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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 this case unless libev 3 compatibility is disabled, as	330	I<not> optional in this case unless libev 3 compatibility is disabled, as
299	libev 3 had an C<ev_loop> function colliding with the struct name).	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		686
606	Like C<ev_default_destroy>, but destroys an event loop created by an
607	earlier call to C<ev_loop_new>.
608
609	=item ev_default_fork ()
610
611	This function sets a flag that causes subsequent C<ev_run> iterations	687	This function sets a flag that causes subsequent C<ev_run> iterations to
612	to reinitialise the kernel state for backends that have one. Despite the	688	reinitialise the kernel state for backends that have one. Despite the
613	name, you can call it anytime, but it makes most sense after forking, in	689	name, you can call it anytime, but it makes most sense after forking, in
614	the child process (or both child and parent, but that again makes little	690	the child process. You I<must> call it (or use C<EVFLAG_FORKCHECK>) in the
615	sense). You I<must> call it in the child before using any of the libev	691	child before resuming or calling C<ev_run>.
616	functions, and it will only take effect at the next C<ev_run> iteration.
617		692
618	Again, you I<have> to call it on I<any> loop that you want to re-use after	693	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	694	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	695	because some kernel interfaces *cough* I<kqueue> *cough* do funny things
621	during fork.	696	during fork.
622		697
623	On the other hand, you only need to call this function in the child	698	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	701	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	702	difference, but libev will usually detect this case on its own and do a
628	costly reset of the backend).	703	costly reset of the backend).
629		704
630	The function itself is quite fast and it's usually not a problem to call	705	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	706	it just in case after a fork.
632	quite nicely into a call to C<pthread_atfork>:
633		707
		708	Example: Automate calling C<ev_loop_fork> on the default loop when
		709	using pthreads.
		710
		711	static void
		712	post_fork_child (void)
		713	{
		714	ev_loop_fork (EV_DEFAULT);
		715	}
		716
		717	...
634	pthread_atfork (0, 0, ev_default_fork);	718	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		719
643	=item int ev_is_default_loop (loop)	720	=item int ev_is_default_loop (loop)
644		721
645	Returns true when the given loop is, in fact, the default loop, and false	722	Returns true when the given loop is, in fact, the default loop, and false
646	otherwise.	723	otherwise.
…		…
657	prepare and check phases.	734	prepare and check phases.
658		735
659	=item unsigned int ev_depth (loop)	736	=item unsigned int ev_depth (loop)
660		737
661	Returns the number of times C<ev_run> was entered minus the number of	738	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.	739	times C<ev_run> was exited normally, in other words, the recursion depth.
663		740
664	Outside C<ev_run>, this number is zero. In a callback, this number is	741	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),	742	C<1>, unless C<ev_run> was invoked recursively (or from another thread),
666	in which case it is higher.	743	in which case it is higher.
667		744
668	Leaving C<ev_run> abnormally (setjmp/longjmp, cancelling the thread	745	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	746	throwing an exception etc.), doesn't count as "exit" - consider this
670	ungentleman-like behaviour unless it's really convenient.	747	as a hint to avoid such ungentleman-like behaviour unless it's really
		748	convenient, in which case it is fully supported.
671		749
672	=item unsigned int ev_backend (loop)	750	=item unsigned int ev_backend (loop)
673		751
674	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	752	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
675	use.	753	use.
…		…
690		768
691	This function is rarely useful, but when some event callback runs for a	769	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	770	very long time without entering the event loop, updating libev's idea of
693	the current time is a good idea.	771	the current time is a good idea.
694		772
695	See also L<The special problem of time updates> in the C<ev_timer> section.	773	See also L</The special problem of time updates> in the C<ev_timer> section.
696		774
697	=item ev_suspend (loop)	775	=item ev_suspend (loop)
698		776
699	=item ev_resume (loop)	777	=item ev_resume (loop)
700		778
…		…
718	without a previous call to C<ev_suspend>.	796	without a previous call to C<ev_suspend>.
719		797
720	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the	798	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
721	event loop time (see C<ev_now_update>).	799	event loop time (see C<ev_now_update>).
722		800
723	=item ev_run (loop, int flags)	801	=item bool ev_run (loop, int flags)
724		802
725	Finally, this is it, the event handler. This function usually is called	803	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	804	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	805	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	806	the watcher callbacks, and then repeat the whole process indefinitely: This
729	is why event loops are called I<loops>.	807	is why event loops are called I<loops>.
730		808
731	If the flags argument is specified as C<0>, it will keep handling events	809	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	810	until either no event watchers are active anymore or C<ev_break> was
733	called.	811	called.
		812
		813	The return value is false if there are no more active watchers (which
		814	usually means "all jobs done" or "deadlock"), and true in all other cases
		815	(which usually means " you should call C<ev_run> again").
734		816
735	Please note that an explicit C<ev_break> is usually better than	817	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	818	relying on all watchers to be stopped when deciding when a program has
737	finished (especially in interactive programs), but having a program	819	finished (especially in interactive programs), but having a program
738	that automatically loops as long as it has to and no longer by virtue	820	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	821	of relying on its watchers stopping correctly, that is truly a thing of
740	beauty.	822	beauty.
741		823
		824	This function is I<mostly> exception-safe - you can break out of a
		825	C<ev_run> call by calling C<longjmp> in a callback, throwing a C++
		826	exception and so on. This does not decrement the C<ev_depth> value, nor
		827	will it clear any outstanding C<EVBREAK_ONE> breaks.
		828
742	A flags value of C<EVRUN_NOWAIT> will look for new events, will handle	829	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	830	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	831	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	832	iteration of the loop. This is sometimes useful to poll and handle new
746	events while doing lengthy calculations, to keep the program responsive.	833	events while doing lengthy calculations, to keep the program responsive.
…		…
755	This is useful if you are waiting for some external event in conjunction	842	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	843	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	844	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.	845	usually a better approach for this kind of thing.
759		846
760	Here are the gory details of what C<ev_run> does:	847	Here are the gory details of what C<ev_run> does (this is for your
		848	understanding, not a guarantee that things will work exactly like this in
		849	future versions):
761		850
762	- Increment loop depth.	851	- Increment loop depth.
763	- Reset the ev_break status.	852	- Reset the ev_break status.
764	- Before the first iteration, call any pending watchers.	853	- Before the first iteration, call any pending watchers.
765	LOOP:	854	LOOP:
…		…
798	anymore.	887	anymore.
799		888
800	... queue jobs here, make sure they register event watchers as long	889	... 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..)	890	... as they still have work to do (even an idle watcher will do..)
802	ev_run (my_loop, 0);	891	ev_run (my_loop, 0);
803	... jobs done or somebody called unloop. yeah!	892	... jobs done or somebody called break. yeah!
804		893
805	=item ev_break (loop, how)	894	=item ev_break (loop, how)
806		895
807	Can be used to make a call to C<ev_run> return early (but only after it	896	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	897	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	898	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.	899	C<EVBREAK_ALL>, which will make all nested C<ev_run> calls return.
811		900
812	This "unloop state" will be cleared when entering C<ev_run> again.	901	This "break state" will be cleared on the next call to C<ev_run>.
813		902
814	It is safe to call C<ev_break> from outside any C<ev_run> calls. ##TODO##	903	It is safe to call C<ev_break> from outside any C<ev_run> calls, too, in
		904	which case it will have no effect.
815		905
816	=item ev_ref (loop)	906	=item ev_ref (loop)
817		907
818	=item ev_unref (loop)	908	=item ev_unref (loop)
819		909
…		…
840	running when nothing else is active.	930	running when nothing else is active.
841		931
842	ev_signal exitsig;	932	ev_signal exitsig;
843	ev_signal_init (&exitsig, sig_cb, SIGINT);	933	ev_signal_init (&exitsig, sig_cb, SIGINT);
844	ev_signal_start (loop, &exitsig);	934	ev_signal_start (loop, &exitsig);
845	evf_unref (loop);	935	ev_unref (loop);
846		936
847	Example: For some weird reason, unregister the above signal handler again.	937	Example: For some weird reason, unregister the above signal handler again.
848		938
849	ev_ref (loop);	939	ev_ref (loop);
850	ev_signal_stop (loop, &exitsig);	940	ev_signal_stop (loop, &exitsig);
…		…
870	overhead for the actual polling but can deliver many events at once.	960	overhead for the actual polling but can deliver many events at once.
871		961
872	By setting a higher I<io collect interval> you allow libev to spend more	962	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,	963	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	964	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	965	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	966	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	967	sleep time ensures that libev will not poll for I/O events more often then
878	once per this interval, on average.	968	once per this interval, on average (as long as the host time resolution is
		969	good enough).
879		970
880	Likewise, by setting a higher I<timeout collect interval> you allow libev	971	Likewise, by setting a higher I<timeout collect interval> you allow libev
881	to spend more time collecting timeouts, at the expense of increased	972	to spend more time collecting timeouts, at the expense of increased
882	latency/jitter/inexactness (the watcher callback will be called	973	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	974	later). C<ev_io> watchers will not be affected. Setting this to a non-null
…		…
929	invoke the actual watchers inside another context (another thread etc.).	1020	invoke the actual watchers inside another context (another thread etc.).
930		1021
931	If you want to reset the callback, use C<ev_invoke_pending> as new	1022	If you want to reset the callback, use C<ev_invoke_pending> as new
932	callback.	1023	callback.
933		1024
934	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))	1025	=item ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())
935		1026
936	Sometimes you want to share the same loop between multiple threads. This	1027	Sometimes you want to share the same loop between multiple threads. This
937	can be done relatively simply by putting mutex_lock/unlock calls around	1028	can be done relatively simply by putting mutex_lock/unlock calls around
938	each call to a libev function.	1029	each call to a libev function.
939		1030
940	However, C<ev_run> can run an indefinite time, so it is not feasible	1031	However, C<ev_run> can run an indefinite time, so it is not feasible
941	to wait for it to return. One way around this is to wake up the event	1032	to wait for it to return. One way around this is to wake up the event
942	loop via C<ev_break> and C<av_async_send>, another way is to set these	1033	loop via C<ev_break> and C<ev_async_send>, another way is to set these
943	I<release> and I<acquire> callbacks on the loop.	1034	I<release> and I<acquire> callbacks on the loop.
944		1035
945	When set, then C<release> will be called just before the thread is	1036	When set, then C<release> will be called just before the thread is
946	suspended waiting for new events, and C<acquire> is called just	1037	suspended waiting for new events, and C<acquire> is called just
947	afterwards.	1038	afterwards.
…		…
962	See also the locking example in the C<THREADS> section later in this	1053	See also the locking example in the C<THREADS> section later in this
963	document.	1054	document.
964		1055
965	=item ev_set_userdata (loop, void *data)	1056	=item ev_set_userdata (loop, void *data)
966		1057
967	=item ev_userdata (loop)	1058	=item void *ev_userdata (loop)
968		1059
969	Set and retrieve a single C<void *> associated with a loop. When	1060	Set and retrieve a single C<void *> associated with a loop. When
970	C<ev_set_userdata> has never been called, then C<ev_userdata> returns	1061	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
971	C<0.>	1062	C<0>.
972		1063
973	These two functions can be used to associate arbitrary data with a loop,	1064	These two functions can be used to associate arbitrary data with a loop,
974	and are intended solely for the C<invoke_pending_cb>, C<release> and	1065	and are intended solely for the C<invoke_pending_cb>, C<release> and
975	C<acquire> callbacks described above, but of course can be (ab-)used for	1066	C<acquire> callbacks described above, but of course can be (ab-)used for
976	any other purpose as well.	1067	any other purpose as well.
…		…
1087		1178
1088	=item C<EV_PREPARE>	1179	=item C<EV_PREPARE>
1089		1180
1090	=item C<EV_CHECK>	1181	=item C<EV_CHECK>
1091		1182
1092	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts	1183	All C<ev_prepare> watchers are invoked just I<before> C<ev_run> starts to
1093	to gather new events, and all C<ev_check> watchers are invoked just after	1184	gather new events, and all C<ev_check> watchers are queued (not invoked)
1094	C<ev_run> has gathered them, but before it invokes any callbacks for any	1185	just after C<ev_run> has gathered them, but before it queues any callbacks
		1186	for any received events. That means C<ev_prepare> watchers are the last
		1187	watchers invoked before the event loop sleeps or polls for new events, and
		1188	C<ev_check> watchers will be invoked before any other watchers of the same
		1189	or lower priority within an event loop iteration.
		1190
1095	received events. Callbacks of both watcher types can start and stop as	1191	Callbacks of both watcher types can start and stop as many watchers as
1096	many watchers as they want, and all of them will be taken into account	1192	they want, and all of them will be taken into account (for example, a
1097	(for example, a C<ev_prepare> watcher might start an idle watcher to keep	1193	C<ev_prepare> watcher might start an idle watcher to keep C<ev_run> from
1098	C<ev_run> from blocking).	1194	blocking).
1099		1195
1100	=item C<EV_EMBED>	1196	=item C<EV_EMBED>
1101		1197
1102	The embedded event loop specified in the C<ev_embed> watcher needs attention.	1198	The embedded event loop specified in the C<ev_embed> watcher needs attention.
1103		1199
1104	=item C<EV_FORK>	1200	=item C<EV_FORK>
1105		1201
1106	The event loop has been resumed in the child process after fork (see	1202	The event loop has been resumed in the child process after fork (see
1107	C<ev_fork>).	1203	C<ev_fork>).
		1204
		1205	=item C<EV_CLEANUP>
		1206
		1207	The event loop is about to be destroyed (see C<ev_cleanup>).
1108		1208
1109	=item C<EV_ASYNC>	1209	=item C<EV_ASYNC>
1110		1210
1111	The given async watcher has been asynchronously notified (see C<ev_async>).	1211	The given async watcher has been asynchronously notified (see C<ev_async>).
1112		1212
…		…
1134	programs, though, as the fd could already be closed and reused for another	1234	programs, though, as the fd could already be closed and reused for another
1135	thing, so beware.	1235	thing, so beware.
1136		1236
1137	=back	1237	=back
1138		1238
		1239	=head2 GENERIC WATCHER FUNCTIONS
		1240
		1241	=over 4
		1242
		1243	=item C<ev_init> (ev_TYPE *watcher, callback)
		1244
		1245	This macro initialises the generic portion of a watcher. The contents
		1246	of the watcher object can be arbitrary (so C<malloc> will do). Only
		1247	the generic parts of the watcher are initialised, you I<need> to call
		1248	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
		1249	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
		1250	which rolls both calls into one.
		1251
		1252	You can reinitialise a watcher at any time as long as it has been stopped
		1253	(or never started) and there are no pending events outstanding.
		1254
		1255	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
		1256	int revents)>.
