In general, you cannot use an C<ev_loop> from multiple threads or other
3034	asynchronous sources such as signal handlers (as opposed to multiple event	3359	asynchronous sources such as signal handlers (as opposed to multiple event
3035	loops - those are of course safe to use in different threads).	3360	loops - those are of course safe to use in different threads).
3036		3361
3037	Sometimes, however, you need to wake up an event loop you do not control,	3362	Sometimes, however, you need to wake up an event loop you do not control,
3038	for example because it belongs to another thread. This is what C<ev_async>	3363	for example because it belongs to another thread. This is what C<ev_async>
…		…
3040	it by calling C<ev_async_send>, which is thread- and signal safe.	3365	it by calling C<ev_async_send>, which is thread- and signal safe.
3041		3366
3042	This functionality is very similar to C<ev_signal> watchers, as signals,	3367	This functionality is very similar to C<ev_signal> watchers, as signals,
3043	too, are asynchronous in nature, and signals, too, will be compressed	3368	too, are asynchronous in nature, and signals, too, will be compressed
3044	(i.e. the number of callback invocations may be less than the number of	3369	(i.e. the number of callback invocations may be less than the number of
3045	C<ev_async_sent> calls).	3370	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
3046		3371	of "global async watchers" by using a watcher on an otherwise unused
3047	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not	3372	signal, and C<ev_feed_signal> to signal this watcher from another thread,
3048	just the default loop.	3373	even without knowing which loop owns the signal.
3049		3374
3050	=head3 Queueing	3375	=head3 Queueing
3051		3376
3052	C<ev_async> does not support queueing of data in any way. The reason	3377	C<ev_async> does not support queueing of data in any way. The reason
3053	is that the author does not know of a simple (or any) algorithm for a	3378	is that the author does not know of a simple (or any) algorithm for a
…		…
3145	trust me.	3470	trust me.
3146		3471
3147	=item ev_async_send (loop, ev_async *)	3472	=item ev_async_send (loop, ev_async *)
3148		3473
3149	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3474	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
3150	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3475	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3476	returns.
		3477
3151	C<ev_feed_event>, this call is safe to do from other threads, signal or	3478	Unlike C<ev_feed_event>, this call is safe to do from other threads,
3152	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3479	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
3153	section below on what exactly this means).	3480	embedding section below on what exactly this means).
3154		3481
3155	Note that, as with other watchers in libev, multiple events might get	3482	Note that, as with other watchers in libev, multiple events might get
3156	compressed into a single callback invocation (another way to look at this	3483	compressed into a single callback invocation (another way to look at
3157	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,	3484	this is that C<ev_async> watchers are level-triggered: they are set on
3158	reset when the event loop detects that).	3485	C<ev_async_send>, reset when the event loop detects that).
3159		3486
3160	This call incurs the overhead of a system call only once per event loop	3487	This call incurs the overhead of at most one extra system call per event
3161	iteration, so while the overhead might be noticeable, it doesn't apply to	3488	loop iteration, if the event loop is blocked, and no syscall at all if
3162	repeated calls to C<ev_async_send> for the same event loop.	3489	the event loop (or your program) is processing events. That means that
		3490	repeated calls are basically free (there is no need to avoid calls for
		3491	performance reasons) and that the overhead becomes smaller (typically
		3492	zero) under load.
3163		3493
3164	=item bool = ev_async_pending (ev_async *)	3494	=item bool = ev_async_pending (ev_async *)
3165		3495
3166	Returns a non-zero value when C<ev_async_send> has been called on the	3496	Returns a non-zero value when C<ev_async_send> has been called on the
3167	watcher but the event has not yet been processed (or even noted) by the	3497	watcher but the event has not yet been processed (or even noted) by the
…		…
3222	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3552	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3223		3553
3224	=item ev_feed_fd_event (loop, int fd, int revents)	3554	=item ev_feed_fd_event (loop, int fd, int revents)
3225		3555
3226	Feed an event on the given fd, as if a file descriptor backend detected	3556	Feed an event on the given fd, as if a file descriptor backend detected
3227	the given events it.	3557	the given events.
3228		3558
3229	=item ev_feed_signal_event (loop, int signum)	3559	=item ev_feed_signal_event (loop, int signum)
3230		3560
3231	Feed an event as if the given signal occurred (C<loop> must be the default	3561	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3232	loop!).	3562	which is async-safe.
3233		3563
3234	=back	3564	=back
		3565
		3566
		3567	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3568
		3569	This section explains some common idioms that are not immediately
		3570	obvious. Note that examples are sprinkled over the whole manual, and this
		3571	section only contains stuff that wouldn't fit anywhere else.
		3572
		3573	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3574
		3575	Each watcher has, by default, a C<void *data> member that you can read
		3576	or modify at any time: libev will completely ignore it. This can be used
		3577	to associate arbitrary data with your watcher. If you need more data and
		3578	don't want to allocate memory separately and store a pointer to it in that
		3579	data member, you can also "subclass" the watcher type and provide your own
		3580	data:
		3581
		3582	struct my_io
		3583	{
		3584	ev_io io;
		3585	int otherfd;
		3586	void *somedata;
		3587	struct whatever *mostinteresting;
		3588	};
		3589
		3590	...
		3591	struct my_io w;
		3592	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3593
		3594	And since your callback will be called with a pointer to the watcher, you
		3595	can cast it back to your own type:
		3596
		3597	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3598	{
		3599	struct my_io *w = (struct my_io *)w_;
		3600	...
		3601	}
		3602
		3603	More interesting and less C-conformant ways of casting your callback
		3604	function type instead have been omitted.
		3605
		3606	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3607
		3608	Another common scenario is to use some data structure with multiple
		3609	embedded watchers, in effect creating your own watcher that combines
		3610	multiple libev event sources into one "super-watcher":
		3611
		3612	struct my_biggy
		3613	{
		3614	int some_data;
		3615	ev_timer t1;
		3616	ev_timer t2;
		3617	}
		3618
		3619	In this case getting the pointer to C<my_biggy> is a bit more
		3620	complicated: Either you store the address of your C<my_biggy> struct in
		3621	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3622	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3623	real programmers):
		3624
		3625	#include <stddef.h>
		3626
		3627	static void
		3628	t1_cb (EV_P_ ev_timer *w, int revents)
		3629	{
		3630	struct my_biggy big = (struct my_biggy *)
		3631	(((char *)w) - offsetof (struct my_biggy, t1));
		3632	}
		3633
		3634	static void
		3635	t2_cb (EV_P_ ev_timer *w, int revents)
		3636	{
		3637	struct my_biggy big = (struct my_biggy *)
		3638	(((char *)w) - offsetof (struct my_biggy, t2));
		3639	}
		3640
		3641	=head2 AVOIDING FINISHING BEFORE RETURNING
		3642
		3643	Often you have structures like this in event-based programs:
		3644
		3645	callback ()
		3646	{
		3647	free (request);
		3648	}
		3649
		3650	request = start_new_request (..., callback);
		3651
		3652	The intent is to start some "lengthy" operation. The C<request> could be
		3653	used to cancel the operation, or do other things with it.