		1257
		1258	Example: Initialise an C<ev_io> watcher in two steps.
		1259
		1260	ev_io w;
		1261	ev_init (&w, my_cb);
		1262	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1263
		1264	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
		1265
		1266	This macro initialises the type-specific parts of a watcher. You need to
		1267	call C<ev_init> at least once before you call this macro, but you can
		1268	call C<ev_TYPE_set> any number of times. You must not, however, call this
		1269	macro on a watcher that is active (it can be pending, however, which is a
		1270	difference to the C<ev_init> macro).
		1271
		1272	Although some watcher types do not have type-specific arguments
		1273	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
		1274
		1275	See C<ev_init>, above, for an example.
		1276
		1277	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
		1278
		1279	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
		1280	calls into a single call. This is the most convenient method to initialise
		1281	a watcher. The same limitations apply, of course.
		1282
		1283	Example: Initialise and set an C<ev_io> watcher in one step.
		1284
		1285	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1286
		1287	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
		1288
		1289	Starts (activates) the given watcher. Only active watchers will receive
		1290	events. If the watcher is already active nothing will happen.
		1291
		1292	Example: Start the C<ev_io> watcher that is being abused as example in this
		1293	whole section.
		1294
		1295	ev_io_start (EV_DEFAULT_UC, &w);
		1296
		1297	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
		1298
		1299	Stops the given watcher if active, and clears the pending status (whether
		1300	the watcher was active or not).
		1301
		1302	It is possible that stopped watchers are pending - for example,
		1303	non-repeating timers are being stopped when they become pending - but
		1304	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
		1305	pending. If you want to free or reuse the memory used by the watcher it is
		1306	therefore a good idea to always call its C<ev_TYPE_stop> function.
		1307
		1308	=item bool ev_is_active (ev_TYPE *watcher)
		1309
		1310	Returns a true value iff the watcher is active (i.e. it has been started
		1311	and not yet been stopped). As long as a watcher is active you must not modify
		1312	it.
		1313
		1314	=item bool ev_is_pending (ev_TYPE *watcher)
		1315
		1316	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		1317	events but its callback has not yet been invoked). As long as a watcher
		1318	is pending (but not active) you must not call an init function on it (but
		1319	C<ev_TYPE_set> is safe), you must not change its priority, and you must
		1320	make sure the watcher is available to libev (e.g. you cannot C<free ()>
		1321	it).
		1322
		1323	=item callback ev_cb (ev_TYPE *watcher)
		1324
		1325	Returns the callback currently set on the watcher.
		1326
		1327	=item ev_set_cb (ev_TYPE *watcher, callback)
		1328
		1329	Change the callback. You can change the callback at virtually any time
		1330	(modulo threads).
		1331
		1332	=item ev_set_priority (ev_TYPE *watcher, int priority)
		1333
		1334	=item int ev_priority (ev_TYPE *watcher)
		1335
		1336	Set and query the priority of the watcher. The priority is a small
		1337	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
		1338	(default: C<-2>). Pending watchers with higher priority will be invoked
		1339	before watchers with lower priority, but priority will not keep watchers
		1340	from being executed (except for C<ev_idle> watchers).
		1341
		1342	If you need to suppress invocation when higher priority events are pending
		1343	you need to look at C<ev_idle> watchers, which provide this functionality.
		1344
		1345	You I<must not> change the priority of a watcher as long as it is active or
		1346	pending.
		1347
		1348	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1349	fine, as long as you do not mind that the priority value you query might
		1350	or might not have been clamped to the valid range.
		1351
		1352	The default priority used by watchers when no priority has been set is
		1353	always C<0>, which is supposed to not be too high and not be too low :).
		1354
		1355	See L</WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1356	priorities.
		1357
		1358	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
		1359
		1360	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
		1361	C<loop> nor C<revents> need to be valid as long as the watcher callback
		1362	can deal with that fact, as both are simply passed through to the
		1363	callback.
		1364
		1365	=item int ev_clear_pending (loop, ev_TYPE *watcher)
		1366
		1367	If the watcher is pending, this function clears its pending status and
		1368	returns its C<revents> bitset (as if its callback was invoked). If the
		1369	watcher isn't pending it does nothing and returns C<0>.
		1370
		1371	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1372	callback to be invoked, which can be accomplished with this function.
		1373
		1374	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1375
		1376	Feeds the given event set into the event loop, as if the specified event
		1377	had happened for the specified watcher (which must be a pointer to an
		1378	initialised but not necessarily started event watcher). Obviously you must
		1379	not free the watcher as long as it has pending events.
		1380
		1381	Stopping the watcher, letting libev invoke it, or calling
		1382	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1383	not started in the first place.
		1384
		1385	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1386	functions that do not need a watcher.
		1387
		1388	=back
		1389
		1390	See also the L</ASSOCIATING CUSTOM DATA WITH A WATCHER> and L</BUILDING YOUR
		1391	OWN COMPOSITE WATCHERS> idioms.
		1392
1139	=head2 WATCHER STATES	1393	=head2 WATCHER STATES
1140		1394
1141	There are various watcher states mentioned throughout this manual -	1395	There are various watcher states mentioned throughout this manual -
1142	active, pending and so on. In this section these states and the rules to	1396	active, pending and so on. In this section these states and the rules to
1143	transition between them will be described in more detail - and while these	1397	transition between them will be described in more detail - and while these
1144	rules might look complicated, they usually do "the right thing".	1398	rules might look complicated, they usually do "the right thing".
1145		1399
1146	=over 4	1400	=over 4
1147		1401
1148	=item initialiased	1402	=item initialised
1149		1403
1150	Before a watcher can be registered with the event looop it has to be	1404	Before a watcher can be registered with the event loop it has to be
1151	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to	1405	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
1152	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.	1406	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1153		1407
1154	In this state it is simply some block of memory that is suitable for use	1408	In this state it is simply some block of memory that is suitable for
1155	in an event loop. It can be moved around, freed, reused etc. at will.	1409	use in an event loop. It can be moved around, freed, reused etc. at
		1410	will - as long as you either keep the memory contents intact, or call
		1411	C<ev_TYPE_init> again.
1156		1412
1157	=item started/running/active	1413	=item started/running/active
1158		1414
1159	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes	1415	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
1160	property of the event loop, and is actively waiting for events. While in	1416	property of the event loop, and is actively waiting for events. While in
…		…
1188	latter will clear any pending state the watcher might be in, regardless	1444	latter will clear any pending state the watcher might be in, regardless
1189	of whether it was active or not, so stopping a watcher explicitly before	1445	of whether it was active or not, so stopping a watcher explicitly before
1190	freeing it is often a good idea.	1446	freeing it is often a good idea.
1191		1447
1192	While stopped (and not pending) the watcher is essentially in the	1448	While stopped (and not pending) the watcher is essentially in the
1193	initialised state, that is it can be reused, moved, modified in any way	1449	initialised state, that is, it can be reused, moved, modified in any way
1194	you wish.	1450	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1451	it again).
1195		1452
1196	=back	1453	=back
1197
1198	=head2 GENERIC WATCHER FUNCTIONS
1199
1200	=over 4
1201
1202	=item C<ev_init> (ev_TYPE *watcher, callback)
1203
1204	This macro initialises the generic portion of a watcher. The contents
1205	of the watcher object can be arbitrary (so C<malloc> will do). Only
1206	the generic parts of the watcher are initialised, you I<need> to call
1207	the type-specific C<ev_TYPE_set> macro afterwards to initialise the
1208	type-specific parts. For each type there is also a C<ev_TYPE_init> macro
1209	which rolls both calls into one.
1210
1211	You can reinitialise a watcher at any time as long as it has been stopped
1212	(or never started) and there are no pending events outstanding.
1213
1214	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
1215	int revents)>.
1216
1217	Example: Initialise an C<ev_io> watcher in two steps.
1218
1219	ev_io w;
1220	ev_init (&w, my_cb);
1221	ev_io_set (&w, STDIN_FILENO, EV_READ);
1222
1223	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
1224
1225	This macro initialises the type-specific parts of a watcher. You need to
1226	call C<ev_init> at least once before you call this macro, but you can
1227	call C<ev_TYPE_set> any number of times. You must not, however, call this
1228	macro on a watcher that is active (it can be pending, however, which is a
1229	difference to the C<ev_init> macro).
1230
1231	Although some watcher types do not have type-specific arguments
1232	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
1233
1234	See C<ev_init>, above, for an example.
1235
1236	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
1237
1238	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
1239	calls into a single call. This is the most convenient method to initialise
1240	a watcher. The same limitations apply, of course.
1241
1242	Example: Initialise and set an C<ev_io> watcher in one step.
1243
1244	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
1245
1246	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
1247
1248	Starts (activates) the given watcher. Only active watchers will receive
1249	events. If the watcher is already active nothing will happen.
1250
1251	Example: Start the C<ev_io> watcher that is being abused as example in this
1252	whole section.
1253
1254	ev_io_start (EV_DEFAULT_UC, &w);
1255
1256	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
1257
1258	Stops the given watcher if active, and clears the pending status (whether
1259	the watcher was active or not).
1260
1261	It is possible that stopped watchers are pending - for example,
1262	non-repeating timers are being stopped when they become pending - but
1263	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
1264	pending. If you want to free or reuse the memory used by the watcher it is
1265	therefore a good idea to always call its C<ev_TYPE_stop> function.
1266
1267	=item bool ev_is_active (ev_TYPE *watcher)
1268
1269	Returns a true value iff the watcher is active (i.e. it has been started
1270	and not yet been stopped). As long as a watcher is active you must not modify
1271	it.
1272
1273	=item bool ev_is_pending (ev_TYPE *watcher)
1274
1275	Returns a true value iff the watcher is pending, (i.e. it has outstanding
1276	events but its callback has not yet been invoked). As long as a watcher
1277	is pending (but not active) you must not call an init function on it (but
1278	C<ev_TYPE_set> is safe), you must not change its priority, and you must
1279	make sure the watcher is available to libev (e.g. you cannot C<free ()>
1280	it).
1281
1282	=item callback ev_cb (ev_TYPE *watcher)
1283
1284	Returns the callback currently set on the watcher.
1285
1286	=item ev_cb_set (ev_TYPE *watcher, callback)
1287
1288	Change the callback. You can change the callback at virtually any time
1289	(modulo threads).
1290
1291	=item ev_set_priority (ev_TYPE *watcher, int priority)
1292
1293	=item int ev_priority (ev_TYPE *watcher)
1294
1295	Set and query the priority of the watcher. The priority is a small
1296	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
1297	(default: C<-2>). Pending watchers with higher priority will be invoked
1298	before watchers with lower priority, but priority will not keep watchers
1299	from being executed (except for C<ev_idle> watchers).
1300
1301	If you need to suppress invocation when higher priority events are pending
1302	you need to look at C<ev_idle> watchers, which provide this functionality.
1303
1304	You I<must not> change the priority of a watcher as long as it is active or
1305	pending.
1306
1307	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
1308	fine, as long as you do not mind that the priority value you query might
1309	or might not have been clamped to the valid range.
1310
1311	The default priority used by watchers when no priority has been set is
1312	always C<0>, which is supposed to not be too high and not be too low :).
1313
1314	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
1315	priorities.
1316
1317	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1318
1319	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
1320	C<loop> nor C<revents> need to be valid as long as the watcher callback
1321	can deal with that fact, as both are simply passed through to the
1322	callback.
1323
1324	=item int ev_clear_pending (loop, ev_TYPE *watcher)
1325
1326	If the watcher is pending, this function clears its pending status and
1327	returns its C<revents> bitset (as if its callback was invoked). If the
1328	watcher isn't pending it does nothing and returns C<0>.
1329
1330	Sometimes it can be useful to "poll" a watcher instead of waiting for its
1331	callback to be invoked, which can be accomplished with this function.
1332
1333	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
1334
1335	Feeds the given event set into the event loop, as if the specified event
1336	had happened for the specified watcher (which must be a pointer to an
1337	initialised but not necessarily started event watcher). Obviously you must
1338	not free the watcher as long as it has pending events.
1339
1340	Stopping the watcher, letting libev invoke it, or calling
1341	C<ev_clear_pending> will clear the pending event, even if the watcher was
1342	not started in the first place.
1343
1344	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1345	functions that do not need a watcher.
1346
1347	=back
1348
1349
1350	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
1351
1352	Each watcher has, by default, a member C<void *data> that you can change
1353	and read at any time: libev will completely ignore it. This can be used
1354	to associate arbitrary data with your watcher. If you need more data and
1355	don't want to allocate memory and store a pointer to it in that data
1356	member, you can also "subclass" the watcher type and provide your own
1357	data:
1358
1359	struct my_io
1360	{
1361	ev_io io;
1362	int otherfd;
1363	void *somedata;
1364	struct whatever *mostinteresting;
1365	};
1366
1367	...
1368	struct my_io w;
1369	ev_io_init (&w.io, my_cb, fd, EV_READ);
1370
1371	And since your callback will be called with a pointer to the watcher, you
1372	can cast it back to your own type:
1373
1374	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1375	{
1376	struct my_io *w = (struct my_io *)w_;
1377	...
1378	}
1379
1380	More interesting and less C-conformant ways of casting your callback type
1381	instead have been omitted.
1382
1383	Another common scenario is to use some data structure with multiple
1384	embedded watchers:
1385
1386	struct my_biggy
1387	{
1388	int some_data;
1389	ev_timer t1;
1390	ev_timer t2;
1391	}
1392
1393	In this case getting the pointer to C<my_biggy> is a bit more
1394	complicated: Either you store the address of your C<my_biggy> struct
1395	in the C<data> member of the watcher (for woozies), or you need to use
1396	some pointer arithmetic using C<offsetof> inside your watchers (for real
1397	programmers):
1398
1399	#include <stddef.h>
1400
1401	static void
1402	t1_cb (EV_P_ ev_timer *w, int revents)
1403	{
1404	struct my_biggy big = (struct my_biggy *)
1405	(((char *)w) - offsetof (struct my_biggy, t1));
1406	}
1407
1408	static void
1409	t2_cb (EV_P_ ev_timer *w, int revents)
1410	{
1411	struct my_biggy big = (struct my_biggy *)
1412	(((char *)w) - offsetof (struct my_biggy, t2));
1413	}
1414		1454
1415	=head2 WATCHER PRIORITY MODELS	1455	=head2 WATCHER PRIORITY MODELS
1416		1456
1417	Many event loops support I<watcher priorities>, which are usually small	1457	Many event loops support I<watcher priorities>, which are usually small
1418	integers that influence the ordering of event callback invocation	1458	integers that influence the ordering of event callback invocation
…		…
1545	In general you can register as many read and/or write event watchers per	1585	In general you can register as many read and/or write event watchers per
1546	fd as you want (as long as you don't confuse yourself). Setting all file	1586	fd as you want (as long as you don't confuse yourself). Setting all file
1547	descriptors to non-blocking mode is also usually a good idea (but not	1587	descriptors to non-blocking mode is also usually a good idea (but not
1548	required if you know what you are doing).	1588	required if you know what you are doing).