		3654
		3655	It's not uncommon to have code paths in C<start_new_request> that
		3656	immediately invoke the callback, for example, to report errors. Or you add
		3657	some caching layer that finds that it can skip the lengthy aspects of the
		3658	operation and simply invoke the callback with the result.
		3659
		3660	The problem here is that this will happen I<before> C<start_new_request>
		3661	has returned, so C<request> is not set.
		3662
		3663	Even if you pass the request by some safer means to the callback, you
		3664	might want to do something to the request after starting it, such as
		3665	canceling it, which probably isn't working so well when the callback has
		3666	already been invoked.
		3667
		3668	A common way around all these issues is to make sure that
		3669	C<start_new_request> I<always> returns before the callback is invoked. If
		3670	C<start_new_request> immediately knows the result, it can artificially
		3671	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3672	example, or more sneakily, by reusing an existing (stopped) watcher and
		3673	pushing it into the pending queue:
		3674
		3675	ev_set_cb (watcher, callback);
		3676	ev_feed_event (EV_A_ watcher, 0);
		3677
		3678	This way, C<start_new_request> can safely return before the callback is
		3679	invoked, while not delaying callback invocation too much.
		3680
		3681	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3682
		3683	Often (especially in GUI toolkits) there are places where you have
		3684	I<modal> interaction, which is most easily implemented by recursively
		3685	invoking C<ev_run>.
		3686
		3687	This brings the problem of exiting - a callback might want to finish the
		3688	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3689	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3690	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3691	other combination: In these cases, a simple C<ev_break> will not work.
		3692
		3693	The solution is to maintain "break this loop" variable for each C<ev_run>
		3694	invocation, and use a loop around C<ev_run> until the condition is
		3695	triggered, using C<EVRUN_ONCE>:
		3696
		3697	// main loop
		3698	int exit_main_loop = 0;
		3699
		3700	while (!exit_main_loop)
		3701	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3702
		3703	// in a modal watcher
		3704	int exit_nested_loop = 0;
		3705
		3706	while (!exit_nested_loop)
		3707	ev_run (EV_A_ EVRUN_ONCE);
		3708
		3709	To exit from any of these loops, just set the corresponding exit variable:
		3710
		3711	// exit modal loop
		3712	exit_nested_loop = 1;
		3713
		3714	// exit main program, after modal loop is finished
		3715	exit_main_loop = 1;
		3716
		3717	// exit both
		3718	exit_main_loop = exit_nested_loop = 1;
		3719
		3720	=head2 THREAD LOCKING EXAMPLE
		3721
		3722	Here is a fictitious example of how to run an event loop in a different
		3723	thread from where callbacks are being invoked and watchers are
		3724	created/added/removed.
		3725
		3726	For a real-world example, see the C<EV::Loop::Async> perl module,
		3727	which uses exactly this technique (which is suited for many high-level
		3728	languages).
		3729
		3730	The example uses a pthread mutex to protect the loop data, a condition
		3731	variable to wait for callback invocations, an async watcher to notify the
		3732	event loop thread and an unspecified mechanism to wake up the main thread.
		3733
		3734	First, you need to associate some data with the event loop:
		3735
		3736	typedef struct {
		3737	mutex_t lock; /* global loop lock */
		3738	ev_async async_w;
		3739	thread_t tid;
		3740	cond_t invoke_cv;
		3741	} userdata;
		3742
		3743	void prepare_loop (EV_P)
		3744	{
		3745	// for simplicity, we use a static userdata struct.
		3746	static userdata u;
		3747
		3748	ev_async_init (&u->async_w, async_cb);
		3749	ev_async_start (EV_A_ &u->async_w);
		3750
		3751	pthread_mutex_init (&u->lock, 0);
		3752	pthread_cond_init (&u->invoke_cv, 0);
		3753
		3754	// now associate this with the loop
		3755	ev_set_userdata (EV_A_ u);
		3756	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3757	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3758
		3759	// then create the thread running ev_run
		3760	pthread_create (&u->tid, 0, l_run, EV_A);
		3761	}
		3762
		3763	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3764	solely to wake up the event loop so it takes notice of any new watchers
		3765	that might have been added:
		3766
		3767	static void
		3768	async_cb (EV_P_ ev_async *w, int revents)
		3769	{
		3770	// just used for the side effects
		3771	}
		3772
		3773	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3774	protecting the loop data, respectively.
		3775
		3776	static void
		3777	l_release (EV_P)
		3778	{
		3779	userdata *u = ev_userdata (EV_A);
		3780	pthread_mutex_unlock (&u->lock);
		3781	}
		3782
		3783	static void
		3784	l_acquire (EV_P)
		3785	{
		3786	userdata *u = ev_userdata (EV_A);
		3787	pthread_mutex_lock (&u->lock);
		3788	}
		3789
		3790	The event loop thread first acquires the mutex, and then jumps straight
		3791	into C<ev_run>:
		3792
		3793	void *
		3794	l_run (void *thr_arg)
		3795	{
		3796	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3797
		3798	l_acquire (EV_A);
		3799	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3800	ev_run (EV_A_ 0);
		3801	l_release (EV_A);
		3802
		3803	return 0;
		3804	}
		3805
		3806	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3807	signal the main thread via some unspecified mechanism (signals? pipe
		3808	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3809	have been called (in a while loop because a) spurious wakeups are possible
		3810	and b) skipping inter-thread-communication when there are no pending
		3811	watchers is very beneficial):
		3812
		3813	static void
		3814	l_invoke (EV_P)
		3815	{
		3816	userdata *u = ev_userdata (EV_A);
		3817
		3818	while (ev_pending_count (EV_A))
		3819	{
		3820	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3821	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3822	}
		3823	}
		3824
		3825	Now, whenever the main thread gets told to invoke pending watchers, it
		3826	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3827	thread to continue:
		3828
		3829	static void
		3830	real_invoke_pending (EV_P)
		3831	{
		3832	userdata *u = ev_userdata (EV_A);
		3833
		3834	pthread_mutex_lock (&u->lock);
		3835	ev_invoke_pending (EV_A);
		3836	pthread_cond_signal (&u->invoke_cv);
		3837	pthread_mutex_unlock (&u->lock);
		3838	}
		3839
		3840	Whenever you want to start/stop a watcher or do other modifications to an
		3841	event loop, you will now have to lock:
		3842
		3843	ev_timer timeout_watcher;
		3844	userdata *u = ev_userdata (EV_A);
		3845
		3846	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3847
		3848	pthread_mutex_lock (&u->lock);
		3849	ev_timer_start (EV_A_ &timeout_watcher);
		3850	ev_async_send (EV_A_ &u->async_w);
		3851	pthread_mutex_unlock (&u->lock);
		3852
		3853	Note that sending the C<ev_async> watcher is required because otherwise
		3854	an event loop currently blocking in the kernel will have no knowledge
		3855	about the newly added timer. By waking up the loop it will pick up any new
		3856	watchers in the next event loop iteration.
		3857
		3858	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3859
		3860	While the overhead of a callback that e.g. schedules a thread is small, it
		3861	is still an overhead. If you embed libev, and your main usage is with some
		3862	kind of threads or coroutines, you might want to customise libev so that
		3863	doesn't need callbacks anymore.
		3864
		3865	Imagine you have coroutines that you can switch to using a function
		3866	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3867	and that due to some magic, the currently active coroutine is stored in a
		3868	global called C<current_coro>. Then you can build your own "wait for libev
		3869	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3870	the differing C<;> conventions):
		3871
		3872	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3873	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3874
		3875	That means instead of having a C callback function, you store the
		3876	coroutine to switch to in each watcher, and instead of having libev call
		3877	your callback, you instead have it switch to that coroutine.
		3878
		3879	A coroutine might now wait for an event with a function called
		3880	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3881	matter when, or whether the watcher is active or not when this function is
		3882	called):
		3883
		3884	void
		3885	wait_for_event (ev_watcher *w)
		3886	{
		3887	ev_set_cb (w, current_coro);
		3888	switch_to (libev_coro);
		3889	}
		3890
		3891	That basically suspends the coroutine inside C<wait_for_event> and
		3892	continues the libev coroutine, which, when appropriate, switches back to
		3893	this or any other coroutine.
		3894
		3895	You can do similar tricks if you have, say, threads with an event queue -
		3896	instead of storing a coroutine, you store the queue object and instead of
		3897	switching to a coroutine, you push the watcher onto the queue and notify
		3898	any waiters.
		3899
		3900	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		3901	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3902
		3903	// my_ev.h
		3904	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3905	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3906	#include "../libev/ev.h"
		3907
		3908	// my_ev.c
		3909	#define EV_H "my_ev.h"
		3910	#include "../libev/ev.c"
		3911
		3912	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3913	F<my_ev.c> into your project. When properly specifying include paths, you
		3914	can even use F<ev.h> as header file name directly.
3235		3915
3236		3916
3237	=head1 LIBEVENT EMULATION	3917	=head1 LIBEVENT EMULATION
3238		3918
3239	Libev offers a compatibility emulation layer for libevent. It cannot	3919	Libev offers a compatibility emulation layer for libevent. It cannot
3240	emulate the internals of libevent, so here are some usage hints:	3920	emulate the internals of libevent, so here are some usage hints:
3241		3921
3242	=over 4	3922	=over 4
		3923
		3924	=item * Only the libevent-1.4.1-beta API is being emulated.
		3925
		3926	This was the newest libevent version available when libev was implemented,
		3927	and is still mostly unchanged in 2010.
3243		3928
3244	=item * Use it by including <event.h>, as usual.	3929	=item * Use it by including <event.h>, as usual.
3245		3930
3246	=item * The following members are fully supported: ev_base, ev_callback,	3931	=item * The following members are fully supported: ev_base, ev_callback,
3247	ev_arg, ev_fd, ev_res, ev_events.	3932	ev_arg, ev_fd, ev_res, ev_events.
…		…
3253	=item * Priorities are not currently supported. Initialising priorities	3938	=item * Priorities are not currently supported. Initialising priorities
3254	will fail and all watchers will have the same priority, even though there	3939	will fail and all watchers will have the same priority, even though there
3255	is an ev_pri field.	3940	is an ev_pri field.
3256		3941
3257	=item * In libevent, the last base created gets the signals, in libev, the	3942	=item * In libevent, the last base created gets the signals, in libev, the
3258	first base created (== the default loop) gets the signals.	3943	base that registered the signal gets the signals.
3259		3944
3260	=item * Other members are not supported.	3945	=item * Other members are not supported.
3261		3946
3262	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3947	=item * The libev emulation is I<not> ABI compatible to libevent, you need
3263	to use the libev header file and library.	3948	to use the libev header file and library.
3264		3949
3265	=back	3950	=back
3266		3951
3267	=head1 C++ SUPPORT	3952	=head1 C++ SUPPORT
		3953
		3954	=head2 C API
		3955
		3956	The normal C API should work fine when used from C++: both ev.h and the
		3957	libev sources can be compiled as C++. Therefore, code that uses the C API
		3958	will work fine.
		3959
		3960	Proper exception specifications might have to be added to callbacks passed
		3961	to libev: exceptions may be thrown only from watcher callbacks, all
		3962	other callbacks (allocator, syserr, loop acquire/release and periodic
		3963	reschedule callbacks) must not throw exceptions, and might need a C<throw
		3964	()> specification. If you have code that needs to be compiled as both C
		3965	and C++ you can use the C<EV_THROW> macro for this:
		3966
		3967	static void
		3968	fatal_error (const char *msg) EV_THROW
		3969	{
		3970	perror (msg);
		3971	abort ();
		3972	}
		3973
		3974	...
		3975	ev_set_syserr_cb (fatal_error);
		3976
		3977	The only API functions that can currently throw exceptions are C<ev_run>,
		3978	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		3979	because it runs cleanup watchers).
		3980
		3981	Throwing exceptions in watcher callbacks is only supported if libev itself
		3982	is compiled with a C++ compiler or your C and C++ environments allow
		3983	throwing exceptions through C libraries (most do).
		3984
		3985	=head2 C++ API
3268		3986
3269	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3987	Libev comes with some simplistic wrapper classes for C++ that mainly allow
3270	you to use some convenience methods to start/stop watchers and also change	3988	you to use some convenience methods to start/stop watchers and also change
3271	the callback model to a model using method callbacks on objects.	3989	the callback model to a model using method callbacks on objects.
3272		3990
3273	To use it,	3991	To use it,
3274		3992
3275	#include <ev++.h>	3993	#include <ev++.h>
3276		3994
3277	This automatically includes F<ev.h> and puts all of its definitions (many	3995	This automatically includes F<ev.h> and puts all of its definitions (many
3278	of them macros) into the global namespace. All C++ specific things are	3996	of them macros) into the global namespace. All C++ specific things are
3279	put into the C<ev> namespace. It should support all the same embedding	3997	put into the C<ev> namespace. It should support all the same embedding
…		…
3282	Care has been taken to keep the overhead low. The only data member the C++	4000	Care has been taken to keep the overhead low. The only data member the C++
3283	classes add (compared to plain C-style watchers) is the event loop pointer	4001	classes add (compared to plain C-style watchers) is the event loop pointer
3284	that the watcher is associated with (or no additional members at all if	4002	that the watcher is associated with (or no additional members at all if
3285	you disable C<EV_MULTIPLICITY> when embedding libev).	4003	you disable C<EV_MULTIPLICITY> when embedding libev).