1549		1589
1550	If you cannot use non-blocking mode, then force the use of a
1551	known-to-be-good backend (at the time of this writing, this includes only
1552	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
1553	descriptors for which non-blocking operation makes no sense (such as
1554	files) - libev doesn't guarantee any specific behaviour in that case.
1555
1556	Another thing you have to watch out for is that it is quite easy to	1590	Another thing you have to watch out for is that it is quite easy to
1557	receive "spurious" readiness notifications, that is your callback might	1591	receive "spurious" readiness notifications, that is, your callback might
1558	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1592	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1559	because there is no data. Not only are some backends known to create a	1593	because there is no data. It is very easy to get into this situation even
1560	lot of those (for example Solaris ports), it is very easy to get into	1594	with a relatively standard program structure. Thus it is best to always
1561	this situation even with a relatively standard program structure. Thus	1595	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1562	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1563	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1596	preferable to a program hanging until some data arrives.
1564		1597
1565	If you cannot run the fd in non-blocking mode (for example you should	1598	If you cannot run the fd in non-blocking mode (for example you should
1566	not play around with an Xlib connection), then you have to separately	1599	not play around with an Xlib connection), then you have to separately
1567	re-test whether a file descriptor is really ready with a known-to-be good	1600	re-test whether a file descriptor is really ready with a known-to-be good
1568	interface such as poll (fortunately in our Xlib example, Xlib already	1601	interface such as poll (fortunately in the case of Xlib, it already does
1569	does this on its own, so its quite safe to use). Some people additionally	1602	this on its own, so its quite safe to use). Some people additionally
1570	use C<SIGALRM> and an interval timer, just to be sure you won't block	1603	use C<SIGALRM> and an interval timer, just to be sure you won't block
1571	indefinitely.	1604	indefinitely.
1572		1605
1573	But really, best use non-blocking mode.	1606	But really, best use non-blocking mode.
1574		1607
…		…
1602		1635
1603	There is no workaround possible except not registering events	1636	There is no workaround possible except not registering events
1604	for potentially C<dup ()>'ed file descriptors, or to resort to	1637	for potentially C<dup ()>'ed file descriptors, or to resort to
1605	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1638	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1606		1639
		1640	=head3 The special problem of files
		1641
		1642	Many people try to use C<select> (or libev) on file descriptors
		1643	representing files, and expect it to become ready when their program
		1644	doesn't block on disk accesses (which can take a long time on their own).
		1645
		1646	However, this cannot ever work in the "expected" way - you get a readiness
		1647	notification as soon as the kernel knows whether and how much data is
		1648	there, and in the case of open files, that's always the case, so you
		1649	always get a readiness notification instantly, and your read (or possibly
		1650	write) will still block on the disk I/O.
		1651
		1652	Another way to view it is that in the case of sockets, pipes, character
		1653	devices and so on, there is another party (the sender) that delivers data
		1654	on its own, but in the case of files, there is no such thing: the disk
		1655	will not send data on its own, simply because it doesn't know what you
		1656	wish to read - you would first have to request some data.
		1657
		1658	Since files are typically not-so-well supported by advanced notification
		1659	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1660	to files, even though you should not use it. The reason for this is
		1661	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1662	usually a tty, often a pipe, but also sometimes files or special devices
		1663	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1664	F</dev/urandom>), and even though the file might better be served with
		1665	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1666	it "just works" instead of freezing.
		1667
		1668	So avoid file descriptors pointing to files when you know it (e.g. use
		1669	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1670	when you rarely read from a file instead of from a socket, and want to
		1671	reuse the same code path.
		1672
1607	=head3 The special problem of fork	1673	=head3 The special problem of fork
1608		1674
1609	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1675	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
1610	useless behaviour. Libev fully supports fork, but needs to be told about	1676	useless behaviour. Libev fully supports fork, but needs to be told about
1611	it in the child.	1677	it in the child if you want to continue to use it in the child.
1612		1678
1613	To support fork in your programs, you either have to call	1679	To support fork in your child processes, you have to call C<ev_loop_fork
1614	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1680	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1615	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1681	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1616	C<EVBACKEND_POLL>.
1617		1682
1618	=head3 The special problem of SIGPIPE	1683	=head3 The special problem of SIGPIPE
1619		1684
1620	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1685	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1621	when writing to a pipe whose other end has been closed, your program gets	1686	when writing to a pipe whose other end has been closed, your program gets
…		…
1719	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1784	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1720	monotonic clock option helps a lot here).	1785	monotonic clock option helps a lot here).
1721		1786
1722	The callback is guaranteed to be invoked only I<after> its timeout has	1787	The callback is guaranteed to be invoked only I<after> its timeout has
1723	passed (not I<at>, so on systems with very low-resolution clocks this	1788	passed (not I<at>, so on systems with very low-resolution clocks this
1724	might introduce a small delay). If multiple timers become ready during the	1789	might introduce a small delay, see "the special problem of being too
		1790	early", below). If multiple timers become ready during the same loop
1725	same loop iteration then the ones with earlier time-out values are invoked	1791	iteration then the ones with earlier time-out values are invoked before
1726	before ones of the same priority with later time-out values (but this is	1792	ones of the same priority with later time-out values (but this is no
1727	no longer true when a callback calls C<ev_run> recursively).	1793	longer true when a callback calls C<ev_run> recursively).
1728		1794
1729	=head3 Be smart about timeouts	1795	=head3 Be smart about timeouts
1730		1796
1731	Many real-world problems involve some kind of timeout, usually for error	1797	Many real-world problems involve some kind of timeout, usually for error
1732	recovery. A typical example is an HTTP request - if the other side hangs,	1798	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1807		1873
1808	In this case, it would be more efficient to leave the C<ev_timer> alone,	1874	In this case, it would be more efficient to leave the C<ev_timer> alone,
1809	but remember the time of last activity, and check for a real timeout only	1875	but remember the time of last activity, and check for a real timeout only
1810	within the callback:	1876	within the callback:
1811		1877
		1878	ev_tstamp timeout = 60.;
1812	ev_tstamp last_activity; // time of last activity	1879	ev_tstamp last_activity; // time of last activity
		1880	ev_timer timer;
1813		1881
1814	static void	1882	static void
1815	callback (EV_P_ ev_timer *w, int revents)	1883	callback (EV_P_ ev_timer *w, int revents)
1816	{	1884	{
1817	ev_tstamp now = ev_now (EV_A);	1885	// calculate when the timeout would happen
1818	ev_tstamp timeout = last_activity + 60.;	1886	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
1819		1887
1820	// if last_activity + 60. is older than now, we did time out	1888	// if negative, it means we the timeout already occurred
1821	if (timeout < now)	1889	if (after < 0.)
1822	{	1890	{
1823	// timeout occurred, take action	1891	// timeout occurred, take action
1824	}	1892	}
1825	else	1893	else
1826	{	1894	{
1827	// callback was invoked, but there was some activity, re-arm	1895	// callback was invoked, but there was some recent
1828	// the watcher to fire in last_activity + 60, which is	1896	// activity. simply restart the timer to time out
1829	// guaranteed to be in the future, so "again" is positive:	1897	// after "after" seconds, which is the earliest time
1830	w->repeat = timeout - now;	1898	// the timeout can occur.
		1899	ev_timer_set (w, after, 0.);
1831	ev_timer_again (EV_A_ w);	1900	ev_timer_start (EV_A_ w);
1832	}	1901	}
1833	}	1902	}
1834		1903
1835	To summarise the callback: first calculate the real timeout (defined	1904	To summarise the callback: first calculate in how many seconds the
1836	as "60 seconds after the last activity"), then check if that time has	1905	timeout will occur (by calculating the absolute time when it would occur,
1837	been reached, which means something I<did>, in fact, time out. Otherwise	1906	C<last_activity + timeout>, and subtracting the current time, C<ev_now
1838	the callback was invoked too early (C<timeout> is in the future), so	1907	(EV_A)> from that).
1839	re-schedule the timer to fire at that future time, to see if maybe we have
1840	a timeout then.
1841		1908
1842	Note how C<ev_timer_again> is used, taking advantage of the	1909	If this value is negative, then we are already past the timeout, i.e. we
1843	C<ev_timer_again> optimisation when the timer is already running.	1910	timed out, and need to do whatever is needed in this case.
		1911
		1912	Otherwise, we now the earliest time at which the timeout would trigger,
		1913	and simply start the timer with this timeout value.
		1914
		1915	In other words, each time the callback is invoked it will check whether
		1916	the timeout occurred. If not, it will simply reschedule itself to check
		1917	again at the earliest time it could time out. Rinse. Repeat.
1844		1918
1845	This scheme causes more callback invocations (about one every 60 seconds	1919	This scheme causes more callback invocations (about one every 60 seconds
1846	minus half the average time between activity), but virtually no calls to	1920	minus half the average time between activity), but virtually no calls to
1847	libev to change the timeout.	1921	libev to change the timeout.
1848		1922
1849	To start the timer, simply initialise the watcher and set C<last_activity>	1923	To start the machinery, simply initialise the watcher and set
1850	to the current time (meaning we just have some activity :), then call the	1924	C<last_activity> to the current time (meaning there was some activity just
1851	callback, which will "do the right thing" and start the timer:	1925	now), then call the callback, which will "do the right thing" and start
		1926	the timer:
1852		1927
		1928	last_activity = ev_now (EV_A);
1853	ev_init (timer, callback);	1929	ev_init (&timer, callback);
1854	last_activity = ev_now (loop);	1930	callback (EV_A_ &timer, 0);
1855	callback (loop, timer, EV_TIMER);
1856		1931
1857	And when there is some activity, simply store the current time in	1932	When there is some activity, simply store the current time in
1858	C<last_activity>, no libev calls at all:	1933	C<last_activity>, no libev calls at all:
1859		1934
		1935	if (activity detected)
1860	last_activity = ev_now (loop);	1936	last_activity = ev_now (EV_A);
		1937
		1938	When your timeout value changes, then the timeout can be changed by simply
		1939	providing a new value, stopping the timer and calling the callback, which
		1940	will again do the right thing (for example, time out immediately :).
		1941
		1942	timeout = new_value;
		1943	ev_timer_stop (EV_A_ &timer);
		1944	callback (EV_A_ &timer, 0);
1861		1945
1862	This technique is slightly more complex, but in most cases where the	1946	This technique is slightly more complex, but in most cases where the
1863	time-out is unlikely to be triggered, much more efficient.	1947	time-out is unlikely to be triggered, much more efficient.
1864
1865	Changing the timeout is trivial as well (if it isn't hard-coded in the
1866	callback :) - just change the timeout and invoke the callback, which will
1867	fix things for you.
1868		1948
1869	=item 4. Wee, just use a double-linked list for your timeouts.	1949	=item 4. Wee, just use a double-linked list for your timeouts.
1870		1950
1871	If there is not one request, but many thousands (millions...), all	1951	If there is not one request, but many thousands (millions...), all
1872	employing some kind of timeout with the same timeout value, then one can	1952	employing some kind of timeout with the same timeout value, then one can
…		…
1899	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is	1979	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
1900	rather complicated, but extremely efficient, something that really pays	1980	rather complicated, but extremely efficient, something that really pays
1901	off after the first million or so of active timers, i.e. it's usually	1981	off after the first million or so of active timers, i.e. it's usually
1902	overkill :)	1982	overkill :)
1903		1983
		1984	=head3 The special problem of being too early
		1985
		1986	If you ask a timer to call your callback after three seconds, then
		1987	you expect it to be invoked after three seconds - but of course, this
		1988	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		1989	guaranteed to any precision by libev - imagine somebody suspending the
		1990	process with a STOP signal for a few hours for example.
		1991
		1992	So, libev tries to invoke your callback as soon as possible I<after> the
		1993	delay has occurred, but cannot guarantee this.
		1994
		1995	A less obvious failure mode is calling your callback too early: many event
		1996	loops compare timestamps with a "elapsed delay >= requested delay", but
		1997	this can cause your callback to be invoked much earlier than you would
		1998	expect.
		1999
		2000	To see why, imagine a system with a clock that only offers full second
		2001	resolution (think windows if you can't come up with a broken enough OS
		2002	yourself). If you schedule a one-second timer at the time 500.9, then the
		2003	event loop will schedule your timeout to elapse at a system time of 500
		2004	(500.9 truncated to the resolution) + 1, or 501.
		2005
		2006	If an event library looks at the timeout 0.1s later, it will see "501 >=
		2007	501" and invoke the callback 0.1s after it was started, even though a
		2008	one-second delay was requested - this is being "too early", despite best
		2009	intentions.
		2010
		2011	This is the reason why libev will never invoke the callback if the elapsed
		2012	delay equals the requested delay, but only when the elapsed delay is
		2013	larger than the requested delay. In the example above, libev would only invoke
		2014	the callback at system time 502, or 1.1s after the timer was started.
		2015
		2016	So, while libev cannot guarantee that your callback will be invoked
		2017	exactly when requested, it I<can> and I<does> guarantee that the requested
		2018	delay has actually elapsed, or in other words, it always errs on the "too
		2019	late" side of things.
		2020
1904	=head3 The special problem of time updates	2021	=head3 The special problem of time updates
1905		2022
1906	Establishing the current time is a costly operation (it usually takes at	2023	Establishing the current time is a costly operation (it usually takes
1907	least two system calls): EV therefore updates its idea of the current	2024	at least one system call): EV therefore updates its idea of the current
1908	time only before and after C<ev_run> collects new events, which causes a	2025	time only before and after C<ev_run> collects new events, which causes a
1909	growing difference between C<ev_now ()> and C<ev_time ()> when handling	2026	growing difference between C<ev_now ()> and C<ev_time ()> when handling
1910	lots of events in one iteration.	2027	lots of events in one iteration.
1911		2028
1912	The relative timeouts are calculated relative to the C<ev_now ()>	2029	The relative timeouts are calculated relative to the C<ev_now ()>
…		…
1918	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2035	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1919		2036
1920	If the event loop is suspended for a long time, you can also force an	2037	If the event loop is suspended for a long time, you can also force an
1921	update of the time returned by C<ev_now ()> by calling C<ev_now_update	2038	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1922	()>.	2039	()>.
		2040
		2041	=head3 The special problem of unsynchronised clocks
		2042
		2043	Modern systems have a variety of clocks - libev itself uses the normal
		2044	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2045	jumps).