3286		4004
3287	Currently, functions, and static and non-static member functions can be	4005	Currently, functions, static and non-static member functions and classes
3288	used as callbacks. Other types should be easy to add as long as they only	4006	with C<operator ()> can be used as callbacks. Other types should be easy
3289	need one additional pointer for context. If you need support for other	4007	to add as long as they only need one additional pointer for context. If
3290	types of functors please contact the author (preferably after implementing	4008	you need support for other types of functors please contact the author
3291	it).	4009	(preferably after implementing it).
		4010
		4011	For all this to work, your C++ compiler either has to use the same calling
		4012	conventions as your C compiler (for static member functions), or you have
		4013	to embed libev and compile libev itself as C++.
3292		4014
3293	Here is a list of things available in the C<ev> namespace:	4015	Here is a list of things available in the C<ev> namespace:
3294		4016
3295	=over 4	4017	=over 4
3296		4018
…		…
3306	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	4028	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
3307		4029
3308	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4030	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
3309	the same name in the C<ev> namespace, with the exception of C<ev_signal>	4031	the same name in the C<ev> namespace, with the exception of C<ev_signal>
3310	which is called C<ev::sig> to avoid clashes with the C<signal> macro	4032	which is called C<ev::sig> to avoid clashes with the C<signal> macro
3311	defines by many implementations.	4033	defined by many implementations.
3312		4034
3313	All of those classes have these methods:	4035	All of those classes have these methods:
3314		4036
3315	=over 4	4037	=over 4
3316		4038
…		…
3378	void operator() (ev::io &w, int revents)	4100	void operator() (ev::io &w, int revents)
3379	{	4101	{
3380	...	4102	...
3381	}	4103	}
3382	}	4104	}
3383		4105
3384	myfunctor f;	4106	myfunctor f;
3385		4107
3386	ev::io w;	4108	ev::io w;
3387	w.set (&f);	4109	w.set (&f);
3388		4110
…		…
3406	Associates a different C<struct ev_loop> with this watcher. You can only	4128	Associates a different C<struct ev_loop> with this watcher. You can only
3407	do this when the watcher is inactive (and not pending either).	4129	do this when the watcher is inactive (and not pending either).
3408		4130
3409	=item w->set ([arguments])	4131	=item w->set ([arguments])
3410		4132
3411	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this	4133	Basically the same as C<ev_TYPE_set> (except for C<ev::embed> watchers>),
3412	method or a suitable start method must be called at least once. Unlike the	4134	with the same arguments. Either this method or a suitable start method
3413	C counterpart, an active watcher gets automatically stopped and restarted	4135	must be called at least once. Unlike the C counterpart, an active watcher
3414	when reconfiguring it with this method.	4136	gets automatically stopped and restarted when reconfiguring it with this
		4137	method.
		4138
		4139	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4140	clashing with the C<set (loop)> method.
3415		4141
3416	=item w->start ()	4142	=item w->start ()
3417		4143
3418	Starts the watcher. Note that there is no C<loop> argument, as the	4144	Starts the watcher. Note that there is no C<loop> argument, as the
3419	constructor already stores the event loop.	4145	constructor already stores the event loop.
…		…
3449	watchers in the constructor.	4175	watchers in the constructor.
3450		4176
3451	class myclass	4177	class myclass
3452	{	4178	{
3453	ev::io io ; void io_cb (ev::io &w, int revents);	4179	ev::io io ; void io_cb (ev::io &w, int revents);
3454	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);	4180	ev::io io2 ; void io2_cb (ev::io &w, int revents);
3455	ev::idle idle; void idle_cb (ev::idle &w, int revents);	4181	ev::idle idle; void idle_cb (ev::idle &w, int revents);
3456		4182
3457	myclass (int fd)	4183	myclass (int fd)
3458	{	4184	{
3459	io .set <myclass, &myclass::io_cb > (this);	4185	io .set <myclass, &myclass::io_cb > (this);
…		…
3510	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.	4236	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
3511		4237
3512	=item D	4238	=item D
3513		4239
3514	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4240	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
3515	be found at L<http://proj.llucax.com.ar/wiki/evd>.	4241	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
3516		4242
3517	=item Ocaml	4243	=item Ocaml
3518		4244
3519	Erkki Seppala has written Ocaml bindings for libev, to be found at	4245	Erkki Seppala has written Ocaml bindings for libev, to be found at
3520	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	4246	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
…		…
3523		4249
3524	Brian Maher has written a partial interface to libev for lua (at the	4250	Brian Maher has written a partial interface to libev for lua (at the
3525	time of this writing, only C<ev_io> and C<ev_timer>), to be found at	4251	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
3526	L<http://github.com/brimworks/lua-ev>.	4252	L<http://github.com/brimworks/lua-ev>.
3527		4253
		4254	=item Javascript
		4255
		4256	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4257
		4258	=item Others
		4259
		4260	There are others, and I stopped counting.
		4261
3528	=back	4262	=back
3529		4263
3530		4264
3531	=head1 MACRO MAGIC	4265	=head1 MACRO MAGIC
3532		4266
…		…
3568	suitable for use with C<EV_A>.	4302	suitable for use with C<EV_A>.
3569		4303
3570	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4304	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
3571		4305
3572	Similar to the other two macros, this gives you the value of the default	4306	Similar to the other two macros, this gives you the value of the default
3573	loop, if multiple loops are supported ("ev loop default").	4307	loop, if multiple loops are supported ("ev loop default"). The default loop
		4308	will be initialised if it isn't already initialised.
		4309
		4310	For non-multiplicity builds, these macros do nothing, so you always have
		4311	to initialise the loop somewhere.
3574		4312
3575	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4313	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
3576		4314
3577	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4315	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
3578	default loop has been initialised (C<UC> == unchecked). Their behaviour	4316	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
3723	supported). It will also not define any of the structs usually found in	4461	supported). It will also not define any of the structs usually found in
3724	F<event.h> that are not directly supported by the libev core alone.	4462	F<event.h> that are not directly supported by the libev core alone.
3725		4463
3726	In standalone mode, libev will still try to automatically deduce the	4464	In standalone mode, libev will still try to automatically deduce the
3727	configuration, but has to be more conservative.	4465	configuration, but has to be more conservative.
		4466
		4467	=item EV_USE_FLOOR
		4468
		4469	If defined to be C<1>, libev will use the C<floor ()> function for its
		4470	periodic reschedule calculations, otherwise libev will fall back on a
		4471	portable (slower) implementation. If you enable this, you usually have to
		4472	link against libm or something equivalent. Enabling this when the C<floor>
		4473	function is not available will fail, so the safe default is to not enable
		4474	this.
3728		4475
3729	=item EV_USE_MONOTONIC	4476	=item EV_USE_MONOTONIC
3730		4477
3731	If defined to be C<1>, libev will try to detect the availability of the	4478	If defined to be C<1>, libev will try to detect the availability of the
3732	monotonic clock option at both compile time and runtime. Otherwise no	4479	monotonic clock option at both compile time and runtime. Otherwise no
…		…
3817		4564
3818	If programs implement their own fd to handle mapping on win32, then this	4565	If programs implement their own fd to handle mapping on win32, then this
3819	macro can be used to override the C<close> function, useful to unregister	4566	macro can be used to override the C<close> function, useful to unregister
3820	file descriptors again. Note that the replacement function has to close	4567	file descriptors again. Note that the replacement function has to close
3821	the underlying OS handle.	4568	the underlying OS handle.
		4569
		4570	=item EV_USE_WSASOCKET
		4571
		4572	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4573	communication socket, which works better in some environments. Otherwise,
		4574	the normal C<socket> function will be used, which works better in other
		4575	environments.
3822		4576
3823	=item EV_USE_POLL	4577	=item EV_USE_POLL
3824		4578
3825	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4579	If defined to be C<1>, libev will compile in support for the C<poll>(2)
3826	backend. Otherwise it will be enabled on non-win32 platforms. It	4580	backend. Otherwise it will be enabled on non-win32 platforms. It
…		…
3862	If defined to be C<1>, libev will compile in support for the Linux inotify	4616	If defined to be C<1>, libev will compile in support for the Linux inotify
3863	interface to speed up C<ev_stat> watchers. Its actual availability will	4617	interface to speed up C<ev_stat> watchers. Its actual availability will
3864	be detected at runtime. If undefined, it will be enabled if the headers	4618	be detected at runtime. If undefined, it will be enabled if the headers
3865	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4619	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
3866		4620
		4621	=item EV_NO_SMP
		4622
		4623	If defined to be C<1>, libev will assume that memory is always coherent
		4624	between threads, that is, threads can be used, but threads never run on
		4625	different cpus (or different cpu cores). This reduces dependencies
		4626	and makes libev faster.
		4627
		4628	=item EV_NO_THREADS
		4629
		4630	If defined to be C<1>, libev will assume that it will never be called from
		4631	different threads (that includes signal handlers), which is a stronger
		4632	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4633	libev faster.
		4634
3867	=item EV_ATOMIC_T	4635	=item EV_ATOMIC_T
3868		4636
3869	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4637	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
3870	access is atomic with respect to other threads or signal contexts. No such	4638	access is atomic with respect to other threads or signal contexts. No
3871	type is easily found in the C language, so you can provide your own type	4639	such type is easily found in the C language, so you can provide your own
3872	that you know is safe for your purposes. It is used both for signal handler "locking"	4640	type that you know is safe for your purposes. It is used both for signal
3873	as well as for signal and thread safety in C<ev_async> watchers.	4641	handler "locking" as well as for signal and thread safety in C<ev_async>
		4642	watchers.
3874		4643
3875	In the absence of this define, libev will use C<sig_atomic_t volatile>	4644	In the absence of this define, libev will use C<sig_atomic_t volatile>
3876	(from F<signal.h>), which is usually good enough on most platforms.	4645	(from F<signal.h>), which is usually good enough on most platforms.
3877		4646
3878	=item EV_H (h)	4647	=item EV_H (h)
…		…
3905	will have the C<struct ev_loop *> as first argument, and you can create	4674	will have the C<struct ev_loop *> as first argument, and you can create
3906	additional independent event loops. Otherwise there will be no support	4675	additional independent event loops. Otherwise there will be no support
3907	for multiple event loops and there is no first event loop pointer	4676	for multiple event loops and there is no first event loop pointer
3908	argument. Instead, all functions act on the single default loop.	4677	argument. Instead, all functions act on the single default loop.
3909		4678
		4679	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4680	default loop when multiplicity is switched off - you always have to
		4681	initialise the loop manually in this case.
		4682
3910	=item EV_MINPRI	4683	=item EV_MINPRI
3911		4684
3912	=item EV_MAXPRI	4685	=item EV_MAXPRI
3913		4686
3914	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4687	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
3950	#define EV_USE_POLL 1	4723	#define EV_USE_POLL 1
3951	#define EV_CHILD_ENABLE 1	4724	#define EV_CHILD_ENABLE 1
3952	#define EV_ASYNC_ENABLE 1	4725	#define EV_ASYNC_ENABLE 1
3953		4726
3954	The actual value is a bitset, it can be a combination of the following	4727	The actual value is a bitset, it can be a combination of the following
3955	values:	4728	values (by default, all of these are enabled):
3956		4729
3957	=over 4	4730	=over 4
3958		4731
3959	=item C<1> - faster/larger code	4732	=item C<1> - faster/larger code
3960		4733
…		…
3964	code size by roughly 30% on amd64).	4737	code size by roughly 30% on amd64).
3965		4738
3966	When optimising for size, use of compiler flags such as C<-Os> with	4739	When optimising for size, use of compiler flags such as C<-Os> with
3967	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of	4740	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
3968	assertions.	4741	assertions.
		4742
		4743	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4744	(e.g. gcc with C<-Os>).
3969		4745
3970	=item C<2> - faster/larger data structures	4746	=item C<2> - faster/larger data structures
3971		4747
3972	Replaces the small 2-heap for timer management by a faster 4-heap, larger	4748	Replaces the small 2-heap for timer management by a faster 4-heap, larger
3973	hash table sizes and so on. This will usually further increase code size	4749	hash table sizes and so on. This will usually further increase code size
3974	and can additionally have an effect on the size of data structures at	4750	and can additionally have an effect on the size of data structures at
3975	runtime.	4751	runtime.
3976		4752
		4753	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4754	(e.g. gcc with C<-Os>).
		4755
3977	=item C<4> - full API configuration	4756	=item C<4> - full API configuration
3978		4757
3979	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and	4758	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
3980	enables multiplicity (C<EV_MULTIPLICITY>=1).	4759	enables multiplicity (C<EV_MULTIPLICITY>=1).
3981		4760
…		…
4011		4790
4012	With an intelligent-enough linker (gcc+binutils are intelligent enough	4791	With an intelligent-enough linker (gcc+binutils are intelligent enough
4013	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by	4792	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
4014	your program might be left out as well - a binary starting a timer and an	4793	your program might be left out as well - a binary starting a timer and an
4015	I/O watcher then might come out at only 5Kb.	4794	I/O watcher then might come out at only 5Kb.
		4795
		4796	=item EV_API_STATIC
		4797
		4798	If this symbol is defined (by default it is not), then all identifiers
		4799	will have static linkage. This means that libev will not export any
		4800	identifiers, and you cannot link against libev anymore. This can be useful
		4801	when you embed libev, only want to use libev functions in a single file,
		4802	and do not want its identifiers to be visible.