		2046
		2047	Neither of these clocks is synchronised with each other or any other clock
		2048	on the system, so C<ev_time ()> might return a considerably different time
		2049	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2050	a call to C<gettimeofday> might return a second count that is one higher
		2051	than a directly following call to C<time>.
		2052
		2053	The moral of this is to only compare libev-related timestamps with
		2054	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2055	a second or so.
		2056
		2057	One more problem arises due to this lack of synchronisation: if libev uses
		2058	the system monotonic clock and you compare timestamps from C<ev_time>
		2059	or C<ev_now> from when you started your timer and when your callback is
		2060	invoked, you will find that sometimes the callback is a bit "early".
		2061
		2062	This is because C<ev_timer>s work in real time, not wall clock time, so
		2063	libev makes sure your callback is not invoked before the delay happened,
		2064	I<measured according to the real time>, not the system clock.
		2065
		2066	If your timeouts are based on a physical timescale (e.g. "time out this
		2067	connection after 100 seconds") then this shouldn't bother you as it is
		2068	exactly the right behaviour.
		2069
		2070	If you want to compare wall clock/system timestamps to your timers, then
		2071	you need to use C<ev_periodic>s, as these are based on the wall clock
		2072	time, where your comparisons will always generate correct results.
1923		2073
1924	=head3 The special problems of suspended animation	2074	=head3 The special problems of suspended animation
1925		2075
1926	When you leave the server world it is quite customary to hit machines that	2076	When you leave the server world it is quite customary to hit machines that
1927	can suspend/hibernate - what happens to the clocks during such a suspend?	2077	can suspend/hibernate - what happens to the clocks during such a suspend?
…		…
1971	keep up with the timer (because it takes longer than those 10 seconds to	2121	keep up with the timer (because it takes longer than those 10 seconds to
1972	do stuff) the timer will not fire more than once per event loop iteration.	2122	do stuff) the timer will not fire more than once per event loop iteration.
1973		2123
1974	=item ev_timer_again (loop, ev_timer *)	2124	=item ev_timer_again (loop, ev_timer *)
1975		2125
1976	This will act as if the timer timed out and restart it again if it is	2126	This will act as if the timer timed out, and restarts it again if it is
1977	repeating. The exact semantics are:	2127	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2128	timeout to the C<repeat> value and calling C<ev_timer_start>.
1978		2129
		2130	The exact semantics are as in the following rules, all of which will be
		2131	applied to the watcher:
		2132
		2133	=over 4
		2134
1979	If the timer is pending, its pending status is cleared.	2135	=item If the timer is pending, the pending status is always cleared.
1980		2136
1981	If the timer is started but non-repeating, stop it (as if it timed out).	2137	=item If the timer is started but non-repeating, stop it (as if it timed
		2138	out, without invoking it).
1982		2139
1983	If the timer is repeating, either start it if necessary (with the	2140	=item If the timer is repeating, make the C<repeat> value the new timeout
1984	C<repeat> value), or reset the running timer to the C<repeat> value.	2141	and start the timer, if necessary.
1985		2142
		2143	=back
		2144
1986	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a	2145	This sounds a bit complicated, see L</Be smart about timeouts>, above, for a
1987	usage example.	2146	usage example.
1988		2147
1989	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)	2148	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1990		2149
1991	Returns the remaining time until a timer fires. If the timer is active,	2150	Returns the remaining time until a timer fires. If the timer is active,
…		…
2111		2270
2112	Another way to think about it (for the mathematically inclined) is that	2271	Another way to think about it (for the mathematically inclined) is that
2113	C<ev_periodic> will try to run the callback in this mode at the next possible	2272	C<ev_periodic> will try to run the callback in this mode at the next possible
2114	time where C<time = offset (mod interval)>, regardless of any time jumps.	2273	time where C<time = offset (mod interval)>, regardless of any time jumps.
2115		2274
2116	For numerical stability it is preferable that the C<offset> value is near	2275	The C<interval> I<MUST> be positive, and for numerical stability, the
2117	C<ev_now ()> (the current time), but there is no range requirement for	2276	interval value should be higher than C<1/8192> (which is around 100
2118	this value, and in fact is often specified as zero.	2277	microseconds) and C<offset> should be higher than C<0> and should have
		2278	at most a similar magnitude as the current time (say, within a factor of
		2279	ten). Typical values for offset are, in fact, C<0> or something between
		2280	C<0> and C<interval>, which is also the recommended range.
2119		2281
2120	Note also that there is an upper limit to how often a timer can fire (CPU	2282	Note also that there is an upper limit to how often a timer can fire (CPU
2121	speed for example), so if C<interval> is very small then timing stability	2283	speed for example), so if C<interval> is very small then timing stability
2122	will of course deteriorate. Libev itself tries to be exact to be about one	2284	will of course deteriorate. Libev itself tries to be exact to be about one
2123	millisecond (if the OS supports it and the machine is fast enough).	2285	millisecond (if the OS supports it and the machine is fast enough).
…		…
2231		2393
2232	ev_periodic hourly_tick;	2394	ev_periodic hourly_tick;
2233	ev_periodic_init (&hourly_tick, clock_cb,	2395	ev_periodic_init (&hourly_tick, clock_cb,
2234	fmod (ev_now (loop), 3600.), 3600., 0);	2396	fmod (ev_now (loop), 3600.), 3600., 0);
2235	ev_periodic_start (loop, &hourly_tick);	2397	ev_periodic_start (loop, &hourly_tick);
2236		2398
2237		2399
2238	=head2 C<ev_signal> - signal me when a signal gets signalled!	2400	=head2 C<ev_signal> - signal me when a signal gets signalled!
2239		2401
2240	Signal watchers will trigger an event when the process receives a specific	2402	Signal watchers will trigger an event when the process receives a specific
2241	signal one or more times. Even though signals are very asynchronous, libev	2403	signal one or more times. Even though signals are very asynchronous, libev
2242	will try it's best to deliver signals synchronously, i.e. as part of the	2404	will try its best to deliver signals synchronously, i.e. as part of the
2243	normal event processing, like any other event.	2405	normal event processing, like any other event.
2244		2406
2245	If you want signals to be delivered truly asynchronously, just use	2407	If you want signals to be delivered truly asynchronously, just use
2246	C<sigaction> as you would do without libev and forget about sharing	2408	C<sigaction> as you would do without libev and forget about sharing
2247	the signal. You can even use C<ev_async> from a signal handler to	2409	the signal. You can even use C<ev_async> from a signal handler to
…		…
2251	only within the same loop, i.e. you can watch for C<SIGINT> in your	2413	only within the same loop, i.e. you can watch for C<SIGINT> in your
2252	default loop and for C<SIGIO> in another loop, but you cannot watch for	2414	default loop and for C<SIGIO> in another loop, but you cannot watch for
2253	C<SIGINT> in both the default loop and another loop at the same time. At	2415	C<SIGINT> in both the default loop and another loop at the same time. At
2254	the moment, C<SIGCHLD> is permanently tied to the default loop.	2416	the moment, C<SIGCHLD> is permanently tied to the default loop.
2255		2417
2256	When the first watcher gets started will libev actually register something	2418	Only after the first watcher for a signal is started will libev actually
2257	with the kernel (thus it coexists with your own signal handlers as long as	2419	register something with the kernel. It thus coexists with your own signal
2258	you don't register any with libev for the same signal).	2420	handlers as long as you don't register any with libev for the same signal.
2259		2421
2260	If possible and supported, libev will install its handlers with	2422	If possible and supported, libev will install its handlers with
2261	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should	2423	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
2262	not be unduly interrupted. If you have a problem with system calls getting	2424	not be unduly interrupted. If you have a problem with system calls getting
2263	interrupted by signals you can block all signals in an C<ev_check> watcher	2425	interrupted by signals you can block all signals in an C<ev_check> watcher
…		…
2266	=head3 The special problem of inheritance over fork/execve/pthread_create	2428	=head3 The special problem of inheritance over fork/execve/pthread_create
2267		2429
2268	Both the signal mask (C<sigprocmask>) and the signal disposition	2430	Both the signal mask (C<sigprocmask>) and the signal disposition
2269	(C<sigaction>) are unspecified after starting a signal watcher (and after	2431	(C<sigaction>) are unspecified after starting a signal watcher (and after
2270	stopping it again), that is, libev might or might not block the signal,	2432	stopping it again), that is, libev might or might not block the signal,
2271	and might or might not set or restore the installed signal handler.	2433	and might or might not set or restore the installed signal handler (but
		2434	see C<EVFLAG_NOSIGMASK>).
2272		2435
2273	While this does not matter for the signal disposition (libev never	2436	While this does not matter for the signal disposition (libev never
2274	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on	2437	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
2275	C<execve>), this matters for the signal mask: many programs do not expect	2438	C<execve>), this matters for the signal mask: many programs do not expect
2276	certain signals to be blocked.	2439	certain signals to be blocked.
…		…
2289	I<has> to modify the signal mask, at least temporarily.	2452	I<has> to modify the signal mask, at least temporarily.
2290		2453
2291	So I can't stress this enough: I<If you do not reset your signal mask when	2454	So I can't stress this enough: I<If you do not reset your signal mask when
2292	you expect it to be empty, you have a race condition in your code>. This	2455	you expect it to be empty, you have a race condition in your code>. This
2293	is not a libev-specific thing, this is true for most event libraries.	2456	is not a libev-specific thing, this is true for most event libraries.
		2457
		2458	=head3 The special problem of threads signal handling
		2459
		2460	POSIX threads has problematic signal handling semantics, specifically,
		2461	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2462	threads in a process block signals, which is hard to achieve.
		2463
		2464	When you want to use sigwait (or mix libev signal handling with your own
		2465	for the same signals), you can tackle this problem by globally blocking
		2466	all signals before creating any threads (or creating them with a fully set
		2467	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2468	loops. Then designate one thread as "signal receiver thread" which handles
		2469	these signals. You can pass on any signals that libev might be interested
		2470	in by calling C<ev_feed_signal>.
2294		2471
2295	=head3 Watcher-Specific Functions and Data Members	2472	=head3 Watcher-Specific Functions and Data Members
2296		2473
2297	=over 4	2474	=over 4
2298		2475
…		…
2433		2610
2434	=head2 C<ev_stat> - did the file attributes just change?	2611	=head2 C<ev_stat> - did the file attributes just change?
2435		2612
2436	This watches a file system path for attribute changes. That is, it calls	2613	This watches a file system path for attribute changes. That is, it calls
2437	C<stat> on that path in regular intervals (or when the OS says it changed)	2614	C<stat> on that path in regular intervals (or when the OS says it changed)
2438	and sees if it changed compared to the last time, invoking the callback if	2615	and sees if it changed compared to the last time, invoking the callback
2439	it did.	2616	if it did. Starting the watcher C<stat>'s the file, so only changes that
		2617	happen after the watcher has been started will be reported.
2440		2618
2441	The path does not need to exist: changing from "path exists" to "path does	2619	The path does not need to exist: changing from "path exists" to "path does
2442	not exist" is a status change like any other. The condition "path does not	2620	not exist" is a status change like any other. The condition "path does not
2443	exist" (or more correctly "path cannot be stat'ed") is signified by the	2621	exist" (or more correctly "path cannot be stat'ed") is signified by the
2444	C<st_nlink> field being zero (which is otherwise always forced to be at	2622	C<st_nlink> field being zero (which is otherwise always forced to be at
…		…
2674	Apart from keeping your process non-blocking (which is a useful	2852	Apart from keeping your process non-blocking (which is a useful
2675	effect on its own sometimes), idle watchers are a good place to do	2853	effect on its own sometimes), idle watchers are a good place to do
2676	"pseudo-background processing", or delay processing stuff to after the	2854	"pseudo-background processing", or delay processing stuff to after the
2677	event loop has handled all outstanding events.	2855	event loop has handled all outstanding events.
2678		2856
		2857	=head3 Abusing an C<ev_idle> watcher for its side-effect
		2858
		2859	As long as there is at least one active idle watcher, libev will never
		2860	sleep unnecessarily. Or in other words, it will loop as fast as possible.
		2861	For this to work, the idle watcher doesn't need to be invoked at all - the
		2862	lowest priority will do.
		2863
		2864	This mode of operation can be useful together with an C<ev_check> watcher,
		2865	to do something on each event loop iteration - for example to balance load
		2866	between different connections.
		2867
		2868	See L</Abusing an ev_check watcher for its side-effect> for a longer
		2869	example.
		2870
2679	=head3 Watcher-Specific Functions and Data Members	2871	=head3 Watcher-Specific Functions and Data Members
2680		2872
2681	=over 4	2873	=over 4
2682		2874
2683	=item ev_idle_init (ev_idle *, callback)	2875	=item ev_idle_init (ev_idle *, callback)
…		…
2694	callback, free it. Also, use no error checking, as usual.	2886	callback, free it. Also, use no error checking, as usual.
2695		2887
2696	static void	2888	static void
2697	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)	2889	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
2698	{	2890	{
		2891	// stop the watcher
		2892	ev_idle_stop (loop, w);
		2893
		2894	// now we can free it
2699	free (w);	2895	free (w);
		2896
2700	// now do something you wanted to do when the program has	2897	// now do something you wanted to do when the program has
2701	// no longer anything immediate to do.	2898	// no longer anything immediate to do.
2702	}	2899	}
2703		2900
2704	ev_idle *idle_watcher = malloc (sizeof (ev_idle));	2901	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
…		…
2706	ev_idle_start (loop, idle_watcher);	2903	ev_idle_start (loop, idle_watcher);
2707		2904
2708		2905
2709	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2906	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
2710		2907
2711	Prepare and check watchers are usually (but not always) used in pairs:	2908	Prepare and check watchers are often (but not always) used in pairs:
2712	prepare watchers get invoked before the process blocks and check watchers	2909	prepare watchers get invoked before the process blocks and check watchers
2713	afterwards.	2910	afterwards.
2714		2911
2715	You I<must not> call C<ev_run> or similar functions that enter	2912	You I<must not> call C<ev_run> or similar functions that enter
2716	the current event loop from either C<ev_prepare> or C<ev_check>	2913	the current event loop from either C<ev_prepare> or C<ev_check>
…		…
2744	with priority higher than or equal to the event loop and one coroutine	2941	with priority higher than or equal to the event loop and one coroutine
2745	of lower priority, but only once, using idle watchers to keep the event	2942	of lower priority, but only once, using idle watchers to keep the event
2746	loop from blocking if lower-priority coroutines are active, thus mapping	2943	loop from blocking if lower-priority coroutines are active, thus mapping
2747	low-priority coroutines to idle/background tasks).	2944	low-priority coroutines to idle/background tasks).
2748		2945
2749	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2946	When used for this purpose, it is recommended to give C<ev_check> watchers
2750	priority, to ensure that they are being run before any other watchers	2947	highest (C<EV_MAXPRI>) priority, to ensure that they are being run before
2751	after the poll (this doesn't matter for C<ev_prepare> watchers).	2948	any other watchers after the poll (this doesn't matter for C<ev_prepare>
		2949	watchers).
2752		2950
2753	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not	2951	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
2754	activate ("feed") events into libev. While libev fully supports this, they	2952	activate ("feed") events into libev. While libev fully supports this, they
2755	might get executed before other C<ev_check> watchers did their job. As	2953	might get executed before other C<ev_check> watchers did their job. As
2756	C<ev_check> watchers are often used to embed other (non-libev) event	2954	C<ev_check> watchers are often used to embed other (non-libev) event
2757	loops those other event loops might be in an unusable state until their	2955	loops those other event loops might be in an unusable state until their
2758	C<ev_check> watcher ran (always remind yourself to coexist peacefully with	2956	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
2759	others).	2957	others).
		2958
		2959	=head3 Abusing an C<ev_check> watcher for its side-effect
		2960
		2961	C<ev_check> (and less often also C<ev_prepare>) watchers can also be
		2962	useful because they are called once per event loop iteration. For
		2963	example, if you want to handle a large number of connections fairly, you
		2964	normally only do a bit of work for each active connection, and if there
		2965	is more work to do, you wait for the next event loop iteration, so other
		2966	connections have a chance of making progress.
		2967
		2968	Using an C<ev_check> watcher is almost enough: it will be called on the
		2969	next event loop iteration. However, that isn't as soon as possible -
		2970	without external events, your C<ev_check> watcher will not be invoked.
		2971
		2972	This is where C<ev_idle> watchers come in handy - all you need is a
		2973	single global idle watcher that is active as long as you have one active
		2974	C<ev_check> watcher. The C<ev_idle> watcher makes sure the event loop
		2975	will not sleep, and the C<ev_check> watcher makes sure a callback gets
		2976	invoked. Neither watcher alone can do that.
2760		2977
2761	=head3 Watcher-Specific Functions and Data Members	2978	=head3 Watcher-Specific Functions and Data Members
2762		2979
2763	=over 4	2980	=over 4
2764		2981
…		…
2965		3182
2966	=over 4	3183	=over 4
2967		3184
2968	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)	3185	=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
2969		3186
2970	=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)	3187	=item ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)
2971		3188
2972	Configures the watcher to embed the given loop, which must be	3189	Configures the watcher to embed the given loop, which must be
2973	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	3190	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
2974	invoked automatically, otherwise it is the responsibility of the callback	3191	invoked automatically, otherwise it is the responsibility of the callback
2975	to invoke it (it will continue to be called until the sweep has been done,	3192	to invoke it (it will continue to be called until the sweep has been done,
…		…
2996	used).	3213	used).
2997		3214
2998	struct ev_loop *loop_hi = ev_default_init (0);	3215	struct ev_loop *loop_hi = ev_default_init (0);
2999	struct ev_loop *loop_lo = 0;	3216	struct ev_loop *loop_lo = 0;
3000	ev_embed embed;	3217	ev_embed embed;
3001		3218
3002	// see if there is a chance of getting one that works	3219	// see if there is a chance of getting one that works
3003	// (remember that a flags value of 0 means autodetection)	3220	// (remember that a flags value of 0 means autodetection)
3004	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	3221	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3005	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	3222	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3006	: 0;	3223	: 0;
…		…
3020	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	3237	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
3021		3238
3022	struct ev_loop *loop = ev_default_init (0);	3239	struct ev_loop *loop = ev_default_init (0);
3023	struct ev_loop *loop_socket = 0;	3240	struct ev_loop *loop_socket = 0;
3024	ev_embed embed;	3241	ev_embed embed;
3025		3242
3026	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	3243	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3027	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	3244	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3028	{	3245	{
3029	ev_embed_init (&embed, 0, loop_socket);	3246	ev_embed_init (&embed, 0, loop_socket);
3030	ev_embed_start (loop, &embed);	3247	ev_embed_start (loop, &embed);
…		…
3038		3255
3039	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	3256	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
3040		3257
3041	Fork watchers are called when a C<fork ()> was detected (usually because	3258	Fork watchers are called when a C<fork ()> was detected (usually because
3042	whoever is a good citizen cared to tell libev about it by calling	3259	whoever is a good citizen cared to tell libev about it by calling
3043	C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the	3260	C<ev_loop_fork>). The invocation is done before the event loop blocks next
3044	event loop blocks next and before C<ev_check> watchers are being called,	3261	and before C<ev_check> watchers are being called, and only in the child
3045	and only in the child after the fork. If whoever good citizen calling	3262	after the fork. If whoever good citizen calling C<ev_default_fork> cheats
3046	C<ev_default_fork> cheats and calls it in the wrong process, the fork	3263	and calls it in the wrong process, the fork handlers will be invoked, too,
3047	handlers will be invoked, too, of course.	3264	of course.
3048		3265
3049	=head3 The special problem of life after fork - how is it possible?	3266	=head3 The special problem of life after fork - how is it possible?
3050		3267
3051	Most uses of C<fork()> consist of forking, then some simple calls to set	3268	Most uses of C<fork()> consist of forking, then some simple calls to set
3052	up/change the process environment, followed by a call to C<exec()>. This	3269	up/change the process environment, followed by a call to C<exec()>. This
…		…
3072	disadvantage of having to use multiple event loops (which do not support	3289	disadvantage of having to use multiple event loops (which do not support
3073	signal watchers).	3290	signal watchers).
3074		3291
3075	When this is not possible, or you want to use the default loop for	3292	When this is not possible, or you want to use the default loop for
3076	other reasons, then in the process that wants to start "fresh", call	3293	other reasons, then in the process that wants to start "fresh", call
3077	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying	3294	C<ev_loop_destroy (EV_DEFAULT)> followed by C<ev_default_loop (...)>.
3078	the default loop will "orphan" (not stop) all registered watchers, so you	3295	Destroying the default loop will "orphan" (not stop) all registered
3079	have to be careful not to execute code that modifies those watchers. Note	3296	watchers, so you have to be careful not to execute code that modifies
3080	also that in that case, you have to re-register any signal watchers.	3297	those watchers. Note also that in that case, you have to re-register any
		3298	signal watchers.
3081		3299
3082	=head3 Watcher-Specific Functions and Data Members	3300	=head3 Watcher-Specific Functions and Data Members
3083		3301
3084	=over 4	3302	=over 4
3085		3303
3086	=item ev_fork_init (ev_signal *, callback)	3304	=item ev_fork_init (ev_fork *, callback)
3087		3305
3088	Initialises and configures the fork watcher - it has no parameters of any	3306	Initialises and configures the fork watcher - it has no parameters of any
3089	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,	3307	kind. There is a C<ev_fork_set> macro, but using it is utterly pointless,
3090	believe me.	3308	really.
3091		3309
3092	=back	3310	=back
3093		3311
3094		3312
		3313	=head2 C<ev_cleanup> - even the best things end
		3314
		3315	Cleanup watchers are called just before the event loop is being destroyed
		3316	by a call to C<ev_loop_destroy>.
		3317
		3318	While there is no guarantee that the event loop gets destroyed, cleanup
		3319	watchers provide a convenient method to install cleanup hooks for your
		3320	program, worker threads and so on - you just to make sure to destroy the
		3321	loop when you want them to be invoked.
		3322
		3323	Cleanup watchers are invoked in the same way as any other watcher. Unlike
		3324	all other watchers, they do not keep a reference to the event loop (which
		3325	makes a lot of sense if you think about it). Like all other watchers, you
		3326	can call libev functions in the callback, except C<ev_cleanup_start>.
		3327
		3328	=head3 Watcher-Specific Functions and Data Members
		3329
		3330	=over 4
		3331
		3332	=item ev_cleanup_init (ev_cleanup *, callback)
		3333
		3334	Initialises and configures the cleanup watcher - it has no parameters of
		3335	any kind. There is a C<ev_cleanup_set> macro, but using it is utterly
		3336	pointless, I assure you.
		3337
		3338	=back
		3339
		3340	Example: Register an atexit handler to destroy the default loop, so any
		3341	cleanup functions are called.
		3342
		3343	static void
		3344	program_exits (void)
		3345	{
		3346	ev_loop_destroy (EV_DEFAULT_UC);
		3347	}
		3348
		3349	...
		3350	atexit (program_exits);
		3351
		3352
3095	=head2 C<ev_async> - how to wake up an event loop	3353	=head2 C<ev_async> - how to wake up an event loop
3096		3354
3097	In general, you cannot use an C<ev_run> from multiple threads or other	3355	In general, you cannot use an C<ev_loop> from multiple threads or other
3098	asynchronous sources such as signal handlers (as opposed to multiple event	3356	asynchronous sources such as signal handlers (as opposed to multiple event
3099	loops - those are of course safe to use in different threads).	3357	loops - those are of course safe to use in different threads).
3100		3358
3101	Sometimes, however, you need to wake up an event loop you do not control,	3359	Sometimes, however, you need to wake up an event loop you do not control,
3102	for example because it belongs to another thread. This is what C<ev_async>	3360	for example because it belongs to another thread. This is what C<ev_async>
…		…
3104	it by calling C<ev_async_send>, which is thread- and signal safe.	3362	it by calling C<ev_async_send>, which is thread- and signal safe.
3105		3363
3106	This functionality is very similar to C<ev_signal> watchers, as signals,	3364	This functionality is very similar to C<ev_signal> watchers, as signals,
3107	too, are asynchronous in nature, and signals, too, will be compressed	3365	too, are asynchronous in nature, and signals, too, will be compressed
3108	(i.e. the number of callback invocations may be less than the number of	3366	(i.e. the number of callback invocations may be less than the number of
3109	C<ev_async_sent> calls).	3367	C<ev_async_send> calls). In fact, you could use signal watchers as a kind
3110		3368	of "global async watchers" by using a watcher on an otherwise unused
3111	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not	3369	signal, and C<ev_feed_signal> to signal this watcher from another thread,
3112	just the default loop.	3370	even without knowing which loop owns the signal.
3113		3371
3114	=head3 Queueing	3372	=head3 Queueing
3115		3373
3116	C<ev_async> does not support queueing of data in any way. The reason	3374	C<ev_async> does not support queueing of data in any way. The reason
3117	is that the author does not know of a simple (or any) algorithm for a	3375	is that the author does not know of a simple (or any) algorithm for a
…		…
3209	trust me.	3467	trust me.
3210		3468
3211	=item ev_async_send (loop, ev_async *)	3469	=item ev_async_send (loop, ev_async *)
3212		3470
3213	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3471	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
3214	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3472	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3473	returns.
		3474
3215	C<ev_feed_event>, this call is safe to do from other threads, signal or	3475	Unlike C<ev_feed_event>, this call is safe to do from other threads,
3216	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3476	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
3217	section below on what exactly this means).	3477	embedding section below on what exactly this means).
3218		3478
3219	Note that, as with other watchers in libev, multiple events might get	3479	Note that, as with other watchers in libev, multiple events might get
3220	compressed into a single callback invocation (another way to look at this	3480	compressed into a single callback invocation (another way to look at
3221	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,	3481	this is that C<ev_async> watchers are level-triggered: they are set on
3222	reset when the event loop detects that).	3482	C<ev_async_send>, reset when the event loop detects that).
3223		3483
3224	This call incurs the overhead of a system call only once per event loop	3484	This call incurs the overhead of at most one extra system call per event
3225	iteration, so while the overhead might be noticeable, it doesn't apply to	3485	loop iteration, if the event loop is blocked, and no syscall at all if
3226	repeated calls to C<ev_async_send> for the same event loop.	3486	the event loop (or your program) is processing events. That means that
		3487	repeated calls are basically free (there is no need to avoid calls for
		3488	performance reasons) and that the overhead becomes smaller (typically
		3489	zero) under load.
3227		3490
3228	=item bool = ev_async_pending (ev_async *)	3491	=item bool = ev_async_pending (ev_async *)
3229		3492
3230	Returns a non-zero value when C<ev_async_send> has been called on the	3493	Returns a non-zero value when C<ev_async_send> has been called on the
3231	watcher but the event has not yet been processed (or even noted) by the	3494	watcher but the event has not yet been processed (or even noted) by the
…		…
3286	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3549	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3287		3550
3288	=item ev_feed_fd_event (loop, int fd, int revents)	3551	=item ev_feed_fd_event (loop, int fd, int revents)
3289		3552
3290	Feed an event on the given fd, as if a file descriptor backend detected	3553	Feed an event on the given fd, as if a file descriptor backend detected
3291	the given events it.	3554	the given events.
3292		3555
3293	=item ev_feed_signal_event (loop, int signum)	3556	=item ev_feed_signal_event (loop, int signum)
3294		3557
3295	Feed an event as if the given signal occurred (C<loop> must be the default	3558	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3296	loop!).	3559	which is async-safe.
3297		3560
3298	=back	3561	=back
		3562
		3563
		3564	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3565
		3566	This section explains some common idioms that are not immediately
		3567	obvious. Note that examples are sprinkled over the whole manual, and this
		3568	section only contains stuff that wouldn't fit anywhere else.
		3569
		3570	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3571
		3572	Each watcher has, by default, a C<void *data> member that you can read
		3573	or modify at any time: libev will completely ignore it. This can be used
		3574	to associate arbitrary data with your watcher. If you need more data and
		3575	don't want to allocate memory separately and store a pointer to it in that
		3576	data member, you can also "subclass" the watcher type and provide your own
		3577	data:
		3578
		3579	struct my_io
		3580	{
		3581	ev_io io;
		3582	int otherfd;
		3583	void *somedata;
		3584	struct whatever *mostinteresting;
		3585	};
		3586
		3587	...
		3588	struct my_io w;
		3589	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3590
		3591	And since your callback will be called with a pointer to the watcher, you
		3592	can cast it back to your own type:
		3593
		3594	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
		3595	{
		3596	struct my_io *w = (struct my_io *)w_;
		3597	...
		3598	}
		3599
		3600	More interesting and less C-conformant ways of casting your callback
		3601	function type instead have been omitted.