		4803
		4804	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4805	wants to use libev.
		4806
		4807	This option only works when libev is compiled with a C compiler, as C++
		4808	doesn't support the required declaration syntax.
4016		4809
4017	=item EV_AVOID_STDIO	4810	=item EV_AVOID_STDIO
4018		4811
4019	If this is set to C<1> at compiletime, then libev will avoid using stdio	4812	If this is set to C<1> at compiletime, then libev will avoid using stdio
4020	functions (printf, scanf, perror etc.). This will increase the code size	4813	functions (printf, scanf, perror etc.). This will increase the code size
…		…
4164	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4957	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4165		4958
4166	#include "ev_cpp.h"	4959	#include "ev_cpp.h"
4167	#include "ev.c"	4960	#include "ev.c"
4168		4961
4169	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	4962	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4170		4963
4171	=head2 THREADS AND COROUTINES	4964	=head2 THREADS AND COROUTINES
4172		4965
4173	=head3 THREADS	4966	=head3 THREADS
4174		4967
…		…
4225	default loop and triggering an C<ev_async> watcher from the default loop	5018	default loop and triggering an C<ev_async> watcher from the default loop
4226	watcher callback into the event loop interested in the signal.	5019	watcher callback into the event loop interested in the signal.
4227		5020
4228	=back	5021	=back
4229		5022
4230	=head4 THREAD LOCKING EXAMPLE	5023	See also L</THREAD LOCKING EXAMPLE>.
4231
4232	Here is a fictitious example of how to run an event loop in a different
4233	thread than where callbacks are being invoked and watchers are
4234	created/added/removed.
4235
4236	For a real-world example, see the C<EV::Loop::Async> perl module,
4237	which uses exactly this technique (which is suited for many high-level
4238	languages).
4239
4240	The example uses a pthread mutex to protect the loop data, a condition
4241	variable to wait for callback invocations, an async watcher to notify the
4242	event loop thread and an unspecified mechanism to wake up the main thread.
4243
4244	First, you need to associate some data with the event loop:
4245
4246	typedef struct {
4247	mutex_t lock; /* global loop lock */
4248	ev_async async_w;
4249	thread_t tid;
4250	cond_t invoke_cv;
4251	} userdata;
4252
4253	void prepare_loop (EV_P)
4254	{
4255	// for simplicity, we use a static userdata struct.
4256	static userdata u;
4257
4258	ev_async_init (&u->async_w, async_cb);
4259	ev_async_start (EV_A_ &u->async_w);
4260
4261	pthread_mutex_init (&u->lock, 0);
4262	pthread_cond_init (&u->invoke_cv, 0);
4263
4264	// now associate this with the loop
4265	ev_set_userdata (EV_A_ u);
4266	ev_set_invoke_pending_cb (EV_A_ l_invoke);
4267	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4268
4269	// then create the thread running ev_loop
4270	pthread_create (&u->tid, 0, l_run, EV_A);
4271	}
4272
4273	The callback for the C<ev_async> watcher does nothing: the watcher is used
4274	solely to wake up the event loop so it takes notice of any new watchers
4275	that might have been added:
4276
4277	static void
4278	async_cb (EV_P_ ev_async *w, int revents)
4279	{
4280	// just used for the side effects
4281	}
4282
4283	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
4284	protecting the loop data, respectively.
4285
4286	static void
4287	l_release (EV_P)
4288	{
4289	userdata *u = ev_userdata (EV_A);
4290	pthread_mutex_unlock (&u->lock);
4291	}
4292
4293	static void
4294	l_acquire (EV_P)
4295	{
4296	userdata *u = ev_userdata (EV_A);
4297	pthread_mutex_lock (&u->lock);
4298	}
4299
4300	The event loop thread first acquires the mutex, and then jumps straight
4301	into C<ev_run>:
4302
4303	void *
4304	l_run (void *thr_arg)
4305	{
4306	struct ev_loop *loop = (struct ev_loop *)thr_arg;
4307
4308	l_acquire (EV_A);
4309	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4310	ev_run (EV_A_ 0);
4311	l_release (EV_A);
4312
4313	return 0;
4314	}
4315
4316	Instead of invoking all pending watchers, the C<l_invoke> callback will
4317	signal the main thread via some unspecified mechanism (signals? pipe
4318	writes? C<Async::Interrupt>?) and then waits until all pending watchers
4319	have been called (in a while loop because a) spurious wakeups are possible
4320	and b) skipping inter-thread-communication when there are no pending
4321	watchers is very beneficial):
4322
4323	static void
4324	l_invoke (EV_P)
4325	{
4326	userdata *u = ev_userdata (EV_A);
4327
4328	while (ev_pending_count (EV_A))
4329	{
4330	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4331	pthread_cond_wait (&u->invoke_cv, &u->lock);
4332	}
4333	}
4334
4335	Now, whenever the main thread gets told to invoke pending watchers, it
4336	will grab the lock, call C<ev_invoke_pending> and then signal the loop
4337	thread to continue:
4338
4339	static void
4340	real_invoke_pending (EV_P)
4341	{
4342	userdata *u = ev_userdata (EV_A);
4343
4344	pthread_mutex_lock (&u->lock);
4345	ev_invoke_pending (EV_A);
4346	pthread_cond_signal (&u->invoke_cv);
4347	pthread_mutex_unlock (&u->lock);
4348	}
4349
4350	Whenever you want to start/stop a watcher or do other modifications to an
4351	event loop, you will now have to lock:
4352
4353	ev_timer timeout_watcher;
4354	userdata *u = ev_userdata (EV_A);
4355
4356	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4357
4358	pthread_mutex_lock (&u->lock);
4359	ev_timer_start (EV_A_ &timeout_watcher);
4360	ev_async_send (EV_A_ &u->async_w);
4361	pthread_mutex_unlock (&u->lock);
4362
4363	Note that sending the C<ev_async> watcher is required because otherwise
4364	an event loop currently blocking in the kernel will have no knowledge
4365	about the newly added timer. By waking up the loop it will pick up any new
4366	watchers in the next event loop iteration.
4367		5024
4368	=head3 COROUTINES	5025	=head3 COROUTINES
4369		5026
4370	Libev is very accommodating to coroutines ("cooperative threads"):	5027	Libev is very accommodating to coroutines ("cooperative threads"):
4371	libev fully supports nesting calls to its functions from different	5028	libev fully supports nesting calls to its functions from different
…		…
4467	=head3 C<kqueue> is buggy	5124	=head3 C<kqueue> is buggy
4468		5125
4469	The kqueue syscall is broken in all known versions - most versions support	5126	The kqueue syscall is broken in all known versions - most versions support
4470	only sockets, many support pipes.	5127	only sockets, many support pipes.
4471		5128
4472	Libev tries to work around this by not using C<kqueue> by default on	5129	Libev tries to work around this by not using C<kqueue> by default on this
4473	this rotten platform, but of course you can still ask for it when creating	5130	rotten platform, but of course you can still ask for it when creating a
4474	a loop.	5131	loop - embedding a socket-only kqueue loop into a select-based one is
		5132	probably going to work well.
4475		5133
4476	=head3 C<poll> is buggy	5134	=head3 C<poll> is buggy
4477		5135
4478	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>	5136	Instead of fixing C<kqueue>, Apple replaced their (working) C<poll>
4479	implementation by something calling C<kqueue> internally around the 10.5.6	5137	implementation by something calling C<kqueue> internally around the 10.5.6
…		…
4498		5156
4499	=head3 C<errno> reentrancy	5157	=head3 C<errno> reentrancy
4500		5158
4501	The default compile environment on Solaris is unfortunately so	5159	The default compile environment on Solaris is unfortunately so
4502	thread-unsafe that you can't even use components/libraries compiled	5160	thread-unsafe that you can't even use components/libraries compiled
4503	without C<-D_REENTRANT> (as long as they use C<errno>), which, of course,	5161	without C<-D_REENTRANT> in a threaded program, which, of course, isn't
4504	isn't defined by default.	5162	defined by default. A valid, if stupid, implementation choice.
4505		5163
4506	If you want to use libev in threaded environments you have to make sure	5164	If you want to use libev in threaded environments you have to make sure
4507	it's compiled with C<_REENTRANT> defined.	5165	it's compiled with C<_REENTRANT> defined.
4508		5166
4509	=head3 Event port backend	5167	=head3 Event port backend
4510		5168
4511	The scalable event interface for Solaris is called "event ports". Unfortunately,	5169	The scalable event interface for Solaris is called "event
4512	this mechanism is very buggy. If you run into high CPU usage, your program	5170	ports". Unfortunately, this mechanism is very buggy in all major
		5171	releases. If you run into high CPU usage, your program freezes or you get
4513	freezes or you get a large number of spurious wakeups, make sure you have	5172	a large number of spurious wakeups, make sure you have all the relevant
4514	all the relevant and latest kernel patches applied. No, I don't know which	5173	and latest kernel patches applied. No, I don't know which ones, but there
4515	ones, but there are multiple ones.	5174	are multiple ones to apply, and afterwards, event ports actually work
		5175	great.
4516		5176
4517	If you can't get it to work, you can try running the program by setting	5177	If you can't get it to work, you can try running the program by setting
4518	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and	5178	the environment variable C<LIBEV_FLAGS=3> to only allow C<poll> and
4519	C<select> backends.	5179	C<select> backends.
4520		5180
4521	=head2 AIX POLL BUG	5181	=head2 AIX POLL BUG
4522		5182
4523	AIX unfortunately has a broken C<poll.h> header. Libev works around	5183	AIX unfortunately has a broken C<poll.h> header. Libev works around
4524	this by trying to avoid the poll backend altogether (i.e. it's not even	5184	this by trying to avoid the poll backend altogether (i.e. it's not even
4525	compiled in), which normally isn't a big problem as C<select> works fine	5185	compiled in), which normally isn't a big problem as C<select> works fine
4526	with large bitsets, and AIX is dead anyway.	5186	with large bitsets on AIX, and AIX is dead anyway.
4527		5187
4528	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS	5188	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
4529		5189
4530	=head3 General issues	5190	=head3 General issues
4531		5191
…		…
4533	requires, and its I/O model is fundamentally incompatible with the POSIX	5193	requires, and its I/O model is fundamentally incompatible with the POSIX
4534	model. Libev still offers limited functionality on this platform in	5194	model. Libev still offers limited functionality on this platform in
4535	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5195	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
4536	descriptors. This only applies when using Win32 natively, not when using	5196	descriptors. This only applies when using Win32 natively, not when using
4537	e.g. cygwin. Actually, it only applies to the microsofts own compilers,	5197	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4538	as every compielr comes with a slightly differently broken/incompatible	5198	as every compiler comes with a slightly differently broken/incompatible
4539	environment.	5199	environment.
4540		5200
4541	Lifting these limitations would basically require the full	5201	Lifting these limitations would basically require the full
4542	re-implementation of the I/O system. If you are into this kind of thing,	5202	re-implementation of the I/O system. If you are into this kind of thing,
4543	then note that glib does exactly that for you in a very portable way (note	5203	then note that glib does exactly that for you in a very portable way (note
…		…
4637	structure (guaranteed by POSIX but not by ISO C for example), but it also	5297	structure (guaranteed by POSIX but not by ISO C for example), but it also
4638	assumes that the same (machine) code can be used to call any watcher	5298	assumes that the same (machine) code can be used to call any watcher
4639	callback: The watcher callbacks have different type signatures, but libev	5299	callback: The watcher callbacks have different type signatures, but libev
4640	calls them using an C<ev_watcher *> internally.	5300	calls them using an C<ev_watcher *> internally.
4641		5301
		5302	=item pointer accesses must be thread-atomic
		5303
		5304	Accessing a pointer value must be atomic, it must both be readable and
		5305	writable in one piece - this is the case on all current architectures.
		5306
4642	=item C<sig_atomic_t volatile> must be thread-atomic as well	5307	=item C<sig_atomic_t volatile> must be thread-atomic as well
4643		5308
4644	The type C<sig_atomic_t volatile> (or whatever is defined as	5309	The type C<sig_atomic_t volatile> (or whatever is defined as
4645	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different	5310	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
4646	threads. This is not part of the specification for C<sig_atomic_t>, but is	5311	threads. This is not part of the specification for C<sig_atomic_t>, but is
…		…
4654	thread" or will block signals process-wide, both behaviours would	5319	thread" or will block signals process-wide, both behaviours would
4655	be compatible with libev. Interaction between C<sigprocmask> and	5320	be compatible with libev. Interaction between C<sigprocmask> and
4656	C<pthread_sigmask> could complicate things, however.	5321	C<pthread_sigmask> could complicate things, however.
4657		5322
4658	The most portable way to handle signals is to block signals in all threads	5323	The most portable way to handle signals is to block signals in all threads
4659	except the initial one, and run the default loop in the initial thread as	5324	except the initial one, and run the signal handling loop in the initial
4660	well.	5325	thread as well.