		3602
		3603	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3604
		3605	Another common scenario is to use some data structure with multiple
		3606	embedded watchers, in effect creating your own watcher that combines
		3607	multiple libev event sources into one "super-watcher":
		3608
		3609	struct my_biggy
		3610	{
		3611	int some_data;
		3612	ev_timer t1;
		3613	ev_timer t2;
		3614	}
		3615
		3616	In this case getting the pointer to C<my_biggy> is a bit more
		3617	complicated: Either you store the address of your C<my_biggy> struct in
		3618	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3619	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3620	real programmers):
		3621
		3622	#include <stddef.h>
		3623
		3624	static void
		3625	t1_cb (EV_P_ ev_timer *w, int revents)
		3626	{
		3627	struct my_biggy big = (struct my_biggy *)
		3628	(((char *)w) - offsetof (struct my_biggy, t1));
		3629	}
		3630
		3631	static void
		3632	t2_cb (EV_P_ ev_timer *w, int revents)
		3633	{
		3634	struct my_biggy big = (struct my_biggy *)
		3635	(((char *)w) - offsetof (struct my_biggy, t2));
		3636	}
		3637
		3638	=head2 AVOIDING FINISHING BEFORE RETURNING
		3639
		3640	Often you have structures like this in event-based programs:
		3641
		3642	callback ()
		3643	{
		3644	free (request);
		3645	}
		3646
		3647	request = start_new_request (..., callback);
		3648
		3649	The intent is to start some "lengthy" operation. The C<request> could be
		3650	used to cancel the operation, or do other things with it.
		3651
		3652	It's not uncommon to have code paths in C<start_new_request> that
		3653	immediately invoke the callback, for example, to report errors. Or you add
		3654	some caching layer that finds that it can skip the lengthy aspects of the
		3655	operation and simply invoke the callback with the result.
		3656
		3657	The problem here is that this will happen I<before> C<start_new_request>
		3658	has returned, so C<request> is not set.
		3659
		3660	Even if you pass the request by some safer means to the callback, you
		3661	might want to do something to the request after starting it, such as
		3662	canceling it, which probably isn't working so well when the callback has
		3663	already been invoked.
		3664
		3665	A common way around all these issues is to make sure that
		3666	C<start_new_request> I<always> returns before the callback is invoked. If
		3667	C<start_new_request> immediately knows the result, it can artificially
		3668	delay invoking the callback by using a C<prepare> or C<idle> watcher for
		3669	example, or more sneakily, by reusing an existing (stopped) watcher and
		3670	pushing it into the pending queue:
		3671
		3672	ev_set_cb (watcher, callback);
		3673	ev_feed_event (EV_A_ watcher, 0);
		3674
		3675	This way, C<start_new_request> can safely return before the callback is
		3676	invoked, while not delaying callback invocation too much.
		3677
		3678	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3679
		3680	Often (especially in GUI toolkits) there are places where you have
		3681	I<modal> interaction, which is most easily implemented by recursively
		3682	invoking C<ev_run>.
		3683
		3684	This brings the problem of exiting - a callback might want to finish the
		3685	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3686	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3687	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3688	other combination: In these cases, a simple C<ev_break> will not work.
		3689
		3690	The solution is to maintain "break this loop" variable for each C<ev_run>
		3691	invocation, and use a loop around C<ev_run> until the condition is
		3692	triggered, using C<EVRUN_ONCE>:
		3693
		3694	// main loop
		3695	int exit_main_loop = 0;
		3696
		3697	while (!exit_main_loop)
		3698	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3699
		3700	// in a modal watcher
		3701	int exit_nested_loop = 0;
		3702
		3703	while (!exit_nested_loop)
		3704	ev_run (EV_A_ EVRUN_ONCE);
		3705
		3706	To exit from any of these loops, just set the corresponding exit variable:
		3707
		3708	// exit modal loop
		3709	exit_nested_loop = 1;
		3710
		3711	// exit main program, after modal loop is finished
		3712	exit_main_loop = 1;
		3713
		3714	// exit both
		3715	exit_main_loop = exit_nested_loop = 1;
		3716
		3717	=head2 THREAD LOCKING EXAMPLE
		3718
		3719	Here is a fictitious example of how to run an event loop in a different
		3720	thread from where callbacks are being invoked and watchers are
		3721	created/added/removed.
		3722
		3723	For a real-world example, see the C<EV::Loop::Async> perl module,
		3724	which uses exactly this technique (which is suited for many high-level
		3725	languages).
		3726
		3727	The example uses a pthread mutex to protect the loop data, a condition
		3728	variable to wait for callback invocations, an async watcher to notify the
		3729	event loop thread and an unspecified mechanism to wake up the main thread.
		3730
		3731	First, you need to associate some data with the event loop:
		3732
		3733	typedef struct {
		3734	mutex_t lock; /* global loop lock */
		3735	ev_async async_w;
		3736	thread_t tid;
		3737	cond_t invoke_cv;
		3738	} userdata;
		3739
		3740	void prepare_loop (EV_P)
		3741	{
		3742	// for simplicity, we use a static userdata struct.
		3743	static userdata u;
		3744
		3745	ev_async_init (&u->async_w, async_cb);
		3746	ev_async_start (EV_A_ &u->async_w);
		3747
		3748	pthread_mutex_init (&u->lock, 0);
		3749	pthread_cond_init (&u->invoke_cv, 0);
		3750
		3751	// now associate this with the loop
		3752	ev_set_userdata (EV_A_ u);
		3753	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3754	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3755
		3756	// then create the thread running ev_run
		3757	pthread_create (&u->tid, 0, l_run, EV_A);
		3758	}
		3759
		3760	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3761	solely to wake up the event loop so it takes notice of any new watchers
		3762	that might have been added:
		3763
		3764	static void
		3765	async_cb (EV_P_ ev_async *w, int revents)
		3766	{
		3767	// just used for the side effects
		3768	}
		3769
		3770	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3771	protecting the loop data, respectively.
		3772
		3773	static void
		3774	l_release (EV_P)
		3775	{
		3776	userdata *u = ev_userdata (EV_A);
		3777	pthread_mutex_unlock (&u->lock);
		3778	}
		3779
		3780	static void
		3781	l_acquire (EV_P)
		3782	{
		3783	userdata *u = ev_userdata (EV_A);
		3784	pthread_mutex_lock (&u->lock);
		3785	}
		3786
		3787	The event loop thread first acquires the mutex, and then jumps straight
		3788	into C<ev_run>:
		3789
		3790	void *
		3791	l_run (void *thr_arg)
		3792	{
		3793	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		3794
		3795	l_acquire (EV_A);
		3796	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3797	ev_run (EV_A_ 0);
		3798	l_release (EV_A);
		3799
		3800	return 0;
		3801	}
		3802
		3803	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3804	signal the main thread via some unspecified mechanism (signals? pipe
		3805	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3806	have been called (in a while loop because a) spurious wakeups are possible
		3807	and b) skipping inter-thread-communication when there are no pending
		3808	watchers is very beneficial):
		3809
		3810	static void
		3811	l_invoke (EV_P)
		3812	{
		3813	userdata *u = ev_userdata (EV_A);
		3814
		3815	while (ev_pending_count (EV_A))
		3816	{
		3817	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3818	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3819	}
		3820	}
		3821
		3822	Now, whenever the main thread gets told to invoke pending watchers, it
		3823	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3824	thread to continue:
		3825
		3826	static void
		3827	real_invoke_pending (EV_P)
		3828	{
		3829	userdata *u = ev_userdata (EV_A);
		3830
		3831	pthread_mutex_lock (&u->lock);
		3832	ev_invoke_pending (EV_A);
		3833	pthread_cond_signal (&u->invoke_cv);
		3834	pthread_mutex_unlock (&u->lock);
		3835	}
		3836
		3837	Whenever you want to start/stop a watcher or do other modifications to an
		3838	event loop, you will now have to lock:
		3839
		3840	ev_timer timeout_watcher;
		3841	userdata *u = ev_userdata (EV_A);
		3842
		3843	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3844
		3845	pthread_mutex_lock (&u->lock);
		3846	ev_timer_start (EV_A_ &timeout_watcher);
		3847	ev_async_send (EV_A_ &u->async_w);
		3848	pthread_mutex_unlock (&u->lock);
		3849
		3850	Note that sending the C<ev_async> watcher is required because otherwise
		3851	an event loop currently blocking in the kernel will have no knowledge
		3852	about the newly added timer. By waking up the loop it will pick up any new
		3853	watchers in the next event loop iteration.
		3854
		3855	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3856
		3857	While the overhead of a callback that e.g. schedules a thread is small, it
		3858	is still an overhead. If you embed libev, and your main usage is with some
		3859	kind of threads or coroutines, you might want to customise libev so that
		3860	doesn't need callbacks anymore.
		3861
		3862	Imagine you have coroutines that you can switch to using a function
		3863	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3864	and that due to some magic, the currently active coroutine is stored in a
		3865	global called C<current_coro>. Then you can build your own "wait for libev
		3866	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3867	the differing C<;> conventions):
		3868
		3869	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3870	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3871
		3872	That means instead of having a C callback function, you store the
		3873	coroutine to switch to in each watcher, and instead of having libev call
		3874	your callback, you instead have it switch to that coroutine.
		3875
		3876	A coroutine might now wait for an event with a function called
		3877	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3878	matter when, or whether the watcher is active or not when this function is
		3879	called):
		3880
		3881	void
		3882	wait_for_event (ev_watcher *w)
		3883	{
		3884	ev_set_cb (w, current_coro);
		3885	switch_to (libev_coro);
		3886	}
		3887
		3888	That basically suspends the coroutine inside C<wait_for_event> and
		3889	continues the libev coroutine, which, when appropriate, switches back to
		3890	this or any other coroutine.
		3891
		3892	You can do similar tricks if you have, say, threads with an event queue -
		3893	instead of storing a coroutine, you store the queue object and instead of
		3894	switching to a coroutine, you push the watcher onto the queue and notify
		3895	any waiters.
		3896
		3897	To embed libev, see L</EMBEDDING>, but in short, it's easiest to create two
		3898	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3899
		3900	// my_ev.h
		3901	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3902	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);
		3903	#include "../libev/ev.h"
		3904
		3905	// my_ev.c
		3906	#define EV_H "my_ev.h"
		3907	#include "../libev/ev.c"
		3908
		3909	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3910	F<my_ev.c> into your project. When properly specifying include paths, you
		3911	can even use F<ev.h> as header file name directly.
3299		3912
3300		3913
3301	=head1 LIBEVENT EMULATION	3914	=head1 LIBEVENT EMULATION
3302		3915
3303	Libev offers a compatibility emulation layer for libevent. It cannot	3916	Libev offers a compatibility emulation layer for libevent. It cannot
3304	emulate the internals of libevent, so here are some usage hints:	3917	emulate the internals of libevent, so here are some usage hints:
3305		3918
3306	=over 4	3919	=over 4
		3920
		3921	=item * Only the libevent-1.4.1-beta API is being emulated.
		3922
		3923	This was the newest libevent version available when libev was implemented,
		3924	and is still mostly unchanged in 2010.
3307		3925
3308	=item * Use it by including <event.h>, as usual.	3926	=item * Use it by including <event.h>, as usual.
3309		3927
3310	=item * The following members are fully supported: ev_base, ev_callback,	3928	=item * The following members are fully supported: ev_base, ev_callback,
3311	ev_arg, ev_fd, ev_res, ev_events.	3929	ev_arg, ev_fd, ev_res, ev_events.
…		…
3317	=item * Priorities are not currently supported. Initialising priorities	3935	=item * Priorities are not currently supported. Initialising priorities
3318	will fail and all watchers will have the same priority, even though there	3936	will fail and all watchers will have the same priority, even though there
3319	is an ev_pri field.	3937	is an ev_pri field.
3320		3938
3321	=item * In libevent, the last base created gets the signals, in libev, the	3939	=item * In libevent, the last base created gets the signals, in libev, the
3322	first base created (== the default loop) gets the signals.	3940	base that registered the signal gets the signals.
3323		3941
3324	=item * Other members are not supported.	3942	=item * Other members are not supported.
3325		3943
3326	=item * The libev emulation is I<not> ABI compatible to libevent, you need	3944	=item * The libev emulation is I<not> ABI compatible to libevent, you need
3327	to use the libev header file and library.	3945	to use the libev header file and library.
3328		3946
3329	=back	3947	=back
3330		3948
3331	=head1 C++ SUPPORT	3949	=head1 C++ SUPPORT
		3950
		3951	=head2 C API
		3952
		3953	The normal C API should work fine when used from C++: both ev.h and the
		3954	libev sources can be compiled as C++. Therefore, code that uses the C API
		3955	will work fine.
		3956
		3957	Proper exception specifications might have to be added to callbacks passed
		3958	to libev: exceptions may be thrown only from watcher callbacks, all
		3959	other callbacks (allocator, syserr, loop acquire/release and periodic
		3960	reschedule callbacks) must not throw exceptions, and might need a C<throw
		3961	()> specification. If you have code that needs to be compiled as both C
		3962	and C++ you can use the C<EV_THROW> macro for this:
		3963
		3964	static void
		3965	fatal_error (const char *msg) EV_THROW
		3966	{
		3967	perror (msg);
		3968	abort ();
		3969	}
		3970
		3971	...
		3972	ev_set_syserr_cb (fatal_error);
		3973
		3974	The only API functions that can currently throw exceptions are C<ev_run>,
		3975	C<ev_invoke>, C<ev_invoke_pending> and C<ev_loop_destroy> (the latter
		3976	because it runs cleanup watchers).
		3977
		3978	Throwing exceptions in watcher callbacks is only supported if libev itself
		3979	is compiled with a C++ compiler or your C and C++ environments allow
		3980	throwing exceptions through C libraries (most do).
		3981
		3982	=head2 C++ API
3332		3983
3333	Libev comes with some simplistic wrapper classes for C++ that mainly allow	3984	Libev comes with some simplistic wrapper classes for C++ that mainly allow
3334	you to use some convenience methods to start/stop watchers and also change	3985	you to use some convenience methods to start/stop watchers and also change
3335	the callback model to a model using method callbacks on objects.	3986	the callback model to a model using method callbacks on objects.
3336		3987
3337	To use it,	3988	To use it,
3338		3989
3339	#include <ev++.h>	3990	#include <ev++.h>
3340		3991
3341	This automatically includes F<ev.h> and puts all of its definitions (many	3992	This automatically includes F<ev.h> and puts all of its definitions (many
3342	of them macros) into the global namespace. All C++ specific things are	3993	of them macros) into the global namespace. All C++ specific things are
3343	put into the C<ev> namespace. It should support all the same embedding	3994	put into the C<ev> namespace. It should support all the same embedding
…		…
3346	Care has been taken to keep the overhead low. The only data member the C++	3997	Care has been taken to keep the overhead low. The only data member the C++
3347	classes add (compared to plain C-style watchers) is the event loop pointer	3998	classes add (compared to plain C-style watchers) is the event loop pointer
3348	that the watcher is associated with (or no additional members at all if	3999	that the watcher is associated with (or no additional members at all if
3349	you disable C<EV_MULTIPLICITY> when embedding libev).	4000	you disable C<EV_MULTIPLICITY> when embedding libev).
3350		4001
3351	Currently, functions, and static and non-static member functions can be	4002	Currently, functions, static and non-static member functions and classes
3352	used as callbacks. Other types should be easy to add as long as they only	4003	with C<operator ()> can be used as callbacks. Other types should be easy
3353	need one additional pointer for context. If you need support for other	4004	to add as long as they only need one additional pointer for context. If
3354	types of functors please contact the author (preferably after implementing	4005	you need support for other types of functors please contact the author
3355	it).	4006	(preferably after implementing it).
		4007
		4008	For all this to work, your C++ compiler either has to use the same calling
		4009	conventions as your C compiler (for static member functions), or you have
		4010	to embed libev and compile libev itself as C++.
3356		4011
3357	Here is a list of things available in the C<ev> namespace:	4012	Here is a list of things available in the C<ev> namespace:
3358		4013
3359	=over 4	4014	=over 4
3360		4015
…		…
3370	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	4025	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
3371		4026
3372	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	4027	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
3373	the same name in the C<ev> namespace, with the exception of C<ev_signal>	4028	the same name in the C<ev> namespace, with the exception of C<ev_signal>
3374	which is called C<ev::sig> to avoid clashes with the C<signal> macro	4029	which is called C<ev::sig> to avoid clashes with the C<signal> macro
3375	defines by many implementations.	4030	defined by many implementations.
3376		4031
3377	All of those classes have these methods:	4032	All of those classes have these methods:
3378		4033
3379	=over 4	4034	=over 4
3380		4035
…		…
3442	void operator() (ev::io &w, int revents)	4097	void operator() (ev::io &w, int revents)
3443	{	4098	{
3444	...	4099	...
3445	}	4100	}
3446	}	4101	}
3447		4102
3448	myfunctor f;	4103	myfunctor f;
3449		4104
3450	ev::io w;	4105	ev::io w;
3451	w.set (&f);	4106	w.set (&f);
3452		4107
…		…
3470	Associates a different C<struct ev_loop> with this watcher. You can only	4125	Associates a different C<struct ev_loop> with this watcher. You can only
3471	do this when the watcher is inactive (and not pending either).	4126	do this when the watcher is inactive (and not pending either).
3472		4127
3473	=item w->set ([arguments])	4128	=item w->set ([arguments])
3474		4129
3475	Basically the same as C<ev_TYPE_set>, with the same arguments. Either this	4130	Basically the same as C<ev_TYPE_set> (except for C<ev::embed> watchers>),
3476	method or a suitable start method must be called at least once. Unlike the	4131	with the same arguments. Either this method or a suitable start method
3477	C counterpart, an active watcher gets automatically stopped and restarted	4132	must be called at least once. Unlike the C counterpart, an active watcher
3478	when reconfiguring it with this method.	4133	gets automatically stopped and restarted when reconfiguring it with this
		4134	method.
		4135
		4136	For C<ev::embed> watchers this method is called C<set_embed>, to avoid
		4137	clashing with the C<set (loop)> method.
3479		4138
3480	=item w->start ()	4139	=item w->start ()
3481		4140
3482	Starts the watcher. Note that there is no C<loop> argument, as the	4141	Starts the watcher. Note that there is no C<loop> argument, as the
3483	constructor already stores the event loop.	4142	constructor already stores the event loop.
…		…
3513	watchers in the constructor.	4172	watchers in the constructor.
3514		4173
3515	class myclass	4174	class myclass
3516	{	4175	{
3517	ev::io io ; void io_cb (ev::io &w, int revents);	4176	ev::io io ; void io_cb (ev::io &w, int revents);
3518	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);	4177	ev::io io2 ; void io2_cb (ev::io &w, int revents);
3519	ev::idle idle; void idle_cb (ev::idle &w, int revents);	4178	ev::idle idle; void idle_cb (ev::idle &w, int revents);
3520		4179
3521	myclass (int fd)	4180	myclass (int fd)
3522	{	4181	{
3523	io .set <myclass, &myclass::io_cb > (this);	4182	io .set <myclass, &myclass::io_cb > (this);
…		…
3574	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.	4233	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
3575		4234
3576	=item D	4235	=item D
3577		4236
3578	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4237	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
3579	be found at L<http://proj.llucax.com.ar/wiki/evd>.	4238	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
3580		4239
3581	=item Ocaml	4240	=item Ocaml
3582		4241
3583	Erkki Seppala has written Ocaml bindings for libev, to be found at	4242	Erkki Seppala has written Ocaml bindings for libev, to be found at
3584	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	4243	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
…		…
3587		4246
3588	Brian Maher has written a partial interface to libev for lua (at the	4247	Brian Maher has written a partial interface to libev for lua (at the
3589	time of this writing, only C<ev_io> and C<ev_timer>), to be found at	4248	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
3590	L<http://github.com/brimworks/lua-ev>.	4249	L<http://github.com/brimworks/lua-ev>.
3591		4250
		4251	=item Javascript
		4252
		4253	Node.js (L<http://nodejs.org>) uses libev as the underlying event library.
		4254
		4255	=item Others
		4256
		4257	There are others, and I stopped counting.
		4258
3592	=back	4259	=back
3593		4260
3594		4261
3595	=head1 MACRO MAGIC	4262	=head1 MACRO MAGIC
3596		4263
…		…
3632	suitable for use with C<EV_A>.	4299	suitable for use with C<EV_A>.
3633		4300
3634	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4301	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
3635		4302
3636	Similar to the other two macros, this gives you the value of the default	4303	Similar to the other two macros, this gives you the value of the default
3637	loop, if multiple loops are supported ("ev loop default").	4304	loop, if multiple loops are supported ("ev loop default"). The default loop
		4305	will be initialised if it isn't already initialised.
		4306
		4307	For non-multiplicity builds, these macros do nothing, so you always have
		4308	to initialise the loop somewhere.
3638		4309
3639	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4310	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
3640		4311
3641	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4312	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
3642	default loop has been initialised (C<UC> == unchecked). Their behaviour	4313	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
3787	supported). It will also not define any of the structs usually found in	4458	supported). It will also not define any of the structs usually found in
3788	F<event.h> that are not directly supported by the libev core alone.	4459	F<event.h> that are not directly supported by the libev core alone.
3789		4460
3790	In standalone mode, libev will still try to automatically deduce the	4461	In standalone mode, libev will still try to automatically deduce the
3791	configuration, but has to be more conservative.	4462	configuration, but has to be more conservative.
		4463
		4464	=item EV_USE_FLOOR
		4465
		4466	If defined to be C<1>, libev will use the C<floor ()> function for its
		4467	periodic reschedule calculations, otherwise libev will fall back on a
		4468	portable (slower) implementation. If you enable this, you usually have to
		4469	link against libm or something equivalent. Enabling this when the C<floor>
		4470	function is not available will fail, so the safe default is to not enable
		4471	this.
3792		4472
3793	=item EV_USE_MONOTONIC	4473	=item EV_USE_MONOTONIC
3794		4474
3795	If defined to be C<1>, libev will try to detect the availability of the	4475	If defined to be C<1>, libev will try to detect the availability of the
3796	monotonic clock option at both compile time and runtime. Otherwise no	4476	monotonic clock option at both compile time and runtime. Otherwise no
…		…
3881		4561
3882	If programs implement their own fd to handle mapping on win32, then this	4562	If programs implement their own fd to handle mapping on win32, then this
3883	macro can be used to override the C<close> function, useful to unregister	4563	macro can be used to override the C<close> function, useful to unregister
3884	file descriptors again. Note that the replacement function has to close	4564	file descriptors again. Note that the replacement function has to close
3885	the underlying OS handle.	4565	the underlying OS handle.
		4566
		4567	=item EV_USE_WSASOCKET
		4568
		4569	If defined to be C<1>, libev will use C<WSASocket> to create its internal
		4570	communication socket, which works better in some environments. Otherwise,
		4571	the normal C<socket> function will be used, which works better in other
		4572	environments.
3886		4573
3887	=item EV_USE_POLL	4574	=item EV_USE_POLL
3888		4575
3889	If defined to be C<1>, libev will compile in support for the C<poll>(2)	4576	If defined to be C<1>, libev will compile in support for the C<poll>(2)
3890	backend. Otherwise it will be enabled on non-win32 platforms. It	4577	backend. Otherwise it will be enabled on non-win32 platforms. It
…		…
3926	If defined to be C<1>, libev will compile in support for the Linux inotify	4613	If defined to be C<1>, libev will compile in support for the Linux inotify
3927	interface to speed up C<ev_stat> watchers. Its actual availability will	4614	interface to speed up C<ev_stat> watchers. Its actual availability will
3928	be detected at runtime. If undefined, it will be enabled if the headers	4615	be detected at runtime. If undefined, it will be enabled if the headers
3929	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4616	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
3930		4617
		4618	=item EV_NO_SMP
		4619
		4620	If defined to be C<1>, libev will assume that memory is always coherent
		4621	between threads, that is, threads can be used, but threads never run on
		4622	different cpus (or different cpu cores). This reduces dependencies
		4623	and makes libev faster.
		4624
		4625	=item EV_NO_THREADS
		4626
		4627	If defined to be C<1>, libev will assume that it will never be called from
		4628	different threads (that includes signal handlers), which is a stronger
		4629	assumption than C<EV_NO_SMP>, above. This reduces dependencies and makes
		4630	libev faster.
		4631
3931	=item EV_ATOMIC_T	4632	=item EV_ATOMIC_T
3932		4633
3933	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4634	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
3934	access is atomic with respect to other threads or signal contexts. No such	4635	access is atomic with respect to other threads or signal contexts. No
3935	type is easily found in the C language, so you can provide your own type	4636	such type is easily found in the C language, so you can provide your own
3936	that you know is safe for your purposes. It is used both for signal handler "locking"	4637	type that you know is safe for your purposes. It is used both for signal
3937	as well as for signal and thread safety in C<ev_async> watchers.	4638	handler "locking" as well as for signal and thread safety in C<ev_async>
		4639	watchers.
3938		4640
3939	In the absence of this define, libev will use C<sig_atomic_t volatile>	4641	In the absence of this define, libev will use C<sig_atomic_t volatile>
3940	(from F<signal.h>), which is usually good enough on most platforms.	4642	(from F<signal.h>), which is usually good enough on most platforms.
3941		4643
3942	=item EV_H (h)	4644	=item EV_H (h)
…		…
3969	will have the C<struct ev_loop *> as first argument, and you can create	4671	will have the C<struct ev_loop *> as first argument, and you can create
3970	additional independent event loops. Otherwise there will be no support	4672	additional independent event loops. Otherwise there will be no support
3971	for multiple event loops and there is no first event loop pointer	4673	for multiple event loops and there is no first event loop pointer
3972	argument. Instead, all functions act on the single default loop.	4674	argument. Instead, all functions act on the single default loop.
3973		4675
		4676	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4677	default loop when multiplicity is switched off - you always have to
		4678	initialise the loop manually in this case.
		4679
3974	=item EV_MINPRI	4680	=item EV_MINPRI
3975		4681
3976	=item EV_MAXPRI	4682	=item EV_MAXPRI
3977		4683
3978	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4684	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
4014	#define EV_USE_POLL 1	4720	#define EV_USE_POLL 1
4015	#define EV_CHILD_ENABLE 1	4721	#define EV_CHILD_ENABLE 1
4016	#define EV_ASYNC_ENABLE 1	4722	#define EV_ASYNC_ENABLE 1
4017		4723
4018	The actual value is a bitset, it can be a combination of the following	4724	The actual value is a bitset, it can be a combination of the following
4019	values:	4725	values (by default, all of these are enabled):
4020		4726
4021	=over 4	4727	=over 4
4022		4728
4023	=item C<1> - faster/larger code	4729	=item C<1> - faster/larger code
4024		4730
…		…
4028	code size by roughly 30% on amd64).	4734	code size by roughly 30% on amd64).
4029		4735
4030	When optimising for size, use of compiler flags such as C<-Os> with	4736	When optimising for size, use of compiler flags such as C<-Os> with
4031	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of	4737	gcc is recommended, as well as C<-DNDEBUG>, as libev contains a number of
4032	assertions.	4738	assertions.
		4739
		4740	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4741	(e.g. gcc with C<-Os>).
4033		4742
4034	=item C<2> - faster/larger data structures	4743	=item C<2> - faster/larger data structures
4035		4744
4036	Replaces the small 2-heap for timer management by a faster 4-heap, larger	4745	Replaces the small 2-heap for timer management by a faster 4-heap, larger
4037	hash table sizes and so on. This will usually further increase code size	4746	hash table sizes and so on. This will usually further increase code size
4038	and can additionally have an effect on the size of data structures at	4747	and can additionally have an effect on the size of data structures at
4039	runtime.	4748	runtime.
4040		4749
		4750	The default is off when C<__OPTIMIZE_SIZE__> is defined by your compiler
		4751	(e.g. gcc with C<-Os>).
		4752
4041	=item C<4> - full API configuration	4753	=item C<4> - full API configuration
4042		4754
4043	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and	4755	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
4044	enables multiplicity (C<EV_MULTIPLICITY>=1).	4756	enables multiplicity (C<EV_MULTIPLICITY>=1).
4045		4757
…		…
4075		4787
4076	With an intelligent-enough linker (gcc+binutils are intelligent enough	4788	With an intelligent-enough linker (gcc+binutils are intelligent enough
4077	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by	4789	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
4078	your program might be left out as well - a binary starting a timer and an	4790	your program might be left out as well - a binary starting a timer and an
4079	I/O watcher then might come out at only 5Kb.	4791	I/O watcher then might come out at only 5Kb.
		4792
		4793	=item EV_API_STATIC
		4794
		4795	If this symbol is defined (by default it is not), then all identifiers
		4796	will have static linkage. This means that libev will not export any
		4797	identifiers, and you cannot link against libev anymore. This can be useful
		4798	when you embed libev, only want to use libev functions in a single file,
		4799	and do not want its identifiers to be visible.
		4800
		4801	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4802	wants to use libev.
		4803
		4804	This option only works when libev is compiled with a C compiler, as C++
		4805	doesn't support the required declaration syntax.
4080		4806
4081	=item EV_AVOID_STDIO	4807	=item EV_AVOID_STDIO
4082		4808
4083	If this is set to C<1> at compiletime, then libev will avoid using stdio	4809	If this is set to C<1> at compiletime, then libev will avoid using stdio
4084	functions (printf, scanf, perror etc.). This will increase the code size	4810	functions (printf, scanf, perror etc.). This will increase the code size
…		…
4228	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4954	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4229		4955
4230	#include "ev_cpp.h"	4956	#include "ev_cpp.h"
4231	#include "ev.c"	4957	#include "ev.c"
4232		4958
4233	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	4959	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4234		4960
4235	=head2 THREADS AND COROUTINES	4961	=head2 THREADS AND COROUTINES
4236		4962
4237	=head3 THREADS	4963	=head3 THREADS
4238		4964
…		…
4289	default loop and triggering an C<ev_async> watcher from the default loop	5015	default loop and triggering an C<ev_async> watcher from the default loop
4290	watcher callback into the event loop interested in the signal.	5016	watcher callback into the event loop interested in the signal.