4661		5326
4662	=item C<long> must be large enough for common memory allocation sizes	5327	=item C<long> must be large enough for common memory allocation sizes
4663		5328
4664	To improve portability and simplify its API, libev uses C<long> internally	5329	To improve portability and simplify its API, libev uses C<long> internally
4665	instead of C<size_t> when allocating its data structures. On non-POSIX	5330	instead of C<size_t> when allocating its data structures. On non-POSIX
…		…
4671		5336
4672	The type C<double> is used to represent timestamps. It is required to	5337	The type C<double> is used to represent timestamps. It is required to
4673	have at least 51 bits of mantissa (and 9 bits of exponent), which is	5338	have at least 51 bits of mantissa (and 9 bits of exponent), which is
4674	good enough for at least into the year 4000 with millisecond accuracy	5339	good enough for at least into the year 4000 with millisecond accuracy
4675	(the design goal for libev). This requirement is overfulfilled by	5340	(the design goal for libev). This requirement is overfulfilled by
4676	implementations using IEEE 754, which is basically all existing ones. With	5341	implementations using IEEE 754, which is basically all existing ones.
		5342
4677	IEEE 754 doubles, you get microsecond accuracy until at least 2200.	5343	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5344	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5345	is either obsolete or somebody patched it to use C<long double> or
		5346	something like that, just kidding).
4678		5347
4679	=back	5348	=back
4680		5349
4681	If you know of other additional requirements drop me a note.	5350	If you know of other additional requirements drop me a note.
4682		5351
…		…
4744	=item Processing ev_async_send: O(number_of_async_watchers)	5413	=item Processing ev_async_send: O(number_of_async_watchers)
4745		5414
4746	=item Processing signals: O(max_signal_number)	5415	=item Processing signals: O(max_signal_number)
4747		5416
4748	Sending involves a system call I<iff> there were no other C<ev_async_send>	5417	Sending involves a system call I<iff> there were no other C<ev_async_send>
4749	calls in the current loop iteration. Checking for async and signal events	5418	calls in the current loop iteration and the loop is currently
		5419	blocked. Checking for async and signal events involves iterating over all
4750	involves iterating over all running async watchers or all signal numbers.	5420	running async watchers or all signal numbers.
4751		5421
4752	=back	5422	=back
4753		5423
4754		5424
4755	=head1 PORTING FROM LIBEV 3.X TO 4.X	5425	=head1 PORTING FROM LIBEV 3.X TO 4.X
4756		5426
4757	The major version 4 introduced some minor incompatible changes to the API.	5427	The major version 4 introduced some incompatible changes to the API.
4758		5428
4759	At the moment, the C<ev.h> header file tries to implement superficial	5429	At the moment, the C<ev.h> header file provides compatibility definitions
4760	compatibility, so most programs should still compile. Those might be	5430	for all changes, so most programs should still compile. The compatibility
4761	removed in later versions of libev, so better update early than late.	5431	layer might be removed in later versions of libev, so better update to the
		5432	new API early than late.
4762		5433
4763	=over 4	5434	=over 4
		5435
		5436	=item C<EV_COMPAT3> backwards compatibility mechanism
		5437
		5438	The backward compatibility mechanism can be controlled by
		5439	C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
		5440	section.
		5441
		5442	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5443
		5444	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5445
		5446	ev_loop_destroy (EV_DEFAULT_UC);
		5447	ev_loop_fork (EV_DEFAULT);
4764		5448
4765	=item function/symbol renames	5449	=item function/symbol renames
4766		5450
4767	A number of functions and symbols have been renamed:	5451	A number of functions and symbols have been renamed:
4768		5452
…		…
4787	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme	5471	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
4788	as all other watcher types. Note that C<ev_loop_fork> is still called	5472	as all other watcher types. Note that C<ev_loop_fork> is still called
4789	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>	5473	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
4790	typedef.	5474	typedef.
4791		5475
4792	=item C<EV_COMPAT3> backwards compatibility mechanism
4793
4794	The backward compatibility mechanism can be controlled by
4795	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
4796	section.
4797
4798	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>	5476	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
4799		5477
4800	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different	5478	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
4801	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile	5479	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
4802	and work, but the library code will of course be larger.	5480	and work, but the library code will of course be larger.
…		…
4808		5486
4809	=over 4	5487	=over 4
4810		5488
4811	=item active	5489	=item active
4812		5490
4813	A watcher is active as long as it has been started (has been attached to	5491	A watcher is active as long as it has been started and not yet stopped.
4814	an event loop) but not yet stopped (disassociated from the event loop).	5492	See L</WATCHER STATES> for details.
4815		5493
4816	=item application	5494	=item application
4817		5495
4818	In this document, an application is whatever is using libev.	5496	In this document, an application is whatever is using libev.
		5497
		5498	=item backend
		5499
		5500	The part of the code dealing with the operating system interfaces.
4819		5501
4820	=item callback	5502	=item callback
4821		5503
4822	The address of a function that is called when some event has been	5504	The address of a function that is called when some event has been
4823	detected. Callbacks are being passed the event loop, the watcher that	5505	detected. Callbacks are being passed the event loop, the watcher that
4824	received the event, and the actual event bitset.	5506	received the event, and the actual event bitset.
4825		5507
4826	=item callback invocation	5508	=item callback/watcher invocation
4827		5509
4828	The act of calling the callback associated with a watcher.	5510	The act of calling the callback associated with a watcher.
4829		5511
4830	=item event	5512	=item event
4831		5513
…		…
4850	The model used to describe how an event loop handles and processes	5532	The model used to describe how an event loop handles and processes
4851	watchers and events.	5533	watchers and events.
4852		5534
4853	=item pending	5535	=item pending
4854		5536
4855	A watcher is pending as soon as the corresponding event has been detected,	5537	A watcher is pending as soon as the corresponding event has been
4856	and stops being pending as soon as the watcher will be invoked or its	5538	detected. See L</WATCHER STATES> for details.
4857	pending status is explicitly cleared by the application.
4858
4859	A watcher can be pending, but not active. Stopping a watcher also clears
4860	its pending status.
4861		5539
4862	=item real time	5540	=item real time
4863		5541
4864	The physical time that is observed. It is apparently strictly monotonic :)	5542	The physical time that is observed. It is apparently strictly monotonic :)
4865		5543
4866	=item wall-clock time	5544	=item wall-clock time
4867		5545
4868	The time and date as shown on clocks. Unlike real time, it can actually	5546	The time and date as shown on clocks. Unlike real time, it can actually
4869	be wrong and jump forwards and backwards, e.g. when the you adjust your	5547	be wrong and jump forwards and backwards, e.g. when you adjust your
4870	clock.	5548	clock.
4871		5549
4872	=item watcher	5550	=item watcher
4873		5551
4874	A data structure that describes interest in certain events. Watchers need	5552	A data structure that describes interest in certain events. Watchers need
4875	to be started (attached to an event loop) before they can receive events.	5553	to be started (attached to an event loop) before they can receive events.
4876		5554
4877	=item watcher invocation
4878
4879	The act of calling the callback associated with a watcher.
4880
4881	=back	5555	=back
4882		5556
4883	=head1 AUTHOR	5557	=head1 AUTHOR
4884		5558
4885	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.	5559	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5560	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
4886		5561

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