4291		5017
4292	=back	5018	=back
4293		5019
4294	=head4 THREAD LOCKING EXAMPLE	5020	See also L</THREAD LOCKING EXAMPLE>.
4295
4296	Here is a fictitious example of how to run an event loop in a different
4297	thread than where callbacks are being invoked and watchers are
4298	created/added/removed.
4299
4300	For a real-world example, see the C<EV::Loop::Async> perl module,
4301	which uses exactly this technique (which is suited for many high-level
4302	languages).
4303
4304	The example uses a pthread mutex to protect the loop data, a condition
4305	variable to wait for callback invocations, an async watcher to notify the
4306	event loop thread and an unspecified mechanism to wake up the main thread.
4307
4308	First, you need to associate some data with the event loop:
4309
4310	typedef struct {
4311	mutex_t lock; /* global loop lock */
4312	ev_async async_w;
4313	thread_t tid;
4314	cond_t invoke_cv;
4315	} userdata;
4316
4317	void prepare_loop (EV_P)
4318	{
4319	// for simplicity, we use a static userdata struct.
4320	static userdata u;
4321
4322	ev_async_init (&u->async_w, async_cb);
4323	ev_async_start (EV_A_ &u->async_w);
4324
4325	pthread_mutex_init (&u->lock, 0);
4326	pthread_cond_init (&u->invoke_cv, 0);
4327
4328	// now associate this with the loop
4329	ev_set_userdata (EV_A_ u);
4330	ev_set_invoke_pending_cb (EV_A_ l_invoke);
4331	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4332
4333	// then create the thread running ev_loop
4334	pthread_create (&u->tid, 0, l_run, EV_A);
4335	}
4336
4337	The callback for the C<ev_async> watcher does nothing: the watcher is used
4338	solely to wake up the event loop so it takes notice of any new watchers
4339	that might have been added:
4340
4341	static void
4342	async_cb (EV_P_ ev_async *w, int revents)
4343	{
4344	// just used for the side effects
4345	}
4346
4347	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
4348	protecting the loop data, respectively.
4349
4350	static void
4351	l_release (EV_P)
4352	{
4353	userdata *u = ev_userdata (EV_A);
4354	pthread_mutex_unlock (&u->lock);
4355	}
4356
4357	static void
4358	l_acquire (EV_P)
4359	{
4360	userdata *u = ev_userdata (EV_A);
4361	pthread_mutex_lock (&u->lock);
4362	}
4363
4364	The event loop thread first acquires the mutex, and then jumps straight
4365	into C<ev_run>:
4366
4367	void *
4368	l_run (void *thr_arg)
4369	{
4370	struct ev_loop *loop = (struct ev_loop *)thr_arg;
4371
4372	l_acquire (EV_A);
4373	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4374	ev_run (EV_A_ 0);
4375	l_release (EV_A);
4376
4377	return 0;
4378	}
4379
4380	Instead of invoking all pending watchers, the C<l_invoke> callback will
4381	signal the main thread via some unspecified mechanism (signals? pipe
4382	writes? C<Async::Interrupt>?) and then waits until all pending watchers
4383	have been called (in a while loop because a) spurious wakeups are possible
4384	and b) skipping inter-thread-communication when there are no pending
4385	watchers is very beneficial):
4386
4387	static void
4388	l_invoke (EV_P)
4389	{
4390	userdata *u = ev_userdata (EV_A);
4391
4392	while (ev_pending_count (EV_A))
4393	{
4394	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4395	pthread_cond_wait (&u->invoke_cv, &u->lock);
4396	}
4397	}
4398
4399	Now, whenever the main thread gets told to invoke pending watchers, it
4400	will grab the lock, call C<ev_invoke_pending> and then signal the loop
4401	thread to continue:
4402
4403	static void
4404	real_invoke_pending (EV_P)
4405	{
4406	userdata *u = ev_userdata (EV_A);
4407
4408	pthread_mutex_lock (&u->lock);
4409	ev_invoke_pending (EV_A);
4410	pthread_cond_signal (&u->invoke_cv);
4411	pthread_mutex_unlock (&u->lock);
4412	}
4413
4414	Whenever you want to start/stop a watcher or do other modifications to an
4415	event loop, you will now have to lock:
4416
4417	ev_timer timeout_watcher;
4418	userdata *u = ev_userdata (EV_A);
4419
4420	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4421
4422	pthread_mutex_lock (&u->lock);
4423	ev_timer_start (EV_A_ &timeout_watcher);
4424	ev_async_send (EV_A_ &u->async_w);
4425	pthread_mutex_unlock (&u->lock);
4426
4427	Note that sending the C<ev_async> watcher is required because otherwise
4428	an event loop currently blocking in the kernel will have no knowledge
4429	about the newly added timer. By waking up the loop it will pick up any new
4430	watchers in the next event loop iteration.
4431		5021
4432	=head3 COROUTINES	5022	=head3 COROUTINES
4433		5023
4434	Libev is very accommodating to coroutines ("cooperative threads"):	5024	Libev is very accommodating to coroutines ("cooperative threads"):
4435	libev fully supports nesting calls to its functions from different	5025	libev fully supports nesting calls to its functions from different
…		…
4600	requires, and its I/O model is fundamentally incompatible with the POSIX	5190	requires, and its I/O model is fundamentally incompatible with the POSIX
4601	model. Libev still offers limited functionality on this platform in	5191	model. Libev still offers limited functionality on this platform in
4602	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5192	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
4603	descriptors. This only applies when using Win32 natively, not when using	5193	descriptors. This only applies when using Win32 natively, not when using
4604	e.g. cygwin. Actually, it only applies to the microsofts own compilers,	5194	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4605	as every compielr comes with a slightly differently broken/incompatible	5195	as every compiler comes with a slightly differently broken/incompatible
4606	environment.	5196	environment.
4607		5197
4608	Lifting these limitations would basically require the full	5198	Lifting these limitations would basically require the full
4609	re-implementation of the I/O system. If you are into this kind of thing,	5199	re-implementation of the I/O system. If you are into this kind of thing,
4610	then note that glib does exactly that for you in a very portable way (note	5200	then note that glib does exactly that for you in a very portable way (note
…		…
4704	structure (guaranteed by POSIX but not by ISO C for example), but it also	5294	structure (guaranteed by POSIX but not by ISO C for example), but it also
4705	assumes that the same (machine) code can be used to call any watcher	5295	assumes that the same (machine) code can be used to call any watcher
4706	callback: The watcher callbacks have different type signatures, but libev	5296	callback: The watcher callbacks have different type signatures, but libev
4707	calls them using an C<ev_watcher *> internally.	5297	calls them using an C<ev_watcher *> internally.
4708		5298
		5299	=item pointer accesses must be thread-atomic
		5300
		5301	Accessing a pointer value must be atomic, it must both be readable and
		5302	writable in one piece - this is the case on all current architectures.
		5303
4709	=item C<sig_atomic_t volatile> must be thread-atomic as well	5304	=item C<sig_atomic_t volatile> must be thread-atomic as well
4710		5305
4711	The type C<sig_atomic_t volatile> (or whatever is defined as	5306	The type C<sig_atomic_t volatile> (or whatever is defined as
4712	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different	5307	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
4713	threads. This is not part of the specification for C<sig_atomic_t>, but is	5308	threads. This is not part of the specification for C<sig_atomic_t>, but is
…		…
4721	thread" or will block signals process-wide, both behaviours would	5316	thread" or will block signals process-wide, both behaviours would
4722	be compatible with libev. Interaction between C<sigprocmask> and	5317	be compatible with libev. Interaction between C<sigprocmask> and
4723	C<pthread_sigmask> could complicate things, however.	5318	C<pthread_sigmask> could complicate things, however.
4724		5319
4725	The most portable way to handle signals is to block signals in all threads	5320	The most portable way to handle signals is to block signals in all threads
4726	except the initial one, and run the default loop in the initial thread as	5321	except the initial one, and run the signal handling loop in the initial
4727	well.	5322	thread as well.
4728		5323
4729	=item C<long> must be large enough for common memory allocation sizes	5324	=item C<long> must be large enough for common memory allocation sizes
4730		5325
4731	To improve portability and simplify its API, libev uses C<long> internally	5326	To improve portability and simplify its API, libev uses C<long> internally
4732	instead of C<size_t> when allocating its data structures. On non-POSIX	5327	instead of C<size_t> when allocating its data structures. On non-POSIX
…		…
4738		5333
4739	The type C<double> is used to represent timestamps. It is required to	5334	The type C<double> is used to represent timestamps. It is required to
4740	have at least 51 bits of mantissa (and 9 bits of exponent), which is	5335	have at least 51 bits of mantissa (and 9 bits of exponent), which is
4741	good enough for at least into the year 4000 with millisecond accuracy	5336	good enough for at least into the year 4000 with millisecond accuracy
4742	(the design goal for libev). This requirement is overfulfilled by	5337	(the design goal for libev). This requirement is overfulfilled by
4743	implementations using IEEE 754, which is basically all existing ones. With	5338	implementations using IEEE 754, which is basically all existing ones.
		5339
4744	IEEE 754 doubles, you get microsecond accuracy until at least 2200.	5340	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5341	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5342	is either obsolete or somebody patched it to use C<long double> or
		5343	something like that, just kidding).
4745		5344
4746	=back	5345	=back
4747		5346
4748	If you know of other additional requirements drop me a note.	5347	If you know of other additional requirements drop me a note.
4749		5348
…		…
4811	=item Processing ev_async_send: O(number_of_async_watchers)	5410	=item Processing ev_async_send: O(number_of_async_watchers)
4812		5411
4813	=item Processing signals: O(max_signal_number)	5412	=item Processing signals: O(max_signal_number)
4814		5413
4815	Sending involves a system call I<iff> there were no other C<ev_async_send>	5414	Sending involves a system call I<iff> there were no other C<ev_async_send>
4816	calls in the current loop iteration. Checking for async and signal events	5415	calls in the current loop iteration and the loop is currently
		5416	blocked. Checking for async and signal events involves iterating over all
4817	involves iterating over all running async watchers or all signal numbers.	5417	running async watchers or all signal numbers.
4818		5418
4819	=back	5419	=back
4820		5420
4821		5421
4822	=head1 PORTING FROM LIBEV 3.X TO 4.X	5422	=head1 PORTING FROM LIBEV 3.X TO 4.X
4823		5423
4824	The major version 4 introduced some minor incompatible changes to the API.	5424	The major version 4 introduced some incompatible changes to the API.
4825		5425
4826	At the moment, the C<ev.h> header file tries to implement superficial	5426	At the moment, the C<ev.h> header file provides compatibility definitions
4827	compatibility, so most programs should still compile. Those might be	5427	for all changes, so most programs should still compile. The compatibility
4828	removed in later versions of libev, so better update early than late.	5428	layer might be removed in later versions of libev, so better update to the
		5429	new API early than late.
4829		5430
4830	=over 4	5431	=over 4
		5432
		5433	=item C<EV_COMPAT3> backwards compatibility mechanism
		5434
		5435	The backward compatibility mechanism can be controlled by
		5436	C<EV_COMPAT3>. See L</"PREPROCESSOR SYMBOLS/MACROS"> in the L</EMBEDDING>
		5437	section.
		5438
		5439	=item C<ev_default_destroy> and C<ev_default_fork> have been removed
		5440
		5441	These calls can be replaced easily by their C<ev_loop_xxx> counterparts:
		5442
		5443	ev_loop_destroy (EV_DEFAULT_UC);
		5444	ev_loop_fork (EV_DEFAULT);
4831		5445
4832	=item function/symbol renames	5446	=item function/symbol renames
4833		5447
4834	A number of functions and symbols have been renamed:	5448	A number of functions and symbols have been renamed:
4835		5449
…		…
4854	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme	5468	ev_loop> anymore and C<EV_TIMER> now follows the same naming scheme
4855	as all other watcher types. Note that C<ev_loop_fork> is still called	5469	as all other watcher types. Note that C<ev_loop_fork> is still called
4856	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>	5470	C<ev_loop_fork> because it would otherwise clash with the C<ev_fork>
4857	typedef.	5471	typedef.
4858		5472
4859	=item C<EV_COMPAT3> backwards compatibility mechanism
4860
4861	The backward compatibility mechanism can be controlled by
4862	C<EV_COMPAT3>. See L<PREPROCESSOR SYMBOLS/MACROS> in the L<EMBEDDING>
4863	section.
4864
4865	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>	5473	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
4866		5474
4867	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different	5475	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
4868	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile	5476	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
4869	and work, but the library code will of course be larger.	5477	and work, but the library code will of course be larger.
…		…
4876	=over 4	5484	=over 4
4877		5485
4878	=item active	5486	=item active
4879		5487
4880	A watcher is active as long as it has been started and not yet stopped.	5488	A watcher is active as long as it has been started and not yet stopped.
4881	See L<WATCHER STATES> for details.	5489	See L</WATCHER STATES> for details.
4882		5490
4883	=item application	5491	=item application
4884		5492
4885	In this document, an application is whatever is using libev.	5493	In this document, an application is whatever is using libev.
4886		5494
…		…
4922	watchers and events.	5530	watchers and events.
4923		5531
4924	=item pending	5532	=item pending
4925		5533
4926	A watcher is pending as soon as the corresponding event has been	5534	A watcher is pending as soon as the corresponding event has been
4927	detected. See L<WATCHER STATES> for details.	5535	detected. See L</WATCHER STATES> for details.
4928		5536
4929	=item real time	5537	=item real time
4930		5538
4931	The physical time that is observed. It is apparently strictly monotonic :)	5539	The physical time that is observed. It is apparently strictly monotonic :)
4932		5540
4933	=item wall-clock time	5541	=item wall-clock time
4934		5542
4935	The time and date as shown on clocks. Unlike real time, it can actually	5543	The time and date as shown on clocks. Unlike real time, it can actually
4936	be wrong and jump forwards and backwards, e.g. when the you adjust your	5544	be wrong and jump forwards and backwards, e.g. when you adjust your
4937	clock.	5545	clock.
4938		5546
4939	=item watcher	5547	=item watcher
4940		5548
4941	A data structure that describes interest in certain events. Watchers need	5549	A data structure that describes interest in certain events. Watchers need
…		…
4943		5551
4944	=back	5552	=back
4945		5553
4946	=head1 AUTHOR	5554	=head1 AUTHOR
4947		5555
4948	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.	5556	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
		5557	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
4949		5558

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